The protolepidodendrid genera Tomiodendron, Ursodendron, Angarophloios, and Meyenodendron have been discovered on the North Slope. These taxa, with the exception of Tomiodendron, are known only from Mississippian (Tournaisian-Visean) units in eastern Siberia and therefore are of uniquely Angaran affinity. The absence of these genera from extensively collected European assemblages strongly suggests that eastern Siberia and northern Alaska were joined, or in very close proximity, during Mississippian time, contrary to most paleogeographic reconstructions. A disjunct relict distribution is discounted on the basis of paleogeograpic reconstructions showing even greater separations between Alaska and Siberia during the Devonian.

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