Dinosaurs were widespread globally at the time of the asteroid impact at the end of the Late Cretaceous period

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New analysis refutes claim that dinosaurs were in decline before asteroid hit

A new study from researchers at the Natural History Museum and University of Bath has looked at the diversity of dinosaurs just before the asteroid that led to their extinction hit
66 million years ago. In contradiction to some current theories, the team found that dinosaurs were not in decline before their extinction and that under different circumstances they might have continued to be the dominant group of land animals on the planet.

Dinosaurs were widespread globally at the time of the asteroid impact at the end of the Late Cretaceous period globally, occupying every continent on the planet, and were the dominant form of animal in most terrestrial ecosystems. However, it is still contentious amongst paleobiologists as to whether dinosaurs were declining in diversity at the time of their extinction.

In order to address this question, the research team led by PhD student at the Museum Joe Bonsor, collected a set of different dinosaur family trees and used statistical modelling to assess if each of the main dinosaur groups was still able to produce new species at this time.

Their study found that dinosaurs were not in decline before the asteroid hit, contradicting some previous studies. The authors also suggest that had the impact not occurred, dinosaurs might have continued to be the dominant group of land animals on the planet.

Lead author of the study, Joe Bonsor, is undertaking his PhD jointly at the Natural History Museum, Milner Centre for Evolution and the University of Bath. Joe explains, ‘Previous studies 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. 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.’

It is difficult to assess the diversity of dinosaurs due to gaps in the fossil record. This can be due to factors such as which bones are preserved as fossils, how accessible the fossils are in the rock to allow them to be found, and the locations where paleontologists search for them.

The researchers used statistical methods to overcome these sampling biases, looking at the rates of speciation of dinosaur families rather than simply counting the number of species belonging to the family.

Joe added, ‘The main point of our paper is that it isn’t as simple as looking at a few family 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 reflect the reality at the time.’

‘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.”

With new dinosaurs being discovered all the time, at an average of 50 a year since the 2000s, the team behind this study hope that the story of dinosaur evolution will only become clearer. For now, it looks likely that had it not been for cosmic intervention our world would be very different today.

The study Dinosaur diversification rates were not in decline prior to the K-pg boundary has been published in the journal Royal Society Open Science and available online here

Notes to editors

The research was funded by the Leverhulme Trust and Natural History Museum.

Natural History Media contact: Tel: +44 (0)20 7942 5654 / 07799690151 Email: press@nhm.ac.uk  

Images available to download here.

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