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Yutyrannus huali
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Yutyrannus (meaning "feathered tyrant") is a genus of proceratosaurid tyrannosauroid dinosaurs which contains a single known species, Yutyrannus huali. This species probably lived during the early Cretaceous period in what is now northeastern China, though there is a chance it may have been from the late Jurassic. Three specimens of Y. huali - all found in the rock beds of Liaoning Province - are known. It is the largest known dinosaur to preserve protofeathers, with all 3 specimens preserving them. However, whether the protofeathers were extensively or sparsely distributed isn't yet clear due to incomplete preservation.
Yutyrannus was a medium-sized bipedal predator, although it was among the largest known of the proceratosaurids. The holotype and oldest known specimen, ZCDM V5000 has an estimated length of 6.4 meters and an estimated weight of about 900 kg with a femur length of 85 cm and an estimated skull length of 90.5 cm. The femoral lengths of the subadult paratypes (ZCDM V5001 and ELDM V1001) are 65 cm and 61.3 cm respectively, with skulls estimated at 80 and 63 cm respectively. Their respective weights can be estimated at 402 kg and 337 kg based on comparison of femoral length with the holotype specimen. The describers established some diagnostic traits of Yutyrannus, in which it differs from its direct relatives. The snout features a high midline crest, formed by the nasals and the premaxillae and which is covered by large pneumatic recesses. The postorbital has a small secondary process, jutting into the upper hind corner of the eye socket. The outer side of the main body of the postorbital is hollowed out. In the lower jaw, the external mandibular fenestra, the main opening in the outer side, is mainly located in the surangular. Yutyrannus would have had an enormous head relative to its body size, exceeding many other carnivorous dinosaurs in this aspect. Its skull was very deep, wide, robust, and full of serrated teeth. Unlike its later relatives such as Tyrannosaurus (but similar to other proceratosaurids like Guanlong), it would have had large and strong three-fingered arms, tipped with sharp claws. It was moderately robust and somewhat long-legged.
Yutyrannus skeletal by Greg Paul. Note that the head on this is undersized given the OP measurements, but it is good otherwise.
 *This image is copyright of its original author Yutyrannus life restoration by Greg Paul.  *This image is copyright of its original author Yutyrannus life restoration by Andrey Atuchin.  *This image is copyright of its original author Yutyrannus skeletals by GetAwayTrike, from top to bottom of ZCDM V5000, ZCDM V5001, and ELDM V1001 and scale bar represents 1 meter for all. Note that the skulls on these are undersized given the OP measurements, but they are otherwise good.  *This image is copyright of its original author  *This image is copyright of its original author  *This image is copyright of its original author GDI of GetAwayTrike's Yutyrannus by SpinoInWonderland, multiply volume by 0.95 to get mass (Note, however, that the torso is somewhat too wide because it is based on the wider-torsoed Gorgosaurus given the absence of a Yutyrannus dorsal view at the time, and correcting this brings it to 900 kg).  *This image is copyright of its original author Yutyrannus skeletals (ZCDM V5000 and ZCDM V5001) by Plastospleen with fixed head size.  *This image is copyright of its original author  *This image is copyright of its original author Yutyrannus skull by Scott Hartman, juvenile specimen ELDM V1001. Note that as deep and robust as this already is, the skull of the adult specimen ZCDM V5000 would have been even moreso.  *This image is copyright of its original author Yutyrannus by Brian Choo. /yutyrannus-56a2543b5f9b58b7d0c91b46.jpg) *This image is copyright of its original author Yutyrannus skull by Kumiko on Wikimedia Commons.  *This image is copyright of its original author Yutyrannus (ELDM V1001) by pilsator.  *This image is copyright of its original author
 (11-25-2020, 10:16 PM)DinoFan83 Wrote: Yutyrannus skeletal by Greg Paul Judging from their physical built, they look much closer to Allosaurids than to Tyrannosaurids. Or they could even be from different clade of Theropoda in my opinion. Quote:Judging from their physical built, they look much closer to Allosaurids than to Tyrannosaurids. Or they could even be from different clade of Theropoda in my opinion. Believe it or not, you're actually not alone with that opinion. Both Darren Naish and Scott Hartman think Yutyrannus is very similar to allosauroids, perhaps moreso than it is to tyrannosauroids. Direct comparisons with allosauroids also support this; in fact, SpinoInWonderland's reconstruction of Carcharodontosaurus' skull here reminds me of Scott Hartman's Yutyrannus skulls in some aspects more than the Yutyrannus skulls remind me of themselves. I personally think Yutyrannus is a tyrannosauroid because all the phylogenetic analyses have recovered it as one, but convergent evolution with allosauroids is probably going on; another group of tyrannosauroids (megaraptorans) were actually thought to be allosauroids for a while, so they're very convergent. (11-26-2020, 09:00 AM)DinoFan83 Wrote:Quote:Judging from their physical built, they look much closer to Allosaurids than to Tyrannosaurids. Or they could even be from different clade of Theropoda in my opinion. I'm curious, how do they perform these phylogenetic analyses?
