Bothriolepis

From Paleos

Bothriolepis was a genus of antiarch placoderms (early armoured fishes). It was a small benthic freshwater detrivore which lived in the Middle and Late Devonian (387–360 million years ago). It was the most successful of all placoderm genera, with more than 100 different species known. It seems to have spent most of its life in freshwater rivers and lakes, but was probably able to tolerate salt water as well because it was spread on all continents. Many paleontologists hypothesize that they actually lived in saltwater, and returned to freshwater to breed, similar to salmon. Its box-like body was enclosed in armor plates, and provided protection from predators.

It had a heavily armoured head fused with the thoracic shield. It had a long pair of pectoral fins, joined at two points: one where the arm leaves the trunk and one a little more than half way along, which would have helped to lift it from the bottom; its heavy body would have sunk quickly back to the bottom as soon as forward momentum was lost. The fins possessed spines, and an articulation to the boxlike trunk. Bothriolepis had a peculiar spiral, sediment-filled gut and probably grubbed in the mud. It may also have used its pectoral fins to stir up the mud that provided its food.

There are two openings through its head: a keyhole opening along the midline on the upper side for the eyes and nostrils and a mouth on the lower side near the front. It also had a special feature on its skull which was a separate partition of bone below the opening for the eyes and nostrils enclosing the nasal capsules called a preorbital recess. It had gills in addition to a pair of pouches off the esophagus that may have functioned as lungs. Bothriolepis had a slender fish-like tail that extends behind the heavily armoured portion, which is unfortunately rarely preserved in fossils.