Dinosaurs were already struggling before the asteroid strike that doomed them to extinction, study finds

Science

CNN 30 June, 2021 - 08:25am 60 views

Updated 9:25 AM ET, Wed June 30, 2021

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The dinosaurs may have already been going extinct before the cataclysmic space rock hit Earth, new findings suggest

Yahoo News 30 June, 2021 - 11:55am

But some dinosaurs had already started to go extinct before the impact, research suggests.

A era of global cooling that started 76 million years ago may have prompted that decline.

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It's tempting to ponder what life on Earth might have looked like had a space rock not hit 66 million years ago. That impact in present-day Mexico doomed the dinosaurs and a majority of land and marine species. In its absence, would humans and other mammals have eventually duked it out with T. rex and triceratops?

The answer is probably not, according to a study published Tuesday.

That research found that six major groups of dinosaurs were slowly going extinct over the 10 million years prior to the crash. The impact's consequences - mile-high tsunamis, raging fires, and a choking cloud of thick dust and sulfur that blotted out the sun - were merely a nail in the dinosaurs' coffin.

"The meteorite is seen as a coup de grâce for dinosaurs, which finished them off," Fabien Condamine, a research scientist at the University of Montpellier in France who co-authored the new study, told Insider.

Condamine and his collaborators suggest that a period of global cooling may have contributed to a decline in the overall number of dinosaur species, which then made it impossible for the animals to recover after the cataclysmic event.

"Many paleontologists think dinosaurs would have continued to live if the asteroid did not hit Earth. Our study brings new information for this question, and it seems that dinosaurs were not in good shape before the impact," Condamine said.

The researchers behind the new study looked at 1,600 fossils from 247 dinosaur species that lived during the late Cretaceous period - from about 100 million to 66 million years ago. That group includes two-legged carnivores like the T. rex, triceratops, and duck-billed dinosaurs.

The team grouped them into six large families, then analyzed how the diversity of species in those families changed over time. The results show that across all six groups, the number of species started to gradually decline 76 million years ago, prior to the space-rock impact.

"We do not find that dinosaur diversity was high and diversifying toward the end of the Cretaceous, as previously thought," Condamine said.

His isn't the first group of scientists to suggest that dinosaurs actually went extinct gradually. A 2016 study found that as species of dinosaurs that had been around on Earth a while went extinct, no newer species replaced them. Although questions lingered as to whether that conclusion was simply the product of an incomplete fossil record, this new study shows that older species did indeed have higher extinction rates than younger ones.

In the late Cretaceous period, the planet began to cool: Starting 80 million years ago, global temperatures dropped by about 13 degrees Fahrenheit (7 degrees Celsius).

Given that dinosaurs relied on the temperature of their environment to regulate their body heat, Condamine said, that change in climate might have played a role in their extinction rates.

"Warm periods favored dinosaur diversification whereas cooler periods led to enhanced extinctions," the study authors wrote.

Another possible explanation for the dinosaurs' decline is a change in the number of herbivore species in the ecosystem. Hadrosaurs, or duck-billed herbivores, seem to have dominated between 76 million and 66 million years ago - out-competing their fellow leaf-eaters like triceratops and the clubbed-tailed, armored ankylosaurs. That contributed to the decline of those other herbivores.

"Removing herbivores can make the entire ecosystems more prone to extinction cascades," Condamine said.

Read the original article on Business Insider

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Dinosaurs Were Already in Big Trouble Before the Asteroid, More Evidence Suggests

Gizmodo 30 June, 2021 - 11:55am

“I have been collecting dinosaurs in North America, Mongolia, China, and other areas for some time, and I have seen huge improvements in our knowledge of the ages of the dinosaur-bearing rock formations,” Phil Currie, a co-author of the study and a paleontologist at the University of Edmonton, said in a statement. “This means that the data are getting better all the time. The decline in dinosaurs in their last ten million years makes sense, and indeed this is the best-sampled part of their fossil record as our study shows.”

