OTP: One True Posture

I’ll summate briefly:

Sauropod neck posture has been debated fairly aggressively among those narrow-discipline sauropod specialists (and occassional avocation biologists) for about a century. Speculation has permitted some people to put sauropods into “snorkel” position deep under water, extending their necks far above their bodies in near-vertical postures, and it has also caused some people to think sauropods were incapable of holding their necks at any real posture above the horizontal, and even then just barely. Attempts to discover the “true” posture has engrossed some researchers, who sought what may be the “Holy Grail” of sauropod neck attitude, the “One True Posture.”

I think they’re all wrong.

Much of this debate has been covered before, and a recent paper (Sander et al., 2011) has sought to make some sense of it, while also proposing their own spin on it:

Sauropods probably employed different neck postures during different activities, like feeding, locomotion and standing at rest, so that reconstructions of neck postures can differ due to different approaches used for the reconstruction[.]

Note that this “spin” is not dismissive of any other theory. It encompasses them all. The problem arises when a theory attempts to dismiss the others, due to some internal property (extension of living animals’ necks, inability of necks to attain extreme postures wityhout exceeding some bony obstacle, etc.). Sander and the entire Sauropod Working Group, of which the quoted paper is the final review summary of, have investigated the posture of necks of more than one sauropod, and find that they tend to differ in attitude. Moreover, the authors (specifically Dzemski and Christian, 2005 & Christian and Dzemski, 2007) argue that different postures are attained at different activities, which just enforces the idea there is indeed no “one true posture.”

So why has the concept of OTP been so prevalent in reconstructing sauropod life strategies? If a sauropod can attain high levels of reach to feed, why must it maintain that posture bar none for any other thing? And why must we restore or reconstruct said posture at any interval? This has engrossed some people (Paul, 1998) who restore skeletal diagrams of sauropods in fast transit, yet alter the neck posture to the extreme (Brachiosaurus brancai, from the Tendaguru Formation of Tanzania, is shown consistently with a more-or-less “swan-like” neck posture [a posture said bird attains primarily when swimming, but not when feeding, flying, or even walking]) [n1]. Dzemski and Christian (2007) have even projected that not all sauropods attain similar neck postures during a single activity, such as feeding, due to varying constraints, regardless of the neck length.

So this isn’t really about extending a really long neck vertically, or preventing the neck from being extended outward. Taylor et al. (2009) argue instead that the neck should always be shown vertically elevated (around 45 degrees, really, but this is a mean, not an explicit value) because mammals and many other terrestrial amniotes hold their necks around this mean when in “alter posture.” Despite not valuing “alert posture” as a valid posture from which to evaluate neck posture in general, the authors generalize the neck system in contradiction of Stevens and Parrish’s ONP (osteological neutral pose), a system by which neck posture is almost always horizontal due to the apparent constraints of the centra and zygapophyses of the neck. Certainly, both arguments are beased on inherent assumptions which have been vastly generalized from a subset of animal behavior, without any firm constraint applied to the range of animal behavior.

Did you know most animals spend virtually all of their time either eating or sleeping? How much time did you think they spent in “alert” or “neutral” posture? Stevens and Parrish imply that feeding and sleeping can be better approximated through constraint to ONP, because the neck is closer to the horizontal in both of these, a finding Dzemski and Christian (2007) actually agree on … for some sauropods. “Alert posture,” presumably, would be the time spent when not eating or resting when an animal would be attentive and wary, essentially doing nothing but sitting, standing, looking, and listening. This is an argument for a “neutral” posture, and because it differs from ONP, it is a good refutation of said ONP, but its meaning in general or systematized posture (as Taylor et al. argue it is) is wrong.

Stevens and Parrish also systematize ONP due to a self-imposed constraint, that of articular neutrality, which would not be exceeded, but this is certainly false based on living animals ranges of movement, and is not found by Dzemski and Christian when assessing a variety of sauropods due to biomechanical investigation of strain and stress, which elevated the neck of Brachiosaurus from the horizontal, as well as Euhelopus (Brachiosaurus was taller) while Diplodocus was kept down.

Feeding strategy also plays a large portion in this. Tree-top foraging is a popular image for sauropods, and it goes well back into the mid 1900s, although popularized only later in (especially by Greg Paul who restored virtually all of his sauropods into elevated tree foragers). Dentition patterns, however, tell a different story, and constrain the diet to a narrower spectrum of plants. Even more problematic, the jaw design and neck length of some sauropods has produced what are likely vastly divergent ecological niches: dicraeosaurids had very short necks, but pencil-like dentition, and likely foraged low to the ground; rebbachisaurids, exemplified by Nigersaurus tiguidiensis taqueti, were likely even lower-ground or surface foragers, despite the longer necks than dicraeosaurids; brachiosaurids and indeed probably also “mamenchisaurs” with their spoon-shaped teeth and long-necks were mid-to-high canopy browsers, and diplodocid sauropods with their pencil-shaped teeth but extremely long necks were low-to-mid browsers.

