Tyrannosaurus rex vs. Stegosaurus armatus

[theropod]

I’d propose the following: help me find those fossils of supposedly 10m+ Stegosaurus, if they exist.
So far, I’ve succeeded in little more than finding some sources, some reliable, some less so, mentioning that Stegosaurus got to around 9m for very large individuals (the 1382mm femur listed in Greg Paul’s datasheet is probably the basis of that, but I’ve got no idea of whether that specimen is even described), not more.

All the actual Stegosaurus specimens I’ve seen so far are way smaller (admittedly many of them are immature and/or actually Hesperosaurus mjosi, but still…), as are all femora of specimens in the literature (e.g. link) and there seems to have been very little work done on its body size.

[dinosauria101]

^Well, I generally find it in miscellaneous dinosaur books and sources on the internet. Once I know a specific source, I'll get that.

[elosha11]

Is there any study or reasonable estimates of how quickly stegosaurus could turn? Because if the T rex can get in front and bite that tiny head, it's over. I'm also a little skeptical that the stegosaurus' tail is long enough or even strong enough to do heavy damage to the T rex unless it got extremly close to the back end, which given the armor, I don't know if T rex would be prone to do. Also keep in mind that T rex has been recorded biting off the horn of Triceratops, so it's possible, (although I wouldn't consider it likely), that T rex could try to similarly immobilize the tail.

I get what dinosauria101 is stating about experience, and T rex not having to deal with such a tail threat. At the same time, I think it's experience with Triceratops might carry over to this conflict, meaning the T rex may have been smart enough to soon recognize a spike/horn-like weapon and know to seek the unprotected head (just like it would to in trying to attack Triceratops from behind). In such a scenario, the T rex might have to get lucky and see the stegosaurus miss with a few strikes and then realize it needed to attack the steg from the front. I could see the T rex then continuously circle the steg, looking for any opening. Thus, my preoccupation with how quickly a stegosaurus could turn.

Also, rock you mentioned T rex could hurt the stegosaurus with its own tail? What evidence is there that T rex used its own tail as a weapon?

[dinosauria101]

Apr 28, 2019 16:47:30 GMT 5 elosha11 said:

I get what dinosauria101 is stating about experience, and T rex not having to deal with such a tail threat. At the same time, I think it's experience with Triceratops might carry over to this conflict, meaning the T rex may have been smart enough to soon recognize a spike/horn-like weapon and know to seek the unprotected head (just like it would to in trying to attack Triceratops from behind). In such a scenario, the T rex might have to get lucky and see the stegosaurus miss with a few strikes and then realize it needed to attack the steg from the front. I could see the T rex then continuously circle the steg, looking for any opening. Thus, my preoccupation with how quickly a stegosaurus could turn.

I can see where you're coming from elosha, but I don't think that'd help Rex too much, if at all. Take a look at these images of Stegosaurus and Triceratops:


They are so radically different that I'm pretty sure Rex would, more often than not, still not know what Stegosaurus is until it's been hit and stabbed.
As for the thagomizer doing damage, we've seen what a smaller subspecies of Stegosaurus that hit a non-vital area and was not hell-bent on killing its opponent did to an Allosaurus fragilis tail vertebra. It punctured right though it, and although it survived, I don't think it would've been much good at fighting right after, which would've allowed the Stegosaurus to retaliate and puncture it until it was dead without any risk to itself. Same applies here, except it's a bigger, stronger species of Stegosaurus hell-bent on killing an unexperienced opponent.
And about the turning speed, I do not know where to look for scientific sources, but I think it's safe to say they needed to be excellent turners in order to survive.

[rock]

Apr 28, 2019 16:47:30 GMT 5 elosha11 said:

Is there any study or reasonable estimates of how quickly stegosaurus could turn? Because if the T rex can get in front and bite that tiny head, it's over. I'm also a little skeptical that the stegosaurus' tail is long enough or even strong enough to do heavy damage to the T rex unless it got extremly close to the back end, which given the armor, I don't know if T rex would be prone to do. Also keep in mind that T rex has been recorded biting off the horn of Triceratops, so it's possible, (although I wouldn't consider it likely), that T rex could try to similarly immobilize the tail.

I get what dinosauria101 is stating about experience, and T rex not having to deal with such a tail threat. At the same time, I think it's experience with Triceratops might carry over to this conflict, meaning the T rex may have been smart enough to soon recognize a spike/horn-like weapon and know to seek the unprotected head (just like it would to in trying to attack Triceratops from behind). In such a scenario, the T rex might have to get lucky and see the stegosaurus miss with a few strikes and then realize it needed to attack the steg from the front. I could see the T rex then continuously circle the steg, looking for any opening. Thus, my preoccupation with how quickly a stegosaurus could turn.

