Mrs Ples
Australopithecus was the precursor to our genus, Homo. lived in Africa, from 4 – 1.9 million years ago and were much more ape-like than later members of the human family; with a small body, small brain and a jaw that juts out (called “prognathism”)1. Now a South African fossil called Mrs Ples has been confirmed to be the oldest ever Australopith2.
Except this isn’t the oldest in terms of geological age. Rather, Mrs Ples was the oldest individual when she died ~2 million years ago3. Mrs Ples is a member of the species Australopithecus africanus, which lived in South Africa shortly after the more famous Australopithecus afarensis (Lucy’s species). Ever since she was discovered in the 1940s4 debate has raged over whether or not she was very young or very old at her time of death. There’s also been debate over whether or not she really did belong to Au. africanus. Or even whether or not she was actually a he2!
A lot of this disagreement stems from “her” rather weird teeth. The roots of Mrs Ples’ teeth are very short, which some took as a sign her teeth hadn’t fully developed (i.e. she was young). Others believed that this was the result of a lifetime of use, which had worn her teeth down. Mrs Ples’ jaw was also a lot more prognathic than typically seen in Au. africanus; hence why some think she might even be a new species2.
The teeth of a young (left) and old (right) chimp; showing how more of the tooth becomes exposed as to compensate for it being worn down
Now a team of palaeoanthropologists from America and the UK have solved the issue by performing CT scans of Mrs Ples and lots of chimpanzees. They found that as chimps get older their teeth get worn down. As this happens the jaw continues to grow, changing shape and pushing the teeth further out (shortening their roots) so they don’t disappear completely. Better to have a funky jaw than loose all your teeth and starve to death! This is a process which occurs in all primates, including humans2.
And it turns out Mrs Ples matches this pattern of development, proving her prognathic jaw and short roots are just a result of the fact she was very old. She’s not a different species after all! Unfortunately jaw growth isn’t regular so this can’t be used to calculate a specific age, but it still looks like Mrs Ples is the oldest Australopithecus found (although they did only compare her to 11 other individuals from this period)2.
This research may also have resolved the debate over whether or not Mrs Ples was actually a Mr Ples. The palaeoanthropologists also found that there was a correlation between the length of the canine root (when jaw growth was taken into account) and overall size of canine. Since larger canines is what distinguishes males from females, they were able to work that Mrs Ples was actually a lady due to her small canines2.
Perhaps we should rename her grandmother Ples, in honor of her grand old age.
References
- Boyd, R., & Silk, J. B. (2009). How humans evolved.
- Villmoare, B., Kuykendall, K., Rae, T. C., & Brimacombe, C. S. (2013). Continuous dental eruption identifies Sts 5 as the developmentally oldest fossil hominin and informs the taxonomy of Australopithecus africanus. .Journal of Human Evolution.
- Herries, A.I.R., Shaw, J. 2011. Palaeomagnetic analysis of the Sterkfontein palaeocave deposits; age implications for the hominin fossils and stone tool industries. J. Human Evolution. 60, 523-539.
- Broom, R. (1947). Discovery of a new skull of the South African ape-man, Plesianthropus. Nature, 159, 672.