Friday, November 27, 2020


Approximately four out of 10 Tyrannosaurus rex fossils are in private or commercial hands, making them unavailable to science. The problems don't go away if museums pay top dollar for them, because their money helps to keep the commercial trade afloat.

The purchase of the dueling dinosaurs that was announced last week (Nov. 17, 2020) by the North Carolina Museum of Natural Sciences  wasn’t the first time a museum has shelled out for an eye-catching tyrannosaur; ahead of that transaction was Sue (Field Museum), Bucky (The Children’s Museum of Indianapolis), Wyrex (Houston Museum of Natural Science), and Trix (Naturalis Museum), totaling five specimens. I argue here that when museums pay the ransom for a dinosaur fossil to the commercial trade, it hurts the science and shouldn’t be done.

Context is everything—Importantly, the context of those five purchases aren’t the same: in the case of Sue the monies from the auction went to the landowner, in the other four the sale satisfied one or more commercial interests. In the case of the dueling dinosaurs, the monies were, presumably, split between the landowners and the two commercial players (Pantuso, 2019). In other words, Sue was not bought off the shelf, whereas the others were.

It should matter to us scientists where the money goes – and if it goes back to the companies who trade in fossils, that fact should give us pause: we become the problem when we give them our money for fossils. It helps to keep them afloat to continue collecting scientifically important fossils, and holding them for ransom from hundreds of thousands to millions of dollars until a museum blinks or a private collector pays out.

Resist. Resist or perish—The monies paid to commercial companies helps to keep them in business. Those companies, at least in the case of T. rex, has deprived science of half the sample size.

An updated comparison of the number of Tyrannosaurus rex fossils collected by commercial interests, in contrast to public trusts. The number of commercially collected T. rex is almost certainly an underestimate, since the trade often keeps its wares in secrecy. Ergo, approximately half of the sample size of T. rex is kept from science.

Half of the specimens of T. rex are inaccessible to science, purely because of the fossil market. This circumstance is simply bizarre, but it is the very one in which I find myself. It is like living in a parallel universe, especially when many of my colleagues don't regard this situation with as much concern as me. In many cases, to give them the benefit of the doubt, they work on species that have higher sample sizes or their work is at a meta-level where high numbers of individuals are not required. But what if they woke up tomorrow morning to discover that half of the fossils they expected to see were gone, and the fossils were held for a ransom of millions of dollars? I don't know how bad the situation is for other dinosaurs and extinct reptiles, but I have noticed that Allosaurus, Diplodocus, Triceratops, and Maiasaura do regularly appear on the auction block.

A colleague has said to me that what they pay for fossils "is only a drop in the bucket" compared with the total annual income of a large commercial outfit. That may be so, but why help keep an exploitative company afloat that sells fossils out of science's hands? Why actively support the commodification of dinosaur fossils? Why play their game? The mean price of a T. rex is 12.4 million USD; this is certainly at the high end for most dinosaurs, but I fail to see how hundreds of thousands of dollars, let alone millions, are trivial sums in a niche (and, in my opinion, illegitimate) market.

Comparison of the monies paid for Tyrannosaurus rex skeletons, which is doled out in the millions of dollars. I do not know the prices paid for Wyrex and Bucky, but I expect that they were sold in the hundreds of thousands of dollars. The sources of prices for Samson, Trix, Sue, and Stan are in my previous post, "Tyrannosaurus rex: 115 years old and royally f***ed." The source for the price of the dueling dinosaurs is from Shaffer (2020).

The problem is increased when museums give the fossil trade a free pass and loads of money to continue as it has, pretending there’s no issue with the trade itself. The public is not alerted to the problem when, with fanfare, museums buy tyrannosaurs.

Don’t be fooled by the hype - the purchase of the dueling dinosaurs does not change the fact that roughly half the sample size of T. rex is still inaccessible to science. Less than 20% of commercially-obtained T. rex eventually wind up in museums. The instance of a T. rex making its way from commercial hands into a public trust is the exception, not the rule.

The proportion of commercially-obtained Tyrannosaurus rex fossils that have made it into a valid museum is less than 20%.

