Darwin re-visited

[Pyrotex]

We haven't discussed this scenario as yet.. and it is quite possible.. but I would think there would be fossils to back this up. Current genome research on simple animals seems to suggest a shared complexity of genes from thebeginning . See cone jellyfish in the news section of this forum.

Ahhh, but the fossils are there. "Wonderful Life" by Gould. The story of the Burgess Shale.

[Thunderbird]

Ahhh, but the fossils are there. "Wonderful Life" by Gould. The story of the Burgess Shale.

 

 

 

This senerio could account for Arthropods, but still fish and gastropods, I can't see or even Imagine the common morphological linkage.

I can Imagine three separate tree's of life sprouting up independently.

[freeztar]

This senerio could account for Arthropods, but still fish and gastropods, I can't see or even Imagine the common morphological linkage.

 

Why does the linkage have to be morphological?

Have a look at this cladogram:

Palaeos Metazoa: Mollusca: Phylum Mollusca

 

Both Arthropods and Lophotrochozoa (including mollusks) are Protostomia.

They diverged at some point prior to the Cambian, or during the emergence of the Pre-Cambrian.

[Thunderbird]

Why does the linkage have to be morphological?

Have a look at this cladogram:

Palaeos Metazoa: Mollusca: Phylum Mollusca

 

Both Arthropods and Lophotrochozoa (including mollusks) are Protostomia.

They diverged at some point prior to the Cambian, or during the emergence of the Pre-Cambrian.

 

These classification techniques on this level are still in debate, for very good reasons. From your page..

 

There is a tendency among researchers in the field of molecular phylogeny to divide the Protostomia into two further groups, the Ecdysozoa and Lophotrochozoa. However, not all molecular phylogeneticists accept this approach.

 

[freeztar]

These classification techniques on this level are still in debate, for very good reasons. From your page..

 

Even if you break Protostomia into two more subgroups, my point still remains.

[Thunderbird]

Even if you break Protostomia into two more subgroups, my point still remains.

 

 

 

 

Both Arthropods and mollusks have a definite common ancestor in Protostomia ?

[freeztar]

Both Arthropods and mollusks have a definite common ancestor in Protostomia ?

 

Good question. Not that I know of, though I will do a bit of digging to see if such a link exists.

 

They are grouped together because of the following:

 

The protostome condition is defined by

 

a spiral and determinant cleavage in the early stages of embryonic development, which means that the fate of the cells is determined as they are formed.

schizocoelous coelom formation. As the archenteron (embryonic gut) forms, the coelom begins as splits within the solid mesodermal mass, with the formation of the blastopore (the original opening) into the mouth.

In both these attributes they differ from deuterostomes.

http://www.palaeos.org/Protostomia

 

To me, this suggests that Protostomians share a common ancestor.

[freeztar]

Here's an interesting tidbit I found while searching for a fossil ancestor of Protostomians:

 

Vernanimalcula has been described as the earliest known member of the Bilateria (animals with bilateral symmetry). It lived some 580 to 600 million years ago. It was between 0.1 and 0.2 mm across (roughly the width of one or two human hairs), and probably fed on microbes on the sea floor. It may have moved over the sea floor by flexing its body. Vernanimalcula means "small spring animal", referring to its appearance in the fossil record at the end of the Marinoan Glaciation (see also Snowball Earth).

 

 

The Vernanimalcula fossils were discovered in the Doushantuo Formation in China. This formation is a Lagerstätte, one of the rare places where soft body parts and very fine details are preserved in the fossil record. The Vernanimalcula fossils show triploblastic structure, a coelom, a differentiated gut, a mouth, an anus, and paired external pits that could be sense organs.

 

The appearance of Vernanimalcula so early in the fossil record has important implications. It greatly reduces the likelihood that animals without coelom (acoelomates), such as flatworms, developed before animals with coeloms. The radiation of animals into many phyla may have occurred before any animal became much larger than microscopic size. The sudden appearance of many animal phyla in the Cambrian Explosion may be an illusion. The Cambrian Explosion may instead represent a (geologically) sudden increase in size and the development of easily fossilized body parts by species in existing phyla.[1][2][3][4]

Vernanimalcula - Wikipedia, the free encyclopedia

 

Interesting...

[Thunderbird]

Here's an interesting tidbit I found while searching for a fossil ancestor of Protostomians:

 

 

Vernanimalcula - Wikipedia, the free encyclopedia

 

Interesting...

