Not deep, but interesting nevertheless.

https://cosmosmagazine.com/palaeontology/big-five-extinctions

PermeateFree said:

Not deep, but interesting nevertheless.

https://cosmosmagazine.com/palaeontology/big-five-extinctions

Excellent. Of course it misses the biggest of all. The end of the Precambrian. 542 million years ago. Loss of Ediacaran fauna worldwide. Proportion of species driven extinct, not sure. Let’s see, 210 genera of metazoa of whom 3 survived – sponges, worms and bilateria. Other than metazoa, some red and green algae, protists and bacteria survived. Say somewhere between 95% and 99% extinction rate, as compared to a 96% extinction rate at the end of the Permian.

Sometime in future I ought to look up DNA comparisons to see which modern species diverged before the Cambrian.

There may have been even bigger extinctions long before that. The arrival and spread of blue-green algae 2.5 billion years ago caused a massive extinction of anaerobic bacteria.

> Biologists suspect we’re living through the sixth major mass extinction.

Not really. More a minor mass extinction.

I’ve seen a chart plotting massive volcanic eruptions (flood basalts) together with the five major mass extinctions. For every one of the five major mass extinctions there was a massive volcanic eruption at close to the same time. This isn’t proof of cause and effect but it is suggestive.

> Sometime in future I ought to look up DNA comparisons to see which modern species diverged before the Cambrian.

Looking at https://academic.oup.com/icb/article/43/1/148/604496

“Molecular data is also providing a new and controversial timescale for the evolution of animal phyla, pushing the major divisions of the animal kingdom deep into the Precambrian.”

“The near-simultaneous appearance in the early Cambrian of the first recognizable members of many animal phyla, at high diversity and with few clear precursors, has been attributed by many researchers an incomplete fossil record (e.g.,Darwin, 1859)”.

“the sudden appearance of animal phyla in the fossil record, the discontinuity between animal body plans, and mutations that bring about discrete body-plan-like changes—have been combined in the hypothesis that the evolution of animal body plans did not occur by the gradual accumulation of small genetic differences, but by relatively few developmental changes with large phenotypic effects”.

Up until now, mollwollfumble has believed that. But arguments against it are found from DNA studies related to much later K-T extinction.

From http://www.pnas.org/content/101/17/6536

“Although the Cambrian explosion is of singular importance to our understanding of the history of life, it continues to defy explanation. This defiance stems, in part, from our inability to distinguish between two competing hypotheses: whether the Cambrian explosion reflects the rapid appearance of fossils with animals having a deep but cryptic Precambrian history, or whether it reflects the true sudden appearance and diversification of animals in the Cambrian.”

“The earliest unequivocally bilaterian fossils are ≈555 million years old. In contrast, molecular-clock analyses calibrated by using the fossil record of vertebrates estimate that vertebrates split from dipterans (Drosophila) ≈900 million years ago (Ma). We estimate that the last common ancestor of bilaterians arose somewhere between 573 and 656 Ma”.

From http://www.pnas.org/content/98/5/2497?ijkey=c45f41cfcad735e5151802203e96e601534d2fb0&keytype2=tf_ipsecsha

Note from the bottom of this figure how far the ancestry of vertebrates, insects and worms extends into the Precambrian. Nowhere near the end of the Precambrian at 524 Ma. Together with the DNA evidence from the K-T extinction, this sheds a completely new light on the extinction rates in the big mass extinctions. ie. there were a lot of organisms that survived these extinctions for which no fossils are known from before the extinction, because they were rare.

mollwollfumble said:

Note from the bottom of this figure how far the ancestry of vertebrates, insects and worms extends into the Precambrian. Nowhere near the end of the Precambrian at 524 Ma. Together with the DNA evidence from the K-T extinction, this sheds a completely new light on the extinction rates in the big mass extinctions. ie. there were a lot of organisms that survived these extinctions for which no fossils are known from before the extinction, because they were rare.

Not also that the human and rat diverged 120 million years ago, which is 52 million years before the first tyrannosaurus.

Ancient history would be very much supposition I imagine, its so long ago, very little evidence remains for what happened and even that is incomplete. Perhaps evolution is both gradual and rapid depending on circumstances.

Cymek said:

Ancient history would be very much supposition I imagine, its so long ago, very little evidence remains for what happened and even that is incomplete. Perhaps evolution is both gradual and rapid depending on circumstances.

Undoubtedly the case.

