An international team of paleontologists has discovered in northern Zimbabwe the fossils of the oldest dinosaurs in Africa, including the almost complete skeleton of a new species of long-necked herbivore 1.8 meters long and between 10 and 30 kilos of weight. These animals lived at the beginning of the Triassic, in the Carnian epoch, 230 million years ago. The finding, published in ‘Nature’, suggests that the planet’s earliest dinosaurs were confined to a temperate region on the southern edge of the ancient supercontinent of Pangea.
The remains are, according to the researchers, a true fossil treasure. Recovering such ancient dinosaurs is a true rarity that, until now, had only been achieved in a few places in the world, mainly in northern Argentina, southern Brazil and India.
The fossils were found during the course of two excavations carried out in 2017 and 2019. They included a herrerasaur dinosaur, relatives of early mammals such as cynodonts, relatives of armored crocodiles such as aetosaurs, and “strange, archaic reptiles.” called Rhynchosaurus.
But the most striking specimen is a new sauropodomorph, a long-necked dinosaur, called Mbiresaurus raathi. According to the researchers, this dinosaur stood on two legs and its head was relatively small. It had small, serrated, triangle-shaped teeth, suggesting that it was a herbivore or potentially omnivore.
“We did not expect to find such a complete and well-preserved dinosaur skeleton,” admits Christopher Griffin, then at the Virginia Polytechnic Institute and State University (Virginia Tech) and now a researcher at Yale University, both in the US. “When I found the femur of mbiresaurus, I immediately recognized it as belonging to a dinosaur and knew that I had in my hands the oldest ever found in Africa. When I kept digging and found the left hip bone right next to the left thigh bone, I had to stop and catch my breath; I knew that much of the skeleton was probably there, still articulated in life position », he recounts.
The scattering by Pangea
The discovery of mbiresaurus has led researchers to propose a new theory about the migration of dinosaurs. Africa, like all continents, was once part of the supercontinent called Pangea. The climate on Pangea is thought to have been divided into strong wet and arid latitudinal belts, with more temperate belts spanning higher latitudes and intense deserts in the lower tropics. Scientists previously believed that these climatic belts influenced and restricted the distribution of animals in Pangea.
“Because dinosaurs initially dispersed under this weather pattern, early dinosaur dispersal should have been controlled by latitude,” Griffin says. “The oldest dinosaurs are known from roughly the same latitudes along the southern temperate climate belt that it was at that time, about 50 degrees south,” she says.
Griffin and his team deliberately headed north from Zimbabwe, as the country fell along this same climate belt, bridging a geographic gap between southern Brazil and India during the Late Triassic Age.
Furthermore, these early dinosaurs were restricted by climatic bands to the south of Pangea, and only later in their history did they disperse throughout the world. The breakdown of these barriers and a northward dispersal wave coincided with a worldwide wet period, or the Carnian Pluvial Event, between 237 and 227 million years ago. After this, the barriers returned, ‘holding down’ the dinosaurs in their various provinces across Pangea for the rest of the Triassic Period.
The authors suggest that climate controls influenced the early composition of terrestrial dinosaurs and other major groups such as mammals, turtles, amphibians, and reptiles, many of which persist to the present day.