Ever since the discovery of the hominds we call Paranthropus robustus in 1938 and Paranthropus boisei in 1959, the dietary habits of these "robust australopithecines" have been controversial. With skulls that seem to have more in common with gorillas than with Homo habilis, another hominid more closely related to us that lived during the same time, it has long been thought that Paranthropus was a dietary specialist. The saggital crest, large and thickly-enameled teeth, and huge jaws of these creatures has long been interpreted as a mark of a diet largely made up of tough, fibrous plants, but a new study published in the open-access journal PLoS disputes the "classic" view. Instead, the authors argue that Paranthropus was a dietary generalist that was able to make use of a broader range of foods than the weaker-jawed hominids more closely allied to our ancestors.
Although no one has the opportunity to observe the behavior of extinct hominids like Paranthropus today, their teeth have provided paleoanthropologists with some important clues as to what they may have been eating. The PLoS study primarily focuses on the patterns of microwear, scratches and pits made on teeth by food as it is being chewed, and the patterns on the teeth of Paranthropus can be compared to patterns on the teeth of living animals so see if they are consistent with a particular kind of diet. The particular creatures used in comparison for this study were the tufted capuchin monkey (Cebus apella), the grey-cheeked mangabey (Lophocebus albigena), the mantled howler monkey (Alouatta palliata), the silvered leaf monkey (Trachypithecus cristata), and the fossil remains of Australopithecus africanus. It should be noted, however, that the fossil teeth mentioned in this study are replicas made from dental impressions taken during the 1990s. Of the original samples of Paranthropus only seven molars replicas preserved any microwear, and I have to wonder if more microwear would be seen on the original teeth.
Further, it is strange that the two living species of gorilla were not used for comparison. Beyond similarities in the skull, both mountain and western gorillas would have provided an excellent baseline to test the Paranthropus teeth against. The western gorillas (Gorilla gorilla) are primarily frugivorous, tougher foods making up a smaller part of the diet (especially when fruit is not available). Mountain gorillas (Gorilla berengei), by contrast, have a diet mostly made up of stems, bark, and roots, fruit being a very small part of what they consume. Within one genus, then, you have two species that have extremely similar morphology but have diets where fruit and tougher foods are consumed in drastically different proportions, and I can't imagine why gorillas were not used in this study.
Such criticism aside, the results of the study revealed that microwear on Paranthropus boisei teeth fell at the bottom of the range of the living primates studied and was distinct from both P. robustus and Australopithecus africanus. The numerous deep pits that are characteristic of a hard-food diet are missing in Paranthropus boisei, and it appears that its diet differed even from the South-African P. robustus even though they look very similar. Indeed, P. robustus microwear patterns appeared to be closer to those of living primates (like the tufted capuchin) that often eat hard food when softer fare like fruit is not available, and P. boisei exhibited even less dental microwear than the South-African robust australopithecine. As the authors of the paper report, it doesn't appear that the individuals of P. boisei that were studied consumed especially tough food "in the days before death" (although this phrase is left frustratingly vague).
The observations made by the authors led them to conclude that P. boisei probably ate softer foods most of the time and rarely ate hard foods, while P. robustus also preferred soft foods but had to "fall back" on tough foods more often. What is not discussed, however, is why robust australopithecines have skulls and dental features that appear to be specialized for processing hard foods. Was there a dietary shift, the group becoming hard-food specialists but then switching over to softer foods? Could some of the robust features have anything to do with sexual dimorphism? With both questions, there is little than can be said. The evolution of the robust australopithecine side branch is still murky, and given the paucity of postcranial evidence and specimens, sexing the remains of these hominids for comparison is presently impossible.
