MESOZOIC MAMMALS; Triconodontidae,
an internet directory: |
PLEASE NOTE: THIS PROJECT IS NOT SCIENTIFIC. IT IS A HOBBY.
"I was looking for information on an old mammal and found this lot. What is this
project?"
It's got lots of information on old mammals. For a short bit of background information, see
here.
| Taxon: Triconodontidae Marsh ,1887
Previous visitors may like to know the layout of this directory area has been altered.
Earlier, all triconodonts were coralled together on a single page, and it got rather
large. It was split into three for reasons of bandwidth economy. Those searching
for amphilestids and various others should file along to the
triconodonts enclosure. Should, however, your
tastes desire gobiconodontids, then feel free to visit the
gobicon 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.
Triconodontidae
At least in part, this does seem to be a monophyletic family of properly related animals.
I'm including Dyskritodon and Ichthyocondon within it, in line with the
scheme of McKenna & Bell, 1997. However, the validity of this is far from established.
As stated by Rose, Cifelli & Lipka, (J.Vert.Paleo 21(3), p.628-632, 2001), the
"monophyly of remaining triconodonts, "amphilestids" and Triconodontidae,
remains uncertain."
In some rather significant studies, these critters and their nearer relations sometimes
claim to belong to Crown-group Mammalia, which
would make them close-ish relatives of all existing mammals. I'll try and add a bit more
info on this as and when I get round to it. For the while, you'll just have to accept my
word for it.
According to Datta & Das (2001), the general tricondontid condition for upper
molars is that the three main cusps are of about equal
height, (A = B = C). However, at least one member, Priacodon, doesn't conform to
this, (A > B > C).
A brief family introduction
Kemp, 2005 (p.150-151) contains a summary of Triconodontidae. The family ranges from the
Upper Jurassic until the early stage of the Upper Cretaceous. As just mentioned, the
three main cusps are generally of similar sized, a cingulum
is well developed and there's: "a unique tongue and groove mechanism for interlocking
adjacent lower molars." A bump (tongue) on the rear of a tooth fitted into a
concavity (groove) at the front of its follower. This probably provided for stability
when delivering a bite.
Interlocking molars
Rougier, Isah & Manabe, 2007 addresses this theme on page 89. Mammalian lower molar
(and molariform) rows frequently have some kind of
interlocking system; bumps at the back fitting into convenient devices on the front of the
following tooth and so on. By the dawn of the Cretaceous, triconodontids had developed
grooves on the front root. These accommodated cusps from the tooth ahead. All North
American Cretaceous members have this system, but Jurassic
Priacodon was of a generation which hadn't gotten around to this refinement.
It's possible something similar was pursued by Morocco's Cretaceous
Dyskritodon as well. Sometimes, a slight measure of
such grooving also occurs for Gobiconodon,
a gobiconodontid rather than a triconodontid. |
| Link:
Mikko K. Haaramo, Triconodontidae
Mikko Haaramo's Triconodontidae
Three cladogrammes. Mikko Haaramo is very thorough, for which I'm grateful.
Genera:
Alticonodon, Arundelconodon,
Astroconodon, Corviconodon,
Dyskritodon, ?Galestes (?= Triconodon),
Ichthyoconodon, Jugulator,
Liaoconodon, Meiconodon,
Priacodon, Tinodon (partly = Priacodon),
Triacanthodon (= Triconodon), Triconodon,
Trioracodon, A HREF="#victoriaconodon">Victoriaconodon,
other reports
Time-Line:
Upper Cretaceous: Alticonodon
Lower Cretaceous: Arundelconodon, Astroconodon, Corviconodon,
Dyskritodon (Morocco), Ichthyoconodon, Jugulator, Liaoconodon,
Meicondon, Triconodon, Trioracodon (Dorset)
Upper Jurassic: Priacodon, Trioraconodon (Wyoming)
Middle Jurassic?: Dyskritodon (India),
Lower Jurassic: Victoriaconodon |
| Species: | Alticonodon lindoei Fox RC, 1969 |
| Place: | Upper Milk River Formation, Alberta |
| Country: | Canada |
| Age: | Campanian, Upper Cretaceous |
| Remarks: |
The type specimen is at UALVP, Alberta. Fox also identified
material as belonging to a second (unnamed) species. |
| Reference: | Fox (1969), Studies of Late Cretaceous vertebrates III. A
triconodontid mammal from Alberta. Canadian Journal of Zoology, 47, p.1253-1256. |
| Genus: Arundelconodon
Cifelli RL, Lipka TR, Schaff CR & Rowe TB, 1999
'Arundel coned tooth' |
| Species: | Arundelconodon hottoni Cifelli RL et al, 1999 |
| Place: | Arundel Clay, Potomac Group, Maryland |
| Country: | USA |
| Age: | Aptian, Lower Cretaceous |
| Remarks: |
Much of what follows is based upon my reading of Cifelli et al, 1999.
As the title of the paper states, this is the first reported Lower Cretaceous mammal
discovered on the US eastern seaboard, a region which has otherwise produced a few remains
of vertebrates from that time, which largely consist of isolate teeth and bones of
hard-to-place dinosaurs, (p.199). Arundelconodon is based on an unusually complete
lower jaw with the last two premolars, and three
molars (m1-m3).
A touch old fashioned
These remains differ from earlier representatives of the family, (Triconodon,
Trioracodon, Priacodon), in details of the
dentition; for example, the crowns of Arundelconodon are higher. However, the
genus also has a significant difference to its North American near contemporaneous
triconodontids, (Astroconodon, Corviconodon, Jugulator). The jaw
retains a feature called the Meckelian groove. (To
avoid any confusion, mainly mine, this is known from some K-triconodonts, such as
Gobiconodon.)
