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Origin of the Palaeognathous Pallet
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:
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
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
2) A (pre)-rhynchokinetic (pre-kinetic)
Ornithomimio-/Hesperornitho-/Ratitomorph (now called Palaeognathous)
3) A (pre)-prokenetic Troodonto-/Neognathomorph (now called Neognathous)
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
(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
S.W.S. Gussekloo and R.G. Bout. 2002:
I?m not asking anyone to waste too much time on this, but what do you think?
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