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.
Reader-friendlier paragraphs:
Some of these critters appear to be forerunners of the northern tribosphenidans,
(Boreosphenida and close relatives), from which a
branch called Theria emerged. That line led to both
marsupial and
placental mammals; eg.
Skippy the Bush Kangaroo and Dame Edna
Everage.
This directory is rather volatile. The title changes about once a year. This latest
incarnation has been influenced by the findings of Martin T, 2002, (see Bibliography). I'm
hoping it'll hold together for a while, and will now try set the scene informally.
Especially in the northern hemisphere of the Upper Jurassic, there were a fair number of
mammals around known as dryolestids and the like.
They were found of eating insects. Compared to the animals represented on this page, (who
also enjoyed insects), they were primitive. This collection represents the northern
mammalian evolutionary action after Dryolestoidea branched off.
A great deal of the discussion on these creatures centres upon teeth; especially the
molars, (which are your largest teeth and can be found either
in the corner of your tooth row, or perhaps soaking in a glass of water overnight). As a
very generalized summary of a basal
zatherian lower molar when seen from the external
perspective, (labial), the tooth has a series of three main
cusps at the front. This area is called the trigonid.
The first is the paraconid, then comes the large protoconid and finally the metaconid.
Behind the trigonid is a kind of heel called the talonid.
Later in the evolutionary history of we northern mammals, this feature came equipped with a
proper basin. There are various other cusps and ridges involved. I'm sorry if some of the
words seem strange, but the subtitle read 'reader-friendlier' not 'friendly'.
Less reader-friendly:
For those of a tidy nature, Zatheria McKenna, 1975 is a
Sublegion within the wider taxon of Cladotheria, which
also includes those aforementioned dryolestids. It's further divided into a couple of
Infralegions: Peramura (which is in effect much the same as Peramuridae -Section B) and
Tribosphenida. Most representatives of Tribosphenida
are therians; marsupials, placentals and their more immediate kith and kin. This directory
takes us near to the House of the Rising therian, but not
quite up to the door. Boreosphenida does that.
Definitions:
As Martin, 2002 makes clear in the Conclusions of the paper, while the fossil record of
pretribosphenic holotherians is increasing, many are represented by scant and fragmentary
material. The picture is further complicated by many anatomical features being
plesiomorphic (primitive), which creates problems for
analysis.
Consequently: "As demonstrated for Nanolestes, these plesiomorphic taxa are
best placed in the stem-lineage of Zatheria. The stem-lineage of a taxon is defined as
the lineage between the last common ancestor of this taxon and its sister-taxon (Ax, 1984,
1985). The stem-lineage of Zatheria lies between the separation of Dryolestoidea and the
last common ancestor of Peramus and Tribosphenida", (p.346). Martin specifies
the inclusion only of Arguimus, Argiotherium, Abelodon, Magnimus,
Minimus, Afriqiamus, Amphitherium and Nanolestes. I'm
inclined to place a couple of other taxa on this page
provisionally, partly because I can't think of where else to put them. |
A. Stem zatherians and zatherians B.
Peramuridae
| A. STEM ZATHERIANS AND ZATHERIANS |
| Taxon: within (or near to) Zatheria McKenna, 1975
This is a fairly diverse collection of animals belonging to a number of families.
Precise relationships are often unclear. Further and better specimens would help.
Link:
Mikko Haaramo's Cladotheria
Mikko Haaramo's Cladotheria
Mikko offers three alternative cladogrammes for this group. This is the most recent,
though not necessarily the most 'correct' of them. Opinions on detail vary and research
and discussion are naturally continuing.
Genera: Abelodon,
Afriquiamus, Amphibetulimus, Amphigonus
(= Amphitherium), Amphitherium, Amphitylus
(= Amphitherium), Arguimus, Arguitherium
(= Arguimus),
Botheration-therium (= Amphitherium), Botheratiotherium
(= Amphitherium), "Heterotherium" (= Amphitherium),
Kennetheredium, Magnimus,
Microderson, Minimus,
Nanolestes, Palaeoxonodon, Thylacotherium
(= Amphitherium), Vincelestes,
other reports
Time-Line:
Lower Cretaceous: Abelodon, Afriquiamus, Arguimus,
Magnimus, Microderson, Minimus, Vincelestes
Upper Jurassic: Nanolestes
Middle Jurassic: Amphibetulims, Amphitherium, Kennetheredium,
Palaeoxonodon |
| Genus: Abelodon Brunet M,
Coppens Y, Dejax J, Flynn J, Heintz E, Hell J, Jacobs L, Jehenne Y, Mouchelin G, Pilbeam DR
& Sudre J, 1990 |
| Species: | Abelodon abeli Brunet et al (& etc), 1990 |
| Place: | Koum Basin |
| Country: | Cameroon |
| Age: | Barremian-Aptian, Lower Cretaceous |
| Remarks: | Apart from the fact that this was a larger
animal than Nanolestes, and both lower and upper molars
are known, I'm lacking information. Seeing as the description was published in French, I
doubt the paper would help me. |
| Reference: | Brunet et al (1990), Nouveaux mammifères du Crétacé intérieur
du Cameroun, Afrique de l'Ouset. C.R. Acad. Sci. Paris Sér. II, 310, p.1139-1146. |
| Genus: Afriquiamus
Sigogneau-Russell D, 1999
‘African mouse’ |
| Species: | Afriquiamus nessovi Sigogneau-Russell D, 1999 |
| Place: | Anoual |
| Country: | Morocco |
| Age: | Lower Cretaceous |
| Remarks: | Martin, 2002 contains some details on the upper
molar, but none on the lower. This tooth was double-rooted,
(p.333). It might be more accurately placed within Peramura. |
| Reference: | Sigogneau-Russell (1999), Reevaluation of Peramura (Mammalia,
Cladotheria) based on new specimens from Lower Cretaceous of United Kingdom and Morocco.
Geodiversitas 21 (1), p.93-127. |
| Genus: Amphibetulimus
Lopatin AV & Averianov AO, 2007
'both sides Betula mouse'
Family: Amphitheriidae Owen, 1846
Remarks: My information is presently restricted to the first page of the publication. 'Betula'
is a Latinized reference to Berezovsk Quarry, the ancient grave yard from whence the fossil
came. |
| Species: | Amphibetulims krasnolutskii Lopatin &
Averianov, 2007 |
| Place: | Berezovsk Quarry, Itat Formation, western Siberia |
| Country: | Russia |
| Age: | Bathonian, Middle Jurassic |
| Remarks: | Only having the first page of the publication
available is rather limiting, but better than nothing. Anyway, the authors refer this
new genus to the family of Amphitheriidae, and regard that concept as home for "the
earliest and most primitive pretribosphenic mammals"; something like great-great-great-etc
grandparents of the something like great-great-great-etc grandparents of
boreosphenidan mammals. Extant boreosphenidans
include myself and Skippy the Bush Kangaroo. However, this comes from a time of Earth tens
of millions of years before the emergence of those descendant lineages. As the most
informative paragraph states:
"Amphibetulimus is assigned to Amphitheriidae based on the following set of
characters: the talonid is larger than that of
Dryolestoidea, bit probably smaller than in more advanced Zatheria; the paraconid is
directed vertically (in Dryolestidae Marsh, 1879, it is inclined anteriorly; jin Paurodontidae
Marsh, 1887, it is low shelflike); the talonid cusp occupies a labial position posterior
to the protoconid (in Dryolestidae, it is positioned lingually; in Paurodontidae, it is at
the midline); the posterior root of the lower molars is only slightly smaller than the
anterior root (in Dryolestidae, it is much smaller."
Holotype
There certainly is one! However, the first page sadly doesn't reveal its catalogue number
or pleasant place of residence. It's also mutely Sphinx-like as regards to the motive
behind the specific name. Somewhat remarkable is that this publication somehow evaded my
radar system until September, 2010.
I should also mention that my sole page is from the English language edition: The earliest
Asiatic pretribosphenic mammal (Cladotheria, Amphitheriidae) from the Middle Jurassic of
Siberia, Doklady Biological Sciences, 417, p.432-434. The original description was in
Russian and the page numbers differ. |
| Reference: | Lopatin & Averianov (2007), (The earliest Asiatic pretribosphenic
mammal (Cladotheria, Amphitheriidae) from the Middle Jurassic of Siberia), Doklady Akademii
Nauk, 417(1), p.136-138. |
| Genus: Amphitherium de
Blainville, 1838
'both sides beast'
Aka: Amphigonus Agassiz, 1838; Amphitylus Osborn, 1888;
Botheration-therium Charlesworth, 1838; Botheratiotherium de Blainville,
1838; Didelphis? (partly); "Heterotherium" de Blainville, 1838;
Thylacotherium Valenciennes, 1838
Family: Amphitheriidae Owen, 1846
Remarks: Ahem. I've been given to understand that Thylacotherium is a synonym of
Phascolotherium Owen, 1838. Perhaps it's somehow both. Heterotherium Fischer
de Waldheim is "a genus of coelebs", (McKenna & Bell, 1997). No, I don't know.
Ask them. There are some very pleasant beers available in Oxfordshire. Maybe they were
excessively sampled in 1838.
The first Mesozoic mammal
"It was about 1812 when a fossil jaw, imbedded in a rock of Jurassic age, was found by
"an ancient stonemason" near Oxford in England and, through W. J. Broderip, then
a student, brought to the attention of Professor Buckland. This was a mammal jaw and it
came from a deposit formed at a time when, according to the geologic theory of that day, no
mammals existed. By 1824 the future dean's convictions had conquered his cautious orthodoxy
and he announced the discovery. By 1840, after a storm of discussion, it was universally
accepted", (Simpson 1935, p.154-155).
The first mention of a Jurassic mammal is in: Buckland W (1824), Notice on
Megalosaurus, Transcriptions of the Geological Society of London, (2), i,
p.390-396.
According to Savage, 1989 (p.4), at least one of these specimens was first found in about
1764.