Dentition
The teeth present are well preserved, though the tips of some cusps are missing and there
are light signs of wear. How many premolars were present in life is unknown, but similarities
to Astroconodon and an unnamed critter from the Cloverly Formation, suggest it may
well have been four, (p.200). If so, the two here must be p3 and p4. These are
four-cusped and actually larger than the molars, with the front representative being a bit
bigger than its surviving colleague. This is a somewhat unusual arrangement. As for the
molars, the length, width and crown height increase
progressively from m1-m3. All teeth have two, clearly divided roots.
Groovy
As with those earlier triconodontids, the Meckel's groove is low on the dentary, which is
probably a basal mammalian
condition, (p.201). It's a widespread feature of early mammals and merits a brief
introduction, (eg. what on earth is it and why's it of any interest whatsoever?).
A short interlude: Why might Meckel's groove be interesting?
The aforementioned Meckel's groove is a space on the dentary
more usually associated with reptiles, (not to mention amphibians, fish and sharks), and
has to do with how crocodiles, turtles, dinosaurs etc open their mouths. Reptile jaws are
differently jointed. (With thanks to
ZOO. 453 - COMPARATIVE VERT. ANATOMY, see the section with the wonderful title,
Splanchnocranium, and don't deny yourself the pleasure of Dermatocranium either.)
Triconodontid transition
Cifelli et al concluded (p.201): "Indeed, Arundelconodon is morphologically
intermediate between Jurassic and Cretaceous taxa, and available evidence suggests that it
represents the sister taxon to remaining triconodontids from the Cretaceous of North
America.".
Holotype
The holotype, USNM 497729, resides in the collection of The Smithsonian Institute,
Washington DC. The species name honours Dr Nicholas Hotton, now deceased.
Additionally
Subsequently, a toothless lower jaw fragment has also been described as cf. A. hottoni,
which suggests that's more or less what it is, but not definitely, (Rose et al, JVP 21(3),
p.628-632, 2001). This came from the same location. Other finds here include dino teeth
which may be from the herbivore Tenotosaurus and its meateating associates,
Deinonychus and Acrocanthosaurus. As the paper subsequently turned up, the
next few paragraphs are based upon my reading of it.
The Cherokee-Sanford brick clay pit doubtlessly delivers material for fine bricks. It also
provides vertebrate fossils including this second
mammalian one. It generally resembles the earlier find, thus its tentative referral,
(p.628). This specimen is USNM 497730, a roughly 1.5cm fragment of right lower
dentary. It's been neglectful of its teeth, but the
alveoli are there for a
canine and five postcanines; probably the final
three premolars and first two molars.
The young one
The dentary is shallower than the holotype, (3.3-3.5mm: 4.4-5.6, p.629), and its surface
texture features distinctive, natural striations ('scratches'). These are characteristics
associated with immature individuals. The inner side preserves a Meckelian groove which
possibly extends as far forwards as the front of the fourth premolar. It's both more
prominent and somewhat longer than in the type specimen, and this may also be related to
relatively youthfulness.
'Adult' premolars
Although no postcanines are available, a radiograph image provides information on what the
teeth had been up to inside the bone. There are no signs of replacement teeth in any stage
of development, (p.630). The alveoli extend all the way down to the mandibular canal.
Replacement wasn't taking place in any position. As this individual was already the
possessor of at least two molars (and possibly more), it seems improbable that the
permanent premolars hadn't begun to develop. Consequently, they'd probably already erupted
and were in use. Evidence of 'adult' premolars at a relatively early stage of life is also
known from Astroconodon denisoni.
Different approaches including eccentric molariforms
Triconodon seems to have retained its fourth
deciduous premolar until after the eruption of m3, at
least according to one individual. As mammalian molars are by definition permanent teeth,
a 'deciduous molar' would be a contradiction in terms. However, some Mesozoic genera
didn't fully understand that.
The type specimen of Gobiconodon ostromi has m1 and m2 in
various stages of eruption, and a fresh m3 waiting below a functioning tooth. Replacement
of molariforms is also known for G. borrissiaki and
Hangjinia. Similar behaviour occurred in
Sinoconodon and
Megazostrodon. This justifies uncertainty
with regards to replacement strategies across the spectrum of
basal Mammalia, and illustrates why the word
'molariform' is often preferred. |
| Reference: | Cifelli et al (1999) First Early Cretaceous mammal from
the eastern seaboard of the United States. Journal of Paleontology, 19(2), p.199-203.
|
| Links:
The University of Texas, DMG Projects
http://digimorph.org/specimens/Arundelconodon_hottoni/
An interesting report, including a photo of the partial jaw.
Baltimore City Paper online, Creatures from the Black Lagoon, May 2002
http://www.citypaper.com/2002-05-08/charmed.html
This is a nicely written report by Tom Chalkley, who paid a visit to Tom Lipka, "a man
obsessively well-versed on Maryland's Age of Reptiles." In the second photo, he’s
holding a partial triconodont jaw. As far as I can tell, it doesn’t seem to be the original
Arundelcondon hottoni.
DML 1999, Thomas Lipka, Goodbye Dr. Hotton!
http://www.cmnh.org/fun/dinosaur-archive/1999Dec/msg00054.html
Pleasant memories of a clearly much missed friend and mentor. |
| Genus: Astroconodon
Patterson, 1951
'star coned tooth'
Remarks: Further material has been reported from Oklahoma. I'm not certain, but I think
the star in question represents Texas. |
| Species: | Astroconodon denisoni Patterson B, 1951 |
| Place: | Trinity Group of Texas, Cloverly Formation of Montana, Wyoming
& Mussentuchit Fauna of Colorado |
| Country: | USA |
| Age: | Aptian - Albian, Lower Cretaceous |
| Remarks: | The species name is in honour of Bob Denison, who
found the specimen. |
| Reference: | Patterson (1951), Early Cretaceous mammals from northern Texas.
