Another small Middle Pleistocene person

Last year I brought up the implications of the small female pelvis from Gona, Ethiopia for body size variation in Homo erectus (see previous post). This individual was much smaller than other Middle Pleistocene Homo fossils, indicating size variation comparable to highly sexually dimorphic gorillas and unlike recent human populations. Before this pelvis, most known Homo erectus fossils were fairly large (comparable to living people), with only a few hints of much smaller individuals (e.g., KNM-ER 427000, KNM-OL 45500). Now joining this petite party, this tiny troop, this little lot, this compact cadre, etc., is KNM-WT 51261, a 750,000 year old molar from Kenya (Maddux et al., in press).

Occlusal area for hominin first molars. The tooth is from Fig. 2 and the plot from Fig. 3 in the paper.

Occlusal area for first molars in the genus Homo. The tooth image is from Fig. 2 and the plot from Fig. 3 in Maddux et al. Lookit how tiny it is!

This ‘new’ specimen substantially increases the range of size variation among early African H. erectus molars, although the expanded range isn’t remarkable compared with later Homo samples such as from Zhoukoudian cave in China or Neandertals. What is different, though, is that most of the highly variable samples show a fairly continuous range of variation, while the WT 51261 molar is a considerable outlier from the rest of the African Middle Pleistocene sample (a lot like the situation with the Gona pelvis). So this tooth re-raises an important question: were smaller specimens like Gona and WT 51261 as rare in life as they are in the fossil record, or was such great size variation common in the Middle Pleistocene? How we reconstruct what kind of animal Homo erectus was differs depending on the answer to this question.

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Inanimate fossils getting older still

Two reports came out last week in the journal Nature, re-dating some European human fossils to before 40 thousand years ago (kya), a few thousand years older than previous evidence for modern-looking people in the region. The media have been reporting these studies as revealing “the first Europeans,” but of course we all know that the first Europeans were the badass hominids, my favorites, from the 1.8 million year old site of Dmanisi.

KC4 maxilla (Higham et al. 2011)

From Kent’s Cavern (United Kingdom) is a partial maxilla, now dated to 44 – 41 kya* (Higham et al. 2011; but see below). The jaw fragment with highly worn teeth was found just above some Aurignacian-like (Upper Paleolithic) blades in 1927. [NB below these 2 blades were 2 other blades of a tool “complex…tentatively associated with Neandertals] The laughable amount of bone makes it rather impossible to say whether the fossil represents a Neandertal or more modern-looking human. The authors examined what little of the morphology was left and concluded that the fossil shared the most similarities with recent humans but only a few with Neandertals. A more rigorous analysis of what this mix of traits means would have been nice (i.e. why would an individual have derived traits of both ‘modern’ humans and Neandertals?). The researchers tried to extract DNA for analysis, but apparently organic remains were too poorly preserved for a good analysis. Bummer.

Cavallo B and C (Benazzi et al. 2011)

A similar older-than-we-thought story is reported by Stefano Benazzi and buddies, who reanalyzed teeth from the Italian site of Grotta del Cavallo (left). After the site was excavated in 1967, the teeth were attributed to Neandertals and the lithics classified as “Uluzzian.” I would be a dirty liar if I said knew anything about the “Uluzzian” industry (try this other site which may be more informative), but apparently it’s seen as transitional between the Neandertal-associated Mousterian and ‘more advanced’ Upper Paleolithic toolkits. So this assemblage could be used to argue that Neandertals were smart enough to upgrade to a sexier stone tool industry shortly before their anatomy (but not their genes!) disappeared. BUT! also like in Kent’s Cavern paper, Benazzi and colleagues examined what little morphology is preserved in the fossil teeth, and (re)assigned them to modern-looking humans. The authors provided nice qualitative and quantitative arguments for the human status of the teeth, though again I have to raise caution that these are only teeth and we have no idea what the rest of the skeleton would have looked like. Researchers also analyzed shells associated with the now-human teeth and dated the site to around 44 kya, making them the oldest probably-human remains in Europe.

Now, according to conventional wisdom, the Neandertals were dullards who made and used the Mousterian stone tool industry. The Mousterian was nice and all, but not nearly as wicked-pisser as the smart and sassy modern-looking humans’ Aurignacian toolkit. The thing is, though, there really hasn’t been really a lot of evidence unequivocally linking modern-looking fossils with Aurignacian artifacts. So both of the recent studies in Nature lend support to the idea that maybe modern humans were the sole makers (and users) of an advanced stone tool industry. But it’s important to remember [1] that the blades ‘associated’ with the Kent’s Cavern jaw can’t really be definitively attributed to a stone tool industry; [2] the blades were deeper in the cave than the jaw, and so may actually be appreciably older than the jaw; and [3] while the teeth from Kent’s Cavern and Cavallo do look most comparable to those belonging to ‘anatomically’ modern humans, we don’t know what the skulls or skeletons containing the teeth looked like. All that said, it’s neat to see the possible appearance of certain anatomy and technology in Europe thousands of years earlier than previously thought. It also re-raises the issue of the degree to which modern-looking humans and Neandertals overlapped in space and time, and what these interactions would have been like (I’d guess terrifying, hilarious and/or sexy).

