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ABSTRACT
Ichnofossils attributed to the ichnogenus Arthrophycus (Hall 1852) have been reported from localities worldwide, including all seven modern-day continents. Arthrophycus is most abundant in Ordovician and Silurian strata and is widely regarded as an ichnostratigraphic indicator of this interval. Occurrences of the ichnogenus from younger strata have been reported, but there is growing consensus that post-Paleozoic records of Arthrophycus are not valid. The oldest confirmed occurrence of Arthrophycus is A. minimus (Mángano et al. Citation2005a) from the Upper Cambrian of Argentina, South America. The youngest confirmed report is A. parallelus (Brandt et al. 2010) from the Upper Carboniferous (Pennsylvanian) of the Michigan Basin, USA. Paleobiogeographic analysis based on the five most widely accepted ichnogenera confirms the hypothesis that Arthrophycus originated in Gondwana during the Late Cambrian and Early Ordovician, expanded to the northern continents during the Mid-Late Ordovician, reaching its acme during the Silurian, before its decline and extinction by the end of the Paleozoic.
Acknowledgments
Our paper is much improved due to the thorough and helpful comments of our reviewers. MES thanks R. L. Anstey, B. Hampton, R. Snider for guidance and encouragement, and her family for their support.