Avemetatarsalia

Various members of the Avemetatarsalia, clockwise from top left: Tupuxuara, Alamosaurus, Tsintaosaurus, Daspletosaurus, Pentaceratops, Common Crane (Grus grus).

• Worldwide

Avemetatarsalia is the name for a clade of archosaurs. This is defined as stem -based taxon that includes all Avesuchia (crown group Archosauria ), which are more closely related to dinosaurs than crocodiles.

Etymology

The name Avemetatarsalia is composed of the Latin word avis for " bird" and the word metatarsus, the anatomical term for the midfoot ( the area between the tarsus and toes). It refers to the bird-like construction of the midfoot ( metatarsal ) as a common feature of the group and was coined by Michael Benton in 1999.

Features

The neck is S-shaped, curved, as is the case with the birds today. The typical construction of the ankle is another characteristic feature of the group. The Gelenkung exists here between the "upper", located closer to the knee ( proximal ) tarsal bones Astragalus and calcaneus and the "lower", closer to the toe lying (distal) Fußwurzelnkochen. This arrangement allows, in conjunction with an extension of the foot, the animals a digitigrade locomotion (gait on the toes ). The sister group of the Avemetatarsalia are the Crocodylotarsi (or Crurotarsi ), consisting of some extinct taxa such as the Phytosauria well as from recent crocodiles, in which the ankle joint between astragalus and calcaneus is what can occur with the entire sole of their representatives.

The name derives from the Avemetatarsalia the construction of the midfoot, the strong to the tarsus - metatarsus complex ( tarsometatarsus ) of modern birds is remembered. The base here is very compact because the metatarsal bones ( metatarsals ) I to IV not yet, as in birds, with each other and with the tarsus fused, but are tightly nestled together. In addition, the midfoot is very long: the length of the metatarsal bones IV, II is more than 50 % of the length of the rail leg ( tibia). In addition, the Avemetatarsalia are characterized by the absence of dorsal osteoderms (on some groups of dinosaurs arose again ).

System

The Avemetatarsalia among the archosaurs. The sister taxon are the Crurotarsi. Cladogram according to Benton ( 2007), " Archosauria " refers to the Pan - archosaurs ( Archosauromorpha ), " Avesuchia " the crown archosaurs:

† Proterosuchidae

† Erythrosuchidae

† Euparkeria

Crurotarsi

Avemetatarsalia

The Avemetatarsalia divided into two taxa: The basal genus Scleromochlus and the highly diverse group Ornithodira. The Ornithodira in turn divided into the Pterosauromorpha ( pterosaurs in the broader sense ) and the Dinosauromorpha (Dinosaurs in the broader sense ) on. Cladogram by Ezcurra (2006):

Scleromochlus

Pterosauria

Lagerpeton

Marasuchus

Pseudolagosuchus

Silesaurus

Eucoelophysis

Herrerasauridae

Theropods (including Aves (birds ) )

Sauropoda

Ornithischia

In some kinship analyzes of basal archosaurs came out that Scleromochlus is not the sister taxon of Ornithodira but the sister taxon of all pterosaurs. In this case, the name " Ornithodira " and " Avemetatarsalia " refer to the same clade.