Pelycosaur

A member of Pelycosauria, a traditional grouping of early synapsids that includes sail-backed animals such as Dimetrodon. The group is not considered a natural clade in modern classification.

Synapsid: A vertebrate with one temporal opening on each side of the skull, including mammals and their extinct relatives. Pelycosaurs belong to the early branches of this lineage.
Dimetrodon: An extinct sail-backed synapsid genus that lived in the Early Permian of North America and Europe. Its distinctive back sail made it the best-known animal traditionally called a pelycosaur.
Therapsid: A diverse group of synapsids that includes mammals and their extinct relatives, often called mammal-like reptiles. Therapsids are a major synapsid branch that followed early forms traditionally called pelycosaurs.
Mammalian jaw: A jaw in which the dentary bone forms the lower jaw and meets the squamosal bone at the jaw joint. Changes in synapsid jaw bones trace a long transition beyond early pelycosaur-grade forms.
Amniote: A vertebrate whose embryo develops within an amnion, including reptiles, birds, and mammals. Pelycosaurs were amniotes, part of the broader group that diversified on land.
Edaphosaurus: An extinct herbivorous synapsid genus with a tall back sail bearing crossbars. It demonstrates that sail-backed pelycosaurs were not all predators.
Mammalia: The class of vertebrates characterized by features including hair and milk-producing mammary glands. Mammals descend from synapsid lineages once grouped with pelycosaurs.
Mammalian middle ear: The middle ear of mammals, whose three tiny bones evolved from bones of the ancestral jaw joint. Its evolutionary history connects synapsid skull changes with the mammalian lineage.
Temporal fenestra: An opening in the skull behind the eye socket that provides space for jaw muscles. The synapsid skull opening is a defining feature of pelycosaur ancestry.
Ophiacodon: An extinct, large-bodied early synapsid genus known from the Permian of North America and Europe. It represents a pelycosaur without the prominent sail of Dimetrodon.

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