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.
Looking for books?
You could visit the
Book Centre and look around.
The best known members of
Metatheria Huxley, 1880 are the
marsupials; koalas, kangaroos and so on. Famously,
this gang hails from Australia, but that's not the limit of their range. Less obtrusive
members occupy South America, (Argentina is home to over twenty living species), and one,
the Virginia opossum, rootles around in North America, even reaching into Canada.
Previously, they were even more widespread. Teeth from Seymour Island attest to
representatives from the Eocene of Antarctica. Fossils of their ancestors are known from
North America, Asia, Europe and Africa. The earliest metatherian known so far comes the
Lower Cretaceous of China, (Sinodelphys). It's a proto-marsupial, rather than a
fully fledged one. Prior to December 2003, the oldest remains had been recovered in North
America, where they became fairly common and diverse during the Upper Cretaceous.
For whatever reasons, unlike the multituberculates,
the North American groups didn't fare well during the Cretaceous-Tertiary transition.
Fossils haven’t come to light beyond the Paleocene, suggesting extinction, perhaps partly
due to pressure of competition from placental
radiations. Slightly more recent remains are known from Europe though, eg. Messel,
Germany, (Lower Eocene, ca. 50 million years ago). Meanwhile, they thrived in the southern
hemisphere. The Virginia opossum is a relatively recent, and very successful immigrant
from Middle America.
Though many people know marsupial females have pouches, (Latin, ‘marsupium’ = 'little bag'),
not all marsupials have learned this. Some don't, eg.
numbats (52 teeth! Good
grief. The photos are rather good). A few even indulge in a rudimentary placenta, (eg.
bandicoots). There’s no evidence to suggest Metatheria was ancestral to
eutherians. We're sister-lines, which emerged from a
common ancestor amongst the therians. This was at some time
before 125 million years ago.
Cifelli, 2004 (p.64) accords Ameridelphia, Szalay, 1982 the rank of Superorder:
"herein I simply expand the concept of "Ameridelphia" to include stem
taxa from the Cretaceous of North America", (p.65).
Living marsupials are generally divided into Ameridelphia and Australidelphia. However,
this becomes problematic when fossil taxa are taken into account. Given that
australidelphians seem to be descendants of American animals, they would logically also be
ameridelphians. (I'm presently following a different approach for the purposes of
paleo-bookkeeping. I'm leaving the relatively early American stem marsupials on this
directory. For later genera, I'm using two cohorts: Alphadelphia, and a more restricted
Ameridelphia. Australidelphia is not directly relevant to this project.)
Mussentuchit fauna, Utah and subsequent radiation
The metatherian component of this fauna has now reached four taxa, (as of July 2004). These
are the geologically oldest marsupials (depending upon definitions) in North America. With
the exception of Kokopellia, the hypoconulid and entoconid on lower
molars are twinned, as is characteristic for marsupials,
(p.62). However, they lack specialisations known from later taxa. Metatherians are both
more numerous and diverse in subsequent North American faunas.
Including Kokopellia, 57 metatherian specimens have been collected at Mussentuchit,
which accounts for 4% of the catalogued total for mammals,
(p.73). The four taxa contribute 17% of the species, (as opposed to 44% for
multituberculates), out of a total of 24.
Well-sampled Upper Cretaceous faunas with fifteen or more species all possess at least six
metatherian taxa, which is equal to or more than the multis. The percentage of marsupial
species in those faunas are, (p.74): Dakota Formation -Cenomanian, 38% of 16 species;
Aquilan Verdigris Coulee Fauna -Santonian-Campanian, 36% of 28 species; Judithian Hill
County Fauna -Campanian, 44% of 16 species; Lancian Formation -Maastrichtian, 41% of 29
species.
It's known that metatherians were established in North America by the start of the Upper
Cretaceous, but where their ancestors were isn't clear. The Trinity fauna of Texas,
(Aptian-Albian), is something like 10-15 million years older than the Mussentuchit assemblage,
and contains a diversity of tribosphenic mammals.
Several have been referred to as marsupials at one time or another, (p.73); eg.
Holoclemensia and
Adinodon. However: "Summing up, none of the tribosphenic mammals now known
from the Trinity Group has unambiguous marsupial
apomorphies." Given the lack of further suitably aged mammal faunas from the
continent, it wouldn't be sensible to assume metatherians were necessarily absent.
However, immigration of ancestors is also a possibility.
The microvertebrates of Mussentuchit have now been so well sampled, that almost all
available mammals have probably been identified, (p.63). The sites which yielded isolated
marsupial teeth were produced by higher-energy deposition, (channels or splay), rather than
floodplains or oxbows, (p.64). |
A. 'Basal' Metatherians B.
Deltatheroida C. Asiadelphia
| Taxon: not that I know of. This section's
presently a bit of a jumble, but it is improving. It contains genuinely basal
metatherians and several other taxa.
Genera: Adelodelphys,
Adinodon, "Adinodus",
Aenigmadelphys, Anchistodelphys,
Apistodon, Arcantiodelphys,
Camptomus, Clemensia (= Holoclemensia),
Dakotadens,
Holoclemensia, Iqualadelphis,
Iugomortiferum, Kokopellia,
Sinbadelphys, Sinodelphys,
other reports
Time-Line:
Upper Cretaceous: Aenigmadelphys, Anchistodelphys, Apistodon,
Arcantiodelphys, Camptomus, Dakotadens, Iqualadelphis,
Iugomortiferum, Madagascar (identity disputed)
Lower Cretaceous: Adelodelphys, Adinodon, "Adinodus",
Holoclemensia, Kokopellia, Sinbadelphys, Sinodelphys |
| Genus: Adinodon Hershkovitz
P, 1995
Remarks: Cifelli, 2004 (p.73) regards this as a nomen dubium; ie. dubious. |
| Species: | Adinodon pattersoni Hershkovitz P, 1995 |
| Place: | Antlers Formation, Texas |
| Country: | USA |
| Age: | Aptian-Albian, Lower Cretaceous |
| Remarks: | This is based on a toothless fragment of
dentary with alveoli which
were originally interpreted as being for four incisors, a
canine, three premolars and
one molar, (Cifelli 2004, p.73). It was referred to
Marsupialia on account of: "a "staggering"
of the incisor series". As well as not being apparent to subsequent studies, this
feature isn't a characteristic of early marsupials.
A second species is indicated by John Alroy. |
| Reference: | Hershkovitz (1995), The staggered marsupial third lower
incisor: hallmark of cohort Didelphimorphia, and description of a new genus and species
with staggered i3 from the Albian (Lower Cretaceous) of Texas. Bonner Zoologische Beiträge,
45, p.153-169. |
| Species: | "Adinodus pattersoni" |
| Place: | |
| Country: | |
| Age: | Cretaceous |
| Remarks: | This is mentioned by Cifelli & Muizon, 1998
(p.535). They consider it a nomen nudum, which means there wasn't a proper description.
Presumably, it's the same material as Adinodon, but I'm a smidgen less than 100%
certain. |
| Reference: | |
| Genus: Adelodelphys
Cifelli RL, 2004
'obscure womb'
Remarks: The genus is obscure in that it's both small and scarce. Delphys is commonly used
for opossum-like marsups. |
| Species: | Adelodelphys muizoni Cifelli RL, 2004 |
| Place: | Cedar Mountain Formation, Utah |
| Country: | USA |
| Age: | Albian-Cenomanian, Lower-Upper Cretaceous |
| Remarks: | The following is based
upon my reading of Cifelli, 2004.
The available supply includes nine upper molars and six
lowers. All four upper positions are represented, (p.65). Material was obtained from
five separate sites. The animal was small and lacked derived
characteristics of Upper Cretaceous taxa. The molar
structure is similar to Kokopellia. However, and in
contrast, the bases of the paracone and metacone are more clearly joined on the upper
molars, (p.66), and there are various other technicalities such as a much deeper
ectoflexus on the M3. In size it compares with
Alphadon perexiguus, (p.67).
The lower molars are mainly known from talonids. These
were relatively wide. Remains of the trigonid suggest it
was low, which is usual for early marsupials. It contrasts to the condition in
Pappotherium and
Holoclemensia, (
Boreosphenida and ?Metatheria respectively).
The holotype, OMNH 25615, studies at Oklahoma. It's an upper right molar, (M1). The
specific name is in recognition of the work of Christian de Muizon. |
| Reference: | Cifelli (2004), Marsupial mammals from the Albian-Cenomanian
(Early-Late Cretaceous Boundary, Utah, Chapter 5 of Bulletin of the American Museum of
Natural History, 285, p.62-79. |
|
Genus: Aenigmadelphys Cifelli RL
& Johanson Z, 1994
'enigmatic uterus'
Aka: Iqualadelphis (partly)
Remarks: 'Delphys' is Greek for 'uterus' and is a frequently used suffix for marsupial
genera. I don't know why.
The remains the genus is based on spent a short while being told they were members
of Iqualadelphis. However, they didn't believe
this suggestion and, subsequently, succeeded in persuading paleontologists
otherwise. |
| Species: | Aenigmadelphys archeri Cifelli RL & Johanson Z, 1994 |
| Place: | Kaiparowits Formation, Utah |
| Country: | USA |
| Age: | Campanian, Upper Cretaceous |
| Remarks: | Some of the following
is based upon my reading of Davis, 2007.
There were difficulties making direct comparisons between specimens impossible, and
that led to the incorrect referral of some fossils to Iqualadelphis for a few
years. They actually represented a previously unknown genus (p.228).
Additional notes
The holotype, a left
molar, and some other specimens are in the Oklahoma
collection. "Aenigmadelphys archeri is considered to be a
marsupial of uncertain suprageneric status by Cifelli and Johanson (1994)",
(Godthelp et al 1999, p.300). |
| Reference: | Cifelli & Johanson (1994), New marsupial from the Upper
Cretaceous of Utah. J. of Vert. Paleont. 14(2), p.292-295. |
| Link:
The Kaiparowits Plateau Wilderness
http://www.suwa.org/WATE/kaiparowits.html
Part of the Southern Utah Wilderness Alliance homepage. This concentrates on the geology,
geography and ecology of the area, rather than the paleontology. The "diverse
raptors" mentioned are birds which catch their prey from above, such as hawks,
falcons, eagles and owls. The Photo Exhibit’s well worth a browse, with some fine views of
the varied and awesome landscape. |
|
Genus: Anchistodelphys Cifelli RL, 1990
|
| Reassigned species: part of A. archibaldi Cifelli, 1990 see
Varalphadon wahweapensis |
| Species: | Anchistodelphys archibaldi Cifelli RL, 1990 |
| Place: | Wahweap Formation, Utah |
| Country: | USA |
| Age: | lower Campanian, Upper Cretaceous |
| Remarks: | Estimated body mass of two
paper clips, 4g. |
| Reference: | Cifelli (1990), Cretaceous mammals of southern Utah, II.
