Edited - I moved sentence around.

The team named the fossil Chosha praecursor, a reference to the Diné word for insect, “ch’osh.” In the Diné (sometimes known as Navajo) creation story, insect people were the land’s first inhabitants.

For a fossil described as a crustacean, it seemed to have an awful lot of insectlike traits, such as a body split into three parts, a pair of antennae and six legs emerging from the central part of the body. Overall, it looked a lot like a modern silverfish. But there was one big difference between this fossil and our current definition of an insect, which has six legs: This one had 24. Today, insects make up more than half the known species of animals, but their early origins are shrouded in mystery.

Very little is known about this transition, because insects and their fellow six-legged arthropods are missing from the fossil record from roughly 385 to 322 million years ago. Paleontologists call this period the “hexapod gap.” But the insect-resembling fossil in Mr. Tihelka’s textbook was from 324 million years ago — just inside the gap.

Its unusual body might reflect a life in transition from water-dwelling crustacean to land-dwelling insect. Some of the legs on its lower body had a flattened shape, which might have helped it paddle in water, while the three pairs of legs in the middle of its body seem more suited to terrestrial living.