Not accounting for muscle and possibly fat may have altered what we think they looked like.
.............and how did bird dinosaurs survive anyway?

shows the modern chicken, if not a direct descendant, has enough characteristics in common with T.Rex to be considered in its immediate family, removed by millions of years.

Most likely the ones that survived where the smallest of the lot, either small adults or young. The young would have had their growth severely stunted by deprivation after the impact had they survived by being sheltered in deep caves, underground in burrows, or deep under water.

Dinosaurs are still with us, they still have feathers instead of fur and lay eggs instead of giving live birth. They just got smaller while that ratlike critter that is the putative ancestor of all mammals got bigger and more diverse.