The coiled channels deep within the ears of fossilized and modern animals reveals that mammals became warm-blooded 233 million years ago.
are a series of coiled tubes filled with a liquid that help an animal track the movements and spatial location of its head, which is crucial for navigation, balance, and motor coordination. The fluid in these canals becomes runnier at warmer body temperatures.
Canals fine-tuned for warm temperatures suggest that their animal owner can create its own internal heat. By looking at the shape and relative size of the inner ear, the researchers say, it’s possible to predict whether an animal was warm- or cold-blooded. When the team used these inner ear measurements to calculate the animals’ body temperatures, they found that their estimates for modern species were very similar to published body temperature data. Based on their body temperature estimates for extinct animals, the team concluded that the transition to warm-bloodedness took place over a 1 million year period, before the first true mammals emerged roughly 200 million years ago.
The study authors suspect that the emergence of endothermy in mammals is tied to genetic changes that resulted in a physiological process that allowed the animal to become “a factory that’s continuously pumping heat,” and the evolution of fur for keeping that precious heat from dissipating into the surrounding air, explains Araújo.The new technique is more accurate for assessing groups of animals than predicting body temperature in individual species.
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