Also, rock you mentioned T rex could hurt the stegosaurus with its own tail? What evidence is there that T rex used its own tail as a weapon?

elosha11 who do you favor here?

[theropod]

OK, this got rather long, but I think there are a couple of points in here that should be of interest to all of the posters here.

1) on experience: Why someone would assume T. rex had no experience dealing with "tail weapons" is beyond me, that is a plain ridiculous proposition considering the elephant in the room that is Ankylosaurus magniventris. If anything, T. rex was probably very familiar with prey that used caudal osteoderms, just as familiar as Allosaurus.

2) elosha11 on turning ability: Kentrosaurus has an extremely posteriorly located centre of mass, and a large moment arm of the forelimbs with respect to the COM, allowing rapid pivoting around the hind feet (Mallison 2011). In addition the forelimbs have good lateral mobility, and the neck has the necessary range of motion to keep sight of an animal standing behind it either by dorsal extension, or lateral flexion (Mallison 2010), at least if it’s tall, like a theropod. All of this likely also applies to Stegosaurus, which is phylogenetically and morphologically very close. That being said, I don’t think a study would have been necessary to accept the proposition that a 6-9 m quadruped could turn faster than a 10-12m biped could run a circle around it, which should have been the null-hypothesis from the start. At the very least, it is obvious which one would have the lower rotational inertia, and considering running around it would require both rotation and linear accelleration at the same time, this would be far slower to achieve even if both had had comparable turning ability.
3) on potency of stegosaur tail strikes: Mallison (2011) also strongly suggests a tail swipe by Kentrosaurus would have generated impact forces high enough to be dangerous to even larger predators, which doesn’t even consider penetrating or slashing trauma. A strike to the face of even a larger theropod from a stegosaur would likely be very dangerous for the predator, even just considering the blunt force of the impact. Actual penetrating trauma on the neck or torso would stand very high chances of being fatal, and it has also been suggested that the spines could cause superficial lacerations that could be debilitating. Granted, T. rex has a more robust skull than most Jurassic theropods, but it’s still just as air-filled, and would probably not be immune from similar attacks from, say, an ankylosaur. Only that Stegosaurus was actually tall enough to realistically whack a T. rex-sized theropod, such as a large Allosaurus in the face, Ankylosaurus was not. In a face-to-tail confrontation between a Stegosaurus and an Allosaurus, the theropod would need a considerable size advantage in order to stand a decent chance of surviving long enough to kill the stegosaur. Over a record-sized Stegosaurus ungulatus, even a monster like the "Epanterias"-holotype might be in for a huge struggle, at least if it was as large as femur length suggests.
4) on biting horns/spikes: T. rex biting the horns of Triceratops was not a good predation tactic, as that horn shows signs of healing (Happ 2008). So this actually represents a pathology resulting from a failed predation attempt, not a purposeful method of attack by the theropod (i.e. probably was more of a defensive method for the T. rex than anything else). It is very likely that for a good chance of success, the theropod would need to make its approach from behind, and strike before it could turn to fully face it.
5) on theropod tails as weapons: T. rex using its tail as a weapon is, frankly, unrealistic. Firstly, it would not be able to generate enough torque to swing it forcefully enough to be a serious danger to a large animal. Secondly, it would risk its own stability in the process, and would require some time to get back into position, because it would basically have to turn its whole body to swing the tail, which would take considerable time (Hutchinson 2007 estimated T. rex would take 1-2 seconds to turn 45°). And finally, theropods might risk breaking their own tails rather than anything else doing that. Especially tetanuran tails, since they are stiffened by long, interlocking zygapophyses of the distal caudals, and certainly not built to withstand being used to strike anything (because of the previous two points, they generally wouldn’t have to be).
6) on real predatory interactions between stegosaurs and theropods: The evidence of probable predation of Allosaurus on Stegosaurus are mostly failed predation. There are two cases of Allosaurus specimens with fatal wounds caused by Stegosaurus thagomizers. There is only one record of a Stegosaurus’ cervical plate bitten by an Allosaurus, apparently without remodeling, which would suggest the stegosaur didn’t survive the attack. There are also quite a few spines with broken and remodeled ends, suggesting successful use for deterring predators. So while that record shows that Allosaurus successfully killed what would have been a very dangerous prey item (both on functional grounds and based on the other fossil evidence) at least occasionally , for now it’s actually 2:1 in favour of the stegosaur here. While it seems that Allosaurus occasionally preyed on Stegosaurus successfully, it is very unlikely that anything but a T. rex-sized freak Allosaurus could take on an individual the size some people are proposing here with any chance of winning. That being said, again, that is not the typical size of Stegosaurus either, not even for S. ungulatus.

7) on taxonomy: Also I would not be too confident that S. ungulatus and S. stenops are even distinct species. Maidment et al. (2008) synonymized all Morrison stegosaur material except for Stegosaurus (=Hesperosaurus) mjosi with S. armatus, although Maidment agrees that S. stenops should be designated as the new type since S. armatus is insufficiently diagnostic (therefore all Stegosaurus material would be S. stenops). In that case, the typical Stegosaurus would be far smaller, enoughly so to make a confrontation with a Tyrannosaurus-sized theropod a mismatch. Average size would probably be no more than 3t ( T. rex is likely between 6 and 7t). However other people (e.g. Carpenter 2010) disagree, citing that this taxon would show too much variation to be a single species (that alone isn’t a good argument, since to distinguish between species at the very least there should at least be evidence for some sort of clustering rather than continuous variation). So I’m not sure whether we should really consider S. ungulatus to be distinct from S. stenops, although of course I’d take no issues with people assuming it in this hypothetical context if they explicitely state so (the thread title however, does not).
8) on size: I would also not be so confident S. ungulatus necessarily got quite as huge as its femur length suggests. The next-largest Stegosaurus femur I know (also attributed to S. ungulatus) is 1.2m long (Gilmore 1914), but it’s midshaft width is just is just 3mm, or 1% bigger than that of a 1.08 m S. stenops femur, so perhaps S. ungulatus, if it was distinct, was longer-legged, or more slender but not that much heavier, or otherwise there was sexual dimorphism. Of course it’s also possible it really got that huge, as there could very well be normal variation or taphonomy at play here. I wouldn’t categorically say femur length is better for scaling between close relatives, but neither would I say this for femur circumference (obviously a femur is a very long bone and by virtue of that, it’s length will have certain constraining effects on body dimensions). In any case though, 9m and 7+t were not normal size.
9) Gilmore (1914) also lists some more femora under Stegosaurus sp., which are quite a bit smaller. Depending on what species they belong to, that could influence what we have to assume was the typical size of S. ungulatus (again, presupposing it is a distinct species). The mounted composite skeleton at the YPM is 5.92m long between perpendiculars (Lull 1910), and probably around 6.9m in axial length and ~3t in mass based on that, so it too is clearly a lot smaller than the 9m behemoth dinosauria is assuming (although the femora as mounted are too long, at over 1.3m, so they cannot be used for scaling up and themselves could belong to a really big specimen).

Bakker, R.T., Zoehfeld, K.W. and Mossbrucker, M.T. 2014. Stegosaurian Martial Arts: A Jurassic Carnivore Stabbed by a Tail Spike, Evidence for Dynamic Interactions between a Live Herbivore and a Live Predator. Geological Society of America (GSA) Annual Meeting, Session.
Carpenter, K. 2010. Species concept in North American stegosaurs. Swiss Journal of Geosciences 103 (2): 155–162.
Carpenter, K., Sanders, F., McWhinney, L.A. and Wood, L. 2005. 17. Evidence for Predator-Prey Relationships. In: Carpenter, K. (ed.), The Carnivorous Dinosaurs, Indiana University Press, Bloomington.
Gilmore, C.W. 1914. Osteology of the armored Dinosauria in the United States National Museum: with special reference to the genus Stegosaurus. U. S. Govt. print. off., Washington DC.
Happ, J. 2008. An analysis of predator-prey behavior in a head-to-head encounter between Tyrannosaurus rex and Triceratops. Tyrannosaurus rex the Tyrant king: 355–370.
Hutchinson, J.R., Ng-Thow-Hing, V. and Anderson, F.C. 2007. A 3D interactive method for estimating body segmental parameters in animals: application to the turning and running performance of Tyrannosaurus rex. Journal of Theoretical Biology 246 (4): 660–680.
Maidment, S.C., Norman, D.B., Barrett, P.M. and Upchurch, P. 2008. Systematics and phylogeny of Stegosauria (Dinosauria: Ornithischia). Journal of Systematic Palaeontology 6 (4): 367–407.
Mallison, H. 2010. CAD assessment of the posture and range of motion of Kentrosaurus aethiopicus H ennig 1915. Swiss Journal of Geosciences 103 (2): 211–233.
Mallison, H. 2011. Defense capabilities of Kentrosaurus aethiopicus Hennig, 1915. Palaeontologia Electronica 14 (2): 1–25.
Lull, R.S. 1910. ART. XXXIX.–Stegosaurus ungulatus Marsh, recently mounted at the Peabody Museum of Yale University. American Journal of Science (1880-1910) 30 (180): 361.

