The mass extinction that took place 65 million years ago wiped out ninety per cent of all vertebrate life. The creatures that survived were not the largest, strongest, fastest or even most intelligent; the future belonged to smaller, more abundant forms of life with higher reproductive rates and less specialised dietary needs.
Rats had long survived, indeed thrived, despite constant human persecution; they spread with those who tried to destroy them, multiplying with the cities that gave shelter and sustenance. When disaster overtook the world they benefited from being able to take refuge underground and eat almost anything; and with their natural enemies gone, along with most competitors, their populations multiplied, migrated and in time diverged. New species emerged to fill the niches of a new ecology that flourished without the interference of industrial societies.
Rattus Deinonychus (terrible claw rat) is an apex predator that retains such ancestral traits as large incisors, grasping forepaws, and a long, mostly hairless tail, though in size and ferocity it greatly exceeds its forebears. No immutable law states carnivores must walk on all fours; and as its second name suggests, R. Deinonychus’ morphology and lifestyle resembles that of ancient dromaeosaurids – a case of convergent evolution. These creatures hunt small game alone and form groups to bring down larger prey. Their tails aid balance while running and jumping, and quarry seized with their forepaws is quickly dispatched with bites and kicks. The quill-like hairs along their spines rise in prelude to attack if they are disturbed while feeding or courting a potential mate.
Other biological traits – an upright stance, binocular vision, opposable thumbs, large brain mass and adult height approaching six feet, to use one ancient measurement – recall another vanished species, and lead some observers to claim that in slightly different circumstances R. Deinonychus would be the creature most likely to develop civilisation; but given its habits and temperament, it is doubtful this alternate world would be any better than our own.