American Journal of Science, 249, p.31-46. |
| Species: | Astroconodon delicatus Cifelli RL & Madsen SK,
1998 |
| Place: | Cedar Mountain Formation, Utah |
| Country: | USA |
| Age: | Albian - Cenomanian, Lower-Upper Cretaceous Boundary |
| Remarks: | Jaw fragments and isolated teeth. |
| Reference: | Cifelli & Madsen (1998), Triconodont mammals from the
medial Cretaceous of Utah, J. of Vertebrate Paleont, 18(2), p.403-411. |
| The uppermost Cedar Mountain
Formation, Utah - Medial Cretaceous
The following is based upon my reading of Cifelli, Kirkland, Weil, Deino & Kowallis,
1997.
The uppermost part of the Cedar Mountain Formation records a rich fauna at the border of
the Lower (Albian) and Upper (Cenomanian) Cretaceous. Radiometric datings of convenient
volcanic ash have yielded an age of about 98 million years. Most the relevant sites are
slightly higher than the ash samples, and thus younger. Some sites are a bit older. In
comparison to the Upper Jurassic and latest Cretaceous, the fossil record for the
intervening time in North America is sparse. Cedar Mountain helps bridge the gap.
At the time of publication, the identified fauna included the oldest evidence worldwide of
hadrosaurid dinosaurs, some derived lizards and a
'marsupial'. (In the latter case,
metatherian would perhaps be a safer word, and the
subsequent description of Sinodelphys from
China added a further 25 million years.) It also boasted the first appearance of North
American tyrannosaurids, pachycephalosaurs and snakes, (p.11163).
Judging by the radical differences between Upper Jurassic and Upper Cretaceous vertebrates,
there must've been many developments taking place. This may have had something to
do with adaptations in response to the relatively rapid radiation of new plants; the
angiosperms. However, other factors could also have been involved; eg. tectonics and
climate.
First catch your fossils
The Cedar Mountain Formation is widely exposed in central Utah. Below is found the
Morrison Formation, and above is the Dakota Formation. As a whole, the Cedar Mountain layers
have a thickness of about 50 metres, (Fig.1 p.11164). The lower couple of metres are
possibly Barremian in age. The strata which provided the fossils for this study were 10 to
20 metres from the top. Concerted collecting at 31 separate sites produced 4,882 specimens
representing 72 taxa. Included are fish, amphibians (with
anurans -frogs), and a variety of reptiles (for instance, five different families of
crocodile). The apparent lack of pterosaurs is surprising. (Update: In Cifelli, 1999, the
specimen count had risen to about 7,000 representing over 80 vertebrate taxa.)
Dinos
Friends of dinosaurs will be happy to know there were plenty around. Responsible for keeping
the place tidy were the meateaters; dromaeosaurines, velociraptorines, troodontids and a
tyrannosaurid. The herbivores were an interesting mix of some old and much new.
Brachiosaurids are more usually associated with the Upper Jurassic, while hadrodaurids
generally turn up later. Remains have also been recovered of hypsilophodontids, a
nodosaurid, a neoceratopsian and even a pachycephalosaurian. Also making an early appearance
is one of the toothy birds of Hesperonithiformes.
Mammals
Among the mammals, triconodontids,
docodontids and
'symmetrodonts' were some of the later representatives of long-established lineages.
Somewhat unusually, there's not much diversity among the omnivorous
Multituberculata. Only a couple of species
originally assigned to Paracimexomyx were
listed, though this was subsequently revised:
Bryceomys intermedius and Cedaromys.
Paracimexomys shares some similarities with the more basal
'plagiaulacidans', although it's probably fairly
close to the founding member of the more derived
cimolodontan multis. The other mammals might be termed the shape of things to come.
Tribotherians, (boreosphenidans in the terminology
of some subsequent publications and this project), include
picopsids, pappotheriids and the
metatherian Kokopellia. Further information
on the mammals can be found below.
Transition
"The Cedar Mountain assemblage lies within an otherwise unrepresented interval in the
terrestrial fossil record of North America", (p.11165). This helps explain why many of
the taxa are new. 33 extended the stratigraphic range in
North America, and 28 did so globally. For example, the brachiosaurid was a late relic.
Sauropods had generally disappeared in North America, although some immigrants arrived
towards the uppermost Cretaceous.
Taken as a whole, the fauna has a flavour which is more Upper than Lower Cretaceous. Many
of the taxa have no known potential antecedents in the somewhat older Cloverly Formation,
(Aptian-Albian). However, their ancestors must've lived somewhere and, in some cases, that
may well have been Asia. With the benefit of hindsight, some of the authors' points have
been overtaken by events. Troodontids have been reported from the Lower Cretaceous of
Asia, but these aren't the first known specimens. Earlier fossils have been identified in
the Upper Jurassic of
Guimarota
in Portugal, and the same seems to be the case for tyrannosaurids. This doesn't counter the
possibilities of Asiatic origins for members of this fauna though.
Faunal exchange schemes
"Geological evidence is consistent with the possibility of a transient, mid-Cretaceous
highland connecting North America and Asia", (p.11166). The constituents of the fauna
suggest there may have been migration, and geological features indicate there would have
been a viable route involving Alaska. The marine faunas known from both sides of Alaska
seem to have been disrupted towards the close of the Albian, which would also be in line
with isolation caused by a landbridge.
The development of flowering plants also shows up in the Cedar Mountain Formation. Unlike
from earlier locations, angiosperm taxa are diverse. This would've confronted herbivores
with new challenges and opportunities. What's clear is that the massive planteaters which
dominated the underlying Morrison strata,
(Diplodocus, Supersaurus, Brachiosaurus and so on), are absent and
there are no close analogues. The one sauropod recorded: "is a small, extremely rare
taxon." At least here, massive bodysize had become obsolete. The new-fangled
hadrosaurid was the dominant defoliator. However, it should be borne in mind that this is
the only relevant fauna presently available. It doesn't represent the rest of North
America.
