An interview with Emily Willoughby, author and artist of Drawing and Painting Dinosaurs

That most obscure theropod taxon Tyrannosaurus chews on bones on the front cover of Emily Willhoughby's new book, Drawing and Painting Dinosaurs: the latest entry into the growing literature dedicated to palaeoartistry. Can we talk about how nice that tyrannosaur knee is? From the Crowood Press website.

The last decade or so has seen the arrival of several notable palaeoart books, articles and book chapters that showcase the works and voices of palaeoart practitioners past and present, such that it seems we’re in a particularly rich literary era for this specialised artform. Among these works are a slowly growing number dedicated to palaeoart methodology: the hows, whats and whys of restoring the life appearance of extinct organisms from fossil remains. In late October of this year, another book in this vein arrived to add to your palaeoart library: Emily Willoughby’s Drawing and Painting Dinosaurs.

I was fortunate enough to be sent a review copy of this new book by Crowood Press, who you may know from my own The Palaeoartist’s Handbook (2018) and the upcoming Witton and Michel volume The Art and Science of the Crystal Palace Dinosaurs (coming May 2022, vintage palaeoart fans!). Much as I wanted to write about Emily's book, my involvement with Crowood presents a conflict of interest to presenting any thoughts I may have, and the fact that Emily kindly contributed artwork to The Palaeoartist’s Handbook only complicates matters further. But in wanting to do something to promote what I think is a useful, welcome addition to our collective palaeoart bookshelf, I reached out to Emily to see if she’d agree to an interview about creating Drawing and Painting Dinosaurs. As you’ll have guessed by now, Emily kindly agreed to answer my questions and the full interview is below.

But before we get to that, we should give a quick introduction to the book in question. Split into eight chapters and two appendices, Drawing and Painting Dinosaurs is a good-sized (280 x 220 mm, 176 pages), well-produced and affordable (RRP £18.99) softback that covers the basics of the palaeoart process as well as reconstruction approaches to several dinosaur groups. Chapters 1-4 cover the basics of palaeoartistry, from restoring anatomy to recreating environments, chapters 5-6 cover restoring pennaraptorans, tyrannosauroids, ornithischians and sauropods, and chapter 8 uses the evolution of feathers as a case study for palaeoartistic prediction. Emily’s qualifications to write such a book, of course, are in no doubt. She is one of the leading palaeoartists of modern times and has been particularly influential in the field of restoring feathered dinosaurs - especially dromaeosaurs. Readers will surely be familiar with Emily’s takes on these animals from her online presence (website, Facebook, Twitter), press release artworks, museum exhibitions and inclusion in landmark palaeoart collections (e.g. Titan Books’ Dinosaur Art II). Even if you’ve been living under a palaeoart-impervious rock for the last decade and somehow missed Emily's stuff, the simple fact is that anyone who can draw and paint dinosaurs like this…

...is clearly someone to pay attention to when they're offering pointers and advice on restoring fossil organisms.

Drawing and Painting Dinosaurs is packed with illustrations - over 250, according to the back cover. Many of them are new (at least, I didn't recognise them from other sources) and it's fun seeing Emily take on taxa we've rarely seen her restore before - giant dinosaur herbivores, big carnivores and so on. You don't need to read a word to realise that this is a must-buy for palaeoart fans: simply having page after page of Willoughby palaeoartworks on your bookshelf is worth the cover price alone. Emily’s world-leading reputation is well-earned for her attention to detail, technical excellence and eye for composition. Eschewing the open plains, giant animals and big skies that have been a staple of dinosaur palaeoart for generations, Emily’s artwork is often more intimate, frequently set in densely forested habitats with fallen logs, patchworks of light and colour, and delicate foliage. Her restorations are not only enormously charismatic but also grounded in observations of modern species, good knowledge of animal behaviour, and an appreciation for real natural spaces. Her combination of skills and approaches makes her Mesozoic dinosaur artwork fantastic to look at and also eminently believable. It's difficult not to think her paintings (especially her more recent and detailed pieces) were not drawn from scenes witnessed with her own eyes. We might not know for certain what Mesozoic dinosaurs looked like or how they behaved, but Emily’s artwork is surely in the right ballpark.

Fortunately for those of us secretly plotting to steal Emily’s artistic essence who’d like to learn to restore dinosaurs with that Willoughby touch, Drawing and Painting Dinosaurs has a greater emphasis on artistry and technique than we’re seen in most other palaeoart guides published to date. The closest comparisons I can think of are Douglas Henderson's palaeoart chapters in the first two Complete Dinosaur books but, with a full book of her own, Emily obviously has a lot more opportunity to discuss her craft. She outlines several methods used in creating her artworks such as painting from models, drawing over articulated fossils, and finding inspiration among real environments, while also giving pointers on matters such as composition, traditional painting techniques and finding basic forms within dinosaur bodies. This approach, combined with her patient, clearly-written text, will make the book especially useful to non-specialists. Technical terms are used here and there, of course (it’s basically impossible to write at length about palaeoart theory without some jargon) but in-text explanations and a glossary make the introduction of such terminology a learning experience, not a barrier to understanding. This is not to imply that the book is just for beginners, of course: there are plenty of useful ideas and takes on dinosaur palaeobiology that will be invaluable to artists of all levels. There were certainly some facts, perspectives and methods that were new to me, for whatever that's worth.

A sample page from Drawing and Painting Dinosaurs, from the Crowood Press website. This page features Emily's drawover of the Mei long holotype, a technique that helps artists not only understand the anatomy of their subjects but also appreciate fossil specimens as the remains of individuals, not as mere scientific concepts. Seeing fossils as the remains of specific creatures forms one philosophical core of the book.

And speaking of the text, I found Drawing and Painting Dinosaurs pleasant to read for its informative, slightly conversational tone. It presents a unique voice in palaeoart discourse, neither written with the disembodied neutrality of a scientist nor with overconfidence about her preferred interpretations of the past. There's an obvious respect for the work and insight provided by scientists but also plenty of informed personal contemplation and opinion on matters of reconstructing anatomy and ancient environments. The book is sprinkled with reflections on specific artworks and projects that give a sense of the enjoyments and frustrations of the palaeoart experience, such as including having artwork dating within days of its completion, the intrigue of reworking a familiar taxon with new data, and the thrill of restoring a newly discovered species. It not only reassures us that Emily is experienced at the trade she’s teaching but gives the book a sense of personality. We're also given insights into how Emily views the past, and her obvious connection to her fossil subjects stands out as something I've not seen expressed in palaeoart literature before. Emily reminds us that fossils are not mere geological phenomena or abstract concepts like species, but the petrified tissues of individuals that lived and died for us to discover millions of years later. It's a sobering, thoughtful take on palaeoart that establishes a personal connection between artist and their extinct subject matter across Deep Time.

One inescapable feature of Drawing and Painting Dinosaurs is its strong focus on dromaeosaurs and related, fully-feathered theropods - especially Deinonychus - for both artistic and case study subjects. These animals really do take centre stage - something like 80% of the artwork features dromaeosaurs or similar dinosaurs - and they serve as go-to species for demonstrating palaeoart principles throughout most of the book. Tyrannosauroids, sauropods and all ornithischians also feature in their own discrete chapters, but Drawing and Painting Dinosaurs is undeniably a show driven by feathered dinosaurs. I feel this is the only aspect of the book that might prove divisive, especially if readers are expecting a more general guide to the life appearance of dinosaur groups. There is value, however, in this doubling down on pennaraptorans. Writing any text like Drawing and Painting Dinosaurs always boils down to a question of breadth vs. depth and, in choosing the former, the book sacrifices some use as a general reference for demonstrating how a deep understanding of a fossil group can enhance our palaeoartistry. Knowing every species, every trace fossil, and every specimen of a clade allows for especially informed and nuanced palaeoartistic approaches, and that’s strongly evident in Emily’s pennaraptoran dinosaur art. For less experienced artists, the amount of information she demonstrates can be transferred from fossils to palaeoartworks may be surprising, and this would not have been so obvious had Emily discussed more clades in less detail. Seeing what can be done with dromaeosaurs and their relatives provides an impetus to learn about our favourite subjects in just as much depth, for which readers are given the right guidance for what to research and where to find it.

The (2017) Jinfengopteryx restoration Emily created for Nature. This image perfectly captures my comment about Willoughby art nailing believability: the colours, the sense of scale and the demeanour of the subject are such that I can totally buy Jinfengopteryx as looking like this. From Emily's website, © Emily Willoughby.

Anyway... this isn't meant to be a review, and here I am writing everything I like about the book. That should give you a flavour of what the book is all about and, as you can tell, I have nice things to say about it. With claxons blazing for those conflicts of interest mentioned above, I recommend anyone interested in palaeoart check it out. But we're not here for my thoughts: let's move on to what we’re actually here to read - Emily’s insights into how the book came to be, the original plans for the project, how she creates her artworks and even some free tips for us budding artists. Huge thanks to Emily for agreeing to this interview, and I hope it inspires you to put Drawing and Painting Dinosaurs on your Christmas list, if it’s not there already.

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MW. It’s felt like a book such as Drawing and Painting Dinosaurs was going to happen eventually: a professional, world-leading palaeoartist imparts their experience and knowledge about illustrating the most popular and in-demand palaeoart subjects. I’ve certainly been around pub tables where artists have discussed it. What made you step up to the plate and think “yep, I’ll take that project on”

EW. It had been a dream of mine to publish a book like this someday, but my experience thus far with bringing book proposals to publishers and agents had been largely disappointing. For my first book, God’s Word or Human Reason?, I and my coauthor sent a total of about a hundred query letters to agents without a single positive response. So when Crowood Press reached out to me and asked if I’d be interested in such a project, there was no hesitation on my part!

