Tuesday, 31 May 2022

The mad, mad, mad stilt-legged tyrannosaurid hatchling (and other efforts at reconstructing baby tyrants)

By now many readers will have seen the excellent, excellent BBC/Apple TV+ documentary Prehistoric Planet, a show being widely celebrated as the most significant televisual portrayal of dinosaurs since 1999’s seminal Walking with Dinosaurs. There’s a huge amount to say about the reaction to Prehistoric Planet as well as how it was put together. I’m proud to say I was involved as a concept artist and consultant but, for now, those of us involved with the show have been (understandably) asked not to give too much away. We can, nevertheless, use the programme as a jumping-off point to discuss some cool dinosaur science, and that’s what I want to briefly do today.

One of the most memorable scenes in Prehistoric Planet is the opener of the first episode, and you might be familiar with it even if you haven’t seen the full series. It’s the sequence featuring the swimming Tyrannosaurus and his juveniles crossing a small body of water to engage in some beach-related foraging. Part of this scene featured in a promotional teaser that dropped so many jaws earlier this year, where Tyrannosaurus juveniles hunted turtles on a beach. If you've somehow missed this, here it is.

The official sneak-peek for Prehistoric Planet, from the Apple TV+ YouTube channel.

It’s easy to buy these superbly rendered, fluffy, long-legged and big-eyed baby tyrants as 100% accurate takes on such animals because they look so real. But under their wireframes and digital rigging, these juvenile dinosaurs are based, in fact, on hypothetical reconstructions, not fossil skeletons. Despite the intense interest in Late Cretaceous North American fossil sites, hatchling tyrant dinosaurs are virtually unrepresented by fossils and the first genuine remains of such animals were only described in 2021, by Greg Funston et al. These important finds constitute a piece of lower jaw, a tooth, and a foot claw from embryonic individuals of Daspletosaurus and Albertosaurus. Each sheds a little light on the size and proportions of baby tyrannosaurs, but we’re still far, far away from a complete picture of their entire osteology. Thus, to date, the only way to restore the life appearance of baby tyrants with some degree of scientific rigour has been to extrapolate their proportions from older, larger individuals. We’ve been attempting this activity for at least 50 years and, even now, we struggle to make accurate, or at least statistically sound, models of baby tyrant appearance.

The first effort at predicting hatchling tyrant anatomy was published in Dale Russell’s 1970 paper on the tyrant dinosaurs of Canada. Russell predicted the proportions of a hatchling “Albertosauruslibratus (=Gorgosaurus libratus today) by calculating scaling trajectories of larger tyrants and projecting them to an individual with a 100 mm long femur. The resultant image is one that might be familiar to many readers, as it has appeared in subsequent dinosaur books and papers. I certainly remember my own first encounter with it in David Norman’s influential 1988 Normanopedia Illustrated Encyclopaedia of Dinosaurs, as it looked very different to the pop-culture plush toy-like baby dinosaurs I was familiar with (hello, The Land Before Time et al.).

Dale Russell's hypothetical Gorgosaurus libratus hatchling, from Russell (1970).

Russel’s prediction shows baby tyrants as long-legged, long-tailed and small-bodied animals that were very different to their parents, a consequence of the pronounced allometry that shaped tyrannosaurs as they grew. The overall animal, he calculated, was dog sized: just over 75 cm from the snout to the end of the tail. Some aspects of Russell’s model, including the shapes of the bones themselves, were created by “juvenilising” the bone shapes of adult albertosaurines and, even today, it's a good-looking skeletal. It certainly matches what we see in other non-avian dinosaur embryos and hatchlings, which are generally leggy animals adapted for precocial, relatively independent early lives. It’s probably this skeleton that a lot of palaeoart and dinosaur documentaries have based their baby tyrants on as, all these years later, it's still one of the only published hatchling tyrannosaur skeletals available.

In 2003 another attempt to predict tyrannosaur hatchling proportions was made by Phil Currie. Armed with more specimens and thus more metric data, Currie was able to provide more informed tyrant scaling regimes and, in theory, give us a superior prediction of hatchling proportions than Russell’s effort of three decades prior. As before, his scaling was to an individual with a 100 mm long femur, and the result was, again, dog-sized. Currie didn't specify what tyrannosaur he was modelling specifically, so his data can be viewed as a generic tyrannosaurid, although albertosaurine scaling metrics were prioritised where they differed significantly from those of tyrannosaurines. Because Currie (2003) only presented the results in a data table and did not illustrate the resultant hypothetical hatchling, I took the liberty to restore the animal with his suggested proportions myself*. And, holy moly…

The stilt-legged tyrant hatchling, restored after the dimensions given in Currie (2003). As explored below, the data behind this reconstruction were identified as unbelievable in Currie's original paper: this is not what Phil Currie (or anyone else) seriously thinks juvenile tyrannosaurus looked like! But it is what models of tyrannosaur ontogeny, as understood in 2003, predicted for a tyrant of hatchling dimensions.

…those are some l-o-n-g legs. They’re slightly maddening to look at, in fact. Like it’s been teleported in from the Nightmare Before Christmas meets Prehistoric Planet Super Crossover Spectacular. While the rest of the animal isn’t too dissimilar to Russell’s baby gorgosaur, the tibia is 60% longer and the metatarsals 220% longer, creating a tiny dinosaur on stilts. The result is a theropod with leg proportions outside of anything known within Dinosauria: even long-legged birds, like stilts, secretary birds and seriemas, are being put to shame. Needless to say, if anyone seriously thought that this is what baby tyrant dinosaurs looked like we’d be considering all sorts of ecological and biomechanical implications. Were baby tyrants waders? Specialists of prairies and open habitats? Did they make money on the side at Mesozoic carnivals as stilt walkers? What the heck is going on?

*I had to take lengths of the vertebral column and manus from Russell (1970), as these were not modelled in Currie (2003).

But, of course, no-one does think that this is what hatchling tyrannosaurs looked like. The outlandish hindlimb proportions of this model were dismissed as unbelievable by Currie (2003) as quickly as they were introduced, and the whole exercise ended with a blunt cautionary note: “there are limitations to what can be done in extrapolating this data.” (Currie 2003, p .663). And before anyone asks, it's worth stressing that Currie's values were not errors or the outputs of wrongful methodology: they're simply what fell out of legitimate, perfectly normal scaling equations. The "limitations" Currie referred to are fundamental difficulties with scaling the proportions of extinct animals outside of observed ranges. Such issues include low sample sizes, our scaling curves being skewed by outliers and overall low confidence intervals, but it's unusual to talk about these as problems for scaling tiny animals. We're generally much more used to these frustrations when trying to scale smaller animals to the size of giant adults. 

And strange as it seems, I admit to finding Currie’s stilt-limbed tyrant baby a more profound example of these issues than our usual subjects of scaling woes, like titanic sauropods or giant pterosaurs, because we know so much more about small dinosaur proportions. It's easy to spot these data as (probably) “wrong” because they're so out of the ordinary, but concerning proportions are harder to intuitively identify in animals beyond the size limits of anything ever witnessed by a person. It's a good reminder that any extrapolation is viewed as shaky from a mathematical perspective, and recalls Knut Schmidt-Nielsen's comments in his classic 1984 book Scaling: why is animal size so important: "unless we fully understand all the pertinent factors involved (and that is not likely to happen in a biological system), going beyond the limits of observation is not simply chancy, but outright perilous” (p. 25). It’s perhaps only when we see relatable, but obviously wrong-looking reconstructions like the one above that we’re confronted with this reality. And while we basically have no choice but to extrapolate and go beyond data limits when dealing with certain unknowns in the fossil record, it's good to come back to Earth from time to time and realise the unreliable nature of the mathematics we're using. So many extrapolations we're familiar and comfortable with might be just as crazy as that lanky-limbed hatchling, we just don't see them as obviously "wrong". 

