New (old) Australopithecus anamensis cranium

August 30, 2019August 30, 2019 / zcofran / Leave a comment

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.

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:

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).

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.

The most complete Australopithecus skeleton

December 11, 2017December 11, 2017 / zcofran / 2 Comments

StW 573, a hominin skeleton more palatably nicknamed “Little Foot,” made its big debut last week:

Ron Clarke showcases the lovingly-excavated skeleton (Photo credit: AP/Themba Hadebe)

The skeleton is remarkable in that it is the most complete australopithecine individual ever discovered, and is among the most complete in the entire hominin fossil record. Below I’ve compared it to the most complete Australopithecus afarensis (KSD-VP-1/1 and AL 288-1), A. africanus (StW 431 and Sts 14), and A. sediba (MH1-2); the Dikika infant would be a neat comparison, too, but I don’t know of any photos of its bones nicely laid out. The other skeletons are practically naked (or dismembered) compared to Little Foot.

Little Foot (red) compared with other australopithecine skeletons. Images not to scale! (Photo credit: The Internet!)

Beyond it’s completeness, the other parts of story of Little Foot are equally fascinating – from its discovery based on already-known fragments to the possibility that it is older than “Lucy” (AL-288). Ron Clarke has painstakingly and I’d say very successfully removed the skeleton from the hard breccia in which the fossils were encased. Having spent the better part of the past two decades with the skeleton, he has argued that Little Foot represents a second hominin species at Sterkfontein, Australopithecus prometheus (Clarke 2013), the species to which hominin fossils at Makapansgat were originally attributed (Dart 1948). With the unveiling of the skeleton, I’d guess that in the coming years we’ll see renewed investigations into the number of species at Sterkfontein, and the general comparison between hominins from there and Makapansgat.

From pictures in the media releases, we can see a few things that weren’t known from previous publications. I’ll outline a few here, but emphasize that these are only superficial observations and will need to be borne out by further research.

“EXPELLIARMUS”

At the top of the trunk, the cervical vertebra seems to have a fairly wide spinal canal, a human-like ‘bulging’ which Meyer and Hausler (2015) suggest might reflect innervation of highly manipulative hominin hands.

Close up of the skull and upper trunk of StW 573, highlighting the cervical vertebral canal (white arrow) and first rib (orange arrow). Original photo credit: AP//Themba Hadebe.

In addition, the first rib may be relatively long front-to-back (as opposed to wide side-to-side), possibly indicating a more barrel-like chest than in other early hominins; the angle of the photo and the clear break between the proximal and distal portions, however, makes this unclear.

Hominin first ribs/bacon, with StW 573 on the far right. Not to scale! Modified from this post.

The distal forelimb (i.e., radius and ulna) are not as elongated as in apes, but the femur is not as elongated as in the genus Homo. From the pictures, the femur neck appears short like in humans, not as elongated as is characteristic for australopiths and early Homo.

Limb proportion comparison. Humerus (top row), radius & ulna (middle), and femur (bottom). Image modified from Asfaw et al. (1999). StW 573 scaled to same humerus length as the human. Note also that all bones are from the right except the StW 573 upper limb.

The apparently short femur neck, similar to humans, contrasts with the wide, flaring ilium of the pelvis. This appears fairly flat, short and wide (Australopithecus af) compared to modern humans’ more strongly curved ilium. But this inference is just from a picture and it’s likely that the fossil needs a bit of reconstruction to uncover the true anatomy.

StW 573 pelvis (left) compared with Sts 14 (A. africanus, middle) and SH pelvis 1 (archaic Homo, right). Sts 14 modified from Berge & Goularis (2010) and SH pelvis 1 from Bonmati et al. (2010).

I’d like to emphasize that these are just first impressions based on press release photos, and actual analysis of the skeleton are necessary to tell if these impressions are correct. As could be expected, the skeleton as a whole looks typically australopithecine, although the short femur neck may be a bit different. As 2017 draws to a close, let’s hope 2018 sees the testing of these predictions.

References

Asfaw B. et al. 1999. Australopithecus garhi: a new species of early hominid from Ethiopia. Science 284: 629-635.