Your text has an especially patient, welcoming quality that carefully explains a lot of information for newbies, encourages readers to draw along as they read, and there are several step-by-step illustration guides. It contrasts with what I’ve come to expect from palaeoart guides, which can slide into machine-gunning anatomical facts and interpretations about extinct animals at the reader. Was this simply your intuitive approach, or something you deliberately crafted when writing your book?

You were actually a pretty big inspiration for the approach I decided to take in this book. Since Crowood also published your wonderful The Palaeoartist’s Handbook, I knew from the outset that I needed to take an approach that would not overlap too much in content and style with your own. I played with a lot of different ideas early on — including, for example, a separate chapter on each medium I typically work in (gouache, digital, pencil, and so on), but felt that approach was too “arty” and not “sciency” enough. Ultimately I wanted to create something that seamlessly entwined the scientific and epistemological bases of paleontology with the hands-on artistic techniques, and this led to a structure that attempted to educate both professional and lay readers by providing context-driven examples.

This book was an enormous education to me in how damned difficult it is to craft a coherent structure of an entirely new book without much outside feedback. The first month or so of its creation was dedicated entirely to what seemed like endless deliberation, revision, and hand-wringing over the structure, approach and focus. I think the decision I went with turned out decently enough, but I still have a lot to learn in this respect.

More terrific Willoughby artwork, The Silky Serikornis (2015). A masterclass of using depth of field to convey scale. From Emily's website, © Emily Willoughby.

Drawing and Painting Dinosaurs has a huge number of images - over 250 - and you created virtually all of them yourself. How much of that was new artwork for this book, and how long did it take to produce? A lot of them seem very recent - were you basically painting 24/7 until the book was finished?

I would estimate that over half of the illustrations are ones that were created specifically for this book, including a large selection of less time-intensive diagrams and sketches. Of the illustrations that were previously completed, many of them were progress shots or thumbnails that haven’t been put to good use until now (I knew there might a good reason someday for me to save progress shots of long-ago artworks!). A handful were also from various projects over the years that never managed to see completion for one reason or another, and some were finished up from early works-in-progress that were subsequently abandoned.

I had about a year total to complete the book from start to finish. I’m still kind of dumbfounded that I managed to get the book together during the same year in which I wrote and defended my Ph.D. dissertation! I have no doubt that’s something I’ll look back on in my twilight years and think “how on earth did I ever have the energy!”

We get to revisit some of your older artworks in Drawing and Painting Dinosaurs which have a slightly different style and mood to your more recent work. Thinking specifically about palaeoart-specific skills, how has your art and approach developed since their creation?

I still have a long way to go, but I like to think that my work has improved tremendously since I first started doing serious paleoart. For one thing, I’ve learned to enjoy reconstructing taxa I’m relatively unfamiliar with, whereas I started out painting feathered theropods and little else. While the new book still largely features dromaeosaurs and their kin, I had a lot more fun than I expected to have on the sauropods, tyrannosauroids, and various ornithischians that were included. For another thing, I’ve expanded my artwork to a variety of media I never worked in regularly early on—oil paint, gouache, acrylics, and graphite.

I’ve also become more comfortable in testing out new ideas and compositions. Recently I’ve been putting more effort into the environment and setting, which I used to think of as a chore that took away from the fun of painting the dinosaurs themselves. But once it starts becoming fun to paint environments, it also becomes easier. My experience is that the single largest improvement in my artwork isn’t so much in a piece’s overall quality per se, but in learning to work more efficiently—better quality per unit time.

As anyone familiar with your portfolio might expect, Drawing and Painting Dinosaurs has a very strong focus on dromaeosaurs and their relatives, especially Deinonychus. What’s the draw of these dinosaurs over sauropods, ornithischians or more rootward theropods?

It’s no secret that my biggest focus in paleoart has always been dromaeosaurs and other feathered coelurosaurs—I’m a feather-fancier, it’s true. Although I did enjoy branching out a bit for this book, dromaeosaurs remain the group of dinosaurs that I find most captivating and arresting. I suppose the reason for this is that feathered dinosaurs were responsible for my introduction to paleoart after a lifetime of obsessive interest in birds and evolution in general. In the early 2000s, I recall reading articles about some of the exquisitely preserved Liaoning fossils, including Sinorthithosaurus, Sinosauropteryx and especially Microraptor. When I first saw a photograph of the fossil of Microraptor in 2003, I was utterly fascinated, and it caused the realization that birds were dinosaurs to register new and profound understanding. The rest is history!

An inescapable conclusion of Drawing and Painting Dinosaurs is that Emily Willoughby ♥ Deinonychus. But her frequent portrayals of this animal are not repeats of palaeoart stereotypes and clichés. In this 2013 painting, Deinonychus is shown opportunistically feeding on a fish, reflecting the less than fussy dietary preferences of living predators. From Emily's website, © Emily Willoughby.

There’s an emotional component to your book that is unusual for discussions about the technicalities of palaeoart. You write about the personal affinities and emotions you’ve developed for certain subjects, and that you regard fossils as not just specimens of not only long-extinct animals, but as long-deceased individuals. An ode to extinct animals, the poem Not Forgotten by Jonathan Kane, ends chapter 1, and you describe Deinonychus as possibly being “the most beautiful animal that ever lived”. There’s a clear attachment to many of your extinct subjects - how much of an influence does this have on your artwork, and do you feel the same about all extinct animals? Or are some subjects “just a job”?

I do think that many natural subjects are beautiful, and it’s hard to not express this when trying to communicate that beauty in my own art. Although I used to think of some natural subjects as “just a job” (especially environments and flora), I feel less that way over time—all natural subjects are beautiful and fascinating, though of course I have my own attachments and biases. Moreover, though, I think that communicating this passion to the public is important to encourage people to think of dinosaurs as real animals, and to cultivate a sense of awe and respect that I feel extinct animals deserve.

You detail both digital and traditional painting techniques in your book. Do you have a preferred medium?

Part of what I enjoy about working in different media is that it’s harder for me to become bored and frustrated. Sometimes I get annoyed at how cluttered and messy my study gets when I work in gouache and (especially) oils for a while, so I switch back to working digitally for a while. Then I may start getting annoyed at how often Photoshop crashes or how Procreate constrains layers and resolution so harshly, so back to gouache it is! Learning and practicing new media is always interesting and keeps me engaged. I need variety. Currently, my favourite medium to work in is Procreate—I love how easy it is to blend, and I can take my iPad to meetings and work. Gouache has always been my traditional medium of choice, but that may change as I work more in acrylics and oils.

I’m also curious to know if you’ve attempted to update traditional paintings when new science forces us to revise older reconstructions.

The one piece of traditional art I spent a lot of time repainting was my 2010 painting of Anchiornis, which I talk about in the book. New to oils at the time, I painstakingly painted a mottled brown and white birdlike critter dashing through a lush green jungle. It was literally days after I was finally satisfied with its completion that the first color study was published, showing that Anchiornis was more likely to be black, grey and red than brown and white. I could have justified the piece as a juvenile, subspecies, or female, but instead I repainted the animal and adjusted the background to the new contrast it required. I’m glad I did, and I sometimes do include minor updates to older pieces, but usually I prefer composing a new piece altogether when new data comes to light.

Emily's 2010 take on Anchiornis huxleyi. This is the second version of this painting which had to be redone after new data on Anchiornis palaeocolour was published shortly after the original's completion. From Emily's website, © Emily Willoughby.

The palaeoart community has long been dominated by males, both in terms of practitioners and fans, such that Drawing and Painting Dinosaurs is among the first, if not the first, palaeoart guide written by a female author and artist. With so much discussion around the lack of diversity in palaeontology, your book feels like an important milestone in diversifying the voices shaping palaeoart. Was this something you were conscious of when creating your book

I don’t think it occurred to me at the time that I was the first, given that there aren’t many paleoart guides out there to begin with. But I’m honoured to represent that milestone if so, and I hope the example may encourage others. I’ve already gotten a few emails and even an interview for a project from a few school-aged girls who want to become palaeoartists, which is frankly one of the very most rewarding things about working in this field to me.

You cover a heck of a lot of ideas and techniques in your book, from finding inspiration among natural settings to building models, to constraining colour patterns using living animals to modifying modern plant leaves to resemble those of the past… and much more. Out of this extensive toolbox, are there any that you regard as especially essential - the one or two that, whatever your approach to palaeoart is, we should all be doing?

Remember that prehistoric subjects were living things, and look to other living things (their anatomy, their ecology and evolution, their behaviour, the way they move and interact in their environment, and so on) for inspiration to capture that sense of lifey-ness that lifeless things are meant to have in paleoart. Although many prehistoric organisms were quite unlike anything alive today, they all share an important thing: they evolved to live and move in their environments. I think that this single injunction can go a long way towards facilitating accurate, interesting, and unique paleoart.

It’s not always wise to ask about the Next Big Project so soon after finishing one, but are there any big Willoughby projects we should look out for soon? Emily Willoughby’s SuperBig Dulux Coffee Table Book of Dromaeosaur Art has a nice ring to it...

So glad that you asked! I am about halfway through a new project: Marks on Time, an illustrated anthology of natural history poetry written by my coauthor Jonathan. This will be a collection of 25 poems about evolution, dinosaurs, and human nature, accompanied by about 40 full-colour and brand-new illustrations. If any publishing agents happen to be reading this, please drop me an email. ;)

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Thanks again to Emily for her interview responses, and I wish her all the success her book deserves. Drawing and Painting Dinosaurs is available now from Crowood Press, priced £18.99, as well as from all the usual book retailers.

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The long, winding road to the first sauropod palaeoartworks

It's a well-verified fact that the best dinosaurs to draw are the sauropods, exemplified here by the mighty Giraffatitan brancai. But the route to this modern realisation was a difficult one. When sauropods were first discovered no one wanted to restore them at all: their fossils were always in the hands of the wrong people, at the wrong time, and our first attempt at restoring their life appearance was many decades after their discovery. A strange story awaits.

