On topic: A Primate of Modern Aspect reviews the anatomy of the Ardipithecus proximal femur.
Clearly, we shouldn’t draw any conclusions about bipedality in Ardi from a third trochanter and hypotrochanteric fossa if even Proconsul had similar characters.
Regarding the "Discovering Ardi" program:
I thought the animation of Ardipithecus walking was kind of wierdly UNhuman like actually. I'd have to go back and look at it again but it seemed kind of li ke a waddler..... NO?
The legs were totally straight; if it had been chimp-like, there would have been a bent-leg stride and more side-to-side.
I think the only thing chimp-like about it was that the toe-off required it to tripod up onto the 1-2 MT/P joints, kind of like a turkey walking. And then there was the arm-swing, which with a 1.5x human length arm looked like Shaggy from Scooby Doo.
And from another reader:
Many people seem to be searching for evidence of exclusive pair bonding among human ancestors in the archaeological record (e.g. Lovejoy's observations in the Ardi program). They are jumping to the wrong conclusion, I think.
Exclusive pair bonding tends to create stronger pairs, but a weaker group. Network bonding (numerous partners both ways) tends to produce weaker individual pairs, but a stronger group. An anology from chemistry might be the differences between graphite and diamond caused by the differences in carbon bonds. In a small group, any bonding behavior that creates strong preferences and strong aversions should inevitably tend to create ready fracture lines within the group. Ultimately, this should tend to decrease the long term viability of both the group and the individuals. Conversely, bonds which criss-cross the group tend to make the loss of any one individual less painful and to make both the group and the remaining individuals more resilient.
This search for pair exclusive bonding evidence seems to be an unwarranted intrusion of modern culture into scientific work.
I think this is a really good point.
I don't know how much you know the field, but Lovejoy's views on pair-bonding are highly ideosyncratic -- they mostly bear influence because he is well-known for other work.
The idea of adapting to social networks is much more the wave of the future. It's not immediately obvious what morphological correlates (if any) we might expect as a consequence of network bonding.
I haven't been able to see all of the "Discovering Ardi" show tonight, but we did get most of the second hour. I just thought I'd jot down some general comments about the production.
First thing -- human evolution show + Mike Rowe narration = awesome. Please, more Mike Rowe. Maybe they could get him to interview the scientists. Ewwww! The roundtable has Paula Zahn. What the heck is that? Why not "Ardipithecus: After the Catch"?
OK, I can't watch that tonight; I've got Mad Men. So back to "Discovering Ardi".
The first hour seems to have been mostly excavation and discovery -- we caught the tail end of that in the second hour, and it seems to have been really well done. The film clips from the Afar are great. It's not obvious how many of them are "dramatic recreations" -- I'd have to see the first hour to get a better picture of that. But to the extent that they've posed the scientists with bones on the ground, it's been well done.
For my taste, they could have included more about the fauna and the fossil plants. The trend in recent years has been to have the "Walking with Dinosaurs" type CGI reconstructions of ancient organisms. I think that producers have the idea that the moving pictures are giving some kind of life to the ancient creatures. A little bit of that isn't a bad thing, but if the entire focus of the show is the CGI, it leaves the impression that the ancient creatures are fictional. That's especially true when you have a "main character" like Ardipithecus. You put it into an ancient CGI environment, and have it interact with one or two other creatures, and walk through some trees, and they're just window dressing. But if you see the actual fossils of the fauna and the plants, I think it conveys the reality that these fossils are themselves the objects of real science, that understanding the ancient paleoenvironment means studying the evolution of all those creatures. Aramis gives such great material to work with, and the film did give show some of the interesting parts of the fauna, and some of the fossil seeds in this hour. But like I said, there could have been more.
Speaking of CGI, they staged a motion-capture session with a small stunt actress, supervised by Owen Lovejoy. The staging wasn't badly done, but we didn't really get the payoff. By the end of the show we had only seen a few short clips of Ardi walking. This definitely fell into the area of "uncanny valley" -- not realistic enough, dark background, kind of creepy-looking. To go from bright desert scenes of the paleontologists in the Middle Awash to this dark, gloomy prehistory was kind of depressing.
The CGI version of Ardi is rendered as a total obligate biped. The knees are fully extended during the stance phase of a stride, there is a toe-off when the leg gets to the most posterior point in the stride, and there is a fully human arm-swing pattern.
This was really the weird part for me. The papers describing Ardipithecus do not come to the conclusion that Ardi had anything like a human pattern of bipedality. Nor, I would add, do the data support that conclusion. Yet here, they spent most of the whole hour leading up to the conclusion that Ardi was an obligate biped -- complete with many supporting sound bites from Lovejoy and Tim White. The only thing detracting from the tidy picture in the film's depiction is that troublesome grasping toe. And even that can be waved away if the toe-off could be accomplished with the second toe.
When the Science flurry of papers came out, I was puzzled by the Matternes reconstruction. It shows a fully upright Ardi striding up a tree branch. Yet the papers emphasized again and again that the hindlimb anatomy of Ardipithecus was likely the primitive condition, present from the human-chimpanzee common ancestor.
Weirdly, the documentary doesn't seem to have much of the "it's not like a chimp" storyline. Only a short mention. But that was the "big story" when the Ardipithecus papers hit the street. Instead, the documentary pushes the "it was a unique biped" storyline.
I don't know any more than these two depictions seem to contradict each other. It seems to me that there was a change of emphasis, or maybe a full-on change of mind, sometime after the documentary's filming and before the release. Reviewers? Whatever is the case, I don't think the anatomy supports the film's representation of the locomotor behavior. The film shows Ardi walking just as if she were Lucy. She didn't walk that way.
I really liked the way the film showed Matternes' work. The process of dialogue that he conducted over the anatomy of the fossil and the reconstruction of missing pieces really showed both the scientific and artistic processes at their best. It is rare that we see this kind of detail in any program about fossil humans. Whether it's CGI hominins or people dressed up in Neandertal get-ups, the assumptions that go into those depictions are always hidden from the viewer. Here, the attention to the artist helps to make those assumptions explicit.
Maybe I'll get to see more later.
UPDATE (2009-10-12): A reader writes:
Discovering Ardi deals with "it's not like a chimp" in the first hour: When we found this skeleton, everyone expected it to look more like a chimp and we were all stunned to find that it does not. Timelines, compared pelves, etc. So someone who sees the program from the beginning hears "it was a unique biped" as reinforcing the notion that it was surprisingly different from apes.
They also speculate on how bipedality and small canine teeth may relate to the success of critters in our branch of the evolutionary shrub, as compared to the apes.
Ah, well then. We do hear about the pelvis. I'll try to catch a rebroadcast of that to see how they handle it.
