MESOZOIC MAMMALS; KUEHNEOTHERIIDAE and Co & "AMPHIDONTIDAE"
| MESOZOIC MAMMALS; KUEHNEOTHERIIDAE and Co
& "AMPHIDONTIDAE", 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.
|
These fossils are the fragmentary remains of the most basal
'symmetrodonts' (very loosely defined). 'Symmetrodonts'
appear to include the ancestors of the therians; the full,
card-carrying members of Mammalia, such as yourself or a
kangaroo. Not surprisingly, some are amongst the earliest representatives; contemporaries
of Morganucodon & Co. However, simply
because a genus is 'primitive', does not necessarily mean that it must have been early.
Strictly speaking, Chronoperates has no business being on a page about Mesozoic
mammals. It's from the Tertiary. But when I try to speak strictly, people laugh.
Furthermore, classification is based upon anatomy, not time. |
A. Chronoperatidae B.
Kuehneotheriidae C. "Amphidontidae"
| Taxon: Chronoperatidae Fox RC, Youzwyshyn GP & Krause DW, 1992 |
| Genus: Chronoperates Fox RC, Youzwyshyn GP &
Krause DW, 1992
'time wanderer'
Remarks: This appears to be a somewhat late representative of its kind; about 120 million
years late. Originally, it was interpreted as a non-mammalian
tritylodontid. Subsequent analysis suggested it to
be a 'symmetrodont'-like something-or-other. To our
notions of orderliness, it appears to have existed during the wrong age, thus the name.
But exist it did. I suppose it's no more surprising than a duck-billed platypus.
It should be mentioned that this reassignment has apparently not been universally accepted.
In Scott et al, 2002, the following appears on page 691: "... the non-mammalian
cynodont Chronoperates paradoxus...". In this case, the et al are Fox and
Youzwyshyn, which suggests they're sticking to their original interpretation. Details of
this paper are in the Bibliography at the foot of this page.
A different perspective on this creature comes Meng et al, 2003. This study concerns a
feature they refer to as OMC, (ossified Meckel's cartilage), in
Repenomamus. A bit of background on
Meckel's groove, (which housed the cartilage is here:
Dryolestes leiriensis). In crude summary,
features on the lower jaw of Chronoperates could be attributed to the presence of
such a cartilage, which is a detail now definitely known from some Mesozoic
mammals such as Repenomamus.
In the words of Meng et al, (p.441-442): "The OMC in Repenomamus provides an
alternative interpretation for the scar on the medial surface of the
dentary in Chronoperates paradoxux, (sic) a
presumably mammal-like reptile from the Paleocene (Fox, Youzwyshyn & Kraus, 1992a).
The scar was considered (Fox et al. 1992a: 234) for lodging 'one or more postdentary bones,
including the splenial.' However, the conclusion was controversial (Fox, Youzwyshyn &
Krause 1992b; Sue (sic), 1992). With the evidence from Repenomamus, a
persisting Meckel's cartilage may be considered to
occupy the scar on the medial surface of the dentary in Chronoperates." |
| Species: | Chronoperates paradoxus Fox et al, 1992 |
| Place: | Alberta |
| Country: | Canada |
| Age: | Upper Paleocene |
| Remarks: | Based on a posterior
mandible housed in the University of Alberta VP collection. "Systematic position
dubious, even at this level, but not a nonmammalian cynodont," (McKenna & Bell,
1997). |
| References: | Fox et al (1992), Post-Jurassic mammal-like reptile from
Palaeocene. Nature 358, p.233-235. |
| Sues HD (1992), No Palaeocene 'mammal-like reptile'. Nature 359,
p.278. |
A. Chronoperatidae B.
Kuehneotheriidae C. "Amphidontidae"
| Taxon: Kuehneotheriidae Kermack DM, Kermack KA & Mussett F,
1968
Kuehneotheriids were micro-mammals, (or mammaliaforms,
which preyed upon and terrorised insects, if that’s possible. Remains are known from the
Rhaetian and early Liassic rocks of Western Europe, Greenland and India.
Kuehneotherium itself is often regarded as the most
basal known member of Holotheria. The
postcanine teeth have three main cusps, two of which are
aligned on the internal side, (lingual). However, the
central cusp is towards the middle part of the crown. If you plot these onto a piece of
paper, you can join them up and the result is a triangle. Mammals such as
Morganucodon had them arranged in a
straightish line, which is more similar to the pattern known from carnivorous non-mammalian
eucynodonts.
Forthcoming developments
I was beginning to despair of ever having a reason to update this directory on
kuehneotheriids, but it looks like things will begin developing. The 2006 Abstracts
of the Society of Vertebrate Paleontology contains a short report by Gill P on
p.67A. She's been examining fossils from a collection of around 1000 isolated
teeth and bits of jaw, and recognises they show two addtional species. Some small
molars are accused of having
plesiomorphic tendencies not apparent on the
other material. The triagulation of the crown is less pronounced and the roots
aren't fully divided. A new cladistic analysis is also promised.
