The phenomenon of psilothermy in the biology of vertebrates

The analysis of specific data on body temperatures and the principles of organization of thermobiological statuses in different groups of vertebrates made it possible to identify and describe the basic property of vertebrates that has become the organizing force of their biology, starting with reptiles. This is psilothermia, a thermoregulatory reaction that directs animals to raise their body temperature (usually above 28-30 °C). It is also a type of thermobiological status in which animals constantly or part of the time during the day raise and keep their body temperature above 28-30°. They do it through heat coming either from outside the body ("relative" ectothermy, bradymetabolic psilothermy, “potential homeothermy" of modern reptiles), or from inside by endogenous thermogenesis (mesometabolic and tachymetabolic psilothermy). That is, they are different degrees of manifestation of endothermy in many extinct groups of reptiles - archosauromorphs, archosaurs, dinosaurs, advanced theriodonts, as well as in birds and mammals). An alternative to psilothermy and the initial condition is hamilothermy, a type of thermobiological status in which animals do not show a psilothermic reaction, resulting in a body temperature that differs little from ambient temperatures, most often below 28-30°. These are fish and amphibians. The mechanism of psilothermy described by us is the most important, basic, fundamental property of higher vertebrates.