Limaysaurus: a Patagonian rebbachisaurid sauropod

Limaysaurus tessonei was a plant-eating diplodocoid sauropod from Early Cretaceous Patagonia. Its type skeleton, found in Argentina’s Neuquén Basin, preserves a partial skull, shoulder and pelvic girdles, limbs and an unusually long series of tail vertebrae. That combination makes it one of the more informative South American rebbachisaurids, although the neck and parts of the skull remain incomplete.

The genus was first named Rebbachisaurus tessonei in 1995 and separated as Limaysaurus in 2004. The best-known specimen supports a medium-sized sauropod, probably about 12–15 metres long, but its mass and neck proportions are modelled rather than measured. The dinosaur catalogue places it beside other sauropods from the region, including Ligabuesaurus and Amazonsaurus, while keeping the revised age of its formation distinct from older published assignments.

Quick facts

Name and discovery

Limaysaurus means “Limay lizard”, combining the name of the Limay River with the Greek sauros, or lizard. The species name tessonei honours Lietto Tessone, who discovered the principal skeleton. It was collected in 1988 near Lake Ezequiel Ramos Mexía, close to Villa El Chocón in Neuquén Province.

The specimen, MUCPv-205, was recovered by researchers associated with the National University of Comahue and Argentina’s Bernardino Rivadavia Natural Sciences Museum. Much of the spine remained articulated, and the find included bones from the skull, shoulder, pelvis and limbs. The type specimen is the name-bearing fossil against which later material is compared; it is not a complete skeleton.

Jorge Calvo and Leonardo Salgado described it in 1995 as Rebbachisaurus tessonei, a South American species of a genus then known from Morocco. Similarities in the shoulder blade and tall dorsal neural arches supported that assignment. Further comparison showed that the Argentine animal differed sufficiently from the Moroccan Rebbachisaurus garasbae. In 2004, researchers established the separate genus Limaysaurus.

Classification and the single species

Limaysaurus belongs to Sauropoda and the diplodocoid branch of the sauropod family tree. Rebbachisauridae includes mainly Cretaceous forms known from South America, Africa and Europe. Their vertebrae often carry elaborate ridges and plates, and their lightened axial skeletons include internal air spaces. The relationship is supported by shared anatomical characters, not by a direct fossil record of ancestry.

Analyses usually recover Limaysaurus among relatively derived rebbachisaurids, near Khebbashia. Some studies use the subfamily name Limaysaurinae for it and other South American genera, but the membership of that group changes between analyses. Rebbachisauridae is the more stable assignment. Only one species, L. tessonei, is currently recognised.

Several isolated bones have been referred to the genus, but they do not all have the same evidential value as MUCPv-205. Material from the Huincul basin’s Lohan Cura Formation was once provisionally labelled Limaysaurus sp. Later anatomical comparisons supported a separate genus, Comahuesaurus. Similarity alone is not enough to add those fossils to the known skeleton of Limaysaurus.

What the skeleton preserves

The holotype includes a braincase and several other rear skull bones, scattered cervical vertebrae, posterior dorsal vertebrae, shoulder and pelvic elements, and almost complete major bones of the forelimbs and hind limbs. The hand is missing. Its most distinctive series is about forty articulated caudal vertebrae, which record how the tail narrowed toward its tip. The neck is less complete, so its total number of vertebrae and full length are not directly known.

Other referred specimens extend the anatomical sample. MUCPv-206 includes cervical and dorsal vertebrae, ribs, a sternal plate and four metacarpals. MUCPv-153 preserves sacral and anterior caudal vertebrae together with parts of the pelvis. These remains help describe variation, but assignments to the genus should remain separate from the type skeleton when the bones do not overlap or cannot be compared securely.

The braincase is particularly useful because rebbachisaurid skulls are rare. CT imaging has been used to reconstruct internal cavities, cranial nerve passages and the right inner ear. The shape of an endocast permits comparison among sauropods, but it does not translate directly into a precise sensory ability. A relatively developed olfactory region, for example, cannot show how strongly an animal relied on smell in daily life.

Body size and locomotion

Published reconstructions put Limaysaurus at roughly 12–15 metres long and about 7–12 tonnes. The span is more informative than a single number: the neck is incomplete, the body proportions have to be restored, and limb-based and volumetric methods do not produce identical mass estimates. It was a substantial sauropod, but the evidence does not place it among the largest known giants.

Several measured bones anchor those estimates. The holotype’s humerus is about 90 centimetres long, its femur about 144 centimetres, and its tibia about 85 centimetres. The upper arm is therefore about 62 percent of femur length, and the forelimbs were shorter than the hind limbs. That proportion suggests a back line rising somewhat toward the hips, rather than the high shoulders of a brachiosaurid.

Four robust limbs supported the trunk. The neck was long relative to most living land animals, but its exact reach and habitual angle are reconstructed because the cervical series is incomplete. The tail was long and tapered. A very thin whip-like tip is plausible by comparison with other diplodocoids, but its soft tissues and exact movement are not preserved in this animal.

Teeth, feeding and gastroliths

The narrow, pencil-shaped teeth were suited to cropping leaves and young shoots rather than chewing them thoroughly. The jaws did not perform mammal-like grinding, so most food processing would have occurred after swallowing. Rebbachisaurids are sometimes modelled as low or middle-level feeders, but the incomplete neck does not let researchers calculate a precise feeding height for Limaysaurus.

Several rounded stones were found beside the holotype’s ribs, and additional stones accompanied MUCPv-206. They have been interpreted as gastroliths, swallowed stones that may have remained in the digestive tract. Their position makes that explanation plausible, but a small number of stones does not demonstrate a powerful grinding “mill” in the stomach. They cannot reveal the exact plant menu either.

No evidence establishes herding, migration routes, courtship, colour or parental care. Multiple fossils from one region may have accumulated at different times. The other dinosaurs in the Candeleros Formation, including the sauropod Andesaurus and theropod Giganotosaurus, belong to the broader regional fauna, but their presence in the same formation does not prove that individual animals met.

Age and the Candeleros landscape

The fossils come from the Candeleros Formation of the Neuquén Basin. Red sandstones, siltstones and other continental deposits record rivers, floodplains, temporary streams and wind-blown sediment. The regional climate was seasonal, with wetter and drier intervals. Vegetation would have been more concentrated along watercourses and places where soils retained moisture.

The formation was traditionally assigned to the early Cenomanian, near the start of the Late Cretaceous. U–Pb dates published in 2026 instead place the studied deposits at approximately 111–106 million years ago, in the Albian of the Early Cretaceous. The newer dates revise the regional chronology; older values remain in reference works because the change is recent. The age describes the rocks and fossil-bearing interval, not an exact birthday for the individual.

Knowing the age matters for comparisons with other South American sauropods. Limaysaurus and Argentinosaurus both come from Patagonia, but the latter is known from a different, younger formation. Geographic proximity across the region does not mean the animals lived at the same time.

What remains uncertain

The genus changed as new comparisons became available: first a species of Rebbachisaurus, then a distinct genus. A second uncertainty concerns Limaysaurinae, whose membership is not recovered consistently. A third concerns the Candeleros age, now revised by new radiometric dates but still described differently in older literature.

The fossils support a medium-sized quadrupedal rebbachisaurid with a partial braincase, robust limbs and a long tail. They do not supply a complete neck, a full skull, a precise body mass, or direct evidence of social behaviour. These limits are part of why the material remains useful: it shows both how much anatomy can be reconstructed from a partial skeleton and where a reconstruction must stop.