The Human Fossil Record, Part 6: The Dispersal of the Australopithecines, Cont’d

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June 20, 2011 Tags: Human Origins

Today's entry was written by James Kidder. Please note the views expressed here are those of the author, not necessarily of The BioLogos Foundation. You can read more about what we believe here.

The South African Forms

As noted in the last post, the discovery of the Taung child in South Africa fueled interest that other hominins could be found as well. With the help of noted anatomist Robert Broom, and anthropologist John T. Robinson, Raymond Dart excavated several other sites in the South African cave system, Makapansgat, Swartkrans, Sterkfontein and Kromdraai, all of which yielded australopithecine remains of both an early gracile form and later robust form. The earlier form, dated to between 3.0 and 2.0 million years ago and to which the Taung find belonged, was called Australopithecus africanus (see Figure 6). Exact dating for these cave sites is hampered by the fact that the cave openings are vertical and it is not clear how the hominins got there. Unlike the east African forms, A. africanus was a very lightly built form, with no crests of any kind. The overall cranial capacity of the finds is between 430 and 520 cubic centimeters, slightly larger than that of A. afarensis and comparable to the east African forms. Like the east African forms, the teeth of this form were larger in the back and smaller in the front than A. afarensis suggesting to some an herbivorous diet.

Slightly more recent in time is A. robustus. This is a scaled-up version of A. africanus and continues the trends seen in that form (See Figure 7). Although having a generally similar facial structure as A. africanus, A. robustus also has crests like the eastern African forms, suggesting a similar dietary adaptation. There is also a continuation of the trend toward larger back teeth and smaller front teeth to accommodate this. While A. robustus and A. boisei are both considered “robust” australopithecines, the considerable differences in their facial architectures suggest to most researchers different evolutionary trajectories.

A recent discovery has been made by Lee Berger and colleagues (Berger et al. 2010) at the site of Malapa in South Africa, of yet another form of Australopithecus, which cannot be accommodated into the sequence of A. africanus and A. robustus, and is different enough from each of them to warrant its own species designation: A. sediba. This form is characterized by having a small cranium with no crests and a flat face, in contrast with all other known australopithecines (See Figure 8). Berger suggests that this form is descended from A. africanus and existed parallel to A. robustus. It has also been suggested that there are post-cranial elements in the hip and leg bones that align it with later Homo, although, at this point, the evidence for this position is scant.

The Odd Men Out: Kenyanthropus Platyops and Australopithecus Bahrelghazali

Up until the last few years, australopithecine evolution had been assumed to have taken place in the entire east African Rift Valley and South Africa. That changed in 1995 when researchers working on the banks of the Sahel River in Chad, discovered what they described as yet another australopithecine, A. bahrelghazali. Nicknamed “Abel”, this find was initially dated to between 3.0 and 3.5 million years ago, and consists only of a jaw fragment with six teeth. Since its discovery, the date of the find has been challenged by Beauvilain (Beauvilain 2008), who argues “Abel was collected at the foot of the shoreline of the last episode of Lake Megachad, which is only a few thousand years old.” While this does not imply that the find is this old, it does cast doubt on the ability to determine just how old it is. The morphology does appear to be australopithecine, however, extending the possible reach of this remarkable genus out to central Africa. Little has been said about it since then, however.

The other find of note was a discovery in northern Kenya, in Lomekwi of a mostly complete but crushed cranium and some facial bones of an individual that shows considerable facial flatness and is lacking in any of the specializations present in the robust australopithecines in terms of dietary adaptations (See Figure 9). It was hence called Kenyanthropus platyops (flat-faced man from Kenya). Dated to approximately 3.5 million years ago, little is known about this find. Its cranial capacity is between that of A. afarensis and A. africanus, at around 400 cubic centimeters (Leakey, et al. 2001). Due to the condition of the cranium, it is difficult to draw any inferences about where this find fits in the phylogeny of the early hominins, and some authors are relegating it to a regional variant of A. afarensis (White 2003). Michael Balter, in fact, recently asked the question Whatever happened to Kenyanthropus platyops?, and the fossil seems to have not generated much interest in recent years.

