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IU's Carlson among international team of six scientists announcing new species of prehistoric human

Indiana University anthropologist Kristian J. Carlson was part of an international team announcing discovery of the fossil remains of a new species of early human that could help rewrite the path of human evolution.


Image by K. J. Carlson

A transparent cranial reconstruction showing dental pattern, upper left, a modified reconstruction of the juvenile skull, center, and the actual fossil cranium from the new species of early hominid, lower right, that may serve as a link between the transition from apelike features toward a hominind with upright stance and increased brain capacity.

Print-Quality Photo

The two partial skeletons, dating from between 1.78 and 1.95 million years old, were discovered in South Africa and appear to represent features and attributes closer to humans -- the genus Homo -- than those from any other of our closest ancestors, the australopithecines. The new species, Australopithecus sediba, was announced April 8 in the magazine Science by principal investigator Lee Berger of the University of the Witwatersrand in Johannesburg, South Africa, and a team of six other researchers that included IU Bloomington's Carlson.

The fossil remains of the two hominids were found about a half-meter apart, embedded in cave deposits at the Malapa excavation site located about 170 miles northeast of Johannesburg and about nine miles northeast of the Sterkfontein World Heritage Site, also called the Cradle of Humankind. The first adult australopithecinewas found in Sterkfontein in 1936.

It has generally been recognized that Australopithicus' lost apelike attributes and began standing upright and evidencing increased brain capacity before evolving into the genus Homo. The Malapa researchers found that the new Au. sediba differs from other australopiths and is aligned to Homo by sharing attributes like increased buttressing of the ilium, expansion of the posterior ilium, and a decrease in the distance between the hip joints and sacroiliac. The new species also differs from the earlier australopiths in having reduced cranial muscle markings, more delicate facial morphology and smaller teeth, as well as in other craniodental and postcranial details.

The new species is still similar to other australopiths by virtue of its small body size and its longer upper limbs with large joint surfaces, among other things, they said.

Paleoanthropologists believe the discovery marks a new link between the traits of the more rugged Australopithecus africanus that was present 1 million years earlier and the later taxon Homo habilis that eventually evolved into Homo erectus.

"Being a member of the team interpreting the Malapa fossils is an extraordinary privilege in that I have an opportunity to be at the forefront of paleoanthropology," Carlson said. "I feel a duty to the field to proceed with cautious scientific analysis, but yet there is also the undeniable excitement of being able to study and interpret previously unknown morphologies and constellations of traits."

As a core member of the Malapa team, Carlson led the analyses of particular components of the discoveries and was responsible for directing all virtual work involving the fossils, as well as several aspects of structural interpretation of morphology in the fossils. Currently a senior researcher and research associate in IU Bloomington's Department of Anthropology, Carlson received his M.A. and Ph.D. in anthropology from IU after receiving B.S. degrees in anthropology and anthropology-zoology from the University of Michigan. He completed post-doctoral work in the Department of Anatomical Sciences, Stony Brook University, and in the Anthropologisches Institut und Museum, Universität Zürich.

Some of his areas of specialization include the examination of morphological variability in extant and fossil ape limb anatomy, experimental analyses of primate gait kinetics and kinematics, and studying form-function relationships in vertebrate limb anatomy. Through examination of computed tomography (CT) scans of bone cross sections Carlson can use mathematical models to estimate bone strengths of primates, modern hunter-gatherers and other mammals.

IU anthropology Professor Kevin Hunt, Carlson's adviser when the student received his Ph.D. in 2002, described the discovery as "amazing" in that it not only creates newly identified links between the australopiths and Homo, but also because it suggests that the transition between the small-bodied Au. africanus and the bipedal H. erectus occurred not only in East Africa, but across the whole of Africa, including South Africa.

"The fossils clearly link fossils in East Africa to South Africa," he said. "Some paleontologists tend to think that we evolved from something in East Africa, and South Africa was just a sort of dead end. This fossil shows that the same trends seen in East Africa were also seen in South Africa -- they're just regional versions of the same thing.

"The discovery is an amazing one. It's late enough that it is contemporaneous with our ancestors that were, at the time, evolving into Homo erectus. The fossils in South Africa tend to be very rugged, with heavy faces and huge molars. These aren't like that, and suggest that they're related to East African fossils that many have put in the taxon Homo habilis," Hunt said. "The intriguing thing is that they still have traits found in the more rugged species, Au. africanus, that is found half a million to a million (or more) years earlier. This suggests that just like humans all over the world have evolved but retained their regional characteristics, we had regional characteristics of Homo habilis at 2 million years ago. The teeth are distinctly smaller than Au. africanus, yet the face looks like a delicate version of Au. africanus."