New (old) Australopithecus anamensis cranium

The Fall semester here at Vassar kicks off next week, and so of course a new fossil discovery is published this week that threatens to upend my course plans and throw my syllabi into disarray. Haile-Selassie and colleagues report a very well-preserved hominin cranium, from the Woranso-Mille region of Ethiopia and dating to 3.8 million years ago. The new cranium shares features with Australopithecus anamensis, a species previously mainly known through jaws and teeth. The fossil is therefore really important since it puts a face to the species’ name, and it is the oldest relatively complete Australopithecus cranium known. When I showed a picture of the fossil to my wife, who is not a paleoanthropologist, all she said was that it looked like the face of a dog who got stung by a bee.

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The new A. anamensis fossil MRD-VP-1 (left), and a dog that lost a fight with a bee. Fossil photo from the Smithsonian‘s coverage.

The big buzz in many news stories about the fossil (for example, Nature, ScienceNews, etc.) is that it rewrites an evolutionary relationship early in human history, with Australopithecus anamensis no longer the ancestor of A. afarensis, but rather the two being contemporaries. That idea is based on a 3.9 million year old frontal bone attributed to A. afarensis from a site called Belohdelie, also in Ethiopia (Asfaw, 1987): basically, the new A. anamensis cranium reveals a hominin with a narrow frontal region of the brain, which lived 100,000 later than A. afarensis with a relatively expanded frontal region:

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Top views of the reconstructed A. anamensis cranium (left), and the Belohdelie frontal (center), and my crappy photoshopped overlay of Belohdelie on A. anamensis (right). Images not to scale.

The lede, “human evolutionary tree messier than thought,” is not terribly interesting or compelling since it seems to characterize most fossil discoveries over the past several years. And in this case I don’t know how well supported the argument is, since the trait in question (narrow frontal region of the braincase or “post-orbital constriction”) can vary dramatically within a single species. The image below is from the paper itself—compare the difference in “postorbital constriction index” (left graph) between the new A. anamensis cranium (MRD) and A. afarensis (in blue). Both sets of fossils fall within the range of chimpanzees (P. troglodytes), and note the great range of variation within gorillas (G. gorilla).

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Part of Figure 3 from the paper by Haile-Selassie and colleagues. On the top is a view from above of fossil humans: Sahelanthropus tchadensis, Ardipithecus ramidus, the new A. anamensis, A. afarensis, and A. africanus. Below the graphs show how species differ in narrowing of the frontal (left) and length of the skull (right).

What I find most interesting about the new find is the great front-to-back length of the cranium—check out how long and narrow the brain-case is of the fossil compared with the later hominins to the right. This is an interesting similarity with the much earlier (6 million years ago) Sahelanthropus tchadensis, which is the left-most fossil in the figure. It makes me really curious to see the brain endocast of A. anamensis and the Sahelanthropus cranium—what was brain shape like for these ancient animals, and what does that mean for the earliest stages of human brain evolution? The Sahelanthropus endocast was presented at a conference six years ago but remains unpublished. Haile-Selassie and colleagues report that they made a virtual reconstruction of the A. anamensis endocast, so hopefully we’ll get to pick its brain soon.

 

The most complete Australopithecus skeleton

StW 573, a hominin skeleton more palatably nicknamed “Little Foot,” made its big debut last week:

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Ron Clarke showcases the lovingly-excavated skeleton (Photo credit: AP/Themba Hadebe)

The skeleton is remarkable in that it is the most complete australopithecine individual ever discovered, and is among the most complete in the entire hominin fossil record. Below I’ve compared it to the most complete Australopithecus afarensis (KSD-VP-1/1 and AL 288-1), A. africanus (StW 431 and Sts 14), and A. sediba (MH1-2); the Dikika infant would be a neat comparison, too, but I don’t know of any photos of its bones nicely laid out. The other skeletons are practically naked (or dismembered) compared to Little Foot.

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Little Foot (red) compared with other australopithecine skeletons. Images not to scale! (Photo credit: The Internet!)

Beyond it’s completeness, the other parts of story of Little Foot are equally fascinating – from its discovery based on already-known fragments to the possibility that it is older than “Lucy” (AL-288). Ron Clarke has painstakingly and I’d say very successfully removed the skeleton from the hard breccia in which the fossils were encased. Having spent the better part of the past two decades with the skeleton, he has argued that Little Foot represents a second hominin species at Sterkfontein, Australopithecus prometheus (Clarke 2013), the species to which hominin fossils at Makapansgat were originally attributed (Dart 1948). With the unveiling of the skeleton, I’d guess that in the coming years we’ll see renewed investigations into the number of species at Sterkfontein, and the general comparison between hominins from there and Makapansgat.

