Immediately after the Carmel Church excavation, Christina and I headed to George Mason University in Fairfax to attend the 7th Secondary Adaptations of Tetrapods to Life in the Water meeting (SecAd). The SecAd meetings occur every three years and have taken place all over the world. This was my second meeting, having attended the fourth meeting in 2005 in Akron.
One of the nice things about the SecAd conferences is that there are talks on all kinds of different marine tetrapods (all in one session), so while there are a lot of whale talks you can also hear about pinnipeds, sea cows, marine birds, and marine reptiles, and more exotic things like desmostylians. People that work on secondarily aquatic animals often face some of the same issues in interpreting anatomy and evolutionary history.
There were 43 talks on the schedule, plus 9 posters, too many for me to review them all. But I wanted to highlight a few of the talks to give an idea of what the meeting is like. Abstracts from the meeting are available online.
Hans Thewissen’s lab had done a lot of interesting and informative work over the years on whale embryonic development. Studying the development of embryos is still one of the most informative ways to determine how new structures evolved and which features are homologous. In this talk, they looked at the development of tooth buds in bowhead whale embryos. Bowheads are toothless baleen whales, but like other baleen whales they had toothed ancestors. This is reflected by the development of embryonic tooth buds (the teeth are usually reabsorbed before birth). They found that, in addition to the genetic information for growing teeth at all, there was still a signal in bowheads for heterodonty (different types of teeth) and polydonty (more teeth than the normal number of mammals), features that haven’t been expressed in the bowhead whale ancestry for at least 30 million years. Moreover, the proteins involved in baleen plate development seem to be the same ones involved in tooth development, which is a bit surprising.
Nathan Smith and colleagues examined the usefulness of of external characters such as feather color in determining relationships when compared to datasets based on skeletal characters or molecular information. As a test case they used sulids, the family that includes gannets and boobies like the Peruvian booby shown below:
Desmostylians are a strange group of Oligocene-Miocene marine mammals from the Pacific Ocean, which are still poorly understood in spite of abundant specimens and fairly intensive study (below is the desmostylian Paleoparadoxia, on exhibit at AMNH):
Gabriel Santos and colleagues reported on a specimen of Desmostylus from California that they interpret as a very elderly individual that had lost all its teeth.
In an entertaining and somewhat stomach-churning talk, Satoshi Maruyama and colleagues gave a detailed description of what happens to a dead dolphin after up to 151 days laying on the beach. In spite of scavengers, flies, and waves, the body holds together remarkably well.
Louis Jacobs and colleagues reported the story of a beaked whale discovered by Jim Mead (who was at the conference) in Kenya in 1964. The skull was lost for 36 years before being relocated The skull was found 700 km inland, and 650 m above sea level, allowing the calculation of rates of uplift in that part of the East African rift system. As an interesting aside, the specimen was lost for 36 years before being rediscovered in a museum collection.
Mark Clementz discussed the use of stable Calcium isotopes in bones for determining the feeding habits of marine animals. The preliminary results indicate that the method shows some promise.
Michelle Campbell and Michael Caldwell described the ear structures of mosasaurs, Cretaceous marine reptiles such as Mosasaurus (below, from South Dakota School of Mines):
Mosasaurs seem to have modifications to the quadrate, the bone that forms the lower jaw joint, to enable them to hear well in the water. Interestingly, some of those features seem to parallel the conditions seen in the ears of whales.
Brian Beatty looked at the teeth of manatees as a model for studying the abrasiveness of diets (manatee mandible below from the Calvert Marine Museum). Because manatees replace their teeth through their entire lives, their tooth wear is a good indication of the abrasiveness of the recent diet of that individual.
Eli Amson and colleagues described bone histology of the aquatic sloth Thalassocnus from Peru (skull below from the Museo de Historia Natural). Thalassocnus ribs and long bones were unusually dense (osteosclerotic), and became more dense over time as the group become more thoroughly adapted to life in the water.
This is just a small sample of the fascinating talks at this year’s SecAd conference, and I’d like to thank the conference organizers for doing a fantastic job. The next meeting is scheduled for 2017 in Berlin.