Tyrantrum is a bipedal, dinosaurian Pokémon that resembles large a theropod. It is predominantly brownish red with scaly patterns on its skin and scattered orange highlights on some scales and ridges. Its head is proportionately large with a blunt, ridged snout and powerful jaws. It has black around its eyes and a light gray lower jaw covered by a beard of white, primitive feathers. Several sharp teeth are visible in the lower jaw, while the upper jaw is lined with orange-tipped, tooth-like projections. Over its eyes are a row of five spikes resembling a crown. Around Tyrantrum's neck is a feathery white ruff that extends over its shoulders similar to a cape. Its underbelly is gray with white borders and there are two orange spikes near the tip of its long tail. Its small forelimbs have only two black-clawed digits each, but it has powerful hind legs with three black claws each. Plated, armor-like ridges cover its knees, back, and the top of its tail.
Before its extinction 100 million years ago, Tyrantrum lived like a king. Its powerful jaws, capable of shredding thick metal plates, made it invincible. It is theorized that its original form was completely covered with a feather-like coat.
Four Tyrantrum debuted in The Tiny Caretaker!, under the ownership of several Scientists, with one of them having evolved from a Tyrunt. Bonnie hoped Clemont would catch the Tyrantrum she had befriended, but because the scientists owned it, she had to bid a sad farewell to it.
Tyrantrum is mostly based on the genusTyrannosaurus, though it also shares characteristics (including the orange facial crest) with the Carnosauria clade. The orange crest is also similar to those seen on Cryolophosaurus. The orange crest and white feathers may also have been inspired by kings (with the crest acting as the crown, the fringe on the lower jaw acting like a beard, and the fringe on the Pokémon's neck acting as a cape). The fringe may also be a reference to the possibility of Tyrannosaurus having feathers.
Tyrantrum may be a combination of Tyrannosaurus or tyrant and tantrum.
Gachigoras may be a combination of ガチ gachi (serious or for real) and チゴラス Chigoras (Tyrunt's Japanese name). It may also come from がっちり gacchiri (stocky).
In other languages
Possibly from ガチン gachin, or ガチガチ gachigachi, チゴラス Chigorasu, and Tyrannosaurus