Rhizodontidae - Anatomy

Anatomy

The upper jaw had a marginal row of small teeth on the maxilla and premaxilla, medium sized fangs on the ectopterygoid and dermopalatine bones, and large tusks on the vomers and premaxillae. On the lower jaw there were marginal teeth on the dentary, with fangs on the three coronoids and a huge tusk at the symphysial tip of the dentary. Apparently, the left and right mandibles have rotated inwards towards each other on biting. This may have been a kinetic mechanism to dig the marginal teeth more deeply into the prey, to help grip slippery or struggling items.

Rhizodonts' trunk was elongated, with pelvic, two dorsal and anal fins much reduced and placed posteriorly The anal and second dorsal fins formed a functional part of the tail. The lateral line system was elaborated on the skull and pectoral girdle - in Strepsodus the main trunk lateral line also had several subsidiary lines running parallel to it. This probably helped rhizodonts detect prey in the turbid, swampy environment where they lived.

Rhizodont pelvic fins are known only from external morphology. They are smaller than the pectoral fins and positioned toward the rear of the body. In comparison to the other fins, the pectoral fins were much enlarged. They had a well-developed internal skeleton surrounded by robust, largely unsegmented lepidotrichia; the whole fin was then covered in deeply overlapping scales. This turned the pectoral fin into a broad paddle.