Reptiliomorpha

The reptiliomorphs (Reptiliomorpha, “reptilian-shaped”) are a clade of tetrapods that combine both reptile and amphibian characteristics. They originated at the beginning of the Carboniferous period, exhibiting both aquatic and terrestrial forms. By the middle of the Permian period, all land forms had become extinct. Only the family Chroniosuchidae and amniotes (which originated in the late Carboniferous) survived the Permian-Triassic mass extinction; the former extended until the end of the Lower Triassic, while the amniotes flourished and continued to diversify.

Reptiliomorphs and the origin of amniotes

It may never be known where the border between non-amniote (amphibian) reptiliomorphs and true amniotes lies, since the reproductive structures involved rarely fossilize. It is not known with certainty which was the first amniote, although several candidates have been proposed, such as the small Solenodonsaurus, Casineria and Westlothiana; these animals laid small eggs, 1 cm in diameter or less, that would have a sufficient volume/surface ratio to develop on land without active gas exchange between the amnion and chorion, which may have been the intermediate stage toward true amniotic egg.

Although the first amniote probably appeared as early as the Middle Mississippian, non-amniote reptiliomorphs (or amphibians) continued to flourish alongside their amniote descendants for many millions of years. Terrestrial non-amniotes had disappeared by the Middle Permian, but many aquatic species reached the end of the Permian and even survived the Permian-Triassic mass extinction, such as chroniosuchids.

Taxonomy

Classification based on Benton (2004).

• Superclass Tetrapoda
  • Superorden Reptiliomorpha
    • Family Caerorhachidae
    • Tokosauridae Family
    • Order Chroniosuchia
      • Bystrowianidae
      • Chroniosuchidae family
    • Order Embolomeri
      • Eoherpetontidae
      • Anthracosauridae
      • Family Proterogyrinidae
      • Eogyrinidae
      • Family Archeriidae
    • Order Seymouriamorpha
      • Kotlassiidae
      • Family Discosauriscidae
      • Seymouriidae
    • Order Cotylosauria
    • Order Diadectomorpha
      • Family Limnoscelidae
      • Family Diadectidae
    • Class Amniota