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.

Pride & Predator

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.

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Australopithecus africanus–a highly strained face?

A cool paper came out today [1] in which researchers used finite element analysis to test hypotheses about the biomechanics of chewing in Australopithecus africanus, a South African hominin that lived probably 3-2 million years ago. Finite element analysis is a technique adapted from engineering in which one creates a virtual model of a structure (here, CT data to make a composite cranium of two fossils, Sts 5 and Sts 52), gives the structure mechanical properties (here, the properties of bone), apply various forces of various direction and magnitude, and then can see how the structure is affected by these loads. It’s an interesting technique that has only recently become popular in physical anthropology, probably as the technology becomes better and cheaper, even though Chris Ruff recommended the technique twenty years ago [2].

The authors used this technique to see if the bony facial structure of A. africanus was adapted specially withstand special bite-loads, specifically at the premolars. For example, A. africanus‘s ‘anterior nasal pillars’—bony struts on either side of the nasal aperture—have long been thought to be buttresses against bite forces, but this had yet to be demonstrated. The authors tried different loading patterns—molars only, premolars only, and molars + premolars–to see how strains were distributed across the cranium.

Regardless of the loading regime, the strains through most of the face were the same. However, when just the premolars were loaded, strains increased noticeably on the nasal margins, compared to the other loading patterns. Thus, the results were consistent with the hypothesis that the face of A. africanus, specifically its anterior nasal pillars, are special adaptations for high-strain bite forces concentrated on the premolars. The results also indicate that the A. africanus cranium was adapted to such a high-force diet, rather than a high-volume (i.e. chewing lots of food) diet, because overall strains were the same regardless of whether the only the molars or all the posterior teth were loaded.

This last result leaves me perplexed as to the significance of a major trend in hominin evolution (except with the inception of Homo): postcanine megadontia. On the whole, through hominin evolution the molars and premolars get bigger and bigger (again, not really in Homo)—this is extreme in A. boisei, one of the latest surviving, “robust” australopiths. Presumably, this tendency toward megadonty increased the amount of food that could be ingested at a given time. But, the paper suggests that premolar loading was, if nothing else, an important selective factor in A. africanus, and presumably later hominins–this explains molarization of premolars (again, most noticeably in A. boisei). But it does not explain why molars should also enlarge, unless molar and premolar size are integrated, that is, under the same genetic and developmental control(s). Hey, that’s a cool hypothesis.… Also, I suppose the results don’t refute the possibility that molar size increased in order to accommodate higher volume of food, but rather they simply indicate that the face was not specially adapted to withstand such a diet.

It would also have been interesting to see how the cranium performed under more loading regimes, expecially of the anterior teeth. What really distinguishes A. africanus from its offshoot A. robustus (and especially A. boisei, to whom I don’t think africanus is ancestral) is its retention of large canines and incisors. How do the crania of these taxa differ in their ability to withstand different dental loading patterns? The DNH 7 skull [3], of a very small female from the S. African site of Drimolen, is probably complete enough to be subject to a similar study.

Anyway, it’s a cool paper that really shows off the promise of ‘virtual anthropology.’

Suggested Reading
1 David S. Strait, Gerhard W. Weber, Simon Neubauer et al., Proceedings of the National Academy of Sciences, USA (2009).
2 C. B. Ruff, Folia Primatologica 53 (1-4), 142 (1989).
3 A. W. Keyser, S. Afr. J. Sci. 96 (4), 189 (2000).

Old bones, new methods

A paper has come out that examines dinosaurs’ sense of smell by using computed tomography (CT) to measure the size of the relative size of dinosaurs’ olfactory bulbs, part of the brain that deals with the sense of smell. This is one example of the really interesting paleontological questions that can be addressed with modern imaging techniques (hint into my NSF proposal…).

The olfactory bulb is a part of the brain that deals with smell. Quite simply, the larger the olfactory bulb, the greater an organism’s reliance upon smelling. As a group, primates rely less on scent than many other mammals, and so their olfactory bulbs are relatively small. Humans have a greatly reduced bulb compared to other primates. Prosimians, the most primitive primates, have much larger bulbs than other primates. Thus, scent plays a larger role for their ecology, possibly due to the fact that many are nocturnal (there’s less light at night, but smells always abound).

This dinosaur study used this logic to infer that Tyrannosaurus rex (probably the ‘sexiest,’ most over hyped dinosaur ever) had a very strong sense of smell. This has important implications about T. rex–was it nocturnal (like all those scenes in Jurassic Park…)? Did scent play an important social role (like modern scent-marking mammals including prosimians)?

Also cool was how the team examined olfactory bulb and brain size. The importance of an scent can be inferred based on an animal’s olfactory bulb size relative to the size of the entire brain. The study used endocasts (naturally preserved impressions of surfaces) of brains and CT scans of skulls to estimate these sizes. This illustrates the usefulness of computed tomography in paleontology. It can be difficult to study certain aspects of fossils non-invasively. By CT scanning a fossil, a digital 3D image of it is created, and this allows researchers to examine all the surfaces (including interior) of the bone, with much better accuracy and resolution than X-rays. In this way, researchers can create ‘virtual’ endocasts, among other things. CT scanning also makes bone (and other material) of different densities distinguishable, so that fossil teeth and the insides of bones can be examined without having to damage them.

CT data are becoming very important not just in medical imaging, but also biological anthropology (Dana knows lots!). Many anthropologists, including the team I met in Vienna this summer, are using CT data to reconstruct fragmentary fossils, uncover tooth shapes in fossil hominins, study brain evolution with ‘virtual’ endocasts, and many other things. This is a very exciting time for anthropology and paleontology, as modern medical imaging techniques have made it possible to address (and ask) research questions that were not possible in the past. In fact, my current NSF graduate research fellowship proposal is seeks to develop a new method for studying cranial variation using CT scans. If I get it (fingers crossed), I’ll keep you all updated with how the research goes. Here’s hoping!

Reference
Zelinitsky D, Therrien T and Koboyashi Y. Olfactory acuity in theropods: paleobiological and evolutionary implications. Proceedings of the Royal Academy B. Corrected proof, in press.