All this said, that stilt-legged tyrant baby still has some utility. While it probably doesn't genuinely reflect what baby tyrants looked like, it does serve as a great visualisation of the allometry expressed through tyrannosaur ontogeny. If we compare the stilt-legged model with a regular-old T. rex, for instance...

The mad stilt-legged hatchling vs. a large adult Tyrannosaurus, based on "Sue".
...we get a good sense of how tyrant bodies grew into their legs as they progressed from hatchling to adults. We can also see that the head length remained about proportionate to femur length and that the arms grew relatively slowly, appearing to "shrink" a bit en route to adulthood (Currie 2003). Of course, in detail, there's actually a mosaic of different allometries occurring through growth: the head doesn't lengthen proportionately, for instance, but it does deepen. The arms and legs don't really "shrink" as one unit, either, but actually at varying rates in different parts of each limb (Currie 2003). Because the stilt-legged hatchling is our understanding of tyrannosaur scaling regimes expressed to an absurd degree, the reality of tyrannosaur ontogeny probably wasn't quite as extreme as the graphic above suggests, but it might not be too far off. Both Russell's (1970) and Currie's (2003) data point to long-legged, shallow bodied tyrant hatchlings and that's the model we should generally follow, even for chunky, robust animals like T. rex and Tarbosaurus. As noted by Currie in the same 2003 paper, "allometric differences among mature specimens of different [tyrannosaurid] species are shown to be trivial when compared with the allometric differences associated with growth". The stilt-legged tyrant (and more recent work and studies on this same topic) makes that crystal clear.

Currie's paper is now almost 20 years old so, to wrap this up, one last question: have we made any progress in being able to reconstruct baby tyrants reliably in recent years? To be frank, no, we don't yet have the data needed to clear the problems outlined above. Things have moved ahead thanks to Greg Funston and colleagues (2021) who, finally, have been able to factor some embryonic tyrant fossil material into their scaling equations. These have generally pointed to animals of the same size and shape as predicted by Currie and Russell, but their 95% confidence intervals (CI) for many predictions are still enormous (which means, in plain terms, that the true proportions may have been very different to the predicted ones). For instance, Funston and colleagues scaled their Albertosaurus embryo dentary to a body length 715 mm, but with a CI range of 496–897 mm. Their (seemingly) larger Daspletosaurus specimen, represented by a toe claw, scaled to 1101 mm long, with a CI of 250–5954(!) mm. Estimates for their femoral lengths were also not well constrained, at least in Daspletosaurus, with CI values of 76–256 mm. Some of the upper ranges of these CIs are consistent with larger tyrant specimens that are already several years old, and they're thus far from the measurements we'd expect from embryos or hatchlings (Funston et al. 2020). Our most charitable assessment is that we're consistently getting the same basic signals about tyrant hatchling form, so we're probably on the right track, but we have a long way to go before we'll have reliable body proportion predictions for tiny tyrants. The discovery of more small tyrannosaurids would go a long way to helping this but, of course, a skeleton of an embryo or hatchling would be the best and most direct way to resolve any uncertainty. 

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  • Currie, P. J. (2003). Allometric growth in tyrannosaurids (Dinosauria: Theropoda) from the upper Cretaceous of North America and Asia. Canadian Journal of Earth Sciences, 40(4), 651-665.
  • Funston, G. F., Powers, M. J., Whitebone, S. A., Brusatte, S. L., Scannella, J. B., Horner, J. R., & Currie, P. J. (2021). Baby tyrannosaurid bones and teeth from the Late Cretaceous of western North America1. Canadian Journal of Earth Sciences, 58(9), 756-777.
  • Russell, D. A. (1970). Tyrannosaurs from the Late Cretaceous of western Canada. National Museum of Natural Sciences, Publications, in Paleontology, 1, 1-34.
  • Schmidt-Nielsen, K., & Knut, S. N. (1984). Scaling: why is animal size so important?. Cambridge university press.

Saturday, 30 April 2022

Introducing The Art and Science of the Crystal Palace Dinosaurs: out next month!

Behold, the cover of The Art and Science of the Crystal Palace Dinosaurs, available for preorder now, and on general sale next month!

Next month sees the publication of what might be one of the more important projects I’ve ever been involved with: a new book, The Art and Science of the Crystal Palace Dinosaurs, co-authored with Ellinor Michel and published by Crowood Press. This is a large, richly illustrated hardback that, as the title suggests, discusses the creation, scientific content, artistry and historic legacy of the world-famous Crystal Palace Dinosaurs, a story we tell in lots of detail and with hundreds of photos, illustrations and diagrams, both vintage and modern.

The good news is that, as of a few days ago, the book became officially available for preorders so palaeoart and history of science aficionados can start bagging copies for delivery next month. The exact publication date has been hard to pin down because of the many global incidents disrupting shipping and transportation, but mid-May is looking like the point when it will be available. You’ll be able to pick it up from just about wherever books are sold, but, with apologies to North American readers, you’re going to have to wait a bit longer for your release as you’re on a different distribution network to us here in the UK (that’s not to say you can’t order it from Europe and have it shipped over to you, of course). The cover price is £30 and, as we’ll detail more below, every sale directly contributes towards the care and maintenance of the Dinosaurs themselves.

With preorders now being taken, we can finally start to talk about our book more openly. The Crystal Palace Dinosaurs can be described, without exaggeration, as some of the most famous pieces of palaeoart in the world and they are true mainstays of dinosaur books and documentaries. They encompass a series of Victorian prehistoric animal sculptures and recreated geological features based in Penge, in the southeastern suburbs of London. The most famous components of the site are the prehistoric animal models, which were built between 1852 and 1855 by their chief architect and artist, Benjamin Waterhouse Hawkins, ostensibly under the watchful eye of Victorian palaeontological mastermind Richard Owen. Much of the original site is still with us today and can be visited freely if you want a glimpse of what cutting-edge palaeontology looked like in the early 1850s. Of the 30 sculptures still standing, the four dinosaurs, representing Iguanodon, Megalosaurus and Hylaeosaurus, are genuine icons of 19th century palaeoart, and a large amount of effort has been exerted over the years to keep the site in fair condition (though read on).

The face that launched this particular ship: the broken Crystal Palace Megalosaurus, as photographed by the Friends of Crystal Palace Dinosaurs in May 2020. As this image shows, the conservation risk to the site is very real and a sense of wanting to do something to help is what got this book rolling.

The origins of our book give a pretty good idea of our aims and hopes for this project. In May 2020 the jaws of the Crystal Palace Megalosaurus were severely damaged in a mysterious incident: the cause is assumed to be final succumbence to weathering or simply vandalism, or a combination thereof. Both, sadly, are common agents of deterioration at the site. The photos of the damaged sculpture shared online were pretty disheartening and, having been working with the Friends of Crystal Palace Dinosaurs to augment their website (you may remember a series of blogposts I wrote related to this project from 2019: part 1, 2, 3 and 4), I wondered if turning my notes and illustrations into a book that we could sell to benefit the sculptures was a good idea. I floated this to Ellinor, who's chair of the Friends of Crystal Palace Dinosaurs, and we then approached Crowood, who you may know from my Palaeoartist’s Handbook and Emily Willoughby’s Drawing and Painting Dinosaurs, to make the project a reality. The pitch was to analyse the Crystal Palace Dinosaurs as an enormous palaeoart project where we looked at their conceptualisation, construction and legacy in context with 19th century palaeontology and palaeoartistry while also, in addition, creating a book that would directly benefit the Dinosaurs themselves. To that end, neither Ellinor nor I have received a penny for producing it: all the usual advances and royalties that go to book authors are instead being donated to the Friends of Crystal Palace Dinosaurs to further their efforts in understanding and maintaining the Dinosaurs and their home.

