Little Foot Finally Extricated

Nature News is reporting on the excavation and description of "Little Foot," a fossil initially discovered twenty years ago by Ron Clarke, at Sterkfontein Cave, in South Africa.  Colin Barras writes:

After a tortuous 20-year-long excavation, a mysterious ancient skeleton is starting to give up its secrets about human evolution.

The first of a raft of papers about ‘Little Foot’ suggests that the fossil is a female who showed some of the earliest signs of human-like bipedal walking around 3.67 million years ago. She may also belong to a distinct species that most researchers haven’t previously recognized.

“It’s almost a miracle it’s come out intact,” says Robin Crompton, a musculoskeletal biologist at the University of Liverpool, UK, who has collaborated with the research team that excavated the skeleton.

Why has this task taken so long and why is it so important? Barras continues:

By late last year, Clarke’s team had successfully removed enough bones to reconstruct more than 90% of the skeleton, and the specimen was unveiled to the world. No other Australopithecus fossil comes close to that level of completeness. For comparison, the most famous Australopithecus — Lucy — is around 40% complete.

Clarke and colleagues have posted a number of papers on the BiorXiv biology pre-print server. One of the papers is titled "The skull of StW 573, a 3.67 Ma Australopithecus skeleton from Sterkfontein Caves, South Africa."  Because these papers are unpublished, they are open-access. 

As Clarke and Kuman notes, this fossil is unlike those of Australopithecus africanus, a species ubiquitous in South Africa but more closely resembles, in some ways, Au. afarensis (Lucy) and Au. anamensis, both of which are north east African variants of Australopithecus and are the earliest members of that genus.  The fossil has been included, taxonomically, with a species originally described by Raymond Dart in 1948: Australopithecus prometheus.  Given its early date, the researchers argue that it cannot be descended from Au afarensis but must be coeval with it.  This suggests that both are descendants of an earlier species that had a large home range. 

More pieces to the puzzle. 

Ardipithecus May Not Have Been Entirely a Facultative Biped After All

In a new article in the Proceedings of the National Academy of Sciences, several researchers have concluded, using 3D morphometric analysis have discovered that Ardipithecus ramidus, while still having facultative (didn't have to but could) bipedalism, when it did walk, its bipedal gait was nearly human.  From the abstract:

We show that hamstring-powered hip extension during habitual walking and climbing in living apes and humans is strongly predicted, and likely constrained, by the relative length and orientation of the ischium. Ape pelves permit greater extensor moments at the hip, enhancing climbing capability, but limit their range of hip extension, resulting in a crouched gait. Human pelves reduce hip extensor moments but permit a greater degree of hip extension, which greatly improves walking economy (i.e., distance traveled/energy consumed). Applying these results to fossil pelves suggests that early hominins differed from both humans and extant apes in having an economical walking gait without sacrificing climbing capability. Ardipithecus was capable of nearly human-like hip extension during bipedal walking, but retained the capacity for powerful, ape-like hip extension during vertical climbing. Hip extension capability was essentially human-like in Australopithecus afarensis and Australopithecus africanus, suggesting an economical walking gait but reduced mechanical advantage for powered hip extension during climbing.

This positions Ardipithecus as the classic intermediate in terms of bipedal locomotion.Although there are many traits in Australopithecus afarensis that are still transitional in terms of the rib cage, dentition and aspects of the hip, it is clear that the major adaptations for bipedalism were in place nearly a million years earlier.  This also suggests that it is not out of the realm of possibility that the fossil footprints in Crete really do reflect a bipedal hominin.  At the risk of positing heresy, the fact remains that we really don't know exactly where hominins first appeared.  This study also reinforced the distinct separation between apes and humans in terms of iliac shape, and that this split must have taken place even further back in time that we have supposed.

The Independent has a news story on this here.  One of the authors, Herman Pontzer remarks:

“It kicks us out of this old paradigm of thinking about human evolution,”...“In that old picture that is everywhere where you have the evolution of man going from crouching thing to upright thing to a human – as much as we have known that is not right, I still think people have it in their heads.”

Australopithecus sediba Voted Off the Island

This does not surprise me.  Science Magazine has a short story which suggests strongly that the characteristics in Au. sediba render it unsuitable for a possible ancestor to the genus Homo. 

