Malapa

[insert clever quip about australopithecus hips]

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A week and a half ago, Kibii and colleagues (2011) published reconstructions and re-analyses of two hips belonging to the 1.98 million-year old Australopithecus sediba. As with many fossil discoveries, these additions to the fossil record raise more questions than they answer. Unless the question was, “did A. sediba have a pelvis?” It did. Here’s a good summary from the paper itself:

Thus, Au. sediba is australopith-like in having a long superior pubic ramus and an anteriorly positioned and indistinctly developed iliac pillar…[and] Homo-like in having vertically oriented and sigmoid shaped iliac blades, more robust ilia, and a narrow tuberoacetabular sulcus…and the pubic body is upwardly rotated as in Homo. (p. 1410, emphases mine)

So far as I can tell, the main way the hips are ‘advanced’ toward a more human-like condition is that the iliac blades are more upright and sweep forward more than in earlier known hominid hips. Here’s the figure 2 from the paper (more sweet pics of the fossils are available here). NB that in both A. sediba hips much of the upper portions of the iliac blades are missing (reconstructed in white; this region is missing in lots of fossils), so it’s possible they were more flaring like the australopith in the center photo.

The authors’ bottom-line, take-home point is that the A. sediba pelvis has features traditionally associated with large-brained Homo – but belonged to a small-brained species (based solely on the ~430 cc MH1 endocast). They argue that this means that many of these unique pelvic features did not evolve in the context of birthing large-brained babies, as has often been thought. They state that these features are thus “most parsimoniously attributed to altered biomechanical demands on the pelvis in locomotion,” and suggest that this hypothetical locomotion was mostly bipedalism but with a good degree of climbing. Maybe, maybe not. This interpretation is consistent with the analysis of the A. sediba foot/ankle (Zipfel et al. 2011).

The weird mix of ancient (australopith-like) and newer (Homo-like) pelvic features in A. sediba really raises the question of how australopithecines moved around. More intriguing is that the A. sediba pelvis has different Homo-like features than the ~1 million year old Busidima pelvis (Simpson et al. 2008), which has been attributed to Homo erectus (largely in aspects of the iliac blades). This raises the question of whether A. sediba is really pertinent to the origins of the genus Homo, and whether the Busidima pelvis belongs to Homo erectus or a late-surviving robust australopithecus (e.g. boisei, Ruff 2010).

Also interesting is that the subpubic angle (in the pic above, the upside-down “V” created by the pubic bones just above the red labels) is pretty low in MH2. This is curious because modern human males and females differ in how large this angle is – females tend to have a large angle which contributes to an enlarged birth canal, whereas males have a low angle like MH2. But MH2 is considered female based on skeletal and dental size. This raises the additional questions of whether human-like sexual dimorphism had not evolved in hominids prior to 1.9 million years ago, and whether the sex of MH2 was accurately described.

Finally, though the authors did a great job comparing this pelvis with those from other hominids, I think a major, more comprehensive comparative review of hominid pelves is in order. How does the older A. afarensis hip from Woranso (Haile-Selassie et al. 2010) inform australopithecine pelvic evolution? What about the possibly-contemporary-maybe-later hip from the nearby site of Drimolen (Gommery et al. 2002)? Given the subadult status of the MH1 individual, it would be interesting to compare with the WT 15000 Homo erectus fossils, or A. africanus subadults from Makapansgat, to examine the evolution of pelvic growth.

ResearchBlogging.org

Lots of interesting questions arise from these fascinating new fossils. “The more you know,” right?

References
Gommery, D. (2002). Description d’un bassin fragmentaire de Paranthropus robustus du site Plio-Pléistocène de Drimolen (Afrique du Sud)A fragmentary pelvis of Paranthropus robustus of the Plio-Pleistocene site of Drimolen (Republic of South Africa) Geobios, 35 (2), 265-281 DOI: 10.1016/S0016-6995(02)00022-0

Haile-Selassie Y, Latimer BM, Alene M, Deino AL, Gibert L, Melillo SM, Saylor BZ, Scott GR, & Lovejoy CO (2010). An early Australopithecus afarensis postcranium from Woranso-Mille, Ethiopia. Proceedings of the National Academy of Sciences of the United States of America, 107 (27), 12121-6 PMID: 20566837

Kibii, J., Churchill, S., Schmid, P., Carlson, K., Reed, N., de Ruiter, D., & Berger, L. (2011). A Partial Pelvis of Australopithecus sediba Science, 333 (6048), 1407-1411 DOI: 10.1126/science.1202521

