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Mass Extinctions (Overall; In General)

Did our ancestors outlive dinosaurs?
A new phylogenic tree suggests ancestors of present-day mammals coexisted with dinosaurs for millions of years and survived whatever wiped out everything else


[Published 28th March 2007 06:01 PM GMT]


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New findings are contradicting a popular theory that the late Cretaceous mass extinction, which eliminated non-avian dinosaurs and most existing fauna 65 million years ago, helped trigger the rise of present-day mammals. Instead, in a report in Nature this week, researchers suggest that ancestors of modern mammals were already present millions of years earlier, and survived this mass extinction event.

"We think that the death of the dinosaurs didn't really have a strong effect, either positive or negative, on the extant groups," including today's mammals, lead author Olaf Bininda-Emonds of the University of Jena in Germany told The Scientist.

Bininda-Emonds and a multidisciplinary team of researchers assembled and analyzed a mammalian "supertree," a comprehensive phylogenetic tree that combines some 2,500 smaller trees, and brings together existing fossil record data and new molecular analyses. "The supertree shows two major diversification peaks: A quick burst of evolution between 100 million years and 85 million years ago and a second peak at about 50 million years ago," Bininda-Emonds said.

According to Bininda-Emonds, by 75 million years ago, 10 million years before the dinosaurs went extinct, all the 18 placental orders were already there. "Then, 50 million years ago, after sitting there for 25 to 40 million years, they suddenly exploded, giving all the forms that we know nowadays," he explained. The authors did find a small peak of mammalian diversification immediately after the dinosaurs disappeared, but most of those mammals went extinct 50 to 55 million years ago.

David Penny, of Massey University in New Zealand and an author of a related News & Views article, considers the supertree a major achievement in itself. "Now there is an evolutionary tree for almost 99% of all the 4,500 species of extant mammals, complete with divergence times estimates, available for further research," Penny told The Scientist.

To date the supertree, the authors used 51,089 base pairs from 66 genes present in the mammalian groups they analyzed. Working under the hypothesis of a molecular clock (a dating method that infers elapsed time from the number of differences in DNA sequences between groups), they chose 30 well-dated fossils to "calibrate" the clock. To Penny, the addition of timing in the tree makes it even more remarkable. But not everybody agrees.

"Most researchers using molecular data in mammal evolution pretty much stop at coming up with the divergence time estimates, but the authors have used them to infer the diversification rate of modern lineages," John Hunter of Ohio State University at Newark told The Scientist. "It's a very creative approach, but I think that applying these early divergence time estimates is probably premature and a little problematic," Hunter cautioned. "The paper's conclusions depend on the accuracy of those estimates, and some are considerably older than a lot of the more modern molecular divergence time estimates that I've encountered lately."

Bininda-Emonds partially agreed, noting that the date estimates contain errors, but even factoring in approximate values for those errors eliminates the possibility that the mass extinction triggered a major mammalian diversification. "Each new molecular study seems to be pushing the divergence dates for mammals a little further back in time, and this is a general pattern in the literature." Bininda-Emonds said.

Hunter also suggested the early divergence time estimates reported in the Nature paper could actually be an artifact, a consequence of higher rates of gene evolution during the big adaptive radiation that affected all mammals as a group after the dinosaur extinction. "To suppose that modern mammals were somehow immune to that is kind of puzzling."

"What we've done is to present a hypothesis for testing, and it's up to others now to verify our claims or to disprove them," Binnda-Emonds concluded.

Graciela Flores
[email protected]

Links within this article

O. R. P. Bininda-Emonds et al., "The delayed rise of present-day mammals," Nature, March 29, 2007.
http://www.nature.com

Olaf R.P. Bininda-Emonds
http://www.personal.uni-jena.de/~b6biol2/

L. Pray, "Modern phylogeneticists branch out," The Scientist, June 2, 2003.
http://www.the-scientist.com/article/display/13825/

David Penny
http://awcmee.massey.ac.nz/people/dpenny/index.htm

D. Penny and M.J. Phillips, "Mass survivals," Nature 446: 501-502, March 29, 2007.
http://www.nature.com

S. Bunk, "The molecular clock," The Scientist,, November 13, 2000.
http://www.the-scientist.com/article/display/12127/

John P. Hunter
http://www.newark.osu.edu/jhunter/

M. L. Phillips, "Genetic evidence for punctuated equilibrium," The Scientist, October 6, 2006.
http://www.the-scientist.com/news/display/25023/


http://www.the-scientist.com/news/home/53035/
 
Has anyone ever asked why the mammals did not compete with the dino's when they were around? They had just as much opportunity to grow and become capable of preying on them.
 
Mammals seems to have been relatively sucessful in their 'small animal' niche at that time. One might ask why the Dino's didn't shrink to compete with the multuberculate shrews. But in some ways they did; the bird line which arose from the theropod dinosaurs were small and must have competed with, preyed upon, and were hunted by early mammals.
 
eburacum: "The connection between impact and volcanism isn't proved or otherwise at the moment."
The period of volcanism which gave birth to the Deccan traps began a number of years before the impact. The apex of activity seemingly at 2 millions years before (see Venkatesen T.R., Panke K., Gopalan K., in Earth and Planetary Science Letters 119). I think that both events played a major role in this extinction. But they seem to be coincidental.
For the Siberian traps at the end Permian, it was suggested that a giant impact could have caused them. Simulations suggest that a crater wider than 100 km collapses, due to crust tension. But no evidence of such an impact has been found. The search for fullerens looked promizing at first, but proved disappointing. The only traces of asteroid from that time, in Antartica, suggest a localized event.

"Mammals seem to have been relatively succesful in their 'small animal niche' at that time."
I am too surprised by the rehearsing of this old cliché, mammals being insignificant animals during the Mesozoic. They included burrowing, tree dwelling, semi-aquatic, fully terrestrial, predatory, herbivory, rodent-like or omnivorous species. Their reproductive and locomotive systems were very varied. In fact, they were in a phase of explosive diversification. Being small never meant being unsuccesful. On the other hand, they seem to have been less succesful at reaching greater size. Because of their endothermy?
Mammals were affected by the K-T extinction, according to a number of paleontologists. Notably, marsupials in North America. As a whole, there was a decline in mammal disparity during Cretaceous. Many groups, like triconodonts, dryolestoids or zatherians became extinct during this period.

