(CNN) - Humans have been performing cranial surgery and drilling holes in other people's skulls for a long time. The oldest example of this procedure, called trepanation, dates to 7,300 B.C., according to findings from a site at the village of Vasilyevka in Azerbaijan. That means cranial surgery was happening as long ago as the Mesolithic period.
Now, for the first time, a definite example of cranial surgery has been found in an animal: specifically, a nearly complete cow's skull discovered at a Neolithic site that dates to 3,400 to 3,000 BC. The investigation of this skull is detailed in a study published Thursday in the journal Scientific Reports.
Trepanation has been found in skulls from all over the world and usually involved drilling, cutting or scraping layers of bone to form a hole. These techniques were used to avoid being forceful and cause further damage or fracturing to the skull. As early as the Neolithic period, symptoms such as seizures, epilepsy, headaches and alterations in behavior were associated with the brain, which is why the holes are usually found in similar locations.
The cow's skull was found at the Stone Age site of Champ-Durand in France, just under 25 miles from the Atlantic coast. The settlement was once an important trade center, specializing in salt production as well as cattle. Archaeological excavations were carried out there from 1975 to 1985, and bones of cows, pigs, sheep and goats have been found.
Cows have been a popular find in other Neolithic sites, and their bones make up about 54% of the uncovered animal remains.
But complete craniums are a rare find; these animals were raised as food, and their skulls were usually broken to retrieve the tongue and brain, the study said. A wild boar skull previously found in Roquefort, France, possibly from the Neolithic period, showed signs of what could be considered surgery. But the only study of the skull was published in 1948, and the skull was never dated.
After the cow's skull was uncovered at Champ-Durand, a 1999 study suggested that the hole in the cranium was the result of the cow being gored by another cow. The lead director of the archaeological excavation asked Fernando Ramirez Rozzi, a paleontologist with the Centre National de la Recherche Scientifique, to study the skull.
Rozzi and his biological anthropologist colleague Alain Froment at the Musee de l'Homme in Paris studied the hole in the skull. They determined that there were no fractures or other evidence of an injury or blow, like goring. There is also no sign of healing around the bone tissue, which means the cow either didn't survive the trepanation process or died shortly after. The other possibility is that it was dead when the hole was formed.
But the researchers, familiar with the scraping and cut marks associated with trepanation, determined that the bone had been scraped intensively -- with the intent to form a hole in the cranium. In other words, this was not accidental.
"The main surprise was to see so evident the scratching on the cow skull reveal trepanation, the scraping marks are exactly similar in the human and cow skull" when compared to human trepanation examples, Rozzi wrote in an email.
The biggest lingering question for the researchers is why the hole was made in the first place. If this was a surgical intervention to help and save the life of the cow, it could be considered the oldest evidence of a veterinarian act. But given that cows were such a popular source of food and that the people lived off the livestock they raised, it's difficult for the researchers to see the reasoning behind surgical intervention.
"What would be the interest to heal a cow which represent the most abundant animal among the archaeological remains?" Rozzi asked.
Another likely scenario is that humans practiced surgical experimentation on animals before trying it on each other. Examples of trepanation in humans have surprised researchers by how perfect and precisely they were carried out, especially in instances in which the patients survived. That kind of skill and technique could be achieved only through practice. And even though we may never know the real reasons and intent behind trepanation found in the archaeological record, it shows us what our ancestors were capable of doing.
"These two possibilities reveal new insights for the Neolithic society," Rozzi said.
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