The Sky People — S.M. Stirling

In the 1960s, the United States and the Soviet Union sent unmanned probes to Mars and Venus -- and discovered worlds teeming with life. At that point, the "Space Race" was on in earnest.

Now, in 1988, Marc Vitrak has been assigned to Jamestown, the U.S.-Commonwealth base on Venus, near the great Venusian city of Kartahown. Set in a countryside swarming with sabertooths and dinosaurs, Jamestown is home to a small band of American and allied scientist-adventurers.

But there are flies in this ointment -- and not only the Venusian dragonflies, with their yard-wide wings. The EastBloc has its own base at Cosmograd, in the highlands to the south, and relations are frosty. Meanwhile, at the western end of the continent, Teesa of the Cloud Mountain People leads her tribe in a conflict with the Neanderthal-like beastmen who have seized her folk's sacred caves.

Then an EastBloc shuttle crashes nearby, and the beastmen acquire new knowledge . . . and AK-47s