Sunday, September 15, 2013


A cast of the Cleveland skull in the Hall of Horns and Teeth at the Museum of the Rockies (Bozeman, MT), where it is presented as a juvenile Tyrannosaurus rex, next to a cast of the subadult MOR 1125.
The impending auction of the ‘Dueling Dinosaurs’ has brought Nanotyrannus back into the pop culture spotlight. I repeat here the evidence that I published in support of the hypothesis that the Cleveland skull is a juvenile Tyrannosaurus rex (Carr, 1999). A critical evaluation of the diagnosis for Nanotyrannus lancensis follows this, and I close with evidence documented by Bakker et al. (1988) that supports the specimen’s referral to T. rex.
What was Bakker et al.’s (1988) characterization of Nanotyrannus? They considered the skull to represent a fully adult individual (skull length: 572 cm) of the most primitive (basalmost) tyrannosaurid from the Late Maastrichtian Hell Creek Formation of Montana, which was sympatric with T. rex. They considered Nanotyrannus to be convergent with T. rex upon an identical and extensive suite of adaptations for stereoscopy and striking behavior (i.e., head-neck kinematics).
Isn’t the Cleveland skull from an adult? No – the basis for adulthood by Bakker et al. (1988) was based on the mistaken notion of suture closure in the skull (Carr, 1999). In fact, very few skull sutures actually close during the ontogeny of tyrannosaurids; regardless, every observable suture in the Cleveland skull is open, aside for the internasal and interparietal sutures, which are closed in other tyrannosaurid juveniles (1999).
Also, the surfaces of the bones in the Cleveland have a distinct striated texture that is typically seen in juvenile dinosaurs (Carr, 1999). A similar texture is seen in adults, but its distribution is patchy and the striae are less dense and distinct than the condition seen in small specimens.
Therefore, based on the absence of suture closure (beyond what is usually seen in tyrannosaurid juveniles), the presence of immature bone grain, and its small size, the Cleveland skull is unquestionably a juvenile tyrannosaurid.
Is the Cleveland skull similar in any way to other juvenile tyrannosaurids? Yes – in virtually every detail; this table summarizes the salient features (Carr, 1999):
Albertosaurus libratus juvenile condition
Is it seen in the Cleveland skull?
Premaxilla, narrow, rostral view
Premaxilla, lateral margin, concave, rostral view
Premaxilla, alveolar region, shallow, rostral and lateral views
Maxilla, mediolaterally narrow, lateral and rostral views
Maxilla, first tooth, incisiform, all views
Maxilla, teeth except the first, labiolingually narrow
Maxilla, ventral jugal process, not breached by neurovascular sulcus
Maxilla, lateral surface along rostral end of the antorbital fossa, not strutlike, lateral view
Maxilla, promaxillary fenestra, tall and not recessed, lateral view
Antorbital fenestra, longer than tall, lateral view
Maxilla, maxillary fenestra, size, small, lateral view
Maxilla, maxillary fenestra, position, midway between the rostral margins of the antorbital fossa and fenestra, lateral view
Lacrimal, rostroventral ala, rostral margin, concave, lateral view
Lacrimal, rostroventral ala, contact with jugal, exceeds that of the ventral ramus, lateral view
Jugal, maxillary ramus, dorsoventrally shallow and long, lateral view
Jugal, pneumatic recess, rostrally restricted slit, lateral view
Jugal, postorbital joint surface approaches the orbit floor, lateral view
Jugal, base of the postorbital process, convex, lateral view
Jugal, caudal margin of the postorbital process, convex, lateral view
Jugal, caudal rim of the joint surface for the lacrimal, subvertical, lateral view
Postorbital, laterodorsal margin, vertically oriented, dorsal view
Postorbital, cornual process, absent, lateral view
Postorbital, subocular prong, absent, lateral view
Frontal, lacrimal notch, long and narrow, dorsal view
Frontal, paired bones are longer than wide, dorsal view
Frontal, dorsotemporal fossa, shallow, dorsal view
Frontal, dorsotemporal fossa, indistinct rostral margin
Parietal, nuchal crest, delicate in form
Parietal, nuchal crest, low in height
Ectopterygoid, jugal ramus, not inflated, ventral view
Ectopterygoid, muscle scar on jugal ramus, caudolateral in position
Supraoccipital, dorsal process, narrow, caudal view
Basioccipital, occipital condyle, shape of an inverted triangle, caudal view
Basioccipital, occipital condyle, form of caudoventral surface, flattened, caudal view
Basioccipital, basituberal web, flat ventral surface, ventral view
Basioccipital, basituberal web, ventral surface is dorsally arched, caudal view
Basioccipital, subcondylar recess, deeply excavated, caudal view
Basisphenoid, pneumatic foramina are small, caudoventral view
Basisphenoid, pneumatic foramina are situated ventrally within the basisphenoid recess, caudoventral view
Basisphenoid, oval scar, smooth and lateroventrally oriented, caudoventral view
Dentary, dorsoventrally shallow, lateral and medial views
Dentary, mediolaterally narrow, ventral view
Surangular, dorsoventrally shallow, lateral view
Surangular, surangular shelf, horizontally oriented, lateral view
Prearticular, dorsal margin is restricted caudally, medial view
Prearticular, caudal ramus is dorsoventrally shallow, medial view
Prearticular, rostral ramus is dorsoventrally shallow and straplike, medial view
Prearticular, rostral ramus, caudodorsal surface is smooth, medial view

