NEW REMARKABLE METAZOANS FROM THE MIDDLE CAMBRIAN (DRUMIAN) MARJUM KONSERVAT-LAGERSTÄTTE OF UTAH, USA

Burgess Shale-type (BST) biotas preserve soft-bodied fossils that critically inform the biodiversity and ecological complexity of the Cambrian Explosion. Although the United States of America contains several Cambrian BST biotas, they have historically featured comparatively lower preservation quality and species richness relative to deposits in Canada (e.g. Burgess Shale) and South China (e.g. Chengjiang). New investigations on the Drumian Marjum biota from Western Utah are progressively reframing our knowledge on the evolution of early animal-dominated communities in Laurentia. With over 150 species, amongst which ca. 60% represent soft-bodied organisms, the Marjum biota is already firmly established as the most diverse Cambrian BST biota in the USA. Dominated by panarthropods and sponges in both species richness and abundance, the Marjum fauna is also characterized by its high quality of preservation. The latter aspect is evidenced by the common fossilization of internal organs, including digestive and neural tissues, and the presence of animal clades with scarce Cambrian records, such as free-swimming ctenophores, and epibenthic dinomischids and graptolites. In this contribution, we present three particularly remarkable new metazoans – a radiodont, an arthropod, and a vertebrate – occurring at the Gray Marjum site. The first new taxon is a hurdiid radiodont, which has proven particularly common in the Gray Marjum beds, and which most closely resembles Cambroraster (Burgess, Chengjiang, Mantou) and Cordaticaris (Zhangxia), forms typically associated with a demersal lifestyle. The second taxon is rare, being known from one, possibly two specimens, and most likely has close affinities with jianfengiid megacheirans, making the first occurrence of this clade outside of the early Cambrian of South China. The last taxon is also rare (one specimen) and represents the first occurrence of vertebrates in the Cambrian of the American Great Basin Region. Cladistic analysis (Bayesian) recovers this new taxon within the vertebrate stem forming a polytomy with Emmonsaspis and Metaspriggina. These three new remarkable metazoans illustrate the preservation quality of the Gray Marjum site in terms of new biodiversity and the fossilization of delicate internal organs including both cuticular and cellular body tissues.