| Named By: | Othniel Charles Marsh in 1878 |
| Time Period: | Late Carboniferous to Early Permian 306-280 Ma |
| Location: | Canada, Nova Scotia. USA, New Mexico - Cutler Formation, Texas - Admiral Formation, Putnam Formation |
| Size: | Up to 3 meters long for the largest species, possibly slightly larger |
| Diet: | Carnivore/Piscivore |
| Fossil(s): | Many specimens allowing for accurate reconstruction |
| Classification: | | Chordata | Synapsida | Pelycosauria | Eupelycosauria | Ophiacodontidae | |
Ophiacodon (meaning "snake tooth") is an extinct genus of synapsids belonging to the family Ophiacodontidae that lived from the Late Carboniferous to the Early Permian in North America and Europe. The genus was named along with its type species O. mirus by paleontologist Othniel Charles Marsh in 1878 and currently includes five other species. As an ophiacodontid, Ophiacodon is one of the most basal synapsids and is close to the evolutionary line leading to mammals.