<P> The evolution of birds is thought to have begun in the Jurassic Period , with the earliest birds derived from theropod dinosaurs . Birds are categorized as a biological class , Aves . The earliest known species in Aves is Archaeopteryx lithographica , from the Late Jurassic period . Modern phylogenetics place birds in the dinosaur clade Theropoda . According to the current consensus , Aves and Crocodilia are the sole living members of an unranked clade , the Archosauria . </P>
<P> The evolution of birds is thought to have begun in the Jurassic Period , with the earliest birds derived from theropod dinosaurs . Birds are categorized as a biological class , Aves . The earliest known species in Aves is Archaeopteryx lithographica , from the Late Jurassic period . Modern phylogenetics place birds in the dinosaur clade Theropoda . According to the current consensus , Aves and Crocodilia are the sole living members of an unranked clade , the Archosauria . </P>
which class is thought to have been descended from dinosaurs
which class is thought to have been descended from dinosaurs
birds
birds