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.
|
Amongst these groups are the earliest known mammals, if
Mammalia is broadly defined. They, or rather their predecessors, seem to have evolved
from non-mammalian cynodonts before the late Upper Triassic. In terms of anatomy,
derived cynodonts, (which persisted until at least the
Lower Cretaceous), and basal mammals were close relatives; so
close, that a clear division cannot be drawn with certainty. |
| Links:
Toby White, Palaeos, Mammaliaformes: Allotheria
http://www.palaeos.com/Vertebrates/Units/Unit420/420.100.html
Anatomy crib notes with a good variety of links. Also addresses the difficulties of seeking
to define what constitutes a mammal. Hadrocodium, a hard to place midget from China,
receives extensive coverage.
John H Burkitt, Mammals, A World Listing of Living and Extinct Species
http://cougarhillweb.org/mammals.pdf
The seriously stunning results of a couple of decades of research.
T Mike Keesey, The Dinosauricon, Ages of the Mesozoic
http://www.dinosauricon.com/times/index.html
Details on funny chronological terms such as Rhaetian etc. Useful for reference.
Remarks: The border between the rocks of the Upper Triassic and the Lower Jurassic in often
not easy to define. For this reason, I rather favour the phrase Rhaetian-Liassic.
|
A. Basal Mammaliaformes B.
Morganucodontidae C.
Megazostrodontidae and Dinnetherium D. Hadrocodium
| Taxon: Mammaliaformes Rowe, 1988
Mammaliaformes includes critters which are often
referred to as mammals, and they were certainly more 'mammalian' than they were anything
else. Its membership may include all the entries on this directory and the orders of
Docodonta and Haramiyida.
Some other groups are also good candidates; eg.
Kuehneotheria. Personally speaking, I'm inclined to think of them as basal mammals. |
| Link:
Mikko K. Haaramo, Mammaliaformes
Mikko Haaramo's Mammaliaformes
Sinoconodontids and friends.
Genera: Adelobasileus,
Archaeodon (= a pseudofossil), Archaeotherium (= Archaeodon),
Gondwanadon, Lufengoconodon (= Sinoconodon),
Sinoconodon, Tikitherium,
other reports
Time-Line:
Lower Jurassic: Sinoconodon
Upper Triassic: Adelobasileus, Gondwanadon, Tikitherium,
Varangéville (France) |
| Genus: Adelobasileus
Lucas SG & Hunt AP, 1990
'unknown king' |
| Species: | Adelobasileus cromptoni Lucas & Hunt, 1990
|
| Place: | Dockum Formation, Texas |
| Country: | USA |
| Age: | Carnian, Upper Triassic |
| Remarks: | Kemp, 2005 (p.138-140) reveals that the basis of
this genus is a heavily crushed, rear section of skull. Details of this 1.5cm fossil are
more mammalian than in close relatives such as
tritheledontids, and that's why it's been widely
welcomed into Mammalia. This animal promises to be very informative regarding the
relationships of trithes, tritylodontids and
basal mammals, but this will only be fulfilled by more
specimens. Jaws should be especially useful, should somebody find any.
Ears and teeth
In some structural respects, the ear is more derived than
in other non-mammalian cynodonts, whilst being less derived than that of any known mammal.
"With respect to several important characters, Adelobasileus shows an
intermediate condition between cynodonts and mammals (Lucas and Luo 1993; Luo et al. 1995).
Additional dental fossils have been discovered (personal communication from SG Lucas) but
not yet described," (Luo, Kielan-Jaworowska & Cifelli (2002).
"Status questionable," (McKenna & Bell, 1997).
Holotype
The holotype, NMMNH P-12971, is a resident of the New Mexico Museum of Natural History and
Science, Albuquerque. |
| Reference: | Lucas & Hunt (1990), The oldest mammal. New Mexico Journal
of Science, 30, p.41-49. |
| Genus: Archaeodon (von Huene),
1925
'ancient tooth'
Aka: Archaeotherium von Huene, 1925 |
| Species: | Archaeodon reuingi (von Huene), 1925 |
| Aka: | Archaeotherium reuingi von Huene, 1925 |
| Place: | Khuaberg, Namibia |
| Country: | Africa |
| Age: | Upper Triassic |
| Remarks: |
This is a pseudofossil. Whilst originally described as a mammal tooth, it's actually a bit
of quartz which formed in a small space inside volcanic lava, (Heinrich 1998, p.269). |
| References: | von Huene (1925a), Triassischer Säugertierzahn aus
Südwestafrika. Centralbl. Min. Geol. Paläont. (B), p.174-181. |
| von Huene (1925b), Archaeodon statt Archaeotherium.
Centralbl. Min. Geol. Paläont. (B), p.303. |
| Genus: Gondwanadon Datta
PM & Das DP, 1996
'Gondwana tooth' |
| Species: | Gondwanadon tapani Datta PM & Das DP, 1996
|
| Place: | Tiki Formation, Madhya Pradesh |
| Country: | India |
| Age: | Carnian, Upper Triassic |
| Remarks: |
This has been reported as a morganucodontid. If
correct, it's very surprising. (With further thanks to David Marjanovic).
Information has just come to hand, courtesy of the Mumbai Grapevine. As many
newsletters often replace old articles with new ones, and because little information on
this genus is otherwise available on the web, I've decided to quote the entire report.
Oldest known mammal fossil discovered in India
Kolkata,Tuesday, September 11, 2001: With the discovery of a tiny rodent tooth as old as
225 million years from the central Indian state of Madhya Pradesh, geoscientists have
reported the oldest known mammal fossil which predates all mammalian records till date. Study
of the two milimetre long molar tooth, unearthed from the
Gondwana supergroup rocks of Tiki village, has led a team of geologists from the Geological
Survey of India (GSI) to postulate that this earliest known mammal was an insect eating
animal of the size of a rat.
Christened Gondwanadon Tapani, in honour of Tapan Roychowdhury who pioneered the study of
early mammals in India, the teeth of the new species was found well preserved in the red
mudstone bed of the Tiki formation.
The Tiki fossil appears to be slightly older than the earliest ever recorded mammalian skull
reported in 1993 from Kalgary in Texas, North America dated around the same period.
"This new record holds promise of throwing more light on the question of evolution of
mammals. More prospecting is in progress," senior geologist of GSI's palaentology
division, who led the discovery, P M Datta told PTI.
The right molar tooth with four cusps arranged in a linear fashion and joined by a continuous
ridge provides an insight into the insect eating habits of the mammal, Datta, who has
co-authored the finding report with fellow geologist D P Das in an in-house publication of
GSI, said.
With thanks for the above to The Mumbai Grapevine
http://www.mumbai-central.com/grapevine/msg00858.html
The Mumbai Grapevine can be contacted at:
news-editor@mumbai-central.com |
| Reference: | Datta & Das (1996), Discovery of the oldest fossil mammal
from India. Indian Minerals, Vol 50(3), p.217-222, (with thanks to the Geological Survey of
India).
Regarding availability of the Journal you may contact:
dydgop4@cal3.vsnl.net.in |
| Genus: Sinoconodon
Patterson & Olson, 1961
'Chinese coned tooth'
Aka: Lufengoconodon ('Lufeng coned tooth') Young CC, 1982
Family: Sinoconodontidae Mills, 1971
Remarks: It's possible that this genus is non-mammalian, "based on the retention of
auxiliary mandibular bones," (Zhang, 1984).
Weird behaviour
This is further supported by Luo 1994 (p.116), (although he does kindly allow the genus to
be a mammal of sorts). Several specimens show very unmammalian dental habits. All adult
mammals who bother with teeth go through two sets. Several Sinoconodon specimens
show evidence of a different inclination. They seem to have replaced their
incisors at least three times, with one
canine having been replaced on at least four occasions; a
neat trick perhaps, but we'd require dentures to replicate it. Our teeth are too
differentiated and specialized. Furthermore: "The alternating replacement of the
incisors and canines and partial replacement of the
postcanines continued as the skull increased in size. Based on this information, I
interpret that the skull of Sinoconodon experienced continuous slow growth, as in
modern diapsid reptiles and in nonmammalian cynodonts." See 'Size range' below for
further details.
Affinities
On pages 117-118, Dr Luo goes on to conclude that: "The overwhelming numbers of
apomorphies... strongly suggest that Sinoconodon
and all other mammals form a robust monophyletic group.
But within this monophyletic group, Sinoconodon differs from
morganucodontids and other mammals in many dental
and skull features. In most of these differences, Sinoconodon retains more
primitive character states than other mammals."
As these critters refused to fully grow up before dying and some of the teeth were subject
to serial replacement, several species and even a separate genus were proposed to
accommodate the variations in size and dental details.
Then again ...
Whether Sinoconodon is a mammal or not rather depends upon definitions. Kemp, 2005
(p.141-142): "Confirmation of its mammalian status is provided by the dentary condyle
and glenoid fossa of the squamosal complete with a postglenoid ridge, the complete
ossification of the internal orbit and the expansion of the
brain case."
The teeth fail to be as sophisticated. The postcanines
are relatively simple, and ones to the front were thrown away rather than directly
replaced. New ones were added to the back of the row.
Size range
Oftedal 2002 (p.234) contains a suggested bodyweight of up to about 500g for the genus, which
would compare to a chubby
brown rat. A range of estimates for different sized specimens is contained in Luo et al,
2001, p.1539, Fig.5B. The available skulls measured between 2.2 and 6.2 centimetres, and
this suggests weights of between 13 and 517 grammes.
| Reassigned species: S. parringtoni Young, 1982 and S. yangi Zhang &
Cui, 1983 see S. rigneyi | |
| Species: | Sinoconodon rigneyi Patterson B & Olson EC, 1961
|
| Aka: | Lufengoconodon changchiawaensis Young CC, 1982; S.
parringtoni Young, 1982; S. yangi Zhang F & Cui G, 1983 |
| Place: | Lower Lufeng Formation, Yunnan |
| Country: | China |
| Age: | probably Sinemurian, Lower Jurassic |
| Remarks: | The following is based upon my reading of Crompton
& Luo, 1993. There's bound to be some overlap with the shorter summary for the genus.
Strictly members only
Mammalia is rather like a fancy dress party for advanced
eucynodonts, where entry is dependant upon being able
to honestly say yes to a suite of questions. The process would be reasonably straightforward
for living candidates. Do you habitually generate heat inside your body, have at least a
little bit of hair about your person, and did you insist upon milk as your first post natal
diet? If you meet each qualification, then your application will be successful. Pigeons
might coo protestingly about the wonders of crop milk for baby birds, (baby pigeons are fed
a kind of milk), but even the most lenient of bouncers would turn them away for blatant
hairlessness. Dolphin hair, however unlikely it sounds, exists.
With living mammals you can check the trustworthiness of their replies easily enough. This
is much more problematic with 200 million year old bits of fossilized tooth and bone. As
checking the blood temperature of a fragment of mineralised jaw won't work, some ticket
inspectors are liable to be more indulgent than others with would be party-goers. The
questions posed will differ, and the starting line of Mammalia is fuzzy anyway. Not that
my opinion is of consequence, but I wouldn't let Sinocondon in.
Utterly unmammalian traits
Some may think me snobbish, but Sinoconodon behaved in some very unmammal-like ways.
The variation is size of individuals points to a strategy of indeterminate growth. As the
animal got older it grew bigger, and only death discouraged this. It was also a serial
tooth replacer. Canines could be renewed at least four
times, (p.30). The postcanines aren't differentiated
into premolars and
molariforms; cingula are poorly developed; upper teeth
and lowers didn't properly occlude. Mammals don't behave like this.
Very mammalian traits
However, as far as can be inferred, this critter was endothermic (it generated heat
internally), presumably had fur and could well have been a milk-suckler. (The anatomy at
the back of the mouth is consistent with that capability.) If Sinoconodon were alive
today, it would be a fascinating aberration but nobody would deny its mammalian credentials
in terms of the three questions above. And these credentials are proclaimed by find
details.
The braincase is expanded in the parietal region, and the medial margin of the
orbit is completely ossified. The characteristic mammalian
jaw joint is strongly developed, with a dentary condyle
below and a concave glenoid fossa on the squamosal above. Sinoconodon and all mammals
appear to share a common ancestor, which didn't give rise to other animals.
Sinoconodontid traits
This genus also had its own specialisations (autapomorphies).
The canine is impressively large and the dentary condyle is massive. Interestingly, compared
to other Liassic mammals, the postdentary bones are proportionately smaller.
Tooth replacement
Sets of teeth are available from a number of individuals of differing sizes, (p.31). The
lack of wear facets demonstrate there was no regular occlusion between upper and lower
postcanines. Some well preserved uppers have a slight buccal
cingulum, while lowers have a more pronounced cingulum to
the front on the lingual side.
A relatively small upper jaw has five incisors. Pits for
replacements are lingual of I2 and I4, and a replacement canine can be seen. There are three
working postcanines with a fourth entering the stage.
Longer jaws sketch this individual's future, had it gotten around to enjoying one. At
least the front two postcanines would have been dispensed with, so as to increase the
length of the diastema. The posterior postcanine was due
to be relatively small and simple. Later, a more typical tooth would have replaced it.
