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The Human Fossil Record, Part 4: Australopithecus Conquers the Landscape

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April 4, 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.

Australopithecus anamensis

In my previous post, I described the discovery of the first Australopithecus in South Africa by Raymond Dart. Beginning with the work of Dart and venerable palaeontologist, Robert Broom, an extensive range of discoveries has been made that continues to the present day.

The earliest known species from the genus that Dart discovered is known as Australopithecus anamensis. Its remains are, sadly, still quite fragmentary. Working at the sites of Kanapoi and Allia Bay in Lake Turkana, in Kenya, Richard Leakey and others unearthed the partial remains of a number of individuals, which are securely dated to between 4.0 and 4.2 million years ago. By comparison, Ardipithecus ramidus (see Figure 1) is dated to around 4.4 million years. More recently 30 specimens of Australopithicus anamensis from at least 8 individuals have been found in Ethiopia and they have been dated at a similar age (see here for an analysis of the rock strata and age of the formations in which the specimens were found.)

Figure 1 Australopithecus in Perspective (from Science Magazine)

Editor's Note: The above diagram is intended as a means of comparison between Australopithecus and its close genetic relatives. It is NOT intended to present a strictly linear progression or imply that gorillas and chimpanzees evolved into present homo sapiens.

Currently, the remains attributed to Australopithicus anamensis consist of several jawbones, some lower faces, more than 50 isolated teeth, skull fragments, several sections of lower arm and a section of a tibia, just below the knee (See Figures 2 and 3). Nonetheless, it is possible, for reasons discussed below, to determine a great deal about how this species moved around, the kinds of things that it ate and, critically, how it differed from its predecessor, Ardipithecus, and the forms that would come after it.

It has been determined that this species inhabited sparse woodland, river bank environments and open grassland, a greater range than that in which Ardipithecus lived. This is based on the similarities between the deposits from Kanapoi, Allia Bay and those of Australopithecus afarensis, the hominin that follows Australopithecus anamensis, temporally. In addition there has been an extensive analysis of accompanying fossil species found at the Ethopian site where specimens from eight A. anamensis individuals have been found.

In addition to the increase in range, certain elements of the skeleton are present that show a clear trend toward the forms that would come later. These include significant changes in how the teeth and palate are arranged, the shape of the teeth (Figure 2), and the morphology of the tibia (Figure 3).

Figure 2 (above, left). Lower Jaw bone of two specimens of Australopithecus anamensis. Figure 3 (below, right). Different views of the same tibia bone from Australopithecus anamensis.

In Ardipithecus, the dentition was very similar to that of modern chimpanzees, with the exception of the size of the canine, which was shortened. The teeth were geared toward a fruit and leaf diet, with occasional meat thrown in, such as you would find in a forest environment.

In Australopithecus anamensis, however, the teeth had much thicker enamel, they were larger and had flatter grinding surfaces that would have been more suited to nuts and other hard foods. This suggests that this hominin would have been well-adapted for life in open grassland and savannah.

The orientation of the tibial shaft indicates that it was positioned directly up and down in relation to the foot and the femur, suggesting that the individual walked completely upright. The length of the radius fragment and its comparison to the tibial fragment further attests that this individual had arms that were elongated, like Ardipithecus. It seems likely, therefore, that like Ardipithecus, A.anamensis spent quite a bit of time off the ground.

It is tempting to speculate about the cognitive abilities of Australopithecus anamensis relative to Ardipithecus ramidus. We have no evidence that Ardipithecus existed outside the forest environment. Based on the taphonomic evidence, we strongly suspect that A. anamensis existed in the fringe and savannah. We do know that the vast majority of modern primates have home ranges that are restricted to one kind of biome. For example, Orang-utans only live in the forests of Borneo and Sumatra while Spider and Howler monkeys only exploit the forest canopies of Central America. While these examples certainly reflect a stable evolutionary response to particular environments, their inability to move beyond these environments and the need for conservation efforts to preserve them reflect a level of cognitive ability that appears to be restricted. If A. anamensis could survive in both the forest/fringe and savanna environments, it suggests an increase in cognitive abilities for this species. More evidence will be necessary to lend credence to this hypothesis.

