A new species of Amphirhagatherium (Choeropotamidae, Artiodactyla, Mammalia) from the Late Eocene Headon Hill Formation of southern England and phylogeny of endemic European 'anthracotherioids'

A new species of artiodactyl, Amphirhagatherium edwardsi sp. nov., is descr ibed from the Late Eocene (Priabonian) Headon Hill Formation of the Hampshi re Basin, southern England. The Haplobunodontidae, in which Amphirhagatheri um is usually placed, has recently been combined with the monotypic Choerop otamidae, both essentially European endemic families. New anatomical inform ation is forthcoming from both the new species and recently published data on related species. A cladistic analysis of taxa included in the two famili es, the possible anthracotheriid Thaumastognathus and the enigmatic Tapirul us, was conducted to test the relationships implied by observed morphologic al similarities. The genus Anthracobunodon is shown to be paraphyletic and is here synonymized with Amphirhagatherium. Choeropotamus and Thaumastognat hus are sister taxa nested with three species of Haplobunodon. Haplobunodon is paraphyletic and polyphyletic, but this clade is too weakly resolved in ternally for reliable taxonomic changes. Lophiobunodon and Tapirulus are si ster taxa nested with a fourth species of Haplobunodon. The synonymy of the Haplobunodontidae with the Choeropotamidae is upheld and close relationshi p of the family with the Anthracotheriidae is argued to be unlikely. Choero potamids are inferred to have had mixed frugivorous and browsing herbivorou s diets. They seem to have diversified in the northern parts of Europe, som e terminal taxa having originated following southward dispersal.