After Evander, 1989, Prothero & Shubin, 1989 and McKenna & Bell, 1997
<==o †Protohippini Gidley, 1907 |--o †Protohippus Leidy, 1858 | |-- †P. vetus | |-- †P. parditus | |-- †P. supremus | |-- †P. simus [P. supremus] | `-- †P. gidleyi `--o †Calippus Matthew & Stirton, 1930 |?- †C. circulus |-- †C. martini |-- †C. cerasinus |-- †C. hondurensis |-- †C. maccartyi |-- (Grammohippus) `--o (?Calippus) |--+-- †C. proplacidus | `-- †C. placidus `--+-- †C. regulus `--+-- †C. sp. `-- †C. elachistus
Reference(s):
- Carroll, R. L., 1988: Vertebrate paleontology and evolution.
–W. H. Freeman and company, New York, 1988, 698. - Carroll, R. L., 1988: Appendix. 594-648.
in Carroll, R. L., 1988: Vertebrate paleontology and evolution.
–W. H. Freeman and company, New York, 1988, 698. - Evander, R. L., 1989: Phylogeny of the family Equidae. 109-127.
in Prothero, D. R. & Schoch, R. M., (eds.) 1989: The evolution of perissodactyls.
–Oxford University Press, New York, New York & Oxford, England, 1989, ix-537 - Gazin, C. L., 1976: Mammalian faunal zones of the Bridger Middle Eocene.
–Smithsonian Contributions to Paleobiology: No. 26, pp. iv-25 - McKenna, M. C. & Bell, S. K., (eds.) 1997: Classification of mammals – above the species level.
–Columbia University Press, New York, 1997, xii-631 - Prothero, D. R. & Schoch, R. M., (eds.) 1989: The evolution of perissodactyls.
–Oxford University Press, New York, New York & Oxford, England, 1989, ix-537