Fishes representative of all Silurian ages were widely distributed in marine environments (carbonate and clastic) in a broad belt within the latitudes 40° N and 40° S of the paleoequator. They are known from fossils of individual scales as well as from rare body molds. A wide variety of agnatha (jawless) fishes are represented by species belonging to the orders Thelodonti, Heterostraci, Osteostraci, and Anaspida. Fishes with a primitive jaw apparatus are represented by members of the subclasses Acanthodii, Elasmobranchii, and Actinopterygii. Different endemic groups developed in Laurentia (known widely from sites in the Canadian Arctic, the Yukon, Pennsylvania, New York, and especially Scotland), Baltica (especially Norway and Estonia), and Siberia (including adjacent Mongolia).
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