Bothriolepis canadensis

Bothriolepis canadensis Whiteaves, 1880

    Upper Devonian

    Escuminac Formation

    Scaumenac Bay

    Canada

    Bothriolepis ("pitted scale" or "trench scale") was the most successful genus of antiarch placoderms with over 100 species found on every continent, including Antarctica . The extinct armored fishes known as placoderms make up what is considered to be the earliest branch of the gnathostome family tree -- the earliest branch of the jawed fishes. Antiarchs are characterized by the fact that their pectoral fins are enclosed in bony tubes (pectoral appendages). Instead of typical fish-like pectoral fins, it bears a pair of rigid arms that are joined at two points. These arms, like the limbs of an arthropod, are articulated by interior muscles. Bothriolepis is a placoderm with a heavily armoured head fused with the thoracic shield. The body was encased in a bony box that had flat sides and bottom and an angled roof. There are two openings through its solidly armoured head -- a keyhole opening along the midline on the upper side for both eyes and nostrils and a mouth on the lower side near the front. The discovey of some undeformed, three-dimensionally preserved specimens led to a review of this fish's morphology. It appears that Bothriolepis had a much more rounded shape than previously thought, and as a direct consequence of the latest reconstructions, it is now believed that its eyes faced forward instead of upward. Bothriolepis does have a slender fish-like tail that extends behind the heavily armoured portion but, because it is almost naked with few scales, it is rarely preserved.

    Reconstruction from Wikipedia.

    Placoderms bore heavy bony armor on the head and neck, often with an unusual joint in the dorsal armor between the head and neck regions; this joint apparently allowed the head to move upwards as the jaw dropped downwards, creating a larger gape. 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. Bothriolepis probably fed on invertebrates such as crustaceans and molluscs or even was a mud-grubber that ingested organic-rich mud for its food.

    Bothriolepis is the most common fish fossil in the shales and sandstones of the Escuminac Formation (Late Devonian, 380 Ma) on the south shore of the Gaspé Peninsula at Miguasha. Abraham Gesner (1797-1864), the provincial geologist of New Brunswick who discovered the site in 1842, referred to this fossil as "a small species of tortoise with foot-marks".

    It seems to be certain that there are at least two, with the second species discovered and described in 1924. Named B. Traquairi, after Scottish paleontologist Ramsey Heatly Traquair, the one and only specimen officially assigned to this species has a more slender body than B. canadensis.

    Because the fossils are found in freshwater sediments, Bothriolepis was originally presumed to have spent most of its life in freshwater rivers and lakes. This idea is now abandoned; many paleontologists now hypothesize that they lived most of their lives in saltwater, and returned to freshwater only to breed.

    http://australianmus.../17865/1289.pdf