Would a fall kill adult Tyrannosaurus rex?

[Vladimír Socha]

Good day to all DMG members!

In 1995 James Farlow and his colleagues published an interesting paper on the effects of 6000 kg galloping T. rex falling on the solid ground. Would these estimates and data still hold? And how bad would the situation be in case of much heavier "Sue" or "Scotty" specimens, with the mass of 8.4 and 8.9 tonnes, resp.? Thank you in advance, VS.

Some interesting parts of the 1995 paper (of course 20 m/s is absolutely unrealistic running speed for an adult T. rex):

Farlow and fellow researchers turned their attention to some theoretical constraints on galloping for a 6,000kg T. rex. Specifically, they were interested in the forces that would be exerted on the body of such an animal if it were to fall while moving at speeds of 10 metres per second or the higher speed of 20 metres per second.

The forces could be broken into two components, a vertical force and a horizontal force. The vertical force would be the same regardless of the speed at which the animal was travelling. Because T. rex had puny arms that would not effectively break the fall, the forces were calculated as direct drops of the mass of the torso and the head from their respective heights. The torso, falling 1.46 metres, would experience an impact force of approximately 260,000 newtons and a deceleration of around 6g while the head, falling 3.46 metres would impact with a force of 99,000 newtons and a deceleration of 14g. This should have been enough to do considerable damage to the skull and rupture vital internal organs.

Do the numbers not mean too much to you? Then think of it this way: the head of a T. rex is about the same size and make up as an adult pig. Imagine what would happen to this hapless piggy if you were to drop it from a height of 3.5 metres. Not a pretty site.

Things only get worse for T. rex when it starts moving and, the faster it moves, the worse it gets. The horizontal component of forces during an impact are more difficult to calculate and require such grizzly factors as the "skid distance" and a "friction coefficient". If the T. rex was running at 20 metres per second (72kmh) and skidded 3 metres on impact, the torso would experience a horizontal force of 300,000 newtons or 7g. The resulting net force of both the horizontal and vertical vectors would run out to 400,000 newtons or 9g for the torso and 110,000 newtons or 16g for the head. At 7g, a fighter pilot blacks out. At 16g his head would pop open.

Tyrannosaurus rex  could avoid these lethal forces by not travelling at such high speeds but even at half that speed (10 metres per second or 36kmh) the risk of serious injury from a fall would still be very high. There is another benefit from going slower; the slower the animal travelled, the better the chance of being able to recover from a stumble before impacting with the ground.

Reference:

Farlow, J. O.; Smith, M. B.; Robinson, J. M. (1995). Body mass, bone “strength indicator”, and cursorial potential of Tyrannosaurus rex. Journal of Vertebrate Paleontology. 15: 713–725.

[Jura]

This paper reminds me of Henderson and Nicholls's 2015 study of the prey lifting potential of Carcharodontosaurus saharicus. Both papers are more like fun thought experiments more than anything else, but they also contain some elegant math to help run one through the process. Something that I've always appreciated about Farlow's work is that he is always the first up to bat when it comes to questioning his study. All his papers come with extensive caveats and alternative takes. The 1995 paper is no different as Farlow et al. provide all the equations necessary to crosscheck the data. You can adjust the values for a larger T. rex here to see what you get. For instance, the net vertical force component equation can be kept largely the same, but the "W" value would be increased to 6,786 kg (75.4% of a 9 tonne animal using the same methods outlined in the paper), leading to a net vertical force of 385,000 Newtons or about 48% more vertical force for the falling behemoth. This is just quick, back-of-the-envelope stuff. More detailed adjustments can be made using more accurate estimates for the torso, head, and limbs. The end results stays the same, though. A massive, fast-running T. rex would not handle a pratfall particularly well.

As an aside, bipedal animals can't gallop. Well...they can, but we call it skipping and it's just about the worst way to travel. :)

Henderson ref:

Henderson, D.M. and Nicholls, R., 2015. Balance and Strength—Estimating the Maximum Prey‐Lifting Potential of the Large Predatory Dinosaur Carcharodontosaurus saharicus. The Anatomical Record, 298(8):1367-1375.

[Heinrich Mallison]

My biggest problems with all these theoretical looks at falling tyrannosaurs are the following two:

- no, animals do not slam down (near-)vertically with all their forward speed. If they did, the same logic would apply to human bikers doing 30+ mph on a bike and falling. They'd die, period. What happens in reality, though, is that the forward motion is translated into a sliding/tumbling/rolling motion. I've fallen with my bike, doing nearly 40 mph. Lots and lots of abrasions, but I did NOT impact the ground at nearly 40 mph, I impacted it at 40 mph TANGENTIAL velocity. Same would be true for a T. rex. A skid distance of 3 m is ABSURDLY low for an animal in which the trunk alone is over 3 m long. I.e.: good math, bad scenario! Call it 10 m, or even 20m, plus rolling instead of simply sliding, and you're getting closer to reality.