Marsupial and marsupial-like mammals from the Wahweap Formation (early Campanian). Journal
of Vertebrate Paleontology, 10(3), p.320-331. |
| Species: | Anchistodelphys delicatus Cifelli RL, 1990 |
| Place: | Utah |
| Country: | USA |
| Age: | Turonian, Upper Cretaceous |
| Remarks: | Weighed around 7g. |
| Reference: | Cifelli (1990), Cretaceous mammals of southern Utah. III.
Therian mammals from the Turonian (early Late Cretaceous). Journal of Vertebrate
Paleontology, 10(3), p.332-345. |
| Genus: Apistodon
Davis BM, 2007
'untrustworthy tooth'
Aka: Pediomys (partly)
Remarks: The genus was established for fossils previously referred to as
Pediomys exiguus Fox, 1971 (see Davis 2007,
p.226). There are no particular affinities with any of the pedis. The generic name
is a disgraceful slur on its honour. The owner was undoubtedly able to rely upon
its most excellent and faithful tooth! It really can't be blamed for any:
"longstanding incorrect classification." Although remains are presently restricted to
upper molars, these provide strong evidence that the
animals themselves had no problems whatsoever with regards to classification, and
knew precisely with whom to share sexual adventures. It wasn't their faults that
much later paleontologists had difficulties working things out.
Technical quibble
This generic entry is followed by a puzzling "TR>". It's the product of a code
error I haven't managed to track down. |
| Species: | Apistodon exiguus (Fox RC, 1971) Davis BM,
2007 |
| Aka: | Pediomys exiguus Fox RC, 1971 |
| Place: | Milk River Formation, Alberta |
| Country: | Canada |
| Age: | upper Santonian, Upper Cretaceous |
| Remarks: | The following is based upon my reading of
Davis, 2007.
The very limited remains available indicate this was a small critter for a
Cretaceous metatherian, so it probably didn't
prey upon dinosaurs. Insects would've evoked more interest than herds of hadrosaurs.
Some upper molar features are typical of basal North American marsups (p.226). The
paracone is taller than the metacone, and the protocone is fairly weedy. However,
cutting blades are strongly developed and stylar cusp C is large. That feature's
positioned behind the ectoflexus bay. This, and
the maked difference in height between the paracone and metacone, are contrasts to
alphadontid norms. The ectoflexus is also
not as deep. A large stylar cusp B (stylocone), small protocone and wide front lobe
of the stylar shelf serve to rule out once proposed affinities with
pediomyids.
The stylar cusp termed C, by Davis, was originally interpreted as being D. However,
that's less likely as it's found only just behind the ectoflexus. Unlike the
condition for "Pediomys" clemencae (see
Protolambda), this cusp remains in a similar position all along the
upper molar series. Further material would be required in order to divulge more
about the possible relationships of this genus.
Holotype
The type fossil, UALVP 5536, is a small molar studying
at the University of Alberta. |
| References: | Fox (1971), Marsupial mammals from the early Campanian
Milk River Formation, Alberta, Canada In Kermack DM & Kermack KA (eds.) Early
Mammals, Zoological Journal of the Linnean Society (Supplement 1) 50,
p.145-164. |
TR>
| Davis (2007), A revision of "pediomyid" marsupials from the
Late Cretaceous of North America, Acta Palaeontologica Polonica, 52(2),
p.217-256. |
| Genus: Arcantiodelphys
Vullo R, Gheerbrant E, Muizon C de & Néraudeau D, 2009
Remarks: The authors have referred this genus to a newly established clade they've named
Marsupialiformes including (from the abstract, which is all I've read): "... the crown
group Marsupialia and primitive stem lineages more
closely related to Marsupialia than to Deltatheroida." |
| Species: | Arcantiodelphy marchandi Vullo R et al, 2009 |
| Place: | Archingeay-Les Nouillers |
| Country: | France |
| Age: | basal Cenomanian, Upper Cretaceous |
| Remarks: | My information is presently restricted to the
abstract.
This critter is presently known from what are termed tribosphenic teeth discovered in the
southwest of France. These are interpreted as having been donated by a marsupial-like
animal rather than a marsupial as such; crudely put, a sort of forerunner of marsups.
The strongest resemblance was found to be with
Dakotadens. As might be surmised from the name, that was a resident of
Cenomanian North America, Utah to be precise. (Honest! It's named after the Dakota
Formation, not the State.)
Assuming the identification is justified, this is the earliest known trace of marsupial-like
mammals from Europe. |
| Reference: | Vullo et al (2009), The oldest modern therian mammal from
Europe and its bearing on stem marsupial paleobiogeography, Proceedings of the National
Academy of Sciences of the United States of America, (published online before print
November 5, 2009. |
| Genus: Camptomus Marsh OC,
1889
'flexible mouse' |
| Species: | Camptomus amplus Marsh OC, 1889 |
| Place: | Lance Formation, Wyoming |
| Country: | USA |
| Age: | Maastrichtian, Upper Cretaceous |
| Remarks: | A bit of insight is offered by Broom, 1914
(p.125). Camptomus amounted to an assortmet of bones which could've belonged to a
(or several) multituberculates, which were generally thought of as marsupials at the time.
Then again, they might be from something else. Among them is a
scapula and an interclavicle. It may be a pretty name but
it doesn't appear to be a very useful one.
Additional Notes
Several specimens are at the Peabody, Yale. The holotype has enjoyed a very varied career;
Campto amp, then multituberculate indet., followed
by reptile indet. It’s now listed as marsupial
indet.
"Type species based on a scapula. Validity questionable," (McKenna & Bell,
1997). |
| Reference: | |
| Genus: Dakotadens Eaton JG,
1993
Remarks: As can be surmised by the name, possibly, this critter hails from the state of
Utah. |
| Species: | Dakotadens morrowi Eaton JG, 1993 |
| Place: | Dakota Formation, Bryce Canyon, Utah |
| Country: | USA |
| Age: | Cenomanian, Upper Cretaceous |
| Remarks: | The animal weighed about three mice, 75g and
there may be a second species.
According to the NAMFS database, it’s a marsupial, closely related to Iugomorotiferum
and Kokopellia.
In a 2009 publication establishing a European genus named
Arcantiodelphys, Vullo and colleagues accuse Dakotadens of membership
of Marsupialiaformes, also a newly established rank. Their conclusions indicate it's a
marsupial-relative rather than a marsup in a strict sense. |
| Reference: | Eaton (1993), Therian mammals from the Cenomanian (Upper
Cretaceous) Dakota Formation, southwestern Utah. J. of Vertebrate Paleontology 13(1),
p.105-124. |
| Genus: Holoclemensia
Slaughter BH, 1968b
Aka: "Clemensia" ('for Clemens') Slaughter, 1968a |
| Species: | Holoclemensia texana Slaughter BH,
1968b |
| Place: | Paluxy Formation, Texas |
| Country: | USA |
| Age: | Albian, Lower Cretaceous |
| Remarks: |
This genus, which is based on teeth, has been variously interpreted. One placement was
within Holoclemensiidae Aplin & Archer, 1987. Until December 2003, I had it listed
in the boreosphenidan family of
Pappotheriidae. It's not clear whether
pappotheriids are within Theria. However, the findings of
Luo et al, 2003 suggest it's one of the most basal members of
Metatheria, (p.1937).
Given that stem-therians, therians, basal eutherians and
basal metatherians are all reasonably closely related, telling them apart can be taxing,
especially when the available evidence is in short supply. A second species is also
indicated.
Cifelli, 2004, (p.73), casts more doubt on the metatherian affinities. The hypoconulid
and entoconid aren't twinned, (lower molars). The
paracone-metacone proportions aren't marsupial-like, (upper molars). Some similarities
might be homoplasies, (convergence).
The holotype lives in the Shuler Museum in Texas. " Holoclemensiidae"
Archer, 1984 was proposed tentatively," (McKenna & Bell, 1997). Clemensia
Packard, 1864 is a North American moth.
|
| Reference: | Slaughter (1968), Earliest known marsupials, Science, 162,
p.254-255. |
| Genus:
Iqualadelphis Fox RC, 1987
Remarks: The following is based upon my reading of Davis BM, 2007.
At times, this genus has been told to be a member -or ally- of a loosely defined
family called Pediomyidae (p.226). However,
this interpretation isn't supported by Davis. His results indicate it's a relatively
small and basal marsup of presently unclear
affinities.
In contrast to other primitive North American
metatherians, eg. Kokopellia, the parastyle
(stylar cusp A) of upper molars is more lingually
positioned, the front of the stylar shelf is reduced to some degree and, resultantly,
the ectoflexus bay is modestly shallow. In
contrast to alphadontids, the paracone and
metacone are close to one another in terms of height, there's the reduction of the
front lobe of the stylar shelf, and no stylar cusp is found in the C position. Ergo,
it's not an alphadontid. Disqualifications from a strictly defined
Pediomyidae include the presence of a stylocone
(stylar cusp B), the stylar shelf front lobe being too wide and the strength of a
particular ridge, the preparacrista.
Good, so what is it?
Iqualadelphis is a relatively primitive North American marsup. More clarity
is presently elusive. Some features are reminiscent of pediomyids, especially
Leptalestes, but these appear to be
superficial similarities (p.227).
Beyond Alberta
A fossil from southwestern Utah was referred to the genus by Eaton & colleagues in
1999 and, in the opinion of Davis, it probably does belon (p.228). At one time,
remains from the Kaiparowits Formation of the same state were also referred. However,
that was incorrect. Later, these formed the basis of
Aenigmadelphys archeri. |
| Species: | Iqualadelphis lactea Fox RC, 1987 |
| Place: | Upper Milk River Formation, Alberta |
| Country: | Canada |
| Age: | upper Santonian, Upper Cretaceous |
| Remarks: | Holotype
UALVP 22823 is imprisoned at the University of Alberta.
Additional notes
Some subsequently collected material from Utah has been rediagnosed as the type
specimen of Aenigmadelphys archeri. Possible second species. Close relative
of Pediomys, (Alroy) but Davis, 2007 doesn't support that conclusion. |
| Reference: | Fox (1987), An ancestral marsupial and its implications for early marsupial evolution, Occasional Paper Tyrrell Museum, Paleo 3, p.101-105. |
| Genus:
Iugomortiferum Cifelli, 1990
|
| Species: | Iugomortiferum thoringtoni Cifelli, 1990 |
| Place: | Wahweap Formation, Utah |
| Country: | USA |
| Age: | lower Campanian, Upper Cretaceous |
| Remarks: | Body weight of around 20g.
A second, unnamed species is indicated. A number of teeth reside in the OMNH collection,
Oklahoma. |
| Reference: | Cifelli (1990), Cretaceous mammals of southern Utah. II.
Marsupials and marsupial-like mammals from the Wahweap Formation (Early Campanian).
Journal of Vertebrate Paleontology, 10(3), p.320-331. |
| Genus: Kokopellia Cifelli
RL, 1993
'for Kokopelli'
Remarks: Kokopelli is a figure from Hopi mythology. He’s a humpbacked, flute playing
deity, and symbolizes fertility, replenishment, music, dance and mischief; a good-time god.