"The bird line which arose from the theroprod dinosaurs were small and must have competed with, preyed upon, and were hunted by early mammals."
There were a number of other very small theropods, directly competing with mammals. Like Compsognathus, Microraptor, or Bambiraptor. But it seems that they failed to fill many ecological niches. Microraptor was a specialized tree-dweller, but didn't last long. Except for the birds Hesperornis and Ichtyornis (and maybe a duck and gull-like species), all at the very end of the Cretaceous, we don't know any aquatic mesozoic dinosaur. But our view may change with new discoveries (as with this new burrowing dinosaur).
 
So dont stay awake worrying about an asteroid strike; just worry.

Extinction by asteroid a rarity: 'Sick Earth' extinctions more likely
http://www.physorg.com/printnews.php?newsid=142595837

In geology as in cancer research, the silver bullet theory always gets the headlines and nearly always turns out to be wrong.

For geologists who study mass extinctions, the silver bullet is a giant asteroid plunging to earth.

But an asteroid is the prime suspect only in the most recent of five mass extinctions, said USC earth scientist David Bottjer. The cataclysm 65 million years ago wiped out the dinosaurs.

"The other four have not been resolvable to a rock falling out of the sky," Bottjer said.

For example, Bottjer and many others have published studies suggesting that the end-Permian extinction 250 million years ago happened in essence because "the earth got sick."

The latest research from Bottjer's group suggests a similar slow dying during the extinction 200 million years ago at the boundary of the Triassic and Jurassic eras.

At the 2008 Joint Annual Meeting of the Geological Society of America, USC doctoral student Sarah Greene drew similarities between ocean conditions at the Triassic-Jurassic boundary and after the end-Permian extinction.

At both those times, bouquet-like structures of aragonite crystals formed on the ocean floor. Such structures are extremely rare in Earth's history, Greene said.

"The fact that these deposits have only been found at these two specific times that are associated with mass extinction suggests at the very least that maybe there's some shared ocean geochemistry … that could be related to the cause of the extinctions," Greene said.

"The Triassic-Jurassic extinction cause is totally up for grabs at the moment," she added.

Also at the meeting, USC doctoral student Rowan Martindale presented results from her studies of coral reefs during the Triassic-Jurassic extinction.

"The coral reefs look actually very similar to modern coral reefs," she said. "At the end-Triassic mass extinction, you lose all your reef systems. And nobody's figured out why that is."

Martindale identified two distinct types of ancient reefs: one dominated by coral and another consisting mainly of mud and debris, possibly held together by bacteria.

A theory for the end-Triassic extinction needs to explain how both types of reefs could have been killed off, Martindale said.

Any knowledge about end-Triassic reef death could be useful in understanding the current reef crisis, widely attributed to climate change.

"We're looking at it as a model to give us any insight that we might have for today's decline for coral reefs," Bottjer said.

Source: University of Southern California
 
Earth in throes of a 'great extinction'
http://www.irishtimes.com/newspaper/wor ... 75601.html
Wed, Jul 29, 2009

EARTH IS experiencing its “sixth great extinction event” with disease and human activity taking a devastating toll on vulnerable species, according to a major review by conservationists.

Much of the southern hemisphere is suffering particularly badly, and Australia, New Zealand and neighbouring Pacific islands may become the extinction hot spots of the world, the report warns.

Ecosystems in Polynesia, Micronesia and Melanesia need urgent and effective conservation policies, or the region’s already poor record on extinctions will worsen significantly.

Researchers trawled 24,000 reports to compile information on the native flora and fauna of Australasia and the Pacific islands, which have six of the most biodiverse regions on the planet.

“Our region has the notorious distinction of having possibly the worst extinction record on Earth,” said Richard Kingsford, an environmental scientist at the University of New South Wales in Sydney and lead author of the report.

“We have an amazing natural environment, but so much of it is being destroyed before our eyes. Species are being threatened by habitat loss and degradation, invasive species, climate change, over-exploitation, pollution and wildlife disease.”

The review, published in the journal Conservation Biology, highlights destruction and degradation of ecosystems as the main threat.

In Australia, agriculture has altered or destroyed half of all woodland and forests. Around 70 per cent of the remaining forest has been damaged by logging. Loss of habitats is behind 80 per cent of threatened species, the report claims.

Invasive animals and plants have devastated native species on many Pacific islands. The Guam Micronesian kingfisher, for example, is thought to be extinct in the wild following the introduction of the brown tree snake.

More than 2,500 invasive plant species have colonised Australia and New Zealand, competing for sunlight and nutrients. Many have been introduced by governments, horticulturists and hunters.

The report sets out a raft of recommendations to slow the decline by introducing laws to limit land clearing, logging and mining; restricting deliberate introduction of invasive species; reducing carbon emissions and pollution; and limiting fisheries. It raises concerns about bottom trawling, and the use of cyanide and dynamite, and calls for early-warning systems to pick up diseases in the wild. – ( Guardian service)
 
Mass Extinctions: 'Giant' Fossils Are Revolutionizing Current Thinking
http://www.sciencedaily.com/releases/20 ... 171413.htm

Large-sized gastropods found in marine sediments in Utah dating from only ~1 million years after the P-T mass extinction. The scale bar represents 1 cm. (Credit: Copyright A. Brayard/J. Thomas)

ScienceDaily (Feb. 11, 2010) — Large-sized gastropods (1) (up to 7 cm) dating from only 1 million years after the greatest mass extinction of all time, the Permian-Triassic extinction (2), have been discovered by an international team including a French researcher from the Laboratoire Biogéosciences (CNRS/Université de Bourgogne), working with German, American and Swiss colleagues. These specimens call into question the existence of a "Lilliput effect," the reduction in the size of organisms inhabiting postcrisis biota, normally spanning several million years.

The team's results, published in the February 2010 issue of the journal Geology, have drastically changed paleontologists' current thinking regarding evolutionary dynamics and the way the biosphere functions in the aftermath of a mass extinction event.

The history of life on Earth has been punctuated by numerous mass extinctions, brief periods during which biodiversity is considerably reduced, followed by phases of re-conquest of the biosphere, corresponding to the diversification of those species that survived. Over the last 540 million years, around twenty mass extinctions, of greater or lesser intensity, have succeeded one another. The most devastating of these, the Permian-Triassic (P-T) mass extinction, which decimated more than 90% of the marine species existing at the time, occurred 252.6 million years ago with a violence that is still unequaled today.

