PLEASE NOTE: THIS PROJECT IS NOT SCIENTIFIC. IT IS A HOBBY.
"I was looking for information on an old mammal and found this lot. What is this project?"
It's got lots of information on old mammals. For a short bit of background information, see here.

The following owes much to Kemp, 2005 (p.162-166). Symmetrodonta as a distinct order of mammals isn't a concept which stood up to scrutiny, but a vaguer version can still be useful. At one time the category contained the families of Kuehneotheriidae, Tinodontidae and Spalacotheriidae, with the kuehneotheriids as the most basal members. A key feature was held to be a triangulated arrangement of main molar cusps. However, that's not in the least unusual for mammals. As it's unclear whether the first family had an intimate relationship with the later two, it was ejected. As it's also unclear whether the remaining two families are in any way closely related, it might require a bit of effort to appreciate why the term is of any use at all. Still, it does convey a rough idea of the sort of grade of molars meant, and it has a long history. Consequently, 'symmetrodonts' is comprehensible (to those who are familiar with it). The molars The molars of 'symmetrodonts' are sort of similar. They're tall, pointy and relatively simple. Those of the later 'symmetrodonts' are usually more simpler than the kuehneotheriid version, in that the cingulum is weakly developed. The triangulated arrangement can be roughly appreciated as follows. The most basal mammalian molars had a straight line of three main cusps: xXx. Shifting the middle one either up or down produces a triangle. In 'symmetrodonts' the central cusp shifted; it moved to the labial in lowers and lingually in uppers. In tindontids and kuehneotheriids, the angle at the apex is over 90°, which is obtuse. It's acute in spalacotheriids. However, as the obtuse condition is primitive, it's not of itself particularly informative about relationships. The cuter acutees At least the acute angled 'symmetrodonts' are related with each other, as shown by that very condition and further specialisations. A second family was established in 2003, Zhangheotheriidae, but Kemp retained Zhangheotherium within Spalacotheriidae in his outline, (p.163): "This group shares certain features with the remainder of Holotheria, indicating a relationship. The most important is the exaggeration of the postvallum-prevallid shearing action, between the back of the upper molar and the front of the lower, which is the functional reason for the development of the acute angulation of the cusps." Additionally The findings of Luo et al 2002, (see Bibliography for details of the paper), place both the tinodontids and spalacotheriids within crown-group Mammalia, as shown by the cladogrammes on pages 14 and 15. Reference for Symmetrodonta Simpson, 1925: Simpson GG (1925), Mesozoic Mammalia II: Tinodon and its allies. American Journal of Science, Series 5 10, p.451-470.

Links: John H Burkitt, Mammals, A World Listing of Living and Extinct Species http://cougarhillweb.org/mammals.pdf A wonderful resource. T Mike Keesey, The Ages of the Mesozoic http://dinosauricon.com/times/index.html A guide to chronological terms such as Albian and Cenomanian.

A. Tinodontidae B. Spalacotheriidae & Zhangheotheriidae

A. TINODONTIDAE

Taxon: Tinodontidae Marsh, 1887 Small mammals, which haven’t been found, with tiny teeth, which have. I was very sceptical as to the integrity of this group. However, a further genus has recently been referred to it. As presented here, the family does apparently serve some purpose. In terms of mammalian evolution, the tinodontids seem to be less derived than the spalacotheriids and Co. However, quite where tinodontids fit within Mammaldom is unclear. Tinodon is described as "a representative of "obtuse-angle" symmetrodonts", as opposed to the spalacotheriids, which are "acute-angle symmetrodonts", (Luo et al 2002, p.10-11). They go on to say, (p.16): "Kuheneotheriidae and Tinodontidae include generally similar taxa, with principal molar cusps arranged in an obtuse triangle (in occlusal view), and upper triangles reversed with respect to lowers." This was previously held to be probably a one-off evolutionary trick, linking these critters to 'descendants' such as Dryolestes, (a "eupantothere"), and the therians, such as myself. However: "The degree of cusp triangulation is quite variable among "obtuse-angle symmetrodonts". The degree of cusp triangulation varies through the molar series in Kuehneotherium (see Parrington 1978). In Tinodon, it is clear that the posterior lower molars show more prominent triangulation than the first lower molar, which is hardly triangulated at all (Crompton and Jenkins 1967). A similar variability in triangulation of cusps in now also documented in Gobiotheriodon (Averianov in press)", (p.16-17). Similar variability is also known from non-"obtuse-angle symmetrodonts" such as Gobiconodon and to a lesser extent Megazostrodon. All this suggests this feature is not the result of a unique evolutionary event, and doesn't reveal much about the systematics, (ie. relationships), among mammalian groups. And that this "obtuse" and "acute" stuff is old hat. Luo et al 2002, (p.17), reach this conclusion: "In summary, we consider that these archaic, "obtuse-angle symmetrodonts" represent a heterogeneous evolutionary grade, and that they lack reliable diagnostic features. All that can be said is that they are probably unrelated to each other or to "acute-angle symmetrodonts". They occupy some basal positions..." (note the use of the plural) "... in mammalian phylogeny that are not very well resolved by the limited anatomical data known from their currently incomplete fossils." Averianov's article on Gobiotheriodon has since been published. Some details are contained in the relevant entry below. Reference: Marsh (1887), American Jurassic Mammals. American Journal of Science 33, p.326-348. Genera: Amphidon (partly =Eurylambda =Tinodon?), Eurylambda (=Tinodon?), Gobiodon (=Gobiotheriodon), Gobion (=Gobiotheriodon), Gobiondon (=Gobiotheriodon), Gobiotheriodon, Menacodon (=Tinodon), Tinodon, Trishulotherium, Yermakia, other reports Time-Line: Lower Cretaceous: Gobiotheriodon, Tinodon (England), Yermakia, Morocco Upper Jurassic: Tinodon (Wyoming) Middle Jurassic: ?England Lower Jurassic: Trishulotherium

Genus: Gobiotheriodon (Trofimov BA, 1980) Trofimov, 1997 Aka: Gobiodon Trofimov, 1974 [nomen nudum] and Cassiliano ML & Clemens WA, 1979, [nomen nudum] and Trofimov, 1980 (preoccupied); Gobion (sic!) Trofimov, 1974 [nomen nudum]; Gobiondon (sic!) Yadagiri P, 1985 Remarks: What with one thing and another, this genus has suffered from some nomenclatural discomfort! Gobiodon refers to a fish, a form of life which I’ve never previously seen associated with the Gobi Desert.

Species:	Gobiotheriodon infinitus (Trofimov BA, 1980) Trofimov, 1997
Aka:	Gobiodon infinitus Trofimov, 1974 [nomen nudum] and Cassiliano & Clemens, 1979, [nomen nudum] and Trofimov, 1980 (preoccupied); Gobion (sic!) infinitus Trofimov, 1974 [nomen nudum]; Gobiondon (sic!) infinitus Yadagiri, 1985
Place:	Höövör (formally known as Khoboor)
Country:	Mongolia
Age:	Aptian-Albian, Lower Cretaceous
Remarks:	Much of what follows is based on Averianov AO 2002, (and thanks are due to the generous donor). This genus seems to be a fairly basal sort of mammal, lacking the further derived dental specializations seen in cladotherians, (eg. dryolestids and myself). Gobiotheriodon retained the 'reptilian' feature of a Meckelian groove on the inside of its jaw, (for some possibly incompetent considerations upon the significance of that, click here and scroll down a bit to the comments following Dryolestes leiriensis). However: "The postdentary trough is missing and there is no clear evidence for attachment of postdentary bones", (p.706). In the broadest sense of the term, it's a "symmetrodont" of some kind or other. Affinities The lack of this postdentary trough thing is more than enough to rule out affinities with the mega old-fashioned kuehneotheriids. Its molars are too complex for its originally proposed membership of the decidedly iffy Amphidontidae. Averianov rejects it as a member of Spalacotheriidae, as it lacks that group's tooth specializations. Gobiotheriodon has too few molars to pair up with Zhangheotherium, (four in comparison to at least six), and various other possibilities are ruled out on the grounds of paucity of evidence. The poor creature needs some company, surely? Happily, despite some dental differences, (which may well have much to do with the more basal nature of Tinodon), Averianov awards Gobiotheriodon a provisional placement within Tinodontidae. "All of these characters distinguishing Tinodon from Gobiotheriodon may be considered as plesiomorphic for the former; loss or modification in Gobiotheriodon is unsurprising, considering its geologically younger age", (p.710). Holotype The holotype, PIN 3101/80, is a 2,6cm long, near-complete mandible containing three molars. This resides in the collection of the Paleontological Institute of the Russian Academy of Sciences, Moscow, although the original description also identified it as PIN 3101/50 in the text. Other referred material includes part of an upper jaw, (which, in the opinion of Averianov, is an unlikely possibility. He states it: "could be currently attributed to as cf. Gobiconodon sp.", (p.707)); and two isolated petrosals which "may belong to Gobiotheriodon", (p.706). A petrosal is the bone case which houses the mammalian internal ear. Catalogue number For some reason, Kielan-Jaworowska et al, 2000 refer to the holotype as being PIN 3101/50 on page 596. This is presumably a typo as it changes back to /80 for the figure on page 597. I've rechecked the Averianov 2002 paper (namely in April 2007), and I didn't make a tieping eror with it.
References:	Trofimov (1974), in Belyaeva EI, Trofimov BA & Reshetov VJ General stages in evolution of late Mesozoic and early Tertiary mammalian fauna in Central Asia, (in Russian). Trudy Sovmestnoj Sovetsko-Mongol'skoj Paleontologiceskoj Ekspedicii 1.
	Cassiliano & Clemens (1979), Symmetrodonta. In Lillegraven JA, Kielan- Jaworowska Z & Clemens WA (eds.), Mesozoic Mammals: the First Two-thirds of Mammalian History, University of California Press, p.151-161.
	Trofimov (1980), Multituberculata and Symmetrodonta from the Lower Cretaceous of Mongolia, (in Russian). Doklady Akademii Nauk SSSR 251, p.209-212.
	Yadagiri P (1985), An amphiodontid symmetrodont from the Early Jurassic Kota Formation, India. Zoological Journal of the Linnean Society 85, p.411-417.
	Trofimov (1997), A new generic name Gobiotheriodon for a symmetrodont mammal Gobiodon Trofimov, 1980. Acta Palaeontologica Polonica 42, p.496.

Links: Acta Palaeontologica Polonica 47 (4) http://www.paleo.pan.pl/acta/acta47/app47-705.pdf Averianov AO, (2002): the full paper on-line. Acta Palaeontologica Polonica 42 (4) http://www.paleo.pan.pl/acta/acta42-4.htm The contents, including mention of the above note. Also contains an abstract on Lower Jurassic sauropod footprints from Poland.

Genus: Tinodon Marsh, 1879 Aka: Amphidon (partly), Eurylambda Simpson, 1929; Menacodon Marsh OC, 1887 Remarks: McKenna & Bell give eury as a junior synonym of tino. Another of life's mysteries is resolved. The Oklahoma Museum of Nat His houses several T.? specimens from the Upper Cretaceous, (Albian), of Utah. I’ve also seen a reference to the Upper Jurassic of Portugal, (Krusat, 1989) The systematic placement of this genus within the mammal scheme of things is unclear. "Data are limited to partial dentition and mandible", (Luo et al 2002, p.10). References: Marsh (1879), Additional remains of Jurassic mammals. American Journal of Science, 18, p.215-216, with 1 fig. in. Marsh (1887), American Jurassic mammals. American Journal of Science, 33, p.326-348. Simpson (1929), American Mesozoic Mammalia. Mem. Peabody Museum 3pt. 1pp I-xv + 171, 62 figs, 32p.

Reassigned species: T. ferox Marsh, 1880 see Priacodon ferox; T. grandaevus see Priacodon grandaevus; T. lulli see Priacodon lulli; T. robustus Marsh, 1879 see Priacodon robustus;

Species:	Eurylambda aequicrurius (Simpson, 1925) Simpson GG, 1929
Aka:	Amphidon aequicrurius Simpson GG, 1925
Place:	Como Bluff, Morrison Formation, Wyoming
Country:	USA
Age:	Upper Jurassic
Remarks:	Part of an upper jaw with an incomplete tooth. This is very possibly the same genus as Tinodon, (which is based on lower jaw material), though this is not yet proven. The holotype, YPM 13639, is at Yale. Rougier et al 2003 report a new find from the same location. This is an upper left, molariform tooth. "The new specimen was collected at Como Bluff Quarry in 1883...," (p.2). Subsequently, it made its way to the collection of the Smithsonian Institute, where it was catalogued as an undetermined mammal tooth, (USNM 2846). Despite tentatively following the interpretation of this genus as being a junior synonym of Tinodon bellus, these authors found it convenient to continue using the 1929 name. Coincidentally, so do I. It's perhaps worth mentioning that upper jaw and teeth remains are far rarer than their lower counterparts. The bone of the lower jaw is significantly stronger, and thus more likely to fossilize.
References:	Simpson GG (1925), Mesozoic Mammalia. II. Tinodon and its allies. Amer. Journ. Sci. 10, p.451-470.
	Simpson (1929), American Mesozoic Mammalia. Mem. Peabody Mus. Nat. Hist. iii (i), p.1-235.

Species:	Tinodon bellus Marsh OC, 1879
Place:	Morrison Formation, Wyoming
Country:	USA
Age:	Upper Jurassic
Remarks:	"Tinodon Marsh 1879, from the Morrison Formation of Wyoming (Jurassic-Cretaceous boundary), stands out among the symmetrodonts as being known by several lower jaws; the type jaw of T. bellus Marsh 1879 has M/1-M/4 in place, while the teeth of a referred specimen are preserved from P/1 to M/4...", (Sigogneau-Russell & Ensom 1998, p.458). T. bellus and T. lepidus material is housed at the Peabody Museum, Yale. There is also a specimen notated as dryolestid indet., which once had the 'MS' name, Tinodon nanus. There are various tinodons and pseudo-tinodons in the collection.
Reference:	Marsh (1879), Notice of new Jurassic mammals. American Journal of Science 20, p.396-398.

