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SKULL BONES
SALT GLANDS
It is a common misconception that big frontal salt glands are seen in
all birds. There is usually a small supraorbital salt gland situated
somewhere either preorbital or overhanging the orbit (Witmer 1997).
However, this has little to do with the endothermy/ectothermy debate
since not all dinosaurs lived near salt water and the nasal gland does
not always mean that a bird can drink seawater. In most birds it is
simply a nasal gland that is homologous to the nasal gland seen in other
sauropsids (Witmer 1997). Only in seabirds does it have the salt
excreting function.
LOSS OF THE PREFRONTAL
Buhler (1992) has argued that many of the typically avian features such
as sandwich brancase construction, flat bones, fusion of bones, loss of
teeth, etc. were evolved to reduce the weight of birds. It is possible,
as postulated by Chiappe et al. (1998), that the prefrontal of birds
(not to be confused with the prefrontal of birds which is the lacrimal)
became fused with the ecthetmoid, the important bone that help allows
streptostyly in birds. In dromaeosaurs, where the ecthemoid is not
present, the prefrontal was probably fused with the frontal or lacrimal
and indepently lost. Another possibilty is that the enalrged
ecthetmoid/prefrontal? of Shuuvia is just simply an enlarged ecthemoid
that is larger than the ecthetmoid seen in other birds. It is also
possible that the prefrontal fused with the frontal in dromaeosaurs and
in birds ossified together with the anterior frontal to become the
ecthetmoid. So many possiblities...
Matt Troutman
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