This is an inside (medial) view of the right side of the lower jaw of an adult mastodon. Most of the rear portion of the jaw is missing, while the front part of the left side of the jaw (1) can be seen toward the left of the photograph.

Two molars are present. The front molar (2) has three pairs of cusps (cones or peaks), the first two of which are worn down. The back molar (3) has four pairs of cusps. Mastodon molars grow in from the back and older teeth are shed from the front. Consequently the back teeth are typically larger and less worn than those in front.

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