“The middle Pliocene gets crowded.” New fossils have recently been announced that were found in East Africa by a team of scientists led by Yohannes Haile-Selassie of the Cleveland Museum of Natural History. According to Haile-Selassie, these fossil fragments constitute a new species of hominin! The creature has been named Australopithecus deyiremeda, combining the word deyi, meaning close, with remeda, meaning relative in the local Afar language. Haile-Selassie et al. argue that Au. deyiremeda is similar in many ways –but also different from0–contemporary species such as Australopithecus afarensis (Lucy!).
I haven’t stopped talking about the fossil since it was announced, so I thought I’d write about it! Disclaimer: this is science in the process, nothing is definitive and not all paleoanthropologists agreed with Haile-Selassie’s conclusions. I’m simply imagining what this could mean if this does, in fact, turn out to be a new species of Australopiths. I try to use language such as”potentially” to reinforce that.
Let’s recap: the team found a couple of lower jaws, as well as that beautiful upper jaw you see in the photo above, and some teeth. So what can paleoanthropologists determine based on some fragmentary bits of jaws and teeth? Well, it turns out, a lot! Teeth have changed dramatically over the course of human evolution, so minute differences tell us a lot about how these creatures were similar and dissimilar from other hominin species. It potentially tells us a bit about what they might have been eating, their behavior, and more. Also, the shape and features of the jaws provide more clues about what they were eating–was it hard to chew? did they need certain types of force? etc–because the shape and features tell us where chewing muscles were located.
So what’s cool about this?!
- This could mean that multiple species co-existed in the Middle Pliocene. In a Nature article, Fred Spoor even called the middle Pliocene “crowded,” which I find amusing and interesting. Prior to this discovery, some paleoanthropologists had already been stating that there is evidence for taxonomic diversity at this point in time, but the fossil record was fragmentary and the primary example Kenyananthropus platyops was very distorted & hard to read. Therefore, Au. deyiremeda adds to the mounting evidence for species co-existing around 3.5 million years ago, which is pretty cool.
- BUT WAIT: Not only did multiple species potentially co-exist, two species were neighbors. This really gets to the heart of how crazy this discovery is: Au. deyiremeda was found approximately 22 miles from the Hadar site that has revealed so many Au. afarensis fossils. I encourage you to really let this sink in. 22 miles. In the vast, East African desert. If this really is a separate species from Au. afarensis then the interesting question is how did they co-exist in such close proximity? Did they happen to be interested in different resources, so the competition was less intense?
If I had to chose one bottom line that I think this find possibly illustrates: Hominin species diversity might permeate human evolution at every stage in the game. It seems as though we are starting to see possible taxonomic diversity at every stage of human evolution (until the present, of course). We potentially see this recently with Homo floresiensis, Neandertals, and Denisovans, we see it in the Middle Pleistocene (200,000-800,000 years ago), and so on. This.is.freaking.cool.
Now, what’s questionable about this?
- Are fragmentary pieces of jaws enough? Some paleoanthropologists are skeptical that a new species can be named based on these fragmentary bits. Those who aren’t big fans of species diversity, such as Tim White, are inclined to put these fossils in with Au. afarensis. The NY Times quoted him as having said “Lucy’s species just got a few more new fossils” in response to the fossil announcement. Paleoanthropologist Bill Kimbel was also cautious about the discovery, stating that “the distinctions [between these fossils and others such as Au. afarensis] are very, very subtle,” Kimbel continued, “I think it’s a judgment call as to whether you think the differences amount to a species-level difference.”
- Is this jaw related to the foot from Burtele? In 2009, a team also led by Yohannes Haile-Selassie 3.4 million year old foot bones were found in Ethiopia. Just like with these jaws, the foot fossils were interesting because they occurred at the same time/place of Au. afarensis, but they looked completely different. The foot had a divergent big toe, sort of like a thumb, that could be used for grasping and climbing trees. The bones suggested that this creature walked upright just like Lucy, but in a very different way. At the time, the team refrained from naming the foot bones a new species. But now that we have this jaw, the question arises if possibly the jaw and the foot belonged to the same creature? Unfortunately, there is no way to prove that yet. But again, think about the possibilities! I think Bill Kimbel summarized the issue well for National Geographic “Figuring out whether or not that very primitive foot is the same critter as the clear australopithecine teeth and jaws…now is of utmost importance,” Kimbel says. “It would mean that you could have australopithecus-like heads with more diverse options for locomotion – which is not a picture we have painted so far.”
Many of these claims are still preliminary, but this could paint a cool picture of human evolution about 3.5 million years ago. Taxonomic diversity raises questions like: if all these species were running around, which one gave rise to us? The tree of life seems to be getting fuller (though some disagree- calling it more of a Saguaro cactus), which makes evolutionary relationships harder to trace and–I think–makes the whole game more fun.
- Nature 521, 483–488 (2015). et al. “New species from Ethiopia further expands Middle Pliocene hominin diversity.”
- Callaway, Ewen “New species of early human discovered near fossil of ‘Lucy’”