MESOZOIC MAMMALS; Gobiconodontidae,
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
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It's got lots of information on old mammals. For a short bit of background information, see
here.
Taxa: Gobiconodontidae Jenkins & Schaff,1988
Repenomamidae Li J, Wang Y Wang Y & Li C,2000
Remarks: Chow & Rich, 1984 established the taxon as
Gobicodontinae, a subfamily. Numbers have expanded since then. Most researchers
regard repenomamids as also belonging to this family, although some place then in
a separate taxon.
This directory is now one of three containing
triconodont mammals. Previously visitors might recall that all groups used to
be on the same page. New discoveries meant that it grew and grew and grew...
Bandwidth economy prompted that collection being divided. Those searching for
amphilestids and various others should file along to the
triconodonts enclosure. Should, however, your
tastes desire triconodontids, then feel free to visit the
triconodontid playground. It's possible the surgery has had odd effects on
internal links, but I've tried to repair them. Feel free to let me know of any
failures. Details such as reference lists may also have been rendered somewhat
erratic.
A bit of gen on gobis
In terms of Mesozoic mammals, some of these
gobiocnodontid guys were enormous. Should our neighbour's cat develop a time-machine, (and he
seems to be a clever puddy), some would be creatures best avoided. They'd be well capable
of beating him up. Of course, compared to many of the contemporaneous dinosaurs,
biggish-moggy-size is still rather modest.
Family feuds
Everybody seems to agree that Gobiconodon and Repenomamus were
closely related, but there is a division of views on familial matters. Some
researchers place the later genus within Gobiconodontidae, whilst others view it as
distinct enough to merit a separate family. As 'disputes' go, this is a very minor
difference in taste. In their recent review, Wang et al, 2006 favour the second
option (p.195), and provide a few reasons. In their usage, repenomamids have three
upper incisors rather than two, the first lower
incisor (i1) isn't enlarged, the molariforms are
taller and 'more piercing', and the main a cusp of the lowers is 'more inflated'.
Others agree but still refer the relevant genus to Gobiconodontidae.
Should anybody think this is a storm in a tea cup, then that'd be a vast
exaggeration. This is more akin to the gentlest of drafts above a large soup
bowl.
Genera: Gobiconodon, Guchinodon
(= Gobiconodon), Hangjinia,
Huasteconodon,
Meemannodon, Neoconodon (= Gobiconodon),
Repenomamus, other reports
Time-Line:
Lower Cretaceous: Gobiconodon, Hangjinia, Meemannodon,
Repenomamus, Spain, England
Lower Jurassic: Huasteconodon (While this genus has been referred to the
family, I have doubts about that. So do the authors.) |
| Genus: Gobiconodon Trofimov
BA, 1978
'Gobi coned tooth'
Aka: Gobioconodon [sic] and (nomen nudum); Guchinodon Trofimov BA,
1978; Neoconodon (nomen nudum)
Remarks: Gobiconodon was also a "Nomen nudum in Trofimov, 1974,"
(McKenna & Bell, 1997).
"Differences in morphology among the four species of Gobiconodon are substantial,
including differences in size, root number of some postcanines, details of cusp morphology,
and development of diastema among the elements of anterior
dentition. These differences are at least as significant
as those used to establish generic differences among other tricondont groups such as
Triconodontidae. For instance, Priacodon, Triconodon and Trioracodon
differ from each other in details similar to those among the species of
Gobiconodon", (Rougier et al 2001, p.17).
A further fossil from Höövör, an upper jaw fragment, was referred to Gobiodon, which
subsequently became Gobiotheriodon. New examination, (Averianov 2002, p.707 -see
Bibliography for fuller details.), suggests this is probably cf.
Gobiconodon.
Dental formula
Information is contained in Wang et al, 2006 (p.195). They report as follows per
side: (uppers): 2 incisors, 1
canine, 3-4 premolars and 4
molariforms; (lowers): 2, 1, 2-3 and 5
respectively. This differs to several earlier offers (Jenkins & Schaff, 1998 and
Li et al, 2003) which were stingier with lower incisors. They only allowed for
one a side.
Kielan-Jaworowska et al, 2000
On page 578, these authors reported skull length estimates for the genus as varying
from 27 millimetres (G. hoburensis) to 106mm, (G. ostromi). Material
has since been added from further afield (Europe and China), but this range of
variation is still about the size of things. The genus contains roughly
mouse- to
rabbit-sized
critters from across the northern hemisphere of the Lower Cretaceous, but their
taste buds wouldn't have tingled with temptation at the scent of plants. The teeth
are those of crunching murderers.
Gobicono-inflation
The number of species (named and unnamed) ascribed to this genus continues to climb.
The Lower Cretaceous of the Isle of Wight coughed up a premolar provsionally
assigned in 2006, and 2007 has seen two more unnamed species arrive from Siberia
(Sweetman, 2006 and Averianov et al, 2007 respectively). As far as I can recall,
the list of countries yielding fossils now reads: Mongolia, USA, China, Spain,
Morocco, England and Asiatic Russia. |
| Species: | Gobiconodon borissiaki Trofimov BA, 1978 |
| Aka: | Gobioconodon borissiaki; Neoconodon borissiaki |
| Place: | Höövör (formally known as Khoboor), Guchin Us County &
Kemerovo Region, Siberia |
| Country: | Mongolia & Russia |
| Age: | Aptian or Albian, Lower Cretaceous |
| Remarks: | This was the first species to be established
(Kielan-Jaworowska et al 2000, p.578). Originally, it was based on fragments of
lower und upper jaws from Höövör. Subsequently, a Siberian
dentary from Shestakov was added. The species
is a middle sized member of the genus, with a skull length of around five
centimetres. Apart from size, there are differences to other speices with regards
to some aspects of the lower teeth. The p4 premolar
is single-rooted. On the m2-m5 molars, cusps known as
e and f are proportionately larger than those of G. ostromi, and the first
incisor and canine
are closer to one another in size. In common with G. ostromi but in contrast
to G. hoburensis, the b and c cusps on molars are built more strongly.
The Siberian material was published by Maschenko & Lopatin in 1998 and is
"rather poor", (Rougier et al 2001, p.3).
Nomen nudum Corner
Averianov & Skutschas 2000, (p.340) states the name was used as a nomen nudum.
Two different papers from 1974 are referenced, (Beliajeva EL, Trofimov BA & Reshetov VJ,
General stages in evolution of late Mesozoic and early Tertiary mammalian fauna in Central
Asia. Trudy Sovmestnoi Sovetsko-Mongol'skoi Paleontologicheskoi Ekspeditsii 1, p.19-45 and
Kalandadze NN & Kurzanov SM, Lower Cretaceous localities of terrestrial vertebrates in
Mongolia. Trudy Sovmestnoi Sovetsko-Mongol'skoi Paleontologicheskoi Ekspeditsii 1,
p.288-295. The first is also referenced for another nomen nudum, Neoconodon
boriassiaki.
