He has studied the oldest known fossil of an ancestral turtle, and he says the new interpretation of turtle embryology may fit well with the fossil record. Last year he and colleagues described Odontochelys semitestacea from a fossil collected in 220-million-year-old marine sediments in southwestern China. The turtle had a standard armored underside but not a full shell on its back. Its ribs widened, but its shoulder blades still lay forward of instead of inside the ribs.
Nagashima speculates that the embryonic fold was evolving a bit at a time and maybe hadn’t reached as far around the body in this ancestral turtle as it does today. Clever suggestion, Rieppel says.
To understand turtle history, paleontologists really need more fossils, says Robert Reisz of the University of Toronto’s Mississauga campus in Canada. In the meantime, the new Japanese paper “clarifies a unique evolutionary event, one that gave rise to a really neat group of animals, our beloved turtles.”
lorenzabar of IN @ Oct 27, 2009 22:13:09 PM