Is there any shape more emblematic of prehistoric life than the silhouette of a sauropod? The combination of long neck, long tail, round body and four robust limbs is universal visual shorthand for anything to do with dinosaurs and, more broadly, extinct life, such that sauropods are bone fide superstars of palaeontological pop-culture. The world-renowned Sinclair logo, Gertie, the leads of The Land Before Time and The Good Dinosaur, the scene welcoming us to Jurassic Park… all sauropods.

Much of the most famous sauropod iconography is, as with so much palaeontological media, related to fully-fleshed sauropod reconstructions rather than their fossil bones, so we can consider much of their popular appeal lying within paleoart. Given the undeniable spectacle and wonder associated with sauropod fossils, where even single bones can be jaw-dropping museum centrepieces, we might imagine that early scientists and palaeoartists jumped at the chance to put flesh on the skeletons of these long-necked reptiles as soon fossil material revealed their basic shape. And yet, this was not the case. The story of how sauropods entered the palaeoart canon and became ambassadors for all things dinosaurian and extinct is a peculiar one, where a full half-century passed between their discovery and their palaeoart canonisation. This is a story of how combative attitudes and egos, missed opportunities and perceived failures in early palaeoartworks stymied life reconstructions of sauropods for much of the 19th century.

(The following post owes much to the history of sauropod research outlined by Mike Taylor (2010) and Mark Hallett and Matt Wedel (2016). Be sure to check these out if you want a more detailed perspective on 19th century sauropod science.)

Fragmentary beginnings

Our tale begins, of course, with the discovery and description of the first sauropods Cetiosaurus and "Cardiodon" by Richard Owen in 1841. As with all the first dinosaur discoveries, our first sauropod fossils were isolated bones from southern Britain. Little could be said about the life appearance of the animals they represented other than that they were enormous reptiles. On account of their size, it was assumed sauropods must have been aquatic and – like all giant sea creatures – carnivorous. Perhaps, it was wondered, they were the arch predators of Mesozoic oceans: the devourers of plesiosaurs and ichthyosaurs. Owen speculated that such a creature must have borne a well-developed caudal fin perhaps similar to that of an ichthyosaur, but this awesome vision of sauropods did not lead to any life reconstructions despite the cavalier reputation of early 19th century Europeans for restoring extinct animals (if you’ve been reading my blog since its origins, you may remember an article on this very topic).

We might wonder why this was the case. After all, animals like Megalosaurus were initially represented by little more material than Cetiosaurus, but they were still restored within just a few years of their discovery. The absence of early 19th century sauropod reconstructions shows, to my mind, some level of nuance about early Victorian palaeoartists. Though often characterised as wild and speculative, the early Victorian palaeoart canon was surprisingly conservative, mainly showing similar scenes populated by the same species in the same anatomical guises. Many of their depictions were also of animals with decent fossil representation like marine reptiles, pterosaurs and fossil mammals, such that the restoration of poorly-represented species, like dinosaurs, can be viewed as exceptional. Moreover, and in further defence of the first palaeoartists, dinosaur anatomy wasn’t a total unknown in the early 19th century. Several species had been attributed characteristic anatomical features such as nose horns, body armour, or distinctive teeth, so there was something to hang restorations around. But sauropods lacked even a basic defining feature, and thus had no way of being distinguished or characterised from other restored giant reptiles. Should vindictive time-travellers ever force early Victorians to draw fleshed-out sauropods, the result would probably be nothing more than generic, giant carnivorous reptiles, perhaps little different to some of John Martin’s whale-sized, lizard-like dinosaurs.

John Martin's frontispiece to G. F. Richardson's 1842 book Geology for Beginners, entitled Age of Reptiles. A lot of early 19th century dinosaur palaeoart was not especially attentive to details of anatomy and form, such that sauropods, if they had been illustrated, probably would have looked much like the (?)Megalosaurus in this piece.

The whale lizard flounders in the palaeoart doldrums

A major step towards understanding sauropod life appearance was made in the late 1860s when a large haul of Cetiosaurus bones were found in Oxfordshire, UK. Described by geologist John Phillips in the 1871 book Geology of Oxford and the Valley of the Thames, this partial skeleton included limb bones, ribs, limb girdles and many vertebrae, and thus provided our first decent insight into the sauropod body plan. In what seems like a cruel twist of fate, no neck or skull bones were recovered, denying knowledge of the most defining characteristic of the group for another few years. Nevertheless, Phillips had enough anatomy to start making the first relatively informed insights into sauropod appearance and behaviour, and he devoted several pages of his book to discussing the size, habits and even skin of Cetiosaurus. Much of what we now think about sauropods was prophesied here, with Phillips describing very large, scaly reptiles that lived on land and ate plants. He made a number of favourable comparisons to Iguanodon in his discussion of Cetiosaurus habits such that he may have imagined it as an especially gigantic large-bodied, quadrupedal herbivore in the vein of Waterhouse Hawkins’ Crystal Palace Iguanodon and Hylaeosaurus. It is curious, therefore, in light of this evident interest, that Phillips did not attempt some sort of reconstruction. He had enough bones to at least construct a decent skeletal diagram. But, OK - maybe reconstructions weren’t Phillip’s thing. With all this anatomical information, surely someone else picked up the baton?

John Phillips' quarry map of a partial Cetiosaurus skeleton found in 1869-70. A lot of the vertebrae and smaller bones are amalgamated into packages in this drawing, but the glut of material is obvious. This was the first significant insight into sauropod life appearance... but not much came of it among Victorian palaeoart. From Phillips (1871).

And it’s at this point that our story becomes rather strange. Cetiosaurus, which was by now as well represented as other animals routinely featured in palaeoart, continued to be snubbed by artists. We have to take a step back from sauropod palaeoart history and expand our scope to the discipline as a whole to understand why. Along with Cetiosaurus, a number of genuinely important, game-changing dinosaur discoveries had been made across Europe in the mid-1800s that included Scelidosaurus (the first complete dinosaur skeleton), Compsognathus, Hypsilophodon, and Archaeopteryx. All were represented by excellent fossils that dramatically enhanced our understanding of dinosaurs and had major implications for reconstructing their life appearance, and yet none were canonised into palaeoart of the day. If you look hard enough you may find some simple line drawings of Archaeopteryx here and there, but there were no lavish paintings, no sculptures or elaborate lithographs celebrating these new animals.

Evidently, Cetiosaurus itself wasn't being snubbed. These superior sauropod remains had arrived while European palaeoart was in a funk that would last several decades, an era when most new palaeoartworks featured restorations recycled from the early 1800s instead of novel reconstructions of newly-discovered species. A contributing factor to suppressed creativity in late 19th century European palaeoart was, ironically, the Crystal Palace Dinosaurs (Secord 2004; Nieuwland 2019). Although popular with the public, most academic response to the 1854 unveiling of these models was negative. Criticisms were many, focusing on their speculated elements, the juxtaposition of modern landscapes with extinct animals, and accusations that they were simply scaled up, monsterised living species. Several Crystal Palace reconstructions were also rapid embarrassed by new fossil data, such that these flagships of Victorian palaeoart were now misleading or confusing the public more than educating them. The Crystal Palace Dinosaurs had given scholars of the 1870s good reason to be sceptical of palaeoart, and the creation of new life reconstructions fell out of fashion for a generation.

American palaeoart to the rescue… sort of

The awakening of American palaeoartistry is one of the few major events that occurred in palaeoart history in the early-late 19th century. While American palaeoartists slowly found their feet, the discovery of excellent sauropod material in western states in the 1870s finally revealed the full spectacle of these amazing, unique animals. Among the first relatively well-known American sauropods was Camarasaurus, found in 1877 and described by Edward Drinker Cope in the same year. These specimens, at last, revealed something of the iconic sauropod neck. Scientists were finally impressed enough to reconstruct a sauropod skeleton, and the result was John A. Ryder’s composite mounted skeleton of a ribless, sail-tailed Camarasaurus, complete with a speculated skull. This mount was around 50 ft long and exhibited at a meeting of The American Philosophical Society in Philadelphia in December 1877, but no images of it were not published until 1914. Nor, for that matter, was it accompanied or followed by a life reconstruction. In fact, I don’t know that anyone has attempted to restore Ryder’s Camarasaurus, so I set aside an hour or so in preparation of this article to finally correct this important injustice. I'd love to see more from different artists - #justiceforRydersaurus!

OK, yes, John A. Ryder's 1877 Camarasaurus skeletal is a little bizarre, but the essence of sauropod form is there. It's a stone-cold crime that no one reconstructed the life appearance of this skeleton, so I've had a go here. Some attempt has been made to give the restoration a classical 19th century, Hawkinsian palaeoart flavour.

The absence of an 1877 Camarasaurus life restoration is all the more curious because of Cope’s association with this specimen. Cope is most famous for his feud with Othniel Marsh and the ‘Bone Wars’ period of American vertebrate palaeontology, but he was also one of the main instigators of American palaeoartistry. During the 1860s Cope produced iconic artworks of dinosaurs known from New Jersey which can be considered among the first flesh reconstructions of recognisable, basically anatomically accurate dinosaurs, as well as well-known depictions of taxa from the Western Interior Seaway. He was an advisor in the 1868 reconstruction of Hadrosaurus by Joseph Leidy and Benjamin Waterhouse Hawkins, and thus had connections to the first grandmaster of palaeoart himself, who was often based in the US for palaeoartistic purposes in the 1860s and 1870s. And yet, around all this, Cope never produced a published sauropod life reconstruction, and nor did his relationship with Hawkins yield any (published) sauropod illustrations. We may ascribe the latter to Hawkins’ dislike of Cope, whom he regarded as an overbearing, fussy collaborator. On at least one occasion he threatened to abandon a project entirely if Cope was involved (Bramwell and Peck 2008). Who knows how the early history of American palaeoart would have played out had these two giants of their disciplines been on better terms.

