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Author Topic:   Rate changes for evolution
Denesha
Inactive Member


Message 3 of 40 (96255)
03-31-2004 6:24 AM
Reply to: Message 1 by Parsimonious_Razor
03-30-2004 8:50 PM


Dear Parsi,
Sudden environmental changes are related to speciation bursts. From Cretaceous and Paleogene fossils, more species appear after transgressive events and flooding. It's quite stable between.
Eldredge and Gould's theory explain some things.
It's a theory.
Denesha

This message is a reply to:
 Message 1 by Parsimonious_Razor, posted 03-30-2004 8:50 PM Parsimonious_Razor has replied

Replies to this message:
 Message 6 by Parsimonious_Razor, posted 03-31-2004 2:41 PM Denesha has not replied

  
Denesha
Inactive Member


Message 21 of 40 (96582)
04-01-2004 7:15 AM
Reply to: Message 20 by mark24
04-01-2004 4:00 AM


Dear Mark24,
Relating fossils with fine accurate datation is alsmost very risky. Shells, bones, teeth don't have the same taphonomic life-time. When PE was edified, little was known concerning the time-averaging. It was assumed that fossils and sediment had same age. This is not fully well supported now.
Denesha

This message is a reply to:
 Message 20 by mark24, posted 04-01-2004 4:00 AM mark24 has replied

Replies to this message:
 Message 22 by mark24, posted 04-01-2004 9:46 AM Denesha has replied

  
Denesha
Inactive Member


Message 23 of 40 (96604)
04-01-2004 10:06 AM
Reply to: Message 22 by mark24
04-01-2004 9:46 AM


Sorry Mark,
I observe time-averaging of more than 50 million years (maxi observed yet) in some Cenozoic sediments. This depend of the tenacity of the fossil. They are often re-incorporated in more recent sedimentation events.
Denesha

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Denesha
Inactive Member


Message 28 of 40 (96652)
04-01-2004 2:43 PM
Reply to: Message 27 by PaulK
04-01-2004 2:25 PM


Yes, I reached the same conclusion.
Denesha

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Replies to this message:
 Message 36 by Brad McFall, posted 04-02-2004 11:33 AM Denesha has replied

  
Denesha
Inactive Member


Message 35 of 40 (96989)
04-02-2004 4:57 AM
Reply to: Message 32 by mark24
04-01-2004 5:37 PM


too short for fossils
Dear Mark24,
I think that 100Ky is too short for speciation based on fossils. This time is more likely a colonisation or secondary invasion time-duration.
Denesha

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Denesha
Inactive Member


Message 37 of 40 (97448)
04-03-2004 7:56 AM
Reply to: Message 36 by Brad McFall
04-02-2004 11:33 AM


Re: this is not rethorical.
Dear Brad,
I will say yes and no. We are limited in our investigation by the fact that we only have fossilized parts of past species.
Paleospecies are only known by that. This is true, unfortunately.
To take account of this subjetivity, it is assumed that mutations have always occured but have not changed the phenotype is most case.
Chronospecies are the best examples.
This inaccuracy is a parameter. A step ahead in objectivity?
Have a nice day,
Denesha

This message is a reply to:
 Message 36 by Brad McFall, posted 04-02-2004 11:33 AM Brad McFall has replied

Replies to this message:
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