Holotype
PIN 3101/09 is much of a right dentary in the collection of the Paleontological
Institute, Moscow. |
| Reference: | Trofimov (1978), The first triconodonts (Mammalia, Triconodonta)
from Mongolia. Dokl. Akad. Nauk SSSR 243, p.213-216. (In Russian). |
| Species: | Gobiconodon hoburensis (Trofimov BA, 1978) Kielan-
Jaworowska Z & Dashzeveg, 1998 |
| Aka: | Guchinodon hoburensis Trofimov, 1978 |
| Place: | Höövör (formally known as Khoboor), Guchin Us County &
Kemerovo Region, Siberia |
| Country: | Mongolia & Russia? |
| Age: | Aptian or Albian, Lower Cretaceous |
| Remarks: |
This is a small representative. The skull length was probably less than a couple of
centimetres (Wible et al 2001, p.15). Other authors report a somewhat larger
size.
The presence of this species at the Shestakovo site in Siberia is cited in Tang et al 2001,
(p.124). However, it's not mentioned by Rougier et al 2001. They refer to G. borissiaki
from Siberia, (p.3). Nor is it in the abstract of Tatarinov and Matchenko, 1998. But it
is mentioned in Maschenko et al, 2002 (p.76). They report the presence of both named species
and even a third, unnamed one for good measure.
Holtype
Kielan-Jawrowska et al, 2000 (p.589) offer a brief outline. The type fossil, PIN
3101/24, is part of a right dentary living at the
Paleontological Institute in Moscow. Further jaw fragements were also collected.
They offer a skull estimate of 2.7cm (one-and-a-bit inches), but the owner
doubtlessly had a big heart and bags of charisma. In contrast to some relatives,
the p4 premolar was double-rooted and, excepting
for the main cusps, those on the molars were more
modestly sized. |
| References: | Trofimov (1978), The first triconodonts (Mammalia, Triconodonta)
from Mongolia. Dokl. Akad. Nauk SSSR 243, p.213-216, (in Russian). |
| Kielan-Jaworowska & Dashzeveg (1998), Early Cretaceous
amphilestid ('triconodont') mammals from Mongolia. Acta Palaeontologica Polonica, 43,
p.413-438. |
| Species: | Gobiconodon hopsoni Rougier GW, Novacek MJ, McKenna
MC & Wible JR, 2001 |
| Place: | Cannonball Member, Oshih Depression (aka Ashile, Oshih Nur) |
| Country: | Mongolia |
| Age: | ?Valanginian-?Neocomian, Lower Cretaceous |
| Remarks: |
This is the largest known representative of the genus and very possibly the earliest. It's
based on two fragments of lower jaw with some teeth in situ. The species name honours Dr
James A Hopson.
Adjudged in terms of the worn gnashers, the holotype is interpreted as coming from "an
old individual", (Rougier et al 2001, p.8).
This location was originally paleontologized by American workers back in the 1920s, who
happily carted off various dinosaurs back to New York. Mammal remains first came to light
in 1997, courtesy of the local researcher, Bolortsetseg Minjin, "thanks to her unique
prowess as a collector," (Rougier et al 2001, p.21).
From the same page: "G. hopsoni (based on teeth size) is approximately the size
of a Didelphis virginiana (skull length of about 12cm)." That's the Virginia
opossum. However, as noted by the authors, the proportions of skull to body size may well
differ. |
| Reference: | Rougier et al (2001), Gobiconodonts from the Early Cretaceous
of Oshih (Ashile), Mongolia: American Museum Novitates, 3348, 30pp. |
| Species: | Gobiconodon ostromi Jenkins Jr FA & Schaff CR, 1988 |
| Place: | Cloverly Formation, Montana |
| Country: | USA |
| Age: | Albian-Aptian, Lower Cretaceous |
| Remarks: | Kemp, 2005 (p.152) includes a brief account. Two
partial skeletons show this species was among the larger versions. The skull is about ten
centimetres long, and the body (without tail) adds 35 more. The skeleton is relatively
robustly built.
The central one of the three main molar cusps is the tallest, reflecting the typical
arrangement in amphilestids. A contrast is that it's
positioned slightly out of line so a degree of obtuse triangulation is involved. As with
triconodontids the lower molars interlock, but the
methodology employed is different. An accessory cusp at the rear fits betwee a pair of
colleagues on the following molar.
Further material is in the Oklahoma collection. The lower molars of this species range in
length from 4,2 - 4,9mm, and it's about double the size of G. borissiaki. Skeletal
remains suggest it was getting on for the size of the existing Virginian opossum, (Clemens
et al, 2003), or a fairly small cat. |
| Reference: | Jenkins & Schaff (1988), The early Cretaceous mammal
Gobiconodon (Mammalia, Triconodonta) from the Cloverly Formation of Montana. J. of
Vert. Paleo, 8(1), p.1-24. |
| Species: | Gobiconodon sp. Rougier GW, Novacek MJ, McKenna MC
& Wible JR, 2001 |
| Place: | Cannonball Member, Oshih |
| Country: | Mongolia |
| Age: | ?Valanginian-?Neocomian, Lower Cretaceous |
| Remarks: |
There's a second species known from this location, though the
remains are not sufficiently well preserved to allow a fuller diagnosis, (Rougier et al 2001,
p.1). Two fragments of jaw were recovered within inches of each other, possibility
indicating that they can from the same creature. The rearmost fragment contains traces of
a Meckelian groove, which is a feature not associated
with living mammals. |
| Reference: | Rougier et al (2001), Gobiconodonts from the Early Cretaceous of
Oshih (Ashile), Mongolia: American Museum Novitates, 3348, 30pp. |
| Species: | Gobiconodon zofiae Li C, Wang Yuanqing, Hu Y &
Meng J, 2003 |
| Place: | Yixian Formation, Liaoning |
| Country: | China |
| Age: | Barremian, Lower Cretaceous |
| Remarks: |
This is from the same site as Repenomamus, below. It's
based on a skull with an articulated lower jaw, (IVPP V12585 in the collection of the
Institute of Vertebrate Paleontology and Paleoanthropology, Beijing). An ossified
Meckel's cartilage has been recognized by Wang et
al, Science vol 294.
In some contrast to Repenomamus, this specimen has two grooves on the inside of the
lower jaw, which are separated by a narrow ridge. This double-grooviness is known from
some other triconodonts, (Meng et al 2003, p.437). |
| Reference: | Li et al (2003), A new species of Gobiconodon
(Triconodonta, Mammalia) and its implication for the age of Jehol Biota, Chinese Scientific
Bulletin, 48 (11), p.1129-1134. |
| Species: | Gobiconodon palaios Sigogneau-Russell D,
2003 |
| Place: | Anoual |
| Country: | Morocco |
| Age: | Berriasian?, Lower Cretaceous |
| Remarks: | |
| Reference: | Sigogneau-Russell (2003), Diversity of
triconodont mammals from the early Cretaceous of north Africa: Affinities of the
amphilestids, Palaeovertebrata, 32(1), p.27-55. |
| Species: | Gobiconodon sp. A Averianov AO,
Skutschas PP, Lopatin, AV, Leshchinskiy SV, Rezvyi AS & Fayngerts AV, 2005 |
| Place: | Bol'shoi Kemchug 3, Krasnoyarsk Territory,
Western Siberia |
| Country: | Russia |
| Age: | Lower Cretaceous |
| Remarks: | The following is based upon my reading of
Averianov et al, 2005 and thanks are due to the supplier.
Fossils indicate the presence of two species inthe Bol'shoi Kemchug 3 fauna of
Western Siberia, and they've so far simply be designated as A and B (p.7).
