Species Taxonomy, Phylogeny, and Biogeography of the Brontotheriidae (Mammalia: Perissodactyla)

A species-level monograph diagnoses Brontotheriidae by an abbreviated face, elongate postorbital cranium and characteristic upper molars, while showing that giant size and frontonasal appendages occur in only part of the family.

Brontotheriidae is an Eocene perissodactyl family revised at species level; its deeper position within Perissodactyla remains less certain than the family’s internal membership.

The atlas’s 53–34 Ma occurrence envelope is provisional; the systematic monograph independently supports an Eocene family record but does not make those numeric endpoints exact origination or extinction times.

Brontotheres were terrestrial Eocene herbivores with folivorous dental evidence and body sizes ranging from small early forms to rhinoceros-sized taxa; one habitat or gait is not generalized across the family.

The revised family is recorded from North America and Asia and rarely eastern Europe; inferred intercontinental exchanges do not establish a single observed dispersal direction.