Burtele Foot Indicates Lucy Not Alone

A new fossil discovery from Eastern Africa called the Burtele foot indicates Australopithecus afarensis, an early relative of modern humans, may not have been the only hominin to walk the plains and woodlands of what is now the Afar region of Ethiopia some 3.4 million years ago.

Researchers openly have questioned whether Au. afarensis, the species to which the famous fossil "Lucy" belongs, was the only living hominin during the late Pliocene of Africa. Lucy's bones provided evidence that she and perhaps other early hominins may have walked upright, but whether or not she was the sole hominin species in her particular geologic time scale has been the subject of much debate.

"There was indeed more than one early hominin species during that time," said Yohannes Haile-Selassie, head of Physical Anthropology at the Cleveland Museum of Natural History and lead author of the findings.

Haile-Selassie and a team of anthropologists and geologists report finding the partial skeleton of a foot that belonged to an early human ancestor that was neither Au. afarensis nor another hominin called Kenyanthropus platyops, a creature that some paleoanthropologists argue was a second hominin that lived at the same time as Au. afarensis.

The journal Nature published the finding today. The National Science Foundation's (NSF) Division of Behavioral and Cognitive Sciences partially funded the research.

Descriptions of Kenyanthropus platyops led some scientists to dispute whether only one hominin inhabited Africa's upper regions 3.9 to 2.9 million years ago mainly due to the distorted nature of the specimen used as the basis for the original published description of Kenyanthropus platyops, said Haile-Selassie.

"Tim White, (a member of the research team who began uncovering Lucy in 1973), argued that Kenyanthropus platyops is a Kenyan version of Australopithecus afarensis and that the subtle differences between the two could be subsumed into an intra-specific variation."

In other words, he argued there was no evidence a second hominin roamed the landscape during the time of Au. afarensis. But Haile-Selassie and his team may have found proof of at least two hominin species.

In Woranso-Mille, a relatively new palaeontological site located in the central Afar region of Ethiopia, researchers dug up a 3.4 million year old partial foot skeleton that does not match the contemporaneous Au. afarensis in form or shape.

Moreover, the skeletal remains infer locomotor adaptations more similar to an earlier, 4.4 million year old hominin, Ardipithecus ramidus, that was discovered by a research team led by White in 1992-1993 in the Middle Awash valley in Ethiopia.

"The Burtele foot differs from Australopithecus afarensis largely by possessing an opposable great toe," said Haile-Selassie, noting the Burtele toe is more like that of Ardipithecus ramidus, inferring similar characteristics for walking, running and jumping.

"This partial pedal skeleton is unique in providing important evidence bearing on the functional morphology and proportions of several early hominin foot elements," the researchers write in their article titled, "A new hominin foot from Ethiopia shows multiple Pliocene bipedal adaptations."

Carolyn Ehardt, program director for Biological Anthropology at NSF, points out that research findings such as this foster appreciation for the complex processes that "shaped the evolutionary history of our species."

"We become increasingly aware of the fact that the evolutionary history of hominins is not unlike that of other groups of organisms in the potential for morphological and behavioral diversity and multiple adaptive pathways characterizing those life-forms during particular evolutionary time periods," she said.

The Burtele foot has some skeletal ratios that fall within the human and gorilla distribution, but outside those of chimpanzees. In addition, the metatarsal of the fourth toe is longer than that of the second toe, a condition seen in some monkeys and Miocene apes.

"Unfortunately this ratio is unknown for both Ardipithecus and Australopithecus," said Haile-Selassie. "But, the finding could indicate the primitive condition for the human family."

The researchers say identifying and naming the species to which the Burtele foot belongs will have to await recovery of more fossils, cranial and dental elements, for example. However, they are sure it does not belong to the species of Lucy, Au. afarensis.

Said Haile-Selassie, "It is probably descended from something like Ardipithecus ramidus."

Joining Haile-Selassie in this research are Beverly Z. Saylor and Bruce M. Latimer of Case Western Reserve University, Cleveland, Ohio; Alan Deino of the Berkeley Geochronology Center, Berkeley, California; Naomi E. Levin of Johns Hopkins University in Baltimore and Mulugeta Alene of Addis Ababa University in Ethiopia.

In addition to NSF, the LSB Leakey Foundation, the National Geographic Society and the Cleveland Museum of Natural History supported this research.

 -NSF-

Castaway Lizards Offer New Look at Evolutionary Processes

Biologists who released lizards on tiny uninhabited islands in the Bahamas have uncovered a seldom-observed interaction between evolutionary processes.

Jason Kolbe, a biologist at the University of Rhode Island (URI)--along with colleagues at Duke University, Harvard University and the University of California, Davis--found that the lizards' genetic and morphological (form and structural) traits were determined by both natural selection and a phenomenon called the founder effect.

Their research results are published online today in the journal Science.

The founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population. It often results in the new population becoming genetically or morphologically different from the original population.

"We rarely observe the founder effect as it happens in nature, but we know that it occurs because islands are colonized by new species over time," said Kolbe.

"What we didn't know was how these evolutionary mechanisms [natural selection and the founder effect] interact with each other."

The scientists learned that differences caused by the founder effect persist even as populations adapt to new environments.

"Evolutionary biologists have been debating the importance of founder effects for more than 70 years," said Sam Scheiner, program director in the National Science Foundation (NSF)'s Division of Environmental Biology, which funded the research. "This study is the first to definitively demonstrate those effects for ecologically important traits."

Kolbe and colleagues randomly collected brown anole lizards from a large island near Great Abaco in the Bahamas, and released one pair on each of seven nearby islands whose lizard populations had been cleared by a recent hurricane.

The source island is forested, while the other islands have short, scrubby vegetation.

Previous research had found that anole lizards living in forests had longer hind limbs than those found in scrub habitat.

Lizards with longer limbs can run faster on the broad perches available in forests, while short-limbed lizards are more adept at moving on the narrower perches found in lower vegetation.

The scientists revisited each of the islands over the next four years to measure the lizards' limb length and collect tissue samples for genetic analysis.

All the new populations survived and increased an average of 13-fold in the first two years, before leveling off.

"We noticed a founder effect one year after starting the experiment, which resulted in differences among the lizards on the seven islands," Kolbe said.

"Some of the islands had lizards with longer limbs and some had lizards with shorter limbs, but that was random with respect to the vegetation on the new islands."

Because the structure of the vegetation on the islands differed from that of the source island, the scientists predicted that natural selection would lead the lizards to develop shorter limbs.

"Over the next four years, the lizards on all the islands experienced a decrease in leg length that is attributable to natural selection," Kolbe explained. "But those that started out with the longest hind limbs still had the longest hind limbs."

The fact that the populations maintained their order from longest to shortest limbs throughout the experiment means that both the founder effect and natural selection contributed to their current differences.

According to Kolbe, the founder effect is rarely observed in nature, with most previous research conducted in the laboratory.

"Ours is the first to study this process experimentally in a natural setting, and we were able to account for multiple evolutionary mechanisms through time," he said. "We manipulated the founding of these islands, but everything else about it was natural."

The next step in the research will be to determine how long the founder effect persists before other factors erase its signature.

Co-authors of the paper are Kolbe; Manuel Leal of Duke University; Thomas Schoener and David Spiller of the University of California, Davis; and Jonathan Losos of Harvard.

The study was also funded by the National Geographic Society.

-NSF-