Nanotyrannus Concluded To Be A Distinct, Separate Species Of Tyrannosaurid, Not A Juvenile T-Rex

[andrewsaurus rex]

Clearly this issue is not resolved.  It's a hot topic and has been for a long time.  One day it will probably be definitively settled, once the right technology comes along.  Until then there will always be opportunities for opponents of one side or the other to criticize methodology used  in coming to a conclusion in favour of, or opposed, to Nanotyrannus as a distinct species.

I just wish there was more pure objective research involved in this issue and less 'personalities'.  It's become an 'us vs them' debate in many ways.  We all simply wants to know the actual answer to the question of Nanotyrannus' legitimacy.  There needs to be a lot more objectivity of pure science involved and a lot less bruised ego.

[Carnoking]

This has always struck me as a particularly volatile subject in the both the field of palentology and the hobby of dinosaurs in general. Just look at how people responded to Safari and PNSO releasing figures billed as "Nanotyrannus".
It would seem that anyone conducting research, publishing papers, or even creating art that goes against the Juvenile Tyrannosaurus dogma are only kicking a hornets nest and inviting the stings.
That said, regardless of who worked on this paper, I'm not willing to dismiss it out of hand and attack those involved because of the controversial conclusions reached therein.
Of course, it is disappointing to see that Longrich is not taking the high road with this one (really sullies the work in my eyes)  but that does not mean those attacking him or anyone involved in the paper just because it goes against a previously "settled" idea are any more in the right.

[VD231991]

I don't agree with Nick Longrich's view of CMNH 7541 and Jane as being young adult specimens because many ontogenetic studies have demonstrated the juvenile nature of CMNH 7541 and Jane. Currie (2003) agreed with Carr (1999) that CMNH 7541 is immature but found no evidence for any other taxa of tyrannosaurids undergoing ontogenetic maxillary tooth count reductions, suggesting that Nannotyrannus lancensis could still be a valid taxon distinguishable from T. rex by its higher maxillary tooth count. Burnham et al. (2018) reported the discovery of a juvenile Tyrannosaurus rex specimen (KUVP 156375) from Montana and noted that this specimen has the maxillary tooth count of T. rex rather than that of the Nanotyrannus lancensis holotype and Jane, so KUVP 156375 may surely support Currie's (2003) view of Nanotyrannus lancensis as distinct from T. rex within Tyrannosaurini. Although LACM 23845 (holotype of Dinotyrannus megagracilis, a junior synonym of T. rex) has no teeth preserved, Longrich agrees with Tom Carr that the Dinotyrannus megagracilis holotype specimen is a juvenile T. rex based on size.

Burnham, Atkins-Weltman, and Jevnikar, 2018. A new juvenile Tyrannosaurus rex from the Hell Creek Formation of eastern Montana provides insights into cranial and dental ontogeny. SVP 78th annual meeting, Albuquerque, New Mexico, p. 99. (PDF link here)

Carr, T.D., 1999. Craniofacial ontogeny in Tyrannosauridae (Dinosauria, Coelurosauria). Journal of Vertebrate Paleontology 19: 497–520.

Currie, P.J., 2003. Cranial anatomy of tyrannosaurid dinosaurs from the Late Cretaceous of Alberta, Canada. Acta Palaeontologica Polonica 48 (2): 191–226.

[Prehistory Resurrection]

So is it the same case as Pachycephalosaurus/ Stigymoloch/ Dracorex and Triceratops/ Torosaurus? By what I see, I conclude that this situation is very much more complex than previously thought.

[andrewsaurus rex]

I've wondered if Nanotyrannus could be a sub species of T. rex..  That would explain the many similarities and yet a few curious differences, like the tooth count and arm proportions.  Perhaps no adult sized Nanotyrannus specimens have yet been discovered.  Perhaps we should be call it Tyrannosaurus rex nanotyrannus?

[Newt]

Subspecies are unfashionable in modern paleontology (and neontology for that matter), and wouldn't be applied to animals that lived in the same place at the same time in any case. If Nanotyrannus were shown to be a distinct taxon of Tyrannosaurus, its proper name would be Tyrannosaurus lancensis.

