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More on respiratory turbinates
The questions about RT that Miller is asking are very pertinent.
In Ruben et al 1996 they measured only the narrow horizontal anterior portion
of theropod nasal passages. A number of birds also have narrow anterior nasal
passages that contain a simple RT, the kiwi being one example, tube nosed
seabirds another. In theropods this part of the nasal passage is fairly easy
to measure because it is largely enclosed by bone (but it is almost always
crushed, as per the "Nanotyrannus" [it's probably a baby T rex] skull). The
problem is that there is a subvertical, posterior part of nasal passage
proper immediately above the internal nares in theropods. (Basically, the
majority of the nasal passage makes an L-shaped loop around the large
auxilary maxillary sinuses in avetheropods). There is no way to reliably
measure the size of this part of the NP because it is almost entirely NOT
enclosed by bone. But being in a broader portion of the skull, it may have
been two, three or more times broader than the anterior passage. In many
birds it is the posterior portion of the NPP that is the broadest and
contains the larger RT directly above the internal nare, again kiwis being an
example. Maybe theropods did the same thing. Since they were insulated
creatures that probably had elevated resting metabolisms my guess is that
they had cartilage RT like most birds. But who knows? In any case RT cannot
be a reliable diagnostic tool for estimating dinosaur energetics because we
cannot determine their presence or development in any dinosaur.
What we do know is that the lizard-like nasal passage restoration of
Dromaeosaurus by Ruben etc. is just plain incorrect. First, they use Phil
Currie's complete skull restoration, which is inappropriate because it's
highly restored. Check out Fig. 1D-E in Currie (1995 JVP 15:578). Of the
snout, only fragments of the premax, maxilla, vomers and palatines are known!
The nasal passage is not preserved at all! (See medial view of skull elements
in Fig. 2 in Currie 1995.) So how can one draw its path? What is much more
informative are complete Velociraptor skulls. These little darlings show that
dromaeosaurs had the standard L-shaped nasal passage of avetheropods, with
the anterior portion running in a long tube just below the snout roof, before
plunging vertically in the mid-section of the skull (because Dromaeosaurus
had the same kind of maxillary sinuses as it realtives, its NP was almost
certainly L-shaped). So, the reality is that the dromaeosaur nasal passage
was long and fairly complex. The same was probably true of Archaeopteryx and
other early birds, which retained the avetheropod maxillary sinus system
marked by auxiliary antorbital fenestra.
Now there, you can all breath easier now.