Reference for Kuehneotheriidae: Kermack, Kermack & Mussett (1968), The Welsh pantothere
Kuehneotherium praecursoris. Journal of the Linnean Society (Zoology) 47, p.407-423.
|
| Genus: Delsatia Sigogneau-Russell D
& Godefroit P, 1997 |
| Species: | Delsatia rhupotopi Sigogneau-Russell D &
Godefroit P, 1997 |
| Place: | Saint-Nicolas-de-Point |
| Country: | France |
| Age: | Norian late-Rhaetian early, Upper Triassic |
| Remarks: |
Known remains seem to be presently restricted to one tiny tooth.
Originally described as a docodont but: "Except for
the facts that paracristid and protocristid break at almost a right angle, and that the
lingual cingulid is discontinuous, Delsatia is very
similar to Kuehneotherium, and I refer it herein to Kuehneotheriidae",
(Averianov 2002, p.711). I've done the same.
Sigogneau-Russell, 2003 also excludes this genus from the Docodonta. |
| Reference: | Sigogneau-Russell & Godefroit (1997), A primitive docodont
(Mammalia) from the Upper Triassic of France and the possible Therian affinities of the
order. Comptes Rendus de l'Académie des Sci., 324(IIa), p.135-140. |
Genus: Kotatherium Datta
PM, 1981
'Kota beast'
| Reassigned species: K. yadagirii Prasad GVR & Manhas BK, 1997 see
Paikasigudodon yadagirii | |
| Species: | Kotatherium haldanei Datta PM, 1981 |
| Place: | Kota Formation, Andrah Pradesh |
| Country: | India |
| Age: | ?Toarcian, ?Lower Jurassic |
| Remarks: |
Whilst often placed within 'Symmetrodonta', this is
broadly similar to Kuehneotherium, (which is also frequently so treated). More recent
studies, (eg. Luo et al 2002; Averianov 2002), strongly conclude that kuehneotheriids are
only "symmetrodonts" in a traditional (and invalid) usage of the term, thus the
quotation marks.
This species is based on one upper molar. "The type
tooth of the genus is remarkable by the extroversion of its small metacone, and for the
extended parastylar wing; moreover there seems to be only a very faint connection between
the paracone and the stylocone, very labially situated, but
this point needs confirmation; the ectoflexus is
accentuated and the labial cingulum bears no cusp between
metastyle and stylocone...", (Sigogneau-Russell & Ensom 1998, p.457-458). |
| Reference: | Datta (1981), The first Jurassic mammal from India. Zool. J.
Linnean Soc. 73p, p.307-312. |
| The Kota Formation, India, Lower Jurassic
The following is largely based upon my reading of Datta & Das, 2001.
The Kota Formation is part of the upper Gondwana Group and fossil yielding locations are
found in Andrha Pradesh, Central India. The age is a subject of continuing enquiry. Some
evidence suggests it may in part be roughly contemporary with the Kayenta Formation, Arizona, the
Clarens of South Africa and the Lufeng Beds of
China.
However, Prasad & Manhas, 2007 indicates the chronological matter is more complex.
They refer to there being a Lower and an Upper Member, and mammal fossils have come
from both (p.1). The Lower is somewhat earlier. Page 2 relates: "Finally, the latest
palynological data indicated a Middle Jurassic to Early Cretaceous age for this
formation." The title of that study refers to "the Jurassic Kota Formation". Not
following those authors, I'm presently assuming the following. Until I've
reason to do otherwise, I'm referring to the lower fauna as ?Lower Jurassic in line
with 'tradition'. I can't yet see grounds for changing that. Mammals from the
upper fauna will here be referred to as ?Middle Jurassic. At least, that's my
intention. This is entirely arbitrary upon my part, and it should not be
treated as in any way valid.
The fauna
As the rock was formed from the silt of rivers and lakes, it's none too surprising to hear
that freshwater swimmers are most numerous among the
vertebrates. The school of local fish includes Indocoelacanthus, which enjoyed
the honour of being the first fossil coelacanth to be discovered in India. A turtle named
Indochelys kept the fish company, and it's very similar to Kayentachelys from
Arizona. An assortment of shelled critters are also known including Darwinella, an
ostracod.
Some remains of terrestrial animals managed to find their way into the water. For example,
there are two prosauropod dinos; Barapasaurus and Kotasaurus. Rarities
among the fossils have been provided by mammals. These are small, isolated teeth but they
had animals attached to them during the Jurassic. Although not numerous, the collection is
becoming reasonably diverse.
There's a morganucodontid, a megazostrodontid
and several 'symmetrodonts' of one sort or anther.
Docodonts and one is now described. More
puzzling is an odd 'triconodont' presently assigned to Dyskritodon; an otherwise
Lower Cretaceous genus from Morocco. This apparent riddle probably can't be resolved
without the assistance of further fossils from here or elsewhere.
Southerners
The significance of this assemblage is enhanced by it being from Gondwana, albeit from an
era when faunal interchanges with the north were still common. Lower Jurassic southern
mammals are presently only known from the Kota Formation and Karoo in southern Africa. A
non-mammalian tritylodontid tooth has been
identified from Antarctica, (which has reportedly since yielded an undescribed
eucynodont). Regardless of the paucity of locations,
none of these fossils are particularly distinctive from contemporary northern lineages.