Therefore, every bone in the Cleveland skull is identical to the condition seen in small juvenile tyrannosaurids, not adults (Carr, 1999). Therefore, we can add the details of the bone structure to the stack of evidence regarding its immaturity.
What about the diagnosis of Nanotyrannus lancensis? Doesn’t it adequately define the new genus and species? This is the heart of the matter because the validity of a taxon rests on its diagnosis. A diagnosis is a list of the anatomical features that set a new taxon apart from its closest relatives; presumably the diagnosis of Nanotyrannus includes indisputably unique features. For Nanotyrannus, let’s consider each character (Bakker et al., 1988) one at a time:
1) “muzzle width greatly constricted to only one fourth the width of the temporal region” (Bakker et al., 1988:3)—This feature is not unique; a narrow snout and wide temporal region is also seen in T. rex. Also, the snout is not as narrow in the Cleveland skull as the authors claim, a condition that has  been exaggerated by mediolateral crushing. This can be seen in the plate of the specimen in dorsal view (1988:28), where  fractures extend across the right jugal and maxilla, and the base of the snout extends rostrally at an unnaturally sharp angle.
2) “extraordinarily wide basicranium between basitubera and basipterygoid processes” (Bakker et al., 1988:3)—This is also seen in adult T. rex (Bakker et al., 1988).
3) “two large pneumatic foramina, placed one behind the other, near the midline of the basisphenoid” (Bakker et al., 1988:3)—This condition is the result of damage (Carr, 1999).
4) “Differs from Daspletosaurus, Gorgosaurus and Alioramus and agrees with Tyrannosaurus, Albertosaurus and Tarbosaurus spp. in having the derived features of a marked expansion of the width across the temple, relative to the skull length…”(Bakker et al., 1988:3)These are not a diagnostic characters since they are seen in other taxa; there is no reason to think that it didn’t evolve once in the common ancestor of Tyrannosauridae and later became lost in several species.
5) “…and basitubera that are displaced forward towards the basipterygoid processes” (Bakker et al., 1988:3)—The same issue applies here as in (4).
6) “Differs from all other tyrannosaurids, except Alioramus, in retaining the primitive characters of a long, low snout…”(Bakker et al., 1988:3)—A long, low snout is typical of juvenile tyrannosaurids, and it has recently been shown (Brusatte et al., 2012) that the extremely long and shallow depth of the snout seen in Alioramus is derived beyond the norm in tyrannosaurids; i.e., the Cleveland skull does not have the condition seen in Alioramus, its snout depth is normal for a tyrannosaurid of its size.
7) “…and maxillary teeth that are strongly compressed side-to-side” (Bakker et al., 1988:3)—Narrow teeth are typical of juvenile tyrannosaurids, and the Cleveland skull does not have unusually narrow teeth in comparison with them (Carr, 1999).
8) “Differs from all other tyrannosaurids in lacking strong ridges and striae along the dorsal surface of the nasal” (Bakker et al., 1988:3)—It turns out that this is not true; a smaller and less mature juvenile T. rex (LACM 28471) has smoother nasals than are seen in the Cleveland skull, indicating that the nasals coarsened with maturity in T. rex (Carr and Williamson, 2004). In other tyrannosaurids, such as Albertosaurus, the nasals are coarse relatively earlier in growth (Carr, 1999).
9) “Differs from Tyrannosaurus in retaining the primitive character of a smooth depressed area for muscle origin on the anterior-ventral corner of the lachrimal” (Bakker et al., 1988:3)—This is the antobital fossa, a pneumatic surface and not an origin for muscle, which is seen in adult T. rex, except that this region is swollen by the internal inflation of the bone by the antorbital air sac system (Carr, 1999). This is a simple growth change that is seen in all tyrannosaurids (Carr, 1999).
Why then is the Cleveland skull referable to T. rex?
To answer this we don’t need to go any further than Bakker et al. (1988), who provided a long list of characters that are only seen in T. rex and the Cleveland skull:
1) “In Tyrannosaurus the basituberal width is enormously expanded, reaching 19% of the skull length…In Nanotyrannus the basituberal web is fully 20% of skull length…”
In other tyrannosaurids the ratio is much lower,  12%-15% (Bakker et al., 1988: 9).
2) “in Albertosaurus, Tyrannosaurus and Nanotyrannus [the main tuberous process of the basal tuber] is reduced in bulk” In other tyrannosaurids, the process is a “swollen development” (Bakker et al., 1988: 9).
Given the modern understanding of tyrannosaurid phylogeny, the reduced condition would have almost certainly have evolved twice, once in Albertosaurus, and again in Tyrannosaurus.
3) “In Nanotyrannus the ventral floor of the basisphenoid is nearly flat between the basituberal and basisphenoid webs, a condition seen in Tyrannosaurus” (Bakker et al., 1988: 12).
