Necessary Assumption

Prompt

In 1860 Bavarian quarry workers discovered the impression of a feather in a limestone slab dating to the Mesozoic era. It had previously been assumed that birds developed only after the close of the Mesozoic era and after the disappearance of pterosaurs, a species characteristic of that era. But there in limest. one lay the imprint of a fully aerodynamic, three-inch-long feather. This, therefore, must have been the earliest bird-­ certainly, the earliest found to that date.