Currently, the oldest known dinosaur fossils date back to about 230 million years ago, and come from sites in Brazil, Argentina and Zimbabwe (today on separate continents, but at that time united in the supercontinent Gondwana). However, the characteristics of all these specimens indicate that they were not the first dinosaurs to exist, but, on the contrary, they were very well adapted creatures that had been evolving for a long time, perhaps even millions of years. That is to say, hidden somewhere, in sites yet to be discovered, there should be dinosaur fossils much older than those that have appeared so far. Somewhere, yes, but where?
Now, a team of paleontologists led by researchers at University College London believe that the remains of those first dinosaurs may be waiting deep in the Amazon rainforest and other equatorial regions of South America and Africa.
An uncertain origin
The new study, just published in ‘Current Biology’carefully analyzed the gaps in the fossil record and concluded that the first dinosaurs probably arose in a warm equatorial region of what was then the supercontinent Gondwana, which at the time encompassed present-day Congo, the Sahara Desert, and the Amazon Basin.
“Dinosaurs are well studied,” explains Joel Heath, lead author of the study, “but we still don’t really know where they came from. The fossil record has gaps so large that it cannot be taken at face value. Our model suggests that the first dinosaurs could have originated in western Gondwana, and at a low latitude. “It is a warmer and drier environment than previously thought, made up of areas similar to deserts and savannahs.”
«So far – continues the researcher -, no dinosaur fossils have appeared in the regions of Africa and South America that once formed this part of Gondwana. “However, this could be because researchers have not yet found the right rocks, due to a combination of inaccessibility and a relative lack of research efforts in these areas.”
Heath and his colleagues’ study was based on fossils and evolutionary trees of dinosaurs and their close reptilian relatives, as well as the geography of the period. And he took into account the gaps in the fossil record in areas of the world where no remains have been found and for which we do not even have complete information.
The first dinosaurs
What we do know is that, when they emerged, the first dinosaurs were vastly outnumbered by their ‘cousins’, the reptiles, including the ancestors of crocodiles, the pseudosuchians (an abundant group that includes enormous species up to 10 meters long). long) and the pterosaurs, the first animals to develop ‘powered flight’, as they flew by flapping their wings instead of gliding, and which grew to the size of fighter planes.
Quite the contrary, the first dinosaurs were much smaller than their descendants: more the size of a chicken or a dog than a Diplodocus. They were also bipedal, since they walked on their two lower limbs, and it is believed that they were mostly omnivores. Dinosaurs were only able to begin to dominate the world much later, when, about 200 million years ago, volcanic eruptions wiped out a good part of their reptilian relatives.
The most likely region
According to the new study, then, dinosaurs, as well as some reptiles, arose in the low latitudes of ancient Gondwana, from where they later spread to the south of the continent and to Laurasia, the adjacent supercontinent in the north, which later divided into Europe. , Asia and North America.
According to researchers, this region is the most likely for the origin of dinosaurs because it is an intermediate point between the place where the first fossils were found, in southern Gondwana, and the area where the fossils of many of their dinosaurs were discovered. close relatives, to the north in Laurasia.
Since it is not known exactly how the oldest dinosaurs were related to each other, Heath and his team decided to test their model on three different evolutionary trees. And the one that agreed best was the one that proposed the Gondwanan origin in the tree that considered the silesaurids (traditionally considered ‘cousins’ of dinosaurs, but not dinosaurs themselves) as direct ancestors of the ornithischian dinosaurs.
Ornithischians, one of the three major groups of dinosaurs that later included the herbivorous Stegosaurus and Triceratops, are mysteriously absent from the fossil record from this early era of the dinosaurs. But if silesaurids turned out to be the ancestors of ornithischians, that gap in the evolutionary tree would suddenly be filled.
Philip Manion, lead author of the study, explains that “our results suggest that the first dinosaurs may have been well adapted to hot, arid environments. Of the three main groups of dinosaurs, one group, the sauropods, which includes brontosaurus and Diplodocus, appeared to retain its preference for a warm climate, remaining in the lowest latitudes of the Earth. And evidence suggests that the other two groups, theropods and ornithischians, may have developed the ability to generate their own body heat a few million years later, in the Jurassic period, allowing them to thrive in colder regions, including the poles. . In total, the dinosaurs’ long reign on Earth lasted more than 135 million years. And it took a great catastrophe on a planetary scale to make them disappear.
Report a bug
#step #closer #mysterious #origin #dinosaurs