| Seymouriamorpha Temporal range: Late Carboniferous[1] - Late Permian | |
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| Fossil of Seymouria in the National Museum of Natural History | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Reptiliomorpha (?) |
| Order: | †Seymouriamorpha Watson, 1917 |
| Subgroups | |
Seymouriamorpha were a small but widespread group of limbed vertebrates (tetrapods). They have long been considered stem-amniotes (reptiliomorphs), and most paleontologists still accept this point of view, but some analyses suggest that seymouriamorphs are stem-tetrapods (not more closely related to Amniota than to Lissamphibia).[2] Many seymouriamorphs were terrestrial or semi-aquatic. However, aquatic larvae bearing external gills and grooves from the lateral line system have been found, making them unquestionably amphibians. Though as they matured, they became more terrestrial and reptile-like. They ranged from 30 cm (1 ft) long lizard-sized creatures to the 1.5 m (5 ft) long Enosuchus. If seymouriamorphs are reptiliomorphs, they were the distant relatives of amniotes. Seymouriamorphs form into three main groups, Kotlassiidae, Discosauriscidae, and Seymouriidae, a group that includes the best known genus, Seymouria. The last seymouriamorph became extinct by the end of the Permian.[3]
Cladogram based on Ruta, Jeffery, & Coates (2003):[5]
| Seymouriamorpha | |
Cladogram based on Klembara (2009) & Klembara (2010):[6][7]
| Seymouriamorpha |
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| Seymouriamorpha |
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