Don't drink the water
Cifelli, 1999 makes it clear that the assemblage is now known as the Mussentuchit local
fauna. The name refers to the unpalatability of a local water source: Musnt tuch it!
Cifelli, 2004 provides an updated number of mammalian species. This now stands at 24, and
the contingent is thought to be at least nearly complete.
Further Mesozoic site summaries can be found at Localities.
Cedar Mountain Formation Mammals (not necessarily taken from the cited paper)
Docodonta
Docodontidae species indeterminate
Triconodonta
Astroconodon delicatus;
Corviconodon utahensis;
Jugulator amplissimus
Multituberculata
Ameribaatar zofiae;
Bryceomys intermedius;
Cedaromys bestia; Cedaromys parvus;
Janumys erebos;
Paracimexomys perplexus;
Paracimexomys robisoni
'Symmetrodonta'
Spalacolestes cretulablatta;
Spalacolestes inconcinnus;
Spalacotheridium mckennai;
Spalacotheridium noblei
Boreosphenida
Pappotheriidae new genus and species
Theria
Picopsidae species indeterminate
Metatheria
Adelodelphys muizoni;
Kokopellia juddi;
Sinbadelphys schmidti;
Pariadens mckennai |
| Species: | Corviconodon montanensis Cifelli, Wible &
Jenkins, 1998 |
| Place: | Cloverly Formation, Montana and Wyoming |
| Country: | USA |
| Age: | Aptian - Albian, Lower Cretaceous |
| Remarks: | |
| Reference: | Cifelli et al (1998), Triconodont mammals from the Cloverly
Formation (Lower Cretaceous), Montana and Wyoming. Journal of Vertebrate Paleontology, 18,
p.237-241. |
| Species: | Corviconodon utahensis Cifelli RL & Madsen SK,
1998 |
| Place: | Cedar Mountain Formation, Utah |
| Country: | USA |
| Age: | Albian - Cenomanian, Lower-Upper Cretaceous Boundary |
| Remarks: | Jaw fragments and isolated teeth. |
| Reference: | Cifelli & Madsen (1998), Triconodont mammals from the
medial Cretaceous of Utah, J. of Vertebrate Paleont, 18(2), p.403-411. |
| Link:
The Journal of Vertebrate Paleontology, 1998, 18(2), p.403-411
http://www.vertpaleo.org/jvp/18-403-411.html
The same reference as for Astroconodon. Also refers to a new but not named genus,
which was later described as Jugulator. |
| Species: | Dyskritodon amazighi Sigogneau-Russell D, 1995 |
| Place: | Anoual |
| Country: | Morocco |
| Age: | Berriasian, Lower Cretaceous |
| Remarks: | According to Rose et al, (JVP 21(3), 2001), the
affinities of this genus are enigmatic. (With thanks to Vince Ward and David Marjanovic). |
| Reference: | Sigogneau-Russell (1995), Two possibly aquatic triconodont
mammals from the Early Cretaceous of Morocco. Acta Palaeontologica Polonica, 40(2),
p.149-162. |
| Species: | Dyskritodon indicus Prasad GVR & Manhas BK,
2002 |
| Place: | Kota Formation, Andrah Pradesh |
| Country: | India |
| Age: | ?Middle Jurassic |
| Remarks: | This is surprising.
Based on a well-preserved, though slightly broken lower molar,
which is somewhat smaller than D. amazighi. The type specimen, VPL/JU/KM/13, resides
in the Palaeontology Laboratory, of Jammu University. "In VPL/JU/KM/13, cusp b is
slightly lingual to a-c line (Fig. 3E), whereas it is a
lingual cingular cusp in D. amazighi; it is relatively smaller than cusp d, but not as
small as in D. amazighi,"(Prasad & Manhas, 2002).
"…there is no basis for invalidating the attribution of VPL/JU/KM/13 to
Dyskritodon as the Indian specimen is remarkably similar to the type species,
Dyskritodon amazighi Sigogneau-Russell, 1995, in its crown morphology," (Prasad
& Manhas, 2002). The Kota Formation is generally regarded as Lower / Middle Jurassic.
The description suggests this may be incorrect, seeing as the dating for Anoual is better
founded on the basis of nannofossils, (ie. very small ones!), and mineralogical data,
(Sigogneau-Russell, 1990).
What time is it?
This either means that Dyskritodon was an astoundingly long-lived genus, (unlikely),
the dating of Kota is very wrong, (unlikely), or something else, (!). Should the Kota and
Anoual deposits represent a similar age, than that would suggest a remarkably late
morganucodontid, Paikasigudodon.
A sauropod from the same formation, Kotasaurus, does a very good impression of
fulfilling expectations for Lower Jurassic sauropods, (with thanks to David Marjanovic).
Other studies cited in the publication also point to a Lower or perhaps Middle Jurassic age. |
| Reference: | Prasad & Manhas (2002), Triconodont mammals from the
Jurassic Kota Formation of India. Geodiversitas 24 (2), p.445-464. |
| Species: | Ichthyoconodon jaworowskorum Sigogneau-Russell D, 1995 |
| Place: | Anoual |
| Country: | Morocco |
| Age: | Berriasian, Lower Cretaceous |
| Remarks: |
According to Rose et al, (JVP 21(3), 2001), the affinities of this
genus are also enigmatic. (With thanks to Vince Ward and David Marjanovic). |
| Reference: | Sigogneau-Russell (1995), Two possibly aquatic triconodont
mammals from the Early Cretaceous of Morocco. Acta Palaeontologica Polonica, 40(2),
p.149-162. |
| Genus: Jugulator Cifelli RL
& Madsen SK, 1998
'cut-throat' |
| Species: | Jugulator amplissimus Cifelli & Madsen, 1998 |
| Place: | Cedar Mountain Formation, Utah |
| Country: | USA |
| Age: | Albian-Cenomanian, Lower Cretaceous |
| Remarks: | Jugulator had a ferocious dagger of a lower
incisor, which inspired its name. It also had powerful jaw
muscles and was equipped to kill. According to one less than serious analogy, these animals
were "like miniature pitbulls on steroids".