Othniel Marsh's 1883 restoration of Brontosaurus - a significant advance over the Ryder sauropod skeletal of just a few years prior.

Cope was, of course, not the only major player in the discovery of American sauropods. Indeed, Cope’s rival, Marsh, probably has a greater legacy with these animals, not only naming more species but also coining the name ‘Sauropoda’. Marsh named and described many now-iconic sauropods including Brontosaurus, Apatosaurus and Diplodocus, and in 1883 he published a Brontosaurus skeletal reconstruction that was, anatomically speaking, vastly superior to Ryder's Camarasaurus. Marsh was thus another person well-placed to facilitate the first artistic resurrection of sauropod life appearance… if only it weren't for his career-long disdain for palaeoart. Here's what he said on this topic in 1875:

I do not believe it possible at present to make restorations of any of the more important extinct animals of this country that will be of real value to science, or the public. In the few cases where materials exist for a restoration of the skeleton alone, these materials have not yet been worked out with sufficient care to make such a restoration perfectly satisfactory, and to go beyond this would in my judgment almost certainly end in serious mistakes. Where the skeleton, etc., is only partly known, the danger of error is of course much greater, and I would think it is very unwise to attempt restoration, as error in a case of this kind is very difficult to eradicate from the public mind… A few years hence we shall certainly have the material for some good restorations of our wonderful extinct animals, but the time is not yet.

(Marsh 1875, quoted in Dodson 1996, p.74)

Marsh’s criticism of palaeoart has a lot of implications for the development of the discipline in general, and almost certainly contributed to the delayed canonisation of sauropods. He held many of the best cards when it came to understanding sauropod life appearance but was the last person who would include a life restoration in a publication. Moreover, his reputation, influence, and longstanding criticism of palaeoart may have further dampened drives to restore newly discovered taxa in Europe, where some of his fiercest denouncement of palaeoartworks were expressed. Marsh’s views were surely a major contributor to the strange fact that the Bone Wars era - one of the most intense periods of discovery and analysis in early dinosaur history – was entirely bereft of associated palaeoart. And while Cope could, in theory, have picked up these palaeoartistic pieces, the ferocity of his feud with Marsh surely meant that he avoided reconstructing Marsh taxa, no matter how spectacular they were. There’s some irony in Marsh and Cope being so instrumental to our early conceptualisation of sauropods but that their various hang-ups - with each other, with other people, and with palaeoart - only kicked the can further down the road.

Finally, a life reconstruction! ...that everyone ignored

By this time - the late 1870s or early 1880s - sauropods had been known to science for about 40 years, with decent, restorable remains on record for at least half that time. Their gigantic size and spectacular anatomy were well appreciated and, thanks to Marsh, their skeletal anatomy had been committed to scientific literature. In these circumstances, surely someone was going to crack and attempt a flesh restoration? Yes, finally, someone did - but not in either of the historic homes of sauropods, Britain and the US. Rather, it was the French author Nicolas Camille Flammarion who provided the first (to my knowledge) sauropod life restoration in his 1886 book Le Monde Avant la Création de l’Homme, courtesy artist J. Blanedet. Behold:

Finally, a sauropod life restoration! J. Blanedet's 1886 Atlantosaurus poses with an elephant for scale. From Flammarion (1886).

Flammarion’s book is a landmark work for depictions of prehistoric life, containing a mix of old and new restorations that went some way to relieving the drought of new reconstructions in the late 19th century. Perhaps reflecting Flammarion’s outsider position from sauropod research, his choice of sauropod was not something well-known like Cetiosaurus, Camarasaurus or Brontosaurus, but the obscure “Atlantosaurus”. This was one of the first discovered Morisson Formation sauropods but, on account of its scrappy remains, it was on its way to becoming a historic footnote in 1886. Today, Atlantosaurus is generally considered a nomen dubium. Obscure taxon choice aside, here, finally, was a sauropod in the flesh. And, all things considered, the reconstruction was pretty good. Marsh’s 1883 Brontosaurus reconstruction was featured in the same book and its shared DNA with the Atlantosaurus illustration is obvious. In the accompanying text, Flammarion describes several sauropods in essentially accurate ways: as gigantic, long-necked animals with small heads, of herbivorous character, and as denizens of terra firma, not lakes and swamps. This was a pretty progressive take on sauropods that built on ideas expressed by Phillips, and they stand in contrast with sauropods’ fast approaching 20th-century relegation to semi-aquatic life.

In a different universe, Flammarion’s Atlantosaurus and other novel reconstructions were the start of a new wave of palaeoartworks based on updated science and newly discovered species. Alas, in our universe, the new artworks in Flammarion’s book made little impression on palaeoart development, and didn’t shake older takes on extinct animals from their foothold in 19th century palaeoart. Even as the 20th century loomed, Hawkinsian, Kuwassegian and Copeian dinosaurs were still populating artworks of Deep Time. From a historic perspective, Flammarion’s Atlantosaurus is more of an Easter egg than the moment sauropod palaeoart truly arrived.

The 1890s: the dam bursts

Joseph Smit's 1892 Brontosaurus, from Henry Hutchinson's Extinct Monsters: A Popular Account of Some of the Larger Forms of Ancient Animal Life. Although not as influential or well known today as the sauropod artworks of Charles Knight, the success of Hutchinson's book would have made this the first life restoration seen by many people, certainly in the English speaking world.

It was only as the sandgrains in the 19th century hourglass ran dry that a collective epiphany about sauropods struck the minds of museum developers, artists and book authors around the world. Finally, after more than a half-century of avoiding sauropod palaeoart, flesh restorations of long-necked dinosaurs entered the mainstream during the 1890s. But, again, it was not America, with its embarrassment of sauropod fossils, that instigated this. Rather, it was a revived British interest in palaeoart that championed sauropods, with one book, in particular, cresting a new wave of new palaeoartistic reconstructions: Henry Neville Hutchinson’s 1892 ;Extinct Monsters: A Popular Account of Some of the Larger Forms of Ancient Animal Life. This featured illustrations by the Danish artist Joseph Smit based on Marsh's skeletal diagrams and the results were so successful that Extinct Monsters was reprinted several times over the next two decades. It was also eventually repackaged with another Hutchinson book, Creatures of Other Days. Smit illustrated both Diplodocus and Brontosaurus in these works, based on Marsh's groundwork, establishing their canonical presence in palaeoart from then onwards.

One of the most iconic palaeoart images of the late 19th century: Charles Knight's 1897 swamp-bound Brontosaurus and grazing Diplodocus. Knight's affiliation with the American Museum of Natural History and the publicity-hungry Henry Osborn brought palaeoart into a new era where dinosaurs would become increasingly dominant art subjects, and sauropods would become superstars.

Shortly after, American palaeoart finally woke up to the splendour of sauropods. The American Museum of Natural History, under the supervision of Henry Osborn, had identified the power of palaeoart as an educational, promotional and commercial tool and realised the role dinosaurs could play in this campaign. The result were sauropod illustrations by Charles Knight, which surely rank as the most famous of all early sauropod artworks. Knight’s iconic 1897 Brontosaurus and Diplodocus in a swamp, produced with direction from Osborn, was among the first of these works, but a lesser-known sketch of a snorkelling Amphicoelias was produced around the same time. The latter is notable for being produced under guidance from Cope, who sketched a rough version for Knight to replicate. Cope’s choice to depict the fragmentarily known Amphicoelias, which he named in 1878, over a better-known Marsh species is surely an instance of their old rivalry dying hard. Many Knight images of sauropods would follow in the next few decades.

In the last year of his life, Edward Drinker Cope tutored Charles Knight in the anatomy of extinct animals so as to help Knight better understand his palaeoart subjects. Among the images they worked on together was this 1897 scene of Amphicoelias, which Cope sketched out for Knight to replicate. Note the interesting stripes and spotting used here. Although now standard in palaeoartworks, such intricate patterning was rare in 19th century palaeoart.

And it’s here, at the turn of the 20th century, that our story picks up with more familiar beats. After their slow adoption into palaeoart and popularised palaeontology, sauropods quickly appeared everywhere dinosaurs were mentioned. American museums put sauropods front and centre of their galleries and, courtesy of Andrew Carnegie, many museums around the world soon sported Diplodocus in their dinosaur halls. Gertie the Dinosaur and the 1925 adaption of The Lost World, where Brontosaurus pioneered cinematic monsters smashing cities for our amusement, made sauropods the focus of early dinosaur films. Life-sized models of sauropods appeared in Europe by 1910 and then in the United States and Russia in the 1930s. Around all this, artists like Knight, Smit, Heinrich Harder and Alice Woodward cemented sauropods into the mainstream palaeoart canon. Surely helped by their palaeoartistic popularity, sauropods had become cultural icons almost overnight.

The story of sauropods entering palaeoart canon is more than a tale of 19th century attitudes to reconstructing extinct animals: it’s also a case study in the vagaries of science communication and gatekeeping. We often discuss why certain facets of science, like dinosaurs, are so popular, while others are not. How much of this reflects the inexplicable, innate interestingness of a topic, and how much of it is manufactured? Many of us would agree that sauropods are some of the most fascinating and spectacular animals to have ever lived but, even when their anatomy was well-realised, this was not enough for mainstream culture to adopt them passively. Even artists and scientists who knew about them were not falling over themselves to restore and promote them, and it really wasn’t until individuals at the turn of the 20th century wanted, or needed, to promote sauropods that they began their journey towards being palaeontological icons. I’ve argued in the past that dinosaurs have a certain fundamental appeal that draws us to them, and that might be true, but stories like this show that our awareness and access to spectacular, easy-sell science, such as that of the biggest dinosaurs to have ever existed, is managed by a privileged few.

