Scientists have answered a longstanding question about mammalian evolution, examining ear anatomy of living and extinct mammals and their close relatives to determine when warm-bloodedness - a trait integral to the lineage's success - first emerged.
Researchers said on Wednesday that the reduced size of inner ear structures called semicircular canals - small, fluid-filled tubes that help in keeping balance - in fossils of mammal forerunners showed that warm-bloodedness, called endothermy, arose roughly 233 million years ago during the Triassic Period.
Mammalian endothermy arrived at an eventful evolutionary moment, with dinosaurs and flying reptiles called pterosaurs - creatures that long would dominate ecosystems - first appearing at about that time. Endothermy offered advantages. Endothermy emerged relatively quickly, in perhaps less than a million years, rather than a longer, gradual process, said paleontologist and study co-lead author Romain David of the Natural History Museum in London.
Determining when endothermy originated through fossils has been tough. As Araújo noted: "We cannot stick thermometers in the armpit of your pet Dimetrodon, right?"