Protoclepsydrops is an extinct genus of early synapsids, found in Joggins, Nova Scotia.[1] The name means 'first Clepsydrops', and refers to it being the predecessor of the other early synapsid Clepsydrops.
Like Archaeothyris, Protoclepsydrops resembled a modern lizard in superficial appearance. However, Protoclepsydrops had primitive vertebrae with tiny neural processes typical of their amniote ancestors. Protoclepsydrops is known from a few vertebrae and some humeri.[2]
Its skeletal remains indicate that it may have been more closely related to synapsids than to sauropsids, making it a possible stem-mammal. If so, it is the oldest synapsid known, though its status is unconfirmed because its remains are too fragmentary. Protoclepsydrops lived slightly earlier than Archaeothyris.[3]