In the aftermath of such events, environmental conditions are severely disrupted: the oceans become less oxygenated, water becomes poisonous, there is increased competition, collapse of food chains, etc. Until now, it has generally been accepted that certain marine organisms, such as gastropods or bivalves, were affected by a drastic reduction in size in response to major disruptions of this nature, both during and after the event. It took several million years for such organisms to return to sizes comparable to those that existed prior to the crisis. This is what scientists call the "Lilliput effect," in reference to the travels of Gulliver (3) who was shipwrecked on the island of the same name, inhabited by very small Lilliputians.

An international team of French, German, American and Swiss paleontologists has recently discovered large gastropod fossils dating from only 1 million years after the P-T mass extinction. The researchers have spent several years studying the re-conquest phase that followed the P-T crisis. By focusing their efforts on fossil-bearing outcrops in Utah dating from the Early Triassic, which have not yet been studied in detail, they have uncovered some outstanding specimens of gastropods, up to 7 cm, which can be termed as "giants" in comparison to those generally found, normally no bigger than 1 cm.

Complementary studies of these new gastropod fauna also indicate that they are not any smaller than older or present-day fauna. This discovery therefore refutes the existence of a Lilliput effect on gastropods during the major part of the Early Triassic or, at the very least, suggests that its importance has been overestimated. Quite surprisingly, the presence of these large gastropods also coincides with an explosive re-conquest of the ocean by organisms such as ammonites (4, 5). Taken together, these events therefore suggest that restructuring of marine ecosystems was already well underway only one million years after the P-T crisis, a very short time after a mass extinction of such magnitude.

The researchers plan to continue to study the fossils discovered in this locality in Utah while searching for other species and groups, such as bivalves, to confirm this new data. However, these findings already suggest that paleontologists are going to have to re-think the immediate and long term impact of mass extinctions on species.

Notes:

(1) The gastropods concerned by this study are mollusks that lived on the sea bed and are related, for example, to present-day land snails.

(2) The Permian-Triassic mass extinction, named after the two geological periods that encompass it, namely the Permian (299 -- 252.6 Ma) and the Triassic (252.6 -- 201.6 Ma), is the greatest mass extinction ever documented. It marks the end of the Primary (or Paleozoic) era and the beginning of the Secondary (or Mesozoic) era.

(3) Gulliver's Travels, written by Jonathan Swift in the 18th century.

(4) Ammonoids, related to present-day nautilus, cuttlefish and squid, are free-swimming cephalopod mollusks with external shells. They disappeared from the world's oceans at the same time as the dinosaurs, 65 million years ago, after having been a major part of the marine fauna for nearly 400 million years.

(5) See also Brayard et al. 2009. Science 235: 1118-1121.
 
Long article:

Dinosaur extinction link to crater confirmed
By Paul Rincon
Science reporter, BBC News, The Woodlands, Texas

An international panel of experts has strongly endorsed evidence that a space impact was behind the mass extinction event that killed off the dinosaurs.

They reached the consensus after conducting the most wide-ranging analysis yet of the evidence.

Writing in Science journal, they rule out alternative theories such as large-scale volcanism.

The analysis has been discussed at the 41st Lunar and Planetary Science Conference (LPSC) in the US.

A panel of 41 international experts reviewed 20 years' worth of research to determine the cause of the Cretaceous-Tertiary (K-T) mass extinction, around 65 million years ago.

The extinction wiped out more than half of all species on the planet, including the dinosaurs, bird-like pterosaurs and large marine reptiles, clearing the way for mammals to become the dominant species on Earth.

Their review of the evidence shows that the extinction was caused by a massive asteroid or comet smashing into Earth at Chicxulub on Mexico's Yucatan Peninsula.

When the 10km-15km space rock struck the Yucatan, the explosive energy released was equivalent to 100 trillion tonnes of TNT - over a billion times more explosive than the bombs dropped on Hiroshima and Nagasaki.

The huge crater that remains from the event is some 180km in diameter and surrounded by a circular fault about 240km in diameter.

"You can actually trace debris right up to the rim of the crater from across the world," Co-author Dr David Kring, from the Lunar and Planetary Institute in Houston, told BBC News.

"You can start in Europe, cross the Atlantic and it just thickens as you approach the Chicxulub impact crater."

etc...

http://news.bbc.co.uk/1/hi/sci/tech/8550504.stm
 
Fossil find resolves ancient extinction mystery
By Victoria Gill
Science reporter, BBC News

Fossils of soft-bodied marine creatures, discovered in south-eastern Morocco
The fossils were preserved in brightly coloured minerals

Researchers have revealed remarkably well preserved fossils of soft-bodied marine creatures that are between 470 and 480 million years old.

Prior to this find, scientists were unsure whether such creatures died out in an extinction event during an earlier period known as the Cambrian.

The fossils were preserved in rocks formed by layers of ancient marine mud in south-eastern Morocco.

They are described in the latest issue of the journal Nature.

The research team that studied the fossils described them as marine animals that lived during the early part of a period that followed the Cambrian, known as the Ordovician.

Professor Derek Briggs from Yale University in New Haven, US, who was an author of the study, told BBC News that the discovery provided "a much more complete record of early marine life than we've ever had before".

The creatures, he explained, closely matched those found in the Burgess Shale of British Columbia, a locality in Yoho National Park, which is famous for yielding rare fossils of soft-bodied marine creatures from the Middle Cambrian period.

"There was an anomaly in the fossil record," said Dr Peter Van Roy, the lead researcher on the study, who is also based at Yale University. "Most of these animals just seemed to disappear at the end of the Middle Cambrian."

The transition between the Cambrian and the Ordovician periods is crucial in evolutionary history.

The "Cambrian explosion" saw the sudden appearance of all the major animal groups. It was followed by the "great Ordovician biodiversification event" when the number of marine animal groups increased exponentially over a period of 25 million years.

Professor Briggs explained: "[These specimens have] shown that some of the organisms that we thought were exclusive to Cambrian actually persisted until the Ordovician."

Dr Jean-Bernard Caron, a palaeontologist from the Royal Ontario Museum in Canada who was not involved in this study, told BBC News that the discovery was "very exciting".

He said that the fossil record had never before demonstrated that certain lineages of Cambrian animals survived until this later period.