Museums: please don’t pay the ransom—The commercial trade in dinosaur fossils has to be shut down; there are many models across the world for the US to follow in terms of managing these nonrenewable resources without a persistent and exploitative commercial trade, such as Alberta, Italy, and so on. In the meantime, museums should just stop buying spectacular specimens, period. And, if any can, they should instead encourage the donation of the fossils to their collections. That would be a great deal less destructive upon science than giving the trade the extra shot in the arm it needs to make the next field season.

Coda—In light of this ongoing mess I can't help but wonder: should fossils bought off the shelf by public trusts be studied at all? The ethics of that stance needs further rumination, but I can already hear the braying of my trolls and their shills: "He can't admit he's wrong about Nanotyrannus!" Nothing could be further from the truth.

Sources Cited

Pantuso, P. 2019. Perhaps the best dinosaur fossil ever discovered. So why has hardly anyone seen it? The Guardian, Wed. July 17.

Shaffer, J. 2020. 'Dueling dinosaurs': world's most complete Tyrannosaurus rex, Triceratops, Raleigh bound. The Charlotte Observer, Tues. Nov. 17.

Saturday, October 31, 2020

Tyrannosaurus rex Among the Bottom Feeders

Over the past few weeks I’ve compiled data on 96 Tyrannosaurus rex fossils that are for sale on eBay, and I present the results here. This survey gives some insights into where the fossils are being collected, which fossils are most frequently sold, the prices sought, and where the sellers are located.

In summary, this is a snapshot of the low-level background noise of the fossil trade that does not conceal itself from the public eye. I take the fossil identifications at face value, since it is more important in this case what it is that people think they are selling (and buying) than what the objects actually are. For what it is worth, I do think that most - but not all - of the identifications are taxonomically accurate.

From where are the T. rex fossils exploited?

The fossils are collected in Wyoming, South Dakota, and Montana. As shown in the graph, Montana is most heavily hit. This exploitation of the northern Rocky Mountain Region for small and isolated T. rex fossils is the same as that of the big-ticket skeletons of T. rex.

Within Montana, T. rex fossils are primarily collected from Carter County and Dawson County. Garfield, McCone, and Powder River counties are also exploited, but less frequently. The high frequency in Carter County is alarming to me, since that is where I do my fieldwork on public lands.

Which parts of T. rex are for sale?

Tooth fragments, teeth, and unidentifiable bone fragments are the primary items sold. In contrast, identifiable parts of the rest of the skeleton (from skull fragments to unguals) are numerically infrequent.

For how much are T. rex parts sold?

The total amount of the 96 fossils in this survey sums to $51,777.96 USD. A comparison of the maximum prices of T. rex fossils shows that, in descending order, teeth, unguals, skull fragments, tooth fragments, and premaxillary teeth are the most highly priced. It is these fossils that break past the $1,000.00 USD price barrier, making these high value items the most vulnerable to being lost to science.

Is there a correlation between size and price of T. rex teeth?

A correlation coefficient of 0.57 was obtained from a quantitative comparison of the data for tooth height and price, indicating a positive correlation. That result means, generally, large teeth are more expensive than small teeth. A single outlier, a 37-millimeter tooth fragment on offer for $6,395 USD was excluded from the comparison; the range in price of the other teeth is from $24 to $2,000 USD.

From where are the T. rex fossils sold?

Most of the fossils (94 of 96) are sold from the continental United States, whereas one fossil each is on offer from Singapore and the United Kingdom.

Despite the fact that the fossils are exploited from only three states, within the US the sellers are as numerous as they are far-flung, from the west coast (California), the east coast (New York), Appalachia (Pennsylvania, West Virginia), the southwest (Arizona, Oklahoma, Texas), the Midwest (Minnesota), the west (Montana, Idaho, South Dakota), the southeast (Florida, South Carolina), the south (Alabama, Tennessee), and the Rocky Mountain Region (Utah). Most of the fossils are sold from (in descending order) Texas, Arizona, and Idaho.

Are the fossils actually T. rex?

Having summarized the primary data, it is now reasonable to ask: do the sellers actually know what they have? In most cases they do, except for the identifications of the skull bones, which, in my opinion, are too incomplete to identify with any accuracy, whereas another complete, identifiable bone is clearly not a dinosaur, let alone T. rex. This means that the sellers in some cases, at best, do not know what it is they have, or, at worst, they are misrepresenting the identification to boost the price.

