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Embrithopoda (cohort Ferungulata, superorder Paenungulata) An extinct order of subungulates of uncertain ancestry and with no known descendants, known by one form, Arsinoitherium, from the Lower Oligocene of Egypt. The animal was the size of a rhinoceros (about 3.4 m long); possibly it dwelt in marshes. It had short massive limbs, one pair of large horns (fused at their bases) growing from its nasal bones and a second, much smaller pair of horns (behind the large pair) from the frontal bone.