I just read the paper. It's interesting, certainly. The arm proportion differences are the most compelling line of evidence to me. Is there any ambiguity about the forelimb material assigned to Nanotyrannus actually belonging to those specimens?

[Duna]

Palaeos has read the article and he says that Nannotyrannus is invalid. I hope he makes a video on that, because his videos have the latest evidence.

[Dynomikegojira]

Subspecies are unfashionable in modern paleontology (and neontology for that matter), and wouldn't be applied to animals that lived in the same place at the same time in any case. If Nanotyrannus were shown to be a distinct taxon of Tyrannosaurus, its proper name would be Tyrannosaurus lancensis.

I just read the paper. It's interesting, certainly. The arm proportion differences are the most compelling line of evidence to me. Is there any ambiguity about the forelimb material assigned to Nanotyrannus actually belonging to those specimens?

Taking this with a huge grain of salt the Dueling Dinosaurs specimens I believe are where the supposed large forearms are from but I'm not 100 percent sure.

[Faelrin]

@Prehistory Resurrection The Torosaurus/Triceratops thing has been debunked a while ago. We have subadult specimens of Torosaurus now confirming the two genera are distinct and separate (among other factor). Depending on one's views on this matter, it is either like that of Dracorex/Stygimoloch/Pachycephalosaurus, or the opposite.


Things of note from this paper (I'm trying to keep an open mind here, even though I know others, including paleontologists prior have found flaws within the data presented, sample size, etc):

Spoiler

-They bring up the controversial matter of Tyrannosaurus potentially having multiple species, and different points brought up from different studies looking at this issue. and stating "We consider this hypothesis viable but in need of further study." I do agree more study is needed, and that there could be potentially be more species out there, but I'm not sure the most recent paper was the most solid in regards to that.
-That the proposed "Nanotyrannus" specimens were not juveniles, but had mature characteristics.
-"Raptorex kriegsteini" was excluded from analysis because it appears to represent a juvenile tyrannosaurine, most likely Tarbosaurus". Wouldn't it have made sense to include it for the purposes of a study such as this? The "Raptorex" specimen has also gone through a controversial classification such as the proposed "Nanotyrannus" specimens. And if they do consider it a juvenile Tarbosaurus, or other  related species, that seems all the more reason why to include it. On a similar note, why not also include both Albertosaurus and Gorgosaurus specimens in something like this (that said later down it does look like they did take a look at Gorgosaurus specimens, but not sure why it wouldn't be mentioned here too)? Prior to stating the above they said this:

"We coded Nanotyrannus lancensis into two previously published character–taxon matrices [1,52] using a composite coding of CMNH 7541, BMRP 2002.4.1, LACM 28471, and the HRS material (Supplementary Information S3, Supplementary Information S4). Coding focused on the skull because the postcrania of BMRP 2002.4.1 are mounted and neither BMRP 2002.4.1 nor BMRP 2006.4.4 are described. Phylogenetic analysis was run in equal-weights parsimony using PAUP* 4.10 b10 [48] (a single character, character 504, was assessed to be potentially redundant and excluded). A second set of analyses was conducted using only ontogenetically stable characters, i.e., characters coding the same in Tarbosaurus adults [53], subadults [34], and young juveniles [54]."

