Proof that paleoanthropology is cool: the Dmanisi hominids (Mzia is the girl on the left and Zezva the dude on the right), tagged onto a storefront in downtown Tbilisi.
Back to the backbone of Homo erectus
Of course the title is referring to all of the back bones. An alternate title may be “The backbone’s connected to the – what bone?” but that’s also kinda cheesy. I’ll do better next time.
Martin Hausler and colleagues (in press) report on newly identified vertebral fragments of the WT 15000 Homo erectus skeleton, perhaps the most complete of an early hominid (this one ~1.5 million years ago). This skeleton, and other early hominids (i.e. Australopithecus africanus), were described as having six lumbar (lower back) vertebrae; the modal number in humans is 5, and 3-4 in the great apes. The issue of vertebral formula (the number of cervical, thoracic, lumbar, and sacral verts) in hominids is interesting because it is unclear what the ancestral condition is: was ancestral pattern to have more lumbars (like australopiths) from which humans and apes lost verts, or is ape pattern is ancestral, and lumbars were gained then lost over the course of human evolution?
The fragments found by Hausler and team establish that the WT 15000 individual – and presumably all H. erectus – possessed only 5 lumbar vertebrae. In the past, the only evidence of the 6th-to-last pre-sacral vertebra was the vertebral body. It was unclear whether this vertebra would have had articular facets for ribs (like a thoracic vertebra) or not (like a lumbar vertebra). The pedicle fragments identified by Hausler and colleagues (figure to the right) have a rib facet, and so indicate that the 6th-to-last vertebra of this skeleton was thoracic. Thus, WT 15000 – and again presumably all Homo erectus – had a modern-human-like vertebral formula.
The evo-devo of the spinal column is interesting because it seems to me that it may not be so outlandish to try to identify and test hypotheses about how spinal column development (segmentation) changed over the course of hominid and ape evolution. In trying to determine how development of vertebral segments evolved it is important to know how ancient the human pattern is, and so the identification of 5 lumbars in WT 15000 at 1.5 million years ago is an important finding. I need to think on this a bit, I’ll hafta get back to you . . .
* figures are from Hausler et al. in press
Reference
Martin Haeusler, Regula Schiess, Thomas Boeni (2011). New vertebral and rib material point to modern bauplan of the Nariokotome Homo erectus skeleton Journal of Human Evolution : 10.1016/j.jhevol.2011.07.004
eFfing Fossil Friday (another late edition)
I’m sitting at a cafe in Tbilisi, departing at 4:00 am tomorrow for America. Readers will notice that I’ve been MIA while working with the second annual Dmanisi Paleoanthropology Field School. I hate to say it but I’m glad I was too busy to blog all the goings-on (though sorry if it disappointed anyone). All in all it was another great year, and we found some great fossils (about which I don’t think I have permission to say anything at all). Here’s this year’s class with their certification of badassery at the site on the last day:
But Dmanisi won’t be the subject of this belated eFfing Fossil Friday. I’d like instead to turn to the question of just what fossils are good for. I’m told that in China, fossil teeth were once interpreted as dragons’ teeth, and so pulverized and sold as medicine. But what good are they to non-medical science? My recent research interests have come to focus on the relationship between evolution and development. Evolutionary developmental biology (“evo-devo”) research has been dominated by studies of genes, gene expression, and model organisms like fruit flies and mice. In such an environment, the question of the relevance of fossils is especially poignant.
But this morning, while planning a human evo-devo course I hope to teach next summer, I stumbled upon a review paper by Rudolf Raff, titled “Written in Stone: Fossils, genes and evo-devo” (2007). I think the abstract sums things up pretty well:
Fossils give evo-devo a past. They inform phylogenetic trees to show the direction of evolution of developmental features, and they can reveal ancient body plans. Fossils also provide the primary data that are used to date past events, including divergence times needed to estimate molecular clocks, which provide rates of developmental evolution. Fossils can set boundaries for hypotheses that are generated from living developmental systems, and for predictions of ancestral development and morphologies. Finally, although fossils rarely yield data on developmental processes directly, informative examples occur of extraordinary preservation of soft body parts, embryos and genomic information.
