The beginning of the equoid radiation

Abstract

With the benefit of newly collected material, primitive equoids are analysed cladistically to determine the detailed relationships of the families Equidae and Palaeotheriidac. The most primitive equid is shown to be Pliolophus. Cymbalophus cuniculus and 'Hyracotherium' sandrae are closely related stem equoids. The Pachynolophidac are not equoids, but most closely related to the primitive tapiromorph family Isectolophidae. Hallensia is sister to these two and therefore also not an equoid. Hyracotherium is restricted to the type species H. leporinum Owen, part of whose lower dentition is made known for the first time. It is closest to a restricted genus Propachynolophus within the family Palaeotheriidae. The original concept of Propachynolophus is polyphyletic. Using the cladogram, newly extended stratigraphic ranges and palaeogeography, an attempt is made to reconstruct the very early speciation and biogeographical history of the group. 'Cymbalophus' hookeri Godinot is recombined in the genus Pachynolophus and 'H.' pernix in Pliolophus. Hallensia louisi sp. nov. and Propachynolophus levei sp. nov. are described. © 1994 The Linnean Society of London.