Berge C and Goularis D. 2010. A new reconstruction of Sts 14 pelvis (Australopithecus africanus) from computed tomography and three-dimensional modeling techniques. Journal of Human Evolution 58: 262-272.

Bonmati A. et al. 2010.Middle Pleistocene lower back and pelvis from an aged human individual from the Sima de los Huesos site, Spain. Proceedings of the National Academy of Sciences 107: 18386-18391.

Clarke RJ. 2013. Australopithecus from Sterkfontein Caves, South Africa. In The Paleobiology of Australopithecus, Reed et al., eds. Dordrecht: Springer Science+Business.

Dart R. 1948. The Makapansgat proto-human Australopithecus prometheus. American Journal of Physical Anthropology 6: 259-284.

Meyer M. and Hausler M. 2015. Spinal cord evolution in early Homo. Journal of Human Evolution 88: 43-53.

Osteology Everywhere: Aerial Ossicles

May 22, 2017May 22, 2017 / zcofran / Leave a comment

Last month I was flying down to New Orleans for the AAPA conference. I was excited to try authentic beignets & sazeracs, present new research, and catch up with colleagues. Midway through the flight I glanced out the window, not expecting to see much. But lo!

twilight

Thankfully there wasn’t something on the wing. But there was something strange out there in the sparkle of sprawling city lights:

What’s that I spy outside the city center?

A bit outside of the main jumble of street lamps appears to be a concentration of light superficially similar to an incus, one of the three auditory ossicles of the middle ear:

Left: An osteologist’s nightmare at 20,000 feet. Right: Ear ossicles from White et al. (2012).

As a good mammal, there are three small bones inside your middle ear. These are fully formed at birth, and help transfer and amplify sound vibrations from your eardrum to your inner ear. It’s nuts. What’s even more nuts is that paleontologists and anatomists have figured out that the tiny, internal incus and malleus of mammals evolved from larger, external pieces of the jaws of our pre-mammalian ancestors. INSANITY!

Cross section of a right ear, viewed from the front. Image credit.

Being so tiny, it’s not surprising that auditory ossicles are not often recovered from skeletal remains, and are pretty rare in the human fossil record. Nevertheless, some are known and their comparison with humans’ ossicles is pretty interesting. The oldest inci I know of are from SK 848 and SKW 18, Australopithecus robustus fossils from Swartkrans in South Africa (Rak and Clarke, 1979; Quam et al., 2013). SK 848 is on the left in the set of images below:

Incus bones in three different views of SK 848, human chimpanzee, gorilla, sock puppet (left to right). Modified from Rak and Clarke, 1979.

SK 848 to differs from humans and African apes in looking more like a screaming sock puppet with a horn on the back of its head. Additional ossicles are known from South African australopithecines, including the older A. africanus from Sterkfontein (Quam et al., 2013). Interestingly, malleus of these hominins is very similar to that of humans, and Quam et al. (2013) think this ossicle may be one of the first bones in the entire skeleton to take on a human-like configuration during hominin evolution. Functionally, this may mean that the frequency range to which human ears are adapted may have appeared pretty early in our lineage as well (Quam et al., 2015).

Who’d’ve thunk we’d learn so much just from looking out an airplane window?

Osteology Everywhere: Cakes or canines?

March 7, 2016March 7, 2016 / zcofran / 1 Comment

I’ve been looking at so many teeth lately, I’m starting to feel like a sadist but with newer magazines.

Yada yada.

Between putting together a talk about dental development in Homo naledi and teaching teeth in my human evo-devo class last week . . .

After these drawings, my students were fully trained and ready to tackle the odontological world.

After these drawings, my students are now fully trained and ready to tackle the odontological world.

. . . I’ve got dentition on the brain. WHICH IS NOT THEIR ANATOMICAL POSITION.

So last weekend some friends and I hit a local pub, a life jacket for my dental inundation. Surely, a pint and a snack will expunge enamel, dissolve dentine, exhume zuby from my brain! We ordered some beer and baursaki, delicious fried bread made out here in Kazakhstan, the perfect snack to go with beer and chechil. Tearing into the pastry, I started to feel at peace, but then was horrified to look down and find myself hoist with my own petard:

Baursak with a bite taken out? Our a hominin canine?