From pictures in the media releases, we can see a few things that weren’t known from previous publications. I’ll outline a few here, but emphasize that these are only  superficial observations and will need to be borne out by further research.

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“EXPELLIARMUS”

At the top of the trunk, the cervical vertebra seems to have a fairly wide spinal canal, a human-like ‘bulging’ which Meyer and Hausler (2015) suggest might reflect innervation of highly manipulative hominin hands.

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Close up of the skull and upper trunk of StW 573, highlighting the cervical vertebral canal (white arrow) and first rib (orange arrow). Original photo credit: AP//Themba Hadebe.

In addition, the first rib may be relatively long front-to-back (as opposed to wide side-to-side), possibly indicating a more barrel-like chest than in other early hominins; the angle of the photo and the clear break between the proximal and distal portions, however, makes this unclear.

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Hominin first ribs/bacon, with StW 573 on the far right. Not to scale! Modified from this post.

The distal forelimb (i.e., radius and ulna) are not as elongated as in apes, but the femur is not as elongated as in the genus Homo. From the pictures, the femur neck appears short like in humans, not as elongated as is characteristic for australopiths and early Homo.

Limb comparison Stw 573

Limb proportion comparison. Humerus (top row), radius & ulna (middle), and femur (bottom). Image modified from Asfaw et al. (1999). StW 573 scaled to same humerus length as the human. Note also that all bones are from the right except the StW 573 upper limb.

The apparently short femur neck, similar to humans, contrasts with the wide, flaring ilium of the pelvis. This appears fairly flat, short and wide (Australopithecus af) compared to modern humans’ more strongly curved ilium. But this inference is just from a picture and it’s likely that the fossil needs a bit of reconstruction to uncover the true anatomy.

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StW 573 pelvis (left) compared with Sts 14 (A. africanus, middle) and SH pelvis 1 (archaic Homo, right). Sts 14 modified from Berge & Goularis (2010) and SH pelvis 1 from Bonmati et al. (2010).

I’d like to emphasize that these are just first impressions based on press release photos, and actual analysis of the skeleton are necessary to tell if these impressions are correct. As could be expected, the skeleton as a whole looks typically australopithecine, although the short femur neck may be a bit different. As 2017 draws to a close, let’s hope 2018 sees the testing of these predictions.

References

Asfaw B. et al. 1999. Australopithecus garhi: a new species of early hominid from Ethiopia. Science 284: 629-635.

Berge C and Goularis D. 2010. A new reconstruction of Sts 14 pelvis (Australopithecus africanus) from computed tomography and three-dimensional modeling techniques. Journal of Human Evolution 58: 262-272.

Bonmati A. et al. 2010.Middle Pleistocene lower back and pelvis from an aged human individual from the Sima de los Huesos site, Spain. Proceedings of the National Academy of Sciences 107: 18386-18391.

Clarke RJ. 2013. Australopithecus from Sterkfontein Caves, South Africa. In The Paleobiology of Australopithecus, Reed et al., eds. Dordrecht: Springer Science+Business.

Dart R. 1948. The Makapansgat proto-human Australopithecus prometheusAmerican Journal of Physical Anthropology 6: 259-284.

Meyer M. and Hausler M. 2015. Spinal cord evolution in early Homo. Journal of Human Evolution 88: 43-53.

New anthropology syllabi for 2017

This Fall I’m teaching three courses at Vassar, two in Anthropology and one in Environmental Studies. Syllabi are posted to my Teaching page in case anyone wants to use them – here are the highlights:

Anth 235: Central Asian Prehistory

Anth 235 site map

I taught this for the first time last Spring, so the Fall syllabus is updated based on how things went in the first go around. This time, students will get more more in depth with the fossil hominins and less on the lithics on the early side. On the more recent end, there are now readings expressly concerned with sites of the Bactrian-Margiana Archaeological Complex, as well as archaeology of both the Tarim and Pazyryk mummies.