Ruff, C. (2010). Body size and body shape in early hominins – implications of the Gona Pelvis Journal of Human Evolution, 58 (2), 166-178 DOI: 10.1016/j.jhevol.2009.10.003

Simpson, S., Quade, J., Levin, N., Butler, R., Dupont-Nivet, G., Everett, M., & Semaw, S. (2008). A Female Homo erectus Pelvis from Gona, Ethiopia Science, 322 (5904), 1089-1092 DOI: 10.1126/science.1163592

Zipfel, B., DeSilva, J., Kidd, R., Carlson, K., Churchill, S., & Berger, L. (2011). The Foot and Ankle of Australopithecus sediba Science, 333 (6048), 1417-1420 DOI: 10.1126/science.1202703

New Australopithecus sediba analyses

/ zcofran / 2 Comments

A slew of papers analyzing the brain, hands, feet, and pelvis of Australopithecus sediba were just published in the journal Science. I have not had a chance to read them yet – nor will I for a few days as I’m in a wedding Saturday [not mine 😦 ] and the partying starts in a few hours. So I’m afraid I won’t be able to report on and interpret these on the blog for a while. Please stay tuned!

CT reconstruction, from Science (follow link above).
The exact same thing happened to me 2 years ago when the Ardipithecus ramidus skeleton was (finally) published. I remember waiting in the Detroit airport to board a flight to St. Louis to begin my platonic soul-mate’s bachelor party, and I get a flurry of emails on my phone announcing the skeleton in the 15 year old closet.
So media beware – whenever I’m in a wedding, badass new fossil studies will be published. 

eFfing Fossil Friday – Renaissance and Designer Fossils

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Sorry I’m a bit late on this one, and that I’ve fallen behind on keeping the blog updated. I’ve been scrambling to make all the observations on, and collect all the data from, these Australopithecus robustus mandibles in a short time. As my advisor likes to remind me, everything always takes 3x longer than you initially anticipate, and this is certainly true of my work here. Yesterday (the actual Fossil Friday), in fact, I probably spent only 30 min with these fossils. Instead, I accompanied Lee Berger and John Hawks on a trip to Malapa – the site that recently yielded fossils of the mysterious Australopithecus sediba – and other sites in the area. To get there, I rented a car and drove on the wrong side of the road for the first time – it was a trippy trip, every time I got in the car I reached to my left for a phantom seat belt, and kept searching for the gear-shift my mind thought was in the door. Nuttiness.
Anyway, I have two thoughts for this edition of eFfing Fossil Friday. First point, related to the great tour from Dr. Berger, is that a ton of hominid fossils are lying in wait for us to re-expose them to the light of day. In South Africa, the classic Plio-Pleistocene sites have been Makapansgat (A. africanus), Sterkfontein (A. africanus) and Swartkrans (A. robustus and early Homo). These sites have variously been worked since the early 20th century. Since then, a number of other hominid-bearing sites – largely in the same area as Sterkfontein and Swartkrans – have been discovered: Gladysvale, Gondolin, Drimolen, and most recently Malapa. Yet still a metric-tonne of work is still being done on the more classic sites (except maybe Makapansgat?).
View of the valley, Malapa is somewhere in the background, I think the green patch of trees near the center, just before the big hill-shadow (?).
But these sites are just the tip of a fossiliferous iceberg. A few years ago when I was working here I accompanied some other researchers on a survey for more fossil sites in the area. What I learned then is that if you look across the Sterkfontein valley in the winter, the dessicated grassland is pimpled with the occasional patch of green trees – these small verdant isles are the tells of underlying cave systems (the caves contain water that plants will cut throats for). What was driven home yesterday at Malapa and other sites Dr. Berger showed us, is that these caves are all over the place, many fossil treasure-troves. What’s more, the A. sediba discovery (and the massive hominid molars from Gondolin) points to the idea that we are only beginning to understand what hominid life was like in the past. There is a rich prehistory still waiting to be discovered in South Africa, and undoubtedly also the rest of the African continent. Human paleontological work is far from exhausted. Let us usher in a Renaissance of field Paleoanthropology!
My next thought is that the process of fossilization can make the fossil-memories of past life quite beautiful. Now, in life the enamel of teeth is white-ish (yellow/brown is also not uncommon), and bone is this off-white/yellowish color. But during the process of fossilization, the original minerals used to make the bone (and less commonly teeth) are replaced by those in the surrounding soil. Often these minerals gussy up the fossils in neat new ways – manganese for example tends to make bone/tooth black.


