The phrase "fossil skulls" refers to the preserved remains of ancient animals' heads. These skulls have turned into stone over time, and scientists study them to understand more about the history and evolution of different species. Full definition
Then he'll make CT scans of fossil skulls of ancient birds and dinosaurs to see when turbinal ridges, and presumably endothermy, first appeared. (discovermagazine.com)
Although H. sapiens might have emerged in East Africa, some researchers also categorize a previously discovered fossil skull from South Africa, tentatively dated to about 260,000 years ago, as H. sapiens. (sciencenews.org)
Neither do fossil skulls previously retrieved from later sediments at the site help to resolve the controversy. (scientificamerican.com)