Reasons for the excitement
Kemp, 2005 (p.167) offers clues as to thoughts of that day: "Since their very
earliest recognition by Dean William Buckland... from the Middle Jurassic Stonesfield
Slate of Oxfordshire, Mesozoic mammals have generated controversy... Transformationists
like Robert Grant denied that they were mammals, because it disturbed their accepted
temporal sequence of Mesozoic reptiles preceeding the exclusively Tertiary mammals. On the
other hand, establishment figures like Buckland himself and Sir Richard Owen welcomed this
apparent refutation of transformationism and had no doubt that they were indeed opossom-like
mammals." (References have been omitted.)
The present supply
Much of the following is based upon my reading of Butler & Clements, 2001.
The world's supply of Amphitherium mandibles has
stood at four since the genus was established. They were all recovered from near Stonesfield.
If anyone knew exactly where they came from, they've been dead for several human generations.
There are presumably more fossils out there somewhere, (eg. the upper teeth), but none have
come to light.
History of the specimens
Simpson studied them in 1928. He concluded there could only be four
premolars present, because no early mammals exceeded this number except for
multituberculates, (p.1). This must've seemed
reasonable enough, seeing as it was backed up by over a century of fieldwork, (albeit not
very thorough). If he'd been working fifty years later, he'd likely have seen things
differently. Some basal
eutherians certainly had five of these teeth, (eg. juvenile Kennalestes). Mind
you, he did add: "so far as is known."
Damage
Back in the early nineteenth century, the fossils were found embedded in blocks of stone.
Since then, they've been cleaned and prepared with varying degrees of care and skill. Some
of these efforts were not careful or skilful enough, (p.2). Sketches made by Owen (1838-1846)
include features which are no longer present. It wasn't until the early 1960s that one of the
specimens, (the Natural History Museum one), was freed from its surrounding matrix. That's
now Amphitherium rixoni. The other three, (Oxford University Museum I, II and III),
are still embedded. Attempts to x-ray these were unsuccessful, so the authors settled for
some gentle cleaning with water.
Molars
Martin, 2002 contains some information on lower molars.
They're larger than the corresponding teeth in Nanolestes, and have a longer
talonid, albeit in a primitive form, (p.344-345).
A useful resource for tooth terminology is
Fasthealth.com.
| Reassigned species: A. prevostii partly = A. rixoni; A.
oweni = A. prevostii | |
| Species: | Amphitherium prevostii (von Meyer, 1832) de
Blainville HMD, 1838 |
| Aka: | A. oweni; A. prevusti; Amphitylus oweni Osborn,
1888; Didelphis ? prevostii von Meyer, 1832 |
| Place: | Stonesfield slate, Oxfordshire |
| Country: | England |
| Age: | Bathonian, Middle Jurassic |
| Remarks: | The following is largely based upon my reading
of Butler & Clements, 2001.
This study contains a redescription of each of the three specimens of this species. I'll
concentrate on Oxford I, which is the type fossil. By the way, the species was established
in 1832 and predates the genus.
Judging by its smaller size, Oxford I is probably the youngest representative of this
species, though it's larger than the A. rixoni individual. The
mandible is fragmentary and exposed only on its
lingual side, (p.3). Six molars
are preserved, (the front three are damaged), and there are four
premolars present. The m1 is shorter than either the p5 or m2. What remains of the
trigonid is proportionately narrower than in the other
molars. It perhaps didn't exceed the main cusp of p5 in height.
A premolar and dental formula
The relatively large size of the slightly damaged p5 makes it resemble the molars. The remains
of its talonid suggest two cusps were present. Fragments of
a lingual cingulum are apparent. The p4 is dominated by a
single cusp at the front. Compared to the p5, the talonid is short. The p3 resembles p4 but
it's smaller. Going further forwards, p2 is heavily damaged on the lingual side. The
mandible is broken in front of that, but there used to be the remains of
alveoli for a double-rooted tooth, (according to Owen,
1842).
Further information is provided by the other specimens. Taken together, the authors conclude
that the lower dental formula was 4 incisors, 1
canine, 5 premolars and 6-7 molars per side.
Differing ages
Oxford II is the largest of the mandibles, and presumably comes from the oldest individual,
(though not necessarily). Osborn used this fossil as the basis for a separate genus and
species, Amphitylus oweni. This was referred to Amphitherium by Goodrich in
1894, (p.6). That specific name was still being used in the 1960s to refer to the only
specimen showing the labial side of the teeth. However, no
basis for a separate species could be recognized by either Simpson, (1928) or in this 2001
study.
Holotype
The holotype, Oxford I, is catalogued as J. 20.074. It studies in the Museum of Oxford
University along with two fellow undergraduate mandibles.
Affinities
Sigogneau-Russell (1999) found that "Amphitherium is closer to
tribosphenidans than to
dryolestoids," (see Afriquiamus above for
the relevant abstract).
A couple of cast specimens of A. oweni are in the collection of the Peabody Museum,
Yale They're labelled as "not verified". |
| References: | von Meyer (1832), Palaeologica, zur Geschichte der Erde und
ihrer Geschöpfe. Schmerber, Frankfurt am Main, xi + 560pp. |
| de Blainville (1838), Doutes sur le prétendu Didelphe de
Stonesfield. Comptes Rendus de l'Académie des Sciences 7, p.402-418. |
| Links:
Hugh Falconer, The Annals and Magazine of Natural History (June 1856)
http://aleph0.clarku.edu/huxley/comm/ScPr/Falc.html
This site’s about as informative as any, despite having been written 145 years ago. (Coming
to think of it, my more site's now far more informative!) Falconer concluded this creature
was more like a 'placental' mammal than a
'marsupial', as then understood, (though it’s now seen
more as a possible, distant proto-both-of-them). At the time, only the three extant,
mammalian lineages were known, and it was generally felt that all species would fit into
them, whether living or extinct. Firstly, very few Mesozoic fossils had been found. And
secondly, Charles Darwin didn’t publish his theory until 1859.
The Peabody Museum VP Catalog
http://george.peabody.yale.edu/vp/
Specimens held at Yale.
The Oxford University Museum, Fossil types
http://www.oum.ox.ac.uk/onlinedb/geotypes/geosearc.htm
And more from Oxford. |
| Species: | Amphitherium rixoni Butler PM & Clemens WA, 2001 |
| Place: | Stonesfield, Oxfordshire |
| Country: | England |
| Age: | Bathonian, Middle Jurassic |
| Remarks: | The following is largely based upon my reading of
Butler & Clements, 2001.
This species is justified by: the smaller size of the
postcanines; the talonid ridge of the p5 extending
directly backwards from the main cusp, (protoconid), with no expansion in the area of the
metaconid; the fully lingual position of the metaconid on
the m1 and m2, (p.6-7).
This is based on a lower mandible which contains five
molars and the last
premolar. The front of the bone is shattered, but fragments of root and
alveoli suggest the original presence of four further
double-rooted premolars. If for a canine, then the first preserved pair of alveoli would
probably be longer than they are. There's no evidence of any replacement teeth beneath the
premolars. However, the less wear displayed by p5 as compared to m1 suggests that at least
that tooth had diphyodont replacement.
Generation gaps
Of all four Amphitherium this one has the slenderest ramus and the least worn teeth.
This is probably because it's the youngest individual, as is the presence of only five
molars, (generally six in A. prevostii). These aren't reasons to establish a
distinct species. My children might think I'm from a different planet, but I doubt they'd
manage to get a reputable journal to accept their argumentation for publication, not unless
they could point to justifications unattributable to my eternal youthfulness.
Getting the measure of things
One thing they could try would be to measure my molars. If I were an Amphitherium,
the length on my molar set wouldn't vary much with age, not once it was established.
Nor would the total length of m1-m5. That's 5.15mm in this species. This is noticeably
below the range for A. prevostii, (5.65-6.0mm). What seems to be the permanent fifth
premolar is also smaller than its known counterparts,
(0.75mm as opposed to lengths of 1.18 and 1.19mm). Then there are the details of the
talonid in p5 and the differences in m1 and m2, which are
mentioned above.
Holotype
The holotype is BMNH 36822 and it works at The Natural History Museum, London. The specific
name honours the now deceased Mr Arthur Rixon, who skilfully prepared the specimen in the
1960s, and thus made a fuller study possible, (p7).
Additional thoughts
Sigogneau-Russell, 2003b discusses this specimen. She finds that a prominent
"antero-buccal cusp" has previously been proposed
as a diagnostic characteristic of this genus, (note- but not this species). However, she
concludes that this 'cusp' is actually a cingulum. It's
hardly noticeable upon the first molar in the series, (m1).
Meanwhile, its analogue is strong on several specimens of Palaeoxonodon,(p.511).
This weakens its usefulness for diagnostic purposes. Variability is evident in different
teeth of this one jaw.
Cheers Mikko
With thanks to Mikko Haaramo for both the notification of the publication, and supplying
the original formulation of this entry.
|
| Reference: | 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. |
Seven Phases of Teeth
(Postcanines)
VI Amphitheriida and Zatheria
The following is derived from and inspired by my reading of Butler & Clements, 2001,
(p.14-16).
For this purposes of this paper, Amphitheriida is restricted to the genus of
Amphitherium. More recent research suggests that Palaeoxonodon may also be a
member of the taxon. The upper postcanines of Amphitherium
are unknown, and there's no direct evidence available concerning dental replacement. The
fifth premolar is probably a secondary tooth in A.
rixoni, and it must have erupted after several molars were already in place, seeing as
it's less worn, (p.14-15).
Zatheria
The oldest fully known postcanines for Zatheria are those which belonged to Peramus,
(next section of this directory). There are eight. Number four is large and for puncturing.
The final three are molars. The fifth upper is like the sixth,
but it's narrower, has a smaller metacone and is double-rooted. It's a
submolariform premolar. When so interpreted, five
premolars accords with Amphitherium, but the presence of only three molars doesn't,
(amphi had six). This, and further reasons, suggest these genera represent lineages which
diverged relatively early in holotherian history.
A deviation on derivation
What follows is my own deviation.
Perhaps because we have a bias for tidy stories with beginnings, middles and ends, there's
a tendency to think evolution implies some kind of ladder leading towards ever greater
improvement. This is counter to the available evidence.
To use a reasonably familiar example, the dinosaur Megalosaurus may have gone
extinct something like 160 million years ago, but that doesn't stop it from being further
derived than a thoroughly live crocodile. This concerns
anatomy. Megalosaurs is less like their last common ancestor than a croc is, and thus
more 'advanced', as well as being long dead. Richard Owen highlighted the relative
sophistication of dinosaurs back in the 1840s, but news travels slowly in some quarters.
