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.
This sub-directory concerns
Crown-group Mammalia, which includes the groups above along with the descendants of
some of the critters involved; Metatheria (marsupials
plus immediate relatives) and Eutheria (placentals plus
immediate relatives). That’s kangaroos & Co and us lot, should anyone be wondering.
This crown-group is defined as the most recent common ancestor of the existing mammalian
lines, (Metatheria, Eutheria and Monotremata -aka
egg-laying platys and echidnas), and all it’s descendants. It’s possible that parts of the
somewhat messy Triconodonta gang might also fall
within this definition, and the multituberculates.
The strength of the case for including both these groups seems to be increasing, so I've
now decided to fall into line with it.
Presently, I’m largely basing the layout of these directories upon:
http://epp.eps.nagoya-u.ac.jp/~seicoro/bio/mammalia.html
I don’t yet know who the author of this Japanese page is, but it’s an impressive piece of
work. However, I have altered some positions according to my own whims and fancies, (and
possible misunderstandings), and added in a few other taxa.
Other reports: Ichnofossils
Colorado, USA
A mammalian ichnogenus has recently been described. This refers to fossilized footprints.
Schadipes crypticus Lockley & Foster, 2003 comes from the Upper Cretaceous
(Campanian-Maastrichtian). Precisely what sort of mammal was wandering about with dinos
and possibly a beetle isn't something I know. (With thanks to Jose Ignacio Ruiz-Omeñaca for
posting notice of the publication on the DML, (17.3.2004). The name translates as Schad's
cryptic foot. It honours Professor Wolfgang Schad for his work on mammals. The specific
name is a reference to the 'hidden location'.
Reference: Lockley M & Foster J, (2003), Late cretaceous mammal tracks from
North America, Ichnos, 10, p.269-276.
Link
UCD's Lockley finds prehistoric mammal tracks
http://newmedia.colorado.edu/silverandgold/messages/3334.html
A brief report on critters doing the rounds at Fossil Trace Golf Course. The Maryland
tracks mentioned are perhaps metatherian, but they've not yet been described.
The following is based upon my reading of Lockley & Foster, 2003.
Scampering with dinosaurs
While working through an I-Spy book about
ten years ago, I was confronted with the challenge of spotting three different kinds of
footprint at, or near, the seaside. My wife had no option but to allow me five points
each for: seagull, human and iguanodontid. The preservation of any particular 140 million
year old footprint is highly improbable. However, many animals do much walking, and such
trace fossils (ichnofossils) are common in some places; for example, in the Purbeck Hills
on the southern coast of England. Such signs of former life can withstand hundreds of
millions of years.
The study by Lockley and Foster is based upon much more recent prints dating back a meagre
70 million years, (give or take a bit). These were made primarily by mammals in Upper
Cretaceous Colorado, (Campanian - Maastrichtian). Two sites are involved, and the tracks
have resulted in the establishment of Schdipes, (p.269). They resemble prints
produced by some modern rodents. However, no body fossils of such animals are known from
the Mesozoic. As the dominant mammals of North America were
multituberculates and
metatherians, those groups provide the most likely
culprits.
From western Colorado
MWC 2226 is a slab of sandstone from the Mesaverde Group, and this is the oldest specimen
involved. It's got maximum sizes of 60 x 50cm and its finder, Dan Chaney, donated it to
the Museum of Western Colorado. About forty tracks are at least partially preserved. All
are mammalian except for one contributed by a small bird. (As there are no indications of
any crutches, I doubt it was one-legged.) For the record, it's about 3.5 x 3cm, (length
and width). The mammalian paws were only around 1.5cm long, and the toe build recorded is
consistent with the rear feet of various mammals; some
eutherians, multis, triconodonts and
metatherians, (p.270). These have been referred to Schdipes sp., (p.271).
Also visible are the impressions caused by rain drops and plants, (p.274). Tracks are
absent where the rain drops occur, so the animals might've been scurrying in a sheltered
area. The bird print looks more weathered, which suggests it was left a bit earlier.
From eastern Colorado
CU-MWC 220.28 and 220.33 are in the University of Colorado-MWC joint collection at Denver.
These tracks, (from the Fossil Trace Golf Course), are less numerous but larger, (2cm or
so). The second mentioned is the holotype of Schadipes and the species ichnogen,
(p.270).
220.28 shows a trackway of six impressions which were previously tentatively referred to a
lizard. This was found by Dr Joanna Wright, and has bow been assigned to this mammal.
It's from a layer about twenty metres lower than the holotype, (p.271). There are traces
of a seventh print but, as the foot involved was smaller, this can't have been contributed
by the same individual. The step length shown by rear paws averages nearly 17.5cm, (stride
length is about double that) and calculations suggest a speed approaching 13kmph, (p.273).
Holotype and generic comments
220.33 shows five partial tracks which may be parts of one series, (p.270). They're spaced
about 12cm apart, and this was found by MG Lockley. The fifth impression is obscured as a
larger animal trod on it. The specimen is a rubber-mould taken during fieldwork, (p.271).
The middle toes (II - IV) are broadly similar in length, while the other two are shorter
and diagonally directed, (when shown).
One of the points demonstrating these are mammalian tracks may be viewed on your hands and
feet, (unless you've been unlucky and / or careless). A quick look will reveal your thumb
(digit I) has two bones in it. Your other fingers are bendier. They contain three
phalanges each, and are digits II - V. The basal mammal
phalangeal formula is 2-3-3-3-3. Lizards and lacertalians have the formula of
2-3-4-5-3(4). As the point is clearest on this specimen, it was selected as the holotype.
The configuration of prints on the plate is consistent with happing. Taken at face value,
all specimens collectively suggest a genus capable of some walking, running and hopping,
which various existing rodents can manage.
From elsewhere
Mammal footprints from the Cretaceous are rarities, and so are fossilized feet. However,
Lower Cretaceous Liaoning is striding forward
impressively. Eomaia,
Jeholodens,
Zhangheotherium and (post publication)
Sinodelphys mean that feet are now known from
Cretaceous Eutheria,
Triconodonta, 'Symmetrodonta' and
Metatheria. All those animals are both too early and
small, but at least the phalangeal formula is consistent with the ichnogenus, (p.273).
The authors also address Cretaceous tracks from elsewhere. The Lower Cretaceous of British
Columbia provides Duquettichnus kooli.
However, this isn't well preserved, and they're uncertain as to which vertebrate group
is involved. While it might be the traces of an early metatherian, the possibility
remains that it's non-mammalian.
The Maastrichtian of Morocco is adorned with Agadirichnus elegans, (p.274). These
prints were assigned to a lacertalian reptile, though they could conceivably be the work of
an extraordinarily large mammal. (As the average length is 11cm, the feet would've been
as long as most complete Mesozoic mammalian bodies.) However, as neither the illustrations
or state of preservation allow more detailed analysis, this possibility is regarded as no
more than tentative, (p.275).
