Atlas Obscura has a story about Elrathia kingii. E. kingii is a very common trilobite found in the Cambrian rocks of Utah. This article is a great summary on how they lived and most importantly... how they grew.
WITH ANY LUCK, HUMANS CHANGE a lot over the course of our time on Earth. As we grow out of our teeny onesies and our teenage styles, the aging process can feel a lot like shedding a past self. But other creatures literally do that: step out of their bodies and grow into a new one. For trilobites—marine arthropods that appeared in the Cambrian period, more than 500 million years ago—molting was a key part of growing up.
Trilobites could crawl out of their exoskeletons more than two dozen times in a single lifespan, typically by arching their bodies, lodging themselves into the sediment, and pushing out of the exoskeleton through the head, which separated into pieces. “The animal pulled itself out of its molt and walked out through the opening,” says Melanie Hopkins, an associate curator of paleontology at the American Museum of Natural History. Hopkins recently researched how a species called Elrathia kingii changed over the course of many, many molts.
