MORE DNA SUPPORT FOR A CETACEA HIPPOPOTAMIDAE CLADE - THE BLOOD-CLOTTING PROTEIN GENE GAMMA-FIBRINOGEN

Recent phylogenetic analyses of DNA sequences suggest that cetaceans ( whales) and hippopotamid artiodactyls (hippos) are extant sister taxa. Consequently, the shared aquatic specializations of these taxa may be synapomorphies. This molecular view is contradicted by paleontologica l data that overwhelmingly support a monophyletic Artiodactyla (even-t oed ungulates) and a close relationship between Cetacea and extinct me sonychian ungulates. According to the fossil evidence, molecular, beha vioral, and anatomical resemblances between hippos and whales are inte rpreted as convergences or primitive retentions. In this report, compe ting interpretations of whale origins are tested through phylogenetic analyses of the blood-clotting protein gene gamma-fibrinogen from ceta ceans, artiodactyls, perissodactyls (odd-toed ungulates), and carnivor es (cats, dogs, and kin). In combination with published DNA sequences, the gamma-fibrinogen data unambiguously support a hippo/whale clade a nd are inconsistent with the palep ontological perspective. If the phy logeny favored by fossil evidence is accepted, the convergence at the DNA level between Cetacea and Hippopotamidae is remarkable in its dist ribution across three genetic loci: gamma-fibrinogen, the linked milk casein genes, and mitochondrial cytochrome b.