Shake Your Tail Feathers: An In-Depth Look at Saurian’s T. rex

Let me first start off by saying that this is not intended as a personal attack on the Saurian team or game. I really admire their aim to communicate modern palaeontological ideas to a wider audience, and the scientific rigour they apply to their reconstructions of prehistoric animals and their environments is superb. I made a generous donation to their crowdfunding campaign that guarantied early access, and I absolutely cannot wait to try it out. That being said, there are a few issues with the science behind their dinosaurs. Here I am going to be talking about one of the biggest, communicated through infographics based on that of the game, which due to their portrayal has sprouted into a widely popular palaeo-meme. I am referring, of course, to their half-feathered Tyrannosaurus rex.

Memefying T. rex

I ran two polls recently over social media, one on Twitter, and one on Facebook, each for a week, to determine the general opinions of my followers/friends, and (in the case of Facebook) those on the palaeoart page. The results were surprising.

poll results

As is clear in the results, the Saurian T. rex has become incredibly popular, and the pattern of feathers they have adopted has become something of a meme within palaeoart, much of it stemming from the detailed infographic they have constructed on the subject (the style of which I have based my figures on here). The basic reasoning is laid out as such:

  1. “Wyrex”, an undescribed Tyrannosaurus rex missing much of it’s tail was recovered with a one or more patches of scaly skin from near the underside of the caudal region.
  2. In an animal’s embryonic development, different types of specialized keratinous epidermal structure cannot grow simultaneously on what are labeled “integument zones”. These are the body, feet, and tail. Modern studies maintain this.
  3. Thus, if part of “Wyrex”‘s tail is scaly, the whole tail must be scaly. 
  4. Similar pattern’s are seen on the dinosaurs Juravenator, Concavenator, and Kulindadromeus, showing that this is a reasonable scenario(1).

While this answer may seem sufficient, the answer is a bit more complicated than the seemingly strait-forward chain of reasoning that Saurian displays.

Scale impressions from Tyrannosaurs

Scale location

It is here that “Wyrex” not being a described find hits the hardest; it is as of yet incredibly hard for those not in possession of the fossil to know where exactly the scales came from. While yes, I agree there is the possibility that these did come from the underside of the tail (which would present quite an exciting example of secondary reticula evolution)(2), the fact remains that the scales from “Wyrex” were not found in undoubtable proximity to the body as most are, but were instead found “near the base of the tail”(1). I am not aware of any site maps of “Wyrex”, so correct me if I am wrong, but could it be that these scales were from the pedal region, or from the footprint of another tyrannosaur visiting “Wyrex” after its death (for motives of cannibalism perhaps)?

Essentially, until an analysis of the specimen is published, we cannot know for sure where these scales came from. This is the big problem with unpublished specimens such as “Wyrex”; we just have the suggestion of the collectors as to the location of the scales. As such I would caution against using “Wyrex” as an indicator for caudal scales, at least until an analysis is performed that concludes their identity.

Additional finds

final fewather phylogeny
The complicated world of published non-paravian theropod skin impressions (not including tracks). While some tyrannosaurid skin impressions have been reported, they are either not published or do not exist anymore.

Several other skin impression of tyrannosaurs reportedly exist, from the animals Daspletosaurus and Gorgosaurus. However, in the former situation, the position of the body is unknown, and in the latter, the specimen has not been studied (I am not even sure if it still exists)(1). The only published impressions from the Tyrannosauridae come from an individual of the genus Tarbosaurus, which preserves a tiny patch of scales from the torso (although the exact location of these are also unknown)(2). While it may seem that due to an abundance of scale impressions, and lack of feather impressions, tyrannosaurs were scaly, it is important to note that feathers require delicate preservation much less common in these areas, and many have likely been destroyed accidentally due to nonrecognition(3)(4). For instance, the fully-feathered Ornithomimus, despite being published in 1890, was only found to be feathered almost 130 years later(4).