New Scientist reports on the "Best of Ig Nobel Prizes 2009". We discover that Harvard anthropologist Dan Lieberman and his colleagues have made a splash:
The physics prize recognises a delicate gravitational study to answer a question that only small children usually dare ask: why don't pregnant women tip over? For four-legged mammals and our knuckle-walking cousins, the maternal load is balanced between front and hind limbs, but for bipedal humans baby and belly protrude perilously.
How could primitive humans have survived when they spent most of their adult lives pregnant or nursing infants, wondered anthropologists Katherine Whitcome of the University of Cincinnati, Ohio, Daniel E. Lieberman of Harvard University and Liza J. Shapiro of the University of Texas, Austin. The answer, they discovered, was that women have a more pronounced curvature in their lower backs than men, shifting the upper part of the trunk backwards so their bodies balance better during pregnancy.
You know, I wouldn't have picked that particular study for this prize, but...well, if I ever am in this position, I'll remember those who blazed the trail before me.
Today is Ardipithecus day. Eleven papers in tomorrow’s issue of Science describe the research on one exceptional skeleton (numbered ARA-VP-6/500, nicknamed “Ardi”) as well as more than thirty other individuals, mostly represented by isolated teeth with a few partial sets of teeth.
I have a lot of material to share about these papers and how they change things in paleoanthropology – so much that I can’t possibly fit it all into one post.
So I’m starting out with a basic overview of the main points, organized as an FAQ. Over the next few days I’ll be exploring some of the most central issues in closer detail: in particular,
How we now interpret the earliest hominins in light of Ardipithecus.
What the skeleton means for our understanding of the human-chimpanzee common ancestor.
How Ardipithecus relates to the first australopithecine, Australopithecus anamensis.
How the crushed pelvis became a 3-d model, and whether we should believe it.
Can Ardipithecus be consistent with genetic estimates of human-chimpanzee divergence time?
What was the locomotor adaptation of Ardipithecus really like?
How was the "Discovering Ardi" documentary feature?
I expect I’ll be posting a new story every day for the next week or so. This initial post will be the central location for the series, and here I’ll try to give the most general-interest information.
I will also have a short article coming out in Seed sometime this week, I will post a link when that is up.
I will be editing this post recurrently – I’ve been speed-writing for the last couple of days and so I have some work yet to do on adding references, fixing typos, rephrasing, etc. This will be a stable document after the first week.
UPDATE (2009-10-03): OK, it's been a couple of days, so I'm closing out the post and adding a jump. I'll continue to update links inside as I round out my reactions to the papers.
If you want a basic description of the facts, here they are. Today’s series of papers is basically unprecedented in paleoanthropology. There are eleven papers in total, giving comprehensive coverage of the anatomy, paleoenvironment, and evolutionary interpretation of a new skeleton of Ardipithecus ramidus and dental remains representing more than 30 additional individuals. They have been published simultaneously in a coordinated effort including excavation, faunal correlation, microscopy, palynology, CT-scanning, three-dimensional reconstruction, isotopic analysis, and lord knows what else.
It’s the closest thing we’ll ever see to a big science effort in the little field of human evolution – like Tim White was building a supercollider under everybody’s noses.
The skeleton has been nicknamed, “Ardi” and it is 4.4 million years old. The site is Aramis, Ethiopia, in the Middle Awash field research area. The skeleton includes most of both arms, except the humeri, both hands, both feet, the right leg, the left ox coxa and part of the right ilium, a bit of sacrum, a couple of vertebrae, and a near-complete skull and dentition. It’s a bit more complete than Lucy, although preserving different parts.
The skull and pelvis were badly crushed, both of these were given CT-assisted reconstructions which are presented in separate papers (Suwa et al., 2009; Lovejoy et al., 2009c). Additionally, the series includes three papers on the paleoenvironment, a complete description of the dentition, and separate papers on the forelimbs and feet. The central paper in the series, by White and colleagues 2009b, is accompanied by a summary paper by Lovejoy examining the human-chimpanzee common ancestor in light of Ardipithecus.
As one of the papers puts it (White et al., 2009b), it represents a previously-unknown “adaptive plateau” for the hominins. Considering that really only three such “adaptive plateaux” were known before this – roughly, australopithecines, robust australopithecines, and humans – that gives some impression of the amount of difference evident in these remains from later hominins.
As I’ll describe, some substantial ambiguities and questions remain, which will no doubt shape the progress of paleoanthropology for many years to come.
White and colleagues 2009b give a detailed overview of the state of preservation of the skeleton
The bony remains of this individual (ARA-VP-6/500) (Fig. 3) (37) are off-white in color and very poorly fossilized. Smaller elements (hand and foot bones and teeth) are mostly undistorted, but all larger limb bones are variably crushed. In the field, the fossils were so soft that they would crumble when touched. They were rescued as follows: Exposure by dental pick, bamboo,and porcupine quill probe was followed by in situ consolidation. We dampened the encasing sediment to prevent desiccation and further disintegration of the fossils during excavation. Each of the subspecimens required multiple coats of consolidant, followed by extraction in plaster and aluminum foil jackets, then additional consolidant before transport to Addis Ababa.
Still, it’s possible to overstate this explanation. Bad preservation of remains is not uncommon in archaeological contexts. In this case extreme care was obviously warranted. But just as important may have been the opportunity to interpret and guide the reconstruction of the fossil using CT scanning and other technological enhancements.
To me, that is the central message of today’s announcement and papers. The big science version of paleoanthropology is one that brings an interdisciplinary and technological approach to fossil remains right from the very start. Coordinating such an extensive interpretive project requires time – in this case, fifteen years.
I can see a shiny nugget of goodness in that depressing span of time. The initial publication of the distorted Sahelanthropus skull led to substantial disagreement about the anatomy of the skeleton. Later CT reconstruction appeared to clarify some aspects of the anatomy. Arguably, it would have been better to delay publication until the CT reconstruction could be done. Obviously White and his team wanted to minimize the opportunity for error in their interpretations. They’ve covered their bases.
But that example also shows the danger of the wait-and-see approach, in that it tends to silence skeptical inquiry. Are there morphological details of the Ardipithecus skeleton that are obscured rather than clarified by reconstruction? At the moment, we don’t know.
Back in the Cold War, CIA analysts and other folks would read carefully through Pravda and other Soviet publications, parsing every word to look for the barest hint of the Politburo’s intentions. There was a word for those people: “Kremlinologists.” It seems to me that somebody quoted in Ann Gibbons’ book, The First Human said that paleoanthropologists basically do the same thing with Ardipithecus — poring through every publication or interview, looking for hints about the fossils hidden from the field for fifteen years. I don’t remember right now who, and I don’t have the book in front of me (I reviewed the book here in 2006).
On the other hand, there are people who follow every Twitter about their favorite celebrity, recording the GPS coordinates of sightings, and “running into” them at the openings of exclusive clubs. There’s a word for these people, too: “stalkers.”
