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How long-necked dinosaurs rose to rule the Jurassic herbivores

A new study suggests that long-necked sauropods, the largest animals to walk on Earth, may have dominated during the Jurassic period thanks to a large explosion of volcanic activity that began about 184 million years ago. The resulting environmental crisis may cause a change in plant life that has given hard-toothed and large-gutted herbivores a powerful advantage over other herbivores.

The finding comes from the discovery of a new fossil of one of the first "true" sauropods in Argentine Patagonia. The sediments bearing the recently described dinosaur, nicknamed Bagualia alba, date precisely to 179 million years ago, paleontologist Diego Pol of the Egidio Feruglio Paleontological Museum in Trelew, Argentina and colleagues report on November 18 in Proceedings of the Royal Society B.

B. alba, the researchers discovered, had the revealing features of true sauropods: large legs, like columns; huge size; long necks relative to body; wide, strong jaws; and large spoon-shaped teeth with thick enamel. Also known as eusauropods, this lineage dominated the Middle and Late Jurassic approximately 174 to 145 million years ago (SN: 10/10/07), giving rise to impressive giants such as Argentinosaurus and Dreadnoughtus schrani (SN: 6/9/15). ).

During the early Jurassic, about 201 to 174 million years ago, Pol says, plant-eating sauropods competed with many other herbivores, including sauropodomorphs, distant relatives such as Mussaurus patagonicus with less powerful jaws and shorter necks (SN: 5). / 20/19). It has not been clear what gave the eusauropod giants in their herbivorous competition, in part because there are relatively few fossils dating back to the transition between the early and middle Jurassic.

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One possible culprit was an environmental crisis that occurred in the late Early Jurassic, an episode of global warming and ocean acidification that led to a number of species extinctions, particularly in the oceans but also on land. Scientists have previously suggested that this episode was related to large volcanic eruptions in the southern hemisphere.

That pulse of volcanism may also have led to a major change in plant life in the region. The early Jurassic was dominated by seed ferns, cycads, and gingkoes, but by the Middle Jurassic, conifers began to bloom in the drier, warmer climate. This, in turn, may have made life difficult for many sauropodomorphs, which disappear from the fossil record after the Early Jurassic.

But B. alba, the study shows, was alive and well 179 million years ago, well after the volcanic aftermath. Pol and his colleagues suggest that B. alba and other eusauropods may have been better placed to sting the very hard leaves of conifers. Pol and his colleagues said his extra powerful jaws and teeth could chew those leaves, and his oversized guts were well-adapted to digest hard plant matter, allowing him to sit and ferment for many days.

Careful dating of the new fossil is a crucial piece of the puzzle, says Pol, because "it provides the first accurate evidence (that) large sauropods became the dominant herbivores in terrestrial ecosystems just after the massive volcanic event."

a hand holding a fossil toothThe tooth of Bagualia alba, discovered in Argentine Patagonia, has the typical thick enamel and spoon shape of sauropods. These characteristics helped the creatures to bite the hard leaves of the conifers, which bloomed after about 180 million years ago. New research suggests that this ability may have allowed sauropods to become dominant in the Jurassic period.Santiago Reuil

The new fossil "is an important complement to our frustrating and incomplete picture of the evolution of the first sauropods," says Paul Barrett, a paleontologist at the Natural History Museum in London. And the coincidence between the fossil age and a significant pulse of volcanic activity in the region is intriguing, he adds.

But, he says, “I’d like to see a little more evidence before extending this to a global event” that has led to changes in the evolution of both plants and dinosaurs. Although this is the first true sauropod fossil found, the lineage of sauropods is thought to date back another 40 million years, to the late Triassic, based on analyzes of the animal's family tree. And scientists know very little about how those earlier sauropods fed, not even where they lived in the world. For example, it is possible that the first true sauropods lived in places where such climatic and floral changes did not occur.

For now, though, “the authors offer a new and interesting idea that we can test with new discoveries in the future,” Barrett says. "If they are right, this would give a good insight into understanding the links between the evolution of the planet, the climate, flora and fauna."

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