The family album of the oldest dinosaurs in the world, in which, until today, species from Brazil and Argentina predominate, has just gained new members: African first cousins.
At 230 million years old, the same age as their South American relatives, the fossils from Zimbabwe are an important piece to understand how dinos began their evolutionary journey.
According to the new study on the topic, which appears in this week’s edition of the scientific journal Nature, the genesis of the dinos was marked by the very different layout of the continents at that time.
Incidentally, it is more appropriate to use the singular: there was then only a single supercontinent, known as Pangea, which means that Africa and South America formed a continuous landmass from west to east, without the Atlantic Ocean in between.
In addition, and more importantly, the areas inhabited by the first dinosaurs were not tropical and subtropical, as in today’s Zimbabwe and Rio Grande do Sul, where their fossils were found.
The arrangement of the supercontinent meant that, at that time, these regions were at a latitude of about 50 degrees in the southern hemisphere—that is, in a temperate zone, equivalent to the position of London or Paris in the northern hemisphere of the modern world.
In practice, it appears that the oldest dinosaurs spent several million years confined to this temperate band of Pangea, which also extended eastward as far as India.
And this for a good reason: the climate of the Triassic period, when the group emerged, had transformed the tropical regions, closer to the Equator, into immense deserts. Therefore, the dinos would have been restricted to their temperate cradle in the southern hemisphere, much more humid and pleasant.
The work that is coming out in Nature is signed by an international team that includes Christopher Griffin, from Virginia Tech University (USA), Darlington Munyikwa, from the Zimbabwe Natural History Museum, and the Brazilian Max Cardoso Langer, from USP in Ribeirão Preto, among other researchers.
The team described the oldest of the African dinosaurs, which was given the scientific name Mbiresaurus raathi. The animal is a primitive member of the group of sauropodomorphs – the same that would end up harboring, tens of millions of years later, the largest land animals of all time, such as the famous brontosaurus.
O M. Raathi, however, it measured only two meters in length, weighing a maximum of 30 kg. With about 90% of its skeleton preserved, the animal was bipedal and had small, serrated, triangular-shaped teeth, probably suitable for a herbivorous diet.
In fact, all these characteristics are very reminiscent of the sauropodomorphs of the old guard that roamed what would one day be the interior of Rio Grande do Sul at the same time, such as the Saturnalia it’s the pampadromaeusboth described by Langer and positioned close to the new African species in the dinosaur family tree.
The team also identified fragmentary fossils of a much larger carnivorous dinosaur from the herrerasaurid group, which could reach six meters in length.
“It’s another sign that it’s a dinosaur fauna very similar to that of South America at the same time, with a herbivore between small and medium in size and a large carnivore. It’s something interesting to see from an ecological point of view” , said Langer to Sheet.
According to him, it is not clear whether the initial diversification of dinosaurs in the temperate and humid regions of the southern hemisphere was directly triggered by these climatic conditions or if, at first, it was just a historical accident of the group’s evolution.
In any case, everything indicates that the animals were only able to cross the tropics and reach the Northern Hemisphere millions of years later, thanks to the so-called “Carnian Pluvial Event”, when the humidity increased globally (the Carnian is the period in which the group appears and diversifies, between 237 million years and 227 million years ago).
“After this event ceases, a separation takes place. [entre as linhagens do hemisfério Norte e do hemisfério Sul]but then the animals were already there”, concludes the Brazilian paleontologist.
From there, the reign of the dinosaurs becomes increasingly globalized.