In other tyrannosaurids the “ceiling of the central basisphenoidal cavity is very tall and the cavity is very deep top-to-bottom” (1988:12). Although the authors are inconsistent in using the terms “ceiling” and “floor”, they are discussing the same feature, namely, the basisphenoid recess.
4) “The occipital condyle…in Nanotyrannus…faces…strongly downward…agreeing with the condition in Tyrannosaurus” (Bakker et al., 1988: 12).
In other tyrannosaurids the condyle presumably faces more caudally than downward.
5) “Moreover, the articular surface on the condyle in Nanotyrannus has been displaced downwards and around onto the ventral surface of the [occipital condyle] neck…again agreeing with [the condition seen in] Tyrannosaurus. Clearly the head was flexed far more sharply downwards in Nanotyrannus and Tyrannosaurus than in more primitive [i.e., all other] tyrannosaurids” (Bakker et al., 1988: 12).
In other tyrannosaurids the articular surface presumably does not extend ventrally onto the neck of the occipital condyle.
6) “…in Tyrannosaurus and Nanotyrannus, the basitubera are displaced forward and project less strongly below the floor of the basicranium” (Bakker et al., 1988:13).
In other tyrannosaurids “the basitubera are located far aft, beneath the occipital condyle, and project strongly downward” (1988:13).
7) “In Nanotyrannus the width of the…entire temporal region is greatly expanded relative to the snout…the breadth between the jaw joints…is 57% of the skull length…[In Tyrannosaurus] the quadratojugal width is 62% of skull length” (Bakker et al., 1988:14).
In other tyrannosaurids this ratio is much lower, ranging from ~33%-42% (1988:14).
8) “As a consequence of the temporal breadth/muzzle breadth ratio in Nanotyrannus and Tyrannosaurus, right and left eyes have a wide overlap of visual fields. Stereoscopy was probably present over a range of 30 degrees or more” (Bakker et al., 1988:15).
In other tyrannosaurids this overlap is not seen.
9) “the orbits face upwards as well as forwards in Tyrannosaurus…In Nanotyrannus, the upward orientation of the orbits is less marked” (Bakker et al., 1988:16).
Although the authors are making a contrast here, it is worth noting that both taxa have orbital fenestrae with an upward component, a condition that is not seen in other tyrannosaurids.
10) “The paroccipital processes of Nanotyrannus agree with those of Tyrannosaurus in being oriented nearly directly outwards and having much less of a backward orientation than that seen in gorgosaurs and daspletosaurs” (Bakker et al., 1988:16).
Arguably, the authors made a better case for referring the Cleveland skull to T. rex than I did (cf. Currie, 2003).
What did Bakker et al. (1988) make of these striking similarities between the Cleveland skull and T. rex? How could they think they had a new genus and species?
Here it is, in their own words:
“Whatever its evolutionary origins, Nanotyrannus seems to have evolved its stereoscopy independently of Tyrannosaurus. The low, long snout and primitive teeth of Nanotyrannus seem to preclude an ancestry from an animal as advanced as Gorgosaurus. The two stereoscopic genera, Nanotyrannus and Tyrannosaurus, are the only well known large predators from the Lancian Age, and it is noteworthy that both have achieved the highest degree of potential stereoscopy known among large theropods…Clearly natural selection was favoring greater precision of depth perception…Thus Nanotyrannus seems to have been shaped by an inexorable law of the evolution between predator and prey, a law that operated to produce ever greater finesse in the choreography of attack behavior” (Bakker et al., 1988:26).
The authors considered this suite of characters to have evolved by convergent evolution in Nanotyrannus and Tyrannosaurus, evidently at the same point in geological time and in the same geographic location. Clearly, that is not a parsimonious hypothesis.
Here’s my train of thought on the matter:
1) The Cleveland skull is of a juvenile tyrannosaurid.
2) The diagnosis of Nanotyrannus lancensis fails under scrutiny: the characters reflect the specimen’s relative maturity, damage to the skull, and characters shared with other tyrannosaurids. Consequently, N. lancensis is an invalid taxon; it entirely lacks defining features.
3) The Cleveland skull shares many specializations that are seen nowhere else except in adult T. rex, the species with which it happens to be sympatric.
4) Therefore, the Cleveland skull is a juvenile T. rex.
5) Ergo, the ‘dueling tyrannosaurid’ cannot belong to a taxon that does not exist.
So what species is the dueling tyrannosaurid?
It isn’t in a legitimate repository, so we can't know this at present. We’ll almost certainly never know if the auction goes ahead and the specimen is sold to a private individual – unless, as a colleague recently suggested to me, the people of the US want to intervene and rescue it for science under a successful argument for eminent domain.

