Seymouriamorpha
| Seymouriamorpha Temporal range: Early Permian - Late Permian |
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| Skeleton of Seymouria in the National Museum of Natural History | |
| Scientific classification | |
| 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 reptiliomorphs, and most paleontologists may still accept this point of view, but some analyses suggest that seymouriamorphs are stem-tetrapods (not more closely related to Amniota than to Lissamphibia). 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. The adults were terrestrial. They ranged from lizard-sized creatures (30 centimeters) to crocodile-sized 150 centimeter long animals. They were reptile-like. 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 Permian.
Cladogram based on Ruta, Jeffery, & Coates (2003):
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