UCMP MYSTERY FOSSIL #48 is . . .
the footprint of a goose

If you said this was a dinosaur footprint, give yourself credit for a correct answer, since many scientists believe that birds are the living descendants of dinosaurs. This track (a trace fossil), and the one in the photo on the right, are from a Miocene trackway found in the Mulholland Formation, Moraga, California. To learn more about birds in the fossil record, look here.