Showing posts with label fossil turtles. Show all posts
Showing posts with label fossil turtles. Show all posts

Tuesday, July 26, 2011

Turtles + Lizards Form A Clade?

Famous for their sluggishness, turtles have been slow to give up the secrets of their evolution and place on the evolutionary tree. For decades, paleontologists and molecular biologists have disagreed about whether turtles are more closely related to birds and crocodiles or to lizards. Now, two scientists from the Mount Desert Island Biological Laboratory in Bar Harbor, Maine, and their colleagues from Dartmouth College and Harvard and Yale Universities have developed a new technique using microRNAs for classifying animals, and the secret is out. Turtles are closer kin to lizards than crocodiles.

To reach their conclusion, published in Nature News and Biology Letters, the research team looked at a newly discovered class of molecules called microRNA. Most of the genetic material or DNA that scientists study provides the code for building proteins, large molecules that form an essential part of every organism. But microRNAs are much smaller molecules that can switch genes on and off and regulate protein production. They are also remarkably similar within related animal groups and provide important clues for identification.

“Different microRNAs develop fairly rapidly in different animal species over time, but once developed, they then remain virtually unchanged,” said Kevin Peterson, a paleobiologist at MDIBL and Dartmouth College. “They provide a kind of molecular map that allows us to trace a species’ evolution.”

Peterson worked with Ben King, a bioinformatician at MDIBL. “My role in the study was to enhance our software so we could find new and unique microRNAs in the lizard genome,” King said. “We identified 77 new microRNA families, and four of these turned out to also be expressed in the painted turtle. So we had the evidence we needed to say that turtles are a sister group to lizards and not crocodiles.”

Though few creatures have been as puzzling as the turtle, the research team plans to use its microRNA analysis on other animals to help determine their origins and relationships as well. It is also developing a web-based platform to share the software with other researchers around the world.

In addition to King and Peterson, the research team included Tyler Lyson and Jacques Gauthier from Yale University, Eric Sperling from Harvard University, and Alysha Heimberg from Dartmouth College.

Tyler R. Lyson, Erik A. Sperling, Alysha M. Heimberg, Jacques A. Gauthier, Benjamin L. King and Kevin J. Peterson. 2011. MicroRNAs support a turtle + lizard clade. Biology Letters doi: 10.1098/rsbl.2011.0477.

Tuesday, November 30, 2010

Holocene Horned Turtles

The Lord Howe Island Horned Turtle,  
Meiolania platyceps, is probably the
best known member of the Meiolaniidae.
It is difficult to describe the uniqueness of turtles.  We all consider them reptiles, but technically, they may not be. See post What are Turtles? While only a few hundred species exists today, the number and diversity of turtles was much greater. The very large (some may have exceeded 3 m) horned turtles (family Meiolaniidae) are members of the Centrocryptodira (Eucryptodire) clade that includes many extinct forms. They are thought to have been herbivorous and were heavily armored with bony frills on their heads and club-like tails. Fossils are distributed in time between the Eocene and the Pleistocene, and the fossils are distributed in space in Australasia and South America, suggesting they evolved prior to the breakup of Gondwana. Now it appears the meiolaniid turtles survived into the Holocene and were eaten by humans.

Arthur W. White at the University of New South Wales, and colleagues have now found remains of meiolaniid turtles at the archeological site at Teouma on the island of Efate in Vanuatu (in the Coral Sea). The meiolaniid turtles were found in cemetery and midden layers that dated between 3100 and 2800 years before present (YBP). The site is close to the coastal inlet of Teouma Bay, and on the eastern bank of a stream fringed by mangrove. The people who lived at this site ate a variety of domesticated animals as well as animals gathered from the environment. Among the remains recovered were limb bones and shell fragments of a new species of meiolaniid turte. The cut marks provide evidence that the turtles were butchered and the lack of skulls and caudal vertebrae suggest the turtles were not prepared at the site. The authors name the new species Meiolania damelipi after Willy Damelip of Ambrym Island, Vanuatu . He was a local archaeologist at the Teouma site. The authors consider its placement in the genus Meiolania tentative.

Gafany, E. S. 1996. The postcranial morphology of Meiolania platyceps and a review of the Meiolaniidae. Bulletin of the American Museum of Natural History, no. 229. 165 pp.

White, A. W., T. H. Worthy, S, Hawkins, S. Bedford, and M. Spriggs. 2010. Megafaunal meiolaniid horned turtles survived until early human settlement in Vanuatu, Southwest Pacific. Proceedings of the National Academy of Sciences 107(35): 15512-15516.