Origin of the Palaeognathous Pallet

[Evan Robinson <evanrobinson2004@hotmail.com>]

A number of functional and neotany studies of the Palaeognathous 
Pterogoid-Palatinum Complex (PPC) by S.W.S. Gussekloo are now available 
on-line. My favorite at the moment:
http://www.etcl.nl/diss/wn/2000/002/Gussekloo.htm

I believe that this is his thesis, the actual reference being: Gussekloo 
S.W.S. (2000) The Evolution of the Palaeognathous Birds, Functional 
Morphology and Evolutionary Patterns. Thesis, Leiden University Netherlands. 
Most of the information in his thesis was published in later papers (some 
listed at the end of this post).

?In this thesis is an attempt is made to solve the question where in avian 
phylogeny and how in avian evolution the bifucation between Neognathae and 
Palaeognathae took place.?

Among the conclusions of this study, and others:

1) The ratites represent a separate solution to pallet detachment, and thus 
are a separate branch of evolution from the Neognathae.
2) There are large differences in the morphology of the Palaeognathae pallet 
and the embryonic stages of a neognathous chicken, indicating a 
non-neotenous origin of ratites.
3) The PPC of the Tinamous is approximately half way between the 
palaeognathous and the neognathous conditions, and contains all of the 
critical elements of both. (Future studies seem to modify this slightly).
4) The Palaeognathae are the most basal group in modern birds and the sister 
group of all other living birds.(I?m not sure that this is actually proven 
here).

Nice.

Also of interest, Zweers et al (1997) hypothesized that after achieving a 
lateral bar reducing, skull flexing fenestration, fossil PPCs evolved into 
three separate lineages of palate detachment evolution:
1) A non-kinetic (akinetic) Dromaeosauro-/Archaeoptery-/Enantiornithomorph 
lineage.
2) A (pre)-rhynchokinetic (pre-kinetic) 
Ornithomimio-/Hesperornitho-/Ratitomorph (now called Palaeognathous) 
lineage.
3) A (pre)-prokenetic Troodonto-/Neognathomorph (now called Neognathous) 
lineage.
Birds are found in the later two.

Gussekloo refines this into:
1) An Akinetic (no kinetic) Dromaeosauridae lineage
2) A Pre-kinetic Ornithomimidae/Troodontidae lineage
2) A Kinetic (Avialae) lineage, the basal member of which resembles the 
Tinamou, and which contains all of the elements required for a split into 
Palaeognathae and Neognathae. The kinetic lineage could have evolved from 
any of the previously mentioned lineages.

Zweer had hypothisized that a possible biting force improvement on the upper 
and lower bill enabled in the kinetic Palaeognathous lineage had allowed 
this particular morphology to survive the K-T boundary. The current study 
finds no increase in said biting force enabled by the Palaeognathous pallet, 
but still suggests that the pallet may have been a factor in the extinction 
event by allowing the upper bill to resist external forces (while grazing on 
tough foliage).

(Although bill flexibility may have been an extinction factor, I would think 
that egg-laying strategy would also have been critical to survive the K-T; 
and statistically, diminutive size seems to be important in most extinction 
events). Perhaps a bill that can probe for grubs (such as that possessed by 
the kiwi and some of the Lithornidae) may also have been a useful structure.

Related studies available on-line:
Gussekloo, S. W. S., Vosselman, M. G. & Bout, R. G. 2001
http://jeb.biologists.org/cgi/reprint/204/10/1735.pdf

S.W.S. Gussekloo and R.G. Bout. 2002:
http://wwwbio.leidenuniv.nl/~EEW/G5/zoo9.pdf

I?m not asking anyone to waste too much time on this, but what do you think?

Thanks,

Evan Robinson

http://www.geocities.com/theeggspot/ratites/phylogenies/phylogenies.html

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