| MESOZOIC MAMMALS; 'basal' Eutheria, an internet directory: |
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.
Looking for books?
You could visit the
Book Centre and look around.
|
Congratulations, it's a placental. (Actually, that's
not quite accurate. All placentals are eutherians, but Eutheria is wider than
Placentalia.) If we accept the morganucodontids as being the first mammals, then it seems to have taken about 90 million years for Eutheria to emerge, though an earlier birthdate shouldn't be ruled out; Eomaia, (May 2002), Barremian, ca. 125Ma. Some of these fossils represent the presence of the major branch of we modern mammals. Still small though they were, their descendants would come to dominate the world, diversifying to take advantage of an astounding variety of ecological niches and inventing football and cricket. The most practical way of constructing this page for now is as a straightforward a-z. |
| Links: Mikko Haaramo's Eutheria
A thoroughly good piece of thoroughness.
T Mike Keesey, The Ages of the Mesozoic http://dinosauricon.com/times/index.html The chronology of the Mesozoic made clear. |
| 'BASAL' EUTHERIA |
| Taxon: Eutheria Huxley, 1880 Remarks: "Eutheria Gill, 1872 covered both marsupials and placentals and until recently lay fallow. Eutheria Huxley, 1880 covered "placentals" and putative "placentals", but not members of the Marsupialia as well," (McKenna & Bell, 1997).
Eutheria literally means 'true beasts'. I'm not sure that
other beasts would appreciate the arrogance of this assertion, but I don't suppose they
mind. They can't read. |
| Link: Platform "Iepen Blijven" http://www.omne-vivum.com/v/603.htm A photo album of various modern eutherians. |
|
Genera: "Beleutinus" (nomen dubium),
Cretasorex, Eodesmatodon,
Eomaia, Eutrochodon,
Helioseus, Idiogenomys,
Kennalestes (partly = Daulestes), Kumlestes (= Daulestes),
Majoria (= Plesiorycteropus), Montanalestes,
Myoryctes (= Plesiorycteropus), Nanocuris,
Neodesmostylus,
Obtususdon, Plesiorycteropus,
Prodelttheridium (nomen nudum),
Telacodon, Tingamarra,
Veratalpa, Wanotherium,
other reports
Time-Line: Quarternary: Plesiorycteropus Pleistocene: Neodesmostylus Miocene: Veratalpa Oligocene: Idiogenomys Eocene: Eodesmatodon, Eutrochodon, Helioseus Paleocene: Obtususdon, Tingamarra, Wanotherium Upper Cretaceous: "Beleutinus", Cretasorex?, Nanocuris, Telacodon, Uzbekistan Lower Cretaceous: Eomaia, Montanalestes, Prodelttheridium (nomen nudum) |
| Genus: "Beleutinus" Bazhanov, 1972 |
| Species: | "Beleutinus orlovi" Bazhanov VS, 1972 |
| Place: | Bostobe Formation, Aral Sea region |
| Country: | Kazakhstan |
| Age: | Santonian, Upper Cretaceous |
| Remarks: |
Averianov & Archibald 2003, (p.14-15), cite this as nomen
dubium, (dubious). Remains consist of a fragment of
dentary with some broken teeth. This might actually be a deltatheroidan, which were proto-marsupials. It's also seen as a possible zalambdalestid, (eg Averianov & Archibald 2003). It was originally referred to Zalambdalestidae, but that seems unjustified, (Wible et al 2004, p.16) The citation details have been taken from the references in Kordikova et al, 2001. |
| Reference: | Bazhanov (1972), Pervaya nakhodka mezozoyskogo mlekopitayushchego Beleutinus orlovi v sovetskom Soyuze. [The first Mesozoic mammal (Beleutinus orlovi) from the Soviet Union], Theriologiya, 1, p.74-80, [in Russian]. |
| Genus:
Cretasorex Nessov LA & Gureev AA, 1981 'Cretaceous shrew' |
| Species: | Cretasorex arkhangelskyi Nessov LA & Gureev AA, 1981 |
| Place: | Kyzylkum Desert |
| Country: | Uzbekistan |
| Age: | Coniacian, Upper Cretaceous |
| Remarks: |
"Nessov (Nesov) and Gureev (Gureyev) believed this almost indeterminate animal to a
Cretaceous shrew because of the pocketed coronoid process of the mandible. However, such a
structure occurs in some mammals that lack a zygomatic arch, e.g. in certain
apternodontids. Cretasorex is apparently not referable to either Sorex or to
Diplomesodon, both of which are currently resident in the Kyzyl Kum area where
Cretasorex was found. That the animal actually represents a shrew remains to be
proven," (McKenna & Bell, 1997). An enquiry arrived in December 2002, regarding the possibilities of a three foot high, bipedal insectivore for a fantasy role-playing game. Cretasorex didn't seem a suitable model! The last I heard, Leptictidium Tobien, 1962, (from the Eocene of Germany), seemed more promising. |
| Reference: | Nessov & Gureev (1981), Nakhodka chelyusti drevneyshey zemleroyki v verkhnem melu pustyni Kyzylkum. Dokl Akad Nauk SSSR 257, p.1002-1004. |
| Genus: Eodesmatodon Zheng J & Chi H, 1978 |
| Species: | Eodesmatodon spanios Zheng J & Chi H, 1978 |
| Place: | |
| Continent: | Asia (southeast) |
| Age: | Upper Eocene |
| Remarks: | I don't know what this is or why it's here. |
| Reference: |
| Genus:
Eomaia Ji Q, Luo ZX, Yuan CX, Wible JR, Zhang JP & Georg JA, 2002 'dawn mother' "First of all, Eomaia is not a placental mammal. It is an early, primitive representative of the lineage that eventually led to placental mammals," said Anne Weil, (in the linked article). She also observed: "Eomaia - 'Dawn Mother' - is exceptionally well-preserved for a 125-million-year-old. Although the fossil's skull is squashed flat, its teeth, tiny foot bones, cartilages and even its fur are visible." |
| Species: | Eomaia scansoria Ji Q, Luo ZX, Yuan CX, Wible JR, Zhang JP & Georg JA, 2002 |
| Place: | Yixian Formation, Liaoning |
| Country: | China |
| Age: | Barremian, Lower Cretaceous |
| Remarks: | The following is based upon
my reading of Ji et al, 2002. Until 1999, it seemed reasonably secure to assume the centre of initial eutherian evolution had been in Asia, which provided the only universally accepted, relevant Lower Cretaceous fossils. They were about 100 million years old. Then North America pushed the record back by ten million years with Montanalestes. Asia retaliated shortly afterwards with Murtoilestes from Transbaikalia, Russia. That set the record back to about 120 million years. Then the Yixian Formation of northeastern China yielded 'dawn mother'; a fossil which merits any and all of the following superlatives: stunning, spectacular, staggering, mind-blowing, beautiful, magnificent, unbelievable and so on and so forth. This is a sensationally well-preserved 125 million year old animal, and the skull and skeleton are known almost completely, (p.816). Prior to this megastar of vertebrate paleontology, the oldest eutherians providing anything like this kind of detail were forty or fifty million years younger. However, Eomaia shows still more audacity. The fur and even some soft body tissue, (eg cartilages from the spine), have been preserved. Apart from at Liaoning, the oldest direct evidence of mammalian fur