Skull ontogeny of the pronghorn (Antilocapra americana) in the comparative context of native North American ungulates

The pronghorn (Antilocapra americana (Ord, 1815)) is the single survivor of a largely extinct, isolated pecoran lineage (Antilocapridae) native to North America. We describe postnatal ontogeny of its skull in a comparative framework inclusive of representatives of other typical North American ungulate linages, all of which partially overlap in geographic distribution and share habitat with A. americana. To describe allometric growth, we took 23 linear cranial measurements in 30 specimens of A. americana and applied bi- and multi-variate statistics. The skull of A. americana generally grew with negative rates in width and height dimensions, and with positive rates in length, including an elongation of rostrum, particularly the nasals, and a relative narrowing of the braincase. We compared skull development in A. americana with development in two cervids (white-tailed deer (Odocoileus virginianus (Zimmermann, 1780)) and wapiti (Cervus canadensis Erxleben, 1777)) and two bovids (bighorn sheep (Ovis canadensis Shaw, 1804) and American bison (Bison bison (Linnaeus, 1758))). The multivariate ontogenetic trajectory of A. americana overlapped greatly with that of Odocoileus virginianus, and differed from the other species in varying degrees. These results indicated an essentially convergent pattern of skull growth with species showing important functional similarities, such as cervids of comparable size and feeding habits.