Babel's Basement by Jane Palmer
Approx. 52,170 words.
Published on October 22, 2010 by
The direct descendent of a carnivorous dinosaur has returned to claim the Earth. Commander Pyg sets up her base in the ancient subterranean Ossiane Empire. Nothing can stop her exterminating the human race apart from an eccentric geologist, sceptical science master, and a few surviving Ossianes.
And none of them know about the comet on collision course with the Earth.