Re: New 'frog-amander' (today's Nature)

[David Marjanovic <david.marjanovic@gmx.at>]

Ah, so Jason's "stem-batrachian" is out. Congratulations on getting it into 
Nature. Let the massacre begin...

(Lots of metaphorical blood will flow over this. I just don't know whose. 
Will be fun to find out. :-) In fact, if the authors are right, almost 
everyone's blood will flow, because almost all phylogenetic analyses have 
found a monophyletic Lissamphibia.)

----- Original Message -----
From: "Tim Williams" <twilliams_alpha@hotmail.com>
To: <dinosaur@usc.edu>
Sent: Thursday, May 22, 2008 1:25 AM
Subject: New 'frog-amander' (today's Nature)

> Not dinosaurs, but still pretty darn cool...
>
> Jason S. Anderson, Robert R. Reisz, Diane Scott, Nadia B. Fröbisch, & 
> Stuart S. Sumida (2004).  A stem batrachian from the Early Permian of 
> Texas and the origin of frogs and salamanders.  Nature 453: 515-518.
>
> First paragraph: "The origin of extant amphibians (Lissamphibia: frogs, 
> salamanders and caecilians) is one of the most controversial questions in 
> vertebrate evolution, owing to large morphological and temporal gaps in 
> the fossil record.  Current discussions focus on three competing 
> hypotheses: a monophyletic origin within either Temnospondyli or 
> Lepospondyli, or a polyphyletic origin with frogs and salamanders arising 
> among temnospondyls and caecilians among the lepospondyls.  Recent 
> molecular analyses are also controversial, with estimations for the 
> batrachian (frog–salamander) divergence significantly older than the 
> palaeontological evidence supports.

This last half-sentence is not true.
http://www.informaworld.com/smpp/content~content=a778976765~db=all~order=page

> Here we report the discovery of an amphibamid temnospondyl from the Early 
> Permian of Texas that bridges the gap between other Palaeozoic amphibians 
> and the earliest known salientians and caudatans from the Mesozoic.  The 
> presence of a mosaic of salientian and caudatan characters in this small 
> fossil makes it a key taxon close to the batrachian (frog and salamander) 
> divergence.  Phylogenetic analysis suggests that the batrachian divergence 
> occurred in the Middle Permian, rather than the late Carboniferous as 
> recently estimated using molecular clocks,

This agrees with the link I gave above.

> but the divergence with caecilians corresponds to the deep split between 
> temnospondyls and lepospondyls, which is congruent with the molecular 
> estimates."
>
> Describes the new stem-batrachian _Gerobatrachus hottoni_ gen. et sp. nov. 
> (Amphibamidae, Temnospondyli).  Although put in the Amphibamidae, this 
> group comes out as paraphyletic.  As the authors put it, "Our analysis 
> finds _Gerobatrachus_ to be the immediate sister taxon to Batrachia (Fig. 
> 4), with the amphibamids _Doleserpeton_, _Amphibamus_ and _Platyrhinops_ 
> as successively more basal taxa.  In addition, the oldest known caecilian 
> _Eocaecilia_ falls within recumbirostrine lepospondyls, sister group to 
> _Rhynchonkos_ and, one step further out, the brachystelechids.  Thus, the 
> available morphological evidence supports the hypothesis of a diphyletic 
> origin of extant amphibians from Palaeozoic tetrapods, with a separate 
> origin of the limbless, largely fossorial caecilians from within the 
> lepospondyls, whereas Batrachia originates within Temnospondyli."
>
> Thus, Lissamphibia is buried, with the phylogenetic analysis recovering 
> batrachians (frogs and salamanders) as temnospondyls, whereas caecilians 
> are lepospondyls.
>
> The discovery is discussed here, with a nice picture of the 'frog-amander' 
> _Gerobatrachus_...
>
> http://www.msnbc.msn.com/id/24761660/

Can't wait to read the paper tomorrow.