Inawentu

MEANING: Imitator

PERIOD: Late Cretaceous

CONTINENT: South America

Inawentu is a titanosaur known from a partial skeleton, including a complete neck with twelve vertebrae. This is the fewest neck vertebrae of any known titanosaur, resulting in a proportionately shorter neck than most titanosaurs. The skull features a wide, squared-off snout that deflects downward, a convergent similarity to the distantly related rebbachisaurids.

Abstract from paper: The evolution of ecosystems during the late Mesozoic on the southern landmasses is complex and still poorly known. Starting from a single vicariant Laurasian–Gondwanan scenario, the paleobiogeographic and biostratigraphic models have become more complex, including vicariant, dispersal, and local extinctions as major drivers of changes in the Cretaceous ecosystems during the isolation and posterior fragmentation of Gondwana. However, the direct effects of replacement and the adaptive evolution of terrestrial vertebrates to fill vacant ecological niches after disruptive ecological events have been poorly discussed. Here, we provide a preliminary description of a nearly complete new titanosaurian sauropod from the Upper Cretaceous of Patagonia, Inawentu oslatus gen. et. sp. nov., that shows remarkable convergent anatomical traits with rebbachisaurid sauropods. A phylogenetic analysis recovers it within a not previously recovered titanosaurian subclade, named Clade A, which would be endemic to the Upper Cretaceous of South America. The convergent evolution between rebbachisaurids and Clade A members is interpreted as the result of the same ecological niche exploitation. The biostratigraphic scenario during the Late Cretaceous of South America leads to interpret rapid speciation of the titanosaurs because of filling the empty ecological niche left by the extinction of the rebbachisaurids, an idea concordant with a regional disturbance event of the ecosystems in this continent between 90 and 85 Ma.

Inawentu 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.

Inawentu is a rinconsaurian titanosaur. Rinconsaurians are a group of derived titanosaurs that lived during the Late Cretaceous, primarily in South America. These dinosaurs were part of the later radiation of titanosaurs that flourished after the decline of other sauropod lineages, showcasing a wide range of body sizes and adaptations suited to the changing ecosystems of the Late Cretaceous.

Rinconsaurian titanosaurs are characterized by elongated neck vertebrae, slender limb bones, and distinctive tail structures, often with strongly curved anterior caudal vertebrae. These features may have contributed to a more flexible neck and tail, perhaps linked to specialized feeding or display behaviors. Compared to their massive lognkosaurian relatives, rinconsaurians were typically more lightly built, though still large by general dinosaur standards. Their fossils, found mainly in Argentina, help illustrate the evolutionary diversity within Titanosauria during its final chapters before the end-Cretaceous extinction.