Preserving life's record
Detailed sketch of an ancient marine creature found in a fossil bed in south-eastern Morocco
Dr Van Roy created illustrations of the ancient marine creatures

The specimens show that poor fossil preservation, rather than mass extinction, was probably responsible for this gap in the fossil record.

Because hard shells fossilise, and are therefore more readily preserved than soft tissue, scientists had an incomplete and biased view of the marine life that existed during the Ordovician.

But the conditions at this Moroccan site, Professor Briggs explained, were special.

"Very thick" marine muds, he said, were laid down in the deep ocean, trapping the creatures' bodies below the influence of storms.

These mud layers also excluded oxygen, creating conditions conducive to forming some of the minerals in which fossils are preserved.

Dr Van Roy, who has been working at this site in for around a decade, discovered this particular group of fossils just one year ago.

But he expects to find even more and he and his team have planned further expeditions to Morocco. "We're only scratching the surface," he said.

"I'm certain there will be more spectacular fossils coming out of this site in the near future."

http://news.bbc.co.uk/2/hi/science/nature/8678459.stm
 
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Prehistoric fish extinction allowed humans to thrive
By John von Radowitz
Tuesday, 18 May 2010

Humans may owe their place on the planet to a mass extinction of fish 360 million years ago, it was claimed yesterday.

The cataclysmic event reset the evolutionary starting point for all vertebrates living today, US scientists said. If it had not occurred, humans and their ancestors may not have evolved, or could have evolved very differently.

Key features shared by all modern mammals, birds and reptiles originated when life re-emerged after the mass extinction, the scientists believe.

"Everything was hit, the extinction was global," said Lauren Sallan, a researcher from the University of Chicago. "It reset vertebrate diversity in every single environment, both freshwater and marine, and created a completely different world."

The Devonian Period, which stretched from 416 to 359 million years ago, is also known as the "Age of Fishes". A broad array of species filled the oceans, rivers and lakes, but most were unlike any alive today.

Armoured placoderms, such as monstrous 30-foot carnivore Dunkleosteus, and lobe-finned fishes similar to modern lungfish dominated the waters. Ray-finned fishes, sharks and four-limbed tetrapods were in the minority. But the picture changed abruptly with the traumatic Hangenberg extinction. "There's some sort of pinch at the end of the Devonian," said Professor Michael Coates, from the University of Chicago. "It's as if the roles persist, but the players change; the cast is transformed dramatically.

"Something happened that almost wiped the slate clean and, of the few stragglers that made it through, a handful then re-radiate spectacularly."


New fossil finds and analytical techniques brought to light the full impact of the Hangenberg event, said the scientists. The research is published in the journal Proceedings of the National Academy of Sciences.

What happened to trigger the mass extinction remains an unsolved mystery. Other scientists have found evidence of substantial glacier formation at the end of the Devonian Period, which would have dramatically affected sea levels. The first appearance of forest-like environments may also have produced atmospheric changes with catastrophic consequences for life.

"It is a pivotal episode that shaped modern vertebrate biodiversity," said Professor Coates. "We are only now beginning to place that important event in the history of life and the history of the planet, which we weren't able to do before."

http://www.independent.co.uk/environmen ... 75594.html
 
Paleoecologists suggest mass extinction due to huge methane release
July 22nd, 2011 in Space & Earth / Earth Sciences

http://www.physorg.com/news/2011-07-pal ... -huge.html

This wide angle view of the Earth is centered on the Atlantic Ocean between South America and Africa.

(PhysOrg.com) -- Micha Ruhl and colleagues from the University of Copenhagen's Nordic Center for Earth Evolution have published a paper in Science where they contend that the mass extinction that occurred at the end of the Triassic period, was due to a "sudden" increase in the amount of methane in the atmosphere due to the effects of global warning that resulted from the spewing of carbon dioxide from volcanoes.

Prior to this research, most scientists have believed that the sudden extinction of nearly half of all life forms on the planet was due solely to the emissions from volcanic eruptions that were occurring in what was to become the Atlantic Ocean. Ruhl et al contend that instead, what happened, was that the small amount of atmospheric heating that occurred due to the exhaust from the volcanoes, caused the oceans to warm as well, leading to the melting of ice crystals at the bottom of the sea that were holding on to methane created by the millions of years of decomposing sea life. When the ice crystals melted, methane was released, which in turn caused the planet to warm even more, which led to more methane release in a chain reaction, that Ruhl says, was the real reason for the mass extinction that led to the next phase in world history, the rise of dinosaurs.

Ruhl and his team base their assertions on studies they've made of the isotopes of carbon in plants (found in what is now the Austrian Alps) that existed during the period before the mass extinction. In so doing they found two different types of carbons and the molecules that were produced during that time frame. After extensive calculations, Ruhl and his team came to the conclusion that some 12,000 gigatons of methane would have had to have been pumped into the atmosphere to account for the differences in the isotopes; something the team believes could only have happened if the methane were to come from the sea floor.

This new research, though dire sounding, may or may not have implications for modern Earth. While it is true that humans have pumped significant amounts of carbon into the atmosphere, amounts that are approaching what Ruhl and his team say led to the earlier methane release, it doesn’t necessarily mean we are on the same path, because as Ruhl points out, things are much different today, the very structure of the planet has changed so much that it would be impossible to transfer what might have been learned about events in Earth’s history 200 million years ago, to what is going on today.

More information: Atmospheric Carbon Injection Linked to End-Triassic Mass Extinction, Science 22 July 2011: Vol. 333 no. 6041 pp. 430-434 DOI:10.1126/science.1204255

ABSTRACT

The end-Triassic mass extinction (~201.4 million years ago), marked by terrestrial ecosystem turnover and up to ~50% loss in marine biodiversity, has been attributed to intensified volcanic activity during the break-up of Pangaea. Here, we present compound-specific carbon-isotope data of long-chain n-alkanes derived from waxes of land plants, showing a ~8.5 per mil negative excursion, coincident with the extinction interval. These data indicate strong carbon-13 depletion of the end-Triassic atmosphere, within only 10,000 to 20,000 years. The magnitude and rate of this carbon-cycle disruption can be explained by the injection of at least ~12 × 103 gigatons of isotopically depleted carbon as methane into the atmosphere. Concurrent vegetation changes reflect strong warming and an enhanced hydrological cycle. Hence, end-Triassic events are robustly linked to methane-derived massive carbon release and associated climate change.
 