Uppers
Species A has donated a couple of isolated molars and
fragments of lower jaw. The M1 upper molar was presumably completely fringed with a
cingulum although, if so, much of the
labial part must be absent due to breakage. The
three main cusps are modestly triangulated in arrangement (about 150°), and cusps B
and C achieve similar heights. An embayment between cusps E and F allowed for
interlocking with the neighbouring tooth. The main cusps of M2 are nearer to
parading in a straight line, although they're slightly triangulated. Only a single
cusp, D, occupies the cingulum, and both flanks of the crown have a concavity near
to the middle.
Downers
Two lower jaw fragments both preserve the area beneath
alveoli for the first three molars. It was a shallow bone with little more depth
beneath the m3 than the m1. Of particular interest is a pit for a dental lamina
lingual of the molar roots. Why that might be of
any interest whatsoever seems a fair question. This small slit is a functional
feature rather than a decorative one, and the point seems to have been to serve as
a convenient facility for the development of replacement molars. It's reasonably
widely known that mammals no longer replace their molars, but this isn't
something all Gobiconodon species appreciated, at least when it came to the
first three. Evidence allows a similar accusation of reprobate replacement tendencies
to be lodged against Repenomamus.
Tooth sizes (p.8):
Uppers: M1 length 1.8mm, width 0.8; Ms 1.8, 0.8
Lower: m5 1.8, 0.8.
And in case anybody thinks there might be some sloppy copy-and-pasting involved with
that, the sizes actually are all the same.
Comparisons
In terms of size, this is a small Gobicono species comparable with G. hoburensis.
However, the lower molar shows more individualized b and c cusps, and there's a clear
E cusp on the cigulum of uppers. |
| Reference: | Averianov et al (2005), Early Cretaceous mammals from
Bol'shoi Kemchug 3 locality in West Siberia, Russia, Russian Journal of Theriology,
4(1), p.1-12. |
| Species: | Gobiconodon sp. B Averianov AO,
Skutschas PP, Lopatin, AV, Leshchinskiy SV, Rezvyi AS & Fayngerts AV, 2005 |
| Place: | Bol'shoi Kemchug 3, Krasnoyarsk Territory,
Western Siberia |
| Country: | Russia |
| Age: | Lower Cretaceous |
| Remarks: | The following is based upon my reading of
Averianov et al, 2005 and thanks are due to the supplier.
In terms of tooth size, this second Kemchug species is about 70% larger than
local species A (p.9), and 20% more than G. zofiae of the Chinese lower
Yixian fauna. Known remains of species B are
presently restricted to a couple of lower postcanines,
and presumably an upper incisor of an appropriate
size and style. That has a 3.5 millimetre high crown with an impressive root adding
around another 6.6mm.
A single-rooted tooth stands accused of being a lower p4 premolar. The b and c cusps
are similar in size. The foremost of this duo, b, is slightly out of line with a and
c, as it stands a bit towards the buccal side. Lovers
of cingula will be pleased to hear that a
lingual cingulum is present, running back between b
and c. A further tooth is probably a lower m5 molar.
Postcanine dimensions
Lowers: p4 length 2.0mm, width 1.4; m5 3.0 and 1.5 respectively.
Comparisons
A tri-cusped p4 with a single root is also known from the somewhat smaller G.
borrisiaki. The corresponding tooth has two roots in some other species. One
entertaining specimen of the considerably larger G. ostromi demonstrates
that some individual variation is possible with this character. One of its p4s is
single-rooted while the other is "incipiently double" (p.10). The lower molar's
identified as an m5 on account of the loweness of it crown proportionate to length,
and the b cusp being a bit higher than the c. |
| Reference: | Averianov et al (2005), Early Cretaceous mammals from
Bol'shoi Kemchug 3 locality in West Siberia, Russia, Russian Journal of Theriology,
4(1), p.1-12. |
| Species: | Hangjinia chowi Godefroit P & Guo DY, 1999 |
| Place: | Ejinharo Formation, Ordos Basin |
| Country: | China |
| Age: | Lower Cretaceous |
| Remarks: | Based a lower left jaw. Rougier et al 2001
suggest the possibility that this might be a juvenile individual and that the genus is
perhaps "a derived gobiconodontid, rather than an
aberrant one as originally proposed", (p.17-18). |
| Reference: | Godefroit & Guo (1999), A new amphilestid mammal from
the Early Cretaceous of Inner Mongolia (PR China), Bull. Inst. Roy. Sci. Nat. Belgique 69,
Supplement B, p.7-16. |
| Genus: Huasteconodon
Montellano M, Hopson JS & Clark JM, 2008
'Huizachal coned tooth'
Remarks: I surely don't need to mention that Huastecos is a culture that emerged in Middle
America, and then fell out of fashion as recently as 1200 years ago. |
| Species: | Huasteconodon wiblei Montellano et al, 2008 |
| Place: | La Boca Formation |
| Country: | Mexico |
| Age: | Lower Jurassic |
| Remarks: | The following is based upon my reading of
Montellano et al, 2008, and thanks are due to Allen P.
If the authors are correct with their referral of this Lower Jurassic genus to the family
Gobiconodontidae, then it would come as a great surprise to me (and quite possibly to
themselves). This would be a remarkable extension for that taxon
which, otherwise, is presently restricted to the Lower Cretaceous. However, the
referral was made in the sure knowledge that it could turn out to be wrong when exposed
to the light of further evidence.
The only available specimen is a small fragment of what was a very small
maxilla (p.1139). It provides a haven for two
molars and alveoli for a
third, and achieves this trick despite being around 2mm in length. (The best preserved
tooth achieves 0.55mm.) Another challenge to unravelling affinities is posed by this
piece of upper jaw not being comparable with taxa known only from lower jaws and/or
teeth. The upper molars are proportionately narrower than those from the Cretaceous
gobicons, the C cusp is unusually small and the D one is impressively large. Roots manage
to exceed the crown in terms of width.
A brief jaw tour
The jaw shows the beginning of the zygomatic process (cheek bone) is located behind the
rearmost of two alveoli (tooth holes) at the rear of the fragment, and that identifies
those two holes as having housed the roots of the last molar in the series. Another
feature is a series of three depressions in the bone. These provided lodgings for the
main cups of lower molars. They're handily position
lingual from the upper teeth and between them; ie. the final depression is internal
from and about equidistant between the two uppers, and so on towards the front.
Wear has been heavy on the molars, and the original architecture isn't entirely clear.
The main cusp, A, is lengthy in terms of front-to-rear and has a rounded tip. B is
located right at the front on the second preserved molar. The identity of rear cusps is
somewhat uncertain. What's likely the C cusp is considerably smaller than a presumably
cingular cusp D. More generally, the reverse size
relationship would be expected. In any case, as A is somewhat lingual of centre, the cusps
achieve a degree of triangulation (approximately 120°). No cingulum is present on the
lingual side, but that absence could've resulted from wear. A
buccal cingulum runs from cusp A to the presumed cusp D.
Affinities???
Of upper dentitions available and invited for interview, the molars of Huasteconodon
share most similarities with Gobiconodon. These include
the somewhat triangulated arrangement of the main cusps, the depressions for housing lower
molar cusp tips, and the wideness of the roots being greater than that of the crown.
However, the fragmentary nature of the only specimen leaves the authors less than fully
confident of their referral of it to Gobiconodontidae. Also cited is the impressive
chronological gap between this genus and other(?) gobicons. As for my level of confidence,
for what little it may count, I'd presently rate that as comparatively lower than the
presumed C cusp.
