Archosaurs Fossil range: Early Triassic - Recent
Living archosaurs include crocodiles (pictured above) and birds.
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Sauropsida Subclass: Diapsida Infraclass: Archosauromorpha (unranked) Archosauria Cope, 1869
Clades
Crurotarsi Aetosauria Crocodilia (crocodiles) Phytosauria Rauisuchia Ornithodira Aves (birds) Dinosauria Pterosauria

Archosaurs (Greek for 'ruling lizards') are a group of diapsid reptiles that is represented today by birds and crocodiles and which also included the dinosaurs. The Early Triassic (also known as Lower Triassic, Buntsandstein, or Scythian) is the first of three epochs of the Triassic period. ... Download high resolution version (1506x1182, 405 KB) Wikipedia does not have an article with this exact name. ... Genera Mecistops Crocodylus Osteolaemus See full taxonomy. ... For other uses, see Bird (disambiguation). ... For other uses, see Scientific classification (disambiguation). ... For other uses, see Animal (disambiguation). ... Typical Classes See below Chordates (phylum Chordata) are a group of animals that includes the vertebrates, together with several closely related invertebrates. ... Clades Subclass Anapsida Subclass Diapsida Infraclass Lepidosauromorpha Infraclass Archosauromorpha Sauropsids are a diverse group of mostly egg-laying vertebrate animals. ... Groups See Text Diapsids (two arches) are a group of tetrapod animals that developed two holes (temporal fenestra) in each side of their skulls, about 300 million years ago during the late Carboniferous period. ... Orders See text Archosauromorpha (Greek for ruling lizard forms) is an Infraclass of diapsid reptiles that first appeared during the late Permian and became more common during the Triassic. ... Edward Drinker Cope Edward Drinker Cope (July 28, 1840–April 12, 1897) was an American paleontologist and comparative anatomist, as well as a noted herpetologist and ichthyologist. ... A clade is a term belonging to the discipline of cladistics. ... Subtaxa Phytosauridae Prestosuchidae Ornithosuchidae Stagonolepididae Rauisuchidae Poposauridae Crocodylomorpha     Sphenosuchia     Crocodilia Crurotarsi (cross-ankles) is a node-based taxon created by Paul Sereno in 1991 to supplant the old term Pseudosuchia. ... Genera Aetosaurus Coahomasuchus Desmatosuchus Longosuchus Neoaetosauroides Paratypothorax Redondasuchus Stagonolepis Typothorax The Aetosaurs (family Stagonolepididae or Aetosauridae) are an extinct clade of heavily armoured, medium to large sized, Late Triassic herbivorous archosaurs. ... black: range of Crocodilia Families Gavialidae Alligatoridae Crocodylidae Crocodilia is an order of large reptiles that appeared about 84 million years ago in the Late Cretaceous Period (Campanian stage). ... Phytosaurs - family Phytosauridae or Parasuchidae - were a group of large (2 to 12 meters long - average size 3 to 4 meters) semi-aquatic predatory thecodonts that flourished during the Late Triassic period. ... Families Family Prestosuchidae Family Rauisuchidae Family Poposauridae Rauisuchia are a poorly known assemblage of predatory and mostly large (often 4 to 6 meters) Triassic archosaurs. ... Superorders Dinosauromorpha    Lagosuchians    Dinosauria Pterosauromorpha    Pterosauria    Scleromochlus    Sharovipteryx Ornithodira is a division of the Archosauromorpha (and perhaps Archosauria) clade. ... For other uses, see Bird (disambiguation). ... Orders & Suborders Saurischia Sauropodomorpha Theropoda Ornithischia Thyreophora Ornithopoda Marginocephalia Dinosaurs were vertebrate animals that dominated the terrestrial ecosystem for over 160 million years, first appearing approximately 230 million years ago. ... Suborders Pterodactyloidea Rhamphorhynchoidea * Pterosaurs (, from the Greek πτερόσαυρος, pterosauros, meaning winged lizard, often referred to as pterodactyls, from the Greek πτεροδάκτυλος, pterodaktulos, meaning winged finger ) were flying reptiles of the clade Pterosauria. ... Groups See Text Diapsids (two arches) are a group of tetrapod animals that developed two holes (temporal fenestra) in each side of their skulls, about 300 million years ago during the late Carboniferous period. ... Reptilia redirects here. ... For other uses, see Bird (disambiguation). ... black: range of Crocodilia Families Gavialidae Alligatoridae Crocodylidae Crocodilia is an order of large reptiles that appeared about 84 million years ago in the Late Cretaceous Period (Campanian stage). ... Orders & Suborders Saurischia Sauropodomorpha Theropoda Ornithischia Thyreophora Ornithopoda Marginocephalia Dinosaurs were vertebrate animals that dominated the terrestrial ecosystem for over 160 million years, first appearing approximately 230 million years ago. ...

