Warm-blooded reptiles?

Since the first fossils of dinosaurs have been found, many scientists agreed that these creatures had a metabolism similar to that of modern reptiles. This means that they were ectothermic (internal temperature equal to that of the external environment). However, other following discoveries led to consider the opposite hypothesis, the endothermy.

The major doubts about dinosaur's mechanisms of thermoregulation arise when we consider the species that lived at polar latitudes. In fact, there are different sites in Australia or Russia where it has been discovered a great variety of dinosaurs, which in some cases lived at temperatures close to zero degrees. As an example in Northern Russia, near Kakanaut, many fossils have been extracted from rocks dating back the Cretaceous, of both carnivores (troodontids, dromaeosaurids, tyrannosaurids) and herbivores (hadrosaurids, ankylosauria and others). There have even been found some hadrosaur eggs, which proves that these animals had a sedentary nature.

A recent research by Holly Woodward, Jack Horner and colleagues at Montana State University (published online on PLoS ONE), proved that dinosaurs who lived at polar latitudes weren't physiologically different from other species, on the contrary of what claimed an earlier study, influenced by the lack of a good number of finds.

The endothermy hypothesis could also be supported by the presence of feathers on many dinosaur species, especially on theropods like dromaeosaurids. This group includes the notorious Velociraptor, and is probably a parallel evolutionary line to that of birds, with whom they could share a common ancestor. Structures like feathers or hair are typical in endothermic animals and are important in thermoregulation, as they act insulating the body and making it less influenced by changes in the environmental temperature.

Another study, published on "Science" and guided by researchers of Bonn University and the California Institute of technology, discovered what the internal temperature of sauropods was. This enormous herbivores had a body temperature similar to that of modern mammals, between 36 °C and 38 °C. They analyzed the teeth of these creatures, which contain carbonates made by different isotopes of carbon and oxygen. Since the temperature at which this compound is formed influences the percentage of ¹³C and ¹⁸O that bind together within the tooth, the higher the temperature was, the lower the frequency of this bond was. Analyzing the quantity of these isotopes, they determined the body temperature of these animals.

All these discoveries, but many others too, seem to prove that the most diversified and successful group of reptiles had a physiology similar to that of mammals, a fact that probably allowed them to colonize almost all the available environments.