Jesairosaurus is an extinct genus of early archosauromorph reptile known from the Illizi Province of Algeria. It is known from a single species, Jesairosaurus lehmani. Although a potential relative of the long-necked tanystropheids, this lightly-built reptile could instead be characterized by its relatively short neck as well as various skull features.
Etymology and discovery
Zarzaïtine fossil material has been known since 1957. Much of the material has been recovered by French expeditions in the late 1950s and 1960s, and deposited at the Laboratoire de Paleontologie (Paleontology department) at the Museum national d'Histoire naturalle in Paris. Algerian fossils were prepared at this institution over subsequent years. Several putative procolophonid skeletons reported in 1971 were later determined to belong to "prolacertiforms" in 1990. The term "prolacertiform" is now considered to refer to an unnatural polyphyletic grouping of early archosauromorphs, distant relatives of crocodylians and dinosaurs (including birds). These hematite-encrusted skeletons were finally prepared and described by Nour-Eddine Jalil as the new genus and species Jesairosaurus lehmani in 1997.
The generic name Jesairosaurus means "Al Jesaire lizard" (although Jesairosaurus is not a true lizard), in reference to the Arabic name for Algeria. The specific name honors J.-P. Lehman for describing for the first time vertebrate material from the Triassic of Algeria.
The holotype of Jesairosaurus lehmani is ZAR 06, a partial skeleton including an articulated and three-dimensionally preserved skull, pectoral girdle, cervical (neck) vertebrae, and a partial left humerus (forearm bone). It is also known from nine paratypes including ZAR 07 (a partial skull), ZAR 08 (a partial skull and postcranial skeletons), ZAR 09 (two partial postcranial skeletons), and ZAR 10-15, various postcranial material including vertebrae, pectoral and pelvic girdles, and even a partial hindlimb in ZAR 15. These specimens were collected in the Gour Laoud, locality 5n003 from the base of lower sandstones of the Lower Zarzaïtine Formation of Zarzaïtine Series, dating to the Anisian-Olenekian stages of the Early to the Middle Triassic.
Description
Skull
Snout bones and palate
The skull is low, with large orbits (eye holes) and a narrow and relatively short preorbital region (portion in front of the eyes). The precise form of the nares (nostrils) is unknown, but they were probably completely surrounded by the large yet narrow premaxillae (paired tooth-bearing bones of the snout tip) based on the structure of the bones of the snout. The ventral process (lower extension) of each premaxilla was long and possessed a large number of tooth positions. Although only 6 teeth were preserved in the right premaxilla of the holotype, there was room for up to 9 or 10 more teeth.
Each maxilla (a tooth-bearing bone on the side of the snout) has a short anterior and dorsal process (forward and upward extensions in the front part of each maxilla), but a long and boxy posterior (rear) process which forms most of the lower edge of the orbit. The front part of the maxilla is concave and has a hole above the third tooth. An estimated 20 to 21 teeth were present in each maxilla. The front edge of each orbit was formed by a prefrontal bone, and a thin lacrimal was present between each prefrontal and maxilla. The lacrimal likely did not form part of the border of either the orbit or nares.
The palatine bones of the roof of the mouth in the front part of the snout extensively contacted the maxillae. Some bones in the front part of the palate (likely the vomers) were also covered in small denticles. Denticles were also present in the back of the palate, likely on the pterygoids and rear parts of the palatine bones. The interpterygoid vacuities (large holes on the side of the palate) were long and thin, while the subtemporal fenestrae (holes in the back of the palate where muscles stretch through) are large.
Postorbital region
The rear lower corners of the orbits are formed by the jugal bones, which extend to the lower part of the skull's postorbital region (behind the eyes). Each jugal had a long and spur-like rear projection which reached as far back as the squamosal bone in the back of the skull. However, this rear projection stretches above each lower temporal fenestra, a hole in the side of the rear part of the skull. This leaves the hole completely open at the bottom, while in many other reptiles the jugal encloses the hole from the bottom.