“It became clear that there were two main factors, first that overall climates were becoming cooler, and this made life harder for the dinosaurs which likely relied on warm temperatures,” Mike Benton, a co-author and paleontologist from the University of Bristol’s School of Earth Sciences, said in the press release. “Then, the loss of herbivores made the ecosystems unstable and prone to [an] extinction cascade. We also found that the longer-lived dinosaur species were more liable to extinction, perhaps reflecting that they could not adapt to the new conditions on Earth.”

To which Guinot added: “[It] became clear that the plant-eating species tended to disappear first, and this made the latest dinosaur ecosystems unstable and liable to collapse if environmental conditions became damaging.”

This study presents a fascinating scenario of decline, and it speaks to an enduring question: What if the asteroid never killed the dinosaurs? We may never know the answer, but as the new study makes clear, things were never going to be the same for the dinosaurs, with or without that fateful asteroid.

Dinosaurs were already in decline before the asteroid wiped them out – new research

The Conversation UK 30 June, 2021 - 11:55am

Chercheur au CNRS en Phylogénie et Evolution Moléculaire, Université de Montpellier

Université de Montpellier provides funding as a member of The Conversation FR.

Some 66 million years ago, on the Yucatán peninsula in Mexico, a 12 kilometre-wide asteroid crashes to Earth. The impact causes an explosion whose magnitude is hard to imagine today – several billion times more powerful than the atomic bomb dropped on Hiroshima.

Most of the animals on the American continent are killed immediately. The impact also triggers worldwide tsunamis. Tons and tons of dust are ejected into the atmosphere, plunging the planet into darkness. This “nuclear winter” causes the extinction of many plant and animal species.

Among the latter, the most emblematic: the dinosaurs. But how were the dinosaurs faring before this cataclysm? This is the question we try to answer in our new study, the results of which have just been published in the scientific journal Nature Communications.

We were interested in six families of dinosaurs, the most representative and the most diversified of the 40 million years that preceded the arrival of the asteroid.

Three of these families were carnivorous: the Tyrannosauridae, the Dromaeosauridae (including the famous velociraptors, made famous by the Jurassic Park movies) and the Troodontidae (small dinosaurs similar to birds).

The other three were herbivores: the Ceratopsidae (represented in particular by the Triceratops), the Hadrosauridae (the richest of all the families in terms of diversity) and the Ankylosauridae (represented in particular by the ankylosaur, a dinosaur covered in bony armour with a club-like tail).

We knew that all these families had survived until the end of the Cretaceous marked by the fall of the asteroid. Our goal was to determine at what rate these families diversified – formed new species – or became extinct.

For five years, we compiled all the known information on these families in order to try to work out how many of them there were on Earth at a particular time, and which species were in each group. In palaeontology, each fossil is given a unique number for the sake of traceability, which allows us to follow it through the scientific literature over time.

The work was tedious – we inventoried most of the known fossils for these six families, which represented more than 1,600 individuals from around 250 species. It’s not easy to properly categorise each of the species and date them correctly: one researcher might have given a record a certain date and species, and then another might re-examine it and make a different analysis. In these cases, we had to make our own calls – if we had too many doubts, we eliminated the fossil from the study.

Once each fossil was properly categorised, we used a statistical model to estimate the number of species that evolved over time for each family. We were thus able to trace the species that appeared disappeared between 160 and 66 million years ago and estimate, again for each family, the rates of speciation – the evolution of new species – and extinction over time.

To estimate these rates, we had to take several confounding factors into account. The fossil record is biased: it is uneven in time and space, and some types of dinosaur simply do not fossilise as well as others. This is a well-known problem in palaeontology when estimating the dynamics of past diversity.

Sophisticated models can account for uneven preservation over time and between species. In doing so, the fossil record becomes more reliable for estimating the number of species at any given time. But it is important to be cautious, because we are talking about estimates, and these estimates may change if we find more fossils, for example, or new analytical models.

Our results show that the number of species was in steep decline from 10 million years before the asteroid strike until the dinosaurs were wiped out. This decline is particularly interesting because it is worldwide, and affects both carnivorous groups such as tyrannosaurs, and herbivorous groups such as triceratops.

Some species declined sharply, like the ankylosaurs and ceratopsians, and only one family out of the six – the troodontids – shows a very small decline, which took place in the last five million years of dinosaurs’ existence.