Paleoanthropologists for the last fifteen years have been a little bit of both. It’s hard to help it – Tim White let slip ten years ago that the skeleton’s locomotor style was like something out of the Star Wars cantina and, well, let’s just say that some people hear his voice and think of Weird Al Yankovic.
If you weren’t following paleoanthropology in 1994, you may not remember Ardipithecus at all. For a brief, shining moment, it was the earliest hominin. Well, except for the Lothagam mandible, but nobody ever seems to remember Lothagam. It doesn’t even show up in the current series of papers.
Then, the species fell under a veil of secrecy. The initial find was from a locality called Aramis, within the Middle Awash field concession worked by Berkeley paleoanthropologist Tim White and colleagues. The news escaped that further fossils from Aramis had been found, including a partial skeleton. After initial examination of the skeleton, White and colleagues (1995) submitted a brief comment to Nature in which they changed the genus name of the first specimens. Instead of Australopithecus ramidus, they would henceforth be Ardipithecus ramidus. After that, silence.
Research at other localities in the Middle Awash uncovered earlier remains, which Haile-Selassie and colleagues 2001; 2004 attributed to a new species of Ardipithecus, Ar. kadabba. These were never the earliest hominins (predated at their initial discovery by Orrorin and later by Sahelanthropus, but at 5.5 million years old they were not far off. In their 2004 paper, Haile-Selassie and colleagues even suggested that all of these terminal Miocene hominins actually represent variations of a single species. An unstated implication is that the species would then be called Ardipithecus tugenensis.
Sileshi Semaw and the Gona Research Project 2005 found Ardipithecus downriver from Aramis, at a locality called As Duma. This represented approximately the same age as the Aramis horizons, and showed that Ardipithecus ramidus was not just a one-off. But the remains were only a few fragments. Based on the paleoecology of the immediate find, they suggested that the species had lived in a ”mosaic” of environments, bringing together elements of the fauna from both woodland, wetland and grassy woodland facies. That interpretation becomes a point of contention in the current series of research articles.
Other hints about Ardipithecus morphology have been dropped over the years. In a key 1999 paper, Owen Lovejoy along with Martin Cohn and Tim White described the Ardipithecus pelvis. They didn’t show it or say it was Ardipithecus, but there it was nonetheless. The interpretations of tooth size in the other, more fragmentary Ardipithecus remains (referred to as “relatively small”) made the body size of the skeleton fairly clear, which enabled interpretation of an radius earlier found at Aramis as a relatively long forelimb. And so on, the main conclusions have been foreshadowed elsewhere.
One thing stood out as a surprise. Ardipithecus had a grasping foot.
Short answer: Yes.
The paper about the foot remains, by Lovejoy and colleagues 2009a, is full of just the kind of impenetrable prose you’d expect for a paper about foot remains. I have a lot of affection for people who know feet, but all the “fulcrumating” has me fulminating.
If we hack through the verbiage, the feet send a clear message:
Several elements of the Ardipithecus ramidus foot are preserved, primarily in the ARA-VP-6/500 partial skeleton. The foot has a widely abducent hallux, which was not propulsive during terrestrial bipedality. However, it lacks the highly derived tarsometatarsal laxity and inversion in extant African apes that provide maximum conformity to substrates during vertical climbing. Instead, it exhibits primitive characters that maintain plantar rigidity from foot-flat through toe-off, reminiscent of some Miocene apes and Old World monkeys. Moreover, the action of the fibularis longus muscle was more like its homolog in Old World monkeys than in African apes. Phalangeal lengths were most similar to those of Gorilla. The Ardipithecus gait pattern would thus have been unique among known primates. The last common ancestor of hominids and chimpanzees was therefore a careful climber that retained adaptations to above-branch plantigrady.
“Unique among primates.” I hate it when they say that.
From the point of view of a foot specialist, this foot has many interesting aspect that can illuminate the evolution of stance and locomotor behavior in Miocene apes and the ancestors of the hominins.
From an Anthro 101 point of view, it’s an ape foot.
Still, Lovejoy and colleagues 2009a; 2009b describe the anatomy of the Ardipithecus foot as clearly different from Australopithecus, but different from chimpanzees also. The confusing thing is that it isn’t intermediate between those two forms. In their account, chimpanzee feet are specialized for more grasping, while the Ardipithecus foot retained a more generalized form. The confusion comes from parallelism in apes after Proconsul, which left Ardipithecus resembling monkeys more than apes in certain aspects of its foot anatomy, but more recent apes more than early apes in others.
The metatarsus of Ar. ramidus, chimpanzees, and gorillas presents a striking contrast to their metacarpus. Like the foot phalanges, the metatarsals also appear to have been universally shortened in all hominoids subsequent to Proconsul. The basis of this universal shortening, however, is somewhat unclear, because tarsal evolution contrasts dramatically in hominids and African apes. The modern ape foot has obviously experienced functional reorganization into a more hand-like grasping organ. The Ar. ramidus foot did not. This suggests that substantial elements of a more lever-based, propulsive structure seen in taxa such as Proconsul and Old World Monkeys [robust plantar aponeurosis; retained quadratus plantae; robust peroneal complex] were preserved in the GLCA/CLCA. These structures were sacrificed in both African ape clades to enhance pedal grasping for vertical climbing (Lovejoy et al., 2009b, 102)
That may be all I want to say about the foot for now. You can see that this is one of the most important anatomical aspects of the specimen in terms of understanding the origins of bipedality. Ardipithecus was not an obligate biped in any sense applied to Australopithecus.
The pelvis of Ardipithecus, as reconstructed by Lovejoy and colleagues 2009c, is intermediate between the chimpanzee and australopithecine morphology. In particular, the blade of the ilium is short and relatively curved compared to the long, flat chimpanzee ilium. But it does not approach the pelvis of Lucy or Sts 14 in those aspects, and the ischium is very chimpanzee-like in shape. The pubic symphysis was shorter than the long chimpanzee morphology, and the auricular surfaces appear consistent with a relatively shorter sacrum than in chimpanzees.
In reconstruction, it looks like a blend of hominin-like and chimpanzee-like anatomies. Lovejoy and colleagues further argue that the proximal femur indicates that a somewhat humanlike gluteus maximus insertion was in fact primitive for apes, with chimpanzees and gorillas having a derived non-humanlike form.
So what does this mean for locomotion? In their description (Lovejoy et al., 2009b), the African ape pelvic morphology is derived as a way of stiffening the lower back, in coordination with shortening the lumbar spine. If the African ape gluteal morphology is also derived (are you counting parallelisms yet?), then neither the ilium nor the proximal femur (excepting the possibility of bone distribution data not observable in Ardi) are useful markers of bipedality.
In other words, even though the Ardipithecus pelvis may look intermediate between chimpanzee and australopithecine morphologies, it’s not indicative of bipedality. Ardipithecus might have the locomotor morphology of the human-chimpanzee common ancestor.
