[topynate]

Maybe you could outrun a fully-grown T. rex. But what about a juvenile?

This is a great zoom talk by Dr. Thomas Holtz about the role played by sub-adult tyrannosaurids: https://www.youtube.com/watch?v=XwxaEsLcU_w

Holtz looks at the hypothesis that juveniles and sub-adults filled the niches that medium-size predators occupied in ecosystems with no tyrannosaurids. If so they'd have needed to have been fast enough to catch smaller prey.