May 30 2013
Old Westbury, N.Y. (May 30, 2013)
— An anatomy professor at New York Institute of Technology College of Osteopathic Medicine
has contributed to a published study that provides clues on the early evolution of one of nature’s unique developments: the turtle shell.
Assistant Professor Gaberiel Bever, Ph.D., is part of a team maintaining that the 260-million-year-old reptile from South Africa, Eunotosaurus africanus, is the earliest known version of a turtle, in part because of its distinctive T-shaped ribs. Those ribs, said Bever, represent an early step in the evolutionary development of the carapace, the hard, upper part of the shell of today’s turtles.
The team’s findings are published in a paper, “Evolutionary Origin of the Turtle Shell” in Current Biology.
“Turtle origins have been a hot topic for a long time,” Bever said, noting that scientists disagree on where turtles fit on the tree of life in part because of a disagreement stemming from the lack of clear transitional fossils – those animals whose remains indicate an intermediate state between ancestors and descendants. Bever added that the differences between molecular studies of living animals and anatomical studies of fossils and living animals also contribute to the disputes about turtle origins.
“Our data supports Eunotosaurus as an important link in that evolutionary chain that eventually produced modern turtles,” said Bever, who is also a research associate with the Division of Paleontology in the American Museum of Natural History. “This is an earlier version of the turtle.”
Previously, the oldest known turtle was a 220-million-year-old reptile from China described in 2008. Establishing Eunotosaurus as part of the turtle lineage thus pushes the age of this evolutionary story back another 40 million years.
Interestingly, Eunotosaurus has been known to science since the 19th century, but Bever said its turtle features were either overlooked or dismissed. One reason, he noted, was that the Eunotosaurus did not have a skin containing bones, which scientists long held was a necessary evolutionary step in the development of the turtle shell. “We were the first to actually include Eunotosaurus in an evolutionary analysis with turtles,” Bever said. “And as soon as we did that, Eunotosaurus was revealed as closely related to everything currently accepted as a turtle.”
(Watch an animation of the turtle's shell development here
Because Eunotosaurus lacks many of the iconic turtle features, such as the portion of the hard shell covering its belly, or plastron, it will remain a controversial species, at least for now. But Bever maintains that the first steps in an evolutionary transformation are likely to be subtle and that the distinctive ribs are strong evidence that Eunotosaurus is an early chapter in the turtle story.
This study is part of a larger research project on reptile anatomy and evolution that includes fieldwork in the Karoo Basin of South Africa, museum research all over the world, and laboratory research at NYIT. He next expects to release a study on the evolution of the turtle’s skull.
Bever’s colleagues on the Current Biology paper are first author Tyler Lyson of Yale University and the Smithsonian Institution, Torsten Scheyer of the Paleontology Institute and Museum in Zurich, and Allison Hsiang and Jacques Gauthier of Yale.
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