To me, that seems shocking. More on this later.
The Middle Awash field team was able to do a very interesting thing in its paleoenvironmental reconstructions. The layer at Aramis containing the Ardipithecus skeleton and other remains is essentially a 3 to 5 meter thick series of paleosol, alluvial silt and fossilized bone and wood of various kinds. It is underlain by a glassy tuff and above by a basaltic tuff, which presumably represents some kind of pyroclastic event that swept through the area. The two tuffs are statistically indistinguishable in age, and the team guesses that the time between them represents something like a thousand years, maybe an order of magnitude more or less. So what they have is a thin sandwich of paleoenvironments, spread over the extent that the twin tuffs cover.
Now, this sandwich outcrops across roughly 9 km of linear distance (White et al., 2009b). So the team could sample distinct localities across this entire transect. What they found was that the line represented a range of habitats from open and grassy at one end to closed and wooded for (most) of the rest. They found Ardipithecus exclusively in associated with the wooded environment – complete with fossil wood, lots of monkeys and tragelaphines. They found no Ardipithecus at all in the localities representing more open environments. White and colleagues 2009a argue that this is a very strong test of habitat preference for Ardipithecus — it liked the trees.
Several aspects of Lower Aramis Member larger mammal assemblage abundance data constitute strong indicators of ancient biofacies and biotope. The locality-specific subassemblages are remarkably consistent in their taphonomy and taxonomy across the 7 km distance from the easternmost (SAG-VP-7) to westernmost (KUS-VP-2) Ar. ramidus localities.
Contemporaneous localities between the two tuffs farther south of the modern Sagantole drainage (SAG-VP-1 and -3, at the southeastern paleotransect pole) are relatively impoverished. They lack this diverse and abundant mammal assemblage and contain no tragelaphines, no monkeys, no fossil wood or seeds, no birds, no micromammals, and no Ardipithecus (table S1). Complementary structural, taphonomic, and isotopic data from localities on this pole of the paleotransect suggest a more open landscape that supported more crocodilians, turtles, and hippopotamids, presumably associated with water-marginal settings more axial in the drainage basin (White et al., 2009a).
That reconstruction makes sense with the locomotor anatomy. It also makes sense with the isotopic data on diet. After sampling carbon and oxygen stable isotopes in five Ardipithecus individuals, they conclude that it had a C4 plant consumption much less than later australopithecines, while higher than the very minimal value in chimpanzees, and that it habitually lived in mesic (not too wet, not too dry) habitat.
The paper by Owen Lovejoy, “Reexamining human origins in light of Ardipithecus ramidus” is possibly the most interesting in the collection. It will take me some more reflection to figure out what I think about the whole paper, but here I can abstract out the main ideas.
Much of the paper is speculative, concerning the “reproductive biology” of the human-chimpanzee common ancestor. In this paper, Lovejoy uses the acronym CLCA for ”chimpanzee last common ancestor,” which I find totally confusing. Since this is so close in time to the human-gorilla common ancestor, I’ll just take advantage of the new taxonomic scheme and call these ancestors the “stem hominines.” Lovejoy’s interest in reproductive biology is longstanding, as it formed the centerpiece of his 1981 article on human origins.
In many ways, this current article is an update of that one, because they arrive at the same singular focus: the association of canine reduction with increasing bipedality. Canines, in Lovejoy’s description, are principally a function of mating biology, and so any indirect evidence we have about the evolution of mating systems in humans or chimpanzees becomes very relevant to the factors that caused hominin origins.
Ardipithecus clearly shows that the canine reduction came first, bipedality later. Lovejoy integrates this fact into his earlier model, that the change in mating biology caused the change in locomotor strategy, as males substituted provisioning and food sharing as modes of mating competition in the place of aggression.
However, I think this is short-sighted. We already know that some degree of canine reduction occurs in several Miocene ape lineages, and that mating competition is highly variable among living apes and primates generally. What Ardipithecus shows, if we assume a connection between it and earlier candidate hominins like Sahelanthropus and Orrorin, is that the reduction of the canines preceded the evolution of effective bipedality by more than three million years. It is very difficult to conceive of mating biology as a cause of the locomotor evolution, when it is so removed from the change in time. It’s as if we stubbornly insisted that bipedality was the cause of stone tool transport.
The most interesting part of this paper is what Lovejoy says about the relevance of chimpanzees. This was also anticipated in an earlier paper, this one by Sayers and Lovejoy 2008, which argued that a chimpanzee model is too restrictive as a way of understanding the initial biology of hominin ancestors. Here, Lovejoy makes that view explicit in terms of the arboreality of Ardipithecus:
The primitive nature of the craniodental and postcranial anatomies of Ar. ramidus suggest that the CLCA, unlike African apes, was predominantly arboreal. However, all of its descendants have since developed relatively sophisticated adaptations to terrestrial locomotion. What was the CLCA’s socio-reproductive structure before these events? Whereas African apes ahve, in the past, almost invariably been selected as CLCA vicars [stand-ins], Ar. ramidus now allows us to infer that they have undergone far too many pronounced and divergent specializations to occupy such a role (Lovejoy, 2009, 74e4).
Lovejoy and colleagues discuss this concept in more detail in the paper outlining the Ardipithecus postcrania (Lovejoy et al., 2009b). I will be spending much more time on this paper, which makes several provocative assertions about developmental biology. But the conclusion of the paper
Ar. ramidus implies that African apes are adaptive cul-de-sacs rather than stages in human emergence. It also reveals an unanticipated and distinct locomotor bauplan for our last common ancestors with African apes, one based on careful climbing unpreserved in any extant form....
Ardipithecus has thus illuminated not only our own ancestry, but also that of our closest living relatives. It therefore serves as further confirmation of Darwin’s prescience: that we are only one terminal twig in the tree of life, and that our own fossil record will provide revealing and unexpected insights into the evolutionary emergence not only of ourselves, but also of our closest neighbors in its crown (Lovejoy et al., 2009b, 105–106).
OK, I don’t remember Darwin saying anything about the neighbors in our crown. But you get the point – the stem hominines weren’t like chimpanzees or gorillas.
Gen Suwa headed the cranial reconstruction (Suwa et al., 2009). Most of Ardi’s skull is represented on one side or the other, except for the basicranium. The team did have the temporal bones from another specimen, ARA-VP-1/500 (previously described by White and colleagues 1994). These temporal bones were too big to fit together with Ardi’s skull, so they digitally shrank them – sort of like reducing on a photocopier.
First of all, they did a really cool thing – they reconstructed the spatial relation of the two temporal bones by aligning the semicircular canals. Those tiny structures of the inner ear are like a miniature three-dimensional coordinate frame – part of the vestibular system that senses the position of the head. I’m sure they’re the first to do that, but it’s pretty neat to be able to align two temporal bones with no contact points between them.