Size and eruption stages evident across the series of jaws indicated upper
canines were replaced at least four times, (p.32). Erupting
incisors on a reasonably sized specimen suggest more than one replacement episode for those
teeth too. With advancing age, the number of upper incisors could reduce to four.
Lower dentition
Not as much is clear about replacement of lower teeth, as less specimens were available.
Growing up seems to have involved the loss of at least one front postcanine. The fourth
postcanine of one individual is small, whereas a larger specimen has a bigger tooth in the
same position, and that suggests replacement occurred. It also proudly displays a fresh,
small postcanine behind it.
Precedents
Losing front postcanines and adding teeth to the back of the row, is a style of behaviour
familiar from some non-mammalian cynodonts, and the same can be said for the pattern of
canine replacement. Various carnivorous critters, (eg. Thrinaxodon and
Probainognathus), also got rid of front
postcanines as they grew older.
Anybody for milk?
I'm very fond of mammary glands, and attempting to get my hands on prized specimens has
sometimes ended with frustration. This problem is far more acute for Mesozoic forerunners.
Despite all their glories, breasts are terribly candidates for fossilisation. How well
endowed Sinoconodon females were, if at all, is a subject firmly veiled by an
unrevealing blanket of mystery. Fossils are silent on this direct matter. However, there
is evidence consistent with suckling capabilities.
Some advice for would be sucklers
Suckling ability is about more than simply owning a mouth and throat. Attempting to suckle
a baby crocodile wouldn't be advisable for a mother, as neither party is endowed for the
job. Even assuming the adult were capable of supplying the goods, there would still have to
be some way for the baby to control the flow of milk into the throat, in order to avoid
technical hitches such as choking to death. Mammalian throats achieve this with a valve at
the back of the mouth, (p.38). The seal is formed by aggressively named muscles and the
rear of the tongue; synchronised actions of the palatoglossal and tensor palatini muscles.
This also requires space for the muscle fibres of the tensor veli palatini to come into
contact with the soft palate.
In most non-mammalian cynodonts, opening and closing the mouth resulted in a tight contact
between a flange of the pterygoid and the coronoid bone. This helpfully stopped the jaws
sliding extravagantly sideways. However, it also meant there was no space available for a
tensor veli palatini. A mammal-style valve to control milk flow wouldn't have been
viable.
Room enough for a tensor veli palatini
This doesn't apply for Pachygenelus, a
tritheledontan. The transverse process of the pterygoid deflected inwards, away from the
coronoid. The contact was also reduced in Sinoconodon. In short, there's no
structural property of the relevant bones which would have impeded mammalian suckling.
Milk would've been an excellent solution for feeding fast growing, endothermic babies.
None of this provides a full-frontal snapshot of Sinoconodon mammary glands.
Nevertheless, there's nothing to rule the possibility out. Given the universality of milk
among all living mammals, the elixir must have a history dating back beyond the most recent
common ancestor of myself and a monotreme.
Come into contact with more breasts at:
Putting the Mamms onto Mammals, 2,700 words on the evolution of lactation and mammary
glands.
Additionally
At least four skulls were assigned to this species, (Zhang 1984, p.5), before other
taxa were synonymised with it. His Table 1 offers an upper
dental formula per side of: three incisors, a
canine, and four
postcanines. However, as variability in numbers has now been established as normal
behaviour in this critter, members aren't obliged to follow that prescription.
Lufengoconodon was based on a skull, jaw and forelimb elements. The dental formula
has been described as being akin to Morganucodontidae,
(Zhang, 1984), but this was before the non-mammalian continual growth habits of
Sinoconodon were recognized. Zhang relates, (p.4), that the skull was low and flat.
The dental formula per side was given as: four incisors, a canine, seven
postcanines; (lowers): four, one and seven respectively.
This may be a juvenile.
A similar fate befell S. parringtoni, which was differentiated from S. rigneyi:
"on the basis of three characteristics: a short and robust rostrum, a larger
canine and a vertically deep skull", (Luo & Wu
1994, p.261). Young's 1982 publication was posthumous. S. yangi was established
mainly because of an extra incisor.
"Status questionable," (McKenna & Bell, 1997). |
| References: | Patterson & Olson (1961), A triconodontid mammal from the
Triassic of Yunnan, p.129-191, in Vandebroek G (ed.), International Colloquiem on the
Evolution of Lower and Non-specialized Mammals. Vol 1. Koninklijke Vlaamse Academie voor
Wetenschappen, Letteren en Schone Kunsten van Belgie, Brussels. |
| Young (1992), [Selected Works of Yang Zhongjian (Young Chung-Chien).]
, Biejing Science Press. [Chinese]. |
| Zhang & Cui (1993), [New material and new understanding of
Sinoconodon.] Vertebrata Palasiatica 21, p.32-41, [Chinese]. |
| Genus: Tikitherium, Datta
PM, 2005
'Tiki beast'
Remarks: The village of Tiki is four kilometres from the fossil locality. |
| Species: | Tikitherium copei Datta PM, 2005 |
| Place: | Tiki Formation, Madhya Pradesh |
| Country: | India |
| Age: | Carnian, Upper Triassic |
| Remarks: | The following is based upon my reading of Datta,
2005.
This study concerns one small tooth from the Carnian rocks of India. It's referred to as
mammalian. This is something like 225 million years old, and I find that surprisingly
early. However, that may merely be my prejudice. Fossils I readily accept as
mammalian have been recovered from strata which are around
ten million years more recent, and there's a reasonable level of diversity including
morganucodontids and
kuehneotherians. That indicates that the ground zero of mammalian origins must have
been somewhat earlier.
The tooth is an upper molariform. (p.200). Considering
its age, it has some surprisingly 'advanced' characteristics. There are three roots. The
buccal (external) side of the crown houses three cusps, and
they're arranged in an obtuse triangle. A further cusp is housed in the rear corner on the
lingual side, and this is involved with two shearing crests.
In front is found a depression described as talon-like.
Given the sophistication, if this tooth is from anything other than a mammal, that would
also qualify as surprising.
Drawing lines
Evolution is messy. Unless a crown-group definition is used, (the most recent common
ancestor of all living representatives, and all of its descendants), where Mammalia starts
is subject to taste. My informal approach is presently anchored on
Morganucodon. Datta employs a somewhat wider concept.
His usage of 'therian' can also be broader as it sometimes
includes kuehneotherians. (The terminology in the paper is less than consistent in some
respects. For example, kuehneotherians are variously "therians", therians and
holotherians.)
The earliest known mammals, a generous approach
This paper has the oldest mammals as Adelobasileus,
Gondwanadon and now Tikitherium. (If the
assignment of Gondwanadon to Morganucodontidae is correct, then that genus would have to
fit within my informal definition.) Datta terms these (and others) non-therians (and
"non-therians")! The next oldest remains are from Rhaetian (and perhaps Norian)
localities in Western Europe. These are something like between 215 - 208 million years in
age.
Towards grinding
(Note: some readers might find it beneficial not to worry too much about the potentially
puzzling mass of names. There won't be a quiz.)
The original eucynodont
postcanines were sectorial; blades for cutting meat.
That's also what the most basal mammals presumably had, albeit
ones for small portions. Kuehneotherians are somewhat more
derived, in that their molars could also manage a bit of grinding, and that allows food
to be more fully processed. Full blown, dual-functional molars required further significant
refinements. Despite the complexities involved, such properly
tribosphenic teeth appear to have evolved twice, (
australosphenidans and boreosphenidans). Several
other mammalian lines also developed grinding capabilities; eg.
Shuotherium and docodonts such as
Simpsonodon.
Despite being much earlier, Tikitherium has characteristics in common with some
later mammals. It had: "derived dental morphology capable of producing a grinding
action", (p.201). However, other aspects set it apart from all known mammals.
On this page, the tooth is termed a molar rather than a molariform, and it's described as
being holotherian. Despite that, it has not been formally placed within
Holotheria, (see page 206).
The tooth
It's an upper left postcanine and well preserved. It's not exactly very big, (p.202).
Seen from the occlusal perspective, the shape is vaguely
like a very clumpy number 7. The upper bar would be on the
buccal side, and that's where the cusps BAC are. The maximum length is 1.3mm with the
internal minimum being about half that. The width at the shaft of the '7' is more uniform;
0.8 - 0.95mm.
When seen from the buccal perspective three cusps are visible. The mighty A dominates and
takes up most the length of the crown. It soars to a height of over a millimetre. Cusp C
arises from its rear slope and apologises its way to a meagre 0.2mm. Cusp B at the front is
more like a minor foothill. The trio are arranged triangularly and the angle BAC is obtuse;
a bit more than 130°.
The tooth has the temerity to possess three roots, (p.203). I've never heard of anything
like that from the Carnian before, though my education may be lacking. I'm aware of
incipiently double-rooted postcanines. Three is a novelty to me, and they appear to be
distinct rather than incipient. Two support the buccal side with the larger one at the
back, (length 0.72mm). A wider root (length 0.50mm) is at the front, and it supports a
cingulum and a cingular cusp E. A smaller root (0.31mm)
is positioned internally. This anchors cusp Z and the talon-like basin towards the rear of
the lingual side.
There are six discernable wear facets on the lingual surface of the crown, (p.204).
Possible affinities
Patterns of cusps are central to the identification of ancient mammals, and reveal information
on relationships. As the complex crown of Tikitherium has characteristics in common
with the teeth of docodonts and
holotherians, the author has no doubts about referring
it to a mammal. However, the sample is limited to only a single specimen, and that
provides room for doubts as to whether these similarities are
homologies.
The external (buccal) surface of basal mammalian postcanines is generally more convex than
the lingual one, and the uppers are relatively wide. That helps identify this as an upper
left tooth.
The general pattern of cusps and proportions are broadly in line with
Woutersia butleri. However, cusp B is much
larger in Woutersia, cusp Z is not widely separated from cusp A by a shallow basin,
and it isn't associated with two shearing crests. There are also less wear facets and they
fail to correspond. As with Kuehneotherium
and 'symmetrodonts', Woutersia upper molars
are double- and not triple-rooted.
The inflated nature of cusp Z and its pair of crests appear to rule out affinities of
Tikitherium with basal holotherians, 'symmetrodonts'
and early cladotherians. Perverse as it may sound,
Tikitherium is too advanced in some details.
Docodonts?
There are resemblances to docodonts, and these include some wear patterns and the general
shape. However, the upper molars of Haldanodon
have four main cusps. Both the buccal and lingual halves of the crown have two each. These
are arranged around a central basin, and they're connected by strong crests. There's no
sign of a triangulated pattern. Docodont molars do have three roots, but the largest, and
not the smallest, is the lingual one. The similarities of wear are only partial.
Tikitherium isn't a docodont.
Shuotherium?
There are similarities with Shuotherium as well, although the upper molar of Shuo is
about twice the size, (p.205). Shuotherium has two main cusps on the
buccal side, and a lingual one associated with two crests.
But there's a whole slew of differences concerning alignment, proportions, crests, wear
facets and further features. Without attempting to summarise I'll content myself with:
"No crests comparable with the pseudo-metacrista, pseudo-precentrocrista, or
pseudo-postcentrocrista are developed in T. copei."
Australosphenidans?
Presently, (ignoring monotremes), australosphenidans
are only known from lower jaws and teeth. That makes comparisons of an upper postcanine
problematic.
A general picture of cutting and grinding
Non-mammalian eucynodonts and basal mammals came equipped with postcanines which could only
shear food. Grinding wasn't possible. Fully blown dual-functional molars are presently
restricted to australosphenidans ('southern cutters') and
boreosphenidans ('northern cutters'). The protocone of an upper tooth is positioned
directly over the basined talonid of a lower. That allows
food to be ground thoroughly. Such molars are tribosphenic,
('cutter-grinders'). Docodonts developed a fair degree of dual-functionality by a different
route.
A Carnian cutter-grinder?
"Cusp Z of the upper molar of Tikitherium shows a little wear on its apex,
which indicates that the cusp made effective contact with the talonid-like surface. This,
along with the accompanied wear marks, would strongly suggest some amount of grinding
action", (p.206). The tooth is a Carnian cutter which could grind a bit.
Holotheria?
Although the tooth was called holotherian on page 201, page 206 contains: "Adopting
the molar cusp triangulation as an important apomorphy
of Holotheria has been shown to lead to instability of the Subclass... This precludes the
formal placement of Tikitherium in the holotherians, though it prominently displays
this character", (reference omitted). Such an arrangement could be a matter of
convergence.
Presently, the affinities of this genus are a puzzle awaiting further evidence. (I wonder
if a comparison with Brasilodon might be
useful. I've got very little information on that taxon, and I'm not sure how reliable it
is. The occlusal outline of postcanines is apparently square, but there is some degree of
triangulation of cusps. I've heard nothing about the roots.)
Holotype
The holotype, Pal./CHQ-009, is in the collection of the Geological Survey of India,
Calcutta. The specific name is for ED Cope, the pioneering paleontologist from 19th
century USA. This honours his contributions to the study of mammalian molars.