We finished writing the book in August 2021 and, I must admit, it was a lot more work than I initially anticipated. This not only reflected the complications of writing a book during Covid-induced national lockdowns but also the volume of material to discuss. Ellinor and I are far from the first scholars to write about the Crystal Palace Dinosaurs, with notable contributions to the literature having been made by Martin Rudwick (1992), Peter Doyle (Doyle and Robinson 1993, 1995; Doyle 2008), Jim Secord (2004), Gowan Dawson (2016), Valerie Bramell and Bob Peck (2008), and Steve McCarthy and Mick Gilbert (1994). Our palaeoart-focus, aided by the modern searchability of digital archives, meant we were able to unearth a lot of obscure details about the Dinosaurs not mentioned elsewhere. My initial thoughts that this would be a quick and straightforward project — perhaps not much more than expanding and stapling my blog series together and writing a few discussion chapters — quickly evaporated when the amount of information to sift through and analyse became apparent. The book ballooned by 20,000 words from my initial projection and it was still a squeeze to get everything in. My somewhat immodest view is that we’ve compiled a new, richer synthesis about the Crystal Palace Dinosaurs through both our own findings as well as coalescing important points raised by other recent authors into our text; in doing so, we’re helping to establish a deeper narrative about this familiar, but still only partially understood site.

A sneak peek at one of the early chapters of the book, focusing on the 1853 New Year's Eve banquet held inside the clay mould of the standing Iguanodon.

Wrangling the story of the Crystal Palace into some sort of order created a book of three parts and 13 chapters:

Part 1. Islands covered by strange figures

1. Historic prehistory in South London

2. Ancient worlds through a Victorian lens: planning the Geological Court

3. Bricks, iron and tiles: rebuilding the past

Part 2. Animals long since extinct

4. The sculptures: Mammals

5. The sculptures: Mosasaurus hoffmanni

6. The sculptures: Flying reptiles

7. The sculptures: Dinosaurs

8. The sculptures: “Teleosaurus chapmani

9. The sculptures: Enaliosaurs

10. The sculptures: “Labyrinthodon

11. The sculptures: Dicynodon

Part 3. A difficult and, perhaps, too bold, attempt

12. The reception and legacy of the Geological Court

13. Past becomes future: the conservation of the Geological Court

You can gauge a lot about the book from that chapter list but, to get a superior sense of what we cover, let’s go into a little more detail.

Part 1. Islands covered by strange figures

The first section serves as an introduction to the world of the Crystal Palace Dinosaurs by discussing the principles and individuals behind their construction as well as the building of the site itself. Very quickly within the narrative, we establish that the label “Crystal Palace Dinosaurs” is not always useful or apt because it omits the major structures that accompanied Hawkins’ palaeontological sculptures: the Geological Illustrations. These are a series of reconstructed geological outcrops that extend around the Dinosaurs' landscape, being created either by importing tonnes of rocks chosen for their age and fossil content from sites around the UK or, alternatively, by recreating complex sedimentary strata using building materials. These rocks were not distributed haphazardly around the park, either, but in realistic stratigraphic congruence: in other words, they are in proper geochronological order, such that Triassic rocks are next to Jurassic rocks, which are then next to Cretaceous rocks, which are then next to "Tertiary" rocks and so on, and the palaeontological sculptures were placed around these in an appropriate geological context. The almost uninterrupted sequence (there are deliberately no Permian rocks) allows visitors to walk continuously from the Devonian to the Quaternary, seeing signature rock types and fossil species along the way.

Our map summarising the full extent, both planned and actual, of the Geological Court. Note the complexity of the geology as well as large numbers of missing models, denoted by red graphics and text, and the extent of never-realised models on the Tertiary Island.

Mapping the strata as real geological features reveals a very sophisticated and complex arrangement of manufactured geology, even incorporating simulated unconformities (missing rock layers, which account for the absence of Permian features) and faults to condense much of the geological column, as it was known in the 1850s, into a small area (Doyle and Robinson 1993). The economic importance of geology to Victorian culture was highlighted with not only a partly artificial coal seam (real coal, partially fake rocks) but a motherflippin’ artificial mine and cave, some 20 m long, within which manufactured stalactites and floatstones, along with mining tools, gave visitors the experience of traversing a real lead mine. The unsung heroes of this forgotten aspect of the park were geologists David Thomas Ansted and James Campell, and we suggest that they need as much recognition as Hawkins or Owen for their contributions to this project. Reflecting this, we mostly refer to the “Geological Court” instead of “Crystal Palace Dinosaurs” throughout the text. This was the name originally given to Crystal Palace’s combined geological and palaeontological display and better encapsulates the full extent of the project. The Geological Illustrations receive a lot of attention in our book, for which we need to tip our hat to Peter Doyle for laying critical interpretive groundwork that we could build on (Doyle and Robinson 1993, 1995; Doyle 2008).

Today located far away from public footpaths is the Carboniferous Mountain Limestone, which contains an artificial cave and lead mine. This is one of the most complex of all the Geological Illustrations and it's also huge: the original Mountain Limestone "outcrop" represented 90 tonnes of real Carboniferous limestone imported from Matlock, in the UK Midlands. This was removed in the mid-20th century so the Mountain Limestone you see now (including in this photo) is a reconstruction from the early 2000s. The cave is original, but is now half-filled with sediment and inaccessible to the public.

Our opening chapters also offer a deep dive into the construction of the models themselves, both in terms of the palaeoartistic principles employed by Hawkins as well as the physical building process. We speak a lot about the importance of 19th century “anatomical correlation” in predicting the life appearance of fossil animals from scrappy bones (Dawson 2016) and analysed photographs and illustrations of the models under construction — some familiar, others less so — to obtain new details of how these often gigantic creations* were assembled. It seems there was no one method behind their realisation, but a mix of techniques that probably depended on practical considerations as well as the availability and cost of materials. The Megatherium was unqiuely carved from blocks of limestone (Doyle 2008) while most of the models were composites of bricks, concrete and metal that could be moved about the site on carts and trollies. The dinosaurs were constructed more like houses, adding bricks, mortar and concrete around deep foundations and enormous iron frameworks (Hawkins 1854). The construction of the Court took place under the eager eyes of international media, and we also use these early chapters to review this interest in the Geological Court. Part of this discussion focuses on the famous 1853 New Year’s Eve banquet in one of the clay Iguanodon moulds. This event has been retold so often that a certain amount of truth has leaked from the original story but, using newspaper accounts and archive material, we think we’ve managed to tidy up what truly happened and answer obvious questions, such as how several dozen people squeezed into a very large, but not enormous dinosaur belly (spoilers: there was an adjoining table, so not everyone sat within the Iguanodon itself. See this Twitter thread if you’d like to know more).

*And I do mean “gigantic”: the Megalosaurus is 12 m long and the Iguanodon and Temnodontosaurus are not much smaller. Photos don’t convey how seriously big some of these sculptures are, and another novelty of our book is providing basic measurements of each one, an obvious aspect to report but, to our knowledge, unrecorded until now. My boots are still drying out from wading through the waters surrounding the marine reptiles.

