Temporal range: Late Carboniferous (Middle Pennsylvanian), 312Ma
Protoclepsydrops was an early amniote, found in Joggins, Nova Scotia. Its skeletal remains indicate that it may have been more closely related to synapsids than to sauropsids, making it a possible synapsid member. If so, it is the oldest synapsid known, though its status is unconfirmed because its remains were fragmentary. Protoclepsydrops lived slightly earlier than Archaeothyris. Like Archaeothyris, Protoclepsydrops resembled modern lizards. However, Protoclepsydrops still had primitive vertebrae with tiny neural processes typical of the amniotes amphibian ancestors.
- Carroll, Robert L. (1964). "The earliest reptiles". Journal of the Linnean Society of London, Zoology 45 (304): 61–83. doi:10.1111/j.1096-3642.1964.tb00488.x. Retrieved 4 May 2012.
- Benton M.J. and Donoghue P.C.J. 2006. Palaeontological evidence to date the tree of life. Molecular biology and evolution. 24(1): 26–53. 
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