An amniote characterized by having a single temporal opening (fenestra) behind each eye socket in the skull, representing the evolutionary lineage that includes mammals and their extinct relatives like pelycosaurs and therapsids.
From Greek 'syn' meaning 'together' and 'opsis' meaning 'arch,' referring to the single temporal arch in the skull. The term was coined in the early 20th century when paleontologists developed classification systems based on skull window patterns.
Synapsids are the rebels of the reptile world who eventually became mammals - they were the first amniotes to experiment with hair, warm blood, and live birth! While dinosaurs ruled the land, early synapsids were already developing the mammalian features that would later allow our ancestors to survive the mass extinction that killed the dinosaurs.
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