DEVONIAN ENTOBIA BORINGS FROM NEVADA, WITH A REVISION OF TOPSENTOPSIS

摘要

Entobia, a sponge boring commonly consisting of interconnected chambers and galleries (i.e., it is camerate), is a dominant agent of bioerosion in Mesozoic and Cenozoic marine carbonates. A similar camerate boring, Topsentopsis devonica, is widely recognized from the Devonian, and its classification is reappraised here. This paper synonymizes Topsentopsis with the senior synonym Entobia, making E. devonica n. comb. the oldest representative of the ichnogenus. New specimens of E. devonica borings in stromatoporoids and megalodont bivalves are described from the Frasnian Guilmette Formation of Nevada, which includes breccias of the Alamo Bolide Impact. The borings occur in skeletal substrates both within and above the impact event breccias, demonstrating their existence prior to the impact and their survival of the catastrophic event. The Nevada discovery extends the geographic distribution of the oldest Entobia to include the western and midcontinental United States, western Canada, and eastern Europe. E. devonica was an important bioerosive agent during the Givetian–Frasnian, but it is unknown following the Frasnian–Famennian mass extinction.