Vastatosaurus

Vastatosaurus rex is the result of Tyrannosaurus rex evolving isolated on Skull Island over millions of years. Females laid their eggs in collected leaf litter in hidden areas of the jungle, and returned to urinate on the eggs periodically. The scent warded off most predators. Infant V-Rexes hatched ready to take care of themselves and began to stalk centipedes and lizards in the island's undergrowth. As they grew, the young V-Rexes began forming small herds with individuals of a similar age for protection. These groups worked together to take down large prey, but with little coordination. At puberty these herds began to disperse, as their burgeoning size made jungle hunting difficult. At that point they moved into more spacious forests and lowlands. Young V-Rexes bore striped camouflage, and remained this way until maturity, as until that point they were small enough to be prey to other species, however it also proved to be a useful feature to hide them as they hunted. The packs of juvenile V-Rexes would often attempt to bully other species away from kills, including the highly intelligent and coordinated Venatosaurus. Because the young V-Rexes had not yet learned to size up opponents, some of their number would sustain injuries or be killed in these contests. Other packs might try to attack a lone Venatosaurus protecting its pack’s chicks, only to be grossly overwhelmed when the Venatosaurus' alarm calls brought the rest of its pack in a voracious attack. Only the fast learners made it to adulthood.

Being fiercely territorial, V-Rexes were known to mark their territory with urine and by roaring in the mornings. Adult male Vastatosaurus preferred the most open spaces available, while adult females preferred to operate on the edge of thick forests to provide cover for nests. Bulls left their usually solitary lives during breeding season. If accepted by a female, the two would hunt in her territory for a few days before she grew tired of him and forced him out. During their hunting excursions, it was not uncommon for younger individuals to sharpen their hunting skills by following the adults and getting quick meals from leftover carcasses. Ambitious young V-Rexes, eager to stake their claims to Skull Island, would take advantage of the older bulls' absences to move into unprotected territory.

Due to their size, Vastatosaurus could easily prey on any of the prey species on the island, but V-Rexes were opportunistic feeders. They understood that it was safer to use their incredible size and strength to intimidate smaller predators off their kills than to hunt for themselves. This practice was made easier by their highly acidic stomach, capable of digesting even the most rancid of rotting meats, and their bone-crunching jaws that allowed them to crack skeletal remains and feed on the marrow. Mainly being ambush hunters, they often used the forests and brush around water to catch animals off guard. They mainly fed on the abundant Ligocristus, but if a young or injured Brontosaurus or Ferrucutus could be found, they would certainly take it. After hunting, their small arms, which grew at a slower speed than the rest of their bodies, were used to keep prey from swinging around by pinning it close to their chests. The greatest challenge facing the V-Rex during the hunt was staying hidden. Adults were dark in color, and were surprisingly stealthy for their size. They could hide in the shadows to mask their movement when stalking prey.

An additional advantage afforded to the Vastatosaurus by their black scale coloration was that they heated the reptiles up quickly in the mornings to give them an edge on the slow-warming species.