Even the megazostrodontids are often included in Morganucodontidae, or at least
Morganucodonta. There's presently no sign of significant Gondwanan endemicism at this
time, but new localities could alter the picture.
Further Mesozoic site summaries can be found at Localities.
Meet the Mammals of the Kota Formation
(at least six genera)
Lower fauna (?Lower Jurassic)
Morganucodonta
Indotherium pranhitai
Note: The genus of Indozostrodon has been referred to Indotherium.
'Symmetrodonta'
Kotatherium haldanei
Upper fauna (?Middle Jurassic)
Morganucodonta
Paikasigudodon yadagirii
Docodonta
Gondtherium dattai.
'Symmetrodonta'
Nakunodon paikasiensis
'Triconodonta'
Dyskritodon indicus |
| Genus: Kuehneon Kretzoi, 1960
Aka: Kühneon; Kuhneon |
| Species: | Kuehneon duchyense Kretzoi, 1960 |
| Place: | Bridgend quarries, South Glamorgan |
| Country: | Wales |
| Age: | Rhaetian-Liassic, Lower Jurassic |
| Remarks: | The following is largely based upon my
reading of Benton et al, 2005 (p.38-39), and thanks are due to the kindly supplier.
Presumably, the generic name was meant to honour Professor Walter Kühne. As a German
'ü' equates to the English 'ue', that should be what's written. The specific name
refers to its hiding place of Duchy Quarry. However, as the sole specimen
disappeared, this issue isn't exactly compelling. It was later noted as being
generically different from Kuehneotherium, but
direct comparison has become impossible.
Ancient Welsh lowlands
As a small, lost fossil isn't much of a conversation piece, we may as well have a
quick chat about old times. The present Vale of Glamorgan was then a lowland area
crossed with modest hills based on limestone laid down during the Carboniferous. The
sea level rose during the Rhaetian, and the hill tops were left as islands. The
weather was tropical or subtropical with a strong rainy season, and erosion and collapse
ate the islands away by Sinemurian times. That put an end to the terrestrial
faunas.
Additional notes
Nomen dubium. "The single tooth upon which the type
and only species... was based, "Duchy 33", has apparently been lost. The name
should be, but has not been, suppressed," (McKenna & Bell, 1997). |
| Reference: | |
| Genus: Kuehneotherium
Kermack, Kermack & Musset, 1968
'Kuehne's beast'
Remarks: Kühne was a German paleontologist, who worked extensively in Glamorgan and Somerset.
He and his wife, who happened to be Jewish, took refuge in Britain from the Nazis. Today,
I fear they'd be in danger of being classified as 'economic refugees'.
Benton et al, 2005 (p.39) states a specimen of the genus was arrested in Jameson Land,
Greenland. |
| Species: | Kuehneotherium praecursoris Kermack, Kermack &
Musset, 1968 |
| Place: | Bridgend quarries, South
Glamorgan |
| Country: | Wales |
| Age: | Lower Jurassic |
| Remarks: | The following is largely indebted to Kemp, 2005
(p.162).
Kuehneotherium was first identified from the
Morganucodon mine of Glamorgan. 'Mine' is a complete exaggeration used to
emphasize the relative scarcity of this genus. In contrast to the well known Morganu,
Kuehneo modestly provided some isolated teeth and occasional fragments of
dentary. All skeletal and skull remains from the deposits
were referred to the much more common animal. That might not be the case should the
critters have been very similar.
Uncommon excitement
Most mammals have, (or are descendants of ancestors which had),
molars with a triangulated pattern of main cusps. This is also the case for
Kuehneotherium, and its discovery caused some excitement. Although remains are
limited, it was interpreted as being near the start of something new;
Holotheria - a taxon
including both this genus and paleontologists. When first described in 1968 the connection
with later mammals seemed obvious enough. However, this has subsequently become less
clear in the light of further discoveries and interpretations.
Cooling down
The lower jaw of Kuehneotherium is gracefully built, (relatively long and shallow),
and there's no distinct angular process. These are contrasts to its contemporary
Morganucodon. But the jaw is simply different rather than more
derived. The trough at the back on the inner side shows
the postdentary bones were still housed there. One complete specimen has a length of 1.4
centimetres. It's only the molars which could be termed more advanced, as one molar cusp
has been repositioned.
Later animals, (the triconodontans), have dentaries
more in keeping with holotherians, (excepting for Kuehneotherium), and their
molars don't generally have a triangulated arrangement of cusps. Should the jaw
similarities of Triconodon and myself be
due to common ancestry, then it's difficult to see how Kuehneo could have been crucial to
both lineages.
Furthermore, triangulation of cusps to some extent has since been observed in other
Mesozoic mammals; Megazostrodon,
Gobiconodon and now it's been claimed for
the 225 million year old Tikitherium. Although
known from only one tooth, that much older animal was probably able to grind food to a
limited degree, in addition to cutting the stuff up. In summary, the affinities of
Kuehneotherium are far from clear.