Species:	Tinodon lepidus Marsh OC, 1879
Aka:	Menacodon rarus Marsh, 1887
Place:	Morrison Formation, Wyoming
Country:	USA
Age:	Upper Jurassic
Remarks:	This species, should it be a distinct species, is also known from lower jaw remains; "... the type of T. lepidus Marsh 1879 keeps only two broken molars (M/2-3); but Menacodon rarus Marsh 1887, which was synonymized with the latter taxa by Simpson (1929) has C to M/3", (Sigogneau-Russell & Ensom 1998, p.458). Reportedly, Simpson also doubted that this species differs specifically from T. bellus. "... synonym of T. bellus according to Cifelli, pers. comm. 2002", (Averianov 2002, p.710).
References:	Marsh (1879), Notice of new Jurassic mammals. American Journal of Science 20, p.396-398.
	Marsh (1887), American Jurassic Mammals. Amer. J. of Sci. 3 , p.326-348.

Link: The Peabody Museum VP Catalog http://george.peabody.yale.edu/vp/

Species:	Tinodon micron Ensom P & Sigogneau-Russell D, 2000
Place:	Durlston Bay, Swanage, Dorset
Country:	England
Age:	Lower Cretaceous
Remarks:	The following is based on my interpretation of Ensom & Sigogneau-Russell, 2000, (with more thanks to the kindly supplier). The holotype, DORCM GS 1110, was described as a somewhat broken lower left molar. It's missing the tips of two of its cusps. Update: it's probably a right molar, (Sigogneau-Russell 2003b, p.524). Five other teeth are also referred to this taxon, one of which is an upper molar. Although not the holotype, "we probably would not have created a new species were it not for the upper molar", (p.774). All known fossils are residents of the Dorset County Museum, Dorchester and originally hale from the upper horizon of the Cherty Freshwater Member at Sunnydown Farm. These lower molars are smaller than those of T. bellus and T. lepidus. They also feature small, lumpy bumpy bits, (cingula), and the cusps are differently angled. And now things get murkier. When it comes to preserved jaw material with teeth, the distinctions between the lower molars of Tinodon and Spalacotherium are clear enough. However, the main characteristics that distinguish Tinodon are also present with a third genus, Spalacolestes, thus: "so that the teeth identified here as belonging to Tinodon could as well be the anterior molars of Spalacotherium evansae; all the more so that on these teeth, and contrary to what is seen in the two other species of Tinodon, the cristids are unequal as they are in Spalacotherium ", (p.775). Similarly, five of the teeth referred to S. evansae "could be posterior molars of this small species of Tinodon..." The decisive element in this puzzle "was the presence or absence of a clear wear facet A... " A strong influence on wear facets is the mode and degree of contact between the upper and lower teeth. If this particular feature is present, Tinodon. If not, Spalacotherium. "Attributed upper molar: In fact, the justification for, and the main interest of, this new Tinodon species resides in the attributed upper molar, DORCM GS 694. We could have designated this tooth as the type, and considered the incomplete lower molars as attributed, but of what genus? The synonymy Tinodon-'Eurylambda' is not proved, but on the other hand it seems ill-advised to create a new 'Eurylambda' species." The problems of paleo-book-keeping. 'Eurylambda' is known from one specimen; a piece of upper jaw with one, incomplete tooth. The anterior labial corner's missing. This is preserved in the Dorset specimen, (which is approximately a third smaller, length 1,2mm as opposed to 1,9; width 0,6 : 0,9), and that's why it's seen as of special interest. I like the conclusion. Whilst noting the discovery of more complete material from North America and China: "Our specimens nevertheless contribute in substantiating the variety of mammals during the middle Mesozoic and in throwing more light on relationships between the faunas of the Morrison Formation of North America and the Purbeck Limestone Group of England, while perhaps obscuring the concept of spalacotheriids!" (p.778). 'Micron' is Greek and means very small. This entry is one of the rare occasions upon which I have spelt Dr Sigogneau-Russell's name correctly, at the first attempt.
Reference:	Ensom & Sigogneau-Russell (2000), New symmetrodonts (Mammalia, Theria) from the Purbeck Limestone Group, Lower Cretaceous, southern England. Cretaceous Research, vol 21, no 6, p.767-779.

Links: Cretaceous Research, vol 21, no 6 http://www.idealibrary.com/links/artid/cres.2000.0227 This abstract also involves Spalacotherium evansae, (French). SVP News Bulletin 174, October 1998 http://www.vertpaleo.org/bulletin/174.pdf The SVP News Bulletin 174, October 1998, includes mention of a Eurylambda tooth from Dorset, reported by Paul Ensom. I strongly suspect, though am not certain, that this must be the one involved here.

Species:	Tinodon sp.
Place:
Country:	Portugal
Age:	Tithonian-Berriasian, Upper Jurassic - Lower Cretaceous
Remarks:	One isolated molar was reported, (Averianov 2002, p.710).
Reference:	Krusat G (1989), Isolated molars of a triconodont and a symmetrodont (Mammalia), from the uppermost Jurassic of Portugal. Berliner geowissenschaftliche Abhandlungen A 106, p.277-289.

Genus: Trishulotherium Yadagiri P, 1984 'Trishul beast' Remarks: A trishul is a three-pronged weapon favoured by Lord Sankara in Indian mythology. The relevant teeth was an earlier parallel.

Species:	Trishulotherium kotaensis Yadagiri P, 1984
Place:	Kota Formation, Andrah Pradesh
Country:	India
Age:	?Middle Jurassic
Remarks:	The following is largely based upon my reading of Yadagiri, 1984, and thanks go to the supplier. Unfortunately, the published article contained significant flaws. As well as establishing this genus, it also included Indotherium, now seen as a possible morganucodontid. The first Mesozoic mammal fossil to be described from India hit the news kiosks of the world in 1981. You may be able to recall the huge queues of wannabe readers, all anxious to get their hands on the reports. It was a small tooth from the Kota Formation of Central India and, surprisingly enough, some editors caused outrage by neglecting to include the story on either the front or back page or, indeed, on any of the pages between them. Angered mobs took the law into their own hands, and burned down the headquarters of some such miscreants. While not condoning such behaviour, I can certainly emphasize with it. While it's true that many other things of some level of significance were going on in the world that year, eg that party in Charminster when she insisted upon showing me her etchings, you would've thought such negligence required some heads to roll. My eyes were left rolling, but that was for a different reason. How different when this description appeared three years later! Very different. She'd moved to Swindon. However, the press reaction was broadly comparable. The new specimens came from a second fossil locality about ten kilometres north of the first one (p.514). Plenty of matrix was collected, soaked and then sorted through sieves of varying mesh sizes. As the desired fossils fit within particular size categories, that sort of treatment gets rid of a lot of the wrong-sized stuff, and that can drastically reduce the amount that needs to be carefully examined. Isolated mammalian molars were found among the remnants along with scraps of jaw and shards of skull from other critters. Two particularly well preserved teeth agreed to cooperate with detailed enquiries but, sadly, they couldn't prevent their answers being somewhat misunderstood. In the paper, the main central cusp is termed the protoconid, the front one the paraconid, and the rear one was accused of being the metaconid. That reflected oft used practice for lower molars at the time but, as these aren't tribosphenic teeth, it would now cause eyebrows to rise on my sides. (Thanks for that expression are due to Mr Usman Bello of Lagos, a bank manager with a wealthy corpse. And Mr Bello Usman. And Dr Usman Williams. And etc.) However, there are several problems. Firstly, the specimens happen to be upper teeth rather than lowers. Secondly, Indotherium was subsequently convicted of being closer to morganucodontid affinities than " 'symmetrodont' ones. I don't like tinkering with published terminology if I feel it can be avoided but, in this instance, I think it's the most conservative course to take. I'm going to use A, B and C respectively for the three relevant cusps. (I've just checked Prasad et al, 2006 for current views on these fossils, which coincidently arrived yesterday. Many thanks.) 'Trishul beast' The original author described the molar as having a well developed lingual and a weakly developed buccal cingulum, and nobody disagrees with that (p.515). However, as the possession of two cingula like these is the sort of behaviour associated with upper molars of this kind of age, everybody seems to disagree about it being a lower left tooth. It's an upper right one. Given the mirror-like qualities involved, that fortunately makes no difference with identifications of front, rear, buccal or lingual orientations. For example, if you'd now like to stare into the mouth of a willing mammalian accomplice, the buccal side of a lower left molar, the external one, is to your right. Now get a pair of pliers and place the tooth into the upper right row. (You might have to make some space.) Buccal remains buccal, blood is spluttering from the mouth, and the eyes of your beloved are now filled with pain, shock and shear horror. Cusps B and C are of similar sizes while A is dominant (p.515). A crest connects A with C, and A is positioned somewhat lingually. As mentioned, the lingual cingulum is more strongly developed than the buccal one. The tooth can be fairly described as tiny: length 0.5mm, width 0.2. It's double rooted. Unfortunately, as the fossil isn't a lower molar, none of the comparisons discussed on page 517 are particularly useful. Holotype GSI SR/PAL/10 is a right upper (not a left lower) molar housed in the paleontological collection of the Geological Survey of India, Southern Region, Hyderabad. The specific name pertains to the Kota Formation. Additional notes This genus seems to be somewhere within 'Symmetrodonta' Simpson, 1925, at least according to McKenna & Bell, 1997. However, the fact that it's not mentioned in the review by Averianov, 2002, leaves me somewhat puzzled. Other sources place the animal within Kuehneotheriidae. My most recent source, (Prasad & Manhas 2001, p.1235), plumps for Tinodontidae. I'm presently following this interpretation, but I don't know how they might define the family. This is based on what was interpreted to be a lower molar. Sigogneau-Russell & Ensom, 1998, (p.458), concluded it was an upper.
Reference:	Yadagiri (1984), New symmetrodonts from Kota formation (Early Jurassic), India. Journal of the Geological Society of India, 25 (8), p.514-621.

Link: M Alan Kazlev, Kuehneotheriidae http://www.kheper.auz.com/gaia/biosphere/vertebrates/trituberculata/Kuenotheriidae.html This page is under construction, though it may take some time. Mr Kazlev is rather busy.

Genus: Yermakia Lopatin AV, Maschenko EN, Averianov AO, Rezvyi AS, Skutschas PP & Leshchinkiy SV, 2005 Remarks: I found mention of this genus by chance on the webpage of Dino Hunter. Many thanks for posting it. Further thanks are due to Jelle Zijlstra for finding the abstract.

Species:	Yermakia domitor Lopatin et al, 2005
Place:	Shestakovo locality, Kemerovo Region, Western Siberia
Country:	Russia
Age:	Lower Cretaceous
Remarks:	The following is based purely on the abstract of the paper, a full copy of which would be most useful. This genus is known from at least one dentary and this seems to be a relatively informative lower jaw. The bone turns dorsally in the area of the incisors and the mandibular symphysis is described as short. An ancient feature is on the inner face of the jaw. This is a Meckelian groove, which was a handy place for storing a bit of cartilage we mammals no longer retain as we get older. Yermakia and various primitive beasties had different views on that. The groove in this case widens like an estuary at the back, grooves along the jaw for a while and then thins progressively. A feature known to its friends as the pterygoid crest is well developed, the pterygoid fossa small, and the coronoid process rises gently. Teeth Preserved are four small incisors and a not very impressive, double rooted canine. A diastema separates that tooth from the postcanine brigade. Its members consist of three premolars and four molars. The premolars are all double rooted and lack a cusp termed b. The angle formed by the trigonid cusps of the molars is obtuse. It ranges from 102° (m1) to 139° (m4). The increase is progressive from front to rear. Affinities The authors refer Yermakia specifically to the family of Tinodontidae. They find it to be more derived than the earlier Tinodon but somewhat primitive in comparison to its nearer contemporary, Gobiotheriodon from Mongolia. This is the first 'symmetrodont' to have been recovered from Russia, and the eucynodont fauna from the locality is presently enjoying a boom in diversity.
Reference:	Lopatin et al (2005), Early Cretaceous mammals from Western Siberia: 1. Tinodontidae, Paleontological Journal, 35(5), p.523-534.

Link: Paleontological Journal, 35(5) http://www.maik.rssi.ru/cgi-bin/search.pl?type=abstract&name=paleng&number=5&year=5&page=523 The Abstract of Lopatin et al (2005) is presently on-line.

Other reports: Anoual, Morocco With regards to a dentary fragment with two molars referred to Donodon, Averianov, 2002, includes: "I think that the dentary specimen referred to D. perscriptoris should be attributed to "Symmetrodonta". The reduction of the lingual cingulid and mesial cingulid cuspule "f" are similarities shared with Gobitheriodon", (p.713). Oxfordshire, England Sigogneau-Russell, 2003b refers two lower molariform teeth from the Bathonian Forest Marble Formation to ?Symmetrodonta indeterminate, (p.524). Of one specimen: "This tooth evokes the anterior molars or [sic] Tinodon Marsh, 1879, but differs by a lower crown and a cingulum not being angled in the middle." The specimens are poorly preserved and may be milk teeth.

