Echinoids show up in the fossil record from the Ordovician (about 450 million years ago), but their fossils are sparse compared to other organisms like bryozoans and crinoids. They may not fossilize well because the skeleton of the first echinoids was made of thin plates loosely held together by soft flesh (in contrast to modern echinoid plates that interlock to make a rigid skeleton). Many modern echinoids live in places with wave action, but the ancient ones probably lived in calm, sheltered waters. Like modern echinoids, some early echinoids had long spines that they could regrow, and tube feet for feeding or locomotion. Their teeth were weaker than modern echinoid teeth, and they may have lived by scavenging food from the ocean bottom. Echinoids diversified during the Triassic and Jurassic, giving rise to the types we see today, including predatory echinoids.

Echinoderms appear in the fossil record more than 500 million years ago, during the early Cambrian. What are usually left behind are hard mouthparts or parts of their skeletons, made of calcite plates. Rarely, an entire skeleton fossilizes, for example in a situation where it was quickly buried in sand. Even a piece of skeleton can provide information, because echinoderms have specific patterns in their skeletons. The echinoderms you see today have five-point (pentaradial) symmetry, often noticeable in five arms. While some of the earliest echinoderms were pentaradial, others had unusual body shapes. The “helioplacoids” had long, oval-shaped bodies with no arms, and a spiral pattern on the surface from tube feet wrapped around a central core. Helioplacoids went extinct even before the end of the Cambrian, as did a variety of other echinoderms, including the star-shaped Somasteroidea. Some echinoderms survived and diversified, becoming dominant in the oceans of the Paleozoic era.