-Another point made is that numerous late Cretaceous formations have been found to have multiple genera of tyrannosaurids, such as Gorgosaurus and Daspletosaurus, and Tarbosaurus and Alioramus, etc, with the Horseshoe Canyon formation being the exception so far (excluding anywhere T. rex is found, since they are proposing "Nanotyrannus" is valid here). They also mention something similar occurs with abelisaurids, of course the Morrison Formation with its variety of large predatory theropods, as well as late Pleistocene mammalian faunas, and extant ones, and marine ecosystems such as during the Miocene with Otodous megalodon and Livyatan, etc, or extant ecosystems with Orca, great whites, etc.
-"Within predator clades, diversity tends to be higher towards the lower end of the mass range; that is, there are fewer species of big cats than small cats, fewer wolves than foxes, many small weasels and ferrets, and just one wolverine [85]. The reasons for these patterns are unknown, but they imply higher speciation rates at low mass, higher extinction at large size, or both. In light of this, one would expect the diversity of small tyrannosaurs to be higher than for large tyrannosaurs." We haven't really seen this so far. The only time we have a smaller tyrannosaur with a larger one is the case of Alioramus and Tarbosaurus. Otherwise it's two large genera, with their various younger forms. And if you go even smaller, well then you have multiple instances of dromaeosaurids and troodontids that occupy a lot of niches in numerous formations, if not ornithomimosaurs and oviraptorosaurs to some degree as well. While Dakotaraptor is likely chimeric, there are some elements that do seem to belong to a large dromaeosaurid, which means at least one medium predator niche was held by a larger dromaeosaurid in at least Hell Creek. However without further study of the material (which likely won't happen knowing DePalma's reputation), or more specimens brought to light, it's hard to say what exactly is going on, and what belongs to what, outside of some twitter and other speculation. The paper does however mention that both Dakotaraptor, and even Acheroraptor are much smaller then T. rex. They do not mention anything about younger tyrannosaurs occupying different niches from the adult forms, which seems like a weird thing to omit. The paper also omits Anzu, Pectinodon, etc, although those are also smaller.
-They suggest that BMRP 2006.4.4 (Petey) clusters with T. rex in their cluster analysis, but also go on to say "This does not seem to result from a strong character signal because (i) the animal lacks cranial material, (ii) the femur was not coded, and (iii) the matrix includes a very large number of subtle characters of the pedal phalanges which (as the material has not been described) we could not verify, but which may drive this pattern. We suspect the placement of BMRP 2006.4.4 is a coding artifact, but further study of the characters and material is needed."
-They plot out tooth length and tooth count, and conclude the two are different. Is this the same argument put forth prior?
-They compare characters in juvenile Tarbosaurus specimens to the proposed "Nanotyrannus" specimens, and suggest there is a possibility they could be juvenile features in the latter, but also state that some of those features are found in adult Alioramus. They state the juvenile Tarbosaurus has features shared between the adult Tarbosaurus and T. rex that the proposes "Nanotyrannus" specimens lack, and "These features appear early in the ontogeny of Tarbosaurus and would presumably occur early in the ontogeny of Tyrannosaurus. The absence of these features in absolutely larger Nanotyrannus specimens is difficult to explain in terms of ontogeny unless Tyrannosaurus had a pattern of development unlike that of Tarbosaurus (Figure 20). Some features of Tyrannosaurinae, especially those related to the skull ornamentation, orbits, and skull roof, appear to develop late, but others appear in even the youngest specimens (Figure 19 and Figure 20). At least some tyrannosaurine features would be expected in Nanotyrannus if it was a juvenile tyrannosaurine, but few, if any, are present." Edit: They claim adult Alioramus exist, but the only specimens I'm aware of are both juveniles? Specifically both the holotype of Alioramus remotus, and A. altai, unless there's specimens out there I'm not aware of, such as potential specimens awaiting description? Specifically they said this, "This means some features seen in Nanotyrannus could conceivably be juvenile characters, but these features do not necessarily mean that the animals are juvenile since they occur in adults of tyrannosauroids such as Alioramus" The papers they link to also only discuss those two juvenile specimens I'm aware of, at least from what I gleaned from quickly skimming them. I'll look at them more in depth tomorrow just to be on the safe side, and see if there any other publications specifically on this genus.
-They also compare juvenile Gorgosaurus specimens to adult Gorgosaurus and state there are similarities, but that the proposed "Nanotyrannus" specimens lack features the juvenile Gorgosaurus specimens have. They suggest that, "For Nanotyrannus to be a juvenile Tyrannosaurus, Tyrannosaurus would have had to have a radically different development pattern than Tarbosaurus or Gorgosaurus. This is not impossible; ontogeny evolves. However, it is more parsimonious to treat Nanotyrannus and Tyrannosaurus as distinct species."
-They also compare the proportions of the manus for the proposed "Nanotyrannus" specimens and T. rex, and conclude that they would need to basically shrink during development.
-They suggest some skeletal features (vertebrae, pectoral girdle, and pelvic girdle, and texture of the skull) in the "Nanotyrannus" specimens show they are close to skeletal maturity, or from young adults, not juvenile animals. They compare these features to other mature, or maturing theropods, including T. rex, and in the case of the skull features, other theropods (mostly tyrannosaurids), and even ceratopsians.
-They suggest an alternative hypothesis for the variation in growth trajectory would be an extreme example of sexual dimorphism (if the specimens are included in T. rex).
-They compare the "smallest unambiguous Tyrannosaurus" LACM 28345 to that of CMNH 7541 (the holotype of "Nanotyrannus"), and ane BMRP 2002.4.1. They also compare UCMP V84133 (T. rex) to the proposed "Nanotyrannus" specimens. Prior to going into detail about doing this, they said, "The hypothesis that Nanotyrannus is a juvenile Tyrannosaurus predicts that the two forms should not overlap in size; that is, all Nanotyrannus will be small, and all Tyrannosaurus will be big. No small Tyrannosaurus should exist. Conversely, if Nanotyrannus is a distinct species, then small juveniles of Tyrannosaurus—approaching the size of Nanotyrannus or smaller—must exist. Juvenile dinosaurs tend to be extremely rare; however, potential juveniles of Tyrannosaurus are known, including a partial skull." So they are only proposing some specimens could belong to a different genus, while confirming some are in fact juvenile T. rex. Yet as we all know that's been very controversial over the years.
-Their phylogenetic placement of "Nanotyrannus" is outside Tyrannosauridae and Tyrannosaurinae, but also finds that Alioraminae is more basal, below "Nanotyrannus". Another dataset shows something similar, with "Nanotyrannus" below Alioraminae, but with Albertosaurinae further down, which would make "Nanotyrannus" a basal member of Tyrannosaurinae. The matrix however shows Bistahieversor outside of Tyrannosauridae. I thought that was accepted to be the case? This is what they claim regarding this, "We repeated our phylogenetic analysis using another dataset, the Brusatte and Carr matrix [1], updated by Wolfe et al. [64]. This matrix produces similar results (Figure 33). Nanotyrannus emerges below Alioraminae but with Albertosaurinae further down the tree. This would make Nanotyrannus a basal member of the Tyrannosaurinae. We note, however, numerous discrepancies between specimens and codings in this matrix, particularly miscodes that appear to force Bistahieversor outside of Tyrannosauridae. This raises issues of whether the backbone of the tree is properly reconstructed; we suspect that the first topology better reflects tyrannosauroid phylogeny..."