The cost upon science of nickel-and-diming T. rex fossils 

These fossils will never make it into a university or museum collection; the information they contain will never be recovered, and the public will not see them. In my fieldwork, these sorts of fossils are important for documenting the stratigraphic distribution of T. rex, the species richness and ecological structure throughout the section, the taphonomy of localities, isotopic ratios of tooth enamel, population structure, ontogeny, and so on. Scientifically, there's a tremendous amount of information about the last million years of the Age of Dinosaurs to be gained by careful collection, documentation, and study of fragmentary bones and isolated teeth.

This nickel-and-diming of T. rex fossils has two immediate effects: it provides incentive for the commercial trade to exploit dinosaur fossils for profit and it reinforces the indifference of the general culture to the problem of the fossil trade. If people really cared about this exploitation, the sellers would, presumably, be run off the platform. Unfortunately the steady stream of fossils that is trickling away from science is evidence that society has yet to respond to this situation for the problem that it really is.

Wednesday, October 14, 2020

Tyrannosaurus rex: 115 Years Old & Royally F***ed

Tyrannosaurus rex is hit very hard by the dinosaur fossil trade; to it approximately half of the sample size has been lost.

How has the most famous and fearsome extinct animal of all time so utterly slipped from the hands of science?


In June of this year I published an extensive study of growth in T. rex based on a sample of 41 scientifically available specimens (Carr, 2020); that is, specimens in the collections of public trusts. There’s several more fossils in public trusts that weren’t included in my study, which brings the number up to 57.

Fifty-seven T. rex specimens sounds pretty good, but that is marginally over half of the potential sample size: there’s at least another 43 in the stockrooms of commercial fossil hunters and in the collections of private collectors who buy them. That means our knowledge of T. rex is half of what it could be because the fossil market has deprived science of half the information.

The study of vertebrate fossils follows ethical guidelines formulated in our corner of the scientific community. To ensure replication of our observations (the universal cornerstone of science), the fossils we study should be accessioned into the permanent collection of a public trust, which in the United States is an accredited museum or university collection. Fossils in private hands lack every protection that a bona fide public trust can provide and so it is unethical to study and publish on them. The recent multimillion dollar auction of the T. rex nicknamed Stan, to an as-yet unknown buyer, is a dire example of why that ethical guideline should be followed given that the fossil had no shield from the legal entanglements of a family conflict (Thompson, 2020).

In order to give you a sense of how bad the situation really is for T. rex, I share here with you numbers based on my own records of commercially held (and brokered) and privately owned T. rex fossils. My sources of information on commercial specimens include published articles (Larson, 2008), auction catalogs, online sources, and, in a few cases, word-of-mouth. I am not interested in naming and shaming, so I will not make publicly available my list of the commercial and private specimens; instead I will keep the focus on the story that the numbers tell.

How many T. rex are in private and commercial hands?

At my latest count, there are 57 specimens (from complete skeletons to single bones and teeth) in public trusts; the count of single bones and teeth are limited to those that I have published, since there are hundreds more of them in museum collections. There are at least 43 specimens (complete to partial skeletons, isolated jaw bones) of T. rex in commercial and private hands (Figure 1).

The count of 43 is an underestimate, because secrecy often surrounds commercially-held T. rex fossils; for example, I will see media reports of previously unheard-of specimens that pop up every six months or so, especially if there is a legal dispute over a fossil or if a skeleton went on public display. On occasion, purely by happenstance, I have learned of important but commercially held T. rex fossils from people who saw a specimen that is otherwise unknown beyond a small circle. Therefore, it is reasonable to infer that the actual number of commercially- and privately-held T. rex fossils must be much higher than my count, but it at least can be said that nearly half of the scientifically informative specimens of T. rex are currently out of the reach of science.

Figure 1. Comparison of the number of Tyrannosaurus rex specimens in public trusts (blue) with those in commercial or private hands (orange).

Sample size gutted

In science, sample size is everything: imagine if our entire knowledge of people was based on only 60 skeletons, where most were adults, we had only a few scraps of teenagers, and of children we had only one skeleton, a skull, and a few bones and teeth. Based on that, we’d know very little about the growth and skeletal biology of people; also, we’d lack a rigorous baseline of data that would enable the study of our evolution among our closest relatives. That situation precisely describes the current scientifically-available sample of T. rex.

