Enamel hypoplasia in Miocene rhinoceroses (Teleoceras) from Nebraska: evidence of severe physiological stress

ABSTRACT

Quarry samples of lower cheek teeth of the Miocene rhinoceros Teleoceras are analyzed for the presence of enamel hypoplasia using macroscopic, thin-section, and scanning electron microscopic techniques. The presence of enamel pits, furrows, and grooves is noted predominantly on, but not limited to, the buccal side of dp4s. The enamel defect is not as common on permanent teeth, but does occur with decreasing frequency on p4s, mls, m2s, and m3s.

Analysis of the formative sequence of deciduous cheek teeth in Teleoceras and the extant rhinoceros Diceros bicornis suggests that the Teleoceras dp4 was developing in the alveolus at the time of birth. Varying degrees of wear on the dp4s exhibiting enamel hypoplasia imply that the defect-producing stress did not result in immediate death. Isolation of the enamel hypoplasia to distinct bands on the Teleoceras dp4s suggests causes linked to non-lethal severe physiological stress due to metabolic disruption or nutritional deficiency occurring at or very near birth. The Teleoceras p4 was probably developing in the alveolus between three and five years of age. The observed p4-hypoplasias appear to reflect physiological stresses not related to weaning, but to some other stressful period such as cow-calf separation prior to the birth of the next offspring.