A FIFTH subspecies of common chimpanzee has been lurking under primatologists鈥� noses for decades, according to a new study of chimp skulls. Colin Groves of the Australian National University in Canberra believes that Pan troglodytes marungensis should join the four already recognised subspecies. 鈥淭he data and the arguments are compelling,鈥� says Tom Butynski, a chimp expert and head of Conservation International鈥檚 East Africa biodiversity hotspots programme.
Current chimp taxonomy recognises P. t. verus and P. t. vellerosus in west Africa, P. t. troglodytes in the centre and P. t. schweinfurthii 鈥� the group into which the smaller animals have traditionally been lumped 鈥� in the east, as well as Pan paniscus, the bonobo or pygmy chimp, south of the Congo river.
Now, from measurements including skull length and the breadth between the orbital cavities of 96 skulls from the P. t. schweinfurthii region, Groves argues that these chimps should be divided into a north-western group 鈥� the 鈥渞eal鈥� P. t. schweinfurthii 鈥� and a south-eastern group, P. t. marungensis. The name marungensis was originally used to label another chimp species, but was culled from chimp taxonomy during a radical overhaul in 1932.
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The 鈥渞eal鈥� P. t. schweinfurthii have large skulls and broad braincases. P. t. marungensis is smaller, relatively broad between the eyes, and with a relatively long palate. P. t. marungensis is also smaller, weighing 30 to 35 kilograms on average, compared with 50 to 60 kilograms for P. t. schweinfurthii.
鈥淧eople have been wondering for a long time why the body weights of chimps at places like Gombe in Tanzania appeared to be so small. Now we find that it is because there is a small, separate subspecies,鈥� Groves says. He suggests that P. t. marungensis might account for about a third of the estimated 50,000 to 100,000 chimps in the schweinfurthii region. His findings are due to be published in the next issue of the journal Australasian Primatology.
While more work is needed to confirm the finding, the debate is not purely academic, but vital for conserving diversity. P. t. marungensis is well protected and has been closely studied by primatologists, including Jane Goodall at her research camp at Gombe. But P. t. schweinfurthii is being hunted for bush meat, and according to the new division, now appears poorly protected.
