Fossilized second molar of a brontothere.

YELL_134174 (1) and (2): These pictures show the second molar of a brontothere that was discovered in Yellowstone National Park in the late 1990s. The tooth is the black-colored part, while the jaw bone is the gray to white fragment.
Megan Norr;
March 2016;
Catalog #20804d;
Original #YELL_134174(2)