To accurately understand the growth changes of T. rex, say, during each major growth stage, or, better yet, during each year, we’d want enough skeletons to capture the entire growth series. That level of knowledge requires a large sample size – in other words, more skeletons! For most living species that occur in abundance, acquiring a large sample size for each year of growth is straightforward, but for rare fossil species, like T. rex, it isn’t.

A statistically rigorous sample size for T. rex would be 30 skeletons for each year of life. Why 30? Nature is messy, and in skeletons that messiness is expressed as variation (i.e., noise) whereas what we’re after is the true pattern of growth (i.e., signal). Generally, a sample size of 30 is sufficient to distinguish between signal and noise.

Therefore, for the main growth stages (juvenile, subadult, young adult, adult, senescent adult) we'd need 150 specimens (30 specimens x 5 growth stages), or, at the other end of the spectrum, we’d need 900 T. rex skeletons (30 specimens x 30 years) to really nail down its year-to-year growth changes. I am well aware that virtually no dinosaur species reaches these sorts of numbers, but the point is that every fossil matters if we're to really understand their growth, biology, ecology, and evolution.

For T. rex, the problem is that science is currently working with only around 60 specimens (7% of what we need for the yearly study) that are in public trusts. This sample size problem is straightforward to help solve: if the 43 specimens that languish in commercial- and private hands were transferred into public trusts, the sample size would reach 100, nudging up the sample size needle in the right direction.

T. rex biology compromised

My research focuses on the growth of T. rex and its close tyrannosaurid relatives. In my study of T. rex, I found that the growth stages represented by the fewest specimens are the small juveniles and subadults. By my count, a fifth of the commercially- and privately held specimens (i.e., nine fossils) represent those rare growth stages, which, if in public trusts, would greatly improve our understanding of how T. rex grew up and evolved (Figure 2).

Figure 2. The proportion of juvenile and subadult specimens (orange), compared with adults (blue) that are commercially- or privately held. The number of juveniles and subadults, the rarest of T. rex fossils, totals to nine specimens.

In which parts of the American West is T. rex most exploited?

According to my tally of the locations where 34 T. rex commercially obtained specimens were found, South Dakota and Montana are the most seriously hit, each with 14 specimens taken (Figure 3). The situation is less severe, but persistent, in Wyoming (four specimens) and North Dakota (2 specimens).

It is notable that the commercial exploitation of T. rex is limited to the Northern Rocky Mountain Region, whereas fossils are not exploited south of Wyoming. This exclusivity may simply be a function of the extensive exposures of the Hell Creek Formation (and equivalents) in the north, the scale of properties upon them, and, perhaps, a high density of commercial outfits, large and small, operating out of South Dakota and Montana.

Figure 3. Comparison of the frequency of commercial exploitation of Tyrannosaurus rex fossils in the northern Rocky Mountain Region of the United States.

How many commercially obtained T. rex have made it into public trusts?

It has been claimed that commercially collected T. rex fossils inevitably make it into public trusts. This is simply not true – by my count, only seven specimens (Bucky, Wyrex, Trix, Sue and two associated T. rex bones, a partial juvenile dentary) are in public trusts.

Figure 4 shows that when Sue and its associated fossils (a lacrimal bone from a juvenile and a partial tibia from a subadult) are counted separately, 14% of commercially collected T. rex fossils made their way into a museum; in contrast, if the Sue locality fossils are counted together, then, arguably, the proportion is only 10%. Either way, science is deprived of the vast majority, from 86- to 90% of the specimens.

Figure 4. The proportion of commercially-collected Tyrannosaurus rex specimens that have been accessioned into the collections of a public trust (orange); the total is from five to seven specimens, depending on how they are counted.

How does the intensity of commercial exploitation of T. rex compare with that of public trusts?

Collection of T. rex fossils by public trusts began in 1892, with the American Museum of Natural History. This activity persisted into the early 1900s, and then stopped. Collection spottily resumed in the 1940s and 1950s that led to the discovery of the infamous Cleveland skull in 1942. After that, forays made by museums ceased until the 1960s, which have continued regularly to the present day (Figure 5).

Over that 128 years of collection, on average, 0.4 scientifically significant T. rex fossils were found each year. Since the 1960s the rate has increased to 0.7 fossils per year.

