Physical Anthropology Update

PHYSICAL ANTHROPOLOGY – RESEARCH UPDATE

(last updated January 2007)
by Phil Stein
Los Angeles Pierce College

A Wee Look at the Little Folks

This is a story of three little skeletons—or parts thereof. Let’s examine these fossils from oldest to youngest.

The Dikika Child

The Dikika child is a wonderful find. It is one of those rare skeletons, relatively complete and well preserved. It is thought to be the skeleton of the juvenile female around 3 years of age. The body was quickly buried in sediment, perhaps by a flood, before it could be altered by the gnawing of scavengers or changes brought about by exposure to the sun, rain, and wind. Of course it is not 100 percent complete, and some parts are distorted—but it is still a rare prize. The skull is fairly well intact, with a natural endocranial cast and a complete set of deciduous teeth. There also is a hyoid bone (only the second one ever found in the hominin fossil record, the other being a Neandertal), and a number of postcranial bones including the scapula, clavicle, several vertebrae, ribs, humerus, phalanges of the hand, femur, tibia, fibula, patella, and a fairly complete foot. It clearly belongs to Australopithecus afarensis.

The find was made in the Afar region of Ethiopia where so many important fossils have been recovered. The site is Dikika, and the skeleton has been cataloged as DIK-1-1. The date of the sediments in which it was found is 3.31 to 3.35 million years ago.

The skeleton shows many transitional features between the Miocene “apes” and the hominins. The cranial capacity (estimated as 275 to 330 cubic centimeters) is similar to that of a 3-year-old chimpanzee. The hyoid bone fits the ape pattern. The shoulder and upper limbs resemble the structures of the apes, with the phalanges of the hand being curved and long. This suggests that A. afarensis was able to move easily in trees. However, the structure of the lower limbs and feet are those of an erect biped. Thus this skeleton supports the hypothesis that A. afarensis, while an erect biped, spent a great deal of time in trees, which is perhaps the only place where a small biped could be truly safe.

The Demise of the Taung Child

However, there is not always safety in trees. When we discuss predation we usually think in terms of big cats and large snakes. Yet for primates more serious predators are carnivorous birds such as eagles and hawks. They come out of the sky and can quickly pick up a small primate in its talons and fly with it to its nest.

Scott McGraw, et al, has published an analysis of primate remains found around nests of African crown eagles in the Tai National Park, Ivory Coast. They collected bones of several species of guenons, colobus monkeys, and potto. Characteristic damage to the bones caused by talons and beak occurs most often on the head, shoulder, pelvis, hands and feet. African crowned eagles weigh about 3.8 kilograms. Most of their prey weighs between 3 and 10 kilograms, but they can kill and transport prey weighing up to 20 kilograms. They also will dismember the larger animals and carry parts of the body to their nests.

The hypothesis that predatory birds exerted a significant selective pressure on hominin populations was initially proposed in 1995. This “bird of prey hypothesis” was based upon an analysis of the bone assemblage at the site of Taung, South Africa. The relative proportions of the different kinds of bones as well as the nature of the damage seen in the bones supported this idea. It is now clear that predatory birds of this size can kill and carry a hominin child to its nest.

Taung, of course, is the site from which the fossil described by Raymond Dart in 1925 was recovered, the first australopithecine and member of the species Australopithecus africanus. Carefully examination of the orbit of the skull clearly shows characteristic puncture marks of a predatory bird.

The Little Hominin from Flores Island—Revisited

“Homo floresiensis,” the skeleton from Flores Island, saddled with the unfortunate nickname of “The Hobbit,” is back again. (See my article in SACC Notes.) T. Jacob, the dean of Indonesian paleontologists, along with other paleontologists from Indonesia, China, Australia, and the United States, are taking pot shots at the unfortunate tiny creature. Only this time it is a detailed, technical article published in the prestigious peer-reviewed journal, the Proceedings of the National Academic of Sciences. Here is a summary of some of the important points they make.

