The Origins of Dinosaurs in the Triassic

The origins of Dinosauria: much ado about nothing

Author:

Langer

Abstract:

Research this century has greatly improved our knowledge of the origin and early radiation of dinosaurs. The unearthing of several new dinosaurs and close outgroups from Triassic rocks from various parts of the world, coupled with improved phylogenetic analyses, has set a basic framework in terms of timing of events and macroevolutionary patterns. However, important parts of the early dinosauromorph evolutionary history are still poorly understood, rendering uncertain the phylogenetic position of silesaurids as either non-dinosaur Dinosauriformes or ornithischians, as well as that of various early saurischians, such as Eoraptor lunensis and herrerasaurs, as either noneusaurischians or members of the sauropodomorph or theropod lineages. This lack of agreement in part derives from a patchy distribution of traits among early members of the main dinosauromorph lineages and requires a more meticulous assessment of characters and homologies than those recently conducted. Presently, the oldest uncontroversial dinosaur records come from Late Triassic (Carnian) rocks of South America, southern Africa and India, hinting at a south-western Pangaea origin of the group. Besides, macroevolutionary approaches suggest that the rise of dinosaurs was a more gradual process than previously understood. Obviously, these tentative scenarios need to be tested by new fossil finds, which should also help close the major gaps recognized in the fossil record of Triassic dinosauromorphs.