Finally, I have some time to do a decent writeup of last Monday's Secret Science Club lecture by paleontologist/physical anthropologist Dr William Harcourt-Smith of the American Museum of Natural History and Lehman College. The lecture began with a quote from Mark Twain, illustrating his opinion of the anthropocentric philosophy:
Man has been here 32,000 years. That it took a hundred million years to prepare the world for him is proof that that is what it was done for. I suppose it is, I dunno. If the Eiffel Tower were now representing the world's age, the skin of paint on the pinnacle-knob at its summit would represent man's share of that age; and anybody would perceive that the skin was what the tower was built for. I reckon they would, I dunno.
After a brief overview of hominin evolution (this graphic, although omitting Homo florensis, is a good depiction of the distribution of humans and their relatives), with discussions of relative brain-to-body size, and the use of microscribe imaging tools in morphological studies, Dr Harcourt-Smith went on to discuss one of his primary fields of inquiry, the development of bipedalism and the morphology of hominin feet.
Humans are the only mammal to habitually walk bipedally, placing one foot in front of the other to walk. Other extant mammals that typically move on two feet move by hopping. There are more living mammal species that lay eggs than there are those that walk on two legs. Evidence of bipedalism dates far back in hominid evolution, with the Laetoli footprints being a beautiful example of evidence that our australopithecine forbears walked erect, and lacked the grasping big toes characteristic of other primate groups. The evolution of bipedalism had long been assumed to have happened in linear fashion throughout the course of hominin evolution, but Dr Harcourt-Smith's research suggests "that there may have been greater diversity in human bipedalism in the earlier phases of our evolutionary history than previously suspected". Different hominins were probably "experimenting" with bipedalism, as suggested by the different "mosaic" of foot bones in fossil hominins- in particular the morphology of the arches of their feet.
Dr Harcourt-Smith's current fieldwork is at an Early Miocene site on the island of Rusinga in Kenya. The site is associated with fossils of the early "ape" Proconsul, which shared its "world" with now-extinct mammal lineages such as creodonts and chalicotheres.
While early paleontological expeditions primarily concentrated on extracting "significant" fossils, current fieldwork involves searching for fossils of all sorts in order to determine what sort of biome characterized the site. Whereas earlier expeditions tended to concentrate on the dramatic fossils, often ignoring the less "significant" fossils which could be useful in determining the prevailing environmental conditions. One anecdote recounted by Dr. Harcourt-Smith illustrates this point- a fossil of a crocodilian was largely ignored by the Rusinga team because it was dismissed as "just a crocodile fossil". When a crocodile expert joined the expedition, the fossil was reevaluated, and may be that of a previously unknown species.
Once again, it was a fantastic lecture. For additional reading Dr Harcourt-Smith regularly wrote blog posts from the field, which make for great reading.
UPDATE: I was somewhat rushed writing this post- I forgot to mention that Dr. Harcourt-Smith mentioned Homo florensis in his lecture, remarking on how large the feet of this little hominin were. He also gave a quick overview of possible reasons for the evolution of a bipedal gait- one theory is that walking on two feet substantially reduces the amount of sunlight, and thus heat, that a body has to deal with. He also cautioned against extrapolating the behavior of extinct hominins from the observed behavior of modern hunters and collectors such as the San. Simply put, the San are modern humans, and exhibit a cultural sophistication that our extinct forebears were unlikely to possess. He also mentioned a recent discovery of a series of footprints dating back to the early days of Homo sapiens, but hinted that the National Geographic Society would come after him if he said anything further about it.