Evrim Yazgin
Cosmos science journalist
A review of the oldest known dinosaurs has revealed that fossil evidence for their origin probably has not yet been discovered.
Most of the earliest dinosaur fossils have been found in South America and Africa.
During the Triassic period (252–201 million years ago), these continents formed the southern part of the supercontinent Pangaea which would eventually break up into Gondwana (South America, Africa, Australia, India, Madagascar) in the south and Laurasia (Europe, Asia, North America) in the north.
Several dinosaur fossils found in Argentina are up to 237 million years old. This includes the lightly built Eodromaeus and Eoraptor which were the size of large dogs, and Herrerasaurus which could be up to 6m long.
More recently, early dinosaurs have been found in Africa. This includes Mbiresaurus which probably stood a metre tall and could be an ancestral form of the giant, long-necked sauropod dinosaurs. Mbiresaurus lived about 231 million years ago.
One dinosaur from Tanzania, Nyasasaurus parringtoni, is believed to be 243 million years old.
Earlier this month, palaeontologists reported the oldest dinosaur from North America – chicken-sized raptor named Ahvaytum bahndooiveche which lived about 230 million years ago. It is the oldest dinosaur found anywhere in Laurasia.
What stands out about these early dinosaurs is that they are different. This suggests that dinosaurs had been evolving for some millions of years earlier. Ahvaytum’s discovery, showing that Laurasian dinosaurs could be at least 230 million years old, adds to the mystery of when and where dinosaurs first evolved.
A new study, published in the journal Current Biology, looked at the current fossil record and used computer modelling to try and fill in the gaps.
The modelling suggests that the earliest dinosaurs probably emerged in a hot, equatorial region of Gondwana that today makes up the Amazon, Congo basin and Sahara Desert.
“So far, no dinosaur fossils have been found in the regions of Africa and South America that once formed this part of Gondwana,” says lead author Joel Heath, a PhD student at University College London (UCL).
“However, this might be because researchers haven’t stumbled across the right rocks yet, due to a mix of inaccessibility and a relative lack of research efforts in these areas.”
The study may also determine how the earliest dinosaurs diversified into the 3 main groups of dinosaurs: theropods (bipedal, mainly meat-eating dinosaurs), sauropods and ornithischians.
Ornithischians include Stegosaurus and Triceratops. They are strangely absent in the early dinosaur fossil record. The model that made the most sense, the researchers found, was one that includes silesaurids as ancestors of ornithischian dinosaurs. Previously, silesaurids have been considered ancient cousins of dinosaurs, but not part of the dinosaur lineage.
“Our results suggest early dinosaurs may have been well adapted to hot and arid environments,” says senior author Philip Mannion, also at UCL. “Out of the 3 main dinosaur groups, one group, sauropods, which includes the Brontosaurus and the Diplodocus, seemed to retain their preference for a warm climate, keeping to Earth’s lower latitudes.
“Evidence suggests the other 2 groups, theropods and ornithischians, may have developed the ability to generate their own body heat some millions of years later in the Jurassic period, allowing them to thrive in colder regions, including the poles.”
