Mesetasaurus

Lore & Background

The holotype material of Mesetasaurus consists of two caudal vertebrae, probably corresponding to the third and sixth positions, discovered in the 1980s. They are permanently housed in the Vertebrate Fossil Collection of the Universidad de la República in Montevideo under the code FC-DPV 3740. In a study published in 2025, Soto Núñez et al. distinguished the more anterior vertebra as 3740A and the more posterior as 3740B, and described them as a new genus and species.

The generic name Mesetasaurus refers to the fossil locality, Meseta de Artigas. The specific name protector honors Uruguayan hero José Gervasio Artigas, also known as 'Protector de los Pueblos Libres'; a bust of him is located near the fossil site.

Phylogenetic analysis by Soto Núñez et al. (2025), using the framework of Pérez Moreno et al. (2025), placed Mesetasaurus within the clade Aeolosaurini, which is divided into two smaller clades (Clade A and Clade B).

Reader's Guide

Mesetasaurus is significant as the second titanosaurian taxon known from the Guichón Formation and the second non-avian dinosaur described from Uruguay, following Udelartitan. Its discovery adds to the sparse record of South American sauropods from the Late Cretaceous of Uruguay. The exact age of the Guichón Formation remains uncertain, with historical suggestions of a Lower Cretaceous age, but the discovery of dinosaur eggshells similar to Sphaerovum and the presence of aeolosaurins (which lived from the Coniacian to Maastrichtian) support a Late Cretaceous age. Mesetasaurus helps clarify the diversity and distribution of aeolosaurin titanosaurs in southern South America. Its classification within Aeolosaurini, a clade split into two subgroups, provides data for future phylogenetic studies. The fossils also contribute to understanding the paleoenvironment of the Guichón Formation, which has yielded remains of Uruguaysuchus, indeterminate iguanodontians, and theropods.

Did You Know?

• The holotype consists of two caudal vertebrae, probably the third and sixth in the tail.
• The specific name 'protector' refers to Uruguayan hero José Gervasio Artigas, known as 'Protector de los Pueblos Libres'.
• The Guichón Formation's age is debated, but Mesetasaurus's describers suggested a Coniacian to Maastrichtian range.