Eocene raoellids (Mammalia, Cetartiodactyla) outside the Indian Subcontinent: palaeogeographical implications

Raoellidae are small fossil cetartiodactyls closely related to the Cetacea. Until now undisputable raoellid remains were reported only from the early Middle Eocene of the Indian Subcontinent, although this Indo-Pakistani endemism has been challenged by several recent works describing potential raoellids from Mongolia, Myanmar and China. In this contribution we address the question of raoellid taxonomic content and definition, through a revision of the dental features of the family. This work, which includes a revision of the putative raoellid material from outside Indo-Pakistan, is primarily based on a re-examination of 'suoid' specimens from Shanghuang (Middle Eocene, coastal China). Our results indicate that the Shanghuang material both substantiates the youngest and easternmost occurrence of Raoellidae and represents the only unquestionable record of raoellids outside the Indian Subcontinent at present. This significantly extends the geographical and chronological range of the family. The occurrence of a raoellid species in the Middle Eocene of coastal China implies that raoellids dispersed from the Indian Subcontinent to eastern Asia during Early or Middle Eocene time. This tempers classical hypotheses of Middle Eocene Indian endemism and eastern Asian provincialism.