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Abstract
The ichnogenus Rusophycus includes a wide range of short bilobate excavations generally attributed to variable feeding behaviors of arthropods, especially trilobites. An unusual Rusophycus assemblage from Upper Ordovician Georgian Bay Formation in Ontario departs radically from previously described examples and presents new challenges for understanding the behavior represented by these traces. This specimen is unique in the arrangement of multiple Rusophycus burrows in a circular, lens-shaped array (as opposed to a linear or random arrangement typical of other Rusophycus assemblages). The size and shape of the individual Rusophycus components are consistent with traces attributed to the coeval trilobite Flexicalymene. Multiple Rusophycus assemblages likely reflect aggregations of trilobites in response to a local concentration of food. The topology of this particular Rusophycus assemblage suggests that the trilobites opportunistically exploited a rich and narrowly restricted food source, perhaps the decaying remains of a buried organism.
ACKNOWLEDGMENTS
An earlier version of this paper was presented at the 2007 Geological Society of America symposium in honor of Dolf Seilacher. The authors thank the symposium organizers and Professor Seilacher for his many contributions to ichnology. DSB thanks the late Connie Snepp of Haslett, Michigan, for bringing the Indiana specimen to her attention; Connie's generous spirit is sorely missed. DMR gratefully acknowledges the collecting acumen and kindness of Dr. Michel Farivar, who found and donated the Ontario specimen to the ROM. We are indebted to Gabriela Mángano and Sören Jensen for their careful reviews and constructive comments, and to Sam Gon for use of his trilobite drawing in .