(With thanks to the
Jowsey Home Zone.) |
| Species: | Kokopellia juddi Cifelli RL, 1993 |
| Place: | Cedar Mountain Formation,
Mussentuchit Formation, Utah & Antlers Formation, Oklahoma |
| Country: | USA |
| Age: | Albian, Lower Cretaceous (or perhaps Upper Cretaceous) |
| Remarks: | The following is largely
based upon my reading of Cifelli, 1993.
The genus is represented by an unusually complete lower jaw, (p.9413). It has the typical
metatherian postcanine
formula of three premolars and four
molars, and several other marsupial-like characters.
As with Sinodelphys, (and unlike further derived
metatherians), the hypoconulid and the entoconid cusps aren't twinned. The hyperconulid is
placed posteriorly rather than on the lingual side.
At least two incisor alveoli
have been preserved, but damage means the incisor count isn't known. The
canine is broken. It's followed by a pair of alveoli for p1
and all the remaining adult teeth. The premolars are conical cusps. The final one, p3, is
tall as in marsupials. The m1 is much smaller than the other molars as with many Upper
Cretaceous marsupials, but unlike most early therians,
including eutherians. "In terms of coronal patterns,
the lower molars much resemble those of the typical Late Cretaceous marsupial Alphadon,
except that the hypoconulid forms a finger-like projection and is more centrally placed at
the back of the talonid, not lingually shifted and twinned
with the entoconid..." (p.9414). As estimated by myself from the drawing, the preserved
specimen is a bit less than 2cm in length. Mouse-sized would seem an appropriate term.
As well as this fossil, the location has yielded further microvertebrate remains. The
mammals include 'symmetrodonts',
triconodonts, tribotherians and
multituberculates
The holotype, OMNH 26361, resides in the collection of the Oklahoma Museum of Natural
History. The specific name honours Jon Judd of Castle Dene, Utah. This is in recognition of
his support for paleontological research and help accorded to fieldworkers.
A second species is indicated, (John Alroy). |
| Reference: | Cifelli (1993), Early Cretaceous mammal from North America and
the evolution of marsupial dental characters. Proceedings of the National Academy of
Science USA, 90, p.9413-9416. |
| Genus: Sinbadelphys
Cifelli RL, 2004
'Sinbad's womb'
Remarks: Stop giggling. The generic name refers to the Head of Sinbad, (rather than other
bits of his body). This is a landmark in the San Rafael Swell, Utah. Delphys is commonly
used for opossum-like marsups. Shouldn't there be two 'd's? |
| Species: | Sinbadelphys schmidti Cifelli RL, 2004 |
| Place: | Cedar Mountain Formation, Utah |
| Country: | USA |
| Age: | Albian-Cenomanian, Lower-Upper Cretaceous |
| Remarks: | The following is based
upon my reading of Cifelli, 2004.
Specimens include thirteen upper molars, (all positions
represented), a deciduous lower
premolar, and fifteen lower molars, (all positions).
These were found at six separate sites, (p.68). This taxon
is small, but not as mini as Adelodelphys. The structure
of the molars is broadly similar. Differences to that genus include less tightly joined
paracones and metacones on the upper molars.
The holotype lives in Oklahoma, (OMNH 26451), and it's named in recognition of the
contribution of David F Schmidt to mammal collections, and the relevant fieldwork. It's a
left upper molar, (M2), minus protocone, (p.67). |
| Reference: | Cifelli (2004), Marsupial mammals from the Albian-Cenomanian
(Early-Late Cretaceous Boundary, Utah, Chapter 5 of Bulletin of the American Museum of
Natural History, 285, p.62-79. |
| Genus: Sinodelphys Luo
Z-X, Ji Q, Wible JR & Yuan C-X, 2003
'Chinese uterus'
Remarks: Another stunner from Liaoning. |
| Species: | Sinodelphys szalayi Luo Z-X, Ji Q, Wible JR
& Yuan C-X, 2003 |
| Place: | Yixian Formation, Liaoning |
| Country: | China |
| Age: | Barremian, Lower Cretaceous |
| Remarks: | This definitely belongs in
a section entitled Basal Metatherians. It's both the earliest
and least derived member yet discovered.
This is based on a near complete skeleton from the most extraordinary Mesozoic fossil field
in the world. Liaoning is famous for its feathery dinosaurs and birds. Less well known
but every bit as astounding are the mammals.
Sinodelphys (Carnegie Museum pages) was a 15cm climber, which weighed about 30g.
As extracted from the linked press release from the Carnegie Museum, Dr Wible said:
"Interestingly, the more primitive mammals of the Yixian feathered dinosaur fauna were
adapted to terrestrial or ground dwelling living. But only the derived
eutherian Eomaia and metatherian Sinodelphys
were scansorial or climbing mammals. This suggests that scansorial adaptations were
important in the divergence of the modern marsupials and placentals."
The authors have no doubts whatsoever that this is a metatherian. Some of the anatomical
features which define that taxon are in the wrists, ankles and front teeth. The construction
of the back teeth show that it was an insectivore. Also preserved are clear impressions
of the fur and other soft body tissue.
Dr Luo provides a concise summary of what this find has done for the fossil record:
"The newly discovered
Sinodelphys extends the duration for the marsupial lineage by 15 million years,
and the earliest record of metatherian skeleton by 50 million years. This new fossil
provided precious, new information about the skeletal anatomy, function and habits of the
earliest metatherians, and sheds light on the evolution of all marsupial mammals."
It's worth bearing in mind that the authors don't refer to this as a marsupial. It's a
metatherian. Metatheria includes both marsupials and their ancestors, which are more
closely related to koalas than pandas.
The following is based upon my understanding of Luo et al, 2003. With thanks to the
donor. For a shorter summary, re-read the above. For both a reliable and a more detailed
account, look at the paper.
Small beginnings
We all start out small, and Metatheria appears to have conformed; somewhere between 25-40g
in bodymass apparently. That's the weight of five to eight teaspoonfuls of water, but
without the spoons.
Sinodelphys is not the first metatherian.
Rather, it's the oldest known representative. However, it does seem close to the root.
The fossil displays many apomorphies, (anatomical
characteristics shared by related organisms), which distinguish it from all known
Cretaceous eutherians (p.1934). It's more
derived than non-crown group
therians, which are those that qualify neither as eutherians
nor metatherians. Meanwhile, in terms of its dental formula, it's less marsupial-like than
critters such as Deltatheridium, which features in the
next section. For one thing, Sinodelphys had one too many
postcanine teeth on the upper jaw, (eight instead of
seven).
Teeth
Many of these marsupial-like features have got thoroughly frightening names, and I'm going
to have to use some. From the same page: "The posterior upper
incisors (I3, I4) are midiolaterally compressed with an
asymmetrical, lanceolate (nearly diamond) outline in lateral view." Each side of the
upper jaws has got four front teeth (incisors -I've got two per side). Seen from the side,
the third and fourth are roughly diamond-shaped. This is a characteristic of
"didelphid-like" marsupials such as American opossums and stem-metatherians,
(where these teeth are known). Neither Cretaceous eutherians nor other therians had teeth
like these.
Unsurprisingly, the incisors are followed by a canine.
Close to this is a premolar (P1), which is angled
forwards. Then there's a gap (diastema) before the P2.
This characteristic is shared with Upper Cretaceous metatherians and later
"didelphid-like" critters, (p.1935). Next are found two further premolars and
four molars, (three on the lower jaw).
Wrists
Wrists contain a number of bones which perform useful functions. They provide flexibility,
stability and stop the fingers falling off. They're quite complex and I'm not going to
mention all the components involved. The lower arm has two main bones. The
ulna attaches to a wrist bone called the
triquetrum. In Asiatherium
and other metatherians, this bone is relatively large. It's joined to a very large
hamate. In these metatherians the other lower arm bone, the
radius, meets a large scaphoid
at the wrist. None of those three wrist bones (triquetrum, hamate or scaphoid) are
enlarged in either Cretaceous eutherians or in more basal mammals. They are in
Sinodelphys. The metatherian (including Sinodelphys) scaphoid is attached
to a relatively small, bean-shaped bone, the trapezium.
Eutherians have a large, rectangular one.
Fingers
If you'd care to wriggle your fingers around, (or indeed those of someone else, but please
ask first), you'll surely notice that most contain three easily recognisable bones. If
you were Sinodelphys, the one joined to the rest of the hand would represent a
metacarpal. We'll call the middle one
phalanx 1, and your claws would be growing on phalanx 2.
Unfortunately, you're a strange mammal instead, but it should nevertheless help give an
appreciation of the rough build of the paw under consideration. (As with some other mammals,
you happen to have an extra phalanx in each finger, and your metacarpals are coyly hidden
in the palm - with thanks to Mickey Mortimer. The same eccentricity applies to your feet).
Among mammals who aren't such aberrations as yourself, phalanx 1 is generally longer than
phalanx 2; often much longer. A table on page 1936 shows some comparisons. In the case of
a fully ground-dwelling marsupial from Central and South America, (Metachirus which
is apparently pouchless and known as a
four-eyed opossum), phalanx 2 is just over 50% as long as its larger companion. In the
committed tree-lover Micoureus,
(woolly mouse opossum -like
myself: "they bite and hiss if cornered."), phalanx 2 is over twice as long. In
Sinodelphys, the ratio is 86%. This is one of the reasons why the authors
concluded this creature was an accomplished climber. There are more features which also
indicate that conclusion, but those two links have provided enough cute photos for the
while.
Feet and all
As regards feet: "Sinodelphys is distinctive from all Cretaceous eutherians
but similar to metatherians in many derived pedal characters." The authors do of
course go into detail, but this argumentation is presently well beyond my limited
understanding, so I think it best to skip to their general summary, (p.1936): "Overall,
Sinodelphys has many derived, marsupial-like features of the skeleton and anterior
dentition, but its molars
and mandible have a mosaic of derived metatherian features
and plesiomorphies shared by
eutherians and taxa outside
the crown Theria."
As should be expected, this basal metatherian lacks some features associated with the
taxon, and maintains some primitive traits (plesiomorphies) of its non-metatherian ancestry.
This is because metatherian evolution is a complex and continuing process, not the result
of one wave of a magic wand. Not all diagnostic characters developed at once, or at the
same rate.
For example, in metatherians generally, (p.1937), lower molars have a couple of exotically
named cusps (entoconid and hypoconulid) which are twinned. In Sinodelphys,
(flicking back to p.1935): "Its lower molars have developed an approximation of the
entoconid to the hypoconulid..." Interestingly, the authors also observe that:
"the entoconid is indistinct or absent..." in some of the generally further
derived deltatheroidans.
Transition
Faced with this highly obliging fossil, the authors wanted to estimate where it fits
within Metatheria, and what information it provides with regard to evolutionary history.
They prepared a series of 380 anatomical pointers, collected data on 84 taxa drawn from
extinct and living mammals and a few non-mammalian
eucynodonts and gave it a vigorous series of runs through a computer, ("...
