Bentonyx sidensis

Bentonyx sidensis is a Middle Triassic rhynchosaur known most clearly from one nearly complete skull found in Devon, England. Its holotype, BRSUG 27200, was first assigned to another species before differences in the braincase, cheek and tooth-bearing surfaces supported a separate name. Later CT work exposed parts of the palate and braincase that could not be examined safely from the outside. The skull also preserves a growing series of worn teeth, but no complete Bentonyx skeleton is known. This profile belongs in the other fossil reptile catalogue, among several unrelated lineages.

Quick facts

A skull moved out of another species

The specimen BRSUG 27200 was originally referred to Fodonyx spenceri. In 2010, Max Langer and colleagues identified differences in its braincase, the rear of the skull, the jugal and the arrangement of the tooth-bearing surface. They named Bentonyx sidensis, using a genus name honouring palaeontologist Michael Benton and a species name connected with the River Sid.

The specimen preserves nearly all of the skull, although parts of the lower edges and rear side are damaged. Much of the lower jaw lies against the skull, which made some internal details difficult to study by ordinary preparation. Naming a distinct species from one skull is possible when the bones preserve a diagnostic combination; it does not mean the whole animal is equally well known.

What CT scans added

A later study scanned the holotype and digitally separated bones from dense surrounding rock. The authors described concealed parts of the palate and braincase and compared them with other Middle Triassic rhynchosaurs. Those observations supported keeping Bentonyx distinct from Fodonyx, Rhynchosaurus, Langeronyx and Stenaulorhynchus.

The scan also made it possible to inspect the internal geometry without breaking the specimen apart. Digital segmentation is still an interpretation: researchers decide where one bone ends and another begins, and damaged or tightly joined surfaces can remain ambiguous. CT imagery adds evidence, rather than turning an incomplete fossil into a complete one.

A tooth surface that grew from the rear

The upper jaw carries a broad tooth-bearing plate. Along the preserved section, the front teeth are low and strongly worn, while teeth farther back retain sharper crowns. This arrangement records a working surface with different wear stages at once. New teeth were added toward the rear and tongue side as the animal grew, rather than simply replacing each functioning crown with a new tooth directly beneath it.

The downturned front of the jaws formed a bony base for a beak. Lower cutting surfaces moved against the upper plates. Together these features support plant processing, but they do not reveal which plants were eaten or the exact motion of every bite. Other rhynchosaurs developed different tooth-plate arrangements later in the Triassic; those comparisons help trace the group's changing feeding anatomy without implying that one genus was a direct ancestor of another.

Devon and the limits of a reconstruction

The skull came from the upper part of the Otter Sandstone Formation near the River Sid. These Middle Triassic deposits formed in a river system under a seasonally dry climate. Other rhynchosaur postcranial bones occur in the formation, but similar animals lived in the same region. Isolated limbs cannot be assigned to Bentonyx just because they came from nearby beds.

The skull fixes the outline of the head and the beaked jaws more securely than it fixes total length, mass or gait. The skin, colour and behaviour are not preserved. An illustration can use a related rhynchosaur to complete the missing body, but those comparisons should remain visible as uncertainty. The animal lived during the Triassic Period; its secure anatomy is concentrated in the single diagnostic skull.