Although the evolution of the robust australopithecine form awaits further fossil discoveries, the available material is starting to reveal a picture of these hominids that differs from the standard story. If studies like this one are correct, Paranthropus was able to consume a wider variety of foods (regardless of whether the lineage evolved as specialists or generalists), their diets perhaps being largely dictated by seasonality of different kinds of food. More research is certainly needed, but the natural history of Paranthropus does not appear to have been as simple as previously supposed. The fact that they could chew up tough foods doesn't mean that they exclusively ate those foods, and a variety of studies is reflecting a more nuanced version of Paranthropus than is often put forward. Unfortunately, since they are on an evolutionary "side line" they are often stereotyped or otherwise brushed aside in the search for our own ancestors, but I am hoping that people like Ungar keep trying to pick away at the lifeways of the robust australopithecines.
Ungar, P.S., Grine, F.E., Teaford, M.F., Petraglia, M. (2008). Dental Microwear and Diet of the Plio-Pleistocene Hominin Paranthropus boisei. PLoS ONE, 3(4), e2044. DOI: 10.1371/journal.pone.0002044
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Thanks for the post!
It's quite a breath of fresh air to read a post and not to have to fight or get frustrated about silliness or craze from the ID nuts. Real science - what a concept.
Brian, the current thinking behind paranthropines, originally presented by Matt Sponheimer of the University of a Colorado a couple years ago, is that if they had a choice between a fig and a tuber, they'd choose the fig like anybody else. However, evolutionary pressures are strongest during the lean times, for obvious reasons, so the exaggerated dentition we see in Paranthropus does not necessarily mean that they were chewing on roots and seeds all day, but only that doing so was beneficial to their survival. It is possible that they only had to fall back onto the more difficult diet 5% of the time or less, but if it is during those times that the less well-endowed among them were dying off, that is still more than enough reason to evolve giant masticatory muscles and dentition.
Ungar has written previously in comparing australopithecine dentition to that of gorillas and chimps, although I don't have the references in front of me at the moment.
Sec; Thanks for the comment. I had heard similar things, but the idea that they were primarily a side-group that munched primarily on tough foods still seems deeply entrenched. During discussions of Paranthropus during a seminar course I had last year (and other conversations with paleoanthropologists) the idea that they were specialists that preferred tough foods still hung on. The reality of the fossil evidence might be different, but the archetype still seems to be in place.
I agree, Sponheimer's work is still fairly new, and Ungar's work is still not as well-known as it should be. During a conversation with Ungar, he said that a gorilla will choose a snickers bar over a bunch of leaves every time, and that made sense to me. It's a matter of differing strategies. Chimps looove figs and will run all over tarnation to find them, whereas gorillas looove to sit on their asses and eat whatever they can reach without having to get up. If there is fruit nearby, huzzah, but they have the dentition to deal with it if not.
I think some very tentative comparisons can be drawn there, with the gracile australopithecines being willing to range widely, and paranthropines being the ones who were either unable or unwilling to seek out better forms of nutrition, and were therefore required to adapt to a rough diet during the lean times.
Where was this paper two months ago? For a Human Evolution class, I wrote a term paper on diet in Paranthropus boisei, only to discover a staggering lack of research compared to P. robustus. With little more than biogeography and guesswork to go on, I hypothesized that P. boisei fed mostly on sedges and other swamp plants, although I also made some whimsical suggestions about wood pith and grasses.
I also wonder why there haven't been any comparisons of paranthropines to Theropithecus, which also had/has many similar cranial and dental adaptations--megadontia, sagittal crest, large zygomatics, etc. I was sort of surprised to see the gelada left out of the extant monkeys referred to in this article.
Fun fact: Paranthropoids are my favorite hominids. I love papers like this, which actually test the dogma. Big skulls with huge muscles = nothing but tubers and dried sticks, right? Probably not!
Brain, nice review. I also reviewed the paper and another possible explaination for the lack of deep pitting in P. boisei dentition. You and also maybe readers of your blog may wanna check my review out.
secularskeptic: That idea was actually proposed first in a series of talks, a book chapter, and eventually a paper, by Laden and Wrangham, but based on work done earlier by Hatly and Kappleman.
Here's a post on that paper.
A lot can be discerned from observations of teeth including eating habits and clues to food that are normally consumed.
dudeee... im writing some essay on australopithecus and i hav to giv evidence supporting my opinion being that they were early apes >_<
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