It seems often that fossils are falling by the wayside. There’s a sentiment that there’s not much information to be gotten from fossils – they’re too incomplete, too few, too inconvenient, at least as compared with extremely high-output data such as that coming from genomics. But Raff is right – we need fossils. Beyond the excellent points Raff raises in the review, I’m working on getting the most out of these seemingly data-poor fossil samples. Because modern computers are so powerful nowadays, I’m using their sheer processing power to test hypotheses about growth and development in fossil samples. These battered bunches of bones are too tiny to be analyzed by traditional methods. But one thing I think is important to take away from this computer-crazy Information Age, is that we now have machines that can handle almost any kind of question one can think to ask, and it’s really inspiring. The sequencing and analyses of ancient Neandertal and Denisova genomes (Green et al. 2010, Reich et al. 2010) are excellent examples of the amazing research that can be done with computers and creativity (and probably also a horde of hard-working math majors).
So this eFFF (or Sunday) is not dedicated to any specific fossil or set of fossils, but rather to all fossils, even the crappy fragments. Gaumarjos, fossils: your secrets are not safe from us.
Reference
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
Raff, R. (2007). Written in stone: fossils, genes and evo–devo Nature Reviews Genetics, 8 (12), 911-920 DOI: 10.1038/nrg2225
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
Gamarjoba from Dmanisi!
It’s been a bit harder to keep things updated as I journey across latitudes this summer. My last post was from Nairobi, and a few days later I arrived in Tbilisi in the Republic of Georgia (lamazi Sakartvelo). I’ve been involved with the 2nd annual Dmanisi Paleoanthropology Field School, which has been going on for about a week now. Things have been going fast and we’ve been having a lot of fun, so it’s a bit too difficult to recap everything so far. But we’ve had a series of lectures from great people in various fields. Here are some highlights:
Our first lecture was by Dr. Bernard Wood, at the site of Dmanisi itself. He discussed some of the progress and pitfalls in the field of Paleoanthropology. Next was Dr. G. Philip Rightmire, who discussed some aspects of hominid morphology and taxonomy. Then Dr. Reid Ferring discussed the geology of the site. As someone who focuses more on the fossils themselves, Ferring’s lecture was refreshingly fascinating for me. In brief, Argon-Argon dating was used to establish that the Mashavera basalt underlying the hominid (and other!) fossils is around 1.85 million years old. Then there were a series of ash falls that led to the soil formation of the site. A little (stratigraphically) above the fossil deposits is a layer dated by paleomagnetism to correspond to the Olduvai polarity reversal, around 1.76(?) million years ago. So the hominid fossils themselves are pretty well constrained to somewhere between 1.85-1.75 million years ago.
Then Dr. Martha Tappan gave a lecture about the taphonomy (site formation and burial processes) of the site; the neighbors invited me in for some delicious ch’ach’a shortly before the lecture, so I’m afraid my memory of this one is a bit foggy. 😦
Last night Dr. Jordi Agusti lectured about the micromammals at Dmanisi, and at some Spanish Pleistocene sites. Micromammals have large litters and short generation times, so they are good indicators for relative dating. Tonight Dr. Adam Van Arsdale will be lecturing about early Homo from Dmanisi and other sites. It’s been a great lecture series so far, and there are sure to be many great more lectures in the next few fast-paced, fun-filled weeks.
We’ve also been excavating the site, working mostly so far on taking down some of the layers stratigraphically above the hominids to hopefully more fossiliferous layers. I injured my hand on some monkeybars at the park yesterday (they seriously ripped off a big layer of skin, so I’m partially mummified), so I was down for the count today, doing lab work in lieu of excavating. I should be ready to go by tomorrow though.
I know I owe the world a few Effing Fossil Friday posts, so I’ll hopefully have those up soon, too. Nakhvamdis!
New beef with boisei – maybe the dingo ate their babies?
Unfortunately, the title is not in reference to a study demonstrating that early hominins fell prey to wild dogs. But Elaine Benes would have appreciated it.
