Revealing The Evolutionary History Of Threatened Sea Turtles
It's confirmed: Even though flatback turtles dine on fish, shrimp, and mollusks, they are closely related to primarily herbivorous green sea turtles. New genetic research carried out by Eugenia Naro-Maciel, a Marine Biodiversity Scientist at the Center for Biodiversity and Conservation at the American Museum of Natural History, and colleagues clarifies our understanding of the evolutionary relationships among all seven sea turtle species.
Naro-Maciel and colleagues used five nuclear DNA markers and two mitochondrial markers to test the evolutionary relationships of all species of marine turtles-leatherback, flatback, green, hawksbill, loggerhead, Kemp's Ridley, and Olive Ridley-and four 'outgroups,' or more distantly related animals. The results formed a well-supported phylogenetic tree, or cladogram, that tells the story of sea turtle evolution and is reported in the journal Molecular Phylogenetics and Evolution.
"The evolution of a specialized diet appears to have occurred three times, independently," says Naro-Maciel. "Many sea turtles are carnivorous generalists. However, hawksbills tend to have a diet of glass-they eat toxic sponges-while the leatherback consumes jellyfish and the green grazes mainly on algae or sea grass." Each of the species with specialized diets is positioned uniquely in the evolutionary tree.
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'Missing link' fossil stuck its neck out
It didn't just have protolimbs, it had a mobile neck as well. More details have emerged about the anatomy of Tiktaalik, the "fishopod" that bridges the gap in evolutionary history between swimming fish and four-legged land-dwelling animals. The new findings bolster its position as a key transition or "missing link" fossil.
The 375-million-year-old fossils first created a stir in 2006, when analyses revealed an organism with features intermediate between fish and land animals, such as wrist-like bone structures at the tips of its fins. The structures would have helped it to crawl in shallow water, qualifying as definite precursors to animal legs.
The initial investigations also revealed a mobile neck, and bony coverings of the gills that suggested the creature could breathe air - making it the most complete fossil of this intermediary stage in evolutionary history.