Early evolution of dinosaurs

Cladogram of tetrapods (Brusatte et al, Earth-Science Reviews 101, 2010, 68)

I’m amazed to find what a wealth of new information there is on dinosaurs. An informative review of the early evolution of dinosaurs appeared this year in Earth-Science Reviews (copy publicly available from one of the authors):

Dinosaurs were remarkably successful during the Mesozoic and one subgroup, birds, remain an important component of modern ecosystems. Although the extinction of non-avian dinosaurs at the end of the Cretaceous has been the subject of intense debate, comparatively little attention has been given to the origin and early evolution of dinosaurs during the Late Triassic and Early Jurassic, one of the most important evolutionary radiations in earth history. Our understanding of this keystone event has dramatically changed over the past 25 years, thanks to an influx of new fossil discoveries, reinterpretations of long-ignored specimens, and quantitative macroevolutionary analyses that synthesize anatomical and geological data. Here we provide an overview of the first 50 million years of dinosaur history, with a focus on the large-scale patterns that characterize the ascent of dinosaurs from a small, almost marginal group of reptiles in the Late Triassic to the preeminent terrestrial vertebrates of the Jurassic and Cretaceous.
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Dinosaurs are members of a speciose clade of vertebrates called the Archosauria (the “ruling reptiles”), which includes birds, crocodylians, and their extinct relatives. Archosaurs are deeply nested within the radiation of land-living vertebrates, and themselves are a subgroup of diapsid reptiles (a more inclusive clade that also includes lizards, snakes, and possibly turtles). The archosaur lineage originated approximately 245 million years ago, just a few million years after the devastating Permo-Triassic mass extinction. This extinction was the most profound period of mass death in geological history and is estimated to have wiped out up to 75–95% of all species. In its aftermath, ecosystems reshuffled and entirely new groups of organisms arose and diversified, including “modern” lineages such as turtles, mammals, lepidosaurs, and archosaurs.