In 1860 Bavarian quarry workers discovered the impression of a feather in a limestone slab dating to the Mesozoic era...

Emil-Kunkin on March 5 at 03:28AM

This is a necessary assumption question, which asks us what the author believes must be the case if their argument is to make sense. Here, the author has concluded that the feather must be from the earliest known bird. However, the feather completely could have come from some other feathered animal, like a feathered dinosaur. So, the author must believe that this is not from another feathered Dino in order for their argument to make sense.