Part 2. Animals long since extinct

The middle of the book is a sculpture-by-sculpture analysis of the palaeontological creations, comprising the mammals, the various marine reptiles, the pterosaurs, dinosaurs, amphibians and Dicynodon. This is the longest section of the book and perhaps the main draw for palaeoart fans. Alas, we still don’t have much insight into Hawkins’ original plans for his sculptures — no relevant notebooks, sketches or correspondence to this effect are known anywhere — but efforts were made to “reverse engineer” the palaeoartistry of each model by comparing what Hawkins produced against palaeontological science of the 1850s. This was similar to the approach I used in my Crystal Palace Dinosaurs blog posts but we go way beyond the details discussed in those articles. Each sculpture is given a photographic montage to show features of interest as well as a diagram showing what fossil specimens or modern animals likely referenced each body part.

An example of the breakdowns given to each restored species at Crystal Palace: what fossils were available to inform Hawkins' restorations? Here, we see how the Iguanodon is really a hodgepodge of different iguanodont material, and not a reconstruction of a single species.

Analysing the sculptures at this level allowed us to break down their “real” identities, and we can see today that many were chimeric mixes of different species. "Labyrinthodon pachygnathus", for instance, can be considered an early attempt at reconstructing the (possible) ctenosauriscid (those neat sail-backed croc-line archosaurs) Bromsgrovia rather than a prehistoric amphibian, and the known reference specimens for Iguanodon do not include any “true” Iguanodon material in the sense that we recognise it now. It’s actually difficult to know what to classify the Iguanodon as in a modern sense, as at least two, and maybe three iguanodont species were factored into its restored form. If we force the issue, Barilium dawsoni, a large iguanodont that was used to establish the size of the Iguanodon sculptures and other components of its anatomy, is perhaps the most dominant species used in the build, so maybe that’s the closest we have to the “true” identity of these sculptures.

Assessing the fossil composition of Hawkins' recreations allowed us to ally species to the Crystal Palace project that are not normally associated with it. They include the possible ctenosauriscid Bromsgrovia walkeri, which is too poorly known to restore itself, but might have resembled Arizonasaurus babbitti. This is a nice reminder that the British fossil record contains a lot of remarkable animals, even if some of their fossils are less than exemplary.

We also compare each species with modern interpretations of the same taxa, and I used these sections as an excuse to sneak in some of my own artwork to show 21st views of the Crystal Palace species. These are all-new restorations rather than recycled images from my 2019 blog posts, and some feature fun callbacks to classic Hawkins imagery. It’s easy to be a little blasé about some of the Crystal Palace taxa because many are well-trodden palaeoart subjects, like Megalosaurus, Megaloceros, Iguanodon etc., but the reality of some of the animals restored for the Geological Court is pretty wild. Leptonectes, for instance, with its grumpy face and massive pectoral fins, is definitely an unusual ichthyosaur, while Cimoliopterus — the animal behind the Chalk pterosaurs — belongs to the long-winged, giant-headed pterosaur group Ornithocheiromorpha. Among everything else, this book was a nice opportunity to draw attention to some lesser-known British fossils that, owing to being poorly preserved, are often overlooked.

I created something like 30 new paintings for The Art and Science of the Crystal Palace Dinosaurs, including this image of the uppermost Triassic ichthyosaur Leptonectes tenuirostris. This reality of this frowny-faced, giant-flippered ichthyosaur is quite different to what was restored at Crystal Palace, where it looks a lot more conventional.

Looking at the sculptures in such detail allowed us to write at length about how excellently executed they are, from their depicted musculature and fine anatomical detailing to their considered behavioural depictions. Hawkins was really ahead of his time by creating palaeoart that showed plausible, realistic-looking animals rather than, as was then common, either super-conservative reconstructions with minimal detailing or, more commonly, fantastic restorations that have more in common with mythology than zoology. Interestingly, we did find evidence that Hawkins considered more aggressive and dynamic posing for at least some of his models before settling on their more sedate poses.

We also compared Hawkins' work to Owen’s publications to gauge how closely Hawkins was working with his consultant. The large number of deviations we found is, we argue, further evidence of Owen being a pretty useless consultant. Owen's contributions to the project have been enormously overstated, with records showing that he neglected to visit the construction site or Hawkins' workshed outside of a handful of instances, and that was also largely ignorant of the appearance of the sculptures until he saw them completed and installed in the park grounds (Secord 2004; Dawson 2016). That Hawkins made some errors Owen could have corrected is entirely consistent with this narrative. Owen also loses points in our dissection of his 1854 Geological Court guidebook, which is often inconsistent with the content of the site itself. Indeed, Owen’s slim overview of the site didn't mention major components of the display, including the bulk of the Geological Illustrations and mammal sculptures. Owen doesn’t quite warrant writing out of the history of the Geological Court, but he definitely needs recasting as a peripheral character who did little to help Hawkins and the Crystal Palace Company accomplish their goals.

The missing paleontological sculptures of Crystal Palace: two pterosaurs, three "Anoplotherium gracile", one Palaeotherium magnum and one female Megaloceros (red arrow). Note the different face on "Palaeotherium minus" and the real antlers on Megaloceros; both have since been replaced with substitutes that no longer resemble the originals. The photographs in this image were kindly provided by the Crystal Palace Foundation.

The final, and perhaps most significant, component of these chapters I want to mention is their discussions of missing models. Exactly how many models and the number of different species they represent has been variably interpreted (e.g. Doyle and Robinson 1993; McCarthy and Gilbert 1994) because of the complex and tumultuous history of certain sculptures. Some have been moved about, mislabelled or even been removed from the site over the last 170 years, leaving researchers to draw different conclusions about what’s left in the park today, and what was there originally. We attempted to get definitive numbers on both counts and concluded that our modern Geological Court holds 30 sculptures of 21 species. In 1855 however, when the Court was at its most complete, it had 37 sculptures and 24 species. That’s a higher count than any previous calculation, but one we’re confident about thanks to data from historic guidebooks, illustrations and photographs. The seven lost models include a fourth Megaloceros (specifically, another model of a reclined doe), the two Jurassic pterosaurs, the large Palaeotherium species P. magnum and, finally, three models of “Anoplotherium gracile”.

The "Megaloceros fawn", which we reidentify as a different animal entirely: "Anoplotherium gracile" or, in modern terminology, Xiphodon gracilis. As explored more below, there is no evidence that this animal represents a juvenile Megaloceros but plenty of evidence to tie it to Xiphodon. How and why this sculpture became associated with the Giant Deer display is not currently understood.

The existence of the latter three sculptures is worth going into a little more because it’s one of our biggest discoveries and ties into another important conclusion. If you’ve visited the Crystal Palace Dinosaurs you’ll know that a small Megaloceros fawn sits close to the three surviving Giant Deer adults in the Quaternary end of the Court. We present evidence that this, in fact, is not a juvenile deer at all, but the sole survivor of a group of four “Anoplotherium gracile”. Known as Xiphodon gracilis today, the presence of this guanaco-like Eocene species among the Crystal Palace fauna has long confused researchers because, despite being mentioned in several guidebooks, it was thought that no obviously Xiphodon-like animals were known at the site, nor were any witnessed in familiar vintage photos or illustrations. Some authors have attempted to reconcile these facts with a more gracile Anoplotherium commune sculpture, assuming that this represented Xiphodon (Doyle and Robinson 1993; McCarthy and Gilbert 1994), but I’ve never found this interpretation convincing. Even in the 1850s scholars knew that A. commune and Xiphodon contrasted in size, build and proportions. The “fawn”, however, is a dead-ringer for historic takes on Xiphodon anatomy, and an image of Hawkins’ workshed shows this same sculpture with three others of the same species (above). Conversely, we found no evidence whatsoever of a Megaloceros fawn existing at the site before modern times. Putting these pieces together, it looks like the blank spots in the history of the displays are large enough to both obscure the loss of three Xiphodon sculptures and also hide the relocation of the surviving Xiphodon alongside the Giant Deer, where it has masqueraded as a juvenile Megaloceros for the entirety of living memory. I admit to finding this as worrying as I do exciting. Discovering not just one Xiphodon but records of four is very cool, but it also shows how enormous the holes in our knowledge of the Geological Court are. If something as fundamental as the existence of a whole set of sculptures can go virtually unrecorded, what else are we missing?