I suppose we are bound to get global warming - fashionable.
It's all too complex, come back Velikovsky, all is forgiven, I say.
 
Old fossils solve mystery of earliest bird extinction
http://www.bbc.co.uk/news/science-environment-14979905
By Leila Battison
Science reporter

Bird fossils are very rare because the bones are fragile and easily damaged.

Related Stories

Feathers fly in first bird debate
Closing the 'three metre gap'

Many early bird species suffered from the same catastrophic extinction as the dinosaurs, new research has shown.

The meteorite impact that coincided with the disappearance of the dinosaurs 65 million years ago, also saw a rapid decline in primitive bird species.

Only a few bird groups survived through the mass extinction, from which all modern birds are descended.

Researchers at Yale University have published their findings in PNAS this week.

There has been a long standing debate over the fate of the earliest "archaic" birds, which first evolved around 200 million years ago.

Whether their populations declined slowly towards the end of the Cretaceous period, or whether they suffered a sudden mass extinction at the Cretaceous-Tertiary (K-T) boundary is unresolved, owing to conflicting evidence.

DNA studies have attempted to date the origin of modern birds; some suggest that they appeared before the extinction of dinosaurs, with large numbers of them surviving through the extinction event.

But the molecular clock suffers from "method issues", explains Dr Longrich of Yale University, and well-dated fossils are needed for "stratigraphic constraint" of the extinctions.

There are problems with the fossil record however. It is incomplete, owing to the extreme rarity of bird fossils.

Bird bones are very difficult to preserve as fossils as they are small and light, and easily damaged or swept away in rivers.

But the new research, headed by Dr Longrich, has made use of fragmentary bird fossils collected up to 100 years ago, from locations across North America.

New diversity
The fossil deposits, in North and South Dakota and Wyoming in the US, and Saskatchewan in Canada, date from the last 1.5 million years of the Cretaceous period.

More precise dating places the bird fossils to within 300,000 years of the extinction event - a very short period on geological timescales.

These fossils had been studied before, but they have been "shoehorned" into modern groups on the basis of their overall similarity.

Dr Longrich and his team have reanalysed and reclassified these important fossil fragments, using features of the shoulder joint to assign the fossils to modern and ancient groups.


Archaic birds like Archaeopteryx looked very different to modern ones
The shoulder bone, or "coracoid" is used for classification because it is the most common bone fragment preserved, and it doesn't vary much between individuals of the same species.

Analysing 24 specimens, the researchers identified 17 species, seven of which were "archaic birds" that are not seen after the K-T mass extinction.

These findings show for the first time a diversity of archaic birds alive, right up until the end of the Cretaceous.

This would mean that the archaic birds went extinct abruptly 65 million years ago, and that modern birds must have descended from just a few groups that survived the event.

'Nail in the coffin'
Among the primitive species identified, there is considerable variation in size, but there are few other specific adaptations.

Modern birds, on the other hand, have a huge range of adaptations to their particular behaviours or living environments.

This variation would have therefore come about during an explosive evolutionary radiation from the few surviving groups, during the first 10 million years or so following the K-T mass extinction.

"It's similar to what happened with mammals following the age of the dinosaurs." said Dr Longrich.

"Given that the extinction affected mammals, reptiles, insects and plants, it would be remarkable if birds survived the event unscathed," the scientists say in an introduction to their research.

There is growing evidence for the theory that the archaic birds survived until the extinction; more and more bird fossils are being found in Madagascar, Mongolia and Europe.

But these fossils are not well dated, unlike the newly analysed fragments from North America.

Dr Longrich said that this evidence was "a nail in the coffin of the idea of a slow decline".

http://www.bbc.co.uk/news/science-environment-14979905
 
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It Took Earth Ten Million Years to Recover from Greatest Mass Extinction
http://www.sciencedaily.com/releases/20 ... 153810.htm

New research reveals that it took some 10 million years for Earth to recover from the greatest mass extinction of all time, some 250 million years ago. (Credit: © byheaven / Fotolia)

ScienceDaily (May 27, 2012) — It took some 10 million years for Earth to recover from the greatest mass extinction of all time, latest research has revealed.

Life was nearly wiped out 250 million years ago, with only 10 per cent of plants and animals surviving. It is currently much debated how life recovered from this cataclysm, whether quickly or slowly.

Recent evidence for a rapid bounce-back is evaluated in a new review article by Dr Zhong-Qiang Chen, from the China University of Geosciences in Wuhan, and Professor Michael Benton from the University of Bristol. They find that recovery from the crisis lasted some 10 million years, as explained May 27 in Nature Geoscience.

There were apparently two reasons for the delay, the sheer intensity of the crisis, and continuing grim conditions on Earth after the first wave of extinction.

The end-Permian crisis, by far the most dramatic biological crisis to affect life on Earth, was triggered by a number of physical environmental shocks -- global warming, acid rain, ocean acidification and ocean anoxia. These were enough to kill off 90 per cent of living things on land and in the sea.

Dr Chen said: "It is hard to imagine how so much of life could have been killed, but there is no doubt from some of the fantastic rock sections in China and elsewhere round the world that this was the biggest crisis ever faced by life."

Current research shows that the grim conditions continued in bursts for some five to six million years after the initial crisis, with repeated carbon and oxygen crises, warming and other ill effects.

Some groups of animals on the sea and land did recover quickly and began to rebuild their ecosystems, but they suffered further setbacks. Life had not really recovered in these early phases because permanent ecosystems were not established.

Professor Benton, Professor of Vertebrate Palaeontology at the University of Bristol, said: "Life seemed to be getting back to normal when another crisis hit and set it back again. The carbon crises were repeated many times, and then finally conditions became normal again after five million years or so."

Finally, after the environmental crises ceased to be so severe, more complex ecosystems emerged. In the sea, new groups, such as ancestral crabs and lobsters, as well as the first marine reptiles, came on the scene, and they formed the basis of future modern-style ecosystems.

Professor Benton added: "We often see mass extinctions as entirely negative but in this most devastating case, life did recover, after many millions of years, and new groups emerged. The event had re-set evolution. However, the causes of the killing -- global warming, acid rain, ocean acidification -- sound eerily familiar to us today. Perhaps we can learn something from these ancient events."