Anth 305: Human Evolutionary Developmental Biology

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This is a seminar version of the first class I ever made on my own, previously taught at the University of Michigan and Nazarbayev University. There have been lots of new discoveries and I’ve published more on this topic since the last time I taught the class. I’m  also excited to see how this class goes as a seminar in which students contribute more to discussion, rather than me rambling on about osteoblasts, morphological integration, and the like.

Enst 187: A Prehistoric Perspective on Climate Change

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This is a 100% brand spankin new class, that uses the climate-denialist argument, “But climate has always been changing,” as a basis for comparing the past and the present. In this First-year Writing Seminar, we’ll compare arguments for defining the “Anthropocene,” examine how climate change may have impacted human evolution, and study archaeological evidence for how climate change has impacted different prehistoric societies.

Osteology Everywhere: Aerial Ossicles

Last month I was flying down to New Orleans for the AAPA conference. I was excited to try authentic beignets & sazeracs, present new research, and catch up with colleagues. Midway through the flight I glanced out the window, not expecting to see much. But lo!

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Thankfully there wasn’t something on the wing. But there was something strange out there in the sparkle of sprawling city lights:

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What’s that I spy outside the city center?

A bit outside of the main jumble of street lamps appears to be a concentration of light superficially similar to an incus, one of the three auditory ossicles of the middle ear:

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Left: An osteologist’s nightmare at 20,000 feet. Right: Ear ossicles from White et al. (2012).

As a good mammal, there are three small bones inside your middle ear. These are fully formed at birth, and help transfer and amplify sound vibrations from your eardrum to your inner ear. It’s nuts. What’s even more nuts is that paleontologists and anatomists have figured out that the tiny, internal incus and malleus of mammals evolved from larger, external pieces of the jaws of our pre-mammalian ancestors. INSANITY!

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Cross section of a right ear, viewed from the front. Image credit.

Being so tiny, it’s not surprising that auditory ossicles are not often recovered from skeletal remains, and are pretty rare in the human fossil record. Nevertheless, some are known and their comparison with humans’ ossicles is pretty interesting. The oldest inci I know of are from SK 848 and SKW 18Australopithecus robustus fossils from Swartkrans in South Africa (Rak and Clarke, 1979; Quam et al., 2013). SK 848 is on the left in the set of images below:

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Incus bones in three different views of SK 848, human chimpanzee, gorilla, sock puppet (left to right). Modified from Rak and Clarke, 1979.

SK 848 to differs from humans and African apes in looking more like a screaming sock puppet with a horn on the back of its head. Additional ossicles are known from South African australopithecines, including the older A. africanus from Sterkfontein (Quam et al., 2013). Interestingly, malleus of these hominins is very similar to that of humans, and Quam et al. (2013) think this ossicle may be one of the first bones in the entire skeleton to take on a human-like configuration during hominin evolution. Functionally, this may mean that the frequency range to which human ears are adapted may have appeared pretty early in our lineage as well (Quam et al., 2015).

Who’d’ve thunk we’d learn so much just from looking out an airplane window?

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ResearchBlogging.orgRead more!

Quam, R., de Ruiter, D., Masali, M., Arsuaga, J., Martinez, I., & Moggi-Cecchi, J. (2013). Early hominin auditory ossicles from South Africa Proceedings of the National Academy of Sciences, 110 (22), 8847-8851 DOI: 10.1073/pnas.1303375110

Quam, R., Martinez, I., Rosa, M., Bonmati, A., Lorenzo, C., de Ruiter, D., Moggi-Cecchi, J., Conde Valverde, M., Jarabo, P., Menter, C., Thackeray, J., & Arsuaga, J. (2015). Early hominin auditory capacities Science Advances, 1 (8) DOI: 10.1126/sciadv.1500355

Rak Y, & Clarke RJ (1979). Ear ossicle of australopithecus robustus. Nature, 279 (5708), 62-3 PMID: 377094

Worst year in review

As we’re wrapping up what may be the worst year in recent global memory, especially geopolitically, let’s take a moment to review some more positive things that came up at Lawnchair in 2016.

Headed home

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Alternate subtitle: Go West
This was a quiet year on the blog, with only 18 posts compared with the roughly thirty per year in 2014-2015. The major reason for the silence was that I moved from Kazakhstan back to the US to join the Anthropology Department at Vassar College in New York. With all the movement there was  less time to blog. Much of the second half of 2016 was spent setting up the Biological Anthropology Lab at Vassar, which will focus on “virtual” anthropology, including 3D surface scanning…

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Cast of early Homo cranium KNM-ER 1470 and 3D surface scan made in the lab using an Artec Spider.