Despite being generally more derived and later than Amphitherium, (Lower Cretaceous
as opposed to Middle Jurassic), Peramus was in some ways also more
basal; ie more similar to Kuehneotherium, the most
basal known holotherian. Its molars are longer and
narrower. "Also, the talonids of the molars of
Peramus fit into grooves between the lingual basal
cusp and the mesiobuccal
cingulum of the trigonids of the following teeth",
(p.15). In those respects, Amphitherium was more derived, as well as long dead. In
most respects that are known, it was also the more basal of the two.
Evolution is about change, and 'improvement' is relative.
Back to the plot
The presence of five premolars in Peramus is
unusual for zatherians, but not unique. It's been argued
that Arguimus shared this characteristic, but that's probably not the case, (p.16).
However, it is known from primitive eutherians; our line.
One of these premolars was subsequently dispensed with, (probably the third), and is unknown
beyond the Upper Cretaceous. The more standard eutherian postcanine formula is four
premolars and three molars (or less in both cases). The
general metatherian condition is 3p and 4m (or less in
both cases). Interestingly, the recently published basal
representative, Sinodelphys, has four
premolars.
Advanced marsups
In terms of decreasing dental replacement, marsupials
are more derived than eutherians, (p.17). Certainly on the lower jaw, the first two
premolars are permanent teeth. Baby kangaroos and opossums don't receive as many visits
from the tooth fairy.
Go to Phase: I Carnivorous non-mammalian cynodonts,
II Basal mammals,
III Kuehneotheriids (basal Holotheria),
IV Cladotheria,
V Dryolestidae,
VI Amphitheriida and Zatheria,
VII Tribosphenic dentition. |
| Genus: Arguimus Dashzeveg D,
1979
'Argui mouse'
Aka: Arguitherium Dashzeveg D, 1994
Remarks: The Argui River is near the locality of Khoobur (aka Khovrboor), which is now more
usually called Höövör. Dashzeveg proposed a family called Arguimidae in 1994 but the validity
of it has been strongly challenged. Furthermore, the genus formerly known as Arguitherium
has fallen into disrepute along with the proposed family of Arguitheriidae. |
| Species: | Arguimus khosbajari Dashzeveg D, 1979 |
| Aka: | A. khosbayari; Arguitherium cromptoni Dashzeveg D, 1994 |
| Place: | Höövör |
| Country: | Mongolia |
| Age: | Aptian-Albian, Lower Cretaceous |
| Remarks: | Misinterpretations and uncertainties in earlier
descriptions led to Lopatin & Averianov offering a drastic revision in 2006. This entry
is now based primarily on my reading of that paper.
Some long dead, scantily preserved eucynodonts can
behave very badly. They like to play tricks on researchers. One such is Arguimus
and that's why it's lumbered with a disgrace, a junior synonym; Arguitherium.
Dating as it does from the Lower Cretaceous of Mongolia, its squeaks were issued in a rather
unfamiliar accent, and that led to misinterpretations; eg. establishing two apparently
quite distantly related genera for specimens from the same species.
It was largely the fault of the postcanine teeth. As is
fairly widely known, mammalian postcanines come in two distinct categories. There are
premolars (the ones you replaced) and
molars (which can only be replaced with dentures). They also
tend to look somewhat different. However, you get shades of grey in this not black and
white world. You can have molariform premolars and only
partially molariform molars. Chuck in the imperfections of preservation and things can get
treacherous. Arguimus was playing tricks of that kind. Fortunately, an increased
number of specimens seem to have brought the miscreant to heel. The genus of
Arguitherium has now been killed off. As the owner of the jaw died during the Lower
Cretaceous, this is one of the few mammals to have perished twice. Some species react to
such behaviour by grounding new religions.
Cleaning the teeth
Five further specimens have since been identified from the Höövör site and they've helped
bring clarity (p.339). The teeth of the holotype are shown to be p4-5 and m1-3. Those on
the type fossil assigned to Arguitherium are confirmed as p4-5 and m1. The known
dental formula per side is: (lowers): 5 premolars and four molars. Particularly sneaky
behaviour was displayed by possession of a premolariform final premolar and an only 'partially
molariform' first molar. That led to it being misidentified as a premolar.
Höövör mammals
A Soviet-Mongolian expedition was busy at the Höövör site from 1969-1972, and the diversity
of mammals is impressive. They include a number of
multituberculates, Gobiconodon, a
'symmetrodont' called
Gobiotheriodon, pretribosphenic Arguimus and a
basal eutherian named
Prokennalestes. As a stem-zatherian, Arguimus could have fitted the role
of a living fossil; a relic of a bygone evolutionary experiment. To be totally disrespectful,
such animals had passed their sell-by date in the northern hemisphere with the close of the
Jurassic. Still, their presence in Mongolia shows their breeding equipment kept functioning
well enough. And mammals don't tend to worry about being out of fashion while having sex.
Arguimus obviously bonked on.
Stem-zatherian! What that?
Zatheria is officially diagnosed as being the most recent common ancestor of myself and
Peramus, and all of its descendants. Check any decent text
book in the world and that's exactly what it will say. Zatherians developed high-tech teeth
which largely conquered the landmasses of the globe. You, me, a dog named Boo and
Peramus -we're all (or were) zatherians. Our earliest known representatives were
munching in the earliest days of the Cretaceous; something like 35 million years prior to
Arguimus orgies in Höövör.
Contrasts
The basal number of lower molars for zatherians appears to have been three per side, and the
talonids were 'pretribosphenic' with a cusp termed the
hypoconulid. Arguimus had four molars and lacked that cusp (p.340). The relatively
deep lower jaw had some 'advanced' characteristics. Unlike an array of mammals (eg.
dryolestidans and
Tendagurutherium) there was no attachment for an 'extra' jaw bone called the
coronoid. Its ancestors had also got rid of
Meckel's groove. That bit of 'non-mammalian' baggage was still being sported by early
eutherians (Eomaia and the aforementioned
Prokennalestes. Arguimus could be termed precocious in that regard.
Lower jaw
Arguimus had a relatively long jaw which deepened from front to back. None of the
seven specimens show any traces of Meckel's groove. The coronoid process of the
dentary ascends steeply at the rear of m4, and there's no
indication of a separate coronoid bone (p.343). There is a faint bump low down at about the
level of the alveoli but its identity is unclear. (Something
similar has been reported for Zalambdalestes
Premolars
Nothing is known of the incisors or
canine, and information on the front premolars is limited. A couple of jaw fragments do
retain alveoli for the front trio which were double rooted (p1-p3). It seems that p2 was the
largest of those. The final pair of premolars is preserved but wear is heavy. The
structure of both is described as premolariform. The
width of p4 remains consistent along its length whereas its partner widens towards the
rear.
Molars
These teeth slope somewhat inwards (lingually), with the
labial side being higher than the lingual.
Talonids are short and only a single cusp adorns them; the
hypoconid. An extension at the back of m1 fits into cusps on either side of the front of
its follower (cusps e and f). Such interlocking systems of various designs are popular with
mammals, as they provide for extra stability of the row. Other molars interlock as well, but
not as strongly. (The system's also variably developed in front molars on different
specimens.)
Despite being a molar, the m1 is 'partially molariform' rather than fully so. Its
protoconid to the front is rather pathetic (p.345). The
more lingually situated metaconid is a bit more beefy but
rates as no more than 'small'. Talonids start out with incipient basins but the effects of
wear rapidly eradicate this facility.
The other molars have metaconids and paraconids of similar height, with both being taller
than on the m1. Their talonids are shorter. The m4 has a lower crown than the m3.
Molars in different stages of wear are available, but none has a clear wear facet on the
lingual side of its hypoconid cusp. Such damage would
result from the effects of a functional protocone of an upper molar. By inference, then,
there can't have been a strong protocone above.
Unmuddying the waters
A summary of shifting and varied opinions on the identity of
postcanines in Arguimus carries on until page 346. It concludes with: "The
foregoing review shows considerable confusion in interpretation of the
dentition in Arguimus and Arguitherium.
Although additional material from the PIN collection are not unconditionally conclusive, study
of all available specimens allow us to make the following observations:..." The authors
then seek to provide five bites of dental clarity.
# The third tooth of the Arguimus type specimen is the same position as the final one
preserved on the jaw previously known as Arguitherium. It's a 'partially molariform'
m1. Teeth in front are premolariform premolars. They have no metaconids, tiny paraconids
(if any) and not much of a talonid. Those m1s are very similar in size and form, and there's
no need for two species (or genera, let alone families). All the relevant specimens fit into
a single taxon (p.347).
# The postcanines aren't that different to Peramus (although
that genus has one less molar). Both have a 'partially molariform' tooth in the procession.
As no pretribosphenic mammal is known with a 'semi-molariform' premolar, that tooth is most
likely a molar.
# The last mental foramen on the jaw varies in position. It can be located as far back as
below the m1 roots, but it's more usually beneath p4 or p5. A similar natural hole occurs
beneath the p5 for Peramus (usually) and Nanolestes.
(In the first genus it's sometimes beneath the rear of p4.)
# The 'partially molariform' tooth of the holotype has suffered greater wear than the following
teeth. This is because it had been in use for longer. First molars erupt before final
premolars, which are replacements for deciduous
predecessors. That heavily indicates it's the m1.
# A complete mandible isn't known. It had been claimed that
alveoli are present on the type fossil for a canine but,
especially as this bone was proportionately long, those are more likely for the first of five
premolars. Five is the number known for sure from Nanolestes (more
basal) and Peramus (more derived despite being
earlier). Unless something new turns up, those two are presently the most relevant points of
comparison.
Killing the family
Features used to define Arguimidae appear to be basal traits
plesiomorphies), and such characters aren't particularly informative (p.348).
Consequently, the establishment of a family turns out to have been unjustified. The genus
is unceremoniously transferred to the stem-lineage of Zatheria with no known familial
affiliations, as was suggested by Martin in 2002.