What could have caused this strong decline? One theory is climate change: at that time, the Earth underwent a period of global cooling of 7 to 8°C.

We know that dinosaurs need a warm climate for their metabolism to function properly. As we often hear, they were not ectothermic (cold-blooded) animals like crocodiles or lizards, nor endothermic (warm-blooded), like mammals or birds. They were mesotherms, a metabolic system between reptiles and mammals and needed a warm climate to maintain their temperature and thus perform basic biological functions. This temperature decrease must have had a very strong impact on them.

It should be noted that we found a staggered decline between herbivores and carnivores: the grass-eaters declined slightly before the meat-eaters. It’s probable that the decline of herbivores caused the decline of carnivores. This is what we call cascade extinction.

One big question remains: what would have happened if the asteroid had not crashed? Would dinosaurs have gone extinct anyway, due to the decline that had already begun, or could they have rebounded?

It’s very difficult to say. Many palaeontologists believe that if the dinosaurs had survived, primates and therefore humans would never have appeared on Earth.

An important fact is that a possible rebound in diversity can be very heterogeneous and group-dependent, so that some groups would have survived and others not. Hadrosaurs, or “duck-billed” dinosaurs, for example, showed some form of resilience to the decline and might have bounced back after the decline.

What we can say is that the ecosystems at the end of the Cretaceous period were under significant pressure due to climatic deterioration and major changes in vegetation, and that the asteroid dealt the final blow.

This is often the case in the disappearance of species: first they are in decline and under pressure, then another event intervenes and finishes off a group that may have been on the verge of extinction anyway.

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Dinosaurs were in decline for 10 MILLION years before they were wiped out, scientists say

Daily Mail 30 June, 2021 - 11:55am

By Sam Tonkin For Mailonline

Dinosaurs were already in decline 10 million years before they were wiped out by the impact of a mass-extinction asteroid, scientists have found. 

Six species including tyrannosaurs, triceratops and hadrosaurs were all evolving and expanding throughout the Cretaceous period, spanning 145 to 66 million years ago.

But they suddenly experienced a downturn about 76 million years ago, researchers said, with rates of extinction increasing and fewer new species emerging.

A combination of global cooling – which saw the Earth's temperature fall by 7°C (12.6°F) – the loss of herbivores and the inability of dinosaurs to adapt to new conditions are thought to be the main reasons for the decline.  

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Struggling to adapt: Dinosaurs were already in decline 10 million years before they were wiped out by the impact of a mass-extinction asteroid, scientists have found

A team of international researchers analysed 1,600 fossils from six dinosaur families: Ankylosauridae, Ceratopsidae, Hadrosauridae, Dromaeosauridae, Troodontidae and Tyrannosauridae.

They found that the speciation rate dipped and extinction rate rose sharply in the last 10 million years of the age of dinosaurs. 

It led to a rapid reduction in the number of species just before an asteroid hit the Earth and wiped out non-avian dinosaurs 66 million years ago.

A combination of global cooling – which saw the Earth's temperature fall by 7°C – the loss of herbivores and the inability of dinosaurs to adapt to new conditions are thought to be the main reasons for the decline.

Many dinosaurs likely relied on warm temperatures to thrive and so struggled to adapt to cooler temperatures and new conditions on Earth, scientists believe. 

Mike Benton, a co-author of the study and professor at the University of Bristol said: 'We explored different kinds of possible causes of the dinosaur decline.

'It became clear that there were two main factors, first that overall climates were becoming cooler, and this made life harder for the dinosaurs which likely relied on warm temperatures.

'Then, the loss of herbivores made the ecosystems unstable and prone to extinction cascade. 

'We also found that the longer-lived dinosaur species were more liable to extinction, perhaps reflecting that they could not adapt to the new conditions on Earth.'

The team of international researchers analysed 1,600 fossils from six dinosaur families: Ankylosauridae, Ceratopsidae, Hadrosauridae, Dromaeosauridae, Troodontidae and Tyrannosauridae. 

One of the key findings was that a decline in the diversity of herbivorous dinosaurs, caused by them being outcompeted by hadrosaurs, may have played a role in the collapse of dinosaur ecosystems.