1000 runs of heuristic search, with unordered multistate characters...", p.1938). The
results suggest that Sinodelphys and a dental taxon, Holoclemensia, are the
most basal known metatherians. The next group to sprout were specimens such as
Deltatheridium. The placement of both those genera within Metatheria has previously
been a matter of some controversy, but this study appears to have resolved the issue. They
also had plenty more to say on subsequent developments, but I think that would go beyond
the scope of this Sinodelphys-centred entry.
Holotype
The species name honours Professor FS Szalay, who is a leading student of mammalian
skeletal evolution. The type fossil's called CAGS00-IG03, and is a resident of the Chinese
Academy of Geological Sciences, Institute of Geology, Beijing. It also includes fragments
of the counterslab, which shows some details not on the main plate. |
| Reference: | Luo, Ji, Wible & Yuan (2003), An Early Cretaceous
tribosphenic mammal and metatherian evolution. Science, 302, p.1934-1940. |
© Z.-X. Luo/Carnegie Museum of Natural History
With many thanks to the Carnegie Museum for allowing the use of this image.
Links:
Sinodelphys szalayi, Carnegie Museum of Natural History
http://www.carnegiemuseums.org/cmnh/research/sinodelphys/index.htm
A reader-friendly introduction to the critter. This also has further links to images of
the fossil.
CMNH - Researches discover the earliest known relative of marsupial mammals
http://www.carnegiemuseums.org/cmnh/news/03-oct-dec/031212sinodelphys.htm
This article is similar but slightly longer. The quotes cited above are drawn from it.
An Early Cretaceous Tribosphenic Mammal and Metatherian Evolution
http://www.carnegiemuseums.org/cmnh/vp/media/Luo-et-al(2003).pdf
The description by Luo et al, 2003 is now freely available on-line in pdf format.
The known Lower Cretaceous mammal fauna of Liaoning, (December 2003):
Eomaia,
Gobiconodon zofiae, Jeholodens,
Maotherium,
Repenomamus,
Sinobaatar,
Sinodelphys (this entry), Zhangheotherium.
What a place! |
| Other reports:
Madagascar
Place: Mahajanga Basin
Age: Maastrichtian, Upper Cretaceous
Remarks: So far, this is the earliest know marsupial fossil from the southern hemisphere.
Or perhaps not. A newer study disputes this diagnosis. In the view of Averianov et al
(2003 -see Bibliography), this "could be referred to a closely related
taxon " of Lainodon, a zhelestid
eutherian of a similar age from Spain. There are
similarities between the fauna of this location, and those of Maastrichtian European
sites.
These authors also mention: "Although marsupials were reported from the Campanian
fauna of the Iberian Peninsula (Antunes et al. 1986), this determination was based on a few
imperfect specimens and is now doubted (Gheerbrant and Astibia 1999). Currently marsupials
are not known from the Late Cretaceous of Europe nor Madagascar."
However, I couldn't help noticing that the fauna listing in the slightly later paper by
Averianov & Archibald 2003, includes cf. Alphadon and cf. Pediomys from
the Campanian of Europe. Both those genera were marsupial (or at least metatherian).
Furthermore, late in 2005, a genus called
Maastrichtidelphys was reported to be loitering in the Masstrichtian rocks near,
er, Maastricht in the Netherlands.
The specimen in question works at the University of Antananarivo, Madagascar, (UA 8699).
Reference: Krause DW (2001), Fossil molar from a Madagascan marsupial. Nature,
vol.412, p.487-498. |
A. 'Basal' Metatherians B.
Deltatheroida C. Asiadelphia
| Taxon: Deltatheroida Kielan-Jaworowska Z,
1975
Most of these critters come from Central Asia. However, given the geographic situation at
the time, it’s not very surprising to learn of a possible American representative, albeit
an even earlier one. Other possible members are Beleutinus and Falepetrus.
The former is presently residing in the 'basal' Eutheria
directory, and was previously also interpreted as a possible Asiatic zalambdalestid.
The latter seems to be an Upper Cretaceous, North American
therian something-or-other.
Doubts have been expressed concerning a relationship between Deltatheriidae & Co with
marsupials. This was partly due to the underived structure of their teeth. However, Luo et
al, 2003 (p.1938) places Deltatheridium unequivocally within Metatheria. Although
towards the base of the taxon, they're more closely related
to marasups than Sinodelphys is.
Delving into taxonomic history, the family of Deltattheridiidae was established by Gregory
& Simpson, 1926. It was originally placed within Insectivora and contained the genera:
Deltatheridium, Deltatheroides and
Hyotheridium, a poorly preserved critter of uncertain affinities, (Wible et al
2004, p.4).
The Gregory & Simpson paper has turned up, and the short summary above is naturally
correct. Those authors observed: "The upper molar teeth are what may be called a
pretritubercular stage of evolution, since the para- and metacones are connate or not
separated from each other and are median in position, in line with the primitive tips of
the premolars, while the so-called "protocones" are internal spurs from the base
of the crown. The lower molars are tritubercular, with shearing paraconid-protoconid
blades and narrow heels" (p.2).
These teeth are strangely primitive and not properly
tribosphenic. That leaves some room for doubt concerning whether deltatheriids
qualify for Metatheria. This wasn't something
considered by Gregory and Simpson, as they called them
placentals with confidence.
In summary
Kemp, 2005 (p.171-173) provides a useful overview. As Mesozoic mammals go, deltatheroidans
are both relatively well known and somewhat difficult to place. This may sound paradoxical,
but it's not their fault. Presently, the most common interpretation sees them as closer
relatives of marsups than
placentals. The original view was the opposite.
The best material has been provided by Deltatheroides
from Mongolia. These animals were kind enough to bequeath skeletons and skull to future
paleontologists. Isolated teeth from North America may also belong to the group, (p.172).
They were fairly large for Mesozoic mammals but not exactly giants. Skull lengths are
about four centimetres. The molars have tall, sharp cusps,
and they suggest the owners were predators capable of seriously beating up small
vertebrates as well as creepy-crawlies.
Shifting loyalties
When discovered in the 1920s, deltatheriids were accused of being placentals, and perhaps
forerunners of post Mesozoic carnivores called creodonts. It was later found out that
their mouths contained three premolars and possibly four
molars per jaw, (p.173), and that points towards marsupials. This interpretation was
strengthened by information on the skeleton. The molars aren't strongly reminiscent of
marsups. Uppers are broad in the stylar region and have small protocones.
Talonids on lowers are too narrow.
Relatives of Skippy the Bush Kangaroo
Nevertheless, the dental differences aren't inconsistent with a
basal position within Metatheria. More complete
and better preserved specimens have provided more similarities. The dental formula is now
known for sure, and it's marsupialish. Per side are found: (uppers): four
incisors, one canine, three
premolars and four molars; (lowers): three, one, four and four repectively. Tooth
replacement was also possibly appropriate. A juvenile individual claims it only ever
replaced its final premolar. (However, that is open to interpretation. For example, Fox
& Naylor, 2006 point out alternative scenarios are also plausible (p.27). The lower
jaw has an inflected angular process. That, along with a couple of details of the
braincase, provides further support.
Size issues
Kielan-Jaworowska et al, 2000 provides a summary on page 601. This includes mention
that order contains "relatively large" mammals for the time of Earth on account of
skull lengths ranging between 4 and 7cm. The largest representative has remained
undescribed for years, and is popularly termed the Guriliin Tsav skull. Quite how
it's managed to avoid formal description is something I can't possibly explain.
Link:
Mikko Haaramo's Deltatheroida
Mikko Haaramo's Deltatheroida
Deltatheroid cladistics at a glance.
Genera: Atokatheridium,
Deltatheridium,
Deltatheroides,
"Deltatheroides" = Sulestes), Deltatherus (= Sulestes),
Khuduklestes, Marsasia (partly = Sulestes),
Oxlestes, Sulestes,
other reports
Time-Line:
Upper Cretaceous: Deltatheridium, Deltatheroides, Oxlestes,
Sulestes, North America, Guriliin Tsav?
Lower Cretaceous: Atokatheridium |
| Genus: Atokatheridium
Kielan-Jaworowska Z & Cifelli RL, 2001
'small beast from Atoka' (Atoka county, eastern Oklahoma) |
| Species: | Atokatheridium boreni Kielan-Jaworowska Z & Cifelli RL, 2001 |
| Place: | Oklahoma |
| Country: | USA |
| Age: | Aptian-Albian, Lower Cretaceous |
| Remarks: | This genus is "based
on an upper molar and a tentatively referred lower molar."
"If a deltatheroidan, the new taxon implies a
significant temporal range extension for the group."
Quotations from the abstract. The species name honours David L Boren, the President of
Oklahoma University. |
| Reference: | Kielan-Jaworowska " Cifelli (2001), Primitive
boreosphenidan mammal (?Deltatheroida) from the Early Cretaceous of Oklahoma. Acta
Palaeontologica Polonica 46(3), p.377-391. |
| Links:
Acta Palaeontologica Polonica 46(3), 2001
http://www.paleo.pan.pl/acta/acta46-3.htm
Included is the abstract.
Campus Connections (Oklahoma University), October 29th, 2001
http://www.ou.edu/connect/campus%20connections/vol7no12.PDF
The tooth suggests this was a proper meat eater. Not satisfied with insects and worms,
Atokatheridium probably set about terrorizing and chewing up vertebrate prey, such
as the dinosaur Deinonychus. (OK, that’s a major exaggeration, though remains are
known from the same site.) In this article, Dr Cifelli enthusiastically observes,
"this animal was a pint-sized black-belt." |
| Genus: Deltatheridium
Gregory WK & Simpson GG, 1926
Family: Deltatheridiidae Gregory & Simpson 1926
'little delta beast'
Remarks: Rougier, Wible & Novacek, 1998 has now arrived (thanks to David N), and
that led to some reorganisation of the notes below.
'Delta' "refers to the triangular cusps on the molars", (with thanks to
Ben Creisler, Dinosaur Mailing List, 18.10.99).
"Described fossils include the dentition, rostral
part of the skull, mandible, and incomplete tarsals",
(Luo et al 2002, p.11). |
| Links:
BBC News, 2.12.1998
http://news.bbc.co.uk/hi/english/sci/tech/newsid_226000/226722.stm
Finds from Ukhaa Tolgod, Mongolia. Michael Novacek highlights the possible marsupial
affinities of the group. Adult and juvenile material was recovered. This link is
reader-friendly and has some nice pics. From the report: "The discovery has allowed
the ancient opossum-like Deltatheridium to be classified firmly as a marsupial."
However, the quotation from Novacek appears less definite: "It's very specialised and
that is the first clear evidence we have of this marsupial-like replacement in these very
weird and ancient creatures." Marsupial-like isn't the same as marsupial. It's a
metatherian.