comes from post-Mesozoic carnivore droppings containing undigested bits of Lambdopsalis. Relative significance Although it might sound premature to voice such an opinion, this is one of the most spectacular finds described in the entire twenty-first century. Should that statement turn out to be an exaggeration, I will happily apologise, (if possible). However, I doubt that will be necessary. This fossil merits excitement. Mammaldom The living world contains three natural categories of mammals. About 270 species, (6%), are marsupials. The three species of egg-laying monotremes are too few to merit a percentage point. The other group are reasonably close relatives of marsupials, and provide around 4,230 species. I'm a member myself. These placentals are a major part of a wider grouping called Eutheria, which contains all critters more closely related to me than with a koala or a kangaroo. While not strictly being a placental mammal, Eomaia is undoubtedly a eutherian. As it's presently both the oldest and most basal representative known, the authors named the genus 'dawn mother'. The specific name, scansoria, refers to scansorial abilities, which means climbing. Features of the legs and feet are only found in clambering and tree-dwelling mammals. This indicates a similar lifestyle for this critter. How big was it, then? What matters is quality, not size. These are my estimates based upon the sketches in the description, (p.817 and 818). The skull, (which is partly represented by impressions rather than solely fossilized bone), has a length of 2.5cm; the neck and body contribute 6-7cm (depending upon how curved the spine was in life); and a reasonably straight tail adds around 7.5cm. Precision concerning the length of a tail is startling. There are 25 separate vertebrae involved, and all of them are half a centimetre or less in size. Not one is missing. Just think for a moment about a fragile structure like that and a 125 million years. This preservation of details is breathtaking. The maximum length of the lower jaw is about 2.2cm. (What's also worth bearing in mind is the care and effort which goes into sketches like these. My estimates are crude in comparison.) More detailed stuff The diagnosis Eomaia differs from other Lower Cretaceous eutherians in details of dentary and dentition. Unlike Montanalestes, the lower jaw retains a Meckelian groove. A further difference from most (but not all) eutherians, is that the angular process towards the back of the jaw is angled slightly inwards. Teeth The dental formula is typical for basal eutherians, and unknown from any metatherians; (uppers): five incisors, one canine, five premolars, three molars; (lowers): four, one, five and three respectively. (Later during eutherian evolution, some of those teeth were dispensed with.) In contrast to less derived boreosphenidans, cusps on the talonid called the entoconid and hypoconid are of near equal sizes, whereas the first cited is relatively smaller in the stem animals. As the molars are fully tribosphenic, it obviously differs from non-tribosphenic mammals. The jaw lacks the primitive postdentary trough, and this is a contrast to the later Australian ausktribosphenids, ( Austribosphenos and Bishops). Wrists The wrist contains an enlarged and long trapezium. The hamate bone is large, but not as oversized as in marsupials (and Sinodelphys which was subsequently described). In contrast, the tapezoid and capitate are relatively small, and the proportions of all these bones is similar to the situation found in living climbing mammals. These wrists hosted hands made for grasping, and that indicates climbing. Hips I've spent much effort studying the hips of a mammal, but scientific enquiry wasn't the objective. Nevertheless, this area of Eomaia contains much of interest, albeit for reasons distinct from my own explorations. "The ilium, ischium and pubis are fused", (p.818). An interesting feature is the presence of epipubic bones. These are universal among mammals excepting for derived eutherians called placentals. As non-mammalian tritylodontids had them too, the characteristic even pre-dates Mammalia, (Reilly & White 2003, p.400.) The build of the hips suggests there wasn't enough room for a wide birth canal, and that points to a mode of reproduction involving poorly developed, new born babies. Not only is Eomaia too basal to be regarded as a member of Placentalia. Embryonic development presumably didn't involve placental feeding. Ankles "The ankle of Eomaia bears strong resemblance to those of Late Cretaceous eutherians..." (reference numbers omitted). It contains a characteristic which is regarded as diagnostic for eutherians. As that concerns details I've no intention of trying to address, I'll just say astragalotibial facet. (Ankle terminology is terrifying.) Fur Impressions of hair are preserved all round the body. There's even a thin layer on the tail. The densest concentration is nearest to the body, and provided insulation. The outer coat was also equipped with longer guard hairs. None of these details are surprising. The flabbergasting aspect is the fossilization of any hairs at all. At the time of publication, this was entirely unprecedented for Mesozoic mammals. Subsequently, several further furry critters have emerged from the former lakelands of the Yixian Formation. Nobody assumed pre-Paleocene mammals had been nudists, but finding fully dressed specimens is highly improbable. Hair virtually never-ever fossilizes. However, Liaoning specialises in improbabilities. Fingers and toes For the purposes of orientation, mammalian hands traditionally contain five (or less) elements technically termed fingers. Each of those has three bones, or two in the thumb. In every digit, the bone nearest to the wrist is a metacarpal, and the other bones are phalanges. The thumb is digit 1 and your little finger is digit 5. You'll have to work out the rest of the sequence for yourself. Conveniently, other than for one exception, these terms and technicalities also apply to feet, which is why I've taken a bit of time to outline them. (The exception is that toes contain metatarsals rather than metacarpals.) These features help to explain: a. how I can count to 21; b. that I'm male. As the situation is broadly similar in the genus of Eomaia, you can use your own paws as visual aids and, I promise, we'll have no need to count even as far as 20. Paws The proportions of the phalanges in front and back feet are similar to those known from existing arboreal animals. For example, the claw bearing phalanx of the third finger is relatively long when compared to the other phalanx, (79%). That ratio tends to be lower in terrestrial mammals, and can be higher in full-time tree dwellers. In the feet, the