|Named By:||Robert R. Reisz in 1972|
|Time Period:||Late Carboniferous, 306 Ma|
|Location:||Canada, Nova Scotia. Czech Republic, Nyrany. USA, Ohio|
|Size:||50 centimetres long|
|Classification:||| Chordata | Tetrapoda | Synapsida | Pelycosauria | Ophiacodontidae ||
Archaeothyris is an extinct genus of ophiacodontid synapsid that lived during the Late Carboniferous and is known from Nova Scotia. Dated to 306 million years ago, Archaeothyris, along with a more poorly known synapsid called Echinerpeton, are the oldest undisputed synapsids known. Protoclepsydrops also from Nova Scotia is slightly older but is known by very fragmentary materials.