Reptiliomorpha

Reptiliomorpha is a tetrapod group comprising amniotes and their closer stem relatives, distinguished by shared ancestry nearer to amniotes than to living amphibians.

Tetrapoda: Tetrapoda is the vertebrate group comprising four-limbed animals and descendants that evolved from four-limbed ancestors. Reptiliomorpha is a major branch within the broader tetrapod evolutionary tree.
Cladistics: Cladistics classifies organisms into groups based on shared derived characteristics and common ancestry. Reptiliomorpha's membership and boundaries are evaluated through phylogenetic character analysis.
Seymouria: Seymouria is an extinct Permian tetrapod genus known from fossils in North America and Europe. Its terrestrial adaptations once encouraged interpretations of Seymouria as closely related to reptiles.
Reptiliomorpha (Laurin and Reisz definition): A phylogenetic definition of Reptiliomorpha as the clade closer to amniotes than to lissamphibians. This explicit definition differs from older classifications that treated the name as a narrower traditional group.
Amniota: Amniota is the tetrapod clade comprising mammals and reptiles, including birds, and their last common ancestor. Amniotes form the living and fossil core of Reptiliomorpha.
Phylogenetic tree: A phylogenetic tree is a branching diagram that represents hypotheses about evolutionary relationships among organisms. Trees show the hypothesized position of reptiliomorph lineages relative to amniotes and amphibians.
Diadectes: Diadectes is an extinct herbivorous tetrapod genus from the Late Carboniferous and Early Permian. Diadectes exemplifies large-bodied, terrestrial stem amniotes often classified among reptiliomorphs.
Anthracosauria: Anthracosauria is a historical name for a group of extinct tetrapods traditionally regarded as reptile-like amphibians. Older authors often used Anthracosauria for taxa now discussed within broader reptiliomorph classifications.
Amphibia: Amphibia is the vertebrate clade comprising frogs, salamanders, and caecilians and their common ancestor. Reptiliomorphs lie closer to amniotes than to this living amphibian lineage.
Synapomorphy: A synapomorphy is a shared derived character inherited from the common ancestor of a group. Shared derived traits help test whether fossil taxa belong on the amniote side of the split.

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