· Additional skeletal material does not include any bones from the braincase, necessary to establish the exceedingly small cranial capacity as being normal. All of the features of the second mandible can be found in Southeast Asian Homo sapiens populations. Only some of the limb bones resemble those of LB1 in size. In fact not one of the 94 descriptive features of the cranium or the 46 features of the mandibles lies outside the range for modern humans living in this region.

· There is evidence of hominin occupation of Flores Island at 840,000 years ago. If a Homo erectus population were to evolve into a distinct species, it would have had to remain isolated from the outside world since that time. The very fact that hominins reached the island meant that they had water craft, and since during the height of the glacial the water barrier was fairly narrow, isolation for a period of over 800,000 stretches the imagination.

· There are many populations in the area of relatively short average stature. These populations include peoples on the Andaman Islands, New Guinea, the Malayan Peninsula, and other areas. Short stature and small body size does not define a hominin species.

· There are a great many forms of microcephaly. LB1 shows a number of distinct deformities in the skull that strongly suggest some type of skeletal abnormality. Among these are neurocranial deformities and a marked asymmetry.

It is perhaps worthwhile to quote parts of the article’s conclusion:

Our reexamination of the original skeletal material shows that there is insufficient morphological or metric evidence for a new hominin species on Flores, where evolution over millennia in total isolation is unproved, unlikely, and at variance with Stegodon migrations and glacial geology. The skeletal material … represents individuals sharing small body size … and other traits previously documented. Such commonalities are expected on grounds of shared environment and relationship in a local group…. [T]he LB1 individual exhibits a combination of characters that are not primitive but instead regional, not unique but found in other modern human populations, particularly some still living on Flores, and not derived but strikingly disordered developmentally.

It is indeed serendipitous that the reports on the Dikika and Flores Island should occur so close in time. It makes for a wonderful contrast on how science should work. The former is a well thought out presentation made after several years of painstaking analysis. The latter is a less measured endeavor whose announcement was accompanied by a great brouhaha in the popular press complete with reconstruction and perhaps one of the most dreadful presentations ever to bear the National Geographic logo.

What makes the debate so interesting as a teaching tool is the ability to represent the two viewpoints side-by-side. The argument for LB 1 is supported by an article in the latest issue of the Journal of Human Evolution by Debbie Argue, et al. Here the authors engage in a statistic analysis of the Flores Island hominin, comparing it with several microcephalic and fossil skulls. They conclude that LB 1 does not match the metrics of several microcephalics, although the authors admit that a larger sample is needed, nor pygmoid skeletal material, but are closest to those of early specimens of Homo.

____________________

References:

A. Argue, et al., “Homo floresiensis: Microcephalic, pygmoid, Australopithecus, or Homo?, Journal of Human Evolutuion, 51 (2006), pp. 360-374.

Z. Alemseged, et al., “A juvenile early hominin skeleton from Dikika, Ethiopia,” Nature, 443 (21 September, 2006), pp. 296-301.

L. Berger, “Brief communication: Predatory bird damage to the Taung type-skull of Australopithecus africanus Dart 1925,” American Journal of Physical Anthropology, 131 (October 2006), pp. 166-168.

T. Jacob, et al., “Pygmoid Australomelanesian Homo sapiens skeletal remains from Liang Bua, Flores: Population affinities and pathological abnormalities,” Proceedings of the National Academy of Sciences, 103 (September 5, 2006), pp. 13421-13426.

W. S. McGraw, et al., “Primate remains from African Crowned Eagle (Stephanoaetus coronatus) nests in Ivory Coast’s Tai Forest: Implications for primate predation and early hominid taphonomy in South Africa,” American Journal of Physical Anthropology, 131 (October 2006), pp. 151-165.

P. L. Stein, “The little people of Flores Island: A lesson in critical thinking,” Teaching Anthropology: SACC Notes, 11 (Spring 2005), pp. 25-28.

J. G. Winn, et al., “Geological and palaeontological context of a Pliocene juvenile hominin at Dikika, Ethiopia,” Nature, 443 (21 September, 2006), pp. 332-336.

Phil Stein
Los Angeles Pierce College
stein2@pacbell.net

last updated: January 3, 2007
Contact Webmaster