… and 3D printing.

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gibbon endocast, created from a CT scan using Avizo software and printed on a Zortrax M200.

This first semester stateside I reworked my ‘Intro to Bio Anthro’ and ‘Race’ courses, which I think went pretty well being presented to an American audience for the first time. The latter class examines human biological variation, situating empirical observations in modern and historical social contexts. This is an especially important class today as 2016 saw a rise in nationalist and racist movements across the globe. Just yesterday Sarah Zhang published an essay in The Atlantic titled, “Will the Alt-right peddle a new kind of racist genetics?” It’s a great read, and I’m pleased to say that in the Race class this semester, we addressed all of the various social and scientific issues that came up in that piece. Admittedly though, I’m dismayed that this scary question has to be raised at this point in time, but it’s important for scholars to address and publicize given our society’s tragically short and selective memory.

So the first semester went well, and next semester I’ll be teaching a seminar focused on Homo naledi and a mid-level course on the prehistory of Central Asia. The Homo naledi class will be lots of fun, as we’ll used 3D printouts of H. naledi and other hominin species to address questions in human evolution. The Central Asia class will be good prep for when I return to Kazakhstan next summer to continue the hunt for human fossils in the country.

Osteology is still everywhere

A recurring segment over the years has been “Osteology Everywhere,” in which I recount how something I’ve seen out and about reminds me of a certain bone or fossil. Five of the blog 18 posts this year were OAs, and four of these were fossiliferous: I saw …

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Anatomy terminology hidden in 3D block letters,

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Hominin canines in Kazakhstani baursaki cakes,

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The Ardipithecus ramidus ilium in Almaty,

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Homo naledi juvenile femur head in nutmeg,

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And a Homo erectus cranium on a Bangkok sidewalk. As I’m teaching a fossil-focused seminar next semester, OA will probably become increasingly about fossils, and I’ll probably get my students involved in the fun as well.

New discoveries and enduring questions

The most-read post on the blog this year was about the recovery of the oldest human Nuclear DNA, from the 450,000 year old Sima de los Huesos fossils. My 2013 prediction that nuclear DNA would conflict with mtDNA by showing these hominins to be closer to Neandertals than Denisovans was shown to be correct.

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These results are significant in part because they demonstrate one way that new insights can be gained from fossils that have been known for years. But more intriguingly, the ability of researchers to extract DNA from exceedingly old fossils suggests that this is only the tip of the iceberg.

The other major discoveries I covered this year were the capuchin monkeys who made stone tools and the possibility that living humans and extinct Neandertals share a common pattern of brain development.

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An unrelated image from 2016 that makes me laugh.

The comparison between monkey-made and anthropogenic stone tools drives home the now dated fact that humans aren’t the only rock-modifiers. But the significance for the evolution of human tool use is less clear cut – what are the parallels (if any) in the motivation and modification of rocks between hominins and capuchins, who haven’t shared a common ancestor for tens of millions of years? I’m sure we’ll hear more on that in the coming years.

In the case of whether Neandertal brain development is like that of humans, I pointed out that new study’s results differ from previous research probably because of differences samples and methods. The only way to reconcile this issue is for the two teams of researchers, one based in Zurich and the other in Leipzig, to come together or for a third party to try their hand at the analysis. Maybe we’ll see this in 2017, maybe not.

There were other cool things in 2016 that I just didn’t get around to writing about, such as the publication of new Laetoli footprints with accompanying free 3D scans, new papers on Homo naledi that are in press in the Journal of Human Evolution, and new analysis of old Lucy (Australopithecus afarensis) fossils suggesting that she spent a lifetime climbing trees but may have sucked at it. But here’s hoping that 2017 tops 2016, on the blog, in the fossil record, and basically on Earth in general.

Osteology Everywhere: Skull in the Stone #FossilFriday edition

It’s that time of year again.

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It’s the end of the year and I’ve got Homo erectus on the brain somethin fierce. Our precedent-erect first popped up in Africa around 1.9 million years ago, quickly spread throughout much of the Old World, and persisted until perhaps as late as ~ 100,000 years ago in Java, Indonesia. This was a very successful species by all accounts, and as a result of its great range and duration, you can imagine it was also pretty variable.

