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Crocodiles and birds are recent archosaurs

Crocodiles and birds are recent archosaurs

Sub-stem : Vertebrates (vertebrata)
Superclass : Jaw mouths (Gnathostomata)
Row : Land vertebrates (Tetrapoda)
without rank: Amniotes (Amniota)
without rank: Sauropsida
without rank: Archosauria
Scientific name
Cope , 1869

The Archosauria are a group diapsider Amniota which the crocodiles (Crocodylia) and birds (Aves) and various fossil groups, including the Flugsaurier (Pterosauria) and the dinosaur comprises. Archosaurs were the dominant vertebrates on land and in the air for much of the Mesozoic Era . Even today they represent a significant part of the vertebrate fauna with over 10,000 species.

Etymology and Definitions

The zoologist Edward Drinker Cope coined the name "Archosauria" because of the temporal arches (Latin singular: arcus temporalis ) that the archosaur skull has due to the openings in its rear part. But it is mostly interpreted with reference to ancient Greek : ἀρχός, archos, "leader, prince" as "the highest standing reptiles ".

The term Archosauria describes the crown group of crocodiles and birds, i.e. includes the last common ancestor of crocodiles and birds as well as all of their descendants. This corresponds to the Archosauria term commonly used in biology.

A second definition preferred by some paleontologists, however, includes other, more original and older groups outside the crown group, such as the Erythrosuchidae , Proterochampsidae , Proterosuchidae and Euparkeria , thus designating a more inclusive taxon. In order to differentiate it from the crown archosaurs in terms of nomenclature, this is also referred to as archosauriformes . Conversely, the crown archosaurs are called Avesuchia to distinguish them from the more inclusive archosauria .


The original archosaur skull (schematic representation) has three cranial windows: pre-orbital windows between lacrimale (l) and maxillary (m) and the two temporal windows between parietal (p), postorbital (po) and squamosum (sq) or postorbital, squamosum, jugale (j ) and quadratojugale (qj).

The most important common features ( synapomorphies ) of archosaurs can be found in the structure of the skull . This originally has a total of three skull windows and is therefore called a triapsid skull . The antorbital window (pre-orbital window) is located in front of the eye socket (orbit); two further skull windows, the so-called temple windows (temporal windows), are located behind the eye socket. The two temple windows show that the archosaurs belong to the diapsids.

However, this is not the case for the archosaurs living today. They have relatively highly specialized skulls that are no longer triapsid. The crocodiles have clearly defined temple windows, but the anterior orbital window is closed in them. In birds, the antorbital window is only indistinct, e.g. Sometimes not at all delimited from the eye socket and the temporal windows are small and also fused with the eye socket.

The lower jaw (mandible) originally also has a window, which is called the mandibular window and is still present in crocodiles. The attachment of the teeth in the jawbone is thecodont, i.e. This means that the teeth each sit in their own tooth socket (alveolus), where they are connected to the bone by connective tissue, and do not have multi-part tooth roots. The teeth of modern birds and some groups of dinosaurs have receded.

Many purely fossil archosaur groups ( aetosaurs , phytosaurs , ankylosaurs ) as well as the fossil and currently living crocodiles had or have a back armored with bone platelets ( osteoderms ) embedded in the skin .

Tribal history

Head reconstruction of Archosaurus rossicus from the Upper Permian of the central Russian Oblast Vladimir

The first appearance of the archosaurs is dated for the crown group (Archosauria or Avesuchia) on the upper Lower Triassic ( Olenekian ), for the Pan group (Archosauria or Archosauriformes) on the upper Upper Permian . One of the oldest representatives of the Pan-Archosauria is Archosaurus rossicus from the Upper Permian.

In the Lower Triassic basal Archosauriformes took over the role of the synapsid apex predators (carnivores at the top of the food chain) from the groups Gorgonopsia and Titanosuchia, which became extinct on the Permian-Triassic border . Another radiation took place in the Upper Triassic with the emergence of the dinosaurs and pterosaurs ( Ornithodira ). In the Jurassic and Cretaceous , the dinosaurs in particular produced enormous diversity. The archosaurs were the dominant group of terrestrial vertebrates during this period. After the mass extinction at the border between the Cretaceous and the Paleogene ( Cretaceous-Tertiary border ) about 65 million years ago, at least one group of the dinosaur line, the birds, has survived to this day.

The crocodile line ( Crurotarsi ) took a completely different development. In the course of the Upper Triassic, their representatives were increasingly displaced from their traditional habitats on land by the dinosaurs and retreated into the water from the Jura onwards, creating the primeval, lizard-like habit that is typical of today's crocodiles.


The formation of the ankle is of central importance for the structure of the Archosauria crown group. The crurotarsi (crocodiles and fossil relatives) are compared to the ornithodira (pterosaurs and dinosaurs including birds) with their mesotarsal joint, in which the astragalus and calcaneus form the joint due to their typical crurotarsal joint, in which the joint between the tarsal bones astragalus and calcaneus occurs with the distal (closer to the toe) tarsal bones.

In contrast, the basal pan and crown archosaurs, which used to be grouped under the name " Thecodontia ", are not a natural family group ( monophylum ), but a paraphylum .

The probable family relationships are given by the following cladogram (according to Benton, 2007) ('Archosauria' here refers to the Pan group):

 Archosauria 1  

 †  Proterosuchidae


 †  Erythrosuchidae


 †  Euparkeria

  Avesuchia 2  

 †  Phytosauridae


 †  Stagonolepididae


 †  Ornithosuchidae


 †  Rauisuchia


 Crocodylomorpha  including  crocodiles  (Crocodylia)

Template: Klade / Maintenance / 3Template: Klade / Maintenance / 4


 †  Scleromochlus


 †  Flugsaurier  (Pterosauria)


 †  Storage peton


 †  Marasuchus


 Dinosaurs  (Dinosauria) including  birds  (Aves)

Template: Klade / Maintenance / Style

Footnotes: 1) Archosauria sensu lato or Archosauriformes; 2) Archosaur crown group


Individual evidence

  1. Pamphlets on Biology: Kofoid collection , vol. 2900 (1878), p. 731 .
  2. Richard J. Butler, Stephen L. Brusatte, Mike Reich, Sterling J. Nesbitt, Rainer R. Schoch and Jahn J. Hornung: The sail-backed reptile Ctenosauriscus from the latest Early Triassic of Germany and the timing and biogeography of the early archosaur radiation . In: PLoS One . 6, No. 10, 2011, p. E25693. doi : 10.1371 / journal.pone.0025693 .
  3. ^ S. J. Nesbitt: The early evolution of archosaurs: relationships and the origin of major clades . In: Bulletin of the American Museum of Natural History . 352, 2011, pp. 1-292. doi : 10.1206 / 352.1 .
  4. D. J. Gower, A. G. Sennikov: Early archosaurs from Russia . In: M. J. Benton, M. A. Shishkin, D. M. Unwin (Eds.): The Age of Dinosaurs in Russia and Mongolia. Cambridge University Press, Cambridge (UK) 2003, pp. 140-159.
  5. ^ S. L. Brusatte, M. J. Benton, J. B. Desojo, M. C. Langer: The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida) . In: Journal of Systematic Palaeontology . 8, No. 1, 2010, pp. 3-47. doi : 10.1080 / 14772010903537732 .

Web links

Commons : Archosauria  - collection of images, videos and audio files