Rhizodus hibberti was the largest freshwater fish ever.

Rhizodus was a very large freshwater sarcopterygian that lived in lakes, swamps and large rivers all over Pangaea throughout the entire Carboniferous period. Rhizodus would have been among the largest fishes in carboniferous freshwater systems, a true "river monster"; the species R. hibberti measured nearly 7 metres (23 ft) in length. It was an apex predator (or macropredator), likely feeding on temnospondyls and lepospondyls it encountered in its range. It had a pair of very long, sharp fangs at the front of its mouth which measured up to 22 cm (8 in) in length. These were the primary defensive and predatory teeth in a mouth filled with additional, smaller sharp teeth.

Unlike other sarcopterygians living at that time, Rhizodus' teeth were designed to rip into small and medium-sized amphibians and other aquatic animals, compared to most species that swallowed their prey whole after subduing them.


The most notable physical characteristic of Rhizodus, compared to other giant rhizodonts (such as Barameda), was its deadly mouth; the species possessed a large pair of 22 cm (8.7 in) fangs, essentially serving as canine teeth. These fangs were the largest teeth in its mouth, which was more or less filled with smaller, but equally sharp, teeth. Like extant large fish and other aquatic predators of today, Rhizodus fed on nearly anything it encountered that could be easily captured and subdued, such as small to medium-sized amphibians or primitive fishes. Rhizodus likely utilized its sharp teeth to catch and kill prey animals, potentially biting down and violently shaking them to death (similar to crocodilians), before tearing them into smaller chunks. This is in contrast to other species that likely swallowed their prey whole (such as other, smaller-toothed sarcopterygians).

Fossilized scale imprints have shown that Rhizodus had large, plate-like armor, similar to the scales seen on the modern-day South American arapaima (Arapaima gigas).


The diet of Rhizodus included medium-sized fishes and tetrapods, such as early amphibians, temnospondyls and lepospondyls. It has been proposed that Rhizodus may have ambushed terrestrial animals as they drank at the water's edge, surprising them from below as with crocodilians, or the giant Wels catfish (Silurus glanis), which ambushes birds and small mammals swimming in shallow water.