Damocles

Damocles serratus is a stethacanthid shark most closely related to Falcatus falcatus, the unicorn shark. It ranges in size to at least two feet. Larger than F. falcatus, they were the next size step up the predator ladder. Considerably larger but very similar spines of a shark are found in rocks from Armagh, Northern Ireland.

Scales are found only on top of the head, the nape of the neck, and the ventral edge of the dorsal spine of males; otherwise these sharks were naked. The pectoral fin had a trailing “whip”, presumably for additional maneuverability. The fish had a nearly symmetrical abbreviate-heterocercal high aspect ratio tail, denoting some cruising ability.

They have many long, sharp cusped cladodont-style teeth in a large mouth; the jaws were rather immobile in a fore and aft direction, but may have had ample lateral mobility. The labial cartilages also bore teeth.

Mature males had a large forwardly pointed dorsal spine with a row of large triangular dependent denticles. Males also had a pointed snout, and denticles borne upon the crown of head and the dorsal surface of the area between spine and head. Females lacked squamation and had a shorter snout.

This is an extremely advanced condition of what started as a separate dorsal fin and spine in the more primitive Stethacanthidae, since the spine and the remnant of the fin are fused.