The carcenosaurus is something of an anomalous species. Each one was once a large reptilian of indefinate species, degenerated by a cancerous catalyst from a creatures bite. Over time, uncountered surface cell-death alters their shape, deforming and mutating until its original species can only be discerned through autopsy. Limbs often fuse together, fracture into new branches of joints or are shed completely as the invasive psuedo-cancer invades deeper. The pattern of the changes often resulting in two distinct final shapes. One resembling some kind of land-bound cephalopod, with tendril-like grasping mouthparts and greatly subdued ambulatory function, and the other form being centipede-like, with non-uniform bone structures forming its legs, and a mouth running almost the entire length of the central body.

Mature individuals are rare, as most juveniles die of natural causes in their incapacitated half-mutated states. Those that do survive long enough to endure the full change will find themselves returning to elevated mobility, and as exclusive carnivores with an anaesthetic saliva to subdue prey. Mature adults have a long lifespan, but that varies greatly between individuals. The nature of these creatures grants them great immunity to poisons and toxins, though eventually the creature willingly allows itself to perish; but not before grappling with several large reptillians in an effort to infect them.

A-Z challenge word : "Carcenosaurus"
Yep. I managed to keep this one close enough to the source word for it to work. Zombie-like cancer-dinosaurs. Gruesome.