SYSTEMATIC PALEONTOLOGICAL INVESTIGATIONS OF THE MARBLE CANYON BURGESS SHALE DEPOSIT AND SURROUNDING AREAS (MIDDLE CAMBRIAN), BRITISH COLUMBIA

Discovered in 2012, the Marble Canyon locality of the Burgess Shale in Kootenay National Park yields one of the richest and best-preserved Cambrian soft-bodied assemblages known to date. Finds include two new middle Cambrian arthropods, the leanchoiliid Yawunik and the isoxyid Surusicaris, as well as exceptionally well-preserved specimens of Metaspriggina, a taxon of critical importance to our understanding of early vertebrate evolution.

A Royal Ontario Museum-led party conducted extensive fieldwork in the area during the summer of 2014 and located several additional fossil localities along the front of the Cathedral Escarpment. The most important and diverse new assemblage is located along the eastern side of Tokkum Creek, nearly 6 km northwest of the 2012 site. It yields a somewhat different assemblage, highlighted by a diversity of arthropods, including many large Misszhouia and Naraoia specimens, and several very large sponges. Thousands of specimens were systematically logged within a 5 meter-thick section during a subsequent seven week long systematic excavation at the 2012 site. Preliminary observations suggest that animals were entombed quickly in dozens of millimetre- to centimetre-thick burial events. The enigmatic worm-like animal Oesia is dominant in the community, and associations with Margaretia, previously regarded as an alga, suggests that this worm lived in a tube. A revision of Oesiais currently underway; exceptionally well-preserved specimens show a tripartite bodyplan that unambiguously point to an enteropneust affinity. The new excavations also confirm the restricted abundance and diversity of epibenthic sessile organisms—mainly sponges and brachiopods—suggesting ecological or environmental controls on their settlement different from those at other local sites.

Complementary geological and geochemical investigations are now underway and, along with detailed analyses of trace fossils and microfossils, will increase our understanding of the nature of the Marble Canyon paleoenvironment and its role in the exceptional preservation of the soft-bodied biota.