Xenacanthus was found exclusively in freshwater environments - like the swampy shallows of North Texas 290 mya, but also all over the world, in places like Europe, Australia, South America and North America - such as the Museum's site near Seymour. It would have slithered through these ancient waters like an underwater snake, using a fin that ran along its back from head to tail.
This Permian oddball was part of an evolutionary line of sharks that first appeared in the Devonian, proliferated like mad through the Carboniferous and Lower Permian periods before taking a final bow towards the end of the Triassic. 220 million years in all - not bad.
Field sketch of Xenacanthus with Diplocaulus - possible prey? (c) Robert T. Bakker
By nature sharks don't make good fossils - most of their bodies are soft cartilage, which decays before the necessary processes can take place. However, Xenacanthus jaws and braincases were hard bone, meaning that we can recover more of this species that most other sharks. In Seymour, the team has found pieces of these, along with lots of Xenacanthus teeth and poison spines. Also in the area - shed teeth and coprolite from Dimetrodon, meaning this wasn't a site Xenacanthus came to relax.