Holotype
PSS no. 10-15 is a fragment of lower jaw in the collection of the Mongolian Academy of
Sciences, Ulaan Baatar. The type fossil of Arguitherium is PSS no. 10-31 and that
species was named in honour of AW Crompton for his work on Mesozoic mammals.
Additional notes
The spelling variation of the specific name is mentioned by Averianov & Skutschas,
2000, (p.340). |
| References: | Dashzeveg (1979), Arguimus khosbajari, gen.n., sp.n.,
(?Peramuridae, Eupantotheria) from the Lower Cretaceous of Mongolia. Acta Polonica
Palaeontologica, 24(2), p.199-204. |
| Dashzeveg (1994), Two previously unknown eupantotheres (Mammalia,
Eupantotheria), American Museum Novitates 3107, p.1-11. |
Lower Cretaceous mammals of Höövör
Much of the following is based upon my reading of Dashzeveg, 1994, although subsequent
sources and developments have been taken into account (hopefully).
The River Argui flows near the fossil site formerly known as Khoobur (and Khovrboor).
Attempting to transcribe Mongolian into English has produced variations. Hopefully,
everybody will now stick to Höövör. That river was honoured in names of two mammalian genera,
one of which (Arguitherium) was brutally annihilated by subsequent opinions in 2006.
It's now regarded as a junior synonym of Arguimus.
The pace of research
Paleontology is more like a marathon than a sprint, but there's never a finishing line in
sight. Often, years can go by between discoveries and published descriptions. Fossils
may require sorting from enormous heaps of debris, initial cleaning, tentatively identifying,
intensive cleaning, conserving, comparing, considering, perhaps arguing about, reconsidering
and then realising that apparently ridiculous thought you jotted down on the back of a
napkin five years ago, made sense... And then there's the matter of convincing somebody
reputable, that your painstakingly researched and written manuscript is worth bothering
with. The most prestigious journals retain Rotweiler researchers, whose main function
appears to be saying: 'Thanks, but no thanks. Next please'. I like to think they bash a
little gong before saying 'next'.
Despite all that care, mistakes can still occur.
Dashzeveg had two small partial jaws from a site then called Khoobar in Mongolia (p.1).
These had been harvested in 1965, and the first was rushed into print after only 14 years
(1979). That was Arguimus. Further considerations on that
appeared with this 1994 description of the second specimen. That's almost three decades
after the fieldwork. Paleontology rarely provides instant gratification.
A variety of further mammals were also found. Dashzeveg cites
Symmetrodonta, Triconodonta,
multituberculates, Eutheria and 'fragments that
represent more primitive mammals'. The age was tentatively put at Aptian-Albian,
Lower Cretaceous.
Further Mesozoic site summaries can be found at Localities.
Meet the mammals of Höövör (7 genera, 10 species)
Multituberculata (3 genera, 4 species)
Arginbaatar dmitrievae;
Eobaatar magnus; E. minor;
Monobaatar mimicus.
Triconodonta (1 genus, 2 species)
Gobiconodon borissiaki; G.
hoburensis.
'Symmetrodonta' (1 genus, 1 species)
Gobiotheriodon infinitus.
Stem-zatherian (1 genus, 1 species)
Arguimus khosbajari.
Eutheria (1 genus, 2 species)
Prokennalestes minor; P. trofimvi.
|
| Genus: Kennetheredium
Sigogneau-Russell D, 2003
'heritage from Kenneth'
Remarks: The generic name is in honour of Kenneth A Kermack, who has worked extensively on
the mammalian fossils of Kirtlington. Whether this genus belongs in this directory is not
yet completely clear. |
| Species: | Kennetheredium leesi Sigogneau-Russell D, 2003 |
| Place: | Kirtlington, Oxfordshire |
| Country: | England |
| Age: | Bathonian, Middle Jurassic |
| Remarks: | These lower molars
have a long talonid and a sloping
cingulum on the internal (lingual) side. There's a high,
slender trigonid with sharp cusps. The paraconid is a bit
shorter than the metaconid. The ordinal and familial relationships are unclear,
(Sigogneau-Russell 2003b, p.521). At least seven specimens have been identified. The
talonid is shorter than in Palaeoxonodon, (p.522).
Holotype
The holotype is a left lower molar known as BMNH J.746. Along with some colleagues, it
lives in the collection of The Natural History Museum, London. The specific name is in
honour of Mr A Lee, who provided the drawings for the paper containing the description. |
| Reference: | Sigogneau-Russell (2003b), Holotherian mammals from the Forest
Marble (Middle Jurassic of England), Geodiversitas, 25 (3), p.501-537. |
| Species: | ?Kennetheredium sp. Sigogneau-Russell D, 2003 |
| Place: | Kirtlington, Oxfordshire |
| Country: | England |
| Age: | Bathonian, Middle Jurassic |
| Remarks: | Six lower molars
may represent a closely related taxon. One difference is the
relative narrowness of the talonid, (Sigogneau-Russell
2003b, p.522). |
| Reference: | Sigogneau-Russell (2003b), Holotherian mammals from the Forest
Marble (Middle Jurassic of England), Geodiversitas, 25 (3), p.501-537. |
| Genus: Magnimus
Sigogneau-Russell D, 1999
'most' |
| Species: | Magnimus ensomi Sigogneau-Russell D, 1999 |
| Place: | Durlston Bay, Dorset |
| Country: | England |
| Age: | Lower Cretaceous |
| Remarks: | Martin (2002) discusses both the lower and upper
molar. The latter differs in various ways from
Nanolestes, the least significant of which is its larger size. It lacks a feature
known as an ectoflexus, has an elongated parastyle and a
relatively small stylocone. As yet, some of this terminology is beyond my understanding,
(p.333).
The species name must be in honour of Paul Ensom, a leading authority on Dorset
paleontology and geology. |
| Reference: | Sigogneau-Russell (1999), Reevaluation of Peramura (Mammalia,
Cladotheria) based on new specimens from Lower Cretaceous of United Kingdom and Morocco.
Geodiversitas 21 (1), p.93-127. |
| Genus: Microderson
Sigogneau-Russell D, 1991 |
| Species: | Microderson laaroussii Sigogneau-Russell D, 1991 |
| Place: | Anoual |
| Country: | Morocco |
| Age: | Berriasian?, Lower Cretaceous |
| Remarks: | A single upper molar,
originally interpreted as a "symmetrodont".
The fact it has the remains of three roots though, show it to be a stem-zatherian, somewhat
more basal in terms of the metacone than Nonolestes,
(Averianov 2002, p.712-713). (Martin 2002 refers to Afriquiamus as a
stem-zatherian. However, its upper molar is double-rooted, p.333). |
| Reference: | Sigogneau-Russell (1991), Nouveaux Mammifères thériens du
Crétacé inférieur du Maroc. Comptes Rendus de lÀcadémie des Sciences, Série II 313,
p.279-285. |
| Genus: Minimus
Sigogneau-Russell D, 1999
'least' |
| Species: | Minimus richardfoxi Sigogneau-Russell D, 1999 |
| Place: | Anoul |
| Country: | Morocco |
| Age: | Lower Cretaceous |
| Remarks: | Martin (2002) contains some details on the lower
molar, but not the upper, (p.333). The location has also
been provided by this paper. The Conclusions suggest a referral to stem-Zatheria.
The species name is in honour of Richard Fox. |
| Reference: | Sigogneau-Russell (1999), Reevaluation of Peramura
(Mammalia, Cladotheria) based on new specimens from Lower Cretaceous of United Kingdom and
Morocco. Geodiversitas 21 (1), p.93-127. |
| Link:
Minimus, Primary Latin
http://www.minimus-etc.co.uk/
This is almost completely irrelevant, though some of the vocabulary might come in handy.
Latin for 7-10 year olds. If you like, you can dress Flavius. |
| Genus: Nanolestes Martin T,
2002
'small predator'
Remarks: David Marjanovic informs me this genus "is a new close relative of
Zatheria". (Thanks for the info!)
In this genus, the lower molars were generally double-rooted
and equipped with a primitive form of unbasined talonid.
The last premolar (p5) wasn't molarized in shape. The
narrow dentary had a well-developed angular process and a
Meckel's groove which extended until below the second
molar, (m2 -and this exciting groove is inexpertly chatted about in the entry for
Dryolestes leiriensis). The lower jaw was
blessed with 30 teeth: 4 incisors, 1
canine, 5 premolars and 5 molars per side. That's a lot
compared to humans, (2; 1; 2; 2-3), but not as toothy as its more basal co-habitees, the
dryolestids, (p.333).
The well-developed angular process of the dentary places this genus within Cladotheria.
However, it also has characters more in common with those primitive dryolestids and
paurodontids. |
| Species: | Nanolestes drescherae Martin T, 2002 |
| Place: | Guimarota |
| Country: | Portugal |
| Age: | Kimmeridgian, Upper Jurassic |
| Remarks: | This is represented by 48 isolated teeth, (upper
and lower), a dentary and a further jaw fragment. From the
abstract: "The former attribution of these specimens to the peramurids cannot be
corroborated."
The following is based upon my understanding of Martin, 2002.
Both roots of the lower molars are well separated and of
about the same size. These teeth have three main cusps; the protoconid is the tallest,
then the metaconid followed by the paraconid. These are slender and pointed. A
fragmentary specimen was sliced up in order to examine the structure of the enamel. This
is very thin, but organized into prisms for strength. Also described are some lower
deciduous premolars.
The informative holtype
Usually, the holotype of a species will be the 'best' specimen. In this case, a single
tooth was selected because it's the most informative fossil for comparative purposes,
given that many taxa are only known from isolated teeth.
However, this species is also represented by some jaw material. Part of a dentary was
given the tentative designation of cf. Peramus by Kühne in 1968. This is preserved
in three fragments; the front and back in original, while the middle part is a cast of the
impression left in the surrounding coal.
The only tooth present is a premolar (p2), but holes (alveoli)
provide information on the former dentalistics. The near horizontal nature of the alveolus
for the first incisor (i1) shows this tooth pointed
forwards. The other three incisors were aligned increasingly toward a vertical plane;
approximately 25°, 45° and 70° respectively.
Roots
The canine was double-rooted, with the front root being
probably slightly larger. A convenient breakage shows it must have bent slightly forward.
