In recent editions of art history texts, the Mesolithic period ("Middle Stone Age") is only briefly mentioned as a "transitory" era between the Paleolithic and Neolithic ("New Stone Age") periods. I think that the word "transitory" is used because the early Mesolithic period was an age of hunting and gathering, whereas the end of the period saw the development of farming. In regards to art, though, I think this period is difficult to discuss because it is hard to interpret Mesolithic art. Soren H. Anderson points out that while some Mesolithic artifacts are decorated, we do not know the intent of the decoration. These objects could have been marked to indicate ownership, gender differentiation, or social rank.1 Any deeper symbolic meaning of these decorations is impossible without a knowledge of the mythology of the Mesolithic people.
Some Mesolithic rock paintings that I like are located on the east coast of Spain. It is very likely that these paintings in shallow rock shelters originated from cave art. Above is a reproduction of a cave painting at Cingle de la Mola, Remigia (Castellon, Spain), c. 7000-4000 BC. The legs are spread wide apart, which suggests that the men in the group are either leaping or marching, perhaps in conjunction with a ritual dance. I think these paintings are interesting because they show individualized, descriptive features like the headdress of the leader. Art historically, these images are important because they show the human figure in a composite view - the torso is shown from a frontal perspective, whereas the legs and head are shown in profile. Obviously, it would be impossible for the human body to contort into this position, but the composite view allows for a more descriptive, detailed depiction of the human body.
There are other interesting artifacts from the Mesolithic period as well, such as amber statues of wild boar from Scandinavia. In Norway, rock engravings of elk, furred creatures (such as foxes) and small whales have been found along the coast and freshwater concourses 1. I especially like the Azilian painted pebbles (shown left, c. 9,050 BC (c. 11,000 BP)) that come from the Mesolithic period. The function of these rocks is unknown; some scholars think that they might be for a cult ritual, but I am drawn to a different interpretation that the painted forms represent letters or numbers (some type of writing system).
If you are interested in learning more about Mesolithic art, you might like to read this book.
1, et al. "Prehistoric Europe." In Grove Art Online. Oxford Art Online, http://www.oxfordartonline.com.erl.lib.byu.edu/subscriber/article/grove/art/T069317pg3 (accessed March 18, 2009).