Extinct reptiles including dinosaurs

Usage examples of archosaur.

This puzzling question will perhaps be answered as new dinosaur specimens are found, and other archosaur and non-archosaur groups become better understood.

The first period followed the separation of dinosaurs from their archosaur ancestors, which took place in the Late Triassic, when the earliest herrerasaurids and prosauropods dominated various other herbivorous and carnivorous vertebrates.

Recent work shows that these reptiles are more closely related to archosaurs and may be included in a larger assemblage called the archosauromorphs.

Most archosaurs went extinct long ago, although two groups remain today: the crocodiles and the birds.

Out of this varied group of Triassic archosaurs arose the dinosaurs which, though initially rare, spread, diversified, and eventually completely dominated the animal communities of the world over the next 150 million years.

But from where within this large grab-bag of archosaurs did the dinosaurs arise?

By studying both fossil and living archosaurus, paleontologists have shown that the archosaurs split into two branches, or lineages, in the Early Triassic.

The vast array of archosaurs and non-archosaurs from the early part of the Late Triassic formed the bulk of the known animal communities in which the earliest dinosaurs appeared.

But among the archosaurs is a group called the pseudosuchians, and their descendants include all the crocodilians.