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Re: tetrapoda



Adam wrote:
 
> Yes the narrow phylogenetic definition of the Tetrapoda does exclude a
> number of basal taxa such as Ichthyostega, Acanthostega etc.. If Laurin's
> new tetrapod phylogeny is correct, then most of the Palaeozoic "tetrapods"
> (eg. temnospondyls, baphetids, embolomeres, gephyrostegids and
> Seymouriamorphs) would actually be excluded from this taxon. Nevertheless
> there is great resistance amongst early tetrapod workers to applying this
> crown group definition of the Tetrapoda, it is analogous to kicking
> Archaeopteryx, Ichthyornis etc. out of Aves because they don't belong to
> the crown group. I think what will settle is either a stem based
> definition like "all taxa more closely related to modern Amphibia and
> Amniota than to Elpistostegids" (Elpistostegids are the closeset known
> taxa to Tetrapoda that still lack limbs and digits) or a node based
> definition like "Elginerpetontidae and all modern amphibians, amniotes and
> all descendants of their common ancestor". The problem with the crown
> group definition of Tetrapoda is that a) people are very used to calling
> limbed vertebrates such as Ichthyostega, temnospondyls and
> seymouriamorphs," tetrapods" and b) there isn't anything else we can call
> them at the moment beyond limbed, near-tetrapod osteolepiforms.
> Tetrapodomorpha does not just apply to these limbed
> near-tetrapods + tetrapods, it is
> infact phylogenetically defined as a stem group including all vertebrates
> more closely related to modern tetrapods than to modern lungfish.
> Therefore such "fishy" taxa as Eusthenopteron are tetrapodomorphs. Whew! I
> seem to have gone on far longer than I intended, I hope this helps clear
> things up.

Yes, it is very interesting information.
Has Laurin's new phylogeny, in which he places Lissamphibia much 
closer to Amniota than previous phylogenies already been published 
formally? What is his sister-group of Amniota?
And which taxa belong in Elginerpedontidae? What about Metaxygnathus, 
Ventastega, Tulerpeton? Has Elpistostegidae priority of 
Panderichthyidae?  Lots of questions (and a bit out of topic...)

Pieter Depuydt