Sauropod Necking: Feedback on ideas please

Hi everyone, I would like to share an essay I wrote and would like to receive feedback. It all goes well, I hope it will help start a discussion.

The possibility of giraffe style necking in sauropods
By: Dakota Hudson

It has been speculated that male sauropod dinosaurs could have used their long necks in combat in a manner similar to modern male giraffes. This behavior is called ‘necking’, and is used by males to establish dominance within groups. Winners of these bouts gain greater reproductive rights as a result. There are two types of necking observed in giraffes: low intensity and high intensity. Low intensity involves the males rubbing and leaning against each other’s necks. Whichever male is able to hold himself more erect is the winner. High intensity, as the name suggests, is far more violent. Here the males will exchange blows to the neck, using the horn-like ossicones on the tops of their heads to deliver the blows.

In order to test this idea, I first hypothesized that perhaps the seemingly repetitive nature of this activity may lead to microfractures in the neck vertebrae which, once healed, would reinforce the bone of the vertebrae making them stronger and harder. This is something that could be detected in well-preserved fossils of sauropod neck vertebrae. So, I did research into the injuries sustained by giraffes to see if this hypothesis was plausible.

Unfortunately, there wasn’t any information about microfractures being found in giraffe necks. While this doesn’t necessarily rule out the possibility, it does render the hypothesis difficult to test to the point of unfalsifiability. However, the available literature did have other information that would be helpful in determining if necking behavior occurred in sauropods.

In high-intensity necking, fractured jaws and neck vertebrae are common injuries among male giraffes. There are even reports of giraffe deaths caused by broken necks due to more violent bouts of necking. These pathologies could possibly be found in sauropod fossils, assuming that well-preserved fossils revealed such injuries. Usually, the only sure-fire way to determine an injury in a fossil is if the organism survived the injury long enough for the injury to have healed. This can be seen in the bone structure. For example, a healed fracture on a rib may have an unusual lump of bone where the fracture occurred. Otherwise, any other damage could be attributed to scavenging, deformation during fossilization, or erosion, etc.

However, at the time of writing this essay, no preserved injuries of this nature have been found in sauropod neck vertebrae or jaws. This could be due to the bias of the fossil record, as complete spinal columns and skulls of sauropods are rare finds. However, other details of anatomy give reasonable doubt to the sauropod high-intensity necking hypothesis.

For starters, male giraffes have dedicated adaptations for high-intensity necking. As mentioned earlier, horn-like ossicones are used to deliver the blows during high-intensity necking. These structures occur in both sexes and may have a role in thermoregulation in addition to being the main weapons used by males in high-intensity necking. The structure of ossicones is highly vascularized (or is full of blood vessels) and is made of ossified cartilage. These structures are fused to the skull at the parietal bones. The ossicones are also covered in skin. Females and young giraffes tend to have tufts of hair on top, while sexually mature males tend to be bald. While cartilage is rarely preserved in the fossil record, many ancient relatives of the giraffe have had at least the ossified portions of their ossicones preserved. Even if no sign of the ossicones survived long enough to be preserved, the points on the skull where the ossicones were fused would be preserved. However, no sauropod skull has been found with anything similar to ossicones or any other possible structure that would play a similar role. Nor have any points of attachment or fusion been found either.

Some have pointed out that some sauropods such as Brachiosaurus and its close relative Giraffatitan have distinctive ‘bumps’ on the tops of their heads which could be potential weapons that could be used in high-intensity necking. However, there are three major points against this: 1.) The struts of bone that make these ‘bumps’ are highly pneumatized and would break easily if used in combat. 2.) The structure of the ‘bumps’ suggests that they contained inflatable nares, and thus it is more probable that they acted as resonance chambers for vocal communication. 3.) The overall structure and position of the ‘bumps’ in comparison to giraffe ossicones lack any contact points that could transfer the force of a blow. Also, the paired ossicones splay somewhat off to the sides of the giraffe’s skull, allowing the ossicones to more effectively make contact when swinging their necks. The ‘bumps’ in brachiosaur skulls are centered and would not be effective in making contact when swung.

Another adaptation found in male giraffes is an increase of calcium deposits on the skull as they get older. These deposits form lumps on the skull which serve to make the skull heavier and more club-like. By contrast, sauropod skulls are typically far more delicate and lighter proportionately. The relative lightness of the sauropod skull is achieved by the large openings in the skull called fenestra. Giraffes do have a similar adaptation in the form of large sinuses. A small and light skull is an excellent adaptation for reducing the amount of weight bore by a long neck.

