Cryptozoic
From the back cover:

Edward Bush is a young artist millions of years from home, sketching the desolate landscapes of the Devonian age.  There he meets Ann, another mind traveler, and they decide to travel together to the later Jurassic age -- where they materialize beside a 20-foot stegosaurus.

Thus begins an extraordinary adventure across aeons of time, from Bush's home time, 2093 A.D., to the utterly alien experience of time uncreated -- the CRYPTOZOIC!
Fiction in English, English Science fiction, Themes, Science fiction, Time travel
Brian W. Aldiss