Sunday 4 March 2012

The canine teeth of Australopithecus anamensis.

Apes have large canine teeth, the males (who sometimes use them for fighting) more so than the females. Modern humans have small canine teeth, similar in size to (and used as extra) incisors, with no difference between the sexes. Australopithecines had bigger teeth than modern humans, but their canines do not appear to be out proportion to their other teeth compared to modern humans. This appears to have been the case in the earliest Australopithecine species, Australopithecus anamensis, having evolved from an ape-like condition in the intermediate genera Sahelanthropus, Orrorin, and Ardipithecus.

In a paper in the March 2012 edition of the South African Journal of Science, Frederick Manthi of the Department of Earth Sciences at the National Museums of Kenya, Michael Plavcan of the Department of Anthropology at the University of Arkansas and Carol Ward of the Department of Pathology and Anatomical Sciences at the University of Missouri describe a new study on a collection of Australopithecus anamensis teeth from Kanapoi in Kenya, dated to between 4.195 and 4.108 million years old.

Teeth of Australopithecus anamensis teeth from Kanapoi. From Manthi et al. (2012).

The team compared the teeth to previously described teeth of Australopithecus anamensis as well as teeth of modern humans (Homo sapiens), Gorillas (Gorilla gorilla), Orang Utans (Pongo pygmeus), Chimpanzees (Pan troglodytes), Bonobos (Pan paniscus) and other early humans (Australopithicus afarensis and Ardipithecus ramidus). Data from other studies and casts of teeth not available were also used.

Manthi et al. concluded that while the canine teeth of Australopithecus anamensis and earlier hominids were reduced in size compared to those of the great apes, they still showed sexual dimorphism (i.e. bigger canines in males than females) at least as late as Australopithecus anamensis. They also noted that all the teeth of the later Australopithicus afarensis (3.77-3.0 million years ago) appeared to be of females (male Australopithecines were larger than females, so even if the tooth proportions were identical, we would expect the teeth of the males to be larger), so that this species could potentially have retained sexual dimorphism in its canine teeth.