RE: something's wrong here: Qianosuchus phylogeny

[Tim Williams <twilliams_alpha@hotmail.com>]

David Peters wrote:

> No wonder the authors were not able to figure out where Qianosuchus nested. 
> They needed the following taxa: Triassolestes, Turfanosuchus, 
> Pseudhesperosuchus.

Just a minor quibble.  _Triassolestes_ is a fossil dragonfly (Tillyard, 
1918), _Trialestes_ is the fossil crocodylomorph (Bonaparte, 1982 - to 
replace _Triassolestes_ Reig, 1963).

> And when all the work is done, you have to step back, take a look at the 
> whole thing and ask yourself: "Does this make sense?" remembering that 
> evolution works in tiny increments.

Two things...

(a) "Does this make sense?" is a question that too often is answered by 
someone who believes that there own opinions have priority over analysis of 
the data.  This is also called "hand-waving".

(b) Evolution does not *always* work in tiny increments.  Here's an example 
of one hypothesis to the contrary...

Sears K.E., Behringer R.R., Rasweiler J.J. 4th, and Niswander L.A. (2006) 
Development of bat flight: morphologic and molecular evolution of bat wing 
digits.  Proc. Natl. Acad. Sci. USA. 103: 6581-6586.

Abstract: "The earliest fossil bats resemble their modern counterparts in 
possessing greatly elongated digits to support the wing membrane, which is 
an anatomical hallmark of powered flight. To quantitatively confirm these 
similarities, we performed a morphometric analysis of wing bones from fossil 
and modern bats. We found that the lengths of the third, fourth, and fifth 
digits (the primary supportive elements of the wing) have remained constant 
relative to body size over the last 50 million years. This absence of 
transitional forms in the fossil record led us to look elsewhere to 
understand bat wing evolution. Investigating embryonic development, we found 
that the digits in bats (_Carollia perspicillata_) are initially similar in 
size to those of mice (_Mus musculus_) but that, subsequently, bat digits 
greatly lengthen. The developmental timing of the change in wing digit 
length points to a change in longitudinal cartilage growth, a process that 
depends on the relative proliferation and differentiation of chondrocytes. 
We found that bat forelimb digits exhibit relatively high rates of 
chondrocyte proliferation and differentiation. We show that bone 
morphogenetic protein 2 (Bmp2) can stimulate cartilage proliferation and 
differentiation and increase digit length in the bat embryonic forelimb. 
Also, we show that Bmp2 expression and Bmp signaling are increased in bat 
forelimb embryonic digits relative to mouse or bat hind limb digits. 
Together, our results suggest that an up-regulation of the Bmp pathway is 
one of the major factors in the developmental elongation of bat forelimb 
digits, and it is potentially a key mechanism in their evolutionary 
elongation as well."


Cheers

Tim

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