Brachiosaurus, Argentinosaurus and Co: The success story of the family of the largest land animals of all time was based on rapid global warming 180 million years ago, new paleontological findings suggest. The advantage of the sauropods was that they had particularly strong teeth compared to their relatives. This made it easier for them to cope with the tough plant species that replaced the previously softer ones in the course of global warming.
A barrel-shaped body with a long tail and neck with a small head: these are the trademarks of the sauropods. They are also famous for their superlatives. The largest land animals in the history of the earth belonged to this group of dinosaurs. Some species reached body lengths of up to 40 meters and weights of 70 tons or more. As bizarre and antiquated as these giants may seem to us, they were definitely models of success for evolution: up to the great mass extinction 65.5 million years ago, the sauropods produced numerous species over millions of years that populated many parts of the world.
Why did the sauropods prevail?
However, they were not among the earliest representatives of the dinosaurs, whose era began around 230 million years ago. During the first fifty million years of their evolutionary history, the dinosaur group, to which the ancestors of the sauropods belonged, were represented by several lines of evolution. These so-called Sauropodomorpha already included some heavyweights, but many were still comparatively small and light – some were only as big as a goat. About 180 million years ago, however, all these groups disappeared relatively suddenly from the stage of evolution – with one exception: the sauropod line survived and then branched out. What caused this development in the early Jurassic period is still a mystery. But now an international team of researchers presents a plausible explanation for the unusual history of the sauropodomorpha.
Their results are based on the investigation of finds in the province of Chubut in Patagonia, Argentina. There the paleontologists discovered the skull of one of the oldest known representatives of the large sauropods. The rock strata from which the dinosaur, baptized Bagualia alba, came, could be dated to an age of 179 million years. As the researchers report, this animal already had the robust teeth typical of the sauropods. Earlier representatives of the Sauropodomorpha, however, had significantly narrower, less stable biters. This is evidence that they ate rather soft and lush vegetation.
Climate change and vegetation change
In this context, the current find provided further exciting clues: In the rocks surrounding the fossil, the researchers found remains of plants that came from the lifetime of Bagualia alba, but also from the era before. They could thus provide indications of changes in the vegetation and thus also of climatic shifts. As the researchers report, the findings indicate that
There was a rapid climate change about 180 million years ago: The mild, warm and humid conditions, in which a diverse and lush vegetation had grown, changed into a hot, dry climate in which apparently only a species-poor and more robust flora could thrive . Specifically, the paleontologists found traces of plants in the younger rock layers that were specially adapted to hot climates, such as certain conifers.
The researchers suspect that it was not just a question of a local change in the climate and flora. They assume a global greenhouse effect that changed conditions on earth around 180 million years ago. According to them, there are indications that increased volcanism during this period released large amounts of the greenhouse gases CO2 and methane into the atmosphere: There are traces of corresponding volcanic eruptions – for example in the Drakensberg in southern Africa.
The others “bit their teeth”
Against the background of the findings, an explanation for the history of the development of the sauropodomorpha and the successful career of the sauropod is emerging: With their narrow, elongated teeth, most groups of the sauropodomorpha were adapted to the rather soft vegetation that shaped the earth before the global warming event . When this flora was replaced by the much tougher, drought-adapted vegetation, these animals eventually died out. However, the sauropods were able to survive as they were the only members of their relatives who had more robust teeth. They were therefore much better adapted to the tough plant food and thus advanced to become the dominant group of herbivorous dinosaurs.
Even the literally outstanding feature of the sauropods could have been linked to this story, the researchers conclude: They suspect that the specialization in the chewy food was also one of the reasons why these animals got bigger and bigger: To cope with the chewy food gigantic bellies were likely beneficial.
Source: Bavarian State Natural Science Collections, specialist article: Proc. R. Soc. B, doi: 10.1098 / rspb.2020.2310