September 30, 2019

Last month, in late August, scientists published a description of a 3.8-million-year-old fossil skull, allowing people to gaze into the face of perhaps our earliest ancestor, Australopithecus anamensis. According to one researcher, the remarkable fossil is the most complete skull of the “oldest-known species” of the human evolutionary tree. The important fossil helps define the ancient human evolutionary family, but it also brings more questions to the often cloudy relationships among that family’s members.

Paleontologists discovered the near-complete skull of Australopithecus anamensis in Ethiopia in 2016. Credit: © Dale Omori, Cleveland Museum of Natural History

A. anamensis belongs to the hominin group of living things that includes human beings and early humanlike ancestors. A team of paleontologists led by Yohannes Haile-Selassie from the Cleveland Museum of Natural History found the hominin skull in 2016 at a site called Woranso-Mille in the Afar region of Ethiopia. The fossil, officially known as MRD-VP-1/1 (MRD for short), was discovered in two halves that fit together, making up a nearly complete skull. The skull’s position in volcanic sediments enabled scientists to determine its age—3.8 million years—with great precision. The anatomical features of the skull helped identify it as A. anamensis, one of the earliest known hominin species. This species was first identified from a handful of fossil skull fragments and other bones discovered at Lake Turkana in northern Kenya in the 1990’s. Those specimens are between 4.2 million and 3.9 million years old.

Scientists used the fossilized Australopithecus anamensis skull to create this image of one of humankind’s earliest ancestors. Credit: © John Gurche/Matt Crow, Cleveland Museum of Natural History

The MRD skull shows that A. anamensis had a small brain, a bit smaller than that of a modern chimpanzee. The skull more closely resembles an ape than a modern human, with a large jaw and prominent cheekbones, but the canine teeth are much smaller and more humanlike. And, like humans, A. anamensis walked upright on two legs. Sediments and other fossils show that the region where the skull was found was arid, but the ancient creature died in a vegetated area near a small stream that entered a lake.

The site in Ethiopia where MRD was discovered is not far from the village of Hadar, where fossils of another early hominin, Australopithecus afarensis, were first discovered in 1974. A. afarensis is known mainly from the partial skeleton of an adult female, the famous “Lucy,” found in deposits dating to about 3.2 million years ago. Other A. afarensis fossils date to nearly 3.8 million years ago, which suggests Lucy and her kind may have coexisted with A. anamensis.

Most scientists, however, think that Lucy and her kind evolved from A. anamensis, and that the transition occurred as one species disappeared and the other took over. Scientists now understand that A. anamensis could still be ancestral to Lucy, but that other A. anamensis populations continued to thrive unchanged as her neighbors. The prehistoric landscape of East Africa had many hills, steep valleys, volcanoes, lava flows, and rifts that could easily have isolated populations over many generations. Over time, the populations eventually diverged. Scientists think that one of these species eventually gave rise to Homo, the human genus.

June 10, 2015

Fossilized jaws and teeth discovered in northern Ethiopia belong to a previously unknown ancient human ancestor that lived 3.3 million years ago, according to scientists who announced the discovery in late May 2015 in the journal Nature. The new species, named Australopithecus deyiremeda by the scientists who described the fossil remains, lived at the same time and in the same region as another early human ancestor.

Yohannes Haile-Selassie, a paleoanthropologist at the Cleveland Museum of Natural History, holds casts of the jaws of Australopithecus deyiremeda, a new human ancestor species from Ethiopia. (Credit: Laura Dempsey, Cleveland Museum of Natural History)

The Ethiopian anthropologist Yohannes Haile-Selassie of the Cleveland Museum of Natural History in Ohio described the fossils, which were found at a site in the Afar region of northeastern Ethiopia. The scientists concluded that the fossils are from an early hominin. Hominins, also called hominids, are the scientific family that includes human beings and early humanlike ancestors. The site is about the same age and only a few miles from Hadar, where fossils of Australopithecus afarensis were first discovered by the anthropologist Donald C. Johanson in 1974.  A. afarensis was an early humanlike creature known in part from a famous fossil skeleton nicknamed “Lucy.” The two species are similar in their anatomy, but they can be distinguished by different shaped jaws. Haile-Selassie believes the fossil jaws and teeth belong to the same species as several fossil foot bones that were discovered at a nearby site in Ethiopia and described in 2012.

The scientists believe the fossils demonstrate that Lucy and her kind were only one of perhaps several hominin species that inhabited the forests and grasslands of East Africa more than 3 million years ago. Each species was adapted to a different habitat and likely had different anatomy and behavior, including how it moved around. However, scientists are not certain if any of these species are direct ancestors to modern humans.

Paleoanthropologists speculate that the distinct jaw shapes of A. deyiremeda and A. afarensis could mean that they used their teeth on different kinds of food. This means that the two species could have lived side-by-side, because they would not have directly competed for food, shelter, and territory. However, not all scientists agree that these new fossils represent a new species of hominin. Some scientists think that the fossils simply demonstrate that physical variation was great among A. afarenis.

Other World Book articles:

• Anthropology (1973-a Back in time article)
• Anthropology (1983-a Back in time article)
• Anthropology (2012-a Back in time article)