There's then a short gap in the dentition, (a
diastema), before a small, also double-rooted premolar
(p1). It must have been similar in size to the preserved p2. The cast of the impression
from the coal includes the alveoli for eight further teeth. With the exception of the
final one, these all possessed two similarly sized roots. Three teeth were further
premolars, which increased gradually in size along the row. The rest of the alveoli
indicate the presence of five molars, the last of which was the smallest and single-rooted.
Advanced jaws
Various details of the dentary ally it more closely with
the further derived Peramus, rather than with those more primitive
dryolestids and the like. More information is
provided by another dentary fragment. This has three premolars in situ, (p3-p5). Both its
slenderness and the morphology of these teeth allow its attribution to this species.
Upper molars are triple-rooted. "At first glance the large number of cusps and
cuspules which surround the trigon basin is rather confusing." After many glances at
the text, I must admit this still applies in my case.
Upstairs uncertainties
The upper dental formula is less certain. There was a badly crushed fragment of
maxilla available, but it fell to pieces when freed from
the coal. Nevertheless, the attached teeth survived. Both their size and nature
correspond with N. drescherae, as is the case for some isolated fossils. One of
these is possibly either a P4 or P5. The ones from the disintegrated jaw are a canine and
P1-P4. These premolars are much smaller than the isolated one, which suggests the
presence of five upper premolars in all. The final upper premolar being enlarged is a
condition also found in Dryolestidae, though they had only four of these teeth. All upper
premolars are double-rooted and the main cusp is
triangular. Upper deciduous premolars, (milk teeth),
have also been identified.
Contrasts of the species and holotype
This is the type species of the genus. Amongst the differences between the two species is
that the lower molar in N. drescherae has a smaller
talonid, which has only two cusps. The holotype is Gui Mam 1002, and it resides in the
collection of the Freie Universität, Berlin. It's a lower right molar. The specific name
honours Frau Ellen Dreschner, who has prepare the fossils from the now closed coalmine of
Guimarota. That means she cleaned the excess matrix off, which can be painstaking work in
the extreme. |
| Reference: | Martin (2002), New stem-lineage representatives of Zatheria
(Mammalia) from the Late Jurassic of Portugal: Journal of Vertebrate Paleontology, 22 (2),
p.332-348.
With thanks to Dinohunter. |
| Species: | Nanolestes krusati Martin T, 2002 |
| Place: | Porto Pinheiro |
| Country: | Portugal |
| Age: | Upper Jurassic / Lower Cretaceous |
| Remarks: | The following is also based upon my understanding
of Martin, 2002, (details in Bibliography).
Material is restricted to one lower and one upper molar.
They compare closely in size and form to N. drescherae but differences in detail
indicate a distinct species, which is not surprising given the more recent age of this
species.
The type fossil, known to its fans as PP 29/67, also lives at the Freie Universität,
Berlin. It's a left lower molar with two of the cusps broken. The specific name honours
the late Dr Georg Krusat. He described the specimen in 1969, but didn't name it. |
| Reference: | Martin (2002), New stem-lineage representatives of Zatheria
(Mammalia) from the Late Jurassic of Portugal: Journal of Vertebrate Paleontology, 22 (2),
p.332-348. |
| Genus: Palaeoxonodon
Freeman EF, 1976
'Ancient Oxfordian tooth'
Family: Amphitheriidae Owen, 1846
Remarks: Most of the following is based upon my reading of Sigogneau-Russell, 2003b,
which places the genus within Amphitheriidae. It was originally interpreted as a possible
peramurid.
This genus is a member of a taxon called
Holotheria, which includes all but the most basal
mammals. It's known mostly from isolated teeth. The lower
molars have a fairly sharp trigonid, a long,
incipiently basined talonid which ends in one, pronounced
cusp, and other interesting features, (p.504). They also have two roots of a similar size.
The dental formula is not presently known.
The trigonid is narrower and sharper than in Amphiterium,
and the beginnings of a talonid basin provide another distinguishment. There are further
differences too.
A number of isolated upper molars are also known from the same location. Most fall into
two groups which are tentatively attributed to Palaeoxonodon, which is the most
common holotherian represented, (p.512). The morphology
and size are consistent with this possibility. When preserved, three roots are present.
Meaning of name
The first part of the generic name is Greek for 'ancient'. 'Oxonia' is the county name in
Latin, and 'odons' switches back to Greek for 'tooth'. |
| Species: | Palaeoxonodon ooliticus Freeman EF, 1976 |
| Place: | Forest Marble Formation, Oxfordshire |
| Country: | England |
| Age: | Bathonian, Middle Jurassic |
| Remarks: | The following is based upon my reading of Freeman,
1979, which isn't the original description. Nevertheless, it includes a description of the
type fossil and a couple of further specimens starting on page 150.
The holotype is a lower molar from the right side of the
dentition. Damage did away with the
paraconid at the front and the tips of both roots (p.152). The
protoconid is tall, sharp and the rear edges curves backwards. The
metaconid is about two-thirds as tall and there seems to
have been no cingulum linkage between it and the
paraconid.
Backstage developments
The most interesting feature is at the rear of the crown. The talonid
heel is better developed than for its contemporary Amphitherium,
but not as well as for the later Peramus. This talonid is
formed primarily by one cusp, and it's presumably the hypoconid. This connects to a ridge
termed the crista olbliqua, which runs from the rear of the metaconid. As with Peramus
(and in contrast to Amphitherium), this ridge features a small cusp at about the
middle. Another low ridge runs from the possible hypoconid and, in association with the
crista obliqua, this encircles a small concaved area; an incipiently basined talonid.
In addition, the lingual talonid rim features two slight expansions, and these are positioned
so as to be plausible candidates for incipient antecedents of two further talonid cusps;
the hypoconulid and the entoconid. If so, then they at a very early stage of
development.
Holotype
The type fossil, BMNH 36508, is a resident of the Natural History Museum, London. It was
originally known by Freeman as FM/K8, but he generously donated important specimens to the
Museum, and they were renumbered. The specific name honours the Great Oolite Series of
rock.
Additional notes
These molars possess no
cingulum on the internal side (lingual) of the
trigonid, and the paraconid is either as large as, or
larger than the metaconid (Sigogneau-Russell 2003b, p.504). There's much variability in
the details amongst these specimens, but such differences occur in other, better
represented genera, (p.506). A main reason for this could be the differing positions of
individual teeth in the tooth row. Unfortunately, few specimens are well enough preserved
to provide much information on wear facets, (p.507).
Savage, 1989 (p.5), has the year of publication as 1979. Although a description did appear
in that year, the original one was earlier. |
| Reference: | Freeman (1976), Mammal teeth from the Forest Marble (Middle
Jurassic) of Oxfordshire, England, Science 194, p.1053-1055. |
| Species: | Palaeoxonodon freemani Sigogneau-Russell D, 2003 |
| Place: | Forest Marble Formation, Oxfordshire |
| Country: | England |
| Age: | Bathonian, Middle Jurassic |
| Remarks: | In contrast to P. ooliticus, these
lower molars have a cingulum
at the front of the internal side (anterior lingual). The
trigonid is a bit wider. The paraconid is generally equal
in size to or smaller than the metaconid, (Sigogneau-Russell 2003b, p.507-508).
The holotype is BMNH J.745. This is a left lower molar in the collection of The Natural
History Museum, London. The specific name honours Mr E Freeman, who began the
paleontological work on the Kirtlington Bone Bed.. |
| Reference: | Sigogneau-Russell (2003b), holotherian mammals from the Forest
Marble (Middle Jurassic of England), Geodiversitas, 25 (3), p.501-537. |
| Species: | Palaeoxonodon antiquus |
| Place: | |
| Country: | |
| Age: | |
| Remarks: | This was listed on the Biosys Index as a
species but it was very possibly a typo. The author of the genus, Eric Freeman,
has forwarded a very plausible explanation. Rather than being a small Middle
Jurassic insectivore, P. antiquus is actually a 400,000 year old elephant of
a similar appearance.
The similarity is in the generic name. This should've been Palaeoloxodon
antiquus aka Elephas antiquus. A close relative named Nellie has
reportedly packed her trunk, and said goodbye to the circus. Off she went with a
trumpety-trump, trump, trump, trump... (I trust everybody knows the song 'Nellie
the Elephant'.) |
| Reference: | |
| Species: | Palaeoxonodon sp. Sigogneau-Russell D, 2003 |
| Place: | Forest Marble Formation, Oxfordshire |
| Country: | England |
| Age: | Bathonian, Middle Jurassic |
| Remarks: | Sigogneau-Russell identified several lower
molars which may represent a further species, (p.508-510).
These contain a mixture of characteristics, when compared to the other species present in
the fauna. |
| Reference: | Sigogneau-Russell (2003b), Holotherian mammals from the Forest
Marble (Middle Jurassic of England), Geodiversitas, 25 (3), p.501-537. |
| The Forest Marble Formation of
Oxfordshire and Dorset (Middle Jurassic)
The following is based largely upon my reading of Sigogneau-Russell, 2003b.
The upper Bathonian Forest Marble Formation is an unusually productive source of Middle
Jurassic mammal fossils. About 700 specimens have been
recovered so far, (p.501). These are mostly isolated teeth, though some jaw material has
also been found. All known lineages of northern Middle Jurassic Mammaldom are represented,
as are non-mammalian tritylodontids. The first
Mesozoic mammals ever identified were found in Oxfordshire and described in the
nineteenth century, (p.502). These came from near Stonesfield and were the only
Middle Jurassic remains known from anywhere until the 1970s.
Two counties
The Kirtlington locality is part of the Forest Marble Formation. There's also a 'sister'
site in West Dorset on the south coast of England, (Watton Cliff). Both locations have
been extensively sampled by paleontologists from London University College, under the
leadership of Professor KA Kermack. The resultant specimens were the reward for
laboriously sieving through many tons of material. As well as the mammals, various other
microvertebrates have also been identified. For purists, the age is thought to be upper
Bathonian.
Arousal in the Kirtlington Mammal Bed
The following is based upon my reading of Freeman, 1979.
