A 145 mm SL specimen of the ostraciid Longhorn Cowfish, Lactoria cornuta (Linnaeus, 1758), collected along the coast of Oman, has only small rudiments of the caudal fin and a much shortened caudal peduncle in which the posteriormost vertebrae are either abnormally developed or fused. The otoliths are too deteriorated to allow aging, but the gonads are mature, and we presume that an adult specimen of this size is several years old. Remarkably, this “tail-less” specimen survived without a functional caudal peduncle and caudal fin, even though the long caudal fin in ostraciid fishes is the main source of the rapid propulsion required for predator avoidance. The anatomical peculiarities of the rudimentary termination of the vertebral column and caudal fin are described and illustrated. We also comment on the potential evolutionary implications of such abnormalities.