EXN.ca, Spectacular fossils unlock secrets of ancient mammals, Tamar Simon
http://exn.ca/Stories/1998/12/02/51.asp
The same story seen from the other side of the Atlantic. This report also claims
"the marsupial mystery has been solved," which I'd say is overstating things
somewhat. |
| Species: | Deltatheridium pretrituberculare Gregory WK &
Simpson GG, 1926 |
| Place: | Ukhaa Tolgod ('Brown Hills'), Bayan Zag, Nemegt, Hermiin
Tsav II & Bayan Mandahu? |
| Country: | Mongolia & China? |
| Age: | Campanian-Maastrichtian, Upper Cretaceous |
| Remarks: | Some people might want to skip the first
few paragraphs. They contain some musings on my nearest main library and the
relevance is tenuous.
Efforts to obtain a copy of the paper by Rougier et al, 1998 included what for me is
an unorthodox approach. I went to the main public library in Nuremberg. In
principle I like the idea of libraries but, surprising as it may sound, I very
rarely find myself in one. Rather than scouring their shelves for literature on
Mesozoic mammals and the like, I'm kind of constructing my own specialised
establishment in the attic. Our nearest library is about half-a-mile away in an
academic institution, and it allows -yea, encourages- access by the general public.
However, seeing as most of its visitors are scholars of ten years of age or younger,
its inventory is rather lacking in paleontological obscuriania.
Christmas was approaching, and pressie-buying options in our immediate neighbourhood
are limited. This prompted a bus and train journey of perhaps ten miles into
Nuremberg in 2006 and, while my olfactory abilities are terrible in comparison
with the talents of even a bloodhound with a severe cold, I nevertheless sniffed
out an opportunity to combine shopping with Rougier et al, 1998. From past
experience, I knew the city library stocked Nature. I'd seen boxes of the things
several years earlier. As the city houses half-a-million strangely derived
primates, a municipal subscription to such a renowned publication in the middle of
Europe is none too surprising. Indeed, the widespread reach of Nature is something
that seems to matter. "Good," I thought, "I've no excuse not to acquire a copy of
that work on Deltatheridium."
The vanished Nature
Unfortunately, it turned out that the half-a-million municipality no longer appears
able to find the resources for a city copy of one of the world's two leading science
journals, let alone both. Nature has become too expensive. That's a shame.
However, the article I was after appeared some years before that issue arose, and
they'd surely not go as far as defoliating the archives of such worthwhile leaves;
specifically pages 459-463 of volume 396. The librarian aunty took pity on my
welling tears, and shook her head in sympathy upon returning from the archives with
sad tidings. All back copies had been thrown into a rudderless boat and cast adrift.
They'd gone, nobody knew where, with the departed sad tidings.
I don't know if the availability of Nature in large German public libraries is of
any concern to the powers that be within the journal. I hope some agenda or other
has room for it but, as this hope is spiced with little optimism, it smells rather
forlorn. Vorloren, by the way, is German for 'lost'.
'Small delta beast'
The following is based largely upon my reading of Rougier et al, 1998, and thanks
are due to the supplier.
The affinities of Deltatheridium have been the stuff of differing opinions,
and this was partly due to the not particularly good preservation of available
specimens. At various times this critter's been accused of being a
eutherian, a
metatherian and a plain therian too
basal for either of those groups. Current opinions
suggest a bit more clarity as nobody now associates it with eutherians. New and
better preserved specimens were found hiding in the vertebrate cemetery of Ukhaa
Tolgod in Mongolia, and information from that pair ruled we eutherians out (p.489).
However, while the authors were convinced about metatherian membership (the group
including marsupials), this hasn't been universally accepted. A notable dissident
is Rich Cifelli of Oklahoma, and one objection concerns the
postcanine teeth. While the numbers and, probably, replacement pattern are both
in keeping with metatherians, the teeth themselves don't make much of an effort at
conforming to norms. They lack details generally associated with Cretaceous
metatherians. Then again, should such characteristics have first crystallized within
Metatheria, than basal members could conceivably have lacked twinned entoconids and
hypoconulids, typical cusp proportions, subsequently tell-tale arrangements of stylar
cusps and so on.
The authors had helpful new specimens to work with as well as access to previously
identified fossils. One newling is a partial skull from an adult with lower jaws,
while the second included skull and jaw remains from a kid. Bits of skeletons
were also recovered. A comparison of all known material suggested only a single
species is justifiable. Previously, two subspecies had been recognized, but the
basis of the distinguishing features were found to be artefacts; tricks played by
preservation conditions.
Teeth
The dental formula per side was found to be: (uppers): 4
incisors, 1 canine, 3
premolars and 4 molars; (lowers): 3, 1, 3 and 4
respectively. This differs from previous reports. While that might make it sound
as if early researchers were very poor at counting, they simply didn't have cooperative
specimens providing evidence of the complete dentition. In contrast to the new
adult, none happened to obviously preserve traces of the very small fourth upper
molar. Consequently, it was thought only three occurred per side. It's actually
set to the lingual side of the metacone on M3.
This postcanine count is typical for Cretaceous metatherians, and out of step with
any contemporary eutherians. Furthermore, the largest lower incisor, i2, is described
as being 'staggered'. I willingly confess to not appreciating what that actually
means, but I'm assured this condition applies for a number of metatherian
lineages.
Head
The head was also found guilty of metatherian tendencies. The
premaxilla has a branch running back to the level of the canine's
alveolus. On the lower jaw, a shelf-like angle
deflects inwards in a marsup style, a feature not found in eutherians of
monotremes. Points regarding the brain case are
similar to marsupials and more basal therians, and the
petrosal shares details with corresponding bones referred to metatherians from
the North American Upper Cretaceous.
Tooth replacement
Mammals are meanies when it comes to tooth replacement. Apart from any very
exceptional freaks, we only replace our teeth by natural processes on a maximum of
one occasion. This is in strong contrast to other toothed animals, which are serial
replacers. For example, imagine being bitten in some body part or other -I'll leave
the choice up to you- by a crocodile. You take a quick look at the damage and
notice a tooth got left in there. Now, it'd be a perfectly normal human reaction
to feel sympathy for the suffering of the croc. "Poor thing," you might
comfortingly say, "what a horrible accident you've had." However, such a reaction
wouldn't actually be appropriate. Crocs are used to losing the odd tooth when
eating, and they have new ones constantly appearing from the conveyor belt. A
replacement will be available for the next meal.
We mammals can't even be bothered to replace our molars at all. There's some
evidence indicating replacement of 'molars' in ancient mammalian lineages, but none
that presently dates from beyond the Lower Cretaceous. Our molars are primary
teeth, and that also applies for late erupting wisdom teeth. However, the habits
of we placentals are extravagant in comparison to marsupials. Other than for the
final premolar, with a miserliness beyond that which even Scrooge could've
exhibited, marsups replace no dental positions. Incisors, canines (if present),
anterior premolars and molars are all primary. Just the final premolar receives
relief from a substitute.
The specimen of junior Deltatheridium provides information on eruption
patters and replacement. The first two of the three lower molars are significantly
worn and fully erupted. The canine and p3 are partly erupted. That also applies for
the third molar whereas the fourth remains in a crypt. X-rays, scanning and
dissection failed to reveal any signs of further replacement teeth. This seems to
mean replacement was restricted to only the third premolars, and that condition
otherwise only applies for metatherians (including marsups).
Timing
While replacement appears to be restricted as in marsups, the order of eruption is
somewhat different. For possums (and apparently
Alphadon), p3 arrives roughly in concert with m4 and after the completion
of the canine. For Deltatheridium, p3 is in advance of m3 and well before
m4 (p.462).
Affinities
The authors ran an analysis of 156 morphological characters and 48 taxa. Six of
those were eventually discarded as only single teeth are known. Deltatheroidans
grouped together near the base of Metatheria, and not as members of an ancestral
lineage for later and / or more derived
metatherians; as an off-shoot from the main line which was subsequently put out of
the breeding business. Some years later, a study of the still more basal
Sinodelphys provided further support for that
conclusion but, as stated, agreement isn't universal.
Holotype
The type fossil, AMNH 21705, is a partial skull with lower jaws visiting the American Museum
of Natural History, New York. It was first offered hospitality there in 1925 and has
remained ever since. The specific name reflects the authors' general opinions on the
evolutionary grade of the teeth.
Additional notes
Granger & Simpson were under the false impression they were looking at an early
placental. As the state of preservation was far
from ideal and the material unfamiliar, avoiding mistakes couldn't have been easy.
The formula for the postcanines is now known to
be: three premolars and four
molars (with thanks to Fox & Naylor 2006, p.27 and
various other authors). The original description cites only three molars (p.7). Gregory
& Simpson actually state their designated 'P4' isn't 'molariform' and the lower 'p4'
isn't 'at all molariform'. I'm not certain how those teeth are now notated; presumably P3
and p3. A fourth molar was found on specimens in 1998.
"The skull was apparently quite stout, with a robust and not greatly pronounced snout"
(p.9). In keeping with the short snout is a stubby lower jaw, and this has a wide coronoid
process towards the rear.
The species name (and this isn't specified in the original description): "refers to
the triangular cusps on the molars; pretrituberculare is a neuter-gender Latin-version of
the term 'pretritubercular,' once used to describe a type of
molar tooth not quite at the evolutionary stage of the 'tritubercular' form found in
later mammals." (Further thanks to Ben Creisler, DML, 18.10.99).
Maastrichtian
An unpublished specimen from the later locality of Khaichin-I, Mongolia, has been
provisionally identified as belonging to this species. This is mentioned by
Bolortsetseg M, Minjin C & Geisler J (2006 Abstracts of the Society of Vertebrate
Paleontology, p.44A). The fossil is a partial dentary. If correct, this extends
the chronological range of the critter. |
| Reference: | Gregory WK & Simpson GG (1926), Cretaceous mammal skulls from
Mongolia, American Museum Novitates, 225, p.1-20. |
| Links:
Nature Science Update, They came from Ukhaa Tolgod, Henry Gee
http://www.nature.com/nsu/981210/981210-4.html
An item with a bit more depth than most.
Ology, Ah Ukhaa! AMNH
http://ology.amnh.org/paleontology/gobi/ukhaa_5am.html
A photo album. Paleontologists at work and play in the desert.
Prehistoric Data Files, Deltatheridium
http://www.angellis.net/Web/DFG-mam/Deltatheridium.htm
I’m delighted when Mesozoic mammals break out from the ghetto of the specialist press and
bask in the glory of the mainstream. However, it can also result in some original
interpretations. As I always believe everything I read; Deltatheridium was obviously
a tiny cat-sized creature, which looked rather like a weasel and an opossum. This strange
summary is culled from an assortment of the near 200 websites which feature the genus. In
reality, the adult jaw is about 5cm long, and the probable body length around 20cm.
Compared to an elephant, that’s tiny. In Mesozoic mammalian terms, it’s quite large, though
perhaps more kitten than cat-large.
American Museum of Natural History Archives
http://digitallibrary.amnh.org/dspace/bitstream/2246/3193/1/N0225.pdf
Gregory & Simpson, 1926 is presently freely accessible in pdf format. |
| Species: | Deltatheridium nessovi Averianov AO, 1997 |
| Place: | Grey Mesa locality, Darbasa Formation |
| Country: | Kazakhstan |
| Age: | lower Campanian, Upper Cretaceous |
| Remarks: | "This new Cretaceous fauna is most similar
to that from the Djadokhta Formation in Mongolia," (Averianov, 1997).