Middle Jurassic mammal fossils have come from several quarries in Oxfordshire (p.135), and
Freeman was able to enhance the haul with specimens from the Kirtlington Old Cement Works
Quarry, which had been dormant since 1929. One layer of the rock face is composed of brown
marl, and this received the name of the Kirtlington Mammal Bed (p.136). Careful searching
uncovered remains of eucynodonts asleep in this bed,
which has a thickness of between four to 25 centimetres. Local stratigraphy suggests those
fossils are a bit more recent than colleagues from Stonesfield (also in Oxfordshire), but
not by all that much. A lack of ammonites is unsurprising in non-marine rock strata.
Nevertheless, as those marine critters happen to be key index fossils for the time, their
absence makes dating things trickier. However, the presence of an ostracod (Glyptocythere
penni) in the Kirtlington clay indirectly points to the Formation correlating with the
Clydoniceras discus Zone.
A bit of a mix
A few interlopers seem to have got into this bed from other layers. Remains are generally
of terrestrial and freshwater organisms, but there are odd fragments of marine residents;
eg. coral and oysters (p.138). As there are marine limestones aplenty around as well, a
bit of reworking of fossils has presumably occurred, and this is supported by extraneous
pieces of oolithic limestone matrix.
The rightful occupants of the bed include bits of various
vertebrates, plenty of ostracods and gyrogonites. There are indeterminate scraps of
plants, but identifiable flora or insects weren't found (p.139). The varied array of
insectivores indicates there were actually plenty of things to sink their teeth into, but
preservation is often biased. While death calls all, fossilisation is much less
democratic.
Vertebrates
A count of the fossils from about 140 kilos of clay is provided. (That was only part of
the material processed.) The most common vertebrate remains were
crocodile teeth. Freeman found 468 complete and 208 partial specimens, and this accounts
for about three-quarters of all teeth recovered. Sizes ranged from 0.8 to 9.5mm. Only three
possessed roots, and this detail indicates most had been shed during life time. Crocs
continually replace teeth, and this habits means they can be numerically over-represented
in fossil faunas. In natural terrestrial communities, a lot of prey animals are required
to feed some predators. Crocs can't actually have been the most common inhabitants, as
such a regime of butchers wouldn't have been viable.
Dinosaurs were also on duty. 34 teeth belonged to
ornithischian gardeners and five came from
theropod killers. The first lot range in length from 0.8
to 5.2mm (p.142), and the second manage 1.6 to 7.4. There was no sign of large dinos in
this bed, but remains are known from the general area. This was Megalosaurus
country.
Other remains include teeth from pterosaurs, fish and
sharks. There were some bones and scutes from dinos and crocs, plates from turtles, limb
bones from frogs and various bits and pieces.
Concentrate...
There's a bit of a peculiarity with the Kirtlington Mammal Bed fauna, and it occurs at
other localities as well (sometimes more strongly). The fossils of some
taxa are concentrated together, despite being isolated.
Seven batches of matrix ranging from about 36 to 140 kilos were processed separately; a
total of about 525 kilos. Each batch was clay collected from much the same place.
"Unexpectedly, it was found that the similarity between the mammal teeth within
an individual batch tended to be greater than between batches..." (reference
omitted).
Furthermore, many teeth seem to have been hollowed out by the expansion of their pulp
cavities; crowns are generally less than complete, with the breakages being clean; and
corresponding fragments weren't found. If these teeth had been transported far by streams,
then a couple of expectations would probably have been met; transport damage and a more
random mix. Despite breakages, the remains are often well-preserved.
... don't constipate
There's a crappy hypothesis which takes these details into account. In 1974, a researcher
called Mellett proposed the notion of coprocoenosis. What d'you mean, pardon? Coprocoenosis!
The concentration of fossils could result from the specimens being dropped as a collection
from the rear end of a larger predator. The gastric acids would destroy most bone, and
account for the breakages and hollowing out of teeth (p.143). This method of preservation
would also provide a protective and buoyant surround for any ejected, undigested material.
In one case a fragment of jaw was found, and it has two noticeable dents. These appear to
be bite marks. The finds from the Kirtlington Mammal Bed are at least consistent with the
possibility of coprocoenosis, and that word could prove to be an interesting addition to
the Scrabble armoury, although I'm not sure whether it'll be found in many dictionaries.
If being eaten were a good route to fossilisation, then it'd also be a bias favouring
smaller mammals, which are more vulnerable to such rude attentions (p.144). Consequently,
it could have caused faunal distortions, as larger mammals would be under-represented on
the menu.
Forest Marble eucynodont fauna:
Note: entries in brackets are from British formations of different ages to the Forest
Marble, although they're also Middle Jurassic. A short article on
Hornsleasow, Gloucestershire
is now available.
Further Mesozoic site summaries can be found at Localities.
Non-mammalian
Tritylodontidae
Stereognathus ooliticus, Oxfordshire, Dorset
(also Gloucestershire and perhaps Isle of Skye).
Freeman, 1979 also describes postcanine tooth parts and
a complete incisor. The latter closely resembles
Oligokyphus, although there's no referral more specific than tritylodontid
(p.163).
Mammals
Morganucodontidae
Wareolestes rex, Oxfordshire
Docodonta
Borealestes serendipitus, (also Isle of
Skye); Borealestes mussetti Oxfordshire;
Cyrtlatherium canei, Oxfordshire;
Krusatodon kirtlingtonensis, Oxfordshire;
Peraiocynodon major, Oxfordshire;
Simpsonodon oxfordensis, Oxfordshire.
Schuotheriidae
Shuotherium kermacki, Oxfordshire;
S. sp. Oxfordshire.
'Haramiyida'
Eleutherodon oxfordensis, Oxfordshire;
Millsodon superstes, Oxfordshire and Dorset;
Kirtlingtonia catenata, Oxfordshire.
Multituberculata
Kermackodon multicuspis, Oxfordshire;
Hahnotherium antiquum, Oxfordshire;
indeterminate, Dorset & Oxfordshire.
'Triconodonta'
Amphilestes borderipii, Oxfordshire;
Phascolotherium bucklandi,
Oxfordshire;
'Symmetrodonta'
indeterminate, Oxfordshire.
Dryolestida
indeterminate, Dorset & Oxfordshire.
Stem-zatherians and Zatheria (This Directory)
Amphitherium prevostii, Oxfordshire;
Amphitherium rixoni; Kennetheredium leesi,
Oxfordshire; Palaeoxonodon ooliticus, Oxfordshire;
Palaeoxonodon freemani, Oxfordshire.
|
| Genus: Vincelestes
Bonaparte JF, 1986
'Vince’s thief'
Family: Vincelestidae Bonaparte JF, 1986
Remarks: McKenna & Bell, 1997 places this genus within
Zatheria. However, in a 2008 review, Bonaparte concluded this genus may be more
closely related with Gondwanan australosphenidans;
thus not Zatheria, Cladotheria or that kind of thing. Whether his view receives support
from other researchers remains to be seen. I'm leaving the entry here for the time
being. |
| Species: | Vincelestes neuquenianus Bonaparte JF, 1986 |
| Place: | La Amarga Formation, Patagonia |
| Country: | Argentina |
| Age: | Hauterivian, Lower Cretaceous |
| Remarks: | Known from remains of nine individuals from the
same site, including six skulls. Different age groups are represented. This
assemblage could be an indication of a social lifestyle. In its day, this was a fairly
hefty mammal, probably reaching over 30cm in length. Hu et al, 2005 (p-13) report a lower
jaw length of 7.4cm in their Supplemental Data, which is only four millimetres
less than known from one of the larger Gobiconodon
species, (G. ostromi).
As viewed by Bonaparte, 2008 (with thanks to the supplier)
Should you have occasion to go into an English supermarket and buy a plastic wrapped block
labelled as being white Cheshire cheese, and then take that back to your den or burrow,
then, after cutting a squidgy slice and tasting it, you may well conclude that the content
is as plastic and enjoyable as the wrapper. This sad realization would leave you with no
appreciation at all of a proper white Cheshire cheese. The consistency of that doesn't
allow for a squidgy slice. It crumbles in joy under even the sharpest blade and leaves
a pile of rubble to be strewed upon the bread. It then melts on your tongue and releases
a wondrous tang of a taste that persists beyond the exit of this crumbly treat down your
throat. In order to know why imitation white Cheshire should be melted down into something
more useful, a small carrier bag perhaps, whereas the proper stuff makes you glad to be
alive, you must compare each with the other and neither with similarly pale chalk. While,
admittedly, chalk can crumble like proper white Cheshire, its taste is only mildly more
pleasing than the non-flavour of the plastic stuff from the supermarket. Should you
please, compare cheese with cheese.
Bonaparte's contention is that previous studies involving Vincelestes have been
comparing chalk with cheese or uncritically accepting such a situation. Until now, this
genus has been compared mainly with Laurasian mammals rather than with Gondwanan ones
(p.81), and this resulted in misleading conclusions. Of those it was compared to, it shared
most similarities with 'advanced' eupantotheres. One conclusion, for example, settled on
an animal more derived than
Henkelotherium but less so than Peramus. If so,
then it would've been fairly close to the ancestral lineage of
therian mammals such as myself and a yapok (a semiaquatic
marsupial from South America). This was seen as a southern expression of an essentially
northern movement.
Why try to compare cheese with chalk?
Earlier researchers were confronted with an unusually generous supply of skulls and other
corpse bits for Vincelestes; an audaciously well represented genus. However, they
also had a problem similar to that experienced by John Cleese in the Monty Python cheese
shop sketch. No matter which kind of cheesy comestible he enquired about, the shop
owner could only admit that particular choice had just sold out, gone off, not arrived or
had been eaten by the cat. There wasn't a crumb of Cheshire or anything else in the
building, and that was regardless of whether imitation or genuine.
That's a slight exaggeration as a very few Gondwanan scraps were available for consultation,
but none of them had much to say of obvious relevance. Comparative anatomy requires
material that can be compared and, back in the 1990s, that meant Laurasian mammals.
The south, Gondwana, has been yielding an increasing trickle of possibly relevant material
since then, although nothing that anywhere near as complete as Vince is known from there
from the Middle Jurassic through to the Upper Cretaceous. Realistic optimism prompts me to
add "as yet". For example, as seems to be the case for some people, skulls are
absentees and upper dentitions are still yearned
for. Nevertheless, new evidence there is.
Are you related with Vince?