Mobility is not the issue, but statitc posture is. No sauropod kept in a single posture, and likely adopted various postures for feeding and travel, at which point it begs the question of why some recent authors concern themselves with this basic and poor assumption there there is or should be “one true posture?”

This isn’t rhetorical: I’d really like to know.

[n1] It should be noted that “swan-like” here refers to the extended S-shape often used for theropod dinosaur reconstructions, rather than the tight-S-shape that swans (and many other birds) often make.

Christian, A. & Dzemski, G. 2007. Reconstruction of the cervical skeleton posture of Brachiosaurus brancai Janensch, 1914 by an analysis of the intervertebral stress along the neck and a comparison with the results of different approaches. Fossil Record 10:38–49.
Dzemski, G. & Christian, A. 2007. Flexibility along the neck of the ostrich (Struthio camelus) and consequences for the reconstruction of dinosaurs with extreme neck length. Journal of Morphology 268, 707–714.
Paul, G. S. 1998. Terramegathermy and Cope’s rule in the land of titans. Modern Geology 23:179–217.
Sander, P. M., Christian, A., Clauss, M., Fechner, R., Gee, C. T., Griebler, E.-M., Gunga, H.-C., Hummel, J., Mallison, H., Perry, S. F., Preuschoft, H., Rauhut, O. W. M., Remes, K., Tütken, T., Wings, O. & Witzel, U. 2011. Biology of the sauropod dinosaurs: the evolution of gigantism. Biological Reviews 86:117-155.
Stevens, K. A. & Parrish, J. M. 1999. Neck posture and feeding habits of two Jurassic sauropods. Science 284:798–800.
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.

This entry was posted in Biological Comparison, Biology, Biomechanics, Paleontology, Science Reporting and tagged . Bookmark the permalink.

5 Responses to OTP: One True Posture

  1. I think you may have read more in to what Taylor et al. (2009) said than they actually did say.

    They actually did not argue for a “one true pose.” In fact, they explicitly said in their paper, “it is important to distinguish the normal alert posture of the head and neck from the feeding posture. Horses carry their heads angled sharply downward (de Beer 1947), and spend much of their time eating near the ground. However, they do not hold their noses just above ground level during locomotion, as diplodocoids have been reconstructed as doing (Stevens and Parrish 1999, 2005a, b; Sereno et al. 2007). In horses, feeding from the ground involves flexing the neck and extending the head, which is a reversal of the usual orientation of those joints in unrestrained alert poses or normal locomotion. We do not doubt that Nigersaurus was similarly capable of feeding in the posture shown by Sereno et al. (2007: fig. 3), but comparative data suggest that this was not the normal posture for Nigersaurus when it was not feeding.”–bold emphasis added.

    So, they were not arguing for a “one true posture” but, more specifically, what the animals would likely do when alert and not restrained.

    Nor do they argue that this posture was general or systematized posture in the sense that this posture was held all the time. While they do argue for a ‘habitual’ posture, this is qualified with various points as noted. They argued that, out of habit, sauropods normally held their necks erect (i.e., not horizontal or sub-horizontal) when unrestrained, alert and not feeding. Hardly what I would call an argument for a “one true posture”, they certainly did not include such dogmatic language in their paper as you seem to suggest (at least in my reading of it). In fact, their paper could be considered an antithesis of the “one true posture” meme. Whether such a meme even exists is questionable, since all of the authors you refer to mention multiple possible posture depending on the current action of the animal.

  2. I’m not going to defend Taylor et al.’s ideas here, but I will note that yet again you’ve misunderstood what they mean by “alert posture.” You write- ““Alert posture,” presumably, would be the time spent when not eating or resting when an animal would be attentive and wary, essentially doing nothing but sitting, standing, looking, and listening.”

    Yet as Naish stated back in 2009 on his blog- “‘alert posture’ is the normal head and neck pose an animal adopts when it is standing or sitting, relaxed, and not engaged in an activity such as foraging, searching or scanning the environment (the specifics are explained in Vidal et al. (1996) and others of the papers we cite). I should add that ‘alert’ is used to mean ‘non-anaesthetised’, rather than ‘stressed/on the lookout for danger’.”

    So “alert” posture has nothing to do with actually being alert. It just indicates the absence of a particular activity like eating, sleeping, running, etc..

  3. I’m actually attacking “alert posture” on two grounds, the first being that it has no given standard why it should be used at all in reconstructing posture of anything, while on the other that (like Stevens and Parrish’s ONP) the functional significance of the posture is horribly canalized in its behavioral support (i.e., it is representative — when it is — of far fewer postures than other alternative postures it is being used to refute).