Meet the teeth
A lower dental formula per side has been provided; 4
incisors, 1 canine, 6
premolars and 4 to 5 molars. (NOTE. Unpublished
research by Pam Gill -mentioned further down this entry under the heading 'Further
Developments'- suggests the molar number was 6.) Both upper and lower molars have
the triangulated arrangement of three main cusps, and it corresponds to the pattern
in more derived holotherians. This allows much of the same terminology to be
employed. The central paracone on uppers is large. At the front of the external
side is an accessory cusp sometimes called the stylocone. At the back and also
somewhat labially positioned is a metacone. Much of
the crown base is girdled by a cuspless cingulum.
The lower counterparts are taller and the cusp arrangement is broadly similar but reversed.
The paraconid at the front and the rear
metaconid are on the lingual
side of the central conid. There's an extra small cusp on the rear of the tooth, and this
is the beginnings of a talonid. The main function was
probably to help the molar better interlock with its neighbour, in order to enhance
stability along the line. The cingulum of lowers is not complete on the labial side.
The triangular arrangement means the cutting edges of the teeth are angled rather than
straight, unlike as in Morganucodon, and this provides enhanced efficiency when
processing food. Items are less prone to getting stuck between the opposing blades.
In addition
Open your mouth
Tooth occlusion resulted overwhelmingly from a simple up and down movement, (Kermack et al,
1965, p.547). As there was little sidewards action the jaws worked much like a pair of
scissors. These teeth could slice but there was little grinding or pounding ability.
Consequently food couldn't be strongly processed prior to swallowing. Well meant parental advice
on the importance of proper chewing, so as to avoid indigestion, would have been
pointless. The kuehneotherikids weren't capable of complying.
Further developments
The 2006 Abstracts of the Society of Vertebrate Paleontology contains a short report
by Gill P, and that includes further information on this species. Her research shows
that the dental system with fully diphyodont; a
maximum of one replacement tooth per position. However, fossils of somewhat more
basal relatives (presently undescribed) suggest this could then have been only
recently established. She has also been busy on the dental formula and offers:
(lowers): 5? incisors, 1 canine, 6 premolars, 6 molars; (uppers): unclear but
presumed to be the same. This differs to the one reported by Kemp by having more
molars.
The old age problem
Fossils of this genus from the Emborough Fissure filling of England may well be Upper
Rhaetian, Triassic. This has also been regarded as Norian, (Kielan-Jaworowska 1992,
p.187-188). |
| Reference: | Kermack et al (1968), The Welsh pantothere Kuehneotherium
praecursoris. J. of the Linnean Soc. (Zoology) 47 (312), p. 407-423. |
| Link:
Micro Vertebrates; ask why! books
http://www.askwhy.co.uk/awwls/00/wlsl60.html
An interesting look at basal mammals, including Kuehneotherium. It‘s a well written
piece; fairly demanding and rewarding for inquisitive non-knowists. |
| Species: | Kuehneotherium sp. |
| Place: | Saint-Nicolas-de-Point /
Boisset & Syren / Medernach & Emborough & Jameson Land |
| Country: | France & Luxembourg & England & East Greenland |
| Age: | Rhaetian, Upper Triassic - Lower Jurassic |
| Remarks: | Based on teeth, which appear to represent
different species than the Welsh form.
The presence of Kuehneotherium is Jameson Land (Greenland) is mentioned in Benton et
al, 2005 (p.39). |
| Reference: | Godefroit , Cuny G, Delsate D & Roche M (1998), Late
Triassic Vertebrates from Syren (Luxembourg). N. Jb. Geol. Paläont. Abh. 210(3), p.305-343.
|
| Emborough Quarry, Somerset
The following is largely based upon my reading of Benton et al, 2005, and thanks go
top the generous supplier.
Emborough Quarry, near Wells in Somerset, is presently the only known mammal locality
in Britain that a broad consensus opinion regards as Triassic (p.31). The possible
Triassic age of several other sites is disputed. If the date supplied by Benton & Co
is correct, then the fossils from Emborough are pre-Rhaetian; something like 220
million years old give or take a few million.
The described mammal fauna is one of the most extensive in the world for the Norian
stage or, and equally correctly, limited to merely two teeth from Kuehneotherium.
There's a molar and a
premolar. The former owner (or owners) doubtlessly had more teeth when alive,
but this meagre swag still suffices to qualify as unusually extensive for the age.
Somehow, I don't think I'll attempt compiling a faunal list for the mammals in this
case.
A rediscovery would be welcome.
Southwest England sort of has another Upper Triassic eucynodont locality, but nobody
quite remembers where it precisely is. A single tooth was found somewhere near
Watchet on the Bristol Channel in the middle of the nineteenth century. This was
described under the name of Hypsiprymnopsis.
It was thought to belong to a 'haramiyidan'. However,
checking that has been made impossible. The sole specimen was lost donkey's years
ago. Doubts have been expressed on the grounds of its unusually large size. That
would be more expected from a non-mammalian
tritylodontid.
Please feel free to rediscover this locality.
Emborough Quarry -take two
And this bit of following is based upon my reading of Fraser, Walkden & Stewart, 1985. As
oft, thanks are due to the supplier. Astute readers may notice some ever so slight
deviations. Certain themes aren't explored in that study.