 

Yes it is. I have read this before and it could possibly be the ancestor we are looking for.

[freeztar]

What did you think of the text I bolded, TB?

It seems to add some credence to your theory while at the same time avoiding the whole CE problem.

[Thunderbird]

What did you think of the text I bolded, TB?

It seems to add some credence to your theory while at the same time avoiding the whole CE problem.

 

It does recognize the problem, and gives one solution.

This is much better than the ole spoung-worm-arthopod-fish senario.

 

These multiple veiw points highlights the fact that there is no clear scenario, if it were the worm-arthropod scenario as suggested earlier there would be no need for the microscopic blastopore scenario,

 

There is no clear line here. The misconception is that there is one clear line

 

One form that really throws a monkey wrench in the whole thing for me is the Gastropod, a spiral shell and a-symmetrical body inside. The orientation of the shell is really weird.

 

The spiral end and the open end with one gill is a right left orientation.

 

The cephalopods however have a symmetrical front back orientation, but even there its hard to say which is which. Its also difficult to see how these animals lived without shells.

it looks like they formed together in a non-linear event, which fits my scenario

[freeztar]

Get your reading glasses out and clear your schedule for the next week or so:

 

The first draft of Charles Darwin's "On The Origin Of Species" is among a wealth of papers belonging to the intensely private man who changed science being published on the Internet on Thursday for the first time.

 

Comprising some 20,000 items and 90,000 images, the release on darwin-online.org.uk is the largest in history, according to the organisers from Cambridge University Library which holds all the Darwin papers.

 

"This release makes his private papers, mountains of notes, experiments, and research behind his world-changing publications available to the world for free," said John van Wyhe, director of the project.

 

"His publications have always been available in the public sphere - but these papers have until now only been accessible to scholars."

 

The collection includes thousands of notes and drafts of his scientific writings, notes from the voyage of the Beagle when he began to formulate his controversial theory of evolution, and his first recorded doubts about the permanence of species.

Darwin's private papers get Internet launch | Top News | Reuters

[Thunderbird]

Get your reading glasses out and clear your schedule for the next week or so:

 

 

Darwin's private papers get Internet launch | Top News | Reuters

 

Cool ! :)

[Biochemist]

What did you think of the text I bolded, TB?

It seems to add some credence to your theory while at the same time avoiding the whole CE problem.

This is a really interesting theoretical point, FT. The notion that the first life form rapidly migrated to multiple phyla, each of which subsequently grew larger is indeed a different perspective on the gravity of the CE events.

 

But it does make the "high gravity" event occur much earlier. It sort of kicks the problem back into history a couple hundred million years. And you are also (essentially) asserting that the phyla were not selected.

 

You see the issue?

[Moontanman]

Here's an interesting tidbit I found while searching for a fossil ancestor of Protostomians:

 

 

Vernanimalcula - Wikipedia, the free encyclopedia

 

Interesting...

 

This is what I have been saying for some time now, the CE was an illusion, tiny hard to fossilize animals preceded the CE by many millions of years. makes a lot of sense to me.

[freeztar]

This is a really interesting theoretical point, FT. The notion that the first life form rapidly migrated to multiple phyla, each of which subsequently grew larger is indeed a different perspective on the gravity of the CE events.

 

But it does make the "high gravity" event occur much earlier. It sort of kicks the problem back into history a couple hundred million years. And you are also (essentially) asserting that the phyla were not selected.

 

How was I asserting that the phyla were not selected for?

Perhaps there were hundreds of phyla, but only the strongest headed into the Cambrian.

(also note that this is not my idea, but I find it interesting)

 

You see the issue?

 

No, not really. :naughty:

[Biochemist]

How was I asserting that the phyla were not selected for?

Sorry, FT. I was a little vague. The "problem" often described associated with the CE is that these 70 (or so) phyla "suddenly" arrived on the scene after a mere 250 million years (or so). Previously, there were 3 phyla. After, there were 70. And then 40 (or so) of the 70 died out to the present day.

 

If we were to assert that all 70 phyla (that is, 70 different body plans) pre-existed the Cambrian, then the time window to generate the body plans get even shorter. I thought we were suggesting above that the initial life form rapidly branched into most phyla. It is pretty difficult to suggest that this was a mutation-driven natural selection process if it occurred.