australopithecus anamensis

New (old) Australopithecus anamensis cranium

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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.

anamensis bee sting

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.

 

Virtual paleontology activity

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Last week Nazarbayev University hosted an Instructional Technology Showcase, in which professors demonstrated some of the ways we use technology in the classroom. This was the perfect venue to show off the sweet skeletal stuff we study in Biological Anthropology, through the use of pretty “virtual” fossils. In the past year I’ve started using CT and laser scans of skeletal remains to make lab activities in a few classes (I’ve posted two here and here). Such virtual specimens are especially useful since it is hard to get skeletal materials and casts of fossils here in the middle of the Steppe. These scans are pretty accurate, and what’s more, 3D printing technology has advanced such that physical copies of surface scans can be created from these virtual models. So for the Showcase, I had a table where passersby could try their hand at measuring fossils both in hand and in silico.

Lower jaw of an infant Australopithecus boisei (KNM ER 1477). Left is the plastic cast printed from the laser scan on the right.

Lower jaw of an infant Australopithecus boisei (KNM ER 1477). Left is the plastic cast printed from the laser scan on the right.

The Robotics Department over in the School of Science and Technology was kind enough to print out two fossils: KNM ER 1477, an infant Australopithecus boisei mandible, and KNM KP 271 a distal humerus of Australopithecus anamensis. They used a UP Plus 2 printer, a small desktop printer that basically stacks layers of melted plastic to create 3D models; they said it took about 9 hours to print the pair. Before the Showcase, I measured the computer and printed models on my own for comparison with published measurements taken on the original fossils (KP 271 from Patterson and Howells, 1967; ER 1477 from Wood, 1991). The virtual fossils were measured using the free program Meshlab, while basic sliding calipers were used to measure the printed casts.

I was pleasantly surprised at how similar my measurements were to the published values (usually within 0.1 mm), since it means that the free fossil scans provided by the National Museums of Kenya are useful not only for teaching, but potentially also for research.

The Virtual Paleontology Lab

The Virtual Paleontology Lab. The Kanapoi distal humerus is held in the foreground while the A. bosei jaw rests on the table. Yes, those are real palm trees.

Knowing that these models are pretty true to life (well, true to death, since they’re fossils), I was curious how students, faculty and staff would do. I picked two fairly simple measurements for each fossil. None of the people that came by to participate had any experience with bones or fossils, or measuring these in person or on a computer. Here are their results:

Boxplots showing participants' data, for two measurements on each of the fossils. The blue stars mark the published values. The red rugs on either side indicate measurements taken on the scans (left side) or printed casts (right).

Boxplots showing participants’ data, for two measurements on each of the fossils. The blue stars mark the published values. The red rugs on either side indicate measurements taken on the scans (left side) or printed casts (right).

For the most part, the inexperienced participants’ measurements are not too far off from the published values. There’s not really an apparent tendency for either cast or computer measurements to be more accurate, although measurements of the Kanapoi humerus are closer than the computer measurements (third and fourth boxes above). In my personal opinion, nothing beats handling fossils (or casts of them) directly, but this little activity suggests students can still make reliable observations using 3D scans on a computer.

Sweet free stuff:
Meshlab software
3D scans of fossils from the National Museums of Kenya

What big teeth you have, indeed

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If our friend Little Red Riding Hood was dumb enough to’ve thought a wolf in babushka threads was her grandma, well, she probably would have played Bingo with a grandmother-mimicking Australopithecus anamensis.
Australopithecus anamensis is the earliest undisputed hominid, found in deposits ranging from 4.2 – 3.9 million years ago in Ethiopia and Kenya (Leakey et al. 1995, White et al. 2006). Now, hominids are allegedly distinguished from other apes by having relatively short canine teeth distinguished by having relatively tall ‘shoulders,’ creating a diamond-shape in front view. Nevertheless, compared with humans these early australopiths had pretty murdersome canines, within the range of female chimpanzee species. (my dictionary is trying to tell me ‘murdersome’ isn’t a word, but I learned long ago not to learn right and wrong from a book)
Such canine form – relatively small with tall shoulders – was important in diagnosing Ardipithecus ramidus (> 4.4 million years) as a hominid back in the roaring 1990s (White et al. 1994). Of course, we learned in the 1980s that many ancient fossil apes looked superficially like hominids because of dental similarities, the result of either parallel evolution or hominids’ retention of primitive features. Indeed, even in light of the recently described Ardipithecus ramidus skull and skeleton, the main similarities with later, undisputed hominids are dental.
With this in mind, I’m struck by the canine of Nakalipithecus nakayamai, an ape from Kenya dating to nearly 10 million years ago (Kunimatsu et al. 2007). This is ape was a pretty important discovery because it began to fill in a rather lonesome Late Miocene ape fossil record in Africa. So, below is a picture of Nakali and anamensis canines, which I’ve tried to properly scale with the cutting-edge techniques of Microsoft Powerpoint (that is absolutely not a plug for Microsoft). On the left is Nakalipithecus, and the 2 on the right are Au. anamensis. The middle one is anamensis from Asa Issie in Ethiopia, and is the largest canine found of any hominid, ever I think. On the right is anamensis from Kanapoi in Kenya, not as big but sharp as shi…
…sh kabob skewers. Well crap, the “hominid feature” of short canine crown with nice shoulders is found in this 10 million year-old ape!
Two mutually exclusive scenarios could explain this similarity: [1] this canine morphology truly is a shared-derived feature of hominids, but hominids and Nakalipithecus just happened to evolve the same morphology independently for no better reason than, say, ennui. [2] This morphology is the ancestral condition for hominids (and chimpanzees and possibly gorillas). The fanciest cladistic methods won’t resolve this issue, only the discover of more badass fossils will. But if [2] is correct, that would deal a tough blow to the case of Ar. ramidus (and Sahelanthropus) behing a hominid. Really, it seems like the distinguishing feature of early hominids was their deplorable lack of distinguishing features.
ResearchBlogging.org
Oy, if bones and teeth are prone to homoplasy (similarity due to parallel evolution and not because of common ancestry), could paleoanthropologists have a special proclivity for it, too (that is, in naming dental hominids)?


Further reading!
Kunimatsu, Y., Nakatsukasa, M., Sawada, Y., Sakai, T., Hyodo, M., Hyodo, H., Itaya, T., Nakaya, H., Saegusa, H., Mazurier, A., Saneyoshi, M., Tsujikawa, H., Yamamoto, A., & Mbua, E. (2007). A new Late Miocene great ape from Kenya and its implications for the origins of African great apes and humans Proceedings of the National Academy of Sciences, 104 (49), 19220-19225 DOI: 10.1073/pnas.0706190104
Leakey, M., Feibel, C., McDougall, I., & Walker, A. (1995). New four-million-year-old hominid species from Kanapoi and Allia Bay, Kenya Nature, 376 (6541), 565-571 DOI: 10.1038/376565a0
Ward, C. (2001). Morphology of Australopithecus anamensis from Kanapoi and Allia Bay, Kenya Journal of Human Evolution, 41 (4), 255-368 DOI: 10.1006/jhev.2001.0507
White, T., Suwa, G., & Asfaw, B. (1994). Australopithecus ramidus, a new species of early hominid from Aramis, Ethiopia Nature, 371 (6495), 306-312 DOI: 10.1038/371306a0
White, T., WoldeGabriel, G., Asfaw, B., Ambrose, S., Beyene, Y., Bernor, R., Boisserie, J., Currie, B., Gilbert, H., Haile-Selassie, Y., Hart, W., Hlusko, L., Howell, F., Kono, R., Lehmann, T., Louchart, A., Lovejoy, C., Renne, P., Saegusa, H., Vrba, E., Wesselman, H., & Suwa, G. (2006). Asa Issie, Aramis and the origin of Australopithecus Nature, 440 (7086), 883-889 DOI: 10.1038/nature04629

Bridging the gap: Australopithecus from Woranso

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Recently discovered Australopithecus fossils from the Ethiopian site of Woranso-Mille help fill a gap between parts of the early hominin fossil record (Haile-Selassie et al, in press). The fossils date to between 3.8-3.6 million years ago (Ma), and consist of several teeth and a jaw fragment. These specimens show a number of features that are intermediate in morphology between the earlier Au. anamensis (4.2-3.9 Ma) and later Au. afarensis from Laetoli (~3.7-3.5 Ma). As a result, the Woranso fossils lend support to the hypothesis that Au. anamensis and Au. afarensis represent a single evolving species (i.e. Kimbel et al. 2006).



I think this is exciting for two reasons. First, the fossils bridge the morphological gap between the older anamensis and younger afarensis fossils. As a result, we get to ‘see’ anagenetic evolution—changes within a single lineage. One topic in evolutionary biology is about the mode and tempo of evolution: are species fairly constant, then evolve into multiple ‘daughter’ species (“punctuated equilibrium”); or does evolutionary change tend to occur more within individual lineages (“anagenesis”)? Obviously neither is mutually exclusive, rather evolution is probably best characterized variously by both processes. Still, in the world of paleoanthropology, where many researchers argue for rapid and constant species turnover within the human lineage, it is cool to see a convincing argument for anagenesis. However, this ignores the meager (but intriguing) K. platyops material (Leakey et al. 2001), dating to around 3.5 Ma, possibly indicating the proliferation of at least two hominin species shortly after 4 Ma.



Second, the morphological intermediacy of the Woranso fossils allow a look at the patterns of evolutionary change within the anamensis–afarensis lineage. The authors note that the teeth of the Woranso hominins are generally more similar to anamensis, but have some derived characters of the later afarensis teeth. If we truly have a glimpse of dental evolution within a single lineage, we can ask questions about the evolution and development (“Evo-Devo”) of teeth. Are changes in these teeth correlated in a way that could be predicted by certain developmental models? Or is selection acting independently on various tooth traits?



References

Haile-Selassie Y, Saylor BZ, Deino A, Alene M, and Latimer BM. New hominid fossils from Woranso-Mille (Central Afar, Ethiopia) and Taxonomy of Early Australopithecus. American Journal of Physical Anthropology, in press.

Kimbel WH, Lockwood CA, Ward CV, Leakey MG, Rak Y, and Johanson DC. 2006. Was Australopithecus anamensis ancestral to A. afarensis? A case of anagenesis in the hominin fossil record. Journal of Human Evolution 51: 134-152.

Leakey MG, Spoor F, Brown FH, Gathogo PN, Kiarie C, Leakey LN, and McDougall I. 2001. New hominin genus from eastern Africa shows diverse middle Pliocene lineages. Nature 410: 433-440.