Over a half-century ago, C. W. Hibbard proposed a climate theory based on imported living giant tortoises (Geochelone) as proxies that suggested the climate adaptations of giant fossil tortoises of the Cenozoic Era (65.5 million years ago to present) were subtropical or tropical across much of North America. This has been a prominent and enduring paleoclimate theory. We show that incorrect assumptions and other problems invalidate this theory. Seven alternative concepts are presented that suggest North American fossil giant tortoises could have evolved necessary adaptations including cold-adaptive morphology, behavioural thermoregulation, burrowing, use of caves as shelters, tolerance of prolonged cessation of food consumption, cryoprotection and supercooling (protection from freezing), and gigantothermy (metabolic and structural thermoregulation) to survive northern winters and in montane areas. This study illustrates the potential danger of using an inappropriate proxy to predict past climates.
Moll, D; Brown, LE
Reinterpretation of the Climatic Adaptation of Giant Fossil Tortoises in North America
Herpetological Journal