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Re: K-Pg extinction global firestorms
Jason Brougham <firstname.lastname@example.org> wrote:
> I agree that it makes the sheltering scenario 'less' improbable, but it is
> still highly improbable as basal birds (palaeognaths, incl. tinamous, and non
> - megapode galliforms) show a highly conserved and almost uniform use of
> simple scrape nests.
> But they spend a great deal of space discussing their evidence and methods so
> it is best if you read the papers rather than have me paraphrase. I'll give
> you the references once more here if that helps.
It's worth noting that a large chunk of Brown and van Tuinen's paper
was copied and pasted from Joseph Brown's PhD dissertation, which is
freely available (see the link below), so there is no need to buy a
copy of _Living Dinosaurs_ just to check their timetree. :-)
David Marjanović <email@example.com> wrote:
>> And according to Phillips et. all (2009) four separate paleognath
>> lineages survived the K-T event.
> So? What calibration dates did they use?
Their primary analysis placed calibrations (with hard lower bounds and
soft upper bounds) on five nodes outside of paleognaths: Archosauria
(normal distribution, 95% of the prior probability density located
between 235 and 250 Ma), Neornithes (normal distribution, 98% range
between 66 and 121 Ma), Galloanserae (uniform distribution, 66–86 Ma),
Aequornithes (lognormal distribution, 97.5% range between 61 and 74
Ma), and Alligatorinae (lognormal distribution, 97.5% range between 64
and 80 Ma). They also ran a second analysis that incorporated two
internal calibrations in addition to the external ones: _Diogenornis_
for the divergence between rheas and other paleognaths and _Emuarius_
for the cassowary/emu split. In hindsight, not using them for the main
analysis seems to have been a pretty good idea -- Alvarenga (2010)
argued that _Diogenornis_ could be more closely related to casuariids
than to rheas.
Mickey Mortimer <firstname.lastname@example.org> wrote:
>> *Vegavis*, itself less than 70 Ma old, doesn't count anymore: the latest
>> phylogenetic analysis of Mesozoic birds (part of the redescription of
>> *Chaoyangia*; Journal of Systematic Palaeontology, online-early; Jingmai
>> O'Connor is one of the authors, probably the first) finds it outside of
>> what should be called Gallanseres. (Possibly even outside Neornithes,
>> because there aren't any other neornitheans in the matrix.)
> Hold on a minute. O'Connor and Zhou's analysis doesn't even include most of
> the characters the Vegavis description used to place it by Anas- lack of a
> pneumatic foramen on the proximomedial surface of ribs; apneumatic coracoid;
> ovoid m. scapulohumeralis cranialis scar; diminutive pectineal process on
> pelvis; numerous hypotarsal cristae.
O'Connor et al. (2011) acknowledged that in the first paper where they
recovered this result:
"The placement of _Vegavis_ outside Neornithes is likely the result of
very low character sampling in this derived clade."
(O'Connor et al. 2011:70)
In the discussion, they further stated that _Vegavis_ can be assigned
to Anseriformes on the basis of "many advanced features absent in
basal ornithuromorphs such as a fully developed hypotarsus" and cited
it as evidence that "by the close of the Cretaceous the
Galliformes–Anseriformes split had already occurred and the radiation
of modern birds was fully underway" (O'Connor et al. 2011: 67). That
said, the sister group relationship of _Vegavis_ and Anatidae is far
less secure -- Mayr (2013) states it's "based on a single character
complex", which seems to be prone to homoplasy. He doesn't question
the position of _Vegavis_ within _Neornithes_, but he notes that its
osteology is quite different from both anatids and the Magpie Goose.
Alvarenga H 2010 _Diogenornis fragilis_ Alvarenga, 1985, restudied: a
South American ratite closely related to Casuariidae. 146 _in_ Miyaki
CY, Höfling E, Donatelli RJ, eds. _Abstracts XXV Int Orn Congr (Campos
de Jordão 2010): recurso eletrônico_. Campos do Jordão: IOC
Mayr G 2013 The age of the crown group of passerine birds and its
evolutionary significance – molecular calibrations versus the fossil
record. Syst Biodivers 11(1): 7–13
O'Connor JK, Chiappe LM, Bell A 2011 Premodern birds: avian
divergences in the Mesozoic. 39–114 _in_ Dyke GJ, Kaiser G, eds.
_Living Dinosaurs: The Evolutionary History of Modern Birds_. London:
John Wiley and Sons