The remains of the first dinosaurs could be undiscovered in the Amazon and other equatorial regions of South America and Africa, according to researchers at University College London (UCL).
Today, the oldest known dinosaur fossils date back to about 230 million years ago and were unearthed further south, in places such as Brazil, Argentina and Zimbabwe. But the differences between these fossils suggest that dinosaurs had already been evolving for some time, pointing to an origin millions of years earlier.
The new study, published in the journal Current Biology, took into account gaps in the fossil record and concluded that the first dinosaurs probably arose in a warm equatorial region on what was then the supercontinent Gondwana, an area of land that today It covers the Amazon, the Congo Basin and the Sahara Desert.
Lead author and PhD student Joel Heath (UCL Earth Sciences and the Natural History Museum, London) comments: “Dinosaurs are well studied, but we still don’t really know where they came from. The fossil record has such big gaps that we can’t tell. can take at face value.
“Our models suggest that the first dinosaurs could have originated in western Gondwana, at low latitudes. It is a warmer and drier environment than previously believed, made up of desert and savanna areas. So far, no dinosaurs have been found. dinosaur fossils 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,” the researchers say in a statement.
The modeling study was based on fossils and evolutionary trees of dinosaurs and their close reptile relatives, as well as the geography of the period. He took into account gaps in the fossil record by treating areas of the globe where no fossils had been found as missing information, rather than areas where no fossils exist.
Initially, the first dinosaurs were vastly outnumbered by their reptilian cousins. Among them were the ancestors of crocodiles, pseudosuchians (an abundant group that includes enormous species up to 10 meters long), and pterosaurs, the first animals to develop powered flight (flying by flapping wings instead of gliding), They grew to the size of fighter planes. Instead, the first dinosaurs were much smaller than their descendants: more the size of a chicken or a dog than a diplodocus. They walked on two legs (they were bipeds) and it is believed that most were omnivores. Dinosaurs became dominant after volcanic eruptions exterminated many of their reptilian relatives 201 million years ago.
The new model results suggest that dinosaurs, as well as other reptiles, may have originated in low-latitude Gondwana before radiating outward, spreading to southern Gondwana and to Laurasia, the adjacent northern supercontinent that later broke up into Europe. , Asia and North America.
Support for this origin comes from the fact that it is an intermediate point between the place where the first dinosaurs were found in southern Gondwana and the place where fossils of many of their close relatives were discovered to the north in Laurasia. Because there is uncertainty about how the oldest dinosaurs were related to each other and their close relatives, the researchers ran their model on three proposed evolutionary trees.
They found the strongest support for a low-latitude Gondwanan origin of dinosaurs in the model that counted silesaurids, traditionally considered cousins of dinosaurs but not dinosaurs themselves, as ancestors of ornithischian dinosaurs. Ornithischians, one of three major groups of dinosaurs that later included the herbivorous Stegosaurus and Triceratops, are mysteriously absent from the fossil record of these early years of the age of dinosaurs. If silesaurids are the ancestors of ornithischians, this helps fill this gap in the evolutionary tree.
Lead author Professor Philip Mannion (UCL Earth Sciences) said: “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 “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.”
