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The Cordillera of North American is a mosaic of allochthonous fault-founded terranes, many of which contain abundant radiolarian chert of Permian age. Permian paleolatitudes for some terranes can be reconstructed by using fusilinid, megafossil, and paleomagnetic data. Cosmopolitan Wolfcampian and older radiolarian faunas extend north as far as the Brooks Range of northern Alaska. By late Wolfcampian or early Leonardian time (Pseudoalbaillella scalprata Assemblage), a marked diversity gradient developed between tropical high diversity faunas and temperate low diversity faunas. Albaillellaria became restricted to terranes with low paleolatitudes, but radially symmetrical cross-axon radiolarians still extended into temperate paleolatitudes. The Brooks Range, Innoko, Angayuch m, and Red Paint terranes of northern and central Alaska all contain low-diversity late Wolfcampian and/or Leonardian faunas. Megafossil data indicate that these terranes may not be enormously displaced. In contrast, the Wrangellia terrane of southern Alaska, which is greatly displaced from low paleolatitudes, contains very diverse tropical Leonardian faunas. Similar faunas occur in the Golconda allochthon of Nevada and are reported from the tropical Bone Spring Limestone (Leonardian) of Texas. By Guadalupian time (Follicucullus scholasticus Assemblage), all distinctive radiolarian lineages were apparently restricted to tropical or subtropical extinctions which first affected temperate faunas during late Wolfcampian or Leonardian time, then affected subtropical or tropical faunas by late Guadalupian or post-Guadalupian time, and culminated in worldwide extinctions in latest Permian or earliest Triassic time. As the transgressive extinctions moved from temperate to tropical paleolatitudes, diverse faunas were replaced by very low-diversity entactiniid faunas and/or nondeposition. The gradual restriction of Permian radiolarian faunas records increasingly unfavorable oceanic conditions that eventually resulted in the worldwide extinction of all but the most adaptable radiolarians.
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