Dragonsdawn (Dragonriders of Pern Series #9)

The beautiful planet Pern seemed a paradise to its new colonists - until unimaginable terror turned it into hell. Suddenly deadly spores were falling like silver threads from the sky, devouring everything - and everyone - in their path. It began to look as if the colony, cut off from Earth and lacking the resources to combat the menace, was doomed.

Then some of the colonists noticed that the small, dragonlike lizards that inhabited their new world were joining the fight against Thread, …