New 13 Million-Year-Old Miocene Ape Discovery in Kenya

National Geographic (and other outlets) is reporting on a new skull discovered in northern Kenya, near Lake Turkana that is 13 million years old and may reflect the morphology of a sister group to the stem group of hominoids, the group that contains modern apes and humans.  Michael Greshko writes:

“We’ve been looking for ape fossils for years—this is the first time we’re getting a skull that’s complete,” says Isaiah Nengo, the De Anza College anthropologist who led the discovery, supported by a National Geographic Society grant and the Stony Brook University-affiliated Turkana Basin Institute.

Roughly the size of a lemon, the skull belongs to a newly identified species of early ape named Nyanzapithecus alesi. Some of its features resemble those of today’s living Old World monkeys and apes, and the face bears a striking resemblance to today’s infant gibbons.

What’s more, N. alesi offers insight into early apes’ brains, the team reports in their study, published today in Nature. With a volume of about seven tablespoons, N. alesi’s brain cavity was more than double that of other Old World monkeys from the time.

The Miocene is generally thought of as the “Age of the Apes” because there were so many genera (30) and species (over 40) of apes pretty much all over the Old World. As the authors note, however, up to this point, most of the remains have been just jaws and teeth.  This skull is an incredible find and will add immensely to our understanding of this time period. 

Was the LCA in Europe????

Was the last common ancestor of apes and humans in Europe?  That seems to be the gist of a study published in the PLoS One.  Nicole Mortillaro, of CBC News reports:

A jawbone discovered by German troops in Athens during the Second World War could be evidence that apes and humans diverged 200,000 years earlier than the current theory says.

Chimpanzees and bonobos are the nearest known relatives to humans, sharing 99 per cent of our DNA. It's believed that we split between five and seven million years ago.

However, researchers analyzing two fossils — a jawbone from a German museum and an upper premolar from a collection in Bulgaria — concluded their ages to be roughly 7.2 million years, and belonging to a pre-human.

From the paper in PLoS:

The split of our own clade from the Panini is undocumented in the fossil record. To fill this gap we investigated the dentognathic morphology of Graecopithecus freybergi from Pyrgos Vassilissis (Greece) and cf. Graecopithecus sp. from Azmaka (Bulgaria), using new μCT and 3D reconstructions of the two known specimens. Pyrgos Vassilissis and Azmaka are currently dated to the early Messinian at 7.175 Ma and 7.24 Ma. Mainly based on its external preservation and the previously vague dating, Graecopithecus is often referred to as nomen dubium. The examination of its previously unknown dental root and pulp canal morphology confirms the taxonomic distinction from the significantly older northern Greek hominine Ouranopithecus. Furthermore, it shows features that point to a possible phylogenetic affinity with hominins. G. freybergi uniquely shares p4 partial root fusion and a possible canine root reduction with this tribe and therefore, provides intriguing evidence of what could be the oldest known hominin.

Hominin, in this case, means humans and their premodern forms.  I think it is more than somewhat suspect to base a far-reaching hypothesis on one trait, even if it is the p⁴ root. It is commonly held that the last common ancestor of apes and humans was in Africa, sometime around 7.5 to 8 million years ago, but we have no fossil evidence to support that position.  While it is certainly true that the further back in time you go, the more ape-like our ancestors get, there is simply no smoking gun.

The world will not end if the LCA is, in fact, in southern Europe, but if it is, then it raises some interesting questions.  For one, if the LCA is in Europe, why are all of its hominin descendants in Africa?  So far, even discounting Sahelanthropus, which is a surface find and was crushed, all of the late Miocene and early Pliocene hominin remains are found in either the Afar triangle (Ardipithecus) or the Tugen Hills, in Kenya (Orrorin tugenensis).  If you add Sahelanthropus, then Chad comes into the picture. Additionally, why have we found no post-split hominids in southern Europe?  So far, all that has come out of the ground in this region is middle to late Miocene apes.

Other hurdles exist to acceptance of this idea.  For one, it is pretty clear that our closest living relatives, genetically, are the chimpanzees, who reside in the tropics of central Africa.   Next on the list is the gorilla, also found in the tropics of Africa.  Why have we found no precursors to these hominoids in southern Europe? 

On the other hand, the fossil find has been securely dated to the Messinian Event, in which the Mediterranean Sea effectively dried up, suggesting the possibility that the ancestors of the Pliocene hominins from North Africa migrated from southern Greece.  If this is so, then it raises the dark and ominous thought that much of the information regarding the LCA lies at the bottom of the Mediterranean Sea. That is terrible to contemplate.  This would also mean that Chimpanzees and Gorillas are the survivors of a group of Miocene apes that ranged from southern Europe to central Africa.  We know that the ancestors of chimpanzees once upon a time occupied the East African Rift Valley, but are now restricted to central and west Africa.   If their original range extended up into Egypt and beyond, then perhaps we are looking at a similar situation for their ancestors, as well.  

