The Evolution of Dinosaurs

Abstract

The ascendancy of dinosaurs on land near the close of the Triassic now\rappears to have been as accidental and opportunistic as their demise and replacement by therian mammals at the end of the Cretaceous. The\rdinosaurian radiation, launched by 1-meter-long bipeds, was slower in\rtempo and more restricted in adaptive scope than that of therian mammals.\rA notable exception was the evolution of birds from small-bodied predatory dinosaurs, which involved a dramatic decrease in body size.\rRecurring phylogenetic trends among dinosaurs include, to the contrary,\rincrease in body size. There is no evidence for co-evolution between\rpredators and prey or between herbivores and flowering plants. As the major land masses drifted apart, dinosaurian biogeography was molded\rmore by regional extinction and intercontinental dispersal than by the breakup sequence of Pangaea.