According to an article by Lupia R (2003), this genus was: "the largest known
Cretaceous mammal", (p.21). That doesn't seem to be correct, but it indicates this was
at least a relatively large representative for the time. I've seem a weight estimate of
750g which probably relates to Jugulator, though that wasn't clear and nor was the
basis for it. If correct, it would've been approximately
hedgehog-heavy,
but presumably more cuddly (when in a good mood).
Another unnamed species has been reported. Coincidentally, Jugulator is also the title of a
record by Judas Priest. |
| Reference: | Cifelli & Madsen (1998), Triconodont mammals from the medial
Cretaceous of Utah. Journal of Vertebrate Paleontology, 18, p.403-411. |
| Genus: Liaocondon Meng J,
Wang Y & Li C, 2011
'Liaoning cuspate tooth'
Remarks: The Jehol Group strikes again!
A couple of years ago, Liaoning's fossil fields decided
to move into the triconodontid business with a couple of species of
Meiconodon, Asia's first tricondontids from the Shahai and Fuxin Formation. The
older Jiufotang Formation (which overlies the famous Yixian Formation) thought about the
possibility of joining in but, naturally enough, it wanted to deliver something more
spectacular. And, naturally enough, it now has.
Odd scraps of jaw and isolated teeth may seem enough for some places, but the Jiufotang
fauna opted for a complete skeleton of a massive (for the time of Earth) 35cm long killer,
with something like 15 or so cm of that being the compete tail. Apparently, it even
succeeds in preserving the incus and
malleus hearing ossicles incorporated into the middle ear
but, via an ossified Meckelian cartilage,
retaining an indirect contact with the lower jaw. The cartilage seems to be aiding the
stability of the ear drum.
According to my notes, this is the first mammal described from the Jiufotang Formation.
Strictly speaking, the authors refer the genus to Eutriconodonta but not to a specific
family. I've placed this entry here among the triconodontids as a matter of
convenience. |
| Species: | Liaoconodon hui Meng J,
Wang Y & Li C, 2011 |
| Place: | Jiufotang Formation, Liaoning |
| Country: | China |
| Age: | lower Aptian, Lower Cretaceous |
| Remarks: | The few notes above have been rapidly scratched
together from internet sources. As I've now got a copy of the description (thanks Allen),
I'll be able to add more at some stage.
The age of this find is around 120 million years old.
Holotype
IVPP V16051 is most of a skeleton now in the collection of the Institute of Vertebrate
Paleontology and Paleoanthropology, Beijing. The specific name honours the recently
deceased paleontologist, Yaoming Hu. |
| Reference: | Meng et al (2011), Transitional mammalian middle ear from a
new Cretaceous Jehol eutriconodont, Nature, 472, p.181-185. |
| Genus: Meiconodon Kusuhashi N, Hu Y, Wang Y,
Hiraswa S & Matsuoka H, 2009
Subfamily: Alticonodontinae
Remarks: This genus manages several firsts. This is the first record of triconodontids
to emerge from the continent of Aisa and, furthermore, the first alticonodontine from
outside of North America. |
| Species: | Meiconodon lii Kusuhashi N, Hu Y, Wang Y,
Hiraswa S & Matsuoka H, 2009 |
| Place: | Shahai or Fuxin Formation, Liaoning |
| Country: | China |
| Age: | Aptian to Albian, Lower Cretaceous |
| Remarks: | So far, all I've seen is the abstract of the
publication in which both species were described. This species has lower molars featuring
a well developed cusp d, a tall cusp a on the m3, and an m4 whereby all main cusps are close
in height. There's also a greatly reduced m5. Which species came from quite where isn't something I yet know.
Thanks are due to Jerry Harris for posting the abstract onto the Dinosaur Mailing List. |
| Reference: | Kusuhasi et al (2009), New triconodontids (Mammalia) from the
Lower Cretaceous Shahai and Fuxin formations, northeastern China, Geobios, doi:
10.1016/j.geobios.2009.06.003. |
| Species: | Meiconodon setoguchii Kusuhashi N, Hu Y, Wang Y,
Hiraswa S & Matsuoka H, 2009 |
| Place: | Shahai or Fuxin Formation, Liaoning |
| Country: | China |
| Age: | Aptian to Albian, Lower Cretaceous |
| Remarks: | So far, all I've seen is the abstract of the
publication in which both species were described. This species is slightly larger than
M. lii, the buccal
cingulum of the m4 molar is apparently sharper, and the cusp d is less well
develped. Which species came from quite where isn't something I yet know.
Thanks are due to Jerry Harris for posting the abstract onto the Dinosaur Mailing List. |
| Reference: | Kusuhasi et al (2009), New triconodontids (Mammalia) from the
Lower Cretaceous Shahai and Fuxin formations, northeastern China, Geobios, doi:
10.1016/j.geobios.2009.06.003. |
| Genus: Priacodon Marsh OC,
1887
aka: Priacondon, Tinodon, Triconodon Owen, 1859
Some Priacodon material from the Morrison Formation of Wyoming was initially
ascribed to the Triconodon genus. Further material has apparently been found in
Portugal.