Check out SK 61, an infant/child Australopithecus robustus. After fossilization, this thing takes on a designer, tortoise-shell coloration (left, above). SK 12, an older adult A. robustus (right, above), is another good example: some subterranean joker has drawn a smiley face beneath his left premolar (circled). So while we are often left with a meager fossil record, at least the fragments we get are voluptuously variegated.

01/01/2011: Looking forward and backward, so fast you may barf

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2010 was a big year for anthropology and lawn-chair-anthropologists. There was laughter and crying, and maybe also some yelling. And smiling. Let’s take a look back at some of the big events of the past year.

  1. Ancient DNA. What a great year for ancient human DNA! In April, Krause and colleagues (2010) announced the sequencing of mitochondrial DNA from a ~50,000 year old girl from Denisova in Siberia. This sequence was twice as divergent from humans as Neandertal mtDNA, which really shocked a lot of people. Then just a week or so ago Reich and colleagues (2010) announced nuclear DNA from the site. The big news was that these ancient humans contributed genes to modern day Melanesians, but not other modern humans sampled. In May, Green and the Pääbo lab announced a draft sequence of the Neandertal nuclear genome. Like with the Denisova story, Neandertal mtDNA is fairly distinct from that of modern humans, and the nuclear genome revealed contribution to some modern humans but not to others. Basically, ancient DNA came out supporting the multiregional model of modern human origins.
  2. Malapa hominids. Lee Berger and researchers announced a new fossil site, Malapa, in South Africa. This site yielded 2 partial skeletons (and others forthcoming), including a very well-preserved skull of a subadult. Superficially the thing looked to me like Australopithecus africanus, though the authors argue that it shows some features derived toward the condition of early Homo. But at an estimated 1.9-1.7 million years old, it’s a little too young to have anything to do with the origin of Homo – not to mention its small 400 cubic centimeter cranial capacity. I really don’t know what to do with Malapa yet.
  3. Woranso-Mille Australopithecus afarensis. This site dates to around 3.6 million years ago, so it’s roughly contemporaneous with Laetoli afarensis, or intermediate in age between Laetoli and later afarensis sites like Maka and Hadar. Haile-Selassie and colleagues described a partial skeleton from the site. This male includes part of the pelvis, which didn’t get much coverage. But it has a 1st rib, scapula and clavicle, indicating a fairly human-like (rather than ape-like) torso shape. So even for how well we know A. afarensis, we’re always learning more about our ancestor.
  4. Saadanius hijazensis and catarrhines. I didn’t blog about this one at the time as I was getting ready to hit the field. But this was exciting because Iyad Zalmout and friends here at UM discovered and analyzed it. Saadanius was found in ~29 million year old deposits in Saudi Arabia, right around the estimated time of origins of apes. The fossil looks like an Aegyptopithecus to my untrained eye, but apparently may be similar to the last common ancestor of apes and old world monkeys.
  5. Field work. I had my first (of hopefully more!) field season at Dmanisi in Georgia. Paleoanthropology would be nothing without fossils, so an important aspect of the job I’d like to do more of is increasing the fossil record. Dmanisi is an amazing place for this, being among the oldest human sites outside Africa, and the interesting ‘intermediacy’ of the Dmanisi hominids between early Homo and more classic H. erectus. We found some great stuff last year, and I anticipate the site will produce more great fossils in the future. Who knows, maybe more fossiliferous deposits will be found in nearby regions?
So it was a helluva year, 2010. What excitement will 2011 bring? Here are some things I’d like to, or expect to, see this year:
  1. More ancient DNA – the surprise that many researchers got from Denisova and Neandertal ancient DNA clearly warrants more work on other ancient DNA. What does that of other fossil humans look like? Will the picture of human origins become further complicated (that is, different from paradigmatic out-of-Africa replacement)? In this regard we need to analyze DNA from more late Pleistocene fossils regarded as ‘anatomically modern.’
  2. a) More about Malapa. I want to say I heard somewhere that there were more hominids than just the 2 presented in the Science paper. These additional specimens will provide further evidence, including what variation within the site was like, and how it fits with other South African specimens. From the appearance of things, these fossils may be late-persisting A. africanus, somehow contemporaneous (roughly sympatric?) with A. robustus and possibly early Homo. Perhaps more work on the geology and taphonomy of Malapa will show it to be older, contemporaneous with the nearby site of Sterkfontein known for abundant A. africanus fossils? Probably not.