Some of the air has gone out of the tires of this paper, as the significance of
kuehneotherians as potential ancestors of the authors has come strongly into question.
As far as the molars are concerned, they look rather like one would expect for an ancestor
of we therian mammals; a triangulated arrangement of main
cusps, the beginnings of a talonid heel, an occlusion
system bringing the front of an upper tooth into contact with the rear of a lower and its
back into action with the anterior of the follower, relatively thin roots... It looks
about right. However, looks can be deceptive.
Seen in the right light, women are emotionally enraptured by the sight of my features,
and want nothing other than to tear off their clothes and have me make love with them; to
them, indeed. Most have been unlucky. In this case, the correct light should shine from
a torch with habitually exhausted batteries. Oh, and a dodgy bulb. Still, it does
brightly flare sometimes. In part, it's a matter of pressing the switch firmly enough
and fiddling with the wires. Some readers might think that's quite enough of my personal
sexual excitements, but I've no inclination to agree with them. I've no wish to feel
sufficed.
Some people, possibly in Arizona, seem to think sex shouldn't be brought into biology.
Teachers of the subject ought to place a fig leaf or paper bag, certainly not a rubber
condom, over the naughty bits, and concentrate on the wholesome parts. I once had a
complaint from Arizona. She praised the Lord that I would surely burn in hell for all
eternity. Naturally, I thanked her for the interest in my future welfare. She wrote back,
noted my politeness showed fear, and compared me to Sadam Hussein. I thanked her for the
interest in my future welfare. I also thanked her Lord for the oft faulty torch.
Returning to Emborough Quarry
Not much of that is actually touched on by Fraser et al, 1985, not directly at least.
Still, it could be implied between the lines. The mammal fossils available were no
longer experiencing sexual desire, if indeed their owner(s) had lived long enough to
develop such interests. They had a couple of teeth from Upper Triassic deposits from
Somerset. (I remember being in a tent with a girl in Somerset, when...) These teeth
were retrieved from sediment within the site of an ancient cave collapse possibly
pre-dating the Rhaetian, and that made them the oldest then known specimens of
kuehneotherians (p.161). At the time, Kuehneotherium
was widely regarded as being a basal therian; at least near to the origins of a lineage
involving myself and that girl I just mentioned. Other purported therians included
kangaroos and various long extinct lineages. Personally, I use a more restricted
definition of Theria, and this doesn't grant membership to
'Kühne's beast'. Nevertheless, the Emborough fossils remain of significance. By a
considerable margin, they remain the oldest mammalian remains from Britain. Associated
fossils attest to the age. These include a small, gliding reptile known as
Kuehneosaurus. The presence of Kuehneotherium, however, put something of
a smudge on the less than pristine distinctiveness of pre- and post-Rhaetian
vertebrate communities. Its lineage had obviously arisen a bit earlier than previously
supposed.
Muddying the dividing waters
There are a number of terrestrial vertebrate fossil localities spreading from Glamorgan
in Wales to Somerset and Gloucestershire in England. They variously date from red Triassic
deposits to Middle Jurassic limestone. A faunal based division had been proposed. The
older Triassic ones -Norian- were supposed to contain only sauropsids ('reptiles').
Younger ones were permitted to host mammals and relatives. Differing flavours among the
sauropsids were also mooted. Emborough's Kuehneotherium put a bite into this neat
picture.
And when she took off her shirt...
Apologies for that quick trip down Memory Lane. It won't happen again. At least, not
with her.
The teeth
Two mammalian postcanines were found, a lower
molar and a premolar. The first is best preserved (p.162). Its central cusp is somewhat
lower than usual for the genus, but a very similar specimen had been found earlier in
Glamorgan. Assigning isolated premolars to a particular genus can be perilous. In this
case, however, the size and look of the thing seem right, and no other mammal has been
found at Emborough. Kuehneotherium's claim is based on default. |
Seven Phases of Teeth
(Postcanines)
III Kuehneotheriids (basal
Holotheria)
The following is derived from and inspired by my reading of Butler & Clements, 2001,
(p.13).
A basal characteristic of Holotheria can be found in the triangularated arrangement of the
three main molar cusps. On uppers the apex is towards the
lingual side, and the opposite is the case for the lowers.
The oldest and most basal holotherian is Kuehneotherium. As most remains are
isolated teeth its dental formulae and development patterns aren't well known. A few bits
of toothless mandible may indicate up to six
premolariforms, with the first four being
single-rooted, and four or five molariforms. During life,
at least the front premolariforms might have been lost, and a further molariform could have
been added at the end of the row.
Go to Phase: I Carnivorous non-mammalian cynodonts,
II Basal mammals,
III Kuehneotheriids (basal Holotheria),
IV Cladotheria,
V Dryolestidae,
VI Amphitheriida and Zatheria,
VII Tribosphenic dentition. |
| Other reports:
Habay-la-Vielle, Belgium
A possible kuehneotheriid tooth has been reported. |
A. Chronoperatidae B.
Kuehneotheriidae C. "Amphidontidae"
| Taxon: Amphidontidae Simpson, 1925
A thoroughly dodgy family
If Rougier, Isha & Manabe, 2007 are correct, then this 'family' is thoroughly
shattered. It wouldn't include Amphidon. However, that's
not actually a reason for changing the name. When it comes to dinosaurs, for example,
Ceratopsidae hasn't had a member known as Ceratops since, if I remember correctly,
the nineteenth century. According to those authors, the genus Amphidon is based on
a very worn tooth of an "amphilestid", and
not a "symmetrodont".
