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 limestone lay the imprint of a fully aerodynamic, three-inch-long feather
This, ttherefore, must have been the earliest bird -- certainly, the earliest found to that date
In the Mesozoic era, no creatures other than birds had such feathers.