FRIDAY, Feb. 18, 2005 (HealthDay News) -- Scientists have dug up what appears to be the oldest intact rabbit fossil, complete with skull, long front teeth, short forelimbs and long hind limbs.
The ancient rabbit, which is described in the Feb. 18 issue of Science, is named Gomphos elkema, in honor of his distinctive dentures; gomphos is the Greek word for tooth.
The discovery of Gomphos adds new information to the picture of evolution, lending credence to the theory that lagomorphs (the group that includes rabbits and pikas) appeared after dinosaurs became extinct. The skeleton is about 56 million years old -- 20 million years older than others like it -- and dinosaurs vanished from earth about 65 million years ago.
The new fossil also supports the hypothesis that lagomorphs and rodents shared a common ancestor that lived very near the time of the extinction of dinosaurs.
"This is an important paper," commented Ken Rose, a professor of functional anatomy and evolution at Johns Hopkins University School of Medicine in Baltimore. "They're presenting something very new and exciting about the origin of rabbits."
David Archibald, a professor of biology and curator of mammals at San Diego State University, described it as "a high quality piece of work."
"It's not necessarily the earliest but one of the most complete specimens," Archibald said.
In a somewhat similar, coincidental discovery, researchers reported in the Feb. 17 issue of Nature that the earliest known Homo sapiens, or modern-day humans, also are older than once thought. New evidence dates humans' appearance on the scene to 195,000 years ago, not 154,000 to 160,000 years ago, as was previously thought.
Gomphos, which was found in southern Mongolia, is one of a group of mammals called Glires, which comprise almost half of all mammals today, said Guillermo Rougier, co-author of the Science paper and an associate professor of anatomical sciences and neurobiology at the University of Louisville School of Medicine in Kentucky.
The availability of a complete fossil, Rougier said, allows scientists to mark the evolution of different organisms with greater precision. "It's as if, in trying to put together the history of the car, you have only the spark plug," he explained. "Now we have the whole car."
"It allows us to adjust and propose new models for the diversification and timing of the origin of living groups," he added.
Gomphos strongly suggests that lagomorphs started diversifying after the big dinosaurs became extinct and that rabbits and rodents have a common ancestor that probably lived among the dinosaurs.
The Mongolian fossil "strengthens the viewpoint that rodents and lagomorphs come from a common ancestor. They're closely related," Rose said. This is a theory that has faded in and out of vogue, he added.
Much of the story lies in the teeth. Gomphos had a pair of incisors in its upper jaw that were arranged like those in lagomorphs, but it also retained a pair of incisors in its lower jaw, a characteristic that is more primitive than any rodent or lagomorph. Other features of the anatomy, however, suggest a rabbit.
"This type of research is like reading a mystery novel," Rougier said. "Fossils are data. They are like the experiments of nature. We go there, we rescue them, we look at their features and we use every one of those features as anyone in history will use an economic report on an old kingdom."
Hopping from rabbits to humans, University of Utah geologist Frank Brown, co-author of the Homo sapiens study, said in a prepared statement that a new look at bones first found in Africa in the late 1960s "pushes back the beginning of anatomically modern humans."
When the bones were first discovered in Ethiopia in 1967, anthropologists estimated they were about 130,000 years old. But a reevaluation by Brown and his colleagues, based on a precise dating of volcanic ash found near the fossils, has now set that date back an additional 65,000 years.
The bones, which now are believed to date to more than 195,000 years ago, are "the oldest well-dated fossils of modern humans [homo sapiens] currently known anywhere in the world," the scientists concluded in a study summary.
More information
For more on the different features of animals, including rabbits and rodents, visit the Animal Diversity Web.
