which class is thought to have been descended from dinosaurs
Evolution of reptiles 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.
Cladistics Cladistics (/kləˈdɪstɪks/, from Greek κλάδος, cládos, "branch")[1] is an approach to biological classification in which organisms are categorized in groups ("clades") based on the most recent common ancestor. Hypothesized relationships are typically based on shared derived characteristics (synapomorphies) that can be traced to the most recent common ancestor and are not present in more distant groups and ancestors. A key feature of a clade is that all descendants stay in their overarching ancestral clade. For example, if within a cladistic framework the terms monkeys/anthropoidea, animals, fishes/vertebrata and worms/bilateria would be used, these terms would include humans. Radiation results in the generation of new subclades by bifurcation.[2][3][4][5]