Tyrannosaurs as "armored prey specialists".

[Hieu Nguyen]

Hello again, 

I have noted that in mainstream media as well as online threads, there seems to be a frequently mentioned idea that large tyrannosaurs evolved their powerful jaws specifically to hunt down "tougher" herbivores such as ceratopsids and ankylosaurs. This is often contrasted with the less robust skulls and slicing bites of large allosauroids. 

I do have to wonder, does this have any actual validity? I know that modern large terrestrial carnivores (hyenas, big cats, Komodo dragons,...) can all hunt down relatively large ungulates despite significant variation in cranial morphology. Could the differences between tyrannosaurid's and allosauroid's skulls be in fact just different evolutionary solutions to the problem of killing large herbivores, instead of specific "specializations"? 

And as a side note - I know that powerful jaws, while certainly effective killing tools, also grant the advantage of osteophagy. Ultilization of kills/carcasses seem to be the only reasonable scenario in which I can see tyrannosaurs outperforming allosauroids? Leaving aside the limited, if any, evidence of interactions between tyrannosaurs and ankylosaurs. 

Thanks in advance to everyone joining the discussion. 

[Jaime Headden]

The main reason for the argument is not tyrannosaurids vs allosaurids, but of tyrannosaurines (Tyrannosaurinae) versus albertosaurines (Albertosaurinae). In this, the skull becomes wider with improved mAME and mPT complexes, massive musccle origin and insertion sites with huge chambers for the passing of these muscles, including a more developed mPTD that passes over the ectoptergoid, deeper and wider dentigerous bones, and a thicker suspensorium regardless of the great adductor chamber width. And, of course, and probably most principally, the much wider teeth. These features all serve to maximize both a grip and pull strategy, with development of massive muscles on the neck and shoulders, as well as an improved bite.

Now, the nuance to this is that anything that size will produce a massive bite force, but that going to ossified dermal structures will always produce a deterrent. So the armor will always be effective at preventing the bite from going through it. So tyrannosaurines, unlike albertosaurines, may have exemplified a counter strategy whereby they simply seized a whole limb or head and just twisted it off. This is Fowler's general interpretation, and it doesn't come without a few caveats, namely that opportunistic feeding and scavenging were still likely employed, and may have been a major part of the prey capture and dismemberment paradigm. That said, the twist and pull theory is well developed to explaining more of the peculiar and robust anatomy of tyrannosaurines compared to either albertosaurines or allosaurids.

Cheers,

--
You received this message because you are subscribed to the Google Groups "Dinosaur Mailing Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email to DinosaurMailingG...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/8a8f6b7b-9603-47ba-9e1f-bc83d9a5e662n%40googlegroups.com.

--

Jaime A. Headden

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

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

[Tyler Holmes]

This argument also really only applies to the Dinosaur Park Formation, where the albertosaurine Gorgosaurus liberatus coexisted the larger, more robust tyrannosaurine Daspletosaurus. Popular books often suggest that Daspletosaurus focused on hunting ceratopsids while Gorgosaurus went after hadrosaurs (since those are just defenceless dino-cows, don'tcha know?) but this has never made a ton of sense to me, since the hadrosaurs are all at least large as the local tyrannosaurs while the ceratopsids are at most half their size. You would expect the more robust predator would probably be taking on more difficult prey, and the herd-dwelling animals with large tails that are possibly faster and heavier than you seem to be the more difficult prey (especially since there are scrappy fossils that suggest Campanian hadrosaurs were getting quite large). Most of the justification seems to rest on the late Maastrichtian sites, where there are no albertosaurines (to date) and the ceratopsids Triceratops and Torosaurus do get quite large (8-10 tonnes). Of course, Edmontosaurus annectens also gets large, with a few specimens approaching or equaling Shantungosaurus in size, but those appear to be quite rare (or maybe they just didn't fossilize well).

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/CAHyo4cRSrz1No-e_qKoYxQTKQEZq6GRFvz4HwXSzSUG4b7CK%2BA%40mail.gmail.com.

[Hieu Nguyen]

To add on to that, I think it’s exceedingly difficult to be certain of prey preference/hunting habits in extinct taxa. And I have seen non-professional arguments/media portrayals extending to tyrannosaur v. allosauroid/carcharodontosaurid as a whole. 

