Re: Waimanu & avian evolution (comments)

[john bois <jbois@verizon.net>]

----- Original Message ----- 
From: "Michael Habib" <mhabib5@jhmi.edu>
To: <dinosaur@usc.edu>
Sent: Friday, May 12, 2006 1:55 PM
Subject: Re: Waimanu & avian evolution (comments)


> 1) Is their method of estimating 'decline' a good one?  The authors
> looked at character evolution (body size) in pterosaurs, but the real
> emphasis seems to be on apparent species diversity.

They are synthesizing a model to explain the pattern of diversity, size, and
extinction of pterosaurs.  From Unwin (2003) they report a long pterosaur
decline in diversity and deem the bolide practically irrelevant because of
it...i.e., other forces were at work.  They note a decrease in diversity of
small sized pterosaurs concurrent with a pre K/T radiation of neornithines
(which they claim is practically cemented by the penguin and other recent
discoveries).  Their hypthothesis is that birds outcompeted or preyed on
pterosaurs forcing them out of the small-flier niche and mandating
specialization at larger sizes.  So, as you say, the main part of the paper
is on the timing of bird radiation--the rest is trying to sequence the data
into a reasonable narrative.

> However, this is
> not an evenly applicable measure.  Due to locomotor differences, it
> should be expected that pterosaur species diversity would be low
> compared to most bird groups (seabirds possible excepted), but may
> still have been represented disproportionately in biomass or geographic
> range.  Any thoughts?

I think it's fair to compare diversity _within_ the pterosaur taxon, and,
noting a decline there, correlate it with a within-taxon rise in neornithine
diversity.  They do make the point somewhere that a species may have
profound ecological impact without being especially diverse or numerous.

> 2) The authors make at least one comment about the possible impact of
> early Falconiforms (which they have placed in the Cretaceous in this
> analysis...I find that dubious for reasons that can be discussed
> later).  Even if the authors are correct about this ancient origin of
> Falconiforms, is there any good reason to assume that the early forms
> were already raptorial?

Probably not...but what is intriguing is the already far-down-the-path to
penguinhood morphology of Waimanu.  Re: Falconiforms...I think what may be
coming more clear is the incredible airworthiness of the aft adaptations for
aerial agility!  In my view, nasty claws and beaks are relatively
off-the-shelf features compared to say, a tail fan.  Is this reasonable?

> Of course, I would also love to hear everyone's thoughts regarding the
> dated tree itself, which is ultimately the most important part of the
> paper.

Interesting that no one here took up that challenge--or, did I miss it?



> > This was discussed earlier on this list, but this is the official
> > paper...
> >
> > Kerryn E. Slack, Craig M. Jones, Tatsuro Ando, G. L. (Abby) Harrison,
> > R. Ewan Fordyce, Ulfur Arnason and David Penny (2006) Early Penguin
> > Fossils, Plus Mitochondrial Genomes, Calibrate Avian Evolution.
> > Molecular Biology and Evolution 23: 1144-1155
>