The Cambrian Explosion in Sirius Passet

The site, in the Franklinian Basin, was discovered serendipitously by geologists in 1984 during regional mapping with the Geological Survey of Greenland. The first fossils turned out to be a Cambrian sponge and trilobites, and blocks from the site later revealed a partly sclerotized fauna with similarities to the much better-known Burgess Shale fauna from the Canadian Rockies. Subsequent expeditions have established large collections of fossils, and taxonomic work has already proved significant in understanding the origins and early evolution of animal phyla. The key properties of the site are the abundance and diversity together with the exceptional preservation of these early animals (Topper et al., 2018); strata are correlated with middle to upper Cambrian Stage 3. Moreover, the environment can be identified as relatively deep-water, at the shelf–slope break, in low-oxygen conditions (Hammarlund et al., 2019). Particularly exciting are the diverse arthropods and related forms (many are predators), some preserving guts, gut contents (Strang et al., 2016) and muscles together with brains and nervous systems (Park et al., 2018). Many new data are available to assess the ecology and taxonomy of individual animals, their phylogeny (Vinther et al., 2014) and the communities in which they lived.