The dinosaur-killing asteroid wiped out ‘everything bigger than a RAT’ 66million years ago and modern animals evolved from there, study reveals
- Fossils discovered in Colorado reveal how mammals and plants bounced back
- All modern mammals – including humans – evolved from rodent-sized ancestors
- What was once a forest became blanketed with ferns after the devastation
No land animals bigger than a rat survived the asteroid which wiped out the dinosaurs 66million years ago, according to scientists.
A remarkable trove of fossils from Colorado has revealed details of how mammals and plants rebounded and grew larger after the devastating impact.
The thousands of specimens let scientists trace that history over a span of a million years, a mere eyeblink in Earth’s lifespan.
The large meteorite smashed into what is now the Yucatan Peninsula of southeastern Mexico around 66m years ago.
It unleashed broiling waves of heat and filled the sky with aerosols that blotted out the sun for months, killing off plants and the animals that depended on them.
More than three-quarters of species on Earth died out.
But life came back, and land mammals began to expand from being small creatures into the wide array of forms we see today – including us.
The ancient Carsioptychus coarctatus mammal is illustrated foraging for plants in a newly diversified forest, 300,000 years after the mass extinction that wiped out the dinosaurs
A trove of fossils has revealed details of how life rebounded after the cataclysm that killed off the dinosaurs
The new find taps into ‘the origin of the modern world,’ said Dr Tyler Lyson, an author of a paper reporting the fossil finds on Thursday in the journal Science.
The fossils of 16 species of animals and more than 6,000 plants were recovered from an area of steep bluffs covering about 10 square miles (17 square kilometers) near Colorado Springs, starting three years ago.
Dr Lyson, of the Denver Museum of Nature and Science, found little in that area when he followed the standard practice of scanning for bits of bone.
But that changed when he began looking instead for rocks that can form around bone. When the rocks were broken open, skulls and other fossils within were revealed.
Dr Lyson said it’s not clear how wide a geographic region the fossils’ story of recovery applies to, but that he thinks they show what happened over North America.
‘We just know so little about this everywhere on the globe,’ he said. ‘At least now we have at one spot a fantastic record.’
Mammals were able to grow larger after the impact because dinosaurs were going extinct, meaning they were less likely to be eaten
The fossils revealed that the area where the meteorite hit had been a forest beforehand, home to dinosaurs like the Tyrannosaurus rex and mammals no bigger than about 17lbs (8kg).
Soon after the disaster, the environment was blanketed with ferns and the biggest mammal around was about as heavy as a rat.
The world was in a warming period, as has been documented in previous studies, after debris clouds from the asteroid blocked out the Sun and sent temperatures plummeting.
By about 100,000 years after the meteorite impact, the forest was dominated by palm trees and mammals had grown to the weight of raccoons.
This was almost as big as they were before the meteorite crash.
The asteroid which wiped out the dinosaurs (illustrated) is believed to have been between six and 10 miles wide (10-15km) and travelling at a speed of around 44,000 miles per hour (70,000kmh)
This photo shows a fern fossil collected from Corral Bluffs, Colorado, which helped to build a picture of how plants evolved after the extinction of the dinosaurs
The world was almost destroyed by wildfires, tsunamis and huge clouds of sulphur the day after the asteroid that killed the dinosaurs hit, according to research. (Artist’s impression)
‘That’s a pretty rapid recovery, or at least one aspect of recovery,’ Dr Lyson said.
By 300,000 years, the walnut tree family had diversified, and the biggest mammals were plant eaters about as heavy as a large beaver.
Based on other studies of their diet, they may have evolved along with those trees, Dr Lyson said.
By 700,000 years, the fossil record shows the first known appearance of legume plants, the family that includes peas and beans.
And it reveals the two largest mammals found in the study, with the larger one weighing about 100lbs (50 kg), roughly the same as a wolf.
That is about 100 times heavier than the mammals that survived the extinction, ‘which I think is pretty fast’ for growth, Dr Lyson said.
The main factor for the mammals growing so much larger, Dr Lyson added, was the disappearance of the dinosaurs, which left an ‘ecological niche’ to be filled.
But the quality and types of food on the landscape probably also played a role and the beans which grew may have provided a ‘protein bar’ growing movement, he said.
He said the mammals were creatures that evolved from animals that had survived extinction or those that immigrated from elsewhere.
Experts not connected to the study were enthusiastic about the findings.
It’s ‘an unparalleled documentary of how life on land recovered’ after the asteroid impact, said P. David Polly of Indiana University in Bloomington.
‘The sheer number of fossil specimens and the quality of their preservation are exceptional’ for this time period, he said.
The fossils’ story certainly represents what happened in central North America and perhaps more broadly, he wrote in an email.
Stephanie Smith of the Field Museum in Chicago said the study’s detailed focus on a single area can help scientists understand the complexity of recovery when combined with results from elsewhere.
WHY DID THE DINOSAURS GO EXTINCT?
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.
Pictured: A collection of four mammal skulls collected from Corral Bluffs, Colorado. From left are skull fragments of Loxolophus, Carsioptychus, Taeniolabis, Eoconodon – all were small mammals
A storm rolls in towards Corral Bluffs, Colorado, outside of Denver. The area represents about 300 vertical feet of rock and preserves the extinction of the dinosaurs through the first million years of the Age of the Mammals
Pictured: Some of the plant fossils retrieved from Colorado. More than 6,000 leaves were collected as part of the study to help determine how and when Earth’s forest rebounded after the mass extinction event
Scientists have previously found little evidence about what happened in the aftermath of the meteorite crash, especially on land, said Jin Meng of the American Museum of Natural History in New York.
The new work, he said, appears to provide ‘the best record on Earth to date.’
Researchers also analyzed thousands of pollen grains to see what plants were alive at various times. Analysis of leaves indicated several warming periods during the period.
Zhe-Xi Luo of the University of Chicago, who did not participate in the work, said the report is remarkable for tying together records for plants, mammals and temperature, giving a ‘holistic picture.’
Scientists expected mammals to recover after the dinosaur extinctions, he said, and the new work ‘is a huge step forward in getting a firm understanding about just how it happened.’
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