Winter in Eden (Eden #2)

Blurb

Winter in Eden is a 1986 science fiction novel by American author Harry Harrison, the second in the Eden series.
It tells an alternate history of planet Earth in which the Extinction of the dinosaurs never occurred. The story began in West of Eden, which depicts a war between a group of Cro-Magnon-level humans and a reptilian race called the Yilanè, who are descended from the prehistoric mosasaur and have become the dominant lifeform on the planet. The central characters from the first book return: Vaintè, an ambitious Yilanè, and Kerrick, a "ustouzou" who was captured by the Yilanè as a boy, raised as a Yilanè, and eventually escapes to rejoin his own people and burn the Yilanè colony city.
The trilogy continues with Return to Eden.