Holotype
The type fossil, IGM 6619, is a fragment of upper jaw now housed at the Institute de
Geologia, Ciudad University, Mexico. The specific name honours paleontologist John R
Wible. |
| Reference: | Montellano et al (2008), Late Early Jurassic mammaliaforms
from Huizachal Canyon, Tamaulipas, Mexico, Journal of Vertebrate Paleontology, 28(4),
p.1120-1143. |
| Genus: Meemannodon
Meng J, Hu Y-m, Wang Y-q & Li C-k, 2005
'Meemann's tooth'
Family: Gobiconodontidae
Remarks: The generic name honours Dr Meemann Chang, a researcher strongly involved in
hunting ancient Yixian fossils. (Thanks are due to George of Athens, who somehow got wind
of the critter a couple of months early.) |
| Species: | Meemannodon lujiatunensis Meng J, Hu Y-m, Wang Y-q &
Li C-k, 2005 |
| Place: | Lower Yixian Fauna, Liaoning |
| Country: | China |
| Age: | Lower Cretaceous |
| Remarks: | The following is based upon my reading of Meng et
al, 2005.
Meemannodon is a further enrichment for a somewhat atypical Lower Cretaceous
fauna; that of the lower Yixian (p.1). In much of the world at that time, mammals were
small but delightful squirts who would've been ill advised to play with even the smaller
small dinosaurs. The prevailing balance of power in the lower Yixian, however, was a far
more sensible one. Towards the top of the known food chain was a triconodont mammal named
Repenomamus giganticus, an immense, modest dog-sized
monster mammal; the largest so far discovered from the entire Mesozoic. This new genus, a
Repeno relative, couldn't match up to that. Nevertheless, for the time of Earth it was
another proportionately enormous mammal; comparable in size to Repenomamus robustus.
A somewhat more modest relative, Gobiconodon zofiae,
has also been recovered from the same locality of Lujiatum (p.2). The lower Yixian is
a-swamped with impressively sized triconodonts.
The only published evidence of a smaller furry friend is found as stomach content in one
of these larger thugs. Whether this size peculiarity is a blip of distortion or a
reasonable reflection of the eco-system is something unknown to me, but the former
possibility strikes me as most likely. Potential distortions that come to mind could
include preservation bias, collecting bias or even a preference for describing bigglings.
Perhaps future finds and / or descriptions will change the impression of a shortage of
smallings. If not, then accounting for the shortage could be interesting.
Meet 'Meeman's tooth'
The former owner of the jaw was similar in size to Repenomamus robustus, Rep gig's
smaller sister species (p.3). However, should a member of that species have become a
dentist providing treatment for its kith and kin, admittedly an unlikely prospect, then it
would've noted peculiarities among the teeth of its contemporary. For example, the first
incisor of Meemannodon is comparatively large, the
cusps of the incisors, the canine and the front
postcanines are noticeably pointy. These are features
shared with Gobiconodon. Distinctions from that genus include the incisors and
canine being implanted in the jaw with a more pronounced tilt towards procumbency, the
first incisor being larger, its follower being smaller, and there being no
diastema separating the premolars and
molars. The molars (or, more properly and in terms of the
paper, the molariforms) have main cusps that are
recurved and comparatively low. The length of these teeth exceeds their height, the m1 is
distinctly smaller than its three erupted colleagues and, in addition, the premolars are
also small.
Jaw and teeth
The known dental formula per side is as follows:
Lowers: 2 incisors, 1 canine, 2 premolars and 5 molars.
The first premolar and final molar aren't yet fully erupted and, such are the effects of
death, never will be. This state of affairs points to a young adult age. The length of
the jaw is a touch over 9cm, and its front is necessarily thickened so as to
accommodate the large first incisor. A groove is apparent on the inner face of the jaw.
This begins at the dentary condyle, runs forwards until it ceases below the second
molar, and it thins along its course. This is the
Meckelian groove.
Excepting for light traces on the cusps of the m3, the teeth are unworn. Incisors, canine
and premolars are all single-rooted. The second incisor is little more than a much smaller
impersonation of the first behind which it's closely positioned. A bit of a gap separates
i2 from the similar but larger canine (p.4). A longer diastema behind the canine ends at
a bump that, in fact, is an apologetic attempt at being a premolar. However, as this p1
was still in the business of eruption, its emergence was cut off before its prime. The
p2 is more substantial, but it still fails to attain the height of even the small second
incisor.
A table of measurements provides lengths, widths and heights. As is my usually mean habit,
I'm just going to mention the lengths here.
Lengths (mm): i1 5.53, i2 2.39, c 2.94, p1 (under construction), p2 2.82, m1 5.33, m2
6.35, m3 7.82, m4 7.43.
In terms of height, the first incisor is easily the dominant tooth. Its height (11.66mm)
leaves it looking down upon everybody else in the row.
The molars (molariforms is the term in the paper) are
double-rooted teeth (p.5), with the rear root being the stronger of the pair. In all
cases, the crown length is superior to the height and there are no
cingula. The cusp tips tilt somewhat backwards. The largest is the central cusp a,
although it's actually a bit forward of the crown midline. A cusp b is to the fore with
larger cusps c and d making up the end of the procession.
The first molar is clearly smaller and less cuspy then the other three fully erupted ones.
Rather than a b cusp as such, there's but a small bump in that position. It also lacks two
further frontal cusps known as e and f. These do occur on the second molar, but are best
expressed on m3 and m4. They have to do with an interlocking system for the rear d cusp
of preceding molars. Another contrast is that cusp b is lower than c on m2, with the
reverse applying for both m3 and m4 (p.6). The m5 is still largely hiding in the bone at
the foot of the coronoid process, a situation that more growth of the animal would have
changed. If the norms applied in this case, then the future adult would presumably have
had a gap between that tooth and the process.
Gobiconodontid tooth type differentiation
According to these authors, but contrary to some previous interpretations of tooth
identity (potentially tricky when, for example, incisors and canines happen to be
similarly shaped), the lower tooth formula for Gobiconodon
and Repenomamus is probably (per side): 2 incisors, 1
canine, 2-3 premolars and 5 molars. Meemannodon also fits within that range. Some
earlier authors had interpreted the gobiconodontid formula differently: 1, 1, 3-4, 5.
The emendation here has resulted from better preserved specimens, particularly in the
case of Repeno.
Welcome to the family
Various characteristics already known from Gobiconodon also apply for
Meemannodon; eg. an enlarged, procumbent first lower incisor, a reduction to only
two incisors and various aspects relevant to the premolars. Molars also employ the same,
albeit primitive interlocking mechanism (p.7), whereby the rear cusp d fits between cusps
e and f of the following tooth. In terms of tooth dimensions, Meemannodon is
larger than all known species of Gobiconodon, although not outrageously so in
comparison to the larger species. In any event, the authors conclude that Gobi is the
closest relative of Meemannodon, and refer the genus to the same family.
However, there are naturally distinctions between these genera. While the incisors and
canine for both are procumbent, this applies more so for Meemann. The newling's i1 incisor
is proportionately greater in size compared to the decreased i2. Meemann has only two
premolars per side rather than three (as interpreted by these authors), and these teeth
are comparatively reduced in size as well as number. It's presumably the third position
that was disposed of by the ancestors. Also, the p2 and m1 molar aren't separated by
any great distance in the dental row. There's a tooth between them for Gobi. However,
the possibility that this p2 is actually a homologue of Gobi's p3, a smaller and more
complex tooth than its other premolars, hasn't been entirely ruled out (p.8).
