The Xenacanthus was a small freshwater shark that went extinct around 200 million years ago. They are a prehistoric genus of sharks. It went extinct at the end of the Triassic period, about 202 million years ago. They were widely distributed and lived from the Devonian to the end of the Triassic period. The name Xenacanthus is a Greek word that means “foreign spine”. Very few complete fossils have been found. Most information about the animal has been found through teeth and spine samples. The Xenacanthus was a freshwater shark.