A. Tinodontidae B. Spalacotheriidae & Zhangheotheriidae

B. SPALACOTHERIIDAE & ZHANGHEOTHERIIDAE

Taxa: Spalacotheriidae Marsh, 1887 Zhangheotheriidae Rougier GW, Ji Q & Novacek MJ, 2003 These small insectivores / carnivores are most commonly found in the Cretaceous rocks of the northern hemisphere. In virtually all cases, remains consist of teeth, with occasional fragments of jaw. The exceptions are the zhangheotheriids, which are known from near complete specimens from China. Luo et al 2002, (p.26), place Spalacotheriidae, as represented by Zhangheotherium), within a modified Trechnotheria McKenna, 1975, which they define as: "the common ancestor of Zhangheotherium (and by extrapolation the monophyletic group of Spalacotheriidae, see Cifelli and Madsen 1999) and crown Theria, plus all of its descendants." In other words, this lot and us share common ancestry. "Spalacotheriids included forms with as few as two premolariforms but as many as seven molariform teeth", (Butler & Clements 2001, p.13. They're sometimes referred to as "acute-angle" symmetrodonts. Reference: Marsh OC (1887), Additional remains of Jurassic mammals. American Journal of Science 18, p.215-216. Shock, horror, non-molar molars Rougier, Isah & Manabe, 2007 includes some disturbing news on page 75. As is widely known, should your circle of acquaintances be wide enough, mammals aren't allowed to replace their molars. Those, should you be wondering, are the large teeth to the rear of your jaws. Indeed, that's reflected in present definitions of a molar; a first generation tooth begind the permolars that experiences no replacement. Mounting evidence indicates that zhangheotheriids (and likely lots of other ancient mammals) hadn't been informed of this. The first 'molar' may look like and have worked like a molar, but it was actually a replacement for an earlier tooth at that position. This primitive form of dental delinquency would appall any right-minded dentists, if that's not a contradiction in terms. This perverse trait is unlikely to have occurred in this particuclar family. The habit could've been widespread among "symmetrodonts" and other groups. For example, it's also now known from gobiconodontid tricondonts.

Links: Mikko Haaramo’s Spalacotherioidea Mikko Haaramo's Spalacotherioidea The cladogrammer’s cladogrammer. Geodiversitas 1999, 21(2), p.167-214 http://www.mnhn.fr/publication/geodiv/g99n2a4.html Spalacotheriid symmetrodonts (Mammalia) from the medial Cretaceous (upper Albian or lower Cenomanian) Mussentuchit local fauna, Cedar Mountain Formation, Utah, USA. The abstract of an article featuring a number of genera by Cifelli RL & Madsen SK. This proposes that Spalacotheriidae is a monophyletic group, (ie: all members are descended from a common ancestor). Whether all the names below are valid is a different matter. Genera: Akidolestes, Heishanlestes, Maotherium, Mictodon, Peralestes (=Spalacotherium), Shalbaatar, Spalacolestes, Spalacotheridium, Spalacotherium, Spalacotheroides, Symmetrodontoides, Symmetrolestes, Yaverlestes, Zhangheotherium, other reports Time-Line: Upper Cretaceous: Mictodon, Shalbaatar, Spalacolestes, Spalacotheridium, Spalacotheroides, Symmetrodontoides Lower Cretaceous: Akidolestes, Heishanlestes, Maotherium, Spalocotherium, Spalacotheroides (Texas), Symmetrolestes, Yaverlestes, Zhangheotherium, East Asia

Genus: Akidolestes Li G & Luo Z-X, 2006 'Point thief' Remarks: The generic name alludes to the pointed rostrum of the jaw. 'Lestes' (thief) has been frequently used for mammals. If they could talk, then insects and worms might explain about some of the problems they encounter.

Species:	Akidolestes cifellii Li G & Luo Z-X, 2006
Place:	Yixian Formation, Liaoning
Country:	China
Age:	Barremian, Lower Cretaceous
Remarks:	The following is based upon my reading of Li & Luo, 2006. I've added certain elements the authors sensibly neglected. Yixian strikes again The Yixian Formation is providing a barrage of fossils which defy superlatives, and it shows no signs of breaking this extravagant habit. There are two mammal-bearing strata, and Akidolestes is the latest addition from the upper fauna (until the next find makes nonsense of this sentence). By the sensational local standards, I suppose this one could be termed unspectacular. It's a small critter a bit over ten centimetres long, with around a third of the length provided by a relatively short tail. It's the third spalacotheroid, so that's no new claim to fame. Akidolestes is the fourth to outrageously flaunt remains of its fur coat. Superficially, there's nothing that's particularly original with yet another furry, terrestrial, insect-annihilating mammal delivered, after a journey of 125 million years, in staggering completeness other than for much of the left skull. Even staggering completeness is no longer surprising for the Yixian. This mammal does have lumbar ribs, but they've been previously sported by Repenomamus from the lower fauna. Now there was a mammal worth interviewing. That genus grew up to lengths of a metre, and ate baby dinos anytime it damned well pleased. Or at least, when it could. That's the road to megastardom. Akidolestes is more like a small face in the crowd, albeit with half its head missing. Lumbar ribs! What they? There's no particular reason why most people would've heard of lumbar ribs. It sounds like a supper for tree-fellers. I'm now going to write in line with my own biases, so a naked woman is obviously essential at this juncture. Should you feel like leaning towards a naked man instead, then feel free to grab one (but mind out where). Time for nudity My wife's not in the room at the moment, so some imagination will be required. As you can see, if you look in through the monitor, I'm sat on the chair somewhat to the side of my usual position. I've cleared a bit of space on the floor, and am now psychically projecting the image of a naked woman standing there. The skilled anatomists among you might notice they can see her face, so they'll be sure they're looking at the front. Most readers will be concentrating on different parts of her body, and have doubtlessly reached a similar conclusion. I'm now letting my hand glide firmly, yet gently, down her neck. Definitely without hurrying, my fingers are pleasingly admiring the warm flesh of her fine mammary glands. This area of the torso is known as the breast region, and it's well worth spending time on the subject. Allowing my hands to slide slowly down and outwards enables me to feel the rib cage. These structures originate from the vertebrae of the upper spine. They're thoracic ribs; the only kind this naked woman has. I've spread my hand flat and am now caressing the skin of the stomach. This is the lumbar region. The bones of this lower part of the spine have no ribs, and this is typical for placental and marsupial mammals. However, that wasn't the case for many non-mammalian cynodonts, various basal mammals or indeed Akidolestes. It also doesn't apply for the egg-laying monotremes such as the platypus. All those critters have or had ribs down there too, although they're much shorter than the thoracic ones, and don't form parts of a protective cage. (They did in earlier synapsids.) All this thinking about a naked woman has somehow distracted me from the paper. There will now be a short interlude. I've got some pressing matters I urgently want to see my wife about. A while later Good. I'm now de-invigorated and everybody knows where our lumbar ribs aren't. The thing about this aspect of Akidolestes, is that their presence was unexpected. Based on what was known from other mammals, nobody would've predicted a spalacotheriid would have had them. The trait is too old fashioned. It's generally somewhat more derived than its zhangheotheriid neighbours such as Zhangheotherium, and they don't have lumbar ribs. Several other features are also surprisingly familiar to fans of monotremes (p.195), whose ancestors diverged from a 'lower' branch of the mammalian bush. I enjoy the word counterintuitive, and such characteristics in this inoffensive, small mammal certainly qualify for it. So unremarkable as this staggeringly complete fossil may appear, he was clearly a wonder. The spur of bone on the back of the ankle means this individual probably was male. Teeth and identity The dental formula per side is: (uppers): 4 incisors, 1 canine, ?5 premolars and ?5 molars; (lowers): 4, 1, 5 and 6 respectively (p.196). The cusps of the last premolar and all the molars are acutely triangulated, with the angle sharpening from front to back along the row. (This means the three main cusps are arranged in the form of a triangle.) The angle's below 50° for the final tooth. This and other features are typical of spalacotheroid dentitions. A crest on the molars termed the protocristid is higher than found in zhangheotheriids. A further distinction lies in the relative sizes of the final premolar and first molar, with the former being the larger of the pair in Akidolestes. This is already enough to debar the animal from admission into the family of Zhangheotheriidae. It has more premolars than Symmetrolestes and outdoes the molar count of both Spalacotherium and Spalacolestes. The coronoid process of the dentary is a gracile construction. This contrasts with the somewhat more recent Heishanlestes, but isn't dissimilar to the zhangheotheriids. In short, this mammal is confidently assigned to Spalacotheriidae. Legs The front legs and shoulders are much like those known from the zhangheotheriids. The back legs are more surprising, as these display similarities with monotremes; presumably convergences. Before reaching that area, I'm allowing my hand to linger low down on the stomach of the naked woman. It's now moving to the side and around her body just above the hip. Feeling the base of her spine is heavenly. I'm not sure how many lumbar vertebrae she has, and I presently couldn't care less. My mind's on other matters. Involuntarily, my fingers are probing the soft... Excuse me. There will now be another interlude. A further while later I can confirm my wife definitely has no lumbar ribs. As established earlier, this contrasts with Akidolestes. That mammal has six vertebrae in the lumbar region, and five are associated with short ribs. These aren't attached to the spine. The bones are free slithers slightly to the side of the vertebrae. A similar condition is found in monotremes, Repenomamus, Fruitafossor and a herd of non-mammalian cynodonts. This trait enjoys a long tradition which we latecomers neglect to follow. We also fail to develop small bones at the front of the hips called epipubes, but all other known mammals other than eutherians have or had them. (Epipubic bones are present in basal eutherians and non-mammalian tritylodontids.) Akidolestes unsurprisingly had these, and they're unusually wide (p.198). This condition is reminiscent of the platypus, but the equivalent bones in other monotremes and Mesozoic mammals tend to be narrower. A number of features are monotreme-like: "The pubis has a prominent tubercule for the psoas minor muscle..."; "In the head, neck and trochanteric area of the femur, Akidolestes is most similar to morganucodontids, eutriconodontans and monotremes (although to a smaller extent for the latter)...". The fibula also has a hypertrophied parafibular process. (That particular bit of bone is much enlarged.) Again, this is also the case for monotremes. Walking the walk Some of these details have significance for how monotremes move. They ensure that the rear legs can't be fully straightened. The limb sticks out somewhat sidewards from the body. The similar construction suggests Akidolestes was a sprawler as well, and this is starkly different to the proud, erect, Didelphis-like posture of Zhangheotherium (p.199). Pausing for paws The relative proportions of bones in fingers and toes can provide revealing clues about lifestyle. Fanatical diggers, swimmers or tree acrobats generally develop telltale specialisations. For example, the latter often have elongated digits for grip. No particular specialisations are evident for Akidolestes. This appears to have been a generalised ground-dweller as with Zhangheotherium and morganucodontans. The relatively short tail seems to me to strengthen this conclusion. It appears complete with sixteen vertebrae. While that's more than I possess, it's not all that many for a mammal. Lumbar ribs in a wider context Lumbar ribs have an ancient pedigree. Sometimes, as in this case, they're found in mammals with close relatives, which are abstainers. Another example is provided by gobiconodontids. Their fellow eutriconodont, Jeholodens, doesn't share this trait. This seems to be an ancient characteristic which has been reactivated on a number of occasions. As a consequence, it doesn't appear overly helpful when trying to establish relationships between groups of mammals. What are they for? Having ribs free of the vertebrae may sound odd but, in monotremes, they come in very useful. By providing anchorage for muscles and the diaphragm they help with movement and breathing. Presumably, especially in the light of further postcranial convergences, Akidolestes benefited in broadly similar ways. The hips of my naked woman are built differently. Her gorgeous skin... Excuse me again. Holotype The type fossil, NIGPAS 139381A and B, is an employee of the Nanjing Institute of Geology and Paleontology. There are two slabs of stone involved, and these are positive and negative impressions of the same animal. The specific name honours the pioneering Utah symmetrodontologist, Rich Cifelli.
Reference:	Li G & Luo Z-X (2006), A Cretaceous symmetrodont therian with some monoteme-like postcranial features, Nature, 439, p.195-200.

Links: Canegie Museum, the full description http://www.carnegiemnh.org/vp/media/Li&Luo(2006).pdf Li & Luo, 2006 is now freely accessible in pdf format. Carnegie Museum, 11.1.2006 http://www.carnegiemuseums.org/cmnh/news/06-jan-mar/101101akidolestes.htm Chinese and American paleontologists discovered a new species of Mesozoic mammal. The Museum's press release includes a link to a couple of images. National Geographic News, 11.1.2006 http://news.nationalgeographic.com/news/2006/01/0111_060111_chimera_fossil.html James Owen took notice of the press release: Extinct Species of "Mosaic" Mammal Found in China. The Hairy Museum of Natural History http://www.hmnh.org/archives/2006/01/11/mesozoic-mammal-akidolestes/ Matt Celeskey investigates 'point thief'.

Genus: Heishanlestes Hu YM, Fox RC, Wang YQ & Li CK, 2005 'Heishan thief' Remarks: The generic name refers to the county from which the fossils came.