An abstract by Datta PM is contained in Albertiana, 30. Somewhat confusingly, the
publication was referred to as being both in press and from 2004. The description finally
appeared early in 2005. (My thanks to the supplier.) |
| Reference: | Datta (2005), Earliest mammal with transversely expanded upper
molar from the Late Triassic (Carnian) Tiki Formation, South Rewa Gondwana Basin, India,
Journal of Vertebrate Paleontology, 25(1), p.200-207. |
| Link:
Albertiana 30
http://www.bio.uu.nl/~palaeo/Albertiana/E-Albertiana/albertiana30.pdf
Go to page 6 for A suggestion for an early Tuvalian time segment for the Tiki Formation,
South Rewa Gondwana Basin, India and other correlatable continental sequences, Datta PM.
This provides a brief round up of the terrestrial vertebrates so far identified. |
| Other Reports:
Varangéville, France
A sinoconodontid tooth, probably a left lower
molariform; Norian (late)-Rhaetian (early), Upper Triassic. This find is included in a
report by Dominique Delsate, which I've unfortunately mislaid. |
A. Basal Mammaliaformes B.
Morganucodontidae C.
Megazostrodontidae and Dinnetherium D. Hadrocodium
| B. MORGANUCODONTIDAE and allies |
| Taxon: Morganucodontidae Kühne WG, 1958
Sometimes cited as the first mammals, these creatures must also have had their mammalian
and near-mammalian ancestors. Morganucodontids were typically shrew-sized insectivores and
probably nocturnal, as far as can be told. On account of tooth similarities, they are
sometimes ascribed to the order of Triconodonta.
However: "Previous studies have shown that morganucodontids are far more primitive
than eutriconodontids in features of the basi-cranium (Rowe 1988; Wible and Hopson 1993;
Rougier, Wible and Hopson 1996) and skeleton (Ji et al. 1999), despite the similarities in
some (although not all) dental characters", (Luo et al 2002, p.14).
Morganucodonta: a brief stroll through paleontological history
Kemp, 2005 (p.142) reports Parrington began the ball rolling in 1941 by describing an
isolated premolar and molar
from Somerset, which had been discovered in a quarry by Kühne. These were referred to a
new genus called Eozostrodon. The molar possessed a straight
line of three main cusps; a pattern broadly similar to both earlier cynodonts and later
triconodontans. The age was held to be Upper Triassic,
although Lower Jurassic is also a possibility. In either case, the time served to enhance
their significance with regards to mammalian origins.
As Kühne happened to be German, he spent much of the Second World War as an internee. He
then resumed hunting fossil mammals, and hit gold in Glamorgan. This much more generous
quarry produced thousands of teeth, jaws and fragments of skeleton. Although clearly
similar to the very limited Somerset remains, he referred much of the trove to a new genus
and called it Morganucodon. This
provoked some nomenclatural inconsistencies with subsequent finds and studies. At one time
or another, both names have been applied for the teeth. Eventually, it was agreed that two
isolated postcanines were inadequate for a diagnosis in
comparison with the Glamorgan material, and the later name received priority.
(Eozostrodon is still sometimes used as a separate genus restricted to Somerset.)
Since then the geographic range of morganucodontans has broadened a bit, and now
encompasses further sites in Western Europe. Oh, and China, South Africa, North America and
India.
How well is Morganucodon known?
As well as jaws and teeth, studies have also probed the postcranial skeleton, and pried into
the inner ears. Short of providing fur, a Mesozoic mammal could hardly have been more
considerate or revealing. "The skull has all the superficial appearance of a small,
modern mammal characterised by the absence of a postorbital bar, slender
zygomatic arch, and expanded braincase consisting
largely of the parietal bone above", (p.143).
Oftedal 2002 (p.234) offers a bodyweight range for the family of between 30-90g. That equates
roughly to between one and four standard
house mice. |
| Link:
Mikko K Haaramo, Morganucodontidae
Mikko Haaramo's Morganucodontidae
An up-to-date cladogramme from an up-to-date cladogrammist.
Genera: Bocaconodon,
Brachyzostrodon,
Eozostrodon (?=Morganucodon),
Erythrotherium,
Hallautherium, Helveticodon (=Helvetiodon),
Helvetiodon, Holwellconodon
, Indotherium, Indozostrodon (=
Indotherium, Kotatherium sp. (= Paikasigudodon),
Morganucodon,
Paikasigudodon, Rostrodon
(?=Morganucodon), Wareolestes,
other reports
Time-Line:
Middle Jurassic: Wareolestes, Peski Quarry (Russia)
Lower Jurassic: Bocaconodon, Erythrotherium, Indotherium,
Morganucodon, Paikasigudodon
Upper Triassic: Brachyzostrodon, Eozostrodon, Hallautherium,
Helvetiodon, Holwellconodon, Morganucodon, Habay-la-Vielle (France),
Syren (Luxembourg), Caturrita Formation (Brazil) |
| Bocaconodon
Montellano M, Hopson JS & Clark JM, 2008
'Boca coned tooth'
Remarks: This genus hasn't been referred by anybody to Morganucodontidae or, indeed, any
other family. Rather, the authors simply refer to it as a mammaliaform of an evolutionary
grade similar to Morganucodon with reagard to the
construction of the lower. I've put it on this directory because I couldn't think of a
better alternative. |
| Species: | Bocaconodon tamaulipensis 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 P.
This manic mammalian killer is presently known from part of a lower right jaw with a
preserved length of 3.7mm (p.1133). As that suffices to provide a home for the two
rearmost teeth and part of a further one, the former owner wasn't exactly a giant. The
teeth show resemblances to those known from Morganucodon and the like. There's a
straight line of three main cusps with the middle one, known affectionately as a, being
much the largest, and positioned slightly fore of the metaphorical crown midway line.
Cusp b is smaller than the rear cusp, c. A d cusp occurs still further back. Contrasts
to Morganu include cusp a being proportionately taller and more recurved, and the
lingual cingulum being
entirely bereft of any cusps or cuspules. That means, among other paucities, there are
no cusps e or g. The inner face of the jaw shows remains of both a postdentary trough and
a Meckelian groove paralleling the lower border. The
former feature contributes to the authors terming the critter a
mammaliaform rather than, in the stricter terms of their paper, a mammal (ie. it wasn't
a member of crown-group Mammalia).
Jaw
The dentary is slender, with its depth but little greater
then the height of the penultimate tooth, the tallest one. Near the base of the jaw is
a shallow Meckelian groove. This feature runs in parallel with the base rather than
converging towards it, as is the case for Morganucodon. The groove widens towards
the rear of the final molar into a deep postdentary trough, as found on many
basal mammals (aka mammaliaforms). The trough would've housed
a rod of "extra" lower jaw bones. Remarkably enough, the future saw fit to relocate those
into the mammalian middle ear.
Teeth
As is usual for triconodont molars, or molariforms,
they don't take their descriptive name overly literally. Both complete crowns actually
feature a centrally located procession of four cusps; from front to rear b, a, c and
d. Those on the foremost tooth are somewhat longer, as befits a longer crown; 1.05mm
against 0.9. A narrow cingulum runs the length of the lingual side of the foremost
molar, but it carries no additional cuspules. The situation is similar for the last molar
excepting that the cingulum is incomplete by the main cusp.
The narrow, cusp-less cingulum is a feature in common with later "triconodonts" and a
contrast to morganucodontids and the like (p.1134). However, the ratios of cusp sizes and
the evolutionary grade of the jaw (eg. with a postdentary trough), are more in keeping with
Morganu. That trough had been gotten rid of by "triconodonts". Bocaconodon is a
basal mammal of presently unclear affinities.
Holotype
The type fossil, IGM6617, resides in the collection of the Instituto de Geologia of
Ciudad University, Mexico. It came from the delightfully named locality of Jim's Joy.
The specific name celebrates the state of Tamaulipas. |
| Reference: | Montellano et al (2008), Late Early Jurassic mammaliaforms
from Huizachal Canyon, Tamaulipas, Mexico, Journal of Vertebrate Paleontology, 28(4),
p.1120-1143. |
| Genus: Brachyzostrodon
Sigogneau-Russell D, 1983
'short girdle tooth'
Datta & Das, 2001, suggests this genus is part of Megazostrodontidae rather than
Morganucodontidae. They also report the genus is based on lower
molars. |
| Species: | Brachyzostrodon coupatezi Sigogneau-Russell D, 1983
|
| Place: | Saint-Nicolas-de-Point & |
| Country: | France & Greenland? |
| Age: | Norian upper-Rhaetian lower, Upper Triassic |
| Remarks: |
The genus and species are based on finds from France. |
| Reference: | Sigogneau-Russell (1983), A new therian mammal from the
Rhaetic locality of Saint-Nicolas-de-Pont (France). Zool. J. of the Linnean Soc. 78,
p.175-186. |
| Species: | Brachyzostrodon maior Hahn, Sigogneau-Russell &
Godefroit, 1991 |
| Place: | Saint-Nicolas-de-Point & |
| Country: | France & Greenland? |
| Age: | Norian upper-Rhaetian lower, Upper Triassic |
| Remarks: | |
| Reference: | Hahn, Sigogneau-Russell & Godefroit (1991), New data on
Brachyzostrodon (Mammalia: Upper Triassic). Geologica et Paleontologica 25,
p.237-249. |
| Genus: Eozostrodon
Parrington FR, 1941
'dawn girdle tooth'
Remarks: This genus is sometimes seen as synonomys with, and was published before
Morganucodon. Usually, it would have taken precedence. However, the material
originally described consisted of two teeth, whereas M. was fair better represented.
Both names have been in use, although the younger one is now generally given priority.
Luo & Wu, 1994 (p.263) still regarded this as a valid genus for some material from
Holwell Quarry, England.
| Reassigned species: E. heikuopengensis Young, 1978 see
Morganucodon heikuopengensis;
E. oehleri see Morganucodon oehleri;
E. problematicus see E. parvus;
E. watsoni see Morganucodon watsoni | |
| Species: | Eozostrodon parvus Parrington FR, 1941 |
| Aka: | E. problematicus Parrington, 1941; Morganucodon
parvus |
| Place: | Hollwell quarries, Somerset |
| Country: | England |
| Age: | Hettangian, Lower Jurassic |
| Remarks: | Benton et al, 2005 provides a brief
summary on page 36. Thanks are due to the suppliers and their photocopiers.
Originally, two species were established for just two teeth from the same quarry.
One of them, E. problematicus, was considered problematic. Later, it opted
to disband the 'species' so as to feel less lonely. While not being overly informative
on great issues of the age, these teeth do at least demonstrate morganucodontids
were active in the area at the time.
The next paragraphs are based upon my reading of Parrington, 1941. Again, thanks
are due to the supplier.
Once there was a war
This paper appeared at rather a taxing time in the history of British paleontology,
what with one thing and another. One of the main issues of the day concerned the
expected, imminent arrival of a large number of German visitors, generally carrying
guns. Tiny Britain, with an Empire reduced to less than a quarter of the available
global supply of land, stood nigh-on alone confronting the very real threat of the
Third Reich. These circumstances may help to explain why the news Parrington had to
relate failed to dominate the front page of The Times, or even the Western
Gazette, whereas my name's been featured in both at one time or another. Remarkable
as it may now seem, few Britons in 1941 spared many thoughts for isolated teeth of
Mesozoic mammals. This potential bombshell of a news story failed to explode in the
press. Nevertheless, despite such distractions as the Nazi threat, British
mammal paleontology carried on as determinedly as National Service, internment and
other circumstances allowed.
Hardly a mouthful
Parrington had only two teeth. Actually, he had more than that in his mouth, but
those weren't the ones he was describing. He had this pair of teeth from a quarry
at Holwell, and the like of them hadn't previously been seen from deposits as old
as these. At the time, the age was generally thought of as being Upper Triassic
(Rhaetian), but they're usually interpreted as Lower Jurassic. Nevertheless, the
oldest comparable specimens then available were Middle Jurassic. This led to the:
"importance of the specimens" (p.140). While sparse, the finds were unprecedented.
"Mammal" teeth had been found in this quarry before, originally in the second half
of the nineteenth century. These had been both more numerous and larger;
"haramiyidan" teeth. That knowledge had encouraged
a German paleontologist, Walter Kühne, to sample the place in the summer of 1939,
and his haul included the fossils Parrington was reporting. Presumably, if Poland
hadn't been invaded and no other event had pressed the starting shots for the encore
of the war to end all wars, the description would've been presented by Kühne.
However, things being as they were, he was otherwise engaged; interred on the Isle
of Mann. German citizens were understandably enough automatically viewed as suspect,
and the British authorities made sure to severely limit their mobility and
activities.
For the purposes of context, Parrington states this paper is: "a brief preliminary
account" (p.141). He was pressed for time.
Similar but...
The pair of teeth both shared similarities, but there were also notable distinctions,
and these prompted the author to tentatively refer them to two species within the
same genus. However, he suspected the actual truth of the matter. One, which he
named Eozostrodon parvus, was a premolar.
E. problematicus was a molar. Later, they
were united into the same species and, if I remember correctly, another specimen
was also assigned to it. (I presently forget quite where I read that, so perhaps
it's a trick played by my memory.) In any case, Parrington shared this opinion.
He didn't enjoy the benefits of hindsight in 1941, and nor did he have a generous
supply of Morganucodon from Glamorgan for
comparisons.
