No matter what you call them – Eohippus, Hyracotherium, or something else – most everyone is familiar with the diminutive “dawn horses” of the Eocene. Sure, dinosaurs get better press, but the connection of these small hoofed mammals to the modern horse (Equus) has turned them into minor paleontological celebrities. In fact, these horses have featured as evolutionary icons for over a century thanks to the perception – long ago proven wrong – that these unassuming creatures initiated a single-file evolutionary march to today’s beloved beast of burden.

Traditionally the relationship of the dawn horses to Equus has been represented by a straight line, either literally or through a series of graded transitional forms. Given this imagery it would be expected