Edgar Rice Burroughs 
People That Time Forgot 
Land That Time Forgot Book 2

In uncharted Caprona, a continent lost from the map of Earth, where Time had stopped and all the primeval creatures of long-gone ages still prowled, Bowen Tyler was lost.Strange mysteries awaited the expedition that went in search of Tyler. A barbaric, warring civilization hid there, trapped between the impassable jungle on one side and an unknown menace on the other.