Warum fleischfressende Dinosaurier wie T. rex winzige Arme entwickelten: „Die Entwicklung winziger Arme in mehreren Gruppen fleischfressender Dinosaurier wurde wahrscheinlich durch die Entwicklung starker, kräftiger Köpfe vorangetrieben, die zum Angriff auf Beute verwendet wurden.“ »

They were all meat eaters

My understanding is that these arms can’t be considered vestigial because they would have actually have evolved off in that time and there are the type of injuries to the arms (wishbone stretching fractures) that make scientists believe they were useful in combat to some degree.

I didn’t read this artifice because if browser issue, but my understanding was the tiny arms were in inverse proportion to the large heavy heads. 

As the head and giant mouth and powerful jaws became an advantage, the arms became less valuable and those dinosaurs with smaller arms could get bigger heads, continuing to diminish arm size, allowing and selecting for  larger and larger and more powerful heads.  

Having both normal sized arms and huge head would be a disadvantage as it would toss of balance, add weight, the arms would not be particularly valuable to hunting or fighting – that giant 6 inch teeth, etc.cant handle. 

TRex had huge head.   

I’s a trade off that offered success.  Like armor plates likely slowing an animal down but offering some protection, or birds or bats and optimizing for flight.  

I think I read this theory many years ago. 
So if there is anything new? 

I favor the pack feeding hypothesis, backed up by tooth marks on arm fossils. Smaller arms were less likely to get munched at the trike buffet.

Source: we dont know and made this all up