When Did Warm Blooded Animals Evolve?

Traditionally, scientists believed that the first true warm-blooded animals were mammal ancestors that appeared around 270 million years ago. Birds would evolve from non-avian dinosaurs a bit later, independently evolving a similar metabolism.

What led to the evolution of warm-blooded animals?

It has been hypothesized that warm-bloodedness evolved in mammals and birds because it provided defense against fungal infections. Very few fungi can survive the body temperatures of warm-blooded animals. By comparison, insects, reptiles, and amphibians are plagued by fungal infections.

When did birds evolve warm blood?

The ancestors of modern birds living in Canada 75 million-years-ago became warm blooded very early in their evolution, a study of dinosaur eggshells revealed. Experts from the Hebrew University of Jerusalem and Yale University studied the chemical bonds of the shells to find the body temperature of the animal inside.