Permian Eugeneodont "Shark" distributions in North America

Eugeneodonts are a group of marine cartilaginous fishes known for possessing a 'buzz-saw-like' whorl of serrated teeth on their mandibles. However not all members of this group were so adapted. During the Permian Period (298-251 million years ago), North America's record of these fishes was dominated by a typical predatory Eugeneodont: Helicoprion davisi, a large bodied, durophagous grazer: Bobbodus schaefferi, and a small bodied durophagous grazer: Agassizodus sp. After sampling four marine vertebrate localities in the field, and analyzing published data on other marine Permian vertebrate sites, a pattern of distribution for these three species emerges. Helicoprion seems to be found in two regions of ancient North America: the mouth of the Permian Basin and the eastern edge of the Panthalassic Ocean. Bobbodus, however, so far seems endemic to the upper portion of the Permian Basin. While neither range of these large fishes overlaps, the range of Agassizodus in the Permian Basin seems to overlap the ranges both animals. We suggest that the cause of this pattern is likely the preference of Helicoprion for colder waters- as evidenced by its occurrence in the Phosphoria Formation of the Rocky Mountains. The grazing Eugenodonts likely preferred the warmer waters of the Permian Basin, because higher benthic productivity would have allowed for easier grazing of hard shelled benthos. The somewhat broader range of Agassizodus compared to Bobbodus may suggest that the former species was more of a generalist in Permian marine ecosystems than the later.