Abstract

Isolated, uncompressed specimens of Pristiograptus dubius, "Pristiograptus" praedeubeli, and "Pristiograptus" ludensis are described from Arctic Canada. Pristiograptus dubius and early forms of "P." praedeubeli are very similar, suggesting a respective, ancestor-descendant relationship. The study shows that "P." praedeubeli and "P." ludensis are generally readily distinguishable, but that the sicular region of the latter shows a much greater variation than previously recognized. End member morphs of "P." ludensis are remarkably similar to "P." deubeli, further confirming a close evolutionary link between them. To facilitate refined biostratigraphic division of the uppermost Wenlock, therefore, large collections of specimens are required to separate those two species when co-occurring.

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