Ophiacodon navajovicus

Ophiacodon 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.

Ophiacodon has a large skull with a deep snout. It has the longest skull of any early synapsid, reaching up to 50 centimetres in one specimen. The jaws are lined with many small teeth. It was larger than most other tetrapods of its time, ranging from 1.6 to 3 metres in length and 26 to 230 kilograms in weight. Specimens of Ophiacodon vary greatly in size.