The Rhynchosaurs

the classic 'triangular' skulls of the rhynchosaurs

Howesia, an early lizard-like rhynchosaur

Rhynchosaurs were herbivorous quadrupeds that enjoyed a worldwide distribution across Pangaea during much of the Triassic Period. They were abundant, representing up to forty to sixty percent of fossil specimens in some locales. Many different species co-existed in the same environments. Early rhynchosaurs were small and lizard-like – such as Meosuchus and Howesia – but as they developed, they grew larger. They averaged about three feet in length, but some – such as Hyperodapedon – could reach up to six feet. Rhynchosaurs disappeared in the Late Triassic Period: they may have met their demise because of the extinction of particular plant material they consumed (such as the Dicroidium flora) or because of losing competition to the rising prosauropod dinosaurs and predatory theropod dinosaurs. Some paleontologists believe that while most rhynchosaurs died out in the Late Triassic, some may have continued into the Early Jurassic before being snuffed out.

Fodonyx, a Middle Triassic rhynchosaur

Rhynchosaurs had stocky bodies and a powerful beak. Rhynchosaurs had triangle-shaped skulls, and in the larger specimens, this triangular facet was more pronounced. Later and larger forms had short, broad, and triangular skulls that became wider than they were long; Hyperodapedon’s skull was nearly twice as wide as it was long! In these Upper Triassic species there was a deep cheek region with the premaxilla – front jawbone – extending outwards and downwards to form the upper beak. Rhynchosaurs had powerful jaws, and the scissors-like action of their beaks enabled them to cut up tough plant material. Some rhynchosaurs had odd ‘tooth plates’ in place of teeth that could be used to mash food. The typical rhynchosaurs diet likely included tough plants such as seed-ferns, conifers, cycads, and ginkgos; they were limited to plants growing at ground level due to their lack of climbing ability. Their hind feet were equipped with massive claws, which scientists speculate were used to dig up roots and tubers by backwards scratching of the hind limbs. 

an artist's rendition of Hyperodapedon

Rhynchosaurs had large eye orbits, indicating that they had good eyesight. They also likely had good olfactory abilities, testified to by a large cavity in their nasal region. As far as hearing goes, it’s debated whether they could hear at all, as their skulls lack a ‘tympanic crest’ to house an eardrum. Some paleontologists speculate that skin membranes around the upper jaw joint permitted the detection of airborne sounds.