Can we assume ancient ecosystems would be as complex as ours

>>As the Ediacaran biota represent an early stage in multicellular life’s history, it is unsurprising that not all possible modes of life are occupied. It has been estimated that of 92 potentially possible modes of life – combinations of feeding style, tiering and motility — no more than a dozen are occupied by the end of the Ediacaran. Just four are represented in the Avalon assemblage. The lack of large-scale predation and vertical burrowing are perhaps the most significant factors limiting the ecological diversity; the emergence of these during the Early Cambrian allowed the number of lifestyles occupied to rise to 30.<< Wiki

In those early days of multicellular life there was apparently not much diversity and hence species. So a high percentage loss is not as critical then as it would be today with our myriad of multicellular species.

>>Biologists suspect we’re living through the sixth major mass extinction. Earth has witnessed five, when more than 75% of species disappeared. Palaeontologists spot them when species go missing from the global fossil record, including the iconic specimens shown here. “We don’t always know what caused them but most had something to do with rapid climate change”, says Melbourne Museum palaeontologist Rolf Schmidt.<< OP

We are currently heading for rapid climate change that will affect vastly more species than at any time in the past. Why moll should think it would only be a small mass extinction is more than surprising.

Cymek said:

Can we assume ancient ecosystems would be as complex as ours

No far from it.

PermeateFree said:

Cymek said:

Can we assume ancient ecosystems would be as complex as ours

No far from it.

That would make sense if they aren’t as they wouldn’t have had time to evolve

PermeateFree said:

>>As the Ediacaran biota represent an early stage in multicellular life’s history, it is unsurprising that not all possible modes of life are occupied. It has been estimated that of 92 potentially possible modes of life – combinations of feeding style, tiering and motility — no more than a dozen are occupied by the end of the Ediacaran. Just four are represented in the Avalon assemblage. The lack of large-scale predation and vertical burrowing are perhaps the most significant factors limiting the ecological diversity; the emergence of these during the Early Cambrian allowed the number of lifestyles occupied to rise to 30.<< Wiki

In those early days of multicellular life there was apparently not much diversity and hence species. So a high percentage loss is not as critical then as it would be today with our myriad of multicellular species.

>>Biologists suspect we’re living through the sixth major mass extinction. Earth has witnessed five, when more than 75% of species disappeared. Palaeontologists spot them when species go missing from the global fossil record, including the iconic specimens shown here. “We don’t always know what caused them but most had something to do with rapid climate change”, says Melbourne Museum palaeontologist Rolf Schmidt.<< OP

We are currently heading for rapid climate change that will affect vastly more species than at any time in the past. Why moll should think it would only be a small mass extinction is more than surprising.

Plus with our incomplete knowledge certain species becoming extinct could cause a huge cascade effect leading to thousands of other dying as well.

PermeateFree said:

Cymek said:

Can we assume ancient ecosystems would be as complex as ours

No far from it.

How ancient are we talking? I fail to see why the Earth during the age of the dinosaurs supported less complex ecosystems?

Witty Rejoinder said:

PermeateFree said:

Cymek said:

Can we assume ancient ecosystems would be as complex as ours

No far from it.

How ancient are we talking? I fail to see why the Earth during the age of the dinosaurs supported less complex ecosystems?

The age of the dinosaurs I was wondering about, it would have been quite complex I imagine to support such large animals.

Witty Rejoinder said:

PermeateFree said:

Cymek said:

Can we assume ancient ecosystems would be as complex as ours

No far from it.

How ancient are we talking? I fail to see why the Earth during the age of the dinosaurs supported less complex ecosystems?

You had a lot of dinosaurs, but few smaller animals like mammals, probably because many dinosaurs were highly effective predators. But probably the most important is the lack of flora diversity and the animals, especially the insects that went with it.

PermeateFree said:

Witty Rejoinder said:

PermeateFree said:

No far from it.

How ancient are we talking? I fail to see why the Earth during the age of the dinosaurs supported less complex ecosystems?

But probably the most important is the lack of flora diversity and the animals, especially the insects that went with it.

This is true.

Cymek said:

Witty Rejoinder said:

PermeateFree said:

No far from it.

How ancient are we talking? I fail to see why the Earth during the age of the dinosaurs supported less complex ecosystems?

The age of the dinosaurs I was wondering about, it would have been quite complex I imagine to support such large animals.

The vegetation was not very diverse and from which each species provides a niche for other species to occupy. Lack of habitat diversity = fewer species.

PermeateFree said:

Cymek said:

Witty Rejoinder said:

How ancient are we talking? I fail to see why the Earth during the age of the dinosaurs supported less complex ecosystems?

The age of the dinosaurs I was wondering about, it would have been quite complex I imagine to support such large animals.

