Pseudosuchia

Pseudosuchia is one of two major groups of archosaurs, which are ancient reptiles. This group includes today's living crocodilians and all archosaurs more closely related to crocodilians than to birds. Even though the name Pseudosuchia means "false crocodiles," true crocodilians are actually part of this group.

The term Pseudosuchia is sometimes used interchangeably with another term, Crurotarsi, though they have slightly different meanings. Scientists have debated their exact relationship, especially regarding a group called Phytosauria. Some believe Phytosauria is closely related to other Pseudosuchians, while others think it branches off earlier.

During the Triassic period, Pseudosuchia included a wide variety of reptiles with different ways of living. Some were large, four-legged top hunters like Saurosuchus, Prestosuchus, and Fasolasuchus. Others were scavengers or small, quick hunters. There were even armored plant-eaters like aetosaurs and two-legged creatures like Poposaurus and Postosuchus. Some strange, bird-like groups had beaks without teeth.

Many of these early groups disappeared before the end of the Triassic period. However, one group, the crocodylomorphs, survived and evolved into many different forms during the Jurassic and Cretaceous periods. Today, the only living members of Pseudosuchia are crocodiles, alligators, caimans, and gavialids.

Origin, decline, and re-use of the clade name Pseudosuchia

The name Pseudosuchia was first used for a group of ancient reptiles that looked like crocodiles. These reptiles lived during the Triassic period. However, by the late 20th century, this name was not used much anymore. Instead, scientists started using the name Crurotarsi to describe these reptiles.

In 2011, a scientist named Sterling Nesbitt suggested that Crurotarsi should include more than just crocodile-like reptiles. He said it should also include birds, dinosaurs that were not birds, and pterosaurs. After this idea was supported by many studies, the name Pseudosuchia started to be used again to talk about crocodile-like reptiles.

Taxonomic history

The name Pseudosuchia was created by Karl Alfred von Zittel in 1887–1890. He used it for three groups that looked like crocodiles but were not actually crocodiles, calling them "false crocodiles."

Later, scientists used the name for many different kinds of ancient reptiles that did not fit into other groups. In the 1980s, scientists Gauthier and Padian gave Pseudosuchia a new meaning. They defined it as all animals more closely related to crocodiles than to birds. This made the name a bit funny because real crocodiles are part of this group. Today, Pseudosuchia is considered the group of reptiles closest to crocodiles, while another group, Avemetatarsalia, includes pterosaurs and dinosaurs, which are closer to birds.

Description

Pseudosuchia is one of the two main groups of Archosauria. Their skulls are often very strong, especially compared to ornithodires. They usually have long, narrow snouts, short and strong necks, and their legs can be sprawled out like typical reptiles or held upright like dinosaurs or mammals, though they achieve this posture differently. Many of these animals have two or more rows of armored plates on their bodies, and some can grow to be three meters or longer.

Evolution

Pseudosuchians first appeared during the late Olenekian in the early Triassic period. By the Ladinian in the late Middle Triassic, they became the main meat-eating animals on land. Their most successful time was the Late Triassic, when they included many different types of species, such as upright-limbed rauisuchians, armored plant-eating aetosaurs, large meat-eating poposaurs, small fast-moving sphenosuchian crocodiles, and a few other groups.

The end-Triassic extinction caused most of these ancient pseudosuchians to disappear, leaving only Sphenosuchia and Crocodyliformes, which are the ancestors of today's crocodiles. It’s often thought that dinosaurs outcompeted these animals, but studies show that volcanic eruptions likely changed the climate, leading to a mass extinction that removed many of dinosaurs' rivals. This allowed dinosaurs to become the main land animals, while crocodiles continued to thrive in water environments.

During the Mesozoic era, while dinosaurs ruled the land, crocodiles evolved to live in rivers, swamps, and oceans, becoming more diverse than they are today. After the end-Cretaceous extinction, dinosaurs disappeared except for birds, but crocodiles survived with little change. Today, crocodiles, alligators, and gharials are the remaining members of this ancient group.

Phylogeny

Pseudosuchia was defined in 1985 as a group that includes crocodiles and all animals more closely related to crocodiles than to birds. Another group, called Crocodylotarsi, was named later, but it means almost the same thing as Pseudosuchia. The name Pseudosuchia means "false crocodiles," but it actually includes true crocodiles too, called Eusuchia.

A third group, Crurotarsi, used to include the same animals as Pseudosuchia, but recent studies show it also includes some other animals, like phytosaurs. So now, Pseudosuchia only includes crocodile-line archosaurs, while Crurotarsi includes more groups, such as phytosaurs, crocodiles, pterosaurs, and dinosaurs.