Megalania

At least a quarter of all dinosaurs were driven to extinction during the the First Age and most of the remainder died during or shortly after the First Unmaking but a few persisted into the the Second Age. The Megalania were one such dinosaur.   Megalania were originally an ambush predator dwelling primarily in temperate and tropical forests. They were ambush predators as they were not good long distance runners. They relied on surprise, a good short distance sprint and venomous bite to take down prey. Their venom was not lethal in and of itself, but it inhibits a subject's ability to move properly for a couple minutes allowing a megalania to finish off disoriented prey with their mighty teeth.   During the First dragons domesticated some megalania to use as guards, herders, and simply companions. Most dragons eventually decided not to bother keeping megalania around, but many giants were quite fond of them and they kept the practice of keeping domesticated megalania alive. Over generations of domestications, selective breeding made the megalania's less venomous, but much faster and hardier runners.   The First Unmaking saw the extinction of wild megalania (who were on their last legs due to dragons enroachment), but the domesticated megalania survived though in most cases they either escaped their masters or were cut loose meaning the domesticated beasts went feral though their ecological niche changed. They were now plains hunters rather than forest ambushers. They were far from the fastest runners in Scarterra but they had great stamina and had good noses so they could track prey and tire them out over time.   Originally, these feral ex-domesticated megalania were peresent on every major land mass, but most of them were hunted to extinction as they hate prey animals that elves and others wanted to hunt. The megalania persisted in remote areas, and the most successful megalania were the ones that adapted to the cold, especially the northern steppes of what is now West Colassia.   Rather than hunt them to extinction, the lost tribe of Moriaclar elves opted to tame them, often using magic. While this term was offensive to actual dragons, the Moriaclar called these beasts "little dragons".   While not as fast as horses and much more expensive to feed, the little dragons could be trained to tolerate wearing heavy armor making them slow but nearly unstoppable juggernauts on the battlefield. Along with their superior horse riding skills, the little dragons were the reason the Moriaclar commanded the most feared soldiers of the Second Age.   Then the Second Unmaking decimated the Moriaclar. A lot of the Moriaclar tried to flee, and they did so on horseback, leaving their little dragons behind. The Moriaclar were one of the first tribes hit by the Unmaking, and early in the Second Unmaking, the Void demons normally didn't bother attacking animals. Once again, the domesticated megalania were cut loose and went feral.   Harsh winters and depleted stocks of prey literally drove the megalania underground where they found a new niche in Scarnoctis but between thousands of years and domestication plus the warping effects of Scarnoctis has evolved megalania into what is effectively a new species barely recognizeable from the creatures they once were.