There is some debate about when archosaurs first appeared. Those who classify the Permian reptiles Archosaurus rossicus and / or Protorosaurus speneri as true archosaurs maintain that archosaurs first appeared in the late Permian. Those who classify both Archosaurus rossicus and Protorosaurus speneri as archosauriformes (not true archosaurs but very closely related) maintain that archosaurs first evolved from Archosauriform ancestors during the Olenekian (early Triassic Period). The Permian is a geologic period that extends from about 299. ... Groups Proterosuchidae     Erythrosuchidae         Euparkeriidae             Archosauria Archosauriformes (Greek for ruling reptiles, + form) are a clade of diapsid reptiles that developed from Archosauromorph ancestors some time in the Late Permian (roughly 250 million years ago). ... Groups Proterosuchidae     Erythrosuchidae         Euparkeriidae             Archosauria Archosauriformes (Greek for ruling reptiles, + form) are a clade of diapsid reptiles that developed from Archosauromorph ancestors some time in the Late Permian (roughly 250 million years ago). ... The Olenekian (also known as the Yongningzhenian) is a stage of the Early Triassic epoch. ... The Triassic is a geologic period that extends from about 251 ± 0. ... A geologic period is a subdivision of geologic time that divides an era into smaller timeframes. ...

Distinguishing characteristics

The simplest and most widely-agreed synapomorphies of archosaurs are: Shared characteristics that define a cladistic grouping. ...

• Teeth set in sockets, which makes them less likely to be torn loose during feeding. This feature is responsible for the name "thecodonts" ("socket teeth"), which paleontologists used to apply to all or most archosaurs.
• Preorbital fenestrae (openings in the skull in front of the eyes but behind the nostrils), which reduced the weight of the skull, a useful feature since most early archosaurs had long, heavy skulls, rather like those of modern crocodilians. The preorbital fenestrae (sometimes called anteorbital fenestrae) are often larger than the orbits (eye sockets).
• Mandibular fenestrae (small openings in the jaw bones), which may have reduced the weight of the jaw slightly.
• A fourth trochanter (ridge for attaching muscles) on the femur. This seemingly insignificant detail may have made the evolution of dinosaurs possible (all early dinosaurs and many later ones were bipeds), and may also be connected with the ability of the archosaurs or their immediate ancestors to survive the catastrophic Permian-Triassic extinction event.

Thecodont (socket-toothed reptile), is a catch-all (paraphyletic) group, now considered an obsolete term, that was formerly used to describe a group of the earliest archosaurs that lived during the Permian and Triassic periods. ... Suborders Eusuchia Protosuchia † Mesosuchia † Sebecosuchia † Thalattosuchia † Crocodilia is an order of large reptiles that scientists believe branched off from class Reptilia about 220 million years ago. ... The Fourth trochanter is a shared characteristic common to archosaurs. ... The femur or thigh bone is the longest, most voluminous, and strongest bone of the mammalian bodies. ... The Permian-Triassic (P-T or PT) extinction event, sometimes informally called the Great Dying, was an extinction event that occurred approximately 251 million years ago (mya), forming the boundary between the Permian and Triassic geologic periods. ...

Archosaur takeover in the Triassic

Mammal-like reptiles were the dominant land vertebrates throughout the Permian, but most perished in the Permian-Triassic extinction event. Lystrosaurus (a herbivorous mammal-like reptile) was the only large land animal to survive the event, becoming the most populous land animal on the planet for a time.^[1] Mammal-like reptiles is a term used to describe the prehistoric animals that appear to be the reptilian ancestors of mammals. ... The Permian is a geologic period that extends from about 299. ... The Permian-Triassic (P-T or PT) extinction event, sometimes informally called the Great Dying, was an extinction event that occurred approximately 251 million years ago (mya), forming the boundary between the Permian and Triassic geologic periods. ... Species Lystrosaurus curvatus Lystrosaurus declivus Lystrosaurus mccaigi Lystrosaurus murrayi Lystrosaurus oviceps Lystrosaurus platyceps Lystrosaurus (meaning shovel reptile, pronounced list-row-sore-uss) was a genus of Early Triassic Period therapsids, which lived approximately 250 million years ago in what is now Antarctica, India and South Africa. ...