I mention that because their reconstruction of the temporals determines the position of the line between the carotid canals on the base of the skull – the bicarotid line. This element of anatomy was very important in our consideration of Sahelanthropus (Wolpoff et al. 2006), as the measure between the bicarotid line and basion was a key indicator of the position of the foramen magnum. Jim Ahern found that this distance actually overlaps substantially between humans and chimpanzees, and most australopithecine crania actually fall into the chimpanzee range. That makes the trait questionable as an indicator of habitual head posture. Here, Suwa and colleagues found that the basion-bicarotid distance in Ardipithecus is as low as seen in the lowest known australopithecine cranium.
Suwa and colleagues advance an old hypothesis for this basicranial form. It’s not about upright posture, it’s about the brain.
The Sahelanthropus and Ardipithecus crania securely associate a relatively short basicranium with small cranial capacity. The hominid basicranial pattern and associated morphologies [such as foramen magnum orientation] are widely held to be related to bipedality and upright posture, despite a lack of empirical evidence to clearly support a functionally based correlation. The Ar. ramidus cranium raises the alternative possibility that early hominid creanial base flexion was associated with neural reorganization that was already present in Sahelanthropus/Ardipithecus, as suggested for Pliocene Australopithecus. Such a hypothetical supposition is in part testable by both future fossil finds and by anticipated advances in our understanding of genomic expression patterns pertaining to brain function, structure, and morphogenesis (Suwa et al., 2009, 68e6).
I say, “old” because that was Raymond Dart’s interpretation of the Taung endocast — it was humanlike because of a neural reorganization.
Are they right? I’ll say this: if the basicranium does not reflect posture in these fossils, then there is no compelling evidence for posture at all.
If brain reorganization was underway in these ancient species, there’s no indication of it in the size of the brain. Ardi, like Toumaï, had a small brain — they estimate only 300–350 ml for its endocranial volume.
The rear of the skull – the nuchal plane of the occipital bone – was not preserved, so the most important remaining comparison with Sahelanthropus is the supraorbital region. This is small in Ardi, and extremely large and thick in Toumaï. Suwa and colleagues propose that this morphology matches the assessment of female sex for Ardi, which seems entirely reasonable. In the context of later Australopithecus, Ardi’s supraorbital torus might even be large for a female of its size. The difference between Ardi and Toumaï in browridge size would be surprisingly large considering the relatively slight difference in size between the two skulls. Still, with only two specimens to compare, a species with very large browridges in males might show this kind of difference on occasion.
This is an interesting omission, no? There’s no cladogram. What we get is this weird phylogenetic diagram that looks like a sectioned spinal cord:
If we could find a way to repair it, Homo would regain feeling.
Setting aside the aesthetics — which I’m sure were a lot of work — this set of scenarios is very unsatisfying. In all three, some version of Ardipithecus is the stem for later hominins. They haven’t shown that at all. None of the scenarios include chimpanzees or gorillas — yet no matter what you think about genetic estimates of divergence, the stem hominines were large and diverse populations with long-term interactions. Maybe these stopped before 6 million years ago, but none of the genetic data suggest that now at all.
Cladograms would oversimplify some aspects that should be considered complex, but maybe we could have one?
White and colleagues 2009b give a long table of “derived” characters in Ardipithecus and Australopithecus, but they are “derived” only with reference to their inferred state in the human-chimpanzee LCA. But elsewhere in these papers, they argue that some of these “derived” characters are actually primitive morphologies for apes, for which chimpanzees are independently derived. For many of the dental features, if we supposed a Miocene ape ancestor, the broadened mandibular body, thicker enamel and so on would look primitive, not derived. In the table, they list upper and lower canine traits separately, and break them up into six or more for each. That’s a quick way of making one morphological change look like twelve or more instances of independent evolution. Talk about atomizing traits!
So I wonder if a real cladistic analysis might not place Ardipithecus with the australopithecines. Especially if it included a proper sampling of Miocene ape taxa.
Maybe worse, a real cladistic analysis that did place Ardi with Australopithecus would probably put the earlier Ardipithecus kadabba as an outgroup to both. That would make Ardipithecus paraphyletic.
I wouldn’t typically care, because I don’t think taxonomic rules should direct the science. But it does seem like a delicious taxonomic dilemma. The likely solution would be to lump Ar. kadabba with either Orrorin or Sahelanthropus, or both. Orrorin kadabba would have priority.
But if one were feeling saucy, she could publish the cladistic analysis on the teeth, point out the dilemma, and then offer a novel genus name for the Kadabba sample. Maybe somebody’s already thought of that — there are a lot of journals out there.
Haile-Selassie Y. 2001. Late Miocene hominids from the Middle Awash, Ethiopia. Nature 412:178–181.
Haile-Selassie Y, Suwa G, White TD. 2004. Late Miocene teeth from Middle Awash, Ethiopia, and early hominid dental evolution. Science 303:1503–1505.
Lovejoy CO. 2009. Reexamining human origins in light of Ardipithecus ramidus. Science 326:74e1–74e8.
Lovejoy CO, Latimer B, Suwa G, Asfaw B, White TD. 2009a. Combining prehension and propulsion: The foot of Ardipithecus ramidus. Science 326:72e1–72e8.
Lovejoy CO, Suwa G, Simpson SW, Matternes JH, White TD. 2009b. The great divides: Ardipithecus ramidus reveals the postcrania of our last common ancestors with African apes. Science 326:100–106.
Lovejoy CO, Suwa G, Spurlock L, Asfaw B, White TD. 2009c. The pelvis and femur of Ardipithecus ramidus: The emergence of upright walking. Science 326.
Sayers K, Lovejoy CO. 2008. The chimpanzee has no clothes: A critical examination of Pan troglodytes in models of human evolution. Curr Anthropol 49:87–114.
Semaw S, Simpson SW, Quade J, Renne PR, Butler RF, McIntosh WC, Levin N, Dominguez-Rodrigo M, Rogers MJ. 2005. Early Pliocene hominids from Gona, Ethiopia. Nature 433:301–305.
Suwa G, Asfaw B, Kono RT, Kubo D, Lovejoy CO, White TD. 2009. The Ardipithecus ramidus skull and its implications for hominid origins. Science 326:68e1–68e7.
White TD, Ambrose SH, Suwa G, Su DF, DeGusta D, Bernor RL, Boisserie JR, Brunet M, Delson E, Frost S, Garcia N, Giaourtsakis IX, Haile-Selassie Y, Howell FC, Lehmann T, Likius A, Pehlevan C, Saegusa H, Semprebon G, Teaford M, Vrba E. 2009a. Macrovertebrate paleontology and the Pliocene habitat of Ardipithecus ramidus. Science 326:87–93.
White TD, Asfaw B, Beyene Y, Haile-Selassie Y, Lovejoy CO, Suwa G, WoldeGabriel G. 2009b. Ardipithecus ramidus and the paleobiology of early hominids. Science 326:75–86.
