By Will Dunham WASHINGTON (Reuters) – 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. Thes…