[Public domain] via Wikimedia CommonsTo support the high rates of oxygen consumption associated with being warm-blooded, the hearts of birds and mammals must pump rapidly and frequently. These high heart rates are made possible by a network of conductive tissue that spreads across the heart, controlling its contraction. The evolutionary origin of this conductive tissue has long been a mystery; it has never been identified in reptiles, the shared ancestors of birds and mammals, leading scientists to wonder whether the conductive network evolved independently in the two taxa.
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