Vitosaura

MEANING: Victoria's lizard

PERIOD: Late Cretaceous

CONTINENT: South America

Vitosaura is an abelisaurid theropod dinosaur that lived during the Late Cretaceous period in what is now Argentina.

Abstract from paper: Abelisauridae is a group of ceratosaurian theropods that thrived mainly in Gondwana during the Cretaceous. Their fossil record is currently represented by more than 25 species, and their most complete and abundant records are from the Argentinean Patagonia. Outside Patagonia, the record of named Argentinean ceratosaurians has been limited to the Cretaceous of the Salta Province, with the noasaurid Noasaurus–represented by a fragmentary skeleton–and the brachyrostran abelisaurid Guemesia–represented by a nearly complete braincase and partial skull roof–. Here, we report a new abelisaurid theropod specimen (CRILAR-Pv 506) from the Late Cretaceous of La Rioja Province, northwestern Argentina. It was found at the Tama locality, in outcrops of the Campanian Los Llanos Formation, and associated with titanosaurian sauropod remains. The new abelisaurid specimen is represented by a first dorsal centrum, a second dorsal vertebra, a partial sacrum, left ilium, pubis and ischium, and other indeterminate elements. A unique combination of character states led us to propose the new genus and species Vitosaura colozacani. Phylogenetic analyses found Vitosaura either as a non-brachyrostran abelisaurid, closely related to Indo-Malagasy species in some trees, or a non-carnotaurinin furileusaurian. However, the interrelationships among abelisaurids are poorly supported. Our comparisons confirm the presence of abelisaurids in the Los Llanos Formation and this is the first named theropod taxon in the Cretaceous of La Rioja Province.

Vitosaura is from the Late Cretaceous. The Cretaceous is the third and final geological period of the Mesozoic Era, with the Late Cretaceous making up roughly the second half of it, lasting from about 100 to 66 million years ago. It was a time of significant evolutionary change, with dinosaurs reaching their greatest diversity before the mass extinction at the end of the Cretaceous.

The Cretaceous was a period with a relatively warm climate, though the Late Cretaceous experienced a global cooling trend, caused by falling levels of carbon dioxide in the atmosphere. The continents were nearing their present positions, but high sea levels flooded low-lying regions, turning Europe into an archipelago, and forming the Western Interior Seaway in North America. These seas were home to a variety of marine reptiles, including mosasaurs and plesiosaurs, while pterosaurs and birds shared the skies.

On land, dinosaurs continued to thrive and diversify during the Late Cretaceous, producing many of the most well-known goups, including tyrannosaurs, hadrosaurs, and pachycephalosaurs. Established Cretaceous dinosaur clades like the ceratopsians, ankylosaurs, and dromaeosaurs continued to flourish. Sauropod species consisted almost exclusively of titanosaurs, which seemed to be confined to the Southern Hemisphere for much of the Late Cretaceous. Flowering plants and grasses diversified and spread, becoming the dominant flora similar to what we see today.

The Cretaceous (along with the Mesozoic) ended with the Cretaceous-Paleogene (K-Pg) extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs, and large marine reptiles, died out. This event, likely triggered by an asteroid impact, is marked by the abrupt K-Pg boundary, a distinct geologic layer separating the Mesozoic and Cenozoic Eras. In its aftermath, mammals and avian dinosaurs rapidly diversified, becoming the dominant land animals of the Cenozoic Era.

Vitosaura is an abelisaur. Abelisauria was a distinctive group of theropod dinosaurs that flourished mainly in the southern continents during the Cretaceous Period. They are part of the larger clade Ceratosauria, which split from other theropods early in dinosaur evolution. Abelisaurs are best known for their unusual body proportions, including deep short skulls often ornamented with ridges, horns, or rough-textured bone, and their extremely small vestigial forearms. Their legs, however, were strong and built for active movement, suggesting they were effective predators.

Fossil evidence of abelisaurs has been found across South America, Africa, Madagascar, India, and parts of Europe, reflecting their dominance in Gondwana during the Late Cretaceous. As ecosystems in the Southern Hemisphere evolved separately from those in the north, abelisaurs took on the top predator roles that tyrannosaurs filled in North America and Asia. Their prevalence in isolated landmasses hints at how regional evolution shaped dinosaur diversity differently across the globe. Despite their strange appearance, abelisaurs were well-adapted hunters, and they remained successful up until the Cretaceous-Paleogene extinction event.