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Re: Moa-Tinamou Clade Found Within Ratites



Just briefly, on the point about transoceanic flight capacity:

Interestingly enough, while pelagic flight as a high frequency behavior (i.e. 
Foraging) does tend to require specific morphology, infrequent transoceanic 
flight (example: migration) is a more fuel-limited behavior. The reigning 
nonstop flight champions (godwits, at 7,242 miles each way) do not have 
specific pelagic adaptations. They are a generalized shorebird and simply carry 
a lot of extra fat and muscle when starting migration. Even passerines can 
cross hundreds of miles of ocean on long distance migrations. They don't have 
marine flight adapted planforms; they essentially brute force it. 

>From a biogeographic deep time perspective, this means that a pretty 
>generalized morph of island bird could hypothetically found distant 
>populations.

Cheers,

--Mike

Sent from my Cybernetic Symbiote

> On May 29, 2014, at 12:16 AM, Tim Williams <tijawi@gmail.com> wrote:
> 
> David Černý <david.cerny1@gmail.com> wrote:
> 
> 
>> Another reason is that the biogeographic distribution of paleognaths
>> in combination with the relatively young age of the clade (supported
>> by several molecular dating analyses)
> 
> 
> I admit to being confused on this point.  If neognaths were present at
> the end of the Cretaceous (e.g., _Vegavis_ and _Austinornis_, both
> regarded as galloanserans), how can palaeognaths be a "young" clade?
> Palaeognathae must be at least as old as these.  I may be
> misunderstanding what you mean by your reference to a relatively young
> age for the palaeognaths - if so, I apologize in advance.
> 
> 
>> requires extensive transoceanic dispersal that flightless birds wouldn't be 
>> capable of.
> 
> 
> This requires not just the ability to fly; it also requires flight
> abilities good enough for long-distance overwater dispersal.  This
> includes the ancestors of kiwi and elephant birds.
> 
> The Miocene apterygid _Proapteryx_ is based on an incomplete femur and
> a tentatively referred quadrate - not much to go on in terms of
> whether it was volant or not, except to say that the inferred size of
> this bird is consistent with it being volant.  But it's possible that
> the kiwi lineage (Apterygidae) was always small, and became flightless
> at quite a small body size.  (Interestingly, _Proapteryx_ lived
> alongside crocodilians and terrestrial mammals in early Miocene New
> Zealand.)
> 
> 
>> Johnston
>> (2011) claimed that the Notopalaeognathae topology is compatible with
>> a strictly vicariant scenario (although he still favored multiple
>> losses of flight over a single re-acquisition of flight in tinamous),
>> but his hypothesis relied on incorrect positions of moa and
>> elephantbirds and an unrealistically old estimate for the age of
>> paleognaths.
> 
> 
> I think we have to be careful here.  I'm reluctant to use words like
> "correct" and "right" in the context of any phylogeny - including
> molecular-based phylogenies.  We cannot "know" the true phylogeny - we
> can only use the evidence available to try and discern the
> phylogenetic signal.  On that score, molecular-based analyses are no
> silver bullet.  They have their own problems, and are underpinned by
> assumptions that in the future may be shown to be wanting.  This
> applies both to the gross topology and to the divergence dates
> ('molecular clock') of a phylogeny.  Even retroposon insertions have
> their bugs (e.g., Churakov et al., 2009; 10.1101/gr.090647.108 w.r.t.
> placental evolution).
> 
> Long story short: I don't think palaeognath phylogeny is set in stone.
> This includes the position of tinamous vis-a-vis ratites.  I have to
> say that, based on the corpus of evidence, that it looks increasingly
> like multiple losses of flight occurred across Palaeognathae.  But one
> or two key fossils could confirm or overturn this hypothesis.
> 
> 
>> It may be even more important to find out where lithornithids -- some
>> of which were highly volant -- belong within the (pan-)paleognath
>> tree. Dyke & van Tuinen (2004) and Worthy & Scofield (2012) recovered
>> _Lithornis_ as a stem-ratite and a stem-paleognath, respectively, but
>> since they also found monophyletic "ratites", their results probably
>> can't be trusted.
> 
> 
> This seems to imply that no morphological-based analysis can be
> trusted, at least where palaeognaths are concerned.  If so, and the
> shared similarities between "ratites" is a consequence of convergence,
> then we need basal/volant members of the individual lineages to
> recover palaeognath interrelationships using morphology.
> 
> 
>> Johnston (2011) and most recently Mitchell et al.
>> (2014) supported a sister-group relationship between _Lithornis_ and
>> tinamous, but I wonder if that's not just a result of the high degree
>> of overall similarity between the two taxa.
> 
> 
> That's okay if the high degree of shared similarity is synapomorphic.
> If _Lithornis_+Tinamidae are nested inside the ratites, then it makes
> it less likely that the shared similarities are plesiomorphic for
> Palaeognathae.
> 
> 
> 
> 
> 
> 
> Cheers
> Tim