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theropod1's avatar

T. rex: the most iconic skull ever

By theropod1
The above is a scalechart of FMNH PR2081, thus far the largest, most massively constructed and most complete T. rex known. In terms of skull size, there are other specimens similar to it, but none surpass it.

Here I scaled the skull based on the mounted version to the Premaxilla-Quadratojugal-lenght from Brochu, 2003. The maximum skull lenght ended up around 5cm longer than that.
The most impressive thing about it and probably a something it is still record holder in is the immense skull width, upwards of 80cm.

And NO, MOR 008 is not larger than sue, it was just incorrectly reconstructed, that's all.
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theropod1's avatar
In Brochu (2003) it seemed like the exoccipital should be more or less hidden by the squamosal in lateral view when both were aligned and the deformation removed, but don’t take my word for it. I might revisit the skull at some point.
theropod1's avatar
Part of it breaks down to how exactly the skull is measured. The other part breaks down to the original skull being crushed and depends on how you correct for that.
kirkseven's avatar
did UCMP 118742 have a bigger skull than sue?
theropod1's avatar
The specimen consists of a single maxilla, which is smaller than sue's maxilla in every measurement.
It's about 96% the size of sue's, so our best bet is that its skull is also around 96% the size of sue's.
kirkseven's avatar
I think its fair to say that it was probably an impressive specimen though
theropod1's avatar
Yes, everything that’s within a few percent of sue’s size is certainly impressive. It’s a shame there’s just a maxilla (but then, fragmentary cranial material is a common kind of shame in giant theropods…).
kirkseven's avatar
 if it was a small headed specimen like AMNH 5027 or the holotype
how large would it be?
theropod1's avatar
UCMP 118742’s maxilla is ~9.1% bigger than AMNH’s and 11.7% bigger than the holotype’s. The specimens are estimated at 11.8m and 11.9m respectively by Scott Hartman.
Dinopithecus's avatar
In some reconstructed T.rex skulls, the teeth are rather long. Some people explain this as the teeth coming out of their sockets (the brown part supposedly the exposed root), but I'm not completely sure if that can be used to explain seemingly long teeth. For example, I recall Jaime A. Headden addressing the same thing for Dilophosaurus and said that the "exposure of the root" is more likely the non-enameled base of the crowns, hence the teeth truly were that long.…

Maybe it's the same case here? I guess it would make sense for hunting, as I recall you saying (on WoA) that the second palate would have served as an obstruction for deep penetration in the absence of long teeth. What do you think?
theropod1's avatar
I’m  aware of that, but firstly I’m not sure I agree with Headden on this one.
Neither crocodiles nor monitor lizards represent a good comparison, since neither of them have teeth that extend beyond the ventral edge of the dentary when the mouth is closed as do Headden’s Dilophosaurus’ teeth.
Also, citation definitely needed regarding exposed unenameled portions in these animals. The only thing I found on the matter suggests the enamel extends down into the alveoli in crocodiles.
"The crocodile enamel has a thickness of about 100–200µm at the crown (Fig. 3A), becomes thinner towards the root and disappears completely just before the onset of the hollow part (Fig. 2A). In this region, an enamel–cementum interface can be observed where a thin cementum layer is present that covers the enamel layer (Fig. 2A)."
From: Enax, J., Fabritius, H.-O., Rack, A., Prymak, O., Raabe, D. and Epple, M. 2013. Characterization of crocodile teeth: Correlation of composition, microstructure, and hardness. Journal of Structural Biology 184 (2): 155–163.

And in monitor lizards, the teeth are commonly buried in the soft tissue almost entirely, so that you can hardly see the crowns in the living animal. They are hardly mounted on stilts of unenamelled dentine that make them stick out. So unless better evidence turns up, I think the convention of treating the enamel-dentine transition as the base of the crown in theropods is well-supported.

Secondly, it isn’t as if I had shortened the teeth in this case (consider one grid intersection is 10cm). There can be little doubt sue’s teeth aren’t preserved in a perfect life-like configuration (because the entire skull is crushed taphonomically), but the teeth as shown here are based on the official dewarped version. Stan is the specimen mounted with weirdly long teeth, not sue. If anything, they end up sticking out a little further than sue’s longest tooth crown (which is 109mm long).

It’d be one thing if the "long toothed" condition was consistent among all specimens, but if there’s so little consistency in T. rex (and among theropods in general), this makes it much more likely that they are artefacts of decomposition than that they are a genuine feature of the animal’s anatomy. And we know that teeth have a certain tendency to slip from their sockets, after all there are also entire, dislodged T. rex teeth known that include the root.