If the tail did have scales

The issues with a completely scaly tail

Simply put, scales have almost no thermoregulatory function(5). While it may be thought at first that an animal of that size would have been a much higher priority to lose heat, the reality is that the climate of Hell Creek was constantly changing. We know this from studies that place a mean annual temperature of about 5-14 degrees celsius(6); there must have been a significant amount of warm weather to sustain the warm-weather fauna of Hell Creek, but enough cold weather to drop the average this much. This means that the area that Tyrannosaurus lived in varied between warm and cold every year, and while this may not be a problem for a cold-blooded reptile (that requires much less food, does not need maintain a constant body temperature, and is able to hibernate in such conditions)(7), we have no indication that Tyrannosaurs could hibernate or use any other mode of rest for surviving the winter, and so was likely active and looking for food year-round.

The tail is a large portion of the surface area of a Tyrannosaur, and if such an area had no ability to thermoregulate, it seems likely that it would have had much more trouble regulating its body temperature than had it been covered in feathers, which can both help retain and lose heat. Considering that feathers were likely the ancestral integument of Tyrannosaurs(8)(9), it seems like there was not much of a motive to lose them and gain back such a large area of feathers. Even if these animals lost feathers in order to be able to dump more heat (assuming retaining heat was not an issue), it seems like they would have simply been replaced by bare skin, like modern ostriches. However, it is important to note that ostriches use their wings to cover their bare skin to warm up(10). As tyrannosaurs did not have this and lived in a much colder climate, it seems likely that their tails would not have been devoid of feathers, especially considering the large tyrannosauroid Yutyrannus had a tail covered in feathers, and yet lived in an area that was as cool, if not warmer, than Hell Creek(6)(8). Please note however, that this is my own personal speculation based on modern animals, and I would recommend a conclusive test be undertaken.

Integument zones

It is maintained in Saurian’s infographic that types of specialized keratinous integument (scales/modified scales and feathers, but not bare skin) cannot coexist on certain zones of the body, as each of these regions develops integument separately from the others, and each cannot grow two different types simultaneously. These “integument zones” are stated to be the main body (including the head, neck, arms, hands, and torso), the feet, and the tail. This claim is supposedly backed up by a series of studies (which I have been unable to find) that supposedly replicate these results in modern birds and crocodilians(1). However, despite what the genes may show, the phenotypes of numerous modern and extinct animals show examples quite to the contrary.


A perfect example of this is the Jurassic coelurosaurian Juravenator starki. This diminutive carnivore, whose phylogenetic position is constantly being debated(11)(12), has been recovered sporting both scales and filamentous feathers simultaneously on its tail. The scale impressions form an almost continuous outline of the ventral surface of the tail, while the feathers, preserved in only in irregular patches due to their delicate preservation, lie just above the sacrum, dorsal to the 10th-14th caudal vertebrae, and dorsal to the 18th-20th caudal vertebrae, after which no caudal impressions are preserved on the dorsal side of the tail(13)(14). Even acting on the conservative assumption that the feathers stop here, it would mean that the feathers and scales coexisted for at least 50% of the tail.

Juravenator is one of only two theropods to be preserved with some scale covering on the tail but feathers on the body, and both show a dorsally feathered tail with a scaly underneath. Unfortunately, the other, Scansoriopteryx(15)(16), is not as closely related to Tyrannosaurus as is optimal, and it is hard to test this more within the non-paravian theropoda. However, there are a few examples of both living and extinct theropods that also diverge from this concept. Kulindadromeus, the only animal to abide by this bald-tailed morph (as stated later), had its upper arms covered in a hybrid of scales and feathers, with the lower arms being scaled, which clearly shows a divergence of integument types on the body zone (a big thanks to Ashley Patch for pointing this out). The proceratosaurid tyrannosauroid Yutyrannus huali preserves filamentous feathers that extend until at least the first part of the tarsus, encroaching on a domain that remains scaly in modern birds(8). Sinocalliopteryx preserves a complete “sock” of tarsal feathers that stop at the toes, and Cathayornis preserves them until halfway down the tarsus(17). The famously well-preserved Anchiornis even preserves scales lying underneath the feathery coating of its legs, from the toes to the tibia(18), which is perhaps the best example in existence to show scales and feathers coexisting.

Inconsistency in the boundaries of feathers and scales suggest that integument zones were not set in stone. Additionally, the only coelurosaurs with known scales on their tails preserve feathers as well.