    Mickey, you note that Naish wrote (in his blog no less) that alert posture has something to do with a non-anaesthetized condition, but this wasn’t made apparent in the paper as justification (at the time) for such a preferential posture from which to contradict other works. The real kicker is that this posture was being used to justify reconstructions and behaviors NOT in “alert” posture. It was being used, rather, as a “one true posture,” a feature that is being found in a variety of other venues (such as “stork-like” pterosaur necks).

    But that’s not the point. “Alert posture” is just as viable a reconstructing method for sauropod neck attitude as ONP. There is nor should be any constraint to prefer using one or the other unless a specified behavior is invoked. If one is, then either of them should NOT be used, and this is where the issue is: More time in an animal’s like is spent sleeping, eating, fighting, etc., than in a “relaxed”/”alert” posture, and such behaviors also contradict a generalized ONP for various behaviors (except, it seems, for diplodocids, where is appears to describe feeding behavior just fine).

  4. A Paleontology Student says:

    [I’m not from US, so please excuse any potential language errors]
    Terms like “alert”, “neutral” or “relaxed” pose are not strictly defined, are they?

    Regarding the final question in the post: I think the answer is related to how we (humans) tend to depict animals – consider how most illustrations of dogs in a “neutral” pose are what you’d expect to see in a dog expo, which differs more than slightly from a position a dog would assume when “doing nothing special”. Heck, even when we take our own pictures we tend to straiten-up: not our most relaxed/natural stance. I think it’s psychological; it has something to do with our need to assign to any given concept what we feel to be a representative mental construct.

    Back to paleontology…
    With what certainty can the range of possible motions be determined from fossil bones (of what wold be considered a well preserved sauropod)?
    Also, would you agree that at any given moment, the posture of the neck (assuming that the animal isn’t doing anything with it and/or it’s head), should be close to the state where the overall body is in balance? (And further, that thus the relative position of the other parts of the body must affect the neck?) I think that physics plays a mayor role here. (A species that could’t maintain balance couldn’t have survived the forces of evolution, right?) On the other hand, do sauropod necks have a significant enough impact on the overall balance?
    Another question: a long massive neck of a large animal requires significant muscle work in order stay above ground, whatever the posture; is there some structural element that lightens the load on the neck muscles, and if so, does it have an impact on neck mobility? If such structures are known, they would have to be different for, say, Brachiosaurus and Diplodocus, considering the differences in body plan?

    Also, I’ve just watched some videos of animals, among them zebras, and while it is true that different activities require different neck postures, I noticed that, for a particular activity, there exist some (enough to be considered significant?) variance in the neck posture adopted by different individuals. In cases where an animal is in locomotion, but doesn’t otherwise exhibit any special activity, the neck posture and shape also respond to movement.

    So, I have to agree with the point that any “one true posture”-based approach would be too narrow.
    Instead, maybe it’s best to determine what was mechanically possible, and than focus on evidence of behavioral patterns?

    As for life restorations, they should probably intentionally be as varied as possible (or reasonable), and augmented with more detailed descriptions of what activity/posture is depicted. Or a consensus should be reached regarding what exactly this optimal/neutral/relaxed/alert posture is.

    Please excuse me for asking so many questions, but it is such an interesting topic. Thanks in advance to anyone who decides to provide some answers and otherwise posts some insightful comments.

    • I presume initially that all we know is the range of motion position possible for a given joint. That said, we may also know, based on a variety of assumptions (mass, velocity, external forces acting on an object in motion, like gravity or torque) a likely attitude for a limb or body (such as when walking, running, etc.) and thus we can assume gait, maximum speed, likely efficiency of either at a given mass and thus conversely we may be able to use this to assume efficient mass.

      When it comes to this, we can also assume energy usage from muscle mass and range of motions with a constraint on intake (how much energy can come from available food sources), and thus dietary needs and the extent to which a neck can be held up. Christian and Dzemski estimate that even at a specific density of .8, the neck of a sauropod like Euhelopus or Brachiosaurus can stay aloft while the animal walked forward, feeding as it went to walking to the next tree; Wedel estimates a likely specific density could be lower for some sauropods (brachiosaurids had cervical vertebrae that were light honeycombs, and thus little solid bone). Even with basic muscle masses, estimated from a variety of sources using only extant birds as an analogue and not inventing unique structures uncommon in reptiles or birds (such as the mammalian type of nuchal tendon complex), the neck can be supported in an elevated state as long as the energy intake equaled or exceeded energy output.

      Greg Paul typically restores skeletons in a “life in the fast lane” style, with a high run or fast walk (for graviportal animals), and his skeletals in dorsal view show the tail’s lateral curvature, as well as of the dorsal spines and neck. In side view, artistry and science forces the skeleton to a pure lateral view, which obscures the degrees of motion likely in such postures. Carol Abraczinkas, who does Sereno’s skeletal diagrams, poses her skeletons (especially for Sarcosuchus) in dynamic frames, often different from one another, but this is a rarity.

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