During the last 4 million years, many of the predatory non-avian theropods that were unique to South America were destroyed during the invasion of the more versatile creatures from the north. The tyrannosaur superfamily of coelurosaurs that first developed in Middle Jurassic times evolved into some of the largest of the carnivorous dinosaurs in the Cretaceous, although some of the spinosaurs (which later died out some time in the Paleogene) approached them in size. As they became larger their heads became heavier and their forelimbs became increasingly smaller. They spread through Eurasia and North America but they have long been extinct in these regions.
A group of tyrannosaurs did manage to filter into the South American continent when a land bridge was temporarily in place about 55 million years ago in the Eocene epoch of the Paleogene (long before the Great American Interchange even began), and there they survived while their relatives died out elsewhere. The line of their evolution continued and they increased in size. The gourmand is a massive creature, 17 meters (60 feet) long and weighing 15 tons. The forelimbs have atrophied entirely, with no trace of either limb bones or shoulder girdle in the skeleton. As the South American tyrannosaurs grew huge, they became too heavy and slow to hunt. They developed a scavenging mode of life, a life now led by the gourmand.
The typically small forelimbs of the ancestral tyrannosaurs were used to steady the animal as it arose from its belly after resting on the ground. In the gourmand this is unnecessary since the hips have moved forward to balance the body perfectly. The legs are jointed in such a way that they lift the body straight upwards off the ground. The animal is a scavenger, moving slowly across the Pampas and swallowing whole the carcass of any dead animal it discovers. The skull is very flexible and the jaws can unhinge to enable it to engulf its prey (such as pterodactyloids). Once it has eaten, the gourmand rests for several days while it digests its meal. It does this while lying motionless in the grass. The armor protects it from attackers during this period.