outer toes (4 and 5) are relatively long. The phalanges, (but not the metatarsals), are longer than the corresponding bones in digit 3. In ground dwellers and clamberers, the phalanges of digits 2 and 3 tend to be the longer. Eomaia claws are more similar to those of scansorial mammals, (climbers), than with fully arboreal ones. In profile, they compare with the dormouse, (Glis), which favours a life in the bushes rather than trees. Overall, the anatomy is consistent with either a scansorial or an arboreal preference. Taking the vertebrae and further elements into account: "These convergences strongly suggest Eomaia was an agile animal with climbing skeletal adaptations, capable of grasping and branch walking, and active both on the ground and in trees or shrubs (for example, like the opossum Didephis, some species of the tree shrew Tupaia, and the dormouse Glis)." A weight estimate of 20-25g is given, and this is about the same as a standard mouse. Was this is the Dawning of the Age of Eutheria... "On the basis of 268 characters sampled from all major Mesozoic mammal clades and principal eutherian families of the Cretaceous, Eomaia is placed at the root of the eutherian tree with Murtoilestes and Prokennalestes. Clearly, these three taxa are closer to living placentals than to living marsupials. Eomaia is placed in Eutheria by numerous apomorphies in the dentition, the wrist and the ankle", (Ji et al 2002, p.820). The diversity among basal eutherians suggests some of the clades arose before Eomaia, (p.821). The next oldest known genus is Murtoilestes, and that dates from close to the Barrmian-Aptian transition. The North American Montanalestes (Aptian-Albian) is anatomically distinctive from its Asiatic contemporaries. Eomaia is the earliest eutherian known, but it wasn't the first to have lived. The lineage was established prior to 125 million years ago, and the search for the oldest representative will continue. Does anyone known the Latin for 'dawn granny'? Holotype The holotype of 'dawn mother' is CAGSO1-IG1 a and b. Both the positive and negative slabs reside at the Chinese Academy of Geological Sciences, Beijing. I'm a fan and this fossil is 'tastic. This is near the start of You in Theria. Nature chose the week of publication to offer me free access to the full on-line edition. As well as the description, it contained an excellent commentary by Anne Weil, which nicely places Eomaia into perspective. It's in English rather than paleo-speak. Dr Luo then generously forwarded a copy of the publication, along with various other papers. Many thanks. An equally astounding basal metatherian from Liaoning, Sinodelphys, was described in December, 2003. |
| Reference: | Ji et al (2002), The earliest known eutherian mammal. Nature (416), p.816-822. |
| Links: Dinosaurier.org, Stefan Jacobasch http://www.dinosaurier.org/nachrichten/news69.htm A report in German. I'm sure English language links will follow shortly. (Good prediction.)
National Geographic News, 24.4.2002 http://news.nationalgeographic.com/news/2002/04/0423_020425_firstmammal.html Earliest Known Ancestor of Placental Mammals Discovered.
Climbing Dawn-Mother, Daniel Bensen http://members.gotnet.net/maier/Dinosaurs/Eomaiascansoria.html A gentle picture with some thoughtfully written comments.
post-gazette.com, Photo Journal http://www.post-gazette.com/journal/photos_bygallery.asp?special=Carnegie+scientists+find+new+mammal A nice gallery of pics. The photo showing the fossil in the hands of Drs Luo and Wible, (don't drop it!), gives an excellent impression of the size. You can click on any of the images to view an enlargement.
Eomaia scansoria, Carnegie Museum of Natural History http://www.carnegiemuseums.org/cmnh/research/eomaia/ A collection of various articles, including a link to the original publication, 4.25.02. |
| Genus: Eutrochodon Roth, 1903 |
| Species: | Eutrochodon sp. Roth, 1903 |
| Place: | |
| Continent: | South America |
| Age: | Middle Eocene |
| Remarks: | The Roth collection in the Museum of La Plata was reviewed by Simpson in 1936. I doubt this is of any relevance to Mesozoic mammals. |
| Reference: |
| Genus: Helioseus Sudre J, 1979 |
| Species: | Helioseus insolitus Sudre J, 1979 |
| Place: | |
| Continent: | Africa (north) |
| Age: | Middle Eocene |
| Remarks: | Presumably hard to place for whatever reason. |
| Genus:
Idiogenomys Ostrander GE, 1983 Aka: Idogenomys |
| Species: | Idiogenomys ozziei Ostrander GE, 1983 |
| Place: | Raben Ranch, Nebraska |
| Country: | USA |
| Age: | Chadronian, Lower Oligocene (or Upper Eocene) |
| Remarks: | Decidedly un-Mesozoic. |
| Reference: | Ostrander (1983), New Early Oligocene (Chadronian) mammals from the Raben Ranch local fauna, Northwest Nebraska. J. of Paleontology 57, p.128-139. |
| Links: Evolution of Tertiary Mammals of North America http://uk.cambridge.org/earthsciences/catalogue/0521355192/default.htm The publisher's blurb for a major study from 1998. Any book priced at 180 pounds must surely qualify as a major study. |
| Genus:
Montanalestes Cifelli RL, 1999 'Montana robber' |
| Species: | Montanalestes keeblerorum (Cifelli RL, 1999) Cifelli RL, 2000 |
| Aka: | Montanalestes keebleri Cifelli RL, 1999 |
| Place: | Cloverly Formation, Montana |
| Country: | USA |
| Age: | Albian-Aptian, Lower Cretaceous |
| Remarks: |
Much of the following is derived from my reading of Cifelli,
1999. This genus is based on associated, partial lower jaws. The right one contained at least four premolars (though the number when alive is unclear) and three molars. "Differs from primitive Tribosphenida (for example, Kermackia), in so far as is known, in having a semimolarized last premolar (lingually placed paraconid, incipient talonid basin, metaconid present) and only three molars; molars differ in having a broader, more fully basined talonid with three cusps consistently present", (p.363). The most comparable known taxon seems to be Prokennalestes from the Upper Cretaceous of Mongolia. Prokennalestes, a definite member of eutheria, is more or less completely known from a number of skulls and skeletons. Montanalestes thus appears to belong within (or very near to) Eutheria. A relatively derived feature of the dentary is the absence of a Meckelian groove, (p.364). In contrast, a roughened depression on the bone could indicate the continuing presence of a coronoid; a small, 'extra' jaw bone. If so, this would be a basal characteristic. At the time of publication, Cifelli didn't quite place this genus within Eutheria. Rather, (p.365): "If Montanalestes is related to Eutheria, as the balance of evidence indicates, then the continent of origin for the group is called into question; evidently, Eutheria enjoyed a far broader Early Cretaceous distribution (echoing