Tetrapod Evolution

[UTEOTW]

Some of you may have already seen this, but there was a nice article in the December Scientific American about recent discoveries on the evolution of tetrapods from fish. In rare form, it is nearly the entire article, only the figures appear to be missing. But I don't know how long it will stay up. Read it why you can.

It seems that we are now in posession of several different stages of the transition and the new information has cleared up previous confusion on how the transition took place.

Reading the article should also give you an idea of how quick the pace of discovery is. There is one fossil that she would like to discuss that would shed even more light on the subject. But it has yet to be described in print so she can only hint at it. In addition, near the end, she laments about the lack of fossils showing how the changes to the rear legs occurred. (The changes from fins to legs in the front is reasonably well established.) As it turns out, the December issue of Nature saw a new specimen of Panderichthys rhombolepis described which illustrates this very area.

http://www.sciam.com/article.cfm?chanID=sa006&colID=1&articleID=000DC8B8-EA15-137C-AA1583414B7F0000

 

[Petrel]

Oodles of stuff on this lately. A new transitional form Devonian fish-like tetrapod has been discovered and reported in Nature. It has fins and scales, but the front fins are jointed! A free access report can be found here.

Creatures with features of both fish and land-living animals have been found before. Fish that may have been beginning to 'walk' in shallow water have been found from about 385 million years ago, and fish with limbs that bear digits have been seen from more than 365 million years ago.

Specimens that fall into the gap, such as Tiktaalik, help researchers to work out the details of this transition. The newly found animal has a structure on its head that looks like a small gill slit that is on its way to becoming an ear, for example, and a long snout that would have been suited to catching prey on land.

 

[Magnetic Poles]

MSNBC reports on it here: http://www.msnbc.msn.com/id/12168265/

 

[Petrel]

I thought this thing was rather small when I first read the brief, but it was 4-9 feet long and ate meat! I wouldn't want to stumble across it!

 

[Gina B]

Looks like an alligator to me.
Are there other pictures of all the bones, or did they just find the head, neck, and a tiny portion of the upper torso like the one pic shows?
I didn't have time to read the whole thing yet.

 

[UTEOTW]

"Are there other pictures of all the bones, or did they just find the head, neck, and a tiny portion of the upper torso like the one pic shows? "

Basically they found the front half, I think. They key parts here are the transitional nature of the front arms. The upper part, down to and including the wrists have changed to be like tetrapod limbs while the fingers are still like the fins of a fish. There are also key parts of the skull caught in an intermediate stage. (From other fossils we know that the front limbs were completely tetrapod like while the rear fins stayed fins until later so the back half, which may or may not be there in the multiple specimens they found, would not be expected to shed much light.

This find has been rumored and hinted at for months. It has lived up to the hype.

Now I will spam my response from teh other thread for more information.

Originally posted by UTEOTW:
</font><blockquote>quote:</font><hr />Originally posted by Mexdeaf:
I wonder what the 'telling anatomical traits of a transitional creature' were?

Here is a long article, first.

http://www.nature.com/news/2006/060403/full/060403-7.html

And I think the two abstracts may answer your question.

The relationship of limbed vertebrates (tetrapods) to lobe-finned fish (sarcopterygians) is well established, but the origin of major tetrapod features has remained obscure for lack of fossils that document the sequence of evolutionary changes. Here we report the discovery of a well-preserved species of fossil sarcopterygian fish from the Late Devonian of Arctic Canada that represents an intermediate between fish with fins and tetrapods with limbs, and provides unique insights into how and in what order important tetrapod characters arose. Although the body scales, fin rays, lower jaw and palate are comparable to those in more primitive sarcopterygians, the new species also has a shortened skull roof, a modified ear region, a mobile neck, a functional wrist joint, and other features that presage tetrapod conditions. The morphological features and geological setting of this new animal are suggestive of life in shallow-water, marginal and subaerial habitats.

A Devonian tetrapod-like fish and the evolution of the tetrapod body plan, Daeschler et al, Nature 440, 757-763 (6 April 2006)

Wrists, ankles and digits distinguish tetrapod limbs from fins, but direct evidence on the origin of these features has been unavailable. Here we describe the pectoral appendage of a member of the sister group of tetrapods, Tiktaalik roseae, which is morphologically and functionally transitional between a fin and a limb. The expanded array of distal endochondral bones and synovial joints in the fin of Tiktaalik is similar to the distal limb pattern of basal tetrapods. The fin of Tiktaalik was capable of a range of postures, including a limb-like substrate-supported stance in which the shoulder and elbow were flexed and the distal skeleton extended. The origin of limbs probably involved the elaboration and proliferation of features already present in the fins of fish such as Tiktaalik.

The pectoral fin of Tiktaalik roseae and the origin of the tetrapod limb, Shubin et al, Nature 440, 764-771 (6 April 2006)

To translate, basically they found a key stage where the fins of the lobe finned fish were about halfway to changing into the arms.legs of tetrapods. The shoulder had moved and changed in a way in which it could support the body in addition to being used for swimming. The arm bones through the wrists had changed to be very much like modern tetrapods. But the fingers were still more like the fins of a fish.

All in all, a spectactular find and another key transitional in the bag. </font>[/QUOTE]This is yet another nail in the coffin of those who claim that there are no transitionals that have been found. This is exactly what was expected to be turned up when they went looking.

 

[SpiritualMadMan]

I really like artists conceptions...

Like fantasy dreams...

What I want to see is a pictural spread of the actual 'monster'...

As it is...

For all we really know is that is is another jaw bone of pig blown up into a major scientific find...

Could be a mutant crocodile or alligator...

One fossile would not allow for reprodcution, either..

Mike Sr.

 

[UTEOTW]

What artists conception?

They found the bones. They found multiple specimens. They even found what they had not previously found before but knew had to be there in the one place that they knew that it had to be!

You are making a serious ethics charge here to say that they deliberately have falsified data and that this "is is another jaw bone of pig blown up into a major scientific find." Do you have any proof at all for such a charge? Have you even read the two papers that were published in Nature today? Can you even tell us where something in the scientific literature at all is just a "jaw bone of pig blown up into a major scientific find."

You have absolutely no basis for your charges. You simply choose to deny the evidence even as it piles higher and higher. YOu instead make serious, unfounded charges against the integrity of those whom you do not even know. Have you not heard that we should not bear false witness? If you have heard of this, then withdraw your accusations or provide your proof.

And it is not just "one fossile [sic]." There are multiple specimens. Not only that, but there are many, many known species on this transitional series that are know known to man.

The "fantasy" lies with those who disbelieve their lying eyes in order to deny the truth.