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First dinosaurs may have evolved in northern Africa and South America
The remains of the earliest dinosaurs could lie beneath the Amazon rainforest and the Sahara Desert.
New research suggests that dinosaurs evolved in a much hotter and drier part of the world than realised, with many early fossils still to be uncovered.
The origins of the dinosaurs are shrouded in mystery – but new research might have revealed the best places to look for clues.
At the moment, the oldest known definitive dinosaurs are 230-million-year-old fossils from Argentina and Brazil, including species such as Eoraptor and Herrerasaurus. However, these animals are already recognisably dinosaurs, which suggests that they had already been evolving for millions of years before.
The hunt for these missing ancestors has so far been largely unsuccessful, but a study published in Current Biology has suggested a possible reason. It might be that palaeontologists haven’t been looking in the right place.
By assessing the fossil record and the dinosaur family tree, the researchers’ models suggest that the first dinosaurs evolved in the dry savannahs and hot deserts of the ancient supercontinent Gondwana. This region would go on to form the Amazon, Congo basin, and Sahara Desert.
Joel Heath, a PhD student who led the new research, says that the finding could “change everything” about the origins of the dinosaurs.
“Until recently, it was thought dinosaurs must have evolved in southern Gondwana, in what is now Brazil and Argentina, because the oldest dinosaur fossils have been found there,” Joel explains. “However, the fossil record has large gaps, so it can’t be taken at face value.”
“Our modelling suggests that that the earliest dinosaurs might have originated in low-latitude Gondwana instead. While no dinosaur fossils have yet been found in these places, this might be due to a mix of inaccessibility and a relative lack of research efforts in these areas.”
While some scientists believe Nyarasaurus could be a very early dinosaur, others believe it's a close relative. © The Trustees of the Natural History Museum, London
Finding the missing dinosaur ancestors
Scientists have named hundreds of species of dinosaurs, but our knowledge of where they came from is still quite shaky. Large parts of the dinosaur fossils record are still missing, especially from the Triassic Period when dinosaurs first evolved.
“While Europe and North America generally have a pretty good fossil record, it’s not the case in other areas of the world,” says Joel. “While some countries, like Brazil, Argentina and China are catching up, there are many places where there only a few fossils have ever been found.”
“This makes it very difficult to understand the dinosaurs’ origin and key moments in their evolutionary history.”
In the past, palaeontologists have tried to understand the relationships of early dinosaurs by assembling a phylogeny, or family tree. By working out how different species relate to each other and where they were found, scientists can track the family tree back to the start to get an idea of where the first dinosaurs might have lived.
However, when the tree is full of gaps there’s a risk that the results might not reflect reality. To address this, Joel and the authors of the new study needed to tell apart where dinosaurs never lived and where their remains simply haven’t been found yet.
“We examined different areas to see what land vertebrate fossils from the Triassic and Jurassic had been found there,” Joel explains. “It’s really unusual if there are no fossils at all, so we took this as a red flag that it might not be a genuine absence.”
“There are two main possibilities. On the one hand, it could mean that the region’s rocks just might not preserve fossils from this time. On the other, it could represent a lack of research.”
By taking this into account, the team have laid out a new scenario for the rise of the dinosaurs.
Early dinosaur fossils could be found underneath the Sahara Desert and other former parts of equatorial Gondwana. © muratart/ Shutterstock
A new dinosaur evolution timeline
The new theory begins near the equator in an arid region of equatorial Gondwana around 250 million years ago following the end-Permian mass extinction event that decimated much of life on Earth.
In the wake of this event, a group of reptiles known as the archosaurs began to evolve into a variety of different forms. This included the ancestors of the dinosaurs, pterosaurs and the crocodile-like pseudosuchians.
While the ancestors of the pterosaurs and pseudosuchians moved north, the predecessors of the dinosaurs stayed in Gondwana. These reptiles eventually evolved into the first dinosaurs. These are thought to have been small, dog-sized omnivorous animals that walked on two legs.
At first, all dinosaurs are thought to have looked quite similar. Major differences only started to appear when they diverged into three main groups – the ornithischians, the theropods and the sauropodomorphs.
Out of these three groups the origin of the ornithischians, which includes species such as Triceratops and Ankylosaurus, is least understood. Rather mysteriously, members of this group don’t appear in the fossil record until long after the other two groups. But Joel and his colleagues think that the answer to this mystery might be hiding in plain sight.
They believe that a group of fossil reptiles called the silesaurids, generally thought to have been the closest relatives of dinosaurs, might actually be the direct ancestors to the ornithischians.
“Our models supported placing the silesaurids at the base of the ornithischians much more than any alternatives,” Joel says. “It doesn’t necessarily mean it’s correct, but it does a better job of filling in this crucial gap in the history of the dinosaurs than other theories.”
While the dinosaurs were already diverging in their early history, their biology confined them to this region of Gondwana for millions of years. Having evolved in a warm climate, the cooler regions north and south of the equator might have hindered their ability to spread further.
Dinosaurs eventually adapted to these cooler regions. It is this that may have allowed them to spread south into Gondwana, where they would eventually become species such as Eoraptor and Herrerasaurus, and north into the Laurasian supercontinent.
“The ultimate test of our models will be if early dinosaurs remain are found in the Amazon, Sahara Desert and other former parts of low-latitude Gondwana,” says Joel. “Finding them would revolutionise our understanding of Triassic ecosystems, and offer key insights into the evolutionary story of the group.”
