Tuesday, September 20, 2011

Extinct lemurs and human evolution


Paranthropus boisei (left) and Hadropithecus (right) (Dumont et al., 2011:Fig1)

In a brief letter to PNAS entitled "Thinking outside the box: A lemur's take on hominin craniodental evolution" Lorrie Godfrey and colleagues respond to a recent article by Cerling and colleagues (discussed here). The Cerling article argued, based on stable isotope data, that the robust east African australopith Paranthropus boisei was likely a grazer.  The main point of the letter is the figure, which shows carbon isotope values for tooth enamel for a variety of hominins, Old World monkeys, and subfossil lemursP. boisei clearly has really high carbon isotope ratios.  The only other primates that can compete are Theropithecus (the grass-eating gelada baboon), and Hadropithecus, a recently extinct lemur that Dumont, Ryan and Godfrey argued just five months ago was unlikely to be a hard object feeder based on skull morphology and finite element modeling.  When you look at the skulls of these guys next to one another, the similarities are really striking! This comes full circle, back to Clifford Jolly's Theropithecus model for hominin diet from 1970, which suggested that australopiths might have had a diet based largely on grass leaves and seeds, instead of the prevailing "nutcracker" ideas. As summed up by Godfrey et al.
"there are important ways in which the diets of Paranthropus and Hadropithecus likely converged. Both probably consumed large quantities of “low-quality” foods (i.e., foods that were relatively high in structural carbohydrates and poor in nutrients and required heavy repetitive trituration). Such conclusions may have important implications for the evolution of the craniodental features that these species share."
UPDATE: 9/22/2012
I failed to notice the Cerling et al. reply to the Godgrey et al. letter to PNAS. They note that Hadropithecus could attain the observed 13C ratios by consuming CAM plants (cacti and suchlike which are common in Madagascar) instead of the C4 plants (grasses, sedges, etc) suggested for P. boisei. Thus, the isotopic and morphological similarities need not suggest any mechanical similarity in the diets of the species.  It seems like it would be useful to compare Hadropithcus with isotope values of lemurs in today's Malagasy spiny forests. Thanks for Chris Kirk for pointing out the omission.
Godfrey et al.'s isotope figure


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