PRIAPULIDS AND THE CAMBRIAN SUBSTRATE REVOLUTION

Priapulids are a group of scalidophoran ecdysozoans whose body fossils are represented in numerous Cambrian Lagerstätten such as the Chengjiang and Burgess Shale biotas. They have been proposed as burrowing animals that were responsible for early Cambrian ichnotaxa, including Treptichnus pedum that defines the Ediacaran-Cambrian boundary as well as other ichnofossils that are commonly identified as Psammichnites, Didymaulichnus, and Mattaia. Here we report additional ichnotaxa that may be produced by priapulids or their relatives. These ichnofossils co-occur with Skolithos in the upper member of the Wood Canyon Formation in the Death Valley area, and they would be identified as Palaeophycus striatus and Bergaueria radiata. They are characterized by horizontal burrows with longitudinal striations and vertical burrows with radiating structures at the lower end. Such structures may have been produced by the scalids and pharyngeal teeth of early Cambrian priapulids or their relatives. These findings shed light on the behavior ecology of Cambrian priapulids. They also add to a growing list of early Cambrian ichnofossils that may have been produced by priapulids, highlighting the important role of priapulids in the Cambrian substrate revolution and contrasting with their limited ecological impact in modern oceans.