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Respiratory turbinates, what they don't mean



There have been some questions posed concerning the energetic implications of
respiratory turbinates in dinosaurs. Its a big subject that cannot be given
its due here, so a few notes. RT are often entirely cartilagenous in every
respect, and leave absolutely no bony trace of their existence (the common
avian condition). The form of RT is also extremely variable. The only way to
disprove their existence in a fossil is by showing that there is not enough
room for them in the main (nonolfactory) nasal passage.

John Ruben claims that theropod dinosaurs do not have enough room for
effective RT because their nasal passages are too small. This is incorrect.
When theropods and birds of similar body mass are compared, the former have
main nasal passages whose volume approaches, equals and often exceeds that of
birds. Most theropods have very big heads, so their nasal passages appear
small relative to the head. However, the same is true of big headed birds
such as diatrymids, phororachids, shoebill storks, toucans and hornbills.
Bang (1971) published the nasal passages of hornbills, and they look tiny
compared to the big head! Most birds have relatively small heads, so the
nasal passages appear large. The belief that birds have bigger nasal passages
than theropods is an illusion caused by failure to reproduce the figures at
the same scale, and to take body size into account. I could go on and on and
on about this, but you will all have to wait until the paper comes out
(finsihing it will have to wait until Ruben's paper comes out sometime this
year).

GSPaul