Lead author, Fabien Condamine, from the University of Montpellier, said: 'We looked at the six most abundant dinosaur families through the whole of the Cretaceous, spanning from 150 to 66 million years ago, and found that they were all evolving and expanding and clearly being successful.

'Then, 76 million years ago, they show a sudden downturn. Their rates of extinction rose and in some cases the rate of origin of new species dropped off.'

Around 10 million years later non-avian dinosaurs were wiped out and more than half the world's species were obliterated. 

Analysis: These graphs show how speciation rate (blue) dipped and extinction rate (red) rose sharply in the last 10 million years of the age of dinosaurs. Run together, this corresponds to a rapid reduction in the number of species (black) just before an asteroid hit 66 million years ago

The Chicxulub asteroid, which slammed into a shallow sea in what is now the Gulf of Mexico, is often cited as a potential cause of the Cretaceous-Paleogene extinction event.

It paved the way for the rise of mammals and the eventual appearance of humans.

'This was a key moment in the evolution of life,' Condamine added. 'The world had been dominated by dinosaurs for over 160 million years, and as they declined other groups began their rise to dominance, including the mammals.

'The dinosaurs were mostly so huge they probably hardly knew that the furry little mammals were there in the undergrowth. 

'But the mammals began to increase in numbers of species before the dinosaurs had gone, and then after the impact they had their chance to build new kinds of ecosystems which we see today.'

Guillaume Guinot, also of the University of Montpellier, said: 'In all cases, we found evidence for the decline prior to the bolide impact.

'We also looked at how these dinosaur ecosystems functioned, and it became clear that the plant-eating species tended to disappear first, and this made the latest dinosaur ecosystems unstable and liable to collapse if environmental conditions became damaging.'  

The new study is published in the journal Nature Communications

Around 65 million years ago non-avian dinosaurs were wiped out and more than half the world's species were obliterated.

This mass extinction paved the way for the rise of mammals and the appearance of humans.

The Chicxulub asteroid is often cited as a potential cause of the Cretaceous-Paleogene extinction event.

The asteroid slammed into a shallow sea in what is now the Gulf of Mexico.

The collision released a huge dust and soot cloud that triggered global climate change, wiping out 75 per cent of all animal and plant species.

Researchers claim that the soot necessary for such a global catastrophe could only have come from a direct impact on rocks in shallow water around Mexico, which are especially rich in hydrocarbons.

Within 10 hours of the impact, a massive tsunami waved ripped through the Gulf coast, experts believe.

Around 65 million years ago non-avian dinosaurs were wiped out and more than half the world's species were obliterated. The Chicxulub asteroid is often cited as a potential cause of the Cretaceous-Paleogene extinction event (stock image)

This caused earthquakes and landslides in areas as far as Argentina.

But while the waves and eruptions were  The creatures living at the time were not just suffering from the waves - the heat was much worse.

While investigating the event researchers found small particles of rock and other debris that was shot into the air when the asteroid crashed.

Called spherules, these small particles covered the planet with a thick layer of soot.

Experts explain that losing the light from the sun caused a complete collapse in the aquatic system.

This is because the phytoplankton base of almost all aquatic food chains would have been eliminated.

It's believed that the more than 180 million years of evolution that brought the world to the Cretaceous point was destroyed in less than the lifetime of a Tyrannosaurus rex, which is about 20 to 30 years.

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Climate change pushed dinosaurs into decline 10 million years before asteroid hit Earth, study says

Yahoo News UK 30 June, 2021 - 11:55am

While paleontologists have been in agreement for some time about the cause of dinosaurs’ eventual demise, until now experts have been divided on whether the reptilian group were thriving or struggling before the sudden end of the Mesozoic Era 66 million years ago. 

Now, an international team of scientists including experts from the University of Bristol have declared that dinosaurs experienced a sudden downturn 76 million years ago, when rates of extinction began to rise.

They pinned this to a period of global cooling on Earth when the mean temperature fell by 7C, putting dinosaurs which favoured warmer temperatures at a disadvantage.

Researchers found that plant-eating species tended to disappear first, which in turn made ecosystems unstable and put other dinosaur families at risk of collapse. 

