Something I Need More Information About

Among the things I wonder about is the dinosaur extinction. There are theories, one of which is becoming more and more accepted: a giant space rock hit just on the northern edge of the Yucatan Peninsula about 65 million years ago. This theory is based on the Cretaceous–Paleogene (K–Pg) boundary (formerly known as the K–T boundary) and the iridium found in high concentration at its stratum. The impact of this space rock is theorized to have wiped out the dinosaurs.

But one thing bothers me... One of the clues in all this is the lack of dinosaur bones found above this layer. Unless the dinosaurs all died off before that impact, wouldn't there be bones and fossils found immediately above that layer? This is why I need more information... because it doesn't quite make sense to me. If the iridium debris floated in the atmosphere for, say, a year or more then there would be time for the dinosaurs to die off and be found below the layer.  But if it fell back to earth in a shorter time then wouldn't we expect to find some dinosaur fossils above the layer? Additionally, it is said this impact driven extinction killed off the non-avian dinosaurs. If so, I surmise that this means avian dinosaur fossils are found above the layer. But wouldn't such a massive amount of debris in the air (not to mention the shockwave and massive winds an impact like this would cause) impact the avian dinosaurs even more than the land-locked ones?


Any experts out there who can explain this to me?