[dinosauria101]

Apr 29, 2019 4:23:43 GMT 5 theropod said:

OK, this got rather long, but I think there are a couple of points in here that should be of interest to all of the posters here.

1) on experience: Why someone would assume T. rex had no experience dealing with "tail weapons" is beyond me, that is a plain ridiculous proposition considering the elephant in the room that is Ankylosaurus magniventris. If anything, T. rex was probably very familiar with prey that used caudal osteoderms, just as familiar as Allosaurus.

2) elosha11 on turning ability: Kentrosaurus has an extremely posteriorly located centre of mass, and a large moment arm of the forelimbs with respect to the COM, allowing rapid pivoting around the hind feet (Mallison 2011). In addition the forelimbs have good lateral mobility, and the neck has the necessary range of motion to keep sight of an animal standing behind it either by dorsal extension, or lateral flexion (Mallison 2010), at least if it’s tall, like a theropod. All of this likely also applies to Stegosaurus, which is phylogenetically and morphologically very close. That being said, I don’t think a study would have been necessary to accept the proposition that a 6-9 m quadruped could turn faster than a 10-12m biped could run a circle around it, which should have been the null-hypothesis from the start. At the very least, it is obvious which one would have the lower rotational inertia, and considering running around it would require both rotation and linear accelleration at the same time, this would be far slower to achieve even if both had had comparable turning ability.
3) on potency of stegosaur tail strikes: Mallison (2011) also strongly suggests a tail swipe by Kentrosaurus would have generated impact forces high enough to be dangerous to even larger predators, which doesn’t even consider. A strike to the face of even a larger theropod from a stegosaur would likely be very dangerous for the predator, even just considering blunt force trauma. Actual penetrating trauma on the neck or torso would stand very high chances of being fatal, and it has also been suggested that the spines could cause superficial lacerations that could be debilitating. Granted, T. rex has a more robust skull than most Jurassic theropods, but it’s still just as air-filled, and would probably not be immune from similar attacks from, say, an ankylosaur. Only that Stegosaurus was actually tall enough to realistically whack a T. rex-sized theropod, such as a large Allosaurus in the face, Ankylosaurus was not. In a face-to-tail confrontation between a Stegosaurus and an Allosaurus, the theropod would need a considerable size advantage in order to stand a decent chance of surviving long enough to kill the stegosaur. Over a record-sized Stegosaurus ungulatus, even a monster like the "Epanterias"-holotype might be in for a huge struggle, at least if it was as large as femur length suggests.
4) on biting horns/spikes: T. rex biting the horns of Triceratops was not a good predation tactic, as many of those horns show signs of healing (e.g. Happ 2008). It is likely this actually represents a pathology resulting from failed predation attempts, not a purposeful method of attack by the theropod (i.e. probably was more of a defensive method for the T. rex than anything else). It is very likely that for a good chance of success.
5) on theropod tails as weapons: T. rex using its tail as a weapon is, frankly, unrealistic. Firstly, it would not be able to generate enough torque to swing it forcefully enough to be a serious danger to a large animal. Secondly, it would risk its own stability in the process, and would require some time to get back into position, because it would basically have to turn its whole body to swing the tail, which would take considerable time (Hutchinson 2007 estimated T. rex would take 1-2 seconds to turn 45°). And finally, theropods might risk breaking their own tails rather than anything else doing that. Especially tetanuran tails, since they are stiffened by long, interlocking zygapophyses of the distal caudals, and certainly not built to withstand being used to strike anything (because of the previous two points, they generally wouldn’t have to be).
6) on real predatory interactions between stegosaurs and theropods: The evidence of probable predation of Allosaurus on Stegosaurus are mostly failed predation. There are two cases of Allosaurus specimens with fatal wounds caused by Stegosaurus thagomizers. There is only one record of a Stegosaurus’ cervical plate bitten by an Allosaurus, apparently without remodeling, which would suggest the stegosaur didn’t survive the attack. There are also quite a few spines with broken and remodeled ends, suggesting successful use for deterring predators. So while that record shows that Allosaurus successfully killed what would have been a very dangerous prey item (both on functional grounds and based on the other fossil evidence) at least occasionally , for now it’s actually 2:1 in favour of the stegosaur here. While it seems that Allosaurus occasionally preyed on Stegosaurus successfully, it is very unlikely that anything but a T. rex-sized freak Allosaurus could take on an individual the size some people are proposing here with any chance of winning. That being said, again, that is not the typical size of Stegosaurus either, not even for S. ungulatus.

