The largest predatory dinosaur of all time, the spinosaurus, swam in the Cretaceous rivers thanks to a long, high and flat tail, never seen before in any other dinosaur: resurfaced from the Moroccan Sahara desert, it was equipped with powerful flexible muscles and joints and moved sideways with an undulating motion like the tail of crocodiles. The discovery is published in Nature by an international group of paleontologists (led by Nizar Ibrahim of the National Geographic Explorer and the University of Detroit Mercy) in which seven Italian researchers participate.
"Now all the books on dinosaurs will have to be rewritten," explains Cristiano Dal Sasso, paleontologist at the Natural History Museum in Milan who took part in the excavations supported by National Geographic. "This tail represents the first unmistakable proof that dinosaurs also invaded aquatic habitats with a completely new and original anatomical model, which erases the false belief that all featherless dinosaurs were forced to inhabit only mainland ecosystems."
Thanks to the excavations conducted between 2015 and 2019 in the Kem Kem desert, paleontologists extracted from a rocky slope almost 40 vertebrae and other bones of the tail of a large dinosaur: "under the scorching sun of the Sahara and almost 50 degrees of temperature , it was a challenge to the limit of the impossible ", recalls Gabriele Bindellini, PhD student of the University of Milan. The bones were enclosed in the same layer from which, a few meters away, the incomplete spinosaurus skeleton published in Science in 2014 as the first semi-aquatic dinosaur had already come to light.
Reconstruction of the appearance of the spinosaurus (source: illustration by Davide Bonadonna)
Paleo-histological analysis confirmed that the bones all belonged to the same young specimen of spinosaurus, more than 10 meters long and weighing more than 3.5 tons. The tail, 5 meters long, had large muscle bundles at the base, while long spines (both above and below the vertebrae) made it high and flat like a long ribbon.
To understand how it works, Harvard biomechanics experts have created a model moved by a robotic arm inside the water tunnel. The results of the tests "show that in the water the tail of the spinosaurus had a propulsion efficiency much higher than the long and thin tails of typically terrestrial carnivorous dinosaurs - explains Dal Sasso - much more similar to that of the tails of living aquatic vertebrates, which swim also good against the current. "" The ribbon-like tail - adds co-author Simone Maganuco - also gave greater stability by reducing the tendency to roll. The large back sail, which perhaps functioned as a reverse keel, could also contribute to this. "