Commercial collection of T. rex fossils began, as far as I can tell, in 1990 with Sue. Since then commercial outfits have collected at least 39 specimens (the number for which I have the year of excavation), which is a collection rate of 1.3 specimens per year (Figure 5). In contrast, public trusts during the same time frame have collected only 28 specimens, resulting in a lower collection rate of 0.93 specimens per year; we can’t keep up.

Based on these data, the commercial market in dinosaur fossils, particularly T. rex, is a very recent phenomenon that has rapidly flushed out half of the sample size away from science.

Figure 5. Comparison of the collection frequency between public trusts (blue) and commercial fossil hunters (orange) from 1892 to the present. Timescale in years is along the x-axis, number of specimens is along the y-axis.

Tyrannosaurus rex is only for the one per cent

It makes me flinch when I hear colleagues breezily discuss the “going market value” of a T. rex, so the worst moment of the Christie’s auction for me (I watched it live online) happened at the end of the affair when a commentator remarked, “Now we know the price of a T. rex - $27.5M.” A comparison of the prices paid for T. rex skeletons shows that people will pay from $5M- to $31.8M USD, with a mean of $14M USD (Figure 6). With prices like that, no museum can alone compete with private interests that will aggressively pursue a bid.

Figure 6. Comparison of the monies (USD) spent on relatively complete adult Tyrannosaurus rex. The price of Sue has been adjusted to its 2020 equivalent (Geggel, 2020). Estimated price of Samson is from Hansen (2009); price of Trix is from Johnson (2016).


In total, these numbers show that over the past 30 years, the commercial exploitation of T. rex fossils has done no favors for science:

(1) The sample size is effectively halved.

(2) The Northern Rocky Mountain Region is cleaned out on an annual basis.

(3) Public trusts are limited to collecting on public lands.

(4) Scientifically important juveniles and subadults are inaccessible.

(5) The market for adult skeletons is accessible only to millionaires.


During the last 30 years of the 115 that it has been known to science, Tyrannosaurus rex has been plundered by commercial exploitation, with no end in sight. This situation doesn’t need to continue, does it?

References Cited

Carr, T. D. 2020.  A high-resolution growth series of Tyrannosaurus rex obtained from multiple lines of evidence. PeerJ 8: e9192.

Geggel, L. 2020. Stan the T. rex just became the most expensive fossil ever sold. Live Science 10-9/2020.

Hansen, K. B. 2009. Samson T. rex fossil displayed at Venetian finds home in Portland. Las Vegas Sun 12-10/2009.

Johnson, S. 2016. Don't worry Sue - Trix is just passing through. Chicago Tribune 8-24/2016.

Larson, N. L. 2008. One hundred years of Tyrannosaurus rex: the skeletons in P. Larson and K. Carpenter (eds.), Tyrannosaurus rex: The Tyrant King, University of Indiana Press, p. 1 - 65.

Thompson, N. 2020. Stan the T. rex's $31.8 million sale cam after family business dispute, court records show. Rapid City Journal 10-9/2020.

Sunday, October 4, 2020

The Disaster of Our Own Making

The looming auction of the privately-owned Tyrannosaurus rex skeleton, nicknamed Stan, is the result of the specimen having found itself in the crosshairs of a liquidation suit. The auction of Stan is a starkly different situation than the one that landed Sue onto the auction block. Sue, fortunately, was rescued from private ownership by a consortium of McDonald’s, Disney, and the Field Museum, sweeping the fossil into the safety of the Field’s permanent research collections and public exhibits.

The difference between Stan and Sue is that, at the time of its auction, Sue did not have a body of scientific literature attached to it; in contrast, Stan does – a staggering 48 peer-reviewed articles in total, by my count (Figure 1). This circumstance opens up (1) the immediate issue of whether or not Stan will wind up safely in a public trust, as did Sue, or whether it will disappear into private ownership; and (2) the farther-reaching issue regarding the publication of such legally vulnerable specimens in the scientific literature.

Figure 1. A histogram showing the annual frequency of 48 peer-reviewed scientific articles that include Stan (BHI 3033).

A. The Best and Worst Outcomes

Our professional scientific society is the Society of Vertebrate Paleontology (SVP), which codifies the expectations, standards, and practices of the science. The ethics regarding the deposition of scientifically important specimens (a bar that Stan exceeds by leaps and bounds) is that:

“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).”

