Swimming Reindeer of Montastruc. Made from the 8in tip of a mammoth tusk. The carving, which is at least 13,000 years old, depicts two deer crossing a river. Their chins are raised as they would be when swimming. At least four different techniques were used to create this masterpiece: an axe trimmed the tusk, scrapers shaped its contours; iron oxide powder was used to polish it; and an engraving tool incised its eyes and other details. Found in 1866, France.