With its fossils dated to 1.98 million years ago, Au. sediba is too young to be directly ancestral to all members of the genus Homo. But Berger and his colleagues proposed in 2010, and again in 2013 in six papers in Science, that given the many humanlike traits in Au. sediba’s face, teeth, and body, the Malapa fossils were a better candidate than Lucy or other East African fossils to be ancestral to Homo erectus, a direct human ancestor that appeared 1.8 million years ago.

In a talk here, though, paleoanthropologist Bill Kimbel of Arizona State University in Tempe analyzed the most complete skull of Au. sediba and systematically shot down the features claimed to link it to early Homo. Kimbel noted that the skull was that of a juvenile—a “7th grader”—whose face and skull were still developing. In his analysis, with paleoanthropologist Yoel Rak of Tel Aviv University in Israel, he concluded that the child already showed traits that linked it most closely to the South African australopithecine Au. africanus, a species that lived in South Africa 3 million to 2.3 million years ago. And had it survived to adulthood, its humanlike facial traits would have changed to become even more like those of Au. africanus.

For example, the breadth of the young Au. sediba’s cheekbones appears narrow, as in early Homo. But by studying other australopithecine, ape, and Homo fossils to see how features of the cheekbones change as individuals grow and chewing muscles develop, Kimbel and Rak could predict how the boy’s face and skull would have looked if he’d grown up to be an adult. The resemblance to Au. africanus is so striking, in fact, that Kimbel thinks Au. sediba is a closely related “sister species” of Au. africanus—and not a long-lost human relative. “We don’t believe … that Au. sediba has a unique relationship to the genus Homo,” says Kimbel.

At this point, it is pretty hard to tell where a precursor might be found. We know that there was considerable variability in australopithecines throughout the Plio-Pleistocene but, as of yet, no good candidate has arisen.What seems to be clear, however, is that there is a general trend toward more modern morphology in the pelvis and hands, as exhibited by Au. sediba.  Whether or not these characteristics are present in other specimens of Au. sediba is, however, unknown.  As Kimbel notes, we need an adult one to see for sure. 

Australopithecus africanus Used Power and Precision Grip

Science Daily, as well as some other outlets are reporting new research on evidence that Australopithecus africanus used their hands in the same way that we use ours.  Focusing on the trabecular (spongy) bone patterns found in the metacarpals, they discovered that the wear and deposition patterns supported the hypothesis that they used their hands to perform precision and power "thumb to forefinger" tasks.  This is a huge step in the direction of making stone tools and using the hands for many other daily jobs.  The authors are quick to point out, however:

All early hominin metacarpal specimens generally exhibit high trabecular bone volume fraction like that of Pan and unlike that of the lower trabecular density of recent H. sapiens. However, the distribution of trabecular bone is similar to the distinct patterns of committed tool users and tool makers, H. sapiens and Neandertals.

This is an excellent example of a transitional trait. They began to adapt the power and precision grips while still maintaining arboreal tendencies and retaining some of the skeletal morphology of their ancestors. One more step on the road to humanity.

BioLogos, Ken Ham and David Menton—A Response, Part II

Point 3:

Because of the rarity of fossil hominids, even many of those who specialize in the evolution of man have never actually seen an original hominid fossil, and far fewer have ever had the opportunity to handle or study one. Most scientific papers on human evolution are based on casts of original specimens (or even on published photos, measurements, and descriptions of them).

So?  Menton seems to think that there is a problem with performing analyses based on measurements that other people have taken.  That is nonsense.  A few years back, I was at a conference where a paper was given in which the author was attempting to show the differences between subtle details on various fossil crania.   The striking criticism of the study was that it was based on casts, not on original fossils and, because of this, the analysis was questionable.  When I did my dissertation on the origins of modern human crania, I had measurements of almost all of the original crania that had been taken either by my advisor or by other researchers in the field, who had then published them.  Almost every paper done on human evolution is based on measurements from the original fossils.  The only examples where this is not happening is where the original skulls are missing, as with the Homo erectus remains from Zhoukoudian, which vanished during the run-up to the second world war, or the European Mladec remains, which were destroyed when the allies bombed the castle in which they were housed.  Even in those cases, copious measurements were taken of the originals and, in the case of the Zhoukoudian remains, comprehensive photos were taken. There is absolutely nothing wrong with doing analyses based on measurements from the original fossils, especially where the photos are clear and detailed. Bill Howells took detailed measurements of the Near Eastern Qafzeh 6 cranium and then kindly sent me the measurements for it.

