Planetfall — E. Robert Dunn

Earth is but a memory to its spacefaring descendents and the coalition of planets known as The System - formed from the progeny from the Earth's first colony planet, Terra. It is a civilization that has cast aside racial and sexual prejudice, a civilization extending itself into unexplored Space ... stopped in its pursuit by the Tauron, a treacherous saurian race that exists to conquer, destroy, and subsume. A war ensues.
Survivors from the sundered planet Aidennia had sought refuge until they could safely make a journey home. They are aboard the podship Pioneer 4 and it is spaceborne once again, plunging into uncharted Space. After weeks of uneventful flight, the Aidennians' voyage is interrupted as Pioneer 4 is abducted by the slipstreams of a gravity well and put in orbit around a world that is lush, a near paradise; another podship and one of its crew are discovered. Eden turns to terror when an alien eugenics project is unveiled. Escape to the Systemite planet of Sheey loses its splendor when the ravages of the Tauron Occupation are revealed. And what seems to be the Aidennians' final battle takes them full circle with the begetters of their odyssey.