The human family was once very diverse, including more than 20 species over the last few million years. Perhaps the weirdest branch on our family tree was Paranthropus. These peculiar hominins lived alongside Lucy and Australopithecus, but looked very different. They had massive jaws, teeth, and jaw muscles; earning them the nickname "nutcracker man". But might they actually have had a penchant for seafood instead?
Discrepancy in the mouth
Despite the nickname, people have debated what "nutcracker man" ate for years. Each piece of evidence seems to point towards something different.
Their large jaws and muscles can generate great power. As such, their initial diagnosis as "nutcrackers" seems justified. Certainly, modern species with a nut (or other tough food) focused diet have similar large jaws and muscles. There's some debate over exactly what tough food they might have eaten. Whilst nuts are the obvious example, roots and tubers (called underground storage organs or "USOs") were common in their environment. And a great source of food. And tough enough to justify a big mouth.
However, stable isotope data disagrees with this a bit. As you eat food, it's incorporated into your bones; leaving a trace of the elements it contained. From this, scientists can infer what you ate. And it looks like Paranthropus ate a fair bit of C4 plants. Things like grasses and sedges. These foods aren't as tough in the traditional sense but are very fibrous and abrasive. Perhaps the large mouth was more of an adaptation for endurance than force. It allowed them to process high volumes of low-quality foods, like grasses.
However, microwear on the teeth tells yet another story. If Paranthropus did eat a lot of tough or abrasive food they should have some damage to their teeth. Specifically, microscopic grooves and gouges from where these abrasive items scratched along the enamel on the top of their teeth. Experiments on modern humans have confirmed such a link. Yet this damage is missing from Paranthropus. Their teeth are far from pristine (showing a lot of macroscopic damage) but don't have enough damage to confirm that they were eating tough or fibrous foods.
Something weird is going on.
Seafood solution
Just now I said that Paranthropus teeth are far from pristine. Well, that's where things get extra strange. Whilst they lack the microscopic damage indicative of eating tough food, that macroscopic damage is consistent with it. They have chipped teeth, worn down crowns, and all the other large-scale damage you'd expect a nutcracker or grass-grinder to have.
The same teeth yield contradictory results!
So some researchers began examining the sides of the teeth. Perhaps they could be the tie-breaker. They studied more than 200 teeth from a dozen species in an effort to see what produces damage to the sides of teeth, and what it might reveal about Paranthropus. The results were interesting, indicating that this cheek-side damage (called buccal wear) was more reliable for telling diet than damage to the top of the tooth. How individuals chew can have a big impact on top damage, whilst side damage remains more consistent.
Armed with this more reliable information, they began searching for a diet that could explain all these weird faecets. Specifically, it needs to have a hard component (explaining the macroscopic damage), yet not too abrasive, and high in C4.
Crabs could fit the bill. Bits of them can be tough, requring a strong jaw and producing macroscopic damage. But once that initial phase is out of the way they're softer and less abrasive, hence why the microwear doesn't show as much damage. Plus, being marine animals they would have an inflated C4 reading, explaining why it initially looked like Paranthropus loved tubers.
Are we crab people now?
So we're crab people now. Living off the fat of the sea. Or at least, our distant cousins were. Or at least, that's one way of reading these results. Even the researchers behind this revelation aren't convinced. Whilst a seafood based diet does match in theory, the practice is very different. Notably, there's a lack of suitable water near to Paranthropus sites. They did leave near lakes, but they were likely too saline in the past to support enough crabs to keep them feeding.
Their skepticism isn't that surprising. The crab idea isn't new, although this extra evidence is. People have long noted how it would match all the weird data observed in a Paranthropus mouth. Yet it didn't take off for the aforementioned reasons (although it may be the case they used what crab was availible in emergencies).
So we're sort of back to square one. Albeit we now have even more data about Paranthropus teeth, what sort of theoretical food might explain this pattern, and what sort wouldn't. It's a baby step towards solving this mystery.
And legally, you aren't allowed to eat baby crabs.
References
Martínez, L.M., Estebaranz-Sánchez, F., Galbany, J. and Pérez-Pérez, A., 2016. Testing Dietary Hypotheses of East African Hominines Using Buccal Dental Microwear Data. PloS one, 11(11), p.e0165447.
Yeakel, J. D., Dominy, N. J., Koch, P. L., & Mangel, M. (2013). Functional morphology, stable isotopes, and human evolution: a model of consilience. Evolution.