References Cited
Bakker RT, Williams M, Currie PJ. 1988. Nanotyrannus, a new genus of pygmy tyrannosaur from the latest Cretaceous of Montana. Hunteria 1: 1-30.

Brusatte, S. L., T. D. Carr, and M. A. Norell. 2012. The osteology of Alioramus, a gracile and long-snouted tyrannosaurid (Dinosauria: Theropoda) from the Late Cretaceous of Mongolia. Bulletin of the American Museum of Natural History 366:1-197.

Carr, T. D. and T. E. Williamson. 2004. Diversity of Late Maastrichtian Tyrannosauridae from western North America. Zoological Journal of the Linnean Society 142:479-523.

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: 191-226.


  1. Replies
    1. There is one problem with your assertion. CAT scanning showed that Nanotyrannus had a differently shaped brain, and it held its head forward a little.

    2. The differences in the endocast and inner ear orientation are the result of extensive damage to the back of the Cleveland skull.

    3. Well I find that a little hard to believe.

    4. Take a look at the image at the head of the post - the laterotemporal fenestra is closed to a narrow slot; the reason for that is the entire back of the skull is crushed forward and up, which has even pushed the palate out of position. This rostralward crushing has collapsed the braincase forward like an accordion; the damage seen externally is consistent with what is seen internally. What is hard to believe is that the space inside of the braincase would be untouched when its encasing bones are so clearly damaged.

    5. What about the "Bloody Mary" specimen? That specimen had 3 foot long arms with bones in that arm were one and a half times larger than in "Sue" does that mean anything?

    6. Nope - privately owned specimens don't mean anything in science. See the corresponding SVP ethics statements.

    7. Well ok.... I'm not entirely convinced that nanotyrannus is invalid, but you made very good points.

  2. Isn't there a referred Nanotyrannus specimen with a dramatically different postcranium (long neck, big arms, etc.)?

    (Yes, this is a half-remembered fragment of conference talk -- what can I tell you, I am sauropod guy.)

    1. Well though I'm not an expert on dinosaurs, I heard that young tyrannosaurids had longer arms than that of adults..

      Williams, S., S. Brusatte, J. Matthews and P. Currie 2010. A new juvenile Tyrannosaurus and a reassessment of ontogenetic and phylogenetic changes in tyrannosauroid forelimb proportions. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2010, 187A.

    2. Yo tampoco soy un experto en dinosaurios pero no me parece posible que los huesos ya formados se encojan, que dejen de crecer durante el desarrollo del resto del cuerpo si es posible, el espécimen "Bloody Mary" poseía brazos mas largos y manos mas robustas que un T. rex adulto, otra cosa que no me parece coherente es la cantidad de dientes, hasta donde yo se ningún animal que pierda dientes conforme avanza su edad.

  3. Given the state of tyrannosaurid knowledge in 1988, would it be reasonable for Bakker et al to conclude otherwise? I'm just curious, since back in 1988 I was more interested in the finer details of Teenage Mutant Ninja Turtles....

    -Caleb Lewis

  4. Caleb: No it isn't reasonable, as explained.

    1. Is that really fair to paleontologists in 1988? Almost no theropod specimens were even recognized as juveniles, besides some Gallimimus and Allosaurus individuals. The few known juvenile tyrannosaurids (e.g. the then unnamed Jordan theropod and Shanshanosaurus) were thought to be small basal tyrannosauroids or even dromaeosaurids. Similarly, there was no consensus the smaller Nemegt tyrannosaurids were young bataar. AFAIK, no one had thought to look for immature bone grain in any Mesozoic dinosaur yet, and there was no consensus of (Alberto(Daspleto(Tarbo,Tyranno))) like we have now to use to find nested traits that suggest synonymy. The sample size of Tyrannosaurus was low enough to make the number of specimens a notable media figure, when now we have more than most species of theropod known from more than just their holotype. The argument Nanotyrannus is a juvenile Tyrannosaurus thus depends on a lot of data which didn't exist in 1988 or wasn't organized yet. Rozhdestvensky (1965) was remarkably prescient decades earlier regarding some of these issues, though his same methodology incorrectly found Lufengosaurus to be young Yunnanosaurus, so we might question whether his seemingly correct tyrannosaurid ideas were validly justified or at least partly luck.

      It's that old standing on the shoulders of giants cliche, and while you are a major giant here, suggesting Currie, Russell, Molnar, Paul, Carpenter, Bakker, etc., basically every theropod worker of the 80s, was unreasonable seems unfair. A valid criticism is that Bakker et al. (1988) never cite or mention Molnar's (1980) description of what would become the type of Dinotyrannus, that was referred to lancensis at the time. It was published 8 years earlier in a well read journal, so should have gotten some comment.

