Pteraspidomorphi

Pteraspidomorphi is an extinct group of early vertebrates, mostly known from the Paleozoic, that included heavily armored jawless forms. Its members are recognized chiefly through fossilized external skeletons.

Vertebrate: An animal with a backbone or an embryonic structure that develops into one. Pteraspidomorphs belong among early vertebrates, before jaws became widespread.
Pteraspidiformes: An order of extinct armored jawless vertebrates known especially from the Devonian. These characteristic pteraspidomorphs had broad head shields and streamlined bodies.
Pteraspid armor: The bony external covering of pteraspidomorphs, often concentrated in a large head shield. Its plates protected the body and provide the clearest fossil evidence of the group.
Ordovician: A geologic period lasting from about 485 to 444 million years ago. Some early pteraspidomorphs, including arandaspids, are known from Ordovician rocks.
Vertebrate phylogeny: The evolutionary relationships among vertebrates, inferred from anatomical and molecular evidence. Different analyses place pteraspidomorphs differently among early vertebrate branches.
Agnatha: A traditional grouping of jawless vertebrates, including living lampreys and hagfishes and extinct forms. Pteraspidomorphs are commonly discussed among extinct jawless vertebrates.
Pteraspis: An extinct genus of armored jawless vertebrates from the Devonian. Its fossils exemplify the group’s shield-like armor and tapering body.
Lateral line: A sensory system that detects water movement through receptors along an aquatic vertebrate’s body. Canals and sensory openings in fossil armor indicate how pteraspidomorphs sensed nearby movement.
Silurian: A geologic period lasting from about 444 to 419 million years ago. Pteraspidomorph fossils document diversification during this interval.
Fossil preservation: The processes by which remains or traces of organisms become preserved in geological materials. Hard armor is preserved far more readily than much of their soft anatomy.

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