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References

• Bramwell, V., & Peck, R. M. (2008). All in the bones: a biography of Benjamin Waterhouse Hawkins. Academy of Natural Sciences.
• Dodson, P. (1998). The horned dinosaurs: a natural history. Princeton University Press.
• Flammarion, C. (1886). Le monde avant la création de l'homme: origines de la terre, origines de la vie, origines de l'humanité. C. Marpon et E. Flammarion.
• Hallett, M., & Wedel, M. J. (2016). The sauropod dinosaurs: life in the age of giants. JHU Press.
• Nieuwland, I. (2019). American Dinosaur Abroad: A Cultural History of Carnegie's Plaster Diplodocus. University of Pittsburgh Press.
• Phillips, J. (1871). Geology of Oxford and the Valley of the Thames. Clarendon 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.
• Taylor, M. P. (2010). Sauropod dinosaur research: a historical review. Geological Society, London, Special Publications, 343(1), 361-386.

Theropod dinosaurs were a bunch of buttheads: the evidence for and development of ideas around theropod cranial combat

When it comes to imagining aggressive behaviour between large Mesozoic theropod dinosaurs, the main game in town is head-biting: individuals grappling with one another by locking jaws around each other’s faces (Tanke and Currie 1998; Peterson et al. 2009). Such actions are well-evidenced by the sometimes significant trauma found on theropod skull fossils, including tooth marks, gouges, and even teeth embedded in facial bones. Clearly, head-biting was a dangerous, bloody activity that could lead to significant injury, and we have to wonder if theropods might have had means of physically settling their differences without tearing each other’s faces apart. After all, while some modern animals don’t have much behavioural grey space between ‘idle’ and ‘psycho’, many species employ means of fighting that prevent, or at least diminish, the need for more violent encounters.

One non-lethal means of theropod interaction explored in dinosaur literature is head-butting, where the various crests, horns and bosses adorning their skulls are transformed into bludgeons, clubs and shoving aids. We don’t see or read much about theropods employing these behaviours in dinosaur popular culture despite its obvious appeal - if you don't find the idea of heckin' big predatory dinosaurs shoving each other around with their heads at least a little bit awesome, you might want to see a doctor. But, actually, theropod head-butting has a reasonable foothold in dinosaur technical literature, with some studies even dedicated to determining its feasibility.

Among the earliest proponents of theropod head-butting were Robert Bakker and Gregory S. Paul, who've been illustrating this behaviour and the anatomy related to it for decades. From left to right: Bakker's (1986) diagram of theropod head ornaments related to head-butting; Paul's (1987, but published in 1988) fantastic flank-butting Ceratosaurus; and a more recent Bakker work showing head-butting Tyrannosaurus from the Beyond Bones blog.

So far as I’m aware, the concept of theropod head-butting was a product of the Dinosaur Renaissance, perhaps an unsurprising occurrence given that it involves regarding theropods as relatively sophisticated, behaviourally-complex animals rather than the pea-brained dullards of pre-Renaissance times. Two of the most influential figures of that revolution - Bob Bakker and Gregory S. Paul - were strong advocates for theropod head-butting. Their famous books The Dinosaur Heresies (Bakker 1986) and Predatory Dinosaurs of the World (Paul 1988) both proposed that theropods engaged in these behaviours (above). Bakker’s take interpreted the stout ridges and crests of theropods such as Allosaurus and Tyrannosaurus as weapons for butting bouts and stressed their significance as nonlethal fighting devices. Paul considered head-butting likely for most theropods with robust cranial ornaments, from the elaborately horned Ceratosaurus and Carnotaurus to the massively-skulled tyrannosaurs. Paul favourably compared the various horns and bosses of such animals to those of giraffes (which, of course, are renowned head clubbers) and has maintained such views in more recent works (e.g. Paul 2016). I’m curious as to whether Bakker and Paul's affinity for drawing theropods played into the formation of these ideas, as they both were among the strongest critics of pre-Renaissance artists for not capturing the diverse morphologies and ornaments of theropod skulls and produced many artworks showing more accurate theropod depictions. Might their more precise renderings of theropod skulls have made them ponder the function of the bosses, ridges and crests they were illustrating?

In subsequent decades theropod head-butting has been mentioned semi-often by theropod workers. A minority of workers have been negative and dismissive of the idea (e.g. Rowe 1989; Molnar and Farlow 1990), but it’s mostly brought up in a confirmatory sense. Most discussions have centred around a few clades - tyrannosaurids (e.g. Bakker 1986, Paul 1988, 2016), carcharodontosaurids (e.g. Sereno and Brusatte 2008; Cau et al. 2013) and especially abelisaurids (e.g. Novas 1989; Mazzetta et al. 1998, 2009; Hieronymus 2009; Snively et al. 2011; Delcourt 2018; Cerroni et al. 2021) - and we now have a suite of typical anatomical features identified as potential head-butting structures, as well as dedicated biomechanical investigations into the plausibility of theropod skull combat (Mazzetta et al. 1998, 2009; Snively et al. 2011; Xing et al. 2015). Evidently, the concept of theropod head-butting is not - as is sometimes the case - an over-eccentric hangover from a particularly adventurous period of dinosaur research, but a legitimate and current behavioural hypothesis supported by a growing amount of data.

The postorbital bone of the carcharodontosaurid Eocarcharia dinops and its prominent orbital boss: a structure made for lateral head-butting? From Sereno and Brusatte (2008).

Let's get into this a little more: what, exactly, are the structures theropod workers are linking to head-butting? As will be well-known to anyone reading this blog, theropods were prone to augmenting their skulls with ridges, bosses, crests and horns, most commonly along the top of the snout and above their eyes. It’s among these that we find potential head-butting structures, but it's not thought that any and all ornaments were suitable for head-butting. Some theropod crests were surely too delicate for physical aggression, probably even allowing for the strengthening properties of their overlying skin tissues (see below). It’s hard to believe that the thin, tall crests of Dilophosaurus were being smacked into other animals, for example, and they instead surely served a purely signalling role (Bakker 1986; Rowe 1989). Indeed, studies of the Dilophosaurus-like crests of Sinosaurus found that they were prone to structural failure under mechanical loading (Xing et al. 2015), and likely ill-suited to weaponisation.

The 'Trix' specimen of Tyrannosaurus, on display in Glasgow 2019, showing the massive postorbital bosses which dominate the posterior skull region of this species. Researchers have associated these with head-butting behaviour, which seems reasonable given their structure, location, and the general grumpy attitude evidenced for Tyrannosaurus.

Head-butting structures are better inferred from the sizeable, prominent and robust components adorning certain theropod skulls. In carcharodontosaurids, ornament indicative of head-butting consists of swollen, laterally-prominent bosses above their eyes (Sereno and Brusatte 2008) or, more unusually, dorsally-prominent domes in the same region (Cau et al. 2017). Unfortunately, taxa with these features - Eocharchia and Sauroniops - are not especially well-known so we can’t see if these features were somehow echoed across the rest of the skull: might they have sported other enhanced bosses and ridges as well? This is not a problem for tyrannosaurids, of course, which have skulls of extreme familiarity to theropod researchers. Both Bakker (1986) and Paul (1988, 2016) have linked the robust nasal bones (forming the top of the snout), lacrimal cornual processes (horns in front of the eye) and postorbital bosses (swollen, rounded structures behind the eye) of tyrannosaurs with head-butting behaviour. Predictions of armoured skin around their eyes and snout (Carr et al. 2017) are consistent with this idea, too. Tyrannosaurus needs special mention here for its uniqueness among theropods - even other tyrannosaurs - in having flattened its lacrimal cornual processes into swollen, highly-textured expansions of the skull roof and inflated its postorbital bosses to a great extent, sometimes even capping the latter with osteoderms (Carr et al. 2017). The enlarged postorbital bosses are among the tallest parts of the skull and also project outward from the eye socket by a considerable margin. Significant rugosities and other properties of these lacrimal and postorbital features indicate a covering of especially thick, toughened skin, but no true horns (despite what you see in lots of artwork and films, there’s nothing pointed or horn-shaped about the ornament of big T. rex specimens). If Bakker and Paul are correct in Tyrannosaurus having a head adapted for head-butting, it’s difficult not to see this reconfiguration as the skull of a theropodan bulldozer: a flattened, shovel-shaped cranium to heave and bash other animals around with.

Tyrannosaurus is unusual among tyrannosaurids for lacking a hornlet in front of the eye, but it compensated for this with armoured cranial skin and two prominent postorbital bosses. Bolted to something like six or more tonnes of angry tyrannosaur, this must have made for one heck of a battering ram. So let's see... if there's BRONTOSMASH!, ArSUMOitherium, then this must be... TYRANNOBUTT? Yes, make it so.

Neither tyrannosaurs nor carcharodontosaurid head-butting has received much in the way of dedicated research attention, however, leaving our best insights into this behaviour coming from abelisaurs, especially Carnotaurus. The head-butting potential of these short- and gnarly-faced, sometimes horned theropods has been remarked on for decades (e.g. Paul 1988; Novas 1989; Mazzetta et al. 1998) and, via Carnotaurus, encouraged several rounds of dedicated biomechanical investigation (Mazzetta et al. 1998, 2009; Snively et al. 2011; Méndez 2012). These initially regarded Carnotaurus cranial combat as a brutal affair, with spinal dampening allowing combatants to impact their heads at rhinoceros-grade speeds of 20 kph (Mazetta et al. 1998). But subsequent investigations have curbed these ideas somewhat, finding that Carnotaurus skulls were incapable of sustaining strong forces during simulated head-butting (Mazetta et al. 2009). Instead, their skulls were better suited to low-velocity impacts, blows that targeted softer parts of animal bodies (e.g. flank butting), or maybe even quasi-static bouts of head-shoving (Mazzetta et al. 2009). This isn’t too surprising: Carnotaurus is a relatively robustly-skulled theropod, but its cranium is still a relatively vacuous, air-filled structure adaptively balancing maximised strength and minimised weight. Compared to the massive and thickened skulls of more dedicated headbutters, theropod skulls look relatively delicate. Abelisaur necks are no longer considered shock absorbers for running impacts either, but their recognition as strong, powerful elements means they still have a role in head-butting hypotheses (Méndez 2012): the utility of a powerful neck in energetic, sustained use of a weaponised head is obvious (Delcourt 2018).