      The supposed unreasonableness of Bakker et al. (1988) also affects your main argument, as some of it depends upon the truth of our current consensus. Accepting Nanotyrannus as a juvenile Tyrannosaurus seems more plausible in a world where Maleevosaurus is just a young Tarbosaurus, Stygivenator is a juvenile Tyrannosaurus, etc.. But if the well-studied Cleveland skull is valid based on newly recognized characters, what does this mean for Maleevosaurus, which has never been studied firsthand since its description to my knowledge? Larson considers Stygivenator a younger Nanotyrannus, for instance, so the former can no longer be used as an example of what juvenile Tyrannosaurus are like.

    I believe I'm holding the key to the answer we all seek.

    1. Very interesting, Bob. Hopefully this will end up in a public institution where it will be available for study, so that it can add to our scientific knowledge instead of being locked away from it.

      Minor quibble - social media can be an excellent tool for science outreach but I feel that referring to the specimen as "T-rex" instead of the more proper T. rex works as a small disservice with regard to educating the general public about general palaeo/bio-science matters. I found it even more jarring because you identified the bone as a femur rather than using the non-technical "thigh".

    2. Hi Robert,

      I second Mark's concern - will that specimen go to a valid museum? Otherwise, it is out of the reach of science, which is what happened to Samson.


    3. Hi Thomas,
      In 2004 Samson was sent to the Carnegie Museum of Natural History, which allowed any and all researchers access to that remarkable skeleton. The skull was also sent to NASA and was allowed to be cat-scanned. Although its in private hands now, I've not heard of the owner refusing any legitimate assess to Samson.
      I understand the importance of this newly discovered juvenile tyrannosaurus and I'm not looking to make it available to private collectors. At this point it's only being offered to institutions, museums and academia, I might also add that 98% of all fossil specimens I've collected are in institutions or museums worldwide.
      I've always had an open door policy with anyone interested and always will.
      Thank you for your concern,
      "Science knows no country, because knowledge belongs to humanity, and is the torch which illuminates the world."
      - Louis Pasteur

    4. Robert,

      The private owner of Samson could roll out a red carpet and slap a set of calipers in my hand, but I wouldn't be able to collect any data from the specimen because it is not in a legitimate repository. To obtain data from such a specimen, I would be in violation of the Society of Vertebrate Paleontology's Ethics guidelines that state,

      "Section 4. Deposition of fossil specimens
      Scientifically significant fossil vertebrate specimens, along with ancillary data, should be curated and accessioned in the collections of repositories charged in perpetuity with conserving fossil vertebrates for scientific study and education (e.g., accredited museums, universities, colleges and other educational institutions)."

      Unless I'm mistaken, Samson is not in such a repository. Therefore, when you sell a scientifically significant fossil such as Samson to a private individual it's lost to science, period. I'm glad you're looking to do the right thing with the small skeleton.

    5. So if a specimen was found that provided conclusive evidence for the existence or nonexistence of Nanotyrannus, complete with soft tissues preserved, and it was sold to a rich young earth creationist who allowed any and all scientists two years to make any observations or run any tests they wanted before he ground up the specimen into dust, you would refuse to look at it on "ethical" principles?

    6. Hi Sue - in a word, yes: such a specimen is out of reach of science if it is not held in a legitimate repository. The touchstone of science is reproducibility of observation, and private collection is no guarantee that the original fossil will be available to science for all time. This is stated explicitly in the ethics guidelines of the Society of Vertebrate Paleontology. Ethical principles are there for good reasons - to protect the integrity of the science and to protect the the specimens - the data - themselves. Private ownership undoes all of that, and knowing this, private overs of fossils must know they aren't in the right. If a specimen is in a private collection, then it is effectively "ground to dust" - no responsible scientist would look at it. To give you a sense of how bad the situation is for T. rex: if all of the privately owned specimens were donated to legitimate museums tomorrow, then the total sample size would almost certainly double.

    7. Its unfortunately true what Mr. Carr said. And these rules are helpful, even if some privately owned specimens are legitimate.

    8. Er, make that even if some privately owned specimens could be legitimate,

    9. Sounds like science's reach has become very short.

      The rosetta philae probe landed on comet 67P. For all intents and purposes this scientific investigation is not reproducible to independent researchers due to logistics and cost. Does NASA not do real science then?

      If a biologist studies the behavior of a highly endangered species that might only have a decade or so left on Earth, is that not science because there is the strong likelihood that future researchers won't be able to observe this behavior themselves?

      Science is not always reproducible. If you care about your science you would surely want to collect as much data as you could when the data was available. I'm not a paleontologist but I would be surprised if no fossil in a museum has been lost or destroyed. Do you never cite the work of previous paleontologists in these cases?

