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). In Strepsodus the tail was diamond shaped and diphycercal; in Gooloogongia loomesi it was nearly so. The lateral line system was elaborated on the skull and pectoral girdle - in Strepsodus (and possibly the other European genera) 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 in which they lived.
In contrast 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. The glenoid fossa was a deep circular dish, allowing good all-round movement of the paddle. This suggests that rhizodonts could generate powerful thrashing and dragging movements, which could be used to manipulate and dispatch prey.
Reconstruction of Strepsodus after Andrews (1985)
Upper part of the pectoral girdle of ?Strepsodus