Molecular Clock Fossil Calibration Consistency

Molecular clocks are a controversal subject among paleontologists. They often conclude on rather different results then studies based souly on the fossil record. An example is the proposed early diversification for plancental mammals during the late Mesozoic, rather than a later diversification supported the fossil record. Molecular clocks depend on two assumuptions: 1) clock-like DNA substitution rates and 2) accurate fossil calibration points. A recent article by Near, Meylan and Shaffer in the journal "The American Naturalist" took a look at fossil calibration points in a clade of fossil turtles. They developed a method to assess the consistency of fossil calibration points by cross comparison of various nodes in a cladogram. This unique method may provide a useful tool to help resolve the differences between molecular clock age estimates and fossil record estimates.

Near TJ, Meylan PA, Shaffer HB. 2005. Assessing concordance of fossil calibration points in molecular clock studies: An example using turtles. AMERICAN NATURALIST 165 (2): 137-146.