Avemetatarsalia

Avemetatarsalia is a group of reptiles that includes all animals more closely related to birds than to crocodiles. This group contains two very important groups: the dinosaurs and the pterosaurs. Dinosaurs were huge land animals that lived during a time called the Mesozoic Era, and one small group of them, called birds, are still alive today. Pterosaurs were the first animals able to fly and 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, and the name was given by a scientist named Michael Benton in 1999. Another name for this group is Pan-Aves, which means "all birds," 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, which 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 and are more closely related to birds than to crocodiles. These creatures have special ankles called "advanced mesotarsal" ankles, which help them move better. Because of this, they usually stood up straight on two legs, like mammals do.

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 very 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-line archosaurs first appear in fossils from about 245 million years ago during the Middle Triassic period. These early fossils come 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 suggest that the group of animals that includes dinosaurs and their close relatives began 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 debate what some of these early footprints really tell us about these ancient animals.

Classification

In 1986, a scientist named Jacques Gauthier named a group of animals called Ornithosuchia. This group included all animals that were more closely related to birds than to crocodiles. Later, in the same year, Gauthier created another name, Ornithodira, for a smaller group that included dinosaurs and pterosaurs. Another scientist, Paul Sereno, added an animal called Scleromochlus to this group in 1991, making it larger.

In 1999, Michael Benton created a new name, Avemetatarsalia, for this group. He chose this name because it included birds and a special ankle joint that these animals had. In 2001, Gauthier suggested using the name Panaves for the same group. Today, scientists sometimes use Avemetatarsalia, Ornithodira, or Panaves when talking about this group of animals. Some scientists think Ornithosuchia should be the correct name because it was used first, but others prefer the other names.

Scientists continue to study and discuss these names and the relationships between these ancient animals.