Part 3. A difficult and, perhaps, too bold, attempt

The last section contains two chapters, one on the complex legacy of the Geological Court and another on its constant battles with degradation. The chapter on the post-development history of the Crystal Palace Dinosaurs is one of the largest in the book and attempts to make sense of a complicated story. It’s fair to say that they were neither the major successes nor major failures they have been portrayed as by different authors, and reactions to the Geological Court have fluctuated enormously in the last 170 years. Early scientific views, for example, were very hostile. Hawkins’ rapidly-dating sculptures vindicated palaeoart sceptics who saw full, elaborate restorations of extinct life as premature and, as has been noted by others (Secord 2004; Nieuwland 2019), the Geological Court seems to have lessened appetites for palaeoart among many, perhaps most, 19th century palaeontologists. It took decades for more sympathetic views to develop among academics (e.g. Hutchinson 1893; Becker 1911) and for palaeoart to regain its early 19th century mojo. Among the public, the Geological Court was a source of equal parts fascination and confusion, as the displays — which lacked any sort of signage or explanation, as per Crystal Palace Company policy — represented content too far from general knowledge for lay audiences to grasp their significance. Some gathered that they were looking at animals that existed before humans (Martineau 1854), but others thought they were grossly-distorted sculptures of living species, or even attempts to show the dangers of intoxication (Owen 1894). As well as cataloguing this diversity of opinion, we also cover the cancellation of the Geological Court’s development, the unrealised models and geological components (in addition to at least a dozen more mammals and birds, planned works included additional Cambrian, Silurian and “Tertiary” Geological Illustrations), vintage Crystal Palace Dinosaur merchandise, and the career impacts of the project for Hawkins and Owen.

A selection of dinosaur palaeoartworks produced after Crystal Palace. It took several decades for scientists to start regularly commissioning artwork of new fossil animals, allowing Hawkinsian dinosaurs to linger in paleoartworks until the late 19th century, as in the lower right images. Novel reconstructions of upright dinosaurs were produced as early as the 1860s (top images), but were rare until palaeoart got its mojo back in the 1890s. Was the scientific backlash against the Crystal Palace Dinosaurs responsible for this dearth of new artworks? There is certainly circumstantial evidence supporting this view.

All this leads to our final chapter, the inevitably stern-faced discussion of the site’s ongoing conservation and maintenance issues. It would have been nice to end the book on a more positive note but it would have been misleading to portray anything other than the truth: that our collective efforts to keep the Geological Court in good condition have not been exemplar and, unless this changes, the long-term outlook for the site isn’t great. We review the patchy conservation history of the site and highlight that no consistent approach to maintenance has ever been followed: repair work has really been a series of occasional interventions, not a routine, regular event. Even more amazingly, outright destruction of some components were justified in the mid-20th century to make way for other Park developments. We can’t be sure, but we think these events were likely responsible for the removal or destruction of the missing palaeontological sculptures. These issues have persisted to modern times and it's a sad fact that the current appearance of the site we're attempting to celebrate is rather sorry. We often had to source photos from the last decade to illustrate the displays in a more intact, less overgrown condition.

A shot from my last visit to the Geological Court in July 2021, showing the extent of overgrowth and degradation among some of the marine reptiles. To give a sense of the scale of the vegetation in this photo, that middle ichthyosaur is one of the largest models at the site: the c. 12 m long Temnodontosaurus. The broken jaw of Ichthyosaurus communis, which you can see in the background, was a recent incident which has now been fixed. Needless to say, allowing the displays to get to this state is pretty criminal, and without a significant, long-term change to maintenance and conservation approaches, we risk losing the site forever.

Thankfully, the Crystal Palace Dinosaurs are now protected against further wanton development by having attained Grade 1 listed status. This recognises the Geological Court as having exceptional historic interest and brings a level of care and protection from Historic England, the public body that manages places of national importance to English heritage. Much is hoped from this relatively recent development and projects to save the site are underway, but we shouldn’t pretend there isn’t a lot of work to do. Behind the visibly crumbling displays are problems as fundamental as subsidence and complex internal damage caused by degradation of their metal frameworks. In addition to dramatic interventions to solve these problems, a regular management strategy to keep on top of perpetual conservation risks is also critical. Without interventions to halt plant growth on the displays and deter human trespassers, the Dinosaurs and Geological Illustrations will quickly fall back into disrepair. Ensuring that the Geological Court endures for another 170 years will not be easy or cheap, and requires a broad shift in how we value the site as a nation. Today, we’re perhaps at a critical point for deciding its future. If we don’t invest our energy and money now, we may be among the last generations to witness something approximating its original grandeur.

TL,DR: buy our book; learn cool things; save some dinosaurs.

And that, in a several thousand-word nutshell, is our book. But this post is really just a teaser of what we have to say: there is so much more to discuss around the Crystal Palace Dinosaurs that we struggled to get everything into this one tome. But for all this, there’s still plenty that we couldn’t write about, because there are enduring mysteries that we were unable to crack. What, for example, are the mysterious Wisbech Museum models of the Crystal Palace species? Do we really not have a single record for what happened to all those palaeontological sculptures, not even in some council development office somewhere? Why were so many models repaired with unsuitable replacement parts at some point in the 20th century? Will anyone, ever, find some of the original designs for the Geological Illustrations or extinct animal restorations? These, and other questions, are for future researchers to look into. For now, we’re happy to have moved the conversation along as far as we have, and to once again be shining the light on the conservation plight of a site unique in its significance to the history of science. We’re especially happy because all this will simultaneously help fund the Friends of Crystal Palace Dinosaurs and their work monitoring and maintaining the Geological Court. Check out The Art and Science of the Crystal Palace Dinosaurs if you want to appreciate the full awesomeness of this very special place.

And finally…

As a quick closing comment, I want to extend a quick personal thanks to a group of people who made this book possible: the folks who support my work at Patreon. Researching, writing and illustrating a book is a huge amount of work and the only way I could commit so much time to a charity project like this was through their monthly donations. So sincere thanks to everyone who supports me there: any positive impact this book has is, in part, related to your continued donations.


  • Becker, H. (1911). Alte und neue Rekonstruktionen ausgestorbener Tiere. Die Umschau.
  • Bramwell, V., & Peck, R. M. (2008). All in the bones: a biography of Benjamin Waterhouse Hawkins. Academy of Natural Sciences.
  • Dawson, G. (2016). Show me the bone: reconstructing prehistoric monsters in nineteenth-century Britain and America. University of Chicago Press.
  • Doyle, P. (2008). A vision of ‘deep time’: the ‘Geological Illustrations’ of Crystal Palace Park, London. In: Burek, C. V. & Prosser, C. D. (eds). The History of Geoconservation. Geological Society Special Publications, 300(1), 197-205.
  • Doyle, P., & Robinson, E. (1993). The Victorian ‘Geological Illustrations’ of Crystal Palace Park. Proceedings of the Geologists' Association, 104(3), 181-194.
  • Doyle, P., & Robinson, E. (1995). Report of a field meeting to Crystal Palace Park and West Norwood Cemetery, 11 December, 1993. Proceedings of the Geologists' Association, 106(1), 71-78.
  • Hawkins, B. W. (1854). On visual education as applied to geology, illustrated by diagrams and models of the geological restorations at the Crystal Palace. Journal of the Society of Arts (78): 443-449.
  • Hutchinson, N. H. (1893). Creatures of other days. Chapman & Hall
  • [Martineau, H.]. (1854). The Crystal Palace. Westminster Review, 62, 534-50.
  • McCarthy, S., & Gilbert, M. (1994). The Crystal Palace Dinosaurs: The story of the world's first prehistoric sculptures. Crystal Palace Foundation.
  • Nieuwland, I. (2019). American Dinosaur Abroad: A Cultural History of Carnegie's Plaster Diplodocus. University of Pittsburgh Press.
  • Owen, R. (1894). The Life of Richard Owen. J. Murray.
  • Rudwick, M. J. (1992). Scenes from deep time: early pictorial representations of the prehistoric world. University of Chicago Press.
  • Secord, J. A. (2004). Monsters at the crystal palace. In: de Chadarevian, S, & Hopwood, N. (eds). Models: the third dimension of science. Stanford University Press. 138-69 pp.