These are all the specimens they are referring to "Nanotyrannus" or as close relatives of such (while also noting how many species there are is unclear):

CMNH 7541	Nanotyrannus lancensis	Hell Creek	Montana	Nanotyrannus lancensis holotype skull; subadult or young adult
AMNH 5050	aff. Nanotyrannus			Partial dentary
BMRP 2002.4.1	Nanotyrannus lancensis (or aff Stygivenator?)	Hell Creek	Montana	"Jane"; skull and skeleton, young adult
BMRP 2006.4.4	cf. Nanotyrannus	Hell Creek	Montana	"Petey"; partial post-cranial skeleton young adult
FMNH PR 2411	cf. Nanotyrannus	Hell Creek	South Dakota	lacrimal
HRS specimen	Nanotyrannus lancensis (or aff Stygivenator?)	Lance	Wyoming	"Zuri"; partial skull and skeleton, young adult; HRS 08423, 08502, 08607, 08486, 08496,
RSM P2347.1	aff. Nanotyrannus	Frenchman Formation	Saskatchewan	Maxilla
KU 155809	Nanotyrannus lancensis (or aff Stygivenator?)	Hell Creek	Montana	Skull and partial skeleton
LACM 28471	Nanotyrannus lancensis (or Stygivenator molnari)	Hell Creek	Montana	Stygivenator lancensis holotype; partial skull, juvenile
MOR 6625	aff. Nanotyrannus			Partial jaws
DDM 344.1	aff. Nanotyrannus			Frontal
"Dueling Dinosaurs"	Nanotyrannus lancensis (or Stygivenator molnari?)	Hell Creek	Montana	Skull and skeleton (Larson, 2013b)

-They also mention specimen NMMNH P-25049, stating it "lacks features allowing referral to Bistahieversor but resembles Nanotyrannus in having a longirostrine skull, low and rounded lacrimal horns, a dentary groove, and a low nasal weakly interlocking with the maxilla. NMMNH P-25049 also resembles juvenile Gorgosaurus [109], but the broad dorsal and ventral margins of the antorbital fossa, the shape of the orbit, and the dentary groove are overall more similar to Nanotyrannus." They also compare the tooth taxon "Aublysodon" from both the Judith River Formation, which seems similar to the "Nanotyrannus" teeth, as well as those from the Dinosaur Park formation, and suggest the features on those might belong to juvenile albertosaurines, when compared to juvenile Gorgosaurus.
-They mention, "We argue that the weight of the evidence favors Nanotyrannus as distinct, but some evidence appears inconsistent with this hypothesis.", and then they explain why. I do know they mentioned numerous times in the paper that more data/samples/material is needed so the authors seem very much aware that more data could change things up.
-They suggest that Nanotyrannus could be the way that it is because of neoteny, which is the case for birds, and even humans.
-They also address the history of the naming of Nanotyrannus, and state that Gilmore, who named it originally, was much more cautious in his work, and that with the exception of Brachyceratops, likely being a juvenile of another genus, nearly all his named genera are still considered valid to this day.
-Not an important point, but I just thought this was humorous and certainly relatable in researching these animals, "probably in part because of the problems that came from trying to navigate the maze of names left behind by those two." (referring to Marsh and Cope)
-They also suggest the sinking of Torosaurus into Triceratops, or Stygimoloch into Dracorex (they linked a 2009 paper from Horner, but like weren't both sunk into Pachycephalosaurus, and doesn't the current evidence support this?) is not supported by the current evidence, as they suggest is the case for keeping Nanotyrannus separate from Tyrannosaurus.

[close]

Ultimately after reading it, I still think they jumped the gun on this, since the Dueling Dinosaurs specimens are still being prepared, and yet to be published on. This especially pertains to this paper since they conclude that it would be one of the proposed "Nanotyrannus" specimens. That would have been wise to wait for those to be prepared and published on, before ultimately including in a study such as this. I will be curious to see future papers on either direction.

I also am curious about how these "Nanotyrannus" specimens compare to Alioramus and Qianzhousaurus specifically. I didn't see very much of that in the paper, aside from the potential phylogenetic placement unfortunately, just more focus on T. rex again, which I get since the whole point of this paper is to say no these particular specimens are not juvenile T. rex specimens, but yeah I think it would been interesting to see if that if "Nanotyrannus" were valid, if it has any relation to those long snout tyrannosaurs. The closest the paper gets to addressing this, aside from the above mentioned placement, is this, "However, primitive tyrannosauroids such as Alioramus [70] retain the primitive condition even as adults and, therefore, resemble the juveniles of Tyrannosaurinae. Because of this, it is illogical to assume that Nanotyrannus must be a juvenile because it lacks features associated with adulthood in Tyrannosaurinae."

Have there been any other papers addressing this in detail? If not I definitely think something like that should be looked into. Qianzhousaurus I know is accepted as a subadult, where as the holotype of both Alioramus remotus and A. altai are juveniles, and which Qianzhosaurus was formerly suggested to be synonymous with Alioramus, it was recently considered to be a valid separate genus again. Above they also say Alioramus retains their condition as adults, but if there are no adult specimens for the genus, how they can state such? The closest we get is the subadult Qianzhousaurus, which is still not yet an adult, yet both Qianzhousaurus and Alioramus are commonly depicted and seem to be accepted to be long snout tyrannosaurs (including recent rigouros media like Prehistoric Planet). If both Qianzhousaurus and Alioramus were to be a unique branch of long snout tyrannosaurs even as adults, it would open the doors to the possibility of something like that also existing in North America as well, since isn't it thought the ancestors of T. rex migrated from Asia, if not its closest relatives are from there? Also Sinoceratops is the only described ceratopsid from Asia, yet all others are from North America, suggesting some faunal interchange between the two continents (if not other possible examples out there as well).


