Dinosaur success in the Triassic: a noncompetitive ecological model.

Abstract

The initial radiation of the dinosaurs in the Triassic (c.200 M yr BP) has been generally regarded as a result of successful competition with the previously dominant mammal-like reptiles. A detailed review, including estimates of relative abundance, gives a different picture of the pattern of faunal replacements. 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 dinosaurs demonstrated their superiority over mammal-like reptiles in massive competitive take-overs. Throughout most of the Triassic, the thecodontians shared carnivore adaptive zones with advanced mammal-like reptiles (cynodonts) until the latter became extinct (random processes, early to late Triassic). Among herbivores, the dicynodont mammal-like reptiles were largely replaced by diademodontoid mammal-like reptiles and rhynchosaurs (differential survival, middle to late Triassic). These groups then became extinct and dinosaurs replaced them and radiated rapidly (opportunism, latest Triassic). The late Triassic extinctions may be linked with floral and climatic changes. Explanations of dinosaur success based on the competitive superiority of their thermoregulation or locomotory capability are unnecessary.-from Author