What is basically done is that a number of traits from every family of dinosaur in the analysis is gathered (for example, let's say an analysis was focusing on ceratosaurids, megalosaurids and carcharodontosaurids, with the addition of some new dinosaurs that didn't seem to belong to any family in particular. Every noticeable trait that each theropod family has and does not share with another, such as details in the skull or limbs for instance, is noted as an indicator that a dinosaur with that trait may belong to that group. If the new dinosaurs shared the majority of the recorded traits with, say, ceratosaurids, they'd be put with them).
I hope that helps.
To put the massive size of this animal's head into perspective, I think a remade version of a size comparison I posted a while back will be quite useful.
Here's a size comparison of the lateral and dorsal views of the skulls of a 2 tonne hippo (60 cm) and 403 kilogram Yutyrannus (ZCDM V5001, 80 cm). Despite the mammal outweighing the dinosaur by a factor of almost 5, and despite how massive a hippo's skull is for its size, its skull is still 1/3 smaller than that of the dinosaur and is considerably less robustly built for its length as well. I'm honestly quite surprised how few have remarked on how proportionally large and robust Yutyrannus' skull is, instead focusing almost solely on the protofeathers.  *This image is copyright of its original author
(01-20-2021, 12:25 AM)DinoFan83 Wrote: To put the massive size of this animal's head into perspective, I think a remade version of a size comparison I posted a while back will be quite useful. Is Lythronax argestes the same size as Yutyrannus?
Based on known specimens, I would say it was not. Greg Paul's estimate of 500 kg for L. argestes is about the same as estimates based on its close relative Daspletosaurus, so unless future finds suggest otherwise, Yutyrannus seems to me the larger.
Old post deleted and redone. I made a couple of errors on the old one and have expanded my information, so this should be more accurate.
Although often overlooked in terms of proportional bite force, I have reason to believe Yutyrannus would have been among the harder-biting theropods for its size because its skull is so proportionally large and robust. However, there have been no bite force studies published, and so my estimates here will be based on comparison to other animals. Exact bite force ballpark is therefore unknown but this is very likely close. Specimens used (both estimated species and species being used as a base for the bite force), their estimated sizes, their estimated skull lengths, and (for the base species) their estimated bite forces: Allosaurus jimmadseni (SMA 0005): 1600 kg based on Randomdinos' chart, 79 cm skull as per discussion in comments of said chart, 8724 newton bite force based on Bates & Falkingham (2012). Sinotyrannus kazuoensis (KZV-001): Can be estimated at a mean of about 1000 kg based on the average estimate of ilium length comparison with the estimates for the Yutyrannus specimens below, 93.1 cm skull based on Daniel Barrera's skeletal. (This is a 'bonus' specimen of which the bite force can tentatively be estimated). Tyrannosaurus spp. (BHI 3033): 6500 kg following Asier Larramendi, 140 cm skull as per the Theropod Database, 35000-57000 newton bite force following Bates & Falkingham. Yutyrannus huali (ZCDM V5000 and ZCDM V5001): The holotype specimen can be estimated at 935 kg as per the above weight estimates, and its skull is estimated at 90.5 cm long by Xu et al. (2012) supplementary information. Also as per the estimates in the above posts, the paratype can be estimated at 419 kg based on femoral length comparisons with the holotype (85 vs 65 cm), and Xu et al. estimates its skull at 80 cm long. Skull comparison and (tentative) bite force estimates: Here is a skull comparison I put together of ZCDM V5001 and SMA 0005, based on the above measurements. Note that MOR 693 was used in place as it had both a good quality lateral and dorsal view available while SMA 0005 did not. As we can see, ZCDM V5001's skull compares very favorably. In regards to bite force, it has all the following going for it: -Larger overall (79 vs 80 cm) despite the animal's size disadvantage of over 3.8-fold. -Much deeper for its