Archosaurs can traditionally be distinguished from other tetrapods on the basis of several synapomorphies, or shared characteristics, which were present in their last common ancestor. Many of these … See more

Synapsids are a clade that includes mammals and their extinct ancestors. The latter group are often referred to as mammal-like … See more

Modern classification
Archosauria is normally defined as a crown group, which means that it only includes descendants of the last common ancestors of its living … See more

Crocodylomorphs, pterosaurs and dinosaurs survived the Triassic–Jurassic extinction event about 200 million years ago, but other archosaurs had become extinct at or prior to the Triassic-Jurassic boundary.
Non-avian … See more

Archosaurs are a subgroup of archosauriforms, which themselves are a subgroup of archosauromorphs. Both the oldest archosauromorph (Protorosaurus speneri) … See more

Since the 1970s, scientists have classified archosaurs mainly on the basis of their ankles. The earliest archosaurs had "primitive mesotarsal" ankles: the astragalus and calcaneum were fixed to the tibia and fibula by sutures and the joint bent about the contact … See more

Hip joints and locomotion
Like the early tetrapods, early archosaurs had a sprawling gait because their hip sockets faced sideways, and the knobs at the tops of their femurs were in line with the femur. In the early to middle Triassic, some archosaur groups … See more