[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: Avian origins: new analysis confirms ancient beginnings

Yep - a storm in a tea cup given that there were crown-group anseriforms 
(_Vegavis_) around in the Late Cretaceous.

Cheers, Tim

> Date: Wed, 6 Feb 2008 04:15:09 +0100
> From: koreke77@yahoo.de
> Subject: RE: Avian origins: new analysis confirms ancient beginnings
> To: dinosaur@usc.edu
> --- Janet m vandenburgh  schrieb:
>> http://www.physorg.com/news121444505.html
>> Avian origins: new analysis confirms ancient
>> beginnings
>> Did modern birds originate around the time of the
>> dinosaurs' demise, or have
>> they been around far longer?
> "...suggesting that they arose more than 100 million
> years ago, not 60 million years ago, as fossils
> suggest."
> I wonder where they dug out *that* gem... they did
> have to dig quite deep in any case. Even BCF can hold
> more in its favor...
> And even BMC states: "DNA points to missing bird
> fossils"
> But we don't know whether they *are* missing. And as
> the news article *does* point out, it is unlikely that
> we would easily recognize them as what they are, if
> it's not nearly complete associated skeletons.
> Supposing _Gallornis straeleni_ was neornithine (which
> at present cannot be falsified) - I think there is no
> mol-clock study that would withstand modern scrutinity
> that suggests *that* early an age for the split.
> (Actually, it is so fragmentary and little-suited to
> large scale phylogenetic morph analyses that the
> mol-clock data is at present the most practical
> argument *against* it being neornithine).
> And of course - since enantios split off from their
> LCA with modern birds more than 125 MA ago and much of
> what diverged in the latter's lineage basal to
> Neornithes almost certainly also split off not too
> late thereafter, the fossil record gives a window of
> about 120-90 MA where the origin of Neornithes can be
> placed with much comfort. May be earlier, may be
> later, but eneither (especially the latter) is very
> plausible at present.
> In other words: the fossil record says "older than 100
> Ma but not *very* much so? Pretty damn likely." We
> apparently have a fair Mesozoic sample - of odds and
> ends, but still - of most Neornithes the mol data says
> we should have.
> Yet this is a most interesting paper in that the
> "Consensus" phylogeny has a few key points, and I
> would have liked to see this dwelled upon more than
> some flimsy straw man about a fossil record that may
> just as well be unrecognized and a time of origin that
> is at least not contradicted by the recognizable
> record.
> Cypselomorphs and Mirandornithes are recovered, as
> well as the loon-tubenose-penguin clade (which ties in
> ever so nicely with the fossil record) as well as a
> "passerimorph" (or whatever) group containing
> woodpeckers, rollers, etc. but not cuckoos. A
> Metaves-Coronaves split is not recovered; rather here
> is a basal polytomy among Neoaves which as certainly
> as anyone can be certain about this must predate the
> K-Pg boundary. Charadriiformes are not the basalmost
> crown clade among Neoaves as they are in several other
> studies.
> Cypselomorphs stand out as oddballs (and
> Falconiformes, which clade with Charadriiformes -
> which IIRC does *occasionally* happen). In the latter
> case, it is known that accipitrids are genomically
> aberrant which may make their rate of molecular
> evolution hard to compute; they certainly have a nasty
> tendency to be not stable in molecular phylogenetic
> analyses, except when they wind up in a polytomy
> rather basal among Neoaves.
> (And yet - the charadriiforms stand apart from all
> other "higher waterbirds". As usual.)
> For the cypselomorphs, something similar may apply;
> they are unique among all major crown avian clades for
> having a metabolism that (in extratropical taxa at
> least) can switch to torpor mode[*] by default. The
> range of conditions under which for example the
> mitochondrial enzymes in a Ruby-throated Hummingbird
> can function is very extreme among birds, probably one
> of the most extreme among homoiotherms in general. It
> is hard to imagine that this has *not*
> influenced/restricted their evolution in some way.
> It looks pretty robust all-around and may well be one
> of those brilliant ones. Nowhere until now was the
> fact that morphological distinctness postdates
> population divergence postdates lineage divergence so
> clearly illustrated. And much of the "supraordinal
> clades" (or whatever you want to call them) gets
> resolved amazingly well. Their interrelationships far
> less so, but the charadriiforms, the
> tubenose-and-allies group, etc had the K-Pg bottleneck
> to cope with, which is likely to have screwed up
> things to a point where the true phylogeny is hardly
> recognizable on the molecular level.[**]
> The provisional PDF version is here:
> http://www.biomedcentral.com/content/pdf/1741-7007-6-6.pdf
> Eike
> [*] As far as I have grokked it, torpor metabolism is
> a rather derived spinoff of poikilothermy, which
> itself is plesiomorphic among amniotes as a whole
> however and almost certainly was not present anymore
> (except in hatchlings) even before Neornithes. It is
> not a neoteny or an atavism in the strict sense (it
> seems) as it is not simply the hatchling metabolism
> being retained or the "reptile" metabolism reemerging;
> hummers, swift, nightjars etc can switch to
> poikilothermy if need be, but they are generally
> homoiotherms, in the case of hummers with a very
> fast-paced and robust metabolism operating at
> extremely high (for an amniote at least) temperatures.
> [**] That the tubenoses-and-allies still clade
> suggests that either their internal divergence just
> postdates the K-Pg boundary or that whatever the
> bottleneck was, it was not strong enough to obscure
> the relationships at least of *these* lineage. This is
> a good candidate for the next major neoavian clade to
> gain widespread recognition.
> E-Mails jetzt auf Ihrem Handy.
> www.yahoo.de/go

Need to know the score, the latest news, or you need your Hotmail®-get your