Diapsida

Diapsida
Various members of the Diapsida Above: North American copper head , star weaver Middle: Mississippi alligator , Heterodontosaurus Below: Tupuxuara , Platypterygius
Systematics
Vertebrates (vertebrata) Jaw mouths (Gnathostomata) Land vertebrates (Tetrapoda) Amniotes (Amniota) Sauropsida Diapsida
Scientific name
Diapsida
Osborn , 1903

The Diapsida (German: Diapsiden ) are a large group of reptiles or Sauropsida . It is the most diverse group of reptiles in the history of the earth . The diapsids include purely land-living representatives, but also aquatic and airworthy forms. Both the adaptation to a life in the water and the ability to fly developed independently of each other in different diapsid groups.

features

Schematic representation of a diapsid skull

The name "Diapsida" refers to the two openings in the cheek or temple region (tempora) behind the eye socket (orbit), which are called the upper and lower temple or temporal window. This skull configuration is called a diapsid skull (see also Amniotic skull types ). The function of the windows lies in the saving of bone substance and, as a result, a weight reduction and a certain flexibility of the skull. They also offer additional paths and points of attachment for the jaw muscles .

The lower opening is bordered by the same skull bones that are involved in the only window in the skull of fossil synapsids: Squamosum (sq), postorbital (po) and jugale (j) and originally also quadratojugale (qj). The upper window is framed by the squamosum, postorbital and parietal (p), with fossil representatives it is not uncommon for the postfrontal to appear.

The diapsid skull is the nominal characteristic of the diapsids, but it represents a rather original state that was changed several times independently in different groups in the course of the evolution of the diapsids:

• The Schuppenkriechtieren , as well as in some early forms of (Squamata), including, for example, include the lizards Archosauromorpha no lower Temporalbogen is present (so-called. Katapside skull configuration). Presumably, neither the lower temporal arch of the bridge lizards nor that of the crocodiles goes back to the original diapside skull configuration of z. B. Petrolacosaurus back, but is secondary from a catapsid state out of new.
• If the turtles belong to the Diapsids, then both temple windows would be completely closed again.
• Even in today's birds, the original diapside skull anatomy is no longer recognizable due to numerous modifications of the skull in the course of adaptation to flying and the development of the musculoskeletal system of the beak.
• In the case of double snakes and snakes, both subgroups of the squamats with partly highly specialized skulls, there are no longer any obvious temple windows.

Systematics

Skull drawing of Youngina , an original diapsid reptile from the Permian of the Karoo Basin in South Africa .

Live reconstruction of the Avicephalen Coelurosauravus from the Permian of Europe and Madagascar

Drawing of the skull of the bridge lizard ( Sphenodon ). In contrast to Youngina , the quadratojugale is not involved in the lower temporal arch here.

Live reconstruction of Arizonasaurus , a large archosaur from the Middle Triassic of North America

Skull of Araripesuchus , a crocodile from the Cretaceous North Africa
( a from the side, b from above, c from below)

Basics

The Diapsida are traditionally a subclass of the class of reptiles (Reptilia). However, the reptiles are not a natural family group ( Monophylum ). Birds and mammals are descended from Permo Mesozoic terrestrial vertebrates , which conform to the classic definition of Reptilia, as they laid hard-shell eggs and were both hairless and feathered. Birds and mammals themselves, however, do not correspond to this classic definition and are therefore traditionally not included in the reptilia. Since this exclusion does not correctly depict evolution, the classic concept of Reptilia has been replaced by the newer concept of Amniota . The amniotes include all terrestrial vertebrates that can reproduce independently of water, regardless of their body covering.

External system

The amniotes are divided into two main lines: the Sauropsida (Reptilia) with today's reptiles and birds and the Synapsida with today's mammals . The Diapsiden are therefore a subgroup of the Sauropsida. If fossil taxa are included , the Sauropsida or Reptilia fall into two major groups: the Eureptilia and the Parareptilia (Anapsida). The diapsids are then a subgroup of the eureptiles.

Amniota	Synapsida   Sauropsida  (Reptilia)    Parareptilia †   Eureptilia    Captorhinidae †   Romeriida    Paleothyris †      Diapsida

Internal system

The recent diapsids are divided into two main groups: the scale lizards (Lepidosauria) with the bridge lizards , " lizards " and snakes and the archosauria with the crocodiles and birds. Here, too, the system is somewhat more complicated when including fossil taxa (see below). According to more recent findings, the turtles are probably also diapsids.

The earliest fossil finds of diapsids come from the Upper Carboniferous North America. These are relatively small, lizard-like representatives, which were described under the names Petrolacosaurus and Spinoaequalis . Both are very original diapsids that lived before the split into Lepidosauria and Archosauria.

• Diapsida
  • Araeoscelidia †
  • Avicephala †
  • Thalattosauria †
  • Younginiformes †
  • Ichthyopterygia †
  • Lepidosauromorpha
    • Eolacertilia †
    • Sauropterygia †
    • Scale lizards (Lepidosauria)
      • Sphenodontia : bridge lizards and extinct relatives
      • Scale reptiles (Squamata): " lizards ", double creeps and snakes
  • Archosauromorpha
    • Choristodera †
    • Prolacertiformes †
    • Rhynchosauria †
    • Trilophosauria †
    • Archosauria
      • Crurotarsi
        • Aetosauria †
        • Phytosauria †
        • Rauisuchia †
        • Crocodylomorpha : crocodiles and extinct relatives
      • Ornithodira
        • Flugsaurier (Pterosauria) †
        • Dinosaur (dinosauria)
          • Birds (aves)

Individual evidence

1. ^ Johannes Müller: Early loss and multiple return of the lower temporal arcade in diapsid reptiles. Natural sciences. Vol. 90, No. 10, 2003, pp. 473-476, doi : 10.1007 / s00114-003-0461-0 .
2. ↑ Michel Laurin, Robert R. Reisz: A reevaluation of early amniote phylogeny. Zoological Journal of the Linnean Society. Vol. 113, No. 2, 1995, pp. 165-223, doi : 10.1111 / j.1096-3642.1995.tb00932.x .
3. ↑ Rafael Zardoya, Axel Meyer: Complete mitochondrial genome Suggests diapsid affinity of turtles. Proceedings of the National Academy of Sciences of the United States of America. Vol. 25, No. 19, 1998, pp. 14226-14231, doi : 10.1073 / pnas.95.24.14226 .
4. ↑ Ylenia Chiari, Vincent Cahais, Nicolas Galtier, Frédéric Delsuc: Phylogenomic analyzes support the position of turtles as the sister group of birds and crocodiles (Archosauria). BMC Biology 2012, 10:65, doi : 10.1186 / 1741-7007-10-65 ( Open Access ).

literature

• Robert L. Carroll: Paleontology and Evolution of the Vertebrates. Thieme-Verlag, Stuttgart, 1993, ISBN 3-13-774401-6 .
• Michael SY Lee: Molecules, morphology, and the monophyly of diapsid reptiles. Contributions to Zoology. Vol. 70, No. 1, 2001 ( online ).

Web links

Commons : Diapsida  - collection of pictures, videos and audio files

• Diapsida - reptiles with two temporal openings Mikko's Phylogeny Archive
• Diapsida in Tree of Life Web Project