The first tooth described was the premolar. It's a relatively simple, double-rooted,
tri-cusped affair, with its central cusp being much the largest. The maximum length
attains a millimetre. Each cusp curves slightly to what Parrington correctly held
to be the rear. That detail also applies for various derived
therapsids including some later mammals (p.142).
One side of the crown is flat while the other is rounded, and it was probably a right
upper premolar. An incipient cingulum on the flat
side suggested perhaps a molar. However, it's a suitable premolar companion for its
problematic friend.
E. problematicus
When complete, this partial molar would've been somewhat longer than 1.5mm. Sadly,
breakage had truncated its full glory. Only two cusps and some accessory cuspules
remain to be admired. Presumably, it too was originally tri-cusped with the middle
member dominant, but that is proportionately less extreme then for the premolar.
Again, the cusp tips curve somewhat towards the rear. Remains of a cingulum are
located at the back and along the side, but its extent is obscured by breakage. It
reminded Parrington of Microleptes (aka
Thomasia) in some ways although, excepting for the cingulum, the tooth is
descriptively triconodont. That perceived mixture seem problematical enough to
inspire the scientific name. However, it hadn't then been possible to compare the
fossil directly with known triconodonts or, naturally enough, those as yet undiscovered
morganucodontids. After all, there was a war going on.
Ancient treasures
Although the Rhaetian date is subject to scepticism, the two teeth were in any case
the oldest then known for any mammal other than those "haramiyidans", if mammals
they be. They're termed "highly aberrant
Multituberculates" in the paper (p.144). Parrington also observes: "Eozostrodon
parvus, indeed, fits very well with the hypothetical ancestral mammalian tooth
postulated by the Cope Osborn Tritubercular theory." Not being overly familiar with
that matter, I'll restrict my enthusiasm to pointing out that it's a premolar rather
than a molar (or, in stricter usage, a
premolariform). That could have significance for comparisons with a
hypothetical construct.
Subsequent developments
In case anybody has missed the news, the 2nd World War ended in 1945. Thankfully,
the efforts of many people ensured the defeat of Nazi German, a country in which I
can now lead my fascinating existence. It also allowed Walter Kühne to get back
to prospecting, collecting and describing Mesozoic mammals. Little more, if any,
of Eozostrodon turned up at Holwell but, nevertheless, the genus did get to
play an active part in something approaching a civil war among some participants in
British paleontology during the 1960s and '70s. A schism opened up and,
as the correct name for Morganucodon became something of a political football
(some demanded it be Eozostrodon on the grounds of seniority), papers from
that time can provide unsuspecting readers with nomenclatural confusion. Theoretically,
differing views on the use of names should simply reflect conflicting interpretations
of generic affiliations. However, in some (not necessarily all) cases, personality
clashes appear to have been involved. This friction about which name to use wasn't
the issue at the centre of difficulties.
Holotype
The original description was intended to be a preliminary account, and a few of the
usual details remained unrevealed. For example, if the fossils involved had
catalogue numbers of some kind, then they weren't disclosed. No was an explanation
given for the origins of the names.
Additional notes
"Commenting on the status of the genus Eozostrodon,
which has often been used interchangeably with Morganucodon, Clemens (1979)
suggested that the identity of Eozostrodon parvus should be restricted to only those
morganucodontids occurring in the Holwell Quarry in England", (Datta & Das, 2001).
I'll follow this suggestion.
A specimen with this name is held at the Peabody Museum, Yale. This was
found by Parrington in 1966. Whether it actually belongs to this genus is another
matter. Referring to Morganucodon, Datta & Das (2001) state that Parrington
wrote about material from Wales in 1941. While the Welsh border isn't a million
miles away, people who live in Somerset have strong reasons for believing themselves
to be in England, and Parrington's paper makes no mention of anything Welsh. |
| Reference: | Parrington (1941), On two mammalian teeth from the
Lower Rhaetic, Annal & Magazine of Natural History, 8, p.140-144. |
| Species: | Erythrotherium parringtoni Crompton AW, 1964 |
| Place: | Poken locality; Red Beds, Stromberg Group, Mafeteng & Upper
Elliot Formation and Clarens Formation |
| Country: | Lesotho & South Africa |
| Age: | Hettangian (late) - Sinemurian / Pliensbachian, Lower Jurassic |
| Remarks: |
The lingual (internal) and buccal
(external) cingula are poorly developed in the upper
teeth, whilst wear patterns are similar to the British Morganucodon, (Datta &
Das, 2001).
This is sometimes referred to the Upper Triassic. According to the findings of Lucas &
Hancox, 2000, (p.6), these formations are Jurassic.
Holotype
The holotype is a juvenile, (Kemp 2005, p.146), and the body is much like
Morganucodon as well. |
| Reference: | Crompton (1964), A preliminary description of a new mammal
from the Upper Triassic of South Africa. Zoological Society of London, Proceedings, 142,
p.441-452. |
| Upper Triassic / Lower Jurassic of Karoo,
southern Africa
The following is based upon my reading of Lucas & Hancox, 2000.
The Karoo Basin of southern Africa contains vast amounts of sandstones and mudstones laid
down between the Upper Permian and Lower Jurassic. Various strata are rich in the remains
of land vertebrates, and the fossils attest to seventy million years or so of evolutionary
action. Non-mammalian eucynodonts are known from the
Lower Triassic. Some of their 'primitive' relatives are also found there and, in the upper
reaches of the complex, so are basal mammals. This paper
concentrates on the Upper Triassic Molteno and lower Elliot Formations. As vertebrate
body fossils are rare and restricted to fish in the first mentioned unit, (which is
probably Carnian in age, p.5), I'll make straight for the Elliot.
This Formation is subdivided into lower, middle and upper components. Below is found the
Molteno and above is the Clarens Formation. In the south, the Elliot is up to 500 metres
thick, though it thins as it progresses northwards, and is less than 200 metres in Lesotho.
The lower Elliot contains an assemblage dominated by prosauropods, (especially
Euskelosaurus). Also present are: Aliwalia, a dinosaur of uncertain
affinities; a large but rare chigutisaurid amphibian; a late
traversodont (
Scalenodontoides); and Basutodon, which is perhaps a rauiscuchian. Also
preserved are various footprints. Comparisons suggest this fauna is probably Norian in
age, (p.6).
The middle and upper Elliot fauna is more diverse, and the rock has been termed the
"Massospondylus range zone". Tritylodon is dominant, but there's
also a rare amphibian, (p.7), a turtle, a sphenosuchian and various dinosaurs,
(Massospondylus, a coelurosaur and several ornithischians). Further eucynodonts
include Pachygenelus, Tritheledon and two basal mammals; Megazostrodon
and Erythrotherium. This fauna seems to date from the Lower Jurassic as is the case
for the overlying Clarens Formation, which shares some of the same
taxa.
Further Mesozoic site summaries can be found at Localities.
The Eucynodonts of the Elliot Formation
Non-Mammalian
Traversodontidae:
Scalenodontoides macrodontes;
Tritylodontidae:
Tritylodon longaevus; T. maximus;
Trithelodonta:
Diarthrognathus broomi;
Pachygenelus monus;
Pattsia likhoelensis;
Tritheledon riconoi
Mammals
Erythrotherium parringtoni;
Megazostrodon rudnerae
Fans of Karoo might like to visit:
# The Permian-Triassic Transition: Think global, die
local,
# The Lower - Middle Triassic in the Karoo Basin. |
| Genus: Hallautherium
Clemens WA, 1980
'Hallau beast' |
| Species: | Hallautherium schalchi Clemens WA, 1980 |
| Place: | Hallau, Schaffhausen |
| Country: | Switzerland |
| Age: | Rhaetian, Upper Triassic |
| Remarks: | Butler & Hooker, 2005 (p.205), state this
genus could be a relative of 'haramiyidans'. According
to their position, that'd imply it wouldn't be a morganucodontid. |
| Reference: | Clemens (1980), Rhaeto-Liassic mammals from Switzerland and West
Germany. Zitteliana, 5, p.51-92. |
| Genus: Helvetiodon Clemens
WA, 1980
'Swiss tooth'
Aka: Helveticodon Tatarinov, 1985
Remarks: "Misspelling or attempted correction," (McKenna & Bell, 1997). |
| Species: | Helvetiodon schutzi Clemens, 1980 |
| Place: | Hallau, Schaffhausen |
| Country: | Switzerland |
| Age: | Rhaetian, Upper Triassic |
| Remarks: | |
| Reference: | |
| Genus: Holwellconodon
?Lucas & Hunt, 1990
'Holwell coned tooth' |
| Species: | Holwellconodon problematicus ?Lucas &
Hunt, 1990 |
| Place: | Holwell Quarry, Frome, Somerset |
| Country: | England |
| Age: | Rhaetian, Upper Triassic |
| Remarks: | Could actually be Lower Jurassic. For the
probable authors thanks are due to Vince Ward. The specific name strong suggests
this is also a synonym of Eostrodon parvus. |
| Reference: | |
| Genus: Indotherium
Yadagiri P, 1984
'Indian beast'
Aka: Indozostrodon Datta PM & Das DP, 2001
Remarks: 'Indian beast' has something to do with the beast having lived in ancient
India. Indozostrodon could translate as 'Indian girdled tooth', and was a
reference to purported similarities with Megazostrodon.
Originally, it was referred to the same family. |
| Species: | Indotherium pranhitai Yadagiri P, 1984 |
| Aka: | Indozostrodon simpsoni Datta & Das, 2001 |
| Place: | Kota Formation, Andrah Pradesh |
| Country: | India |
| Age: | ?Toarcian, ?Lower Jurassic |
| Remarks: | The following is based upon my reading of
Yadagiri, 1984. In that he established both this genus and
Trishulotherium. Unfortunately, mistakes render much of the discussion
irrelevant.
The original description is beset with difficulties. The specimen is an upper molar
rather than a lower one, and that throws some terminology out of kilter. To add more
spice, time has outmoded the terms used and, rather than being from a
"symmetrodont", the tooth appears closer to the
morganucodontids. As a consequence, I feel compelled to change the terminology used for
cusps. I'm using A rather than "protoconid", B for "paraconid" and C instead of
"metaconid". A is the main central cusp, B stands to the front of the tooth, and I'll
let you figure out the sort of position occupied by C.
Taking those points into account, the specimen is a reasonably complete cheek tooth
missing part of the rear (p.519). Cusp A is large, broader than tall, and its base is
conjoined with that of a substantial, but smaller cusp C behind. Cusp B is a faintly
distinct bump. Both sides of the crown have well developed
cingula, a characteristic associated with upper molars,
and the buccal one plays host to some small cuspules.
It's a double-rooted molar, with the front one being considerably stronger and larger
than the rear one. That large root has a length of 0.92mm. Compare that with the
height, for example, of the main cusp, which is but 0.25. The latter figure's more like
the depth of the rear root. Both roots taper along their courses.
Hindsight saw fight to make the opening sentence of the discussion section appear
somewhat ironic: "Indotherium does not compare with any known symmetrodonts, except
sharing a few common features." As it's not a "symmetrodont" tooth, and happens to be
an upper rather than a lower...
This was all rather a long time ago, but something strikes me concerning the Acknowledgements'
section of the paper on page 520, and it could be significant. A number of people are
thanked for having provided assistance in various ways, but none of the names seem to
pertain to anybody with an obvious track record in the literature on Mesozoic mammals.
That's not the case for Yadagiri's 1985 description of a further Kota genus,
Nakunodon. Hindsight has treated that work
much more kindly.
Holotypes
GSI SR/PAL/11 is an upper right molar (not a lower left). It's in the collection of
the Geological Survey of India, Southern Region, Hyderabad. The specific name derives
from the River Prahita.
As for the molar formally known as Indozostrodon, the fossil was found five km
west of Yamanapalli. It's known to its fans as GSI Type No. 20795 and resides in the
collection of the Geological Survey of India, Calcutta. The specific name honours
Professor GG Simpson, whose work on triconodonts has been of immense significance.
Additional notes
Prasad, Verma & Parmar, 2006 discussed the status of Indozostrodon (p.102-103),
and came to the conclusion that they couldn't distinguish it from Indotherium.
This upset the genus a great deal. Rather than listening to its anguished screams for
any longer, they stamped it to death. My psalm to that no longer valid taxon has been
copied in here. However, I haven't yet attempted to check what I
wrote on the subject some years ago.
This genus was originally assigned to Kuehneotheriidae.
This present interpretation is based on the findings of Prasad & Manhas (1997), which
concerned a further find. (With thanks to David Marjanovic.)
To add to the fun: "But they also mistook the new tooth for a lower
molar, as Yadagiri (1984) did for the type," (Prasad
& Manhas, 2002). 'They' refers to Prasad & Manhas, 1997. Would it be churlish of me
to mention the following: "Pant Quarry (Early Jurassic), Glamorganshire, England,"
(Prasad & Manhas, 2002). Glamorgan is in Wales. This genus still seems most similar to
the morganucodontids.
