page_title: Eupelycosauria
section_title: Classification
hierarchical_section_title: Eupelycosauria / Classification
caption_attribution_description: English: Archaeothyris, pencil drawing.
context_page_description: The Eupelycosauria originally referred to a suborder of 'pelycosaurs', but has been redefined to designate a clade of synapsids that includes most pelycosaurs, as well as all therapsids and mammals. They first appear during the Early Pennsylvanian epoch, and represent just one of the many stages in the acquiring of mammal-like characteristics, in contrast to their earlier amniote ancestors. The defining characteristics which separate these animals from the Caseasauria are based on details of proportion of certain bones of the skull. These include a long, narrow supratemporal bone, and a frontal bone with a wider connection to the upper margin of the orbit.
context_section_description: The following cladogram follows the one found on Mikko's Phylogeny Archive.
caption: Archaeothyris belongs to the Ophiacodontidae and appears in the Early Pennsylvanian
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