A re-examination of a 1970s fossil has revealed that Hallucigenia, one of the oddest creatures from the Cambrian period, may have fed on the corpse of a comb jelly. The discovery shows spines from seven Hallucigenia individuals scattered over the remains of the gelatinous organism. This provides a rare glimpse into the ancient animal's possible diet and behavior.
Hallucigenia, a bizarre small animal up to 5 centimeters long with a worm-like body, multiple legs, and sharp spines on its back, lived in the deep seas during the Cambrian period, from about 539 million to 487 million years ago. Initially, paleontologists reconstructed it upside down, mistaking its spines for legs. The creature, related to velvet worms, tardigrades, and arthropods, was first identified in fossils from the Burgess Shale deposits in British Columbia, Canada.
Little was known about Hallucigenia's lifestyle, particularly its diet, as no preserved gut contents have been found in its fossils. Javier Ortega-Hernández at Harvard University recently re-examined a fossil from the original 1977 description that had not been studied since. This specimen, measuring 3.5 cm by 1.9 cm, is the damaged remains of a soft-bodied, gelatinous organism identified as a comb jelly, or ctenophore.
Over the comb jelly, Ortega-Hernández found Hallucigenia spines from seven individuals. He proposes that the comb jelly died and sank to the sea bed, attracting a swarm of Hallucigenia that fed on it, likely using suction feeding. The group was then rapidly buried in mud and fossilized together, capturing this interaction.
Ortega-Hernández declined an interview, noting the findings are from a preprint not yet peer-reviewed. Paleontologist Allison Daley at the University of Lausanne finds it convincing, describing it as a 'snapshot' of a brief moment, possibly minutes or hours, preserved in the fossil record. She notes that in the nutrient-scarce deep waters, scavenging such soft prey with suction would be effective.
However, Jean-Bernard Caron at the Royal Ontario Museum is skeptical. He argues that the proximity of the fossils does not prove interaction; underwater mudslides might have brought them together. Caron also suggests the spines could result from moulting as the animals grew, rather than feeding.
The findings, detailed in a bioRxiv preprint (DOI: 10.64898/2025.12.28.696761), offer new insights into Cambrian ecosystems but await peer review for confirmation.