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Author Topic:   Is evolution of mammals finished?
Lithodid-Man
Member (Idle past 1218 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 32 of 213 (385699)
02-16-2007 9:06 PM
Reply to: Message 20 by MartinV
02-11-2007 9:43 AM


Marine K-T extinctions
And might be there were no vacant niches in the oceans at all. Yet land mammals pushed back all species from their "local maximums" there. Might be that on the land there were much more emtied niches as in the ocean at that time and yet the evolution was driven in some cases by internal forces to the sea whatever it cost.

Anyway I have never heard about adaptive radiation of water species during the period discussed. The greatest adaptive radiation in the ocean I know about occured during cambrian explosion. So preliminary I would not bet a nickel on it.

Then you would be wise as you would lose your nickle, sorry. The K-T event devastaed shallow water marine ecosystems. The ammonites, huge predatory cephalopds (coiled shells 3 meters across) were extremely widespread and diverse. These probably had a top-down control on prey items (IOW Cretaceous bad time to start evolving from terrestrial to aquatic). Belemites, another group of cephalopods were also extinct after this event. Rudists were very large bivalves (not closely related to any living bivalves) that formed massive reefs in Cretaceous seas and kilo for kilo probably accounted for most of the aquatic biomass in shallow seas. Completely absent after the Creataceous.

Echinoids (sea urchins and their kin) lost pretty much all of their diversity as did brachiopods. Large numbers of fish families became extinct. Marine phytoplankton groups like diatoms and coccolithophores crashed in both numbers and diversity. In the large vertebrate world (those that might have occupied niches to be later filled by pinnipeds and cetaceans) all of the marine reptiles went extinct. This, btw, includes the marine crocodylians. The group including modern marine crocodiles are not known until the Tertiary so your statement in another post about no change in crocodile diversity is, well, a crock (just an aside, and maybe this was an error, but you might want to avoid citing undergraduate web projects as primary sources. Especially when those sources do not contain the info you claim anyhow).

Nearly all of our shallow water marine mollusks and echindoderms are families which diversified since the K-T event. Decapod crustaceans (crabs, lobsters, shrimp) evolved prior to the event but exploded in diversity during the Tertiary.

Edited by Lithodid-Man, : Forgot to add what did diversify during the Tertiary!


Doctor Bashir: "Of all the stories you told me, which were true and which weren't?"
Elim Garak: "My dear Doctor, they're all true"
Doctor Bashir: "Even the lies?"
Elim Garak: "Especially the lies"

This message is a reply to:
 Message 20 by MartinV, posted 02-11-2007 9:43 AM MartinV has responded

Replies to this message:
 Message 34 by MartinV, posted 02-17-2007 8:51 AM Lithodid-Man has responded

  
Lithodid-Man
Member (Idle past 1218 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 42 of 213 (385905)
02-18-2007 12:35 AM
Reply to: Message 34 by MartinV
02-17-2007 8:51 AM


Re: Marine K-T extinctions
Yet sharks seems to thrive as well as once. For instance:

(from the Big Shift article)
The most recent elasmobranch radiation coincided with the mammalian radiation which eventually produced ourselves. Modern elasmobranchs are thus the distilation of millions of years of experiments in How to Build a Predator.

You either failed to read or failed to understand your source. The page you cited, "The Big Shift by Richard Martin (http://web.ncf.ca/bz050/bigshift.html) is about the diversification of elasmobranchs after the K-T event. Meaning that the species which survived the event subsequently filled the niches left empty. In the quote above Martin states clearly "The most recent elasmobranch radiation coincided with the mammalian radiation..." (bold mine). He is talking about what occured after the event which destroyed nearly all shallow water and terrestrial species over 50 kg.

MartinV writes:

Some types of sharks became even non-predatory animals - Basking shark, White shark. So I would say there were not enough "emptied niches" for all predatory sharks.

First of all, and I am sure it is a typo, white sharks are indeed predatory. The evolution of 'filter feeding' (btw, I hate that term. In my classes it is known as the "F-word" because I take off points when I see it used on a paper) has absolutely nothing to do with a lack of emptied niches. It makes no more sense than to say whales evolved to swim because all of the walking niches were filled. Suspension feeding (<-- used instead of the F-word) typically evolves as predators specialize in capturing small but abundant prey.


Doctor Bashir: "Of all the stories you told me, which were true and which weren't?"
Elim Garak: "My dear Doctor, they're all true"
Doctor Bashir: "Even the lies?"
Elim Garak: "Especially the lies"

This message is a reply to:
 Message 34 by MartinV, posted 02-17-2007 8:51 AM MartinV has responded

Replies to this message:
 Message 43 by MartinV, posted 02-18-2007 7:47 AM Lithodid-Man has not yet responded
 Message 48 by RAZD, posted 02-18-2007 2:06 PM Lithodid-Man has not yet responded

  
Lithodid-Man
Member (Idle past 1218 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 55 of 213 (386036)
02-19-2007 6:59 AM
Reply to: Message 54 by MartinV
02-19-2007 2:49 AM


Re: Marine K-T extinctions and opportunity
Yet cold-blooded reptiles could survive quite well.
It seems like warm-bloodeness was disatvantage during K/T boundary - but only for dinos. For mammals it was somehow advantageous.

It wasn't cold or warm bloodedness that made the decision ultimately. It was a giant freakin rock that killed everything on the planet (except maybe deep sea oganisms) over 50 kg in size. Trees, dinosaurs, mammals, reptiles, birds, sharks, the like. The clock was reset at the K-T boundry. Very few species survived, but those species quickly evolved to fill the empty niches. Birds made it, mammals made it. Some evidence from Alaska suggests that even some dinos made it for a short time.

I think size was the ultimate factor. Little things or those who could hibernate did better than those who were swift and powerful. In the terresrial realm it was the mammals who were excluded from dino niches. They undoubtedly suffered massive extinctions. But only two main lineages exist today (Protheria and Theria).


Doctor Bashir: "Of all the stories you told me, which were true and which weren't?"
Elim Garak: "My dear Doctor, they're all true"
Doctor Bashir: "Even the lies?"
Elim Garak: "Especially the lies"

This message is a reply to:
 Message 54 by MartinV, posted 02-19-2007 2:49 AM MartinV has not yet responded

  
Lithodid-Man
Member (Idle past 1218 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 67 of 213 (386188)
02-20-2007 5:33 AM
Reply to: Message 65 by MartinV
02-20-2007 5:21 AM


Re: Marine K-T extinctions and opportunity
MartinV writes:

My point is that they entered environment with fully adapted predators and yet there was enough space and nurture for them too. If the nurture is really no problem as you seems to admit with your "shopping store" story I see no selective pressure in the Nature at all. All development subsequently was a matter of "internal factors" .

This whole post makes absolutely no sense. I am assuing you were wasted when you wrote this and should be given an opportuninty to repost your point.

Eagerly await the repost.


Doctor Bashir: "Of all the stories you told me, which were true and which weren't?"
Elim Garak: "My dear Doctor, they're all true"
Doctor Bashir: "Even the lies?"
Elim Garak: "Especially the lies"

This message is a reply to:
 Message 65 by MartinV, posted 02-20-2007 5:21 AM MartinV has responded

Replies to this message:
 Message 68 by MartinV, posted 02-20-2007 9:53 AM Lithodid-Man has not yet responded

  
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