Ann Gibbons reports on a recent conference investigating the interaction of climate change and Plio-Pleistocene human evolution “Where’s the beef? Early humans took it.” I like her description of Lars Werdelin’s work:
After comparing fossils of 78 species of carnivores that lived during five different periods of time between 3.5 million years ago (when large carnivores were at their peak) and 1.5 million years ago, Werdelin found that all but six of 29 species of large carnivores (animals that weighed more than 21.5 kilos) had gone extinct in that time. Moreover, the mass extinction began just before H. erectus appeared in the fossil record 1.9 million years ago. He also found that the community of carnivores alive 2.5 million to 2 million years ago ate a much broader range of foodwith species within a community filling a wider range of dietary niches. By 1.5 million years ago, just hypercarnivores that ate only meat, such as lions and leopards, had survived while omnivores that scavenged and ate a wider range of foods, like civets, had disappeared. "Even I was surprised by the dramatic drop," Werdelin says.
It will be interesting to see more details of this work as it is published. The picture described here seems fairly different from Werdelin’s 2005 paper with Margaret Lewis
With the present focus on hominins as potential competitors, maybe the expansion in scope to a greater number of omnivores made the difference to the analysis. On the other hand, it’s hard to see how recent carnivores can be purer meat-eaters than extinct sabretooths like Megantereon. Lewis and Werdelin’s 2007 book chapter
While the appearance of stone tools at 2.6 Ma has no apparent effect upon carnivorans, the appearance of Homo ergaster after 1.8 Ma may have been at least partly responsible for the decrease in the carnivoran origination rate and the increase in the extinction rate at this time. The behavior of H. ergaster, climate change, and concomitant changes in prey species richness may have caused carnivoran species richness to drop precipitously after 1.5 Ma. In this situation, even effective kleptoparasitism by H. ergaster may have been enough to drive local populations of carnivorans that overlapped with hominins in dietary resources to extinction. Possibly as a result, the modern guild, which evolved within the last few hundred thousand years, is composed primarily of generalists.
We should probably add to the picture the evidence for dispersal into and out of Africa, which is unclear at the moment for carnivores
On that note, there are some incredible carnivore materials from Malapa that may really add to the picture of carnivore-hominin relations. The first of these were published last fall by Brian Kuhn and colleagues, including Werdelin
UPDATE (2012-04-25): Adam Van Arsdale writes that Dmanisi provides even more evidence about carnivore-human interactions: “Early Homo and the carnivore guild”.
The Dmanisi fauna in general, including the carnivores, are only just beginning to be more widely published. A 2011 paper by Hemmer and colleagues discusses a possible large cheetah-like carnivore found at the site. This 2010 paper by Sotnikova and Rook looks at Canid evolution in Eurasia more broadly, but discusses the abundant Canid material from Dmanisi in some depth.
Kate Wong gives some more information about Werdelin’s presentation: “Rise of Humans 2 Million Years Ago Doomed Large Carnivores”.