Story Source:

The above story is reprinted from materials provided by University of Bristol.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Zhong-Qiang Chen, Michael J. Benton. The timing and pattern of biotic recovery following the end-Permian mass extinction. Nature Geoscience, 2012; DOI: 10.1038/ngeo1475

http://www.sciencedaily.com/releases/20 ... 153810.htm
 
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Asteroid that killed the dinosaurs also wiped out the 'Obamadon'
December 10th, 2012 in Other Sciences / Archaeology & Fossils

In the foreground, the carnivorous lizard Palaeosaniwa stalks a pair of hatchling Edmontosaurus as the snake Cerberophis and the lizard Obamadon look on. In the background, an encounter between T. rex and Triceratops. (Artwork by Carl Buell)

The asteroid collision widely thought to have killed the dinosaurs also led to extreme devastation among snake and lizard species, according to new research—including the extinction of a newly identified lizard species Yale and Harvard scientists have named Obamadon gracilis.

"The asteroid event is typically thought of as affecting the dinosaurs primarily," said Nicholas R. Longrich, a postdoctoral associate with Yale's Department of Geology and Geophysics and lead author of the study. "But it basically cut this broad swath across the entire ecosystem, taking out everything. Snakes and lizards were hit extremely hard."

The study was scheduled for online publication the week of Dec. 10 in the Proceedings of the National Academy of Sciences.

Earlier studies have suggested that some snake and lizard species (as well as many mammals, birds, insects and plants) became extinct after the asteroid struck the earth 65.5 million years ago, on the edge of the Yucatan Peninsula. But the new research argues that the collision's consequences were far more serious for snakes and lizards than previously understood. As many as 83 percent of all snake and lizard species died off, the researchers said—and the bigger the creature, the more likely it was to become extinct, with no species larger than one pound surviving.

The results are based on a detailed examination of previously collected snake and lizard fossils covering a territory in western North America stretching from New Mexico in the southwestern United States to Alberta, Canada. The authors examined 21 previously known species and also identified nine new lizards and snakes.

They found that a remarkable range of reptile species lived in the last days of the dinosaurs. Some were tiny lizards. One snake was the size of a boa constrictor, large enough to take the eggs and young of many dinosaur species. Iguana-like plant-eating lizards inhabited the southwest, while carnivorous lizards hunted through the swamps and flood plains of what is now Montana, some of them up to six feet long.

"Lizards and snakes rivaled the dinosaurs in terms of diversity, making it just as much an 'Age of Lizards' as an 'Age of Dinosaurs,'" Longrich said.
The scientists then conducted a detailed analysis of the relationships of these reptiles, showing that many represented archaic lizard and snake families that disappeared at the end of the Cretaceous, following the asteroid strike.

One of the most diverse lizard branches wiped out was the Polyglyphanodontia. This broad category of lizards included up to 40 percent of all lizards then living in North America, according to the researchers. In reassessing previously collected fossils, they came across an unnamed species and called it Obamadon gracilis. In Latin, odon means "tooth" and gracilis means "slender."

"It is a small polyglyphanodontian distinguished by tall, slender teeth with large central cusps separated from small accessory cusps by lingual grooves," the researchers write of Obamadon, which is known primarily from the jaw bones of two specimens. Longrich said the creature likely measured less than one foot long and probably ate insects.

He said no one should impute any political significance to the decision to name the extinct lizard after the recently re-elected U.S. president: "We're just having fun with taxonomy."

The mass (but not total) extinction of snakes and lizards paved the way for the evolution and diversification of the survivors by eliminating competitors, the researchers said. There are about 9,000 species of lizard and snake alive today. "They didn't win because they were better adapted, they basically won by default, because all their competitors were eliminated," Longrich said.

Co-author Bhart-Anjan S. Bhullar, a doctoral student in organismic and evolutionary biology at Harvard University, said:

"One of the most important innovations in this work is that we were able to precisely reconstruct the relationships of extinct reptiles from very fragmentary jaw material. This had tacitly been thought impossible for creatures other than mammals. Our study then becomes the pilot for a wave of inquiry using neglected fossils and underscores the importance of museums like the Yale Peabody as archives of primary data on evolution—data that yield richer insights with each new era of scientific investigation."
Jacques A. Gauthier, professor of geology and geophysics at Yale and curator of vertebrate paleontology and vertebrate zoology, is also an author.
More information: "Mass Extinction of Lizards and Snakes at the Cretaceous-Paleogene Boundary", PNAS, 2012.

Provided by Yale University

"Asteroid that killed the dinosaurs also wiped out the 'Obamadon'." December 10th, 2012.

http://phys.org/news/2012-12-asteroid-d ... madon.html
 
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Australia's deadly eruptions were reason for the first mass extinction

A Curtin University researcher has shown that ancient volcanic eruptions in Australia 510 million years ago significantly affected the climate, causing the first known mass extinction in the history of complex life.

Published in the journal Geology, Associate Professor Fred Jourdan from Curtin's Department of Applied Geology, along with colleagues from several Australian and international institutions, used radioactive dating techniques to precisely measure the age of the eruptions of the Kalkarindji volcanic province -- where lavas covered an area of more than 2 million square kilometres in the Northern Territory and Western Australia.

Dr Jourdan and his team were able to prove the volcanic province occurred at the same time as the Early-Middle Cambrian extinction from 510-511 million years ago -- the first extinction to wipe out complex multicellular life.
"It has been well-documented that this extinction, which eradicated 50 per cent of species, was related to climatic changes and depletion of oxygen in the oceans, but the exact mechanism causing these changes was not known, until now," Dr Jourdan said.

"Not only were we able to demonstrate that the Kalkarindji volcanic province was emplaced at the exact same time as the Cambrian extinction, but were also able to measure a depletion of sulphur dioxide from the province's volcanic rocks -- which indicates sulphur was released into the atmosphere during the eruptions.

"As a modern comparison, when the small volcano Pinatubo erupted in 1991, the resulting discharge of sulphur dioxide decreased the average global temperatures by a few tenths of a degree for a few years following the eruption.

"If relatively small eruptions like Pinatubo can affect the climate just imagine what a volcanic province with an area equivalent to the size of the state of Western Australia can do."

The team then compared the Kalkarindji volcanic province with other volcanic provinces and showed the most likely process for all the mass extinctions was a rapid oscillation of the climate triggered by volcanic eruptions emitting sulphur dioxide, along with greenhouse gases methane and carbon dioxide.
"We calculated a near perfect chronological correlation between large volcanic province eruptions, climate shifts and mass extinctions over the history of life during the last 550 million years, with only one chance over 20 billion that this correlation is just a coincidence," Dr Jourdan said.