The only southern hemispheres previously interviewed about possible links with Vince were
living, breathing monotremes or, at least, specimens
that had very recently been living, breathing monotremes (p.82). There was no obvious
close affinity. What can now be done is a comparison with a wider selection of mammals,
both Laurasian and Gondwanan, based upon features of lower jaws and those teeth (p.83).
Bonaparte duly adapted and emended 90 relevant characters from an already compiled data
matrix, and sought the assistance of a computer analysis. This resulted in
Vincelestes claiming to have closer affinities with
australosphenidans rather than Laurasian
cladotherians (p.85).
The dental fashion of this critter has been termed pretribosphenic. Upper
molars have a small protocone (or perhaps an equivalent)
and lowers are blessed with a small talonid. While such
features should occur on forerunners (and their descendants) of mammals with fully
tribosphenic dentitions, their significance in this
case is unclear. For example, there's also the possibility of these characters having
been reduced rather than being incipient. In any case, Bonaparte found nothing compelling
to tie Vince into an intimate relationship with Laurasian tribosphenic mammals, although
he does address the presently unevidenced possibility of something being discovered which
could, conceivably, connect the northern boreosphenidans
with southern australosphenidans. That's put no stronger than voicing a
possibility.
Additional notes
Hear, hear
Vincelestes has been kind enough to provide some information on its inner ears. The
coiling of the bony cochlear canal exceeds 270°,
which is a higher degree than is known from any of the egg-laying
monotremes, (Luo et al, 2002, p.28). (Blame me for the
next four sentences.)
Monotremes have also further enhanced their hearing abilities, but they used a different
trick. Rather than lengthening the bony canal still more, monotremes have worked on their
aural membranes. As our cochlear canals are even further coiled, this might suggest that
prototribosphenidans such as Vincelestes, were effectively proto-northern-
tribosphenidans. The southerners had branched off long before. Then again, there's also
the possibility that these developments occurred independently.
Skull and teeth in brief
Kemp, 2005 (p.167) reports this large mammal possessed a relatively short and sturdy skull.
The dental formula per side is: (uppers): four incisors, one
canine, two premolars and
three molars; (lowers): one, one, two and three respectively.
"The upper canine is huge, the first and last
postcanines small. The lower molars have low cusps and a small
talonid with only a single cusp. The upper molars are a curious shape, being very wide
laterally, and narrow medially."
The affinities of this animal aren't very clear. Partly, this may be due to the
postcranial material not yet having been described. However, that possibly won't help all
that much, as so many mammals aren't known from skeletons. The main obstacle is the sheer
peculiarity of its teeth.
From the abstract of Sigogneau-Russell (1999): "Vincelestes does not qualify as
a pretribosphenic mammal." (This is linked to the entry for Afriquiamus above).
Nevertheless, I’ll leave the entry here for want of a usable alternative.
The animal was equipped with epipubic bones, (Wible et
al 2004, p.15). |
| Reference: | |
| Other reports:
Germany?
Location details not yet available
17.2.2004. The first perhaps mammalian fossil in the Cretaceous of Germany has been
recovered, but knowledgeable whispers suggest it's possibly something else. The fossil is
reportedly about 3,5cm of edentulous jaw. Preserved are
the 'point-like' alveoli for
'premolars', and more squarish ones for 'molars'.
Other fossils from this new locality include remains of: small theropods, part of the toe
of a larger one, teeth and part of the hips of an iguanodontid, evidence of crocs, part of
a pterosaur and many fragments of tortoises. All finds are disarticulated and excavations
are continuing. No information on the whereabouts of the site is available. My thanks go to
the thoroughly reliable, and presently anonymous, source. Amongst other things, they're
hoping to find some of the teeth. |
A. Stem zatherians and zatherians B.
Peramuridae
| Taxon: Peramuridae Kretzoi, 1946
This family constitutes the infralegion of Peramura McKenna, 1975. The 'group' is
therefore something of a problem. According to Kielan-Jaworowska et al (2002), and
doubtless others, Peramura is not monophyletic; ie. its members are not the descendents of
a common ancestor unique to the taxon. Rather, they have some
similar anatomical characteristics, (especially dental characteristics), which may partly
have something to do with convergence, as well as inheritance. Nevertheless, some of these
characteristics give a very good impression of being ancestral to full-blown tribosphenic
molars. Hopefully, future finds and studies will make things
tidier, from a paleobook-keeping perspective.
Genera: Kiyatherium, Leptocladus
(= Peramus), Peramus, Pocamus,
Spalacotherium (partly = Peramus), Tendagurutherium,
other reports
Time-Line:
Lower Cretaceous: Kiyatherium, Peramus, Pocamus, France
Upper Jurassic: Tendagurutherium
Middle Jurassic: ?England |
| Genus: Kiyatherium
Maschenko EN, Lopatin AV & Voronkevich AV, 2002 |
| Species: | Kiyatherium cardiodens Maschenko EN, Lopatin AV
& Voronkevich AV, 2002 |
| Place: | Shestakovo 1, Kemerovo Region |
| Country: | Russia |
| Age: | Lower Cretaceous |
| Remarks: |
This genus is also mentioned in a further paper by the same
authors from 2002, (and they're listed in the same order). They state it's a peramurid,
(p.76). Details are in the bibliography at the end of this directory. As the description
of this genus is referenced in that, the Kiyatherium paper must have been published
first, so I'll refer to it here as 2002a.
Maschenko et al, 2002a is on-line and linked below, (though the page numbering differs to
the reference in Maschenko et al, 2002b). As it's in Russian, my understanding is even
more limited than usual. However, the authors clearly place this critter within
Peramuridae.
Holotype and teeth
The holotype is part of an upper jaw and has the number 16/2-50. I can't decipher which
collection it's within for sure, but I think it's the Paleontological Museum of the Tomsk
State Museum. As upper jaw fragments go, it appears to preserve a good array of teeth.
The description seems to mention the canine,
premolars 1-5 and molars
1-3. Hatched lines on the drawing might well indicate that the second premolar is absent.
Premolar 5 is clearly double rooted, and the roots are broadly similar in the length. The
distance from the canine to the final molar is 14mm. |
| Reference: | Maschenko, Lopatin & Voronkevich (2002a), [New Early Cretaceous
mammal from West Siberia.] Doklady Akademii Nauk. T.386 No.5, p.715-716, [in Russian]. |
| Genus: Peramus Owen R, 1871
?'Pyramid' (from the Greek for 'something that rises')
Aka: Leptocladus Owen R, 1871, Spalacotherium (partly) |
| Species: | Peramus tenuirostris Owen R, 1871 |
| Aka: | Spalacotherium minus Owen R, 1854 |
| Place: | Purbeck Limestone Group, Durlston Bay, Dorset |
| Country: | England |
| Age: | Lower Cretaceous (or Upper Jurassic) |
| Remarks: |
"Data limited to characters of the dentition and
mandible", (Luo et al 2002, p.11). A specimen is in
the collection of the National History Museum in London, (BMNH 47739). Kielan-Jaworowska et
al, 2002 (p.482), state Peramus is: "widely believed to be a proximal relative
of living therians (e.g., Butler 1990; Rougier et al.
1998)." It seems to be close to our ancestry and they label it as a "stem
zatherian", (eg. p.481 and p.484).
A brief look at the teeth
Kemp, 2005 (p.167) helpfully reports the number of
postcanines is eight. Five are probably premolars,
but four is also a possibility. Lower molars have
talonids with two cups; a hypoconid and a hypoconulid, and
they're linked by a crest. There's no entoconid and the talonid is incipiently basined.
"The upper molars are triangular and although no protocone has evovled, there is a
narrow cingulum on the
lingual side of the crown that is the incipient homologue of the protocone."
These incipient features were of themselves functional, as they improved the shearing
ability.
Another look at the not-protocone
Talking of dental intricacies, (and from Kermack et al 1965, p.546, which is the description
of the more derived critter, Aegialodon):
"Mills (1961, 1964) discussing Peramus says 'the
lingual cingulum of the upper
molars is developing towards a definitive protocone'. We have examined the Peramus
material in the British Museum, and we have no doubt that he is correct. Peramus,
however, lacks a lingual wear facet on the
talonid, so that a definitive protocone, in the sense of a
fully developed cusp, could not have existed here. This is the most fundamental difference
between the dentition of Aegialodon and that of
Peramus."
In the case of Peramus, a distinct cone, (the protocone), is present in an
incipient form. This is not known from more basal mammals.
It's been deduced as present in Aegialodon, although that genus is known purely from
one lower, left molar. The wear facets provide some information about the properties of the
corresponding, upper molar.
Spalacotherium minus, which was about half the size of
Spalacotherium tricuspidens, was later
found to be synonymous with P. tenuirostris, (Ensom & Sigogneau-Russell, 2000). |
| References: | Owen (1854), On some fossil reptilian and mammalian remains
from the Purbecks. Quarterly Journal of the Geological Society of London 10, p.420-433. |
| Owen, (1871), Monograph on the fossil Mammalia of the Mesozoic
formations. Palaeontological Society Monograph, 24, p.1-115. |
| Species: | Peramus sp. Sigogneau-Russell, 1999 |
| Place: | Anoual |
| Country: | Morocco |
| Age: | Berriasian?, Lower Cretaceous |
| Remarks: | This receives a mention in Sigogneau-Russell,
2003b (p.528). It seems to be an upper molar (SA 37), and
may be a deciduous tooth. |
| Reference: | Sigogneau-Russell (1999), Reevaluation of Peramura (Mammalia,
Cladotheria) based on new specimens from Lower Cretaceous of United Kingdom and Morocco.
Geodiversitas 21 (1), p.93-127. |
| Genus: Pocamus Canudo JI &
Cuenca-Bescós G, 1996
'Poca mouse'
Poca is the name of the particular locality. |
| Species: | Pocamus pepelu Canudo JI & Cuenca-Bescós G, 1996 |
| Place: | upper Camarillas Formation, Galve |
| Country: | Spain |
| Age: | lower Barremian, Lower Cretaceous |
| Remarks: | The following is based upon my reading of Canudo &
Cuenca-Bescós, 1996.
This species is based upon an upper premolar (P5). This
would be the equivalent of M1 of some authors. The view expressed in this paper, (p.222),
is that peramurids had five upper premolars and three molars.
