Paris, April 21: For the first time, a definite example of cranial surgery has been found in a cow from Stone age that suggests that animal trials were held before graduating to humans, a study said. The near complete cow’s skull was discovered at a Neolithic site dating back to 3,400 to 3,000 B.C., a CNN report said. It was found at the Stone Age site of Champ-Durand in France, 25 miles from the Atlantic coast.