Dino demise

MNH - T rex

Last Friday afternoon at around 5.30pm, just as I was about to go home after a busy week, the phone rang. It was BBC Radio Oxford asking if I would appear on the breakfast show at 7.50am the following Monday morning. They wanted me to talk about a new study published this week about the extinction of the dinosaurs…

The research, led by Dr Steve Brusatte from the University of Edinburgh, suggests that perhaps dinosaurs were rather unlucky not to have survived a meteorite impact 66 million years ago. The paper, which is published in Biological Reviews, suggests that a number of other factors were already weakening the dinosaurs’ survival chances, presenting a perfect storm of bad luck.

Commenting on this research on the BBC Oxford show, I explained to presenter Phil Gayle that the dinosaurs died out at the end of the Cretaceous period when an asteroid hit what is now the coast of Mexico (apart from the earliest birds, which had already evolved from dinosaurs and mostly survived).

Hilary at the BBC Oxford radio studio in Summertown, talking to Mike Reid on BBC Radio Berkshire, later the same day.

Hilary at the BBC Oxford radio studio in Summertown, talking to Mike Reid on BBC Radio Berkshire, later the same day.

But even before their extinction, the end of the Cretaceous was a time of great change. The climate became cooler than it ever had been during the 160 million years of dinosaur reign, and sea levels were changing quite dramatically, although this was not so out of the ordinary. More unusually, there was a massive amount of volcanic activity going on in India, forming one of the largest volcanic features on Earth – the Deccan Traps. This caused acid rain and cooling of the atmosphere in the short-term.

On top of this there was the enormous impact, thought to have been an asteroid around 6 miles in diameter. It left a crater over 100 miles wide and 10 miles deep near Chicxulub in Mexico. The impact would have caused massive earthquakes and tsunamis, acid rain, and a temporary removal of the ozone layer. A thick cloud of dust thrown up by the impact would have darkened the Earth and cooled the planet by several to a few tens of degrees.

This shaded relief image of Mexico's Yucatan Peninsula show a subtle, but unmistakable, indication of the Chicxulub impact crater. Most scientists now agree that this impact was the cause of the Cretatious-Tertiary Extinction, the event 65 million years ago that marked the sudden extinction of the dinosaurs as well as the majority of life then on Earth. Image: NASA/JPL-Caltech, modified by David Fuchs at en.wikipedia [Public domain], via Wikimedia Commons.

The Chicxulub impact crater in Mexico.
Image: NASA/JPL-Caltech, modified by David Fuchs at en.wikipedia [Public domain], via Wikimedia Commons.

Unfortunately, due to the coarseness of the fossil record scientists have found it difficult to reach a consensus on which environmental change, if any, caused the dinosaurs’ demise. Was it solely due to the massive asteroid impact? Was it just temperature change? Was it a combination of all four factors, or even none at all?

The new study uses the most up to date information on the fossil record, and combines this with new and powerful statistical techniques to try and shed more light on these questions. The researchers found that the extinction of the dinosaurs was abrupt, coinciding almost exactly with the asteroid strike, although there was no evidence to suggest that dinosaurs around the world were already dying out before then, as some people have claimed.

However, they did find a decrease in the diversity of plant-eating dinosaurs in North America shortly before the impact; this might have disrupted the food chain and made the dinosaurs more susceptible to extinction. The decrease in diversity could have been caused by climate change, sea-level change or the volcanic activity, but without more data it’s still not possible to pin the reason down.

The findings led Dr Brusatte to suggest that if the asteroid hit at any other time in the dinosaurs’ history, they might well have survived. They were essentially just very unlucky, he claims. This is an interesting idea, but unfortunately there’s no way we can test it in a scientific way. A 6-mile wide asteroid hitting the Earth is an experiment you can only really run once, and it’s one I personally don’t want to see repeated!

It’s amazing that these incredible creatures, including the largest carnivore that ever lived on land, T. rex, could have become extinct in such a short space of time. They ruled the earth for nearly 160 million years and seemed invincible. The end of the Age of Reptiles seems somewhat poetic. And it makes me wonder, what might give rise to the end of the Age of Mammals?

Hilary Ketchum, Earth Collections manager

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