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.
![](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2002/02/1006.jpg?resize=100%2C135&ssl=1)
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.