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Re: Moa-Tinamou Clade Found Within Ratites
evelyn sobielski <firstname.lastname@example.org> wrote:
> Did anyone count how often paleognath phylogeny was "resolved" yet?
And I would guess that palaeognath phylogeny will be resolved again
some time in the future, . :-)
With tinamous nested inside ratites, the most favored hypothesis is
that the palaeognaths underwent multiple losses of flight, leading to
the various flightless ratites we see today. The alternative
hypothesis - that the palaeognath clade is primitively flightless, and
tinamous regained flight from a flightless ancestor - isn't given much
truck. This "secondary volant" hypothesis is considered unlikely
because secondary loss of flight is very common across Aves, but there
are no known examples of bird lineages that have lost and regained
flight (although apparently it happens in insects).
However, it's worth noting that tinamous are extremely poor fliers.
It's not just that tinamous are reluctant to fly (in fact, they will
do almost anything to avoid it), their flight abilities are also
extremely weak. This is a result of the short, rounded wings as well
as their low aerobic metabolism (which sets them apart from ratites,
and is a consequence of having a relatively small heart and lungs).
One source (Clive Roots' _Flightless Birds_) even describes tinamous
as "semiflightless". Their morphology is consistent with birds that
are in the process of losing the power of flight - although tinamous
have been 'stuck' in this morphology for millions of years.
It is even conceivable that the weak flight abilities of tinamous are
a consequence of regaining flapping flight abilities from ancestors
that were technically flightless but retained the anatomical equipment
associated with flight in rudimentary form - as many flightless birds
do. Thus, tinamous could have evolved from ancestors that were
technically flightless, and shifted to (weak) flapping flight by
secondarily expanding the flight muscles, but not doing much else (for
one, the cardiovascular system was poorly adapted for sustained
flight). The various ratite lineages, on the other hand, went all the
way and dispensed with flight abilities completely, becoming bigger in
Then again, it may be that the most recent common ancestor of ratites
and tinamous was a perfectly decent flier after all, and
flightlessness (and near-flightlessnes in the tinamous) arose several
times within the palaeognath clade. Palaeognaths may have begun as
rather small, volant birds with excellent flight abilities (unlike the
tinamous). Key to this is _Proapteryx_, the fossil kiwi (apterygid)
from the early Miocene of New Zealand, which was smaller than extant
kiwis and possibly volant (Worthy, 2013). If basal apterygids were
indeed volant, it improves the chances for kiwi ancestors to have
arrived in NZ via overwater dispersal.
> And do Baker et al (2014) address the concerns of Smith et al (2013)
> Kimball et al (2013?)
> and Yuri et al (2013)
> regarding the need to test any
> "new phylogenomic sequences from 1,448 nuclear DNA loci totalling almost one
> million base pairs"
> (and RGCs just as well) on whether they actually retain phylogenetic signal?
> An additional question: considering we have no problems getting the
> artificial (Paleognaths,(Passerines,other neognaths)) or
> (Paleognaths,(Galloanseres,(Passerines,other Neoaves))) quite robustly
> supported - how can we be sure (Ostrich,other paleognaths) is not artificial?
> Ben Creisler <email@example.com> schrieb am Mi, 14.5.2014:
> Betreff: Moa-Tinamou Clade Found Within Ratites
> An: firstname.lastname@example.org
> Datum: Mittwoch, 14. Mai, 2014 04:24 Uhr
> From: Ben Creisler
> Here's the citation and link for the new paper on ratite
> Allan J. Baker, Oliver Haddrath, John D. McPherson and
> Alison Cloutier (2014)
> Genomic Support for a Moa-Tinamou Clade and Adaptive
> Convergence in Flightless Ratites.
> Molecular Biology and Evolution (advance online
> doi: 10.1093/molbev/msu153
> One of the most startling discoveries in avian molecular
> is that the volant tinamous are embedded in the flightless
> but this topology remains controversial because recent
> phylogenies place tinamous as the closest relative of a
> ratite clade. Here, we integrate new phylogenomic sequences
> from 1,448
> nuclear DNA loci totalling almost one million base pairs
> from the
> extinct little bush moa, Chilean tinamou and emu with
> sequences from ostrich, elegant crested tinamou, four
> neognaths and
> the green anole. Phylogenetic analysis using standard
> models and heterogeneous models robust to common topological
> recovered compelling support for ratite paraphyly with the
> little bush
> moa closest to tinamous within ratites. Ratite paraphyly was
> corroborated by eight independent CR1 retroposon insertions.
> of morphological characters reinterpreted on a 27-gene
> topology indicates that many characters are convergent in
> the ratites,
> probably as the result of adaptation to a cursorial life