Hypuronector limnaios (Olsen 1979, Colbert & Olsen 2000) ~12 cm in length, Carnian, Late Triassic, was originally considered a "deep tail swimmer" but later discoveries provide evidence that this clade was primarily arboreal. Hypuronector was derived from a sister to Jesairosaurus and was a sister to Vallesaurus, a basal drepanosaurid. Half the length of the smallest Jesairosaurus, Hypuronector is known from a headless skeleton, similar to that of other drepanosaurids, but lacking a caudal hook.
Distinct from Jesairosaurus the skull would have been much smaller, judging by the mandible. Mandibles are known from other specimens. The dentary was toothless anteriorly.
The taller anterior dorsal spines formed a distinct "hump" over the scapula, some of which were anteroposteroly expanded, nearly touching one another. Other vertebrae had taller neural spines. Posterior caudal spines leaned anteriorly following a slight upward bend in the caudal series. The hyper-elongated chevrons were fused to the caudal centralia, forming a deep, leaf-like tail. Gastralia were absent.
The scapula had narrowed to a minimum. Clavicles were absent. The humerus was more slender. Metacarpal III was the longest. Metacarpals IV and I were subequal.
The pelvis was narrower, taller and deeper. The metatarsals were extremely short. The penultimate phalanges were the longest. Pedal unguals II-IV were aligned, very deep and trenchant. Pedal digit V was elongated, subequal to IV. |