@suspsy You claimed "Longrich seriously didn't bother to include the Jane specimen in the study. That's . . . very bad." in an earlier post, but Jane was definitely mentioned throughout the paper, which both @Nyrorosaurus and S @SidB pointed out. A simple search brings up the name Jane 19 times, with an additional 31 for BMRP 2002.4.1, which also includes captions for figures and tables. That's quite a bit, so I'm surprised you would claim something like that (and I initially liked your comment, as I had yet to read the paper, and thought your comment was in response to what the paper said, since you claimed as such), which is demonstrably false.

The Jane specimen (BMRP 2002.4.1) is also represented in these images (and others):

Spoiler

[close]

Edit: Fixed some spelling (my spell check somehow wasn't working earlier), and italicized some names. Also added an edit pointing out an additional part of the paper in the notes section where they were claiming there were adult Alioramus specimens, which I'm not currently aware of. I'll do more research on this tomorrow.

[suspsy]

I was referring specifically to Figure 18, in which the authors used the 13 largest T. rex skulls and a few purported Nano skulls, but omitted Jane completely. Meant to specify that in the first place, but just plain forgot. Been a busy week.

[Faelrin]

@suspsy Thanks for the clarification, and sorry to hear. Hope you can catch a good break afterwards. Looking back at the previous discussion in this thread, I wonder if this is also what @TaranUlas was getting at, so sorry to single you out in particular in regards to this.

Anyways that is an absolutely strange omission on their part, considering how much of the paper refers to it, or includes it in most sections of the paper. Specifically they plot out Nanotyrannus as having around 16-18 dentary teeth, but the Jane specimen seems to have less then that (when compared to the images in figure 12). Again the plot something similar for the maxillary teeth, but once again the Jane specimen seems to have less then that (when compared to the images in figures 4 and 5). The sample size also seems way too small with only 3 for Nanotyrannus, unless those are the only specimens with decent skull and teeth material. Looking at the referred specimen list above it seems there are more specimens then three that could have been used, but that again depends on how good the material was, however that still doesn't explain why Jane was left out, when it seems to be decently preserved on this front. Hopefully when there is another paper on this topic, that aspect is addressed and corrected (unless a previous paper already did so).

That said where in the paper did they mention what specimens they used for that part of the paper (figure 18)? Was that something in the supplementary material? Edit: Just wondering if I missed something that's all. I spent like all day picking at this paper, with numerous distractions and breaks in between, and I'm not really inclined to do it again, lol. It's possible I also came across it, but already forgot because my short term memory is terrible.

[andrewsaurus rex]

this is an obvious point but couldn't part of the problem be that some specimens are Nanotyrannus and other specimens are juvenile T. rex and the two distinct animal specimens are getting lumped into the same slot ie either all are Nanotyrannus or all are juvenile T. rex.  It's very difficult to make fine determinations from portions of fossilized skeletal remains that are over 66 million years old and have possibly been distorted a bit during the fossilization process.

As a modern day example, a male lion's skeleton is more similar to a male tiger's skeleton than it is to a female lion's skeleton.  So imagine millions of years from now, if researchers had little knowledge of cats discovering a female lion fossil and a male lion fossil.  They could easily be considered two different genera. 

That's the kind of difficulty there is today in making determinations in subtle differences in fossilized remains.

[Faelrin]

A @andrewsaurus rex The paper didn't exactly do that though. They did say some specimens were T. rex no doubt, but the question is if the particular (11) specimens they are assigning to Nanotyrannus are different enough or are juvenile T. rex. The large consensus seems to be they are juveniles, but nonetheless I do find some of the points raised interesting (in my notes section above), and look forward to seeing papers released that dispute those. Some of the data sets or sample size did seem pretty poor as well, which doesn't work well in its favor despite some of the other arguments being pushed forth based on the interpretation of the fossil evidence at hand.