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Old 01-06-2010, 05:57 PM   #755258  /  #1
Per Ahlberg
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Default New paper on the origin of tetrapods

Hi all,

I have a new paper on the origin of tetrapods coming out in tomorrow's Nature. For those of you in the UK, the story will be running on the BBC television news at 6 pm. It is a major discovery with surprising implications that will not, I think, be uncontroversial.

As usual, PM me for a pdf of the paper.
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Old 01-06-2010, 06:01 PM   #755265  /  #2
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This means it'll be online tonight.
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Old 01-06-2010, 06:02 PM   #755268  /  #3
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Damn, you beat me. I've been hearing about this from my friend at Nature for weeks now!
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Old 01-06-2010, 06:02 PM   #755269  /  #4
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New, interesting phylogenies?

Delish.
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I suppose it's good for society that I'm not an alpha wolf then.
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Old 01-06-2010, 06:07 PM   #755275  /  #5
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http://www.nature.com/nature/journal...ture08623.html

Quote:
Tetrapod trackways from the early Middle Devonian period of Poland

The fossil record of the earliest tetrapods (vertebrates with limbs rather than paired fins) consists of body fossils and trackways. The earliest body fossils of tetrapods date to the Late Devonian period (late Frasnian stage) and are preceded by transitional elpistostegids such as Panderichthys and Tiktaalik that still have paired fins. Claims of tetrapod trackways predating these body fossils have remained controversial with regard to both age and the identity of the track makers. Here we present well-preserved and securely dated tetrapod tracks from Polish marine tidal flat sediments of early Middle Devonian (Eifelian stage) age that are approximately 18 million years older than the earliest tetrapod body fossils and 10 million years earlier than the oldest elpistostegids. They force a radical reassessment of the timing, ecology and environmental setting of the fish–tetrapod transition, as well as the completeness of the body fossil record.
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Old 01-06-2010, 06:07 PM   #755276  /  #6
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It's out. Front cover:

http://www.nature.com/nature/journal/v463/n7277/covers/

News and Views:

http://www.nature.com/nature/journal...l/463040a.html

The paper itself:

http://www.nature.com/nature/journal...ture08623.html
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Old 01-06-2010, 06:07 PM   #755277  /  #7
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Beaten again! Bastards!
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Old 01-06-2010, 06:11 PM   #755282  /  #8
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Well, holy fucking shit.
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Old 01-06-2010, 06:13 PM   #755285  /  #9
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of course you tell us this at 3 mins to 6. I haven't missed it have I?
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Old 01-06-2010, 06:13 PM   #755287  /  #10
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Per, I'm reminded of your debate with the creationist fastnet when the paper says:

Quote:
Two large trackways from Valentia Island, Ireland36, have been dated radiometrically to 385 million years ago. At the time of publication this was taken to imply an Eifelian (early Middle Devonian) age39, which clashed with the occurrence of the Late Devonian index fossil (for Laurussia) Bothriolepis in the same strata. However, subsequent recalibration of the timescale indicates that 385 million years ago corresponds to the Givetian–Frasnian boundary33. This is consonant with the biostratigraphy but nevertheless suggests an earlier origin for tetrapods than indicated by the body fossil data.
39 being the trackway reference that he brought up, that I don't think you were familiar with at the time (might be wrong about that). Now you've got a paper on trackways; funny how things work out I guess.
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Old 01-06-2010, 06:15 PM   #755290  /  #11
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Quote:
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of course you tell us this at 3 mins to 6. I haven't missed it have I?
Doubt it, not with the plot against Gordon Brown. Just turned it on myself. Will be on later, hopefully they don't drop it due to the big political news.
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Old 01-06-2010, 06:22 PM   #755298  /  #12
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Per on the news now!
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Old 01-06-2010, 06:25 PM   #755303  /  #13
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No Per. Booooo. An OK report, some Henry Gee and some "re-writing of the textbooks" from the reporter..
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Old 01-06-2010, 06:25 PM   #755304  /  #14
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Is there a listing of the specific interpretation of evidence which indicates that the animal responsible for the trackway was a tetrapod? It would be interesting.
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Old 01-06-2010, 06:30 PM   #755310  /  #15
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Ed Yong has a write up:

http://scienceblogs.com/notrocketsci..._million_y.php

Includes comments from other researchers:

Quote:
The implications of the Polish tracks are so controversial that reactions from other palaeontologists have been, understandably, mixed. Ted Daeschler and Neil Shubin, who discovered Tiktaalik, both find the study intriguing, but not definitive.

Last edited by SteveF; 01-06-2010 at 06:33 PM.
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Old 01-06-2010, 06:32 PM   #755316  /  #16
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Quote:
Originally Posted by FIGUER View Post
Is there a listing of the specific interpretation of evidence which indicates that the animal responsible for the trackway was a tetrapod? It would be interesting.
Yes. For example:

Quote:
Stride length, relative spacing of the prints, and the absence of a body drag demonstrate that Muz. PGI 1728.II.16 is a tetrapod trackway. Elpistostegids and other tetrapodomorph fishes all have straight ‘knees’ and ‘elbows’, and shoulder and hip joints that face posteriorly23, 24, 25, 26, 28. In early tetrapods, by contrast, the knees and (in particular) elbows of the short, sprawling limbs allow greater flexion, and the shoulder and hip joints face laterally. The relative stride length shows that both fore- and hindlimbs were oriented anterolaterally at the anterior extremity of the movement arc, with the manus and pes placed on the ground well anterior to the respective shoulder and hip joint (Fig. 2b). This would be impossible for an animal with the girdle morphologies documented in Tiktaalik and Panderichthys23, 24, 25, 26, 28, and in any case the absence of a sacrum would prevent the fish from lifting its tail clear off the substrate (Fig. 2b). Assuming standard early tetrapod proportions8, 18, 21, the total length of the track maker was probably in the region of 40–50 cm.
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Old 01-06-2010, 06:36 PM   #755320  /  #17
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The money shot:

Quote:
FIGURE 5. Phylogenetic implications of tracks.



a, Phylogeny of selected elpistostegids and stem tetrapods, based on refs 10, 12, 19 and 20, fitted to Devonian stratigraphy. The grey bar indicates replacement of elpistostegids by tetrapods in body fossil record. b, Effect of adding the Zachel strokemie tracks to the phylogeny: the ghost ranges of tetrapods and elpistostegids are greatly extended and the ‘changeover’ is revealed to be an artefact. Pan, Panderichthys; Tik, Tiktaalik; Elp, Elpistostege; Liv, Livoniana; Elg, Elginerpeton; Ven, Ventastega; Met, Metaxygnathus; Aca, Acanthostega; Ich, Ichthyostega; Tul, Tulerpeton. ANSP 21350 is an unnamed humerus described in ref 17. The bars are approximate measures of the uncertainty of dating. These are not statistical error bars but an attempt to reflect ongoing debate.
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Old 01-06-2010, 06:53 PM   #755346  /  #18
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I'm honestly not too surprised that you're finding better representation of tracks than trackmakers; we see the same thing in track communities in the Penn-Permian, especially in cases where parareptile tracks significantly precede body fossils of parareptile trackmakers. I don't really see how Shubin and Daechler could possibly claim this was ambiguous, but this really shits in their "Tiktaalik is the perfect transitional fossil" salad.

It is interesting that this is a tidal marine environment, though. That would offer some additional credence to the marine status of Tulerpeton as being something more than a fluke. I can see this being misused, though, by some other folks in the field.
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Old 01-06-2010, 06:56 PM   #755352  /  #19
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Quote:
Originally Posted by SteveF View Post
The money shot:

Quote:
FIGURE 5. Phylogenetic implications of tracks.



a, Phylogeny of selected elpistostegids and stem tetrapods, based on refs 10, 12, 19 and 20, fitted to Devonian stratigraphy. The grey bar indicates replacement of elpistostegids by tetrapods in body fossil record. b, Effect of adding the Zachel strokemie tracks to the phylogeny: the ghost ranges of tetrapods and elpistostegids are greatly extended and the ‘changeover’ is revealed to be an artefact. Pan, Panderichthys; Tik, Tiktaalik; Elp, Elpistostege; Liv, Livoniana; Elg, Elginerpeton; Ven, Ventastega; Met, Metaxygnathus; Aca, Acanthostega; Ich, Ichthyostega; Tul, Tulerpeton. ANSP 21350 is an unnamed humerus described in ref 17. The bars are approximate measures of the uncertainty of dating. These are not statistical error bars but an attempt to reflect ongoing debate.
The interesting thing here is that the changeover may be an artifact...but of what? It's possible that it's a statistical artifact, or it's possible that there's a point in time where tetrapods quickly replace elpistostegalid-grade tetrapodamorphs. The latter would be an interesting paleoecological and evolutionary event in and of itself.
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Old 01-06-2010, 06:57 PM   #755353  /  #20
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ok report. got to tick off most of the media reporter boxes though. those people should just shut up, really.
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Old 01-06-2010, 06:57 PM   #755355  /  #21
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There are some tiny fishes in the river that runs besides my house which walk, not only on the bottom, but also outside the water over wet stones. They use their two front fins like little feet, but also swim.
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Old 01-06-2010, 07:11 PM   #755378  /  #22
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Quote:
Originally Posted by FIGUER View Post
There are some tiny fishes in the river that runs besides my house which walk, not only on the bottom, but also outside the water over wet stones. They use their two front fins like little feet, but also swim.
Is the water there brackish?
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Old 01-06-2010, 07:30 PM   #755416  /  #23
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So cool it's come around the horn into hotness!

I certainly pm'd Per for a copy of the whole thing!

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Old 01-06-2010, 07:39 PM   #755438  /  #24
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Quote:
They force a radical reassessment of the timing, ecology and environmental setting of the fish–tetrapod transition, as well as the completeness of the body fossil record.
Radical? Radical would be 'Sorry everyone ... we don't think tetrapods evolved from fish after all ... chock another one up for the creationists.' I'll be watching for that announcement. Then I'll say you're a radical, Per. (Ducks behind desk to avoid flying eggs and rotten tomatoes)
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Old 01-06-2010, 07:43 PM   #755443  /  #25
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Quote:
Originally Posted by TestyCalibrate View Post
Quote:
Originally Posted by FIGUER View Post
There are some tiny fishes in the river that runs besides my house which walk, not only on the bottom, but also outside the water over wet stones. They use their two front fins like little feet, but also swim.
Is the water there brackish?
Not most of the time. It's a neo-tropical creek with constant and rapid flow of relatively clear water. I have some in an aquarium. I could try getting some pictures, but as they are less than an inch in length it might not provide much visual information.

While I have been visiting-living on the site for two decades, it was only several weeks ago that I first saw them. I noticed huge schools of them swimming up-river, thousands of them, and then to my surprise saw that they were swarming over the wet stones when they reached the falls. They looked like worms in rotten meat or like a mass of tiny snakes.
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