But archosaurs quickly became the dominant land vertebrates in the early Triassic. The two most commonly-suggested explanations ^{[citation needed]} for this are: The Triassic is a geologic period that extends from about 251 ± 0. ...

• Archosaurs made quicker progress than mammal-like reptiles towards erect limbs, and this gave them greater stamina by avoiding Carrier's constraint. This is unconvincing since Archosaurs became dominant while they still had sprawling or semi-erect limbs, similar to those of Lystrosaurus and other mammal-like reptiles.
• The early Triassic was predominantly arid, because most of the earth's land was concentrated in the supercontinent Pangaea. Archosaurs were probably better at conserving water than mammal-like reptiles:
  Modern diapsids (lizards, snakes, crocodilians, birds) excrete uric acid, which can be excreted as a paste. It is reasonable to suppose that archosaurs (diapsids and ancestors of crocodilians, dinosaurs and birds) also excreted uric acid, and therefore were good at conserving water. The aglandular (glandless) skins of diapsids would also have helped to conserve water.
  Modern mammals excrete urea, which requires a lot of water to keep it dissolved. Their skins also contain many glands, which also lose water. Assuming that mammal-like reptiles had similar features, as argued e.g. in Palaeos [1], they were at a disadvantage in a mainly arid world. The same well-respected site points out that "for much of Australia's Plio-Pleistocene history, where conditions were probably similar, the largest terrestrial predators were not mammals but gigantic varanid lizards (Megalania) and land crocs."

Carriers constraint is the observation that air-breathing vertebrates which have two lungs and and flex their bodies sideways during locomotion find it very difficult to move and breathe at the same time, because: the sideways flexing expands one lung and compresses the other. ... Species Lystrosaurus curvatus Lystrosaurus declivus Lystrosaurus mccaigi Lystrosaurus murrayi Lystrosaurus oviceps Lystrosaurus platyceps Lystrosaurus (meaning shovel reptile, pronounced list-row-sore-uss) was a genus of Early Triassic Period therapsids, which lived approximately 250 million years ago in what is now Antarctica, India and South Africa. ... This article is about Earth as a planet. ... In geology, a supercontinent is a land mass comprising more than one continental core, or craton. ... For other uses, see Pangaea (disambiguation). ... Groups See Text Diapsids (two arches) are a group of tetrapod animals that developed two holes (temporal fenestra) in each side of their skulls, about 300 million years ago during the late Carboniferous period. ... Uric acid (or urate) is an organic compound of carbon, nitrogen, oxygen and hydrogen with the formula C5H4N4O3. ... Urea is an organic compound with the chemical formula (NH2)2CO. Urea is also known as carbamide, especially in the recommended International Nonproprietary Names (rINN) in use in Europe. ... This article or section does not cite its references or sources. ... Species Many, see text. ... Binomial name (Richard Owen, 1859) Megalania is an extinct giant monitor lizard. ...

Main types of archosaurs

Primitive mesotarsal ankle. Adapted with permission from Palaeos

Since the 1970s scientists have classified archosaurs mainly on the basis of their ankles.^[2] The earliest archosaurs had "primitive mesotarsal" ankles: the astragalus and calcaneum were fixed to the tibia and fibula by sutures and the joint bent about the contact between these bones and the foot.
Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... FIG. 270– Left talus, from above. ... The calcaneus is the large bone making up the heel of the human foot. ... This article is about the vertebrate bone. ... For other uses, see Suture (disambiguation). ...

Crocodilian form of crurotarsal ankle. Adapted with permission from Palaeos

The Crurotarsi appeared early in the Triassic. In their ankles the astragalus was joined to the tibia by a suture and the joint rotated round a peg on the astragalus which fitted into a socket in the calcaneum. Early "crurotarsans" still walked with sprawling limbs, but some later "crurotarsans" developed fully erect limbs (most notably the Rauisuchia). And modern crocodilians are "crurotarsans" which can walk with their limbs sprawling or erect depending on how much of a hurry they are in.
Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... A crurotarsal ankle is one which can bend between the astragalus and calcaneum. ... Subtaxa Phytosauridae Prestosuchidae Ornithosuchidae Stagonolepididae Rauisuchidae Poposauridae Crocodylomorpha     Sphenosuchia     Crocodilia Crurotarsi (cross-ankles) is a node-based taxon created by Paul Sereno in 1991 to supplant the old term Pseudosuchia. ... The Triassic is a geologic period that extends from about 251 ± 0. ... For other uses, see Suture (disambiguation). ... Families Family Prestosuchidae Family Rauisuchidae Family Poposauridae Rauisuchia are a poorly known assemblage of predatory and mostly large (often 4 to 6 meters) Triassic archosaurs. ...

Reversed crurotarsal ankle. Adapted with permission from Palaeos

Euparkeria and the Ornithosuchidae had "reversed crurotarsal" ankles, with a peg on the calcaneum and socket on the astragalus.
Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... A crurotarsal ankle is one which can bend between the astragalus and calcaneum. ... Binomial name Euparkeria capensis Broom, 1913a Is considered to be one of the dinosaurs ancestors. ... Genus Ornithosuchus Venaticosuchus Riojasuchus The Ornithosuchidae is a family of quadrupedal and facultatively bipedal crurotarsan archosaurs. ...

"Advanced" mesotarsal ankle. Adapted with permission from Palaeos

The earliest fossils of Ornithodira ("bird necks") appear in the Carnian age of the late Triassic, but it is hard to see how they could have evolved from the "crurotarsans" - possibly they actually evolved much earlier, or perhaps they evolved from the last of the "primitive mesotarsal" archosaurs. Ornithodires' "advanced mesotarsal" ankle had a very large astragalus and very small calcaneum, and could only move in one plane, like a simple hinge. This arrangement was only suitable for animals with erect limbs, but provided more stability when the animals were running. The ornothodires differed from other archosaurs in other ways: they were lightly-built and usually small, their necks were long and had an S-shaped curve, their skulls were much more lightly built, and many ornothodires were completely bipedal. The archosaurian fourth trochanter on the femur may have made it easier for ornothodires to become bipeds, because it provided more leverage for the thigh muscles. In the late Triassic the ornithodires diversified to produce pterosaurs and dinosaurs.^[3] Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Superorders Dinosauromorpha    Lagosuchians    Dinosauria Pterosauromorpha    Pterosauria    Scleromochlus    Sharovipteryx Ornithodira is a division of the Archosauromorpha (and perhaps Archosauria) clade. ... The Carnian is a stage on the geologic time scale occuring from 228 +/- 2 to 216. ... The Triassic is a geologic period that extends from about 251 ± 0. ... Bipedalism is standing, or moving for example by walking, running, or hopping, on two appendages (typically legs). ... Suborders Pterodactyloidea Rhamphorhynchoidea * Pterosaurs (, from the Greek πτερόσαυρος, pterosauros, meaning winged lizard, often referred to as pterodactyls, from the Greek πτεροδάκτυλος, pterodaktulos, meaning winged finger ) were flying reptiles of the clade Pterosauria. ... Orders & Suborders Saurischia Sauropodomorpha Theropoda Ornithischia Thyreophora Ornithopoda Marginocephalia Dinosaurs were vertebrate animals that dominated the terrestrial ecosystem for over 160 million years, first appearing approximately 230 million years ago. ...

Hip joints and locomotion

Like the early tetrapods, early archosaurs had a sprawling gait because: Groups See text. ...

• Their hip sockets faced sideways.
• The knobs at the tops of their femurs were in line with the femur.

In the early to mid Triassic, some archosaur groups developed hip joints which allowed (or required) a more erect gait. This gave them greater stamina, because it avoided Carrier's constraint, i.e. they could run and breathe easily at the same time. There were two main types of joint which allowed erect legs: The femur or thigh bone is the longest, most voluminous, and strongest bone of the mammalian bodies. ... The Triassic is a geologic period that extends from about 251 ± 0. ... Carriers constraint is the observation that air-breathing vertebrates which have two lungs and and flex their bodies sideways during locomotion find it very difficult to move and breathe at the same time, because: the sideways flexing expands one lung and compresses the other. ...

• The hip sockets faced sideways but the knobs on the femurs were at right angles to the rest of the femur, which therefore pointed downwards. Dinosaurs evolved from archosaurs with this hip arrangement.
• The hip sockets faced downwards and the knobs on the femurs were in line with the femur. This "pillar-erect" arrangement appears to have evolved more than once independently in various archosaur lineages, for example it was common in Rauisuchia and also appeared in some aetosaurs.

