Bothriolepis

From Wikipedia, the free encyclopedia

Bothriolepis
Fossil range: Late Devonian

Kingdom:	Animalia
Phylum:	Chordata
Subphylum:	Vertebrata
Class:	Placodermi
Order:	Antiarchi
Family:	Bothriolepidae
Genus:	Bothriolepis Eichwald, 1840

Bothriolepis ("pitted scale" or "trench scale") was the most successful genus of antiarch placoderms, if not the most successful genus of any placoderm, with over 100 species found on every continent. It was a small benthic freshwater detrivore which lived in the Middle and Late Devonian (387–360 million years ago). Because the fossils are found in freshwater sediments, Bothriolepis is presumed to have spent most of its life in freshwater rivers and lakes, but was probably able to enter salt water as well because its range appeared to have corresponded with the Devonian continental coastlines. Many paleontologists hypothesize that they were anadromous, that is, they actually lived in saltwater, and returned to freshwater to breed, similar to salmon. Its box-like body was enclosed in armor plates, providing protection from predators.

It had a heavily armoured head fused with the thoracic shield. It had a long pair of spine-like 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 throw sediment (mud, sand or otherwise) over itself.

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, 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, according to scientific speculation, may have functioned as lungs. Bothriolepis had a slender fish-like tail that extended behind the heavily armored portion, which is unfortunately rarely preserved in fossils.