According to McKenna & Bell, (1997), this name is "preoccupied by Indotherium
Kretzoi, 1942, a synonym of Aprotodon, a rhinoceros, but a new name has not yet been
proposed." A genus of this name featured on a 20 riels coin in Cambodia. The rhino
sounds more likely than a morganucodontid.
The artist formerly known as Indozostrodon
This presumably requires some re-writing and editing, but that hasn't yet taken
place.
The following is based upon my reading of Datta & Das, 2001.
Improbable as it may sound, my copy has been partly translated in atrocious German and the
page numbers are missing.
In the terminology employed in this paper, Triconodonta
is divided into five families; Morganucodontidae, Triconodontidae, Amphilestidae,
Sinoconodontidae and Megazostrodontidae. This is not the scheme I'm following, but it
explains why the authors refer this genus to Triconodonta.
Remains are not exactly plentiful. They're restricted to one upper right
molar. It's got three main cusps, (ie. triconodont). The one
nearest to the front of the mouth is B, the middle one A and the one nearest the
jaw-cranium joint is C. This is standard enough terminology for triconodont teeth in
general. In this case, A is somewhat set off towards the
lingual (tongue) side and C, which is the smallest main cusp, is twinned with it. A
shelf-like cingulum provides a girdle around the lower
tooth. It's especially well-developed on the buccal surface,
though there's a distinctive interruption in the middle. Seen from the
occlusal view, the crown is vaguely kidney-shaped in
outline. Also preserved are wear facets. These provide information on how the tooth
worked, just as semi-circles worn into old flagstones can indicate the former presence of a
long gone door.
This tooth is double rooted. Its length is about 1.2mm and the width is slightly less than
half of that. Cusps A and C slant jauntily backwards, whilst B is proudly vertical. Those
two are also set at a higher level than B. However, in terms of height A and B are about
equal. The authors are particularly keen on the well-developed, girdling cingula, (plural
of cingulum). These carry several minor cusps.
Wider issues
So what? One of the pleasing aspects of this paper, is the overview it provides of the
differences between the families mentioned within it. In
Morganucodontidae: "the relative height of
the cusps is A > C > B." A's the biggest whilst B's the smallest, and I'm going to
refer to that here as "morganucodontid". The different condition in
Indozostrodon combined with the wear facet patterns exclude this fossil from
inclusion. However, a couple of paragraphs later, with reference to the British
Morganucodon, comes: "The cusps of the upper molars
are of equal size while on the lower molars cusp A > C > B." I suppose
Mammalia has always produced eccentrics. We're all
supposed to have seven neck vertebrae, but nobody
remembered to inform sloths or manatees. The authors also find distinguishing differences
to Dinnetherium, and various amphilestids and triconodontids, (which doesn't mean
the same as triconodontans).
That "morganucodontid" upper molar cusp height pattern is presumably a
basal condition, or is it coincidental that it's also found
in Sinoconodon and Megazostrodon? Perhaps. However, it disqualifies this
tooth from those genera, (A = B > C). Nevertheless, it's Megazostrodon which is
most similar. Its upper molars (especially M3 and M4) are kidney-shaped from above. They
also display strong, girdling cingula and the buccal one has that familiar central
interruption. Cusps A and C are "closely attached".
The roots offer further support for an appropriate placement within Megazostrodontidae.
Sinoconodon has an incomplete division. Morganucodon and Dinnetherium
have complete division, but this begins above the gum level. In Megazostrodon,
Brachyzostrodon (known from lower molars) and Indozostrodon, this division
commences at the gum level. For the reasons mentioned above and further ones, the authors
felt a new genus was necessary. They appear to have been in error on that point. |
| References: | Yadagiri (1984), New symmetrodonts from Kota formation (Early
Jurassic), India. J. Geol. Soc. India, p.514-521. |
| 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. |
| Links:
Coin Lode
http://www.coinmall.com/clode/listsl.htm
No. ML-1400, priced at 45,00($?).
J. of Vert. Paleont., Vol. 21(3), p.528-534, Indozostrodon
http://www.vertpaleo.org/jvp/21-528-534.html
"Remarkable similarity of this new taxon with other
triconodont mammals points to a Pangaean distribution of these early mammals and supports
the thesis that the continents were confluent at least up to the Early Jurassic and
intercontinental migration was taking place," (from the abstract). 'Triconodont' is
sometimes used very broadly. |
| Links:
Enchanted Learning.com
http://www.enchantedlearning.com/subjects/mammals/extinct/Morganucodon.shtml
I like this description. It's very straightforward. Ask a small child for help, if you'd
like to colour the picture in. It'd be best to paint over the ears though, or perhaps
disguise them as vegetation in some way. As David Marjanovic has pointed out, where
evidence is known, it shows that basal mammals didn't have
external ears. Have a look at a convenient duck-billed platypus.
The Natural Canvas
http://www.thenaturalcanvas.com/Mammals/pages/4280.html
From the catalogue of a fossil trader, (nothing to do with me). This is a photo of a rather
well preserved Morganucodon tooth from Wales. If you click on the upwards pointing
arrow, there are various other images.
Digimorph, University of Austin, Morganucodon sp.
http://digimorph.org/specimens/Morganucodon_sp/
And this is a photo of a reasonably well preserved skull from China. |
| Species: | Morganucodon parvus |
| See: | Eozostrodon parvus Parrington FR, 1941 |
| Species: | Morganucodon watsoni Kühne WG, 1949 |
| Aka: | Eozostrodon watsoni |
| Place: | Bridgend quarries, South Glamorgan |
| Country: | Wales |
| Age: | Lower Jurassic |
| Remarks: | The following is based upon my reading of
Kühne, 1949, and thanks are due to the generous supplier and their helpful
photocopier.
Having roamed his way through the Carboniferous limestone deposits of Somerset in
search of fissure fillings dating from later times, the inexhaustible Walter Kühne
followed his educated nose across the Welsh border into Glamorgan, as he knew
similar geological conditions also prevailed in that part of Cymru. And that meant
the chance of finding Mesozoic mammals. "If we can as 'ave 'em frum Zumerzet," the
German paleontologist possibly didn't quite say to himself, "then I tain't as zee
why them theres 'cross the Bristol Channel mayn't as 'ave zum un all." Still, even
if he didn't quite use that dialect, then 'e thunked sumint along them lines, an'
went to take a gander (English paleospeak meaning 'to have a look'). This began in
the summer of 1947 (p.345).
Several promising localities were identified, and one of them provided a couple of
handfuls of a grey rock containing fossils. Kühne found that on a spoil heap, but
came across no signs of any more of this stuff. That's one of the problems with
fissure and channel fillings in commercial quarries. These can be small accumulations
of material, and rock extraction can quickly eradicate them. This well may have
been the cause for the scant supply. On the other hand, quarrying can also expose
new storehouses of fossils as by products. Fossiling is thus something of a lottery,
but tenacious is a word typically descriptive of many paleontologists, and tenacity
can stack the odds in your favour. A decisive factor in searching for vertebrate
fossils can be identifying the right sort of place in which to look. Kühne was a
master of the art.
This small amount of grey stuff was taken back to London for interrogation. It
confessed to possessing indeterminate scraps of bone but nothing of much interest.
However, re-examination with a microscope revealed a pair of broken roots, and a well
preserved tooth was hidden in the matrix. Another visit to the locality, Duchy
Quarry, resulted in a larger amount of such matrix, presumably from a different
exposure. At the time of publication, that hadn't been fully processed. What Kühne
then had no way of knowing, was that this area was gearing up to deliver more
mammal specimens than he would have bothered to hope for. The subsequent avalanche
provided representatives of nigh on every part of Morganucodon's body,
although without managing anything like a single even vaguely articulated
skeleton.
A bit of wider context
Duchy Quarry is on the bank of a valley to the south of Bridgend, and its vertebrate
fossils date from the Lower Jurassic. This was the third location in Western Europe
to provide non-haramiyidan mammal remains from
the Rhaetian-Liassic. The first such find had been relatively recent. Kühne came
up with it himself in 1939 at Holwell Quarry, Somerset.
What with the rude interruption of World War Two, it had been an eventful sort of
decade. The other locality, Hallau in Switzerland, had yielded twenty teeth that
still awaited description. Further sites have since been added in Glamorgan,
Somerset, France, Belgium and Luxembourg.
Drawing a line
At the time, it was usual to think of mammals as
being descended from reptiles called cynodonts.
There's been a conceptual change to this. While mammals are descended form
cynodonts, the inference is that this makes us cynodonts as well, on account of our
ancestry. Furthermore, as cynodonts weren't descendants of the last common ancestor
of all living reptiles, then the lineage that gave rise to mammals weren't reptiles.
That lineage was -and is- Synapsida; the sister
lineage of reptiles (or sauropsids as may be preferred.
I mention this semantic spaghetti as Kühne was uncertain whether this tooth belonged
to a mammal or: "...an animal still technically a reptile." Resolution would've
required having the back of the lower jaw. The uncertainty concerned the jaw-skull
joint. If there'd been an articular-quadrate
joint, then Moganuc could've been given a membership card for Reptilia, as then
generally understood. However, a
dentary-squamosal one would've allowed admittance into the Club Mammalia. When
jaws later became available, it turned out both joints were present, with the
mammalian one being dominant.
While such an issue may have provided conversation material for some bored
researchers, the animal itself wisely couldn't have given a tinker's cuss. And as
for Kühne: "However, I consider it futile to give this point any importance." I
think this point is worth mentioning here as the authors of some paleo-books for
general readers, should they deign to mention Mesozoic mammals at all, can still
lay some weight upon this piece of less-than-trivia.
Evolution's borders are fuzzy blurs; spectra.
To tell the tooth
Kühne didn't have much to go on in 1949. He had one fossil tooth, more matrix to
process and, hopefully, more to find. He made the most of all those resources, and
lots more fossils provided plenty more information on Morganucodon. But
that was for later. In this study, he had only a molar (or
molariform) to describe. With a length of 1.5mm, it wasn't exactly as large as
a sauropod. However, it was in unusually good
condition, and he did have a microscope.
The molar has three main cusps centrally aligned along the middle of the crown. The
central cusp is the largest, and the rearmost comes second (p.346). Guess which
one's the smallest. This is a triconodont-like pattern. As the front cusps on such
teeth are usually smaller, it was clear enough which end was most likely the front.
Further finds have since confirmed that assumption. There was a
cingulum with small cusps on one side of the crown,
and this suggested that was the lingual side of a
lower molar. In known triconodonts, uppers have cingula on both sides.
In contrast to the previously described Eozostrodon,
which has often been seen as synonymous, the tips of the cusps don't tilt back
towards the rear. Furthermore, the middle region of the cingulum differs. These
were reasons to establish a distinct genus (p.348).
Holotype
The type fossil is a lower right postcanine which,
in 1949, was in the collection of Walter Kühne (p.349). It came from fissure
fillings in Duchy Quarry. As for the specific name, let's all say it together with
Sherlock Holmes: "It's elementary, my dear Watson." The Watson meant was Prof. DMS
Watson, and the name was minted: "as a sincere compliment".
Additional remarks
According to Datta & Das, 2001, the upper molars of
morganucodontids have three main cusps. Going from the front of the mouth towards the
jaw-cranium joint, these are termed B, A and C respectively. They give the relative height
of these cusps within the family as being A > C > B. (A's the largest, whilst B's the
smallest. Whilst this applies to the lower molars of the British Morganucodon, they
state that the cusps of the upper molars are of more-or-less equal height and arranged in a
straight line. These teeth also have internal (lingual) and
external (buccal) shelves known as
cingula which house a number of cuspules. The ones on the buccal cingulum are
"very small". The central cuspid of the lower molar (a) occludes with the
lingual side of the upper molar between B and A. This sort of detail leaves characteristic
wear facets.
Walter Kühne was probably the only German paleontologist to spend the Second World War in
Britain, much of it in internment. He collected fossils extensively in Glamorgan and
Somerset.
Some Savage comment
Savage, 1989 (p.5) has the name of the author in brackets. I've
no idea why as it appears with none in the original publication. Of more general
interest, he also reports the area was then subject to a warm to hot climate with
rainy seasons, possibly rather like monsoon conditions, (p.6). "The seasonal
rains would provide nourishment for a wide range of small plants, mostly seed-ferns
and small conifers. These would attract insects, and both plants and insects would
attract mammals." |
| Reference: | Kühne (1949), On a triconodont tooth of a new pattern from a
fissure-filling in South Glamorgan. Proc. of the Zool. Soc. of London, 119, p.345-350.
|
| Bridgend Quarries, Rhaeteo-Liassic,
Glamorgan
The following is based upon my reading of Benton et al, 2005, and thanks are due to
the supplier.
There are three sites (or groups of sites) of (probably) broadly similar age
vaguely centred on the Bristol Channel; the Holwell
Quarries and Windsor Quarry of Somerset and
the Bridgend Quarries in Glamorgan. While there is some faunal overlap between
them, the eucynodonts nevertheless manage to
be surprisingly distinct. Holwell eucynodonts boil down to
'haramiyidans' in the starring role with a few assistants. Windsor Hill is alive
with the sound of music from oodles of
Oligokyphus with no other voices for accompaniment. Glamorgan, meanwhile,
was showing solid support for insectivorous morganucodontids along with fringe votes
for kuehneotheriids. Rather as with
Conservative Party candidates in much of South Wales, haramiyid voters have been
identified as well, but they're very scarce.