Seeing the snack, I saw the very thing I’d been fleeing – a hominin canine tooth. Inadvertently, I’d almost exactly replicated Sts 50, a lower left canine crown and broken root from the South African site of Sterkfontein.

Left: Sts 50, lower left canine. Right: bitten fried bread. Images not to scale. ANTIMERES?

They’re nearly identical but from opposite sides (the fancy word for which is “antimeres”). Note the tall-shouldered, sharp apex of the crown, and the little distal tubercle, the little ‘bump’ at the far left in the left picture above. The mesial, or front, crown shoulder is notably taller than the distal tubercle. At probably around 3 million years ago, Sts 50 likely belongs to Australopithecus africanus, and retains an ape-like asymmetrical crown shape compared to the more incisor-shaped canines we humans have today.

Left to right: Homo baursaki, three South African canines, and a modern human (from White et al. 2012). Images not to scale.

Hominin canines and definitely no cakes. Left to right: Homo baursaki, three canines from early Pleistocene South Africa, and a modern human (from White et al. 2011). Images not to scale. Note how much less asymmetrical the modern human canine crown (far right) is compared to the fossil hominins. Teeth 1, 2, 4, and 5 are from the right side while the center, Sts 50, is from the left.

Apparently all you need to go back in time is some beer and baursaki.

Gracile & robust Australopithecus

October 25, 2015 / zcofran / 3 Comments

Last week, I introduced my Human Evolution students to the “robust” australopithecines. It was a very delicate time, when we had to have a grown up, mature conversation about adult things. I reminded the students that they’re only human, but they must resist urges that seem only natural. No matter how much they want to, even if their friends are doing it, they must not act on the deep, dark desire to say that “robust” vs. “gracile” Australopithecus differ in their body build.

Don’t do it, Homo naledi. Don’t talk about body size when you mean to talk about jaw and tooth size. Illustration by Flos Vingerhoets.

Every semester, students (who don’t read and/or pay attention to lecture) think that the difference between these two groups has to do with the species’ body sizes. This is a misconception that has reached the highest echelons of reference:

At least one person is not citing their source here. F-.

Apple and Google, at least one person here is not citing their source: F-. Also, is no one else surprised that this term is allegedly specific to anthropology?

No. In the case of australopiths, “gracile” and “robust” refer to the relative size of the jaws, teeth and chewing muscles (all contributing to the “masticatory apparatus”). Traditionally, graciles include the ≥2 million year old Australopithecus afarensis and africanus, and robusts include the later A. boisei and robustus. The discovery of an A. aethiopicus cranium (Walker et al. 1986) somewhat blurred the lines between the two groups but it is usually included with the robusts (who are often collectively called Paranthropus). John Fleagle’s classic textbook (1999) illustrates the gracile-robust dichotomy very nicely:

Comparison of gracile (left) and robust (right) craniodental traits. From Fleagle, 1999.

So to recap: Jaws and teeth, people! To the best of my knowledge, there’s little or no evidence that the various australopithecines differed appreciably in body size (McHenry and Coffing, 2000), stoutness, or muscularity. Although the OH 80 partial skeleton, attributed to Australopithecus boisei based on tooth size and proportions, includes a humerus with very thick cortical bone and a radius with a crazy big insertion for the biceps muscle – it was a very large and muscular A. boisei (Domínguez-Rodrigo et al., 2013). Nevertheless, gracile and robust australopithecine species differ most notably in their jaws and teeth, not bodies. Maybe this is why Liz Lemon was so confused about the term “robust”?

Good god, Lemon.

Today, these are somewhat antiquated terms. Back when the only hominins known to science were the species listed above, it was easy to make a distinction. However, as the fossil record has expanded of late, the gracile-robust dichotomy becomes blurry. Australopithecus garhi (Asfaw et al., 1999) has overall tooth proportions comparable to graciles, but absolute tooth sizes and sagittal cresting like robusts. The recently described Australopithecus deyiremeda has tooth sizes and proportions like graciles but lower jaws that are very thick, like those of robust australopithecines (Haile-Selassie et al., 2015).

So in light of all the confusion and blurring distinctions, maybe it’s time to scrap “gracile” vs. “robust”?

Further reading: The “robust” australopiths (Constantino, 2013).

