Spinosaurus News ~

[DinoFan83]

Quote:Would it be possible for Spinosaurus to have pneumatized cervical vertebrae but then reduction/obliteration of such more caudally? The thought came to me from this quote from Ibrahim et al. (2020):

"With much additional spinosaurid material now available for other taxa such as Baryonyx, Suchomimus and Ichthyovenator, we know that the extent of lamination and pneumaticity varies not only along the presacral column of single individuals as might be expected, but also between spinosaurid genera."

From Lakin and Longrich (2019), an indeterminate spinosaurid's thoracic vertebra lacked pneumatization.:

"FSAC-KK-18121 is a partial anterior thoracic vertebra. The neural arch is completely absent and the articular facet of the centrum is poorly defined. There is no central pneumatic foramen, nor is the parapophysis present on the centrum (Fig. 6G&6J), supporting the diagnosis of an anterior thoracic vertebra."

I do agree that if those pneumatized cervicals really did belong to Spinosaurus, it is likely for the airsacs to have been limited to the neck or otherwise reduced elsewhere. Assuming that Spinosaurus had any airsacs at all, the only advantageous place to really have them would be that region; there's not really a whole lot that would benefit it from airsacs elsewhere.

Quote:I am unsure what trends are in other dinosaurs. However, a pneumatized skull and cervical column would allow easy access to air and above water vision which could fit with the aquatic behavior.

While you are correct that airsacs in the neck allow for greater ease in above-water activities, it is important to keep in mind that crocodilians are able to maintain a float and vision above water simply by inhaling, so Spinosaurus may not have necessarily needed airsacs to get a good breath, good view above water, etc.
I'm not saying the assignments of pneumatic cervicals were definitely wrong, but that not having airsacs wouldn't necessarily be a disadvantage for the above activities.

Quote:Whatever the case, the obliterated medulla of the long bones need to be reconciled with the cervical pneumatization (assuming those are correctly assigned). A floating animal (<1 density) would either mean Spinosaurus stayed at the surface or the density is wrong if Spinosaurus was a sinking animal.

I think the most parsimonious scenario if we were to assume that the animal had both pneumatic cervicals and very dense long bones is that the overall density could be changed at will by inflating and deflating the airsacs as needed. In this scenario, with the airsacs inflated, the whole density would be slightly less than water for an easier time floating, but with the airsacs deflated when the animal was underwater (as it presumably would be most of the time), there wouldn't be anything preventing it from being at least as dense as water if not moreso. Reply