Dr Jourdan said the rapid oscillations of the climate produced by volcanic eruptions made it difficult for various species to adapt, ultimately resulting in their demise. He also stressed the importance of this research to better understand our current environment.

"To comprehend the long-term climatic and biological effects of the massive injections of gas in the atmosphere by modern society, we need to recognise how climate, oceans and ecosytems were affected in the past," he said.

Journal Reference:
F. Jourdan, K. Hodges, B. Sell, U. Schaltegger, M. T. D. Wingate, L. Z. Evins, U. Soderlund, P. W. Haines, D. Phillips, T. Blenkinsop. High-precision dating of the Kalkarindji large igneous province, Australia, and synchrony with the Early-Middle Cambrian (Stage 4-5) extinction. Geology, 2014; 42 (6): 543 DOI: 10.1130/G35434.1

http://www.sciencedaily.com/releases/20 ... 124327.htm
 
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... The first person to find evidence that Earth's history was punctuated by global extinctions was palaeontologist Jack Sepkoski, who studied species diversity across geological time.

As well as proposing a "big five" of mass extinction events, Sepkoski also found evidence of a smaller extinction peak slightly earlier in the Permian in marine organisms called foraminifera in what is now China. Although further evidence of extinctions around this time has been found, all of it was in the tropics, suggesting that the event was a regional, not global, affair.

But now David Bond of the University of Hull, UK, says there is evidence of a major marine extinction at the same time in the Arctic. Brachiopods – hard-shelled marine animals – left the most visible evidence of their demise. The fossil record Bond has uncovered in Spitsbergen, Norway, and in Greenland suggests that more than 50 per cent of all marine genera died during the event, with some groups losing 80 per cent of their genera. Ammonites and corals suffered heavily. Bond reported his findings on 19 October to the Geological Society of America meeting in Vancouver, Canada. "We can now say this is a real global mass extinction," he says.

Because, on a geological scale, these two Permian extinctions occurred so close together, species numbers might not have had time to recover from the first before the second began, says Bond, and so whole groups of organisms might have been fatally weakened. For example, three-quarters of trilobite genera went extinct in the earlier Permian extinction, leaving only five surviving genera that were then wiped out at the end of the Permian. In contrast, other mass extinctions have been separated by at least 50 million years (see chart). ...

http://www.newscientist.com/article/mg2 ... E6DofmsW8k
 
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...Some of Earth’s past mass extinctions have been caused by the impacts of extraterrestrial objects, such as the asteroid that struck near Mexico’s Yucatán Peninsula and wiped out the dinosaurs about 66 million years ago. Others have occurred during extended periods of geological disruption that include region-smothering volcanic eruptions. Both kinds of catastrophes seem to occur on a cycle of about 30 million years, notes Michael Rampino, a geoscientist at New York University in New York City. “It’s always been a mystery as to how extraterrestrial impacts could cause these long-lived geological effects,” he says. But invisible dark matter, he proposes, could trigger both extraterrestrial impacts and geological upheavals in one fell swoop.

Scientists still don’t know what dark matter is, but its gravitational pull on other objects in space shows that there’s a lot of it out there. Researchers estimate that in the plane of the galaxy, each square light-year contains about one solar mass of dark matter. Like the clouds of dust and gas that astronomers can see, clouds of dark matter may be perturbing the orbits of distant comets, causing them to fall into the inner solar system where they can strike Earth ...

http://news.sciencemag.org/earth/2015/02/did-dark-matter-kill-dinosaurs
 
Catastrophes that could end the world

THE eruption of Tambora 200 years ago was the largest volcanic blast of modern history, killing something like 100,000 people in what is today Indonesia, producing an ash cloud that covered a million square kilometres and temporarily changing the global climate. The veil of sulphate particles which Tambora created in the stratosphere cooled the planet’s continents by an average of about 2ºC in the following year; local changes were in some places much more severe, and there was agricultural chaos in North America, Europe and China. Volcanoes are nasty; other natural disasters—such as storms, floods and earthquakes—only have global effects because of the interconnectedness of human societies and economies, while large eruptions have direct geophysical effects worldwide. Yet volcanoes are not the only existential threats humanity faces. Which catastrophes could actually end human civilisation?

What would a Tambora-like eruption mean for the modern world?

A repeat of Tambora would have similar climatic effects, though it is possible that in today’s world their human impact would not be so severe. But the next large eruption could be a lot bigger than that. In terms of the volume of rock the eruption of the volcanic caldera at Taupo, in New Zealand, 26,500 years ago, was well over ten times the size of Tambora; that of Toba, in Indonesia, 75,000 years ago was almost 100 times larger than the 1815 blast. The area covered by ash from Toba to a depth of a centimetre or more has a population of about 2 billion people today. The climatic effects of an eruption do not increase linearly with its size, but if it arrived without years of warning (time to allow massive precautionary stockpiling) a repeat of the Toba eruption today would be a devastating blow to food security on a global scale and could be expected to cause tens of millions or hundreds of millions of casualties. Some researchers believe that the Toba eruption was sufficiently devastating to Homo sapiens, which may well then have been found at that time only in east Africa, as to almost wipe the species out. That could explain why modern humans have a very low level of genetic diversity compared with other apes.

The only other natural disasters of similar consequence are impacts by asteroids and comets, which can massively disrupt the climate in similar ways. ...

http://www.economist.com/blogs/econ...plains-10?fsrc=scn/tw/te/bl/ed/catastrophesEE
 
I think we should hold a candle vigil for all the people killed in the Cambrian Explosion :bomb:
https://en.wikipedia.org/wiki/Cambrian_explosion
This appalling act of terror was clearly the work of hostile extraterrestrial forces intent on colonizing our planet.
Lest we forget. (what the Cambrian explosion was)
Too soon?
 
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Every cloud has a silver lining

A team of researchers from several institutions across the U.S. has found evidence suggesting that there was an explosion of diversity in fish after the end-Cretaceous mass extinction. In their paper published in the journal Nature Ecology and Evolution, the team describes their genetic study involving more than 1800 species of fish and what they found.

