How many finger does allosaurus have?

Tyrannosaurus has two proper functioning fingers plus a smaller, residual nonfunctional third finger.

The most primitive dinosaurs have five fingers on their hands. The first three fingers (I-II-III) have claws and the last two fingers (IV-V) didn't have claws.

As theropods (the group the T.rex belongs) evolved the goup lost the two non-clawed fingers (IV-V), reducing the number of fingers to three. Most theropods have three.

Nitpick: The correct abbreviation of Tyrannosaurus rex is Capital T [Dot] lower case rex.

So T.rex (Scientific names are in italics).

Other incorrect abbreviations: T rex, T Rex, T-Rex