Leonerasaurus

Discovery

The fossils of Leonerasaurus were recovered near Cañadón Las Leoneras, an affluent of the left margin of the Chubut River, southeast of Sierra de Taquetrén in Chubut Province, Central Patagonia, Argentina. The Las Leoneras Formation is probably Early Jurassic, interpreted as Pliensbachian to Toarcian or late Sinemurian to Toarcian. The overlying Lonco Trapial Formation, with volcanic facies from the Middle Jurassic, constrains the younger boundary, but a Late Triassic age cannot be ruled out due to a poorly defined lower constraint. The generic name references the Leoneras lithostratigraphic unit, while the specific name taquetrensis refers to the Sierras de Taquetrén.

Description

Leonerasaurus taquetrensis is known from a single incomplete individual, with much of the remains found in articulation. The specimen includes parts of a dentary and teeth, neck and trunk vertebrae, a sacrum, portions of the pectoral and pelvic girdles, and several limb bones. It measured about 2.40 meters in length, 1 meter in height, and weighed roughly 70 kg. The only skull element preserved is the anterior part of the right dentary.

Near the symphysis, the bone is straight and gently arched medially, similar to basal sauropods, unlike the broadly arching region in eusauropods. The ventral edge is damaged but does not appear deflected as in some basal sauropodomorphs. A longitudinal ridge seen in some other basal sauropodomorphs is absent, possibly due to damage. Thirteen teeth or tooth fragments were found in the dentary, with two empty alveoli indicating at least 15 teeth on one side.

The teeth and alveoli are angled forward by about 60°, resembling eusauropods and juvenile Mussaurus. Tooth height and width decrease from front to back, and neighboring teeth overlap. Anterior teeth likely lacked serrations or had them only at the crown tips, as in eusauropods, while a not erupted tooth from the back of the jaw has large denticles similar to basal sauropodomorphs. This pattern of front teeth without denticles and rear teeth with denticles also occurs in juvenile Mussaurus and Melanorosaurus.

Unlike eusauropod teeth, no high-angle wear facets are present. The anterior teeth are spoon-shaped with a convex outer surface and concave inner surface, resembling basal sauropods, but the surface texture is more like that of basal sauropodomorphs.