The Place of Australopithecus

It is tempting to look at these remains and think privately, “these are nothing but apes. What is the fuss?” Such has been the viewpoint of the Institute for Creation Research’s Duane Gish (Gish and Research 1985) and John Morris, who remarked “From the neck down, certain clues suggested to Johanson that Lucy walked a little more erect than today's chimps. This conclusion, based on his interpretation of the partial hip bone and a knee bone, has been hotly contested by many paleoanthropologists”(Morris 1994). This is incorrect. There was never any doubt in any of the researcher’s minds that from A. afarensis, the australopithecines walked upright, albeit with a gait not quite like that of modern humans. It is, further, instructive to compare the skulls of australopithecines and chimpanzees side by side (Figure 10). This shows several of the characteristics in the australopithecines that are derived relative to the ape condition. First, the brain case is decidedly larger, on the order of 100 cubic centimeters, and, second, the teeth do not extend beyond the tooth row as they do in the chimpanzee. While this comparison is certainly artificial in that the chimpanzee is a modern animal, the fact remains that the brains of australopithecines were already advanced beyond any known ape species either then or now. As importantly, however, is that the foramen magnum hole is always at the bottom of the skull in all australopithecine remains for which that area of the skull is present, indicating bipedality (movement on two rear legs), a condition never found in apes.

The Oldowan Tool Tradition

At the site of Gona, in Ethiopia, stone tools were unearthed dating to between 2.4 and 2.6 million years ago. More advanced than those used by A. afarensis, these consisted of crude choppers, bifaces and rudimentary blades. Other tools have been found at Olduvai (the type site) but none in direct association with any hominin remains. While it is thought that the users of these tools may have been australopithecines, there is simply no direct evidence to support this.

The Extinction of the Australopithecines

In both east and south Africa, the australopithecines hold sway until approximately 1.2 to 1.1 million years ago. Then they simply disappear. Remains are few enough that it is not possible to say for sure why or over what period of time this happened. As can be surmised from the evidence of the dentition and facial muscles, the australopithecines became very dietarily specialized, leading them down a restricted evolutionary path. Consequently, the most widely supported explanation for their extinction is that they were simply out-competed by the new kid on the block: Homo, which first makes its appearance around 2.3 million years ago. With the advent of Homo came a hominin with a vastly expanded braincase and direct association with stone tools.

We have now covered the ground between the earliest demonstrable hominins, in Ardipithecus and the most prolific ones, the australopithecines. Next, we will move to forms that begin to show the characteristics that we can recognize, from a physical perspective, as human.

Bibliography

Asfaw, B., T. White, O. Lovejoy, B. Latimer, S. Simpson & G. Suwa (1999) Australopithecus garhi: A New Species of Early Hominid from Ethiopia. Science, 284, 629-635.
Beauvilain, A. 2008. The contexts of discovery of Australopithecus bahrelghazali (Abel) and of Sahelanthropus tchadensis (Toumai): unearthed, embedded in sandstone, or surface collected? In South African Journal of Science, 165-168. African Online Scientific Information System PTY LTD.
Berger, L. R., D. J. de Ruiter, S. E. Churchill, P. Schmid, K. J. Carlson, P. H. G. M. Dirks & J. M. Kibii (2010) Australopithecus sediba: A New Species of Homo-Like Australopith from South Africa. Science, 328, 195-204.
Cerling, T. E., E. Mbua, F. M. Kirera, F. K. Manthi, F. E. Grine, M. G. Leakey, M. Sponheimer & K. T. Uno (2011) Diet of Paranthropus boisei in the early Pleistocene of East Africa. Proceedings of the National Academy of Sciences.
Dawson, C. & A. S. Woodward (1913) On the discovery of a palaeolithic Human Skull and Mandible in a flint-bearing gravel overlying the Wealden (Hastings Beds) at Piltdown, Fletching (Sussex). Quarterly Journal of the Geological Society, 69, 117.
Gish, D. T. & I. f. C. Research. 1985. Evolution: The challenge of the fossil record. Creation-Life Publishers, Master Book Division.
Grine, F. 2007. Evolutionary History of the" robust" Australopithecines. Aldine de Gruyter.
Morris, J. D. 1994. The Young Earth. Master Books.
Oakley, K. P. & C. R. Hoskins (1950) New Evidence on the Antiquity of Piltdown Man. Nature, 165, 379-382.
Walsh, J. E. 1996. Unraveling Piltdown: the science fraud of the century and its solution. Random House.
Weiner, J. S., K. Oakley & W. Le Gros Clark (1953) The solution of the Piltdown problem. Bulletin of the British Museum (Natural History) Geology, 2, 141-146.
hite, T. (2003) Early Hominids--Diversity or Distortion? Science, 299, 1994.


James Kidder holds a Ph.D. in Biological Anthropology from the University of Tennessee (UT). He currently employed as an instructor at UT, and as a science research librarian at Oak Ridge National Laboratory. He has been involved in the Veritas Forum at UT and runs the blog "Science and Religion: A View from an Evolutionary Creationist/Theistic Evolutionist."