And additionally, if fossil evidence is anything to go by, T. rex seemed to have targeted both ceratopsids and hadrosaurs as its main prey items. Both did not offer extensive “armor” postcranially - certainly not to the extent of ankylosaurids. 

I should also note that I find the argument that ceratopsids and ankylosaurids evolved specialized predator defense weapons rather weak. 

[Gregory Paul]

The presumption that there was only one Tyrannosaurus species in the TT-zone is now disputed by multiple studies by myself, Sancarlo, Persons, Zanno, Napoli, Saitta, Longrich (and see https://www.google.com/search?client=safari&hs=ttuU&sca_esv=4b9c4fb793c57767&channel=mac_bm&udm=7&sxsrf=ANbL-n4kR0vxe2cVBzdN6R1rOOeiuP_bBg:1774405954947&q=nicholas+longrich+tyrannosaurus+species+imperator&sa=X&ved=2ahUKEwjT54algbqTAxWKjokEHemyHP0Q8ccDKAR6BAgWEAY&biw=1573&bih=911&dpr=1#fpstate=ive&ip=1&vld=cid:c3afed72,vid:4e_yDs3GBkY,st:0),. In the upper section there was a level of divergnce in robusticity versus gracility that literally exceeded that between Gorgo and Daspleto, apparently being the two species stout T. rex (with the wild and wacky postorbital Mickey Mouse bosses seen on Scotty and Tufts Love) and gracile T. regina with rather run of the mill tyrannosaurid style bosses. Obvious candidates for prey segregation. 

As far as I can tell the giant Edmontosaurus are so far from the lower TT-zone (if anyone knows otherwise please say so with the information) which may be E. copei what as far as I know is not yet known from the upper TT-zone (but some specimens may be from there, or not, any information would be appreciated). So far the only specimens I know are from high in the zone are rather modest sized E. annectens. 

GSPaul

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/5471e192-0f4a-40a2-b93b-3a5114141158n%40googlegroups.com.

[Hieu Nguyen]

I am not sure if it is appropriate to base assumptions off of taxa that are highly controversial/of very uncertain validity.

[Milo Gaillard]

To add to your point, the Maastrichtian sites aren’t a reliable enough justification, because there’s also Nanotyrannus, which is smaller, more gracile, and sleeker than any albertosaurine that’s ever been found, in contrast to the much larger, bulkier, and more powerful Tyrannosaurus. It’s not like Nanotyrannus primarily hunted Edmontosaurus while Tyrannosaurus was mainly focused on Triceratops, Torosaurus, and Ankylosaurus.

Sent from my iPhone

On Mar 24, 2026, at 17:40, Tyler Holmes <tyle...@gmail.com> wrote:



To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/CAP7CPGbseVXnefSvVzJz%3Ds7Pw3_NqKmpJ_2nD3bPxC8DDW4vkg%40mail.gmail.com.

[Franco Sancarlo]

Even if you do not support the multiple species of Tyrannosaurus (for wich we need more studies on the argument) the fact that in the lower tt-zone the robusticity variability is lower seems a fact (based on the actual data that I've seen). In the upper tt-zone the difference in robusticity is pretty big, so even if they are the same species, this is important to the debate. to my knowledge the giant hadrosaur of 13 plus ton are found only in the lower tt-zone, in the upper seems like that they were smaller (might be wrong, correct me if I am), the lower tt-zone E.copei and upper tt-zone E. annectens are pretty different and might not even be the same genus (Ford personal comment) so that might shows that between the lower and high tt-zone the differences in fauna was higher than previously thought,  this might also support the change of diet of Tyrannosaurus in 2 species. 

But we need more studies on the argument and I might be completely wrong 

Sorry for the bad english 

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/ece41430-75d7-4ff7-88a0-296066521e59n%40googlegroups.com.

[Gregory Paul]

The nanos, stygis, larsonvenators & gilmoretyrannians were not hunting the giant herbivores, and when it comes to Tyranno are only relevant to their competition with its less gracile, dinky armed, blunter toothed juveniles, which were lower in number so far. 

GSPaul

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/DEA8CFAA-365F-48D3-91CC-C78BDB3442AE%40gmail.com.

[Gregory Paul]

Also Ankylosaurus is apparently absent from the lower TT-zone, which might have been inhabited by a giant nodosaur. 

