Avemetatarsalia

Avemetatarsalia is a group of reptiles that includes all animals more closely related to birds than to crocodiles. This group has two very important parts: the dinosaurs and the pterosaurs.

Dinosaurs were huge land animals that lived during a time called the Mesozoic Era. One small group of them, called birds, are still alive today. Pterosaurs were the first animals able to fly. They lived during the same time as the dinosaurs but went extinct at the end of the Cretaceous Period.

Avemetatarsalia began in the Triassic Period, a time long ago. The name was given by a scientist named Michael Benton in 1999. Another name for this group is Pan-Aves, which means "all birds." This is because it includes every animal, living or not, that shares a closer family tie to birds than to crocodiles.

Besides dinosaurs and pterosaurs, there were other interesting animals in this group during the Triassic Period. One of the earliest groups was called aphanosaurs. They were four-legged meat-eaters. There were also animals called pterosauromorphs, which are closer to pterosaurs, and dinosauromorphs, which are closer to dinosaurs. Some of these early relatives of dinosaurs and pterosaurs include small insect-eating reptiles like lagerpetids and silesaurids.

Description

Avemetatarsalia is a group of reptiles that share a common ancestor. They are more closely related to birds than to crocodiles. These creatures have special ankles that help them move. Because of this, they usually stood up straight on two legs.

Many of these animals had feathers or similar structures. Pterosaurs, one group of avemetatarsalians, were the first vertebrates to fly. They had wings made of skin stretching from their ankles to a long finger. Birds came later and developed flight using their arms and special flight feathers. These animals were often lighter and smaller-headed compared to their crocodile relatives.

Origin

Further information: Origin of birds

Bird-like reptiles first appeared in fossils from about 245 million years ago during the Middle Triassic period. These early fossils are from a small creature called Asilisaurus. There are also older footprints from Poland that might be from even earlier relatives, dating back to around 249 million years ago. These footprints show that the group of animals that includes dinosaurs and their close relatives started to appear not long after a big event that changed Earth long ago. The rise of these creatures, including dinosaurs, happened slowly over many millions of years. Some scientists discuss what these early footprints might tell us about these ancient animals.

Classification

In 1986, a scientist named Jacques Gauthier named a group of animals called Ornithosuchia. This group included animals more closely related to birds than to crocodiles. Later that year, Gauthier made another name, Ornithodira, for a smaller group with dinosaurs and pterosaurs. In 1991, another scientist, Paul Sereno, added an animal called Scleromochlus to this group.

In 1999, Michael Benton created the name Avemetatarsalia for this group. He chose this name because it included birds and a special ankle joint. In 2001, Gauthier suggested using Panaves for the same group. Today, scientists use names like Avemetatarsalia, Ornithodira, or Panaves for this group. Some think Ornithosuchia is the right name because it was used first, but others like the other names.

Scientists keep studying these names and the links between these ancient animals.