Absence of the Guttural Pouch in a Newborn Indian Rhinoceros Demonstrated by Three-Dimensional Image Observations

Abstract

CT scanning and its related three-dimensional image techniques were applied for a carcass head of a newborn Indian rhinoceros (Rhinoceros unicornis) to clarify if the guttural pouch is well-developed or not in the early growth stages of this species. Observations from the sections of the CT three-dimensional reconstructed image reveal that the guttural pouch is not present around the stylohyoid bone in a new born Indian rhinoceros. Since the absence of the guttural pouch has been confirmed also in adult rhinoceros, we can point out that the guttural pouch does not disappear during the growth stages, but is originally absent in the newborn. Although the well-developed guttural pouch in the horse and ass has attracted anatomists, we can conclude that the guttural pouch is not commonly observed in the perissodactyls, but in a few species of Equus, and that the guttural pouch is adapted only to restricted roles in the smaller taxa within perissodactyls.