A new soft-bodied fauna: The Pioche Formation of Nevada

A new Burgess Shale-type soft-bodied fauna crossing the Lower-Middle Cambrian boundary in the Comet Shale Member of the Pioche Formation in Lincoln County, Nevada, contains common remains of soft-bodied ecdysozoan taxa. These fossils provide important new information about the nature and variety of Cambrian soft-bodied organisms. Arthropod taxa include one species of Canadaspis Novozhilov in Orlov, 1960, one species of ? Perspicaris Briggs, 1977, three species of Tuzoia Walcott, 1912, and at least two species of Anomalocaris Whiteaves, 1892. A priapulid referable to Ottoia Walcott, 1911a, was also recovered. A comprehensive review of Tuzoia is given. Some specimens from Early Cambrian sections are replaced by hematite, resulting in iron staining similar to that in such other Early Cambrian soft-bodied faunas as the Kinzers Formation in Pennsylvania. Some taxa in the Comet Shale, and in other Early and Middle Cambrian soft-bodied faunas, have prodigious geographic ranges that spanned much of Laurentia and even other Cambrian cratons. Moreover, these taxa ranged across the Early-Middle Cambrian boundary relatively unscathed. This is in contrast to many trilobite taxa that had narrow geographic ranges in the Early Cambrian and high levels of extinction at the Early-Middle Cambrian boundary.