And it gets even trickier if anatomical ape-ness is not homologous, given how diverse modern ape locomotion is! (none of this is to detract from the paper, of course -- it is a valuable way of addressing the question).

Especially because there isn't even a firm consensus on what those ape anatomical specializations are for, something this paper dodges a bit by combining "suspension, orthograde stand, cling, and postural bridge" into a single "versatile postures" (i.e., "ape stuff") category.

Of course, the causal link could still go either way (certain scientists get their work published more so the taxa they work on appear more often, or specific taxa are published more often so the scientists who work on them get their work published more often).

This is very cool, thank you so much for doing it! I'd be very curious if the preference for certain taxa is confounded by an overrepresentation of specific scientists.

Last week, amidst the hoopla over a new Speen, @fishfetisher.bsky.social suggested a review of naming papers in fancy journals in response to a post by @daveyfwright.bsky.social - I got bored after work and now I have (some) data!

🧵👇

#FossilFriday
#CharismaticTaxaAreOverrated

Thanks for this! I tried using this form when the videos first came out but never got a reply. I kinda figure the heavily cited paragraph I sent was above the pay grade of whatever intern was supposed to reply to those 😅. It's probably worth trying again, though.

Given this widespread educational use, is there a way to report errors? Not small nitpicks; I'm aware of two complexly videos (one SciShow one Eons) in my field that answer the titular question wrong. That's a good track record given the number of videos, but I'd still love to see them fixed!

This is great. It's not as in depth as the suggestions here, but at my JC in grad school we always asked two questions at the end: "What is the most valuable thing we can take from this paper?" and "What's the next step we would take related to that most valuable thing?" It was fantastic.

Yes! There is some debate about whether Pierolapithecus diverged before or after orangutans (I feel the evidence is stronger for 'before').

A great question about the context of Sahelanthropus from @fossilhistory.bsky.social. Figured I'd share it and my best attempt at answering it, rather than letting it linger in replies.

Thank you! You are absolutely right about the context. It is definitely frustrating that such an important fossil is plagued by so much uncertainty. The size and lack of repeated bones is consistent with one species or even individual, but it will likely be impossible to prove without more fossils.

I'd be surprised if they are from entirely different species, but it's not impossible. Maybe this is literally the human-chimp split? With the femur being from the human line and the ulna from the chimp line? This is getting into some pretty serious speculation territory, though, so I should stop!

If the femur and ulnae are from different but similarly-sized individuals of the same species, it adds a uncertainty to e.g. our analysis of length ratios, but wouldn't change our qualitative observations of a bipedal signal in the femur coexisting with some very chimp-like features of the ulna.

An arguably bigger issue with Sahelanthropus’s context is whether the bones are actually associated. The size of the bones and the lack of repeating elements are consistent with them being from the same individual, but it is not possible to positively demonstrate that.

If it turns out that Sahelanthropus is actually older than currently thought, branching off before the split between humans and chimps, our analysis would contradict all current hypotheses and would definitely necessitate rethinking our major conclusions (and generating an entirely new hypothesis)!

This conclusion isn’t altered if the fossils are actually younger than currently thought—this combination is still only predicted by the chimp-like LCA hypothesis. Being ‘earliest’ is nice, but the same hypothesis is supported whether bipedalism emerged immediately or after 1-2 million years.

Our analysis suggests that a clear bipedal signal in the femur exists alongside an ulna that is chimpanzee-like in overall appearance, especially a type of curvature that is characteristic of knuckle-walking. This combination is predicted only by the chimpanzee-like LCA hypothesis.

What we really need to test these hypotheses is a fossil from after the split between chimps+humans gorillas but not too deep into the family trees of any of those lineages. Sahelanthropus is one of the only fossils that fits the bill.

The problem with these models is that these fossil taxa all branched off before the last common ancestor of chimpanzees, humans, gorillas, and probably also orangutans lived, which means while they can be useful for generating hypotheses, they aren’t useful for testing them.

As an alternative, researchers point to various fossil apes and suggest these should be models for the LCA’s locomotion. Fossils that have frequently been put forward for this purpose include Proconsul, Pierolapithecus, and recently Danuvius.

But so far there are no fossil apes that resemble chimpanzees, and besides chimps have been evolving as long as we have, so many (probably most) researchers have called this basic explanation into doubt.

There are several hypotheses: The simplest model is that LCA locomotion resembles that of a chimpanzee or bonobo. They are our closest relatives and generally move in a similar way to our next closest relatives, gorillas. So this explanation is sort of a default in the absence of other evidence.

The scientific debate we address is about how the last common ancestor of chimpanzees and humans moved. This form of locomotion would be the precursor to bipedalism, and because evolution is a historical process understanding that precursor is essential to understanding how bipedalism emerged.

That said, the conclusions emphasized in the article you linked aren’t really our main conclusions. The fact that “Upright walking… [emerged] long before later evolutionary changes such as larger brains or tool use” was first proposed in 1925 and was extremely well established long before our paper.

Great question! The context of Sahelanthropus is disappointingly ambiguous. Different dates would affect whether this can be called the earliest evidence. For now any point in the established date range makes this ‘earliest’, but I wouldn't be totally shocked if the range gets updated at some point.

Happy to try to answer some!

(and yes, I know I am part of the 'suspension discourse' 😅)

I've been looking forward to this one! I find the suspension discourse fascinating. We so often talk about 'suspension' as if it is a single thing that primates either do or don't, but there's quite a range in both quantity and type! I really appreciate the explicit values discussed in this paper!

The short version is that geometric morphometric shape analyses link the Sahelanthropus postcranial remains with extant great apes (and especially chimps in the ulna), but we identify some qualitative characters of the femur that strongly imply bipedal locomotion.

Earliest evidence of hominin bipedalism in Sahelanthropus tchadensis Limb bones of the earliest known hominin, Sahelanthropus, are chimpanzee-like in shape but demonstrate adaptations for bipedalism.

This was one of those exciting papers to write where many of the results genuinely surprised me. I'm proud of the work we did on this one, and huge thanks to Scott for leading and to all my co-authors, as well as the reviewers for important feedback! www.science.org/doi/10.1126/...