Phylogenetic relationships of the Cretaceous frog Beelzebufo from Madagascar and the placement of fossil constraints based on temporal and phylogenetic evidence.

The placement of fossil calibrations is ideally based on the phylogenetic analysis of extinct taxa. Another source of information is the temporal variance for a given clade implied by a particular constraint when combined with other, well-supported calibrations. For example, the frog Beelzebufo ampinga from the Cretaceous of Madagascar has been hypothesized to be a crown-group member of the New World subfamily Ceratophryinae, which would support a Late Cretaceous connection with South America. However, phylogenetic analyses and molecular divergence time estimates based on other fossils do not support this placement. We derive a metric, Δt, to quantify temporal divergence among chronograms and find that errors resulting from mis-specified calibrations are localized when additional nodes throughout the tree are properly calibrated. The use of temporal information from molecular data can further assist in testing phylogenetic hypotheses regarding the placement of extinct taxa.