Ischyodus

Ischyodus is an extinct genus of cartilaginous fish belonging to the subclass Holocephali, which includes the modern-day chimaeras. Fossils are known from Europe (including Russia), North America, and New Zealand.

Ischyodus was rather similar to the present-day chimaera Chimaera monstrosa, which is found in the Atlantic Ocean and Mediterranean Sea. Just like C. monstrosa, Ischyodus had large eyes, a long whip-like tail, small lips, large pectoral fins and dorsal fin, and a dorsal spike attached to the front of the dorsal fin. The spike probably served as a method of protection against predators, and may have been venomous, as it is in modern chimaeras.[1]

Dental plates of at least two species, Ischyodus rayhaasi and Ischyodus dolloi, have been found at several sites in North Dakota.