* T. rex was a dinosaur, an animal. Animals are multicellular organisms, meaning they are made up of many cells.

* Prokaryotes and eukaryotes are classifications of cells. Prokaryotes are simple cells without a nucleus or other membrane-bound organelles. Eukaryotes are more complex cells that have a nucleus and other organelles.

* T. rex wasn't a single cell. It was a complex organism made up of trillions of cells.

Therefore, T. rex is not a prokaryote or eukaryote. It is a multicellular organism made up of eukaryotic cells.