References
Asfaw B, White T, Lovejoy O, Latimer B, Simpson S, & Suwa G (1999). Australopithecus garhi: a new species of early hominid from Ethiopia. Science (New York, N.Y.), 284 (5414), 629-35 PMID: 10213683

Domínguez-Rodrigo, M., Pickering, T., Baquedano, E., Mabulla, A., Mark, D., Musiba, C., Bunn, H., Uribelarrea, D., Smith, V., Diez-Martin, F., Pérez-González, A., Sánchez, P., Santonja, M., Barboni, D., Gidna, A., Ashley, G., Yravedra, J., Heaton, J., & Arriaza, M. (2013). First Partial Skeleton of a 1.34-Million-Year-Old Paranthropus boisei from Bed II, Olduvai Gorge, Tanzania PLoS ONE, 8 (12) DOI: 10.1371/journal.pone.0080347

Haile-Selassie Y, Gibert L, Melillo SM, Ryan TM, Alene M, Deino A, Levin NE, Scott G, & Saylor BZ (2015). New species from Ethiopia further expands Middle Pliocene hominin diversity. Nature, 521 (7553), 483-8 PMID: 26017448

Walker, A., Leakey, R., Harris, J., & Brown, F. (1986). 2.5-Myr Australopithecus boisei from west of Lake Turkana, Kenya Nature, 322 (6079), 517-522 DOI: 10.1038/322517a0

Blood spattered Easter eggs from Raymond Dart

August 23, 2015August 23, 2015 / zcofran / Leave a comment

Some of the more colorful ideas and text in the anthropological literature are courtesy of Raymond Dart.

Dart, hammering away to remove a fossil from some breccia. I hope. Image credit.

Dart, hammering away at some breccia to remove a fossil. I hope. Image credit.

In 1925, Dart identified the Taung fossil as a close relative of humans, and coined the scientific name, Australopithecus africanus. This was a pretty good idea, as Taung was the first in what is now a large collection of fossils attributed to this species.

Taung was such an important discovery, you can now walk across it as you enter the fossil collections at Wits University.

Taung was such an important discovery, you can now walk across it not once, not twice, but thrice! as you enter the fossil collections at the Evolutionary Studies Institute at Wits University.

Some of Dart’s ideas that made it into print, though, were a bit more fanciful. Aside from his description of Taung, he is probably most famous for hypothesizing the “osteodontokeratic” culture, the idea that the myriad broken animal bones in Makapansgat cave were in fact tools used by australopiths for hunting and murder. MURDER! It was a neat idea at the time, but his vision of bloodthirsty, bone-dagger-wielding australopithecines is not accepted today (nor back when he was writing).

Dart was trained as an anatomist, and much of his work was devoted to writing up australopithecine fossils discovered at site of Makapansgat in South Africa. These are probably the best descriptive papers I’ve found in all the literature, as Dart’s whimsical visions of violence and bloodshed occasionally made their way into otherwise dry scientific prose.

In 1948 he very casually put it out there, that the front teeth of the MLD 2 mandible were lost in “fatal combat . . . presumably by a bludgeon” (emphasis added). Of course, the teeth were probably lost long after the poor kid died, rather than being knocked out “at the hands of a kinsman more expert than himself in the accurate application of directed implements” (Dart, 1948: 393-394). But Dart’s version is certainly more interesting than the more likely taphonomic explanation.

The MLD 2 mandible, poor kid, as illustrated in Dart (1948). Note that the incisor tooth sockets are empty, likely the result of taphonomy rather than bloodsport.

Dart (1958) later described the MLD 7 ilium, which he’d presumed to be a female, from the same site as MLD 2. Dart recounted the violent demise of MLD 2, raising the possibility of a similar death for the MLD 7 individual: “The adolescent boy [MLD 2] … was killed by a bone-smashing blow on the chin from a club or fist. Did brother and sister share here in death the same cannibalistic fate?” (emphasis added) Bloodshed, cannibalism, Australopithecus according to Dart had it all. Although these are unlikely characterizations of australopithecines, there is evidence of cannibalism in later fossil humans.

