UCMP MYSTERY FOSSIL #34 is . . .
Confuciusornis

The exact age of Confuciusornis is still hotly debated but it may be about as old as the earliest known bird, Archaeopteryx. It is the oldest known toothless bird and one of the most numerous in the fossil record—over a hundred specimens have been found. Confuciusornis exhibits sexual dimorphism—the males had the long tail feathers (left) while the females (above) did not. Find out more about Confuciusornis and other fossil birds here.