Triceratops

[DinoFan83]

It's a well known fact that Triceratops was among the most robust dinosaurs of all. But just how robust, really, was it? The answer may surprise you!

To answer this question, we need to look at available mass estimations and measurements of its limb bones in the literature. Case in point: Going by SpinoInWonderland's GDI, a Triceratops with a 2.5 meter skull weighs at least 10.5 tonnes (possibly 11 due to the reasons I have outlined earlier in this thread), and this would equate to about 14.6 tonnes for AMNH 5040, whose estimated skull length is 275 cm going by GetAwayTrike's skeletal. 
For limb bone length, given the skull length of 2.5 meters, the femur length is 151.8 cm, which would then equate to a femur length of 167 cm for AMNH 5040. And according to Benson et al. 2014, the humerus to femur ratio in a single Triceratops individual (AMNH 5033) is 78 cm to 103.4 cm, meaning an estimated humerus length of 126 cm for AMNH 5040.

What, you may ask, does this have to do with how robust Triceratops is?

That shall soon become very apparent. Following Benson, the 103.4 cm femur has a circumference of 49.9 cm, and the 78 cm humerus a circumference of 49.2 cm. These measurements equate to the estimated 167 cm femur and 126 cm humerus of AMNH 5040 having circumferences of 80.6 and 79.5 cm, respectively.

And how robust does the resulting animal turn out to be?

Putting it mildly, Triceratops ends up as a very good contender for the most proportionally robust dinosaur ever discovered! The mass estimation for AMNH 5033 in the linked file is stated to be 14 tonnes based on limb bone circumference (this, coincidentally, is a very close match for the volumetrically-derived mass of our largest Triceratops specimens that I have outlined above), which would equate to a circumference-based mass of 59 tonnes (!) for a 14.6 tonne animal extrapolating to AMNH 5040's predicted limb bone sizes.  

What else has limb bones of similar thickness? A 45-75 tonne Notocolossus (humerus circumference 77 cm), a 46 tonne Ruyangosaurus (femur circumference 79.7 cm), and a 55+ tonne Patagotitan (humerus circumference 78.2 cm). And the even more impressive thing is that not only are these animals roughly 3-5 times as big as the ceratopsian, they are titanosaurs, notorious for having very proportionally robust limbs as Greg Paul (2019) noted, so despite all that AMNH 5040 very likely has limb bones of comparable circumference, which does go to show how incredibly robust an animal that Triceratops was.
For further comparison, given the disparity between the mass indicated by limb bone strength relative to mass indicated by volume, Triceratops has limb bones proportionally 59.3% more robust than the vast majority of extant terrestrial tetrapods (these animals tend to produce much more accurate results with the equations of Campione and Evans (2012)), which is just as impressive.

All things considered, given this extreme robusticity combined with its large size and top-tier offence/defence, it's very easy to see why Triceratops did so well during the Cretaceous and why its fossils are so common. If I was a T. rex, I'd definitely have kept my distance! Reply