アメリカ自然史博物館のインスタグラム(amnh) - 10月15日 04時33分

#NationalFossilDay Puzzle 5/6: The left and right frontal bones that make up the “forehead” in mammals may look thick, but they are far from solid. Underneath the forehead are frontal sinuses, numerous cavities between the nose and the brain lined with a sticky membrane. The extent of the frontal sinus varies across mammals, with the greatest sinus development found in heavy land mammals like elephants, and in bone-crushing predators like hyenas. The extent of sinus development can be estimated on this skull by how much the forehead appears "inflated": The part of the forehead near the bottom of the photo is “inflated,” but the top and back (right side of photo) of the head are occupied by a solid bony crest.

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