The Bridgend Quarries (p.37)
A quartet of Bridgend quarries have contributed mammalian remains and, collectively,
they deserve many congratulations upon their successful efforts. Take a bow
Ewenny Quarry, Duchy Q, Port Alun Q and Pant Q. As with the similarly aged localities
on the English side of the Bristol Channel, the fossils come from the in-fillings of
fissures in the underlying rock. Again, an important pioneering role was performed
by the dynamic Walter Kühne, a German researcher. He struck mammal after being
released from wartime internment and, as that was one of his motivations for coming
to Britain in the first place, his enforced patience (or quite possibly impatience)
on the Isle of Mann received much sought after recompense. Other motivations were
also involved in his emigration to Britain; for example, not being killed by the
Nazis. With Communist tendencies and a Jewish wife, Kühne was immensely unpopular
in some German quarters.
Subsequent excavations in Glamorgan were conducted by Kenneth Kermack & Co from the
University of London and, indeed, the on-going efforts of other researchers. Of
late, these have become more difficult due to an increased use of industrialized
quarrying methods. Even so, the fossil collections continue to grow. An increase
in the number of eucynodont taxa may be relied upon.
This isn't the most adventurous prediction I've ever dared, as I happen to have read
that at least one new species of kuehneotherians are likely to be described in the
not too distant future. Spores of a plant, Hirmeriella, from three of the
quarries mean the dating as Hettangian-Sinemurian seems secure for these
remains.
Taking a brief gander* at the fauna (p.38)
* In the interests of spreading international understanding, 'to take a gander' is
UK slang for 'having a quick look'. It doesn't imply half-inching** a bird
(**stealing).
The most common vertebrate isn't actually a male bird,
as they hadn't then been invented. Nor had female ones. It's a small reptile
named Gephyrosaurus bridensis. Second place, however, is claimed by our own
heroic relative, Morganucodon watsoni. Pant Quarry has dished up some record
of tritylodontids and
'haramiyidans'. In the second instance, the use of the singular would perhaps
be better in keeping with one partial tooth.
In terms of eucynodonts, the Lower Jurassic fossil mines of Glamorgan represent
Morganucodon country. This vast killer, with a skull length that could exceed
2.5 centimetres in some cases, practiced a merciless reign of terror against small,
squiggly things. A fair amount is known about its skeleton, and the sum of this
knowledge is supplemented by broadly similar, more complete critters from elsewhere;
most helpfully Megazostrodon of Lesotho.
Presumably the skeleton of another Glamorgan killer,
Kuehneotherium, was also rather similar. That would explain why no parts
have been recognized for the less common genus. All mammalian skeleton parts habitually
claim to belong to Morganu and, so far, no distinguishing features have been decoded.
Nevertheless, as most jaws are from Morganu, it'd be odd if the same wasn't the case
for limb bones, ribs and so on.
Slaughter in ancient Morgannwg
It was originally thought that the dentition of these two mammals were of potentially
Earth-changing significance. The hunt was on for the ancestors of
placentals and
marsupials, and the molars of Kuehneo looked like
the sort of thing expected. Whereas Morganu had rather blunt cusps arranged in
approximately a straight line along the crown, Kuehneo boasted of taller cusps
organized into a triangular constellation. There are also differences in the molar
roots. They taper for Kuehneo, and that's generally also the case for later
mammals. Morganu roots have a habit of dilating inside the bone, and this has been
compared with a wide-mouthed gun barrel; a blunderbuss. The end is wider than the
stem. That provides for stronger anchorage. As a consequence of the less well held
system favoured by Kuehneo, there's a tendency for those jaws to be found toothless.
Such differences, and more, suggest this pair weren't fierce competitors for
resources. 'Kuehne's beast' presumably murdered with more discrimination, but
doubtlessly with proper enthusiasm for the task at paw. Meat-eating mammals of
this size have high body heating costs, and they have to be suitably murderous.
While such ancient small insectivores wouldn't necessarily have had the fuel
consumption levels required by modern counterparts, eg. shrews, plenty of killing
was surely an important item on the daily agenda.
Further Mesozoic site summaries can be found at Localities.
Meet the eucynodonts of Bridgend quarries,
Glamorgan
(4 genera, 4 species)
Non-mammalian Eucynodontia (1 genus, 1
species)
Tritylodontidae indeterminate.
?Mammalia (1 genus, 1 species)
'Haramiyida' indeterminate
Mammalia (2 genus, 2 species)
Morganucodon watsoni;
Kuehneotherium praecursoris.
Additional kuehneotherians are to be expected. A genus called
Kuehneon was established for a single
tooth but, seeing as it promptly got lost, it's not exactly a useful concept. |
| Species: | Morganucodon oehleri Rigney, 1963 |
| Aka: | Eozostrodon oehleri |
| Place: | Dark Red Beds, Yangcaodi,
Lower Lufeng Formation & |
| Country: | China & Wales |
| Age: | probably Sinemurian, Lower Jurassic |
| Remarks: | Described on the basis of a relatively well
preserved skull which, along with other fossils, was smuggled out of China during the
establishment of the People's Republic.
When named, this was the finest specimen of a pre-Upper Cretaceous mammalian skull in the
world, (Zhang 1984, p.3). It was a relatively large species for the genus. The known
dental formula per side is apparently: (uppers): four premolars
and three molars; (lowers): three and four respectively.
The lower molars have distinctive cingula on the
labial side. (Note: In Table 1 of the translation of Zhang,
1984, the lower postcanine count is given as four and four.) |
| Reference: | Rigney (1963), A specimen of Morganucodon from Yunnan.
Nature 197, 1122. |
| Species: | Morganucodon heikuopengensis (Young CC, 1978) |
| Aka: | Eozostrodon heikuopengensis Young, 1978; M.
heikoupengensis |
| Place: | Dark Red Beds, Lower Lufeng Formation,
Ch'u-Hsiung Yi, Yunnan |
| Country: | China |
| Age: | probably Sinemurian, Lower Jurassic |
| Remarks: | Zhang, 1984 (p.4) reports that a number of skulls
were collected in 1972, and two represent this species. Both came supplied with
mandibles. It doesn't differ much from M. oehleri.
The known tooth count per side is five premolars and three
molars. Other than that, the distinguishments include the
very close proximity of the canine and first premolar; and
the first molar being the tallest, rather than the second.
However, the 'extra' premolar could be an effect of age, aka ontogenetic variation.
Studies by both Mills and Parrington in 1971 "showed that the anterior premolars are
progressively lost in older individuals of M. watsoni", (Luo and Wu 1994, p.263).
The same may apply to this species. |
| Reference: | Young (1978), [New materials of Eozostrodon.] Vert.
Palasiatica v. 16, p.1-3, [Chinese]. |
| Link:
The Berkeley on-line Specimen Catalogue
The Berkeley Catalogue
Several Morganucodon fossils are held in California, including this holotype.
|
| Species: | Morganucodon peyeri Clemens WA, 1980 |
| Place: | Hallau |
| Country: | Switzerland |
| Age: | Rhaetian, Upper Triassic |
| Remarks: |
Based on upper molariform teeth. Datta & Das (2001)
state there's a close resemblance to the British species. The specific name presumably
honours B Peyer, who reported on the Hallau bonebed in 1956. |
| Reference: | Clemens (1980), Rhaeto-Liassic mammals from Switzerland and
West Germany. Zitteliana, 5, p.51-92. |
| Species: | Morganucodon sp. |
| Place: | Kayenta Formation, Arizona |
| Country: | USA |
| Age: | Sinemurian (late) / Pliensbachian (early), Lower Jurassic |
| Remarks: | The following is based upon my reading of
Jenkins et al, 1983, and thanks are due to the supplier.
The cited paper inclides some information on the Kayenta Morganucodon, although
that the main star of the show. Specimens reported consisted of a crushed skull, body
bones and four isolated teeth (p.1233). The molar length
of 1.11mm fits with legths for the genus known from elsewhere, but there are differences
in construction. Upper molars of the Kayenta critter have B cusps that are more strongly
developed than the C ones, and the lingual
cingulum is interrupted in the middle, rather than being
continuous, as is usual for M. watsoni. Cuspules on the
buccal cingulum are larger, and more akin to
Megazostrodon. These differences would probably suffice for a separate
species. However, the available specimens were seen as inadequate for establishing
one. |
| Reference: | |
Seven Phases of Teeth
(Postcanines)
II Basal mammals
The following is derived from and inspired by my reading of Butler & Clements, 2001,
(p.11-12).
In the mouths of Mesozoic mammals premolariform
teeth were simpler than molariform ones. However, it's
probably not the case that the last premolariform tooth of Morganucodon is homologous
to its 'counterpart' in more derived lineages, and the same
applies to the first molariform. Nevertheless, similarities exist for these primitives and
holotherians. Mostly, the last premolariform has a main
cusp which is higher than that of the first molariform, and a less elaborate crown. (This
isn't always so. The p4s of multituberculates were
complex).
There are a couple of mechanical factors to mention. The maximum force is always located
nearest to the muscles at the rear of the jaw. Vertical movement is greater at the front.
The optimal position for crushing and grinding is where the force is strongest. Teeth for
holding and stabbing require more room to work.
Primitive mammals
The basal stage of mammalian
postcanine occlusion was direct contact between uppers and lowers when the jaws closed,
but the teeth lacked specialisations for precision. Newly erupted postcanines didn't occlude
well, and the wear on relatively weak enamel, (proper prismed enamel wasn't then available),
was heavy. Minimal replacement of teeth helps reduce problematic occlusion, whilst not
living very long deals with difficulties caused by dental erosion.
The best known postcanine dentitions of basal mammals have
been supplied by Morganucodon and Dinnetherium, (next section of this
directory). There's clear differentiation between
premolariform and molariform teeth. The crowns of
the latter are multicusped. Most of both have two roots. The wear facets show the effects
of reasonably stable occlusion. The last premolariform was a replacement for a molariform.
However, the dentition was in some ways more reminiscent of non-mammals. A small and perhaps
youthful member of M. oehleri seems to possess an early set of teeth. "The fossil
suggests that the postcanine dentition was replaced at least once prior to initiation of
loss of anterior premolariforms", (p.12). Therians
don't replace molars. These teeth are strictly primary.
The number of premolariforms and molariforms wasn't fixed in all lineages. M. watsoni
has up to five of the latter, M. oehleri four and M. heikuopengensis three.
In M. watsoni, the last molariform appeared late in life. Variation in relative size
could be due to replacement.
A bit more sophisticated
In other relatively basal lines, a juvenile Triconodon
preserves the final premolariform under a deciduous
tooth. In Haldanodon, (Docodonta), milk
molariforms gave way to permanent premolariforms. With
multituberculates, all premolars were diphyodont
except for the specialised p4, (though this doesn't apply to Pauchoffatiidae). The two
molars multis had were both
monophyodont.
An interjection: Who are you calling derived?
The following paragraphs are prompted by Crompton & Luo, 1993 (p.35).
Although early mammals are generally further derived than non-mammalian
eucynodonts, (ie. less like the most recent common
ancestor), this needn't and doesn't apply in every respect. The bodies of all organisms
contain old (and even archaic) features combined with more recent variations and some
novelty. Morganucodontids were blessed with impressive occlusion between upper and lower
teeth. The crowns weren't only properly aligned. The morphology was complementary, so
further food processing advantages accrued. This is derived.
However, the teeth had to be filed down by usage before well-defined wear facets and
cutting edges were in prime form. Totally unworn crowns were not optimally effective.
In this respect, some earlier and contemporary non-mammals were more sophisticated, as the
structure of newly erupted uppers and lowers complemented each other with minimal wear.
This applies to some relatively late traversodontids,
and also to tritylodontids; both herbivorous
groups. The astonishingly advanced occlusion of 225 million year old travies failed to
ensure their future success. Dinosaurs with cheap, disposable teeth conquered and expanded
the niches of middle-sized to large (and ridiculously enormous) plant-eaters.
Go to Phase: I Carnivorous non-mammalian cynodonts,
II Basal mammals,
III Kuehneotheriids (basal Holotheria),
IV Cladotheria,
V Dryolestidae,
VI Amphitheriida and Zatheria,
VII Tribosphenic dentition. |
| Genus: Paikasigudodon
Prasad GVR & Manhas BK, 2002
'Paikasigudem tooth'
Aka: Kotatherium Prasad & Manhas, 1997 |
| Species: | Paikasigudodon yadagirii (Prasad & Manhas, 1997)
Prasad GVR & Manhas BK, 2002 |
| Aka: | Kotatherium yadagirii Prasad & Manhas, 1997 |
| Place: | Kota Formation, Andrah Pradesh |
| Country: | India |
| Age: | ?Middle Jurassic |
| Remarks: |
The generic name is derived from the village of Paikasigudem. The type
specimen, VPL/JU/KM/10, resides in the Palaeontology Laboratory, of Jammu University.