All of science is built on what came before and the observations of the those scientists are absolutely invaluable.

Point 4:

Since there is much more prestige in finding an ancestor of man than an ancestor of living apes (or worse yet, merely an extinct ape), there is immense pressure on paleoanthropologists to declare almost any ape fossil to be a “hominid.” As a result, the living apes have pretty much been left to find their own ancestors. 

More nonsense.   There are palaeoprimatologists that spend their entire lives researching the prehistory of non-human primates.  A check of Google Scholar revealed over forty-nine thousand papers dealing with non-human fossil primates.  One of the most productive and exciting aspects of fossil primate studies is the search for the last common ancestor (LCA).  This involves an in-depth study of Miocene apes.  Another area of important study is the origin of the large-bodied primates and the split between the Old World and New World monkeys.  When Menton states that the living apes have been left to find their own ancestors, he forgets the media circus that surrounded the find of the fossil primate Ida, which shed light on the origin of primates as a group. 

Point 5:

In contrast to man, apes tend to have incisor and canine teeth that are relatively larger than their molars. Ape teeth usually have thin enamel (the hardest surface layer of the tooth), while humans generally have thicker enamel. Finally, the jaws tend to be more U-shaped in apes and more parabolic in man.

The problem in declaring a fossil ape to be a human ancestor (i.e., a hominid) on the basis of certain humanlike features of the teeth is that some living apes have these same features and they are not considered to be ancestors of man. Some species of modern baboons, for example, have relatively small canines and incisors and relatively large molars. While most apes do have thin enamel, some apes, such as the orangutans, have relatively thick enamel. Clearly, teeth tell us more about an animal’s diet and feeding habits than its supposed evolution. Nonetheless, thick enamel is one of the most commonly cited criteria for declaring an ape fossil to be a hominid. 

Menton may be correct in his statements about enamel thickness.  Enamel thickness may be a better indicator of dietary adaptations than of morphology, but, where primates are concerned, that is only true of enamel thickness.  It is not true of tooth morphology.  Primatologists have no trouble telling baboons from humans.  They do not have the same features.  Fossil and modern baboons are quite different from humans, even human ancestors.

In 1924, when the well-trained anatomist Raymond Dart was given the deposits that had the Taung child in them, he knew immediately that the teeth did not belong to any fossil baboon.  It wasn't the thickness of the enamel that tipped him off.  The dimensions were similar to those of an infant human and the morphology of the canine and the premolars was like that of humans. Remember, at this time, there were very few other prehuman ancestors with which to compare it, and no australopithecines.

Teeth are, actually, one of the most conservative features on a skeleton and change very little over time.  For example, the Y-5 molar pattern that we have in our mouths is first found in Aegyptopithecus, from the Oligocene epoch, some 30 million years ago. Furthermore, one of the ways we can tell the new world primates from the Old World primates is the number of teeth they have.  New World monkeys have two incisors, one canine, three premolars and three molars in each quarter of the mouth.  All Old World monkeys and apes are lacking the extra premolar (bicuspid, if you are a dentist).  We have this same pattern. 

These differences are either glossed over or not mentioned by Menton, who simply declares, based on enamel thickness, that the teeth are similar and completely disregards information that doesn't fit his narrative. 

Part III here.  

Phillip Tobias Has Died

Phillip Tobias, a preeminent anthropologist who worked tirelessly to raise the standard for palaeoanthropology in South Africa, has died. From the Scotsman:

But for Tobias’ endeavours, the honours would probably have gone to East Africa, the territory of the more famous Leakey team, Louis and Mary. The Leakeys were great self-publicists and they made sure that East African discoveries – especially those they made in the Olduvai Gorge in Kenya’s Rift Valley – featured prominently in international media at a time when South Africa was mostly renowned for its apartheid policies.

However, Tobias, who was an anti-apartheid activist as well as a distinguished scientist, lived long enough to see the tide turn and South Africa take centre stage in the great debate on humanity’s origins. The huge shift in perceptions was largely Tobias’ doing. It was no mean feat to keep the torch alight for evolutionary studies in a land governed by white right-wing Christian fundamentalists who passionately dismissed the idea of evolution.

