Description and Classification

Yamanasaurus was a type of sauropod dinosaur, a group known for their very large size, long necks and tails, four pillar-like legs, and herbivorous diet. Specifically, it belongs to the Titanosauria clade, which were the dominant large herbivores in the Southern Hemisphere during the Late Cretaceous. Within titanosaurs, Yamanasaurus is classified as a saltasaurid, and more precisely, it is often placed within the group Aeolosaurini. This group includes other relatively small and slender titanosaurs like Aeolosaurus and Gondwanatitan.

The known fossils of Yamanasaurus are quite limited, consisting of a partial sacrum (fused vertebrae from the hip region), a section of a tail vertebra, and part of a radius (a bone from the forearm). Based on these remains, scientists estimate that Yamanasaurus was a relatively small titanosaur, perhaps only about 6 meters (20 feet) long. This is significantly smaller than giants like Argentinosaurus or Patagotitan, but typical for many members of the Aeolosaurini. Its vertebrae show features common in titanosaurs, such as procoelous sacral vertebrae (concave on the front end and convex on the back).

Distinguishing Features

Yamanasaurus can be identified by a combination of features found in its bones, particularly when compared to other titanosaurs. These include:

• Its relatively small size for a titanosaur, making it one of the smaller known saltasaurids.
• The middle-to-front part of its tail vertebrae had a solid internal bone structure, rather than being extensively hollowed out with air sacs (pneumatized), which is different from some other related titanosaurs.
• The sacral vertebrae (hip bones) are procoelous, meaning they have a concave surface on the front and a convex surface on the back, helping them articulate strongly.
• The proximal end (the part closest to the elbow) of its radius bone had a somewhat rectangular shape with specific joint surfaces for the ulna and humerus.

Paleoenvironment and Diet

The fossils of Yamanasaurus were found in the Río Playas Formation in southern Ecuador. During the Late Cretaceous Maastrichtian age, this area was likely a coastal or near-coastal environment, possibly with river systems and floodplains. The climate would have been warm. As a sauropod, Yamanasaurus was a herbivore. It would have used its long neck to browse on plants, likely feeding on a variety of vegetation available in its habitat. Its small size compared to other titanosaurs might have allowed it to access different food sources or live in different types of environments than its larger relatives.

Significance and Ongoing Research

The discovery of Yamanasaurus is highly significant for several reasons. It was the first named non-avian dinosaur found in Ecuador, which fills a gap in our knowledge of dinosaur distribution in South America. It shows that titanosaurs, specifically aeolosaurins, lived much further north in western South America during the latest Cretaceous than previously confirmed. This finding helps paleontologists understand how different dinosaur groups were spread across the continent before the mass extinction event that wiped out the non-avian dinosaurs.

Ongoing research on Yamanasaurus will likely focus on finding more complete fossil remains. More bones would help scientists better understand its anatomy, its exact size, and its relationship to other titanosaurs like Saltasaurus and Neuquensaurus. Further study of the Río Playas Formation will also provide more details about the ancient environment Yamanasaurus lived in and the other animals and plants that shared its world. Understanding Yamanasaurus helps paint a clearer picture of the diversity and evolution of dinosaurs in South America just before the end of the Cretaceous period.