Another challenge to the hypothesis involves the paucity of non-technological evidence of a kind we would expect to find transmitted from east to west; cave paintings of a kind associated with the Cave of Altamira in Spain, for example, are without close parallel in the New World. In response, Bradley and Stanford contend that it was "a very specific subset of the Solutrean who formed the parent group that adapted to a maritime environment and eventually made it across the north Atlantic ice-front to colonize the east coast of the Americas" and that this group may not have exhibited the full range of Solutrean cultural traits. A carved piece of bone depicting a mammoth found near the Vero man site in Florida was dated between 20,000–13,000 BP. It is described as possibly being the oldest art object yet found in the Americas and may provide some evidence for the Solutrean hypothesis. Art historian Barbara Olins has compared the Vero carving to "Franco-Cantabrian" drawings and engravings of mammoths. She notes that the San of southern Africa developed a realistic manner of representing animals similar to the "Franco-Cantabrian" style, hinting that such a style could have evolved in North America independently.