"The tooth is a double rooted, bean-shaped, excellently preserved left upper
molar," (Prasad & Manhas, 2002). The original
description falsely interpreted it as a lower molar. The new diagnosis refers this fossil
to Morganucodontidae instead of Tinodontidae, (
'Symmetrodonta'). |
| References: | Prasad & Manhas (1997), A new symmetrodont mammal from
the Lower Jurassic Kota Formation, Pranhita-Goadavari valley, India. Geobios 30, p.563-572.
|
| Prasad & Manhas (2002), Triconodont mammals from the Jurassic
Kota Formation of India. Geodiversitas 24 (2), p.445-464. |
| Genus: Rostrodon ?Young CC, ?1978 |
| Species: | Rostrodon heikuopengensis ?Young CC, ?1978 |
| Place: | Lufeng |
| Country: | China |
| Age: | Rhaetian-Liassic, Lower Jurassic |
| Remarks: |
In the translation of Zhang, 1984, (see Bibliography), this
name appears in the summarized table immediately before the References, but not in the text.
It’s listed as being based on two skulls, as is Eozostrodon heikuopengensis, (aka
Morganucodon). I can find no confirmation elsewhere. I’m assuming it’s an unusual
spelling of Eozostrodon, rather than a proposed generic name. For certainty, I
think I'd have to learn Chinese and consult Zhang’s original paper and those of Young CC
from 1978. That seems slightly beyond the scope of this project and vastly beyond my
capabilities. |
| Reference: | |
| Genus: Wareolestes Freeman
EF, 1979
'Ware's brigand'
Remarks: The genus is named in honour of Dr Martin Ware, as he contributed much to the
work on the Kirtlington Mammal Bed. The Greek word 'lestes' is often used for meat-eaters
and has various English equivalents. 'Brigand' is specified in this case. |
| Species: | Wareolestes rex Freeman EF, 1979 |
| Place: | Forest Marble, Oxfordshire |
| Country: | England |
| Age: | Bathonian, Middle Jurassic |
| Remarks: | The following is based upon my reading of Freeman,
1979.
When described (p.158), 'Ware's brigand' was known from just a single tooth and, as far as
I'm aware, that paucity hasn't yet been enriched. Nevertheless, it happens to be
impressively large for a morganucodontid lower molar; about
twice the size as the Welsh Morganucodon. If the rest
of the doubtlessly beautiful body followed suit, then this would've been a
black rat-sized
killer with a mean attitude. However, psychologically profiling a murderer from only one
tooth would probably raise objections from any defence lawyer.
Other distinctions?
Size really is the main issue, as the tooth is otherwise much like Morganucodon.
There's a centrally located row of three principle cusps, with the central one being much
the largest. From front to rear these cusps are termed b, a and c. Right at the back is
an additional smaller cusp d. A further accessory cusp, g, is
lingual of a. This is sometimes called a kühneocone. The
buccal side of the crown has a fairly unimpressive
cingulum. There's a lingual cingulum as well (p.160), and that houses three accessory
cusps in all, with the already mentioned g being tallest. Wear and damage could've erased
traces of more.
There was a pair of strong roots, but both have been broken off. Despite being considerably
younger than Morganucodon, the molar shows no particular derivations on the basic
model. For example, triconodonts had main three main
cusps which were more equal in size compared to morganucodontids, and also reduced those
found on the cingulum. Wareolestes shows no hints towards those directions.
Holotype
BMNH 36523 is a near complete lower molar in the collection of the Natural History Museum,
London. Before donating it Freeman used the number FM/K 25. The specific name, rex,
is Latin for 'king' and it has two meanings in this usage. Firstly, the molar is
relatively large compared to many contemporary mammals (length 2.31mm, width 1.24).
Secondly, it alludes to Mr EJ King.
Additional notes
Luo et al 2002, (p.21), rate this as a "questionable genus". |
| Reference: | Freeman EF (1979), A Middle Jurassic Mammal Bed from
Oxfordshire, Palaeontology, 22(1), p.135-166. |
| Other reports:
Habay-la-Vielle, Gaume, Belgium
http://home.pi.be/~nerodj2/Npagehtm/txtvtp2_hb1.htm
Dominique Delsate summarizes a Rhaetian site in Lorraine, (in French). Mammalian and
non-mammalian teeth have been recovered, and the techniques employed are described: take a
couple of hundred kilos of sand and start sieving.
Syren, Luxembourg
Centre de Recherches Lorraines: Dominique Delsate
http://www.multimania.com/crcrl/articles/syrencrl.htm
Morganucodontid teeth have been identified in the Grand Duchy; Rhaetian, Upper Triassic. A
further site in France, Varangéville, (Norian upper-Rhaetian lower).
Peski Quarry, Russia
Acta Palaeontologica Polonica 46(1), Gambaryan PP & Averianov OA
http://www.paleo.pan.pl/acta/acta46-1.htm
A report from 2001 of a morganucodontid femur from the
Bathonian, Middle Jurassic. The site is 100 km southeast of Moscow.
Caturrita Formation, Brazil
Lucas & Heckert 2002, includes mention of "a supposed Erythrotherium-like
mammalian mandible fragment", (p.34). They conclude that this location is Carnian,
though it has previously been seen as slightly younger than that, (Norian). |
A. Basal Mammaliaformes B.
Morganucodontidae C.
Megazostrodontidae and Dinnetherium D. Hadrocodium
| C. MEGAZOSTRODONTIDAE AND DINNETHERIUM |
| Taxon: Megazostrodontidae Gow, 1986
McKenna & Bell (1997) places this family and Dinnetherium within
Docodonta, whilst other authors put more emphasis on
possible affinities with morganucodontids.
Genera: Dinnetherium,
Megazostrodon,
other reports
Time-Line:
Lower Jurassic: Dinnetherium, Megazostrodon |
| Genus: Dinnetherium
Jenkins Jr FA, Crompton A & Downs WR, 1983
Family: Dinnetheriidae? Megazostrodontidae? Gow, 1986
'Dinne beast'
Remarks: Dinne is a Navajo word for the Navajo, and they know well enough what
they're called. |
| Species: | Dinnetherium nezorum Jenkins Jr FA, Crompton A
& Downs WR, 1983 |
| Place: | Kayenta Formation, Arizona |
| Country: | USA |
| Age: | Lower Jurassic |
| Remarks: | The following is based upon my reading of
Jenkins et al, 1983, and thanks are due to the tireless photocopying supplier.
The Kayenta Formation of Arizona outcrops in the Adeii Eechii Cliffs on land belonging to
the Navajo, and it generously agreed to supply fossils from terrestrial
vertebrates of a Lower Jurassic community. This
included mammals and close relatives (p.1233). Previously, sites in Europe, China and
southern Africa had been responsible for providing such critters, and the Kayenta rocks
for it time that somebody started flying the flag of North America. This fauna turned
out to have much in common with localities in distant places which, given the comparative
unity of global landmasses at that time, isn't all too surprising. The fossils mentioned
by Jenkins & Co included a non-mammalian tritylodontid,
a possible 'haramiyidan', a
morganucodontid and members of the single new
taxon they then established; nine specimens of
Dinnetherium. Far duller members of the community included the usual variety of
dinosaurs, crocs, turtles, lizards, pterosaurs and amphibian but, to be frank, who cares
about such rabble?
The interesting animals, the eucynodonts feature
Oligokyphus and
Morganucodon, both of which also dominated the landscapes of Europe and
China.
It's Dinne time
The basic arrangement of main molar cusps is
morganucodontid-like. There's a line of three of them running straight along the
length. The central cusp, however, is as tall as found for
Kuehneotherium. Lower molars interlock with one another by means of a front
cuspule fitting between the rear e and f on the tooth in front. The situation is
similar upstairs, but convention requires the use of capital letters for upper cusps.
Central cusp a occluded between the upper cusps B and A, and this habitual activity
caused a "nearly horizontal, V-shaped facet" on the front of B. Eventually, if the
owner survived for long enough, this dental interaction led to cusp B being smashed to
smithereens. The result of cusp A working against C was the infliction of a vertical
facet on the lower participant.
The lower jaw differs in some measure from both Morganucodon and
Kuehneotherium, and appears to be further derived
than either of them. The lateral ridge of the dentary
has: "a flange-like ventrolateral extension". Furthermore, there's what's termed a
"pseudoangular process". This is a small projection sticking out below approximately
level with the front area of the coronoid process.
Do the chew
The jaw movements required for eating were somewhat different than for many contemporary
mammals. The wear facets mean some measure of rotation was involved. Cusp a was the
first to engage between A and B, but rotation was than required to allow A to inflict
the wear facet on the buccal side of c (p.1234). This system is further derived than
that of, for example, Morganucodon.
At the time this paper was written, there was a tendency to regard Liassic non-haramiyidan
mammals as being either morganucodontids or kuehneotheriids. That reflected the stuff
that had turned up. Dinnetherium served to demonstrate the picture was
unsurprisingly more complex. It fitted into neither family. The authors saw the option
of amphilestid affinities as being
unattractive, although it could have passed a diagnostic exam in that subject. Similarities,
though, appeared to rest upon relatively basal characteristics, and the family had (and
has) an inadequate definition.
Holotype
The type fossil, MNA V3221, is part of a right mandible imprisoned at the Museum of Northern
Arizona, Flagstaff. The specific name honours the Nez family of Gold Spring for their
assistance to researchers.
Additional notes
The genus is known primarily from teeth and jaw
fragments, but some skull material has also been collected. I've read that the animal was
about 10 cm long and weighed perhaps 20-30 grammes. Seeing as it's lower jaw reached a
length of 5 cm, (according to an illustration in Crompton & Luo 1993, p.34), I doubt
this proposed body-length should be taken too literally. I'm inclined to double it. Some
specimens reside in the Museum of Comparative Zoology, Harvard University. I've seen this
genus referred to as a docodont and a morganucodontid. I've also seen it mentioned as
Upper Triassic, but have found nothing to substantiate that.
"In fact, the basic traits of the amphilestid dentition
are already present in the Early Jurassic Dinnetherium", (Rougier et al 2001,
p.19). Amphilestids are a poorly defined grouping often placed within
Triconodonta. The quotation doesn't reflect an
attempt to place this genus within it.
Grown ups only
Crompton & Luo, 1993, (p.34), found: "All the available jaws of Dinnetherium
appear to be from adult individuals (Figs. 4.4. and 4.5). The
postcanine row is differentiated into molars and
premolars. In some of the smaller jaws the anterior
postcanines were replaced, and in older individuals the molars and premolars are
extensively worn. This suggests a diphyodont dentition.
In an older specimen, the second premolar is lost and the
alveolus is plugged with spongy bone, similar to the pattern seen in Morganucodon
and Sinoconodon."
Crompton and Luo continue: "The structure and occlusion of Dinnetherium molars
are similar to those of Morganucodon. The main cusp a of a lower molar occludes
between B and A of an upper molar, as in Morganucodon (Fig. 4.5). The difference is
that in Dinnetherium lower molar cusps b and c are of equal height in unworn crowns,
and are positioned symmetrically on either side of a, whereas in Morganucodon cusp b
is lower than c and closer to a than c. The wear facets on the lower molars of
Dinnetherium are close to vertical, while those on the upper are close to horizontal.
The lower jaw apparently rotated around its horizontal axis during occlusion." The jaw
was capable of a greater range of movements than were possible for Morganucodon.
Similar wear patterns are known from at least some triconodonts.
Cusps
Upper molars: The three main cusps are arranged in a row, with the middle one, (A), being
much larger than B or C. B is more robust than C. They're otherwise broadly similar to the
corresponding teeth in morganucodontids, in that they display large internal and external
(lingual and buccal)
cingula. In contrast to the megazostrodontids, the
buccal cingulum is continuous. That feature is addressed in the entry for
Indotherium. The main cuspid of the lower molar (a), occluded between B and
A on the upper tooth, which produced nearly horizontal, v-shaped embrasures. This could
lead to the virtual obliteration of B in worn specimens. This information is my
interpretation of Datta & Das, 2001. |
| Reference: | Jenkins, Crompton & Downs (1983), Mesozoic mammals from
Arizona. New evidence of mammalian evolution. Science 222, p.1233-1235. |
| Genus: Megazostrodon
Crompton AW & Jenkins Jr FA, 1968
'large girdle tooth'
Family: Megazostrodonidae Gow, 1986 |
| Species: | Megazostrodon rudnerae Crompton & Jenkins,
1968 |
| Place: | Elliot Formation |
| Country: | Lesotho |
| Age: | Hettangian / Sinemurian, Lower Jurassic |
| Remarks: | There's are fairly complete specimen of this
mousey-sized
animal. One source offers a bodylength of 12cm. Judging by the several hundred webpages it
features on, Megazostrodon seems to have many admirers. It's also modelled for a
postage stamp issued by the Republic of Comoros in June 1999.
The Elliot Formation has sometimes been assigned to the Upper Triassic. This is not the
opinion of Lucas & Hancox, 2000, (p.6). |
| Reference: | Crompton & Jenkins (1968), Molar occlusion in Late
Triassic mammals, Biological Review, 43, p.427-458. |
A. Basal Mammaliaformes B.
Morganucodontidae C.
