Millerosteus minor Miller, 1858

Millerosteus minor Miller, 1858

Middle Devonian

Eifelian

Caithness

Scotland

Millerosteus minor (named after Hugh Miller, a Scottish geologist and paleontologist 1802-1856) was a small arthrodire placoderm, rarely exceeding 15cm. 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. Arthrodires possessed jaws but no teeth. Razor-sharp bony dental plates formed sort of a beak and allowed to gnaw on prey.

Arthrodires (“jointed neck”) are characterized by 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. In addition, it also had an internal joint between its neck vertebrae and the back of the skull, allowing for the mouth to be opened even wider and being able to feed on rather large prey. Millerosteus probably fed on invertebrates such as crustaceans and mollusks or even was a mud-grubber that ingested organic-rich mud for its food. Arthrodires possessed a heavily armored head- and neck-region. The slender fish-like body and the heterocercal tail that extends behind the heavily armored portion is, because it is almost naked or only covered with small scales, rarely preserved.

Millerosteus is a rather common fish in the Middle Devonian flagstones around Caithness.