Averianov & Archibald 2003, (p.6), contains mention of both D. nessovi and
'Deltatheridium' nessovi. As this is written differently, they are
presumably referring to different specimens. "The systematic position of
'Deltatheridium' nessovi is uncertain; it may actually belong to
Deltatherus, but more dental information is required for this assessment."
That doesn't necessarily apply to the whole species. |
| Reference: | Averianov (1997), New Late Cretaceous mammals of southern
Kazakhstan. Acta Palaeontologica Polonica 42(2), p.243-256. |
| Flaming Cliffs and Brown Hills,
the Upper Cretaceous desert of Mongolia
The following is loosely based upon my reading of Loope, Mason & Dingus, 1999, with
further details from Norrell, Gaffney & Dinus, 1995 (p.194-197). Thanks to DC for
providing the first paper.
Southern Mongolia can boast of several stunningly good locations for Upper Cretaceous
terrestrial fossils. The classic locality was known as Flaming Cliffs when visited by
three expeditions from the American Museum of Natural History in the 1920s. The name is
still used, but it's also often called Nemegt. It would be wrong to say those expeditions
succeeded beyond the wildest dreams of the ogranisers, as the original objective was early
human remains rather than excellently preserved dinosaurs
and some reasonably complete mammalian skulls. At the time, many (white) Westerners
preferred to think human origins lay in Asia rather than Africa, although the available
evidence suggested otherwise. What they actually found didn't feature in any of their
dreams.
Anything but a pic-nic
The three campaigns were conducted under enormously difficult conditions. For one thing,
southern Mongolia was a very long way from New York. Ensuring supplies in this remote
region was a piece of logistical brilliance. As if that weren't enough, there were also
the knock-on effects of the Soviet revolution and subsequent civil war. That left parts of
Mongolia involutarilly hosting bands of anti-Bolshevik militia. Oh, and a newly installed
Bolshevik regime in the capital city of Ulan Baatar, which wasn't exactly pro-US. And
bordering China was disadvantageous as well, what with the collapse of central authority
and civil war there. Did I mention the problematic armed horsemen? Amidst the general
regional chaos, many of the locals were understandably distrustful of strangers and distant
governments, and felt it best to be armed to the teeth. Firing guns was one method of
getting round language difficulties.
Despite looking for the wrong fossils in entirely the wrong place (at a completely
inopportune time), the determination required for these expeditions deserved to be rewarded.
The yield was very rich indeed and no researchers were killed, although bullets whizzed by
on various occassions.
As time goes by...
Mongolia then became a no go area for Western paleontologists. Eventually, Polish
expeditions resumed the fieldwork and enjoyed much success. Subsequent Soviet projects
were less well rewarded. However, by the 1990s, the political landscape had changed.
Scientists from the West were again welcome, and joint projects with Mongolian paleontologists
were on the agenda.
Brown Hills
A full-scale expedition involving the American Museum of Natural History took place in 1992,
and another site was found further south in 1993. This was Ukhaa Tolgod ('Brown Hills').
It's about the same age as Nemegt and (especially in terms of mammals) even richer. This
small locality has produced hundreds of mammalian skulls and some complete skeletons. Loope
et al 1999 mention 20 species of vertebrates and a
thousand skeletons and skulls (and that count was published in 1995).
Mongolia: modern and Cretaceous
Climatic and environmental conditions vary considerably within modern Mongolia, which is
hardly surprising seeing that the country has an area about three times that of France.
Nevertheless, I hope it's not too unfair to describe such a large place as generally fairly
arid uplands. Average rainfall is about 25% that in France. Given its position in the centre
of the largest continent on the planet, far from the nearest ocean, frequent lashings of
rain shouldn't be expected. However, most of the land is semi-arid steppe rather than true
desert. Horses are a national passion and that indicates plenty of grass.
It was central Asiatic upland 75 million years ago as well and, at least around the fossil
mines, even more arid than today. This was a region dominated by sand dunes. These were
driven by the wind and allowed sandstone to form.
Death in the desert
It's been argued that violent winds caused animals to buried by sand, and that explains the
origins of the fossils. Loope and colleagues have their doubts about the scenario. At
Ukhaa Tolgod remains are found next to former dunes, but not in stone of clearly eolian
formation. The matrix of the rock shows no particular structure. Generally, if formed by
wind action, sand would be deposited in layers, as it would arrive at different times with
settling occurring intermittantly. The authors think these unstructured deposits resulted
from sudden events; dune slides.
Who pulled the trigger?
It might sound like a killer beyond suspicion in an arid area, but these investigators
conclude the evidence points the finger at heavy rain. Calculations suggest sudden influxes
of water could've destabilised the upper fifty centimetres of dune surface, and sent vast
weights of sand hurtling down on the leeward side, burying anythig in the wong place at the
wrong time.
The leeside of a large dune isn't usually prone to collapse. Water drainage is good, and
they don't frequent places with lots of rain. There's every reason to think much the same
applied 75 million years ago. While the wildlife has certainly changed, what are now termed
the laws of physics haven't. However, the scenario assumes occasional heavy deluges rather
than normal rates of rain (p.708).
Calcitic zones
The rock from both fossil localities contains cross-strata with plenty of calcite. As no
source for that could be found in the contributing sand, the required calcium presumably
came from the atmosphere, and accumulation rates would've been relatively slow. This
suggests the dunes could have been stable for millennia. Calcitic zones of between five and
ten centimetres are evident at intervals.
These zones are consistent with a generally stable climate (p.710). However, the build up
radically reduced the capacity of dunes to absorb water, in the unlikely event of much
falling from the typically cloudless sky. Mathematical modelling was employed to explore the
possible effects of abnormally heavy storms. Water draining through the fine, surface
sands does little more than make things a bit damp, as it can flow readily. Pressures
begin to build up when it reaches the calcitic zone, as water accumulates more rapidly
than it can drain off to the sides (p.711). If the innudation is generous enough, severe
sandslides are inevitable.
Reality steps in
At least, sandslides happened in the mathematical model. It's perhaps easier to stimulate
a major storm in the middle of a desert, than it is to imagine such a thing happening. But
they can occur. The authors mention a storm which hit Rapid City in South Dakota in 1972,
(although this area wouldn't qualify as desert). 25 centimetres of rain fell in six hours,
and resulted in flooding. The calculations suggest, that a similar downpour in the Mongolian
Upper Cretaceous would have instigated a collapse of the top fifty centimetres of sand.
Further Mesozoic site summaries can be found at Localities.
Meet the mammals
The first group of localities listed here are probably a bit older than Ukhaa Tolgod. All
locations are in Mongolia unless otherwise stated, and the letters following the species
refer to the faunas in which they occur. The source used is Kielan-Jaworowska et al,
2003 p.277.
i. Djadokhta Formation (and equivalents) (11 genera, 14 species)
Locations: Bayan Zag (BZ), Törgrög (T), Bayan Mandahu (BM) - PR China.
Multis (6 genera, 7 species) - Sloanbaatar
mirabilis BZ; Bulganbaatar nemegtbaataroides BZ;
Kamptobaatar kuczynskii BZ;
Djadochtatherium matthewi BZ, T, BM;
Kryptobaatar mandahuensis BM; K. dashzevagi
BM, T; ?Tombaatar sabuli BM.
Therian (1 genus, 1 species) - Hyotheridium dobsoni BZ.
Eutherians (2 genera, 4 species) - Kennalestes
sp. BM; K. gobiensis BZ, T;
Zalambdalestes sp. BM; Z. lechei BZ, T.
Metatherians (including deltatheroidans 2 genera, 2 species) -
Deltatheroides cretacicus BZ;
Deltatheridium pretrituberculare BZ, ?BM.
ii. Ukhaa Tolgod beds (9 genera, 9 species)
Locations: Ukhaa Tolgod.
Multis (6 genera, 6 species) - ?Sloanbaatar
mirabilis; ?Kamptobaatar kuczynskii;
Djadochtatherium matthewi;
Kryptobaatar dashzevagi;
Chulsanbaatar vulgaris;
Tombaatar sabuli.
Eutherians (2 genera, 2 species) -
Zalambdalestes lechei; Ukhaatherium
nessovi.
Metatherians (including deltatheroidans 1 genus, 1 species) -
Deltatheridium pretrituberculare.
|
| Genus: Deltatheroides
Gregory WK & Simpson GG, 1926
'delta beast form'
Family: Deltatheroididae Kielan-Jaworowska & Nessov, 1990
Remarks: "Dr Nesov preferred to spell his name Nessov in English," (McKenna &
Bell, 1997). |
| Species: | Deltatheroides cretacicus Gregory WK &
Simpson GG, 1926 |
| Place: | Bayan Zag |
| Country: | Mongolia |
| Age: | Campanian, Upper Cretaceous |
| Remarks: | The following is based upon my reading of Gregory
& Simpson, 1926.
This genus is broadly similar Deltatheridium in as far
as it's known. The reasons for referring it to a distinct genus concerned the
'premolars', the last of which turned out to be a molar in
both animals. Regardless of that, there are distinctions in these postcanine teeth, and
they seem to be more substantial than variation within a single genus would permit.
Deltatheroides is also a bit more robustly built (p.11).
Holotype
AMNH 21700 is the front of a skull in the collection of the American Museum of Natural
History, New York. The specific name is a reference to the Cretaceous, although the authors
didn't provide a translation.
Additional notes
A second species is indicated. Further material is at the Institute of Paleobiology,
Warsaw. Finds are presently restricted to the one location.
Kielan-Jaworowska et al, 2000 provide some discussing on pages 602-603. Apart from
being somewhat longer, 20-35%, there's no obviously compelling difference from
Deltatheridium. It's unclear as to whether a
separate genus is required, but dealing with the issue is best left to a time when
more specimens are available. |
| Reference: | Gregory & Simpson (1926), Cretaceous mammal skulls from
Mongolia. Am. Museum Novitates, 225, p.1-20. |
| Puzzling Cretaceous insectivores
The following is based upon my reading of Simpson, 1928b, which was a review of then
recently described insect-eaters from Mongolia.
The Asiatic Expeditions of the American Museum of Natural History were rewarded with a
collection of the finest Mesozoic mammals then known, and mammalogists were highly pleased.
The haul of fame included a multituberculate
(Djadochtatherium) and five species of
small insectivores; Deltatheridium pretrituberculare,
Deltatheroides cretacicus, Hyotheridium
dobsoni, Zalambdalestes lechei and
Z. grangeri. All had been described prior to this study, but Simpson felt further
consideration was required concerning the affinities of the insectivores. Previous
authors, including himself, had failed to resolve the issue and he hoped to move matters
forward (p.1). It's now about eighty years later, and the affinities of
zalambdalestids and deltatheriids are still the stuff of discussion and disagreement.