7) on taxonomy: Also I would not be too confident that S. ungulatus and S. stenops are even distinct species. Maidment et al. (2008) synonymized all Morrison stegosaur material except for Stegosaurus (=Hesperosaurus) mjosi with S. armatus, although Maidment agrees that S. stenops should be designated as the new type since S. armatus is insufficiently diagnostic (therefore all Stegosaurus material would be S. stenops). In that case, the typical Stegosaurus would be far smaller, enoughly so to make a confrontation with a Tyrannosaurus-sized theropod a mismatch. Average size would probably be no more than 3t ( T. rex is likely between 6 and 7t). However other people (e.g. Carpenter 2010) disagree, citing that this taxon would show too much variation to be a single species (that alone isn’t a good argument, since to distinguish between species at the very least there should at least be evidence for some sort of clustering rather than continuous variation). So I’m not sure whether we should really consider S. ungulatus to be distinct from S. stenops, although of course I’d take no issues with people assuming it in this hypothetical context if they explicitely state so (the thread title however, does not).
8) on size: I would also not be so confident S. ungulatus necessarily got quite as huge as its femur length suggests. The next-largest Stegosaurus femur I know (also attributed to S. ungulatus) is 1.2m long (Gilmore 1914), but it’s midshaft width is just is just 3mm, or 1% bigger than that of a 1.08 m S. stenops femur, so perhaps S. ungulatus, if it was distinct, was longer-legged, or more slender but not that much heavier, or otherwise there was sexual dimorphism. Of course it’s also possible it really got that huge, as there could very well be normal variation or taphonomy at play here. I wouldn’t categorically say femur length is better for scaling between close relatives, but neither would I say this for femur circumference (obviously a femur is a very long bone and by virtue of that, it’s length will have certain constraining effects on body dimensions). In any case though, 9m and 7+t were not normal size.
9) Gilmore (1914) also lists some more femora under Stegosaurus sp., which are quite a bit smaller. Depending on what species they belong to, that could influence what we have to assume was the typical size of S. ungulatus (again, presupposing it is a distinct species). The mounted composite skeleton at the YPM is 5.92m long between perpendiculars (Lull 1910), and probably around 6.9m in axial length and ~3t in mass based on that, so it too is clearly a lot smaller than the 9m behemoth dinosauria is assuming (although the femora as mounted are too long, at over 1.3m, so they cannot be used for scaling up and themselves could belong to a really big specimen).

Bakker, R.T., Zoehfeld, K.W. and Mossbrucker, M.T. 2014. Stegosaurian Martial Arts: A Jurassic Carnivore Stabbed by a Tail Spike, Evidence for Dynamic Interactions between a Live Herbivore and a Live Predator. Geological Society of America (GSA) Annual Meeting, Session.
Carpenter, K. 2010. Species concept in North American stegosaurs. Swiss Journal of Geosciences 103 (2): 155–162.
Carpenter, K., Sanders, F., McWhinney, L.A. and Wood, L. . 17. Evidence for Predator-Prey Relationships. In: Carpenter, K. (ed.), The Carnivorous Dinosaurs, Indiana University Press, Bloomington.
Gilmore, C.W. 1914. Osteology of the armored Dinosauria in the United States National Museum: with special reference to the genus Stegosaurus. Govt. print. off., .
Happ, J. 2008. An analysis of predator-prey behavior in a head-to-head encounter between Tyrannosaurus rex and Triceratops. Tyrannosaurus rex the Tyrant king: 355–370.
Hutchinson, J.R., Ng-Thow-Hing, V. and Anderson, F.C. 2007. A 3D interactive method for estimating body segmental parameters in animals: application to the turning and running performance of Tyrannosaurus rex. Journal of Theoretical Biology 246 (4): 660–680.
Maidment, S.C., Norman, D.B., Barrett, P.M. and Upchurch, P. 2008. Systematics and phylogeny of Stegosauria (Dinosauria: Ornithischia). Journal of Systematic Palaeontology 6 (4): 367–407.
Mallison, H. 2010. CAD assessment of the posture and range of motion of Kentrosaurus aethiopicus H ennig 1915. Swiss Journal of Geosciences 103 (2): 211–233.
Mallison, H. 2011. Defense capabilities of Kentrosaurus aethiopicus Hennig, 1915. Palaeontologia Electronica 14 (2): 1–25.
Lull, R.S. 1910. ART. XXXIX.–Stegosaurus ungulatus Marsh, recently mounted at the Peabody Museum of Yale University. American Journal of Science (1880-1910) 30 (180): 361.

theropod by lack of experience, I meant with stegosaurs and thagomizers, not tail weapons. Even Stegosaurus and Ankylosaurus are rather different, and since T rex hasn't seen anything with tail spikes as a weapon (in a sense, something of a cross between a Triceratops and Ankylosaurus). Judging by comparison of these images, Rex is still facing something very brand new.


