would sauropods rear up and stomp down at predators as viable defense behavior?

[Chaos Soahc]

A few days ago, thanks to the myriad of help and ideas about sauropods withstanding the force from rearing and going back down, I wanted to ask whether rearing up and stomping down would be a viable way to defend itself an example of this kind of behavior comes from this YouTube link https://m.youtube.com/watch?v=czNfKI6FX_Y&ra=m.

Any comments on this, I am super grateful for any comments

[Chaos Soahc]

Also any hypotheses or predictions on how effective or powerful this tactic would be is much appreciated as well as potential downsides or reasons against this behavior

[Jaime Headden]

It should be said that, a sauropod's greatest defense is its size. This is true for large herbivores in every environment: merely being huge confers a great deal of advantage over the environment. Predators tend not to be very large in relation to the largest "prey species" in their environment, the contrast between humpback whales and orcas, for instance, is an order of magnitude (40t and 15m vs 6t and 8m, which means at double their length, humpbacks are greater than four times as massive). Elephants and lions (or tigers, considering). The main contradiction here would be sperm whales, which focus on smaller prey and are the largest carnivores in the ocean, but do not predate on other whales (generally). Sharks are similar; like all other predators, they tend to favor prey species *smaller* than themselves.

This sort of predator/prey sorting is by necessity. An elephant can kick. A hippo has a vicious bite. Rhinos are very strong, and that horn is a deterrent. Simply being huge may not be an absolute defense, but there are quite often much less troublesome, namely smaller, prey to be had. Juveniles, for instance, or the sick, infirm. They will tend to be "left behind" their social groups, or cannot be protected absolutely, when predators "raid" such groups seeking to peel parent from child.

But when it comes to defense, you'll notice that armored or spiked "prey" tend to be smaller than the largest herbivores in their environment, which puts them closer to "a good meal" range and not "waste your weeks' energy budget trying to kill with cooperation," which is how Savuti lions take down large prey. The cost has to be worth it for them to even try.

But to the specific question, I did mention elephants can kick? A leg capable of supporting at any one time one quarter to one third of an animal's entire body mass in the 20+ ton range is going to have a phenomenal amount of power behind it. This was the point of Taylor, Wedel, and Cifelli naming Brontomerus "thunder thighs," opining that (tongue in cheek) a massive femoral retractor would confer a massive rearward swing of the hind leg. Now, we can quibble about the necessity of such a thigh for the sake of merely kicking, and not being the natural capability of an animal elevating its entire body weight on just the hindlimbs, but it stands that, the ability to support 20+ tons means each of your legs will hit like a truck. For an animal in motion, momentum adds to this and any claws at the end of the leg will become extremely dangerous, even if they're not "razor sharp" (which, let's be honest, they're used for digging, they're not going to be sabers but spades).

So the answer to your question would be: alright, maybe. But they wouldn't need to. And as Heinrich said, and a few papers have suggested, the maths on tail movement itself is as much a matter of "really large thing imparting momentum and force to smaller thing" and the natural consequences of smaller things not having the resilience to withstand such forces. Big tail hits smaller animal = pain. The tailtip doesn't need to be a whip when the middle of the tail is just as dangerous, if not more so.

Cheers,

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Jaime A. Headden

The Bite Stuff: http://qilong.wordpress.com/

"Innocent, unbiased observation is a myth" - P. B. Medawar (1969)

[Tristan Stock]

To continue Jaime's points, most extant large herbivores do not utilize rearing stomps for defense more so because it takes a long wind-up of rearing and coming back down when you could just have a simple and quick action (kicking) that is gonna break the predator's bones and cause massive internal damage regardless. That's also why most defensive weapons are fast-acting, like squamates deterring predators with speedy tail whips, jabbing gemsbok horns (which have a shown anti-predator function ala Mills 1990), and various spray and chemical defenses, which all come out fast. Big, showy, and slow ritualized behaviors are much more effective for display, hence why they are deployed in ritualized combat, because your life isn't (in that moment) on the line, but others of your species are often nearby and judging you, so it's important to deescalate situation and prove you are the more fit individual to prevent confrontations from getting physical with big shows of strength.

