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RE: Nesting birds (was RE: Marsupial forelimbs... or rather hindlimbs)



> > Come to think of it, avians are basally ground
> nesters -- 
> > when did tree-nesting begin? (And which clade is
> it limited to?)
> > 
> Tinamous, ratites, galliforms (basally), and
> anseriforms (basally) seem to
> all be ground nesters.
> 
> Of course, the relationships among Neoaves are
> rather... Um... Uncertain.

Not *that* uncertain... except where it is relevant
here :(

> If we use Livezey & Zusi,

...which is perhaps not such a good idea - but in the
present scope it is OK


> Pelecaniformes and their branch of Natatores have
> examples that nest low in
> the trees, while Procellerariformes, penguins, (and
> I believe loons and
> grebes) are ground nesters.
> 
> In Terrestrornithes: anyone know about the nesting
> habits of gruiforms,
> turniciforms, ralliforms, and charadriforms? (These
> represent one of the two
> clades within the land birds).

And are probably - with maybe the exception of
charadriiforms (which include turniciforms) - closer
to "Natatores" than to other "higher landbirds" (at
least that's what about every modern analysis *except*
L&Z says)

Ground-nesting is the plesiomorphy.
I am not 100% that they are *all* ground-nesters, but
the Anseriformes are neither; in any case we can be
fairly sure that the original condition is
ground-nesting in both.

> The remaining clade
> of land birds are
> unquestionably tree nesters basally.

IF it is a clade. I'd lean towards the alternative
that tree-nesting evolved multiple times
independently.[*]

> So that state seems to polarize well up within
> terrestrornithine neoavian
> neognath birds; it is not a basal avian condition at
> all.

"Metaves" (which would be Cretaceous as a distinct
lineage) include a happy-go-lucky mix of both.

The stork-heron-"core gruiform"-whatnot assemblage
contains both too, and this at least, while it may not
be monophyletic, is part of a polytomic (at present)
clade that is found by almost anyone except L&Z (the
main question is: does this clade contain
Charadriiformes or not? At present, I'd guess it's 70%
in favor of "not")

I may be wrong on this, but: IIRC there is no known
neornithine taxon from the Mesozoic for which there is
any reasonable indication that it might have been a
tree-nester.

I would not go as far as to suggest that niche
separation according to nesting habits was a major
factor in the early-Pg avian radiation, but it is food
for thought.

[*] The problem is: what we know is the status quo.
But what the condition was in the Pg representatives
of everything between core Gruiformes and the
woodpecker-cuckoo-songbird shrubbery - is far less
clear. Eagles for example show that a niche shift can
occur in as little as a few million years. Many
songbirds are fairly catholic as regards where they
build their nest; there is considerable diversity in
Passeroidea for example yet there is no good data
suggesting they originated before the mid-late
Miocene.

So where did proto-herons nest? Sophiornithids?
Pseudasturids? We don't know, but especially the
former I think are crucial. Was _Proardea amissa_
still a ground-nester? What exactly is _"Phasianus"
alfhildae_ and where did it nest?


Regards,

Eike




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