that of the triconodont mammal Gobiconodon) and an earlier evolutionary radiation than previously envisaged." Subsequent publications might suggest that the author is psychic. In 2002, an undoubted and earlier eutherian was described, (Eomaia from Liaoning in China). Adding to the portrayal of prescience is a further Liaoning species first published in July, 2003; a new species of the aforementioned Gobiconodon. Clearly, basal representatives of the line which led to Placentalia were scampering around Asia at least 125 million years ago, (something like 15 million years earlier than this genus). As eutherians were around and the known remains of Montanalestes look eutherian, that's most probably what they represent. Ask Luo et al 2002, p.11. The critter had an estimated body length of ca. 6cm. As the species name is actually in honour of the Keebler family, it was later adjusted in accordance with Latin grammar. There’s possibly a second, unnamed species. The holotype, in the Oklahoma Museum of Natural History, is OMNH 60793. |
| Reference: | Cifelli (1999), Tribosphenic mammal from the North American Early Cretaceous. Nature, 401, p.363-366. |
| Links: Richard Cifelli, Nature 401 http://w3.frontier.esto.or.jp/d1/saji/nature.pdf Includes the first few paragraphs of the article in pdf format.
The Shawnee News-Star Online, 28.9.99 http://www.news-star.com/stories/092899/new_jawbones.shtml A reader-friendly report for non-specialists. Intelligent journalism. |
| Genus:
Neodesmostylus Khomenko, 1927 'new Desmostylus' |
| Species: | Neodesmostylus sp. Khomenko, 1927 |
| Continent: | Asia |
| Age: | Pleistocene |
| Remarks: | I don't know what this genus is hanging around here for either. The age indicates the last ice-age. Old Desmostylus was from the Miocene and was "probably related to Sirenia and Proboscidea, but not a member of either as far as is known." (With thanks to David Marjanovic.) |
| Reference: |
| Genus: Nanocuris
Fox RC, Scott CS & Bryant HN, 2007 'Dwarf razor'
Nanocuris is a somewhat curiously named dental deviant, and some of its
perversity can be read about below. As nanos is Greek for 'dwarf', it
generally gets called into use for particularly small taxa; eg. Nanotyrannus,
a relatively mini tyrannosaurid (or perhaps a baby). However, in this case the
remains available happen to have been left lying around by one of the largest
mammals from its fauna. There will now be a brief pause for puzzled head
scratching... |
| Species: | Nanocuris improvida Fox, Scott & Bryant, 2007 |
| Place: | Frenchman Formation, Saskatchewan |
| Country: | Canada |
| Age: | Maastrichtian, Upper Cretaceous |
| Remarks: | The following is based upon my reading of
Fox et al, 2007, and thanks are due to the supplier. This paper concerns a fossil assigned by the authors to Placentalia, but I tend to prefer the somewhat wider concept of Eutheria (p.1). This is because I don't happen to know whether it's a descendant of the most recent common ancestor of myself and all other living placentals. Regardless of that semantic difference, it represents another advance in the knowledge about the diversity of Mesozoic mammals in terms of morphology. Only a partial jaw is presently available, but it contains teeth of a style never previously observed for a Cretaceous mammal. The molars have more resemblance with some later mammals, the mesonychians but, as these similarities are probable matters of convergence, similar tools for performing similar work, there's no suggestion of kinship. This new oddling has been allowed to form its own isolated family of unknown ordinal affinities, and it'd be pleased to meet any close relatives from either its home is the Frenchman Formation of Saskatchewan or further afield. Should you happen to be a nanocurid, then please get in touch. If earlier assignments of several other local fossils were correct, then this particular Upper Cretaceous fauna had something of a typically post-Cretaceous flavour among its eutherians. Other finds have included a "condylarth" and a taeniodont. Those might be strange words for some, but no matter. These usually refer to furry critters from the Paleocene or more recent times. Other North American Cretaceous faunas haven't displayed this sort of mood. Obviously, it'd be interesting to know whether the inhabitants of the Frenchman fauna were, in part, ancestors of the subsequent placental radiation in North America. Less obvious is how the truth of that could be substantiated. It's an intriguing possibility, but might not be the case. Tribosphen-conservatives Most Upper Cretaceous therian mammals were conservative with regards to their molar form. They'd inherited relatively high-tech ones known as tribosphenic. Lowers have a grinding bowl at the back in the form of a multi-cusped talonid heel, and this aids the processing efforts of an industrious protocone on the tooth above. The front half of the crown houses a three-cusped trigonid, and these cusps fit between valleys separating upper cusps from one another. These are dual-purpose molars for a mix of shearing and grinding of food. Some neat adaptations arose, but all appeared content with fairly modest variations on similar themes. (A bit of refreshment on elephants came from a quick re-reading of Skizzen aus den Lebensschicksalen der Elefantenstamme von Dr Günther Schlesinger, Kosmos Handweiser für Naturfreunde 1913, Heft 3, Seiten 89-94. An extremely close acquaintance of mine uploaded an English translation of that in 2006: A brief history of elephants. The article was aimed at interested general readers.) Later therians showed more diversity could bring rewards in the right circumstances. Elephants, for example, seem to have begun their careers with molars more like those sported by extant hippos; cutters for dealing with softer plants; eg. Moeritherium of the Eocene. However, over time, the molars of elephants stretched and developed into things more like severe files; as with those found in a workshop rather than the tax office. To get some idea of how elephant molars go to work, why not stick your hand between two such files and ask a friend or, even better, somebody who really hates you to get to work with a demonstration? Elephants have no particular relevance to Nanocuris, but they do illustrate the sort of rather radical changes that occur in fossil localities separated by not all that many millions of years. As this trend in elephants had strong links with the increasing popularity of plants hardly available during the Cretaceous and involved biggish to mammoth mammals, then expecting something along those lines to turn up would be optimism to the point of severe mental derangement. Even so, nearly 50% of both eutherian and metatherian history happens to date from the Cretaceous. Both lineages had already been launched at least sixty million years prior to the famous K-T mass die in(s), events which occurred but sixty-five million years before next Thursday afternoon, and Cretaceous therians are therefore hardly in a position to say they didn't have enough time to try radical derivations. Excuses along those lines won't wash. A Cretaceous eutherian pervert Basal therian, metatherian and eutherian approaches to life all involved beating up smaller honoured victims, and terminally depriving them of their valuables. Naturally, the already dead would also be willingly defiled if opportunities arose. 