Few constructed shelters are known for the Mousterian. This absence may result from a lack of preservation, since large numbers of Mousterian sites exist in exposed areas, suggesting that Neandertals did not need caves or rock shelters to survive. The few examples of shelters that exist were made from durable materials, such as animal bone. It may simply be that shelters were made of wood or other nonpreservable materials. Indeed, there is evidence even before the Mousterian for wooden stakes and post molds such as this pre-Mousterian example from the French cave of Combe-Grenal.