The story of how dinosaurs came to rule our planet has captivated scientists and the public alike for generations. Now, an intriguing new study on fossils suggests we might be looking in the wrong places for their earliest ancestors.
While we’ve found countless dinosaur fossils in places like Argentina and Zimbabwe, the very first dinosaurs might have emerged from the steamy equatorial regions of ancient Earth – areas that today make up the Amazon rainforest, Congo basin, and Sahara Desert.
Gap in the dinosaur fossil record
The oldest known dinosaur fossils date back around 230 million years and have been found in Argentina, Brazil, and Zimbabwe.
However, the differences between these fossils indicate that dinosaurs had already been evolving for millions of years before these specimens emerged. This implies an even earlier origin, but direct fossil evidence of this has yet to be found.
The new study, published in the journal Current Biology, addresses this issue by using advanced modeling techniques to account for gaps in the fossil record.
The researchers analyzed fossils, evolutionary trees, and ancient geography to reconstruct the likely emergence of dinosaurs.
Instead of assuming that fossils have not been found in certain areas because they never existed there, the study treats those regions as simply missing data.
“Dinosaurs are well studied but we still don’t really know where they came from. The fossil record has such large gaps that it can’t be taken at face value,” noted study lead author Joel Heath from University College London.
First dinosaurs and their world
According to the study, the earliest dinosaurs likely appeared in western low-latitude Gondwana, a region that was hot and dry, resembling today’s deserts and savannas. This challenges the previous assumption that dinosaurs first evolved in more temperate environments.
Despite the study’s findings, no fossils from these early dinosaurs have been discovered in the Amazon or central Africa.
Heath suggests that this is due to a combination of accessibility issues and a lack of focused research in these regions.
The world of early dinosaurs was vastly different from the one their descendants would later dominate. During the Late Triassic period, dinosaurs were only a minor part of a diverse ecosystem filled with other reptilian creatures.
These included the ancestors of crocodiles, known as pseudosuchians, some of which grew up to 10 meters (33 feet) long.
Another major group in this prehistoric world was pterosaurs, the first vertebrates to develop powered flight. These flying reptiles would eventually evolve into species as large as modern fighter jets.
In contrast to their massive successors like Diplodocus or Tyrannosaurus rex, the earliest dinosaurs were much smaller, typically the size of a chicken or a medium-sized dog.
They walked on two legs, making them agile hunters and scavengers, and most were likely omnivorous. Their small size and adaptability may have helped them survive in the challenging environments of early Gondwana.
The rise of dinosaurs
For millions of years, dinosaurs remained in the shadow of their reptilian cousins. That changed around 201 million years ago, when a series of massive volcanic eruptions led to the end-Triassic mass extinction.
This catastrophe wiped out many of the dominant reptile species, creating an ecological vacuum that the surviving dinosaurs quickly filled.
With their competitors gone, dinosaurs began to spread and diversify, eventually becoming the dominant land animals for the next 135 million years.
The modeling study suggests that dinosaurs and other reptiles may have first evolved in low-latitude Gondwana before spreading outward.
They expanded southward into what is now Argentina and Zimbabwe, and northward into Laurasia, the northern supercontinent that would later split into Europe, Asia, and North America.
This idea is supported by fossil evidence showing that some of the dinosaurs’ closest relatives, including early crocodile-like reptiles, were found in northern Laurasia.
Missing link in dinosaur evolution
One of the study’s key findings concerns the evolutionary relationship between early dinosaurs and their close relatives. There is ongoing debate about how different groups of dinosaurs evolved from their reptilian ancestors.
To address this, the researchers tested their model against three different evolutionary trees. The strongest support for a Gondwanan origin came from a model that classified silesaurids, traditionally seen as distant cousins of dinosaurs, as direct ancestors of ornithischians.
This finding is significant because ornithischians – one of the three major dinosaur groups, which later included the stegosaurs and Triceratops species – are mysteriously absent from the fossil record in the earliest years of dinosaur history.
If silesaurids were indeed their ancestors, this would help fill a major gap in the evolutionary tree and provide a clearer picture of how dinosaurs diversified over time.
Dinosaurs and climate adaptation
The study also sheds light on how dinosaurs adapted to different climates over millions of years. “Our results suggest early dinosaurs may have been well adapted to hot and arid environments,” noted Professor Philip Mannion, a senior author of the study.
This is particularly evident in sauropods, the group that includes massive plant-eaters like Brontosaurus and Diplodocus. These dinosaurs appear to have retained their preference for warm climates, remaining in lower latitudes throughout their existence.
On the other hand, theropods – the group that includes T. rex and modern birds – and ornithischians seem to have developed the ability to generate their own body heat.
This adaptation allowed them to expand into colder regions, including the polar regions, by the time of the Jurassic period. This shift in climate tolerance may have contributed to their long-term evolutionary success.
Future research on dinosaur fossils
Despite the study’s compelling findings, direct fossil evidence of the earliest dinosaurs in the Amazon, Congo, or Sahara remains absent.
Future expeditions to these regions may uncover this elusive evidence that could redefine our understanding of dinosaur origins.
If dinosaurs did originate in equatorial Gondwana, as the study suggests, their earliest ancestors may still lie buried beneath the dense rainforests of the Amazon or the shifting sands of the Sahara.
These areas remain some of the least-explored fossil sites on Earth, meaning that the missing chapters of dinosaur evolution may still be waiting to be revealed.
As paleontologists continue to refine their understanding of early dinosaur evolution, this study highlights the importance of exploring new frontiers in fossil research.
The true story of dinosaur origins is still being written, and future discoveries in these regions could change everything we thought we knew about the dawn of the dinosaurs.
The study is published in the journal Current Biology.
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