    b) More hominid sites and fossils in South Africa. One thing that was neat about Malapa was that it was from slightly outside the rest of the South African ‘cradle’ sites like Sterkfontein, Kromdraai, Drimolen, and Swartkrans. When I was in the area in 2008 I went with some researchers on survey of the Sterkfontein valley, new sites are definitely being sought. Perhaps 2011 will see the discovery of more Malapa-like sites?
  3. Human fossils from East Asia. Maybe even ancient DNA recovery from the region. East Asia has long been thought to be a potential ‘center’ of human origins. Earlier in the year, fossils coming from Zhirendong suggest some of the earliest evidence of chin, arguably a ‘modern human’ feature. Recent fossil and genetic discoveries ought to usher a renewed vigor in examining human evolution in Asia.

That’s all I feel like doing for now. Happy New Year, all!

ResearchBlogging.org
References
Berger, L., de Ruiter, D., Churchill, S., Schmid, P., Carlson, K., Dirks, P., & Kibii, J. (2010). Australopithecus sediba: A New Species of Homo-Like Australopith from South Africa Science, 328 (5975), 195-204 DOI: 10.1126/science.1184944
Cann, R., Stoneking, M., & Wilson, A. (1987). Mitochondrial DNA and human evolution Nature, 325 (6099), 31-36 DOI: 10.1038/325031a0
Green, R., Krause, J., Briggs, A., Maricic, T., Stenzel, U., Kircher, M., Patterson, N., Li, H., Zhai, W., Fritz, M., Hansen, N., Durand, E., Malaspinas, A., Jensen, J., Marques-Bonet, T., Alkan, C., Prufer, K., Meyer, M., Burbano, H., Good, J., Schultz, R., Aximu-Petri, A., Butthof, A., Hober, B., Hoffner, B., Siegemund, M., Weihmann, A., Nusbaum, C., Lander, E., Russ, C., Novod, N., Affourtit, J., Egholm, M., Verna, C., Rudan, P., Brajkovic, D., Kucan, Z., Gusic, I., Doronichev, V., Golovanova, L., Lalueza-Fox, C., de la Rasilla, M., Fortea, J., Rosas, A., Schmitz, R., Johnson, P., Eichler, E., Falush, D., Birney, E., Mullikin, J., Slatkin, M., Nielsen, R., Kelso, J., Lachmann, M., Reich, D., & Paabo, S. (2010). A Draft Sequence of the Neandertal Genome Science, 328 (5979), 710-722 DOI: 10.1126/science.1188021
Haile-Selassie, Y., Latimer, B., Alene, M., Deino, A., Gibert, L., Melillo, S., Saylor, B., Scott, G., & Lovejoy, C. (2010). An early Australopithecus afarensis postcranium from Woranso-Mille, Ethiopia Proceedings of the National Academy of Sciences, 107 (27), 12121-12126 DOI: 10.1073/pnas.1004527107
Krause, J., Fu, Q., Good, J., Viola, B., Shunkov, M., Derevianko, A., & Pääbo, S. (2010). The complete mitochondrial DNA genome of an unknown hominin from southern Siberia Nature, 464 (7290), 894-897 DOI: 10.1038/nature08976
Liu W, Jin CZ, Zhang YQ, Cai YJ, Xing S, Wu XJ, Cheng H, Edwards RL, Pan WS, Qin DG, An ZS, Trinkaus E, & Wu XZ (2010). Human remains from Zhirendong, South China, and modern human emergence in East Asia. Proceedings of the National Academy of Sciences of the United States of America, 107 (45), 19201-6 PMID: 20974952
Reich D, Green RE, Kircher M, Krause J, Patterson N, Durand EY, Viola B, Briggs AW, Stenzel U, Johnson PL, Maricic T, Good JM, Marques-Bonet T, Alkan C, Fu Q, Mallick S, Li H, Meyer M, Eichler EE, Stoneking M, Richards M, Talamo S, Shunkov MV, Derevianko AP, Hublin JJ, Kelso J, Slatkin M, & Pääbo S (2010). Genetic history of an archaic hominin group from Denisova Cave in Siberia. Nature, 468 (7327), 1053-60 PMID: 21179161
Zalmout IS, Sanders WJ, Maclatchy LM, Gunnell GF, Al-Mufarreh YA, Ali MA, Nasser AA, Al-Masari AM, Al-Sobhi SA, Nadhra AO, Matari AH, Wilson JA, & Gingerich PD (2010). New Oligocene primate from Saudi Arabia and the divergence of apes and Old World monkeys. Nature, 466 (7304), 360-4 PMID: 20631798

