Biology of North American tortoises

Chelonians have fascinated people for centuries and have been the object of biological studies for nearly as long. Perhaps the long life span and harmless demeanor of most species contribute to their wide appeal. they also represent a link to the distant past because their characteristic shell separated this line of ectotherms from all other reptiles and all other animals in the age of dinosaurs (Pough et al. 1989). However, the origins of chelonians remain a mystery.