Echinerpeton

Echinerpeton Temporal range: Late Carboniferous, 308 Ma PreЄ Є O S D C P T J K Pg N ↓
Life restoration of Echinerpeton intermedium
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Synapsida
Family:	incertae sedis
Genus:	†Echinerpeton Reisz, 1972
Type species
†Echinerpeton intermedium Reisz, 1972

Echinerpeton is an extinct genus of synapsid, including the single species Echinerpeton intermedium from the Late Carboniferous of Nova Scotia, Canada. Along with its contemporary Archaeothyris, Echinerpeton is the oldest known synapsid, having lived around 308 million years ago. It is known from six small, fragmentary fossils, which were found in an outcrop of the Morien Group near the town of Florence. The most complete specimen preserves articulated vertebrae with high neural spines, indicating that Echinerpeton was a sail-backed synapsid like the better known Dimetrodon, Sphenacodon, and Edaphosaurus. However, the relationship of Echinerpeton to these other forms is unclear, and its phylogenetic placement among basal synapsids remains uncertain.

Echinerpeton is known from six specimens, five housed in the Museum of Comparative Zoology and a sixth in the Redpath Museum: the holotype MCZ 4090, which consists of a partial postcranial skeleton and some jaw fragments; MCZ 4091, which includes vertebrae and an interclavicle; MCZ 4092, a left maxilla or upper jaw bone; MCZ 4093, a partial right maxilla; MCZ 4094, including three neural arches or vertebral spines; and RM 10057, consisting of a right maxilla, neural arch, rib, and a phalanx or finger bone. Since all other specimens besides the holotype are isolated bone fragments, their assignment to the same species is not certain. The maxillae are distinct in having straight lower margins, distinct from the often curved jaws of ophiacodontids and sphenacodontids but similar to the straight jaws of some other synapsids like Archaeothyris, Haptodus, and Varanops. The dentary or lower jaw bone has a slight upward curve. The teeth of both the upper and lower jaws are small and cone-shaped, some having slightly serrated edges, and are only differentiated by slight differences in length (some other synapsids have teeth that vary greatly and shape across their jaws). The three forward-most dentary teeth are angled slightly outward as in more derived synapsids such as Dimetrodon and Sphenacodon. Several features, including straight-margined maxillae and simple conical teeth, are also seen in the earliest reptiles.