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Hominin brain sizes. Boxes and whiskers represent sample tendencies and points are individual specimens. 1 = Australopithecus, 2 = Early Homo (cf. habilisrudolfensis), 3 = Dmanisi H. erectus, 4 = Early African H. erectus, 5 = Early Indonesian H. erectus, 6 = Chinese H. erectus, 7 = Later Indonesian H. erectus, 8 = modern humans.

Despite this great variation, H. erectus skulls generally share a common visage: long and low cranial vault, low forehead, protruding brow ridges, fun tuberosities and tori in the back. You’d recognize them anywhere. Including the sidewalk!

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Homo erectus in front of Ploenchit Tower, Bangkok (lateral view, front is to the right).

The relief in this sidewalk slat superficially looks like a trace fossil of partial H. erectus cranium, the face either missing (from the lower right) or taphonomically displaced toward the left side of the tile (see here for actual H. erectus trace fossils). This looks really similar to H. erectus from Indonesia, not surprising given its discovery in Thailand. Why, it could have come straight out of Figure 6 from a 2006 paper by Yousuke Kaifu and colleagues:

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Left lateral views of Javanese H. erectus crania, modestly modified from Kaifu et al. (2006: Fig. 6). Front is to the left this time.

Using my insane photo editing skills, I’ve inserted the Ploenchit Tower trace fossil (reversed) within the horde of heads presented by Kaifu et al., above. Like many of the real fossils, the Ploenchit specimen is missing the face (due to taphonomy), the supraorbital torus or brow ridge juts out from a low-rising forehead, and the occipital bone also projects out about from the otherwise rounded contour of the cranium. Note that there is a good deal of variation in each of these features among the real fossils.

What a happy holiday accident to find a Homo erectus cranium on the street!

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ResearchBlogging.org Reference
Kaifu Y, Aziz F, Indriati E, Jacob T, Kurniawan I, & Baba H (2008). Cranial morphology of Javanese Homo erectus: new evidence for continuous evolution, specialization, and terminal extinction. Journal of human evolution, 55 (4), 551-80 PMID: 18635247

Osteology Everywhere: Skeletal Spice

The American winter holiday season is steeped in special spices, such as nutmeg, cloves, cinnamon, and whatever the hell pumpkin spice is. I guess as part of the never-ending War on Christmas, each year this sensory and commercial immersion begins earlier and earlier. Since these have become old news, I’d pretty much forgotten about the seasonal spicecapade until just the other day. In prep for minor holiday gluttony, I was grinding fresh nutmeg when I made a startling discovery. Nutmeg is not just the fragrant fruit of the Myristica fragrans tree. No, there’s something far more sinister in this holiday staple.

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Merely nutmeg?

The ground section looks superficially like an unfused epiphyseal surface, whereas the rounded outer surface is more spherical. It turns out, in the most nefarious of all holiday conspiracies since the War on Christmas, nutmeg halves are nothing more than unfused femur heads! Compare with the epiphyseal surface of this Homo naledi femur head:

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Nutmeg (left) and H. naledi specimen UW 101-1098 (right).

This immature H. naledi specimen was recently published (Marchi et al., in press), and the associated 3D surface scan has been available for free download on Morphosource.org for a while now. It fits onto a proximal femur fragment, UW 101-1000, also free to download from Morphosource.

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Modified Fig. 11 from Marchi et al. It’s weird that only H. naledi bones were found in the Dinaledi chamber, but even weirder is the underreported presence of nutmeg.

Like most  bones in the skeleton, the femur is comprised of many separate pieces that appear and fuse together at different, fairly predictable ages. The shaft of the femur appears and turns to bone before birth, and the femur head, which forms the ball in the hip joint, usually appears within the first year of life and fuses to the femur neck in adolescence (Scheuer and Black, 2000). So we know this H. naledi individual was somewhere between 1–15ish years by human standards, probably in the latter half of this large range.

So there you have it. Osteology is everywhere – the holidays are practically a pit of bones if you keep your eyes open.

ResearchBlogging.orgREFERENCES

Marchi D, Walker CS, Wei P, Holliday TW, Churchill SE, Berger LR, & DeSilva JM (2016). The thigh and leg of Homo naledi. Journal of Human Evolution PMID: 27855981.

Scheuer L and Black S. 2000. Developmental Juvenile Osteology. New York: Elsevier Academic Press.