The molars also offer differences. The cusps for Meemann lean backwards rather than
attempting to stand to attention like the guards at Buckingham Palace. These teeth are
comparatively elongated with lower crowns. There are no cingula whereas a cingulid is
usually (but not always) present for Gobi. Additionally, the m1 of Meemannodon
is notably smaller than the other molars.
Distinctions from Repenomamus include the lower first incisor of that genus not
being enlarged (p.9). The molars of Rep are higher crowned and adapted more for piercing
its prey, and the central cusp a is more inflated. As is the case for Meemann, these
teeth also lack a cingulid.
Holotype
With a name like IVPP V 13102, the holotype must be in the collection of the Institute of
Vertebrate Paleontology and Paleoanthropology, Beijing. The specific name honours
Lujiatun, where the fossil was found.
Additional notes
All the following notes were scribbled together prior to obtaining the paper by Meng and
colleagues. I first saw a copy in 2009.
My information was limited to a translation of a
short Chinese webpage, which does have a photo. A link is below, but non-Chinese
speakers would probably be better served by Googling. As a 2006 paper (Wang et al)
has turned up, I can add some points from it. But first comes my own original
attempts to try to fathom things out from a picture.
A look at the photo
As Meso mammals go, this is another biggy. The photo shows much of the left of a
dentary, and the scale provided suggests a length of around
nine centimetres. There are two incisors, with the
i1 being much the largest. It points diagonally forwards. The
canine does much the same, but this is roughly the same size as the i2. It's
rather pathetic.
I can see a diastema between that tooth and the first of
two modest premolars. The four multicusped
molars look much more fun. The cusps slant somewhat
rearwards, and at least two of those teeth are blessed with an extra cusp at the back.
Oh yeah, there's a slight breakage between the premolars, and that makes the
preservation of those partial.
A guess at which part of the Yixian Formation
The Yixian has remains of two faunas, with the most recent one radiometrically dated at
about 125 million years. This dentary seems to be from the older fauna, as far as I can
see. My reasoning is that the fossil has been preserved in three dimensions. Specimens
from the younger Yixian have been habitually flattened by pressure. Consult the paper for
certainty.
If my assumption is correct, then the mammals from the lower Yixian are a very peculiar
collection. There are four genera of closely related meat-eaters and (as yet) nothing else.
I'm lacking measurements for Gobiconodon zofiae. However,
this Meemannodon and Repenomamus robustus are
enormous as Mesozoic mammals go, with body lengths of around half a metre. There's only
one known species which was certainly bigger, and that's Yixian's R. giganticus.
This pack of Cretaceous carnivores is utterly without parallel.
As far as I went, I did OK
Wang et al, 2006 (p.195) assures me I went for the right fauna; the lower Yixian.
While that wasn't exactly difficult to work out, I'm mildly proud of myself. This
review also states Meemannodon is a gobiconodontid; a closer relative of
Gobio than Repeno. It doesn't tell me much more on this particular subject.
|
| Reference: | Meng J, Hu Y-m, Wang Y-q & Li C-k (2005), A new
triconodont (Mammalia) from the Early Cretaceous Yixian Formation of Liaoning, China,
Vertebrata PalAsiatica, 43(1), p.1-10. |
| Link:
The Database of Paleontology Species
http://www.dinosaur.net.cn/DataBase/p_museum.asp?id=28502
This short Chinese page contains some brief details (in Chinese). For those of us who
speak only otherwise, there are photos offering before an external and internal view of the
jaw and three more detailed pics of the teeth. The photos may take a bit of time to
load. |
| Genus: Repenomamus Li J,
Wang Y, Wang Y & Li C,2000
'reptile-mammal'
Remarks: This genus is also termed Repenomamus the Magnificent, (on this
directory anyway).
Idiot
Wang et al, 2006 contains brutal accusations of remarkable stupidity for this genus
on page 196. Admittedly, they don't explicitely throw them, but that may be from fear
of upsetting this dynamic killer. Between the lines, I sense the presence of
derisive jealousy. How else can I understand the following? "Compared to the most
primitive mammaliaform Morganucodon
and Sinoconodon, however, the braincase
of Repenomamus is proportionally narrow or small." Although the comment is
made in the context of discussions on the possible motor of brain expansion, having
been responsible for the transportation of middle ear ossicles from the lower jaw to
their new abode -which is obviously dependent upon expansion which, in the
brain case of this genus, doesn't seem to have occurred... I think they were
rude to even mention such a delicate and personal matter in public.
Calling somebody stupid isn't particularly polite, and all the more so when it
happens to be true. Never mind how feeble-minded this cretin of a mammal was.
Writing stuff like that down is inexcusable.
There are a couple of difficulties in making assumptions about comparisons of
intelligence for the critters just mentioned, and that isn't actually what the
authors were addressing. They were talking about the relative proportions of the
brain cases. Firstly, as all the critters are long dead, the possibilities of
behavioural research are severely limited. Secondly, larger animals frequently have
comparatively smaller brain boxes than littler ones. Even the smaller Repeno was
considerably bigger than Morganucondon.
Additional notes
Averianov et al, 2007 (p.3) provides some discussion on this genus. They point out
that the possibility has been voiced of Rep perhaps being a junior synonym of
Hanglinia. Personally, I'm not particularly partial to
the generic name of Repenomamus (we mammals are
synapsids, not reptiles), but I hope this opinion doesn't turn out to prevail.
Hangji is presently based on a toothless jaw of a juvenile, and its tooth formula
has been subject to challenge. According to the original authors, it had 3
incisors, 1 canine,
perhaps 2 premolars and 2
molars per side. However, the formula could actually be 1, 1, 1-2 and 1-4
respectively, and that would be closer to gobiconodontid norms. Given its youthful
age, the lack of a second incisor and fifth molar (both present for Rep), could be
the result of kidding around (ie. being young). These teeth may not have gotten
around to erupting.
Even so, the lack of any actual teeth makes comparisons of limited value at present,
thus the possibility is simply noted. Toothier specimens might one day sing more
instructively, either in tones of yea or nay.
Replacement 'molars'
Rougier, Isah & Manabe, 2007 carries shocking news on page 75. CT scanning revealed
the presence of tooth buds on a specimen of Repno for at least some of the 'molar'
positions. They indicate replacement was going on. Disgraceful!
A key part of current definitions of molars necessitates them being teeth of the first
generation; ie. ones that don't get replacements. By persisting with this filthy,
non-mammalian habit, those teeth fail to strictly qualify as molars despite their
molar-like build and function. The correct word would be
molariform. As such a term could frighten the
uninitiated away, and the subject holds plenty of interest for lay
readers, my tendency is to stick with more familiar language even if it's not quite
correct. For example, it's interesting that some primitive mammals replaced their
molars, as that's not something any living ones do. In this regard, they were more
primitive than us lot, be we mice or people. |
| Species: | Repenomamus robustus Li J, Wang Y, Wang Y & Li C,
2000 |
| Place: | Yixian Formation, Liaoning |
| Country: | China |
| Age: | Barremian, Lower Cretaceous |
| Remarks: |
The first block of this entry is based upon my understanding of
Li et al, 2001 (see Bibliography). This is an English language description, for those of
us who are unacquainted with one of the most widely spoken languages on the planet.
