J. Rex

Perhaps the dinosaur closest to Jurassic World's Indominus rex (barring the enhanced intelligence and ability to change color) was Saurophaganax maximus, or as some paleontologists regard it, Allosaurus maximus. Regardless of its true identity, this predator was a close relative and contemporary of Allosaurus, though significantly larger.

Skeletal sketch of the type specimen at the Sam Noble Oklahoma Museum of Natural History, with skin, muscle, and keratin outlines.

Saurophaganax (color scheme still pending) chomps into a diplodocoid's tail.

Both of these drawings were challenging to execute and while I'm mostly happy with both, I wish had came up with a better target for the lunging head in the second drawing. Allosaurs are believed to have slammed their jaws into their victims, causing them to bleed to death before eating them in earnest. An allosaur that attacked an Apatosaurus or Diplodocus from the tail would either be exceptionally petty, considering the more fatty, vulnerable flanks, or exceptionally stupid and risky, given that these tails may have been these sauropods' best weapons.