First triconodont mammal from the east coast!

[Tompaleo@aol.com]

Hello all,

The following is a short synopsis (by special request) of the aforementioned 
mammal (JVP, 19:2, p. 199-203) which was discovered by yours truly last year 
while crawling around the Arundel Clay. In fact, it was found a mere two 
weeks after Dinofest in Philly!

Many of you by now are at least somewhat familiar with the fauna of the 
Arundel Clay (Potomac Group; Aptian) of Maryland either by my occasional 
missives to this list or by other members or by the growing body of 
literature dealing with this subject. 

The dinosaur site at which I have been toiling at for nearly a decade is the 
last of it's kind. It is the last open pit quarry that is being mined for the 
clay (Arundel clay) where once, dozens of such pits existed over a century 
ago. Such luminaries in paleontology as Leidy, Marsh, Hatcher, Bibbins, Lull 
and Gilmore have all contributed to our knowledge of the fauna contained in 
the Arundel. Among these are turtles, crocodiles, invertebrates, plants, and 
dinosaurs representing all three of the major clades (saurischia, theropoda 
and ornithischia).
Recently, hybodont sharks were reported as well. But no mammals. That all 
changed with the discovery of a left dentary with five teeth in place. I was 
later to learn of a second, edentulous jaw being found about the same time. 
Ken Rose and myself are now working on a short paper describing it and 
hopefully will be in press by years end.

I have been advised that it is among the 10 best preserved triconodontid jaws 
in the entire world and it is certainly the first and only one ever described 
from the Lower Cretaceous of Maryland or from the East coast for that matter!

Basically the specimen is the holotype for a new genus and species of 
triconodont mammal for which we erected the taxon Arundelconodon hottoni. In 
short "cone tooth from the Arundel" and its specific epithet is given in 
honor of Dr. Nicholas Hotton III of the Smithsonian institution in 
recognition for his lifetime contributions to vertebrate paleontology and as 
far as I am concerned, for his personal interest in my work and for helping 
me to gain access to the site so many years ago!

The specimen preserved is the left dentary which preserves 2 rather large 
premolars and 3 molars. All the teeth are rather labio-lingually compressed. 
More so than you'd expect for a mammal but this critter is rather primitive. 
Another interesting aspect of the jaw is its having an interlocking "groove 
and ridge" system between the molars. Further testament to it's primitiveness 
is the presence of a Meckelian Groove on the medial (labial) side. 

Rich Cifelli of the University of Oklahoma, and who did the bulk of the 
comparative and descriptive work along with Chuch Schaff of  Harvard, also 
reports that while there are similarities with triconodonts from the Cloverly 
Fm. of Montana and Wyoming, from the Trinity Grp of Texas, and from the Cedar 
Mt. Formation of Utah, all of which are at least partially contemporaneous 
with the Arundel Clay, that the Maryland form is more primitive.  
Triconodonts from these units appear to be more derived because they lack the 
Meckelian Groove (among other aspects) except the Arundel form. It is 
believed that the presence of the groove is shared with more primitive 
mammals and mammal-like reptiles (e.g., therapsids)! 

The presence of such a primitive triconodontid along with palynological data 
arguing for a late early Aptian - mid Aptian age for the Arundel Clay seems 
to confirm the belief that the Arundel Clay is older than the Western 
Interior genera (and by definition the units that contain them) but 
interestingly is not of itself conclusive proof of a faunal tie with European 
tricondonts or of South American genera.

As I stated previously, we now have a second edentulous jaw. This specimen 
appears to be the right ramus and is somewhat smaller. 
Since Ken Rose and I are working on getting this one in print as well, it's 
best that I stop here.

Meanwhile I have been working since June (and between the usual distractions 
and other field trips) on an NSF -  funded screen washing project in concert 
with Cifelli and the UOk . I have to date washed about 3/4 ton of matrix (by 
myeslef and with only 20 screen boxes)and  will be taking this concentrate to 
the UOk  in about two weeks to kerosene and heavy liquid concentrate and from 
there it will be picked by microscope in the hopes of finding more 
microvertebrates including lizards and hopefully more mammals!

Hope this is of interest!

Cheers!

Thomas R. Lipka
Paleontological/Geological Studies