Which dinosaur had huge jaws and tiny arms?

Tyrannosaurus rex, whose arms are the standing joke of palaeontology - about a metre long on a nine-tonne animal, with two fingers. They are not vestigial, though: the bones carry heavy muscle attachments and the arms could probably curl a couple of hundred kilograms. Nobody is sure what for. Proposals include holding prey, gripping a mate, and pushing itself up off the ground.

The head is where the animal invested. Bite force estimates run to around 35,000 newtons, the strongest of any land animal that has ever lived, delivered through thick conical teeth built to crush rather than slice - and there are Triceratops and Edmontosaurus bones with T. rex tooth marks that went through bone, plus fossilised droppings full of bone fragments.

The picture has changed enormously in thirty years. The tail-dragging upright posture of old museum mounts is wrong; it stood horizontal, balanced at the hip. Its close relatives had feathers and it very likely had at least some. And the recurring argument about whether it hunted or scavenged has mostly been settled with the obvious answer, which is both - there is a healed Edmontosaurus vertebra with a T. rex tooth embedded in it, meaning the animal was attacked, and got away.