Why is it impossible for a cat fossil to be found in the same sedimentary rock layer as a dinosaur?

it is impossible to find a cat fossil in the same layer of sedimentary rock as that of a dinosaur because dinosaurs existed long time ago before the mammals with bigger size such as that of cat came into existence. Dinosaurs became extinct about 65 millions years ago whereas cats came into existence about 50 millions years ago which means that cat appeared on the earth 15 millions after extinction of dinosaurs making it impossible for the duo to be found in the same layer of sedimentary rock.     

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