Species:	Heishanlestes changi Hu YM, Fox RC, Wang YQ & Li CK, 2005
Place:	Badaohao, Heishan County, Liaoning
Country:	China
Age:	Aptian, Lower Cretaceous
Remarks:	The following is based upon my reading of Hu et al, 2005. Heishanlestes is the third new 'symmetrodont' genus to appear from the strata of Liaoning Province in the last eight years, but this is both the most recently alive and poorest known of them. Rather than being from the fabulous treasury of the Yixian Formation, Heishanlestes hails from a less salubrious coal mine. As well as being geologically younger, the taxon is more closely related with the spalacotheriids of North America. Remains are restricted to lower jaws with teeth, but at least they're relatively well preserved, (p.1). The animal possessed four premolars which were closely packed together, and probably acted to crush foodstuff. This was then passed back to the six molars for cutting. An interesting feature is that the molars are differentiated into three distinct subgroups. The first displays a trigonid with obtuse-angled triangulation, while the other five are acute-angled. The last pair have a large cusp at the centre of the trigonid, and this isn't homologous with the anatomy of any other known mammal. A further point of significance is that all postcanines are in situ (p.2). That presently qualifies as extremely unusual. Collection and conditions Three specimens were obtained from small coal mines in the field seasons of 1994 and '95. These are in Badaohao, Heishan County, and correlate with the Shahai Formation. Fossils recovered include further mammals (triconodonts, multituberculates, a relative of Aegialodon and eutherians), various molluscs, fish, lizards and teeth and egg shell from dinosaurs. Below is found the Jiufotang Formation which shares elements with the famous Yixian Jehol fauna. The remains from Badaohao must be younger than that, and an estimated age for the Shahai is Aptian, (p.3). That's about 121 - 112 million years ago. Size The 'Heishan thief' was typically sized for a Mesozoic mammal; small. The holotype is a jaw a touch longer than 1.7cm, although the front of this dentary, (where the incisors and canine were housed), is missing. A canine is included with another specimen. Dental formula The known numbers of teeth per side are: (lowers): ? incisors, 1 canine, 4 premolars and 6 molars, (p.4). Anybody anxious for information on the upper teeth should make their way to the coal mine in question and find some. Incisors As not much of the jaw is missing, the front teeth were presumably relatively small. This would be in line with Spalacotherium. In contrast, Zhangheotherium boasted of an enlarged first incisor. There probably wasn't room for such an implement in this mouth. Canine The tooth is preserved on one jaw fragment, but it was in the early stages of eruption. The alveolus is larger than the unicusped canine within it, and that suggests this is a replacement for a deciduous predecessor. The number of roots is unknown. Its equivalents are double-rooted in Spalacotherium tricuspidens and single-rooted in zhangheotheriids. Premolars The four premolars are unusually crowded together. A projection at the front of each overlaps with the rear of the tooth in front, (p.7), forming a tighter unit a bit like a line of interlocking shields. The first molar also overlaps with the p4, but whether the situation is similar for the p1 and canine is unclear. Each tooth has an ovoid area of wear behind and to the lingual side of the main cusp. The whole unit seems to have provided a crushing process for breaking down foodstuff. The largest premolar is p4. The p1 was probably a bit bigger than ps 2 and 3. Each is oval in outline from the occlusal perspective. With the exception of p1, they are certainly double-rooted. Only one root is visible for the first tooth in the series, but that could conceivably divide inside the bone. Wear on p4 suggests this tooth may also have participated in some cutting of food in concert with its upper partners, (p.8). Molars Each of the six molars is double-rooted. A surprising feature is that they're divided into three distinct models. Had they not been found on the jaw the authors state these would probably have been assigned to at least different genera. The m1 has an obtuse-angled arrangement of trigonid cusps (140°), with the paraconid and metaconid marginally more lingually situated than the protoconid. All other molars have acute triangulation, with it being most extreme in the second type (55°, 48° and 46° for ms 2, 3 and 4 respectively). These teeth are considerably taller on the labial side than they are on the lingual, as is known from other spalacotheriids. The angles in m 5 and 6 are 50° and 60°. This pair are adorned with an extra and strong cusp on the lingual aspect of the trigonid. A parallel with other Mesozoic mammals is unknown. Wear on m1 suggests some crushing activity; evidence of the functional transition along the postcanine row as a whole, (p.10). As with the premolars, projections at the front of the crown interlock with the proceeding tooth. The two rearmost molars are the smallest and lowest in the row, (p.12), with the m6 being much smaller than the m5. The tallest feature of these crowns is that presently unique cusp between the paraconid and metaconid. There's no hint of anything similar on the teeth in front, let alone in other mammals. Jaw The dentary is relatively slender, (p.13), with the maximum depth of the horizontal ramus below the m6. Small mental foramina are present on the external side of the bone beneath the canine and the second and third premolars. There's no sign of a Meckelian groove Behind the tooth row is a nearly complete coronoid process. This has suffered some crushing and part of the rear border is missing. The process ascends more or less at 90° behind the molars, and there's little rearwards curvature until about two-thirds of the way up. A small, rough depression is on the medial surface, (p.14). This is perhaps an attachment point for an 'extra', small jaw bone; a coronoid. Other possibilities include it being an artefact of distortion. More specimens could provided clarity. The absence of an angular process below the coronoid process is usual for 'symmetrodonts'. A spalaco molar stock take Six lower molars is the number also reported from zhangheotheriids, (although one interpretation placed this as five for Zhangheotherium). Symmetrodontoides canadensis manages six or seven. The latter figure is favoured by Spalacotherium triscuspidens and Spalacolestes cretulablatta. However, in all those animals, size and shape of molars alter gradually along the row. None have three distinct types as in Heishanlestes. The unusual m1 is similar to a tooth assigned to Symmetrodontoides candensis, although this identification may not be correct. It could be from a closer relative of this 'Heishan thief', and the same possibility exists for some further specimens from Utah, (p. 16). The m2-m4 are more typical of spalacotheriids. The crowns are short and wide with a protoconid towards the rear and no talonid. Other features, such as the acute triangulation of cusps and lack of a cusp f, (in contrast to mammals such as Tinodon), occur in all spalacos as well, (including zhangheotheriids). Affinities and geography As Heishanlestes is more similar to Spalacolestes and Symmetrodontoides than Spalacotheroides is, the authors place the genus within the otherwise North American subfamily of Spalacolestinae, although this produces doubts concerning the monophyletic status, (p.18). Be that as it may, the relationship is clear enough. Closely related mammals were scampering around in both North America and China. This is far from being a unique case. It's been speculated that spalacolestines were able to survive in North America because eutherians were rare. However, Heishanlestes lived in an area alongside of eutherians. Nevertheless, spalacotheriids became rarities beyond the middle of the Cretaceous, and their disappearance coincides with the radiation of we therians. Holotype The type fossil, IVPP V 7480, is an employee of the Institute for Vertebrate Paleontology and Paleoanthropology, Beijing. The specific name honours Professor Zhenglu Chang, who has done much over the past five decades for the studies of stratigraphy and paleontology in the region.
Reference:	Hu et al (2005), A new spalacotheriid symmetrodont from the Early Cretaceous of northeastern China, American Museum Novitates, 3475, pp.1-20.

Genus: Maotherium Rougier GW, Ji Q & Novacek MJ, 2003 'Mao's beast' Family: Zhangheotheriidae Rougier et al, 2003 Remarks: I haven't seen the paper, but this is reportedly named in honour of the late Charirman Mao Tse-Deng. Unfortunately or otherwise, I'm informed that may be incorrect. (With thanks to Mark Isaak's Curiosities of Biological Nomenclature ('Named after People: Political and Military Figures). Brief information is provided by Wang et al, 2006 (p.197-198). This sounds like a hum-dinger of a fossil. It's complete (and even furry). In essence, it's a somewhat inflated version of Zhangheoterhium with a few differing details. Lower jaw halves are supplied with one more molar. Skeletal differences include the proportions of limb bones, the number of vertebrae and, in this critter, an unfused sternum.

Species:	Maotherium sinensis Rougier GW, Ji Q & Novacek MJ, 2003
Place:	Yixian Formation, Liaoning
Country:	China
Age:	Barremian, Lower Cretaceous
Remarks:	This genus is mentioned in the recent Carnegie Museum Press Release, which accompanied the publication of Sinodelphys szalayi. It's referred to as a symmetrodont. It's in the family of Zhangheotheriidae, (Tsubamoto et al 2004, p.337). Thanks are due to Dinohunter for posting notice of the description, which will hopefully turn up somehow or other.) From the abstract: "This paper describes a complete specimen of a symmetrodont mammal with well-preserved hairs and soft tissue from the basal part of the Yixian Formation in the Sihetun area, Beipiao, western Liaoning."
Reference:	Rougier, Ji & Novacek (2003), A new symmetrodont mammal with fur impressions from the Mesozoic of China, Acta Geologica Sinica, 77 (1), p7-14.

Links: Sinodelphys szalayi, Carnegie Museum of Natural History http:www.carnegiemuseums.org/cmnh/research/sinodelphys/index.htm Maotherium gets a mention. Acta Geologica Sinica, 2003 The abstract... ...is on-line.

The Yixian Formation, China, Lower Cretaceous The following is loosely based upon my reading of Luo, 1999. However, various bits and pieces of information aren't mentioned in that paper; for example... I live about forty miles from Solnhofen, which is one of the most incredible places in the world for stunningly well-preserved, Mesozoic fossils. Its most famous Upper Jurassic resident was Archaeopteryx. Seven specimens have turned up over the last 150 years, though one is presently regarded as belonging to Wellnhoferia, (a close relative). That makes Archie a well-represented dino-bird. Seeing the quality of the fossils in the Bürgermeister-Müller-Museum and other collections provides a staggering experience, and mind-blowing's an appropriate term. However, the fossils from the Yixian Formation of Liaoning, northwest China, have conspired to make Solnhofen seem relatively mundane, which it certainly isn't. They make all superlatives woefully inadequate and keep on coming. The Times they are A-changing The Upper Jurassic / Lower Cretaceous transition produced profound changes within both the terrestrial flora and fauna of the world. The flowering plants (angiosperms) budded, blossomed and then went on to gloriously seed. This seems to have powered the emergence of nectar-feeding flies and subsequent adaptation among many other insects; eg. bees and butterflies. The pterosaurs were joined on the wing and challenged by strange dinosaurs known as birds. New groups of outlandish mammals took to their paws; metatherians and eutherians including marsupials and placentals respectively. And this locality, slap bang in the chronological middle (ca. 124 million years BP), provides exquisite evidence of these episodes. When Dr Luo describes the Yixian Formation as: "one of the richest and most important sources of fossils from the Mesozoic era...", I feel compelled to object on the grounds of false modesty. These fabulous finds are powerful enough to condemn even the hard-hearted of paleontologists to tears of joy. I can hear Thomas Huxley sobbing with pleasure in his grave. Shooting Star Fossil fish, arthropods and plants have been coming from these beds since the 1920s, though these were mostly forms which were purely Asiatic during the Lower Cretaceous. This endemicism made biostratigraphic comparisons with specimens from further afield difficult, and didn't shed much light on wider evolutionary matters. But, after relatively modest beginnings, Liaoning began firing on the most astounding cylinders and more than made up for lost time. The aforementioned Huxley had linked dinos with birds in the 1860s but, perhaps as the evidence available consisted of similarities between a couple of specimens of Archaeopteryx and a small, non-birdy compatriot called Compsognathus, this reasonable interpretation fell somewhat out of favour for nigh-on a century. Further work and more fossils helped revive its fortunes from the 1960s. Then Liaoning began batting in earnest and it was soon game over, (though there are one or two dissenters). One of the most basal coelurosaurs, Sinosauropteryx, seemed to be equipped with fluffy feathers. The same was the case for the primitive maniraptors Protarchaeopteryx and Caudipteryx. And, since Luo's paper was written, we've even been blessed with the appearance of Microraptor gui; a non-birdy dromaeosaur with aerodynamically adapted feathers and leg wings. A four-winged dinosaur may sound bizarre, but it's appropriate enough for Liaoning. Also present in the fauna are Confusciusornis and Changchengornis, both of which are more derived birds than my friend Archaeopteryx of Solnhofen. Desolation Row The increasing mammalian element (two more species added in the first nine months of 2005) is an intriguing cocktail of 'old' and 'new'. Sinobaatar is a relatively old-fashioned 'plagiaulacidan' multituberculate. Fairly late occurring 'symmetrodonts' (this directory) and triconodonts are also known. More derived are Sinodelphys ( Metatheria) and Eomaia (Eutheria). Both animals are the earliest and most basal representatives of their respective lineages. As was Maotherium ('Symmetrodonta'), these fossils came supplied with the oldest directly evidenced fur coats in the world. An interesting flowering plant (angiosperm) is Archaefructus. The female reproductive structure, the carpel, is typical enough. However, this plant lacked petals, and it seems to be a transitional proto-flower. Watching the River Flow The basal nature of some of these mammals and dinosaurs shows affinities with groups known from earlier times in North America and Europe, and this is also reflected by other vertebrates. The pterosaurs resemble those from Solnhofen. Such patterns might suggest an Upper Jurassic age for Yixian too, but that's not the case. Volcanic material has supplied a reliable dating, (Argon 40 / Argon 39 basis). This formation is Lower Cretaceous. Consequently, some of these lineages were effectively 'living fossils' of their time, which supports the view that Central and Eastern Asia were isolated during the Upper Jurassic and lowest Cretaceous. (Further evidence for this has been provided by the persisting presence of non-mammalian tritylodontids from Lower Cretaceous locations in Siberia and Japan. As yet, there's no indication of any such fossils in Liaoning, but I live in admittedly diminishing hope.) I'll be your Baby Tonight "Primitive fossil taxa may not always be older than their more derived relatives." According to my understanding, populations aren't reliable analogues of individuals. They don't come with built-in lifespans. A lineage can continue for as long as it has individuals willing and able to produce viable off-spring. A duck-billed platypus is far more basal than a woolly mammoth, but I know which species derives the most satisfaction from sex. Tangled Up in Blue A note for fossil collectors. Occasionally, Yixian 'mammals' are offered for sale on the open market. Up until now (July 2005), they've all had one thing in common. They're fakes. Some are complete forgeries, while the better efforts are composites of perhaps a few mammalian remains, enhanced with much other microvertebrate material. Just because an offered specimen happens to be composed of fossil bone, it would be hasty to assume it's genuine. Probability suggests otherwise. I'm not going to mention a list of faults with the photographed 'Zhangheotherium' I saw this month, as that could be a useful resource for producing better quality forgeries. However, as a clue, it'd be worth thinking about whether the 'animal' depicted could have ever managed to walk. My understanding of the legal situation isn't extensive. Nevertheless, as things stand, should a genuine specimen somehow make it onto the market, (and that is highly unlikely), it will have been obtained by theft somewhere along the line. No Yixian mammals have ever been granted an export licence. Should you be informed that an appropritate authority, (such as the Institute of Vertebrate Paleontology and Paleoanthropology, Beijing), has verified the fossil, it could well be a good idea to check. This would almost certainly be news to them. Ideally, there should be no market for such fossils. Yixian mammals are far too important for any one person to claim ownership. Further Mesozoic site summaries can be found at Localities. Meet the mammals of the Yixian Formation (13 genera and 14 species) Multituberculata (1 genus) Sinobaatar lingyuanensis Triconodonta (6 genera) Gobiconodon zofiae; Jeholodens jenkinsi; Juchilestes liaoningensis; Meemannodon lujiatunensis; Repenomamus robustus; R. giganticus; Yanoconodon allini 'Symmetrodonta' (3 genera) Akidolestes cifellii; Maotherium sinensis; Zhangheotherium quinquecuspidens Metatheria (1 genus) Sinodelphys szalayi Eutheria (2 genera) Acristatherium yanensis; Eomaia scansoria To be accurate, the Yixian Formation has a number of members. The Repenomamus sisters, Gobiconodon and Meemannodon are from the lower fauna, and this dates to between 128 and 139 million years ago. The other mammal fossils are younger; around 125 million years.