Professor Mike Benton from the University of Bristol's School of Earth Sciences, one of the study’s co-authors, said: “In the analyses, we explored different kinds of possible causes of the dinosaur decline.

“It became clear that there were two main factors, first that overall climates were becoming cooler, and this made life harder for the dinosaurs which likely relied on warm temperatures. 

“Then, the loss of herbivores made the ecosystems unstable and prone to extinction cascade. We also found that the longer-lived dinosaur species were more liable to extinction, perhaps reflecting that they could not adapt to the new conditions on Earth.”

Fabien Condamine, lead author from France’s Institut des Sciences de l'Evolution de Montpellier, said: “We looked at the six most abundant dinosaur families through the whole of the Cretaceous, spanning from 150 to 66 million years ago, and found that they were all evolving and expanding and clearly being successful.

“Then, 76 million years ago, they show a sudden downturn. Their rates of extinction rose and in some cases the rate of origin of new species dropped off.

“This was a key moment in the evolution of life. The world had been dominated by dinosaurs for over 160 million years, and as they declined other groups began their rise to dominance, including the mammals. 

“The dinosaurs were mostly so huge they probably hardly knew that the furry little mammals were there in the undergrowth. 

“But the mammals began to increase in numbers of species before the dinosaurs had gone, and then after the impact they had their chance to build new kinds of ecosystems which we see today.”

Researchers accounted for paleontological uncertainties including incomplete fossil records and age-dating discrepancies by running modelling software millions of times before agreeing on the most probable date of decline.

Phil Currie, a co-author of the study, from the University of Edmonton, in Alberta, Canada, said: ”We used over 1,600 carefully checked records of dinosaurs through the Cretaceous. 

“I have been collecting dinosaurs in North America, Mongolia, China, and other areas for some time, and I have seen huge improvements in our knowledge of the ages of the dinosaur-bearing rock formations. 

“This means that the data are getting better all the time. The decline in dinosaurs in their last 10 million years makes sense, and indeed this is the best-sampled part of their fossil record as our study shows.”

The findings were published in the journal, Nature Communications.

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Scientists propose wild new theory for what originally killed the dinosaurs

Inverse 30 June, 2021 - 11:55am

The asteroid was only the “fatal coup de grâce,” new research suggests.

Then the asteroid hit, wiping out three-quarters of life on Earth.

These events describe the Cretaceous–Paleogene (K–Pg) mass extinction event, a famously monumental moment that occurred approximately 66 million years ago. It’s a riveting tale we’ve heard time and time again since grade school.

But research published Tuesday in the journal Nature Communications finds it’s not exactly accurate — at least when it comes to the extinction of dinosaurs. New research suggests their death was more gradual than sudden.

“I actually did not expect such a long decline,” lead author Fabien Condamine, a research scientist at the French National Center for Scientific Research, tells Inverse.

This new Nature Communications study takes it a step further, debunking the commonly held belief that asteroids primarily caused the dinosaur extinction.

The asteroid may have been a death knell, but dinosaurs were on their way out long before Chicxulub made an appearance on the Yucatán Peninsula in Mexico, the study suggests.

In fact, the decline in dinosaur populations likely began 76 million years ago during the Campanian period — 10 million years before the asteroid hit. The researchers write that two factors may have had the most impact on the dinosaur decline:

The dual blows that killed the dinosaurs were not necessarily the double asteroids, but environmental and population factors that emerged much earlier, the researchers say.

“Further analyses indicate that the global dinosaur decline could have been precipitated by the decline of herbivores,” Condamine explains, adding that herbivores are essential “keystone species” in ecosystems.

His research suggests dinosaurs weren’t able to recover from these dual blows. The rates of new species of dinosaurs emerging could not keep up with the extinction rates, leading to a decline in dinosaur diversity.

In fact, the dinosaur decline was so severe, Condamine and colleagues posit that the T-rex may have only had one species left on planet Earth by the time the asteroid made impact.

He spent years working alone and putting together a fossil record of the six major dinosaur families from the Late Cretaceous Period.

“I am passionate about the debate on the extinction of dinosaurs, and I thought the time was ripe to test again the hypothesis of an extinction due solely to the asteroid impact versus the hypothesis of a long-term diversity decline,” Condamine says.

