The origin of the small, Miocene horse Archaeohippus is poorly known. A recently collected specimen from the late Oligocene or earliest Miocene (Arikareean) of Florida represents Archaeohippus mannulus, sp. nov. It includes a complete upper dentition, a partial left dentary with dp1–m3, and most of the right and left manus. It is the most nearly complete skeleton of an Arikareean Archaeohippus. Distinguishing characteristics of A. mannulus include: on upper P2–P3, anteroposteriorly narrow hypocone with a pronounced medivallum ridge originating on the metaloph; lower cheek teeth with a mediolaterally broad and flat hypoconulid; and extremely small body size with very gracile limb elements. Body mass of this individual is estimated at 10 kg. The revised generic diagnosis includes derived features of Archaeohippus relative to Miohippus and Anchitherium such as crochets on upper cheek teeth and reduced tridactyly, which link it with Parahippus, merychippine-grade equids, hipparionines, and equines.