Genus: Mictodon Fox, 1984

Species:	Mictodon simpsoni Fox, 1984
Place:	Upper Milk River Formation, Alberta
Country:	Canada
Age:	Campanian, Upper Cretaceous
Remarks:	Known from a single tooth. The cusp arrangement and slender roots suggest a milk tooth of a spalacolestine symmetrodont. Symmetrodontoides canadensis would be a possibility, seeing as it's known from the same formation, (Averianov 2002, p.712). The holotype, UALVP 16273, is in the collection of the University of Alberta. "Assignment to Tinodontidae is uncertain," (McKenna & Bell, 1997). Quite. That's why I've relocated this entry to Spalacotheriidae.
Reference:	Fox (1984), A primitive, "obtuse-angled" symmetrodont (Mammalia) from the Upper Cretaceous of Alberta, Canada. Canadian Journal of Earth Sciences 21, p.1204-1207.

Link: The University of Alberta http://www.biology.ualberta.ca/wilson.hp/UALVP/UALVPtypelist.html A list of type specimens in the UALVP Collections.

Genus: Shalbaatar Nessov LA, 1997

Species:	Shalbaatar bakht Nessov LA, 1997
Place:	lower Bissekty Formation, Dzharakuduk
Country:	Uzbekistan
Age:	middle-upper Turonian, Upper Cretaceous
Remarks:	Originally, the remains were held to be a multituberculate, which are commonly called Something-or-other-baatar. However: "According to Z. Kielan-Jaworowska (personal communication 2000), the posteriorly placed masseteric fossa excludes Shalbaatar from Multituberculata, because this indicates absence of the "backward masticatory power stroke" that is characteristic of the group", (Averianov 2002, p.713). On re-examination, Averianov identified several features known from spalacotheriids. He places it unreservedly within Spalacotheriidae, and possibly even within the otherwise American subfamily, Spalacotheriinae. He also points to similarities between the Bissekty fossils and those known from the Upper Cretaceous of North America. Several vertebrate taxa are common to both places, including the eutherian mammal Paranyctoides, (p.713-714). A further fragment of toothless dentary has been recovered from the Aitym Formation, (possibly upper Turonian-Coniacian). This formation is about 30 metres above the Bissekty. The second specimen is thus somewhat later than S. bakht, and does display some contrasts. It may represent a different species, but this will only become clear with further and better specimens, (Averianov & Archibald 2003, p.5). Holotype The genus is based on an edentulous fragment of lower jaw, which means it ain't got any teeth left. This is ZIN 82622 and lives at the Zoological Institute of the Russian Academy of Sciences, St. Petersburg.
Reference:	Nessov (1997), Cretaceous Non-marine Vertebrates of Northern Eurasia, (in Russian). University of Saint Petersburg, Institute of the Earth Crust, Saint Petersburg. 218pp. (Posthumous edition by Golovneva LB & Averianov AO.)

Genus: Spalacolestes Cifelli RL & Madsen SK, 1999 'mole-like thief'

Species:	Spalacolestes cretulablatta Cifelli RL & Madsen SK, 1999
Place:	Cedar Mountain Formation, Utah
Country:	USA
Age:	Albian (late) - Cenomanian (early), Upper Cretaceous
Remarks:	This mighty beast probably weighed about four grammes, (two paperclips). A number of mini-teeth are in the collection of the Oklahoma Museum of Natural History, some of which were previously assigned to Spalacotheroides sp. Kirkland et al, 1997. About fifty enigmatic, smaller premolars (and two associated jaw fragments) have also been recovered from this location. They're unusual for Mesozoic mammals, in that they're low crowned, and the probably posterior specimens show a highly molarized form, (Cifelli, 1999 -see Bibliography for details). These are probably milk teeth. They can be confidently grouped into three types, (Taxa 1-3), and probably represent the juveniles of the three spalacotheriids from the local fauna. "Most groups of mammals known from the Cedar Mountain Formation, ( Multituberculate, Triconodonta, Tribosphenida) can be immediately dismissed from consideration, because their dentitions contain no teeth that are remotely similar to those described herein. The only mammalian group known from the Cedar Mountain Formation by taxa of appropriate size, morphology, and abundance is the Symmetrodonta", (p.257-258). The sizes and relative quantities of these teeth correspond closely to those of the three spalacotheriid species, and the fossils come from precisely the same sites. Therefore, the most abundant and middling-sized Taxon 1 probably represents young Spalacolestes cretulablatta; the smaller specimens of Taxon 2, Spalacotheridium noblei; the two larger specimens of Taxon 3, Spalacolestes inconcinnus, (p.260).
Reference:	Cifelli & Madsen (1999), Spalacotheriid symmetrodonts (Mammalia) from the medial Cretaceous (upper Albian or lower Cenomanian) Mussentuchit local fauna, Cedar Mountain Formation, Utah. Geodiversitas 21 (2), p.167-214.

Link: Mussentuchit (OMNH V868) http://flatpebble.nceas.ucsb.edu/nam/listfiles/Mussentuchit_(OMNH_V868).html An inventory of the fossil site.

Species:	Spalacolestes inconcinnus Cifelli RL & Madsen SK, 1999
Place:	Mussentuchit, Cedar Mountain Formation, Utah
Country:	USA
Age:	Albian (late) - Cenomanian (early), Upper Cretaceous
Remarks:	This holotype also lives at the Oklahoma Museum of Nat Hist.
Reference:	Cifelli & Madsen (1999), Spalacotheriid symmetrodonts (Mammalia) from the medial Cretaceous (upper Albian or lower Cenomanian) Mussentuchit local fauna, Cedar Mountain Formation, Utah. Geodiversitas 21 (2), p.167-214.

Genus: Spalacotheridium Cifelli RL, 1990 'small Spalacotherium' A species is also present in the Santonian Straight Cliffs Formation of Utah, (Eaton, 2005 see link).

Link: Santonian mammals from southern Utah..., Eaton JG, 2005 http://gsa.confex.com/gsa/2005RM/finalprogram/abstract_86565.htm An abstract from the 57th Annual Meeting of the Rocky Mountain Section.

Species:	Spalacotheridium mckennai Cifelli RL, 1990
Place:	Cedar Mountain Formation, Utah
Country:	USA
Age:	Albian (late) - Cenomanian (early), Upper Cretaceous
Remarks:	Known from at least two locations.
Reference:	Cifelli (1990), Cretaceous mammals of southern Utah. III. Therian mammals from the Turonian (early Late Cretaceous). J. Vert. Paleontology. 10, p.346-360.

Link: Vertebrate Paleontology in Utah, Medial Cretaceous vertebrates from the Cedar Mountain Formation, Emery County, Utah: the Mussentuchit local fauna Vertebrates from the Cedar Mountain Formation An extensive report on fossil vertebrates from Cifelli & Co. This is the text version of a pdf file, from the Utah Geological Survey.

Species:	Spalacotheridium noblei Cifelli RL & Madsen SK, 1999?
Place:	Cedar Mountain Formation, Utah
Country:	USA
Age:	Albian (late) - Cenomanian (early), Upper Cretaceous
Remarks:	A seriously small creature, with an estimated bodyweight of about 2,5 grammes. This species was named in honour of the Noble Foundation, in recognition of financial support. Remains can be admired at the Oklahoma Museum of Nat Hist. A microscope would be useful. The fauna from this locality is known as the Mussentuchit local fauna, (Cifelli 1999, p.247-248). About 80 vertebrate taxa have been identified on hand of over 7000 specimens, over a thousand of which are mammalian, (p.257). These are still subject to studies, but there are more than 20 species. These include multituberculates, triconodontids, spalacotheriids and various tribosphenic critters. Amongst these are Kokopellia, which may be an early metatherian. A radiometric dating suggests the remains are about 98 million years old.
Reference:	Geodiversitas

Link: The Daily Ardmoreite http://www.ardmoreite.com/stories/092999/new_dino.shtml 'Dinosaur now a 'Noble' creature'. This is a good, readable report. Mussentuchit, I’m delighted to discover, was named with reference to the local water, which is rich in alkaline and undrinkable, (Musn’t-touch-it). If only the inflictor of the atrocious headline had been a twentieth so inspired.

Genus: Spalacotherium Owen R, 1854 'mole-like beast' Aka: Peralestes Owen R, 1871 Remarks: Based on the evidence provided by Zhangheotherium, Peralestes appears to represent the upper teeth of Spalacotherium, which enjoys seniority. (This is included in the link to Z. by Hu et al, 1997). S. & P. are known from the same Dorset site. Reference: Owen (1854), On some fossil reptilian and mammalian remains from the Purbecks. Quarterly Journal of the Geological Society of London 10, p.420-433. Apparently, a further publication from the same year is Owen (1854), Discovery of Spalacotherium in the Purbeck beds. Bull. Soc. géol. France XI (2), 482.

Reassigned species: S. minus Owen, 1854 see Peramus tenuirostris

Species:	Spalacotherium tricuspidens Owen, 1854
Place:	Durlston Bay, Dorset, and Wealden, Hastings Beds
Country:	England
Age:	Lower Cretaceous
Remarks:	This creature was something like 15cm long and is known from several lower jaws. Collectively, these preserve the teeth from the canine to the m6, (Sigogneau-Russell & Ensom, p.459). The holotype works at The Natural History Museum in London. It's known to its friends as BMNH 46019, (Gill, 2004) and is part of a dentary.
Reference:	Owen (1854), On some fossil reptilian and mammalian remains from the Purbecks. Quarterly Journal of the Geological Society of London 10, p.420-433.

Links: Dr Ian West, Purbeck Type-Section, Durlston Bay, Middle Purbeck Strata http://www.soton.ac.uk/~imw/durlmid.htm Spalacotherium is mentioned in this extensive geological report. Dr Ian West, Jaws and Teeth from Beckles' Mammal Pit http://www.soton.ac.uk/~imw/gif/pujaw.gif A sketch of S. tricuspidens and a couple of friends.

Species:	Spalacotherium longirostris (Owen, 1871)
Aka:	Peralestes longirostris Owen, 1871
Place:	Durlston Bay, Dorset
Country:	England
Age:	Lower Cretaceous
Remarks:	Peralestes appears to represent the upper dentition of Spalocotherium. The type specimen seems to reside in the Natural History Museum, London. It's an upper jaw and shows the teeth P3-M6, (three premolars and six molars), though they have been slightly damaged, (Sigogneau-Russell & Ensom 1998, p.459).
Reference:	Owen (1871), Monograph of the fossil Mammalia of the Mesozoic formations. Palaeontographical Society 24, i-vi +, p.1-115.

Link: The Peabody Museum, Yale Vertebrate Paleontology Catalogue http://www.peabody.yale.edu/cgi-bin/Get.Specimen?vp.PU.17219-Peralestes.sp A model is in the collection of the Peabody Museum. They also have cast material of Spalacotherium sp. This is in part ascribed to the Bathonian of Oxfordshire, which seems extremely odd.

Species:	Spalacotherium taylori Clemens WA & Lees PM, 1971
Place:	Wealden, East Sussex
Country:	England
Age:	Lower Cretaceous
Remarks:	Known from a single, and very small tooth. It's a lower molar with a complete labial cingulum, which is a shelf-like bump on the side, (Ensom & Sigogneau-Russell 2000, p. 774).
Reference:	Clemens & Lees (1971), A review of English Early Cretaceous mammals. In Early mammals (eds Kermack DM & Kermack KA). Linnean Society of London 50, (Supplement I to the Zoological Journal), p.117-130.

