Uruguayan paleontologists have identified a remarkable new species of eorosaur, a titanosaur, based on a pair of well-preserved coccyx bones discovered near the Uruguay River in the 1980s.
Mesetasaurus protector roamed the Earth in what is now Uruguay from 86 million to 72 million years ago during the late Cretaceous period.
This newly discovered species belongs to a group of sauropod dinosaurs known as titanosaurs. The Aeolosaurini lineage thrived across South America during the closing stages of the Cretaceous period.
“Titanosaurs represented the most abundant and diverse sauropod clade of the Late Cretaceous, with numerous genera identified, particularly in South America,” stated Dr. Matias Soto Nuñez from the University of Lepsidade de la Repubblica and his colleagues.
“They had been present since the Valanginian (approximately 137 to 132 million years ago), achieved massive body sizes during the Albian-Cenomanian (113 to 94 million years ago), and were the only sauropods to survive the Cretaceous extinction event (67 million years ago).”
Numerous lineages, including the Aeolosaurini family, thrived in South America, such as Andesauridae, Diamantinasauridae, Saltasauridae, Rogoncosauridae, and Rhynchosauridae.
“This unique clade is an essential component of the South American late Cretaceous fauna,” the researchers added.
“The unique morphology of the caudal vertebrae allows for easy identification, making them valuable for biostratigraphy.”
The two caudal vertebrae attributed to Mesetasaurus protector were collected from the Meseta de Artigas site in the Guichon Formation, Paysandu Department, northern Uruguay.
The specimen was discovered on a slight outcrop of reddish sandstone, suggesting it belonged to a single individual.
“Cataloged as FC-DPV 3740A and FC-DPV 3740B, this specimen is among the best-preserved sauropod vertebrae ever found in Uruguay,” the paleontologists noted.
To determine the phylogenetic placement of Mesetasaurus protector, researchers utilized a comprehensive dataset and compared it with numerous other titanosaurs to construct the dinosaur family tree.
Findings indicate that this dinosaur is deeply embedded within the Aeolosaurini family, in close relation to Aeolosaurus lionegrinus and Ardatitan Maximus from Argentina and Brazil.
This discovery points to the existence of multiple lineages of giant herbivorous dinosaurs in present-day Uruguay during the Late Cretaceous, rather than a solitary population.
“Mesetasaurus protector is the second sauropod found in Uruguay, distinct from the lineages of titanosaurs previously discovered, such as Uderartitan Celeste,” the researchers explained.
“Notably, this is the second confirmed record of an aeolosaurid in Uruguay, adding to the caudal vertebrae found in the late Cretaceous Asensio Formation related to Aeolosaurus.”
A paper detailing the discovery of Mesetasaurus protector was published online on July 8, 2026, in the journal Ameginiana.
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Matias Soto Nuñez et al.. A new aeolosaurid (sauropod, titanosaur) from the Late Cretaceous of Uruguay. Ameginiana published online on July 8, 2026. doi: 10.5710/amgh.19.06.2026.3689
Source: www.sci.news