In fact, the flagship publication of the SVP, the Journal of Vertebrate Paleontology (JVP) requires that “All specimens used in diagnostic descriptions, in illustrations, or in taxonomic discussions must be properly curated and reposited in a recognized public or private, non-profit institution.” So the best possible outcome for the auction is for Stan to find itself accessioned into the collections of a genuine public trust so that it can be ethically studied and published. However, the $6 to $8-million expected price does not raise much hope for that happy outcome.

Most museums – even the biggest and most prosperous among them - do not have millions of dollars to spend on single objects; that magnitude of money is best put toward hiring staff, expanding facilities, developing new exhibits, funding field programs for decades, and so on. With museums out of the way as candidates to make a winning bid, the auction is opened up to private interests, where Stan could disappear into a private collection, never to be seen again.

This has happened before: a T. rex skeleton, nicknamed Samson, was auctioned in 2009 to a private individual and, as far as I know, it is on display in a corporate headquarters somewhere in the continental US, inaccessible to science. As long as a scientifically important specimen is in a private collection, it cannot be studied since there is no guarantee of access to it by scientists or its long-term whereabouts, especially upon the death of the owner or some other happenstance, such as liquidation of a company and the specimen lumped in with financial assets.

Given the expected price on Stan, there is a very high probability that Stan will go the way of Samson; in a similar fashion, the recently discovered painting by Leonardo da Vinci, the so-called “Salvator Mundi,” was snatched out of the hands of the academic art world by a private collector with limitless lucre (

Therefore, my hopes aren’t high for Stan making it into a public trust.

At this juncture, it is worth asking: if Stan is sold to a private collector, never to be seen again, what do we do with the science that is published on it?

B. The Way Forward

In my view, there are two options.

We disregard the data and results that have been published on Stan. This is the approach I’ve taken in my own research: I make the effort to vet and exclude any specimens in the scientific literature that are privately owned. Also, I do not study or publish on privately owned specimens.

We just carry on and continue to use the published data on Stan. If we do this, we do so knowing that those observations cannot ever be repeated, and we’ll be unable to test the hypotheses that they were a part of initially. This circumstance is problematic because testing observations is the cornerstone of science; if we continue to include Stan in our scientific articles that decision puts the literature in a fraught, if not compromised, situation.

In the end, our actions as scientists have contributed to the potentially high scientific cost of the auction, which blasts past the skeleton directly into the scientific literature, a territory we thought was beyond the mundane reach of commerce. Arguably, even if Stan is auctioned to an accredited museum, its history must give us pause before studying fossils of similar vulnerability, should ever the temptation arise to upend our reason.

So we must do what we can to ensure that Stan, upon auction, becomes part of a desirable museum collection; that is the position that the SVP has taken ( Otherwise, the consequences for the science could be titanic.

Sunday, November 19, 2017

Links to interview series on things tyrannosauroidean

Hi All,

I was recently interviewed by Arsen Kazaryan on things tyrannosauroidean for his youtube channel.

Here are the links to the first four parts:

Part 1 - Daspletosaurus horneri & Carr et al. 2017:

Part 2 - Tyrannosaur family tree, tyrannosaur skin, tyrannosaur skin diagram:

Part 3: Tyrannosaurus, tyrannosaur ontogeny, upcoming publication:

Part 4: Dinosaurs in media, research tips and advice

Depending on the feedback on these, I will do a follow-up Q&A post.


Friday, July 14, 2017

Introducing Daspletosaurus horneri: short video summary

Here's a link to a short video that I did with Carthage College that hits the main points of our recent publication on Daspletosaurus horneri:

Monday, April 3, 2017

Introducing Daspletosaurus horneri, the Two Medicine Tyrannosaurine: Ontogeny

In our recent publication (Carr et al., 2017), we presented a cladistic growth series for Daspletosaurus horneri in Figure 3. The complete list of growth changes that we recovered are listed, in code form, in the supplementary materials. In the interests of saving you the trouble of scrolling up and down multiple pages at a time, I have put together an illustrated summary of the growth stages here. For convenience, the codes are listed in each heading. 

