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RE: Moa-Tinamou Clade Found Within Ratites



> From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] On Behalf Of Tim 
> Williams
>
> 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.

Perhaps what is meant is crown-group palaeognaths, rather than the total group?

> > 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.

Thank you! I was going to bring this up!! Not all island fauna are secondarily 
flightless!

> > 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).

Quite so. The easiest test of this in the world is the observed fact that 
different molecular analyses can produce discordant results, and single 
analyses produce greatly more than 1 most parsimonious tree. Both of these 
indicate that the data are not 100% decisive, and that for a variety of reasons 
there are ambiguities in the record. This is true for bones, it is true for 
soft tissues, it is true for genes, it is true for genomes. Those who are 
trapped in the "my technique yields the TRUE answer" mentality have to grow out 
of the 1990s and move on...

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216                        
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661               

Faculty Director, Science & Global Change Program, College Park Scholars
http://www.geol.umd.edu/sgc
Fax: 301-314-9843

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA