The Size of Mammal Ancestors' Ear Canals Reveal When Warm-Bloodedness Evolved
Published:27 Jul.2022 Source:Field Museum
One of the things that makes mammals, mammals is that we're warm-blooded -- our bodies have high metabolisms that maintain our internal temperature independent of our surroundings, unlike cold-blooded animals like lizards that have to bask in the sun. Among modern animals, only mammals and birds are warm-blooded, and our ability to keep ourselves warm has enabled mammals to survive in icy weather and make long migrations. But it's been a mystery exactly when mammals evolved their high metabolisms. In a new study in Nature, scientists point to an unlikely source for determining when ancient mammal ancestors became warm-blooded: the size of tiny structures in their inner ears.
It's hard to tell whether a fossil animal was warm-blooded -- we can't take the temperature of a creature that lived hundreds of millions of years ago, and we can only guess at whether its behavior matched an active, warm-blooded metabolism or a slower cold-blooded one. But a team of researchers led by London's Natural History Museum, the University of Lisbon's Instituto Superior Técnico, and the Field Museum in Chicago realized that animals' ears provide an indirect clue about their body temperatures.