This hypothesis is even disrupted in modern birds. In the grouse family, the Ruffed Grouse (Bonasa) has a Sinocalliopteryx-like “sock”, as well as snowshoe-like feathery projections that it grows in the winter(19), while its close relative the Rock Ptarmigan (Lagopus) has a complete covering of the pes in feathers, only stopping at the reticulae(20). In eagles, variation is shown between, for example, the Booted Eagle (Hieraaetus)(21) and the Bald Eagle (Haliaeetus)(22), which show different levels of tarsal feather covering. These are just a few examples of modern coelurosaurs that disprove the hypothesis that feathers and scales cannot coexist on the same integument zone, subtracting from the likelihood that Tyrannosaurus had a fully scaled tail.

Comparative anatomy

The three examples used by the Saurian team in their analysis all seem to follow the trend set by their Tyrannosaurus. However, only one of these examples actually fits, and it is Kulindadromeus, an ornithischian. The two other theropods tell different stories.


Concavenator was originally described with a series of bumps present on the posterior side of the ulna, a trait that was taken as evidence of quill knobs(23). As such, it did not seem that far-fetched that it was covered with feathers in real life, excluding the tail, which preserved scales(1). However, further analyses showed that the bumps actually lay on the anterior side, and were they to support quills, the quills would have stuck forward through the radius(24)(25). Additionally, skin impressions from the abdomen of it’s close relative, Allosaurus, show a scaly torso, further casting doubt on this hypothesis(26). For now, it seems that Concavenator was fully scaly.


Juravenator (explained in brief above as well) was a peculiar little coelurosaur from the Solnhofen beds. First described with only scales lining the tail, further in-depth analyses in 2006 and 2010 found traces of filamentous feathers lining the top of the tail and hips(13)(14). This was represented in the infographic. The problem? The feathers were drawn in the wrong place (perhaps a mistake by interpreting the tendinal fibres shown in Fig. 5 of the redescription as the feathers). In reality, the impressions showed patches of feathers running down the top of the tail until caudal vertebra 20, as shown in the UV scans in the last few pages of the paper. This means that the feathers covered at least 50% of the dorsal surface of the tail (no impressions were preserved beyond there)(14).

In all, the only animal that abides with this bald-tailed interpretation is Kulindadromeus, which isn’t even a theropod(27). It should be noted however, that Juravenator lies in a phylogenetic position very close to the base of the Tyrannosauroidea, be it a compsognathid or otherwise(11)(12). Since it is the closest relative to Tyrannosaurus found with scaly impressions from the tail in addition to other epidermal impressions on the body, I would like to suggest to the Saurian team that they base their Tyrannosaurus on this animal. While there is of course a definite difference in size between the two, it is not much more than that between Tyrannosaurus and Kulindadromeus, the only known dinosaur with this pattern. As such, if the “Wyrex” specimen is to be accepted as evidence, the integument covering the rest of the body should be modeled off of its closest-known relative to sport scales on the tail and feathers on the body, and should therefore sport tail feathers to at least the 20th caudal vertebra along the tail’s dorsal surface.


tyrannosaur bitey

Basically, determining the scale covering of Tyrannosaurus rex is a lot more complicated than it initially presents itself. While there may be some genetic evidence for separated integument zones(1), numerous extinct and extant species completely disprove this hypothesis. Additionally, the only two coelurosaurs that preserve scales on the tail also preserve feathers on the dorsal surface, and due to the close phylogenetic position of one to the Tyrannosauroidea(13)(14)(15), it seems most logical to base Tyrannosaurus‘ physical appearance on this.

I recognize that, as they have recently mentioned, the Saurian team is very close to pre-release, and as such is not able to preform many edits on their animals(28). I would however suggest that they, for the full release of the game, redesign their Tyrannosaurus rex based on other Tyrannosaurs and/or Juravenator in order to maintain the excellent scientific accuracy that they have exhibited so far.

That’s all for now. See you soon

Henry Sharpe


Works cited:

1 Palmer, R J. “Saurian-T. Rex Infographic.” DeviantArt. N.p., n.d. Web. 08 Apr. 2017.

2 Larson, Pete. “T. Rex Skin (Wyrex), Above, Is a Perfect Match for the Skin from an Emu’s Foot (below).” Twitter. Twitter, 25 Sept. 2014. Web. 08 Apr. 2017.

