Mini/Jurassic Park

The minis found in Jurassic Park fanfiction are mini-Tyrannosaurus rex. This can be shortened to mini-T. rex.

Mini-T. rex have two thick legs and two short arms. They walk with their body held horizontally, tail straight back and head pointed forwards. As a mini, they love bacon, of course, but will enjoy pretty much any meat. Except Slorp.

Canon Origin
Tyrannosaurus rex was an actual dinosaur inhabiting prehistoric Earth, including the Real World. As with all dinosaurs, knowledge of T. rex is limited to what the fossil record has revealed. There is still contention whether T. rex was a predator or scavenger, but it does seem to have had binocular vision and strong smell and hearing. They very likely had feathers on at least some parts on their bodies.

The Tyrannosaurs in the JP series are cast as predators, but depicted as featherless. (That theory didn't develop until after most of the books and movies had been released.) The first JP novel had an adult and child T. rex, while the movie had only one adult. In both versions, a T. rex kills a minor character early. In the film, the T. rex rather hilariously saves the day at the last minute by attacking the Velociraptor pack while the humans escaped via helicopter. The movie T. rex can only see movement, contradicting the better-than-human vision they are now believed to have.

The sequel, The Lost World, has a mating pair of T. rex with a baby. In the novel, they get to eat another minor character, but in the movie, the male and baby are actually brought to San Diego, where the daddy escapes and goes on a rampage through the city and its inhabitants before being lured back to the boat with the baby, and subsequently returned home.

A T. rex appears briefly in the third JP film, getting killed and eaten by a Spinosaurus.

Minis

 * Jurassic park (adopted by Agent Cadmar)