Crurotarsi

From Tokaia

The crurotarsians are a group of archosaur reptiles; they are, by definition, all forms closer to crocodiles than to birds. Their main feature is the distinct scute armour; it has, however, been lost in some marine crocodilians and phytosaurs, while it gave rise to the feather-like scales in the ornithoideans.

In Terra Alternativa

In our world, crurotarsians had been among the dominant vertebrate groups in the Triassic period; however, as dinosaurs evolved, they were eventually replaced and only crocodilians survived.

Since dinosaurs never evolved on Terra Alternativa, crurotarsians remained as dominanat, and in fact only pterosaurs and synapsids competed with them. They are/were divided into four main groups:

• Rauisuchia: a linage of carnivorous like crurotarsians, which mostly resembled quadrupedal theropods, aside from the bizarre poposaurids, which were mostly ornithomimid like forms.

• Aetosauria: herbivorous cruratarsians, akin to stegosaurs and ankylosaurs.

• Phytosauria: one of the two linages of aquatic crurotarsians, later replaced by crocodilians.

• Crocodilia: the typical aquatic reptiles known as crocodiles, alligators and gharials, although as a group they were far more diverse.

In addition, the bird-like ornithoideans evolved from early crocodilians.

During most of the Mesozoic, the first three orders of crurotarsians dominated land ecosystems; however, towards the Cretaceous period crocodilians rised in dominance, although a few members from the other groups still hanged on to life. At the K-T event, nearly all crurotarsians were eliminated, with the exception of semi-aquatic crocodilians and the flying ornithoideans.

In What if Dinosaurs

The evolutionary history of crurotarsians is similar to that of our world; however, crocodiles are quite more diverse, having not experienced the K-T event.

See Also

Crurotarsi on wikipedia.