Equidae is a taxonomic group.
Equidae ( sometimes known as the horse family ) is the taxonomic family of horses and related animals , including the extant horses , donkeys , and zebras , and many other species known only from fossils . Taxonomy ( from [ wiktionary : τάξις , τάξις ] taxis , `` arrangement '' , and [ wiktionary : νόμος , - νομία ] - nomia , `` method '' ) is the science of defining and naming groups of biological organisms on the basis of shared characteristics .