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Spinosaurus News ~
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 Quote:I feel a caveat with the pneumaticity is that it is not uniform. A pneumatic neck won't help the animal stay much afloat of the rest of the body is dense (which seems to be the case here). At best, the animal will have a floaty head/neck which can reduce the cost of elevating its head above water to breath but the body would still be a sinking rock. Yes, that's what I was referring to, my bad. The earlier suggestions in the thread were precisely as you have said. Quote:Looking at these cross-sections, Spinosaurus matches most closely with those that spend a significant time submerged. The hippo for instance is not a fast moving dolphin (however, it can actually be deceptively fast) but spends a significant time in the water. Good finding. Let it be known that I do not actually find the assignment of the pneumatic vertebrae likely on the whole, my previous post was operating under a 'assuming that x (assignment of pneumatic vertebrae) and y (new lifestyle) are correct, which they aren't necessarily but it's what will be assumed for the sake of demonstration'. Quote:Dr. Ibrahim also made a great point to counter the most recent paper in this article, where he states: ^This I can agree on. I actually think a relatively slow-moving ambush lunge predator would have a very hard time with any airsacs, given their potential to mess up buoyancy and reveal its presence to its prey. Now hearing about it, Ibrahim's newest point makes sense IMO. More than the one from Hone and Holtz, actually. Because you don't need to be a crocodilian-like swimmer to ambush big and slow moving fish.  (01-28-2021, 10:28 PM)DinoFan83 Wrote:Quote:I feel a caveat with the pneumaticity is that it is not uniform. A pneumatic neck won't help the animal stay much afloat of the rest of the body is dense (which seems to be the case here). At best, the animal will have a floaty head/neck which can reduce the cost of elevating its head above water to breath but the body would still be a sinking rock. What studies are available on determining the average thoracic density? How would the lungs and rest of the viscera affect the density relative to 1 g/ml?
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). |
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