Ceratopsian horns and frills – what drove their evolution?

So I have another new paper out on sexual selection and what this means for dinosaurs. This one has been led by my PhD student Andy Knapp (follow him on Twitter here) and he agreed to write about it here:

Ceratopsians are among the most instantly recognisable dinosaurs thanks to their enormous, elaborately-adorned skulls. The frills and horns of ceratopsians have been the subject or ongoing debate in palaeontological circles since the discovery of Triceratops in the late 19^th century. Triceratops is known to everyone, specialists and non-specialists alike, and remains the classic example of ceratopsian skull morphology, with three large forward-pointing horns and a thick, shield-like frill extending back from the rear of the skull. It seemed obvious to early palaeontologists that these features had evolved for protection. The trouble is that Triceratops is almost alone in possessing this precise combination of features. Many of the larger ceratopsians that we know of didn’t have such large horns, and most had large, weight-saving fenestrae in their frills which would offer little protective value in life. In recent years the large number of known ceratopsian species has increased with a steady stream of new discoveries, each with its own characteristic horn and frill morphologies. These discoveries have posed a whole load of new questions as to what their purpose was.

Large, elaborate features with no obvious use – such as the frills and horns seen in ceratopsians – are expensive to grow and maintain, and obvious parallels in living creatures involve sexually selected features. The most extravagant examples of sexually selected features, as realised by Darwin in his book The Descent of Man, involve extreme sexually dimorphism in traits and/or overall size; peacock tails, elephant seals, etc. In contrast, there is no convincing evidence of sexual dimorphism in any ceratopsian taxa. This has led some researchers to reject the hypothesis of sexual selection as an explanation for exaggerated features in ceratopsians and other dinosaurs, and suggest that instead these features have evolved for species recognition.

Species recognition is the idea that being able to differentiate members of your own species is vital in herding, protection and mating. Basic examples of ‘species recognition’ are everywhere in nature; zebras don’t have trouble telling lions apart from other zebras! The more specific idea that physical traits evolve as a mechanism to allow differentiation is controversial. There are a few known examples of divergence of traits in closely-related taxa where hybridisation could be detrimental to fitness, a process known as reproductive character displacement. This is distinct from ecological character displacement, where sympatric taxa that fill similar ecological niches diverge in traits associated with resource acquisition. The rock nuthatches Sitta neumayer and S. tephronota exist across central Asia in partially overlapping ranges. Where they are sympatric, the distinctive dark eye stripe, ubiquitous across the rest of the two species’ ranges, fades in intensity in the population of S. neumayer. This has been interpreted as an adaptation to prevent hybridisation between the two species. Crucially, other known examples of reproductive character displacement involve minor modifications to pre-existing, often sexually selected features.

Reproductive character displacement is not expected to operate where a taxon exists in isolation, because there is no evolutionary pressure for traits to diverge. This prediction allows us to test the hypothesis of species recognition as an explanation for the presence of distinctive traits in extinct taxa for which we have good geographical information. Ceratopsians fit these criteria well. They were widespread across North America and Asia, speciose, and many species are known from relatively complete remains. We compiled and assessed a list of 350 cladistic character traits for a 46 well-known ceratopsian species and compared how the traits generally considered ornamental, and thus contenders to be species recognition traits, varied between sympatric and non-sympatric species. We also examined at other traits; those that were internal and therefore not visible during the animal’s life, and those that were external but not considered to function as a display trait. We then conducted a pairwise comparison of each possible species pair for three distinct character classes; internal, display, and external non-display.

We then compared the results for species pairs known to be sympatric and, therefore, likely to encounter one another in life, with non-sympatric species pairs. For each category we found increasing character divergence with increasing phylogenetic distance as expected, but, crucially, found no difference between the disparity of the display characters of sympatric species and those of non-sympatric species. This suggests that interaction between species has no effect on the evolution of ornaments in ceratopsians, and that species recognition is not a contributing factor to ornament evolution. Of course, it is entirely plausible that ceratopsians were able to identify conspecifics by their ornamentation, but this would have been a byproduct of ornamentation, not a cause.

The ruling out of species recognition as a driver of ornament evolution, at least in ceratopsians, shortens the list of possible explanations. Avoiding hybridisation would benefit both parties and so the evolution of distinguishing features should tend towards a zero-cost exercise. In contrast, ceratopsian skulls are the largest of any terrestrial vertebrate and impose certain limitations on their bearers. Computer models of ceratopsians have shown their massive skulls shifted their centre of mass further forwards than other quadrupedal dinosaurs. Compared with the hadrosaurs that they shared the ancient river deltas of what is now Canada’s Dinosaur Provincial Park, this made them poor swimmers and liable to drown when crossing bodies of water. This obvious handicap, along with the sheer cost of growing and maintaining such a large component of overall body mass that has no obvious mechanical or ecological function, points to an explanation that favours investment in high-cost structures.

An additional result of our analysis was that at the lowest phylogenetic distances, ornamental traits were around ten times more diverse than internal traits and three times more diverse than non-ornamental external characters. This suggests a general trend for rapid evolution of ornamental traits. Rapid evolution and high-cost are both hallmarks of sexually selected features. If the frills and horns of ceratopsians are sexually selected, as has been previously suggested, they are distinct from extant taxa in being both highly exaggerated and sexually monomorphic. This combination suggests strong sexual selection that applies more-or-less equally to both sexes. Some evidence for ceratopsian ornamentation being sexually selected has been demonstrated previously, and this study both adds to this evidence and rejects a competing hypothesis. Ultimately, our findings open up further avenues for exploring the life history and ecology of these fascinating and enigmatic creatures.