Admittedly, they're more similar than the comparison with Triceratops, but they're still very different, and I find that backs up my doubts of Rex's experience in the field. 

[theropod]

Apr 29, 2019 5:06:17 GMT 5 dinosauria101 said:

Apr 29, 2019 4:23:43 GMT 5 theropod said:

OK, this got rather long, but I think there are a couple of points in here that should be of interest to all of the posters here.

1) on experience: Why someone would assume T. rex had no experience dealing with "tail weapons" is beyond me, that is a plain ridiculous proposition considering the elephant in the room that is Ankylosaurus magniventris. If anything, T. rex was probably very familiar with prey that used caudal osteoderms, just as familiar as Allosaurus.

2) elosha11 on turning ability: Kentrosaurus has an extremely posteriorly located centre of mass, and a large moment arm of the forelimbs with respect to the COM, allowing rapid pivoting around the hind feet (Mallison 2011). In addition the forelimbs have good lateral mobility, and the neck has the necessary range of motion to keep sight of an animal standing behind it either by dorsal extension, or lateral flexion (Mallison 2010), at least if it’s tall, like a theropod. All of this likely also applies to Stegosaurus, which is phylogenetically and morphologically very close. That being said, I don’t think a study would have been necessary to accept the proposition that a 6-9 m quadruped could turn faster than a 10-12m biped could run a circle around it, which should have been the null-hypothesis from the start. At the very least, it is obvious which one would have the lower rotational inertia, and considering running around it would require both rotation and linear accelleration at the same time, this would be far slower to achieve even if both had had comparable turning ability.
3) on potency of stegosaur tail strikes: Mallison (2011) also strongly suggests a tail swipe by Kentrosaurus would have generated impact forces high enough to be dangerous to even larger predators, which doesn’t even consider. A strike to the face of even a larger theropod from a stegosaur would likely be very dangerous for the predator, even just considering blunt force trauma. Actual penetrating trauma on the neck or torso would stand very high chances of being fatal, and it has also been suggested that the spines could cause superficial lacerations that could be debilitating. Granted, T. rex has a more robust skull than most Jurassic theropods, but it’s still just as air-filled, and would probably not be immune from similar attacks from, say, an ankylosaur. Only that Stegosaurus was actually tall enough to realistically whack a T. rex-sized theropod, such as a large Allosaurus in the face, Ankylosaurus was not. In a face-to-tail confrontation between a Stegosaurus and an Allosaurus, the theropod would need a considerable size advantage in order to stand a decent chance of surviving long enough to kill the stegosaur. Over a record-sized Stegosaurus ungulatus, even a monster like the "Epanterias"-holotype might be in for a huge struggle, at least if it was as large as femur length suggests.
4) on biting horns/spikes: T. rex biting the horns of Triceratops was not a good predation tactic, as many of those horns show signs of healing (e.g. Happ 2008). It is likely this actually represents a pathology resulting from failed predation attempts, not a purposeful method of attack by the theropod (i.e. probably was more of a defensive method for the T. rex than anything else). It is very likely that for a good chance of success.
5) on theropod tails as weapons: T. rex using its tail as a weapon is, frankly, unrealistic. Firstly, it would not be able to generate enough torque to swing it forcefully enough to be a serious danger to a large animal. Secondly, it would risk its own stability in the process, and would require some time to get back into position, because it would basically have to turn its whole body to swing the tail, which would take considerable time (Hutchinson 2007 estimated T. rex would take 1-2 seconds to turn 45°). And finally, theropods might risk breaking their own tails rather than anything else doing that. Especially tetanuran tails, since they are stiffened by long, interlocking zygapophyses of the distal caudals, and certainly not built to withstand being used to strike anything (because of the previous two points, they generally wouldn’t have to be).
6) on real predatory interactions between stegosaurs and theropods: The evidence of probable predation of Allosaurus on Stegosaurus are mostly failed predation. There are two cases of Allosaurus specimens with fatal wounds caused by Stegosaurus thagomizers. There is only one record of a Stegosaurus’ cervical plate bitten by an Allosaurus, apparently without remodeling, which would suggest the stegosaur didn’t survive the attack. There are also quite a few spines with broken and remodeled ends, suggesting successful use for deterring predators. So while that record shows that Allosaurus successfully killed what would have been a very dangerous prey item (both on functional grounds and based on the other fossil evidence) at least occasionally , for now it’s actually 2:1 in favour of the stegosaur here. While it seems that Allosaurus occasionally preyed on Stegosaurus successfully, it is very unlikely that anything but a T. rex-sized freak Allosaurus could take on an individual the size some people are proposing here with any chance of winning. That being said, again, that is not the typical size of Stegosaurus either, not even for S. ungulatus.