While this adaptation is shared by both sauropods and giraffes, as stated above male giraffes tend to have more or less “weaponized” skulls. No such “weaponization” has been observed in sauropod skulls. Such “weaponization” could be well preserved in the fossil record if it existed. This would be due to the fossilization favoring bone and other hard tissues.

Another difficulty that casts doubt on high-intensity necking is the anatomical differences in the structure of giraffe and sauropod necks. One of the reasons why dinosaurs, especially sauropods, grew to titanic sizes was due to the presence of hollow bones. Hollow, or pneumatized, bones, allowing bones to be light while retaining strength. This is a trait that modern dinosaurs, birds, have inherited and adapted for flight. The pleurocoels, or hollow spaces in the bones, are most prominent in dinosaur vertebrae. This is most noticeable in sauropods in their iconic long necks.

In addition to saving weight in the bones themselves, the lighter weight of sauropod necks also reduced the need for what would otherwise be unfeasibly massive amounts of supportive muscle and other connective tissues. Giraffes, in contrast, have solid vertebrae and are proportionally more heavily muscled when compared to sauropod necks. These traits make giraffe necks more resilient to blows caused by necking. This is not to say that sauropod necks couldn’t take a blow. However, given the large size of many sauropods’ necks, the forces that would be involved would dwarf anything seen in giraffe high-intensity necking. This is of course assuming if the range of motion and flexibility of sauropod necks is comparable to that of giraffes.

Since sauropod necks had less connective tissues proportionally than giraffes, it is likely that high-intensity necking would be extremely dangerous for sauropods due to lack of connective tissue to provide some protection from necking. Such behavior would not be conducive for the survival of a population without protective adaptations that would enable this behavior.

Another consideration that lends itself for doubt, is the biomechanics of how sauropod necks move. There is still considerable debate over how flexible sauropod necks were, with many studies giving conflicting results. Unfortunately, until this debate is resolved, biomechanics will be left out of this essay for now. However, even if the biomechanics allowed for the needed flexibility to engage in high-intensity neckings, the above doubts still hold weight. If such flexibility is shown to be true, it is more likely that it is an adaptation for something else such as feeding.

In a tentative conclusion, I find that high-intensity necking in sauropods is unlikely due to the lack of adaptations needed for such behavior in anatomy and the lack of pathologies that would be associated with necking.

UPDATE (09/30/2021): One group of sauropods, the apatosaurines (diplodocids like Brontosaurus and Apatosaurus) have heavily built neck vertebrae and a recent study has suggested the underside of their necks may have pairs of keratin covered osteoderms on the dorsal ends of the neck vertebrae. These could have been used for intraspecific shoving matches between individuals reared up into the tripodal stance. While this is not the same as giraffe necking, it is analogous behavior and a potential exception to my earlier hypothesis featured above.

Sources

Taylor, M.P. (2014). “Quantifying the effect of intervertebral cartilage on neutral posture in the necks of sauropod dinosaurs”. PeerJ. 2: e712. doi:10.7717/peerj.712. PMC 4277489. PMID 25551027.

Franz, R.; Hummel, J.; Keinzle, E.; Kölle, P.; Gunga, H-C.; Clauss, M. (2009). “Allometry of visceral organs in living amniotes and its implications for sauropod dinosaurs”. Proceedings of the Royal Society B: Biological Sciences. 276 (1662): 1731–1736. doi:10.1098/rspb.2008.1735. PMC 2660986. PMID 19324837.

Taylor, M.P.; Wedel, M.J.; Naish, D. (2009). “Head and neck posture in sauropod dinosaurs inferred from extant animals” (PDF). Acta Palaeontologica Polonica. 54 (2): 213–220. doi:10.4202/app.2009.0007. S2CID 7582320.

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): 213–220. doi:10.4202/app.2009.0007.

Stevens, K. A. (1999). “Neck Posture and Feeding Habits of Two Jurassic Sauropod Dinosaurs”. Science. 284 (5415): 798–800. doi:10.1126/science.284.5415.798. PMID 10221910.

Taylor MP, Wedel MJ, Naish D, Engh B. 2015. Were the necks of Apatosaurus and Brontosaurus adapted for combat? PeerJ PrePrints 3:e1347v1 Were the necks of Apatosaurus and Brontosaurus adapted for combat? [PeerJ Preprints]

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I was sitting there waiting for the keratin forms in apatosaurus. There it is at the end.

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