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Topic: New fossil caecilians! (Read 305 times) previous topic - next topic

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New fossil caecilians!
Just in time for Bili's birthday, although I should have posted it yesterday.

So maybe Lissamphibia is polyphyletic after all. Or at least crown Lissamphibia has to include a whole bunch of other stuff if you want to keep it monophyletic. Maybe. I'd be interested in any criticisms anyone has on that.

Stem caecilian from the Triassic of Colorado sheds light on the origins of Lissamphibia Jason D. Pardo, Bryan J. Small,and Adam K. Huttenlocker (2017) PNAS, doi:10.1073/pnas.1706752114

Quote
The origin of the limbless caecilians remains a lasting question in vertebrate evolution. Molecular phylogenies and morphology support that caecilians are the sister taxon of batrachians (frogs and salamanders), from which they diverged no later than the early Permian. Although recent efforts have discovered new, early members of the batrachian lineage, the record of pre-Cretaceous caecilians is limited to a single species, Eocaecilia micropodia. The position of Eocaecilia within tetrapod phylogeny is controversial, as it already acquired the specialized morphology that characterizes modern caecilians by the Jurassic. Here, we report on a small amphibian from the Upper Triassic of Colorado, United States, with a mélange of caecilian synapomorphies and general lissamphibian plesiomorphies. We evaluated its relationships by designing an inclusive phylogenetic analysis that broadly incorporates definitive members of the modern lissamphibian orders and a diversity of extinct temnospondyl amphibians, including stereospondyls. Our results place the taxon confidently within lissamphibians but demonstrate that the diversity of Permian and Triassic stereospondyls also falls within this group. This hypothesis of caecilian origins closes a substantial morphologic and temporal gap and explains the appeal of morphology-based polyphyly hypotheses for the origins of Lissamphibia while reconciling molecular support for the group's monophyly. Stem caecilian morphology reveals a previously unrecognized stepwise acquisition of typical caecilian cranial apomorphies during the Triassic. A major implication is that many Paleozoic total group lissamphibians (i.e., higher temnospondyls, including the stereospondyl subclade) fall within crown Lissamphibia, which must have originated before 315 million years ago.
Why do I bother?

  • Faid
Re: New fossil caecilians!
Reply #1
Those caecilians are shaking our confidence daily

Ill see myself out
Who even made the rule that we cannot group ducks and fish together for the simple reason that they are both aquatic? If I want to group them that way and it serves my purpose then I can jolly well do it however I want to and it is still a nested hierarchy and you can't tell me that it's not.

Re: New fossil caecilians!
Reply #2
If you insist on going up against them when death is on the line, what do you expect?
Why do I bother?

  • Bilirubin
  • Ain't nothing ta fuck wit'
Re: New fossil caecilians!
Reply #3
LOOK AT THIS PAPER TEETH

  • Monad
Re: New fossil caecilians!
Reply #4
Can't access it :(

Re: New fossil caecilians!
Reply #5
Neat paper. Looks like it was written by a third grader. :stuckup:
Love is like a magic penny
 if you hold it tight you won't have any
if you give it away you'll have so many
they'll be rolling all over the floor

Re: New fossil caecilians!
Reply #6
First author is a grade-A douche

Re: New fossil caecilians!
Reply #7
That moment where you realise you started a interdepartmental fight...
Why do I bother?

Re: New fossil caecilians!
Reply #8
Just in time for Bili's birthday, although I should have posted it yesterday.

So maybe Lissamphibia is polyphyletic after all. Or at least crown Lissamphibia has to include a whole bunch of other stuff if you want to keep it monophyletic. Maybe. I'd be interested in any criticisms anyone has on that.

Stem caecilian from the Triassic of Colorado sheds light on the origins of Lissamphibia Jason D. Pardo, Bryan J. Small,and Adam K. Huttenlocker (2017) PNAS, doi:10.1073/pnas.1706752114

Quote
The origin of the limbless caecilians remains a lasting question in vertebrate evolution. Molecular phylogenies and morphology support that caecilians are the sister taxon of batrachians (frogs and salamanders), from which they diverged no later than the early Permian. Although recent efforts have discovered new, early members of the batrachian lineage, the record of pre-Cretaceous caecilians is limited to a single species, Eocaecilia micropodia. The position of Eocaecilia within tetrapod phylogeny is controversial, as it already acquired the specialized morphology that characterizes modern caecilians by the Jurassic. Here, we report on a small amphibian from the Upper Triassic of Colorado, United States, with a mélange of caecilian synapomorphies and general lissamphibian plesiomorphies. We evaluated its relationships by designing an inclusive phylogenetic analysis that broadly incorporates definitive members of the modern lissamphibian orders and a diversity of extinct temnospondyl amphibians, including stereospondyls. Our results place the taxon confidently within lissamphibians but demonstrate that the diversity of Permian and Triassic stereospondyls also falls within this group. This hypothesis of caecilian origins closes a substantial morphologic and temporal gap and explains the appeal of morphology-based polyphyly hypotheses for the origins of Lissamphibia while reconciling molecular support for the group's monophyly. Stem caecilian morphology reveals a previously unrecognized stepwise acquisition of typical caecilian cranial apomorphies during the Triassic. A major implication is that many Paleozoic total group lissamphibians (i.e., higher temnospondyls, including the stereospondyl subclade) fall within crown Lissamphibia, which must have originated before 315 million years ago.


Okay so summary here:

If we're right, Lissamphibia is still monophyletic. This is consistent with the molecular phylogenies and the age of Lissamphibia is right in the middle of modern molclock estimates for the origin of the amphibian crown.

Again, if we're right, Lissamphibia is a LOT more inclusive, and most "temnospondyls" are actually true lissamphibians. Small size in caecilians and salamanders is convergent rather than a shared, derived characteristic. Soft tissue features shared between caecilians and frogs/manders can probably be extended downward into most fossil amphibians. The evolutionary history of the pedicellate bicuspid tooth is unclear; it would seem to be convergent based on the distribution of unicuspid nonpedicellate teeth across total-group amphibians, but there may be some "deep homology" there.

But yeah.

Re: New fossil caecilians!
Reply #9
That moment where you realise you started a interdepartmental fight...

<-first author

  • Bilirubin
  • Ain't nothing ta fuck wit'
Re: New fossil caecilians!
Reply #10
That moment where you realise you started a interdepartmental fight...

<-first author
Neat paper. Looks like it was written by a third grader. :stuckup:

Re: New fossil caecilians!
Reply #11
Who cares about froggies anyway? Moar dinoes!
Believer in High Powers, and naturally, logarithms.
Pikkiwoki is the one true god.

  • Doobie Keebler
  • I've got a lot of problems with you people
Re: New fossil caecilians!
Reply #12
If my recollections of Jurassic Park serve me correctly, we are going to need the frogs to make moar dinoes, soooo.....
"I'm over 70 and have never seen such , arrogance, incompetence and Ill -intentions as this President and his aids."    The Dotard     (posted 12 days after his 68th birthday)

Re: New fossil caecilians!
Reply #13

Re: New fossil caecilians!
Reply #14
That moment where you realise you started a interdepartmental fight...

<-first author
Reported for revealing personal information  ;)

Seriously though, we'll done. :happydance:
Why do I bother?