Recent University of Michigan Ph.D. Jeremy DeSilva gets some nice press about his work demonstrating that fossil hominins didn't climb like chimpanzees:
"Frankly, I thought I was going to find that early humans would be quite capable, but their ankle morphology was decidedly maladaptive for the kind of climbing I was seeing in chimps," DeSilva told LiveScience. "It kind of reinvented in my mind what they were doing and how they could have survived in an African savannah without the ability to go up in the trees."
This is a good example of the comparative method in paleoanthropology. We can't observe the behavior of extinct species; we can only observe the behavior of their living relatives. We can observe the anatomy of fossil specimens, but testing hypotheses about their behavior requires us to understand the relationship between anatomy and behavior in living species. We've known about the anatomy of fossil hominid ankles for a long time, but it's not so obvious how the anatomical differences between them and chimpanzee ankles relates to behavior.
The paper's abstract:
Whether early hominins were adept tree climbers is unclear. Although some researchers have argued that bipedality maladapts the hominin skeleton for climbing, others have argued that early hominin fossils display an amalgamation of features consistent with both locomotor strategies. Although chimpanzees have featured prominently in these arguments, there are no published data on the kinematics of climbing in wild chimpanzees. Without these biomechanical data describing how chimpanzees actually climb trees, identifying correlates of climbing in modern ape skeletons is difficult, thereby limiting accurate interpretations of the hominin fossil record. Here, the first kinematic data on vertical climbing in wild chimpanzees are presented. These data are used to identify skeletal correlates of climbing in the ankle joint of the African apes to more accurately interpret hominin distal tibiae and tali. This study finds that chimpanzees engage in an extraordinary range of foot dorsiflexion and inversion during vertical climbing bouts. Two skeletal correlates of modern ape-like vertical climbing are identified in the ankle joint and related to positions of dorsiflexion and foot inversion. A study of the 14 distal tibiae and 15 tali identified and published as hominins from 4.12 to 1.53 million years ago finds that the ankles of early hominins were poorly adapted for modern ape-like vertical climbing bouts. This study concludes that if hominins included tree climbing as part of their locomotor repertoire, then they were performing this activity in a manner decidedly unlike modern chimpanzees.
DeSilva's conclusion is straightforward and easy to illustrate. Chimpanzees climb vertical tree trunks pretty much like a logger does. A logger slings a strap around the trunk and leans back on it. Friction from the strap holds him up as he moves his feet upward; spikes on his boots hold him while he moves the strap.
Of course, chimpanzees don't have spikes on their feet, and they don't use a strap. Instead, their arms are long enough to wrap around the trunk, and they can wedge a foot against the trunk by flexing their ankle upward -- dorsiflexing it -- or grip the trunk by bending the ankle sideways -- inverting the foot -- around it. The paper includes a photo that shows the chimpanzee style of climbing clearly:
Photo of chimpanzee climbing a tree, from DeSilva (2008)
You might wonder, yeah so what? Isn't it obvious that chimpanzees climb this way?
Well, it wasn't so obvious which features of the ankle might adapt chimpanzees to this style of climbing. By watching the chimpanzees (and other apes) DeSilva was able to determine the average amount (and range) of dorsiflexion and inversion of the feet while climbing, and could also assess the extent to which dorsiflexion is accomplished at the ankle joint (as opposed to the midfoot). In this case, the observations were pretty obvious -- chimpanzees were habitually flexing their ankles in ways that would damage a human ankle. Then, by examining the bony limits on human ankle flexibility, DeSilva showed that fossil hominins shared the same constraints on ankle movement as recent people. They couldn't have climbed like chimpanzees.
I would say that the ankle-joint observations match the rest of the skeleton. It seems pretty obvious that Australopithecus afarensis and later hominids couldn't possibly have climbed in the chimpanzee-like manner described in DeSilva's paper, because the hominins' arms were too short. If a logger tried to climb with his arms instead of a strap, even spikes on his feet would be relatively ineffective holding him up. Dorsiflexion would be hopeless -- the normal component of force against the tree trunk would be insufficient to prevent slipping.
Humans who aren't loggers use a different strategy to climb vertical tree trunks -- they put a large fraction of the surface area of their legs directly in contact with the trunk. Wrapping legs around and pressing them together gives the necessary friction to hold the body up.
If you're like me, you'll remember this climbing strategy ruefully from gym class, where "rope climbing" is the lowest common denominator of fitness tests. The sad fact is that many otherwise-normal humans fall on the wrong side of the line between mass and muscle power. Straining my groin muscles to the max, I still could never pull my way up a rope.
There's nothing magical about getting a human to climb. Ladders, after all, are relatively easy for the large fraction of the population who can't climb a rope or tree trunk. The trick with a ladder is that friction is organized in a more effective way for our ankle mechanics and arm length. But you don't need to schlep a ladder, if you can manage a little extra arm strength and a low enough body mass.
Australopithecines were light in mass, and from what we can tell, they had strong arms. So they had what it takes for humans today to climb trees effectively -- not like chimpanzees, but like humans. Up to A. afarensis, every early hominin we know about lived in an environment that was at least partially wooded.
In his comments about the paper, DeSilva hypothesizes a trade-off between climbing ability and effective bipedality, so that early hominins could not have effectively adapted to both. I don't think a chimpanzee-like ankle would have been any use with arms as short as australopithecines'. So I don't see the necessity of a trade-off in ankle morphology. A. afarensis -- long before any evidence of stone tool manufacture -- had very non-apelike arms, hands and thumbs.
But there's one significant question that DeSilva omits discussing: StW 573. Clarke and Tobias (1995) describe the foot of StW 573 as having a big toe that is abducted (sticks out) from the foot, intermediate between the chimpanzee and human condition. They conclude:
[W]e now have the best available evidence that the earliest South African australopithecine, while bipedal, was equipped to include arboreal, climbing activities in its locomotor repertoire. Its foot has departed to only a small degree from that of the chimpanzee. It is becoming clear that Australopithecus was not an obligate terrestrial biped, but rather a facultative biped and climber (Clarke and Tobias 1995:524).
DeSilva studied the talus, not the toe. StW 573 has a talus, and although it is not in DeSilva's sample, it probably would place very close to the other hominins in his comparison. Even Clarke and Tobias described its talus as humanlike -- their argument for an intermediate form was based mostly on the toe.
But still, it's hard to believe that australopithecines would retain a chimpanzee-like big toe, if they couldn't use that big toe by inverting or dorsiflexing their foot in any significant way. By all other accounts, an abducted hallux would only impede effective bipedality. It is of no use at all for a human-like pattern of climbing. The only remaining utility would be for small-branch grasping, but small branches would seem unlikely as a support for hominin arboreality.