Compare Mark Witton’s reconstruction of the same specimen and Manabu Sakamoto’s reconstruction of Stan (where he remarked on the tooth-thing):
"It's evident that a lot of the teeth have shot out of the sockets after the animal had died so that much of the roots are exposed. Presumably, this version should be closer to what the tooth row would have been like in life; I don't suppose roots would be exposed too much in life..."

That the secondary palate would impede penetration deeper than tooth crown length is perfectly consistent, with the fact that the teeth are already so relatively long, and that the bite was evidently reliant on huge amounts of force. So yeah, I think if T. rex wanted to inflict a deep-going injury it would have to properly crush down on what it bit and damage it through blunt force.
Dinopithecus's avatar
Interesting about the first part.

I didn't say you resized them, it's just that the outer tooth length I see in various specimens tends to vary (with roots sticking out in some and not so in others).

The crowns appear to be ~15cm here, which is consistent with figures I tend to hear for Tyrannosaurus' tooth length (just in case you're interested where I heard them, I first read it from Darren Naish's "100 years of Tyrannosaurus rex" blog post on the old Tetrapod Zoology, so I figured it was reliable). I guess that's large in absolute terms, but I'm not sure if I would really call them relatively long, especially considering how they belong to a ~6 tonne animal.
theropod1's avatar
As for the 15cm, I think it’s one of many rough figures floating around the web, possibly based on an exaggerated tooth length resulting from slippage. Since it sais "over 15cm" I could even very well imagine Naish was actually referring to the whole tooth, including the root. In any case, there are precise figures in the literature that are better to rely on, the longest T. rex tooth crown on record is short of 12cm tall, the average is about 7cm. The tallest of sue’s tooth crowns are approaching 11cm, as I already mentioned.

I didn’t actually measure the length of the tooth crowns in my reconstruction, since I based them directly on the uncrushed skull restoration of sue, but if they are that long, then they actually do have the roots sticking out here anyway.

In any case, that’s among the longest teeth of any theropod, and I really don’t see any justification to say they should be longer than shown here.

Saying that we should assume it had longer teeth because they could be useful is a bit of a fallacy.
Extant durophages don’t have relatively longer teeth either (the opposite is often the case because their teeth need to be robust), precisely because they rely on bite force, not on excellent penetrative abilities of their teeth. The same is the case here, the teeth are exceptionately massive, but not exceptionately long (still they are among the largest theropod tooth crowns together with Spinosaurus and Carcharodontosaurus).

As a theropod, T. rex has a different tooth design in some regards (i.e. it’s teeth are way more pointed than the crushing teeth of mammals, they probably served as spikes, not boltcutters), but that doesn’t mean that if you give it saber teeth by assuming its tooth roots sticked way out of their sockets that would be consistent with a massive bite force and adaptions for it (such as the secondary palate, reduced cutting abilities, wide skull…).

Smith, Joshua B.; Vann, David R.; Dodson, Peter (2005): Dental Morphology and Variation in Theropod Dinosaurs: Implications for the Taxonomic Identification of Isolated Teeth. The Anatomical Record, 285 (A) pp. 699-736.
Dinopithecus's avatar
"short of 12cm" Is this referring to Sue's longest crowns?

I never actually made the assumption that "x had to be this way, otherwise, it couldn't *insert certain activity*" (actually, anyone who reads that would see just how flawed it is), I was simply wondering about the whole tooth crowns and roots thing and what affect that would have on the living animal.

How long are the teeth of the two theropods you mentioned? I *THINK I recall you saying ~10cm for Carcharodontosaurus on Carnivora (Carchy vs. Rex thread) and I *THINK I also recall you saying Spinosaurus had the longest theropod teeth on record.

*because I hate to state something from memory that turns out to be wrong.
theropod1's avatar
Me too, so I'll get back to you later.

Sue's longest crown is 10.9cm (short of 11cm), the longest of all T. rex tooth crowns is a little longer than that, at 11.7cm (short of 12cm).

Well, the situation seems to be that T. rex simply needed huge amounts of force to bite deeply, which of course it had.
What do you think about the Witmer Lab reconstructions?
To me the skull seems a bit thin, primarily the snout, from various places I have seen 40-50 cm wide (at the maxilla) and at the widest point of the skull 80-85 cm or more.

If the head were only that small it would seem strange going with a torso that is very wide as depicted in this article:…
theropod1's avatar
The original skull was 94.5cm wide in the temporal region, and it was dorsoventrally crushed, making it wider than it was in life. I see nothing wrong with those width measurements. The witmer lab-reconstruction is excellent as far as I can tell, but I think it bases on BHI 3033, not FMNH pr 2081.

An animal’s torso doesn’t really tell us how wide its skull is going to be, and this skull is already extremely wide for theropod standards, both in absolute terms and compared to its lenght and the size of the ribcage.
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