archosaurian, adj.
/ahr"keuh sawr'/, n.
any reptile of the subclass Archosauria, including the dinosaurs, pterosaurs, and crocodilians and characterized by two pairs of openings in the temporal region of the skull.
[1965-70; < NL Archosaurus, taken as sing. of Archosauria, equiv. to Gk archo-, comb. form of archós ruler, chief + saûr(os) -SAUR + NL -ia -IA]

* * *

Any of the various advanced reptiles in the subclass Archosauria ("ruling reptiles"), including all thecodonts, pterosaurs, dinosaurs, birds, and crocodilians.

The first known archosaurs appeared 242–227 million years ago during the Triassic Period. All early archosaurs possessed an ankle specialization that aided in upright posture, and most had long hindlegs and short forelimbs. Unlike the teeth of earlier reptiles, which were set in a shallow groove, the teeth of archosaurs were (and are) set in sockets.

* * *

▪ reptile subclass
      any of various reptiles, including all crocodiles (crocodile) and birds (bird) and all descendants of their most recent common ancestor. Archosaurs (“ruling reptiles”) are members of a subclass that also includes the dinosaurs (dinosaur), the pterosaurs (pterosaur) (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 (phytosaur), 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 245 million to 228 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 hindlegs 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.

      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 (Cretaceous Period). 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.

* * *

Universalium. 2010.

Игры ⚽ Поможем написать курсовую

Look at other dictionaries:

  • Archosaur — Taxobox name = Archosaurs fossil range = Early Triassic Recent image width = 250px image caption = Living archosaurs are crocodilians and birds. regnum = Animalia phylum = Chordata classis = Sauropsida subclassis = Diapsida infraclassis =… …   Wikipedia

  • archosaur — noun Etymology: New Latin Archosauria, from Greek archōn + sauros lizard Date: 1933 any of a subclass (Archosauria) of reptiles comprising the dinosaurs, pterosaurs, and crocodilians • archosaurian adjective or noun …   New Collegiate Dictionary

  • archosaur — noun Any reptile of the taxon Archosauria; includes the extinct dinosaurs, plesiosaurs, pterosaurs and ichthyosaurs and the modern crocodiles …   Wiktionary

  • archosaur — [ α:kəsɔ:] noun Zoology & Palaeontology a reptile of a large group that includes the crocodilians together with the extinct dinosaurs and pterosaurs. Origin 1930s: from mod. L. Archosauria, from Gk arkhos chief or arkhōn ruler + saur …   English new terms dictionary

  • archosaur — ar·cho·saur …   English syllables

  • archosaur — pal ar•cho•saur [[t]ˈɑr kəˌsɔr[/t]] n. pal ram any reptile of the subclass Archosauria, including the dinosaurs, pterosaurs, and crocodilians • Etymology: 1965–70; < NL Archosaurus < Gk árcho(s) leader, ruler +saûr(os) saur …   From formal English to slang

  • archosaur — noun extinct reptiles including: dinosaurs; plesiosaurs; pterosaurs; ichthyosaurs; thecodonts • Syn: ↑archosaurian, ↑archosaurian reptile • Derivationally related forms: ↑archosaurian (for: ↑archosaurian) …   Useful english dictionary

  • Galtonia (archosaur) — Taxobox| name = Galtonia fossil range = Late Triassic regnum = Animalia phylum = Chordata subphylum = Vertebrata superclassis = Tetrapoda classis = Sauropsida subclassis = Diapsida unranked ordo = Archosauria unranked familia = Crurotarsi genus …   Wikipedia

  • List of dinosaurs — Mounted skeletons of Tyrannosaurus (left) and Apatosaurus (right) at the AMNH. This list of dinosaurs is a comprehensive listing of all genera that have ever been included in the superorder Dinosauria, excluding class Aves (birds, both living and …   Wikipedia

  • Longisquama — Taxobox name = Longisquama image width = 200px image caption = Illustration of Longisquama insignis fossil range = Early Triassic regnum = Animalia phylum = Chordata classis = Sauropsida subclassis = Diapsida unranked ordo = Avicephala? familia …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”