'' 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 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 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. The 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 environments 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. ==Phylogeny==