Thanksgiving.

[g-boy]

Geologically we do know which came first. The first feathered animals showed up in the late-Jurassic with Archaeopteryx. But that was a dinosaur, that is a reptile, with feathers. From the fossil record, we can see the intermediates that show dinosaurs (specifically saurischia) evolved into birds, and those birds made it through the Cretaceous/Tertiary boundary (the mass extinction associated with the asteroid that hit the Caribbean), and then spread along with mammals during the Cenozoic and what we have presently. The current cladograms regarding reptiles, dinosaurs, and the evolution of dinosaurs into birds are pretty good and accurate from the information we have. Dinos came a good 150 million years before birds.