Another project having to due with archaeocetes has been the determination of the dental eruption sequence in dorudontines. I have worked out the basic sequence in Dorudon and Zygorhiza, and I have also discovered that dorudontines replace their deciduous premolars. This is an unusual condition for mammals. The dental eruption sequence is illustrated below. The molars erupt first from front to back. This is followed by the premolars, erupting from back to front, and at the same time the incisors plus canine, erupting from front to back.
In addition to my interest in cetacean evolution, I have
pursued and am pursuing a number of other areas of exploration. One is
on statistical range extension that I have worked on with Philip D. Gingerich
of the University of Michigan Museum of Paleontology. One paper on this
subject is available on-line at Palaeontologica Electronica. http://www-odp.tamu.edu/paleo/1998_2/ging_uhen/issue2.htm
This method uses the known distribution of fossils in the
stratigraphic record and a few assumptions about fossilization and collection
to place confidence intervals on the first and last occurrence of a taxon.
I am also involved with Lori Marino of Emory University on a project
using Computed Tomography to image the internal anatomy of fossil whale
skulls. We have used the technology to measure the endocranial volume
of fossil whales. Modern cetaceans have very large brains for their body
size (not unlike we primates) and we are trying to figure out when that
increase in brain size occurs in whale evolution to test hypotheses of
the function of large brain size in cetaceans and primates. Click the
image below to view some of the CT Scans.
Click to view CT images.
I also have a paper in press with Maureen O'Leary of the State University of New York at Stony Brook on wear facets on archaeocete molars. Archaeocetes have vertical wear facets on their molars that are not found in their terrestrial relatives. This indicates that archaeocetes used a different feeding mechanism than their terrestrial ancestors. This makes sense if whales originally began as terrestrial animals that started feeding in the water. This paper will be out in Paleobiology soon