I doubt E. copei is a different genus -- as much as I like Anatotitan. 

The English is good. 

GSPaul

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/CADJSBGpVdoMUu3UqMqfYMaEoeLDRDZRTvhLVDyTnGW0dnfLf_w%40mail.gmail.com.

[Tyler Holmes]

That the largest Edmontosaurus specimens come from the same time period and geographic area as the largest Tyrannosaurus specimens (such as Sue, Cope, Goliath) is very interesting, but there are also large ceratopsids from that same area (such as "Triceratops maximus", which could be Triceratops horridus or Torosaurus latus). That correlation doesn't really help us with the "robust tyrannosaurs focused on ceratopsids while gracile species hunter hadrosaurs" hypothesis because even in schemes were there are multiple Tyrannosaurus species in the late Maastrichtian, no one has suggested the lower TT-zone contains more than one Tyrannosaurus species, so we don't have a second large predator to partition with (I doubt small non-tyrannosaurid eutyrannosaurs were exerting competitive pressure on predators 8-10 times their size). 

That leaves us with the Dinosaur Park Formation (two taxa), the Two Medicine Formation (three taxa), the Judith River Formation (three or four taxa), and the Kirtland Formation (at least two taxa). Several of these contain large to giant hadrosaurs and the Kirtland Formation may also have a large ceratopsid (though OMNH 10135 may actually be from the underlying Fruitland Formation). These would be the best places to test niche partitioning amongst similarly-sized tyrannosaurs. 

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/597282938.151343.1774441868986%40mail.yahoo.com.

[Gregory Paul]

I cannot overemphasize that there is currently no compelling evidence of a size change in Tyrannosaurus. The skeletons of the three largest semi-complete skeletons -- high placed Scotty and Stan (which we all hope will survive the ongoing war) and bottom of HC Sue, share the same basic dimensions and volume with masses in the 7.5 t zone (higher masses are based on errant, bloated Jackie Gleason restorations). I don't know off the top of my head what is going on with fragmentary specimens but those are subject to statistical fluctuations. 

And let's no go too far with what was going on with TT-zone Edmontosaurus. How tied the biggies are to stratigraphy is not yet certain. And while one of the E. copei skulls and a mandible are apparently low placed, the level of the type and another skull are not known and according to people who work in those formations cannot be determined at this time. This is a reason I limit my published comments on these to the field guides and will not attempt a technical paper on the subject, not enough data (very different from Triceratops, Tyrannosaurus, Ankylosaurus, pachycephalosaurs, more similar to the baso-eutyrannosaurs for which the strato data is usually poor). 

GSPaul

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/CAP7CPGZRQnW1r8s2z6HgeH3RP0K8tqv4briBkbPx%3Dpj0a1F7Og%40mail.gmail.com.

[Gregory Paul]

Also, there do not seem to be any E. copei skulls from the Canadian TT-zone deposits which are all high up. If any know otherwise please advise. 

GSPaul

[Franco Sancarlo]

Denversaurus (type specimen) to my knowledge is from the lower tt-zone, there are also specimens from the Lance formation.

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/597282938.151343.1774441868986%40mail.yahoo.com.

[Gregory Paul]

I am referring to the presence of any Ankylosaurus from the lower TT-zone, or giant nodosaurs -- Denversaurus is not 5+ tonnes.

GSPaul

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/CADJSBGqQxx6zncyGLxVv5wVPMtB3EnLpKwAZG3e64YkhidzvcA%40mail.gmail.com.

[Franco Sancarlo]

To my knowledge BHI 6225 (see Burns 2016 phd thesis for all the data) seems to be quite bigger that the holotype skull of Denversaurus (if we reconstruct it like Bakker 1988 did)

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/917872400.3911.1774460845727%40mail.yahoo.com.

[Hieu Nguyen]

I'm pretty sure the bottom line here is that there is pretty much no evidence for tyrannosaurids as a whole elvoving powerful bites to specifically target "tougher/more armored" herbivores. It could just have been for effectively killing (and then efficiently exploiting the carcass of) large prey species as a whole. As for the idea that "gracile" vs. "robust" tyrannosaurids represent different morphologies for targeting different prey items, I find it very speculative at the moment, to say the least.