Human evolution: the place of Paranthropus (Introduction)

by David Turell , Thursday, November 23, 2023, 19:23 (156 days ago) @ David Turell

It seems they coexisted with more advanced Homo species:

https://www.newscientist.com/article/mg26034660-800-how-did-paranthropus-the-last-of-th...

"Spurred on by the discovery of more fossils, researchers are finally reassessing this addition to our evolutionary tree – and their work suggests it was one of the oddest. Paranthropus may have been a skilled tool-maker, but it also potentially grazed grass like a cow and communicated with low rumbles like an elephant. The question now is, can the research bring us closer to understanding how the last of the ape-people survived in a world that was dominated by early humans?

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"But in this grand picture of hominin evolution, Paranthropus sticks out like a sore thumb. Its brain was similar in size to that of the ape-like hominins, and its teeth were exceptionally large. But it lived late in the story – an ape-like hominin alongside the human-like species. “We have evidence of Paranthropus from 2.8 to 1.4 million years ago,” says Kaye Reed at Arizona State University.

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"In particular, we learned decades ago that it had “this really almost dish-shaped face that is caused by the cheekbones getting so big to allow for these huge chewing muscles”, says Angeline Leece at Southern Cross University in New South Wales, Australia. It also had “hyper-thick enamel” and “enormous back teeth”, she says. Indeed, it has been argued that, relative to its weight, Paranthropus had the biggest jaws and teeth of any primate that ever lived. It is understandable, then, that researchers initially concluded that these ape-people dined on hard foods. The first skull of P. boisei – found by palaeoanthropologist Mary Leakey in the 1950s – actually became known as “Nutcracker Man”.

"As we have learned more about Paranthropus in the past 20 years, it has become clearer that the catchy nickname isn’t really suitable....Instead, the growing consensus is that Paranthropus probably ate a lot of tough, chewy foods, including grasses. The evidence for this is particularly clear for P. boisei. Analyses of the carbon in their teeth show that they ate a lot of plants that used C4 photosynthesis – which basically means grasses and the grass-like sedges.
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"...described the first partial skeleton of P. boisei, in the form of 1.34-million-year-old arm and leg bones found in Tanzania’s Olduvai gorge. The bones were big and chunky, confirming that it wasn’t just Paranthropus‘s teeth that were robust.

"More bones appeared a few years later, discovered by Green and his colleagues at Ileret in Kenya...Given the “massive” upper arm bone, Green says it is likely that Paranthropus was better at climbing trees than modern humans.

“It makes sense for me,” says Reed. Paranthropus wasn’t particularly fast and had no natural armour. “How are you going to defend yourself against three different species of hyenas, sabre-toothed cats, lions, giant-sized predators?” she says. “Climb a tree.”

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"P. robustus from a site in South Africa had distinctively shaped cochleas, the part of the ear that turns sounds into signals for the brain. The cochleas would have been unusually sensitive to low-frequency noises. Braga suggests that Paranthropus could make low-pitched sounds, which would travel great distances.

"This is all quite different from anything we imagine as human: something that chewed grass like a cow, rumbled like an elephant and climbed trees like a chimpanzee. In other words, we are left with the impression that Paranthropus were nothing like our human ancestors in terms of diet and behaviour. Arguably, then, we are close to solving the mystery of how and why they survived for so long in a world increasingly dominated by humans: Paranthropus just weren’t competing with humans for food or living space.

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"A 2021 study of sediments from Kenya found evidence that carbon dioxide levels rose between 1.3 million and 0.7 million years ago, causing P. boisei‘s favoured grasses to become less common. This shift in vegetation would have created a pressure to evolve or die.

“'That would make sense,” says Leece. Paranthropus was “the mammoth of the hominins”, she suggests, referring to the latter’s presumed demise due to rapid changes to dietary flora in its habitat. “They got so far down this hyper-specialised adaptive route that when they hit another source of pressure, they weren’t able to adapt away from it quickly enough. That left them kind of cornered in a niche that was no longer viable for them.”

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"But Paranthropus wasn’t just an evolutionary dead end. For one, it is a reminder that for most of hominin history, many species coexisted. “It’s an absolute anomaly for us to be the only species of hominin on the landscape right now,” says Leece.

"For another, there is still the intriguing – if speculative – idea that Paranthropus live on in all of us, having interbred with early humans and so potentially contributed small amounts of DNA to our species. They and early humans probably shared a common ancestor around 3 million years ago, and it can take a long time before seemingly separate species can no longer interbreed. (my bold)

Comment: this article changes my view of Paranthropus as very ancient. We need their DNA to answer the question of interbreeding.