3 Thompson, Helen. “Five Things We Don’t Know About Tyrannosaurus Rex.” Smithsonian Institution, 15 Apr. 2014. Web. 08 Apr. 2017.

4 Zelenitsky, D. K., F. Therrien, G. M. Erickson, C. L. Debuhr, Y. Kobayashi, D. A. Eberth, and F. Hadfield. “Feathered Non-Avian Dinosaurs from North America Provide Insight into Wing Origins.” Science 338.6106 (2012): 510-14. Web.

5 Hone, Dave. “Why Did Dinosaurs Evolve Feathers?” The Guardian. Guardian News and Media, 05 June 2013. Web. 09 Apr. 2017.

6 Arens, Nan Crystal, and Sarah E. Allen. “A Florule from the Base of the Hell Creek Formation in the Type Area of Eastern Montana: Implications for Vegetation and Climate.”Geological Society of America Special Papers Through the End of the Cretaceous in the Type Locality of the Hell Creek Formation in Montana and Adjacent Areas (2014): 173-207. Web.

7 Rohring, Brian. “Animal Survival in Extreme Temperatures.” American Chemical Society. N.p., Oct. 2013. Web. 09 Apr. 2017.

8 Xu, Xing, Kebai Wang, Ke Zhang, Qingyu Ma, Lida Xing, Corwin Sullivan, Dongyu Hu, Shuqing Cheng, and Shuo Wang. “A Gigantic Feathered Dinosaur from the Lower Cretaceous of China.” Nature 484.7392 (2012): 92-95. Web.

9 Xu, Xing, Mark A. Norell, Xuewen Kuang, Xiaolin Wang, Qi Zhao, and Chengkai Jia. “Basal Tyrannosauroids from China and Evidence for Protofeathers in Tyrannosauroids.” Nature431.7009 (2004): 680-84. Web.

10 “Ostrich.” Toronto Zoo | Ostrich. N.p., n.d. Web. 09 Apr. 2017.

11 Hendrickx, Christophe, Scott Hartman, and Octavio Mateus. “AN OVERVIEW OF NON-AVIAN THEROPOD DISCOVERIES AND CLASSIFICATION.” PalArch’s Journal of Vertebrate Palaeontology 12.1 (2015): n. pag. Web.

12 Cau, Andrea, Tom Brougham, and Darren Naish. “The Phylogenetic Affinities of the Bizarre Late Cretaceous Romanian TheropodBalaur Bondoc(Dinosauria, Maniraptora): Dromaeosaurid or Flightless Bird?” PeerJ 3 (2015): n. pag. Web.

13 Goehlich, U. B., H. Tischlinger, and L. M. Chiappe. “Uravenator Starki (Reptilia, Theropoda) Ein Neuer Raubdinosaurier Aus Dem Oberjura Der Suedlichen Frankenalb (Sueddeutschland): Skelettanatomie Und Weichteilbefunde.” N.p., 2006. Web.

14 Chiappe, Luis M., and Ursula B. Göhlich. “Anatomy of Juravenator Starki (Theropoda: Coelurosauria) from the Late Jurassic of Germany.”Neues Jahrbuch für Geologie und Paläontologie – Abhandlungen 258.3 (2010): 257-96. Web.

15 Headden, Jaime. “The Fisherman & the Sinosauropteryx.” The Bite Stuff. N.p., 30 Sept. 2014. Web. 09 Apr. 2017.

16 Zhang, Fucheng, Zhonghe Zhou, Xing Xu, and Xiaolin Wang. “A Juvenile Coelurosaurian Theropod from China Indicates Arboreal Habits.” Naturwissenschaften 89.9 (2002): 394-98. Web.

17 Zheng, X., Z. Zhou, X. Wang, F. Zhang, X. Zhang, Y. Wang, G. Wei, S. Wang, and X. Xu. “Hind Wings in Basal Birds and the Evolution of Leg Feathers.” Science 339.6125 (2013): 1309-312. Web.