7) on taxonomy: Also I would not be too confident that S. ungulatus and S. stenops are even distinct species. Maidment et al. (2008) synonymized all Morrison stegosaur material except for Stegosaurus (=Hesperosaurus) mjosi with S. armatus, although Maidment agrees that S. stenops should be designated as the new type since S. armatus is insufficiently diagnostic (therefore all Stegosaurus material would be S. stenops). In that case, the typical Stegosaurus would be far smaller, enoughly so to make a confrontation with a Tyrannosaurus-sized theropod a mismatch. Average size would probably be no more than 3t ( T. rex is likely between 6 and 7t). However other people (e.g. Carpenter 2010) disagree, citing that this taxon would show too much variation to be a single species (that alone isn’t a good argument, since to distinguish between species at the very least there should at least be evidence for some sort of clustering rather than continuous variation). So I’m not sure whether we should really consider S. ungulatus to be distinct from S. stenops, although of course I’d take no issues with people assuming it in this hypothetical context if they explicitely state so (the thread title however, does not).
8) on size: I would also not be so confident S. ungulatus necessarily got quite as huge as its femur length suggests. The next-largest Stegosaurus femur I know (also attributed to S. ungulatus) is 1.2m long (Gilmore 1914), but it’s midshaft width is just is just 3mm, or 1% bigger than that of a 1.08 m S. stenops femur, so perhaps S. ungulatus, if it was distinct, was longer-legged, or more slender but not that much heavier, or otherwise there was sexual dimorphism. Of course it’s also possible it really got that huge, as there could very well be normal variation or taphonomy at play here. I wouldn’t categorically say femur length is better for scaling between close relatives, but neither would I say this for femur circumference (obviously a femur is a very long bone and by virtue of that, it’s length will have certain constraining effects on body dimensions). In any case though, 9m and 7+t were not normal size.
9) Gilmore (1914) also lists some more femora under Stegosaurus sp., which are quite a bit smaller. Depending on what species they belong to, that could influence what we have to assume was the typical size of S. ungulatus (again, presupposing it is a distinct species). The mounted composite skeleton at the YPM is 5.92m long between perpendiculars (Lull 1910), and probably around 6.9m in axial length and ~3t in mass based on that, so it too is clearly a lot smaller than the 9m behemoth dinosauria is assuming (although the femora as mounted are too long, at over 1.3m, so they cannot be used for scaling up and themselves could belong to a really big specimen).

Bakker, R.T., Zoehfeld, K.W. and Mossbrucker, M.T. 2014. Stegosaurian Martial Arts: A Jurassic Carnivore Stabbed by a Tail Spike, Evidence for Dynamic Interactions between a Live Herbivore and a Live Predator. Geological Society of America (GSA) Annual Meeting, Session.
Carpenter, K. 2010. Species concept in North American stegosaurs. Swiss Journal of Geosciences 103 (2): 155–162.
Carpenter, K., Sanders, F., McWhinney, L.A. and Wood, L. . 17. Evidence for Predator-Prey Relationships. In: Carpenter, K. (ed.), The Carnivorous Dinosaurs, Indiana University Press, Bloomington.
Gilmore, C.W. 1914. Osteology of the armored Dinosauria in the United States National Museum: with special reference to the genus Stegosaurus. Govt. print. off., .
Happ, J. 2008. An analysis of predator-prey behavior in a head-to-head encounter between Tyrannosaurus rex and Triceratops. Tyrannosaurus rex the Tyrant king: 355–370.
Hutchinson, J.R., Ng-Thow-Hing, V. and Anderson, F.C. 2007. A 3D interactive method for estimating body segmental parameters in animals: application to the turning and running performance of Tyrannosaurus rex. Journal of Theoretical Biology 246 (4): 660–680.
Maidment, S.C., Norman, D.B., Barrett, P.M. and Upchurch, P. 2008. Systematics and phylogeny of Stegosauria (Dinosauria: Ornithischia). Journal of Systematic Palaeontology 6 (4): 367–407.
Mallison, H. 2010. CAD assessment of the posture and range of motion of Kentrosaurus aethiopicus H ennig 1915. Swiss Journal of Geosciences 103 (2): 211–233.
Mallison, H. 2011. Defense capabilities of Kentrosaurus aethiopicus Hennig, 1915. Palaeontologia Electronica 14 (2): 1–25.
Lull, R.S. 1910. ART. XXXIX.–Stegosaurus ungulatus Marsh, recently mounted at the Peabody Museum of Yale University. American Journal of Science (1880-1910) 30 (180): 361.