Additional notes
These beasties are further derived than kuehneotherians,
and have been viewed as reasonably close relatives of the
spalacotheriids. However, new findings suggest
this is actually a junk taxon.
Averianov 2002 cites it as a nomen dubium; ie. dubious. Purely for convenience, I'll
maintain using it for the while.
Rougier et al 2003 (p.11) are perhaps even more dismissive: "We think, therefore, that
Amphiodontidae as a distinct family of Mesozoic mammals is probably unwarranted, and that it
is based on an artificial grouping of badly preserved and poorly known fossils."
Reference for Amphidontidae: Simpson GG (1925), Mesozoic Mammalia II: Tinodon and its
allies. American Journal of Science, 10, p.451-470.
"In one group of symmetrodonts, the poorly known
amphidontids, the postcanine dentition consisted of only
four premolariforms and four
molariforms", (Butler & Clements 2001, p.13).
Genera: Amphidon, Amphiodon (=Amphidon),
Manchurodon, Nakunodon,
other reports
Time-Line:
Upper Jurassic: Amphidon, Manchurodon
Middle Jurassic:
Lower Jurassic: Nakunodon |
| Genus: Amphidon Simpson GG,
1925
'paired tooth'
Aka: Amphiodon
Remarks: Amphiodon, which I’ve seen used, is actually a genus of hiodontid fish, as
well as apparently being a junior synonym for another fish, Poecilanthe.
A second species, A. aequicrurius Simpson, 1925, was subsequently rediagnosed under
the name Eurylambda aequicrurius, which is very possibly the upper teeth of
Tinodon, Tinodontidae. |
| Species: | Amphidon supperstes Simpson GG, 1925 |
| Aka: | Amphiodon supperstes |
| Place: | Como Bluff, Morrison Formation,
Wyoming |
| Country: | USA |
| Age: | Upper Jurassic |
| Remarks: | The most recent thing I've read is Rougier,
Isah & Manabe, 2007 (p.100). They think it probable that this genus is probably a
clapped out "amphilestid" triconodont,
rather than any kind of "symmetrodont". The sole
known specimen experienced a great amount of war on its rear 'molars'. Interestingly,
this doesn't apply for the first in the series, and that indicates it erupted later (p.101).
As, by definition, mammalian molars aren't allowed to be
replacement teeth, that would render it a molariform
non-molar. Some ancient mammals didn't adhere to modern codes of behaviour.
Additional notes
Remains consist of a lower jaw with five 'molars'. The m1
"has an obtuse-angled crown with a trigonid angle of
~145°", (Averianov 2002, p.711). This is its sole qualification for being a
'symmetrodont' and it might be something else. An
aberrant amphilested is one suggestion.
Further support for that possibility has arrived. Rougier et al 2003, (p.11): "The type
and only known specimen of Amphidon supperstes seem to be better interpreted as an
"amphilestid" with worn-down molars rather than a typical "symmetrodont"."
"Amphilestids" are within or near to Triconodonta.
Lopatin et al, 2010, briefly address this genus. They mention a future intention of
revision the family of Amphidontidae to include a number of "amphilestid" genera (p.282),
ax presently categorized. I'm not going to take that future plan into account yet beyond
stating it. However, t'was they who formally assigned Siberia's
Acinacodusto this family.
Holotype
The Peabody Museum, Yale, houses the holotype, which was collected by Reed WH in 1880, (YPM
13638). |
| Reference: | Simpson GG (1925), Mesozoic Mammalia. II. Tinodon and
its allies. Amer. Journ. Sci. 10, p.451-470. |
| Genus: Manchurodon Yabe H &
Shikama T, 1938
'Manchuria tooth' |
| Species: | Manchurodon simplicidens Yabe OH & Shikama T,
1938 |
| Place: | Zhadzyao Coal Mine, Tuchengzi Formation, Liaoning |
| Country: | China |
| Age: | Upper Jurassic (Middle according to the authors, Low Cret said
others.) |
| Remarks: | Two fossils were found, and they may represent
the same individual, (Zhang 1984, p.6). The most instructive was the central portion of a
right mandible, which was described as including the
following postcanine teeth: three
premolars and five molars.
The molars have only one dominant cusp; the protoconid.
It's relatively high and on the labial side. There's a
cingulum behind the metaconid,
but no basined talonid. The premolar cusps are more
pointed but lower than those of the molars. A later interpretation transformed the first
'molar' into a premolar, thus rendering the count 4:4, (p.6).
Originally, a resemblance to Amphidon was reported, and the
age was thought to be Middle Jurassic. Remembering that this is only a partial mandible,
its length of nearly 3cm is surprisingly large for a mammal of that age. The other fossil
is a fragmentary scapula.