- leopards can run at nearly 40 mph (35-37 mph have been measured). Am I the only paleontologist who has even seen video of a fall at that speed? Golly, they usually are pretty fine! However, even IF they sustain pretty shocking looking injuries, e.g. the tail has a 90° kink, large bloody patches on the torso and limbs, half the skin on the face hangs off [this is based on an actual video in a BBC documentary] - a year later the same leopard was filmed lounging in an acacia tree, carefully keeping watch over the just-killed antelope. Scared but healthy and happy! So, big predators do get hurt, and hurt bad - and still live!

What do we see in T. rex? According to Lipkin and Carpenter, a large amount of broken and healed bones consistent with falling on their anterior trunks at high speeds.  

https://www.researchgate.net/profile/Kenneth-Carpenter-2/publication/314895700_Looking_again_at_the_forelimbs_of_Tyrannosaurus_rex/links/58c70de0aca27232ac8297b6/Looking-again-at-the-forelimbs-of-Tyrannosaurus-rex.pdf

golly, who would have thunk!

Does that mean T. rex was impervious to bad falls? NO! Obviously, just as with humans and their eggshell skulls, a bad, unlucky fall could kill them. But then, humans need absolutely no forward velocity to die from falling over. You fall (usually) backwards, you hit your head, you can die. Same for a T. rex: a fall could, if unlucky, lead to a mortal injury. Just not often. *shrug*

_______________________________________________________
Dr. Heinrich Mallison

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email: heinrich...@gmail.com
blog: dinosaurpalaeo.wordpress.com

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[Eric Snively]

385,000 N is dramatic certainly. Spread out in  a belly flop with  2 m^2 of body in contact with the ground, however, gives 192.5 kPa. Not enough to dent a scale. On the pubis though; ouch.

[Adrian Boeye]

Late reply, but Alexander also had something on the 1995 paper (https://www.nature.com/articles/379121a0). His main point was largely that even if a T. rex was capable of running at high speeds (something which is highly unlikely) and faced risk of injury, it almost certainly still would run at said high speeds. Notably, other animals like giraffes still move pretty quickly despite the risk to themselves and animals like monkeys also swing through trees quickly despite similar risk.  Granted, as others have pointed out, how animals fall generally is fairly survivable, even at higher speeds since they are not landing straight. An adult T. rex probably isn't moving that fast either, and most of the results from models I have run indicate it is a problem of force generation and ability to support high contact forces, rather than fears of dying from a fall. As such, a T. rex moving at a slower clip and not falling straight down (sliding and skidding some distance) while also transmitting that force over a broad area would likely be pretty survivable. Unpleasant, and in some extreme cases risking some degree of injury? Definitely. But always fatal? Probably not. All said though, Farlow et al. (1995) is still an excellent paper and represents serious quantitative analysis which is almost always a good thing in these matters.

Best,

Adrian

Reference-

Alexander, R. Tyrannosaurus on the run. Nature 379, 121 (1996). https://doi.org/10.1038/379121a0

[e w]

Hi,

"how animals fall generally is fairly survivable, even at higher speeds since they are not landing straight" - and since in most non-extreme-r non-aquatic fauna, the reprocutive fitness of individuals who are not usually capable of stumbling/crashing/falling survivably declines to zero even in the medium term.

Physical fragility within one's niche is not a viable strategy if you're not capable of pumping out extreme amounts of descendants at a young age, which T.rex wasn't. Nonwithstanding that, ever so often an individual exceeds their physical structural limits, because most animals are curious and investigative, getting into places and postures that are intrinsically unsafe - and that even cats, which are amazingly adapted to survive accidents and injuries, are often enough killed by their curiosity is proverbial.

So the shortest answer to the T.rex question is probably: "totally could, but usually wouldn't".


Best,

Eike

Am Mittwoch, 23. Juli 2025 um 15:58:07 MESZ hat Adrian Boeye <aboe...@coa.edu> Folgendes geschrieben:

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[Gregory Paul]

Most if not all known nonavian dinosaurs were r-strategists that laid lots of rather small eggs -- even sauropod eggs are not large compared to the one put out each year by your Aepyornis -- and Tyranno began reproducing at about half adult mass according to 1125 with its medullary tissue. So a female Tyanno might have deposited maybe 200 eggs before croaking fairly young as they seem wont to have done. Far more reproductive output than K-strategist elephants of equal size. 