He’s not a paleontologist by profession, so he solicited the help of co-author and Canadian paleontologist Phil Currie — whom he likens to “Professor Graham in Jurassic Park” — to help with his preliminary analyses of the dinosaur fossil record. This analysis suggested dinosaur populations were in decline before the asteroid event.

Led by Condamine, the subsequently four-person research team compiled a dataset of 1,600 fossils representing 247 dinosaur species from six major families, including the Tyrannosaurs and the herbivores known as Hadrosaurs.

“Although the dinosaur fossil record provides invaluable data [...] it is biased and incomplete,” the researchers write in the paper.

They turned to a tool called PyRate to estimate how the diversity of dinosaur species changed over time. The tool helps researchers analyze the rates of speciation — the emergence of new species — and extinction from incomplete fossil records.

Next, the researchers looked at differences in diversity among different dinosaur groups, specifically comparing carnivores and herbivores.

Finally, they used statistical models to determine the effects of certain factors, such as changes in dinosaur diversity and warming temperatures. This allowed them to determine what may have caused dinosaur decline.

But this study, like others before it, suggests that the most popular rendition of their demise isn’t the most accurate one. This research also challenges the timeline of dinosaur extinction, proposing it starting far earlier than previously assumed.

“From the perspective that our results add a new stone in our understanding of dinosaur diversification until the end, it's likely the study will be controversial among paleontologists,” Condamine says.

Condamine explains that paleontologists have typically viewed dinosaur extinction in one of two ways: sudden extinction or a more gradual decline.

“Perhaps our study will be seen as a proponent of one side,” Condamine says. He also adds that “even if we show the dinosaurs were in decline well before the asteroid hit the ground, we also support the idea that the meteorite was the fatal coup de grâce” that wiped out the remaining dinosaurs. (A asteroid fragment that lands on Earth is known as a meteorite.)

As we stare down our own climate crisis, it’s startling to think that dinosaurs were contending with their own changing climate — albeit, a cooling world rather than a warming one.

“Such a debate is not only about dinosaurs, but the diversification of organisms in general and how they respond to global events,” Condamine says.

Dinosaurs’ large forms could not maintain constant body temperatures in a chillier world. Their inability to adapt to their changing climate seems like a grim precursor when we consider how many animal species are failing to adapt to fluctuating global temperatures today.

Among the species most affected by the climate crisis are some dinosaurs’ descendants: birds.

These future fossil discoveries might provide insight into other environmental or genetic factors that could have led to the dinosaurs’ demise, the researchers write. Although the study covers six important dinosaur families, it doesn’t provide a full picture of what happened to all dinosaur species.

“I think future studies can build upon our results by adding more dinosaur families, for instance, or testing other environmental variables as putative causes of the extinction,” Condamine says.

But it’s inarguably an important first step to figuring out what led to their extinction.

“Studying dinosaurs is a complex but passionate topic, and I anticipate that our results will motivate people to look at their data and results through a new lens,” Condamine says.

Dinosaurs declined before meteor strike: study

FRANCE 24 30 June, 2021 - 11:55am

Dinosaurs may have been in decline millions of years before the meteor strike often attributed to their extinction, according to research published Tuesday examining the role played by changing climate.

The Chicxulub meteor, which slammed into what is now Mexico's Yucatan peninsula around 66 million years ago, is thought to have led to the Cretaceous-Paleogene extinction event that killed off three quarters of life on Earth -- dinosaurs included.

Now new research suggests that a number of species of the terrible lizards may have been declining up to 10 million years before the meteor strike.

Research published in the journal Nature examined data from 1600 dinosaur remains found across the planet to model how common certain species of carnivorous and herbivorous dinosaurs were in the late Cretaceous.

The team found that species decline began around 76 million years ago.

Fabien Condamine, from the University of Montpellier's Institute of Evolutionary Science and lead study author, said his team had followed the decline of six families of dinosaur, comprising nearly 250 distinct species.

"We have a peak in diversity around 76 million years ago," he told AFP.

"Then there's a decline that lasts 10 million years -- that's more than the entire duration of the Homo genus."