The genus is described on the basis of a reasonably well-preserved specimen, (p.782). The
authors summarize a number of derived
mammalian characteristics: the strongly developed
jaw joint (dentary-squamosal); a reduced number of teeth; well differentiated postcanine
teeth into premolars and
molars; the presence of a dorsal process on the
premaxilla which doesn't contact with the nasal; the
closed medial wall of the orbit (eye-hole); and a
finger-shaped promontorium on the petrosal,
(which is the bony casing of the inner ear).
However, they also point to a number of 'reptilian' anatomical features, and term this the
most basal of the three Jehol taxon, which had then been
described. The others were Jeholodens (below) and Zhangheotherium
(Spalacotheriidae).
Big
The most striking feature of this genus is its size. The skull is over 10cm long (p.783).
This makes it the one of the largest Mesozoic mammals yet found. (5cm in length is
relatively big for a skull.) Update: it's got an even larger sister, as can be
appreciated by the second species introduced below.
Dentition
Compared to its some of its contemporaries, it had a low number of upper
teeth. The formula is 3.1.2.4. This means three incisors,
one canine, two premolars and four molars per side. Of
these, the canine is similar in size to the I3, the premolars have a conically shaped main
cusp, whilst the molars have an impressive main cusp (A), in conjunction with the weakly
built B and C.
Skull and jaw
The skull was preserved in a three dimensional condition, and was in tight occlusion with
the lower jaws. Between the nasal and premaxilla, the authors noted the presence of a large
septomaxilla, which is not the sort of feature any existing mammal possesses. It's a
decidedly 'reptilian' bone. Other primitive features apparently include (p.785): a
'postdentary bar', (subsequently rediagnosed as a fossilized
Meckel's cartilage -Meng et al, 2003, p.433); the
lack of an angular process; the relatively simple structure of the molars with their
indistinct cusp separation; a smallish braincase and "the morphology of the lambdoid
crest and the occiptal plate is special, which is similar to some "mammal-like
reptiles", but more primitive than other mammals. Considering the above characters
and also the large body size of Repenomamus, the lineage represented by this taxon
should have diverged early from the main stem in the evolution of mammals."
Holotype
The species name refers to the relatively large size of the critter. The holotype is
IVPP V 12549 and it lives in the Institute of Vertebrate Paleontology and
Paleoanthropology, Beijing, (p.783).
"Four nearly complete Repenomamus adult skulls with articulated lower
jaws", are known, (Wang Y, Hu Y, Meng J & Li C 2001, An ossified Meckel's
cartilage in two Cretaceous Mammals and Origin of the Mammalian middle ear, p.357-?. I've
only got page 357!).
An increasingly healthy population
Meng et al, 2003 (p.433) suggests this genus may be breeding. The headcount seems to have
reached seven reasonably complete or partial skulls, (a couple in association with partial
skeletons), and a partial lower jaw. Several specimens show the ossified Meckel's
cartilage, known as OMC in this paper; a feature a bit over 3cm in length. Fired up with
enthusiasm, these authors also took another look at a previously undescribed element from
the skull of Zhangheotherium, (Spalacotheriidae), from the same location. This also
seems to be the remains of Hr Meckel's cartilage. Quite what these creatures did with
their cartilages isn't clear.
Should it be of interest, (p.436): "The
meckelian groove is distinct in all lower jaws of Repenomamus. It lies along
the lower part of the dentary. The posterior portion of
the groove that holds the OMC is broad and has a rounded base."
This was an exceptionally large Mesozoic mammal. The dentary is over 8cm long, "with
a skull almost 11cm long", (Weil, 2002). There seems to be a close relationship to
Gobiconodon, which has also been reported from the same location. With thanks to
David Marjanovic.
R. robustus (IVPP V13605) the Magnificent
This block is largely based upon my reading of Hu et al, 2005.
This individual is a Mesozoic eucynodont megastar.
In conjunction with its bigger sister, R. giganticus, it hit the world press with a
resounding explosion when described in January 2005. The choice of diet was the decisive
factor. It temporarily sent the visiting figures of this directory into previously
unimaginable territory; four figures on a single day. Normally, four fingers are
sufficient for a head count. The monthly bandwidth allowance was obliterated, but I can
only congratulate the Repenomamus sisters for achieving the seemingly impossible.
Diet: having a bite to eat
An understanding of Mesozoic mammalian diets is generally a matter of deduction from tooth
morphology. As tooth shape in living mammals is usually a reliable guide, it's reasonable
to assume the same applied in the distant past. A deceased member of this species has
taken a different approach. Including the tail, this individual was nearly 60cm long and
probably weighed between four and six kilos. It thoughtfully died before it had digested
its last meal.
The world was plagued by dinosaurs at the time, and this mammal had an effective way of
lessening the problem. It ate them. Admittedly, adult sauropods would have involved biting
off a bit more than it could have imperfectly chewed, but a very young Psittacosaurus
was dealt with decisively. The dino had a body length of about 14cm, and Repeno saved it
from any future worries about further growth.
The Happy Eater
This was a good meal and not a snack. The torso of the mammal is only around three times
the length of the thoroughly savaged baby. The bits of dino which are still identifiable
include a leg, an arm, toes and teeth. The skull and remainder of the skeleton are broken
up, but all elements are packed together in a restricted area of where the stomach used to
be. Most of the swallowed teeth are sufficiently worn to show the dinner invitation wasn't
delivered to an embryo in an egg.
The fact that this last meal is so easily recognisable demonstrates it hadn't been chewed
very effectively. This is none too surprising given the archaic mammalian teeth Repeno's
jaws were equipped with. They weren't capable of thorough chewing. Nevertheless, they
could certainly create a deadosaurus.
A few other bones show the Psittacosaurus had company in the stomach. Some ingested
vertebrae and ribs are mammalian. Repeno was also a
mammal murderer. Which victim formed the first course is unclear, but I suspect it was the
furry one. Thinking back to Christmas dinner, I wouldn't have bothered swallowing a mouse
or shrew-sized creature afterwards, had one been on offer. This must've been a really
good day for the predator. Who knows what tomorrow might have brought? In this case it
failed to show up.
Remains
As well as being unusual for containing bits of dinosaur, this fossil also happens to be
stunningly complete and articulated. Apart from most of the tail there's not a lot
missing. As with its bigger sister there are 20
thoracic vertebrae with most of the ribcage, shoulders and hips. All the main limb
bones have been preserved along with much of a front and back foot. These are short and
wide. They're plantigrade paws for a primarily terrestrial resident. This is a megastar
who kept its feet firmly on the ground. |
| Reference: | Li, Wang, Wang & Li (2000), A new family of primitive
mammal from the Mesozoic of western Liaoning, China. Kexue Tongbao 45(23), p.2545-2549, [in
Chinese]. |
| Species: | Repenomamus giganticus Hu Y, Meng J, Wang Y & Li C,
2005 |
| Place: | Yixian Formation, Liaoning |
| Country: | China |
| Age: | Barremian, Lower Cretaceous |
| Remarks: | Mesozoic mammals were typically small critters, (or
smaller), and interest is restricted to a few admirers. For some unknown reason, 25 metre
sauropods seem to receive more public attention than one centimetre long jaw fragments or
minute isolated teeth. Even a complete skeleton of
Ukhaatherium, (12 centimetres not counting the tail), provokes minimal interest
beyond the fan base of committed Meso Mammal Ultras. Why a 12 metre tyrannosaurid should
enjoy a higher profile is hard to understand. If you want to give your kid, (or yourself),
a cuddly Ukhaatherium, then no toy shop on the planet will have one in stock.
