Waptia fieldensis Walcott, a mandibulate arthropod from the middle Cambrian Burgess Shale.

Jean Vannier,Rod S. Taylor,Cédric Aria,Jean-Bernard Caron

doi:10.1098/rsos.172206

Abstract

Waptia fieldensis Walcott, 1912 is one of the iconic animals from the middle Cambrian Burgess Shale biota that had lacked a formal description since its discovery at the beginning of the twentieth century. This study, based on over 1800 specimens, finds that W. fieldensis shares general characteristics with pancrustaceans, as previous authors had suggested based mostly on its overall aspect. The cephalothorax is covered by a flexible, bivalved carapace and houses a pair of long multisegmented antennules, palp-bearing mandibles, maxillules, and four pairs of appendages with five-segmented endopods—the anterior three pairs with long and robust enditic basipods, the fourth pair with proximal annulations and lamellae. The post-cephalothorax has six pairs of lamellate and fully annulated appendages which appear to be extensively modified basipods rather than exopods. The front part of the body bears a pair of stalked eyes with the first ommatidia preserved in a Burgess Shale arthropod, and a median ‘labral’ complex flanked by lobate projections with possible affinities to hemi-ellipsoid bodies. Waptia confirms the mandibulate affinity of hymenocarines, retrieved here as part of an expanded Pancrustacea, thereby providing a novel perspective on the evolutionary history of this hyperdiverse group. We construe that Waptia was an active swimming predator of soft prey items, using its anterior appendages for food capture and manipulation, and also potentially for clinging to epibenthic substrates.

Highlights

Our current understanding of early animal evolution and ecology has seen major improvements in recent years
While Briggs [50] had originally described them as crustacean antennules (A1) in Canadaspis, Aria & Caron [69] suggested that these paired projections in hymenocarines may represent vestigial homologues of the frontalmost appendages of more basal panarthropods, arising from the ocular protocerebral somite
We provide in electronic supplementary material, S22, an alternative topology resulting from the inclusion of selected larval taxa, as was done in a previous iteration of this dataset [9]

Summary

Introduction

Our current understanding of early animal evolution and ecology has seen major improvements in recent years. The integration of fossil and neontological datasets using modern cladistic approaches has helped clarify the wider evolutionary relationships of many previously problematic fossil taxa, a consensus has yet to emerge as to the phylogenetic position of many clades. Future progress in this field remains more than ever critically dependent on adding robust fossil evidence. In this context, several iconic fossil forms remain, perhaps surprisingly, still largely unknown despite their potential role in revealing key insights into early animal evolution and the ecological structure of Cambrian communities. A revision is especially timely given the recent reappraisal of the bivalved arthropod Branchiocaris and its close relatives from the Burgess Shale (protocaridids) as early mandibulates [9], implying that many of the species with bivalved carapaces (including Waptia as part of the order Hymenocarina, revised here) may likewise shed light on the early radiation of mandible-bearing euarthropods

Methods

Findings

Discussion

Conclusion