"Virtually the entire dentition, most of the mandible, and parts of the skull are
known", (Luo, Kielan-Jaworowska & Cifelli 2002, p.9). |
| Species: | Priacodon ferox (Marsh, 1880) Marsh OC, 1887 |
| Aka: | Tinodon ferox Marsh, 1880 |
| Place: | Como Bluff, Wyoming |
| Continent: | USA |
| Age: | Upper Jurassic |
| Remarks: | At least one specimen lives at Yale, (YPM 606). |
| References: | Marsh (1880), Notice of Jurassic mammals representing two new
orders. Am. J. Sci. (3) xx: 235-239. |
| Marsh (1887), American Jurassic mammals. Am. J. Sci.(3) xxxiii,
p.326-348. |
| Species: | Priacodon fruitaensis Rasmussen TE &
Callison G, 1981 |
| Place: | (Burro) Morrison Formation,
Colorado |
| Country: | USA |
| Age: | Upper Jurassic |
| Remarks: |
The following is based upon my interpretation of Engelmann and Callison, 1998.
This critter is now known from a lower left jaw, part of the right with
molars and the last premolar,
much of the upper jaws, a single-rooted canine, fragments of
the skull, part of the left front leg, bits of a tibia and
toes, and some vertebrae. Not all this material is well
preserved or described in the paper, (p.349).
Jawing
As well as the aforementioned premolar, the lower right jaw (mandible) contains four molars.
Although incomplete and damaged, the bone appears to be relatively deep in comparison to
its length. As the authors cite "the large and well-defined masseteric fossa" as
being particularly distinctive, (p.350), I thought I'd best mention it. Amongst various
technical details they observe: "Of particular interest is a small, anteriorly-oriented
pit at the anteriormost margin of the fossa." Where the relevant portion is preserved,
this is apparently present among all Como Bluff triconodonts.
Both the main upper jaw bones, (the right and left maxillae),
are reasonably intact, (p.351). This means that the cheek teeth series is completely known.
It was also surprising. Priacodon and Trioracodon are broadly similar:
"Indeed, this difference in dental formula is the only diagonstic distinction between
Priacodon (P3/3, M4/4) and Trioracodon (P4/4, M3/3)", (p.357). That
means that P. should have three premolars and four molars per side on the upper and
lower jaws, whilst T. can boast four premolars and three molars. In the original,
lower jaw-based description, this specimen conformed admirably. However, the maxillae
rebelled and display the Trioracodon pattern. This was against expectations. The
authors doubt this is sufficient reason to erect a separate genus. Rather, "we think
the problem lies in the assumption that triconodont dental morphology can be interpreted in
the same terms as more modern mammals. It is possible,
even likely, that triconodont dental formulas may be much more variable among individuals
of the same population or may continue to change throughout the lifetime of the individual
to a much greater extent than in therian mammals. This may
also allow for a greater range of variation of adult size within a species. If this is
the case, the assignment of P. fruitanensis and the Como Bluff triconodonts are in
question. A thorough review of triconodonts is needed to resolve this question. Until this
has been done it is best to leave the generic placement of P. fruitanensis as it
stands."
Holotype
The holotype is known affectionately as LACM 120451. This charming name originally referred
to a lower left jaw, though various other associated elements have been subsequently
identified and described, (p.348-349).
The wider fauna
P. 344: "Fruita, Colorado. A diverse fauna of mammals has been recovered from
quarries in a small area near Fruita, Colorado. The locality is remarkable for the
completeness of the preservation of many of the specimens. Some of the material has been
described (Rasmussen and Callison, 1981) but much more remains undescribed." |
| Reference: | Rasmussen & Callison (1981), A new species of triconodont
mammal from the Upper Jurassic of Colorado. J. of Paleont. 55, p.628-634. |
| Species: | Priacodon grandaevus Simpson GG, 1925 |
| Aka: | Tinodon grandaevus |
| Place: | Como Bluff, Wyoming |
| Continent: | USA |
| Age: | Upper Jurassic |
| Remarks: | |
| Reference: | Simpson (1925), Mesozoic Mammalia. I. American triconodonts
(Parts 1 & 2). II. Tinodon and its allies. III. Preliminary comparison of Jurassic
mammals, except multituberculates. Am. J. Sci. (5) x: I. 145-165, 332-358; II. 451-470;
III. 559-569. |
| Species: | Priacodon lulli Simpson GG, 1925 |
| Aka: | Tinodon lulli |
| Place: | Como Bluff, Wyoming |
| Continent: | USA |
| Age: | Upper Jurassic |
| Remarks: | |
| Reference: | Simpson (1925), Mesozoic Mammalia. I. American triconodonts
(Parts 1 & 2). II. Tinodon and its allies. III. Preliminary comparison of Jurassic
mammals, except multituberculates. Am. J. Sci. (5) x: I. 145-165, 332-358; II. 451-470;
III. 559-569. |
| Species: | Priacodon robustus (Marsh, 1879) Simpson GG,
1925 |
| Aka: | Tinodon robustus Marsh, 1879 |
| Place: | Como Bluff, Wyoming |
| Continent: | USA |
| Age: | Upper Jurassic |
| Remarks: | |
| References: | Marsh (1879), Notice of new Jurassic mammals. Am. J. Sci.
(3) xviii: 396-398. |
| Simpson (1925), Mesozoic Mammalia. I. American triconodonts
(Parts 1 & 2). II. Tinodon and its allies. III. Preliminary comparison of Jurassic
mammals, except multituberculates. Am. J. Sci. (5) x: I. 145-165, 332-358; II. 451-470;
III. 559-569. |
| Genus: Triconodon Owen R, 1859
'three coned tooth'
Aka: ?Galestes; Triacanthodon Owen, 1871
The proposed name Galestes is apparently mentioned in The Student's Elements of
Geology written by Charles Lyell in 1870. According to an on-line version: "Professor
Owen has proposed the name of Galestes for the largest of the mammalia discovered in
1858 in Purbeck, equalling the polecat (Mustela putorious) in size. It is supposed to
have been predaceous and marsupial."