Holy Effing Crap II: Australopithecus from Malapa

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Lee Berger and colleagues report in Science today on 2 incredibly well preserved skeletons – including perhaps the best-preserved hominid skull in South Africa, in some ways as good as or better than Sts 5 (Australopithecus africanus). The specimens come from a site called Malapa in South Africa, dating to around 1.9 – 1.7 million years ago. The authors argue that it is so unique in its features that it warrants a new species – Australopithecus sediba – linking the earlier A. africanus with later Homo habilis. Is it really a new species? In my personal opinion, there’s not much distinguishing it from A. africanus.
The amazingly preserved skull is of a subadult, maybe 11 years old. The highly angled root of the zygomatic, positioned just above the M1 alveolus is classic A. africanus. It really reminds me of Sts 17, or possibly Sts 52 in the lower face. The prognathism is modest and lacks the anterior nasal pillars which tend to be fairly pronounced in A. africanus; in this regard it is quite comparable to specimens like TM 1512. Like Sts 52, it has multiple infraorbital foramina. The cranial capacity is estimated at 420 cubic centimeters (cc), which is pretty small, but within the estimated A. africanus range of variation. The authors say that the relatively low position of the temporal lines, spaced far apart from the sagittal suture, and the fact that the zygomatic arches do not flare to the sides, are features more like Homo than like A. africanus. But the specimen is only 11 years old; while the brain is finished growing, the face and chewing muscles probably aren’t. So if this were a fully adult specimen, I’m sure both of these features would come to look more like A. africanus.
The upper and lower first and second molars increase in size posteriorly, and have a distinct protostylid (enamel shelf along the side of one of the cusps) which has a very high frequency in A. africanus. The upper molars, while not totally complete, preserve something that I’ve noticed and I’m sure is in the literature, that the M1 is fairly small and squared compared to the generally larger and not-quite-as-square M2. In a few words, then, the skull seems to fit comfortably in the range of A. africanus variation.
Perhaps the least A. africanus-like aspect of the skull is the supraorbital torus. The supraorbital, or brow, is generally a modestly expressed in most africanus specimens that preserve it. The Malapa specimen is much more similar, to my eye, to later Homo in its projection and arching over the eyes. What could this mean? Moss and Young’s (1960) functional matrix model of looking at the cranium views the supraorbital as a function of the relative position of the brain to the orbits. Perhaps the spatial relationship between the vault and the face which becomes characteristic of later homo becomes established in earlier in the lineage. Other than the supraorbital, this specimen seems purely A. africanus to me. In all, the contour of the vault may not be too different from younger Dmanisi specimens like D2700 or 2280; that Malapa lacks the occiput gives an artificially short front-to-back look to the specimen. The face, however, is totally A. africanus.
Perhaps one of the most striking images is the lateral view. This photo looks strikingly similar to a subadult chimpanzee, albeit with a taller face and less prognathic snout. Maybe I’ve just seen a subadult ape before that this thing reminds me of.
So, this is an immensely exciting set of fossils. Is there a new species of Australopithecus? I wouldn’t bet my life on it. If you go with the widely held idea, that A. africanus or something like it was ancestral to later A. robustus on the one hand, and our Homo ancestors on the other, this thing would fall on the Homo side of that split. So in this case, since we’re not seeing anagenetic evolution – evolutionary change within a lineage – but rather branching, how do you name this thing? It might be slightly more derived toward a Homo than either its “pure” africanus ancestors and A. robustus evolutionary cousins, does this make it Homo? The issue is that adaptively its morphology doesn’t seem to be different from A. africanus, which would argue against the generic distinction. But if its later ancestors become H. habilis and nothing else, then I suppose this would make it a “chronospecies” of H. habilis. So maybe we should call this thing H. habilis? I think most people would argue with this simply on the brain size issue. And the brain is way smaller than any proclaimed Homo specimen.
Taxonomically, this will be a tough call.
References
Berger L, de Ruiter DJ, Churchill SE, Schmid P, Carlson KJ, Dirks PHGM, and Kibii JM. 2010. Australopithecus sediba: A New Species of Homo-like Australopith from South Africa. Science 328: 195 – 204
Moss ML and Young R. 1960. A functional approach to craniology. American Journal of Physical Anthropology 18: 281 – 292