Eocyclotosaurus (Greek ‘èoos’ = dawn, ‘kyklos’ = circle, 'ous' = ear ) is an extinct genus of mastodonsauroid temnospondyl from the Middle Triassic (Anisian).

It lived between 247 and 242 million years ago in both North America, Germany, France and the British Isles during the early Triassic.

[7] The tabular horn is situated on the side and toward the back of the body / laterally directed and suturing with the squamosal posteriorly.

[10] The reduction of the cross section  of its skull and the elongation of its nasal bones was an adaptation to reduce drag during lateral movement of the head, increasing the efficiency of aquatic feeding.

[9] By the early Anison, most major crown clades were present: heylerosaurids (Eocyclotosaurus), mastodonsaurids, stenotosaurids.

[1] The origin of the genus Eocyclotosaurus was at the Spanthaian and Anisian boundary, separate from Cyclotosaurus in the late Ladiunian.