I photographed these turtles about 10 days ago in Lake Artemesia in College Park, Maryland. The one on the left is an eastern painted turtle, (Chrysemys picta picta), while the one on the right is a red-eared slider (Trachemys scripta elegans). The piece of log they were on is a favorite basking spot of the turtles in the lake, for I often see at least one on it.
Although one is tempted to think that the ancestors of extant turtles were aquatic and that some of their descendants evolved to become terrestrial, a recent study suggests the opposite. Joyce & Gauthier1 demonstrated that extant turtles have different forelimb morphologies depending on whether they are aquatic or terrestrial (shorter hands on land for walking, longer hands in water for swimming). When they applied this analysis to the forelimbs of two of the closest extinct relatives of turtles, the results indicated that the earliest turtles were land animals.
More information on these turtles and turtle evolution:
Red-eared slider (Trachemys scripta elegans)
Amphibians and Reptiles of Long Island, Staten Island and Manhattan
Fossil Turtle Newsletter
Transitional Vertebrate Fossils FAQ
Appreciations to Butch Norden of Maryland DNR for his help with the identifications.
1. Joyce, W.G. & Gauthier, J.A. 2004. Palaeoecology of Triassic stem turtles sheds new light on turtle origins. Proc. R. Soc. Lond. B, 271:1–5. full text pdf
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