Families Family Prestosuchidae Family Rauisuchidae Family Poposauridae Rauisuchia are a poorly known assemblage of predatory and mostly large (often 4 to 6 meters) Triassic archosaurs. ... Genera Aetosaurus Coahomasuchus Desmatosuchus Longosuchus Neoaetosauroides Paratypothorax Redondasuchus Stagonolepis Typothorax The Aetosaurs (family Stagonolepididae or Aetosauridae) are an extinct clade of heavily armoured, medium to large sized, Late Triassic herbivorous archosaurs. ...

Extinction and survival

Crocodilians, pterosaurs, dinosaurs, and champsosaurs survived the Triassic-Jurassic extinction event about 195 million years ago, but other archosaurs became extinct. Champsosaurus is a semiaquatic reptile known from the Late Cretaceous of North America, and a member of the Choristodira. ... Comparison of the intensity of the T-J extinction event, labeled here End Tr to other extinction events in the last 500 million years. ...

Non-avian dinosaurs and pterosaurs perished in the Cretaceous-Tertiary extinction event, but crocodilians, champsosaurs, and birds (last suviving dinosaur group) survived. Birds are descendants of archosaurs, and are therefore archosaurs themselves under phylogenetic taxonomy. Badlands near Drumheller, Alberta where erosion has exposed the KT boundary. ... In biology, phylogenetics (Greek: phylon = tribe, race and genetikos = relative to birth, from genesis = birth) is the study of evolutionary relatedness among various groups of organisms (e. ...

Champsosaurs became extinct in the Oligocene. The Oligocene epoch is a geologic period of time that extends from about 34 million to 23 million years before the present. ...

Crocodilians (which include all modern crocodiles, alligators, and gharials) and birds flourish today, and it is generally agreed that birds have the most species of all air-breathing vertebrates. Genera Mecistops Crocodylus Osteolaemus See full taxonomy. ... For other uses, see Alligator (disambiguation). ... Binomial name Gavialis gangeticus (Gmelin, 1789) The gavial (Gavialis gangeticus) is one of two surviving members of the family Gavialidae, a long-established group of crocodile-like reptiles with long, narrow jaws. ...

Archosaur lifestyle

Diet

Most were large predators, but members of various lines diversified into other niches:

• aetosaurs were herbivores and some developed spectacular armor.
• A few crocodilians were herbivores, e.g. Simosuchus.
• The large crocodilian Stomatosuchus may have been a filter feeder.

Genera Aetosaurus Coahomasuchus Desmatosuchus Longosuchus Neoaetosauroides Paratypothorax Redondasuchus Stagonolepis Typothorax The Aetosaurs (family Stagonolepididae or Aetosauridae) are an extinct clade of heavily armoured, medium to large sized, Late Triassic herbivorous archosaurs. ... Filter feeders (also known as suspension feeders) are animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized structure, such as the baleen of baleen whales. ...

Land, water and air

Archosaurs are mainly portrayed as land animals, but:

• The crocodilians dominated the rivers and swamps and even invaded the seas (the Teleosaurs and Metriorhynchidae). The Metriorhynchidae were rather dolphin-like, with paddle-like forelimbs, a tail fluke and smooth, unarmoured skins.
• Their descendants the pterosaurs and the birds dominated the air.

Paleo Template Project The teleosaurids were marine crocodilians similar to the modern gharial. ... Paleo Template Project Metriorhynchids were a group of aquatic crocodilians that lived in seas during the Jurassic and Cretaceous periods. ... Suborders Rhamphorhynchoidea Pterodactyloidea Pterosaurs (TEH-row-sore, winged lizards) were flying reptiles of the clade Pterosauria. ...

