A peritidal Burgess‐Shale‐type fauna from the middle Cambrian of western Canada

Burgess-Shale-type (BST) faunas have proven critical for mapping the Cambrian assembly of animal-dominated ecosystems, but have so far only been reported from fully subaqueous deposits. Here we integrate evidence from ichnofossils, sedimentary features, and small carbonaceous fossils (SCFs) from the middle Cambrian (Late Guzhangian, Series 3) Pika Formation of western Jasper
National Park, Alberta (Canada) to document a unique BST fauna, occupying a peritidal habitat near the outer margin of a large epicratonic sea. Finely laminated shales with mudcracks and dumbbell-shaped Arthraria-type burrows denote a periodically emergent, dysoxic mudflat setting. This same facies yields SCF priapulids, annelids and wiwaxiids typical of deeper-marine sediments. Recovery of
Cirratuliformia-like annelid chaetae further identifies the likely source of Arthraria burrows and associated faecal pellets.These findings show that Cambrian marine metazoans, including probable members of crown-group orders, ranged beyond permanently subaqueous deposits. The expanded palaeoenvironmental range of the BST taxa from the Pika biota denotes remarkably broad ecological tolerances, suggesting the existence of a guild of Cambrian metazoan generalists able to colonize at least transiently subaerial settings. Their occupation of offshore peritidal ecologies may have preluded to more extensive metazoan colonization of high-energy, siliciclastic marginal marine environments.