Hupehsuchus nanchangensis (Young and Dong 1972, Carroll and Dong 1991) Early Triassic ~242 mya, ~1 m in length was originally and is currently considered an enigma with no obvious close relations. Here Hupehsuchus was derived from Stereosternum and was a sister to the basal ichthyopterygid Utatsusaurus. Hupehusuchus represents the last in its lineage.
Compared to a small Stereosternum, the skull of Hupehsuchus had a longer, flatter rostrum without teeth. The premaxilla was longer than the maxilla. The lacrimal and prefrontal were smaller. The posterior skull was shorter and taller. The quadratojugal was restricted to the quadrate. The palate was further modified toward the ichthyosaur configuration.
The cervicals were shorter. The dorsals neural spines were were much taller and topped with ossifications that further increased their height. The dorsal ribs were thinner and enclosed a deep, round torso. The tail was deeper with shorter caudals. The transverse processes were reduced.
The scapula and coracoid are not fused. The clavicle reached the top of the scapula. The humerus was reduced to a small stout rectangle with a concave posterior rim. An extra finger was present between #4 and #5, essentially duplicating #4. The unguals were reduced to discs and the entire hand was likely transformed into a paddle that was much larger than the foot.
The ilium was reduced, as was the hind limb. All five digits were aligned. This was made possible by addng phalanges (hyperphalangy) to the medial digits and subtracting one from digit IV. It appears likely that the hind limbs was also tranformed into a flipper.
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