They are using the “molecular clock” technique to determine that:
Their analyses suggest that the ancestors of modern echinoids likely emerged during the Early Permian, and rapidly diversified during the Triassic period in the aftermath of a mass extinction event, even though this evolutionary radiation does not seem to have been captured by the fossil record.
Additionally, the results suggest that sand dollars and sea biscuits likely emerged much earlier than thought, during the Cretaceous period about 40 to 50 million years before the first documented fossils of these creatures. The authors say this result is remarkable, as the tough skeleton of the sand dollars, their buried lifestyles, and their extremely distinct morphologies imply that their fossil record should faithfully reflect their true evolutionary history.eLife, “Early evolution of sea urchins” at ScienceDaily (March 22, 2022)
One wonders if that technique is not too risky in the absence of a fossil record. But “earlier than thought” has been a good bet in principle. Not so good for the “long, slow process of evolution” stuff though.
The paper is open access.
You may also wish to read: Bryozoa add to Cambrian Explosion’s impact: 35 million years earlier than thought So they are complex and that much closer to the dawn of life. At ENST: In Nature News and Views, Andrej Ernst and Mark A. Wilson write, “Bryozoan fossils found at last in deposits from the Cambrian period.” They had been “conspicuously absent” till now.