theropod by lack of experience, I meant with stegosaurs and thagomizers, not tail weapons. Even Stegosaurus and Ankylosaurus are rather different, and since T rex hasn't seen anything with tail spikes as a weapon (in a sense, something of a cross between a Triceratops and Ankylosaurus). Judging by comparison of these images, Rex is still facing something very brand new.


Admittedly, they're more similar than the comparison with Triceratops, but they're still very different, and I find that backs up my doubts of Rex's experience in the field. 

Well, how exactly would they be different in the appropriate response to them? I get that a tail can move in a very different manner from a horn, which might surprise a predator unaccustomed to animals using tails as weapons, but a stegosaur tail would move relatively similarly to an ankylosaur one, so are you suggesting that T. rex would be too stupid to tell apart a tail from a head, or recognize when a tail was located at face height instead of ankle height?
Have you ever known an extant terrestrial predator mistake its prey's body parts for one another or just walk right into a horn or spike? I haven't, generally it takes extant prey animals quite a bit if effort to make predators connect with their pointy bits.

Also animals generally have an innate respect of pointed structures, whether they are horns on a ceratopsian, thagomizers on a stegosaur, pikes, or bayonets shouldn't really matter. There's no reason to assume dinosaurian predators were any different from extant animals in this regard, since they evolved alongside at least as many pointy structures as modern predators. It would know perfectly well to rrcognize and avoid a tail, and it would know perfectly well to recognize and avoid pointy bits sticking out of it.

Also you are already suspending so manyconcepts of realism matching ul two species further apart from each other than T. rex and humans, that it would seem weird to not also presuppose both animals would be aware, at the very least, if the danger posed by the other. After all that's one of the few assumptions here that could increase realism, since real predators and their prey tend to be familiar with each other, barring introduced predators in island biomes.

[dinosauria101]

Well I initially was thinking that T rex, although it likely would've been able to figure out the danger, probably wouldn't be able to do so before getting stabbed and killed, or seriously injured. Stegosaurus also differs from Ankylosaurus in terms of extreme tail flexibility (comparable to monkeys), so I thought that might work in its favor as well.
Could I have missed something though?

[theropod]

Well not really, unless a theropod was already standing right besides it, which it wouldn't be able to do anyway. I think Carpenter et al. and Bakker et al. show what happened to theropods that made that mistake. They didn't get to make it twice. But if approaching from the rear, they'd probably get hit in the face even before that.

[dinosauria101]

Ah, okay. I think I still favor Stegosaurus, but not 70-80 percent, rather just 65-70 percent.

[theropod]

I am not trying to convince you of whom to favour. Firstly I don't really care, and more importantly I don't really have an opinion (you might get me to to the former if this were Allosaurus, the latter would still be difficult, as I outlined).
I'm just providing you with the scientific data in the hopes that it will aid the rest of you in having a more informed, considered discussion.

That being said, there are subjects, such as the specimen-level taxonomy and measurements of Stegosaurus, that I don't have a very good overview of.

[dinosauria101]

^Well, I was just pointing out you did change my opinion. Good contribution to the thread!

[Infinity Blade]

as many of those horns show signs of healing (e.g. Happ 2008)

Horns? Wasn't only one horn actually conclusively shown to be bitten by Tyrannosaurus? The same source you mention does mention seven unhealed broken Triceratops horn cores at the collection of Shenandoah University...but a lot of other things could have broken those (even post mortem damage).

[theropod]

Apr 29, 2019 9:40:34 GMT 5 Infinity Blade said:

as many of those horns show signs of healing (e.g. Happ 2008)

Horns? Wasn't only one horn actually conclusively shown to be bitten by Tyrannosaurus? The same source you mention does mention seven unhealed broken Triceratops horn cores at the collection of Shenandoah University...but a lot of other things could have broken those (even post mortem damage).

My bad, for some reason I thought there was another paper about that.
thanks or catching that