Dinosaurs were so successful it may have contributed to their demise, new research has found.
The rapid expansion of the huge reptiles across the globe meant they were running out of space on Earth long before they went extinct.
Researchers suggest that the dinosaurs were in decline long before the killer asteroid hit 65 million years ago because they had clogged up every habitat on Earth.
They claim they may have been ‘too successful for their own good’.
This seriously impeded their ability to produce new species, which left them vulnerable to extinction, researchers at the University of Reading found.
Fossil evidence shows dinosaurs originated in the late Triassic Period around 230 million years ago in South America, when the continent was part of the huge land mass called Pangea.
The origin of enormous reptiles closely followed the world’s largest extinction event, known as the Great Dying.
The event killed roughly nine in 10 marine species and seven in 10 land species, creating a ‘blank canvas’ for the rise of the dinosaurs, researchers said.
During the next 150 million years a diverse range of dinosaur species evolved, from the Tyrannosaurus rex to the gigantic, long necked Diplodocus.
But after rapidly expanding across the globe from South America, the reptiles were unable to adapt as land ran out, scientists found.
Study coauthor Dr Chris Venditti said: ‘Early dinosaurs had a blank canvas and spread quickly across the devastated Earth, taking up every opportunity in their path.
‘Virtually every door was open to them as there was no competition from other species.
‘The inability of the dinosaurs to adapt rapidly enough as the Earth became full may explain why they were in decline prior to the asteroid strike, and why they were so susceptible to almost total extinction when it hit.’
The study, published in Nature Ecology and Evolution, for the first time reveals the paths taken by the dinosaurs as they expanded out of South America.
By tracking the geographical positions of fossil evidence left in the wake of the reptiles’ rise to dominance, they showed that the dinosaurs covered the planet ‘in a frenzy of movement’.
They spread unchecked across the huge available space, at a rate of 621 miles (1,000 kilometres) every million years.
They dominated every terrestrial habitat, across all the continents as they drifted apart from Pangea, over the course of 170 million years.
Lead author Ciara O’Donovan said: ‘This honeymoon period could not last forever, and the dinosaurs eventually filled every available habitat on Earth.
‘There was nowhere new for species to move to, which may have prevented new species from arising, contributing to the dinosaurs’ pre-asteroid decline.
‘In essence, they were perhaps too successful for their own good.’
This saturation of the Earth caused the dinosaurs to become increasingly specialised to live in their existing environment.
This resulted in a fundamental change in the way they evolved and produced new species, curbing their progress and leaving them vulnerable to extinction.
The sudden huge changes to their environment caused by the asteroid strike 65 million years ago was enough to finish them off.
The new study links to previous University of Reading research, which showed that dinosaurs were in decline 50 million years before the deadly asteroid strike hit.
Ms O’Donovan said: ‘Fossil evidence has shown us where the dinosaurs started out and where they died, but there is an important middle period that little was known about.
‘Our research fills this gap in prehistory by revealing how the dinosaurs spread, how fast they moved and what directions they moved in through time.’