Osteostraci

fossil vertebrate order

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July 1, 2026

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Osteostraci is an informal term for an extinct group of armored, jawless, fishlike vertebrates that appeared during the early Paleozoic Era. These creatures are considered ostracoderms, a classification that also includes living hagfish and lampreys. The name "Osteostraci" is derived from Greek words meaning "bone" and "shell," reflecting their armored nature.12

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agnathan
Form and function
Some Osteostraci, for example, possessed a flattened head shield and, although possessing a powerful swimming tail, appear to have been bottom dwellers. The size and shape of the mouth suggest that they were filter feeders. The laterally compressed, fishlike form of the anaspids (such as Pharyngolepis)…
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Some Osteostraci, for example, possessed a flattened head shield and, although possessing a powerful swimming tail, appear to have been bottom dwellers. The size and shape of the mouth suggest that they were filter feeders. The laterally compressed, fishlike form of the anaspids (such as Pharyngolepis)…
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agnathan
Annotated classification
†Order Osteostraci Head covered in broad bony shield, undersurface of head covered with tiny scales, gill openings on undersurface, eyes dorsal, nostril median and placed on top of head, areas of bony shield covered with tiny tesserae. About 7 families. Early Silurian to Late Devonian (443.8–358.9…
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†Order Osteostraci Head covered in broad bony shield, undersurface of head covered with tiny scales, gill openings on undersurface, eyes dorsal, nostril median and placed on top of head, areas of bony shield covered with tiny tesserae. About 7 families. Early Silurian to Late Devonian (443.8–358.9…
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fish
Agnatha: early jawless fishes
…jawless fishes of the order Osteostraci. Somewhat later in the Silurian from the same region, layers contain fragments of jawed acanthodians, the earliest group of jawed vertebrates, and of jawless fishes. These layers lie between marine beds but appear to be washed out from fresh waters of a coastal region.
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…jawless fishes of the order Osteostraci. Somewhat later in the Silurian from the same region, layers contain fragments of jawed acanthodians, the earliest group of jawed vertebrates, and of jawless fishes. These layers lie between marine beds but appear to be washed out from fresh waters of a coastal region.
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