Re: RATITES REVISITED

["Matthew Troutman" <m_troutman@hotmail.com>]

>As for what is 'iffy' and what is not, well, again, interpretation of 
>these things as hypermorphic is no more iffy than are paedomorphic 
>interpretations PLUS I have a hard time with some of the paedomorphic 
>features because they are just plain wrong. For example, it is stated 
>that unfused skull sutures in adult palaeognaths etc prove 
>paedomorphy. This may or not be true (when bones fuse is a 
>complicated factor that does not always equate with ontogeny), but, 
>in my experience, adult ratites actually have fully fused skull 
>sutures. Whereas ironically, in tinamous, there are at least two 
>skull sutures that _never_ fuse. If ratites are supposed to be big 
>paedomorphic palaeognaths, with tinamous as an outgroup, then the 
>fused ratite skull hardly equates with logical paedomorphosis.

     Actually lithornithids would be a better outgroup, tinamous have 
been allied with the galliforms most recently.  And, correct me if I'm 
wrong, lithornithids have completely fused skulls. 

Regarding the chick similiarity problem: 
 
>For palaeognaths, I don't think this has anything to do with 
>paedomorphosis: it could just as parsimoniously be used as evidence 
>indicated the relatively primitive status of palaeognaths in the 
>ornithurine tree. Adult palaeognaths are as much like their juveniles 
>as lizards, crocodiles and non-avian dinosaurs were like theirs, so 
>far as we know. Furthermore, the fact that adult palaeognaths lack 
>the globose porportionally inflated cranium and huge eyes of their 
>juveniles **can**, again, be used as counter-evidence for 
>paedomorphosis in this taxon: in paedomorphy that has been described 
>for hominin hominids, phocoenid odontocetes and alligatoroid 
>crocodylians, adults have 'juvenile-like' skulls. I can't see this in 
>palaeognaths.

     The similiarity is seen also at the metabolic level. Flightless 
birds have a lower metabolism than other birds and this can be 
considered a similiarity with juveniles.  As for the similiarity in 
skulls, I guess it can be considered a matter of opinion, for I think 
that the unfused bones, the disproportionate eyes,  and  the large, 
robust skull all conform to a 'juvenile-like' skulls. However, I must 
now concede that the example of the similiarity to juveniles in adult 
flightless birds is not as strong as I have made it out to be.

      The best evidence for paedomorphic ratites is the similiarities 
that they share with other flightless birds ( vestigal humerus, 
thick-walled and disproportionate hindlimbs, etc ) which can be 
considered paedomorphic characteristics due to the starling experiment. 

Matt Troutman

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