Epidermal correlates covering the heads of abelisaur species, from Delcourt (2018). Carnotaurus stands out with its indications of especially reinforced, cornified snout and horn tissues - a 'carnivorous bull' indeed.

Further information on abelisaur head-butting stems from their facial skin. The rugose surface textures of abelisaur skulls are indicative of particular skin types, such as cornified sheaths (think bird beaks and cow horns), cornified pads (muskox heads) or thickened, armoured dermis (rhino and hippo skin) (Sampson and Witmer 2007; Hieronymus 2009; Delcourt 2018; Cerroni et al. 2021; Hendrickx and Bell 2021). These are exactly the tough, reinforced skin types we’d expect to see in animals that used their heads as clubs or shoving implements, and it’s been noted that these dermal types, in extant animals, correlate with intraspecific fighting (Hieronymus 2009). We’ve touched on these data before, discussing that abelisaur faces may have looked quite different to their skulls thanks to thick skin. This is especially so for Carnotaurus, which had a snout covered by an extensive cornified pad. Because the evidence for thick, armoured skin on abelisaur faces is especially prominent compared to other theropods, it seems reasonable to infer a behavioural emphasis on head-butting within the group.

Carnotaurus sastrei, a species that - among theropods at least - is probably the most head-butting adapted of all. Exactly how its head, equipped with a cornified pad and sheathed horns, was used in aggressive behaviours has been interpreted differently over the years and boils down to assumptions of shock-absorption capability: was it a high-impact or low-impact headbutter, a shover, or a flank-butter? Whichever it was, it certainly looked awesome.

But these neat dermal insights bring complications along with insight, adding important caveats to the biomechanical studies outlined above. We know from living animals that head-butting capability is best modelled by factoring both bony and soft-tissue data (e.g. Drake et al. 2016), and that such simulations can turn bone-only models of skull strength on their heads. So far as I know, no studies of abelisaur cranial strength in head-butting simulations have modelled their armoured and cornified skin tissues yet, and so we await such analyses before real confidence can be drawn about abelisaur head-butting capability. The same is true, of course, of any other theropod we’d want to investigate head-butting behaviour for. I'm sure I'm not the only one thinking such studies, and other insights into this relatively unexplored but fascinating facet of theropod palaeobiology, would be very welcome additions to dinosaur research.

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References

• Bakker, R. T. (1986). The dinosaur heresies: new theories unlocking the mystery of the dinosaurs and their extinction. William Morrow.
• Cau, A., Dalla Vecchia, F. M., & Fabbri, M. (2013). A thick-skulled theropod (Dinosauria, Saurischia) from the Upper Cretaceous of Morocco with implications for carcharodontosaurid cranial evolution. Cretaceous Research, 40, 251-260.
• Carr, T. D., Varricchio, D. J., Sedlmayr, J. C., Roberts, E. M., & Moore, J. R. (2017). A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system. Scientific Reports, 7(1), 1-11.
• Cerroni, M. A., Canale, J. I., & Novas, F. E. (2021). The skull of Carnotaurus sastrei Bonaparte 1985 revisited: insights from craniofacial bones, palate and lower jaw. Historical Biology, 33(10), 2444-2485.
• Delcourt, R. (2018). Ceratosaur palaeobiology: new insights on evolution and ecology of the southern rulers. Scientific reports, 8(1), 1-12.
• Drake, A., Donahue, T. L. H., Stansloski, M., Fox, K., Wheatley, B. B., & Donahue, S. W. (2016). Horn and horn core trabecular bone of bighorn sheep rams absorbs impact energy and reduces brain cavity accelerations during high impact ramming of the skull. Acta biomaterialia, 44, 41-50.
• Hieronymus, T. L. (2009). Osteological Correlates of Cephalic Skin Structures in Amniota: Documenting the Evolution of Display and Feeding Structures with Fossil Data (Doctoral dissertation, Ohio University).
• Mazzetta, G. V., Fariña, R. A., & Vizcaíno, S. F. (1998). On the palaeobiology of the South American horned theropod Carnotaurus sastrei Bonaparte. Gaia, 15(185), 192.
• Mazzetta, G. V., Cisilino, A. P., Blanco, R. E., & Calvo, N. (2009). Cranial mechanics and functional interpretation of the horned carnivorous dinosaur Carnotaurus sastrei. Journal of Vertebrate Paleontology, 29(3), 822-830.
• Méndez, A. H. (2012). The cervical vertebrae of the Late Cretaceous abelisaurid dinosaur Carnotaurus sastrei. Acta Palaeontologica Polonica, 59(3), 569-579.
• Molnar, R. E., & Farlow, J. O. (1990). Carnosaur paleobiology. In: Weishampel, D. B., Dodson, P., & Osmólska, H. (eds.). The Dinosauria. University of California Press. 210-224 pp.
• Novas, F. E. (1989). Los dinosaurios carnívoros de la Argentina. PhD thesis, La Plata: Universidad Nacional de La Plata.
• Paul, G. S. (1988). Predatory dinosaurs of the world: a complete illustrated guide. Simon & Schuster.
• Paul, G. S. (2016). The Princeton Field Guide to Dinosaurs. Princeton University Press.
• Peterson, J. E., Henderson, M. D., Scherer, R. P., & Vittore, C. P. (2009). Face biting on a juvenile tyrannosaurid and behavioral implications. Palaios, 24(11), 780-784.
• Rowe, T. (1989). The early history of theropods. Short Courses in Paleontology, 2, 100-112.
• Sampson, S. D., & Witmer, L. M. (2007). Craniofacial anatomy of Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar. Journal of Vertebrate Paleontology, 27(S2), 32-104.
• Sereno, P. C., & Brusatte, S. L. (2008). Basal abelisaurid and carcharodontosaurid theropods from the Lower Cretaceous Elrhaz Formation of Niger. Acta Palaeontologica Polonica, 53(1), 15-46.
• Snively, E., Cotton, J. R., Witmer, L., Ridgely, R., & Theodor, J. (2011). Finite Element Comparison of Cranial Sinus Function in the Dinosaur Majungasaurus and Head-Clubbing Giraffes. In Summer Bioengineering Conference (Vol. 54587, pp. 1075-1076). American Society of Mechanical Engineers.
• Tanke, D. H., & Currie, P. J. (1998). Head-biting behavior in theropod dinosaurs: paleopathological evidence. GAIA: revista de geociências, (15), 167.
• Xing, L., Wang, Y., Snively, E., Zhang, J., Dong, Z., Burns, M. E., & Currie, P. J. (2015). Model-based identification of mechanical characteristics of Sinosaurus (Theropoda) crests. Acta Geologica Sinica, 89(1), 1-11.

A tale of plesiosaur tails: vertical fins or horizontal flukes?

The giant elasmosaurid Albertonectes vanderveldei forages for invertebrates and small prey deep underwater. From this posterolateral view, the vertical tail fin is unmissable - but should I have drawn it as a horizontal fluke instead? Welcome to yet another challenge for restoring the life appearance of plesiosaurs!

It’s fair to assume that, when painting or sculpting plesiosaurs, most palaeoartists favour attention to their heads, necks and flippers, these being the most characteristic parts of their anatomy and the components most of our audience will focus on. Plesiosaurs are, of course, famously tricky animals to restore with any degree of certainty, their body plans being entirely unlike anything alive today, their mechanism of swimming - underwater flight with two sets of flippers - being the source of much debate and controversy, and their fossil record giving us few direct insights into their soft-tissue anatomy. So here’s more good news: in recent years another part of plesiosaur anatomy has joined their flippers and necks in artistic and scientific contention, their tails.

Plesiosaur tails have traditionally been little more than afterthoughts in palaeoartworks: cone-shaped structures tapering from the body without much in the way of interesting features. In the last decade or so, however, research interest in plesiosaur caudal anatomy and the resurrection of certain historic observations (e.g. Dames 1895; Smith 2007, 2013; Wilhem 2010; Sennikov 2015, 2019; Otero et al. 2018) has seen plesiosaurs with more interesting tails making regular palaeoartistic appearances. This artistic shift initially showed plesiosaur tails having fish- or ichthyosaur-like vertical fins but, more recently, newer research has made a case for another configuration, horizontal tail flukes (note the terminological distinctions), and such reconstructions are now also appearing with regularity. These fins and flukes, it must be stressed, are not mere whimsy or speculation but based on osteological correlates for some kind of extensive skin structure around the tail tip, and we should clarify that no-one thinks these represent a hitherto unappreciated propulsive organ - plesiosaurs do not suddenly have five ‘engines’ for swimming. Instead, these fins or flukes surely represent devices to act as some kind of rudder or stabilising aid, perhaps helping to offset the impact of swimming around with those giant necks and heads.

Recent skeletal reconstructions of plesiosaurs (or parts thereof) showing different interpretations of caudal rudder anatomy. It is increasingly common to see these features in plesiosaur skeletals and this compilation image could be much bigger, but I've restricted it to those from papers specifically making cases for fins or flukes.

One thing is clear: the evidence for tail rudders in plesiosaurs is pretty strong in several plesiosaur clades and any credible palaeoart of these animals should show them with some kind of fin, flipper or fluke at the tail tip. But, clearly, our current conflicting interpretations of plesiosaur tail anatomy can’t both be correct. I’ve gone back and forth on these ideas in my plesiosaur art over the last couple of years and decided that it was time I looked into this in more detail. What is the evidence for tail fins or flukes in plesiosaurs, and which is most compellingly argued for? Can we even make a call on this topic at the moment? Let's find out.

One of several plesiosaur artworks I've drawn recently showing a fluked tail, rather than (as was my previous preference) a fin. This is Plesiosaurus dolichodeirus scavenging a pterosaur carcass, because plesiosaurs are meant to eat pterosaurs in palaeoart, consarnit.

Something old is new... etc. etc.

First, let's briefly familiarise ourselves with the history of this controversy. It may seem that notions about plesiosaur caudal fins and flukes are part of the Brave New World of changing up old reconstructions of fossil reptiles for radical new ones, but that’s not the case here. Actually, osteological features and soft-tissue remains evidencing caudal rudders in plesiosaurs were identified in the 19th century, and even the dichotomy of interpretation between fins vs. flukes is over 100 years old. Our modern discussions of these concepts are a revival of relatively early investigations into plesiosaur functional morphology and life appearance.

The holotype of Seeleyosaurus guilelmiimperatoris, famous for having a soft-tissue outline around its tail. This specimen was the only plesiosaur fossil on record with direct bearing on the fin vs. flipper controversy, but the tail soft-tissues have been painted over and are no longer accessible for study. Yeah, frustrating, right? From Dames (1895).

The concept of plesiosaur caudal fins was first broached by Richard Owen, who proposed that lateral compression of the terminal tail vertebrae of Archaeonectrus rostratus indicated a caudal fin (Owen 1865). Owen’s observation had little impact on reconstructions of plesiosaurs at the time, but seeming confirmation of his prediction arrived a few decades later when, in 1895, a specimen of the Jurassic plesiosaur Seeleyosaurus guilelmiimperatoris was described with a soft-tissue outline around much of tail tip (Dames 1895). To date, this specimen remains the only fossil on record that provides direct confirmation of a caudal fin or fluke but, alas, it can no longer be investigated or even validated as the soft tissue component of the fossil has been painted over (BUT - see update at the end of the post). This presents a problem deeper than merely obscuring the body outline. Many marine reptile specimens were often ‘improved’ with forged soft-tissues and realigned bones by 19th century preparators such that anything especially amazing and interesting - like the only known plesiosaur tail fin outline, for instance - really needs verification from modern researchers to be accepted as genuine. I’m not aware of any plesiosaur experts who consider the Seeleysoaurus soft-tissues especially suspicious, but this inescapable caveat hangs around any discussion of this specimen: we can only put so much stock in any interpretation of it, modern or historic. This said, scholars of the late 1800s certainly regarded the body outline as genuine, leading to a few late 19th and 20th-century palaeoartworks in which Seeleyosaurus and other plesiosaurs sported tall, diamond-shaped tail fins. Among the most famous of these were the reconstructions published in Wilhelm Dames' 1895 Die plesiosaurier der süddeutschen Liasformation and the generic pliosaurid reconstruction published by Newman and Tarlo (1967).

Neither finned nor fluked plesiosaurs really caught on in historic palaeoart, but finned reconstructions almost did. Here's a rarely seen example: Woodward's (1896) reconstruction of "Plesiosaurus" macrocephalus, from A Guide to the fossil reptiles, amphibians, and fishes in the Department of Geology and Palaeontology of the British Museum (Natural History).

Not everyone accepted Seeleyosaurus as evidence of caudal fins in plesiosaurs, however. Both Fraas (1910) and Wegner (1914) felt that their caudal skeletons were indicative of a horizontal fluke, citing the absence of a tail bend, the dorsoventral flexibility of the vertebrae, and the size of the caudal ribs as evidence of this feature. I’m not aware of any historic reconstructions showing this configuration (this is not to say that none exist, of course) and assume that fluked plesiosaurs gained even less traction in technical literature and artwork than their finned counterparts. This left most academic and artistic consideration of plesiosaur caudal anatomy assuming featureless, tapering tails for the next century, despite the continued cataloguing of peculiar caudal anatomy in plesiosaurs - most notably, their fused terminal tail vertebrae, recalling the pygostyles of birds (see review by Smith 2013). Today, such structures are considered part of the evidence package for a caudal rudder, but this significance seems to have been mostly overlooked in older publications.

Evidence for fins, evidence for flukes

The story of plesiosaur caudal rudders is thus one of three parts: an initial set of pro-rudder proposals and observations; a period of relative disinterest in the idea; and our modern era of belated engagement with those original hypotheses. This latter stage began about 10-15 years ago when observations made by Owen and Dames were resurrected and augmented by modern plesiosaur experts to make a case for plesiosaur tail fins. Perhaps the most in-depth investigations supporting finned tails to date are those by Benjamin C. Wilhelm (2010) and Adam Stuart Smith (2007, 2013), both of whom looked at the tails of Jurassic plesiosaurs and identified features also seen in swimming animals with vertical caudal fins. Using the relatively completely known tails of the cryptoclidids Cryptoclidus and Muraenosaurus, Wilhelm (2010) catalogued a suite of anatomies correlating with vertical fin lobes, including a relatively large neural spine close to the tail tip (the 17th caudal vertebra in Cryptoclidus); several neural spines with expanded ends; a shift in the orientation of the neural spines at the tip of the tail (from posteriorly-directed to anteriorly-directed) and lateral compression of the terminal caudal vertebrae (see diagram, above). These features recall the finned tails of mosasaurs, Triassic ichthyosaurs and thalattosuchians (e.g. Lindgren et al. 2013; Renesto et al. 2020), where enlarged neural spines mark the start of a caudal fin and shifting neural spine orientations characterise the vertebrae embedded in the fin itself. As with tail-finned reptiles and fish, plesiosaur tails had increased flexion in two regions, both at the tail base and immediately anterior to the enlarged and reorientated neural spines. A slight vertical peduncle - a thinning of the tail structure to minimise its drag profile when being moved through water - was also identified anterior to the enlarged neural spine region. By analogy with the preserved soft-tissues of other marine reptiles, Wilhelm’s study allowed for a prediction of the possible fin outline for cryptoclidids: a small triangular lobe with a concave posterior margin on the upper side of the tail (above). This is quite different from the diamond-shape interpreted by Dames and others from the Seeleyosaurus fossil, but Wilhem’s thesis argues that a large ventral lobe is not suggested by that fossil and we can infer - if Wilhelm’s reconstruction is correct - that only a small amount of material is missing from the dorsal margin (see diagram, below).

Advocates for plesiosaur tail fins highlight similarities between their tail anatomy (see illustrations, above) and those of certain finned marine reptiles, such as early ichthyosaurs and mosasaurs. There are indeed obvious similarities, although the plesiosaur fin supports are clearly far less developed than the examples shown here - a reflection, almost certainly, of tails being adapted for locomotion vs. those adapted for ruddering. Images from Renesto et al. (2020) and Lindgren et al. (2013).

Although working with more fragmentary material, Smith (2007, 2013) found similar features to those reported in Benjamin Wilhelm’s thesis, as well as further evidence of finned tails. This included lateral compression at the tail tip of Rhomaeleosaurus, as well as peculiar ‘node’ vertebrae that might indicate a zone of flexion or even a slight downturn of the tail tip - another feature of finned tails. A wedge-shaped vertebra was noted in another rhomaleosaurid, Macroplata, which might indicate a slight tail downturn, although this taxon curiously lacks laterally compressed distal vertebrae. Agreeing with Benjamin Wilhelm’s thesis, as well as Wilhelm and O’Keefe’s (2010) examination of further caudal material, Adam's study concluded that the flexibility evidenced in the proximal tail region would allow the caudal fin of plesiosaurs to augment steering and stability.

A few years after these works reignited interest in plesiosaur caudal rudders, artistic and academic champions of fluked plesiosaurs also resurrected, retooled and expanded the initial observations and arguments made by Fraas and Wegner (e.g. Sennikov 2015, 2019; Otero et al. 2018). At the core of these proposals were ideas that plesiosaur tails were more convergent with those of whales and manatees than with swimming reptiles or fish, and thus suited to dorsoventral motion and sporting horizontally-aligned soft-tissues at their tips. Some researchers have endorsed this idea by including fluked reconstructions in their papers (e.g. Sachs et al. 2016). 

Were plesiosaur tails reptilian variants of sirenian-like caudal anatomy? Again, there are similarities, especially in the great width of the vertebrae. In lieu of decent sirenian skeletons online, I've borrowed these Florida manatee (Trichechus manatus) skeleton replica images from Bone Clones.

Some of the evidence for plesiosaur flukes is the same as that used for finned reconstructions, such as the two zones of flexion in the plesiosaur caudal skeleton, and the recognition of a distinctive, often stiffened vertebral region at the end of the tail (Sennikov 2015, 2019). This is representative of fluked and finned tails having functional similarity, each essentially being the same thing operating in different planes. Fluke-specific evidence includes the presence of long caudal ribs along much of the tail length which, in making some vertebrae wider than tall, are suggested to create a relatively wide, flat tail with restricted lateral movement (Sennikov 2015, 2019; Otero et al. 2018). Otero et al. (2018) noted that the tips of the caudal ribs of Aristonectes are fibrous for potential attachment of extensive soft-tissue, potentially implying a much wider tail than shown by osteology alone (something seemingly confirmed by soft-tissue data of Mauriciosaurus). The absence of convincing downturned tail tips has also been flagged up, even for taxa with ‘node’ vertebrae (Otero et al. 2018), and has been negatively compared against the finned condition of ichthyosaurs and marine crocodylomorphs (Sennikov 2019). The small size or absence of chevrons, and the low, variable orientation of caudal neural spines, are features thought to have allowed the fluke to move vertically and independently of the rest of the tail (Otero et al. 2018; Sennikov 2019). The plesiosaur torso - a pachyostotic, relatively inflexible trunk - has also been regarded as similar to that of sirenians and thus potentially indicative of a fluked tail (Sennikov 2019). For the fluke model to be correct, of course, the traditional interpretation of Seeleyosaurus having some kind of tail fin has to be wrong. Sennikov (2019) states that this is indeed the case, and provides an alternative view where the Seeleyosaurus soft-tissues represent a horizontally-aligned structure within which the vertebrae have fallen over. The asymmetry of the fluke as preserved is explained as a result of vertebral displacement, soft-tissue decay and incomplete fossilisation.

