The phylogeny and taxonomy of Hippopotamidae (Mammalia: Artiodactyla): a review based on morphology and cladistic analysis.    From Wordnik.com.  [More on what I saw at the zoo] Reference

On the origins of Hippopotamidae together with descriptions of two species, a new genus and a new subfamily from the Miocene of Kenya.    From Wordnik.com.  [More on what I saw at the zoo] Reference

Whales probably evolved from anthracobunid artiodactyls, a stem group that may be closely related to Hippopotamidae.    From Wordnik.com.  [PLoS ONE Alerts: New Articles] Reference

Boisserie J-R, Lihoreau F, Brunet M (2005) The position of Hippopotamidae within Cetartiodactyla.    From Wordnik.com.  [PLoS ONE Alerts: New Articles] Reference