†Calippus regulus Johnston 1937 (horse)
Synonym: Calippus anatinus Quinn 1955
- Calippus regulus: Its type locality is Grant Lease, which is in a Miocene terrestrial horizon in Texas
- Calippus anatinus: Its type locality is Buckner Ranch Site 1, which is in a Clarendonian terrestrial horizon in the Goliad Formation of Texas.
Ecology: ground dwelling grazer
Average measurements (in mm): P3 14.5 x 14.7, P4 14.5 x 14.7, M1 14.0 x 13.4, p3 14.7 x 8.5, p4 14.7 x 8.5, m1 14.3 x 6.9