      The sample size of T-rex might double, but aren't there a good number of T-rexes in museums compared to other large dinosaur types? And isn't that due, in good part, to the efforts of amateur/commercial collectors?

    10. A few further thoughts:

      What is a 'legitimate repository"? If Mr. Carr decided to open up his own museum, unaffiliated with another museum or a university, would he expect other researchers to view it as legitimate?

      Is there a guarantee that a public museum will keep fossils "available to science for all time"? Ignoring the complete absurdity of any institution, public or private, claiming to guarantee that their fossils will be curated for the rest of human history or that even the institution itself will exist indefinitely, there are other issues with this line of thinking. No laws or regulations strictly prohibit a public museum from getting rid of their fossils or even selling them in auction (This has indeed happened before - Can you, Mr. Carr, promise me that the US government will never become disillusioned by the fossils collections at the Smithsonian and that no politicians will ever cut funding to support the curation of its fossils? Not to mention that some fossils that are kept in public institutions are not accessible for many years (e.g., Ardi and Quetzalcoatlus).

      I was not aware of the SVP ethics guidelines, but after looking at their website, I also see the following: "Seciton 5: Information about vertebrate fossils and their accompanying data should be disseminated expeditiously to both the scientific community and the interested general public". I see that you often quote Section 4, but never mention Section 5.

      If private fossil collectors are indeed in the wrong, as you claim, should they just give away all their fossils to you and your colleagues, regardless of the amount of time, money, and effort, they put into their collections? That seems like a ridiculous thing to expect of them.

      About specimens being in private collections as essentially being as worthless as dust - Are you saying that no privately owned specimen has ever made it into a public institution?

  6. A nice post, but if I were reading it in 2013 and thought Nanotyrannus were valid, it would be quite unconvincing. Note I do provisionally agree with you that Nanotyrannus are juvenile Tyrannosaurus, so here I'm arguing as Devil's Advocate.

    Notably it's only really engaging with the first and worst arguments for Nanotyrannus' validity. Sure Bakker's 25 year old ideas are flawed, but any modern defense of the genus includes a swath of newly recognized characters, and of course Jane. So yes, Bakker was wrong to think the Nanotyrannus type had extensive cranial fusion. But Larson (2013) reports Jane has presacral neurocentral, scapulocoracoid and pelvic fusion. By not addressing these characters (also including glenoid position, subnarial foramen position, quadratojugal pneumaticity, maxillary tooth count, etc.), your analysis loses most of its force.

    There's also the problem of using similarity to juvenile stages of other species as an argument. In the 4 stage ontogeny of your 1999 paper, Albertosaurus simply never gets to stage 4. It stops at what is stage 3 in Daspletosaurus. Indeed, in 1996, you used this to argue Daspletosaurus are just adult Albertosaurus. You later changed your mind on this, but couldn't Nanotyrannus be a tyrannosaurine that never grows past stage 1? This makes your huge table moot, just as a huge table of stage 3 characters listed as "Yes!" in Albertosaurus would not mean it was a subadult Daspletosaurus.

    A related point is that Larson agrees Nanotyrannus could be the sister taxon of Tyrannosaurus, so your long list of characters they share works well for both hypotheses. We don't need to assume Bakker's odd phylogeny with a basal Nanotyrannus convergent with Tyrannosaurus for the genus to be valid.

    Further, it implies a taxon can be invalidated merely by finding the original diagnosis wanting. Let's see how that works for Tyrannosaurus, based on Osborn's (1905) original diagnosis.
    1. "Carnivorous Dinosaurs attaining very large size." Tarbosaurus got as large as the average Tyrannosaurus, so this is invalid even within Tyrannosauridae.
    2. "Humerus believed to be of large size and elongate (Brown)." This was based on an incorrectly identified bone.
    3. "No evidence of bony dermal plates (Brown)." This was to distinguish it from Dynamosaurus, whose holotype had incorrectly referred plates.
    Well, guess Tyrannosaurus is an invalid taxon we can't refer the Cleveland skull to...

    Finally, couldn't the Cleveland skull be a juvenile and a valid genus, just without known adult specimens? That's what you argue for in Alioramus, which is (1) based on two specimens of juvenile tyrannosaurid, (2) has an original diagnosis which relies entirely on characters claimed to be ontogenetic in the case of Nanotyrannus (long snout, high tooth count, compressed teeth, etc.), (3) has derived characters only known in the sympatric Tarbosaurus, so is by your reasoning (4) therefore juvenile Tarbosaurus. Yes, Alioramus has additional suggested apomorphies, but so does Nanotyrannus and they seem to be of equal import (e.g. additional pneumatic features in each). So I'd like to know why you came to divergent conclusions in these similar cases.

  7. Hi Mickey,

    Thank you for your comments! I have decided that my response to them will be a post entry in the near future.



