Fossil may solve mystery of what one of the weirdest ever animals ate

Revisiting fossils from the 1970s has shed new light on the peculiar scavenging habits of Hallucigenia. Recent analysis suggests that a group of these enigmatic creatures may have been feasting on the remains of a comb jelly, providing insight into their evolutionary behavior.

Measuring up to 5 centimeters in length, Hallucigenia sported a worm-like body with numerous legs and long spines along its back. Initially misinterpreted due to its unusual anatomy, this ancient creature dwelled in the depths of the sea during the Cambrian period, around 539 to 487 million years ago. Its fossils, first discovered in the Burgess Shale deposits in Canada, reveal its evolutionary relationship to velvet worms, tardigrades, and arthropods.

Despite its distinctive appearance, little is known about the dietary preferences of Hallucigenia as no fossilized gut contents have been preserved. However, a recent study by Javier Ortega-Hernández at Harvard University has uncovered a fascinating ecological interaction involving Hallucigenia.

Ortega-Hernández’s reexamination of a Burgess Shale fossil, originally described in 1977, revealed the presence of a comb jelly, or ctenophore, measuring 3.5 cm by 1.9 cm. Strikingly, the fossil also displayed Hallucigenia spines scattered across the comb jelly, indicating a group of seven individuals feeding on the gelatinous organism. This scenario suggests that the comb jelly likely perished and sank to the seabed, where the Hallucigenia seized the opportunity to scavenge and feed, possibly through suction feeding, before being buried in mud and eventually fossilized.

While Ortega-Hernández’s findings propose a compelling narrative of ancient scavenging behavior, not all experts are entirely convinced. Palaeontologist Allison Daley at the University of Lausanne acknowledges the significance of the discovery, describing it as a snapshot of a brief moment in time captured in the fossil record. Given that Hallucigenia inhabited nutrient-poor deep-sea environments, scavenging on rich food sources like comb jellies would have been a strategic survival tactic.

Contrarily, Jean-Bernard Caron at the Royal Ontario Museum raises skepticism about the interpretation, suggesting that the co-occurrence of Hallucigenia and ctenophore fossils may not necessarily indicate direct interaction. He proposes an alternative explanation where the fossils were deposited together due to undersea mudslides. Caron also speculates that the presence of Hallucigenia spines could be attributed to molting rather than feeding behavior.

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