This Brain Remained Intact in a 310 Million-Year-Old Fossil

The discovery suggested that horseshoe crab brains haven’t changed much and that there are more ways for soft tissues to be preserved in the fossil record.

Brain tissue is innately squishy. Unlike bones, shells or teeth, it is rich in fat and rots quickly, seldom making an appearance in the fossil record. So when Russell Bicknell, an invertebrate paleontologist at the University of New England in Australia, noticed a pop of white near the front of a fossilized horseshoe crab body where the animal’s brain would have been, he was surprised. A closer look revealed an exceptional imprint of the brain along with other bits of the creature’s nervous system. Unearthed from the Mazon Creek deposit in northeastern Illinois, and dating back 310 million years, it’s the first fossilized horseshoe crab brain ever found. Dr. Bicknell and his colleagues reported the find last month in the journal Geology.