Bernice Summerfield 9.2 - The Adolescence of Time
Big Finish Productions Audio Book

Earth is still suffering the after-effects of the asteroid (or something) which collided with the planet many years ago: the dust cloud which blots out the sun shows no sign of settling and the dinosaurs are doomed. Above the cloud, colonies of winged reptiles – more intelligent than any we know of – are fighting to survive. A strange creature calling itself Summerfield appears in their midst: is it destined to save them?