Asterolepis (fish)
Asterolepis is an extinct genus of antiarch placoderms from the Devonian of North and South America and Europe. They were heavily armored flat-headed benthic detritivores with distinctive jointed limb-like pectoral fins and hollow spine. The armor plate gives the Asterolepis a box-like shape. Its pectoral fins are also armored but the caudal and dorsal fin are not. The first fossils were named by M. Eichwald in 1840 after noticing star-like markings on the fossils. Etymology "Aster-" means star while "-lepis" means scales. Confusion surrounded the first fossils discovered of this genus, as naturalists were unable to ascertain their place among fishes and they were first named Chelonichthys. Later very fine specimens were found in the Old Red Sandstone of Russia and Professor Asmus of Dorpat sent them to the British Museum, noticing fossils exhibited star-like markings. That is when the name Chelonichthys was abandoned for Asterolepis which Eichwald proposed. Description Primitive features such as jaw ossifications, a palatoquadrate, and a Meckel's cartilage are present in the Asterolepis that are important features shared between antiarchs and other Gnathostomata. Additionally the Asterolepis has box-like dermal armour covering the head and thorax with highly modified pectoral fins that are enclosed in interlocking dermal plates protecting a cartilaginous endocranium and gill region. Also, the vertebral column and the pectoral girdle are cartilaginous. The Asterolepis does not have an anal fin or pelvic fins. However it does have a caudal and dorsal fin. Both are covered in similar scales. Armour plates The Asterolepis has multiple interlocking dermal plates that form its body armour; anterior ventro-lateral (AVL) plate, posterior lateral plate, posterior ventro-lateral (PVL) plate, anterior median dorsal (AMD) plate, two anterior dorsolateral (ADL) plates, two mixilateral plates, and one posterior median dorsal (PMD) plate. The area considered to be the face is also armored with interlocking dermal plates; nuchal plate, paired paranuchal plate, paired postmarginal plate, postpineal plate, premedian plate, paired lateral plate, and semilunar plate. The cheek region of the head shield is formed by three bones: prelateral, opercular/ sub-marginal, and infraprelateral plates where the prelateral and submarginal plates form the lateral region and the infraprelateral plates form the ventral region The paired pectoral fins are also plated with plates of the dorsal central series (CD1-CD4), plates of the medial marginal series (MM1-MM4), and the plates of the lateral marginal series (ML1-ML4). The postpineal plate is broader than longer. The premedian plate is thickens as you move posterior. The posterior wall of the premedian plate concaves to form the anterior wall of the orbito-nasal cavity and shows prerostral process. The pineal plate is small, trapezoidal, thin bone that covers the most posterior part of the orbito-nasal cavity. It has a rough ornamented surface and a smooth visceral surface that has a round pineal pit. Also, rough postero-ventro-laterally facing processes in the antero-lateral projections of the plate are present. The medial marginal plate 4 of the pectoral fin displays short spaced spines that go lateral which are absent on the distal part of the plate.