With the benefit of eight decades of hindsight
On page 11 Simpson presents a concise list of seven conclusions, and subsequent studies
and discoveries have shown much to be decidedly off-target. This is likely to happen to
anybody pursuing fresh areas, as following generations of researchers have got unfair
advantages. They've usually got more, better and a wider variety of fossils to refer to;
they've got more literature to consult; new methods of preservation and study may well be
available; somebody's been kind enough to make mistakes previously for their benefit.
The first of these conclusions is correct about zalambdalestids and deltatheriids being:
"...related to diverging groups", but not exactly in the way intended. They're
far more divergent than appreciated. Finds made near the end of the twentieth century
support the placement of the deltas towards the base of
Metatheria, and that makes them closer relatives of
marsupials. What with publishing deadlines and the like, Simpson couldn't have waited
for the 1990s. Besides, there's nothing bad about getting some things wrong for sensible
reasons, as a cake needs baking before the icing can be applied.
Invisible ancestors
Simpson was also faced with a trap set by expectations.
Placental mammals radiated spectacularly in the Paleocene of North America, and there
were no obvious candidates for ancestors known from the local Cretaceous fossil record.
(There's been a modest change; Schowalteria.)
Generally, however, there's still little sign of suitable, North American predecessors.
Unless the Paleocene placentals grew on trees or were delivered by aliens, their ancestors
must've been having sex somewhere. (I've seen it suggested that
Protungulatum did arrive on a spaceship but, as far as I'm aware, trees
haven't previously been cited.)
There was an intriguing and vast empty space in the Cretaceous map of Mammalia; the whole
of Asia. Various authors, with Osborn and Matthew to the fore, pointed out that unknown
space could've been populated by the mysterious ancestors. If so, then when fossils came
to light, basal placentals were to be expected. (In current
terminology, there's usually a distinction drawn between Placentalia and
Eutheria, with the latter being a somewhat broader
concept. A lack of non-placental eutherian fossils meant that distinction would have
been rather pointless in 1928. There's little value in labelling a box, unless you've
got some use for it.)
Bingo
These insectivores were in the right time and place and looked suitable for the role. The
zalams are relatively basal eutherians, perhaps even qualify
for Placentalia, and a hypothesis based on an invasion of North America by Asian hordes is
still viable. In the case of one Upper Cretaceous genus,
Paranyctoides, the earliest fossils have been found is Asia, and later ones show
up in America. Various other vertebrates, including
dinos, indicate faunal exchanges occurred several times.
That doesn't settle the issue, as other scenarios are consistent with the available
evidence. For example, placental radiation could've been underway in the Upper Cretaceous of
North America in areas with poor fossilization conditions. The extensive local record doesn't
provide information on all habitats. Rather, it's but a relatively small survey of particular
parts. The aforementioned Schowalteria attests to taeniodonts in Cretaceous
NAm, and they're regarded as placentals. However, these two scenarios aren't mutually
exclusive. Both immigration and endemic radiation may have contributed ancestors for
Paleocene developments.
Given the hopeful anticipation, an enthusiastic reception for the Mongolian insectivores
was inevitable and, given the relatively poor condition of the teeth, somewhat inaccurate
interpretations were at least probable.
Revision
Gregory and Simpson originally pointed to possible connections of zalams to later,
placental insectivores then called zalambdodonts (p.3), and thus the name. 'Zalambdodont'
refers to a particular form of molar. They did note clear differences. For example, the
Cretaceous teeth have paracones and metacones, which are both more separated and positioned
further on the buccal side of the crown, when compared with
any living insectivores. Arguably more to the point is that the ancient Mongolian skulls
showed no obvious tendencies in a zalambdodont direction. In his reconsidered view, based
mainly on further information concerning the molars, Simpson found closer affinities with
lepticted insectivores more likely, and pushed the zalambdodonts closer to the
deltatheriids.
"The crucial evidence of the molars continues this confusing resemblance to two groups
now widely separate, but points much more definitely toward the erinaceomorphs",
(hedgehogs and relatives). This confusion has much to do with zalams having no close
affinities with either group, despite the resemblances. However, comparative anatomy is
dependant upon having specimens to usefully compare something with.
The skull, jaws and postskeletal elements are discussed (p.4-6). The skull is said to
provide little clarity on affinities: "... beyond strongly confirming reference to the
Insectivora" (p.6). Rather than affinities, resemblances have much to do with being
small mammals with similar lifestyles.
Salt and Pfeffer
A footnote addresses the thoughts of a German researcher named G Pfeffer, who had contested
the referral to Insectivora in 1927. He apparently challenged the interpretation of zalams
as placentals. According to Simpson, the main basis for the objection rested on an
assumption that placentals simply must have first appeared at the start of the Tertiary. If
that's an accurate representation, then Pfeffer's case merited a large pinch of salt. In
the language of the time, Placentalia and Eutheria were synonyms, as far as I'm aware.
Zalambdalestes certainly qualifies as eutherian (as used today).
Deltatheriidae
The remains of Deltatheridium and Deltatheroides
were as broadly similar as the names suggest, but there are a few distinctions. (The
following dental positions are as interpreted in 1928, but problems became apparent.
Deltatheroidans are now known to have three premolars and four molars both up and down.
This is confirmed by Fox and Naylor, 2006.)
According to the 1928 view, Deltatheroides had no P1 upper
premolar (this seems to be generally incorrect); a
single-rooted P2; P3 shorter than 'P4'; and the 'P4' has a slight
lingual heel. ('P4' is presumably M1). With
Deltatheridium you find: a P1; P2 is double-rooted; P3 and 'P4' (presumably M1) are
similar in length; and 'P4' boasts a stronger heel. It also donated more information than
its friend and was better preserved.
Hyotheridium is still poorly known. Its snout was
relatively long and slender, but it neglected to fossilize much else. The actual affinities
are consequently obscure. The only particular links with Deltatheriidae are: it was a
mammal from much the same place and time.
Incorrect affinities
In 1926, Gregory & Simpson falsely accused deltatheriids of being intimately involved
with subsequent placental mammals including some creodonts (p.7). The fossils were none too
pleased as, unlike the paleontologists, they'd met their parents and knew they were
(probably) basal metatherians. Giving birth to placental babies struck them as perverse.
Simpson listened to their enraged squeaks but, although sympathetic, found it hard to
understand their unfamiliar accents. He hadn't heard much Cretaceous Mongolian before and
a translator wasn't available. He assured them they were probably cousins of an Eocene
North American called Didelphodus. The deltatheriids quietened down on hearing
that name, as it sounded like a marsupial. While Didelphodon may have been a
pleasing companion for some, it happened to be another placental.
Blame evolution
Simpson had met North American metatherians from the Cretaceous, and they come equipped with
various helpful characteristics, especially on the molars. For example, a couple of cusps
on the talonid heel of lowers are conveniently twinned
(the entoconid and hypoconulid), while uppers have pleasant rows of extra cusps on the stylar
shelves, which are useful balconies located on the buccal
side. There are other such traits as well and, as a set, they spell out m-e-t-a-t-h-e-r-i-a-n
(marsupial in the terminology of the day). Some of these (such as the twinned talonid
cusps) weren't present on basal metatherian molars, and none of those had been encountered
previously.
Two Eocene placentals, Didelphodus and the poorly known Phenacops, were
singled out as perhaps having 'special affinity' with the Cretaceous deltatheriids, and
Simpson felt confident enough to suggest the former could be part of the family. Subsequent
research strongly indicates otherwise.
Link:
North American Museum of Natural History Archives
http://digitallibrary.amnh.org/dspace/bitstream/2246/3112/1/N0330.pdf
Simpson, 1928b is presently freely accessible in pdf format. |
| Genus: Khuduklestes Nessov LA,
Sigogneau-Russell D & Russell DE, 1994
'Khuduk thief' |
| Species: | 'Khuduklestes bohlini' Nessov LA, Sigogneau-Russell &
Russell, 1994 |
| Place: | Tsondolein-Khuduk |
| Country: | China |
| Age: | medial Cretaceous |
| Remarks: | Finding information on this required patience,
and the result is not exactly exciting. The following came from Averianov & Archibald,
2005 (p.593). The sole fossil presently known is a single piece of spine. As the locality
hasn't been extensively sampled, more material might turn up in the future. |
| Reference: | Nessov et al (1994), A survey of Cretaceous tribosphenic
mammals from Middle Asia (Uzbekistan, Kazakhstan and Tajikistan), of their geological
setting, age and faunal environment, Palaeovertebrata, 23, p.51-92. |
| Genus:
Oxlestes Nessov LA, 1982 |
| Species: | Oxlestes grandis Nessov LA, 1982 |
| Place: | Sheikhdzheili local fauna,
Khodzhakul Formation |
| Country: | Uzbekistan |
| Age: | lower Cenomanian, Upper Cretaceous |
| Remarks: | This is based on a couple
of fused cervical vertebrae, and was originally considered
a deltatheroidan: "but these vertebrae could be referable to the purported zhelestid
Eozhelestes Nessov, 1997, the largest
mammal in the assemblage", (Averianov & Archibald 2003, p.14). Another possibility
is a now larger, unnamed zhelestid from the same
fauna (Averianov & Archibald 2005, p.605). |
| Reference: | Nessov (1982), Drevneyshiye mlekopitayushchiye SSSR. (The
most ancient mammals of the USSR.) Ezheg. Vses. Paleontol. O-va. 25, p.228-242. |
| Genus: Sulestes Nessov LA,
1985
Family: Deltatheridiidae Gregory & Simpson, 1926
Aka: Deltatheroides Nessov, 1993; Deltatherus Nessov, 1997; Marsasia
(partly).
For the synonymy I'm following the findings of Archibald & Averianov, 2005 (p.11 and
16). |
| Species: | Sulestes karakshi Nessov LA, 1985 |
| Aka: | Deltatheroides kizylkumensis Nessov LA, 1993; Deltatherus
kizylkumensis (Nessov 1993); Marsasia aenigma Nessov LA, 1997. |
| Place: | Bissekty Formation,
Dzharakuduk |
| Country: | Uzbekistan |
| Age: | middle-upper Turonian, Upper Cretaceous |
| Remarks: |
A partial, right upper molar has been identified from a
higher level of much the same locality, (the Aitym Formation, upper Turonian - Coniacian),
which could also belong to this genus. It at least qualifies as deltatheriid.
A specimen of Sulestes, (CCMGE 35/12000), may be visited in the collection of
Chernyshev's Central Museum of Geological Exploration, Saint Petersburg. A second species
from Central Asia is possible.
Euthanasia I
Averianov & Archibald, 2003 contains: "There are two deltatheroidans in the
Bissekty Formation, Sulestes karakshi Nessov, 1985 and Deltatherus
kizylkumensis (Nessov, 1993), the latter known by the lower
dentition and an
edentulous maxillary fragment", (p.5-6).
However, with the aid of an increased supply of metatherian specimens from the local fauna,
the same authors concluded only one deltatheroidan species is present. Deltatherus
began its short career as Deltatheroides in 1993, only to be laid to rest as part of
Sulestes.
