1. a member of a major group of vertebrates that includes mammals and their extinct relatives, characterized by having a single opening in the skull behind each eye socket
Usage: paleontology; zoology

1. relating to or characteristic of synapsids
Usage: paleontology; zoology

Examples

• Early synapsids dominated terrestrial ecosystems before the rise of dinosaurs.
• The fossil skull showed the characteristic single temporal opening of a synapsid.
• Mammals are the only surviving group of synapsids today.
• Scientists discovered synapsid remains dating back 300 million years.
• The synapsid lineage eventually gave rise to all modern mammals.
• This synapsid species had features that were transitional between reptiles and mammals.