The ancestors of large herbivorous dinosaurs lived in large colonies in which pups were raised together
Some dinosaurs, at some point in evolution, became social animals. This is well known, and it appears to underlie the evolutionary success of some dinosaur species, including large herbivores.
It was believed that such behavior began in the late Jurassic period, but paleontologists’ hypothesis has so far lacked scientific evidence. A brand new study, published in the scientific journal Scientific Reports, reveals that such behavior can be dated as much as 40 million years earlier than previously believed. E non solo: la vita in branco dei dinosauri era molto più simile a quella che ci si aspetterebbe dai grandi mammiferi di oggi.
Il progenitore del brontosauro
Lo studio, che porta la firma del professor Jahandar Ramezani del MIT, ha analizzato i resti rinvenuti in un sito in Patagonia, databili intorno a 200 milioni di anni fa, appena all’inizio del periodo Giurassico.
Il sito su cui si sono concentrate le ricerche risale nello specifico a 193 milioni di anni fa, e rappresenta la più antica evidenza della vita sociale dei dinosauri: come spiega il dottor Ramezani “sappiamo da tempo che i dinosauri più avanzati, specie i grandi sauropodi, vivessero in branco; la domanda è sempre stata: quando è iniziato questo comportamento?”.
Back then, the brachiosaurus and brontosaurus had not made their appearance on Earth – it would still take 50 million years – and the large herbivores that populated vast areas of the planet were the sauropodomorphs, the group of huge, long-necked dinosaurs to which the largest land animals that ever existed also belong.
The research focused specifically on Mussaurus, a giant sauropod that inhabited areas of South America about 200 million years ago.
The new findings show that not only the sauropodomorphs had already learned to live “in society”, but that they raised their pups by age and in a manner similar to what happens in the communities of mammals.
The social life of sauropods
The study examined more than 100 eggs and 80 skeletons of Mussaurus, from new excavations but also from acquisitions that date back to the seventies.
The findings of Ramezani’s team are exceptional: the largest of the adult specimens found in Patagonia could reach a weight of more than 1.5 tons, and it appears that the youngest specimens walked on four legs.
The fossils were found fairly close together, Ramezani explains, and many of the fossils were grouped by age class, including some nests in which up to 30 eggs were found all together.
Among the most important of the discoveries presented in the new study is a grouping of 11 juvenile specimens, the same size, that appear to have died together and buried together. The burials of the adult specimens, on the other hand, appear to be for singles or at most pairs.
“The division by age is the key to everything,” says Ramezani, “it shows us that we are not talking about a simple family structure, where young and old are together.” He continues, “we’re talking about colonies of many dinosaurs that were in charge of caring for their young and eggs together.”
It’s likely that dinosaurs had begun living in groups even before the appearance of Mussaurus: this, Ramezani says, could be the very reason these and other dinosaurs were able to dominate Earth’s ancient ecosystems.
To complete the picture of early dinosaur social behavior, Ramezani concludes, we await the publications of other studies, especially from the remains of sauropodomorph colonies in China and South Africa.