Protoclepsydrops was a Synapsid from Carboniferous Nova Scotia.  It was one of the first Synapsids (this group evolved into the mammal-like reptiles) Therapsids, and eventually the true mammals.  It was also one of the first Amniotes (reptiles) and lived alongside other primitive amniotes like Hylonomus and Petrolacosaurus.
Community content is available under CC-BY-SA unless otherwise noted.