These gruesome Easter Eggs come to mind as I’m reading his 1956 paper about brain evolution. Here, Dart (1956: 28) says that hominins began walking on two legs after a dietary shift: “The forest-loving vegetarian anthropoids clung to their four-handed climbing and fruit while the terrestrial predaceous australopithecines, depending on their speed of foot and deftness of hand, lusted after flesh!” (emphasis added) Today, this idea would simply be written as, monkeys and apes live in trees and eat fruits while australopithecines lived on the ground and ate meat. But Raymond Dart wouldn’t stand for this. Oh no.

My grad school advisor, Milford Wolpoff, used to lament that students today don’t want to read anything older than the past 5-10 years. But Dart is a shining example of some of the rewarding Easter Eggs that await those who dig deeper into the literature. [I’m reminded also of Don Cousins describing “the colossal poundage of the lowland gorilla ‘Phil,’ who lived in the St. Louis Zoo from 1941-1958″ (1972: 269, emphasis added].

Some good, older stuff

Cousins D (1972). Body measurements and weights of wild and captive gorillas, Gorilla gorilla. Zoologische Garten NF Leipzig 41, 261-277.

Dart, RA (1925). Australopithecus africanus: The Man-Ape of South Africa Nature, 115 (2884), 195-199 DOI: 10.1038/115195a0

Dart, RA (1948). The adolescent mandible of Australopithecus prometheus American Journal of Physical Anthropology, 6 (4), 391-412 DOI: 10.1002/ajpa.1330060410

Dart RA (1956). The relationships of brain size and brain pattern to human status. The South African Journal of Medical Sciences, 21 (1-2), 23-45 PMID: 13380551

Dart, RA (1958). A further adolescent australopithecine ilium from Makapansgat American Journal of Physical Anthropology, 16 (4), 473-479 DOI: 10.1002/ajpa.1330160407

Osteology Everywhere: Vertebeer Fest

July 27, 2015July 27, 2015 / zcofran / Leave a comment

This past weekend was witness to the Summer Beer Festival, the annual showcase of Michigan’s brewing splendor. Dozens of breweries brought out batches of beer, from classics we know and love, to inspired innovations meriting a MacArthur Fellowship. There was an embeerrassment of boozes. Dark Horse Brewing Company, from Marshall, MI, put on quite the show:

Dark Horse Brewing Co. pumping out the brews and blasting t-shirts into the crowd.

Besides towering over the bacchanal hordes, the Dark Horse beer fort also offered IPAs infused with pretty much anything that might pair well with hops. They even steeped habañero peppers in one, and it was maximally boss.

Beer still my heart.

Having sampled only a small part of rich the smorgasbord on tap, a rest by the river was in order. The Festival was on the banks of the mighty Huron River, an excellent place to sit and sip Arcadia‘s scotch ale, taking in the evening under cloud-peppered, cerulean skies. Such a calm and relaxing setting would surely offer respite for a brain besieged by bones. Right?

Every year for the Festival they replace the river water with beer.

Wrong! Peering through beer goggles over the shimmer of the river, seeking signs of Bigfoots lurking on the opposite shore, I locked eyes with a large, wooden vertebral body.

An eyeless frown marks the ventral surface of this centrum.

The human spine is composed of anywhere from 31-34 vertebrae (not counting the coccyx or tail bone). The body or “centrum” is the large, blocky portion of the bone, which is separated from other such bodies by intervertebral discs; it is literally a pile of bodies, stacked one on top of the other. And the intervertebral discs are remnants of the notochord, the embryonic structure that unites you and me and all other humans with all other animals known as chordates. Anyway, kiss my grits if this old tree stump across the mighty Huron River here doesn’t look like a lower thoracic or upper lumbar vertebral body, the metaphoric shark fin of a giant trunkless human waiting to pounce from the placid waters.

a) Our mystery vertebra. b) a lumbar vertebra from White et al. (2012). c) views of the right and front side of the Australopithecus africanus fossil StW H41, from Sanders (1998, Fig. 1).

a) Our mystery river vertebra. b) a lumbar vertebra from White et al. (2012). c) views of the right and front side of the Australopithecus africanus fossil StW H8/H41, modified from Fig. 1 of Sanders (1998).