Large modern herbivores like elephants, horses, etc. don't really rear up to take on a predator. If anything they tend to hunch down and kick, and if the predator is downed in any way, they run up and try to smother and bite it. A common anti-predator response for elephants is to try and crush what they view as a threat by kneeling down and pinning the threat between the ground and their head, often followed by standing up and pushing down onto said threat with one foot, often with gory results. Equids do a similar behavior by biting and kneeling their full weight onto the threat. Much faster and more effective than taking a second or two to tilt your mass backwards to put a bit extra oomph into a bit step, at which point the target might have moved out of the way. The obvious thing a sauropod is to do if a predator is harassing you is to just try and kick in their general direction with any of your four legs, or swing at them quickly with your gigantic neck or tail, both of which would cause big damage and knock them over. Then when they're getting up, the sauropod could still choose to rush up to the downed predator and put one foot on them to cause massive internal bleeding and bone fractures. One of the reasons why they were likely exceptionally dangerous animals to ever consider targeting as adults, since it's so simple for one small mistake to just end the predator's life, while a giant sauropod would take a lot of time to be worn down by the full onslaught of even the largest theropod.

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[Jerry Harris]

I would add to the excellent discussion here that hypothesizing that a sauropod would rear up and then come down on an attacking predator kind of assumes that in the time during which the sauropod rears up, the attacking predator is standing still, awestruck by the spectacle, and is so bedazzled that it doesn't move out of the way of the falling sauropod and thus gets crushed. (Natural selection at its finest, certainly.) No darting in to attack the sauropod's now vulnerable belly, no dashing out of range until the sauropod resumes quadrupedality; just standing there gawping, slack jawed.

I'm being completely facetious here, of course, but I agree with others in this thread that kicking, tail whipping, etc. would be speedier and much more effective as defense strategies. Even if the sauropod already was reared, feeding in a tall tree or something, the tree would be in the way of the sauropod coming down speedily.

[Jura]

Continuing the trend here, I don't think that rearing such as that shown in the YouTube video would have been all that effective against a predator for all the same reasons mentioned before. I think it looks good for theatrics but real animals would be unlikely to waste their time on such a risky move. This may even be truer for sauropods since their heads are already so far away from their bodies that raising up to stomp down on a would-be predator would involve temporarily going blind to where the predator is at that moment. 

A more likely scenario would be turning the body sideways towards the predator, inflating itself as much as possible to look more intimidating and readying the tail in preparation to strike. All of this would probably only hold true for small sauropods and juveniles of large sauropods. I doubt many if any predators ever gave large adults much trouble. At that size, the animals could just steamroll over their attacker without so much as a second thought.

[Mike Taylor]

I'm broadly in agreement with Jaime's post, but there's one point of correction.

He wrote "This was the point of Taylor, Wedel, and Cifelli naming Brontomerus "thunder thighs," opining that (tongue in cheek) a massive femoral retractor would confer a massive rearward swing of the hind leg."

The distinctive thing about Brontomerus morphology is the size of the preacetabular blade, which indicates extensive anterior musculature -- the femoral protractors, which would enable a powerful forward kick.

At least, that's one of the things these muscles might have done. To quote the paper directly (pp. 89-90):

Functional anatomy.—The functional significance of the
unusual ilium of Brontomerus is difficult to interpret due to

the absence of functionally related skeletal elements such as
the pubis and ischium, posterior dorsal and anterior caudal
vertebrae, and femur. In life, these elements work together as
a functional complex, each affecting the function of the oth−
ers. Some speculation is warranted, however.
    The large preacetabular blade of the ilium provides an an−
chor for large protraction muscles, which would have al−
lowed the leg to be moved forwards powerfully; this is sur−
prising as femoral retraction is required for forward locomo−
tion, requiring large muscles to pull the femur backwards,
and the ilium of Brontomerus offers almost no attachment
area for posteriorly located muscles. The caudofemoralis
muscle is the main power generator in locomotion for extant
reptiles, and osteological correlates such as the fourth tro−
chanter of the femur indicate that this was also true of
non−avian dinosaurs. This muscle connects the femur to the
tail, so in the absence of proximal caudal vertebrae and chev−
rons of Brontomerus it is not possible to determine whether
the femoral retractors were enlarged in proportion with the
protractors. If so, then this increase in musculature would in−
dicate that Brontomerus may have been unusually athletic
for a sauropod. Another possibility is that powerful femoral
protraction was useful for delivering a strong kick (Fig. 12).
    As well as protractors, the preacetabular blade of the

ilium also anchors abductors (i.e., muscles which draw the
leg laterally away from the median plane). These muscles are
important for creating abduction torque when standing, and
may have facilitated occasional bipedal stance or even lim−
ited bipedal walking.
    A third possibility is that the proportionally large leg
muscles were required to drive unusually long legs. The
large anterior expansion of the scapula provides weak addi−
tional support for this hypothesis. If this interpretation were
correct, Brontomerus might have resembled a giraffe in gross
morphology.

The paper is free to read at

https://app.pan.pl/archive/published/app56/app20100073.pdf

if anyone wants more detail.

-- Mike

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