Paleontologists in Argentina have identified a new species of eusauropod (true sauropod) dinosaur that lived 179 million years ago, just after the mysterious disappearance of non-eusauropod sauropodomorphs.

Life reconstruction of Bagualia alba. Image credit: Jorge González.

Life reconstruction of Bagualia alba. Image credit: Jorge González.

The newly-identified dinosaur lived in what is now Patagonia, Argentina during the Early Jurassic epoch.

The ancient creature was a type of eusauropod, a group of long-necked, strictly herbivorous, quadrupedal dinosaurs that thrived from the Early Jurassic through the Late Cretaceous.

Named Bagualia alba, the animal is in fact the oldest eusauropod dinosaur known to date.

Sauropodomorpha is the first major dinosaurian group that diversified into multiple herbivorous lineages recorded throughout the world,” said Dr. Diego Pol from the Museo Paleontológico Egidio Feruglio and CONICET and his colleagues from Argentina, the United States and Germany.

“The first 40 million years of sauropodomorph evolution are characterized by the coexistence of diverse lineages with great disparity in body size, feeding biomechanics and locomotion types, ranging from small (less than 10 kg) bipedal species to the large (greater than 5 tons) quadrupedal early sauropods.”

“By the Middle Jurassic, eusauropod dinosaurs were the only surviving sauropodomorph lineage.”

The remains of at least three individuals of Bagualia alba — including a partial skull and cervical vertebrae — were found at the same site in Bagual Canyon in the Cañadón Asfalto Basin, central Patagonia.

“Sauropods became the dominant group of large herbivores in terrestrial ecosystems after multiple related lineages became extinct towards the end of the Early Jurassic,” the paleontologists explained.

“The causes and precise timing of this key faunal change, as well as the origin of eusauropods, have remained ambiguous mainly due to the scarce dinosaurian fossil record of this time.”

“The terrestrial sedimentary successions of the Cañadón Asfalto Basin document this critical interval of dinosaur evolution.”

To shed light on the extinction of sauropodomorphs, Dr. Pol and co-authors examined fossil flora and fauna of the Cañadón Asfalto Basin.

They found evidence for severe perturbations to the ancient climate and a drastic decrease in the floral diversity, characterized by the rise of conifers with small scaly leaves, after a massive magmatic event that impacted southern Gondwana between 180 and 184 million years ago.

They believe that the non-eusauropod sauropodomorphs went extinct after soft vegetation was replaced by much tougher greenhouse vegetation.

Bagualia alba and other eusauropods recorded after the event invariably display characters that may have been critical for their success after this environmental change,” the researchers said.

“Their elongated neck provided maximal feeding envelopes and browsing heights and their large body size has been related to an expansion of gut capacity and fiber digestibility.”

“Their deep and robust skulls and mandibles indicate high bite force and their long jaw gape and large and broad teeth with thick enamel (greater than 700 µm) and extensive shearing wear facets have been interpreted as adaptations to obligate high-fiber herbivory and bulk feeding on tough, fibrous plant material.”

The team’s paper was published in the Proceedings of the Royal Society B: Biological Sciences.

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D. Pol et al. 2020. Extinction of herbivorous dinosaurs linked to Early Jurassic global warming event. Proc. R. Soc. B 287 (1939): 20202310; doi: 10.1098/rspb.2020.2310