'Small razor' had broadly similar attitudes, but it was equipped to tackle such tasks somewhat differently. Its weaponry had undergone refinement. The body, or rather part of a jaw, was exhumed during excavations in a quarry that began in 1994 (p.2). It happened to contain parts of a Tyrannosaurus and, rather than saying the sensible thing, "oh how boring. Let's just leave it there for the weather to erase and go and have a beer", a team of paleontologists felt moved to extract the daft dino. Still, they probably had a beer or two whilst doing so. Digging a trench round part of this monstrosity brought a far more interesting fossil to light; Nanocuris. The K-T boundary in the local strata is exquisitely marked by all kinds of stuff ("boundary clay, iridium anomaly, diagnostic palynofloral change, magnetostratigraphy (the boundary is contained in chron 29R), and radioisotopic dates..."), and this excavation occurred 28 metres or so below it. The Upper Cretaceous date is unambiguous. A giant 'dwarf razor' It may sound a tall order to deduce the size of a long dead animal from a couple of fragments of jaw, but comparing it with other bits of jaws provides a good basis for at least a sensible approximation. This critter was of fairly similar dimensions to Cimolestes magnus and Schowalteria, and the second named is known from more extensive remains. It was big enough for most Western families to find enough meat for a meal. Most contemporary mammals would hardly have amounted to a snack for the cat. There are two fragments of dentary, but both are parts of the same jaw. The front bit houses a canine and part of a premolar, while the second has the four rear teeth and the lower part of the coronoid process; a muscle attachment area immediately behind the tooth row. The fragments were noticed close to one another, sizes match and they're in the same sort of general condition. What remains of the teeth isn't in very good shape (p.3). The canine was a strong, somewhat procumbent tooth with its base curving along its course. Presumably, that curvature continued along the rest of its course, but some's missing. (Merely from the graphics, it manages to remind me of an incisor. However, as the authors have plenty of experience and had much time to carefully examine the fossil from all available angles, I'd put my money on their opinion.) The single root of the canine's accommodated within most of the depth of the dentary (p.5), and proceeds back until at least the front of the postcanines. Little can be said of the incisors as that area is absent, but they were likely small. A modest diastema separates the canine from remains of a double-rooted premolar. Most of that crown has been drastically eradicated. The break in the bone behind it was relatively recently inflicted, and this occurred prior to recognition of the fossil. That could've been during or after the quarrying. In any event, the fracture shows part of an alveolus going down more than halfway into the bone, and which was larger than both of those for the first premolar. It must've held the root of a larger tooth snug behind the p1. The bigger bit Logically enough, the fracture at the front of the larger chunk of jaw's also fresh. That piece contains three and a bit teeth; presumably p4 and the three molars. The talonid of the first tooth is rather wrecked, but it was strongly developed. It's relatively long and juts back beyond the root. The first two molars have also been left in ruins. The third's intact but was subjected to erosion. However, it's clear that these teeth were notably narrow, and they shorten progressively along the line (or should that be regressively)? The rear root of m1, for example, has a length of 2.5 times its width whereas its front partner is only a bit longer than broad. That suggests again a long and narrow talonid behind, possibly, a slightly wider trigonid. The story is similar for the smaller m2. Number three is more generous with information. Despite attaining an impressive length of 3.2mm, it's nevertheless the smallest of the trio. Erosion of the enamel may have removed some details, but the basic structure remains for visitors to admire. Four cusps are evident. What's left of the paraconid is a raised area a touch lingual at the front of the crown (p.6). This feature is further obscured as it got a chip knocked out of its old block. The protoconid is tall, pointed, narrow and triangular in profile. Its tip is vertical, showing no inclination of any backwards tilt. Behind, and lingual, stands a small swelling of the mini metaconid. The para- and metaconids are both far labial of positions for previously described tribosphenic critters of the Mesozoic and, with all three cusps close to form a straight line, the trigonid is abnormally narrow. The trigonid angle is given as 180°. For other eutherians of the time, it's generally less than 90° on final lower molars. Two crests descend from the main cusp to link it with its junior colleagues. The one running to the rear carries on horizontally along the talonid. A swelling at its rear is presumably a nigh on extinct hypoconulid cusp. What this talonid lacks is any trace of a basin, and no signs of other cusps termed the hypoconid and entoconid. That's not previously been seen for Cretaceous therians. All such lower molars are supposed to be equipped with talonid basins. Apparently, the ancestors involved in the production of Nanocuris failed to bear that in mind, and set about simplifying the design. The jaw bone itself is oddly deep for a Cretaceous therian relative to the tooth height, and it deepens continually from front to rear. Generally, the deepest are of such jaws occurs beneath the molars, and things tend to get shallower in both directions. This is technically termed "boat-shaped" (by these authors). 