As part of my Latitudes Tour, I’m in Nairobi for a couple of days, hoping to spend some quality time with the young Australopithecus boisei kids at the Nairobi National Museum. Recall (that is, if I’ve mentioned it here?) that my dissertation research is on growth of the lower jaw, in Australopithecus robustus as compared to modern humans. The study of growth obviously requires analyzing individuals across different age groups (an “ontogenetic series” is the fancy term). Admittedly, then, the focus on A. robustus is chiefly because this species has the largest ontogenetic sample of any early hominin (tho at nearly 15 non-adults, it’s still not as large as one could hope). Also because A. robustus was totally badass.
Australopithecus boisei makes an important comparison for A. robustus, because the two species are allegedly evolutionary ‘sisters’ – the “robust” australopithecines (though I’m personally not convinced that these two are each other’s closest relative). So their growth should be pretty similar. At the same time, though, A. boisei shows much greater adaptations to heavy chewing – they’ve been referred to as “hyper-robust.” So comparing growth in these species should elucidate how their differences arise.
Problem is, there just aren’t enough kids. Wood and Constantino (2007) published a pretty comprehensive review of A. boisei, including a 1.5-page table of the skulls and teeth attributed to the species. So far as I know, only 4 specimens in that table are non-adult mandibles, and so far as I can tell, they’re all about the same age (right around the age that the first permanent molar comes in). There are so many jaws of adult A. boisei (although many of these are abraded mandibular bodies lacking teeth) — where are all the damned kids?
A quick look at pairs of infant and juvenile jaws of the two species suggests they both increase in size fairly dramatically between when they only have baby (a.k.a. “deciduous” or “milk”) teeth and when the first permanent molar comes in. But this is just a preliminary observation based on two specimens of each species, so this has to be taken with a grain of salt.
On second thought, maybe I’ll propose the nearly untestable hypothesis that bone-eating hyenas ate the boisei babes, and that’s why we don’t have their jaws. What could have been nicely preserved young boisei bones are instead coprolites (fossilized poops). Spectacular, yes, but it’s also been hypothesized that many of the A. robustus fossils we know and love came to us as carnivores’ scraps.
Further reading:
Wood, B., & Constantino, P. (2007). Paranthropus boisei: Fifty years of evidence and analysis American Journal of Physical Anthropology, 134 (S45), 106-132 DOI: 10.1002/ajpa.20732
eFfing Fossil Friday – Renaissance and Designer Fossils
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.
eFFING FOSSIL FRIDAYS!
I’m going to do my best to keep up with the blog during by Big Summer Adventure, and one thing I’d like to do is “F-ing Fossil Friday!” in which I focus on fossils for a bit. We’ll see if I can make this pan out.
Today I got out the rest of the Australopithecus robustus mandibles at the Transvaal Museum (above), save for I think maybe 1. As you can see from the picture, taphonomy (what happens to an animal’s remains between death and our digging them up) creates a serious challenge for the study of variation in this species. I’m focusing on ontogenetic variation – differences associated with growth and development. In spite of its fragmentary nature, so far as I know this is the best ontogenetic series of any fossil hominid (I should probably look more into A. afarensis here, too). In the bottom left you’ll see SK 438, the youngest in the sample, whose baby teeth haven’t quite come in all the way. Poor little guy! At the top right corner is SK 12, probably the oldest individual and also a big bugger.
One thing that I’ve noticed so far, only a preliminary observation that I need to actually run some numbers on, is that as individuals get older, the length of their tooth row (molars and premolars) gets shorter. This is because of the tendency for teeth to move forward during growth – “mesial drift” – and for adjacent teeth to literally wear into one another, their ends becoming flatter and flatter. While I should have realized this, it was surprising at first to find some dimensions of the lower jaw actually decreasing during growth. Now, I still have to run some tests to see if this is a biologically significant phenomenon. But it’s always nice to learn something new, even after just 2 days back with my best extinct buddies.
Stay tuned to future eFfing fossil Fridays!
