Pelycosaur
order of tetrapods
Pelycosaur ( PEL-ih-kə-sor) is an older term for basal or primitive Late Paleozoic synapsids, excluding the therapsids and their descendants. Previously, the term mammal-like reptile was used, and Pelycosauria was considered an order, but this is now thought to be incorrect and outdated. The terms stem mammals, protomammals, and basal or primitive synapsids are instead used where needed.
Because Pelycosaur excludes its own descendants, the advanced synapsid group Therapsida, the term is paraphyletic and contrary to modern formal naming practice. Thus the name pelycosaurs, similar to the term mammal-like reptiles, fell out of favor among scientists by the 21st century, and is only used informally, if at all, in the modern scientific literature.
Etymology
The modern word was created from Greek pélyx meaning 'basin' and saûros meaning 'lizard'. The term pelycosaur has been fairly well abandoned by paleontologists because it no longer matches the features that distinguish a clade.
In phylogenetic nomenclature, "Pelycosauria" is not used formally, since it does not constitute a group of all organisms descended from some common ancestor (a clade), specifically excluding therapsids, which are descended from pelycosaurs. Instead, it represents a paraphyletic "grade" of basal synapsids leading up to the clade Therapsida.
Eupelycosauria is used as a proper monophyletic group to designate the clade that includes most pelycosaurs, along with the Therapsida and Mammalia.
“Pelycosaur” enters the record as order of tetrapods. Crown Archives preserves that source wording while asking what Pelycosaur, order and tetrapods can confirm, complicate or overturn.
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Named sources, stable identifiers and responsible institutions provide the strongest route from overview to verifiable evidence. The source revision retrieved here is dated Jul 5, 2026. The linked authority identifier is Q319520. None of the 0 selected statements returned an explicit reference.
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This entry incorporates text from “Pelycosaur” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.