Population Dynamics of Archaeohippus blackbergi (Mammalia; Equidae) from the Miocene Thomas Farm Fossil Site of Florida

Abstract

The Thomas Farm fossil site, Gilchrist County, Florida, is the most fossiliferous Hemingfordian terrestrial site east of the Mississippi River. Taphonomy indicates that the formation of the fossil deposit occurred over a period of at most thousands of years, a geologic instant. Thomas Farm contains one of the earliest and numerically largest populations of the small equid Archaeohippus. Although the sample of mandibles is small (MNI=30), I was able to recognize nine age grades for Archaeohippus blackbergi. As the age at which a female Equus gives birth to her first offspring (3-3.5 years) approximately correlates with eruption of the third molar (3.5-4 years), it is estimated from tooth eruption data that a female A. blackbergi yielded her first foal between 1.5-2 years of age. A mortality spike for individuals with m3 coming into occlusion is interpreted as representing mortality due to intraspecific combat between males. Potential longevity for A. blackbergi is estimated at about 5 years.