The name "Vastatosaurus rex" means "Ravager-Lizard-King". "Ravager" comes from the Latin term "Vastato", or "Vasto", which means "devastate, ravage, or to lay waste." "Lizard" comes from the ancient Greek word "sauros", which was combined with a Greek and Latin root to get the word "saurus". "King" comes from "rex", which is the Latin word for "king".
Vastatosauruses look much like their Cretaceous ancestors, having the build of a theropod, with digitigrade legs, small arms, and a muscular neck that supports a large head.
The creature's head is rounded, much like a Tyrannosaurus, however, their snouts are much shorter in comparison, with the jawline bearing a few less teeth as well. The overall tooth design remains the same as a T. rex however, being very thick, and blunt, used for deep puncturing of its prey. The tooth design works in tandem with the Vastatosaurus immense jaw strength, allowing for immediate deep injuries, over light, less penetrative slashing.
The dinosaur's arms still retain a short length, however, an additional digit has been added bringing up the count of fingers from the iconic two, to three, much like a dinosaur from the Allosauridae family. Its feet, much like its predecessors are tri-toed and are broad in design, aiding in supporting the creature's weight.
Unlike its ancestors however, the Vastatosaurus features a legitimate waist, with a large amount of space between the rib-cage and hips of the creature. This allows for the creature to make quick turns in the jungle.
Its skin is a greenish gray hue, possessing scales along the spine and generally smooth skin everywhere else. The skin turns into a pale tan color along the creature's underside. Its eyes are a blazing and distinct orange, as well.
The roar of the V. rex is very loud, and raspy in tone, more akin to a yell, over a deep bellow like most media's presentation of dinosaurs shows.
These dinosaurs don't display intelligence on the level of King Kong, however, during the events of the film, the group of Vastatosauruses seen showed a surprising level of cunning, being able to distract, group attack and ambush Kong during their fight.
As lone predators outside of groups, these creatures displayed a conscious effort to act as ambush predators, taking their prey by surprise, as seen with the V. rex's first attack on the Foetodon, and then the two subsequent attacks on Ann Darrow.
While Ann Darrow was being chased by a Foetodon, a Vastatosaurus rex appeared and killed by Foetodon by crushing it with its jaws. Upon seeing Ann, the V. rex chased after her. Ann managed to hide on a fallen tree, but a second V. rex appeared and attacked her. Thankfully, King Kong arrived and rescued Ann. The V. rex attacked Kong, and was soon joined by the other one.
Kong took on both V. rexes, only to find himself attacked by a third one. Kong quickly killed one V. rex by smashing its head with a boulder. The other two V. rexes then tackled Kong off a cliff, causing them to become tangled in vines. Kong battled one of the V. rexes through the mess of vines and tried to reach Ann. However, as more vines snapped, Ann fell onto one of the V. rex's jaws, to which Kong held it open with a large amount of vines. Said vines began to give way, making the one V. rex slowly drop towards another, who had its own mouth open awaiting the small prey item's descent. However, as Kong leaped down to kick its mouth shut, the former mouth was able to close, and Ann was sent falling from the action, leading to her landing on the V. rex's snout. The resulting squirming of the dinosaur resulted in the vines breaking entirely, sending both Ann and the carnivore to the forest floor.
Kong however, dealt with the former rex, seemingly killing it, before dropping down into the same area, right behind Ann. Ann retreated behind Kong and allowed him to defend her. After a vicious struggle, Kong grabbed the V. rex's jaws and pried them apart until they snapped, killing the mighty saurian.
V. rexes have been shown to understand and coordinate group efforts in taking down large prey, much like modern predators, and their hypothesized prehistoric counterparts. To add to this, despite their large stature and generally loud presences, Vastatosauruses can remain whisper quiet if need be, being able to take a Foetodon, Ann Darrow, and Kong by complete surprise.
The jaws of the Vastatosaurus are extremely powerful, following the lineage of powerful jaws granted by the family of dinosaurs known as Tyrannosauridae, most famously, that of the Tyrannosaurus rex. The same principles apply to its tooth design, which is akin to a railroad spike in design which, when used in tandem with its powerful bite, could easily prove supremely painful, or outright fatal to its targets.
Vastatosauruses displayed immense physical strength with a lone specimen being a solid match for Kong, let alone the three that attacked him at once.
Endurance and Stamina
They have shown to be able to take punishment from Kong well enough enough to continue fights that other predators would attempt to escape from. Their reinforced skull allows them to take a lot of trauma as well, as multiple V. rexes took strikes and blows to the head from Kong, only to get back up and keep fighting.
Speed and Agility
Due to their ribcage and waist design, these dinosaurs have supreme agility in comparison to their predecessors. In addition, they also possess a long stride which can be used in tandem with their footspeed to allow them to cross large distances in a surprisingly quick fashion.
Despite their strength, the lack of length to their forearms results in the V. rex having a shortcoming in physical combat. This vulnerability was exploited by Kong, who was able to keep a V. rex at bay easily, with the latter unable to push forward without proper forearm length, until its partner came in to assist.