    1. I'm looking forward to Thomas' reply. But I can give a brief one of my own: Alioramus was a potential juvenile Tarbosaurus, but the subsequent discovery of a specimen which was more clearly a juvenile Tarbosaurus but distinct from Alioramus causes us to reject this hypothesis.

      As I have stated for a decade and a half or so, that's all I'd need to be convinced of the validity of Nanotyrannus: either a juvenile Tyrannosaurus of the same ontogenetic status as Nano but is distinct from it, OR an adult Nanotyrannus which is distinctly not Tyrannosaurus.

      Until such a situation, parsimony suggests we accept the simpler solution: the taxon known only from juveniles and the sympatric taxon known only from subadults and adults which share apomorphies with each other are most likely the same taxon.

    2. I'd actually go the other way with this and view Alioramus as a juvenile Tarbosaurus. The differences between Alioramus' two known specimens and the few Tarbosaurus of similar size are mostly those known to vary ontogenetically (so could be explained by size not exactly correlating to skeletal maturity) or individually (especially pneumatic and ornamentation characters). There's enough variety in adult Tyrannosaurus rex to cause that whole rex vs. X debate, so seeing similar variety in juvenile Tarbosaurus seems expected. It's also not as if we have multiple Tarbosaurus subadults which all have one state and multiple Alioramus that all have another- due to incompleteness it's actually two Alioramus maxillae vs. a larger Tarbosaurus maxilla, the jugal, postorbital and tibia of "altai" vs. one similar-sized Tarbosaurus example, two Alioramus surangulars vs. a different Tarbosaurus than the last two, etc.. The very fact we have five subadult Mongolian tyrannosaurines but only two Hell Creek subadults also makes it more likely the former will show more variation.

      Finally, it should be noted Brusatte et al.'s (2009) description of Alioramus "altai" coded Alioramus as if it were adult, so it seemed more different from Tarbosaurus in the cladogram and matrix.

  8. This is an excellent article,

    Could you comment on Currie's (2003a) claim that the maxillary tooth counts vary between Nanotyrannus (14) and Tyrannosaurus (11-12) and that there's little evidence to suggest that the number of maxillary teeth becomes reduced during ontogeny (Currie 2003b). I'm not convinced by this argument myself but I'd just like to play devil's advocate a little and get your thoughts on it.

    1. Hi Kyle,

      If the Cleveland skull is a juvenile T. rex, and all of the available evidence indicates this is so, then we have to accept the occurrence of ontogenetic tooth loss in that species. In 1999, I also hypothesized that the loss happened at the front of the tooth row. The variation seen in adults is consistent with the tooth loss hypothesis.


  9. Hello Carr. Well I am really surprised because I though that you said that Nanotyrannus was a juvenile T. rex. But clearely the Cleveland skull (and Jane's) are from immature specimens (well, there were found triceratops skulls with unfused bones that were bigger than some skulls with fused bones, but the difference between these skulls may not be bigger than what we see in the Cleveland skull and adult tyranosaurids). Well, as Nanotyrannus shows many similarities to Albertosaurus, couldn't Nanotyrannus be a young Albertosaurus?

    1. The similarities to Albertosaurus are either ontogenetic or reflect common ancestry. The heart of the matter is that the Cleveland skull and Jane have features that are only seen elsewhere in adult T. rex, ergo the simplest explanation for that is they ARE juvenile T. rex. How is that so difficult to grasp?!

    2. I see. But have you ever thought that the similarities between T. rex and Nanotyrannus may also reflect fommon ancestry? I took a look at the skull of the Cleveland skull and to Jane's and I saw that they show may characteristics that we would not expect from a teenage T. rex: they show horn like lacrimal bones that adult T. rexes lack, they show somewhat circular orbits when adult T. rexes have "glasses shaped" orbits, the sagital crest (I think this is the name of that crest like bone that is located above the lateral temporal fenestrae) of the Cleveland skull looks nothing like what we see in adult T. rexes, and while teenagers should have an overhaul skull shape and proportions very similar to that of an adult, nanotyrannus has a long, low snout when adult T. rexes show shorter, high snouts (also remember that babies and juveniles always have proportionally shorter , and sometimes higher, snouts if compared to adults). The overhaul shaoe of the skull of Nanotyrannus looks nothing like that of an adult T. rex... and specimens with half of their maximum size have similar skull shape if we compare them to adult specimens.

    3. I see. But have you ever thought that the similarities between T. rex and Nanotyrannus may also reflect fommon ancestry?

      They are – all members of the same species descend from a single common ancestor.

