Allometric studies on the skull of living and fossil Equidae (Mammalia: Perissodactyla)

Abstract

ABSTRACT New material for a study of the allometric growth of muzzle length versus braincase length in the skull of living and fossil Equidae is presented. The classical allometric growth formula y = bx α is used in its logarithmic transformation log y = α log x + log b (or Y = αX + B), where y is muzzle length and x is braincase length. During fetal development of the skull of the domestic horse the a value decreases steadily from 1.58 to 1.00 at the time of birth, and subsequently it remains at 1.00 (static allometry). Phylogenetic changes in skull dimensions are explained in terms of the allometric equation and two explanations for these changes are offered. The first suggests that α and B remain constant while X and Y increase. The second suggests that α remains constant while B varies: this brings about a change in skull shape. We propose a provisional interpretation of this evolution at the level of genetic determination.