Metabolism

The metabolism of archosaurs is still a controversial topic. They certainly evolved from cold-blooded ancestors, and the surviving non-dinosaurian archosaurs, crocodilians, are cold-blooded. But crocodilians have some features which are normally associated with a warm-blooded metabolism because they improve the animal's oxygen supply:

• 4-chambered hearts. Mammals and birds have 4-chambered hearts. Non-crocodilian reptiles have 3-chambered hearts, which are less efficient because they allow oxygenated and de-oxygenated blood to mix and therefore send some de-oxygenated blood out to the body instead of to the lungs. Modern crocodilians' hearts are 4-chambered, but are smaller relative to body size and run at lower pressure than those of modern mammals and birds. They also have a bypass which makes them functionally 3-chambered when under water, conserving oxygen.
• a secondary palate, which allows the animal to eat and breathe at the same time.
• a hepatic piston mechanism for pumping the lungs. This is different from the lung-pumping mechanisms of mammals and birds but similar to what some researchers claim to have found in some dinosaurs.^[4][5]

So, why did natural selection favour the development of these features, which are very important for active warm-blooded creatures but of little apparent use to cold-blooded aquatic ambush predators which spend the vast majority of their time floating in water or lying on river banks? The secondary palate exists in species with separate nasal cavities and oral cavities, in order to separate the two. ... Human respiratory system The lungs flank the heart and great vessels in the chest cavity. ... For other uses, see Natural selection (disambiguation). ...

Some experts believe that crocodilians were originally active, warm-blooded predators and that their archosaur ancestors were warm-blooded. Developmental studies indicate that crocodilian embryos develop fully 4-chambered hearts first and then develop the modifications which make their hearts function as 3-chambered under water. Using the principle that ontogeny recapitulates phylogeny, the researchers concluded that the original crocodilians had fully 4-chambered hearts and were therefore warm-blooded and that later crocodilians developed the bypass as they reverted to being cold-blooded aquatic ambush predators. ^[6][7] Ontogeny recapitulates phylogeny, also called the biogenetic law or the theory of recapitulation, is a now discredited hypothesis in biology first espoused in 1866 by Ernst Haeckel. ...

If the original crocodilians were warm-blooded and other "crurotarsan" archosaurs were also warm-blooded, this would help to resolve some evolutionary puzzles:

Terrestrisuchus

• The earliest crocodilians, e.g. Terrestrisuchus, were slim, leggy terrestrial predators whose build suggests a fairly active lifestyle, which requires a fairly fast metabolism. And some other "crurotarsan" archosaurs appear to have had erect limbs, while those of rauisuchians are very poorly adapted for any other posture. Erect limbs are advantageous for active animals because they avoid Carrier's constraint, but disavantageous for more sluggish animals because they increase the energy costs of standing up and lying down.
• If early archosaurs were completely cold-blooded and (as seems most likely) dinosaurs were at least fairly warm-blooded, dinosaurs would have had to evolve warm-blooded metabolisms in less than half the time it took for mammal-like reptiles to do the same.

Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Terrestrisuchus (land crocodile) is an extinct genus of crocodylian that was about 50 cm (1 ft 8 in) long. ... Families Family Prestosuchidae Family Rauisuchidae Family Poposauridae Rauisuchia are a poorly known assemblage of predatory and mostly large (often 4 to 6 meters) Triassic archosaurs. ... Carriers constraint is the observation that air-breathing vertebrates which have two lungs and and flex their bodies sideways during locomotion find it very difficult to move and breathe at the same time, because: the sideways flexing expands one lung and compresses the other. ... The physiology of dinosaurs has historically been a controversial subject, particularly thermoregulation. ...

Phylogeny

 Avesuchia `--Archosauria |--Crurotarsi | |-?Ctenosauriscidae | `--Crocodylotarsi | |--Ornithosuchidae | `--+--Phytosauria | `--Suchia | |--Prestosuchidae | `--Rauisuchiformes | |--Aetosauria | `--Rauisuchia | |--Rauisuchidae | `--+--Paracrocodylomorpha | `--Crocodylomorpha (crocodiles and relatives) `--Ornithodira |--Pterosauromorpha | |--Scleromochlus | `--Pterosauria `--Dinosauromorpha `--Dinosauriformes `--Dinosauria |--Ornithischia `--Saurischia `--Aves (birds) 

