Azendohsaurus

Azendohsaurus is an extinct genus of herbivorous archosauromorph reptile from roughly the late Middle to early Late Triassic Period of Morocco and Madagascar. The type species, Azendohsaurus laaroussii, was described and named by Jean-Michel Dutuit in 1972 based on partial jaw fragments and some teeth from Morocco. A second species from Madagascar, A. madagaskarensis, was first described in 2010 by John J. Flynn and colleagues from a multitude of specimens representing almost the entire skeleton. The generic name 'Azendoh lizard' is for the village of Azendoh, a local village near where it was first discovered in the Atlas Mountains. It was a bulky quadruped that unlike other early archosauromorphs had a relatively short tail and robust limbs that were held in an odd mix of sprawled hind limbs and raised forelimbs. It had a long neck and a proportionately small head with remarkably sauropod-like jaws and teeth. Azendohsaurus used to be classified as a herbivorous dinosaur, at first as an ornithischian but more often as a 'prosauropod' sauropodomorph. This was based only on its jaws and teeth, which share derived features typically found in herbivorous dinosaurs. The complete skeletal material from Madagascar, however, revealed more basal characteristics ancestral to Archosauromorpha and that Azendohsaurus was not a dinosaur at all. Instead, Azendohsaurus was actually a more primitive archosauromorph that had convergently evolved many features of the jaws and skeleton shared with the later giant sauropod dinosaurs. It was found to be a member of a newly recognised group of specialised, mostly herbivorous archosauromorphs that was named the Allokotosauria. It is also the namesake and typifier of its own family of allokotosaurs, the Azendohsauridae; initially the only member, the family now includes other similar allokotosaurs, such as the larger, horned azendohsaurid Shringasaurus from India. Several other groups of archosauromorphs also adapted to herbivory in the Triassic, sometimes with dinosaur-like teeth that also caused confusion in their classification. Azendohsaurus is notable, however, for also convergently evolving a similar body shape to sauropodomorphs in addition to its jaws and teeth. Azendohsaurus and sauropodomorphs likely independently evolved to fill a similar ecological niche as long-necked, relatively high browsing herbivores in their environments. However, Azendohsaurus predates the large Late Triassic sauropodomorphs it resembles by several million years, and did not evolve similar body plans under the same environmental conditions. It may then have been one of the first herbivores to fill the high-browsing role that only large sauropodomorphs were thought to occupy during the Triassic, expanding the known ecological diversity of herbivorous archosauromorphs outside of dinosaurs in the Triassic Period. Azendohsaurus is also significant as it may be one of the earliest endothermic archosauromorphs known, and suggests that a warm-blooded metabolism was ancestral to the later archosaurs, including the dinosaurs. Azendohsaurus was a stocky mid-sized reptile estimated to be roughly 2–3 metres (6.6–9.8 ft) long. It had a small, box-shaped head with a short snout on a long neck that was raised above the shoulders. The body was broad, with a barrel-shaped chest and shoulders much taller than the hips, together with an unusually short tail. Its posture was semi-sprawled, with sprawling hind limbs and slightly elevated forelimbs. The limbs themselves are relatively short and particularly robust, with digits that are shorter and stouter compared to other early archosauromorphs, each with notably large, curved claws on all four feet. Superficially its appearance is comparable to that of sauropodomorph dinosaurs, along with various details of its skeleton, suggesting Azendohsaurus converged on similar traits for a relatively high-browsing, herbivorous lifestyle. A. laaroussii is poorly known compared to A. madagaskarensis, and the two species are only known to differ in minor details of the jaw bones and teeth. Additional skeletal material of A. laaroussii has been reported from the type locality of the original skull fragments, but have yet to be formally described as of 2015. The skull of A. madagaskarensis is almost completely known, and is robustly built with a short and boxy shape and a deep snout. The premaxillae are gently curved at the front of the upper jaw, forming a blunt, round snout tip, while the lower jaws have a deep, down-turned tip like those of sauropods. The bony nostrils are fused into a single (confluent) opening that faces forwards at the front of the snout, similar to those of rhynchosaurs. The skull has a number of traits convergent with sauropodomorphs, including the downward curving dentary, a robust dorsal process of the maxilla, and several features of the teeth. The process on the maxilla usually indicates the presence of an antorbital fenestra in archosauriforms, but in Azendohsaurus this space is occupied by the lacrimal bone in front of the eyes. This is a unique arrangement unknown in other Triassic archosauromorphs, except for the related Shringasaurus. The orbits are almost entirely occupied by the large sclerotic rings, suggesting large eyes. The lower temporal fenestra is open at the bottom, separating the jugal and the quadratojugal bones (a primitive trait for archosauromorphs). Also like other early archosauromorphs, Azendohsaurus has a small (3–5 mm across) parietal foramen ('third eye') on the roof of the skull. The lower jaw is especially convergent with those of sauropodomorphs, with an articular joint where the jaw hinges positioned below the level of the tooth row and downward curving dentaries, as well as the similarly shaped teeth. These features are variously found in other herbivorous Triassic archosauromorphs, but this combination is only known in Azendohsaurus and sauropodomorphs. The teeth are all roughly leaf-shaped (lancoelate) with expanded crowns and bulbous bases that are fused to the jaw bones (ankylothecodont). However, the upper and lower teeth are distinctly heterodont, and can be readily distinguished from each other. The upper teeth are relatively short and broad at their base, with 4–6 denticles on each surface, similar to ornithischians; the lower teeth are almost twice as tall and have twice as many denticles, more closely resembling the teeth of sauropodomorphs. The four premaxillary teeth are the longest teeth in the upper jaw, and are more recurved back in shape than the rest.