Among the most peculiar creatures ever to roam the Earth is Hallucigenia, a scavenger that thrived on the carcasses of Kushi jelly. Recent studies have reinvigorated our understanding of this enigmatic organism first discovered in the 1970s.

Hallucigenia measured approximately 5 cm in length and boasted an insect-like body with multiple legs and lengthy, sharp spines along its back. Its unusual morphology led paleontologists to initially reconstruct it upside down, mistaking its vertebrae for legs.

This unique creature inhabited the deep sea during the Cambrian period, roughly 539 to 487 million years ago, when various major animal groups emerged. Hallucigenia was first identified in the Burgess Shale formation in British Columbia, Canada. It shares evolutionary ties with velvet worms, tardigrades, and arthropods, a group that includes insects and spiders.

Despite the wealth of fossils, much about the lifestyle of ancient creatures such as Hallucigenia remains a mystery. For instance, researchers have yet to determine what they fed on, as existing fossils have not preserved intestinal contents.

Harvard University’s Javier Ortega Hernandez has conducted a thorough investigation of the Burgess Shale fossils. He revisited the original description of Hallucigenia in 1977, which had not been revisited until now.

Among the findings was a fragment of a severely damaged, soft-bodied gelatinous organism measuring 3.5 cm by 1.9 cm, which Ortega Hernández identified as a comb jelly (ctenophore).

He proposed that the spines attributed to Hallucigenia represent a group of seven individuals that voraciously fed on a dead Kushi jelly, which had drifted to the ocean floor. This event likely involved suction feeding, as they were all eventually enveloped in sediment and transformed into fossils.

Ortega Hernández opted against interviews for New Scientist since this research is currently pending peer review.

“This represents a fascinating ecological interaction,” remarks paleontologist Alison Daly from the University of Lausanne, Switzerland, referring to these findings as “snapshots” that capture fleeting moments in the fossil record, lasting perhaps only a few minutes or hours.

As noted by Daly, Hallucigenia thrived in the nutrient-poor depths of the ocean, so it’s plausible that these creatures survived by rapidly locating and consuming abundant food sources like deceased Kushi jelly. “Suction feeding is highly effective for soft-bodied organisms,” she comments.

However, Jean-Bernard Caron of the Royal Ontario Museum in Toronto expresses some skepticism. The fact that fossils of ctenophores were found in proximity to Hallucigenia does not definitively indicate interaction, he suggests, as an underwater landslide could have transported them to the same resting place.

Furthermore, Caron proposes an alternative interpretation: the discovered fossils may simply be detached spines, indicating that these creatures may have shed their skin as they grew.

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