Euthanasia II
They gave the erstwhile asiadelphian, Marsasia, similar treatment, although some
material was also reassinged to Paranyctoides,
a eutherian. The directory entry for Marsasia read: "We assign Marsasia to
Marsupialia on the basis of the following characters: inflected angular process, shape of
the dentary similar to that in Asiatherium,
postcanine dental formula, inferred from
alveoli for p1-3, m1-4, and structure of m4 more similar
to Cretaceous marsupials than eutherians," (Averianov & Kielan-Jaworowska 1999).
This referral was considered tentative.
Marsasia was based on a few, mainly
edentulous fragments of lower jaw. One preserves a molar (m4), (Kemp 2005, p.198). In
their 2003 paper, (p.15), Averianov and Archibald indicated a second species was present
in the same fauna. That isn't in line with their 2005 study. |
| References: | Nessov (1985), Redkiye kostnyye ryby, nazemnyye yashcheritsy
i mlekopitayushchiye zony limanov i primorskikh nizmennostey mela Kyzylkumov. (Rare bony
fish, terrestrial lizards and mammals from the lagoonal zone of the littoral lowlands of
the Cretaceous of the Kyzylkum.) Ezheg. Vses. Paleontol. O-va. 28, p.199-219. |
| Nessov (1997), Cretaceous Nonmarine Vertebrates of Northern Eurasia.
In, Goloneva LB, Averianov AO (Eds.), (University of St Petersburg, Institute of
Earth Crust, Saint Petersburg, 218pp. (In Russian) |
| Link:
Acta Palaeontologica Polonica 44(1), 1999
http://www.paleo.pan.pl/acta/acta44-1.htm
An abstract concerning a dentary fragment. Averianov & Kielan-Jaworowska (1999).
Marsupials from the Late Cretaceous of Uzbekistan. |
| Other reports:
North America
Reference: Fox RC (1974), Deltatheroides-like mammals from the Upper Cretaceous of
North America. Nature, 249 (5455), p.392, 1 fig.
Remarks: This might refer to material from Lull 2 Quarry of the Maastrichtian Lancian
Formation in Wyoming. Trochu, Alberta is another possibility. Check the paper and let me
know.
Guriliin Tsav, Mongolia
An undescribed skull is known from the Upper Cretaceous site, which has been classed as a
deltatheroidan. "In our opinion, however, it cannot be excluded that the
"Guriliin Tsav skull" belongs to Stagodontidae, a family of Late Cretaceous
marsupials otherwise known from North America", (Kielan-Jaworowska et al 2003, p.276) |
A. 'Basal' Metatherians B.
Deltatheroida C. Asiadelphia
| Taxon: Asiadelphia Trofimov & Szalay,
1993
"Also said to be new in 1994," (McKenna & Bell, 1997).
As yet, a rather poorly known group, (especially by myself). This order is presently
restricted to Asia.
Genera: Asiatherium,
Sailestes, other reports
Time-Line:
Upper Cretaceous: Asiatherium, Sailestes |
| Genus: Asiatherium
Trofimov BA & Szalay SF, 1994
'Asia beast'
Family: Asiatheriidae Trofimov & Szalay, 1994
Remarks: "Nomen nudum in Trofimov & Szalay, 1993 (...) and in Szalay,
1994," (McKenna & Bell, 1997).
Kielan-Jaworowska et al, 2000 provide a concise summary on page 603.
The postcanine dentition meets a suite of norms
for Cretaceous metatherians. There are three premolars and four molars per side,
and the final premolar isn't molariform. The
change from one tooth morphological type to the other is abrupt, and not graduated
as is generally the case for Cretaceous eutherians.
The talonid of lower molars has the hypoconulid and
entoconid cusps appropriately 'twinned'. Elements of the ear architecture are also
in line with marsupials (and their ancestors), and more support comes from various
characters of the skeleton.
In short, this critter seems a good candidate for affinities with the North American
Cretaceous marsupials, but it's too late to be considered as personally responsible
for their origins. The similarities are numerous enough to make parallelism an
improbable explanation for them all. More likely, it's a result of common
descent. |
| Species: | Asiatherium reshetovi Trofimov BA & Szalay SF,
1994 |
| Place: | Üüden Sair |
| Country: | Mongolia |
| Age: | Campanian, Upper Cretaceous |
| Remarks: | The following is largely
based upon my reading of Trofimov & Szalay, 1994.
They authors unequivocally refer to this genus as a
marsupial, (p.12569). Remains include the skull, both
mandibles and most of the postcranial skeleton. For
those who are tempted to think of placentals as being
the bee's knees of mammalian sophistication, and assume that all other lineages are past
their use by dates: "It appears an inescapable conclusion that the first
metatherians had a more derived dental formula (and
probably replacement pattern) than the earliest dental
eutherians, regardless of what specific derivation from a
therian ancestry is contemplated." In these respects I'm still more primitive than
Asiatherium. They also suggest that Asiadelphia and Deltatheroida represented
ancient metatherian lineages. Sinodelphys certainly provides no contradiction.
"Because unequivocally derived attributes of the
protometatherian or protoasiadelphian are nearly impossible to separate at present..."
The proposed order of Asiadelphia came with a "diagnosis", rather than a diagnosis.
Some of the characteristics cited probably predate Metatheria. To the best of my
understanding, these would therefore be of limited diagnostic use. Also established was the
family Asiatheriidae.
Splat
Should there have been lorries trundling around in the Mesozoic, then one of them appears
to have run Asiatherium over. Its crushed skull and sidewards splayed rear legs make
the fossil look something like a road kill victim. Maybe it was hit by a large, speeding
dinosaur. The bodylength of about 7cm, (tail not included), and a skull of about 2cm
suggest a large dino mightn't have been required.
Dental details
The postcanine dental formula is three
premolars and four molars,
which is obligingly metatherian. In contrast to Deltathoida and North American Cretaceous
marsupials, the p3 isn't significantly taller than the m1. The paraconid is only the most
pronounced labial cusp on the m4, (p.12570). As with
Kokopellia, the metaconids of the first three molars are taller than the paraconids,
but there are a number of distinctions in the talonids. Also,
the entoconid and hypoconulid are somewhat more twinned, as is known from
Protalphadon and
Alphadon, but not as in deltatheroidans.
An early bird
Until Sinodelphys came along, this specimen had the earliest known, reasonably
complete metatherian skeleton. "The crushed skull... has been reconstructed and shows,
in many respects, what may be considered primitive therian conditions in additions to a
suite of apomorphies. The
nasal structure contacts the lacrimal structure, and the jugal structure contacts the
glenoid fossa, both being primitive, probably late synapsid traits [see particularly
Sinoconodon...]", (figure and reference
numbers omitted).
As for what kind of lifestyle Asiatherium might have led, page 12571 perhaps provides
a clue: "The derived condition (within Metatheria) of
the distal femur is also characteristic in a number of
terrestrial metatherian lineages such as caenolestids and peramelids." It should be
said that the authors don't speculate upon lifestyle, but they do also mention the then
semi-arid environment, (12572).
Holotype
The type fossil, (PIN) no. 3907, is resident in the Paleonotological Institute of the
Russian Academy of Sciences, Moscow. The species name honours the deceased Yuri V Reshtov,
who was a pioneer of fieldwork in Central Asia, and made important contributions to the
study of early ungulate evolution.
In addition
"As the earliest known putative metatherian known by an associated skeleton (Trofimov
and Szalay 1994). Asiatherium is of further interest because the
dentition is strikingly unlike that of North American,
Cretaceous marsupials (Cifelli and Muizon 1997) and because features of its auditory region
have a bearing on the evolution of characteristics typically associated with Marsupialia
(Szalay and Trofimov 1996)", (Luo et al 2002,p.11). |
| Reference: | Trofimov & Szalay (1994), New Cretaceous marsupial from
Mongolia and the early radiation of Metatheria. Proceedings of the Nat. Acad. of Sci. of
the USA, 91(26), p.12569-12573. |
| Genus: Sailestes Nessov LA,
1982 |
| Species: | Sailestes quadrans Nessov LA, 1982 |
| Place: | Bissekty Formation,
Dzharakuduk |
| Country: | Uzbekistan |
| Age: | middle-upper Turonian, Upper Cretaceous |
| Remarks: | The affinities of this genus aren't completely
clear, but knowledge is restricted to one upper molar. It's
probably an M1. The morphology is fairly reminiscent of
Paranyctoides maleficus, which is a eutherian.
The simplest difference to grasp is that the crown in Sailestes is narrower,
(Archibald & Averianov 2001, p.8). Other differences are also present, and these are
sufficient to have raised uncertainties regarding wider affinities.
The overall morphology and the 'postvallum shear', (p.10), suggest this could be an upper
tooth of Marsasia from the same location. In any case, it's most
likely a metatherian.
Holotype
The holotype, CCMGE 7/11758, is a resident of Chernyshev's Central Museum of Geological
Exploration, Saint Petersburg. This lone tooth has a length of 1.5mm.
As the fauna table in Averianov & Archibald 2003, (p.15), lists this genus as a member
of Asiadelphia, I placed it here. |
| Reference: | Nessov (1982), Drevneyshiye mlekopitayushchiye SSSR. (The
most ancient mammals of the USSR.) Ezheg. Vses. Paleontol. O-va. 25, p.228-243. |
| Other reports:
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| Help:
Should anybody have any further information, I'd be pleased to hear of it.
Regarding references and Bibliography:
I haven't and can't verify all the references, so beware. Traditional papers used in
constructing this page are in the bibliography. If you feel these are too few, then send
some more.
With thanks to all the featured sources.
back to top
Trevor Dykes, January 2002 Latest update: 8.11.2009
ktdykes@arcor.de |
Bibliography:
Archibald JD & Averianov AO (2001), Paranyctoides and allies from the
Late Cretaceous of North America and Asia, Acta Palaeonotologica Polonica, 46 (4), (Proof
Version).
Archibald JD & Averianov AO (2005), Mammalian faunal succession in the Cretaceous
of the Kyzylkum Desert, Journal of Mammalian Evolution, 12 (1/2), p.9-22.
Averianov AO & Archibald JD (2003), Mammals from the Upper Cretaceous Aitym
Formation, Kyzylkum Desert, Uzbekistan. Cretaceous Research 00 (2003), p.1-21.
Averianov AO & Archibald JD (2005), Mammals from the mid-Cretaceous Khodzhakul
Formation, Kyzylkum Desert, Uzbekistan, Cretaceous Research 26, p.593-608.
Averianov AO, Archibald JD & Martin T (2003), Placental nature of the alleged
marsupial from the Cretaceous of Madagascar. Acta Palaeontologica Polnica 48(1),
p.149-151.
Broom R (1914), On the structure and affinities of Multituberculata, Bulletin of the
American Museum of Natural History, 33(8), p.115-134.
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marsupial dental characters. Proceedings of the National Academy of Science USA, 90,
p.9413-9416.
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(Albian-Cenomanian) Cedar Mountain Formation of Utah. Journal of Mammalian Evolution, 6 (3),
p.247-270.
Cifelli RL (2001), Early Mammal Radiations, Journal of Paleontology, vol 75 (6),
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paper yet!)
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