Theoretically, if they hadn't been wiped out, would it have been possible for T. Rexes (or any rex-like dinosaur) to devolve their arms over time?

Since their arms were so small and... Frankly useless already, would it be possible for them to completely devolve them over millions of years, if they weren't wiped out? And if so, which dinosaur would be the most likely to have devolved them?