Tajaroceras is an extinct slender cephalopod from the uppermost Lower Ordovician of western North America, belonging to the Orthocerid family Troedssonellidae.
Along the ventral side, within the siphuncle, is a continuous rod, much like that found in a group known as rod-bearing Baltoceratidae.
On the dorsal side, overlying within, are annular deposits that grow forward to form a continuous lining that ultimately rests against the ventral rod, leaving a small opening slightly above the center.
Tajaroceras, first described by Hook and Flower (1976), has been found in the Upper Cassinian Wahwah Limestone in Western Utah and in the equivalent Florida Mountains Formation in Southern New Mexico and is the probable ancestor of the Troedssonellidae, being followed in overlapping sequence by Buttsoceras.
The type, Tajaroceras wardae, was found 55–65 ft above the base of the Wahwah Ls in the Ibex area of western Utah.