Megazostrodontidae and Dinnetherium D. Hadrocodium
| Genus: Hadrocodium Luo Z-X, Crompton AW & Sun AL,
2001
'larger full head'
Remarks: A tiny critter with a relatively large brain capacity. This is the most mammal-
like known mammaliaform. |
| Species: | Hadrocodium wui Luo Z-X, Crompton AW & Sun AL,
2001 |
| Place: | Lower Lufeng Formation, Yunnan |
| Country: | China |
| Age: | Sinemurian, Lower Jurassic |
| Remarks: | The following is largely based upon my reading of
Luo et al, 2001.
Before preparation, this near-complete skull was mentioned as a juvenile
Morganucodon, in Crompton & Luo, 1993. However,
when all the details were visible, it clearly represented an entirely different, and far
more derived critter.
The skull's 1,2cm long and 0,8cm across at its widest point. In the view of the authors,
it's not a juvenile anything. Despite being tiny, they found it to be an adult, (or
perhaps sub-adult). Scaling based on relationships between body mass and skull size for
extant, diminutive, insect-hungry mammals suggests that this complete Hadro was something
like paper-clip long, (disregarding the tail), and paper-clip heavy, (ca. 2g). The only
smaller extant mammal is a micro-bat from Asia, though the
Etruscan shrew
isn't much larger. Imagine a furry animal sitting comfortably within the bowl of a
teaspoon, and that's about the scale of things.
I ain't nobody's baby
The skull has a number of characteristics associated with adult or subadult
mammals, both ancient and modern, (p.1535). These include
a large diastema between the
canine and first postcanine tooth, as in older
individuals of Morganucodon, Sinoconodon and
Kuehneotherium. Younger specimens of those
animals are blessed with a first premolar which was
subsequently lost without replacement in adults.
Furthermore, the molars of Hadrocodium have wear
facets, and they indicate the teeth had been used for processing food. The skull has a
feature termed: "a fully functioning temporomandibular joint, (TMJ), which only
appears beyond the suckling stage of early growth in extant
monotremes... and therians", (reference numbers
omitted). The dentary also lacks a
Meckelian groove on the inside. That's a
characteristic I carelessly lost during my embryonic career, but this wasn't the case for
the more basal mammals of Yunnan.
A brief interlude for some scepticism
However, other researchers have since pointed to possible 'juvenile' characteristics. From
Meng et al 2003, (p.443): "In our earlier work (Wang et al., 2001) we have questioned
whether the type specimen of Hadrocodium is a postsuckling juvenile. We still consider
it an adequate question. When many potential juvenile features of Hadrocodium, such
as its small size, erupting first upper postcanine tooth, only two molars, a slender
mandible, a proportionately large space between m2 and the
coronoid process, a large promontorium, and a large brain vault, are considered in
combination, the possibility that V8275 is a postsuckling juvenile cannot be unambiguously
excluded."
Back to page 1535, relationships
A comparative analysis of 90 characteristics of skull and teeth suggests Hadro is more
closely related to me than it is with Adelobasileus,
Sinoconodon, morganucodontids and Haldanodon.
Various derived features indicate it's in a sister taxon of a
clade including existing mammals and the extinct
triconodontids
Jaws
A suite of these characters can be found on the mandible. This lacks a postdentary trough,
a medial ridge and a medial concavity on the mandublar angle, which contrasts with the
situation in more basal mammals and nonmammalian cynodonts. These features have to do with
the accommodation of 'extra' bones on the lower jaw which neither Hadrocodium or
myself keep there. These 'extras' include the forerunners of my
malleus and incus. I store
those safely in my ears.
Brains
Hadro received its name because it was unexpectedly brainy for a 195 million year old. The
cranial vault is enlarged. It's actually proportionately wider than for any other Jurassic
mammal presently known, let alone in comparison with its more primitive contemporaries and
predecessors. Partly, this is because the animal was tiny. A brain requires sufficient
mass in order to function, and this means mini-animals typically must devote more body space
for this purpose. I allow my brain about 2.5% of my volume, and it seems satisfied with
the arrangement. Among other extant animals, some tree shrews provide a more generous 3%,
and various small birds flutter above 8%. This doesn't mean they're necessarily that much
more intelligent, although I've never managed to beat a humming bird at chess. A percentage
isn't offered for Hado. (Perhaps one could be obtained by cracking the skull open, but
there's only one specimen.) However, the smallness of the critter isn't sufficient on its
own to account for the size of the brain in this case.
TMJ
The temporomandibular joint is formed by the dentary and
squamosal. It's what we mammals keep our jaws attached to the skull with.
Basal mammals retained a small, primitive joint as well, but
Hadrocodium had dispensed with that. Unless you've had an appalling accident, one
TMJ should be located on each side. If you'd care to place an upwardly pointing finger next
to the front of your ear, then you're near enough to the right location. Draw a line across
the top of your head to the other side, (that might require assistance), and you'll notice
it's a little bit behind the orbits, which is generally (but
not always) the case for mammals. There's space between the two joints which should contain
brain. (If not, then your reading abilities are astonishing in the circumstances.) The
authors discuss some derived characteristics in connection
with the TMJ of Hadro, but I don't feel confident enough to attempt any comments on those.
Nevertheless, the TMJ will be mentioned again below.
Ears (p.1536)
The petrosal has a feature termed the promontorium, and
it houses the cochlea. In this instance, it's proportionately larger than in more basal
mammals. However, this is at least partly probably a reflection of overall bodysize.
Miniaturisation has its limits.
Dentition
The dental formula per side present in this individual is: (uppers): 5
incisors, 1 canine, 2
premolars and 2 molars;
(lowers): 4, 1, 2 and 2 respectively. (This is explicitly stated in References
and Notes, point 15.) This strikes me as being an unusually low number of postcanine
teeth.
The molars are 'triconodont-like' and suggest an inordinate fondness of beetles and other
creepy-crawlies. They're double-rooted and have three main cusps, with the middle one (a
or A according to whether the tooth is lower or upper) being dominant. The lower molars
feature two accessory cuspules.
Incremental Mammalisation
All living mammals share lots of similarities with each other, but these took time to
evolve. We're all endothermic ('warm blooded'), have hair (albeit drastically reduced in
some cases, eg. whales), and began our post-natal lives as milk addicts. All these
characteristics probably pre-date Mammalia. Living mammals,
and no other extant animals, have a TMJ formed by the dentary-squamosal, a lower jaw
consisting of only one bone, three small bones in the ear for processing sound, and many
more things in common besides.
Basal mammals had the same TMJ, but they also possessed a second joint; the
articular-quadrate. The lower jaw was
multi-boned and there was only one ossicle in the ear. Hadrocodium is the earliest
known mammal with only a single jaw joint. Furthermore, the bones of the middle ear were
not attached to the dentary, (p.1537), and the brain vault (and presumably the brain) were
enlarged. This genus extended the clearly documented history of those traits back by 45
million years, although that has much to do with the rarity of suitable specimens. Not
many sites yield anything like complete skulls.
How does an old jaw joint end up in the ear?
This is not presently understood. The process involves a shift of three small bones. The
original angular equates to the ectotympanic ring, the articular has become the
malleus and the quadrate forms the
incus. In the marsupial, Monodephis, that trio ossify
and stop growing before brain development is complete. The continuing growth of the brain
and basicranium are in progress at the same stage as the middle ear bones separate from the
jaw. As Hadrocodium possesses both an expanded brain case and a lower jaw lacking
those bones, it's postulated that brain expansion could provide the driving mechanism for
the shift.
Body mass and customer service
The figure of two grammes in weight is an estimate, but it wasn't plucked out the air. 64
species of lipotyphlans (insectivores) agreed to help out. Among these living mammals
there's a well-established correlation between the length of the skull, (p.1538), and the
mass of the whole body. Two grammes is what would be expected from a twelve millimetre
head. The diminutive stature of Hadrocodium means that the range of sizes among
modern lipotyphlans is quite closely matched in Lower Jurassic Yunnan; two grammes to half
a kilo. As a consortium, the eucynodonts were able
to cater for a wide spectrum of clients. Whether an insect was big or small, there was a
eucynodont available to attack it.
How clever was Hadrocodium?
I don't know, and it's not something the authors discuss. They point out the brain
capacity is relatively large, but offer no considerations upon the animal's ability, when it
comes to tackling the Daily Telegraph crossword. Cleverness isn't simply a matter of
relative size. If it were, then mice and people would be equally good at setting traps for
each other. And nor is it a matter of absolute size. If otherwise, then sperm whales
would probably be unbeatable on quiz shows.
What the authors do provide is Figure 3. This shows a range of extinct and extant mammals.
Brain capacity isn't compared. The comparison offered is the width of the imaginary line
between the two TMJs which is taken up by the brain vault. Among
Sinoconodon, Morganucodon and
Haldanodon, (all more basal critters with
doubly jointed jaws), the brain vault accounts for between 43 and 58% of that width. For
the half dozen in the sample with singly jointed jaws, (Hadro, two extant
monotremes, an extinct
multituberculate, a Cretaceous eutherian and the
Virginia opossum), the range is between 60 and 87%. This genus is just 1% behind the leader,
the duckbilled platypus. To repeat, that doesn't
necessarily reflect brain capacity, relative volume or effectiveness. (Both the multi and
possum would've increased their score markedly by shoving their brains forwards, as they
widen significantly behind the TMJ. However, that would probably have decreased their
intelligence due to severe cases of death.)
Holotype
The holotype, IVPP 8275, lives at the Institute of Vertebrate Paleontology and Paleoanthropology in
Beijing. The specific name honours Dr X-C Wui, who discovered the skull in 1985.
With thanks to Toby White for initially posting the link.
Additional notes
Postdentary trough
Wang et al, 2006 p.195 carries a short pen picture of Hadrocodium. They report
that the original description stated there was no postdentary trough on the lower
jaw. Such features were popular with Lower Jurassic mammals, as they were good places
to store small, 'extra' jaw bones that we no longer keep there. However, Wang & Co
state a trough is present on the internal side of the jaw. If so, then this raises
questions concerning the number of little ossicles catching good vibrations in the
middle ear. I've got three in each of my ears, and two are derived from what were
originally bits of multi-boned jaws. These authors found nothing further indicating
the animal to be a juvenile. |
| Reference: | Luo, Crompton & Sun (2001), A new mammaliaform from the
Early Jurassic and evolution of mammalian characteristics Science 292, p.1535-1546.
|
| 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, September 2001 Last update: 16.9.2009
Ktdykes@arcor.de |
Back to top
| With further thanks due to:
The Society of Vertebrate Paleontology's Bibliography of Fossil Vertebrates (John Damuth)
http://www.bfvol.org/
Yale Peabody Museum, Collection Search (VP)
http://george.peabody.yale.edu/vp/
Zhang Fakui (1984): The Fossil Record of Mesozoic Mammals in China, Vertebrata
PalAsiatica, Vol. XXII No. 1, January 1984, p. 29-38. (Translated by Will Downs in
May, 1986 with minor revisions in 1999.) Courtesy of:
The Polyglot Paleontologist
http://www.uhmc.sunysb.edu/anatomicalsci/paleo/terms.html
Professor Pascal Godefroit, for supplying the interesting and informative papers on
the microvertebrates of Western Europe.
Dr Zhexi Luo, for further papers and kind words of encouragement.
Shirley Sparks, for kindly supplying the paper by Dr Savage.
HitBox Central, and
Animation Library for the animations. |
Bibliography:
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.
Butler PM & Hooker JJ (2005), New teeth of allotherian mammals from the English
Bathonian, including the earliest multituberculates, Acta Palaeontologica Polonica, 50(2),
p.185-207.
Crompton AW & Luo Z (1993), Relationships of the Liassic Mammals Sinconodon
, Morganucodon oehleri and Dinnetherium, p.30-44, (Chapter 4 of)
Mammal Phylogeny--Mesozoic Differentiation, Multituberculates, Monotremes, Early Therians,
and Marsupials, (eds. Szalay S, Novacek MJ & McKenna MC), Springer-Verlag.
Datta PM (2005), Earliest mammal with transversely expanded upper molar from the
Late Triassic (Carnian) Tiki Formation, South Rewa Gondwana Basin, India, Journal of
Vertebrate Paleontology, 25(1), p.200-207.
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.
Freeman EF (1979), A Middle Jurassic Mammal Bed from Oxfordshire, Palaeontology,
22(1), p.135-166.
Godefroit P (1997), Reptilian, therapsid and mammalian teeth from the Upper Triassic
of Varangéville (northeastern France). Sciences de la Terre 67, p83-102.
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, Stuttgart.
Heinrich W-D (1998), Late Jurassic Mammals from Tendaguru, Tanzania, East Africa.
Journal of Mammalian Evolution, Vol5 (4), p.269-290.
molars
Jenkins FA, Crompton AW & Downs WR (1983), Mesozoic mammals from Arizona: New
evidence of mammalian evolution. Science 222, p.1233-1235.
Kühne, WG (1949), On a triconodont tooth of a new pattern from a fissure-filling
in South Glamorgan, Proceedings of the Zoological Society of London, 119,
p.345-350.
molars
Lucas SG & Hancox PJ (2000), Tetrapod-based correlation of the nonmarine Upper
Triassic of Southern Africa. Albertiana 25, p.5-9.
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