The vegetation was not very diverse and from which each species provides a niche for other species to occupy. Lack of habitat diversity = fewer species.

Flowering plants didn’t exist did they, is that certain would they fossilise and if not we assume they didn’t exist
I wonder if a minimum number of flora/fauna exists to support a long term ecosystem.

Cymek said:

PermeateFree said:

Cymek said:

The age of the dinosaurs I was wondering about, it would have been quite complex I imagine to support such large animals.

The vegetation was not very diverse and from which each species provides a niche for other species to occupy. Lack of habitat diversity = fewer species.

Flowering plants didn’t exist did they, is that certain would they fossilise and if not we assume they didn’t exist
I wonder if a minimum number of flora/fauna exists to support a long term ecosystem.

They evolved a little over 100 million years ago, but needed habitat diversity to develop to any extent. The slow development was because they needed a more open environment rather than the closed fern and conifer forests.

PermeateFree said:

Cymek said:

Can we assume ancient ecosystems would be as complex as ours

No far from it.

I was just reading about a scientific study of this.

It was concluded that Ediacaran ecosystems were 12% as complex as ours. In the sense that Ediacaran ecosystems utilised 12% of the environmental niches (feeding strategies) used by organisms today.

mollwollfumble said:

PermeateFree said:

Cymek said:

Can we assume ancient ecosystems would be as complex as ours

No far from it.

I was just reading about a scientific study of this.

It was concluded that Ediacaran ecosystems were 12% as complex as ours. In the sense that Ediacaran ecosystems utilised 12% of the environmental niches (feeding strategies) used by organisms today.

What sort of margin of error does that have though, out of all the fossils found I wonder how many species aren’t represented, could be in the order of 1 out a 100,000 species becomes fossilised and only 1 or 2 out of a million of that species dies in a manner allowed them to become fossilised.

Cymek said:

mollwollfumble said:

PermeateFree said:

No far from it.

I was just reading about a scientific study of this.

It was concluded that Ediacaran ecosystems were 12% as complex as ours. In the sense that Ediacaran ecosystems utilised 12% of the environmental niches (feeding strategies) used by organisms today.

What sort of margin of error does that have though, out of all the fossils found I wonder how many species aren’t represented, could be in the order of 1 out a 100,000 species becomes fossilised and only 1 or 2 out of a million of that species dies in a manner allowed them to become fossilised.

The same creatures were spread far and wide indicating limited diversity.

PermeateFree said:

Cymek said:

mollwollfumble said:

I was just reading about a scientific study of this.

It was concluded that Ediacaran ecosystems were 12% as complex as ours. In the sense that Ediacaran ecosystems utilised 12% of the environmental niches (feeding strategies) used by organisms today.

What sort of margin of error does that have though, out of all the fossils found I wonder how many species aren’t represented, could be in the order of 1 out a 100,000 species becomes fossilised and only 1 or 2 out of a million of that species dies in a manner allowed them to become fossilised.

The same creatures were spread far and wide indicating limited diversity.

It seemed to have worked though, some of the ecosystems lasted a long time, I wonder how our present day ecosystem would last if humans didn’t exist. Seems that often some sort of huge outside event triggers an extinct event and most life resets. If we didn’t have asteroids strikes, volcanoes, ice ages, etc could an eco system last for billions of years. Changes would be gradually allowing adaption instead of just dying

Cymek said:

mollwollfumble said:

PermeateFree said:

No far from it.

I was just reading about a scientific study of this.

It was concluded that Ediacaran ecosystems were 12% as complex as ours. In the sense that Ediacaran ecosystems utilised 12% of the environmental niches (feeding strategies) used by organisms today.

What sort of margin of error does that have though, out of all the fossils found I wonder how many species aren’t represented, could be in the order of 1 out a 100,000 species becomes fossilised and only 1 or 2 out of a million of that species dies in a manner allowed them to become fossilised.

I can answer that. There are at least two places in the world where entire Ediacaran ecosystems were buried at once. These are called Ediacaran assemblages. The analysis was done on these assemblages, comparing them to modern assemblages.

Cymek said:

PermeateFree said:

Cymek said:

What sort of margin of error does that have though, out of all the fossils found I wonder how many species aren’t represented, could be in the order of 1 out a 100,000 species becomes fossilised and only 1 or 2 out of a million of that species dies in a manner allowed them to become fossilised.

The same creatures were spread far and wide indicating limited diversity.

