Brachiopods have an extensive fossil record, first appearing in rocks dating back to the early part of the Cambrian Period, about 525 million years ago. They were extremely abundant during the Paleozoic Era, reaching their highest diversity roughly 400 million years ago, during the Devonian Period. At the end of the Paleozoic, however, they were decimated in the mass extinction that marks the end of the Permian Period, about 250 million years ago. This event, known as the Permo-Triassic mass extinction, may have killed more than 90 percent of all living species. It was the largest of all extinction events (larger than the major extinction at the end of the Cretaceous period that killed the dinosaurs).
Although some brachiopods survived the end-Permian extinction, and their descendants live in today’s oceans, they never achieved their former abundance and diversity. Only about 300 to 500 species of brachiopods are exist today, a small fraction of the perhaps 15,000 species (living and extinct) that make up the phylum Brachiopoda. Brachiopods live only in the sea, and most species avoid locations with strong currents or waves.