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Re: [dinosaur] Early amphibians evolved distinct vertebrae for habitat invasions (free pdf)



> We demonstrate that temnospondyls were likely ancestrally terrestrial and had 
> several early reinvasions of aquatic habitats.

That conclusion depends on two things:

â the interpretations of the lifestyles of a lot of temnospondyls. If you ask 
me, all the "semiaquatic" ones (orange in fig. 4) were as aquatic as an eel or 
a European catfish (*Silurus*), and that may even hold for some of the 
"terrestrial" ones (green). The mere lack of lateral-line canals doesn't make 
*Saharastega* terrestrial, and similar things hold even for *Eryops*.

â the phylogeny. Mind you, I have nothing against the phylogeny in fig. 4; it 
is entirely reasonable. But so are 5 or 10 _very_ different alternatives for 
the lower half of the tree (lower in that figure, I mean). Take any analysis of 
temnospondyl phylogeny, tweak the outgroup sample or the character sample, and 
everything tumbles around at random (pers. obs.). We know basically nothing 
about large-scale temnospondyl phylogeny; it was frankly not possible to do 
this study at this point, and it will remain impossible for years.

It's quite a frustrating state of affairs: every year, a study or two comes out 
that requires a robust phylogeny of early limbed vertebrates in general or 
temnospondyls in particular, but no such phylogeny exists, because nobody 
manages to get the huge amount of work funded that is necessary to make one. 
And so, people who need a phylogeny before their short-term grant runs out 
resort to flimsy supertrees or pick a published tree they happen to like, and 
they all run a huge risk of "garbage in, garbage out". For the time being, 
these studies aren't even falsifiable.

By the way, although it doesn't matter for this study, I can't resist pointing 
out that we don't even know if the temnospondyls were "early amphibians" or 
outside the tetrapod crown-group. The updated phylogenetic analyses in Daza et 
al. (2020), accompanying the description of *Yaksha*, the albanerpetid in 
amber, move the needle a bit further toward the latter possibility...