Cladoselache is a cladoselachid cladoselachiform cartilaginous fish from the Late Devonian-Mississippian of the United States of America. It was named in 1894 by Bashford Dean. It was a truly unique shark at the time, as it had traits of both primitive and advanced sharks.
Physiology
Cladoselache bore a resemblance to modern sharks; it was a cartilaginous fish with a streamlined body, a large, blunt head with big jaws, triangular pectoral and dorsal fins, a crescent-shaped caudal fin, a mid-sized head with a blunt nose and large jaws. However, it had many traits that set it apart from its modern brethren, such as a thin, slender body, head more similar in shape to that of a bony fish, massive pectoral fins, and a large, hook-like spine in front of its dorsal fin. Its body was covered in smooth skin, with a clump of pointed scales situated on the edges of its fins, around its eyes, and on its lips.
Diet
Cladoselache was a predator, preying on ray-finned bony fish, conodonts (lamprey-like basal chordates), crustaceans, and smaller sharks. Its teeth had smooth edges and multiple points, and were used to get a hold of struggling prey as the shark swallowed them whole.
Ecology
As an early shark, Cladoselache was one of the most efficient swimmers during the Devonian; its slender, streamlined body allowed it to move through the water with ease, and its large, crescent-shaped tail fin was used to propel itself through the water with powerful, side-to-side movements. Why Cladoselache evolved to be so fast and agile is unknown; some may speculate that it developed this lifestyle to catch fast-moving prey such as bony fish and conodonts, while others may theorize that it evolved this way in order to evade the formidable jaws of the large placoderm Dunkleosteus. In order to hunt, Cladoselache would swim up to a small aquatic animal, grab it with its toothy jaws, and swallow it tail-first. An interesting thing to note is that unlike modern sharks (as well as primitive sharks like Stethacanthus, Cladoselache lacked the claspers used for the transferring of sperm during reproduction; some possible theories about how it found a way around this issue include internal fertilization, but these theories are yet to be demonstrated.