Re: NON-PAEDOMORPHIC RATITES

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

>De Beer also coined the term hypermorphosis, this time meaning the 
>evolutionary development of features in descendants extended beyond 
>the adult stage of ancestors, or 'overstepping'. The very fact that 
>flightless birds, particularly ratites, are so big compared to other 
>birds implies that they are hypermorphic - they apparently have grown 
>to sizes extending well beyond those of their ancestors.

    Another explanation for this is that since many of the larger 
flightless birds are folivores and or nearly so, a larger size would be 
needed to accomadate the larger gut and to edge out competition for the 
food source.

>Other 
>features, some previously explained as paedomorphic - the 
>well-developed aftershaft of ratite feathers, uniformly distributed 
>feathers (arguably overstepping of the very extensive apteria seen in 
>juvenile carinates), ossification of the procoracoid, thick-walled 
>long bones - can be equally, or more, parsimoniously interpreted 
>as hypermorphic. Diverse designs in ratite pelves imply 
>hypermorphosis, because paedomorphosis is supposed to have a 
>homogenising effect and embryonic bird pelves are all similar.

    The feather features can be explained by paedomorphosis as well as 
hypermorphosis, but the other features are more iffy. I find that the 
chicks of flightless birds are similiar to their parents in most all of 
their features evindence that paedomorphosis is the most likely 
explanation for avian flightlessness. 


Matt Troutman

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