After the end-Cretaceous mass extinction—the one that killed off the dinosaurs—mammals became much more diverse and dominant. Without the dinosaurs to feast on them, they were free to prosper. Much less is known about what went on in the oceans. In this new effort, the researchers have added some new pieces to that puzzle.

Prior research has suggested that the asteroid or comet that smashed into the Earth approximately 65 million years ago killed off more than the dinosaurs—approximately 50 percent of all species worldwide disappeared. These include many sharks and other reptiles, leaving a void of sorts in the world's oceans that allowed fish to flourish. And flourish they did, according to the researchers with this new effort.

To learn more about what happened with sea creatures after the end-Cretaceous mass extinction, the researchers collected tissue samples from 118 acanthomorph species, looking specifically at 1,000 DNA sequences that were similar across the genomes of their samples—as part of that effort, they searched for variations in genetic sequences that offered clues regarding how closely related the fish were to one another.

https://phys.org/news/2018-03-genetic-explosion-diversity-fish-end-cretaceous.html





Read more at: https://phys.org/news/2018-03-genetic-explosion-diversity-fish-end-cretaceous.html#jCp
 
Every cloud has a silver lining
A team of researchers from several institutions across the U.S. has found evidence suggesting that there was an explosion of diversity in fish after the end-Cretaceous mass extinction. In their paper published in the journal Nature Ecology and Evolution, the team describes their genetic study involving more than 1800 species of fish and what they found.
https://phys.org/news/2018-03-genetic-explosion-diversity-fish-end-cretaceous.html
Read more at: https://phys.org/news/2018-03-genetic-explosion-diversity-fish-end-cretaceous.html#jCp

In relationship to this topic, there are few things more fascinating and mysterious than the Cambrian Explosion. To this day science is still unable to understand the causes of the sudden upswing in genetic diversity that occurred. The payday for a discovery like that would be a Nobel Prize, with the likelihood of free superpowers, and I am only joking a little bit. You want Fortean? It has it all.
 
In relationship to this topic, there are few things more fascinating and mysterious than the Cambrian Explosion. To this day science is still unable to understand the causes of the sudden upswing in genetic diversity that occurred. The payday for a discovery like that would be a Nobel Prize, with the likelihood of free superpowers, and I am only joking a little bit. You want Fortean? It has it all.

But who planted the bomb?

Putin?

Or was it a black flag op?
 
I don't think it's fair to say that "science is unable to explain" the Cambrian explosion, so much as there are competing theories - which is what science is all about, really.

No offence to yourself, as it's not the context in which you used it, but I always find a phrase like "science is unable to explain" does scientists a disservice, and has a bit too much of an air of the E.L. Wisty-voiced "did you know..." pub bore to them!

I suppose the Cambrian explosion's closest comparison would be to the sudden emergence of flowering plants - things just ticking along quite nicely, then a sudden drastic change in so many directions at once.

The explanation I always remember hearing for the explosion was about changes in the amount of Oxygen in the atmosphere, though apparently that one's considered doubtful now, and it might be about a sudden increase in the levels of calcium in the ocean, meaning organisms were able to develop skeletons and so on.
 
The explanation I always remember hearing for the explosion was about changes in the amount of Oxygen in the atmosphere, though apparently that one's considered doubtful now, and it might be about a sudden increase in the levels of calcium in the ocean, meaning organisms were able to develop skeletons and so on.
The organisms that created the chalk sediments extracted CO2 from the biosphere and bound it into a solid form (chalk is calcium carbonate). This meant that oxygen became a larger proportion of the atmosphere as the CO2 was used up.
 
I don't think it's fair to say that "science is unable to explain" the Cambrian explosion, so much as there are competing theories - which is what science is all about, really.
No offence to yourself, as it's not the context in which you used it, but I always find a phrase like "science is unable to explain" does scientists a disservice, and has a bit too much of an air of the E.L. Wisty-voiced "did you know..." pub bore to them!
I suppose the Cambrian explosion's closest comparison would be to the sudden emergence of flowering plants - things just ticking along quite nicely, then a sudden drastic change in so many directions at once.
The explanation I always remember hearing for the explosion was about changes in the amount of Oxygen in the atmosphere, though apparently that one's considered doubtful now, and it might be about a sudden increase in the levels of calcium in the ocean, meaning organisms were able to develop skeletons and so on.

So... All of a sudden this planet experiences a sudden and inexplicable increase in the number of discrete species of life. These are often entirely bizarre creatures with odd numbers of limbs and lacking symmetry. It is, in effect the diametric opposite of what normally happens to life here, namely mass extinction events, or business as usual with species slowly evolving from prior versions. Out of nowhere in a tiny time frame in terms of evolution, suddenly there is a boom in living diversity that is unseen prior or since. Science says it could have been caused by variously, radiation, increased oxygen, or a major evolutionary advance such as vision. There is in fact no solid evidence to support any of these hypotheses. The most popular is the oxygen increase theory, but it is hotly debated, and I don't buy it. While skeletons definitely appear post Cambrian Explosion, the majority of organisms produced in the period still didn't develop skeletons, similarly there were plenty of predators prior too. In short, all the answers presented are wobbly in the extreme. Something caused a massive but apparently benign increase in species diversity and we don't know what it was with anything approaching certainty. In short "science is unable to explain" in any way that satisfies the scientific community itself.

TO INTERESTED PARTIES:
Here is a nice primer article for those who want in on the debate. It's great and has plenty of footnote links to increase your expertise in the field:
https://www.nature.com/news/what-sparked-the-cambrian-explosion-1.19379#/life
 
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Scientists re-counted Australia's extinct species, and the result is devastating

Source: theconservation.com
Date: 2 December, 2019

It’s well established that unsustainable human activity is damaging the health of the planet. The way we use Earth threatens our future and that of many animals and plants. Species extinction is an inevitable end point.

It’s important that the loss of Australian nature be quantified accurately. To date, putting an exact figure on the number of extinct species has been challenging. But in the most comprehensive assessment of its kind, our research has confirmed that 100 endemic Australian species living in 1788 are now validly listed as extinct.

Alarmingly, this tally confirms that the number of extinct Australian species is much higher than previously thought.

https://theconversation-com.cdn.amp...3A%2F%2Fwww.google.com&amp_tf=From%20%251%24s
 
Isn't that really just a small percentage compared to the known animal and plant species that are at an underestimate at 28k? My point being that it isn't as apocalyptic as the headline and we can do more in the future to learn and remedy.
 
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