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TruthSeeker - #62748

June 20th 2011

Hi-
Throughout this essay, there are many pictures of skulls. I am curious as to whether or not full or mostly full skeletons have yet been found near these skulls? If not, are ideas as to why only skulls fossilized and remained from the bodies…?


Jimpithecus - #62754

June 20th 2011

What typically happens in depositional environments is that the hardest stuff fossilizes the easiest.  Those parts are teeth and skulls.  The long bones will usually break up and, hopefully, some parts of them will fossilize.  The vast majority of fossil remains are skull parts and teeth.  That is not to say that there are not other parts but those things are the hardest. 

We did get very fortunate in that there was almost an entire vertebral column found belong to an A. africanus individual, showing clearly the double-s that is characteristic of bipedality. In the case of a Neandertal (Kebara), we got almost an entire skeleton—minus the head!  A Homo erectus skeleton was found on the shores of Lake Turkana, at the site of Nariokotome that I will discuss in a future post, that is 90% complete.  It was phenomenal.  Everything from the top of the head to the bottom of the foot.  That is rare, though.  Most of the time, it is heads and teeth. 


Paul D. - #62757

June 20th 2011

Dr. Kidder, what do you think are the odds we will ever get a sample of Australopithecus or H. erectus well enough preserved to do DNA sequencing on? The sequencing of Neanderthal and Denisovan DNA to demonstrate that they were parallel hominin lineages still blows my mind.


Jimpithecus - #62785

June 21st 2011

Paul, about the furthest we can go back is around 60 to 70 thousand years before the strands start to break down.  The problem with the australopithecines is that they are completely fossilized and, consequently, rock.  Jurassic Park, while really cool, is not possible. 

About the Denisovans: there is considerable evidence that they are not specific in the sense of being unable to interbreed with other populations.  It is best to view them as an isolated population of a highly polytypic species (modern humans). 


KevinR - #62764

June 21st 2011

How are the ages of these fossils determined? It would be educational to know the precise process followed by those who discover these items.
I think it would also make a great deal of sense to perform carbon-14 dating on them and compare that to the other methods used to determine the age, if it isn’t in the standard set of tests that get done. The reason is simply that C-14 dating will immediately tell whether the skull is older than 50k years or not. Of course if one then comes up with a date less than that then the immediate reaction would be to reject it as contamination. Even if there’s no evidence of such contamination. This is the normal evolutionary process.


beaglelady - #62781

June 21st 2011

Why would it make a great deal of sense?


Jimpithecus - #62787

June 21st 2011

Depending on inferred age of the deposits, different dating techniques are used.  Not all of them are radiometric.  For example, the early modern humans in the Near East were dated using thermoluminescence and electron spin resonance dating, both of which rely on the counting of electrons in a sample that has been superheated.  For fossils that are older than around 500 thousand years old, Argon-Argon dating is the best way to determine ages. 

It is important to remember that, while it sounds like there is some circularity in the determination of which method to use, the half-lives of the elements are well-known and an educated guess can be made about how old something is in a relative way.  Then the absolute method nails it down. 


Jimpithecus - #62798

June 22nd 2011

This is only true, however, if you don’t think the earth was created six thousand years ago.


Uncle Bonobo - #62779

June 21st 2011

“I think it would also make a great deal of sense to perform carbon-14 dating on them and compare that to the other methods used to determine the age, if it isn’t in the standard set of tests that get done.”

All you wanted to know from a Chistian perspective:

http://www.asa3.org/ASA/resources/wiens.html


Jimpithecus - #62788

June 21st 2011

I would also read an article by Davis Young on radiometric dating called How old is it?  How do we know? A review of dating methods, Part II: Radiometric Dating:
mineral, isochron and concordia methods that appeared in Perspectives on the Christian Faith.

Great.  Link creator doesn’t work.  Here is the earl: http://www.asa3.org/ASA/PSCF/2007/PSCF3-07Young.pdf


DanB - #62987

June 28th 2011

“All you wanted to know from a Chistian perspective”

Thanks for the link and I will certainly read it with great interest.

However, I am a little concerned with presenting one scientific point of view as the “Christian” perspective.  Given that the Bible isn’t a science text book and how different scientific processes work isn’t central to Christian doctrine I would hesitate to say that something is “from a Christian perspective”.  I would think you can (and probably do) have Christians who have radically different opinions on matters science, just as you have Christians who have differing political views, views on economics, social views, etc.


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