Spinosaurus News ~

[DinoFan83]

I believe lungs/airsacs are modeled based on the extent and distribution of skeletal features (like pneumatic foramina) that suggest them. For example, Bates et al. (2009):

Quote:The CAD environment allows easy incorporation of objects within reconstructed body volumes. This enabled us to reconstruct the size and shape of embedded respiratory structures on the basis of osteological and phylogenetic inferences of anatomy [52]–[54], without being restricted to simplified geometric shapes.

The 3 giant modeled theropods were Acrocanthosaurus specimen NCSM 14345 as well as T. rex specimens MOR 555 and BHI 3033, and they were all about the same density (91.2%, 92.5%, and 90.5% as much as water respectively), which averages out to 91.4% as dense as water. This is basically the same density as Scott Hartman's GDI estimates (though the result are wrong, the density does not seem to be given how close it is to the study), which assumed a density 91.3% of water.

However, both of these estimates were made well before the revision on non-avian dinosaur density by Larramendi, and they had originally assumed the animals in question to have been as dense as water before the lungs and airsacs were modeled. Larramendi, in contrast, estimated terrestrial non-avian theropods to have been a mean of 97% as dense as water when the lungs and airsacs were taken into account, meaning that the body parts (eg: neck, thorax) that had lungs and airsacs modeled within them were probably some 6.2% denser than water if there were no airsacs.

But that's not all. As close as it may be to the density of water, 0.97 is almost certainly too low a specific gravity for the neck of whatever the owner of those cervicals was (should anyone be wondering about this). If Janensch (1947) is anything to go by, T. rex would have had a lot more cervical pneumatophores than any of the specimens Lakin & Longrich describe given that the latter authors do not suggest the cervicals they describe had pneumatophores in the cervical ribs, neural arches, and centra all at once.

Quote:The precaudal vertebral column was heavily pneumatized, with pneumatopores penetrating the centra and neural arches of all presacral vertebrae, the cervical ribs, and the anteriormost four sacral centra

In summary, it appears the studies that have tried to estimate thoracic density had probably underestimated it by some 6.2%. This suggests that things like viscera would have been what brought up the density, as none of the pre-2020 estimates appear to have accounted for them. So a plausible density for an airsac-free theropod thorax could be 6.2% denser than water (such density can be used on Spinosaurus' thorax for instance). Reply