The mandible has since been lost and the original description is brief. All lower
premolars in
spalacotheriids and Zhangheotherium are double-rooted. With
Manchurodon, at least one was single-rooted. Though often referred to Amphidontidae,
Averianov (2002) finds this thoroughly unconvincing: "There is insufficient basis to
posit a special relationship between the two genera, and Manchurodon is considered
herein as "Symmetrodonta" incertae sedis", (p.711-712). |
| Reference: | Yabe & Shikama (1938), A new Jurassic Mammalia from South
Manchuria. Imp. Acad. Tokyo Proc. 41, 4, p.353-357. |
| Link:
The Polyglot Paleontologist
http://www.uhmc.sunysb.edu/anatomicalsci/paleo/terms.html
The Fossil Record of Mesozoic Mammals in China, (1984), by Fakui Zhang, (as translated by
Will Downs), was obtained courtesy of the Polyglot Paleontologist. The full citation is
contained in the Bibliography. The Poly Pal is a great resource. |
| Genus: Nakunodon Yadagiri
P, 1985
'Nail tooth'
Remarks: As is obvious to all true lovers of Sanskrit, nakuna refers to a nail.
The tooth is kind of nail-like as it had only one effective cusp. |
| Species: | Nakunodon paikasiensis Yadagiri P, 1985 |
| Place: | Kota Formation, Andrah Pradesh |
| Country: | India |
| Age: | ?Middle Jurassic |
| Remarks: | The following is based upon my reading of
Yadagiri, 1985, and thanks go to the supplier. As pointed out by (among others)
Prasad et al, 2006 (p.102), some of the terminology used in now inappropriate for a
non-tribosphenic mammal. I'm going to add inverted commas as I think fit; eg
"paracone". Obviously, they weren't used by the author.
This study concerns a well preserved, right upper molar
from the Kota Formation of Andhra Pradesh. It provided evidence for the fourth
taxon of supposedly Lower Jurassic mammal from those faunas,
although a more recent age now seems likely. Tentatively, it was referred to a rather
dubious "symmetrodont" family known as
Amphidontidae (p.411). There's no convincing reason for believing these 'amphidontids'
have any particular connections with each other, but it kind of serves as an assembly
area for some poorly known critters possibly sharing vague similarities of molar teeth.
Included was Amphidon from North America and this then
new Indian genus. However, the fossils available wouldn't have given even a very small
fairy the need to break out into sweat. A third possible member,
Manchurodon from China, wouldn't even cause the fairy to wake up. What remains
there were fell victim to the Second World War, and the only evidence left comes from its
1938 description. But, despite the scantiness of remains, a couple of fossils don't merit
being swept under the carpet. Their owners were real parts of the wildlife, albeit small
parts, and it's not their fault more information isn't yet available. Besides, I like it
when my wife's dressed as scantily as possible.
Typically, mammals from this sort of age had multi-cusped molars, and evolutionary
enhancements tended to result in increasingly complex crowns. Cusps were being shifted
and added, and dental sophistication enabled enhanced food processing abilities for more
complete exploitation. But that was merely typical. Trend-breakers can also flourish,
given the right circumstances. 'Amphidontids' made their livings by simplification.
Their molars had but a single cusp worthy of the name; the "paracone" on uppers, the only
tooth known for Nakunodon, and the "protoconid" on lowers.
The crown has only one effective cusp (p.415), and is surrounded by a strong
cingulum. Its efforts were supported by a pair of short,
thick roots. It's generally well preserved despite a small chip missing from the old
block. The main cusp accounts for most of the available space, and could be in danger of
offending against anti-monopoly legislation. A small bump marks the
pathetic "metacone" whereas the "parastyle" is a little bit longer. As is often the case,
the buccal face of the main cusp is convex. This sort of
habit is helpful when it comes to working out the orientation of isolated molars, and it
also shows this to be a tooth from the right side. Of the roots, the front one's about
twice the dimensions of the rear one (p.416).
'Amphidontid' problem cases
'Amphidontids' have got about three things in common: small teeth from Mesozoic mammals;
extremely scarce to no longer existent fossils; a single effective molar cusp - "functionally
monocusped". The inventory presently reads: Amphidon, one specimen; Nakunodon,
one tooth; Manchurodon, a sketch and some words. There was a near complete lower
jaw, but once there was a war. To what extent Amphidon actually shares the
'family characteristic' is less than clear. Further preparation showed it to be heavily
worn. In life, its accessory cusps could have been larger.
Nevertheless, 'amphidontids' do at least give hints of diverse approaches to life among
Mesozoic mammals, and provide hope that new discoveries could add more meet and spice to
this presently extremely thin soup.
Holotype
GSI SR/PAL/12 entertains guests in the collection of the Geological Survey of India,
Hyderabad. The specific name reflects the locality of Paikasigudem.
Additional notes
A single, monocusped upper molar. "The most striking
feature of Nakunodon is a complete cingulum,
especially thick and robust lingually, with a
protocone-like eminence at the junction of the pre- and post-cingula. The affinities
of Nakunodon remain problematic, but there exists no basis to classify it with
Amphidon", (Averianov 2002, p.712).
