After all these posts, I’d understand if you were sick of this thing by now, but there is still (sadly for you) some more to discuss. One thing that has been left untreated until now on the blog is the size of Zhuchengtyrannus. Knowing the media would immediately want to know*, we did suggest that this was an 11 m long, 4 m tall and 6 ton animal, but really, how accurate are these? And where does that place it among other theropods?
*Indeed, despite including this in our press pack, I was still regularly asked about this, and was asked for ‘real life’ examples as well.
Well first off the easy stuff – we can measure the bones we do have and that gives us a 64 cm maxilla and a 78 cm dentary, though the latter would probably have been a bit longer in life. These obviously make up a significant part of the skull, but it would have been much longer when complete. As noted before, tyrannosaurines are generally pretty conservative so we can compare the sizes of these bones to their equivalents in other specimens for comparison. There are two adult Tryannosaurus specimens with maxillae just 1 and 2 cm longer than that of ZT with one having a bigger and the other a smaller dentary, so it’s immediately fair to call this about T. rex sized. However, the specimen known as ‘Sue’ is a real monster of a rex with a maxilla some 79 cm long, which is a fair bit bigger bigger. There are several Tarbosaurus specimens in the low 60s for maxilla length, with one (I can only imagine is a juvenile) at 49 and a pretty big one at 73. Several other more basal tyrannosaurid and tyrannosaurine taxa get close, but are not quite as big as ZT.
Obviously we just have one specimen and it’s impossible to know if it was a big or small or very average specimen. Assuming the latter, it’s very slightly bigger than most specimens of Tarbosaurus and slightly smaller than most Tyrannosaurus ones. That means it’s basically about the same size as these two, and lying in between on average.
From that of course we take our other estimates of size – while Sue is about 13m long, the others are more like 11 and so in the paper we suggest that ZT was between 10 and 12 m long (or more simply, 11 m to the press). In hindsight the 4m tall might be a bit much, but not by a huge amount, and as ever with measures like this, vary a lot with what the animal is or could do. If it stretched or tilted the head up (OK, perhaps straw grasping a bit) it would probably be over 4. So onto the mass, which is inevitably the most contentious, if only because it’s the hardest to determine.
Long time readers will be aware of the huge range of masses that have been posited for all manner of dinosaurs over the years. While the ranges have been narrowing and the values converging there is still quite a lot of disagreement. Add to that the natural levels of variation between individuals and even the fluctuations of individuals (sometimes they’re fat, other times, thin) and it should be obvious that even if our calculations were 100% accurate, you would still need a range of figures for a given species and even a single individual. For an animal this size that could easily mean that a single specimen could vary by as much as a few hundred kilos and as a species perhaps the biggest and smallest were well over a ton apart or even two. As such any reasonable number is going to be ‘about’ right and with estimates for T.rex typically being around 6 tons (though up to 8 have been suggested) then 6 is a perfectly reasonable number for ZT, and though we really are extrapolating from less than half a skull, the group as a whole is conservative enough that I’d be surprised if we were much out with any of these numbers.
So where does this put this critter in the pantheon of predatory theropods? Well obviously Tyrannosaurus is bigger and Tarbosaurus is pretty much the same. I don’t think anyone would argue that (in terms of length at least) that Spinosaurus, Giganotosaurus and Mapusaurus are not bigger (and here’s a good chance to link to this old image of mine). After that, well, I’m kinda out of bigger ones. While admittedly ZT is in the same position as some possible other rivals (i.e. we have enough o make a good guess but not enough to be certain) I don’t think it unreasonable to suggest that Zhuchengtyrannus sits in the all time top half dozen.