Van es thinks it is possible there is a functional protrusion at the peak of the head. It appears in the photo to have been worked. In paleoart, sometimes a "bump on the head" was used to help portray proboscidean creatures. Please note how The Netherlands figure stone has a second bump in the middle representing the peak of the (mammoth's?) back. In the carved ivory example pictured below, there is a similar peak to the back of the mammoth.
Jan's web site is under reconstruction at this writing and with some limited images and content still available. Please visit it in the future for a excellent study of figure stones from The Netherlands and Holland. Originsnet.org has a nice gallery of his finds from another site at Boukoul.
This example in carved ivory dated to around 35,000 B.P. demonstrates how the art of the Wooly Mammoth accounts for the rounded part of the mammoth's head and the high, arched, back. It is from a Speigel article from 2007.