The team found two possible explanations for the falling dinosaur diversity identified in the fossil records and their own computer modelling.

For one, the pace of the species decline corresponded with a strong cooling of the global climate around 75 million years ago, when temperatures fell up to eight degrees Celsius.

Condamine said that dinosaurs were adapted to a mesothermal climate -- predominantly warm and damp -- that had prevailed for tens of millions of years throughout their time on Earth.

"With strong cooling, like other large animals, they likely weren't able to adapt," he said.

The second possible decline explanation came as something of shock to the team.

Whereas both herbivores and carnivores would have been expected to be impacted at roughly the same time, the team found a two-million year lag between their respective declines.

"So the decline of the herbivores, which were the prey, would therefore have cascaded into a decline in meat-eaters," said Condamine.

The study concluded that not only did a cooling climate and reduced diversity among herbivores lead to the dinosaurs' slow decline, it also left the various species unable to recover after the meteor strike.

"These factors impeded their recovery from the final catastrophic event," it said.

New Research Shows Dinosaurs Were in Decline for Million Years Before the Final Asteroid Death Blow

SciTechDaily 30 June, 2021 - 11:55am

If rocks from Earth containing microbial life entered Venus’s orbit in the past, this life may have adapted to Venus’s atmospheric conditions.

The death of the dinosaurs 66 million years ago was caused by the impact of a huge asteroid on the Earth. However, paleontologists have continued to debate whether they were already in decline or not before the impact.

In a new study, published today (June 29, 2021) in the journal Nature Communications, an international team of scientists, which includes the University of Bristol, show that they were already in decline for as much as ten million years before the final death blow.

Lead author, Fabien Condamine, a CNRS researcher from the Institut des Sciences de l’Evolution de Montpellier (France), said: “We looked at the six most abundant dinosaur families through the whole of the Cretaceous, spanning from 150 to 66 million years ago, and found that they were all evolving and expanding and clearly being successful.

“Then, 76 million years ago, they show a sudden downturn. Their rates of extinction rose and in some cases the rate of origin of new species dropped off.”

The last march of dinosaurs. Credit: Jorge Gonzalez

The team used Bayesian modeling techniques to account for several kinds of uncertainties such as incomplete fossil records, uncertainties over age-dating the fossils, and uncertainties about the evolutionary models. The models were each run millions of times to consider all these possible sources of error and to find whether the analyses would converge on an agreed most probable result.

Guillaume Guinot, also of the Institut des Sciences de l’Evolution de Montpellier, who helped run the calculations, added: “In all cases, we found evidence for the decline prior to the bolide impact.

“We also looked at how these dinosaur ecosystems functioned, and it became clear that the plant-eating species tended to disappear first, and this made the latest dinosaur ecosystems unstable and liable to collapse if environmental conditions became damaging.”

Graphs showing how speciation rate (blue) dipped and extinction rate (red) rose sharply in the last 10 million years of the age of dinosaurs. Run together, this corresponds to a rapid reduction in the number of species (black) just before the impact of the asteroid 66 million years ago. Credit: Fabien L. Condamine

Phil Currie, a co-author of the study, from the University of Edmonton (Alberta, Canada), said: “We used over 1,600 carefully checked records of dinosaurs through the Cretaceous.

“I have been collecting dinosaurs in North America, Mongolia, China, and other areas for some time, and I have seen huge improvements in our knowledge of the ages of the dinosaur-bearing rock formations.

“This means that the data are getting better all the time. The decline in dinosaurs in their last ten million years makes sense, and indeed this is the best-sampled part of their fossil record as our study shows.”

Professor Mike Benton from the University of Bristol’s School of Earth Sciences, another co-author, added: “In the analyses, we explored different kinds of possible causes of the dinosaur decline.

“It became clear that there were two main factors, first that overall climates were becoming cooler, and this made life harder for the dinosaurs which likely relied on warm temperatures.

“Then, the loss of herbivores made the ecosystems unstable and prone to extinction cascade. We also found that the longer-lived dinosaur species were more liable to extinction, perhaps reflecting that they could not adapt to the new conditions on Earth.”