Wealden mammals, Southeast England - Lower Cretaceous The following is very loosely based upon part of Clemens WA, 1963. The Weald is an area in southeast England. In the nineteenth century, geologists found a sequence of rock layers were particularly well exposed there, and took to calling them Wealden. These rocks, (which are in places generous suppliers of fossils), were deposited during the Lower Cretaceous. A more precise age was difficult to pin-point. In the paper by Clemens they're referred to as pre-Aptian. More recent research indicates they're Valanginian - Berremian (132 - 121 million years ago). There can be little room for dispute about the most widely known Wealden genus. Iguanodon was first named in 1825 on the basis of sparse fossils from Sussex. Better material turned up in Belgium in 1878. For some reason, the discovery of forty of the things in a coalmine was deemed somehow newsworthy. This was clearly blown out of all proportion, as not all of them were complete. Iguanodon became a global celebrity, and that just goes to show the power of advertising. I could write more about this animal but who wants to be bored by ten metre dinosaurs? Animals with far more personality were living in the ancient Weald, and you don't need telling they were mammals. Remains are ever so slightly less than complete, but Clemens reported on ten undoubtedly Mesozoic mammalian specimens and a few of less certain pedigree; all of them teeth. In keeping with this tasteful minimalist approach, I should mention that I haven't got a complete copy of his paper. I'm restricted to a few pages. Still, some is better than none. I also have the benefit of some subsequent studies by other authors. Bone Beds As well as being very rare, mammalian fossils from the Wealden are difficult to find due to their tiny size. Further complications are provided by the elusiveness of the source rock, and the temperamental nature of the eroding cliffs. Promising spots can disappear due to collapses. With perseverance and luck, the Cliff End Bone Bed can be found near Hastings in Kent, which is immediately east of Sussex. This mighty layer of hard and coarse-grained sandstone can attain thickness of over ten centimetres, but not much over. (Clemens states: "never more than 4 or 5 inches thick".) Despite that apparent paucity, researchers still managed to collect up an impressive quantity of rock to process; several hundredweight. (Considerably more was subsequently worked through.) Processing the rock involved the use of diluted formic acid for dissolving extraneous material. The remainder was then washed, dried and sieved through differently sized meshes. Smaller particles then required further chemical treatment prior to examination. This yielded five mammalian teeth. A second location, the Paddockhurst Bone Bed, donated three further specimens in 1960. (More detail on the processing is given below.) Clearly, a great deal of muscle work must have been required. Furthermore, as these fossils are a millimetre or so in length and had to be picked from among loads of other tiny things, it's obvious that an enormous amount of intense concentration was also called for. It sounds like a lot of trouble for a few teeth It does, but the research didn't only turn up mammal fossils. At the time, this was the only known source for mammals of this age in the world. Upper Jurassic specimens were known from the Morrison Formation of North America and, (as interpreted at the time), Dorset in England. (The Purbeckian of Dorset is now thought to be lowermost Cretaceous.) Apart from the two teeth found previously in Kent, the next oldest fossils were from the Trinity Sand of Texas, (Albian). This left a gap in the record of around 30 - 35 million years, and the Wealden provided the chance of partly bridging it. A brief history: some right, some less so The first announcement of a Wealden mammal was made in 1891 by A Smith-Woodward. I've heard he was good when it came to fossil fish, but not so sure with us hairy animals. One of Smith-Woodward's later publications was Eoanthropus, the notorious 'Piltdown Man' forgery. Smith-Woodward wrote about a specimen from the collection of the Natural History Museum, London (BMNH M13134). He interpreted it as a molar from Plagiaulax, a multituberculate. Subsequently, the tooth suffered damage, and all that's left is a bit of root. The identification was less than convincing and, as far as can be told, it's probably not mammalian. Lydekker published further news in 1893. He assigned an incisor, (BMNH M5691), to Multituberculata. This was done with the observation that it was indistinguishable from the corresponding tooth of a rodent. As rodents had never been found in the Lower Cretaceous, he concluded it was most likely from a multi. More specifically, the incisor resembles those known from Theriodmys so closely, that's probably what it is. The problem here is provenance. The fossil was found in a block among a heap of stone on the shore, and then spent three decades neglected in a private collection. Doubts were expressed as to whether the remaining matrix was from the locality. Although it was said to have been encased in Tilgate Grit, this was incorrect. That would be sandstone. As GG Simpson pointed out in 1928, the matrix was crumbly clay. The block of stone was presumably transported. This could have occurred due to either tidal action or as a consequence of road building. Smith-Woodward described three further specimens in 1911. These were collected by Teilhard de Chardin and Peiletier at Cliff End, and two are from Wealden mammals. The bone bed of origin couldn't be found at the precise location in 1960. Cliff erosion had very possibly either destroyed or buried it. BMNH M10480 is the holotype of Loxaulax valdensis. BMNH M10481 is part of a lower molar, (m2), and probably from the same species. The third tooth wasn't catalogued, but the short description matches what's now BMNH M20241, which was collected in 1911 near Hastings. This is regarded as indeterminate and not clearly mammalian. Until collecting resumed in 1960, remains of undoubted mammals from the Wealden (and much of the Lower Cretaceous) were limited to two molars of Loxaulax valdensis. In the terminology of Clemens (1936), the new finds provided further information on that species, and attested to the presence of a symmetrodont and a eupantothere. Unfortunately, my partial copy preserves no further details. Kermack et al, 1965 provides further information on the locality, and goes into events Clemens had departed. A water bed? The Cliff End bonebed may well be in the sea, which would account for difficulties with precisely locating it, (p.536). Bits of it are most commonly found on the beach following spring and autumn storms. These can be enthusiastic. In one instance, a block weighing a couple of tons was left balancing on a ledge about three metres up the cliff face. The location was rediscovered by Professor P Allen and collecting recommenced in 1960. That's when Dr Clemens arrived on a post-doctoral placement at the University College of London. Of the five mammalian specimens recovered between then and the autumn of the following year, four teeth were from multis and the other was an upper molar at least allied with Laolestes (Melanodon). Fieldwork continued, (p.537). The Paddockhurst Park locality proved to be very limited in scope and was probably exhausted. All attentions turned to Cliff End and nine more teeth were recovered. One of them was immediately recognised as something special. This was Aegialodon, a close relatives of animals such as myself and a wombat. The rock In line with the information above, the fossils are reported as coming from a layer of rough sandstone with a thickness of between 5 and 12.5 centimetres. Ripple marks show which side was up. The grains are of variable sizes; 0.24 to 5 millimetres in diameter, and the black fossils are of similar dimensions. Ancient conditions This material was probably deposited in a brackish area, where fresh and salt waters chose to network with each other. A river estuary is a good candidate. The London Platform was being drained by rivers flowing southwards, and that land may have been home sweet home for the terrestrial vertebrates. They surely didn't live in the sea. Various fish account for 90% of the recognisable vertebrate fossils, and most come from Lepidotes mantelli. Pycodont teeth are well represented, and 15 to 20% of fossils have been contributed by sharks; at least four species of hybondont. In percentage terms the mammalian contingent doesn't merit a quiet squeak. Bits of reptile are more common. However, quality is of great importance. How to find Wealden mammals First catch your rock. That's the relatively straightforward part. The grains and fossils are held together by a calcareous cement, and it needs dissolving, (p.538). A solution involving 10% formic acid is a good option. It's: relative speedy, easier to clean off, and not as poisonous as other possibilities. Speedy in this context means a block of about 75cm² with a thickness of 10cm will require a mere two or three months of continual submergence in order to disintegrate. (The figures in the paper are in inches; 12 square inches and 4 inches thick.) Continual submergence isn't quite meant literally, as the acid periodically gets tired and needs replenishing. Blocks were removed and washed when bubbling stopped, and any loose material was collected. This spent a day in running water to cleanse off any calcium salts and silt. Such impurities can cause damage and clogging when sieving. The rock was then placed in fresh solution and so on and so forth. Eventually, the block was fully dissolved and sorting could begin. Sieves After cleaning the loose material required light baking to dry it (60°F). It was then sent through a set of three sieves with differing meshes, (approximately between 2.4mm down to 0.42mm). Anything passing through the whole series was discarded. Elements as substantial as about 1.4 millimetres and larger were sorted purely by eye and hand. However, most material wasn't as large. It was also mixed in with a lot of quartz. Sink or swim The fossils are denser than most the other material, and that quality caused them to sink more eagerly. Fossils and much unwanted debris can thus be sorted by floatation. In this case, the floatation liquid was a mixture of tetrabromoethane and dibromoethane, and this was a relatively cheaper option. The drawback is the poisonous fumes. A fume cupboard, a convenient draft and as little exposure to the toxins as possible helped minimalize danger to researchers. (They can be difficult to replace.) It's now time to add your debris and stir, (preferably without breathing in). In the unlikely event that the liquids are mixed to the correct proportions, the fossil fragments and some extraneous material will obligingly sink. The mixture will more probably require refining adjustments. This procedure left 95% of the loose material on the surface to be sieved off. All of that is rubbish. Now add more material. Drying Eventually, there'll be a satisfying quantity of heavier material in your toxic soup, (p.539). This can be retrieved and bathed in pure alcohol, which both limits exposure to the fumes and allows as much as possible of the floatation liquid to be recycled. ('Relatively cheaper' still meant expensive.) The lighter material was also treated for similar reasons. As a further detox stage, both accumulations were left to dry at their leisure. The uninteresting rubbish, (95% of the total), could then be disposed of. The potentially interesting 5% was left for to air for two more days. Efficiency As is clear, this entire process is intensely time consuming and sounds amazingly dull in comparison to prospecting á la Jurassic Park. It was the most efficient means available. Finding tiny teeth can require sorting through extraordinary quantities of rubbish. And now for the laborious bit... Having isolated and detoxified the heavier material, each seriously small particle requires looking at individually. This is best done with the help of a numbered grid of squares as a background for orientation and a good microscope. Afterwards, the researchers may be left wanting to bathe in alcohol. The following informal list of Wealden mammals has come from subsequent sources. Further Mesozoic site summaries can be found at Localities. Meet the Mammals of the Wealden (Lower Cretaceous) (4 genera, 5 species) Multituberculata (1 genus, 1 species) Loxaulax valdensis Dryolestoidea (1 genus, 1 species) Laolestes (Melanodon) hodsoni 'Symmetrodonta' (1 genus, 2 species) Spalacotherium taylori; S. tricuspidens Boreosphenida (1 genus, 1 species) Aegialodon dawsoni

Species:	Spalacotherium henkeli Krebs B, 1985
Place:	Castellar Formation, Galve
Country:	Spain
Age:	lower Barremian, Lower Cretaceous
Remarks:	This species is based on a few cheek teeth. These somewhat larger than those of the other species, (Sigogneau-Russell & Ensom 1998, p.459).
Reference:	Krebs (1985), Theria (Mammalia) aus der Unterkreide von Galve (Province Teruel, Spanien). Berliner Geowissenschaften Abh., Reihe A 60, p.29-48.

Species:	Spalacotherium evansae Ensom P & Sigogneau- Russell D, 2000
Place:	Durlston Bay, Swanage, Dorset
Country:	England
Age:	Berriasian, Lower Cretaceous
Remarks:	The following is based upon my reading of Ensom & Sigogneau-Russell, 2000, (with thanks to the kindly supplier). The Purbeck Limestone Group of southeast Dorset was the second source of Mesozoic mammals discovered in the world. Only the Forest Marble Formation in Oxfordshire began work earlier, (and that also occurs in west Dorset). Descriptions of Purbeckian mammals from Durlston Bay near Swanage date back to 1854. A new inland site was discovered roughly five kilometres west at Sunny down Farm in 1986, (p.767). Among the finds are fossils assigned to both Spalacotherium and Tinodon. Most came from two strata of the Cherty Freshwater Member at Sunnydown. Four additional specimens had been recovered at Durlston Bay. S. evansae The new species is represented by a fragmentary partial lower right jaw and remains of a further thirty or so isolated teeth, (p.768). As well as being smaller than their equivalents in S. tricuspidens and S. henkeli, they differ in the incompleteness of the labial cingulum, and the even greater equality of root size (as far as can be told). The incomplete cingulum is also a distinction from the only known specimen of S. taylori, which falls within the size range of this species. Some of the molars have a tinodontid-like cuspule f. A pipsqueak The jaw fragment is 3.7 millimetres long, and the molar lengths run from 0.37 to 1.1mm, averaging out at around 0.73, (Table 1, p.769). This was a seriously small mammal. Jaw The front of the fragment contains two alveoli for roots, with the second being a bit longer than the foremost, (p.770). Next in line is a complete molar. The protoconid is tall and thin. The paraconid was probably not as high as the metaconid, but the latter cusp is broken. The tooth has a lingual cingulum which features a cusp e and cusple f at the front. The rear of the crown possesses a low, sharp hypoconulid cusp. The remnants of the roots suggest similar sizes and the division is halfway along the paraconid. The next molar has lost most of its crown, but it was considerably smaller. The third preserved tooth is even tinier. It shares a suite of characteristics with the final molar of Spalacolestes. Referred teeth Most specimens are fragments. Among them are lower and upper molars. Four were found to probably represent juvenile gnashers: "They are very thin transversely, with particularly long and thin roots", (p.773). But: "Whether these milk teeth belong to Tinodon or Spalacotherium is uncertain; however, the similarity with the tooth from Galve, where S. henkeli was identified (Krebs, 1985), has led us to prefer the latter attribution." Lower molars of 'symmetrodonts' typically feature two similarly sized roots, a lingual cingulum and a small, sharp hypoconulid. The labial cingulum of these teeth, (albeit partial), the compressed trigonid and the sharp high protoconid are signatures of Spalacotherium. Generally, spalacotheriids favoured a complete labial cingulum, (p.774). However, that also doesn't apply for Spalacotheroides or Zhangheotherium (if so classified). The abstract is linked to Tinodon micron, (above). Holotype The holotype, DORCM GS 355, is in the collection of the Dorset County Museum, Dorchester. The specific name honours Dr Susan Evans, "in recognition of her major contribution to the discovery and study of Mesozoic microvertebrate remains in Great Britain."
Reference:	Ensom & Sigogneau-Russell (2000), New symmetrodonts (Mammalia, Theria) from the Purbeck Limestone Group, Lower Cretaceous, southern England. Cretaceous Research, vol 21, no 6, p.767-779.

Link: The Dorset County Museum Geology Department http://home.clara.net/dorset.museum/page9.html Nostalgia break: I wasn't very old when I first went to this museum. It's full of stuff on the archaeology, history, culture, geology, paleontology, natural history and etc of Dorset. Dino footprints; Thomas Hardy memorabilia; ichthyosaurs; an old font from the church of Melbury Bub, which is where I'm reliably informed my father was baptized; dead people from the old days and stuffed animals from the surrounding countryside. We took our daughter along when she was about three. A couple of German tourists were struggling somewhat with reading the stuffed animal labels. Our daughter, who's Anglo- Deutsch, childed around the room with great enthusiasm, gleefully announcing "Fledermaus - bat. Fuchs - fox. Dachs - badger..." The German tourists were much astounded and stopped struggling. On leaving the museum, turn right and walk a couple of hundred yards further up the road. The 17th century Old Tea House does a great cream tea.

