This early ocean predator was a giant ‘swimming head’

2021-09-08

The mothership has landed. Two years after scientists dubbed one of Earth’s first sea-dwelling predators the “Millennium Falcon” for its sci-fi carapace, the same researchers have identified an even larger spaceshiplike creature at the same site, in Canada’s Burgess Shale. The half-meter-long arthropod, described in a study out today, was essentially a giant “swimming head” that prowled the Cambrian seas half a billion years ago, says Joseph Moysiuk, a paleontologist at the University of Toronto (U of T) who helped uncover the fossil in 2018. “The first word that comes to mind when I think of this new species is big.”

Titanokorys gainesi, whose head takes up nearly half the length of its body, was covered in a domed, spike-tipped carapace that inspired its Latin name: “Titan’s helmet.” The creature likely swam along the ocean floor, Moysiuk says, flushing prey from the mud with appendages built like “baskets of spines” (see video, above). And whereas its spiky helmet might have helped with that digging, its eyes, which sat at the back of its carapace, facing straight up, would have been useless for finding prey. Those were probably for spotting other predators—threats to Titanokorys itself.

“Predation was a big evolutionary innovation that happened during the Cambrian,” says co-author Jean-Bernard Caron, curator of invertebrate paleontology at the Royal Ontario Museum and a paleontologist at U of T. “Here, we are illustrating the complexity of that.”

Titanokorys belongs to a diverse group of arthropods called radiodonts that split from the ancestors of spiders, insects, and horseshoe crabs by 520 million years ago, soon after the Cambrian explosion of animal diversity. At a time when vertebrates—the lineage that led to us—were little more than pinkie-size fish, radiodonts terrorized the Cambrian seas. The ranks of these now extinct creatures included Anomalocaris, a predator with front-facing eyestalks and a pair of clawlike appendages on its face, and Cambroraster falcatus, the species with the sleek head carapace reminiscent of Han Solo’s spaceship.

All radiodonts shared three traits, Caron says: a circular mouth that looks like a pineapple cross-section and contains flesh-ripping teeth, a pair of spiny appendages in front of the mouth, and large compound eyes. This new species fits all those traits onto a supersize, carapace-covered head. Allison Daley, a paleontologist at the University of Lausanne who was not involved in the new research, says she is “delighted” by the find.

“It’s one of those discoveries that you never forget,” Moysiuk says. It was the end of the day during a dig near Marble Canyon in Canada’s Kootenay National Park, when Caron decided to split open one last rock. “And lo and behold, he uncovered this absolutely massive, spaceship-shaped carapace just shimmering there in the Sun,” Moysiuk says. “Everyone was pretty stunned.” After taking a few selfies, the team carefully wrapped the specimen in newspaper and packed it in a big metal can to safely helicopter it down the mountain.

At first, the researchers thought the fossil might simply be a supersize Cambroraster, because that species was found in abundance at the same site. But the shape and size of the new fossil—and 11 related specimens—were just too different. It had to be something new, Moysiuk and Caron write today in Royal Society Open Access. Daley says the authors make a “very convincing argument” that Titanokorys should get its own genus.

Finding Titanokorys at the same site as Cambroraster underscores the diversity of Cambrian ecosystems, Caron adds—and the remarkable abundance of predators. Earth’s early seas must have had enough prey to feed a large range of hunters coexisting in the same space, including some animals that have so far eluded paleontologists.

Next summer, the researchers hope to go out and search the site for a more complete Titanokorys fossil, with its full body intact. They might even find a new and even more outlandish species hidden away within the rocks.

science.org, 8 September 2021
; https://www.science.org