Ligabuesaurus: a large Early Cretaceous sauropod

Ligabuesaurus leanzai was a large herbivorous sauropod from Early Cretaceous Patagonia. Its fossils come from the Lohan Cura Formation of Neuquén Province, Argentina, and include teeth, vertebrae, shoulder and pelvic bones, and substantial parts of both forelimbs and hind limbs. The skull and much of the spine are missing, but the postcranial material is unusually rich for a sauropod of this age.

Its classification has changed. The original description in 2006 called it an early titanosaur; a detailed 2022 revision instead placed it among non-titanosaurian Somphospondyli, close to the evolutionary radiation that includes Titanosauria. Length estimates of 18–24 metres and mass estimates around 17–29 tonnes are reconstructions with different uncertainties. The dinosaur catalogue lists Ligabuesaurus alongside the Patagonian rebbachisaurids Limaysaurus and Amazonsaurus, whose skeletons preserve different anatomical evidence.

Quick facts

Name and discovery

The genus name honours Giancarlo Ligabue, an Italian patron and researcher. The species name leanzai commemorates Argentine geologist Héctor Leanza, who reported fossils from Cerro de los Leones near Picún Leufú. The name therefore records two people connected with the history of the find.

Expeditions led by José Bonaparte worked in exposures of the Lohan Cura Formation from 1996 to 2004. Material from Quarry 4 formed the basis of the new genus. In 2006, Bonaparte, Bernardo González Riga and Sebastián Apesteguía described Ligabuesaurus leanzai. Its holotype is catalogued as MCF-PVPH-233.

The first description included a block of teeth, cervical and dorsal vertebrae, shoulder blades, upper arm and hand bones, a femur, lower-leg bones, an ankle bone and much of the right foot. Some quarry material was prepared later and received separate museum numbers. A 2022 revision used field notes and photographs to reassess where the collected elements had lain and added more vertebrae, limb-girdle elements and a partial skeleton from a nearby quarry.

Classification and its revision

Ligabuesaurus is a sauropod within Titanosauriformes, the broad group that includes brachiosaurids, somphospondylans and titanosaurs. Its first description placed it inside Titanosauria and compared it with the Thai genus Phuwiangosaurus. Later analyses did not consistently support that placement.

The detailed 2022 study recoded nearly two hundred anatomical characters and incorporated bones that had not been described in 2006. Its analysis recovered Ligabuesaurus as a non-titanosaurian somphospondylan: more derived than Sauroposeidon in that tree but outside the narrower Titanosauria. The result puts it close to early titanosaur evolution without making it a titanosaur in the strict sense.

Classification is an inference from shared anatomy. New bones and a broader comparison can change a position even when the genus remains valid. For that reason, older sources still calling Ligabuesaurus an early titanosaur reflect its original placement, not a different fossil animal. Its importance is that large non-titanosaurian titanosauriforms remained part of South American ecosystems during the early radiation of titanosaurs.

What the fossils preserve

The Quarry 4 assemblage probably represents one large individual. The researchers found no duplicate bones from the same side, the sizes were broadly compatible, and the elements fit a disarticulated carcass. Some bones are compressed or distorted by burial, which complicates measurements and explains why not every apparent difference should be treated as a biological feature.

The material includes teeth, several cervical and dorsal vertebrae, an anterior caudal vertebra, rib fragments, both scapulae and coracoids, humeri, part of a radius, metacarpals, pelvic fragments, both femora, tibiae and fibulae, an astragalus and a substantial part of the foot. The nearly complete left femur and associated hind-limb elements are especially useful for proportions.

A second partial skeleton from Quarry 3 includes neck and dorsal vertebrae, ribs and a scapula. A well-preserved isolated tooth has also been referred to the genus. These additional remains permit comparisons among individuals, but they are not pieces of one composite skeleton. The skull remains unknown.

The original authors described a block of ten teeth as part of the right upper jaw. The 2022 revision found no jaw bone in the block and interpreted it as a tooth row held together by tissue before burial. That reassessment removes a supposed piece of the skull from the direct record. A full muzzle in a reconstruction must therefore be based on related sauropods.

Size, limbs and posture

Length estimates generally range from 18 to 24 metres. The spread reflects an incomplete neck, missing tail sections and different choices for restoring body proportions from related somphospondylans. It is more accurate to give a range than to present one total as a measured fact.

Mass has a firmer, though still model-based, anchor. Circumferences of the humerus and femur were entered into an equation that produced roughly 23 tonnes, with an error of about 5.9 tonnes. A practical interval is around 17–29 tonnes. That estimate does not mean the animal was weighed, and it depends on the chosen formula and the condition of the bones.

The middle cervical vertebra is elongated, and the researchers considered the neck relatively long. Compression affects its proportions, so derived elongation indices differ. The vertebrae contain pneumatic spaces and bony partitions that reduced skeletal mass while retaining structural support. Broad, diamond-shaped neural spines on rear neck and front back vertebrae help diagnose the genus.

The humerus is comparatively slender; the femur is nearly straight and expands strongly near the hip. An older humerus-to-femur ratio of about 0.9 encouraged a reconstruction with unusually long forelimbs and a high shoulder. Measurements from the more complete femur reduced the ratio to roughly 0.8, closer to many non-brachiosaurid sauropods. The high-shouldered outline is not demonstrated by that older figure.

The foot preserves five metatarsals and several phalanges. One phalanx has a deep depression considered distinctive. Features of the coracoids and pubic bones suggest a post-juvenile or intermediate growth stage, but they do not provide a precise age for the individual.

Habitat, diet and behaviour

The fossils come from the lower part of the Cullín Grande Member of the Lohan Cura Formation in the southern Neuquén Basin. Fine sandstones and mudstones record a distal river floodplain under a semi-arid climate, with channels and low areas flooded at intervals. The landscape could support large herbivores without being a permanent swamp.

Other fossils from the regional system include freshwater invertebrates, turtles, crocodyliforms, pterosaurs, plants and dinosaurs. The assemblage describes a continental ecosystem. It does not prove that every listed animal shared the same moment or habitat patch.

Broad, worn teeth support plant cropping and swallowing with little chewing. A long neck would have expanded the animal’s feeding reach, but neither the preferred height nor the plants it ate are known. Two specimens from nearby quarries do not establish a herd: their remains could have accumulated at different times. No nest, trackway, skin impression or other direct evidence records its social life, colour, speed or care of young.

Older images and open questions

Several familiar claims need qualification. First, the 2006 label “titanosaur” is not the placement recovered by the later detailed analysis. Second, Ligabuesaurus has no preserved upper jaw or nearly complete skull; only teeth are known from the head region. Third, the high-shouldered body often shown in older art relied on a limb ratio revised after the better-preserved femur was studied.

Finally, about 23 tonnes is an equation-based estimate with a broad error range, not a precise weight. A length of 18–24 metres is likewise reconstructed from incomplete bones. Ligabuesaurus was a large sauropod, but the available material does not establish it as one of the biggest dinosaurs.

The strongest conclusion is anatomical and evolutionary: this was a large Albian sauropod with substantial limb and vertebral material, and its current placement lies among non-titanosaurian somphospondylans close to Titanosauria. Missing skull and vertebral sections, plus the uncertainty of modelled dimensions, remain part of any responsible reconstruction.