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Re: Inglourious New Papers
> Are these mechanisms different across the different taxa or
> for different skeletal elements? (Or both?)
> In other words, what does this say about palaeognathes
> primitively volant/nonvolant?
It might not be easy to recognize. AFAIK the first step into flightlessness
"always" involves reduction of the sternal keel[*], and there are not that many
ways to achieve this - arrested evelopment (as they do indeed find in all the
ratites). Some more years of evo-devo studies and we'll probably know which
genes to check for how they are mutated... that might give an answer. If we go
not already have it by then.
The data in the paper is not very dense in that regard, but as it seems the
sternum ossifies some time before hatching in the tinamou and only after
hatching (or around hatching?) in the ratites. The wing elements' ossification
is quite disparate. As is to be expected - only one ratite per major lineage is
represented. If you'd add for example a cassowary, its close relationship to
the Emu would probably stand out.
As regards phylogeny:
"Recent phylogenetic hypotheses based on molecular data suggest that tinamous
may be derived within palaeognaths, either as sister group to the Australasian
ratites (emu, cassowaries, kiwis) (Hackett et al., 2008) or as sister group to
the rheas (Harshman et al., 2008). This is in contrast with the traditional
viewpoint, supported by both morphological and
molecular data, that tinamous are basal to all other extant ratites.
Developmental data are equivocal on the debate, and are made difficult to
interpret because of the close association between embryology and morphology.
In spite of this, it should be noted that tinamous lack many of the unique
developmental features characteristic of rheas, including the
delayed ossification of the caudal region and the fusion of phalanges on manual
digit IV, and thus there is little support for the hypothesis of Harshman et
I would not discount it though. The eggshell data, IIRC, also places tinamous
close to rheas.
I'd believe vertebral ossification pattern is more independent of flight
ability than tail or hand ossification. They report atlantal arch ossification
to be accelerated compared to posteriad(? is that the word) vertebral arches in
the emu (and kiwis), less accelerated in the tinamou, equally fast in the rhea,
and its ossification is delayed in the ostrich. Typical pattern for birds is
slight acceleration (i.e. tinamou pattern is probably plesiomorphic).
4 lineages, no clear trend, but FWIW the character state in the flighted
lineage is embedded within the spectrum of those of the flightless lineages.
Also, ostriches have never (IIRC) been considered by anyone or suggested by any
data to be any close to tinamous compared to other ratites.
Make of that what you will.
[*] as you lose muscle mass, which is probably the key advantage triggering
evolutionary loss of flight. If you *can* pull it off and survive to reproduce,
you'll save a lot of resources: