The Wide World of Paleontology: Winter 2008

This quarter saw the return of our department's paleontology discussion group, and over the course of the last few months we've gone over several papers of note. Here are some of the paleontological highlights from the first quarter of 2008:

• Two of my former MSc supervisors, Sarda Sahney and Mike Benton, published a paper on faunal recovery after the Permian-Triassic extinction. Their research yielded two particularly interesting results. First, extinction at the P-T boundary was the last of three extinctions that occurred during the late Permian. Second, ecological recovery took much longer than had previously been thought. Though some organisms - in particular the pig-like reptile Lystrosaurus - survived the extinction and thrived afterwards, ecosystem complexity remained low until 30 million years into the Triassic. You can read Sarda's much more detailed explanation of the paper's findings on her blog.
• My current advisor, Samantha Hopkins, has also published a paper this year. It deals with the issue of rodent body size estimation. In particular, it emphasizes that previous estimates likely overestimate the size of the giant South American rodent Phoberomys, which had been described as "buffalo-sized." Just before this paper came to press, an even larger South American rodent was reported: the cumbersomely-named Josephoartigasia, which was estimated by the authors to weigh 10,000 kg (11 English tons). Unfortunately for fans of giant rodents, this reckoning is likely also too high, though it still would have been a massive animal, far larger than any rodent alive today (as is made abundantly clear in the picture at right at which the skull of Josephoartigasia is compared to a living rat).
• On the paleoclimate front, Wolfram Kürschner and his colleagues published a study of Miocene plant stomata, orifices in leaves that allow carbon dioxide to enter the cells. The density of these openings varies with atmospheric CO2 content, and as such they provide a proxy for climatic conditions. This line of evidence is significant because marine and terrestrial isotopic studies show different climate signals. Stomatal data confirm the pattern observed in the terrestrial isotopic record, showing a period of global warming (the mid-Miocene climatic optimum) between 17 and 15 million years ago, followed by a prolonged period of global cooling.
• Perhaps my favorite paper of the quarter was a description of the Eocene fossil bat Onychonycterus. Before the discovery of this specimen, all fossil bats looked for all intents and purposes like modern forms. This was frustrating, as these fossils told us nothing about the early evolution of bats. Onychonycterus effectively settles one major debate that had been raging in the paleochiropteral community; its ear showed none of the features associated with echolocation in modern species, demonstrating that bats took to the air before evolving "sonar." Even more interesting are the implications for the evolution of bat flight. Onychonycterus has wings similar to those seen in modern bats that fly by intermittent fluttering and gliding. What's more, it had relatively long legs and large claws on its wings, both of which would have made it an adept climber. Taken together, these lines of evidence suggest that the first flying bats were climbing trees and gliding rather than evolving wings from the "ground up" to help them catch insect prey. Another glimpse of early bat evolution was provided by fossil from the Fayum of Egypt, where - among others - a giant species was recently described.
• There were several other stories in paleontology that we didn't discuss in our group that deserve mention anyway. Fellow Bristol and Chicago alumnus Steve Brusatte has described two new carnivorous dinosaurs from Africa. Dinosaurs weren't the only big things around in the Mesozoic, though, a point underscored by the discovery of a giant, dinosaur-eating frog (shown at right). Our Primate ancestors seem to have been part of the dinosaurs' world for longer than expected as well, and our own species seems to have evolved into more diverse niches than we had previously realized. One thing our species is not, according to a U of O anthropologist, is a duck-killer. The debate over how old ducks and their relatives really are rages on, but at least one contentious issue seems to have been solved: if a modern lion and an extinct marsupial "lion" got in a fight, who would win?