OK, so let's look at that claim, and check our bases here, see if we can proceed to a conclusion that is solid.
If I recall, relatively few 'feathered' dino birds exist in the record. Is this right? If so, we need to look at where the few were found, precisely.
We need to look at the basis of the claim that they are more recent.
If you can do that, we can move on to deducing what went on. Of course the birds showing up later should be obvious, if we understand that life on earth (with some exceptions) started in Eden. Moved out from there. So birds would need to wait till it was suitable, and safe to start living and dying in an area. The fact that they arrived in many places after the dinos illustrates that.
Liaoning Province is one place a lot of that stuff was found. Can you tell us about where in the record it was in the rock? Did they find these things right under big dinos?
Or was it simply "dated" by the usual faith based methods?
If you can't deal with that, we are left only with the fact that birds came in the record later than the time the big dinos died there. That is what is expected in the exit from Eden.