A whole lot more investigation needs to be done and more fossil remains need to be found to shore up the European LCA hypothesis.  Given that this new information does not come from newly discovered fossils does not raise my hopes. 

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.  

Orrorin tugenensis: As Close to the Last Common Ancestor As We Have Gotten?

Based on work by SUNY Stoney Brook, it has been learned that the femur of Orrorin tugenensis, the six-million year-old presumed hominin, also called the "millenium man," has a mix of traits that align it with not just early hominins but late Miocene apes.  Science Daily reports:

According to Dr. Almécija, their study for the first time compared the six-million-year-old Millenium Man femur (called BAR 1002'00) using state-of-the-art morphometric techniques to not only other available hominin fossils but also great apes, hylobatids (ie, gibbons and siamangs), and most importantly to fossil apes that lived in the Miocene. The analysis included more than 400 specimens.

"We discovered that Orrorin's femur is surprisingly 'intermediate' in both age and anatomy between quadrupedal Miocene apes and bipedal early human ancestors," said Dr. Almécija. "Our paper provides quantitative results of the Orrorin femur as a unique mosaic and stresses the need to incorporate fossil apes into future analyses and discussions dealing with the evolution of human bipedalism, an investigation that should stop considering chimpanzees as default living 'starting point' models."

As the authors note, this is not so different from what was concluded about the gait of Ardipithecus ramidus and that the examination of that hominin led to the idea that, perhaps, modern apes are poor models for early hominin morphology and that the modern apes diverged from the last common ancestor (LCA) in entirely different directions. It is exciting to get to a point where there are obviously transitional characters between hominins and non-hominins. 

The other thing that is quite striking is that there is no obvious dividing line between being a quadruped and a biped and that the transition took some time and was gradual.  Don Johanson, in Lucy: The Beginnings of Humankind, word:

You don’t gradually go from being a quadruped to being a biped. What would the intermediate stage be–a triped? I’ve never seen one of these.

It appears that he may have been wrong, at least about the gradual part.

For the Want of a Chromosome Pair

Slate has an article on how we ended up with 46 chromosomes. Despite the colloquial writing style, there is some good information about how we got one less set of chromosomes than Chimpanzees, our closest relatives. Sam Kean writes:

Around a million years ago, in some fateful man or woman in Africa, what were the 12th and 13th human chromosomes (and still are the 12th and 13th chromosomes in many primates) got entangled at their tips. Instead of separating cleanly, 12 and 13 fused together, like one belt buckled onto another. This amalgam eventually became human chromosome 2.

Fusions like this are not uncommon—one in every 1,000 babies has some sort of chromosomal fusion—and most go unnoticed because they don’t upset anyone’s health. (The ends of chromosomes contain few genes, so often nothing gets disrupted.) However, a fusion by itself can’t explain the drop from 48 to 46. A fusion leaves a person with 47 chromosomes, not 46, and the odds of two identical fusions in the same cell are remote. And even after the drop to 47, the person still has to reproduce to pass on the trait, a serious barrier.

He would have to find a person also with 47 chromosomes and, despite the possibility of many miscarriages, one in thirty-six would inherit both fused chromosomes and have 46. This must have had some sort of selective advantage because that is the form in which we find ourselves today. It has been suggested that there was a genetic bottleneck (Venema also writes about this) and it is possible that this was the point that the 46 variant took over. it is thought-provoking, if speculative. One thing is certain: we have fewer chromosomes than chimpanzees and it is because of a chromosomal fusion. The key here is that we and chimpanzees share a last common ancestor.

Gorilla DNA Sequenced

According to a story out of the LA Times, the gorilla genome has been completely sequenced. Eryn Brown writes:

By comparing the new gorilla DNA sequence with reference genomes of humans, chimpanzees, orangutans and macaques, scientists have already made a few surprising insights into the crucial periods when we diverged into separate species.

For instance, the new genetic data bolster fossil evidence that gorillas split off as a separate species about 10 million years ago and that humans and chimps parted ways about 6 million years ago. Previous genetic evidence had seemed to point to a more recent split, prompting a contentious debate between genetics experts and fossil scholars, said Durbin, who leads the genome informatics group at the Wellcome Trust Sanger Institute in Hinxton, England.

This is good because it means that the last common ancestor can be as far back as six to seven million. Does this make Sahelanthropus or Orrorin hominins? Not necessarily but now it is a more easily acceptable position..

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