Skull geometric morphometric analysis among two cottontail rabbits Sylvilagus Gray, 1867 (Mammalia: Lagomorpha)

Abstract

Within the genus Sylvilagus Gray, 1867, Sylvilagus brasiliensis (Linnaeus, 1758) and Sylvilagus floridanus (J.A. Allen, 1890) are some of its recognized species, for whom morphological studies in both species are extensive. Therefore, a comparative study was conducted between the cranial conformation using techniques of geometric morphometrics. For this purpose we studied a total of 31 S. brasiliensis and 16 S. floridanus skulls. Pictures were obtained and 12 anatomical landmarks were situated on the dorsal aspect. There did not appear differences between sexes but indeed between both species, both in size and shape. S. brasiliensis presented a shorter but wider the skull of than S. floridanus. Anatomical points were not particularly important as muscular attachments neither host externally important functional structures (as it might be those related to the view); due to this fact and that both species share similar ecological requirements it is plausible to think that detected differences were merely due to changes derived from the size differences –S. brasiliensis is smaller than S. floridanus-. In other words: the cranial size reduction would not imply a mere reduced form version (a “harmonic reduction”), but it would require heterotopic changes, e.g. a redesign structural derivative of the size reduction. We assume these regional differences in cranial structure to be due more to changes in development patterns between both species rather than a difference in their life strategies, in view of the similar ecological requirements for both.