Averianov settles for Holotheria incertae sedis. |
| Reference: | Yadagiri (1985), An amphidontid from the Early Jurassic Kota
formation, India. Zoological Journal of the Linnean Society, London, 85, p.411-417. |
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| Help:
Should anybody have any further information, I'd be pleased to hear of it.
Regarding references and Bibliography:
I haven't and can't verify all the references, so beware. Traditional papers used in
constructing this page are in the bibliography. If you feel these are too few, then send
some more.
Trevor Dykes, October 2001 Last update: 25.10.2010
Ktdykes@arcor.de |
Bibliography:
Averianov AO, (2002), Early Cretaceous "symmetrodont" mammal
Gobitheriodon from Mongolia and the classification of "Symmetrodonta".
Acta Palaeontologica Polonica 47 (4), p.705-716.
Benton MJ, Cook E & Hooker JJ (2005), British Mesozoic fossil mammal GCR
sites, Chapter 2 of Benton, Cook & Hooker, Mesozoic and Tertiary fossil mammals and
birds of Great Britain, Geological Conservation Review Series, No. 32, Joint Nature
Conservation Committee, Peterborough, p.27-66.
Butler & Clemens (2001), Dental morphology of the Jurassic holotherian mammal
Amphitherium, with a discussion of the evolution of mammalian post-canine dental
formulae. Paleontology, 44 (1), p.1-20.
Datta PM & Das DP (2001), Indozostrodon simpsoni, gen. et sp. nov., an
Early Jurassic megozostrodontid mammal from India. Journal of Vertebrate Paleontology,
Vol. 21(3), p.528-534.
Fraser NC, Walkden GM & Stewart V (1985), The first pre-Rhaetic therian mammal,
Nature, 314, p.161-163.
Godefroit P (1997), Reptilian, therapsid and mammalian teeth from the Upper Triassic
of Varangéville (northeastern France). Bull. De l’Inst. Des Sci. Nat. de Belgique,
Sciences de la Terre 67, p.83-102.
Godefroit P & Battail B (1997), Late Triassic cynodonts from Saint-Nicolas-de-
Port (north-eastern France). Geodiversitas, 19 (3), p.567-631.
Godefroit P, Cuny G, Delsate D & Roche M (1998), Late Triassic Vertebrates from
Syren (Luxembourg). N. Jb. Geol. Paläont. Abh. 210(3), p.305-343.
Kemp TS (2005), The Origin and Evolution of Mammals, Oxford University Press,
pp.331.
Kermack KA, Lees PM & Mussett F (1965), Aegialodon dawsoni, a new trituberculosectorial
tooth from the lower Wealden. Proceedings of the Roy. Soc., London, B, 162, p.535-554.
Kielan-Jaworowska Z (1992), Interrelationships of Mesozoic Mammals, Historical
Biology, 6, p.185-202.
Lopatin AV, Maschenko EN & Averianov AO (2010), A new genus of triconodont
mammals from the Early Cretaceous of western Siberia, Doklady Biological Sciences, 433,
p.282-285.
Luo Z-X, Kielan-Jaworowska Z & Cifelli RL (2002), In quest for a phylogeny of
Mesozoic mammals. Acta Palaeontologica Polonica 47 (1), p.1-78.
McKenna MC & Bell SK, (1997), Classification of Mammals Above the Species Level.
Columbia University Press.
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.
Prasad GVR & Manhas BK (2002), Triconodont mammals from the Jurassic Kota
Formation of India. Geodiversitas 24 (2), p.445-464.
Prasad GVR & Manhas BK (2007), A new docodont mammal from the Jurassic Kota
Formation of India, Palaeontologica Electronica, 10, p.1-11.
Prasad GVR, Verma O & Parmar V (2006), An overview of the Mesozoic
mammalian fossil record of India, Mesozoic Terrestrial Ecosystems 2006,
p.101-104.
Rougier GW, Spurlin BK & Kik PK (2003), A New Specimen of Eurylambda
aequicrurius and Considerations on "Symmetrodont" Dentition and Relationships.
American Museum Novitates 3398, p.1-15.
Scott CR, Fox RC & Youzwyshyn GP (2002), New earliest Tiffanian (late Paleocene)
mammals from Cochrane 2, southwestern Alberta, Canada. Acta Palaeontologica Polonica 47 (4),
p.691-704.
Sigogneau-Russell D (2003), Docodonts from the British Mesozoic. Acta Palaeontologica
Polonica 48(3), p.357-374.
Sigogneau-Russell D & Ensom P (1998), Thereuodon (Theria, Symmetrodonta)
from the Lower Cretaceous of North Africa and Europe, and a brief review of symmetrodonts.
Cretaceous Research, 19, p.445-470.
Yadagiri P (1985), An amphidontid from the Early Jurassic Kota formation, India,
Zoological Journal of the Linnean Society, London, 85, p.411-417.
Zhang F (1984), The Fossil Record of Mesozoic Mammals in China (translated by Will
Downs 1986, with minor revisions in 1999). Vertebrata Pal Asiatica, Vol. XXII No. 1,
p.29-38 |
