Study Reconsiders Early Evolution of Sea Urchins

Genome-scale analysis of evolutionary relationships and times of origin of sea urchins and their relatives prompts re-evaluation of their fossil record. A study led by researchers at Scripps Institution of Oceanography at UC San Diego provides new insight on the origins and early evolution of echinoids, a group of marine animals that includes modern sea urchins, sand dollars, and their relatives. The work suggests that modern echinoids emerged some 300 million years ago, survived the Permo-Triassic mass extinction event, the most severe biodiversity crisis in Earth's history, and rapidly diversified in its aftermath. These findings help address a gap in knowledge caused by the relative lack of fossil evidence for this early diversification. There are more than 1,000 living species of echinoids, including sea urchins, sand dollars and sea biscuits, which live across different ocean environments ranging from shallow waters to abysses. Throughout history, the hard spine-covered skeletons of these creatures have left a large number of fossils. However, despite this remarkable fossil record, their emergence is documented by few fossil specimens with unclear affinities to living groups, making their early history uncertain.