A recent study concludes that prehistoric birds, unlike modern birds, were cold-blooded  This challenges a widely held view that modern birds descended from warm-blooded birds  The conclusion is based on the existence of growth rings in prehistoric birds' bodily structures, which are thought to be found only in cold-blooded animals  Another study, however, disputes this view
It concludes that prehistoric birds had dense blood vessels in their bones, which suggests that they were active creatures and ttherefore had to be warm-blooded
Modern birds did not evolve from prehistoric species of birds.