KC4 originally
(Higham et al. 2011)

A fun lesson also comes from the Kent’s Cavern study. Higham and colleagues report that the KC4 human maxilla was excavated in 1927 and analyzed by Sir Arthur Keith, a well-trained anatomist and paleoanthropologist famous in his day. Keith described the fossil as containing a canine, second premolar and first molar (right, compare with above). Higham and colleagues, however, noticed that what Keith described as a second premolar was in fact a first premolar. The teeth are so worn they mostly lack information about their form and features, so this mistake probably didn’t really mislead anatomists in any way. Still, it goes to show that even experts like Keith can make mistakes or overlook the things they know best, and this is not the first time I’ve seen this happen with fossils. So always (politely) question those giants whose shoulders you’re standing upon.

*Update (07 Nov): John Hawks points out that the KC4 maxilla itself was not used to obtain the older radiocarbon age estimate. In 1989 the maxilla was directly dated to around 30 kya, over 10 ky younger than the new estimates. Higham and friends thought this date was too young, based on methodological grounds. An attempt to redate the KC4 maxilla based on one of the teeth yielded too little collagen (organic material) to produce a date. Bummer again! The new estimate is instead based on radiocarbon dates obtained from animal bones that were excavated from above and below the human jaw. So this ‘redating’ of the Kent’s Cavern maxilla is very interesting, but should be taken with a grain of salt.

ResearchBlogging.org
See for yourself
Benazzi, S., Douka, K., Fornai, C., Bauer, C., Kullmer, O., Svoboda, J., Pap, I., Mallegni, F., Bayle, P., Coquerelle, M., Condemi, S., Ronchitelli, A., Harvati, K., & Weber, G. (2011). Early dispersal of modern humans in Europe and implications for Neanderthal behaviour Nature DOI: 10.1038/nature10617

Higham, T., Compton, T., Stringer, C., Jacobi, R., Shapiro, B., Trinkaus, E., Chandler, B., Gröning, F., Collins, C., Hillson, S., O’Higgins, P., FitzGerald, C., & Fagan, M. (2011). The earliest evidence for anatomically modern humans in northwestern Europe Nature DOI: 10.1038/nature10484

Dmanisi Homo erectus: I’ll have what she’s having

Speaking of diet in fossil humans … Herman Pontzer and buddies just published a brief analysis of fine-scale tooth wear in the Dmanisi Homo erectus specimens.

Source: http://bit.ly/uD1LWo

Teeth are useful as hell in life. Humans’ teeth are critical not only for eating, sporting a sexy smile, and biting people (right), but also for speech and song (“f,” “th” and “v” sounds). Some parents even harvest their childrens’ exfoliated baby teeth. The things we do with teeth.

Teeth are also really useful for studying long-dead people and animals – teeth may preserve pretty well for millions of years, they can be used to estimate an individual’s age-at-death, and their shape and composition can be used to learn about diet. In a vile act of revenge, the food that sustains us also scrawls its Nom Hancock into the surfaces of our teeth. So, scientists can study the microscopic marks (= “microwear”) on tooth surfaces to see what kinds of foods were eaten shortly before death. Peter Ungar, an author of the current paper, has done a lot of work here, and his website is worth checking out if you’re interested in learning more. Microwear can’t really tell you exactly what an animal was eating, but can tell you whether the animal mostly ate grasses, leaves, hard objects like nuts, and so forth.

So Pontzer and colleagues (in press) examined the microwear on some of the lower molars of the youngest members of the nearly 1.8 million year old (Ferring et al. 2011) Homo erectus group from Dmanisi in the Republic of Georgia. To the left is a picture of the jaws, from the paper (from another paper. How meta of me). The microwear patterns of these badass early humans fit cozily within the variation exhibited by other Homo erectus specimens.

Microwear in Homo erectus is pretty variable, but still rather distinct from other fossil groups like robust Australopithecus, and a little less distinct from their putative ancestor H. habilis. This suggests that something special about Homo erectus was the species’ great dietary breadth – Homo erectus‘ key to colonial and evolutionary success might not have been the adoption of a key dietary resource, but rather the ability to utilize a wide range of food resources. Atkins diet be damned. What’s neat is that the Dmanisi hominids, though kind of primitive (Australopithecus-like) in terms of brain size and some aspects of skull shape, nevertheless demonstrated key behaviors of H. erectus, namely colonization (Dmanisi is the oldest reliably-dated hominid site outside Africa), and dietary flexibility. This really suggests the success of our ancestors was due to some behavioral innovation, aside from advances in stone tool technology.

