Dragonsdawn (Pern, #9)

In the beginning, before Thread, before the Dragons, before the Holds and the Weyrs and the elite Dragonriders of Pern, was just the great ships gliding through space with nearly six thousand colonists prepared to tackle the mighty task of beginning a new world on a strange planet.

It was a jewel of a planet, with rivers and seas and mountains, and breathable air and growing things. Then came the terror. The strange, unidentifiable circles in the grass suddenly revealed a meaning, and every living thing was at risk. Many died -- a horrible and consuming death. All resources, every man, woman and child had to fight the terrible nightmare of Thread.

But a new creature was about to save the planet. From the delicate fire lizards a new life was born -- a new symbiosis between man and beast.