length. -Notably wider for its length. -Fused nasal bones (these aren't exactly visible, but tyrannosauroids have them), increasing rigidity and thus bite force. And while I'm not aware of how to factor in the fused nasals, the length, depth, and width can be used for a tentative extrapolation of ZCDM V5001's bite force - based on my combined measurements of length, jugal-postorbital depth, eye socket width, and anterior anteorbital fenestra width, ZCDM V5001's skull is some 14.9% larger overall. That suggests a bite force estimate for the specimen of 11517 newtons (8724x1.149^2). This tentative estimate for ZCDM V5001's bite force also allows for estimations via skull length for the bite forces of ZCDM V5000 (90.5/80 (11517)^2=14739 newtons) and KZV-001 (93.1/80 (11517)^2=15598 newtons), as their skulls seem to be similarly solidly built. Now, you may be wondering at this point how Yutyrannus (and 'bonus' Sinotyrannus as well) compare to the provided bite force estimates for Allosaurus and Tyrannosaurus on a 'pound for pound' basis. Assuming the above is relatively accurate, they stack up better than one might expect. Proportional bite force compared to Allosaurus: 1600/419 (11517)^0.667=28151 newtons can be estimated as the bite force for a hypothetical SMA 0005-sized ZCDM V5001. 1600/935 (14739)^0.667=21091 newtons can be estimated as the bite force for a hypothetical SMA 0005-sized ZCDM V5000. 1600/1000 (15598)^0.667=21342 newtons can be estimated as the bite force for a hypothetical SMA 0005-sized KZV-001. If this is roughly on point, the estimates suggest ZCDM V5001 could bite about 3.23 times as hard as an equally sized Allosaurus, and ZCDM V5000 would be able to bite 2.42 times as hard (which gives us a mean 'pound-for-pound' Yutyrannus bite force 2.83 times as great as that of Allosaurus). Similarly, the 'bonus' KZV-001 would bite some 2.45 times as hard. I don't find this surprising in the least, given how all 3 tyrannosauroids have larger and more solidly built skulls than the allosauroid despite substantial disadvantages in size. Proportional bite force compared to Tyrannosaurus: 6500/419 (11517)^0.667=71705 newtons can be estimated as the bite force for a hypothetical BHI 3033-sized ZCDM V5001. 6500/935 (14739)^0.667=53723 newtons can be estimated as the bite force for a hypothetical BHI 3033-sized ZCDM V5000. 6500/1000 (15598)^0.667=54362 newtons can be estimated as the bite force for a hypothetical BHI 3033-sized KZV-001. Both Yutyrannus specimens and 'bonus' Sinotyrannus compare to BHI 3033 very well in terms of 'pound-for-pound' bite force. ZCDM V5000 is very close to the proportional upper end of 35000-57000 newtons Bates & Falkingham gave to BHI 3033, while ZCDM V5001 significantly exceeds even the upper end of it(!), and with the mean proportional bite force of both Yutyrannus specimens being greater than the range (62714 newtons), this suggests that Yutyrannus just might have been able to match up to or exceed similarly sized bone crushing tyrannosaurids for bite force. Our 'bonus' Sinotyrannus also fits well into the given range, close to the upper end. Such high proportional bite forces for Yutyrannus (and Sinotyrannus) may come as a surprise to many, but given the quite large skulls the used specimens have for their size compared to BHI 3033, it is perhaps less such. In the order written above, if they were hypothetically the same size, the estimated specimens would possess skulls 42.5% larger, 23.4% larger, and 24.2% larger respectively (and as the link shows, these skulls are no less robust for their length than that of BHI 3033), so I personally do not find it to be a stretch to say that while Yutyrannus-grade tyrannosauroids were not bone crushers like giant tyrannosaurids were, they could be able to match or exceed the high bite force proportionally (if only by their proportionally larger heads). In summary, I can say that without testing this, I never would have known the bite forces of Yutyrannus and its kin could have been so proportionally high. And it also does show well that you don't need to be a bone crusher at all for a high proportional bite force on par with or greater than a bone crusher.
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. |
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