'Dwarf razor's place in the scheme of things Narrow lower molars with cusps in more-or-less straight lines is a trademark of Eutriconodonta Incorporated among Mesozoic mammals or, at least, it was until now. However, that design doesn't happen to involve an impressive, albeit unbasined talonid. Those triconodonts didn't do talonids. Some pretribosphenic mammals developed incipiently basined talonids, eg. Peramus, but not elongated ones (p.7). While it can't be entirely ruled out that Nanocuris could be a remarkably late peramuran, or something of the sort, the complete shortage of any such fossils beyond the Lower Cretaceous makes it improbable. It should be held in mind that the pair of molars further forward could, perhaps, have featured a 'better' degree of talonid development, possibly even basined, but it could still only have involved unusually narrow talonids due to the shortage of space. The authors conclude, rather than being a member of a pretribosphenic lineage that refused to go into retirement, this critter's what I'll term a post-tribosphenic one. That's not a word they use, but I think it's fair enough. These teeth had become specialized simply for artistic, elegant, brutally murderous shearing of unwilling flesh, and their owner couldn't be bothered with wasting energy on grinding bones or making bread. Cut, cut and cut again; yummy raw meat. The narrow molars decrease in size along the row, and that combination of both narrowness and decrease appears to be presently unique among Mesozoic therians. That prompted comparisons with some later ones. Borhyaenoid marsupials, extinct South American carnivorous marsups, were consulted, but they raised several objections. "Our molars increase in size along the line," they pointed out, "and besides, if we bother having talonids at all, then they're only short ones." Several placental creodont lineages of the Paleocene and beyond also reported progressive size increases and further differences. Some rather derived mesonychians (aka Acreodi), mesonychids and hapalodectids, confessed to possessing similarities, but they pointed to their tendencies to reduce talonids on m3, and prefer to store their metaconids lingually of and sometimes a bit forward of protoconids not, as here, behind them. "This Nanocuris was nothing to do with us", they all agreed. Then what am I? The question mark's worth making a note of. Assuming, on the grounds of probability, this fossil doesn't come from an astonishingly late supposed-to-be-extinct lineage (or a previously undetected one), then hanging it onto one of the two main therian branches appears to be the only available option. The inferred postcanine formula of four premolars and three molars indicates Eutheria. Metatherians of the age, as far as is known, favoured three premolars and four molars. However, as the inferred formula involves missing bone and teeth, its reliability is worth questioning, and the authors attempted interpreting things differently. The identity of the positions preserved on the front portion of the dentary aren't subjected to such treatment in this study, not publicly anyway. Personally, I'd have liked some reasoning for identifying the first preserved position as a canine. Perhaps it's so obvious, it didn't merit a mention. The authors are satisfied the rear fragment housed one premolar and three molars, and their confidence suggests they must have good reasons. The question addressed was whether the first tooth could be a p3. If so, that could indicate a metatherian. However, it'd still leave a total of only three molars, a count not known for any Cretaceous metatherian. Although damaged, the talonid was strong rather than small, and that's in keeping with eutherians. And, if it were a molar, then it would also be odd, although not entirely without some precedent. Generally, Cretaceous metatherian molars increase in size from the front to number three or even four ( stagodontids). The m2 would be the largest in this instance, a situation that's only known so far for Glasbius intricatus. A decrease in size from m1 to m3, but not in combination with this narrowness, is known from zalambdalestid eutherians and various Tertiary placental mammals. On the grounds of probability, the authors opt for eutherian affinities (p.8). Odd ball Perhaps enraptured by its beauties and eccentricities, the authors felt moved to reward Nanocuris with a family level, Nanocuridae. This was done because it appears to be sufficiently distinct from anything else known. It presumably also represents an otherwise unknown order of enigmatic affinities, but officially establishing one should await further information. Holotype RSM P2523.260 is a much loved resident at the Royal Saskatchewan Museum in Regina. The specific name is Latin for 'not anticipating', as this animal possessed unexpectedly derived specialisations for the time of Earth. |
| Reference: | Fox et al (2007), A new, unusual therian mammal from the Upper Cretaceous of Saskatchewan, Canada, Cretaceous Research. (My copy's an 'Article in Press' edition that doesn't carry full citation details.) |
| Genus:
Obtususdon Xu Q, 1977 Aka: Obtusudon |
| Species: | Obtususdon hanhuaensis Xu Q, 1977 |
| Place: | Qianshan Basin, Dou-mu Formation, Anhui Province |
| Country: | China |
| Age: | Nongshanian, Upper Paleocene |
| Remarks: | This seems to fit somewhere within the order Notoungulata. A cast of the holotype is in the Peabody collection. |
| Reference: | Xu (1977), Two new genera of old Ungulata from the Paleocene of Qianshan Basin, Anhui. Vertebrata Palasiatica 15(2), p.119-125. |
| Link: Order Notungulata, Martin Jehle |
| Genus:
Plesiorycteropus Filhol, 1895 'near the aardvark' Aka: Hypogeomys G Grandidier, 1912 (partly); Majoria ('for Major') Thomas, 1915; Myoryctes Forsyth Major, 1908
Remarks: This is a hard-to-place but recent fossil genus. It has been considered as
aardvark-like, but such similarities might be a matter of convergence. It appears it was
some kind of digger, with vaguely basal hangovers. The order Bibymalagasia has been
proposed. Though irrelevant to the project in hand, it sounds quite interesting. Reference: Forsyth Major (1908), A giant sub-fossil rat from Madagascar, Myoryctes rapeto, gen et sp nov. Geol Mag V (5), p.97-98, figs. 1, 2. |
| Link: Abstract for Bulletin 220, AMNH |
| Species: | Plesiorycteropus madagascariensis Filhol, 1895 |
| Aka: | Majoria; Myoryctes rapeto; Hypogeomys boulei Grandidier, 1912 (partly) |
| Place: | near Belo |
| Country: | Madagascar |
| Age: | Recent |
| Remarks: |
A burrower the size of a small dog, this creature probably had a taste for ants, etc. The
wildlife of the island suffered a fair few extinctions about a thousand years ago. This
genus was one of the victims. Holotype MNHNP 328 is a partial skull of probably a juvenile or subadult discovered by M. Grevé in November, 1894 or possibly earlier. It struts its stuff in the collection of the Museum National d'Histoire Naturelle, Paris. The specific might just have some geographical connection, but this is merely my guess. The specimen was collected somewhere near Belo in the middle of the west coast. |
