Stethacanthus altonensis

Stethacanthus looked like it had an anvil growing out of its back. This strange shark's dorsal fin hardly resembled that of modern sharks; Stethacanthus' was thick, flat on top and covered by small extra-rough scales. Experts think only males had this strange fin, and used it to attract females and to fight off rivals. However, scientists haven't found any females yet. They speculate that the female might have been so different from the male that it has been accidentally classified as a different species."Tail Power: Like modern sharks, Stethacanthus had a streamlined body and a powerful tail for propulsion. It was one of the fastedt swimmers for its size during the Devonian Period, chasing down smaller fish and putting its small but sharp teeth to use.""No Girls Allowed? All Stethacanthus fossils found so far have been from males. Experts think females didn't have the oddly-shaped dorsal fin, and that another species of ancient shark, called Symmorium, might actually be the Stethacanthus female."

Anvil Shark
Stethacanthus' strange feature was its thick, anvil-shaped dorsal fin. On top, the fin was flat and covered by rough scales, and there was a matching rough patch on the shark's forehead. Most experts think the shark used its odd-looking fin to impress females, and fought rivals with the rough skin patches. Two males competing for a female would have gone head-tohead, literally, "gripping" each other with their rough patches and pushing as hard as they could. The shark that could push its rival back the farthest would win.

Stethacanthus shared prehistoric seas with the super predator, Dunkleosteus (above)."Watch Out for Dunky: As with all creatures that lived in the Devonian seas, Stethacanthus had to keep watch for Dunkleosteus. Dunkleosteus was the king of the seas back then, and could have killed the small-bodied Stethacanthus with a single bite.""Take a Ride: A few experts think that Stethacanthus may used its spiny dorsal fin and the rough skin on its forehead to hitchhike. It could attach itself to the underside of a much larger fish and hang on for the ride."

Did You Know?
The name "Stethacanthus" means "chest spike."

Timeline: Stethacanthus lived from 380 to 300 million years ago, during the Devonian and Carboniferous Periods.