Thinking on it, our mystery river vertebra doesn’t just look like any old human centrum, it is a ringer for the second lumbar vertebra of StW H8/H41, a series of the 11th thoracic to 4th lumbar vertebrae of Australopithecus africanus from Sterkfontein (see the red arrow in c, above). Sanders (1998) notes that this short segment of an early hominin spine shows clear adaptation to walking upright like we humans do today, although the size of the vertebral bodies is both absolutely and relatively small compared to ours, just as is seen in other Australopithecus fossils.

And what better way to celebrate this monumental discovery than returning to the Beer Festival – hooray beer!

Osteology Everywhere: Ilium Nublar

June 30, 2015 / zcofran / 1 Comment

Jurassic Park is objectively the greatest film ever made, so I don’t need to explain why I recently watched it for the bajillionth time. Despite having seen this empirically excellent movie countless times, I finally noticed something I’d never seen before.

Hold on to your butts. What's that on the screen in front of Ray Arnold?

Hold on to your butts – what’s that on the screen in front of John Arnold? (image credit)

The film takes place on the fictitious island “Isla Nublar,” a map of which features prominently in the computer control room when s**t starts to go down. Here’s a clearer screenshot of one of Dennis Nedry‘s monitors:

Isla Nublar from the JP control room. Quiet, all of you! They’re approaching the tyrannosaur paddock…. (image credit)

It dawned on me that the inspiration for this island is none other than MLD 7, a juvenile Australopithecus africanus ilium from the Makapansgat site in South Africa:

Figure 1 from Dart, 1958. Left side is MLD 7 and right is MLD 25. Top row is the lateral view (from the side) and bottom row is the medial view (from the inside). These two hip bones are from the left side of the body (see the pelvis figure in this post). Note the prominent anterior inferior iliac spine on MLD 7, a quintessential feature of bipeds.

Isla Nublar is basically MLD 7 viewed at an angle so that appears relatively narrower from side to side:

MLD at a slightly oblique view (or stretched top to bottom) magically transforms into Isla Nublar.

MLD 7 at a slightly oblique view (or stretched top to bottom) magically transforms into Isla Nublar.

It’s rather remarkable that some of the most complete pelvic remains we have for australopithecines are two juveniles of similar developmental ages and sizes from the same site. In both, the iliac crest is not fused, and joints of the acetabulum (hip socket) hadn’t fused together yet. The immaturity of these two fossils matches what is seen prior to puberty in humans and chimpanzees. Berge (1998) also noted that MLD 7, serving as an archetype for juvenile Australopithecus, is similar in shape to juvenile humans, whereas adult Australopithecus (represented by Sts 14 and AL 288) are much flatter and wider side to side. Berge took this pattern of ontogenetic variation to match an ape-like pattern of ilium shape growth. This suggests a role of heterochrony in the evolution of human pelvic shape, or as Berge (1998: 451) put it, “Parallel change in pelvic shape between human ontogeny and hominid phylogeny.” In layman’s terms, ‘similar changes in both pelvic growth and pelvis evolution.’

eFfing #FossilFriday: toolmakers without tools?

January 24, 2015January 24, 2015 / zcofran / Leave a comment

Matt Skinner and colleagues report in today’s Science an analysis of trabecular bone structure in the hand bones of humans, fossil hominins and living apes. Trabecular bone, the sponge-like network of bony lattices on the insides of many of your bones, adapts during life to better withstand the directions and amounts of force it experiences. This is a pretty great property of the skeleton: bone is organized in a way that helps withstand usual forces, and the spongy organization of trabeculae also keeps bones fairly lightweight. Win-win.

An X-ray of my foot. Note that most of the individual foot bones are filled with tiny 'spicules' (=trabeculae) of bone. Very often they have a very directed, or non-random, orientation, such as in the heel.

An X-ray of my foot. The individual foot bones are filled with narrow spicules (=trabeculae) of bone. Very often they have a directed, or non-random, orientation: in the calcaneus, for instance, they are oriented mostly from the heel to the ankle joint.

This adaptive nature of trabecular bone also means that we can learn a lot about how animals lived in the past when all they’ve left behind are scattered fossils. In the present case, Skinner and colleagues tested whether tool use leaves a ‘trabecular signature’ in hand bones, looking then for whether fossil hominins fit this signature. Their study design is beautifully simple but profoundly insightful: First, they compared humans and apes to see if the internal structure of their hand bones can be distinguished. Second, they tested whether these differences accord with theoretical predictions based on how these animals use their hands (humans manipulate objects, apes use hands for walking and climbing). Third, they determined whether fossil hand bones look more like either group.

