Deep origin of articulation strategies in panarthropods: evidence from a new luolishaniid lobopodian (Panarthropoda) from the Tulip Beds, Burgess Shale

Abstract

The evolution of articulated sclerites via soft membranes, termed arthrodization, is arguably one of the most critical innovations in animals. Defining the megaphylum Arthropoda, the arthrodization of appendages, or arthropodization, likely predated that of the body, the combination of both being diagnostic of true arthropods (Euarthropoda) – all of these innovations occurring during the Cambrian explosion. Here, thanks to dozens of exceptionally preserved fossils from the Cambrian Wuliuan Stage Burgess Shale (Tulip Beds locality on Mount Stephen, British Columbia, Canada), we show that a distinct but comparable system of imbricated sclerotic elements evolved in the paraphyletic sister group of arthropods, the lobopodians. Entothyreos synnaustrus gen. et sp. nov. has characteristic body plan features of the Collinsovermidae (order Luolishaniida), including anterior limbs for suspension-feeding and stout anchoring posterior limbs. Uniquely, however, E. synnaustrus also displays segmental sclerotic sheets along the trunk, covered in a thin layer of integument, as well as overlapping sclerotized annuli on posterior-most limbs. While the latter elements likely served a protective function, the dorsolateral trunk sheets, which also carry spines, may have facilitated body erection and suspension-feeding. Other luolishaniids possess separate ring-like structures connecting the base of metameric spines which are covered by the apical layer of the lobopodian integument. E. synnaustrus and related taxa illustrate, therefore, an arguably parallel evolution of arthropod-like morphoanatomical features early during the rise of panarthropods. This finding broadens our perspectives on the uniqueness of major synapomorphies and the importance of including canalization in macroevolutionary narratives.

http://zoobank.org/urn:lsid:zoobank.org.pub:D4A01784-E587-481A-AB04-A812B4AAE422

Keywords:

• Cambrian
• Burgess Shale
• Panarthropoda
• lobopodian
• arthrodization
• convergence

Acknowledgments

Burgess Shale fossil material was collected by the Royal Ontario Museum under several Parks Canada Research and Collection permits from 1989 to 2016. We are grateful to Danielle Dufault (ROM) for the illustrations and to Sharon Lackie (Windsor) for providing Environmental Scanning Electron Microscopy images of specimens. We also thank two anonymous reviewers and Associate Editor Gregory Edgecombe for their insightful and constructive comments. This research was supported by a NSERC Discovery Grant (#341944 to J-B.C.). J-B.C. acknowledges the Dorothy Strelsin Foundation (ROM) for the purchase of a Leica M205C stereomicroscope which was used in this research and the French Embassy in Ottawa, Canada for a travel grant to CA. This is Royal Ontario Museum Burgess Shale project number 93.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental material

Supplemental material for this article can be accessed here: http://dx.doi.org/10.1080/14772019.2024.2356090.

Associate editor: Gregory Edgecombe

Additional information

Funding

Burgess Shale fossil material was collected by the Royal Ontario Museum under several Parks Canada Research and Collection permits from 1989 to 2016. We are grateful to Danielle Dufault (ROM) for the illustrations and to Sharon Lackie (Windsor) for providing Environmental Scanning Electron Microscopy images of specimens. We also thank two anonymous reviewers and Associate Editor Gregory Edgecombe for their insightful and constructive comments. This research was supported by a NSERC Discovery Grant (#341944 to J-B.C.). J-B.C. acknowledges the Dorothy Strelsin Foundation (ROM) for the purchase of a Leica M205C stereomicroscope which was used in this research and the French Embassy in Ottawa, Canada for a travel grant to CA. This is Royal Ontario Museum Burgess Shale project number 93.