An ancient crustacean found in amber, little more than a fossilized speck, may reveal a critical point in the evolutionary history of one of Earth’s most versatile animals: crabs. This 100-million-year-old fossil, discovered in Myanmar, is helping researchers resolve a prehistoric puzzle about when crabs started to move away from the seas.

The tiny crab’s preservation is “spectacular,” says Yale University paleontologist Javier Luque, lead author of a new study describing the specimen in the journal Science Advances. Luque and colleagues were able to see details of the animal’s jointed legs, claws, compound eyes, and even its gills through the amber.

Paleontologists are unsure whether the new fossil represents an adult crab or a juvenile, but the crab is so