Several details make me uncertain of Charles Lyells's attention to accurate
plaeobook-keeping. If the on-line version is accurate, he refers to five mammalian 'upper
maxillaries' from Stonesfield in Oxfordshire. Three must have been the lower jaws of
(Amphitherium). He also reports on the
discovery of the dinosaur Compsognathus from the same place. This was from the
Solnhofen Formation of Bavaria, which isn't generally regarded as part of Oxfordshire.
Lyell further states Triconodon: "is supposed to have been a small
insectivorous marsupial, about the size of a hedgehog." It's more usually reported as
something like
cat-size.
It's also not a marsupial. However, that was indeed Owen's interpretation.
| Reassigned species: T. bisulcus Marsh, 1880 see
Trioracodon bisulcus | |
| Species: | Triconodon mordax Owen, 1859 |
| Place: | Purbeck Limestone Group, Durlston Bay, Dorset |
| Country: | England |
| Age: | Berriasian (early), Lower Cretaceous |
| Remarks: | Indeterminate material has also been reported from
the Morrison Formation, Wyoming, though some or all of this may since have been referred
to Priacodon. |
| Reference: | |
| Links:
Southampton University, Jaws and Teeth from Beckles' Mammal Pit
http://www.soton.ac.uk/~imw/gif/pujaw.gif
A sketch of jaws and teeth. Also portrayed are Plagiaulax becklesi, a
multituberculate, and Spalacotherium
tricuspidens, a symmetrodont. Encouraged by Richard Owen, Samuel Beckles excavated a
number of mammal fossils from Durlston Bay in 1857. Further finds are still being made
from nearby, though the exact location of Beckles' pit isn't known.
Jurassic Page, The Gallery
http://member.aol.com/jurassicta/pl24e.htm
A fine illustration. |
| Genus: Trioracodon Simpson
GG, 1928
aka: Triconodon
Remarks: Some Trioracodon material is in the collection of the Natural History Museum,
London. Luo et al 2002 (p.9-10) list remains as being the
dentition, mandible and incomplete cranium material. They carry on to cite the genus
as a representative of earliest Cretaceous, European Triconodontidae. Whether the North
American material is still regarded as appropriately diagnosed is something I don't know. |
| Species: | Trioracodon bisulcus (Marsh, 1880) Simpson 1929 |
| Aka: | Triconodon bisulcus Marsh, 1880 |
| Place: | Morrison Formation, Wyoming |
| Country: | USA |
| Age: | Upper Jurassic |
| Remarks: | |
| References: | Marsh (1880), Notice of Jurassic mammals representing two new
orders. Am. J. Sci. (3) xx, p.235-239. |
| Simpson (1929), American Mesozoic Mammalia. Mem. Peabody Mus. Nat.
Hist. iii (i), p.1-235. |
| Species: | Trioracodon ferox (Owen, 1871) |
| Aka: | Triconodon ferox Owen, 1871 |
| Place: | Purbeck Limestone Group, Durlston Bay, Dorset |
| Country: | England |
| Age: | Berriasian (early), Lower Cretaceous |
| Remarks: | Kemp, 2005 (p.151) mentiones Triconodon
ferox. A complete lower jaw is available, and it measures eight centimetres; a
dwarf-cat sized carnivore.
A specimen known as BMNH 47775 is employed by The Natural History Museum of London. |
| Reference: | Owen, (1871), Monograph on the fossil Mammalia of the Mesozoic
formations. Palaeontological Society Monograph, 24, p.1-115. |
| Link:
Ian West, Durlston Bay pages
http://www.soton.ac.uk/~imw/durlston.htm#correl
This homepage includes a useful index of three extensive articles on the geology and
paleontology of Durlston Bay. As reported by Paul Ensom, these Dorset mammals show links
with the Upper Jurassic fauna of Morocco and North America. |
| Species: | Trioracodon major |
| Aka: | Triconodon major |
| Place: | Purbeck Limestone, Dorset &
Morrison Formation, Wyoming? |
| Country: | England & USA? |
| Age: | Upper Jurassic? - Lower Cretaceous |
| Remarks: | The presence of this species in the Purbecks is
confirmed by the table contained in Savage, 1989, (p.5). |
| Reference: | Owen, (1871), Monograph on the fossil Mammalia of the Mesozoic
formations. Palaeontological Society Monograph, 24, p.1-115. |
| Species: | Trioracodon oweni Simpson GG, 1928 |
| Place: | Purbeck Limestone, Dorset & Morrison Formation, Wyoming? |
| Country: | England & USA? |
| Age: | Upper Jurassic? - Lower Cretaceous |
| Remarks: | This species is also listed in Savage, 1989.
Confirmation on the Morrison Formation would be welcome. |
| Reference: | Simpson (1928), A Catalogue of the Mesozoic Mammalia in the
Geological Department of the British Museum, London, British Museum. |
| Genus: Victoriaconodon
Montellano M, Hopson JS & Clark JM, 2008
'Victoria coned tooth'
Remarks: The referral of this genus to the family is less than confident. For what it's
worth, I rate it as improbable. The generic name honours the town of Ciudad Victoria, the
nearest town to the locality. |
| Species: | Victoriaconodon Montellano et al, 2008 |
| Place: | La Boca Formation |
| Country: | Mexico |
| Age: | Pliensbachian, Lower Jurassic |
| Remarks: | The following is based upon my reading of
Montellano et al, 2008, and thanks are due to Allen H.
Victoriaconodon is presently known from about half-a-centimetre of lower jaw
preserving remains of four teeth (p.1137). These are interpreted as being three
premolars and the first
molar based upon triconodontid norms. Such critters have final lower premolars
that are considerably larger than the first molar, and that applies in this case too. If
this is indeed a member of the family of Triconodontidae, then its early age -Lower Jurassic-
would be remarkable. This gang otherwise ranges from the Upper Jurassic into the
Cretaceous. The Mexican record would add something like thirty million years more.
