For decades, paleontologists have debated the origin and dispersal of dinosaurs across the planet. Until recently, the prevailing view posited that these creatures appeared in the southern hemisphere, on the supercontinent Gondwana, before gradually migrating north to a region called Laurasia. However, a groundbreaking discovery in what is now Wyoming, United States, suggests that dinosaurs were present in the northern hemisphere millions of years earlier than previously thought. This revelation upends classic theories and redefines our understanding of the early evolution of dinosaurs.
A discovery that challenges established theories about dinosaurs
A team from the University of Wisconsin-Madison recently studied the fragmentary bones of a dinosaur discovered in the Popo Agie geological formation, located in present-day Wyoming. Using high-precision radioisotope dating techniques, researchers were able to establish the age of the fossils as well as the surrounding rocks: approximately 230 million years. These remains are now considered oldest dinosaur fossils ever found in the northern hemisphere. The analyzes also revealed slightly older fossil footprints, suggesting that dinosaurs or their close ancestors already inhabited this region before this specific species appeared.
This discovery therefore pushes back the presence of dinosaurs in the northern hemisphere to a time comparable to that of the first dinosaurs identified in Gondwana, which thus changes our understanding of their early dispersal. It also confirms that Laurasia, the northern half of Pangea, played a much more significant role in dinosaur evolution than previously assumed.
The characteristics of Ahvaytum bahndooiveche
These remains belong to a new species, Ahvaytum bahndooivechea small dinosaur that lived near the equator of Laurasia. Despite the absence of a complete skeleton, the bones discovered, in particular fragments of legs, make it possible to identify Ahvaytum bahndooiveche like a dinosaur and a early relative of sauropods. The latter, famous for including gigantic species like titanosaurs, descend from small, much more modest ancestors.
Ahvaytum bahndooiveche measured approximately 30 centimeters high and 90 centimeters longwhich included a long tail. Contrary to the popular image of imposing dinosaurs, this specimen was the size of a chicken. Although researchers have not found its skull, they suggest that it was likely omnivorous like other dinosaurs in its lineage. These characteristics thus highlight the diversity and humility of the beginnings of dinosaurs.
A special period
The period when he lived Ahvaytum bahndooiveche also coincides with a major climatic episode known as of Carnian pluvial episode which took place between 234 and 232 million years ago.
This episode, triggered by increased volcanic activity associated with the fragmentation of Pangea, profoundly transformed the global climate. Massive eruptions released significant amounts of carbon dioxide and other greenhouse gases into the atmosphere, causing global warming and subsequent intensification of precipitation.
-These abundant rains altered the vast arid deserts that until then dominated many regions of the supercontinent into humid and fertile areas. These new ecosystems provided ideal conditions for the development of biodiversity, including the diversification of dinosaurs and many other terrestrial and aquatic species. These ecological transformations would have enabled groups of primitive dinosaurs to quickly adapt to varied environments and to colonize territories that were until then inhospitable.
A necessary revision of evolutionary theories about dinosaurs
The discovery ofAhvaytum bahndooiveche also sheds new light on the emergence of dinosaurs. For a long time, paleontologists assumed that dinosaurs had a single origin in one region of Gondwana (the southern part of Pangea), from where they would have slowly dispersed northward. This hypothesis was mainly based on the analysis of fossils, mostly found in the southern hemisphere. However, Ahvaytum bahndooiveche challenges this well-established theory.
Evidence now suggests that dinosaurs may have evolved simultaneously in different regions of Pangeaparticularly in the northern hemisphere, instead of being limited to a single point of origin. Similarities between fossils discovered in Laurasia and those in Gondwana indicate that distinct lineages may have diverged earlier than previously thought, each adapting independently to local conditions. This idea of parallel evolution in the two hemispheres is echoed in the fossil records and in climate models of the time, which show that favorable habitats were not exclusive to the south.
This perspective expands our understanding of the diversity and adaptability of early dinosaurs. It highlights their ability to occupy a variety of ecological niches from the earliest stages of their evolution. It could also explain why dinosaurs survived and thrived after the ecological crisis that marked the end of the Triassic period, when many other species became extinct.
Ultimately, the discovery ofAhvaytum bahndooiveche emphasizes that the northern hemisphere was not a simple passive receptacle for migrating dinosaurs from Gondwana, but an active theater of their early diversification.
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