18 Hartman, Scott. “Anchiornis: Putting Skin on the Bones…with Science!” Scott Hartman’s Skeletal N.p., 28 Feb. 27. Web. 09 Apr. 2017.

19 Holland, Mary. “Ruffed Grouse Winter Adaptations.” Naturally Curious with Mary Holland. N.p., 08 Dec. 2012. Web. 09 Apr. 2017.

20 “Do Ptarmigans Have Snowshoes? – Activity.” N.p., n.d. Web. 09 Apr. 2017.

21 “Booted Eagle Photo.” ARKive. N.p., n.d. Web. 09 Apr. 2017.

22 “Bald Eagle Photo.” ARKive. N.p., n.d. Web. 09 Apr. 2017.

23 Ortega, Francisco, Fernando Escaso, and José L. Sanz. “A Bizarre, Humped Carcharodontosauria (Theropoda) from the Lower Cretaceous of Spain.” Nature467.7312 (2010): 203-06. Web.

24 Mortimer, Mickey. “SVP 2015 Day 4.” SVP 2015 Day 4. N.p., 01 Jan. 1970. Web. 09 Apr. 2017.

25 Cau, Andrea. “Le Papille Ulnari Di Concavenator Non Sono Papille Ulnari.” Theropoda. 03 Mar. 2016, n.d. Web. 09 Apr. 2017.

26 “Re: Allosaurus Skin.” Dinosaur Mailing List. N.p., 14 Aug. 2004. Web. 09 Apr. 2017.

27 Godefroit, P., S. M. Sinitsa, D. Dhouailly, Y. L. Bolotsky, A. V. Sizov, M. E. Mcnamara, M. J. Benton, and P. Spagna. “A Jurassic Ornithischian Dinosaur from Siberia with Both Feathers and Scales.” Science 345.6195 (2014): 451-55. Web.

28 “Saurian DevLog #17 – Hurricane Clarissa » Saurian.” Saurian. N.p., 30 Mar. 2017. Web. 09 Apr. 2017.


8 thoughts on “Shake Your Tail Feathers: An In-Depth Look at Saurian’s T. rex”

  1. Excellent post.

    However, I must note that:

    -The position of the scales on the juvenile Allosaurus specimen is on the shoulder

    -Sciurumimus, according to the latest phylogenetic test, is a coelurosaur.

    -The case of Concavenator quill knobs is still unresolved. For instance, there was one study in 2015 that said that “quills” are unlikely, but another in the same year, which was mentioned in the 2015 SVP stated the “quills” are likely and are shown by the fossil.


    1. Thanks for the input on Allosaurus, I will edit that. Sciurumimus is a mistake, thanks for pointing that out, I accidentally placed the coelurosaur label in the wrong place.

      As for Concavenator, while there was a presentation in the 2015 SVP meeting that noted the unlikely possibility of the knobs being muscle attachment points based on their location, but failed to take in to account the likelihood that they were actually located on the anterior surface (the ulna seems to have been dislocated), which was mentioned in a series of posts by Mortimer and Cau. While I don’t think these have been published, it still remains that the proposal of quill knobs was hinged on their location on the posterior surface of the ulna, and now a number of scientists have essentially proven this wrong, so I’m siding with the conclusion that they were not actually quill knobs.


      1. Spanish paleontologist Francisco Ortega has assured to me that the quill knobs are on the posterior side of the ulna. And at least until January 2017 the idea that they betray a feather structure of any sort is the only held hypothesis .


      2. I myself have not seen any evidence to show that the ulna is not dislocated in the fossil, so I’m still staying away from the quill concept. If the describers would publish some sort of response (I’m not sure if they have already) that disproves this, than I will embrace the quill idea. Did Ortega mention anything particular about why the knobs were on the posterior side?


      1. BTW, IIRC, Saurian’s Rex, at least the top, first-half portion, is naked skin, though I could be wrong.


  2. (can’t find a better place to put my answer)
    I’m not sure if Ortega got into further details and I don’t remember what thread was that. I’ve just ask him and I’m waiting for his answer. I’ve been told that another paleontologist, Elena Cuesta, talks about the issue in her Doctoral Thesis but don’t know if it is available.


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