Ostracoderms (lit. 'shell-skins') are the armored jawless fish of the Paleozoic Era. The term does not often appear in classifications today because it is paraphyletic (excluding jawed fishes and possibly the cyclostomes if anaspids are closer to them) and thus does not correspond to one evolutionary lineage. [1] .

Ostracoderm, an archaic and informal term for a member of the group of armoured, jawless, fishlike vertebrates that emerged during the early part of the Paleozoic Era (542–251 million years ago). Ostracoderms include both extinct groups, such …

The ostracoderms were primitive vertebrates, small to medium in size. Their body form was fish-like, usually flattened dorsoventrally, with a huge head and gill region, a tapering but muscular trunk and some sort of tail fin.

Ostracoderms ("shell-skinned") are any of several groups of extinct, primitive, jawless fishes that were covered in an armor of bony plates. Their fossils are found in the North American and European strata of the Ordovician, Silurian, and Devonian periods of the Paleozoic era, approximately 400 million years ago.

After about 30 million of years of coexistence, the ostracoderms finally went extinct, leaving the jawed fishes to take over the waters. Scientists don’t know what factors led to the “shelled-skin” fishes’ demise.

Ostracoderms are especially interesting because they represent the oldest known vertebrate fossils in the late Cambrian and Ordovician rocks dating back to nearly 500 million years. They are the remote ancestors of all the vertebrates including man.

The Ostracodermi is divided into 2 subclasses and 5 suborders which are as follows: A single, large, slit-like median nostril on the top of the head between the eyes. The Monorhina has been divided into three orders: Order 1. Euphanerida: Silurian.

Ostracoderms ranged from 3 to 10 inches long, and were characterized by flat, thick bodies with a pair of side fins for steering. They had cartilaginous internal skeletons covered by bony external armor that protected their cephalic and pectoral regions.

The meaning of OSTRACODERM is any of various primitive, extinct jawless fish (class Agnatha) of the Lower Paleozoic with a bony covering of plates or scales serving as a protective armor and which on the broad head usually form a bony shield of fused plates.

Ostracoderms encountered first as fragmented fossils. Occurs in the rocks of late Cambrian and middle Ordovician periods. Quite abundant during the upper Silurian and Devonian periods. Ostracoderms were the first vertebrates. They were popularly called armoured fishes. They were jawless vertebrates. They lived in freshwater.