Image: Forelimbs of T. rex and Carnotosaurus
The short left forelimbs of theropods Carnotosaurus (left) and Tyrannosaurus rex (right). These forelimbs may have been small but the muscles were strong.
- © Australian Museum
Some theropod dinosaurs such as Carnotosaurus and Tyrannosaurus rex had large hand claws but very short arms that did not reach their mouths. The short arm length may be related to the massive heads of these theropods. An increase in head size relative to the body required a decrease in arm size to retain balance.