Problematic as it is, proposals of plesiosaur rudder shape have to contend with the now-lost Seeleyosaurus data to some extent. Some fin models posit that not much has happened to the caudal region of the Seeleyosaurus holotype, whereas the fluke model requires a little more modification. While the fin model seems simplest, the fluke version hardly seems implausible.

Fins vs. flukes, head to head (er... tail to tail?)

Having briefly reviewed this evidence, can we see which of these models seems strongest? I stress my word choice in that sentence: our understanding of plesiosaur soft-tissues is not yet sufficient to make claims of absolute certainty, so any conversation on them should be peppered with appropriate caveats and considerations. This is a case where it’s much easier to be a researching scientist, where “we don’t yet know” is a perfectly acceptable response, than a palaeoartist, where you have to come down on one side of a debate or another. So, with the proviso that I’m not sure we can really make a definitive call yet… and with some urging of readers to check the papers mentioned above for themselves to make up their own minds... and with appropriate caution… and having now run out of ways to stall writing this sentence... I find myself... more persuaded by arguments for a tail fin at present. The fin hypothesis seems to explain more of the peculiar anatomy of plesiosaur tail tips than its rival, and it presents an overall simpler, and thus more likely correct, interpretation of our available data. The highlighted similarities between plesiosaur tails and those of certain other fin-tailed swimming reptiles are prudent observations not yet accounted for in the fluke model and, when thinking about the evolution of such features, it seems a shorter developmental distance for a plesiosaur to evolve a fin than a fluke. I’m especially thinking of the switch from primarily lateral to vertical spinal flexion, the former being ancestral to reptiles and thus common to many in swimming reptile species. Significant vertical caudal flexion has developed among diapsids of course, in birds, and some swimming birds even use their tail fans in a rudder-like fashion (Felice and O’Connor 2014), so we shouldn’t rule out this capability for plesiosaurs entirely. Moreover, this is not to say that the observations from Team Fluke are redundant. Maybe the wide, potentially muscular tails of plesiosaurs were indeed capable of an unusual amount of vertical motion, even with a fin? If, indeed, plesiosaur tails operated as ruddering aids, some surely had a big job on their hands: there’s no way moving those giant necks and heads didn’t have a tremendous rotational impact when swimming and their tails may have had an important role in keeping their owners on course. A weedy tail with limited mobility in either plane might not have been up to that task. It would be neat to see simulations of this sort of thing.

I also agree with Wilhelm’s (2010) assessment of the Seeleyosaurus tail outline, which looks - so far as can be seen in Dames’ (1895) illustrations, more like a vertical structure than a horizontal one. I’m not sure how much stock we should place in interpretations of the drawings of this specimen given that the original soft tissues are now inaccessible, but, for what it’s worth, the relatively neat margins and asymmetry of the tissue outline, the general position of the vertebrae and location of possible ‘fin’ tissues above the tallest neural spines look consistent with a small dorsal lobe (sensu Wilhelm 2010), while a fluked interpretation relies on a fair amount of distortion from decay and disarticulation. But there is certainly plenty of ambiguity around that specimen and I could be convinced otherwise. Needless to say, more plesiosaur specimens with soft-tissues preserved around the tail tip would be incredibly useful in this discussion.

Plesiosauria was a diverse group with a huge array of body proportions, sizes and lifestyles. Did the gigantic pliosaur Kronosaurus queenslandicus share the same caudal rudder shape and size as Cryptoclidus? We need more research to say either way.

Of course, this tentative endorsement of vertical fins comes with many caveats. Despite the antiquity of proposals that plesiosaurs bore a soft-tissue rudder on their tails, these discussions are still in their infancy. Very few studies have directly addressed this topic and our analyses have, thus far, been largely limited to qualitative descriptions and comparisons with other vertebrates. Our taxon sampling is also relatively limited and has not yet incorporated the most extreme examples of plesiosaur size or body plans. I can’t be the only one wondering what the extremely long-necked elasmosaurids and giant pliosaurids were doing with their tails and, given the innumerable studies linking tail shape to ecology in swimming animals, it’s not crazy to assume plesiosaurs of different lifestyles might have had differently shaped rudders. We may even already be finding evidence of such variation, it being observed (for example) that elasmosaurids may not have had the mobile terminal tail region identified in some cryptoclidids (Otero et al. 2018). Moreover, might plesiosaurs have done something unusual with their tails, such that the fin vs. fluke dichotomy is an oversimplification of a more complex organ befitting their unique swimming style? Could other structures - keels or projecting stabilisers - have augmented a larger fin? It will be interesting to see what further research reveals and, in particular, what quantified comparisons between the caudals of plesiosaurs and those of fluked and flippered animals have to tell us. Many of the features discussed above are relatively subtle - a taller neural spine here, a slight wedging of the centrum there. Careful, quantified comparisons of a suite of features with modern and extinct analogues may help us distinguish whether fins or flukes are the better tail rudder model, or if such analogues are useful guides at all.

And that, with one foot off the fence on this matter, but still not feeling like a conclusion has really been reached, is where we'll leave off for now. Hopefully, more definitive evidence for plesiosaur tail morphology will appear soon but, until then, the best thing artists can do is not take the comments above as gospel: check out the papers discussed here (most are open access or otherwise available online) to make up your own mind which is the better-supported model. I suspect I'm still going to remain uncertain about my plesiosaur tails for some time, but there's comfort knowing that this isn't really something we can be especially confident about until more data is gathered.

UPDATE: 28/09/2021 (the day after posting). In what is clearly good news, it turns out that the paint covering the Seeleyosaurus holotype soft-tissues has been removed and that the specimen is, at time of writing, under study by plesiosaur expert Sven Sachs. You can see a photo of the restored specimen at Sven's website, here. The paint was actually removed some years ago but this has not, to my knowledge, been mentioned in more recent papers discussing this specimen, hence the error in reporting here. Thanks to Sven and others who have pointed this out.

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References

• Dames, W. (1895). Die plesiosaurier der Süddeutschen Liasformation. Abhandlungen der
• Königlich Preussischen Akademie der Wissenschaften zu Berlin 1895, 1–81.
• Felice, R. N., & O’connor, P. M. (2014). Ecology and caudal skeletal morphology in birds: the convergent evolution of pygostyle shape in underwater foraging taxa. PLoS One, 9(2), e89737.
• Fraas, E. (1910). Plesiosaurier aus dem oberen Lias von Holzmaden, Palaeontographica, 57, 3–4, 105–140.
• Lindgren, J., Kaddumi, H. F., & Polcyn, M. J. (2013). Soft tissue preservation in a fossil marine lizard with a bilobed tail fin. Nature Communications, 4(1), 1-8.
• Newman, B. & Tarlo, B. (1967). A giant marine reptile from Bedfordshire. Animals, 10, 61-63
• Otero, R. A., Soto-Acuña, S., & O'keefe, F. R. (2018). Osteology of Aristonectes quiriquinensis (Elasmosauridae, Aristonectinae) from the upper Maastrichtian of central Chile. Journal of Vertebrate Paleontology, 38(1), e1408638.
• Owen, R. (1865). A monograph on the fossil Reptilia of the Liassic Formations. Part 3. Sauropterygia. Monograph of the Palaeontographical Society, 17, 1–40, pl. 1–16.
• Renesto, S., Dal Sasso, C., Fogliazza, F., & Ragni, C. (2020). New findings reveal that the Middle Triassic ichthyosaur Mixosaurus cornalianus is the oldest amniote with a dorsal fin. Acta Palaeontologica Polonica, 65(3), 511-522.
• Sachs, S., Hornung, J. J., & Kear, B. P. (2016). Reappraisal of Europe’s most complete Early Cretaceous plesiosaurian: Brancasaurus brancai Wegner, 1914 from the “Wealden facies” of Germany. PeerJ, 4, e2813.
• Sennikov, A. G. (2015). New data on the herpetofauna of the Early Triassic Donskaya Luka locality, Volgograd Region. Paleontological Journal, 49(11), 1161-1173.
• Sennikov, A. G. (2019). Peculiarities of the Structure and Locomotor Function of the Tail in Sauropterygia. Biology Bulletin, 46(7), 751-762.
• Smith, A. S. 2007. Anatomy and systematics of the Rhomaleosauridae (Sauropterygia: Plesiosauria). Unpublished PhD thesis, School of Biology and Environmental Science, National University of Ireland, University College Dublin.
• Smith, A. S. (2013). Morphology of the caudal vertebrae in Rhomaleosaurus zetlandicus and a review of the evidence for a tail fin in Plesiosauria. Paludicola, 9(3), 144-158.
• Wegner, T. (1914). Brancasaurus brancai Wegner, ein elasmosauride aus dem Wealden Westfalens. Borntraeger.
• Wilhelm, B. C. (2010). Novel anatomy of cryptoclidid plesiosaurs with comments on axial locomotion (Doctoral dissertation, Marshall University Libraries).
• Wilhelm, B. C., & O'keefe, F. R. (2010). A new partial skeleton of a cryptocleidoid plesiosaur from the Upper Jurassic Sundance Formation of Wyoming. Journal of Vertebrate Paleontology, 30(6), 1736-1742.