Wednesday, 30 March 2022

Tyrannouroboros: how everything old is new again in recent proposals of Tyrannosaurus taxonomy

Tyrannosaurus engages in some closed-mouth vocalising, but which species of Tyrannosaurus is this? It might seem that, up until recently, there would be only one answer, but this is actually an old question dating back to at least the early 1970s. Hey, writing about this sounds like a fun idea for a blog post. Oh look, someone else thought so too - read on...

Even aliens living on the far side of the Moon are aware that, last month, independent researcher and palaeoartist Gregory S. Paul led a team of authors proposing that our traditional take on Tyrannosaurus rex was wrong. According to Paul et al. (2022), this classic genus does not contain just one species, but actually three: the stocky, geologically older T. imperator, and two descendant, coexisting younger species, T. rex and T. regina. As documented in the New York Times and elsewhere in numerous articles, the response from tyrant dinosaur experts was not enthusiastic; to the contrary, most workers concluded that the study was underwhelming and unlikely to change the status quo. It’s not my intention to provide a detailed breakdown on this paper as relevant experts have already done this in recent weeks on various news and social media sites. It'll suffice to say that, while some of the ideas floated by Paul et al. are certainly interesting, the vague, very short diagnoses of the three species, the failure to provide strong statistical support for “robust” and “gracile” morphotypes within our T. rex inventory, and the inability to assign several well-preserved partial skeletons to the new species will likely prove sufficiently problematic to prevent widespread adoption of this new scheme. I hear a response is already being written.

But one, perhaps surprising, reaction to Paul and colleagues’ (2022) research is that most experts really weren’t shocked by the idea of several species within the T. rex hypodigm, and several even remarked that the idea itself is plausible even if our data, for the time being, do not support it. While the exact geological longevity of Tyrannosaurus rex is open to question (Paul et al. 2022), it was at least around for close to one million years (Brusatte and Carr 2016) and existed in varying habitats across a wide spread of western North America, from southern Alberta to the Texas/Mexico border, and from Utah to the Dakotas (Sampson and Loewen 2005). Compared to other theropods, that’s a broad spatiotemporal spread and one that could conceivably contain hitherto unappreciated variation that requires close analysis to uncover.

And it’s this topic of looking closely at our T. rex sample that I want to discuss today. It might seem that Paul and colleagues’ proposal is a radical dismantling of a fossil icon, and, indeed, this status is emphasised by Paul et al. themselves, who remark in their supplementary data and press work that they are “likely to displease many who are enamoured with the tyrant lizard king Latin moniker”, but that their "mini-revolution" will “force people to face the issue”. But, viewed more broadly, their study is actually only the latest in a long line of research that has expanded or shrunk our inventory of T. rex fossils and toyed with the idea of multiple Tyrannosaurus species. Indeed, even the features said to characterise the T. regina, rex and imperator are familiar from older publications (e.g. Larson 2008a). The result is that, when reviewing older literature on Tyrannosaurus taxonomy in light of these recent discussions, it’s difficult to avoid a sense that these seemingly-new ideas are not only re-treading old ground, but maybe even tripping over it.

T. rex taxonomy: the early(ish) years

Graphic summary of the classification of Tyrannosaurus specimens (cranial material alone shown here) in the late 20th century. This illustration and those that follow do not represent the entirety of T. rex material known at any one time, but focus on named T. rex specimens that have been proposed as distinct taxa at one time or another. Note the comment below on the spelling of "stanwinstonorous", as some confusion surrounds this.

Despite the long-held celebrity of Tyrannosaurus and it being known to science for over a century, most of what we’ve learned about this animal has been discovered in the last 30 years. In fact, little of note was published on T. rex during the mid-20th century and only a few significant specimens were uncovered (Larson 2008b). This corresponds with little taxonomic work and means we can skip ahead to start this story around 1970. Tyrannosaurus fans will realise that this omits discussion of the historic taxa “Dynamosaurus” and “Manospondylus” but, given that they were satisfactorily dismissed by Osborn (1906, 1917) and have no chance of being revived today, we can gloss over the earliest history of T. rex studies with only one important note: rushed as it was, Henry Osborn’s (1905) naming and type designation for Tyrannosaurus rex were extremely solid. So remember that, in spite of everything that follows in this article, and whatever else future generations have to say about the number of Tyrannosaurus species, T. rex itself is not going anywhere.

Rushing through that earliest period of Tyrannosaurus research puts us in the mid-20th century when, following a world war-induced hiatus in North American palaeontology, collectors and researchers returned to the field during the 1960s and ‘70s to resume exploration of American fossil resources. Among many important discoveries were new specimens of Tyrannosaurus and, at this point in history, each one was significant because T. rex was still only represented by a few examples. As our sample size grew from a few to a handful, and then to a dozen and more, it became apparent that no two T. rex individuals were exactly alike: T. rex evidently held a large amount of intraspecific variation within its population (Carpenter 1990). With this observation came the question of how much difference could be permitted in these fossils before specimens could no longer be identified as T. rex. The first rumblings on this never made it to print but were included in an unpublished 1972 thesis by then-student Douglas “Quetzalcoatlus” Lawson, who named Tyrannosaurusvannus” for a relatively small, seemingly unusual tyrannosaurid maxilla from the Texan Javelina Formation. T. “vannus” never became “official” in the eyes of zoological nomenclature because it was never formally published and, in any case, Lawson revised his interpretation soon after, referring the same bone to T. rex itself (Lawson 1976). But in a later, 1990 review of T. rex variation, Kenneth Carpenter independently opined that this maxilla might represent a distinct southern Tyrannosaurus species. Others (Brochu 2003; Carr 2020) have been less convinced that it represents a new species, with Brochu (2003) suggesting that if the Texan maxilla was not T. rex, it must still represent a very close relative.

FMNH PR2081, better known as "Sue", represents one extreme of Tyrannosaurus form in being an especially large and robust example of the genus. These features have seen this specimen (shown here in its older, more prominent place in the Field Museum of Natural History) at the centre of many discussions of T. rex diversity and disparity. Photo by Connie Ma, from Wikimedia, CC BY-SA 2.0.