Subtaxa Phytosauridae Prestosuchidae Ornithosuchidae Stagonolepididae Rauisuchidae Poposauridae Crocodylomorpha     Sphenosuchia     Crocodilia Crurotarsi (cross-ankles) is a node-based taxon created by Paul Sereno in 1991 to supplant the old term Pseudosuchia. ... Genus Ornithosuchus Venaticosuchus Riojasuchus The Ornithosuchidae is a family of quadrupedal and facultatively bipedal crurotarsan archosaurs. ... Genera  ?Centemodon Paleorhinus Angistorhinus Brachysuchus Smilosuchus Leptosuchus Rutiodon Pseudopalatinae Nicrosaurus  ?Belodon Pseudopalatus Redondasaurus Angistorhinopsis Mystriosuchus Phytosaurs - family Phytosauridae or Parasuchidae - were a group of large (2 to 12 meters long - average size 3 to 4 meters) semi-aquatic predatory archosaurs that flourished during the Late Triassic period. ... Genera Batrachotomus Mandasuchus Prestosuchus Ticinosuchus Saurosuchus Yarasuchus Prestosuchidae are a group of Triassic carnivorous archosaurs. ... Genera Aetosaurus Calyptosuchus Coahomasuchus Desmatosuchus Longosuchus Neoaetosauroides Paratypothorax Redondasuchus Stagonolepis Tecovasuchus Typothorax The Aetosaurs (family Stagonolepididae order Aetosauria) are an extinct clade of heavily armoured, medium to large sized, Late Triassic herbivorous archosaurs. ... Families Family Prestosuchidae Family Rauisuchidae Family Poposauridae Rauisuchia are a poorly known assemblage of predatory and mostly large (often 4 to 6 meters) Triassic archosaurs. ... Genera Rauisuchus Fasolasuchus Lotosaurus Heptasuchus Tikisaurus ?Teratosaurus ?Postosuchus Rauisuchidae are a group of large (upto 6 meters or more) predatory Triassic archosaurs, and constitute advanced representatives of the larger group Rauisuchia. ... Groups see taxonomy The Crocodylomorpha are an important group of archosaurs that include the living crocodilians and their extinct relatives. ... Superorders Dinosauromorpha    Lagosuchians    Dinosauria Pterosauromorpha    Pterosauria    Scleromochlus    Sharovipteryx Ornithodira is a division of the Archosauromorpha (and perhaps Archosauria) clade. ... Suborders Rhamphorhynchoidea * Pterodactyloidea Pterosaurs (, from the Greek πτερόσαυρος, pterosauros, meaning winged lizard, often referred to as pterodactyls, from the Greek πτεροδάκτυλος, pterodaktulos, meaning winged finger ) were flying reptiles of the clade Pterosauria. ... Schleromochlus is the name of an archosaur from the early Triassic era, sharing many similarities in form with the pterosaurs which evolved years later, leading to speculation that it may have been an ancestor. ... Suborders Rhamphorhynchoidea Pterodactyloidea Pterosaurs (TEH-row-sore, winged lizards) were flying reptiles of the clade Pterosauria. ... Clades Lagerpeton Dinosauriformes Dinosauromorpha is the name of a superfamily of archosaurs that includes any direct ancestors of dinosaurs, or the order Dinosauria itself. ... Clades Dinosauria Eucoelophysis Lagosuchus Lewisuchus Marasuchus Pseudolagosuchus Sacisaurus Silesaurus Dinosauriformes is a clade of archosaurian reptiles that include the dinosaurs and their most immediate relatives. ... Orders Saurischia    Sauropodomorpha    Theropoda Ornithischia Dinosaurs are giant reptiles that dominated the terrestrial ecosystem for most of their 165-million year existence. ... Suborders Thyreophora Cerapoda    Ornithopoda    Marginocephalia Ornithischia is an order of beaked, herbivorous dinosaurs. ... Groups Sauropodomorpha    Saturnalia    Prosauropoda    Sauropoda Theropoda    Eoraptor    Herrerasauridae    Ceratosauria    Tetanurae       Aves(extant) Saurischians (from the Greek Saurischia meaning lizard hip) are one of the two orders/branches of dinosaurs. ... For other meanings of bird, see bird (disambiguation). ...

References

Further reading

• Benton, M. J. (2004), Vertebrate Paleontology, 3rd ed. Blackwell Science Ltd
• Carroll, R. L. (1988), Vertebrate Paleontology and Evolution, W. H. Freeman and Co. New York

An editor has expressed a concern that the subject of the article does not satisfy one of the guidelines for inclusion on Wikipedia on one of the following topics: If you are familiar with the subject matter, please expand the article to establish its notability, citing reliable sources. ... Robert L. Carroll (b. ...

External links

• UCMP
• Paleos reviews the messy history of archosaur phylogeny (family tree) and has an excellent image of the various archosaur ankle types.
• Mikko's Phylogeny Archive Archosauria