139-6 Predator or scavenger? Hallucigenia illuminates the ecology of Cambrian lobopodians

Session: Evolution of Life in the Cambrian Seas: Biotic, Biogeochemical, and Sedimentological Contexts, Part II

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The armoured lobopodian Hallucigenia sparsa embodies the seemingly uncanny nature of the animals that evolved during the Cambrian Explosion over 500 million years ago. Initially regarded as an evolutionary oddball, the exceptional preserved anatomy of H. sparsa has been substantially revised, leading to a better understanding of its relationships with other lobopodians and phylogenetic affinities with extant panarthropod phyla. However, the ecology and behaviour of H. sparsa remain largely enigmatic owing to the difficulties of interpreting its functional morphology and the perceived lack of modern analogues. Restudy of an extraordinary composite fossil assemblage from the middle Cambrian Burgess Shale demonstrates swarm-like behaviour of several diminutive H. sparsa individuals scavenging on a dead ctenophore. The lack of grasping, masticatory, or piercing mouthparts in H. sparsa points to suction feeding as a viable strategy to consume the gelatinous carcass. Reassessment of the functional morphology of H. sparsa reveals analogues with extant pycnogonids, including an elongate anterior end with a terminal mouth, enlarged oral chambers followed by a cuticular denticles in the foregut. These observations suggest that suction feeding is ancestral for the onychophoran stem lineage and highlights the critical ecological role of hallucigeniid lobopodians in degrading soft-bodied carcasses in Cambrian benthic ecosystems.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8070

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