I have my doubts about the referral and, it seems fair to say, so do the authors. The
justification is decidedly thin. However, so is the available evidence. For example,
most the synapomorphies for tricondonotids cited in
the paper happen to be missing information for this genus. What is known is that the final
premolar is certainly larger than the first molar.
As well as the aforementioned teeth, the jaw also provides part of an
alveolus (presumably for the canine), and a further hole
for a premolar.
A glance in the mouth (lower jaw only)
Although the tops of the m1 cusps look rather like a manic dentist has attacked them with
some kind of saw, there's no conceivable way they could've attained anything like the height
of the overwhelmingly dominant main cusp of the preceding tooth. Such a disparity between
a final premolar and first molar is a triconodontid trait, and especially so in the case
of Priacodon, held to be a comparatively
basal representative. Also pleasingly tric-like is the
progressive increase in premolar size from front to rear. However, similar songs could be
sung for Morganucodon (p.1138) although, in
that libretto, the premolar-molar height differential is much less extreme. The morphology
of the premolars is also similar to triconodontids. At the front is a well developed cusp
b and, on the posterior teeth, cusp c earns the distinction of being termed prominent. A
small cusp d also puts in an appearance. However, not typical for trics is the presence of
an e cusp. also not typical is the great height difference between the main cusps on the
crowns. Excepting for Priacodon, such tric teeth display a more egalitarian attitude
to altitude. Still, this could be explained by primitiveness. After all, this is tens of
millions of years earlier than the main triconodontid choir.
The interpretation of the alveoli, one for a canine and one for a premolar, puts the
number of lower premolars at four. (Whether there's some recognisable difference between
the alveoli to support that interpretation, for example, their positions and distance from
each other, isn't stated, as far as I noticed.) Priacodon had three. Four is the
count for Triconodon but, in that instance, the first is
a double-rooted tooth rather than a presumably single-rooted one. A detail ruling out
affinities with morganucodontids is the lack of
evidence for a Meckelian groove on the jaw. The former
owner may have possessed such a thing further back (or may have not) but, if one was there,
then it doesn't reach as far as the first molar, let alone the final premolar. At least
some triconodontids and "amphilestids" also have a groove going that far forward.
A matter of size
The fragment is 5.7mm long and of somewhat variable depth (1.65mm beneath p1, 2.1 below
p4). The postcanine lengths are:
p2 0.7mm; p3 0.95; p4 1.3; m1 about 1.1.
Affinities
The comparative analysis performed indicates Victoriaconodon, although
considerably earlier, may nevertheless be more derived
than Priacodon but more basal than other known triconodontids. However, the
evidence supporting this is weak; the number of premolars has perhaps increased from
three to four (if the original tric count was as for Priacodon), tooth crown height
seems to be less than 50% of the jaw depth, and the jaw depth increases from front to rear.
"None of these characters inspires confidence."
For example, the height of most the molars isn't actually known. Perhaps rear ones were
taller.
Holotype
IGM 3493 is an inmate of the Institute de Geologia of Ciudad University, Mexico. The
specific name refers to the unequal height of the main cusps, a contrast to the typical
condition for triconodontids. |
| Reference: | Montellano et al (2008), Late Early Jurassic mammaliaforms
from Huizachal Canyon, Tamaulipas, Mexico, Journal of Vertebrate Paleontology, 28(4),
p.1120-1143. |
| 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 Latest update: 15.4.2011
(Many of the entries were originally on a different page and date back to May 2001).
Ktdykes@arcor.de |
| With further thanks for assistance due to:
Dr Richard Cifelli, Oklahoma Museum of Natural History, for his insights on
Jugulator, tolerance of my sense of humour and etc.
Mr David Marjanovic, for corrections and suggestions.
Dr Zhexi Lou for the encouragement, kind words and various papers.
Shirley Sparks, for kindly supplying the paper by Dr Savage.
HitBox Central for the thrilling animations.
Dr John Alroy, for information concerning Jugulator, via his
North American Fossil Mammal Systematics Database,
Serdar Mayda.
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
Polyglot Paleonotologist
http://www.uhmc.sunysb.edu/anatomicalsci/paleo/terms.html
This homepage is packed with goodies, especially for the keen anatomist. |
Bibliography:
Cifelli RL (1999), Therian teeth of unusual design from the Mid-Cretaceous
(Albian-Cenomanian) Cedar Mountain Formation of Utah. Journal of Mammalian Evolution,
6 (3), p.247-270.
Cifelli RL, Kirkland JI, Weil A, Deino AL & Kowallis BJ (1997), High-precision
Ar40/Ar39 geochronology and the advent of North America's Late Cretaceous terrestrial
fauna, Proc. Natl. Acad. Sci. USA, vol94, p.11163-11167.
Cifelli RL, Lipka TR, Schaff CR & Rowe TB (1999), First Early Cretaceous mammal
from the eastern seaboard of the United States. Journal of Paleontology, 19(2),
p.199-203.
Engelmann GF & Callison G (1998), Mammalian Faunas of the Morrison Formation,
Modern Geology, Vo 34 (4), p.343-379.
Kemp TS (2005), The Origin and Evolution of Mammals, Oxford University Press,
pp.331.
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.
Lupia R (2003), Exploring the large world of small fossils, Earth Scientist Magazine,
The University of Oklahoma, p.18-23.
McKenna MC & Bell SK, (1997), Classification of Mammals Above the Species Level.
Columbia University Press.
Meng J, Wang Y & Li C (2011), Transitional mammalian middle ear from a new
Cretaceous Jehol eutriconodont, Nature, 472(181), p.181-185.
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.
Prasad GVR & Manhas BK, (2002), Triconodont mammals from the Jurassic Kota
Formation of India. Geodiversitas 24 (2), p.445-464.
Rose KD, Cifelli RL & Lipka TR, (2001), Second triconodont dentary from the
Early Cretaceous of Maryland, Journal of Vertebrate Paleontology, 21(3),
p.628-632.
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.
|