Source: http://bit.ly/vCTfeR

Now, these Dmanisi H. erectus kids’ teeth wore like other H. erectus, and it would be reasonable to infer that this is because they ate similar foods. This makes it all the more mysterious that the other Dmanisi jaws, from older adults, have teeth completely worn to shit (sorry to swear). D3444/3900 (left) are the cranium/mandible of an individual who was missing all their teeth, except maybe a lower canine – the earliest example of edentulism in the human fossil record (Lordkipanidze et al. 2005). D2600 (below) is a very large mandible with teeth so worn that the pearly-white first-molar crowns were gone and the internal pulp cavity (and nerve) were exposed. (Interestingly, D2600 is so large that some researchers initially argued it represented a different species from the other jaws – yet Adam Van Arsdale presented evidence that this extreme tooth wear may actually be responsible for making jaws relatively taller in early humans).

Source: http://bit.ly/u6bk6h
So what’s curious is why the older Dmanisi hominids should show such an extreme amount of tooth wear compared to other H. erectus, but microwear on the young suggests their diet was the same (that is, just as diverse in texture) as others in the species. Was Dmanisi-level tooth wear (and tooth loss) comparable to other H. erectus, and we just happen not to have found them at other sites? (KNM-ER 730 from Kenya is the next-most worn early Homo that next comes to mind) Is there another aspect of diet we don’t know about, that caused the Dmanisi teeth to wear especially quickly? Or were these early Homo from Dmanisi actually living longer than other H. erectus? I suspect the second is more likely, but that’s a hypothesis that remains to be tested.
ResearchBlogging.org
Read more, dammit!
Ferring, R., Oms, O., Agusti, J., Berna, F., Nioradze, M., Shelia, T., Tappen, M., Vekua, A., Zhvania, D., & Lordkipanidze, D. (2011). From the Cover: Earliest human occupations at Dmanisi (Georgian Caucasus) dated to 1.85-1.78 Ma Proceedings of the National Academy of Sciences, 108 (26), 10432-10436 DOI: 10.1073/pnas.1106638108
Lordkipanidze, D., Vekua, A., Ferring, R., Rightmire, G., Agusti, J., Kiladze, G., Mouskhelishvili, A., Nioradze, M., de León, M., Tappen, M., & Zollikofer, C. (2005). Anthropology:  The earliest toothless hominin skull Nature, 434 (7034), 717-718 DOI: 10.1038/434717b
Pontzer H, Scott JR, Lordkipanidze D, Ungar PS. In press. Dental microwear texture analysis and diet in the Dmanisi hominins, Journal of Human Evolution (2011). DOI:10.1016/j.jhevol.2011.08.006

Tooth formation rates – what do species comparisons really mean?

A paper just came out in PNAS, by Tanya Smith and others, in which they estimate tooth-crown formation times in a large sample of modern humans (n=>300 individuals), a modest sample of Neandertals (n=8), and a poor sample of ‘fossil Homo sapiens‘ (n=3). Teeth form by the periodic deposition of enamel (the hard, white part visible in teeth in the mouth) and dentin (forms the tooth root and internal part of the crown). These periodicities are fairly regular (though variable), thus allowing researchers to estimate how long it took for teeth to develop. As previous studies have shown, Smith and colleagues find that Neandertals formed most of their teeth faster than modern humans.

Growth and development are part of an organism’s life history strategy, and so the observation that Neandertals (and other fossil human species/lineages) form their teeth faster than modern people suggests that perhaps they ‘lived faster’ and died younger than us. It has also been used as evidence that Neandertals are a different species from modern humans.
But I don’t know how well the latter taxonomic argument works. Along these lines, I wish the authors had discussed the meaning of the estimated crown formation times for their fossil ‘modern’ humans (Qafzeh 10 & 15 from Israel ~100 thousand years ago, and Irhoud 3 from Morocco ~160 thousand years ago). The boxplot summaries of crown extension rates (above) show that Neandertals are, indeed, generally fast relative to the large modern sample. However the fossil-modern humans (asterisks, which I’ve circled in red) show a bizarre, not easily interpretable pattern. For the central upper incisors (I1), fossil-moderns are either within the Neandertal range or an outlier at the high end of the human sample. For the lower second incisor (I2) the two fossil-moderns are either waaaaaay above the human range, or a little below it -either way it’s outside the human range. In addition, the sole fossil-modern lower first molar has a lower rate than the modern sample – suggesting an even slower development time. Only the fossil-modern canine formation time fits comfortably within the range of modern humans. Given this wide range of variation in tooth crown formation times in the very small sample of fossil-modern humans, I don’t think we can use this information to make taxonomic arguments.
I think these dental histology studies are very interesting, but I don’t know how much stock we can put in any taxonomic interpretations of them. That Neandertal teeth form faster than modern humans’ is old news, and the discussion focused solely on the neandertal-modern human comparison. It’s too bad that the really interesting part of the paper – the variation in formation time displayed by the fossil-moderns – got no discussion.
The paper
Smith TM et al. 2010. Dental evidence for ontogenetic differences between modern humans and Neandertals. Proceedings of the National Academy of Sciences, in press.