By Sid Perkins
A sandstone quarry that normally supplies flagstone for hearths and custom countertops recently served up a rare scientific find nearly half a billion years in the making: fossils of an armada of jellyfish that stud the sites stone slabs.
At least seven thin layers in the quarry near Mosinee, Wis., contain impressions left by thousands of jellyfish stranded on what was a tropical beach about 495 million years ago. Some specimens measure more than 50 centimeters across, making them the largest jellyfish in the fossil record, says James W. Hagadorn, a paleontologist at the California Institute of Technology in Pasadena.