Hallucigenia sparsa – A Reassessment of its Ecology and Functional Morphology

Hallucigenia sparsa, a lobopodian from the Burgess Shale, has traditionally been interpreted as a soft-limbed, bottom-walking organism. But there are also morphological arguments for believing that it spent much time suspended above the seafloor. This paper considers four possible modes of life; firstly, feeding on carrion on the seabed, secondly, walking on the substrate, thirdly, suspension among macroalgae, and fourthly suspension feeding. It proposes a model of asymmetry in limb orientation to assist with grasping, along with long projecting spines to increase rotational inertia. Finally, by analogy with a present-day species, it proposes how each of the first three of these modes could have co-existed, presenting a model of a suspended scavenger using its claws to grasp macroalgae, and dropping down to feed opportunistically. It does not seek to refute the phylogenetic placement of Hallucigenia.