Thermoregulation in Extant Reptiles: Patterns, Constraints, and Evolutionary Implications

The Class Reptilia have traditionally been classified as ectothermic vertebrates; however, accumulating evidence demonstrates that thermoregulation in extant reptiles is physiologically, ecologically and evolutionarily heterogeneous. Although the taxon Reptilia is paraphyletic under cladistic taxonomy, the term remains useful when referring to extant non-avian, non-mammalian sauropsids, including Testudines, Crocodylia, Rhynchocephalia, and Squamata. This review synthesizes current knowledge on reptilian thermoregulation, emphasizing ectothermy, heterothermy, mesothermy, and inertial homeothermy (gigantothermy). We examine the roles of body size, metabolic rate, habitat, phylogenetic inertia, and evolutionary constraints in shaping thermal strategies. Special attention is given to exceptional cases such as leatherback sea turtles and tuatara, as well as implications for extinct reptilian lineages, including Dinosauria and marine reptiles. We argue that most extant reptiles are better characterized as obligate ectothermic heterotherms rather than simple ectotherms and discuss how ongoing anthropogenic climate change may challenge their thermal ecology and evolutionary resilience.