Australopithecus afarensis

In 1973, working with a local team of fossil hunters, Maurice Taieb went to an arid stretch of land in the Afar Triangle of Ethiopia to an area called Hadar. A year later, Don Johanson, a member of his team discovered one of the most famous of all fossil hominin discoveries ever made. Exploring 3.4 and 3.6 million years old deposits, he discovered the fragmentary remains that constituted 40% of the skeleton of a small adult female (Figure 4) . This individual was nicknamed “Lucy” after the Beatles' song "Lucy in the Sky with Diamonds" which played in the camp during the analysis of the remains. The team named the species she represented Australopithecus afarensis, because she had been found in the Afar triangle. Johanson, together with M. Edey, went on to pen the New York Times Bestseller Lucy: The Beginnings of Humankind. This book catapulted Lucy onto the national stage and fueled research into the biological origins of humankind (Johnanson and Edey 1980).

When Lucy was examined, it was found that the shape and position of the the teeth and jaw as well as the hip and long bone fragments put her almost perfectly intermediate be tween the ape position and the human position. Although she had the overall size and rib cage structure of a chimpanzee, her pelvis and leg bones were perfectly adapted for bipedalism (for a discussion on bipedalism, see this post and this video.) It was in the teeth and palate that the clearest transitional characteristics existed (Figure 5, right). In modern humans (5c), the dental arcade (tooth row) is in the shape of a parabola, like the Gateway Arch in Saint Louis. In apes (5a), it is a sharp “U” shape. In A. afarensis (5b), it is intermediate, tending toward the ape condition.

In apes, there is a space (diastema) between the canine and the second incisor (bicuspid, if you prefer) to allow room for the long lower canine when the ape closes its mouth. In A. afarensis, the canine is human-sized and the diastema, while still present, is smaller. In apes, the first premolar is rotated relative to the tooth row and has a very high cusp so that it creates a sharpening surface for the opposite canine when the two teeth come together. In Lucy, the cusp is somewhat lower and the premolar is only slightly rotated. In humans, the cusp does not extend above the tooth row and there is no rotation at all.

The case for habitual bipedalism received added support from a site much further south than where Lucy had been found. In 1976, Andrew Hill, a digger in Mary Leakey’s team, working at the site of Laetoli, in Tanzania, unearthed a set of hominin tracks that had been covered by a now extinct volcano. These footprints, which extend approximately 80 feet across the plain, have been securely dated at 3.6 million years and show where two individuals walked side-by-side (Figure 6). The tracks are significant in that they demonstrate that the individuals who made them had arches and practiced the characteristic “toe-off” pattern of gait practiced only by hominins. The presence of A. afarensis skeletal remains nearby at the same level provided the link to the footprints.

By the time A. afarensis appears in the lineage all clear evidence of spending time in the trees was gone. On the foot, the arch had become prominent and the big toe, which had been slightly off-set in Ardipithecus and possibly Australopithecus anamensis, was firmly in-line with the other toes. The presence of the arch allowed for easy toe-off locomotion and would have been disadvantageous in climbing trees because it contributes to the rigidity of the foot. This was a species that was not just optimized for bipedality, it had become its only form of locomotion Furthermore, as noted, taphonomic evidence indicates that this species could exist in the forest and fringe environments. Its presence in both the Afar triangle and near Lake Turkana (nee Lake Rudolf) further suggests that it had a range of several thousand miles (Figure 7, left).

Kimbel and others have suggested that the similarities in traits between A. anamensis and A. afarensis represent an ancestor-descendant relationship, with A. afarensis representing the more advanced stage in hominin evolution(Kimbel et al. 2006).



Stone Tools: A Cognitive Shift

With Australopithecus afarensis came another striking evolutionary development. While A. anamensis and A. afarensis have been shown to have adapted to the forest/fringe and savannah environments, it is with A. afarensis that we have the first evidence of behavior that is directly cognitive in nature: the use of stone tools. At the site of Dikika, in Ethiopia, very near the site of recovery of an almost complete A. afarensis skeleton, animal bones were discovered dated to at least 3.39 million years ago that demonstrate distinctive signs of human action: cut marks. As McPherron et al. write:

The cut marks demonstrate hominin use of sharp-edged stone to remove flesh from the femur and rib. The location and density of the marks on the femur indicate that flesh was rather widely spread on the surface, although it is possible that there could have been isolated patches of flesh. The percussion marks on the femur demonstrate hominin use of a blunt stone to strike the bone, probably to gain access to the marrow. (McPherron et al. 2010) (For video summary of discovery, see here)

These authors are quick to point out that there is no way to determine whether or not these marks were made by tools that were modified for this purpose or made with the first available sharp rock, although the authors note that rocks found in association with the bones had been transported over six kilometers from their original location. This reflects advanced behavior by these hominins, though, including the first consumption of meat known in the fossil record.