One possibility is that Clarke and Tobias were simply mistaken. That appears to be the explanation favored by Harcourt-Smith and Aiello (2004:412), who cited Harcourt-Smith's 2002 thesis:
Recent multivariate analyses of the Stw 573 tarsal bones (medial cuneiform, navicular and talus) using geometric morphometric techniques demonstrate that this fossil had a very ape-like talus, a navicular that was intermediate between apes and modern humans, and a human-like medial cuneiform inferring a lack of any hallux opposability (Harcourt-Smith, 2002). This finding contrasts with the findings of Clarke & Tobias (1995), but is does not change the fact that Stw 573 would still have a different combination of morphologies in the foot than does A. afarensis.
This view was also supported by McHenry and Jones (2006), who concluded that all known hominin feet appear to lack any "ape-like ability to oppose the big toe." They also point to the Laetoli footprint trails, most observers of which agree that the big toe was adducted, not abducted.
I tend to favor that explanation -- australopithecines simply didn't have a grasping foot. But they may not have shared the medial longitudinal arch, at least not in the human configuration, and without it one might doubt that their gait featured as strong a toe-off as that of later humans. Who knows?
Meanwhile I can recommend Harcourt-Smith and Aiello's review for those who want to read more about bipedality and climbing in early hominins. It's not the last word but it is a good introduction to the literature.
UPDATE (2009/04/15): A reader writes to suggest also the 1987 paper by Bruce Latimer, James Ohman and Owen Lovejoy. I recommend it for anyone who wants to dig deeper into australopithecine ankle morphology. I've added it to the bibliography below.
DeSilva JM. 2009. Functional morphology of the ankle and the likelihood of climbing in early hominins. Proc Nat Acad Sci USA 106:6567-6572. doi:10.1073/pnas.0900270106
Clarke RJ, Tobias PV. 1995. Sterkfontein Member 2 foot bones of the oldest South African hominid. Science 269:521-524.
Harcourt-Smith WEH, Aiello LC. 2004. Fossils, feet and the evolution of human bipedal locomotion. J Anat 204:403-416. doi:10.1111/j.0021-8782.2004.00296.x
Latimer B, Ohman JC, Lovejoy CO. 1987. Talocrural joint in African hominoids: Implications for Australopithecus afarensis. Am J Phys Anthropol 74:155-175.
McHenry HM. Jones AL. 2006. Hallucial convergence in early hominids. J Hum Evol 50:534-539. doi:10.1016/j.jhevol.2005.12.008
Elizabeth Culotta reports from the Vertebrate Paleontology meetings about an analysis of the hominid femur from Galili, Ethiopia.
In the view of Viola and his Vienna colleague Horst Seidler, the bone is more primitive than Lucy's femur and resembles that of a much earlier hominin, Orrorin tugenensis, thought to be about 6 million years old. They suspect that it came from Au. anamensis, a species that lived about 4 million years ago and is widely considered to be Lucy's ancestor.
Details of the femur's anatomy, such as a long neck of bone leading to a large femoral head (the "ball" of the hip's ball and socket joint), suggest that its owner--whatever its name--was bipedal, Viola said. But other clues imply that it may also have climbed trees, he added. For example, a thick layer of dense cortical bone is evenly distributed around the femoral neck. In upright walkers like us, that cortical bone is unevenly distributed. "Both Orrorin and this femur seem to show several traits which indicate bipedalism but also retain signs of arboreal behavior," Viola says. That suggests that our ancestors' move out of the trees was a long process.
Culotta has quotes from other experts either way. I have no strong opinion -- the even distribution of cortical bone is likely a sign of locomotor flexibility, but that might mean arboreality, a less stereotyped pattern of bipedality, or some other pattern of activity.
I tend to be more convinced by ecological arguments in favor of the continued use of trees/ For example, pre-afarensis hominids are always found in wooded environs. The dental pattern of later hominids emerged very slowly, plausibly reflecting a shift from fruits toward the products of grasses and other savanna foods, but this pattern may be post-Ardipithecus. And early hominids never attain the body size of later Homo, despite the advantages of larger size in a terrestrial habitat. Plausibly, this is because climbing remained important, and large body size made climbing harder.
That's a very circumstantial argument. From that perspective, the femur doesn't conflict with the idea that the locomotor requirements included climbing. But it's not very strong evidence in favor of the hypothesis, either.
The article is short, and doesn't mention the history of the Galili field site, including the conflicts over excavation rights and territorial boundaries. Those details are reviewed in Ann Gibbons' book, a great introduction to many of the field sites and current personalities (I reviewed it here).
There have been few publications on the Galili site. Roberto Macchiarelli and colleagues (2004) described the first hominid tooth found at the site, and this year, Ottmar Kullmer together with Seidler and others described the paleoecology and chronology of the site. Their paleoecological reconstruction places Galili as open woodland to bushland, and is perhaps the most open of the pre-4.0-myr sites. They suggested that the field site represents a transitional time period from A. anamensis to A. afarensis, which would be chronologically just after the Asa Issie sample at 4.1-4.2 myr, but possibly overlapping with Allia Bay.
Culotta E. 2008. Two legs good. Science 322:670-671. doi:10.1126/science.322.5902.670b
Kullmer O, Sandrock O, Viola TB, Hujer W, Said H, Seidler H. 2008. Suids, elephantoids, paleochronology, and paleoecology of the Pliocene hominid site Galili, Somali region, Ethiopia. Palaios 23:452-464. doi:10.2110/palo.2007.p07-028r
Machiarelli R, Bondioli L, Falk D, Faupl P, Illerhaus B, Kullmer O, Richter W, Said H, Sandrock O, Schäfer K, Urbanek C, Viola TB, Weber GW, Seidler H. 2004. Eaerly Pliocene hominid tooth from Galili, Somali region, Ethiopica. Collegium Anthropologium 28:65-76.
There's nothing especially surprising about the functional interpretations in Richmond and Jungers' paper about the Orrorin BAR 1002'00 femur. They conclude it was an australopithecine-like biped, because it shared several features with australopithecine femora: in particular, it has a long, narrow, anteroposteriorly flattened neck and a broad thick proximal shaft.
In this, they mirror the conclusions of the original description of the Lukeino fossils by Senut et al. (2001). Richmond and Jungers also reiterate the evidence for arboreality in the Lukeino fossils, including the well-developed musculature of the distal humerus and the chimpanzee-like curved finger bone. I wonder why their analysis could not have made something more out of the other two femoral fragments, one of which is fairly large (but lacking the head). Still, the paper reiterates the quite good evidence for bipedality in the most complete femoral specimen.
I wonder sometimes how closely people actually read the papers they comment on. The associated coverage, including Ann Gibbons' article, has made a lot out of a small point in the paper, but I think that the commenters have it wrong.
