Scientists have long theorized that dinosaurs were on the decline before the catastrophic asteroid impact wiped them out 66 million years ago –but new study suggests the prehistoric beasts may have been thriving.
Previous works used fossil records to assess diversity of dinosaurs, but researchers in the latest study say how bones are preserved and other factors produce sampling bias.
Teams from the University of Bath and the Natural History Museum collected a set of different dinosaur family trees and used statistical modelling to assess if each of the main dinosaur groups was able to produce new species at the time.
This allowed them to examine the rates of speciation of dinosaur families rather than counting the number of species belonging to the family, revealing some groups, such as hadrosaurs and ceratopsians, were flourishing on Earth before the mass extinction.
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Scientists have long theorized that dinosaurs were on the decline before the catastrophic asteroid impact wiped them out 66 million years ago –but new study suggests the prehistoric beasts may have been thriving
Lead author Joe Bonsor is undertaking his PhD jointly at the Milner Center for Evolution at the University of Bath and the Natural History Museum.
‘Previous studies done by others have used various methods to draw the conclusion that dinosaurs would have died out anyway, as they were in decline towards the end of the Cretaceous period,’ he said.
‘However, we show that if you expand the dataset to include more recent dinosaur family trees and a broader set of dinosaur types, the results don’t actually all point to this conclusion – in fact only about half of them do.’
Bonsor and his team note that the reason other studies may went in the other direction is because gaps in the fossil record make it difficult to assess dinosaur diversity.
Teams from the University of Bath and the Natural History Museum collected a set of different dinosaur family trees and used statistical modelling to assess if each of the main dinosaur groups was able to produce new species at the time
This is due to how bones are preserved as fossils, how accessible the fossils are in the rock to allow them to be found and the locations where palaeontologists search for them.
In the study, the team used statistical methods to overcome these sampling biases, examining the rates of speciation of dinosaur families rather than counting the number of species belonging to the family.
‘The main point of our paper is that it isn’t as simple as looking at a few trees and making a decision – the large unavoidable biases in the fossil record and lack of data can often show a decline in species, but this may not be a reflection of the reality at the time,’ Mr Bonsor said.
‘Our data don’t currently show they were in decline, in fact some groups such as hadrosaurs and ceratopsians were thriving and there’s no evidence to suggest they would have died out 66 million years ago had the extinction event not happened.’
There have been multiple studies that lean to the idea that dinosaurs were thriving, while others suggest they were on the decline before the asteroid impact.
A study conducted in 2016 by a team from the universities of Reading and Bristol found dinosaurs may have been teetering on the edge 50 million years before the impact.
This allowed them to examine the rates of speciation of dinosaur families rather than counting the number of species belonging to the family, revealing some groups, such as hadrosaurs and ceratopsians (pictured), were flourishing on Earth before the mass extinction
They suggest the lack of diversity is what ultimately led to their demise.
The group also used statistical analysis of the dinosaur family tree and compared these with fossil records.
Just last year, a separate analysis from Imperial College London, University College London and University of Bristol leaned towards the recent study’s results.
This group took on the speculations that the creatures were on the decline due to huge pressures from climate change.
They looked at the changing climate coupled with the distribution of dinosaur species in North America, where many dinosaur fossils were found.
The team found habitats that could support them were much more widespread than originally thought, but these areas were less likely to preserve fossils.
Far more fossils were found in the western half, from the newly forming Rocky Mountains, which created perfect conditions for fossilizing dinosaurs.
In contrast, the eastern half of the continent was far less suitable for fossilization.
This means that far more dinosaur fossils are found in the western half, and it is this fossil record that is often used to suggest dinosaurs were in decline.
HOW THE DINOSAURS WENT EXTINCT AROUND 66 MILLION YEARS AGO
Dinosaurs ruled and dominated Earth around 66 million years ago, before they suddenly went extinct.
The Cretaceous-Tertiary extinction event is the name given to this mass extinction.
It was believed for many years that the changing climate destroyed the food chain of the huge reptiles.
In the 1980s, paleontologists discovered a layer of iridium.
This is an element that is rare on Earth but is found in vast quantities in space.
When this was dated, it coincided precisely with when the dinosaurs disappeared from the fossil record.
A decade later, scientists uncovered the massive Chicxulub Crater at the tip of Mexico’s Yucatán Peninsula, which dates to the period in question.
Scientific consensus now says that these two factors are linked and they were both probably caused by an enormous asteroid crashing to Earth.
With the projected size and impact velocity, the collision would have caused an enormous shock-wave and likely triggered seismic activity.
The fallout would have created plumes of ash that likely covered all of the planet and made it impossible for dinosaurs to survive.
Other animals and plant species had a shorter time-span between generations which allowed them to survive.
There are several other theories as to what caused the demise of the famous animals.
One early theory was that small mammals ate dinosaur eggs and another proposes that toxic angiosperms (flowering plants) killed them off.