[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: CNN on Lungs and Feathers
Regarding the discussion concerning the meaning of the presence of pneumatic
verterbrae and other skeletal adaptations in theropods.
The importance of pneumatic vertebrae is that they essentially prove the
presence of air-sacs in theropods. This is according to Britt (in the
Encylopedia of Dinosaurs) and Reid (BYU Geol. Studies 1996).
The next question is whether theropods had the skeletal adaptations needed to
ventilate more ventral and posterior air-sacs. It is important to understand
that many avian adaptations are not critical to this system. Large ossified
sternal plates, ossified uncinate processes, and broad ribs are all absent in
various birds, especially nonflying forms. At the same time dromaeosaurs had
large sternal plates and ossified uncinate processes. So go figure. Anyway,
what IS needed are long posterior ribs with well developed double heads that
allow them to be highly mobile. These can change the volume of posterior
air-sacs, and they most certainly are present in theropods, especially
avetheropods which have the most bird-like trunks of any tetrapods. Because
theropods had both pneumatic bones, and ribs able to operate air-sacs, they
had a preavian respiraotry complex.
Back to birds, there have been arguments that enantiornithines had rather low
metabolic rates, in part because they lacked ossified sternal ribs that may
be needed to achieve the high aerobic exercise capacity of flying birds. Yet
Late Cretaceous Neuquenornis had ossified sternal ribs and a sternum as large
as in modern birds. Looks like the fossil bird's aerobic flight capacity was
as high as in living examples.
As for croc-lungs in dinosaurs, Phil Currie has just returned from examining
the type Sinosauropteryx slab. And no Virginia, Ruben et al's septum does not
exist, it's complete air from top to bottom. So much for that notion.