Global warming has triggered the evolution of giant dinosaurs

The word “dinosaur” tends to evoke giant animals with massive bodies, long necks and tails, and small heads. These “dinosaurs par excellence” actually represent an important subgroup of Dinosauria, the so-called Sauropoda (“long-necked dinosaurs” in popular culture). Sauropods were truly amazing animals and included the largest known land animals, with a body length of up to 40 meters and a weight of 70 tons or more.

However, these giant animals did not appear directly at the beginning of the dinosaur era. For the first 50 million years of their evolutionary history, Sauropodomorpha – the lineage to which sauropods belong – were represented by different groups of animals from bipedal to quadrupedal. Although some of them reached large body sizes of around 10 meters in length and a few tons in weight, these groups also included smaller and lighter-bodied animals, some of which were no larger than a goat. In addition, all of these animals had thin teeth, indicating that these animals ate plants and fed on soft, lush vegetation. However, towards the end of the early Jurassic period, around 180 million years ago, all of these groups suddenly disappeared and only one lineage survived and thrived: the sauropods. What caused this fauna change during the early Jurassic has remained enigmatic so far.

In Proceedings of the Royal Society B, an international team of researchers led by Argentine paleontologist Diego Pol and including Munich researcher Oliver Rauhut from Bayerische Staatssammlung für Paläontologie und Geologie and Ludwig-Maximilians-University now report new evidence on the possible cause of these changes. In the province of Chubut, Argentine Patagonia, the fossil remains of one of the oldest known large sauropods have been discovered, which the team named Bagualia alba, and placed it right in its temporal and ecological context. Therefore, the strata from which the new sauropod comes could be dated to 179 million years ago, just after the mysterious disappearance of the other sauropodomorphic groups. Plant fossils in the rock strata just before that time and at the time Bagualia lived provide evidence of the climate and ecology in which these animals lived.

Therefore, the data indicate that about 180 million years ago there was relatively rapid climate change, from a warm and humid temperate climate, in which lush and diverse vegetation flourished, to a strongly seasonal, very hot and dry climate, characterized from a less diversified flora and dominated by forms that show adaptations for warm climates such as some conifers. These environmental changes have apparently been driven by a greenhouse effect due to climate gases such as CO₂ and methane caused by the increase in volcanism at that time; evidence of these volcanic eruptions has been found on many southern continents, such as the Drakensberge in southern Africa, for example.

With their thin teeth, non-sauropodan sauropodomorphs adapted to the soft vegetation that flourished before this global warming event, but when this flora was replaced by much harsher greenhouse vegetation, these animals became extinct. Sauropods represented the only group of sauropodomorphs with much stouter teeth, well adapted for such tough vegetation, and so they flourished and became the dominant group of herbivorous dinosaurs at that time. Indeed, the specialization for this type of vegetation was probably one of the reasons why these animals reached their gigantic size: since large digestion chambers are needed to cope with such food, there was a general trend for these animals. to get bigger and bigger.

Supplied by the Bavarian state collections of natural sciences