SKULL BONES

["Matthew Troutman" <m_troutman@hotmail.com>]

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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