Here's the story: When the Orrorin materials were first published, Brigitte Senut and Martin Pickford put forward the argument that these may be more closely related to Homo than to known australopithecines. They based their argument mainly on Orrorin's relatively thick-enameled molars, which they viewed as different from the thin-enameled molars of Ardipithecus, but lacking the enlarged dentition of Australopithecus. So, they suggested that Orrorin might be a plesiomorphic ancestor of Homo, and that Ardipithecus and Australopithecus represent divergent lineages derived in their dental anatomy.
I don't find that suggestion very compelling, because it seems to put too much faith in the absence of evolutionary reversals. There's no reason why a large-molared australopithecine should not have given rise to small-molared Homo, particularly since smaller-toothed Homo habilis is apparently derived from earlier, larger-toothed "Homo" specimens like A. L. 666-1 and Omo 75-14. And Haile-Selassie, Suwa and White (2004) claimed that the Orrorin, Sahelanthropus, and Ardipithecus dentitions were so similar that they might represent one taxon. So the dental contrasts among these early hominids are probably not great enough to justify the idea that Orrorin is an exclusive Homo ancestor.
The femur also formed a part of this phylogenetic story, with Senut and Pickford having noted the lack of extreme australopithecine-like features in the femur. The Orrorin femur has a less exaggerated neck length than many australopithecine specimens, it is larger than many, and appears to have a higher neck-shaft angle. To the extent those features differ from later Australopithecus, they resemble the human anatomy.
Richmond and Jungers address this argument very briefly in their last paragraph, by noting that the functional elements of the Orrorin femoral anatomy are entirely consistent with the australopithecine pattern of bipedality:
The similarity between O. tugenensis and australopith femora weakens support for scenarios in which O. tugenesis is ancestral to Homo to the exclusion of A. afarensis (4). Instead, the overall primitive hominin morphology of the O. tugenensis femur, along with primitive dental anatomy, is consistent with the more parsimonious hypothesis that it is a basal member of the hominin clade.
I think that's fair, as far as it goes. The overall morphological pattern of this femur, with its long neck and broad shaft, is much like known australopithecine femora. But to go a bit further, their metric comparisons show BAR 1002'00 to be the most Homo-like of the early hominid femora they examined, and their phenetic cluster puts it basal to the other australopithecines. That's pretty much exactly what Senut et al. have consistently said. So I have a hard time understanding how those observations refute the idea that Orrorin has a more Homo-like femur than later australopithecines!
Again, I don't put much stock in the phylogenetic argument for an Orrorin-Homo link. I don't see any difficulty deriving Homo from Australopithecus, especially given the likely effects of body size evolution on the locomotor pattern. And at least one or two early Homo femoral specimens, like KNM-ER 1481, share most of the Australopithecus-like pattern of proximal femur anatomy. But this paper surely doesn't add anything new to the critique of Senut and Pickford's preferred phylogenetic hypothesis. The details simply don't detract from their story.
Richmond BG, Jungers WL. 2008. Orrorin tugenensis femoral morphology and the evolution of hominin bipedalism. Science 319:1662-1665. doi:10.1126/science.1154197
Gibbons A. 2008. Millennium ancestor gets its walking papers. Science 319:1599-1601. doi:10.1126/science.319.5870.1599
Haile-Selassie Y, Suwa G, White T. 2004. Late Miocene teeth from Middle Awash, Ethiopia, and early hominid dental evolution. Science 303:1503-1505.
Senut B, Pickford M, Gommery D, Mein P, Cheboi K, Coppens Y. 2001. First hominid from the Miocene (Lukeino Formation, Kenya). C R Acad Sci Paris, Sciences de la Terre et des planètes 332:137-144.
There's a new paper by Tim White in the "In Press" portion of Comptes Rendus Palevol, titled "Early hominid femora: The inside story". It has a short introduction to the importance of the Orrorin proximal femur to understanding the evolution of hominid bipedality.
That short introduction is followed by an four-page-long description of White's correspondence attempting to get photographs, scans, and measurements of Orrorin. He quotes his own e-mails. With dates. I've never seen anything quite like it in a journal.
The review ends with this paragraph:
It is unclear why the Orrorin discovery team and its associates will not publish the comparatively very simple conventional radiography and conventional photography of the unglued BAR 1002'00 femoral neck that we have urged on numerous occasions (see above) since 2001. Martin Pickford and Brigitte Senut mysteriously did not join the list of authors who responded to our last, published request for these data in our February 2005 letter to Science. Their American colleagues responded: "it is our understanding that the initial studies were carried out under serious constraints of time and other resources [...] and we have made it clear that we plan to rescan and study the existing fossils if funds are made available" [5 (p. 845)]. We were again disappointed because we had asked for the publication of new data, not the promotion of a funding request for documentation long overdue.
This quote refers to the 2005 exchange between Ohman, Lovejoy and White on the one hand and Eckhardt, Galik and Kuperavage on the other. Read it too.
The cited response ends with this paragraph:
As far as phylogenetic speculations, a fuller understanding of the first several million years of human ancestry awaits the outcome of studies (already under way by other members of our research group) of the equivocal hominoid remains from Chad, as well as some much more comprehensive results from the by now decade-long analysis of the Ardipithecus (née Australopithecus) ramidus fossils, the reported fragility of which nonetheless should not preclude the making of CT scans and publication of what they show.
Well, I know which of these folks have shared data with me...
I have an idea for a contest. Please send your best punchline for the following joke, and I'll post the top ten (let me know if you want credit!):
How is Bigfoot different from a Miocene hominid?
Eckhardt RB, Galik K, Kuperavage AJ. 2005. Questions about the Orrorin femur. Science 307:845. Full text
Ohman JC, Lovejoy CO, White TD. 2005. Questions about the Orrorin femur. Science 307:845. Full text
White TD. 2006. Early hominid femora: the inside story. Comptes Rendus Palevol (in press). Full text (subscription)
Elizabeth Pennisi has a short piece in Science describing David Carrier's ideas about leg length and fighting in early hominids.
David Carrier, a comparative physiologist at the University of Utah in Salt Lake City, has jumped into the fray with a provocative idea about Lucy's legs. In earlier studies with dogs, he had found that short legs provide mechanical benefits during fights. Pit bulls' short limbs, for example, aid stability and are tough enough to sustain attack without breaking.
Carrier contends that Lucy and other australopithecines also had bodies built for defense against each other: Their short legs may have provided a competitive edge when males battled rival suitors.
This is basically the wrestler vs. distance runner physique story. And it could be true -- but is it a primary cause or a secondary one? Depends how they were fighting, I should think.
The interesting part is that it is not an argument based on optimal energy expenditure. But is it safe to use sexual dimorphism as a proxy for male competition? And were australopithecines really very sexually dimorphic?
Boy, there sure seem to be a lot of unknowns lately.
Pennisi E. 2006. Was Lucy's a fighting family? Look at her legs. Science 311:330. Full text (subscription)
