A bizarre fossil of a Cambrian creature that looked like an “alien fish taco” reveals how a single group with jaws came to account for around 90 percent of all animal species on Earth

Around 500 million years ago a strange creature with bulging eyes, a rudderlike tail and 30 pairs of spiny limbs extending from its cigar-sized body swam through Earth’s seas. Most of its legs couldn’t touch the ocean floor because they were tucked inside a protective shell that wrapped almost entirely around its midsection. And like a tiny King Neptune, it wielded a mysterious trident-shaped tooth between external jawlike structures in front of its mouth.

Though it looked more like an alien fish taco, it was an arthropod called Odaraia alata. The creature, spanning about 20 centimeters long, likely met its end very suddenly, buried underneath a thick layer of sediment. But the circumstances that spelled the animal’s doom also immortalized it in the fossil record.