Protoclepsydrops

Protoclepsydrops was an early amniote from about 314 million years ago. Its remains were found at the Joggins Fossil Cliffs World Heritage Site. The dating of this site has been debated, with dates from 320 million years ago (mya) to 305 mya being suggested.p39 It is now settled as 314.5–313.4 mya +/- 1.1 million years.p40
The skeletal remains of "Protoclepsydrops" suggest it may have been a synapsid. If so, it is the oldest synapsid known, though its status is unconfirmed because its remains were fragmentary. "Protoclepsydrops" lived slightly earlier than "Archaeothyris", which was definitely a synapsid. Like "Archaeothyris", "Protoclepsydrops" had a body shape which resembled modern lizards.