Reptiliomorpha

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Reptiliomorpha
Fossil range: Early Carboniferous - Middle Triassic (non-amniote)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Superclass: Tetrapoda
Superorder: Reptiliomorpha
Säve-Söderbergh, 1934
Major Sub-Groups

Reptiliomorpha is a name given either to reptile-like tetrapods, or to amniotes and those tetrapods related to them.

Contents

[edit] Changing Definitions

The name Reptiliomorpha was coined by Professor Gunnar Säve-Söderbergh in 1934 to designate various types of late Paleozoic reptile-like labyrinthodont amphibians.

However Alfred Sherwood Romer used the name Anthracosauria instead, and this has been used until quite recently e.g. Carroll 1988.

In 1956 Friedrich von Huene included both amphibians and anapasid reptiles in the Reptiliomorpha. This included the following orders: 1. Anthracosauria, 2. Seymouriamorpha, 3. Microsauria, 4. Diadectomorpha, 5. Procolophonia, 6. Pareiasauria, 7. Captorhinidia, 8. Testudinata.

In 1997 Michel Laurin and Robert Reisz (1997) adapted the term in a cladistic sense. Michael Benton (2000, 2004) mades it the sister-clade to Batrachomorpha. However, when considered a linnean ranking, Reptiliomorpha is given the rank of superorder and only includes reptile-like amphibians [Systema Naturae 2000]. More recently Reptiliomorpha has been adopted as the term for the largest clade that includes - according to the technical definitions of the phylocode which only refers to species or genus level organisms - Homo sapiens but not Ascaphus truei (a primitive frog) (International Phylogenetic Nomenclature Meeting 2003). Or, as Toby White (Palaeos website) puts it, more like dogs than frogs (i.e. mammals but not amphibians).

[edit] Characteristics

Dr Michael Benton (2000, 2004) gives the following characteristics for the Reptiliomorpha:

  • narrow premaxillae (less than half the skull width)
  • vomers taper forward
  • phalangeal formulae (number of joints in each toe) of foot 2.3.4.5.4-5

[edit] Evolutionary history

During the Carboniferous and Permian periods, tetrapods evolved along a number of parallel lines towards a reptilian condition. Some of these tetrapods (e.g. Archeria, Eogyrinus) were elongate, eel-like aquatic forms with diminutive limbs, while others (e.g. Seymouria, Solenodonsaurus, Diadectes, Limnosceles) were so reptile-like that until quite recently they actually have been considered true sauropsids, and it is likely that to an observer they would have appeared like small or large reptiles.

Although the first amniote probably appeared as early as the latest Mississippian period (Middle Carboniferous), reptilomorph tetrapods continued to flourish alongside their fully reptilian descendents and relatives for many millions of years.

By the middle Permian the terrestrial forms had died out, but several aquatic groups continued to the end of the Permain, and in the case of the Chroniosuchids survived the end Permian mass extinction, only to die out at the end of the Early Triassic. Meanwhile, the single most successful daughter-clade of the Reptiliomorphs, the Amniotes, continued to flourish and to inherit the Earth.

[edit] Taxonomy

Classification after Laurin & Reisz (1997):

  • Superclass Tetrapoda
    • Superorder Reptiliomorpha
      • Family Caerorhachidae
      • Family Tokosauridae
      • Order Chroniosuchia
        • Family Chroniosuchidae
      • Order Emblomeri
        • Family Eoherpetontidae
        • Family Anthracosauridae
        • Family Proterogyrinidae
        • Family Eogyrinidae
        • Family Archeriidae
      • Order Seymouriamorpha
        • Family Kotlassiidae
        • Family Discosauriscidae
        • Family Seymouriidae
    • (unranked) Cotylosauria

[edit] References and External links

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