アメリカ自然史博物館のインスタグラム(amnh) - 10月14日 23時53分

Happy #NationalFossilDay 2015 (1/6)! To celebrate the wonderful fossil resources around the country, Z. Jack Tseng (@tseng_zj), a National Science Foundation postdoctoral researcher in the Division of Paleontology at the American Museum of Natural History, has a puzzle for you! In the next couple of hours, we’ll present pieces of a fossil from the Age of Mammals (65 million years ago to present). Can you figure out which group of animals it belongs to, using clues that reveal its lifestyle?

To begin: this photo shows the lower-back part of the skull, which was recovered in 15-million-year-old rocks in Nebraska. The dark, rounded hole near the photo’s center is the entrance into the left ear region, where you will find tiny internal ear bones that help transmit sound—a signature of living mammals. (Reptiles have similar structures, but they are part of the jaw, not the ear.) The size of the ear chamber, which is enclosed by a bony bulb-like covering (called the bulla) below the entrance, is in part associated with the range of hearing frequencies (larger chambers for lower-frequency hearing). The bulla in this photo is relatively small for the size of the skull.

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