You'll have to make it yourself.
However, now and then a find will turn up which refuses to accept indifference, and they're
usually from Liaoning. The squeaks are so alluring that even the BBC and CNN fall to their
charms. The Repenomamus sisters weren't content with that. These are fossils with
attitude. They didn't just squeak their way into global awareness. They roared. And the
world turned round in astonishment. Repeno didn't live in the shadow of dinosaurs. It ate
them.
The following is based upon my reading of Hu et al, 2005. (My thanks go to the suppliers.)
A superstar is born
Until the start of 2005, the largest Mesozoic mammal
represented by anything like reasonably complete remains was Repenomamus robustus.
It was about the size of a Virginia opossum or a cat. This second species, R.
giganticus, has just grabbed the record with its powerful jaws and has no intention of
letting go. This compares to a large Tasmanian devil or, (for those with less adventurous
tastes in pets), a respectable dog. Its 50% bigger than its sister.
Along with Gobiconodon zofiae these fossils come from
the lowest member of the Yixian Formation, and they're consequently somewhat older than
the other Lower Cretaceous Liaoning mammals. Their age is somewhere between 128 and 139
million years. The volcanic tuffs have preserved a large assemblage of 3-dimensional
vertebrate skeletons, and they may all have been the victims of a single catastrophe. The
death list includes frogs, reptiles, dinosaurs and these mammals.
Remains
Presently, one specimen has been identified for this species but the completeness is
fantastic. It's not quite enough for a round of 'head, shoulders, knees and toes', but
this is only because the paws are missing. The other requirements have been fulfilled
along with the spine, ribs, tail, limbs and so on. For example, the animal clearly had
epipubic bones because one's still joined to the
pelvis. It looks as if the critter lay down on its side,
fell asleep and forgot to wake up. It must've been under a cosy blanket, as nobody had a
chance to play around with the remains. There's no indication of violence or scavenging,
and this is consistent with a bout of natural eco-terrorism.
What a whopper
The aforementioned Ukhaatherium (12cm not including the tail) is a fairly respectable
size for a Mesozoic mammal. In most other cases, remains are so limited that lengths have
to be estimated. A measuring tape can be used for R. giganticus. The skull's 16cm
in length, the body's a bit over 52cm, and what remains of the tail is in excess of 36cm.
(The first sixteen caudal vertebrae are present, so it can't
have been too much longer.) Repenomamus giganticus was literally over a metre long,
(assuming it held its tail in an odd way).
Body and limbs
"In both species of Repenomamus, the lumbar and
thoracic vertebrae; are well differentiated",
(p.151). There's a clear division of breast and lumbar regions to the body, and this is
typically mammalian. The 20 thorarcic vertebrae and associated ribs define the breast
area, and six lumbar vertebrae form the lower region of the spine. The trunk of the body
is relatively long when compared with therians, and the legs
are short and robust. Based on data for living mammals the authors offer a weight estimate
of 12-14 kilos.
Head
In comparison with its sister, R. giganticus has a skull with stronger sagittal and
lambdoid crests, and a stronger zygomatic arch.
Teeth
The dental formula per side is: (uppers): three incisors,
one canine, two premolars
and four molars; (lowers): two, one, two and five respectively.
(The paper refers specifically to premolariforms and
molariforms, but I tend to be less formal.) This is a
relatively low number of postcanines for what is a
fairly basal mammal.
The large and pointed incisors are the strongest members of the
dentition. In league with the canine and premolars, these are tools for catching,
holding and tearing. The build of the jaw provides plenty of space for muscles. The
combination of tall front and small rear teeth is share with many meat-eating
non-mammalian synapsids. As the molars are small and not particularly sharp, they
couldn't have been used for effective chewing, when compared to the art as practiced by
further derived mammals.
Natural Born Killer
The teeth and muscles fit best with an active predator rather than a more wimpish scavenger.
This animal tore its prey apart and gulped it down in raw, warm chunks. This was served
with blood rather than ketchup, but doubtlessly swallowed with plenty of relish.
Biological age and growth pattern
All postcanines have at least partly erupted, and most
show much wear. As the teeth had much work experience, their owner must've been an adult.
However, the fifth lower molar has only just appeared and isn't at all worn. The m3 is in
the process of erupting, as are a couple of other teeth; P1 and i1. This individual was a
relatively young adult.
The epiphysis and the shafts of long bones are fused. This suggests body growth had
ceased. These animals reached a full adult size and stuck with it. This is a strategy of
determinate growth rather than continual, and it's typically mammalian.
Reasons for establishing a new species
An obvious distinction between the two species is size. However, that alone isn't
necessarily a sure indication. In an extreme case from living
Mammalia, male elephant seals can be 60% longer than their mates. (That's unusual and
seals are aquatic specialists. Such a differential between the sexes isn't found in most
terrestrial species.) Even more extreme ranges of size are known from non-mammalian
eucynodonts, (eg. Chiniquodon), but it's
unknown whether this was influenced by sex.
In this instance, there are a suite of further distinctions. For R. giganticus the
incisors are proportionately larger; the upper canine is double-rooted; the first upper
premolar is much smaller than the canine; upper molars have a complete
lingual and a partial
labial cingulum; pits on the palate for the
accommodation of lower molars are shallower.
On the lower jaw, the mandibular symphasis is deeper; the jawbone is more robust; the
incisors, canine and premolars are less widely spread; cusps c and d on the molars are
larger.
Holotype
The holotype, (IVVP V14155), is in the collection of the Institute of Vertebrate
Paleontology and Paleoanthropology, Beijing. The specific name is naturally enough a
reference to the unusually large size for a Mesozoic mammal.
(Thanks are due to Verrengia JB (12.1.2005), Fossil is proof of Mammal eating dinosaur, The
Associated Press, and Guy Leahy for posting notification on the Dinosaur Mailing List.
The same article provided information on the eating habits of R. robustus.)
An amazement induced anecdote
This publication initiated an incredible surge in traffic. Although there's a counter at
the foot of this directory, I'd never looked at it until 14.1.2005. I was staggered to
find it read exactly 3,000 and the bandwidth allowance for the month had disappeared. My
guestimate is that something like 1,750 visitors must've arrived on the 12th and 13th,
possibly at a ratio of around 25:75%. Usually, the combined total would've been in single
figures. I mention this because: a. I'm still gobsmacked, and b. as an anecdotal
illustration of the worldwide interest this description provoked. If you'll excuse, I'm
off to the shops to buy some more bandwidth to keep this project on-line. |
| Reference: | Hu, Meng, Wang & Li (2005), Large Mesozoic mammals fed on
young dinosaurs, Nature, 433, p.149-152. |
| Other reports:
Vallipón, Teruel, Spain
What follows is based largely upon Cuenca-Bescós & Canudo, 2003 (see Bibliography).
Although not diagnosable below the family level, this fossil is the first evidence of
Gobiconodontidae from Europe. These creatures clearly spread across the northern
hemisphere. At this location, remains are presently restricted to a single tooth.