      I took a look at the skull of the Cleveland skull and to Jane's and I saw that they show may characteristics that we would not expect from a teenage T. rex: they show horn like lacrimal bones that adult T. rexes lack, they show somewhat circular orbits when adult T. rexes have "glasses shaped" orbits, the sagital crest (I think this is the name of that crest like bone that is located above the lateral temporal fenestrae) of the Cleveland skull looks nothing like what we see in adult T. rexes,

      Most of this is accounted for in Carr (1999) and Carr and Williamson (2004).

      and while teenagers should have an overhaul skull shape and proportions very similar to that of an adult,

      Your evidence is…? Obviously, they don’t!

      nanotyrannus has a long, low snout when adult T. rexes show shorter, high snouts (also remember that babies and juveniles always have proportionally shorter , and sometimes higher, snouts if compared to adults).

      The snout to skull length ratios are identical – T. rex adults have tall, not short snouts.

      The overhaul shaoe of the skull of Nanotyrannus looks nothing like that of an adult T. rex... and specimens with half of their maximum size have similar skull shape if we compare them to adult specimens.

      The only difference is dorsoventral height, just like other tyrannosaurids.

    4. What evidence I have that teenagers must be similar to adults? Simple: every single animal. Even in amphibians we see that individuals with half the maximun size look far more like the adults than the babies. Now in reptiles and birds the babies already look a bit like the adults, so I do not have to comment about the teenagers.

      You just have to take a look at phitos of skulls of immature animals and you will see that their anout is eighter shorter or exactly like that of an adult (and their orbits start to have similar shapes.

      "Most of this is accounted for in Carr (1999) and Carr and Williamson (2004)." only because authorities say so it does not mean it is true. A teenage specimen should not show way different shaped bones if compared to a fully mature specimen.

      The snout size in proportion to the overhaul skull is no way similar in nanotyrannus and T. rex. I have compared the images and I put the skulls at the same height (by height I mean the distance of the top of the lateral temporal fenestrae to the bottom of the lower jaw) and the snout of nanotyrannus became way longer than that of the T. rex (I used AMNH 5027 to compare).

      And I forgot that babies have a proportionally larger head. So juveniles should ahow eighter larger or proportionally equal heads if compared to adults (while nanotyrannus shows a proportionally SMALLER head).

    5. And let's take a look at what you claim: albertosaurus and nanotyrannus have tons of similarities and even if you take a fast look you will see how they are almost identical, but these similarities are surely just ontogenic or reflection of common ancestry.

      Adult T. rexes and nanotyrannus appear to have no similarity if you take a fast look (nanotyrannus shows different shaped orbits, aditional bones to the lacrimal bones that give nanotyrannus a horn like bone that T. rex lacks, their sagital crests are completely different, etc) and even if thei have some similarities these could be just ontogenic or reflct common ancestry: no matter because nanotyrannus is surely a young T. rex even if it shares more similarities with the more similar sized albertosaurus.

    6. I realize you don't like authorities, but there's an excellent list of similarities between the type specimen of Nanotyrannus and adult T. rex in Bakker et al. (1988), which I later added to in Carr (1999).

    7. You distorced my argument: I said that only because an authority says so it does not mean it is true. The authority must give arguments just like every other person.

      This might be an excelent list, but you just need to take a fast look to see that nanotyrannus (or whatever should that species be called) looks far more like an albertosaurus.

      And it is just like I said: if having similarities with T. rex makes it a young T. rex, why similarities with albertosaurus does not make it a young albertosaurus?

  10. To my mind, our conversation is over and I'll provide no further replies; but to send you on your way, I provide you with a reading list of the relevant scientific literature that bears on the this question. This isn't a dodge - I just have the impression that there's nothing I can say to persuade you and we'll just stay locked in a perpetual and tedious exchange that will just bore our readers. So here's the list: Gilmore, 1946; Rozdhestvensky, 1965; Russell, 1970; Bakker et al. 1988; Paul, 1988; Carpenter, 1992; Carr, 1999; Currie, 2003; Carr and Williamson, 2004. To my mind Roz '65 is the watershed work - he points the way for the rest of us to follow and if we don't, it's to our peril.

  11. So you will just run away? Really? If you are so certain of your position, why don't you give me your arguments? Actually: do you have it?

    And if you do not mind: scientific literature means nothing IF what is written there is based on fallacies or poorly examined theories. I am 100% certain that there was scientific literature at the time that dinosaurs were though to be 100% scaly with their tails on the ground.

    You also seem to forget about all the characteristics that Jane and the Cleveland skull show that do not match with what we would expect from a teenage T. rex: young animals with half of their maximum size never show aditional bony structures (nanotyrannus' horn like bone on it's lacrimal bone), they must show an orbit shape that looks like (even a little bit) like what is found in adults (while nanotyrannus shows a circular orbit, adult T. rexes show a somewhat "glasses shaped" orbit) and the fact that young infividuals must have eighter a shorter, higher snout or be proportionally equal (you just have to observe the growth pattern of reptiles, birds and mammals... and in this case compare the skulls like I did here

    Do you know Scott Hartman? He has the same position as you in this aspect. But it was better to discuss with him because he actually SHOWS ARGUMENTS.