| References: | Filhol H (1895), Observations concernant les mammiferes contemporains des Aepyornis a Madagascar, Bull. Mus. Hist. Nat., Paris, 1, p.12-14. |
| Forsyth Major, CI (1908), A giant sub-fossil rat from Madagascar, Myoryctes rapeto, Geol. Mag. (series 5), 5, p.97-98. | |
| Grandidier, G (1912), Un nouvelle espece subfossile d'Hypogeomys, 1'H. Boulei, G. G. Bull. Mus. Nat. Hist. Nat., Paris, 18, p.10-11. |
| Link:
AMNH Bestiary http://www.amnh.org/science/biodiversity/extinction/Resources/Bestiary/Bibymalagasia.html A brief, comprehensible description of a definitely non-Mesozoic mammal. |
| Species: | Plesiorycteropus germainepetterae MacPhee RD, 1994 |
| Place: | |
| Country: | Madagascar |
| Age: | Recent |
| Remarks: | I've got a copy of MacPhee, 1994 but, as
the subject is somewhat beyond the scope of my core interests, I doubt I'll get
around to giving the paper the attention it'd would require. Even the abstract on
page six is long, as abstracts go. MacPhee addresses proposed affinities with
the aardvark (Orycteropus), and accepts there are similar
derived characters. However, these also tend to be
shared with other digging mammals such as anteaters. They're adaptations for
pursuing the same sort of trade, and can be blamed on convergence rather than
shared ancestry. "Accordingly, the view that Plesiorycteropus is
unambiguously aardvarklike in its morphology and adaptations is not supported in this
study." Holotype Jumping forward to page 34 allows me to mention MNHNP 327, the type fossil resident at the Museum National d'Histoire Naturelle, Paris. It's a partial adult skull, and the specific name honours Dr Germaine Petter from the MNHNP. A complete femur was allocated to this species. As well as being somewhat smaller, the new species differs in some details of the skull. One particularly significant characteristic is shared; extinction. Size and bye bye A series of calculations came up with body weight estimates ranging from between around 6 to 12 kilos. The variation results from comparions with differently built animals. The time of extinction of this genus is considered on page 159. Presumably, as no mention of anything of this sort appears in early chronicles, the animal was deader than the dodo prior to Europeans arriving in Madagascar. That would suggest before around 1650. A popularly cited figure for this extinction is about a thousand years ago. It's easy enough to remember, and roughly coincides with the end of an extinction wave that beset the wildlife of the island. |
| Reference: | MacPhee RD (1994), Morphology, adaptations and relationships of Plesiorycteropus and a diagnosis of a new order of eutherian mammals, Bulletin of the American Museum of Natural History, 220, p.1-214. |
| Genus:
Prodelttheridium Trofimov BA, 1984 Remarks: This generic name wasn't in connection with a formal description. This means it's a nomen nudum. The spelling of the name seems rather odd. I've taken it from Wible et al 2001, p.16. The material is still undescribed. |
| Species: | Prodelttheridium kalandadzei Trofimov BA, 1984 |
| Place: | Höövör |
| Country: | Mongolia |
| Age: | Albian-Aptian, Lower Cretaceous |
| Remarks: |
"In light of the name, this form was presumably thought to
have affinities with the basal metatherian Deltatheridium (Gregory & Simpson, 1926;
Rougier et al., 1998) and, therefore, to occupy a position between Vincelestes and
Late Cretaceous eutherians", (Wible et al 2001, p.16). The formulation chosen places this between V. and Late Cret eutherians, which means it could represent a non-eutherian. A formal description would help. |
| Reference: | Trofimov in Reshetov & Trofimov (1984), Review and study of fossil mammals from the USSR. In Sokolov & Kucheruk (eds), Theriology in the USSR, p.6-29. |
| Genus: Telacodon Marsh OC, 1892 |
| Species: | Telacodon laevis Marsh OC, 1892 |
| Aka: | T. leavus |
| Place: | Lance Formation, Wyoming |
| Country: | USA |
| Age: | Maastrichtian, Upper Cretaceous |
| Remarks: | Simpson, 1951 provides some information. As with Batodon in the same study (p.9), Marsh established this genus for lower jaw material preserving premolars but not molars. Telacodon had the shorter canine. Several specimens, including the type fossil, are at the Peabody, Yale. |
| Reference: | Marsh (1892), Discover of Cretaceous Mammalia, Part III, American Journal of Science, 43, p.249-262. |
| Link: NAFMS, Lull's Locality 5 http://flatpebble.nceas.ucsb.edu/nam/listfiles/Lull's_Locality_5.html |
| Species: | Telacodon praestans Marsh OC, 1892 |
| Place: | Lance Formation, Wyoming |
| Country: | USA |
| Age: | Maastrichtian, Upper Cretaceous |
| Remarks: | This species is briefly discussed in Simpson,
1951 (p.10). This was based on part of a lower jaw with two molars. However, as it's probably metatherian, it can't be sensibly regarded as belonging to this genus. I've got no idea about current thinking on this fossil, assuming there is some. Simpson relates a similar fate befell a fossil referred by Marsh to Batodon tenuis. |
| Reference: | Marsh (1892), Discover of Cretaceous Mammalia, Part III, American Journal of Science, 43, p.249-262. |
| Genus: Tingamarra Godthelp H, Archer M, Cifelli RL, Hand SJ & Gilkeson CF, 1992 |
| Species: | Tingamarra porterorum Godthelp et al, 1992 |
| Place: | Murgon, Queensland |
| Country: | Australia |
| Age: | Upper Paleocene or Lower Eocene |
| Remarks: | This was described as a condylarth of
sorts, a proto-ungulate. If correct, it's fifty million years earlier than terrestrial
placentals were supposed to have reached Australia. However, it's affinities now seem less
than clear, (Kemp 2005, p.209). Although it lacks some typical characteristics, others have
interpreted it as a marsupial; either an ameridelphian
or a specialised australidelphian. In contrast to typical marsups, the entoconid and
hypoconulid of the molar talonid aren't twinned. Tingamarra's based on a single tooth, though other possible bones have been identified. A certain eutherian in the same fauna is Australonycteris clarkae Hand, Novacek, Godthelp & Archer 1994. This is among the oldest records of a bat I've heard of. Tingamarra's the name of the property, while Murgon is the township. The age was originally considered to be Lower Eocene, but radiometric dating has subsequently shown the fossils are possibly somewhat older, (with thanks to Brian Choo for the update). |
| Reference: | Godthelp et al (1992), Earliest known Australian Tertiary mammal fauna. Nature (London) 356, p.514-516. |
| Links: Australia's Lost Kingdoms http://www.lostkingdoms.com/facts/factsheet13.htm An accessibly written summary.
