Taco-Shaped Creature Had a ‘Major Edge’ in Evolution—and 30 Pairs of Spiny Legs .NguyenNghia

Around 540 million years ago, the world witnessed the Cambrian explosion: a fast-paced period of evolution that produced more advanced organisms than ever before. Now, paleontologists at Canada’s Royal Ontario Museum have discovered surprising physical features on one of this timespan’s most iconic creatures, a taco-shaped, shrimp-like arthropod called Odaraia alata. The study was published in Proceedings of the Royal Society B on Wednesday.

“The head shield of Odaraia envelops practically half of its body including its legs, almost as if it were encased in a tube,” Alejandro Izquierdo-López, a paleontologist and lead author of the study, says in a statement. “Previous researchers had suggested this shape would have allowed Odaraia to gather its prey, but the capturing mechanism had eluded us, until now.”

Odaraia was about eight inches long—a size that, for its time, was pretty big—and sported a large head, big eyes, a rudder-shaped tail and a surprisingly taco-like shell. Paleontologists first discovered Odaraia fossils in the Burgess Shale—a landmass in the Canadian Rockies famous for its excellent preservation of soft-bodied fossils—more than a century ago.

But despite various studies during the 1980s, two questions have continued to plague scientists: Did Odaraia have a mandible, and how did it feed?

“Many things about Odaraia were still secret to us,” Izquierdo-López tells the New York Times’ Rebecca Dzombak.

For the new study, paleontologists examined around 150 fossils of Odaraia that had not been analyzed before, and as a result, they were finally able to provide answers. Odaraia did have a mandible lined with tiny teeth as well as an odd, trident-shaped tooth between its jaws. This makes Odaraia one of the earliest mandibulates, or arthropods with mandibles.

“I’m gobsmacked,” Russell Bicknell, a paleontologist at the American Museum of Natural History who was not involved in the study, tells the New York Times. “It’s nuts how beautiful these animals are.”

This discovery helps scientists study the evolution of mandibles, which would have given creatures “a major edge over competing organisms, [because they] could break larger structures into pieces and gain access to new types of food,” Izquierdo-López tells Scientific American’s Ashley Balzer Vigil.

The study also revealed the odd-looking creature’s feeding mechanism. Paleontologists discovered that Odaraia possessed more than 30 pairs of legs covered in large spines and small spikes, which would have interlocked to create a makeshift fishing net. It swam upside-down and likely used its legs to propel water through its shell, snaring tiny organisms in the tangle of spikes and sending them toward its mouth.

“Odaraia was capturing food from the water column using its spiny legs,” Izquierdo-López tells Gizmodo’s Isaac Schultz.

Researchers had previously concluded Odaraia was a filter feeder. But because its upside-down feeding strategy could catch slightly more substantial prey—and because its large eyes are a common feature of predators—Odaraia might have been part filter feeder and part predator, he adds to the New York Times.