One of the most beautiful things I have ever seen, is the rock art of the Wadi Mathendoush (in the Libyan Sahara), which was created almost ten thousand years ago. You will see all kinds of wild animals: elephants, rhinoceruses, hippopotamuses, giraffes, and crocodiles. Obviously, the desert was more fertile back then, and indeed, it seems to have been some kind of savana. (Petrified forests are additional evidence.) You will also find rock paintings of ostriches, cattle, horses, and dromedaries in the desert, but these are younger.
I have made a page on the history of those ancient works of art, which you can find here. It is one of the pages I love best. The Wadi Mathendoush is here, and finally, there is a brief note on a related subject: the Troglodytes, or cave men. I recommend starting here, and I promise you will find it interesting.