Murgon http://www.amonline.net.au/fossil_sites/murgon.htm A look at the fossil site in Queesland. Quite a place.
Cadbury Yowie and the Lost Kingdoms http://www.yowiepower.com/lostkingdoms/ditty2.htm Paleontology meets chocolate. |
| Genus: Veratalpa Ameghino, 1905 |
| Species: | Veratalpa sp. Ameghino, 1905 |
| Place: | |
| Continent: | Europe |
| Age: | Miocene |
| Remarks: | ?????? |
| Reference: |
| Genus:
Wanotherium Tang & Yan, 1976 Aka: Wannotherium |
| Species: | Wanotherium xuanchengensis Tang & Yan, 1976 |
| Place: | Xuancheng Basin, Anhui Province |
| Country: | China |
| Age: | Upper Paleocene |
| Remarks: | A couple of cast specimens are at Yale. |
| Reference: |
| Other reports: Bissekty Formation and Aitym Formations, Kyzylkum Desert, Uzbekistan An upper molar, with anatomical affinities to Daulestes, has been recovered from the Aitym Formation, (upper Turonian - Coniacian). It's about 50% larger than those of D. nessovi. Larger molars have also been reported from the somewhat older Bissekty Formation, and these seem to imply the presence of two or more species in that fauna. Studies continue. (Averianov & Archibald 2003, p.6-7.) |
| Bonus Link:
Some notes on Taxonomy and Zoological Classification http://www.nafcon.dircon.co.uk/zoology_class.html The alternative title is What do we mean by species, genus and family? A bit of background and history on classification. |
| Help:
Should anybody have any further information, I'd be pleased to hear of it.
Regarding references and Bibliography:
With thanks to all the featured sources.
Trevor Dykes, January 2002. Latest up-date: 29.9.2007 |
| With further thanks due to:
The Prehistoric Data Files http://www.angellis.net/Web/PDfiles/marsups.pdf
Martin Jehle, Paleocene mammals of the world, Cohort Placentalia http://www.paleocene-mammals.de/pal2.htm An excellent reference. Some Mesozoic remains feature.
BIOSIS, The Index to Organism Names http://www.biosis.org.uk/triton/indexfm.htm
The Society of Vertebrate Paleontology BFV Online, (John Damuth)
The Peabody On-line VP Catalogue http://george.peabody.yale.edu/vp/
Dr John Alroy, North American Fossil Mammal Systematics Database http://www.nceas.ucsb.edu/~alroy/nafmsd.html Weight guestimates and nomenclatural details.
David Marjanovic, for suggestions, corrections and lessons in Russian grammar. |
| Bibliography: Averianov AO & Archibald JD (2003), Mammals from the Upper Cretaceous Aitym Formation, Kyzylkum Desert, Uzbekistan. Cretaceous Research 00 (2003), p.1-21. Cifelli RL (1999), Tribosphenic mammal from the North American Early Cretaceous. Nature, 401, p.363-366. Fox RC, Scott CS & Bryant HN (2007), A new, unusual therian mammal from the Upper Cretaceous of Saskatchewan, Canada, Cretaceous Research, 'Article in Press' edition, p.1-9. Ji Q, Luo ZX, Yuan C-X, Wible JR, Zhang JP & Georgi JA (2002), The earliest known eutherian mammal, Nature 416, p.816-822. Kemp TS (2005), The Origin and Evolution of Mammals, Oxford University Press, pp.331. Kordikova ZB, Polly PD, Alifanov VA, Rocek Z, Gunnell GF & Averianov AO (2001), Late Cretaceous and early Tertiary microvertebrates from the North Eastern Aral Sea Region of Kazakhstan, Journal of Paleontology, 75 (2), p.390-400. MacPhee RD (1994), Morphology, adaptations and relationships of Plesiorycteropus and a diagnosis of a new order of eutherian mammals, Bulletin of the American Museum of Natural History, 220, p.1-214. McKenna MC & Bell SK (1997), Classification of Mammals Above the Species Level. Columbia University Press. Reilly SM & White TD (2003), Hypaxial Motor Patterns and the Function of Epipubic Bones in Primitive Mammals, Scienec 299, p.400-402. Simpson GG (1951), American Cretaceous insectivores, American Museum Novitates, 1541, p.1-19. Weil A (2002), Mammalian evolution: Upwards and onwards, Nature 416, p.798-799. Wible JR, Novacek MJ & Rougier GW (2004), New data on the skull and dentition in the Mongolian Late Cretaceous eutherian mammal Zalambdalestes, Bulletin of the American Museum of Natural History, 281, p.1-144. Wible JR, Rougier GW, Novacek MJ & McKenna MC (2001), Earliest Eutherian Ear Region: A Petrosal Referred to Prokennalestes from the Early Cretaceous of Mongolia. American Museum Novitates 3322, p.1-44. |
A somewhat later and more