archosaur
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What is an archosaur?
An archosaur is any reptile belonging to the subclass Archosauria, which includes crocodiles and birds as well as all descendants of their most recent common ancestor. Archosaurs also include dinosaurs, pterosaurs (flying reptiles), and several extinct groups, mainly from the Triassic Period (251 million to 200 million years ago). The first known archosaurs appeared in the Middle Triassic Period (about 246 million to 229 million years ago). The teeth of archosaurs are set in sockets, unlike other living reptiles whose teeth are set in shallow grooves.
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What types of reptiles are included in the archosaur group?
The archosaur group includes a diverse array of reptiles, both living and extinct. Archosaurs are divided into two main branches: Pseudosuchia, which includes crocodiles and related extinct groups, and Ornithosuchia, which includes birds, dinosaurs (from which birds evolved), pterosaurs, and some extinct Triassic forms. Crocodilians are descendants of archosaurs and are the closest living relatives to dinosaurs besides birds.
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How are archosaurs different from other reptiles?
Archosauria is a subclass of reptiles that includes crocodiles, birds, dinosaurs, pterosaurs, and several extinct groups. Archosaurs are diapsids, meaning they possess two openings in the skull behind the eye. Unlike other reptiles, archosaur teeth are set in sockets rather than shallow grooves. Most archosaurs have long hind legs and short forelimbs, with a large opening on the snout in front of the eye (antorbital fenestra) and another at the junction of three bones in the lower jaw (mandibular fenestra). The first archosaurs appeared during the Middle Triassic Period, about 246 million to 229 million years ago.
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Which modern animals are descended from archosaurs?
The archosaur subclass includes crocodiles and birds and all descendants of their most recent common ancestor. Archosaurs are divided into two branches: Pseudosuchia, which includes crocodiles, and Ornithosuchia, which includes birds. The first known archosaurs appeared in the Middle Triassic Period (about 246 million to 229 million years ago). Birds evolved in the Late Jurassic. Crocodiles and birds still remain today, while other dinosaurs and the pterosaurs became extinct by the end of the Cretaceous period. Crocodilians are scaly, carnivorous reptiles that include crocodiles, alligators, caimans, and gharials and are descendants of the archosaurs that lived on Earth more than 200 million years ago.
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What characteristics did ancient archosaurs have?
Archosauria is a subclass of reptiles that includes crocodiles and birds, as well as all descendants of their most recent common ancestor. Archosaurs are also called "ruling reptiles".
Most archosaurs had long hind legs and short forelimbs. They also possessed distinct characteristics such as a large opening on the snout in front of the eye (antorbital fenestra) and another at the junction of three bones in the lower jaw (mandibular fenestra). Unlike other living reptiles, the teeth of archosaurs are set in sockets.
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How did archosaurs influence the evolution of dinosaurs and birds?
The archosaur subclass significantly influenced the evolution of both dinosaurs and birds. Archosaurs, or "ruling reptiles," are distinguished by features such as socketed teeth and holes in the skull and lower jaw.
The archosaurian branch, Ornithosuchia, includes dinosaurs (from which birds evolved) and pterosaurs. The earliest archosaurs appeared in the Middle Triassic period. Most had long hind legs and short forelimbs.
Experts debate whether flight evolved through gliding or aerial launching by a running terrestrial ancestor. Feathered dinosaurs did not survive the end of the Cretaceous Period, but birds did and then flourished.
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archosaur, (subclass Archosauria), any of various reptiles, including all crocodiles and birds and all descendants of their most recent common ancestor. Archosaurs (“ruling reptiles”) are members of a subclass that also includes the dinosaurs, the pterosaurs (flying reptiles), and several groups of extinct forms, mostly from the Triassic Period (251 million to 200 million years ago).
The true archosaurs are divided into two branches. The Pseudosuchia branch includes crocodiles and all other archosaurs more closely related to crocodiles than to birds. Pseudosuchians comprise mostly extinct Triassic groups such as phytosaurs, aetosaurs, prestosuchids, rauisuchids, and poposaurs. All were carnivorous except the armoured, herbivorous aetosaurs. The second archosaurian branch, the Ornithosuchia, includes birds and all archosaurs more closely related to birds than to crocodiles. In addition to the dinosaurs (the group from which birds evolved and to which they formally belong), ornithosuchians include pterosaurs and some extinct Triassic forms such as lagosuchids and lagerpetontids.
The first known archosaurs appeared in the Middle Triassic Period (about 246 million to 229 million years ago). They evolved from an earlier group of diapsid reptiles, diapsids having two openings in the skull behind the eye. These, along with protorosaurs, rhynchosaurs, trilophosaurids, proterosuchians, erythrosuchids, and proterochampsids, belong to a larger assemblage called the Archosauromorpha. Most archosaurs had long hind legs and short forelimbs. All archosaurs had a large opening of uncertain function on the snout in front of the eye (antorbital fenestra) and another at the junction of three bones in the lower jaw (mandibular fenestra). Unlike other living reptiles, whose teeth are set in a shallow groove, the teeth of archosaurs are set in sockets.
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Although most archosaurs were egg layers, there is evidence that some species gave birth to live young. The oldest known example of such a live-bearing form is Dinocephalosaurus, an archosauromorph—that is, a form more closely related to archosaurs than lepidosaurs (the lineage containing modern lizards and snakes, their direct ancestors, and their close relatives)—which lived about 245 million years ago.
The two branches of archosaurs developed different patterns of locomotion. The pseudosuchians have a generally crocodile-like ankle that flexes in the middle so the foot can twist against the ankle as it walks sprawled out. However, this ankle joint can also stiffen so that the animal moves in a “high walk,” as seen in crocodiles. The ornithosuchians, on the other hand, have an ankle that swings in only one plane (fore and aft), so they are obliged to walk upright and put one foot in front of the other as birds do. These differences seem to have characterized the archosaurian branches from the earliest times in their history. In correlation with this difference, nearly all pseudosuchians are typically quadrupedal, walking on four legs, whereas nearly all ornithosuchians are typically bipedal, walking on two.
The Triassic saw the first broad diversification of archosaurs, and, although most groups became extinct by the end of that period, dinosaurs, crocodiles, and pterosaurs survived and proliferated during the Jurassic and Cretaceous periods. Birds evolved in the Late Jurassic, and, although the other dinosaurs and the pterosaurs became extinct by the end of the Cretaceous, the crocodiles and birds still remain.