Dinosaur Success in the Triassic: A Noncompetitive Ecological Model

Abstract

The initial radiation of the dinosaurs in the Triassic period (about 200 million years ago) has been generally regarded as a result of successful competition with the previously dominant mammal-like reptiles. A detailed review of major terrestrial reptile faunas of the Permo-Triassic, including estimates of relative abundance, gives a different picture of the pattern of faunal replacements. Dinosaurs only appeared as dominant faunal elements in the latest Triassic after the disappearance of several groups of mammal-like reptiles, thecondontians (ancestors of dinosaurs and other archosaurs), and rhynchosaurs (medium-sized herbivores). The concepts of differential survival (competitive) and opportunistic ecological replacement of higher taxonomic categories are contrasted (the latter involves chance radiation to fill adaptive zones that are already empty), and they are applied to the fossil record. There is no evidence that either thecodontians or dinosaur demonstrated their superiority over mammal-like r...