Fabien Condamine added: “This was a key moment in the evolution of life. The world had been dominated by dinosaurs for over 160 million years, and as they declined other groups began their rise to dominance, including the mammals.

“The dinosaurs were mostly so huge they probably hardly knew that the furry little mammals were there in the undergrowth. But the mammals began to increase in numbers of species before the dinosaurs had gone, and then after the impact they had their chance to build new kinds of ecosystems which we see today.”

Firstly the impact of asteroid had a localied effects for extintion as per some proofs yet obtained with restriction. However simultanios phenomena are aviable as earth’s periodic puĺse theory for extinction of dinosaurs by volcanic eruptions.But do not run away partial credit for this theory,which states impact of asteroid caused mass extinction of dinosaurs 66 million years ago.Congratulation and thanks to the author.

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Large Dinosaurs Were Prone to Extinction Way Before The Asteroid, New Study Argues

ScienceAlert 30 June, 2021 - 11:55am

The collision set off a cascade of environmental devastation, with debris in the atmosphere cutting off life-giving sunlight. Earth's surface temperatures plunged. Animals perished. 

Well, that's what most paleontologists think happened. 

While evidence for this end-Cretaceous impact is indisputable, debate within the paleontological community has been ongoing as to whether dinosaur extinction was abrupt or gradual

The extinctions do coincide with a period of long-term environmental upheaval, largely the result of the continued breaking up of the supercontinents Laurasia and Gondwana. High sea levels, cooling climates, the spread of new habitat on land, as well as massive volcanic activity, may have all played significant roles in the mass extinction event. 

Up until now, analysis of fossil data has yielded no convincing evidence of a decline in dinosaur species before their extinction. A phylogenetic study in 2016, which used dinosaur timetrees, challenged the idea of a sudden extinction, but this conclusion proved to be contentious. 

The fossil record is a notoriously difficult source of evidence, with critiques of that study pointing to gaps in the dinosaur fossil record and sampling biases which could have led to the under-reporting of certain Cretaceous dinosaur species. 

Now, a new study has lent additional evidence to the hypothesis that non-avian dinosaurs were already teetering on the edge of extinction before the cataclysmic events of the infamous asteroid impact.

Led by French National Center for Scientific Research phylogeneticist Fabien Condamine, the authors of the new study claim that methodological developments in data analysis have allowed them to take into account certain biases in fossil data, along with uncertainties around the ages of fossils. 

The team analysed 1,600 dinosaur fossils to assess the speciation and extinction rates of six major dinosaur families: Ankylosauridae, Ceratopsidae, Hadrosauridae, Dromaeosauridae, Troodontidae, and Tyrannosauridae. 

The team found that the diversity of non-avian dinosaurs started to decline approximately 76 million years ago - that's 10 million years prior to the Yucatán impact. They suggest the decline is linked to increased extinction rates in older species, who may have lacked evolutionary novelty and were unable to adapt to changing environmental conditions.

"These results imply that warm periods favored dinosaur diversification whereas cooler periods led to enhanced extinctions," state the authors. 

Ecological and physical factors point to a cooling climate as a catalyst for the decline of dinosaur species in the late Cretaceous. These cooling temperatures likely spelled trouble for large dinosaurs in particular, since they relied on a warm climate to maintain a stable body temperature. 

"A physiological explanation for the cooling-driven extinction could be the hypothesis that if sex determination in dinosaurs was temperature dependent, as in crocodiles and turtles, sex switching of embryos could have contributed to diversity loss with a cooling global climate at the end of the Cretaceous," the team added

The researchers also point to additional factors, such as hadrosaurs outcompeting other herbivores - their teeth show they were able to eat a greater variety of plants than more specialized competitors. With herbivores playing an interconnected role in the food web, their decline may have been detrimental to a number of additional dinosaur species. 

In the end, data from the new study suggest that the final extinction of dinosaurs really could not be solely attributed to a massive asteroid impact.

While the study could not point directly to the precise ecological mechanisms which underlay the effects of global cooling on dinosaur speciation and extinction rates, the results support the idea that long-term environmental changes likely made non-avian dinosaurs prone to extinction, even before a giant space rock smashed up their home planet. 

The study was published in Nature Communications.

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