GSPaul

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[e w]

Hi,

It's not just the raw egg output. In dinos it had to be elevated due to the high infant mortality, but that mortality was *not* due to dying after stumbling, but mostly predation: Juvenile dinosaurs were *the* food for contemporary large predators; there was not much else available in sufficient numbers to keep a population of reproducing T.rex or whatever fed, particularly after scavenging mammals and small (par)avians started to contest large carrion in significant numbers. To an adult theropod superpredator, it was hardly energy efficient to chase away every small scavenger from a carcass; they simply had to put up with losing food to them.

Elephants (and whales, humans etc) are EXTREMELY K-selected. It's not a binary thing, but a continuum. Dinos were closer to r than their size suggests, but the population dynamics were probably in no way close to the boom-crash cycles of extreme r strategists like aphids, most rodents, many fairy shrimp etc.
Greenland sharks reproduce a lot like dinosaurs (sizeable litters, start reproducing fairly early relative to maximum possible age) but they're still so K-selected (their extreme gestation time is a major factor) that their population dynamics are optimized for safely (=slowly but surely) getting the population to carrying capacity *and keeping it there*, and they're consequently highly vulnerable to overfishing.

That is the main divider: K population dynamics are optimized towards maximum resource utilization in the long run, r population dynamics are optimized towards boom-crash cycles caused by fluctuating or stochastic resource availability.
Most dinosaurs were probably more K- than r-selected, and certainly were not "extreme" r strategists.

Maybe small polar dinos were truly r - populations exploding in late spring, collapsing by midwinter, and reproduction effectively semelparous.
Elsewhere, keeping the mature individuals alive was probably more important to persistence of dinosaur gene pools than producing a generation or more per year to react to changing resource availability.

Anyway, the original question was about "adult" T.rex, and we know they had to be physically sturdy for a significant proportion of juvies to reach full-grown age.
(Unrelated: Do we have any T.rex fossils with indication of *senescence*? Or did they simply grow asymptotically - "effectively, not anymore" from some point on - and stay reproductive until killed by some disaster/accident or by disease or in combat?
Coming to think of it, there do not seem to be many studies about senescence in non-avian dinosaurs in general, no? It's more of a homeotherm thing AFAICT, but then again, even giant tortoises do seem to get senescent, albeit very slowly.)


Best,

Eike

Am Mittwoch, 23. Juli 2025 um 19:47:11 MESZ hat 'Gregory Paul' via Dinosaur Mailing Group <dinosaurma...@googlegroups.com> Folgendes geschrieben:

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[Adrian Boeye]

Hello,

I think that is a very well articulated point as well, that kind of physical fragility is a severely maladaptive and would not be sustainable in all but the most extreme populations. Your shortest answer is about as succinct and accurate as it can be. 

> "Unrelated: Do we have any T.rex fossils with indication of *senescence*? Or did they simply grow asymptotically - "effectively, not anymore" from some point on - and stay reproductive until killed by some disaster/accident or by disease or in combat?" 

I would point you to Carr (2020), which does a phenomenal job reconstructing an aging cycle for Tyrannosaurus. It has been sometime since I have read the article so I can't give a good answer on senescence but specimens like Sue are easy to point to for wracking up so many pathologies. Almost certain we also have some signs of arthritis in at least one specimen of Tyrannosaurus, but I am having trouble recalling which animal it was (might just be Sue). 

Best,

Adrian

Reference-

Carr, T. D. (2020). A high-resolution growth series of Tyrannosaurus rex obtained from multiple lines of evidence. PeerJ, 8, e9192. 

[Vladimír Socha]

Sue is now estimated to be 28 - 33 years old at the time of death, IIRC. Type specimen of Meraxes gigas, OTOH, lived almost to its 50th year...

Dne pátek 25. července 2025 v 5:48:09 UTC+2 uživatel Adrian Boeye napsal:

[JamaleIjouiher]

Sorry, but I have to disagree with the assertion that mammals and birds were contesting scavenging rights with large theropods to the point that the latter were excluded. 

On the Serengeti, despite a diverse assemblage of predators, both mammalian and avian, glutting themselves, there is still an estimated surplus of 26 million kg of carrion left over to rot. And that's in an ecosystem with vultures, a group that has become so specialised that they are almost obligate scavengers at this point. Its also in an ecosystem without sauropods, that would become meat mountains after death, something without precedent in extant terrestrial ecosystems -  a whale-fall on land would be the closest analogue. 

So, their should be plenty of carrion left over for any theropod super-predator, with most of it actually going to waste. 

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Jamale Ijouiher

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