It seemed to have worked though, some of the ecosystems lasted a long time, I wonder how our present day ecosystem would last if humans didn’t exist. Seems that often some sort of huge outside event triggers an extinct event and most life resets. If we didn’t have asteroids strikes, volcanoes, ice ages, etc could an eco system last for billions of years. Changes would be gradually allowing adaption instead of just dying

Not much Ediacaran fauna survived and their linage did not persist.

mollwollfumble said:

PermeateFree said:

Cymek said:

Can we assume ancient ecosystems would be as complex as ours

No far from it.

I was just reading about a scientific study of this.

It was concluded that Ediacaran ecosystems were 12% as complex as ours. In the sense that Ediacaran ecosystems utilised 12% of the environmental niches (feeding strategies) used by organisms today.

If you compared Ediacaran marine with recent marine, how would that work out?

I mean, land had yet to be colonised.

PermeateFree said:

Cymek said:

PermeateFree said:

The same creatures were spread far and wide indicating limited diversity.

It seemed to have worked though, some of the ecosystems lasted a long time, I wonder how our present day ecosystem would last if humans didn’t exist. Seems that often some sort of huge outside event triggers an extinct event and most life resets. If we didn’t have asteroids strikes, volcanoes, ice ages, etc could an eco system last for billions of years. Changes would be gradually allowing adaption instead of just dying

Not much Ediacaran fauna survived and their linage did not persist.

I would also be interesting to see if life forms were recycled, ie a insect existed 100 millions years ago and evolved again a second time and the DNA is the same (could that happen I wonder or would slight difference exist due to the climate being different)

Cymek said:

If we didn’t have asteroids strikes, volcanoes, ice ages, etc could an eco system last for billions of years. Changes would be gradually allowing adaption instead of just dying

It’s an interesting question. I think now that the answer is no. (If you had asked me even six months ago then my answer would have been different).

Consider the Tyranosaurs for instance, as a genus they lasted just 2 million years. There was no disaster that called them into existence, but in that short geological time they took over North America.

Cymek said:

PermeateFree said:

Cymek said:

It seemed to have worked though, some of the ecosystems lasted a long time, I wonder how our present day ecosystem would last if humans didn’t exist. Seems that often some sort of huge outside event triggers an extinct event and most life resets. If we didn’t have asteroids strikes, volcanoes, ice ages, etc could an eco system last for billions of years. Changes would be gradually allowing adaption instead of just dying

Not much Ediacaran fauna survived and their linage did not persist.

I would also be interesting to see if life forms were recycled, ie a insect existed 100 millions years ago and evolved again a second time and the DNA is the same (could that happen I wonder or would slight difference exist due to the climate being different)

The are many cases of things evolving more than once. The eye and sight is a good example.

mollwollfumble said:

Cymek said:

If we didn’t have asteroids strikes, volcanoes, ice ages, etc could an eco system last for billions of years. Changes would be gradually allowing adaption instead of just dying

It’s an interesting question. I think now that the answer is no. (If you had asked me even six months ago then my answer would have been different).

Consider the Tyranosaurs for instance, as a genus they lasted just 2 million years. There was no disaster that called them into existence, but in that short geological time they took over North America.

The ecosystems are unlikely to survive, but some of the animals from them may and adapt to a new ecosystem that develops from the new environment.

PermeateFree said:

Cymek said:

PermeateFree said:

Not much Ediacaran fauna survived and their linage did not persist.

I would also be interesting to see if life forms were recycled, ie a insect existed 100 millions years ago and evolved again a second time and the DNA is the same (could that happen I wonder or would slight difference exist due to the climate being different)

The are many cases of things evolving more than once. The eye and sight is a good example.

Complete animals or plants I mean, DNA would have limited expression even if that number is quite high

Cymek said:

PermeateFree said:

Cymek said:

I would also be interesting to see if life forms were recycled, ie a insect existed 100 millions years ago and evolved again a second time and the DNA is the same (could that happen I wonder or would slight difference exist due to the climate being different)

The are many cases of things evolving more than once. The eye and sight is a good example.

Complete animals or plants I mean, DNA would have limited expression even if that number is quite high

DNA is applicable to the species and its linage. So if one species goes extinct the DNA continues on in others, and if the extinct species has left an unoccupied niche, then a related species might move in to fill it. It is all about habitat and its occupants.

Cymek said:

PermeateFree said:

Cymek said:

I would also be interesting to see if life forms were recycled, ie a insect existed 100 millions years ago and evolved again a second time and the DNA is the same (could that happen I wonder or would slight difference exist due to the climate being different)

The are many cases of things evolving more than once. The eye and sight is a good example.