Figure 8. Cut Marks on 3.35 Million year old Bovid Femur (from Nature)

With Australopithecus afarensis, however, a new hominin was on the landscape—a hominin that could adapt to new environments and, to a limited degree, adjust the environment around them to meet their needs. Without the adaptations necessary to remain in the trees for any length of time, and with the ability to balance and walk in a truly human fashion, the fact that they no longer needed to use the hands for support or grasping, freed them up for other uses. As A. afarensis moved about the landscape, these uses became evident: they modified what they had at their disposal.

It is unfortunate that we do not know whether these hominins created the tools to make these marks or used what was available to them. If they brought stones with them to butcher animals, though, it means that they were the first hominins that did more than react to their environment; they modified it to their uses.

Next, the diversification and extinction of the australopithecines and the rise of the genus Homo.

Notes

1. Johnanson, D. & M. Edey. 1980. Lucy: The beginning of humankind. New York: Simon & Schuster.

2. Kimbel, W., C. Lockwood, C. Ward, M. Leakey, Y. Rak & D. Johanson (2006) Was Australopithecus anamensis ancestral to A. afarensis? A case of anagenesis in the hominin fossil record. Journal of human evolution, 51, 134-152.

3. McPherron, S. P., Z. Alemseged, C. W. Marean, J. G. Wynn, D. Reed, D. Geraads, R. Bobe & H. A. Bearat (2010) Evidence for stone-tool-assisted consumption of animal tissues before 3.39 million years ago at Dikika, Ethiopia. Nature, 466, 857-860.

4. Ward, C., M. Leakey & A. Walker (1999) The new hominid species Australopithecus anamensis. Evolutionary Anthropology: Issues, News, and Reviews, 7, 197-205.


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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Jimpithecus - #57368

April 8th 2011

In the second paragraph of the paper, Woodmorappe writes:

Creationists have shown that the geological column presents no problem to
Flood geology.  It is nothing more than a hypothetical classification scheme
based on selected rock outcrops in Europe, and used flexibly to classify
rocks around the world.

He then cites for this information two studies, one by Henry Morris and Gary Parker, neither of whom have any geological training whatever and another study by himself. (By the way, “John Woodmorappe” is a pseudonym.  His actual name is Jan Peczkis.  The weird part is that he has been known to quote himself in the third person) He then fails to mention that there is not a scrap of mainstream geological literature that supports this position.  In fact, Christian geologist Carol Hill has written that there is not a shred of evidence to support flood geology. 

Woodmorappe doesn’t seem to understand the concept of sampling here.  He complains that Morton overreaches.  He writes:

“Common sense teaches us that 16 miles (at
most) which exists, out of a total of 100 or 200 miles, is a
very incomplete column!  It remains primarily an invention of
the uniformitarian imagination, and a textbook orthodoxy.  So, although
there are places where lithologies referable to all ten of the Phanerozoic
systems can actually be seen superposed, creationists remain more than
justified in highlighting the essential non-existence of the standard
geologic column. “
 


Morton clearly states:

“In point of fact, Morris and Parker define the
geologic column in a silly fashion. There is no place on earth that has
sediments from every single day since the origin of the earth. No geologist
would require this level of detail from the geologic column. But if there are
sediments left at a given site once every hundred thousand years or so, then at
the scale of the geological column, the entire column would exist. There would
still be erosional surfaces contained in that column and that would mean that on
some days no sediment was left at a given location to mark the passage of those
days.”

What Morton is trying to point out is that there is a sample of each of the ten phanerozoic periods represented and that they are in order, which follows the predictions of uniformitarianism and evolutionary theory.  Woodmorappe writes:

Without first
assuming the validity of the geologic column, and using it as
a tool to find times as well as areas of non-deposition, there is no way of
independently knowing anything about ostensible long-term areal trends in
sedimentary deposition.  That is, without the complete geologic column as a
reference, who can possibly know how much of the Earth’s
surface has been depositional simultaneously in any period of several tens
of millions of years (i. e. the average duration of a geologic period)?

This is nonsense.  There are plenty of areas of the world in which large sections of the geological column exist that show long stretches of time.  There is no assumption required.  It is straight observation.  If you have ABCD in one area and BC[erosion facies]E in another and C[erosion facies]EFG in another, it does not take a wild guess to see that they are related but that there might be depositional hiatuses.  This insistence on focusing on one area of the world to make your case about the whole planet doesn’t work. 


Jimpithecus - #57369

April 8th 2011

That last comment was supposed to be a direct response to Dennis’ comment number 57254.  For some reason, it didn’t put it there.


Maurizio - #57406

April 8th 2011

Thanks for making this observation Jimpethicus. Just look at the reference list…All ICR and CEN articles….That pretty much sums up this completely ..one-sided piece. It loses all credibility.


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