Son of Man — Robert Silverberg

The classic science fiction novel, now back in print Clay is a man from the 20th Century who is somehow caught up in a time-flux and transported into a distant future. The earth and the life on it have changed beyond recognition. Even the human race has evolved into many different forms, now coexisting on the planet. The seemingly omnipotent Skimmers, the tyrannosaur-like Eaters, the sedentary Awaiters, the squid-like Breathers, the Interceders, the Destroyers -- all of these are "Sons of Man". Befriended and besexed by the Skimmers, Clay goes on a journey which takes him around the future earth and into the depths of his own soul. He is human, but what does that mean?