Dinosaurs changed to birds and other reptiles over time.
You are missing one point. The dinosaurs that evolved into birds did so long before the K-T boundary. The first birds evolved over 100 million years ago, the K-T boundary was ~65 million years ago.(1) The non-avian dinosaurs became extinct as did the common ancestral species that evolved into birds. Many dinosaur species became extinct before the birds evolved. Most of the Triassic dinosaurs were extinct prior to the Jurassic, and most of the Jurassic species were extinct before the Cretaceous, including the birds common ancestor.
(1)
The Ancestors Tale Richard Dawkins, p256.
There is no better love between 2 people than mutual respect for each other WT Young, 2002
Who gave anyone the authority to call me an authority on anything. WT Young, 1969
Since Evolution is only ~90% correct it should be thrown out and replaced by Creation which has even a lower % of correctness. W T Young, 2008