Vivere come un Sauroposeidon

[Vladimír Socha]

Good day!

I'd like to ask especially sauropod experts here, are there any new hypotheses about the efficiency of cardiovascular system in giant sauropods with enormous necks and their heads held pretty high - as much as 18 meters above the ground in Sauroposeidon proteles? How thick and tough were the veins and arteries walls in Mamenchisaurus sinocanadensis and Supersaurus vivanae with their necks over 15 meters long? What extreme anatomical and physiological adaptations were at play in their hearts, lungs, veins etc? Around 2000 it was suggested that just pumping blood up to the head on an elevated neck for long would have used about half of its energy intake. Also, it was estimates that moving blood to such a heigth (dismissing posited auxiliary hearts in the neck) would require a heart 15x as large as of a similar-sized cetacean! And you've probably seen how big is the heart of Balaenoptera musculus...

The above have been logically used to argue that the long neck must instead have been held more or less horizontally, even in titanosaurs and brachiosaurids. OTOH research on living animals demonstrated that almost all extant tetrapods hold the base of their necks sharply flexed when alert, showing that any inference from bones about habitual "neutral postures^" is deeply unreliable. So they probably were holding their heads 15 or more meters above the ground, about three or even for times higher than tall giraffes. Will paleontology shed light on these miracles of nature (and nature engineering) one day?

And also, does the idea of sauropods not being able to submerge completely (because they wouldn't be able to breathe) still hold? Especially a study by Kermack (1951) demonstrated, that if the animal were submerged in several metres of water, the pressure would be enough to fatally collapse its lungs and airway. We now know of course, that these early studies were flawed as they ignored that the bodies of sauropods were heavily permeated with air sacs. Even the heaviest sauropods would hence have been buoyant and would not have been able to submerge their torsos completely below the surface of the water. They would practically float, and would not have been in danger of lung collapse due to water pressure when entering the deeper waters or even swimming. Any thoughts on this?

Thank you in advance, VS.

References:

Kermack, K. A. (1951). A note on the habits of sauropods. Ann. Mag. Nat. Hist. 4 (44): 830–832.

Choy, D. S.; Altman, P. (1992). The cardiovascular system of barosaurus: an educated guess. Lancet. 340 (8818): 534–536.

Stevens, K. A.; Parrish, J. M. (1999). Neck posture and feeding habits of two Jurassic sauropod dinosaurs. Science. 284 (5415): 798–800.

Seymour, R. S.; Lillywhite, H. B. (2000). Hearts, neck posture and metabolic intensity of sauropod dinosaurs. Proc. Biol. Sci. 267 (1455): 1883–1887.

Henderson, D. M. (2004). Tipsy punters: sauropod dinosaur pneumaticity, buoyancy and aquatic habits. Proceedings of the Royal Society of London B. 271 (Suppl 4): S180–S183.

Taylor, M. P.; Wedel, M. J.; Naish, D. (2009). Head and neck posture in sauropod dinosaurs inferred from extant animals. Acta Palaeontologica Polonica 54 (2), 2009: 213–220.

Seymour, R. S. (2009). Raising the sauropod neck: it costs more to get less. Biol. Lett. 5 (3): 317–319.

Sander, P. M.; et al. (2011). Biology of the sauropod dinosaurs: the evolution of gigantism. Biological Reviews. 86 (1): 117–155.

Cobley, M. J.; Rayfield, E. J.; Barrett, P. M. (2013). Inter-Vertebral Flexibility of the Ostrich Neck: Implications for Estimating Sauropod Neck Flexibility. PLOS ONE. 8 (8): e72187.

Henderson, D. M. (2013). Sauropod Necks: Are They Really for Heat Loss?. PLOS ONE. 8 (10): e77108.

Taylor, M. P.; Wedel, M. J. (2013). Why sauropods had long necks; and why giraffes have short necks. PeerJ. 1: e36.

Stevens, K. A. (2013). The Articulation of Sauropod Necks: Methodology and Mythology. PLOS ONE. 8 (10): e78572.

Moore, A. J.; et al. (2023). Re-assessment of the Late Jurassic eusauropod Mamenchisaurus sinocanadorum Russell and Zheng, 1993, and the evolution of exceptionally long necks in mamenchisaurids. Journal of Systematic Palaeontology. 21 (1).

[Jura]

The short answer here is that nothing new (mathematically) has been done in this field since Seymour's treatment. I and others think that Seymour has been a bit too iron fisted (pun intended) with the physiology calculations, but they still remain the most recent treatment. We have some sauropods that show good evidence for raised necks at their base (e.g.,  Euhelopus zdanskyi), but that is no guarantee that the neck stayed that way all the way to the head, nor does it mean that much larger sauropods were doing the same. Sauropod neck position remains a conundrum, especially from a cardiovascular point of view.

[Gregory Paul]

For an extensive technical examination of the issue of neck posture see https://anatomypubs.onlinelibrary.wiley.com/doi/full/10.1002/ar.23617

The results show that most sauropods usually carried their necks erect, including one case of cervicals fused in that position (diplodocoids had horizontal necks). How this was accomplished BP wise remains unclear. The Kent Stevens work about all sauropod necks being low has faded because it is not in accord with sauropod anatomy and animal biology. There has been some recent work on giraffes that indicates they have some sort of siphon. I know Seymour and he is not happy with the work on sauropod neck posture, but agrees it looks like they did have high held heads. 

That pneumatic sauropods could not sink is a reason they were not highly aquatic. Hippos in contrast are so dense SG ~1.1 they cannot surface swim (and are at risk of drowning if they get into water too deep for them to stand and snorkel, same probably for armored dinosaurs, maybe ceratopsians), see https://anatomypubs.onlinelibrary.wiley.com/doi/full/10.1002/ar.24574 

- be warned, it's a heavy read;) no really, it is.  

GSPaul 

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