Let’s hear it for the Null!
via Carl Zimmer, Dr. Jon Brock in his blog, “Cracking the enigma,” has some thoughts on why null hypotheses don’t suck so bad as so many people think. Null hypotheses are generally along the lines of, “there is no difference between these groups,” or “this variable has no effect on something,” or “there is no relationship between variables.” The more general statistical statement behind the null hypothesis is usually along the lines of “this phenomenon can be explained just as well by a completely random process.” I’d agree with Brock that it seems that a good many researchers (not me!) view the null hypothesis as a bore or meaningless. But I like his final thought:
This brings me neatly to my final point. In research on disorders such as autism or Williams syndrome, a significant group difference is considered to be the holy grail. In terms of getting the study published, it certainly makes life easier. But there is another way of looking at it. If you find a group difference, you’ve failed to control for whatever it is that has caused the group difference in the first place. A significant effect should really only be the beginning of the story.
Bloodsport in Australopithecus africanus?
A few months ago in a post about the ilium and cannibals, I relayed a quote by Dr. Raymond Dart who was the first to recognize (and name) the hominid genus Australopithecus, back in 1925. I’d also mentioned that he was described [in a reference that escapes me] as “blood-thirsty.” This macabre descriptor came to mind again, as I’m reading his (1948) description of the MLD 2 mandible, of a juvenile A. africanus from Makapansgat cave in South Africa (figure is from the paper):
“[Individuals represented by MLD2 and another skull fragment] met their death by manually applied violence. The fractures exhibited by the mandible show that the violence, which probably occurred in fatal combat, was a localized crushing impact received by the face slightly to the left of the midline in the incisor region, and administered presumably by a bludgeon… this youth probably met his fate at the hands of a kinsman more expert than himself in the accurate application of directed implements” (p. 393-394)
This rather fanciful hypothesis may reflect Dart’s alleged bloodlust, and the condition of the fossil likely reflects damage that occurred after death during the sometimes abusive process of fossilization.
Reference
Dart, R. (1948). The adolescent mandible of Australopithecus prometheus American Journal of Physical Anthropology, 6 (4), 391-412 DOI: 10.1002/ajpa.1330060410
100,000 year old child skeleton on National Geographic
National Geographic aired a special tonight about a recently-excavated child’s skeleton (they focused on the skull) from Grotte des Contrebandiers in Morocco, dated to around 108,000 years ago. So far as I know this material has not been fully published (aside from a brief blurb in Science).
The program presented work of archaeologists, paleontologists, reconstruction artists, taphonomists, and lots of other people, hoping to figure out who the kid was and such. All in all it was pretty cool, I’d recommend checking it out if you didn’t see it. Or again if you did see it.
While I think it was a great program and the researchers involved are doing a terrific job, I had two main notes: first, I wish they’d treated the topic of growth-n-development a little more. They noted that the child (5-6 years old possibly) looked really “modern” because of its flat face. But looking at it, it didn’t really have that flat of a face, especially for a child. They talked about how human-like (rather than Neandertal-like) the kid was, but they only compared it with adults – children tend to have relatively smaller faces and larger brain-cases than adults (right), so it’s no wonder it looked more like an adult human than the adult Neandertal from Amud (Israel) that they compared it with. It would’ve been great to see more comparisons with other late Pleistocene hominid kids, such as from Skhul/Qafzeh or La Quina. A future program, perhaps.
Second, they kept asking whether the kid was “a Homo sapien.” I know it’s counterintuitive for English-speakers, but “H. sapiens” is the singular and plural of humans’ scientific name. Silly, right, cuz it doesn’t even get paid twice as much. But you’ll have take that up with C. Linnaeus. I am a Homo sapiens. You are a Homo sapiens. Fifty people are a gaggle of Homo sapiens.
Anyway it was a cool show. Check it out!
Figure credit: Fig. 2 from Bogin. 2003. The human pattern of growth and development in paleontological perspective. In Patterns of Growth and Development in the Genus Homo, eds. Thompson JL, Krovitz GE and Nelson AJ. New York: Cambridge University Press: 15-44.
Lawnchair Anthropology 
