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Fossil confirms that early arthropods molted

A 505-million-year-old fossil provides hard proof of what scientists had previously only suspected: Ancient arthropods shed their exoskeletons during growth, just as their modern relatives do.

Arthropods, a class of animals named after the jointed legs characteristic of its member species, includes creatures as diverse as king crabs, insects, and scorpions. Many periodically shed their hard outer skins as they grow. Arthropods make up about three-fourths of all known living and extinct species.

Scientists have found some fossils of trilobites—aquatic arthropods that dominated many ancient seafloor ecosystems but went extinct about 250 million years ago—near matching bits of fossilized exoskeleton. None of those fossils, however, portrays the very act of shedding, says Desmond H. Collins of the Royal Ontario Museum in Toronto.

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