Hyperodapedon in particular was part of the subfamily Hyperodapedontinae, a specialized rhynchosaurian subgroup with broad skulls, beaked snouts, and crushing tooth plates on the roof of the mouth.

Some of the early South American finds were described under the name Scaphonyx, which is often considered a junior synonym of Hyperodapedon.

Huxley's correspondence was added as a postscript to Roderick Murchison's broader discussion on the age of the Elgin area sandstones.

Hyperodapedon was the third reptile to be discovered in the area, behind Stagonolepis and "Telerpeton" (Leptopleuron), and reinforced Huxley's new hypothesis that the Lossiemouth Sandstone was Mesozoic in age, rather than Paleozoic.

[7] Hyperodapedon huxleyi was named by English naturalist Richard Lydekker in 1881 based on fossils from the Lower Maleri Formation of India.

[10] For much of the 20th century, Paradapedon huxleyi was entangled with debates over the validity of Parasuchus hislopi, a species which was first mentioned by Huxley (1870) and formally described by Lydekker (1885).

[8][10] One of the syntype fossils of Parasuchus hislopi was a collection of bones including a partial braincase, osteoderms (bony scutes), teeth, and other associated material.

[10] Assisted by the discovery of new complete skeletons, Parasuchus hislopi is still considered a valid phytosaur taxon to the present day.

[13] Arthur Smith Woodward (1907) named a new genus and species, Scaphonyx fischeri, for a small number of reptile vertebrae and phalanges from the Upper Santa Maria Formation, in the Brazilian state of Rio Grande do Sul.

Huene (1926) informally proposed multiple new names to describe the reptile fossils he had collected: Cephalonia, Cephalastron, Cephalostronius, and Scaphonychimus.

Sill also demonstrated the synonymy of Cephalonia lotziana and Scaphonyx fischeri, with fossils of the latter simply having been recrystallized into a more inflated state via diagenetic processes.

[13] Diagnostic features of H. huenei include the absence of an infraorbital foramen, a single dentary blade, and fusion between the supraoocipital and opisthotic bones of the braincase.

Cranial autapomorphies (unique diagnostic features) include a basipterygoid process which is longer than wide[clarification needed] and a crest-shaped maxillary cross section next to the main longitudinal groove.

[4] The upper temporal bar faces dorsally and is raised above the level of the ventral margin of the orbit (eye socket).

Rhynchosaurs are archosauromorph diapsids, meaning that they are reptiles more closely related to archosaurs (such as crocodilians and birds) rather than lepidosaurs (such as lizards).

Within Rhynchosauria, Hyperodapedon is the namesake of Hyperodapedontinae, a smaller clade meant to encompass Late Triassic rhynchosaurs while excluding more basal taxa such as Rhynchosaurus and stenaulorhynchines.

Several of the new genera had been used in the past (Scaphonyx for H. sanjuanensis, Macrocephalosaurus for H. mariensis, Paradapedon for H. huxleyi, Supradapedon for H. stockleyi) while others are newly named (Beesiiwo, Oryctorhynchus).

The neck and cervical ribs also hosted strong attachment points for muscles related to stabilizing, swinging, and lowering the heavy head.

In its maximum rearward position, the humerus points nearly straight back and lies flat against the body, twisting the forearm inwards and narrowing the stance of the forelimb as a whole.

The forelimbs were likely secondary to the hindlimbs during locomotion, since the shoulder joint was small and weak while its associated muscles were poorly positioned for strong movement.

The ideal posture to maximize stride length was semi-erect, with the thigh about 45° below the horizontal (when seen from both the front and the side) at the start and end of its 90° arc.

Despite its heavyset body, the limb proportions of Hyperodapedon were similar to active and relatively agile dinosaurs such as Protoceratops.

[7] Several lines of evidence support the idea that Hyperodapedon and other rhynchosaurs used their hindlimbs for scratch digging, a versatile type of burrowing behavior utilized by animals such as turtles, ground squirrels, armadillos, and pangolins, among others.

The pelvis and tibia had room for dense musculature, and the stout interlocking toe phalanges would have been reinforced with strong ligaments.

Overall, Hyperodapedon had a more aggressive developmental strategy than most reptiles, and its metabolism was likely more similar to early archosauriforms like Proterosuchus and Erythrosuchus.

[26] Fossils of the mandible and cranium of H. huxleyi from the Maleri Formation show bite marks most likely made by phytosaurs, indicating that these reptiles likely would have preyed on Hyperodapedon.