This comes from the Artoles Formation in NE Spain. At Vallipón, the lower 30 - 50 cm of
the eight metre thick formation is fossiliferous. It's probably late Barremian and
represents an assemblage of marine and terrestrial creatures, accumulated by both the flow
of shallow streams and tidal action, (p.575). So far, 43 different vertebrate
taxa have been identified. Mammals are known from isolated
teeth; Multituberculata,
Theria?, Docodonta and a gobicon, (p.576).
The tooth described is a left upper molar, (M3 or M4), which
now resides in the collection of Zaragoza University. It's relatively small, (about 1,7mm
long and 1,1mm wide), and reasonably complete. There's a discontinuous
cingulum along the internal (
lingual) side, and the tooth was double-rooted. Seen from above (occlusal) the outline
is described as "pillow-shaped", (the authors use the inverted commas). Being
unacquainted with the pillows of either author, I'll settle for roughly rectangular with a
constriction in the middle.
As this page is devoted to triconodonts, the presence of three main cusps is no surprise,
(B-A-C -front of the mouth to back). The biggest cusp is A. This is set off towards the
internal edge. If you felt inclined to draw lines from B-A-C-B, you'd end up with an
obtusely angled apexed triangle. Various wear facets are also discernable. A breakage
shows that the enamel was thin and prismatic after a fashion. A hole can be seen below the
front of the crown. This is the pulp cavity. Its small size suggests this tooth belonged
to an adult.
A rough rectangle with a mid constriction can be described as being a figure-of-eight kind
of outline. This is typical for gobiconodontid upper molars.
The wear facets also compare well with Gobiconodon, as does a wide and
well-developed cingulum on the
lingual side, and the prismatic enamel. However, the size means this must have belonged
to a relatively small representative, (p.578). The authors estimate it as five or six times
smaller than G. ostromi and G. hopsoni, with its size between G.
hoburensis and G. borissiaki, (p.579).
This material was also mentioned in Cuenca Bescós B & Canudo JI (1999), A Lower
Cretaceous Traveller: Gobiconodon: ("Triconodont", Mammalia) from Vallipón
(Upper Barremian, Teruel, Spain), IV European Workshop on Vertebrate Paleontology (1999)
Albarracin, Spain, p.51-52.
Link
Acta Palaeontologica Polonica, 48(4), p.575-582
http://app.pan.pl/acta48/app48-575.pdf
Cuenca Bescós B & Canudo JI (2003).
The Isle of Wight, England
A microvertebrate site being worked by Steve Sweetman has reportedly yielded a
gobiconodontid. With thanks to DinoWight: see the entry for
24.9.2004.
A description was published in 2006 and Steve has kindly sent a copy. The reference
is: Sweetman SC (2006), A gobiconodontid (Mammalia, Eutriconodonta) from the Early
Cretaceous (Barremian) Wessex Formation of the Isle of Wight, southern Britain,
Palaeontology, 49(4), p.889-897.
As the paper's now here, further information will be added at some point. The
single speciemen presently available is a premolar
from Yaverland Point, and a referral to Gobiconodon is tentative. In any
case, it's from a gobiconodontid.
Manzongshan, China
Wang et al, 2006 (p.196) reminds me of Tang et al, 2001. They'd reported gobiconodontid
specimens among fossil collections and, for some or no reason, I neglected to add a
note here. They've still not been described but come from two horizons probably
ranging from the Barremian to Aptian. |
| 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 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, November 2002, relaunched November 2007
Latest update: 18.9.2009
(Many of the entries were originally on a different page and date back to May 2001).
Ktdykes@arcor.de
With thanks to
The Society of Vertebrate Paleontology's Bibliography of Fossil Vertebrates (John Damuth)
http://www.bfvol.org/
BIOSIS: The Index to Organism Names
http://www.biosis.org.uk/triton/indexfm.htm |
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.
Averianov AO, Skutschas PP, Lopatin AV, Leshchinskiy SV, Rezvyi AS & Fayngerts
AV (2005), Early Cretaceous mammals from Bol'shoi Kemchug 3 locality in West
Siberia, Russia, Russian Journal of Theriology, 4(1), p.1-12.
Chow M & Rich THV (1984), A new triconodontan (Mammalia) from the Jurassic of
China, Journal of Vertebrate Paleontology, 3(4), p.226-231.
Clemens WA, Wilson GP & Molnar RE (2003), An enigmatic (Synapsid?) tooth
from the Early Cretaceous of New South Wales, Australia. Journal of Vertebrate
Paleontology, 23 (1), p.232-237.
Cuenca-Bescós G & Canudo JI (2003), A new gobiconodontid mammal from the Early
Cretaceous of Spain and its palaeogeographic implications. Acta Palaeontologica Polonica,
48 (4), p.575-582.
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.
Kielan-Jaworowska Z, Novacek MJ, Trofimov, BA & Dashzeveg D (2000), Mammals
from the Meozoic of Mongolia, p.573-626 in Benton MJ, Shishkin MA, Unwin AM
& Kurochkin EN (Eds.), The age of dinosaurs in Russian and Mongolia, Cambridge
University Press.
Li J, Wang Yuan, Wang Yuanqing & Li C (2001), A new family of primitive mammal
from the Mesozoic of western Liaoning, China, Chinese Science Bulletin, Vol 46 (9),
p.782-786.
Maschenko EN, Lopatin AV & Voronkevich AV, (2002), A new genus of the
tegotheriid docodonts (Docodonta, Tegotheridae) 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.
Meng J, Hu Y, Wang Yuanqing & Li C, (2003), The ossified Meckel's cartilage and
internal groove in Mesozoic mammaliaforms: implications to origin of the definitive
mammalian middle ear, Zoological Journal of the Linnean Society, 138,
p.431-448.
Meng J, Hu Y-m, Wang Y-q & Li C-k (2005), A new tricondont (Mammalia) from the
Early Cretaceous Yixian Formation of Liaoning, China, Vertebrata PalAsiatica, 43(1),
p.1-10.
Montellano M, Hopson JA & Clark JM (2008), Late Early Jurassic mammaliaforms
from Huizachal Canyon, Tamaulipas, Mexico, Journal of Vertebrate Paleontology, 28(4),
p.1120-1143.
Rougier GW, Isah S & Manabe M (2007), An Early Cretaceous mammal from the
Kuwajima Formation (Tetori Group), Japan, and a reassessment of triconodont phylogeny,
Annals of Carnegie Museum, 76(2), p.73-115.
Rougier GW, Novacek MJ, McKenna MC & Wible JR (2001), Gobiconodonts from the Early
Cretaceous of Oshih (Ashile), Mongolia. American Museum Novitates, 3348, 30pp.
Tang F, Luo Z-X, Zhou Z-H, You H-L, Georgi JA, Tang Z-L & Wang X-Z (2001),
Biostratigraphy and paleoenvironment of the dinosaur-bearing sediments in Lower Cretaceous
of Mazongshan area, Gansu Province, China. Cretaceous Research 22, p.115-129.
Weil A (2002), Mammalian evolution: Upwards and onwards, Nature 416, p.798-799.
Wang Y-Q, Hu Y-M & Li C-K (2006), Review of recent advances on study of
Mesozoic mammals in China, PalAsiatica, 44(2), p.193-204.
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.
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