Species:	Spalacotherium hookeri Gill, P, 2004
Place:	Durlston Bay, Dorset
Country:	England
Age:	Berriasian, Lower Cretaceous
Remarks:	The following is based upon my reading of Gill, 2004, Most Purbeckian Mesozoic mammals were either collected in the 1850s or since the late 1980s, (p.748). This one was found by the author in 1969, but further searching of the precise location hasn't turned up more material. It's probably marginally older than S. evansae, as it came from a slightly lower layer of rock. The main difference from the type species, S. tricuspidens, is size. The new species is 40% or so smaller, although both individuals were adult. Distinctions to the other species are stronger, and include details of the molars. The only specimen is part of a lower left jaw with the rear five molars in place. The last in the series is the smallest tooth. Along with its distinctive shape, this allows a confident identification of it as being the m7. (This genus has seven lower molars.) Consequently, the foremost preserved tooth must be the m3. An alvelous attests to the former presence of the m2, and that pair were of similar size. Also included in the paper are descriptions of four isolated teeth from the Wealden strata of southeastern England. These fossils were found some decades ago, and also belong to the genus, (p.749-750). One may be a deciduous, lower premolar. The trigonid has an obtuse angle and the enamel is relatively thin. Although the teeth of this species are similar in form to S. tricuspidens, there are a couple of differences on the jaw, (p.751). In the new species, Meckel's groove extends further forward until at least below the m2. Behind the final molar, a feature termed the coronoid process seems to ascend more gradually. However, crushing could have provided some distortion, and the features may represent variation in individuals. Further specimens would be required to show whether these characteristics are of diagnostic value. Considering they've been dead for a long time, spalacotheriids and friends seem to be breeding profusely at present. (Thanks are due to the supplier of the paper.) The holotype, BMNH 44970, resides at The Natural History Museum, London, where Dr Jerry Hooker can also be found. The specific name is in recognition of his contributions to the study of fossil mammals. Judging by the photo, the holotype's a bit over half a centimetre long.
Reference:	Gill P (2004), A new symmetrodont from the Early Cretaceous of England, Journal of Vertebrate Paleontology, 24(3), p.748-752.

Genus: Spalacotheroides Patterson, 1955 'Spalaco form'

Species:	Spalacotheroides birdwelli Patterson, 1955
Place:	Paluxy Formation, Texas & Massentuchit, Utah and Wyoming
Country:	USA
Age:	Lower Cretaceous - Upper Cretaceous (early)
Remarks:	According to Cifelli et al, 2000, this is a nomen dubum. Several specimens, including the holotype, live in the collection of the Peabody Museum, Yale.
Reference:	Patterson (1955), A symmetrodont mammal from the Early Cretaceous of northern Texas. Fieldiana. Zool. 37, p.689-693, fig. 145.

Link: Certaceous Dinosaur Faunas of the Central Colorado Plateau http://www.dinosaurweb.com/papers/cretaceous/table3.htm The Mussentuchit fauna list of Dinosaur Web.

Genus: Symmetrodontoides Fox RC, 1976 'symmetrodont form' Remarks: The latest known and most specialized North American spalacotheriid genus, if that's where this genus belongs. JF Bonaparte has apparently expressed the opinion that this taxon belongs within Dryolestida, (with thanks to Mikko Haaramo for the notification.) McKenna & Bell give Fox, 1976 as the year of description. I'm sure they have their reasons and they're probably correct. Averianov confirms this. I have also seen 1979 cited. Reference: Bonaparte (1999), New Dryolestida (Theria) from the Late Cretaceous Los Alamitos Formation(Argentina)and paleogeographical comments. in Leanza HA, (ed.) 1999: Abstracts of VII Int. Symposium on Mesozoic Terrestrial Ecosystems. Buenos Aires, A1-A65

Species:	Symmetrodontoides canadensis Fox, 1976
Place:	Upper Milk River Formation, Alberta
Country:	Canada
Age:	early Campanian, Upper Cretaceous
Remarks:	This holotype, UALVP 8588, is a partial right dentary in the collection of the University of Alberta. There are a couple of lower jaw fragments with teeth in situ, (Sigogneau-Russell & Ensom 1998, p.461).
Reference:	Fox (1976), Additions to the mammalian local fauna from Upper Milk River Formation (Upper Cretaceous), Alberta. Canadian Journal of Earth Sciences 13, p.1105-1118.

Species:	Symmetrodontoides foxi Cifelli RL & Madsen, 1986
Place:	Wahweap Formation & Paunsaugunt Plateau, Utah
Country:	USA
Age:	Santonian (late) or Campanian (early), Upper Cretaceous
Remarks:	Weighed about four paperclips, (8g). The type fossil, a lower molar, is housed at the Oklahoma Museum of Nat Hist.
Reference:	Cifelli & Madsen (1986), An Upper Cretaceous symmetrodont (Mammalia) from southern Utah. J. Vert. Paleont. 6, p.258-263.

Link: A New Vertebrate Fossil Locality Within the Wahweap Formation (Upper Cretaceous) of Bryce Canyon National Park and Its Bearing on the Presence of the Kaiparowits Formation on the Paunsaugunt Plateau http://www2.nature.nps.gov/geology/paleontology/pub/grd3_3/brca1.htm An interesting article by Eaton JG, Munk H, & Hardman MA. This relates to finds made in 1997.

Species:	Symmetrodontoides oligodontos Cifelli RL, 1990
Place:	Straight Cliffs Formation, Utah
Country:	USA
Age:	Turonian, Upper Cretaceous
Remarks:	The holotype, also in Oklahoma, is a corroded right lower molar. According to Sigogneau-Russell & Ensom, 1998, this is an even smaller species, (p.461).
Reference:	Cifelli (1990c), Cretaceous mammals of southern Utah. III. Therian mammals from the Turonian (early Late Cretaceous). J. Vert. Paleontology. 10, p.332-345.

Genus: Symmetrolestes Tsubamoto T, Rougier GM, Isaji S, Manabe M & Forasiepi AM, 2004 'symmetric hunter'

Species:	Symmetrolestes parvus Tsubamoto T, Rougier GM, Isaji S, Manabe M & Forasiepi AM, 2004
Place:	Kitadani Formation, Fukui Prefecture
Country:	Japan
Age:	Barremian?, Lower Cretaceous
Remarks:	The following is based upon my reading of Tsubamoto et al, 2004. Following the establishment of Zhangheotheriidae for the 'symmetrodonts' of Liaoning late in 2003, Shalbaatar was left on its own as the only Asiatic member of the sister family, Spalacotheriidae. To avoid feelings of isolation Japan agreed to yield this new genus as a companion. The complete shearing surfaces, higher crowns and fuller cingulids of the lower molars mean it's more advanced than the Chinese zhangheotheriids, (p.329). However, it also differs from its closer relatives in the presence of more lower premolars (five) and less molars (four). In addition, the transition between the two types of tooth is more gradual. The presence of both this relatively basal spalacotheriid and zhangheotheriids in East Asia prompts the authors to raise the possibility of Asiatic origins for Spalacotheriidae. If correct, then this would imply a presently unevidenced history stretching back to the Jurassic. Remains presently consist of a lower right jaw, which was found in a block of stone in central Japan, (p.330). This also contained a fragment of bone, bits of egg shell and the tooth of an iguanodont dinosaur. The age is not absolutely clear, but Barremian is at least likely, (p.331). The specimen is fragmentary and preserved in two pieces. As they were prepared from opposing sides, re-assembly is made difficult. Five teeth are present. These are probably the final premolar (p5) and four molars (m1-m4). However, this diagnosis is based upon the shape of the teeth as evidence regarding replacement patters is lacking. The premolar has a length of just over a millimetre. The molars range from about 0.6 (m4) to 0.7mm. Family concerns Page 332 offers a revised diagnosis for the family. Differences to other 'symmetrodonts' include: the strong pterygoid crest on the dentary and a wide and upright coronoid process. The postcanine teeth have a continuous shearing crest and high crowns. The lower molars contain reduced talonids and near continuous cingulids on the buccal and lingual sides, with that latter characteristic being lost in Spalacotheroides. Dentition As well as the teeth, the jaw also contains alveoli for further gnashers. Nine holes are complete with three other probables, (p.333). The likely lower dental formula was four incisors, one canine, five premolars and four molars, (although i3+ and p4+? is safer -p.334). The first incisor is pretty much horizontal. As it doesn't protrude beyond the front of the jaw and lacks wear, this was probably unerupted and is visible due to a convenient break in the bone, (p.335). The best preserved tooth is the final premolar, (p5), but it's damaged. As premolars go, it's relatively complex. Of the molars, m4 is the smallest and simplest. It was probably single-rooted. Although upper teeth aren't known, its structure suggests if there was an M4 counterpart, then it was most likely to have been much reduced, (p.336). Postcanine peculiarity With spalacotheriids in general, molars tend to be more generously supplied than premolars, (p.337). However, although the p5 in this case can be reasonably termed molar-like, it seems to be a premolar and resembles what was originally termed the m1 in Zhangheotherium. That interpretation was doubtful for a couple of reasons. Firstly, the tooth was much less worn than its colleagues which suggests it was more recently erupted. Secondly, an additional specimen has been found which shows replacement occurring at that position. That's very un-molar-like behaviour. Among Spalacotheriidae, a more usual number of premolars is three, (p.339), while molars go up to seven. If Symmetrolestes does possess five and four respectively, this may be a reflection of its relatively primitive position within the family. The holotype, NSM PV 20562, is a resident of the National Science Museum, Tokyo. The specific name is Latin for 'small'. As the fossil has a length of roughly 1.8cm, mouse-sized shouldn't be too misleading.
Reference:	Tsubamoto et al (2004), New Early Cretaceous spalacotheriid "symmetrodont" mammal from Japan. Acta Palaeontologica Polonica, 49 (3), p.329-346.

Link: Acta Palaeontologica Polonica, Tsubamoto et al, 2004 http://app.pan.pl/acta49/app49-329.pdf The description is on-line and freely accessible.

Genus: Yaverlestes Sweetman SC, 2008

Species:	Yaverlestes gassoni Sweetman SC, 2008
Place:	Wessex Formation, Isle of Wight
Country:	England
Age:	Barremian, Lower Cretaceous
Remarks:	The paper has arrived and is being read. Thanks are due to David N. Remains include a partial dentary and some isolated teeth. In contrast to other euro-spalacos, this one fits within the presently largely North American subfamily of Spalacolestinae.
Reference:	Sweetman SC (2008), A spalacolestine spalacotheriid (Mammalia, Trechnotheria) from the Early Cretaceous (Barremian) of southern England and its bearing on spalacotheriid evolution, Palaeontology, 51(6), p.1367-1385.

Genus: Zhangheotherium Hu Y, Wang Y, Luo Z & Li C, 1997 'Zhang He’s beast' Family: Zhangheotheriidae Rougier GW, Ji Q & Novacek MJ, 2003 Remarks: The generic name honours Mr Zhang, who both harvested and generously donated the holotype from his personal collection of fossils. He has reportedly donated all his extensive collection to one institution or another. The genus briefly summarised: "Its hands, however, have relatively short, straight fingers, with gently curved, broad claws.", (Weil, 2002), the inference being that it was a moderate ground dweller-clamberer by habit, rather than any kind of arboreal acrobat.

