How Old are Turtles? A Paleontological Perspective.
In a recent paper published in Journal of Vertebrate Paleontology, Danilov and Parham present an interesting analysis of two Middle Jurassic fossil turtle lineages. They estimate the phylogenetic relationships of these extinct lineages using discretely coded morphological characters, and bracket the estimated age for the crown node of all living turtles based on the oldest fossils. As the the figure from their paper shows, there has been debate as to the timing of turtle (Testudines) diversification. Previous estimates range from the Triassic-Jurassic boundary to the Late Jurassic.
Recent molecular divergence time estimates from Charles Marshall (presented at the 2008 Evolution meetings in Minnesota) and a team composed of Peter Meylan, Brad Shaffer, and yours truly result in an age for living turtles that dates to the Triassic-Jurassic boundary (our study), or well into the Triassic (Marshall's study). Regardless of this disagreement among molecular estimates and inferences from the fossil record, Danilov and Parham's paper presents a nice summary of the problem and a clever way to investigate the origin of turtles with the fossil record.
Danilov, I. G. and J. F. Parham 2008. A reassessment of some poorly known turtles from the Middle Jurassic of China, with comments on the antiquity of extant turtles. Journal of Vertebrate Paleontology 28: 306-318.
Dechronization is authored by evolutionary biologists interested in the development and application of methods for estimating phylogeny and making phylogeny-based inferences. The goal of the blog is to provide a forum for discussion of the latest research and methods, while also providing anecdotes, tidbits of natural history, and other related information.