How the demise of the dinosaurs led to super-sized mammals

The demise of the dinosaurs created the ecological opportunity for the diminutive prehistoric mammals of the time to become the largest creatures on Earth today, scientists have demonstrated conclusively for the first time.

A worldwide study of fossilised mammals has demonstrated beyond any doubt that it was the extinction of the dinosaur some 65 million years ago that was the key trigger leading to the explosive growth of the warm-blooded mammals.

Although it was long suspected that this was the reason for the transition from dinosaur dominance to mammalian supremacy, a thorough investigation of fossil mammals dating back 140 million years has confirmed that we would not have elephants today had it not been for the death of Argentinosaurus, one of the biggest-ever dinosaur, and others like it.

The study found that for the first 40 million years or so of their existence, the mammals were mostly small, shrew-like creatures that lived in a narrow range of habitats.

However, after the dinosaur disappeared, the mammals evolved relatively rapidly into much larger creatures capable of exploiting a wide variety of ecological niches, from leaf-eating giant sloths to tundra-munching mammoths.

"Basically, the dinosaur disappear and all of a sudden there is nobody else eating the vegetation. That's an open food source and mammals start going for it, and it's more efficient to be aherbivore when you're big," said Jessica Theodor of the University of Calgary in Canada. "You lose dinosaur 65 million years ago, and within 25 million years the system is reset to a new maximum for the animals that are there in terms of body size. That's actually a pretty short time frame, geologically speaking. That's really rapid evolution," Professor Theodor said.

The study in the journal Science found that many different types of mammals grew into gigantic forms on different continents. The biggest was a hornless rhinoceros-like herbivore that lived in Eurasia 34 million years ago called Indricotherium transouralicum, which weighed 17 tons and stood 18ft high at the shoulder – four times the size of a modern elephant.

Being big is an advantage in a habitat with a large landmass of lots of vegetation, although it can make species vulnerable to sudden extinction if the environment changes rapidly.

With the dinosaur gone, and no other large animals already on Earth to take their place, the scene was set for the mammals to evolve into bigger and bigger forms that could better exploit the natural resources available to them.

"Nobody has ever demonstrated that this pattern is really there. People have talked about it, but nobody has ever gone back and done the math. We went through every time period and said 'OK, for this group of mammals that's the biggest one?' And then we estimated its body mass," Professor Theodor said. John Gittleman of the University of Georgia, who took part in the study, said that the fossil record for mammals was better than for many other animals, which was a key factor that helped to nail down the main conclusion.

"Once dinosaur went extinct, mammals evolved to be much larger as they diversified to fill the ecological niches that became available.

"This phenomenon was well documented in North America. We wanted to know if the same thing happened all over the world," Dr Gittleman said. "Having so many different lineages independently evolve to such similar maximum sizes suggests that there were similar ecological roles to be filled by giant mammals across the globe," he said.

Suggested Topics
Start your day with The Independent, sign up for daily news emails
News
Kim Wilde began gardening in the 1990s when she moved to the countryside
peopleThe singer is leading an appeal for the charity Thrive, which uses the therapy of horticulture
Sport
Alexis Sanchez celebrates scoring a second for Arsenal against Reading
football
Life and Style
health
Voices
An easy-peel potato; Dave Hax has come up with an ingenious method in food preparation
voicesDave Hax's domestic tips are reminiscent of George Orwell's tea routine. The world might need revolution, but we like to sweat the small stuff, says DJ Taylor
News
i100
News
Japan's population is projected to fall dramatically in the next 50 years (Wikimedia)
news
ebooks
ebooksA special investigation by Andy McSmith
  • Get to the point
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Recruitment Genius: Project Implementation Executive

£18000 - £23000 per annum: Recruitment Genius: They work with major vehicle ma...

Recruitment Genius: Chiropractic Assistant

£16500 per annum: Recruitment Genius: A Chiropractic Assistant is needed in a ...

Recruitment Genius: Digital Account Executive - Midlands

£18000 - £26000 per annum: Recruitment Genius: They work with major vehicle ma...

Recruitment Genius: Web Developer

£28000 - £30000 per annum: Recruitment Genius: This company provides coaching ...

Day In a Page

NHS struggling to monitor the safety and efficacy of its services outsourced to private providers

Who's monitoring the outsourced NHS services?

A report finds that private firms are not being properly assessed for their quality of care
Zac Goldsmith: 'I'll trigger a by-election over Heathrow'

Zac Goldsmith: 'I'll trigger a by-election over Heathrow'

The Tory MP said he did not want to stand again unless his party's manifesto ruled out a third runway. But he's doing so. Watch this space
How do Greek voters feel about Syriza's backtracking on its anti-austerity pledge?

How do Greeks feel about Syriza?

Five voters from different backgrounds tell us what they expect from Syriza's charismatic leader Alexis Tsipras
From Iraq to Libya and Syria: The wars that come back to haunt us

The wars that come back to haunt us

David Cameron should not escape blame for his role in conflicts that are still raging, argues Patrick Cockburn
Sam Baker and Lauren Laverne: Too busy to surf? Head to The Pool

Too busy to surf? Head to The Pool

A new website is trying to declutter the internet to help busy women. Holly Williams meets the founders
Heston Blumenthal to cook up a spice odyssey for British astronaut manning the International Space Station

UK's Major Tum to blast off on a spice odyssey

Nothing but the best for British astronaut as chef Heston Blumenthal cooks up his rations
John Harrison's 'longitude' clock sets new record - 300 years on

‘Longitude’ clock sets new record - 300 years on

Greenwich horologists celebrate as it keeps to within a second of real time over a 100-day test
Fears in the US of being outgunned in the vital propaganda wars by Russia, China - and even Isis - have prompted a rethink on overseas broadcasters

Let the propaganda wars begin - again

'Accurate, objective, comprehensive': that was Voice of America's creed, but now its masters want it to promote US policy, reports Rupert Cornwell
Why Japan's incredible long-distance runners will never win the London Marathon

Japan's incredible long-distance runners

Every year, Japanese long-distance runners post some of the world's fastest times – yet, come next weekend, not a single elite competitor from the country will be at the London Marathon
Why does Tom Drury remain the greatest writer you've never heard of?

Tom Drury: The quiet American

His debut was considered one of the finest novels of the past 50 years, and he is every bit the equal of his contemporaries, Jonathan Franzen, Dave Eggers and David Foster Wallace
You should judge a person by how they peel a potato

You should judge a person by how they peel a potato

Dave Hax's domestic tips are reminiscent of George Orwell's tea routine. The world might need revolution, but we like to sweat the small stuff, says DJ Taylor
Beige is back: The drab car colours of the 1970s are proving popular again

Beige to the future

Flares and flounce are back on catwalks but a revival in ’70s car paintjobs was a stack-heeled step too far – until now
Bill Granger recipes: Our chef's dishes highlight the delicate essence of fresh cheeses

Bill Granger cooks with fresh cheeses

More delicate on the palate, milder, fresh cheeses can also be kinder to the waistline
Aston Villa vs Liverpool: 'This FA Cup run has been wonderful,' says veteran Shay Given

Shay Given: 'This FA Cup run has been wonderful'

The Villa keeper has been overlooked for a long time and has unhappy memories of the national stadium – but he is savouring his chance to play at Wembley
Timeless drama of Championship race in league of its own - Michael Calvin

Michael Calvin's Last Word

Timeless drama of Championship race in league of its own