Species:	Zhangheotherium quinquecuspidens Hu et al, 1997
Place:	Jiansahngou Beds, Yixian Formation, Liaoning
Country:	China
Age:	Barremian, Lower Cretaceous
Remarks:	The following is based upon my reading of Hu et al, 1997. Until this publication, 'symmetrodonts' had been subjects of plenty of studies, but the available evidence was severely restricted to occasional fragments of jaw and isolated teeth. Naturally enough, this left much room for speculation. Teeth are generally a good indication of favoured foodstuff, and so a diet based largely upon creepy-crawlies was a safe enough conclusion. The small size of the teeth, (molars with lengths of about a millimetre or so), and the jaw fragments suggested animals of roughly shrew- or mouse dimensions, rather than anything likely to rival dinosaurs. However, the rest of the anatomy was hypothetical; presumably more derived than basal mammals, but less so than ones with tribosphenic or near-tribosphenic teeth. (This is ignoring australosphenidans, as that concept postdates this description.) Mr Zhang, an experienced and self-taught amateur, stepped in where professionals hadn't managed to tread, and changed the state of knowledge. He found a specimen more complete than anybody had probably ever dared to dream of, and donated it for study, (p.137). Aptly, there's now a family named in his honour. The first specimen consisted of a near complete skeleton, a partial skull and teeth. This allowed the hypothetical expectations to be tested, and they were pretty accurate. In the terminology as used in the paper, the animal was an 'archaic therian', although this project uses Theria in a more restricted sense. (The nearest equivalent term I presently employ is Holotheria.) Getting the measure of things As a table of lengths is provided, it would be churlish not to mention some. The dentary is a bit over three centimetres. This is longer than the corresponding element in the Liaoning eutherian, Eomaia. Taking a shot in the arm, the humerus measures 2.2cm, the ulna half a millimetre less, and the radius 1.7cm. The legs are a bit longer: femur 2.2cm, tibia and fibula 2.35cm. For the teeth, the lower molar lengths range from 1.1 to 1.8 millimetres (1.5 is the mean), and the uppers (M3-M5 only) 1.6 to 1.8mm. There are six lowers. Ignoring the less well represented tail, the complete animal had a length of about fifteen centimetres, (nose to other end). This is actually quite large compared to many 'small' insectivores. (The bodylength is based on the sketch and photos on page 138.) Family concerns Although originally assigned to Spalacotheriidae, a new family was established in 2003; Zhangheotheriidae. Its members are more basal than spalacos, even the earlier ones. ["The Chinese Zhangheotherium, having rounded, conical molar cusps that lack connecting crests (Hu et al. 1997), apparently did not achieve the dental specialization characteristic for Spalacotheriidae... and should be excluded from this taxon, although it may be a sister taxon to Spalacotheriidae", (Averianov 2002, p.713).] Teeth The dental formula per side is given as: (uppers): 3 incisors, 1 canine, 2 premolars and 5 molars; (lowers): 3, 1, 2 and 6 (5 is correct) respectively. Dental formula updates However, Tsubamoto et al, 2004 (p.339) suggests the holotype has five lower molars rather than the six originally described. The front-most is likely to be a premolar. In a subsequently identified specimen, it was in the process of being replaced. Another possibility is that the holotype could be a juvenile and not in possession of a complete set of adult teeth. The closely related Maotherium has six molars, the final one of which is extremely reduced in size. Wang et al, 2006 (p.197) has the lower formula revised to 3, 1, 3, 5 -not 6, but the revison isn't their doing. They do see a further complicating factor. In terms of its construction, the 'premolar' presently designated as p3 is similar to the molars, and there's a possibility it's actually the first of those teeth. This uncertainty reflects the fact that, in contrast to extant mammals, some more basal versions replaced at least some 'molars'. Returning to the original description, (p.138), the lower molars have relatively robust and rounded main cusps. The uppers also differ in that a cusp termed B' is hypertrophied; ie particularly big. That doesn't mean it's anything like the largest cusp on the tooth. The central cusp, (A or a respectively), dominates the crown. Referring to the lower molars, (p.139): "Zhangheotherium resembles other known spalacotheriid symmetrodonts... in that the central cusp (a) and the two accessory cuspules (b,d) of the lower molar form an acute triangle. [I suspect the accessory cuspules are actually b and c, rather than d.] The associated upper and lower teeth of Zhangheotherium could occlude into the embrasures of the opposing tooth row, a pattern unique to spalacotheriids among archaic therians... This suggests that the teeth were used more for crushing and puncturing than shearing..." (The omissions are reference number, 'spalacotheriids' includes what are now zhangheotheriids, and 'archaic therians' equates to holotherians in this project.) Judging by the sketch, the other lower teeth are fairly unremarkable. The first incisor is a couple of millimetres in height, and slants forwards and upwards. The other two are about half the size. The canine's fairly tame. Seen from the side, the profile of the premolars is roughly triangular. They're about the same height as the canine and molars. They're nothing like the morphology of the tooth designated m1. However, should it be a premolar, it must be a deciduous one. They typically have more complex crowns. Implications for Dorset The cusp pattern of the upper molars is reminiscent of Peralestes. As mentioned in the text to Figure 2, (p.138), the lowers are more similar with Spalacotherium. These Purbeckian genera are known from the same Dorset location, and only from upper and lower material respectively. By inference, there's a strong probability that the fossils represent only one genus. However, probability and certainty aren't the same. Lower jaw development "The dentary has a dorsally curved condylar process and a posteriorly tilted coronoid process", (p.139). There is no angular process, and that lack is old fashioned. I appreciate many people will have little idea what these 'processes' might be. In this instance, they're particular branches of the lower jaw, and they serve some function or other. Anchoring points for muscles is a common use. An angular process can often be found low down on and towards the rear of mammalian dentaries. However, it emerged in animals more derived than this genus. Characteristics typical of existing mammals didn't arrive as a single package. They evolved at various times. There are other features of this lower jaw which won't be found in modern mammals. There's a channel on the inside called the Meckelian groove. In this case, it's narrow and becomes shallower and fainter towards the front. A rugose area along the anterior of the groove could indicate the presence of an 'extra' bone known as a splenial, and a rough area at the base of the coronoid process is consistent with the retention of a poorly developed coronoid bone. It's often stated that mammalian lower jaws are composed of a single bone called the dentary, and this is now the case. Relatively early non-mammalian synapsids had lower jaws made from up to eight separate bones per side. (Between four and six are still popular with reptiles, including birds who generally favour five, Sidor 2003, p.605.) During synapsid history, most these bones gradually faded and then vanished, or were relocated, but this took time. Multi-boned lower jaws were still in use by some mammals of the Cretaceous. Dryolestidans may be anatomically more derived than spalacos and zhangheoteriids, (although there's no consensus on this as yet). At least in the case of Henkelotherium, a much reduced coronoid bone has been inferred as still present. Ears In mammals, the inner ear is encased in one bone called a petrosal, and this seems to be universal across Mammalia. The cochlea is housed in a feature termed the promontorium, and the shape provides an indication as to the form of its contents. In more derived mammals, the promontorium is oval and bulbous. This allows room for a cochlear canal which is coiled by at least 270°. In Zhangheotherium, Sinoconodon, morganucodontids, triconodonts and multituberculates, this feature is cylindrical and finger-like in shape. The cochlea is straight or slightly curved, but not properly coiled. Vertebrae Like virtually all living mammals, the neck consists of seven cervical vertebrae. As this was also the case in the nearly- eucynodont Thrinaxodon, (pers comm Dr Ferdinand Abdala, 2004), this basic number was presumably already established at least 250 million years ago. Strictly speaking, it's no longer universal. Both sloths and manatees are non-conformists in this regard, and there may be others. (Mit bestem Dank an Frank, who raised the subject at some stage in 2003.) Going further down the body, there are thirteen throacic vertebrae, on which can be found the ribs. Six lumbar and three or four caudal vertebrae are represented by impressions. Arms The upper arm bone is robust, (p.140). "Distally, the humerus has an incipient trochlea for the ulna, a therian apomorphy... that is absent in multituberculates..." (reference numbers omitted). A prominent, spherical unlnar condyle on the humerus resembles the condition in 'non-therian' mammals, (non-holotherian in this project.) Hips and feet The bones of the pelvis are slender, and the rod-like ilium is about three times the length of the ischium. On the back of the foot is a feature known from Gobiconodon, existing monotremes and (to my knowledge) at least some multis, (eg Kryptobaatar). This is a spur of bone on the heel. In living monotremes, this feature is generally restricted to adult males. With reference to only the platypus, it's associated with venom. The presence of this spur suggests the holotype is also a male, (although that point isn't directly expressed in the description). Zhang-she-otherium For those of a romantic disposition: There's some good news for Zhangheotherium from Luo et al 2002, p.68. He, (and it very probably was a he), can look forward to female companionship. That spur of bone is missing in the case of a second specimen. Assuming this is s a sexual dimorphic characteristic, then we might be able to look forward to the patter of tiny paws, as long as they fancy each other. While no breeding programme is planned, experience suggests that such formalities are sometimes superfluous. Where there's a will there's a way. Systematics The description reports the following, (p.140): "The sister-taxon relationship between therians and multituberculates... is strongly supported by the evidence from Zhangheotherium, such as the clavicle-interclavicle joint and some features of the femur, corroborate the therian affinities of multituberculates..." (reference numbers omitted). However, it's now 2004 rather than 1997 and there's little consensus. The available evidence is improving, but it's still thin. Acute-angled 'symmetrodonts' are generally regarded as holotherians, and are probably within Crown-group Mammalia; the most recent common ancestor of myself and a platypus, and all of its descendants. In some respects, (eg the retention of an interclavicle in the pectoral girdle), the anatomy is more basal than known from Henkelotherium, a dryolestidan. However, that's insufficient to indicate a more basal position within Mammalia. The interclavicle is present in existing, adult monotremes and, embryonically, in marsupials. Holotype The holotype, IVPP V7466, works at the Institute of Vertebrate Paleontology and Paleoanthropology, Beijing. The specific name refers to the three main and two accessory cusps on the lower molars.
Reference:	Hu et al (1997), A new symmetrodont mammal from China and its implications for mammalian evolution. Nature 390, p.137-142.

Links: Nature 1997 http://perso.club-internet.fr/jflhomme/pef/mammif_chinois.pdf The description in PDF format. C News Science, 24.11.1997 http://www.canoe.com/CNEWSScienceArchive/nov24_mouse.html Some observations from Zhexi Luo. The Shenzhen Daily, 30.3.2001 http://pdf.sznews.com/szdaily/2001/0330/15.htm A nice article on the amateur fossiler, Zhang He. Mr Zhang has reportedly donated 5,000 further fossils to the Shenzhen Extinct Life Fossils Museum in the Fairy Lake Botanical Garden. Deservedly, they’ve made him curator for life. Contrary to this report, Confuciusornis does not predate Archaeopteryx. It’s a about 20 million years younger.

Other reports: East Asia Abstracts submitted to The Society of Vertebrate Paleontology Annual Meeting 2004 include: Early Cretaceous spalacotheriid "symmetrodont" (Mammalia) from East Asia, lead author Takehisa Tsubamoto. This may have something to do with Symmetrolestes, but I'm not certain.

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Help: Should anybody have any further information, I'd be pleased to hear of it. Regarding references and Bibliography: I haven't and can't verify all the references, so beware. Traditional papers used in constructing this page are in the bibliography. If you feel these are too few, then send some more. With thanks to all the featured sources. Trevor Dykes, October 2001 Last update: 29.7.2009 Ktdykes@arcor.de

With further thanks due to: Prehistoric Data Files, Angellis http://www.angellis.net/Web/PDfiles/MarsupS-em.htm This site hosts one huge index, culled from a hundred or so paleontological books and journals. It’s frequently of use, either to fill in gaps or for cross referencing. BIOSIS, The Index to Organism Names http://www.biosis.org.uk/triton/indexfm.htm The Society of Vertebrate Paleontology BFV Online, (John Damuth) http://www.bfvol.org/ Dr John Alroy's North American Fossil Mammal Systematics Database John H Burkitt, MAMMALS, A World of Living and Extinct Species http://cougarhillweb.org/mammals.pdf Welcome back on-line. The exciting animations have come courtesy of HitBox Central, Animation Library and best animations.com .

Bibliography: Averianov AO, (2002), Early Cretaceous "symmetrodont" mammal Gobitheriodon from Mongolia and the classification of "Symmetrodonta". Acta Palaeontologica Polonica 47 (4), p.705-716. Averianov AO & Archibald JD (2003), Mammals from the Upper Cretaceous Aitym Formation, Kyzylkum Desert, Uzbekistan. Cretaceous Research 00 (2003), p.1-21. Butler & Clemens (2001), Dental morphology of the Jurassic holotherian mammal Amphitherium, with a discussion of the evolution of mammalian post-canine dental formulae. Paleontology, 44 (1), p.1-20. Canudo JI & Cuenca-Bescós G (1996), Two new mammalian teeth (Multituberculata and Peramura) from the Lower Cretaceous (Barremian) of Spain. Cretaceous Research 17, p.215-228. Cifelli RL (1999), Therian teeth of unusual design from the Mid-Cretaceous (Albian-Cenomanian) Cedar Mountain Formation of Utah. Journal of Mammalian Evolution, 6 (3), p.247-270. Cifelli RL (2001), Early Mammal Radiations, Journal of Paleontology, vol 75 (6), p.1214-1226. Clemens WA (1963), Wealden Mammalian Fossils, Palaeontology (partial copy without page numbers). Ensom P & Sigogneau-Russell D (2000), New symmetrodonts (Mammalia, Theria) from the Purbeck Limestone Group, Lower Cretaceous, southern England. Cretaceous Research 21, p.767-779. Gill P (2004), A new symmetrodont from the Early Cretaceous of England, Journal of Vertebrate Paleontology, 24(3), p.748-752. Hu YM, Fox RC, Wang YQ & Li CK (2005), A new spalacotheriid symmetrodont from the Early Cretaceous of northeastern China, American Museum Novitates, 3475, p.1-20. Hu Y, Wang Y, Luo Z & Li C, (1997), A new symmetrodont mammal from China and its implications for mammalian evolution. Nature 390, p.137-142. Ji Q, Luo Z & Ji S (1999), A Chinese triconodont mammal and mosaic evolution of mammalian skeleton. Nature 398, p.326-330. Kemp TS (2005), The Origin and Evolution of Mammals, Oxford University Press, pp.331. Kielan-Jaworowska Z, Novacek MJ, Trofimov, BA & Dashzeveg D (2000), Mammals from the Meozoic of Mongolia, p.573-626 in Benton MJ, Shishkin MA, Unwin AM & Kurochkin EN (Eds.), The age of dinosaurs in Russian and Mongolia, Cambridge University Press. Li G & Luo Z-X (2006), A Cretaceous symmetrodont therian with some monoteme-like postcranial features, Nature, 439, p.195-200. Luo Z (1999), A refugium for relicts. Nature, vol 400, p.23-25. Luo Z-X, Kielan-Jaworowska Z & Cifelli RL (2002), In quest for a phylogeny of Mesozoic mammals. Acta Palaeontologica Polonica 47 (1), p.1-78. McKenna MC & Bell SK, (1997), Classification of Mammals Above the Species Level. Columbia University Press. Prasad GVR & Manhas BK (2001), First docodont mammals of Laurasian affinity from India. Current Science, 81 (9), p.1235-1238. Prasad GVR, Verma O & Parmar V (2006), An overview of the Mesozoic mammalian fossil record of India, Mesozoic Terrestrial Ecosystems 2006, p.101-104. Rougier GW, Isah S & Manabe M (2007), An Early Cretaceous mammal from the Kuwajima Formation (Tetori Group), Japan, and a reassessment of triconodont phylogeny, Annals of Carnegie Museum, 76(2), p.73-115. Rougier GW, Spurlin BK & Kik PK (2003), A New Specimen of Eurylambda aequicrurius and Considerations on "Symmetrodont" Dentition and Relationships. American Museum Novitates 3398, p.1-15. Sidor CA (2003), Evolutionary trends and the origin of the mammalian lower jaw, Palaeobiology, 29(4), p.605-640. Sigogneau-Russell D (2003b), Holotherian mammals from the Forest Marble (Middle Jurassic of England), Geodiversitas, 25 (3), p.501-537. Sigogneau-Russell D & Ensom P (1998), Thereuodon (Theria, Symmetrodonta) from the Lower Cretaceous of North Africa and Europe, and a brief review of symmetrodonts. Cretaceous Research, 19, p.445-470. Tsubamoto T, Rougier GW, Isaji S, Manabe M & Forasiepi AM (2004), New Early Cretaceous spalacotheriid "symmetrodont" mammal from Japan. Acta Palaeontologica Polonica, 49 (3), p.329-346. Wang Y-Q, Hu Y-M & Li C-K (2006), Review of recent advances on study of Mesozoic mammals in China, PalAsiatica, 44(2), p.193-204. Weil A (2002), Mammalian evolution: Upwards and onwards, Nature 416, p.798-799. Yadigiri P (1984), Journal of the Geological Society of India, 25(8), p.514-521. Zhang Fakui (1984), The Fossil Record of Mesozoic Mammals in China. Vertebrata PalAsiatica, Vol XXII (1), p. 29-38, (as translated by Will Downs, May 1986 with minor revisions in 1999). This was obtained courtesy of the Polyglot Paleontologist. http://www.uhmc.sunysb.edu/anatomicalsci/paleo/terms.html