Tobias was partly responsible for the changes in attitudes in South Africa that led to the downfall of apartheid and, along with many biological anthropologists of the time, championed the idea that race, as a biological concept, is meaningless. He will be missed.

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New Explanation for Brain Evolution in Australopithecines

Science Daily is reporting on new examinations of the famous Taung brain endocast that provides insights into human evolution. They write:

"These findings are significant because they provide a highly plausible explanation as to why the hominin brain might grow larger and more complex," Falk said.

The first feature is a "persistent metopic suture," or unfused seam, in the frontal bone, which allows a baby's skull to be pliable during childbirth as it squeezes through the birth canal. In great apes -- gorillas, orangutans and chimpanzees -- the metopic suture closes shortly after birth. In humans, it does not fuse until around 2 years of age to accommodate rapid brain growth.

The second feature is the fossil's endocast, or imprint of the outside surface of the brain transferred to the inside of the skull. The endocast allows researchers to examine the brain's form and structure.

The argument is that the metopic suture stays open in hominins longer to allow the brain to grow more postnatally, something we have known for some time. It is the new imaging techniques that have allowed us to get a better handle on this. The endocast has been around for almost ninety years and has been subject to all kinds of studies, some of which have led to riotous disagreements between researchers. More pieces of the puzzle.

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Nature News Story on Au. sediba

Nature News has a story on the Australopithecus sediba skeleton described by Lee Berger and colleagues.  Ewen Callaway writes:

At around 420 cubic centimetres, A. sediba 's puny brain compares to those of other Australopithecus specimens and chimpanzees. But a high-resolution synchrotron scan of the brain's impression on the skull shows enlarged frontal areas that are normally associated with humans and linked to higher cognitive abilities, such as planning. A. sediba's pelvis also looks wider than those of other australopiths, raising doubts about the idea that the human pelvic shape evolved to accommodate large-brained babies. "Whatever is driving a relatively human-like shape of the pelvis, it is not a big brain," says Berger. The orientations of its leg and ankle bones suggest that A. sediba walked upright, and its nearly complete ankle resembles that of a human. But its long arms, and some features of its feet and shin bones, are similar to those of a chimpanzee. Taken together, these features suggest that A. sediba was adapted for both bipedalism and tree-dwelling.

This is a wonderful mosaic. As I wrote yesterday, though, it is not clear where it fits. There are three possibilities: A. africanus gives rise to A. sediba and A. habilis and A. rudolfensis.  Here, the two species of early Homo have been demoted and all three have transitional characteristics that represent a general trend toward modernity (after Walker and Wood).

The second scheme has A. africanus giving rise to A. sediba, which then goes extinct, and H. habilis and H. rudolfensis (in some fashion), one of which then gives rise to H. ergaster.  This posits that the traits present in both early Homo and A. sediba represent a general trend toward modernity. 

 

The third scheme has  A. garhi giving rise to early Homo with A. africanus giving rise to A. sediba, which then goes extinct.  The advantage of this is that A. garhi has modern-like limb proportions and is found in northeast Africa, not far from early Homo, while A. africanus and A. sediba are both found in south Africa.

 

Which one of these is right?  Are any of them right?  Who knows.  What we do know is that these critters have relationships to each other in some way, shape or form.  

Did Australopithecines Have Bonding Patterns Like Modern Chimpanzees?

The Guardian has a story on research done with Australopithecus africanus and A. robustus teeth that suggests that, while the men did not wander far from their birth site, the women did. Ian Sample writes:

“Here we have the first direct glimpse of the geographic movements of early hominids, and it appears the females preferentially moved away from their residential groups,” said lead author, Sandi Copeland at the Max Planck Institute for Evolutionary Anthropology in Leipzig.

A similar situation is seen among modern chimpanzees, where females tend to move out of their groups, in part because males form strong ties that help them protect a troop's territory.

“By virtue of the fact that the males choose to remain, the females are indirectly forced to leave their communities in order to avoid close inbreeding. It could be that among these early hominins, female dispersal has some correlation to close cooperative behaviour between males,” Copeland added.

Another piece of the puzzle.