NEW YORK, NY.- About 70% of the animals on Earth — including centipedes and bees, shrimp and crabs — are arthropods with mandibles, or pincerlike jaws. To understand how organisms with this anatomical feature became so diverse and successful over the last 500 million years, scientists looked inside the tacolike shell that protected an enigmatic creature that once swam in prehistoric seas.

Odaraia alata, an arthropod, roamed the shallow seas of the middle Cambrian Period approximately 508 million years ago. Sometimes compared by scientists to modern-day shrimp, Odaraia was nearly 8 inches long, which was large for the time. Its unique hard covering, which may remind you of Taco Tuesday, most likely helped propel it through water, at times upside down.

An analysis of fossils, published Wednesday in the journal Proceedings of the Royal Society B, presents the first solid evidence that Odaraia had mandibles and probably collected food in the open ocean, not only near the seafloor. The study fills critical gaps in the evolutionary record of arthropods and the establishment of marine food webs.

Paleontologists have been puzzling over Odaraia for more than a century. They proposed, first in 1912 and later in 1981, that the sea bug could filter-feed with mandibles, as shrimp and barnacles do today. But the fossil evidence was inconclusive.

“Many things about Odaraia were still secret to us” even after the comprehensive 1981 analysis, said Alejandro Izquierdo López, a paleontologist who led the new study while at the University of Toronto.

Izquierdo López measured and documented 150 previously unanalyzed Odaraia alata specimens from the collections at the Royal Ontario Museum. He selected 24 fossils with exceptional preservation for closer study, which yielded exquisite details about the animal’s head and legs. Such features rarely survive geologic burial, but the fossils were originally found in British Columbia, Canada, in the Burgess Shale, a rock formation with unusually high rates of high-quality preservation of soft body parts. Izquierdo López’s specimens were no exception.

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

The fossils had clear mandibles lined with tiny teeth. Set between the jaws was an odd, single tooth, most likely used to help grind food.

“It looks like a trident,” Izquierdo López said. “That was something that has not been seen in any other Cambrian animals.”

His analyses also revealed that Odaraia’s “very bizarre” legs were covered in dozens of large spines and hundreds of smaller spikes. The legs would have interlocked to create a mesh, similar to a fishing net. The animal could have used its cascade of legs to funnel water through its tube-shaped shell, capturing plankton and other prey in the net. It would then send the food up to its mouth, where the mandibles and tooth would grind it up.

The fossil findings support previous ideas that Odaraia was a filter feeder. But relatively large gaps between the leg spines suggested that the animal could have captured prey up to 1 centimeter long. Odaraia also has some of the largest eyes compared with its body size among animals of that time, a common feature in predators.

Izquierdo López posited, then, that Odaraia could have been part filter feeder, part predator. “It’s an idea worth continuing to explore,” he said.

“This is an animal that hit on suspension feeding, which is pretty innovative for this deep in time,” Bicknell said. The fossils provide “stunning insight into how we think this kind of animal functioned.”

That flexibility could have helped Odaraia thrive in the water column, setting the stage for the evolutionary success of other mandible-bearing arthropods. Even if its taco-shaped shell is no more, its way of eating has survived for half a billion years.

Scientists are not sure what Odaraia’s closest living relative is; the taco-shaped shell hasn’t been seen since the animal roamed the Cambrian seas. Some forms of shrimp are potential relatives of Odaraia, but there’s more to learn, Izquierdo López said.

Both paleontologists, if given the opportunity, would subject Odaraia to a taste test.

“They were probably quite meaty,” Izquierdo López said. “I’d probably do something with parsley and garlic.

“You’d just have to take off a lot of legs,” he added.

As for Bicknell, who is a dual national of New Zealand and Australia: “Honestly? Shrimp on the barbie.”

This article originally appeared in The New York Times.