Comparison of first metacarpals (the thumb bone in your palm) between a chimpanzee (left), three australopithecines, and a human (right). In each, the palm side is to the left and the wrist end of the bone (proximal) is down. Image by Tracy Kivell, and found here.

Looking at the image above, it’s difficult to spot trabecular differences between the specimens with the naked eye. But computer software can easily measure the density and distribution of trabecular bone from CT scans. With these tools, researchers found key differences between humans and apes consistent with the different ways they use their hands. Neandertals (humans in the past 100 thousand years or so) showed the human pattern, not unexpected since their bones look like ours and they used their hands to make tools and manipulate objects like we do.

What’s more interesting, though, is that the australopithecines, dating to between 1.8-3.0 million years ago, also show the human pattern. This is an important finding since the external anatomy of Australopithecus hand bones shows a mixture of human- and ape-like features, with unclear implications for how they used their hands. Their trabecular architecture, reflecting the forces their hands experienced in life, is consistent with tool use.

This is a very significant finding. Australopithecus africanus fossils from Sterkfontein aren’t associated with any stone tools; bone tools are known from Swartkrans, though it is unclear whether Australopithecus robustus or Early Homo from the site made/used these. In addition, in 2010 McPherron and colleagues reported on a possibly cut-marked animal bone from the 3.4 million year old site of Dikika in Ethiopia, where Australopithecus afarensis fossils but no tools are found. Skinner and colleagues’ results show that at the very least, South African Australopithecus species were using their hands like tool-makers and -users do.

This raises many fascinating questions – were australopithecines using stone tools, but we haven’t found them? Were they using tools made of other materials? What do the insides of Australopithecus afarensis metacarpals look like? What I like about this study is that it presents both compelling results, and raises further (testable) questions about both the nature of the earliest tools and our ability to detect their use from fossils.

Kryptonians’ DNA in the Sts 71 fossil

April 15, 2014January 5, 2016 / zcofran / 1 Comment

I don’t love flying. In fact I’m writing this post in a traffic jam on the tarmac of Frankfurt International between a 9 hour and a 5 hour flight. On a related note, reclining your seatback all the way for most of a long flight does in fact make you the worst person on earth.

Hey, guy, how’s that 10th X-Men movie? What kind of shampoo is that I smell? Why yes, I do work best when I can’t open my computer fully. What a joyous way for us to learn all about each other, new best friend!

A plus of all this airtime, though, is that I can get caught up on recent movies I’ve missed living under the proverbial rock of research and teaching. On the ~7500 mile trip from Kazakhstan to Kanada I got to watch Man of Steel, a new take on an ancient comic. It was tacky and entertaining and there are some interesting takes on biology, but it had a boss paleo surprise.

The best part of the movie is at the beginning when The Gladiator steals a mysterious “codex” as his planet Krypton plunges catastrophically into implosive oblivion. Amid the chaos, Russel Crowe swims through some chamber, and what does he encounter?

The codex? No, it’s…

Sts seventy f*ing one

Sts 71 is my favorite fossil I’ve seen because it looks totally badass (not a scientific reason, but it’s the truth). It comes from Sterkfontein cave in South Africa, dates to probably around 2.5 million years ago, and is attributed to the species Australopithecus africanus.

I realize I’m behind the times here, but in case you haven’t seen the movie but are planning to, then read no further (SPOILER ALERT). In the film, this codex/fossil apparently contains the genetic code for the entire species of Kryptonians (whose resemblance to living humans is so remarkable it requires a statistically impossible amount of parallel evolution). Now, the oldest DNA recovered from a fossil is from a horse that lived about 700 thousand years ago (Orlando et al., 2013). Sts 71 is some 3-4 times older than that, and illusorily contains the genomes of a billion human-like aliens with super powers.

What a badass fossil.

Lawn Chair Anthropology

Biological anthropology, paleontology, evolution, and development, by Dr. Zachary Cofran

Australopithecus africanus