The following convention is followed for the labels in all of the images: a solid leader line extends to a feature that can be seen in lateral view, whereas a dashed line points toward a feature that is out of the plane of view. At this stage, all of the images that I can offer are in lateral view. Therefore, some features are simply not labeled, but they are listed following the illustration. Be forewarned that some features, although they are labeled, may not be clearly seen or not seen at all; i.e., some labels indicate simply where to look and I apologize in advance for that limitation.

GROWTH STAGE 1 (exemplar:  MOR 553S/

This growth stage is represented by the juvenile paratype dentary. No mature features were recovered for this growth stage since all of its characters were scored as "0". Regardless, this specimen reveals many juvenile features for the dentary, including small body size, as inferred from the length of the tooth row.

GROWTH STAGE  2 (exemplar: AMNH FARB 5477): 1 (1)

This growth stage is represented by a juvenile maxilla. One unambiguously optimized feature was recovered for this growth stage, large size, as given by the length of the tooth row. This maxilla has many features that are representative of the juvenile condition, and they are labeled in the figure below.

GROWTH STAGE 3 (exemplar: MOR 590): 2 (1), 6 (1), 8 (1), 11 (1), 14 (1), 19 (1), 20 (1), 21 (1), 22 (1), 28 (1), 30 (1), 33 (1), 34 (1), 37 (1), 38 (1), 40 (1), 42 (1), 43 (1), 45 (1), 49 (1), 50 (1), 52 (1), 53 (1), 164 (1).

This growth stage is represented by the imposing skull and jaws of the type specimen, MOR 590. Given the limitations of the data set, all 24 of the unambiguously optimized features pertain to the maxilla.

Several features cannot be seen from the side, and including them in the diagram would unnecessarily crowd the image. All of these descriptions pertain to the mature state, which is coded as a "1", the numbers correspond to the character number in the supplementary information for Carr et al. (2017); they include:

40. Base of the medial interfenestral strut is positioned at or behind the midlength of the lateral strut.

42. Caudal antromaxillary fenestra is close to the anteroventral margin of the internal antorbital fenestra.

43. Epiantral recess is deeply excavated.

45. Palatal process of the maxilla is sigmoid in shape.

49. Margin of the choana on the maxilla is positioned caudally, where it extends along the level of alveoli 7-10.

50. Distinct depressions for dentary teeth below the rostral end of the palatal process.

52. Interdental plates are positioned close to the alveolar margin of the bone.

GROWTH STAGE 4 (exemplar: MOR 3068): 135 (1), 136 (1), 141 (1), 144 (1), 145 (1), 147 (1), 148 (1), 153 (1), 155 (1), 156 (1), 158 (1), 161 (1).

This growth stage is represented by a referred partial mandibular ramus, and all 12 of the unambiguously optimized characters pertain to the lower jaw.

Two additional characters cannot be seen in this view:

156. Dorsoventrally shallow medial bar.

161. Massive and rostrally extending medial ridge on the caudal process of the splenial.

GROWTH STAGE 5 (exemplar: MOR 1130): 134 (1), 137 (1), 138 (1), 142 (1), 143 (1), 146 (1), 150 (1), 151 (1), 152 (1), 157 (1), 159 (1), 162 (1), 163 (1).

This growth stage is represented by the majestic paratype adult; all 13 unambiguously optimized characters pertain to the mandibular ramus. The limited data set results in only a batch of characters unambiguously optimized for the caudal- and mid-regions of the mandibular ramus.

Two characters of the splenial cannot be seen in this view:

162. Bar below the rostral mylohyoid foramen of the splenial is dorsoventrally deep.

163. Fossa along the dorsal margin of the rostral mylohyoid foramen is absent, where the corresponding surface is convex.

Concluding thoughts

Although we successfully obtained a growth series for D. horneri, the incomplete nature of the majority of the specimens results in a limited account of the changes across the entire skull from stage to stage. Instead, we obtained a patchy picture of the sequential changes that happened during growth, which will hopefully be filled by future discoveries of complete juveniles.

Also, at this point we did not provide any explanation for the changes that occur; that will be the subject of a future work (by me) that will make comparisons across derived tyrannosauroids (Bistahieversor + Tyrannosauridae).

References cited

Carr, T. D., D. J. Varricchio, J. C. Sedlmayr, E. M. Roberts, and J. R. Moore. 2017. A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system. Scientific Reports. Doi: 10.1038/srep44942.