It was a full slate for me today, as there were lots of whale and other mammal talks. Aaron Wood et al. presented on a new specimen of the Eocene horse Hyracotherium from Wyoming with a well-preserved vertebral column (the specimen above is from the National Museum of Natural History). Their functional analysis of the flexibility in the column indicates that Hyracotherium was capable of rapid acceleration. As a tiny forest dweller (see the life-sized model below at AMNH, with Tim for scale), they suggested that it may have used the same flight strategy as a rabbit; freezing, then rapidly bounding away if spotted.
Bruce Shockey et al. presented a talk on the knee-locking mechanism in rhinos. As indicated in the photo below of the modern genus Rhinoceros from the National Museum, this consists of an enlargement of the inside of the femur (thigh bone–green arrow) and a hook on the patella (knee cap–red arrow). These interlock to fix the knee and ankle into a straight position, preventing the leg from bending unless the patella is pulled to the side by a muscle. This allows the rhino to stand for hours on end without getting tired. Their relatives, the horses, have a somewhat similar mechanism that involves a cartilage hook.
Lisa Cooper et al. presented a paper on the thickened ribs in Indohyus, an Eocene herbivore that they believe is ancestral to the whales (as described in an earlier post).
The afternoon session was all whales. Robert Boessenecker and Jonathan Geisler reported a new and very well-preserved specimen of the small baleen whale Herpetocetus from California. I don’t have a photo of Herpetocetus, but it’s closely related to Piscobalaena from Peru (below):
Their studies indicate that the remingtonocetids were living in estuarine environments, which makes them behavorially intermediate between slightly older and slightly younger whales from the same area (although remingtonocetids are too specialized to be ancestral to modern whales).
Mark Uhen et al. presented preliminary findings on Eocene whales from Peru, possibly including the oldest whales known from the southern hemisphere. I saw some of these specimens a few years ago on one of my visits to Peru:
Meredith Staley and Larry Barnes presented on other toothed mysticetes, this time from the early Miocene of California. Three different species from this locality are the youngest known toothed mysticetes. I was able to photograph one of the partially-prepared skulls when I was visiting the Los Angeles County Museum a few years ago (the arrows are pointing to teeth):
I don’t have a good report on the last poster session, because I had to present my own poster and didn’t get a chance to see many others. As I mentioned a few days ago, I reported on the Rappahannock sperm whale and its similarities and differences with Zygophyseter. I have finally decided that the Rappahannock whale is not Zygophyseter varolai, although it may be related. Both the Rappahannock whale and Zygophyseter have a long connection between the jugal and squamosal bones, which is not found in other sperm whales. However, as can be seen in the image below, the shape and size of these bones is quite different in Zygophyseter (top) and the Rappahannock whale (bottom). The Rappahannock whale has a much more massive lacrimal, jugal, and zygomatic process, and a longer jugal, even though the length of the zygomatic processes are the same.
Zygophyseter image modified from: Bianucci, Giovanni, & Landini, Walter. (2006). “Killer sperm whale: a new basal physeteroid (Mammalia, Cetacea) from the Late Miocene of Italy”. Zoological Journal of the Linnean Society 148: 103-131.
On Sunday morning I head back home, after a very informative four days.