Radiation and Divergence Times of Batoidea.

We present a time-scaled analysis based on morphological characters to estimate the divergence ages for the major batoid clades. Two approaches were used: tip-dating, which allows the extinct taxa to be included as terminals, assessing the phylogenetic relations and their divergence time simultaneously; and basic and minimum branch length ('a posteriori' methods) that date a pre-existing unscaled topology, given a set of stratigraphic data for the taxa involved. We used stratigraphic indexes to compare the divergence ages recovered by both methods. The tip-dating approach obtained a more resolved topology and slightly better stratigraphic index scores than the other methods. Overall the tip-dating analysis recovered slightly earlier divergence ages than the rest of the time dating analyses and the known fossil record of the groups. However, these divergence ages were not as old as those estimated by molecular analysis. Our results suggest the diversity increase through the Late Jurassic–Early Cretaceous might not be gradual, and that Early Cretaceous diversity could be significantly higher. As several divergence events are placed in the Early Cretaceous, there is a suggestion that an active period of cladogenesis leads to the Late Cretaceous high diversity. The last divergence events recovered by the present analysis occurred in the Paleogene and led to the extant groups of batoids. [ABSTRACT FROM AUTHOR]