Paleontologists in Argentina’s Patagonia have recently discovered the back half of a new rebbachisaurid sauropod, now named Astigmasaura genuflexa. This enormous plant-eater roamed Earth roughly 95 million years ago, during the Late Cretaceous. It measured around 18 meters (59 feet) long and weighed over 10 tons.
Scientists found this specimen found in 2017 and published a preliminary description of it in 2024. Now, the authors have formally named the unique genus and species, and provided a comprehensive description. New laboratory work on the specimen by the researchers has provided new bone elements and improved the previous morphological description.
Rebbachisauridae were medium-to-large sauropods that grazed close to the ground using highly specialized skulls, lightweight skull-support structures, and slender limbs. They flourished mainly on the ancient supercontinent Gondwana, especially in South America and North Africa. In fact, Patagonia has given us more than half of all known Rebbachisauridae dinosaur discoveries.
From Patagonia to the World
The fossil comes from the El Orejano locality of the Huincul Formation in Patagonia’s Neuquén Basin. The Huincul Formation is already known for remarkable dinosaur diversity, including other rebbachisaurids (like Cathartesaura and Sidersaura), giant titanosaurs (like Argentinosaurus), and various theropods and ornithischians. It may have been a bustling dinosaur metropolis!
Remarkably, this particular specimen is only the second known rebbachisaurid found with its hindlimbs, hip, and front tail preserved. This is a significant find for unraveling rebbachisaurid anatomy. It shows more anatomical diversification in the family than we were aware of until now.
The discovery of Astigmasaura improves our knowledge of dinosaurs
According to lead author Flavio Bellardini, Astigmasaura genuflexa shares typical rebbachisaurid traits. We can see tall neural spines on anterior tail vertebrae, four-rayed neural laminae, unequal hemal arches, flattened upper tibias, and thigh bones with inward-leaning lower ends.
It also combines distinctive anatomical features unseen in any other sauropod, setting it apart as a unique species. The new fossil provides new information about the caudal (tail) and pelvic girdle morphology of rebbachisaurids. This was poorly known until now.
“This new record”, Bellardini said “not only provides new morphological information about the caudal and pelvic girdle anatomy of Rebbachisauridae, which is poorly known to date, and suggests a greater taxonomic diversification within the family during the last stages of its evolutionary history than known before.”