This was only the start of the buzz circulating around the concept of Tyrannosaurus having multiple species, which gained further traction in the 1980s. Again, the amount of variation in T. rex specimens was generating conversation, and both Horner and Lessom (1993) and Larson (2008) give Robert Bakker credit for observing features in Tyrannosaurus skeletons that might distinguish certain morphotypes from others. It’s reported that Bakker was so confident in this that only a slightly increased T. rex sample size might have seen him formally propose more Tyrannosaurus species before the turn of the millennium. It was perhaps these rumours and conversations that prompted Paul (1988) to muse on multiple Tyrannosaurus species in his influential book Predatory Dinosaurs of the World. Despite acknowledging variation in T. rex dentition and limb structure, Paul concluded that no, the Tyrannosaurus specimens known in the late 1980s were not diverse enough to represent more than one species. But other researchers weren’t so sure. Molnar (1991) responded to Paul’s comments by questioning whether we had enough T. rex specimens to draw any firm conclusions about the number of species they really represented, and suggested that the question would remain open until we acquired more data. Others were more confident that Paul was wrong. Donald Glut (1997) recorded that researcher Stephen Pickering privately issued manuscripts in 1996 proposing that several T. rex specimens, including the famous “Sue” skeleton, represented a new species that he named Tyrannosaurus "stanwinstonorous"* after the special effects pioneer responsible for the animatronic dinosaurs in Jurassic Park and its sequels. Pickering argued that multiple features of the skull and the trait of adults being 6-7 % larger than Tarbosaurus or T. rex distinguished "stanwinstonorous" from other tyrannosaurs, but — as with Lawson’s T. “vannus” — lack of widespread publication prevented this name from entering scientific consideration.

*Added 31/03/2022: Pickering spelt this name "stanwinstonorum" in his original manuscripts, but Glut — which is where I obtained my information from — spelt it "stanwinstonorous". "stanwinstonorum" is thus the intended and "correct" spelling for this taxon, but the situation is confused by Glut's 1997 encyclopaedia being an ICZN-compliant publication, which Pickering's privately disseminated manuscripts are not. Ergo, "stanwinstonorous" is now mentioned in technical literature, while "stanwinstonorum" isn't. Given the informal status of stanwinstonorum/ous we probably don't need to worry about this too much, but this inconsistency is worth highlighting.

So, even as palaeontologists circled Tyrannosaurus looking for specimens to split from the T. rex hypodigm in the late 20th century, no formal proposals were published. But taxonomic acts relevant to T. rex were being carried out as smaller, often fragmentary North American tyrannosaurs that we’d eventually recognise as Tyrannosaurus were receiving names or reclassification. With some of these specimens having been found decades prior, fairly convoluted taxonomic histories are associated with them (see Carr and Williamson 2004 for a summary). Here, let’s just cut to the chase and list them with their final, accepted binomials: Dinotyrannus megagracilis (Paul 1988; Olshevsky and Ford 1995), Stygivenator molnari (Paul 1988; Olshevsky and Ford 1995) and — most famous of all — Nanotyrannus lancensis (Gilmore 1946; Bakker et al. 1988). Despite recognition that at least some of these species (D. megagracilis and S. molnari) were based on juvenile or subadult material, the idea that they may represent subadults of T. rex was not considered, and the validity of N. lancensis was hinged, to some extent, on it being a subadult or adult that reached maturity at a smaller size and lighter frame than T. rex itself (Paul 1988; Bakker et al. 1988). This thinking reflects, in part, a period in vertebrate palaeontology dominated by typological approaches where specimens were assigned to species based on morphology alone without factoring in the influences of growth or individual variation. Under such schemes, it was rare, though not unheard of (Rozhdestvensky 1965; Russel 1970), to ally juvenile theropod specimens with adult specimens.

A 21st century T. rex hypodigm

T. rex taxonomy made simple: everything is T. rex! There are, of course, dozens more specimens we could show here: this graphic only shows the skulls of specimens thought to represent different Tyrannosaurus species at one time or another.

A more holistic philosophy toward the classification of fossil species has, in the last few decades, replaced such thinking and allows us to realise that, for example, a young juvenile specimen might look very different to an old adult. This can make characterising fossil species more difficult, but the results are more rewarding as we get more detailed and realistic insights into the life histories and ecologies of ancient animals. Such practices have typified most recent taxonomic work on Tyrannosaurus, emphasising the need to investigate features of specimen growth stage (e.g. bone fusions, histological evidence of specific age etc.) alongside morphology when considering what is, and what isn’t, Tyrannosaurus rex (e.g. Carr 1999, 2020; Carr and Williamson 2004; Woodward et al. 2020).

These works have shown that Tyrannosaurus was even more variable than initially realised, not only being differentiated in build and size as an adult but also looking entirely different as a juvenile. As is now well-known to Tyrannophiles, T. rex grew from a dog-sized, slender-snouted hatchling to a supersized, gnarly-skulled adult with unprecedented robustness among theropods. Carr (2020) characterises T. rex growth as undergoing “secondary metamorphosis” at the onset of sexual maturity, in which it transformed from a slender, “bird-meets-horse” juvenile body plan to a robust, deep-snouted, massive-bodied adult form. The result is an interpretation of Tyrannosaurus rex that occupied a range of disparate anatomies throughout its lifespan, within which small tyrants like “D. megagracilis” and “S. molnari” can be absorbed into a well-substantiated growth sequence (Carr and Williamson 2004). And yes, while a minority favour Nanotyrannus as a distinct taxon (e.g. Larson 2013), it also plots neatly into this system without issue (Carr 1999, 2020; Currie 2003; Woodward et al. 2020).

It's strange to think that this fleet-footed predator is the same species as that 6-10 tonne tank we were recently discussed as a head-butter, but the evidence that T. rex underwent this radical transformation is very strong. This dramatic transformation is also surely one of the major complicating factors in our attempts to unravel Tyrannosaurus taxonomy.

This hypothesis does more than just tidy up T. rex taxonomy. It also establishes that Tyrannosaurus was probably not a “normal” theropod in terms of its ecological role, and that there may be a good reason why this one species occupied such an expanse of time and space in Maastrichtian North America. The 30-odd year lifespan of one Tyrannosaurus encapsulated the ecological potential of several grades of predatory dinosaurs (Holtz 2021), and we might expect such an adaptable animal to have a long evolutionary history and wide geographic range. We might also predict an unusual amount of variation in our T. rex samples because, if this one species was undergoing such a transformation across three decades of growth, it would have transitioned through a large number of “morphs”. Coupled with distortion caused by fossilisation and the dusting of individual variation we’d expect among a reasonable sample of biological entities and we're going to find a lot of variation among our Tyrannosaurus fossils. It’s an interesting idea that explains a lot of weirdness around our T. rex sample, perhaps more parsimoniously than greater taxonomic granularity or sexual dimorphism. But on those topics…

Larson’s Tyrannosaurus x

Graphic summary of select skulls referred to T. rex and T. "x" by Larson (2008). As above, this is not a comprehensive assessment, but shows where important, name-bearing specimens end up in Larson's scheme.

Developing in parallel to this “everything is Tyrannosaurus” interpretation were research projects that argued to split T. rex apart. The drip of new Tyrannosaurus specimens that started in the 1960s and ‘70s had turned into a relative torrent in the 1990s, such that researchers of the 2000s had dozens of T. rex specimens to examine. This was a large enough sample that we had some hope of teasing more obvious trends or patterns out from the statistical noise of individual variation and we might, finally, get some perspective on whether T. rex was one species or several.

In 2008, Pete Larson specifically addressed this issue (Larson 2008a). He noted that some adult Tyrannosaurus skeletons can be much stockier and more heavily built than others and ascribed this to sexual dimorphism for a variety of reasons, most of which are now doubted. But he also highlighted variation in cranial pneumatic features, tooth counts and the number of small "incisiform" teeth at the front of their lower jaw. These, Larson argued, were more likely to be taxonomic differences. Only a few specimens possessed a full suite of distinctive features that separated them from T. rex proper, including the giant skull MOR 008, the privately-owned “Sampson” skeleton, and the iconic AMNH 5027. Larson set these aside from the T. rex hypodigm but erred on the side of caution by not establishing a new taxon: instead, he gave this potential second Tyrannosaurus species a nickname: Tyrannosaurus x”.

The holotype dentary of T. rex shows one small "incisiform" tooth in this photo presented by Larson (2008). The presence or absence of a second small tooth at the front of the lower jaw has been suggested to denote a distinct Tyrannosaurus species, but different authors disagree over the true variation of this feature.