Complete animals or plants I mean, DNA would have limited expression even if that number is quite high

I’d be very surprised if the same DNA sequences evolved a second time or more. Too much variability in the moulding environment. Might get a similar organism, but I suspect the randomness would not allow exactness.

PermeateFree said:

The are many cases of things evolving more than once. The eye and sight is a good example.

That’s an interesting one. In CSIRO I came across a single celled alga with eyes. Not the Euglena (see below) but very similar.

https://www.britannica.com/science/eyespot-biology

“Eyespot, also called stigma, a heavily pigmented region in certain one-celled organisms that apparently functions in light reception. The term is also applied to certain light-sensitive cells in the epidermis (skin) of some invertebrate animals (e.g., worms, starfishes). In the green one-celled organism Euglena, the eyespot is located in the gullet, at the base of the flagellum (a whiplike locomotory structure). A cup-shaped mass of pigment rods shields a sensitive area of the flagellar base from light coming from the direction of the opposite end of the organism. The light-sensitive region apparently influences flagellar motion in such a manner that the organism moves toward light.”

Now Animals and Fungi are classed together in the Opisthokonta. The name comes from the Greek meaning “flagellum”. Euglena are from the group of protists containing flagella.

So could it be that the eye is ancestral to all animals? It’s just a hypothesis, but an interesting one. If so, then the eye didn’t develop independently in different animals, and what developed differently is the lens(es) of the eye.

mollwollfumble said:

PermeateFree said:

The are many cases of things evolving more than once. The eye and sight is a good example.

That’s an interesting one. In CSIRO I came across a single celled alga with eyes. Not the Euglena (see below) but very similar.

https://www.britannica.com/science/eyespot-biology

“Eyespot, also called stigma, a heavily pigmented region in certain one-celled organisms that apparently functions in light reception. The term is also applied to certain light-sensitive cells in the epidermis (skin) of some invertebrate animals (e.g., worms, starfishes). In the green one-celled organism Euglena, the eyespot is located in the gullet, at the base of the flagellum (a whiplike locomotory structure). A cup-shaped mass of pigment rods shields a sensitive area of the flagellar base from light coming from the direction of the opposite end of the organism. The light-sensitive region apparently influences flagellar motion in such a manner that the organism moves toward light.”

Now Animals and Fungi are classed together in the Opisthokonta. The name comes from the Greek meaning “flagellum”. Euglena are from the group of protists containing flagella.

So could it be that the eye is ancestral to all animals? It’s just a hypothesis, but an interesting one. If so, then the eye didn’t develop independently in different animals, and what developed differently is the lens(es) of the eye.

There are so many types of eye, the eyes of insects and those of a bird of prey, fish, etc., to being just being light sensitive. Eyes are so diverse and spread over such distantly related groups it is difficult to see any linear progression.

Cymek said:

I would also be interesting to see if life forms were recycled, ie a insect existed 100 millions years ago and evolved again a second time and the DNA is the same (could that happen I wonder or would slight difference exist due to the climate being different)

I’d be extremely surprised (to the point of disbelief) if two organisms with identical DNA evolved at different times. Consider the relatively simple DNA shift that causes field crickets (Teleogryllus oceanicus) to lose their chirping ability: we know it’s happened at least twice, in two different populations of crickets, with different DNA mutations. See, for instance, Rapid Convergent Evolution in Wild Crickets, Current Biology, Vol 24, issue 12, May 2014.

btm said:

Cymek said:

I would also be interesting to see if life forms were recycled, ie a insect existed 100 millions years ago and evolved again a second time and the DNA is the same (could that happen I wonder or would slight difference exist due to the climate being different)

I’d be extremely surprised (to the point of disbelief) if two organisms with identical DNA evolved at different times. Consider the relatively simple DNA shift that causes field crickets (Teleogryllus oceanicus) to lose their chirping ability: we know it’s happened at least twice, in two different populations of crickets, with different DNA mutations. See, for instance, Rapid Convergent Evolution in Wild Crickets, Current Biology, Vol 24, issue 12, May 2014.

I was about to say I totally agreed. And I still do totally agree.

But I happen to know of a couple of cases where the same DNA mutation has occurred multiple times. Not too unexpected, and these are micro-changes, not cases of convergent evolution.

Case 1. Down syndrome. The loss of chromosome 21 has occurred independently many times.
Case 2. Achondroplasic dwarfs. A mutation on chromosome 4.
Case 3. Albinism. Shared by animals as diverse as mammals, birds, fish, molluscs, insects, echinoderms.

These are not necessarily good examples because different DNA mutations can have the same physical effects.