Dinosaurs doing well before asteroid impact

July 29, 2014 by Hayley Dunning
Dinosaurs doing well before asteroid impact
Artist's impression of the impact. Credit: John Sibbick.

A new analysis of fossils from the last years of the dinosaurs concludes that extra-terrestrial impact was likely the sole cause of extinction in most cases.

Although some groups of were declining in certain populations, dinosaurs in general were doing well before the impact of a 10km-wide asteroid or comet.

The impact caused huge tsunamis, earthquakes and wildfires. Everything over 25kg went extinct, paving the way for small birds and mammals to flourish in the aftermath.

Other pressures

The impact is well-established as the final cause of the demise of the dinosaurs. However, several other major changes were occurring on Earth at the time, leading to the suggestion that dinosaurs were already declining, and that the impact was the final straw.

Dinosaurs went extinct at the end of the Cretaceous period, 66 million years ago. Over the last few million years of the Cretaceous, environmental changes included huge temperature variations, sea-level swings and massive outpourings of volcanism in India.

Using the most up-to-date records of assemblages occurring in the last 18 million years of the Cretaceous, a team of researchers from some of the top institutions and dinosaur museums around the world, including Dr Paul Barrett from the Natural History Museum, conclude that in most cases the impact was the 'smoking gun for the cause of the extinction.'

Dinosaurs doing well before asteroid impact
Some large herbivores, such as triceratops, may have been declining in certain areas.

Little decline

In some regions, there was evidence of certain groups of large herbivores declining in species diversity, which could make the communities that depend on them for food more vulnerable to extinction from external pressures such as an impact.

Overall, though, dinosaur species diversity appeared to be relatively stable despite the large-scale changes occurring over the last few million years.

New fields of study

However, the work is based largely on sites in North America, where the most complete and continuous dinosaur fossil records from the end of the Cretaceous have been described.

'It is unusual for so many experts from a consortium of world-leading intuitions to reach consensus over a big question like this,' said Dr Barrett.

'Having this agreed view helps to set an agenda to guide palaeontologists interested in finding more evidence regarding the speed and structure of the extinction.' This agenda includes looking at regions with the potential for the same detailed records as in North America, including sites in Spain and China.

Zooming in on the cause

The timing of the impact also coincides with a pulse in volcanic activity from India. The dinosaur fossil record is not yet complete enough to say what effect the increase in dust, sulphur and carbon dioxide in the atmosphere from the volcanism would have had on dinosaur communities immediately prior to the impact.

With focused research on this time period across the globe, Dr Barrett is hopeful we can gain an even clearer understanding of the timing and tempo of the .

'This will give us a much clearer picture of our past and perhaps even an understanding of the environmental and ecological factors that could cause or accelerate extinctions in the future.'

Explore further: Dinosaurs fell victim to perfect storm of events, study shows

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5 / 5 (1) Jul 29, 2014
Do we really have the level of granularity in the fossil and geological records to be making these sweeping claims?

Most of these factors are going to be point events, with a limited duration of impact -even "climate changes" not lasting beyond the hundreds to thousands of years. At some point the selective pressure of an event (plague, food availability, etc...) or environmental change has reached its peak, and the species which are successful in the "new" environment are dominant and on the rise. The outlier to these events is the asteroid impact, which presented the opportunity to so rapidly modify the global environment beyond the pace of evolution for the vast majority of terrestrial species.

To me, saying that there were a "perfect confluence of events" which led to the demise of the dinosaurs is analogous to saying that having a slight headache and an ulcer contributed to your death in a head-on collision.
5 / 5 (1) Jul 29, 2014
Just yesterday Natural History Museum was mentioned as a participant in the study claiming "Dinosaurs fell victim to perfect storm of events"
It's embarrassing for an institution like Natural History Museum to make such contradictory claims on a daily basis.
5 / 5 (1) Jul 29, 2014
I have long wondered whether the near-simultaneous Chicxulub Impact and the formation of the Deccan Traps were simple coincidence, or whether the blast wave of the impact could have propagated through the mantle, *reconverging* near the antipodal point of the impact, and retaining enough energy (due to re-focusing) to rupture the crust and actually cause the eruption of the Deccan Traps.
Whydening Gyre
3 / 5 (2) Jul 29, 2014
Just yesterday Natural History Museum was mentioned as a participant in the study claiming "Dinosaurs fell victim to perfect storm of events"
It's embarrassing for an institution like Natural History Museum to make such contradictory claims on a daily basis.

Are you saying that article and this one are contradictory? Doesn't seem so to me...
5 / 5 (1) Jul 30, 2014
Are you saying that article and this one are contradictory? Doesn't seem so to me...

"Dinosaurs doing well before asteroid impact" and "At this time, the dinosaurs' food chain was weakened by a lack of diversity among the large plant-eating dinosaurs on which others preyed ... their ecosystems were vulnerable."
seems pretty contradictory to me.

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