Other interpretations have suggested the presence of four in both cases.
Not exactly large
The fossil in question is a slightly broken, rootless crown, and is very small, (length
0,72mm, width 0,37mm). It resembles the P5 known from Peramus tenuirostris.
However, it lacks a lingual
cingulum, and a further shelf with two small cusps. The are other differences of
detail too, (p.223). There's a large cutting surface evident between two of the cones,
(paracone and metacone), which can be interpreted as a feature called an incipient
protocone. The protocone is a characteristic of the further derived 'tribosphenidans',
(boreosphenidans in the structure I'm presently
trying to follow).
Affinities
From the same page: "The cladogram proposed by Prothero (1981) shows Peramura as a
sister group of the Tribosphenida, being the last group characterized by the addition of a
protocone. As we propound the large shearing surface of Pocamus to be an incipient
protocone and include this genus in Peramura, we postulate that Peramura shares with
Tribosphenida the derived condition of a protocone and reduced dental formula." In
crude summary, they're closely related.
Holotype
The holotype (MPZ 95/173) is in the collection of the Universidad de Zaragoza, and the
species name honours Professor Jose Luis Sanz for his contribution to the study of Spanish
vertebrates of the Mesozoic. |
| Reference: | Canudo & Cuenca-Bescós (1996), Two new mammalian teeth
(Multituberculata and Peramura) from the Lower Cretaceous (Barremian) of Spain. Cretaceous
Research, 17 (2), p.215-228. |
| Genus: Tendagurutherium
Heinrich W-D, 1998
'Tendaguru beast' |
| Species: | Tendagurutherium dietrichi Heinrich W-D, 1998 |
| Place: | Middle Saurian Bed, Tendaguru |
| Country: | Tanzania |
| Age: | Kimmeridgian-Tithonian, Upper Jurassic |
| Remarks: |
The following is based upon my reading of Heinrich, 1998.
The only known specimen is a crushed and distorted fragment of lower jaw. It was recovered
by the German Tendaguru expedition of 1909-13, though identified much later. The fossil
came to light in the Humboldt Museum in Berlin, after about 500kg of matrix was finally
dissolved in acetic acid, (p.271).
Fashion trends
This genus is known from a 6.5mm fragment of lower jaw, (p.274), with some old fashioned
characteristics. These include a groove at the back between the condyle of the
dentary and the angular process (a subcondylar groove),
a Meckelian groove running partly along the base of
the jaw, and the presence of an 'extra' bone called the coronoid. Also preserved is one
molar.
Jaw
The bone is crushed, bent, distorted and snapped abruptly in front of the final tooth.
Nevertheless, the rear is intact excepting for the top of the coronoid process. What
remains there are show the tooth bearing ramus was slender. Quite a way behind the molar,
(there's space enough for another tooth but no suggestion of one), the coronoid process
ascends steeply; at about 80°. A triangular coronoid bone is joined to the lower front
corner of that process; a decidedly 'un-mammalian' feature. Some evidence indicates that
further lower jaw bones may also have been retained, (the splenial and prearticular are
both possibilities). However, this is unclear in both cases, (p.278).
Molar
The trigonid of cusps at the front has been completely
preserved, but most of the talonid is missing. The tallest
cusp is the protoconid. While the
metaconid is taller than the
paraconid, this is at least largely the result of differing levels of wear. The
protoconid is further forward than the metaconid, which is more
lingually positioned than the paraconid.
The base of the protoconid has a developed labial
cingulum with an accessory cusp. Further accessory cusps
are situated at the foot of the front of the paraconid and to the anterior on the labial
side of the crown. That pair would've overhung the talonid of the preceding tooth.
One cusp of the talonid is found to the rear on the labial
side, (p.279). It may have been the hypoconid. The crown has a length of 1.1mm and the
trigonid is 0.6mm wide. The angle of cusp triangulation
for the trigonid is around 60°.
Affinities
The molar and well-developed angular process on the dentary are signatures of
'eupantotheres', (p.282); cladotherians in the scheme
followed by this project. However, it retains some relatively primitive traits. For
example, the condylar groove. Another local resident,
Brancatherulum, has no sign of such a feature.
Of all the mammals interrogated, Peramus appears to be the
closest. This is based on a comparison of the final lower molar. They share a similar
arrangement of main cusps, accessory cusps at the front, no lingual cingulum and a large
talonid, (p.283). But the dentary is clearly different; eg.
that subcondylar groove. This genus was only tentatively referred to Peramuridae,
(p.285).
What is this subcondylar groove thing for?
It presumably housed something, and a likely possibility is more lower jaw bones. It's
suggested that the angular bone and the articular complex weren't entirely separated from
the rear of the dentary, (p.286), an idea which receives much support from embryological
development in marsupials.
The tri-boned mammalian inner ear incorporated erstwhile jaw bones. The
incus formed from the quadrate of the skull. The lower jaw
contributed the malleus (articular) and the
ectotympanic (angular). In the case of
Tendagurutherium and more basal mammals, a mandibular
eardrum would account for the presence of the subcondylar groove, if that's where it was
positioned.
Holotype and present home
The holotype (MB.Ma.46910) is in the collection of the Humboldt Museum, Berlin. I was there
in 1995 and must’ve missed it. This was possibly due to the impressive dinos,
Archaeopteryx and the unusual spelling of Schrewsbury. Then again, this was
actually because it hadn't been identified and may well not be on display. Nevertheless,
should you find yourself in Berlin, this is a place well worth visiting. The species is
named in honour of Wilhelm-Otto Dietrich, who was the first to fully describe a Mesozoic
mammal from Africa, (Brancatherulum tendagurense in 1927).
(Additional thanks for information are due to Vince Ward.) |
| Reference: | Heinrich (1998), Late Jurassic Mammals from Tendaguru,
Tanzania, East Africa. Journal of Mammalian Evolution, Vol5 (4), p.269-290. |
| Other reports:
France, Cherves-de-Cognac
Excavations are underway in a gypsum quarry in the wine country of southwestern France.
The age of the location is reckoned to be Berriasian and correlates closely with the
Purbeck beds of Dorset. It seems to represent a coastal environment characterized by a
retreating sea and estuary deposits. Amongst the reported finds are remains of fish,
crocs, sharks, dinos and eggshell. Oh yes, and a couple of mammal teeth. At least one of
these is said to be from a peramurid.
With thanks to David Marjanovic for posting the following report and Steve Sweetman for
suggesting contact details, (which I haven't yet followed up 18.12.2003).
Link
David Marjanovic, DML, 26.6.2003
http://www.cmnh.org/dinoarch/2003Jul/msg00449.html
England, Forest Marble Formation, Oxfordshire
Sigogneau-Russell, 2003b (p.528) includes discussion on a left upper molariform tooth,
recovered from the Middle Jurassic Kirtlington Bone Bed. It shows resemblance to
Peramus sp. from Morocco. She refers it to ?Peramuridae. The reference details
are in the Bibliography at the end of this directory. |
| 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.
back to top
Trevor Dykes, December 2001. Last update: 5.9.2010.
ktdykes@arcor.de |
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 & Skutschas P (2000), A eutherian mammal from the Early Cretaceous
of Russia and biostratigraphy of the Asian Early Cretaceous vertebrate assemblages.
Lethaia 33(4), p.330-340.
Bonaparte JF (2008), On the phylogenetic relationships of Vincelestes neuquenianus,
Historical Biology, 29(2), p.81-86.
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.
Dashzeveg D, (1994), Two previously unknown eupantotheres (Mammalia, Eupantotheria),
American Museum Novitates, 3107, p.1-11.
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.
Freeman EF (1979), A Middle Jurassic Mammal Bed from Oxfordshire, Palaeontology,
22(1), p.135-166.
Heinrich W-D (1998), Late Jurassic Mammals from Tendaguru, Tanzania, East Africa.
Journal of Mammalian Evolution, Vol5 (4), p.269-290.
Hu Y, Meng J, Wang Y & Li C (2005), Large Mesozoic mammals fed on young
dinosaurs, Nature, 433, p.149-152 and the Supplemental Data, p.1-15.
Kemp TS (2005), The Origin and Evolution of Mammals, Oxford University Press,
pp.331.
Kermack KA, Lees PM & Mussett F (1965), Aegialodon dawsoni, a new trituberculosectorial
tooth from the lower Wealden. Proceedings of the Roy. Soc., London, B, 162, p.535-554.
Kielan-Jaworowska Z, Cifelli RL, & Luo Z-X (2002), Dentition and relationships of
the Jurassic mammal Shuotherium, Acta Palaeontologica Polonica, 47(3), p.479-486.
Lopatin A & Averianov AO (2006), Revision of a pretribosphenic mammal Arguimus
from the Early Cretaceous of Mongolia, Acta Palaeontologica Polonica, 51(2), p.339-349.
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.
Martin T (2002), New stem-lineage representatives of Zatheria (Mammalia) from the
Late Jurassic of Portugal: Journal of Vertebrate Paleontology, 22 (2), p.332-348.
Maschenko, Lopatin & Voronkevich (2002a), [New Early Cretaceous
mammal from West Siberia.] Doklady Akademii Nauk. T.386 No.5, p.715-716, [in Russian].
Mascheko EN, Lopatin AV & Voronkevich AV, (2002b), A new genus of the
tegotheriid docodonts (Docodonta, Tegotherianae) from the Early Cretaceous of West Siberia.
Russian Journal of Theriology, 1 )2), p.75-81.
McKenna MC & Bell SK, (1997), Classification of Mammals Above the Species Level.
Columbia University Press.
Savage RJG (1989), British mammals of the Mesozoic Era, Biological Journal of the
Linnean Society, 38, p.3-7.
Sigogneau-Russell D (2003b), Holotherian mammals from the Forest
Marble (Middle Jurassic of England), Geodiversitas, 25 (3), p.501-537.
Simpson GG; Olson EC (1935/1976), The First Mammals, The Quarterly Review of Biology,
51, 50th Anniversary Special Issue, 1926-1976, p.45-73. (Note: this is a reissue with an
introduction by Olson. The remainder of the paper is by Simpson, and has the page numbers
154-180.)
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. |
