Yutyrannus huali

[DinoFan83]

I think this post may help clear up some of the stuff written above, and give better insight as to what the written information actually looks like.

So, with all the disclaimers on the above posted skeletals that the heads may be too small as well as with no skeletal posted so far showing a very big-headed animal as the OP says, I have little doubt some have read this thread and wondered 'Is Yutyrannus actually as big headed as the text says? Even if the heads are supposedly undersized, none of the images support that'.

And for those who have, I in all honesty don't blame you.

Literally every skeletal of the animal I know of - be it any of the skeletals posted above, Franz-Josef73's skeletal, or Plastospleen's/Ashley Patch'es skeletal - depict the skull as too small despite all the other bone measurements being consistent with what has been published. And if every skeletal failed to depict such a big-headed animal, without the proper knowledge of the context you'd never know it wasn't as those skeletals show it.

To that end, I have taken a moment to slightly modify one of the above skeletals (Ashley's) in order to be more coherent with the published skull length measurements from Xu et al. (2012) supplementary information, linked in the above post. Measurements adjusted based on skull length to femur length ratios as written in the image. 

With the proper measurements, it is clearly visible how large the skull of Yutyrannus really is relative to its body size, especially that of ZCDM V5001. Undoubtedly one of the most big-headed theropods of all, we're looking at an animal beaten a mere 4.2% on a proportional basis than the biggest-headed theropod I am aware of.
The skull is also very deep and robust, as can be seen both in the above chart and in the other posts.

*This image is copyright of its original author

Something you may be wondering at this point is that, if the published measurements really indicate the head is that big, then just why did every skeletal make it too small? 
While I cannot say for sure as I'm not the one who made them, I have a number of theories, all of which may have been playing a role in the skulls coming out as too small was when everything else was just fine. They are as follows:

-Measurements of the skulls not accessed. The original paper on Nature is paywalled, and non-paywalled versions like on ResearchGate or WebArchive do not have the link to the supplementary information, the only place that gives skull measurements.
To compound the problem, while the supplementary information with the Nature paper is free, it's not shown as a major part of the paper at all and is therefore easy to miss if you're not looking for it. So I think it is likely that not knowing about the supplementary information and having to work off of what was in the skull measurement-free paper played a role in how the skulls of those skeletals turned out to be too small (more on this below).

-The crushed skulls potentially being shorter than the uncrushed skulls. On his blog, Scott Hartman goes over how this can really mess a theropod skull up.

Quote:The reconstruction above is based on one of the beautifully preserved skulls (there are 3!); like everything else found in the Yixian Formation, the specimens have been squashed flat. Relatively robust bones like a femur hold up fairly well, but skulls really don't. They tend to be highly three-dimensional in shape, and are made out of relatively thin elements. In particular, on theropod skulls the top and rear of the skull tend to fold upward as the head undergoes the pancake treatment of diagenesis.

And this is just one of quite a few cases where a crushed theropod skull ends up differently from an uncrushed one. Let''s take Acrocanthosaurus for example. 
Currie & Carpenter (2000) list NCSM 14345's crushed skull at 129 cm long.

Quote:There has been some crushing and distortion of the skull, mostly towards the back (Fig. 2). For example, the left postorbital was broken in at least two places, and had pulled away from its suture with the frontal, the ventral part rotating medially. Minor crushing and distortion are also evident in the posterior half of the jaws. The skull (Figs 2; 3) is almost 129 cm long (premaxilla to quadrate) with a preorbital length of 85 cm

The uncrushed version, however, is 140 cm following the scalebar in Eddy & Clarke (2011), and this length is also consistent with the given maxilla length of 82.3 cm.
Basically, since crushed theropod skulls can very well be shorter than they would be uncrushed and since the 3 Yutyrannus skulls were figured that way with no non-supplementary measurements, this could have been another factor for all those skeletals to have undersized skulls.

-The authors could have drawn the skulls too small in the figures, or got the scalebars for them wrong. This wouldn't be so unprecedented, skeletals and figures of dinosaurs in their description papers are sometimes quite off both in terms of the anatomy of preserved remains and in terms of scalebars.

In a nutshell, I believe no proper measurements outside the elusive supplementary material, crushing of the skulls that may have shortened them, and erroneous proportions/scalebars in the figures of the non-supplementary paper (or any combination of those three) are the factors that lead to every skeletal of Yutyrannus so far having an undersized skull. Reply