Periotic anatomy ofArsinoitherium(Mammalia, Embrithopoda) and its phylogenetic implications

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Abstract
The description of two previously unknown petrosal specimens of Arsinoitherium highlights a number of derived ungulate characteristics. A phylogenetic analysis based on ungulate periotic anatomy implies that perissodactyls, sirenians, proboscideans, and arsinoitheres are united by the absence of a subarcuate fossa, derived course of the facial nerve, and open stylomastoid foramen. The form of the fenestra ovalis and fenestra rotundum links proboscideans, sirenians, and arsinoitheres. Absence of a discrete cochlea aqueduct implies a sister-group relationship between arsinoitheres and proboscideans. Artiodactyls are primitive in all respects except for the complete enclosure of the epitympanic recess by the tegmen tympani. The phylogenetic position of hyracoids is equivocal with the possibility of amastoidy and absence of promontorial grooves being independently derived.