Thread: Extinction and Evolution

Could a mass extinction lead to an increased level of evolution for those species remaining? There would be niches left unfilled that other species could move into and over time adapt to fill as well as the specie that was removed from it.

*cough*the age of mammals.. *cough* P–Tr extinction *cough*

*cough*I'm not well versed in evolutionary history.*cough*

Originally Posted by Chemboy

*cough*I'm not well versed in evolutionary history.*cough*

Sorry man. Didn't mean that in an obtuse way. The mass extinction of dinosaurs 65 mya led to the success and diversification of mammals. The Permian-Triassic mass extinction took place around 250 mya. It was the Earth's most severe extinction event, with up to 96 percent of all marine species and 70 percent of terrestrial vertebrate species becoming extinct. Also, it's the only mass extinction event involving insects.



From Wikipedia (concerning the results of the Permian mass extinction, or the Great Dying, as it's colloquially known):

Lystrosaurus, a pig-sized herbivorous dicynodont therapsid, constituted as much as 90% of some earliest Triassic land vertebrate faunas.[10] Smaller carnivorous cynodont therapsids also survived, including the ancestors of mammals. In the Karoo region of southern Africa the therocephalians Tetracynodon, Moschorhinus and Ictidosuchoides survived but do not appear to have been abundant in the Triassic.[64]
Archosaurs (which included the ancestors of dinosaurs and crocodilians) were initially rarer than therapsids, but they began to displace therapsids in the mid-Triassic.[10] In the mid to late Triassic the dinosaurs evolved from one group of archosaurs, and went on to dominate terrestrial ecosystems for the rest of the Mesozoic.[65] This "Triassic Takeover" may have contributed to the evolution of mammals by forcing the surviving therapsids and their mammaliform successors to live as small, mainly nocturnal insectivores; nocturnal life probably forced at least the mammaliforms to develop fur and higher metabolic rates.

Originally Posted by Chemboy

Could a mass extinction lead to an increased level of evolution for those species remaining? There would be niches left unfilled that other species could move into and over time adapt to fill as well as the specie that was removed from it.

Think K-T boundary - extinction of dinosaurs (except the birds) and the number of niches that thereby opened up for the mammals. (About 65mya.)

ok. thanks. I did know about mammals becoming more prominent after the dinosaurs, but that kind of thing isn't toward the front of my mind so I didn't think of it as an answer to my question. Makes sense.

Any extinction event changes the environment and so creates opportunities. Potential competitors have been eliminated. It is not just on the large scale referred to by Gotspeiler and sunshine warrior, but any small scale extinction, even of a single species will change the opportunities for surviving species.

Originally Posted by Chemboy

Could a mass extinction lead to an increased level of evolution for those species remaining? There would be niches left unfilled that other species could move into and over time adapt to fill as well as the specie that was removed from it.

Hell yeah. This is actually a pretty huge field in paleontology that has discovered a lot of interesting evolutionary effects.

For example, there is a continuum of taxa from disaster to disaster-opportunist to opportunist that essentially thrive in the aftermath of mass extinctions and then fade away into obscurity after a few million years when the biosphere has fully recovered.

This shock interval is also associated with the idea of 'permissive ecology', namely that there are intervals of evolution where selectionis altered/limited allowing for unique body plans to arise that aren't necessarily 'fit'. This is one of the ideas behind some of the very odd and interesting phylums that arose in the Cambrian but have not been seen since.

Additionally, there are other effects such as Lazarus taxa: fossils that 'rise from the dead' in the sense that they are present before the mass extinction, disappear for a few million years after the extinction, but then mysteriously show up again in overlying strata.

that sounds very cool. I'd like to learn more about that now. Not that I have much extra time these days... Thanks.

Relates to the discussion in another thread about 'regular background rate' of evolution vs 'Punctuated Equilibrium" - where catastrophic changes lead to very fast evolution in spurts.

Lie the cambrian explosion? But, as a consequence of that, there was an extinction in the Cambrian.

Permian, KT, triassic extinctions all triggered massive evolutionary spurts, however.

I am unfamiliar with the end of the PreCambrian - is there was also a major shift in the geology denoting a global change in environment?

I understood that the Cambrian explosion is mainly interpreted due to life evolving the chitonous shell.

Was that explosion over the course of millenia or possibly mere decades? At what rate is evolutionary change considered 'breakneck speed'?

Originally Posted by C_Sensei

Was that explosion over the course of millenia or possibly mere decades? At what rate is evolutionary change considered 'breakneck speed'?

The explosion was over a few million years, but this saw the emergence of entire phyla, not just new species, or genera or families.
It is possible that the change was triggered by emergence from a snowball Earth episode in which almost all the oceans froze over.

Originally Posted by Ophiolite

Any extinction event changes the environment and so creates opportunities. Potential competitors have been eliminated. It is not just on the large scale referred to by Gotspeiler and sunshine warrior, but any small scale extinction, even of a single species will change the opportunities for surviving species.

Maddening to conservationists of the Pacific Northwest: we see tremendous expansion of biodiversity after clearcutting old growth forest.

Originally Posted by Pong

Maddening to conservationists of the Pacific Northwest: we see tremendous expansion of biodiversity after clearcutting old growth forest.

Mow down a conservationist and a diverse team of uniformed police, detectives, forensic experts, reporters and casual bystanders spring up in their place.

Originally Posted by Ophiolite

Originally Posted by C_Sensei

Was that explosion over the course of millenia or possibly mere decades? At what rate is evolutionary change considered 'breakneck speed'?

The explosion was over a few million years, but this saw the emergence of entire phyla, not just new species, or genera or families.
It is possible that the change was triggered by emergence from a snowball Earth episode in which almost all the oceans froze over.

all chichlid species in lake victoria evolved in 12.000 years.

That's no time whatsoever on the geological time scale.

Originally Posted by pong

Maddening to conservationists of the Pacific Northwest: we see tremendous expansion of biodiversity after clearcutting old growth forest.

That is 1) irrelevant to a discussion of evolution; 2) probably false. No one has done a good survey of biodiversity in an old growth forest in the Pacific Northwest; and 3) not a big concern of "conservationists". They measure biodiversity over larger areas, and clearcutting old growth reduces the biodiversity of the larger area - the clearcut stuff is common elsewhere and quickly replaced wherever extinguished, the old growth rare and irreplaceable.