The decade following Larson’s proposal has not provided much support for his suggested split in Tyrannosaurus specimens. In part, this reflects weak statistical support for the alleged taxonomic and sexual morphotypes. Joshua Smith’s (2005) assessment of T. rex dental characteristics and their utility in systematics can be seen as a blind test of size variation in the second dentary tooth, for instance, but failed to find significant characteristics of this in examined specimens. Mallon (2017) specifically looked for evidence of Tyrannosaurus sexual dimorphism along the parameters outlined by Larson but failed to find the sort of bimodal character distribution that would, in theory, result from differentiated sexes. More recently, Thomas Carr’s gigantic 2020 ontogenetic analysis of 44 T. rex specimens also found no taxonomic significance to Larson’s proposed dental and skull characters, nor did it recover evidence for sexual dimorphism. Moreover, it also failed to cluster the specimens ringfenced by Larson as T. "x". The size of Carr's analysis really has to be emphasised; by cataloguing up to 1850 features in 44 specimens, this investigation is, by far, the most in-depth analysis of anatomical variation within Tyrannosaurus (and maybe any dinosaur), and its failure to recover conclusions similar to those of Larson's 2008 study does not look good for the T. "x" hypothesis. Indeed, the scope and depth of Carr's investigation sets a high bar to clear for any different interpretation of T. rex variation, and that brings us to…

…Paul et al. (2022): the “mini-revolution for the dinosaur long universally called T. rex

The suggested T. rex taxonomy of Paul and colleagues (2022) and its potential fallout from collisions with older schemes. Again, this is not a comprehensive breakdown of which T. rex specimens go where in this taxonomy, it only shows the treatment of key, named specimens.

As will now be clear, a finger has been hovering over the big red button marked “new Tyrannosaurus species” for decades now, and someone, somewhen, was going to push it eventually. In this context we can see Paul et al. (2022) as simply being the team that took the plunge, offering to give yet another interpretation of Tyrannosaurus ;taxonomy by splitting T. imperator and T. regina from T. rex. And as will also now be clear to anyone familiar with Paul and colleagues’ arguments, there is a certain historic familiarity to some of their ideas: the characters used are very similar to those used by Larson for characterising T. "x"; specifically, regina, rex and imperator are distinguished by features of skeletal robustness and the number of smaller incisiform teeth in the lower jaw. To be fair, how these are quantified and measured is slightly different in Paul et al., but there's undeniable conceptual overlap. I suspect this is one reason the paper has not received the most enthusiastic response among tyrant dinosaur experts, who will not only have experienced a sense of deja vu from the concept of new Tyrannosaurus species but also immediately thought of those analyses which have already investigated and dismissed the taxonomic potential of robustness and dentary incisiforms. And, OK, we need to be careful not to be arrogant or dismissive in these considerations: it’s really easy to say “other analyses didn’t find this result, so you’re probably wrong”, but if a new paper is essentially arguing points that have already been shown as doubtful, it’s fair to point to the same studies that dismantled those ideas the first time around.

And it’s not only in character choice that the past might catch up with the conclusions drawn by Paul et al. As outlined above, T. rex taxonomy has enough history and complications under its skin that it’s hard to create, as Paul et al. attempt, a totally fresh Tyrannosaurus classification without running into leftovers from older proposals. For instance, Paul et al. refer the holotype of Dinotyrannus megagracilis to their new species T. regina, arguing that the megagracilis type is an incomplete juvenile specimen and thus a nomen dubium, and therefore unsuited to be the holotype for their new species. But, unless my understanding of ICZN rules is totally wrong, I’m not sure that’s how nomenclatural rules will shake out. For megagracilis to be identified as regina it must show at least some of the features Paul et al. assert are unique to T. regina; this being the case, it (theoretically) has features distinguishing it from T. rex as well. If a specimen can be identified to species level it cannot be a nomen dubium, and this should would allow megagracilis to re-enter the field as a valid, non-T. rex species. And if megagracilis is the same species as regina, then megagracilis has nomenclatural priority by 34 years: the "Tyrant Queen" becomes… "Tyrant Big Skinny". Note that megagracilis is also a Paul (1988) taxon, so it’s regina’s own senior author complicating the attempted, and admittedly pretty neat, emperor-king-queen naming scheme.

The imperator name is potentially at risk from an older name too, as highlighted by tyrannosaur expert/palaeontology social media machine Thomas Holtz in the New York Times. The holotype of Nanotyrannus lancensis stems from the lower portion of the Hell Creek Formation where imperator, according to Paul et al., is said to have existed independently from rex and regina. Given that the lancensis type specimen is clearly a juvenile animal, and most probably Tyrannosaurus (Carr 1999; Woodward et al. 2020), parsimony suggests it should be the same species as T. imperator. Paul et al. (2022) are non-committal about Nanotyrannus as a separate genus, noting its questionable status but not coming down on either side of the debate around its validity. But whether we regard the generic name as warranted or not, if Nanotyrannus is the juvenile of a stratigraphically older species of Tyrannosaurus, lancensis would have nomenclatural priority over imperator. The Tyrant Emperor would become humdrum T. lancensis.

Variation within Tyrannosaurus as illustrated by Paul et al. (2022): how many species do you see? What's worth noting in this graphic is that two specimens (B, RSM 2523.8; and F, AMNH 5027) are not referred with confidence to any Tyrannosaurus species by Paul and colleagues, which seems remarkable given their relative completeness.

It’s also interesting to see how Paul and colleagues’ conclusions compare to those of previous workers. Of note are that specimens highlighted by others as potential new Tyrannosaurus taxa — such as AMNH 5027, the Texan maxilla — are considered indeterminable by Paul et al., and that Larson (2008a), despite utilising the same dentary tooth character, retained the holotypes of regina and imperator in T. rex. There’s nothing wrong with different projects drawing contrasting taxonomic conclusions, of course, but this shows that attributes as basic as specimen tooth size are being interpreted very differently by different authors. This demonstrates the difficulty, and perhaps the degree of subjectivity, associated with carving our Tyrannosaurus dataset into multiple species. Perhaps the clusters of specimens we're identifying as distinct "species" are strongly influenced by our own opinions on what features are taxonomically important, and also how we choose to measure and characterise those features? The discussion of Tyrannosaurus dentary incisiform size by Paul et al. is telling in this regard, highlighting the existence of “borderline” specimens that could be interpreted one way or another. Differing takes on such specimens probably account for the varied views proposed by different researchers.

The end? Probably not...

The take-home here is a simple one: T. rex is a tricky animal to split into multiple taxa, but the problem is not because researchers are wedded to the idea of there being one species of this animal. To the contrary, exactly the opposite is true: people have been trying to blow T. rex into smaller taxonomic units for half a century! Rather, it's because what seems like a straightforward job of naming a few new tyrannosaur species is complicated by the enormously variable nature of the T. rex dataset and also the lesser-known, but still important, taxonomic considerations of past workers. I admit to seeing Paul and colleagues’ work as less of a “mini-revolution” than the latest contribution in a decades-long conversation about the variation apparent in Tyrannosaurus specimens. Their work is distinguished, of course, by finally erecting new Tyrannosaurus species after 50 years of researchers tossing this idea around, and in this respect, Paul et al. have moved the conversation on. But in doing this, a greater spotlight is now shone on past attempts to investigate Tyrannosaurus variation, including the legitimacy of species previously sunk into T. rex as well as the value of anatomical characters already of doubtful value in dividing up the T. rex sample. It’s the response to these that will determine how far our understanding of Tyrannosaurus diversity has been moved by these new proposals.

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