 

Knapp A, Knell RJ, Farke AA, Loewen MA and Hone DWE (2018). Patterns of divergence in the morphology of ceratopsian dinosaurs: sympatry is not a driver of ornament evolution. Proc. R. Soc. B. 20180312. http://dx.doi.org/10.1098/rspb.2018.0312

 

References

Brown WL and Wilson EO (1956) Character displacement. Systematic Zoology. 5: 49-64

Darwin, C. (1871). The Descent of Man and Selection in Relation to Sex. London, John Murray

Henderson DM (2014). Duck Soup: The floating fates of hadrosaurs and ceratopsians at Dinosaur Provincial Park, in Eberth D and Evans D (eds). Hadrosaurs. Bloomington: Indiana University Press. pp. 459-466

Hone, D.W.E., Wood, D., and Knell, R.J. (2016). Positive allometry for exaggerated structures in the ceratopsian dinosaur Protoceratops andrewsi supports socio-sexual signalling. Palaeontologica Electronica. 19.1.5A: 1-13

Knell RJ, Naish D, Tompkins JL, and Hone DWE (2012). Sexual selection in prehistoric animals: detection and implications. Trends in Ecology and Evolution. 28; 38 – 47

Maidment SCR, Henderson DM, and Barret PM (2014). What drove reversions to quadrupedality in ornithischian dinosaurs? Testing hypotheses using centre of mass modelling. Naturwissenschaften. 101: 989 – 1001

Padian, K. and Horner, J.R. (2010). The evolution of ‘bizarre structures’ in dinosaurs: biomechanics, sexual selection, social selection or species recognition? Journal of Zoology. 283; 3 – 17

Buried Treasure – Matt Wedel

I’m not quite sure whether I’m supposed to be talking about my favorite paper out of my little flock, or the one that I wish had gotten more attention. But it’s okay, because the answer in both cases is the same: my 2012 paper on long nerves in sauropod dinosaurs. It’s freely online through Acta Palaeontologica Polonica.

This one is my favorite for several reasons. I think it’s the most personal of my papers, in that there was no obvious need for it, and probably no-one else was ever going to write it. Whereas with pneumaticity I just got in at the right time – that work was going to be done by someone, and probably sooner rather than later. I also like the long nerve paper because all it required was thinking. I didn’t discover anything, and I didn’t do any real work. In fact, at the outset I was basically thinking of it as sort of a stunt paper. If it had any broader meaning at first, it was merely, “Ha ha, I thought of this before anyone else did.”

But that’s the great thing about science – if you pick up any given thread and follow it, you may soon find yourself in a labyrinth of possibilities, like Theseus and Ariadne in reverse. That happened with the sauropod nerve project, which has spun off in a couple of new directions for me. One is thinking more about the peripheral nervous systems of extinct animals, which has attracted almost zero attention so far. It’s pretty esoteric – nerves leave even less of a trace on the skeleton than air sacs – but there are some interesting and useful inferences that we can draw (to find out what those are, wait for the paper!). The second spin-off is that writing the 2012 paper fired my interest in the physiology of neurons, and in fact kicked off some conversations and potential collaborations with neuroscientists. That is a career wrinkle I never anticipated.

Still, I have to admit that it is a paper without a lot of obvious applications. It hasn’t been cited much – about half as many times as other papers of mine from around that time – but I have been happy to see it cited in a variety of fields, including neuroscience, computer science, and linguistics. That’s satisfying because I cited works from a variety fields in writing the paper in the first place. In part that was because cell biology in giant dinosaurs is an inherently cross-disciplinary problem, and in part because the example of the recurrent laryngeal nerve in the giraffe has become widely known and referenced across so many fields.

My goal now is to build on the 2012 paper with at least a couple of follow-ups to show paleontologists that, yes, there is some actual science to be done here, beyond the gee-whiz aspects. That was the subject of my talk at SVPCA last year. And as I said at the end of that talk, if you’re interested in the interplay of evolutionary novelty and developmental constraint across multiple levels of biological organization, thinking about the cell physiology and comparative anatomy of large animals is a fertile playground.

Guest Post: Producing Protoceratops art

The little ceratopsian Protoceratops (and indeed art on Protoceratops) has been a big thing for me in recent years as I’ve been lucky enough to work on some very special specimens and have them illustrated in life.  As is so often the case though, one new specimen begets some new opportunities and today sees the publication of a new paper on the ongoing issue of sexual selection and social dominance signals using some of these specimens in the dataset. The paper is freely available online here and I’ve also written about it here, but the paper also contains some lovely new palaeoart of signaling dinosaurs by Rebecca Gelernter who has kindly agreed to talk about her work here.

When I plan a piece of paleoart, I try to make the animal I’m restoring as complete as possible. I want to make it look like a real, tangible creature with adaptations that make sense for its life history. I particularly enjoy showing behavior, which made this a really intriguing project to work on.

First off, I had to figure out what my Protoceratops should look like. Anatomically, this was pretty straightforward, thanks to the wealth of fossil photos, papers, and books Dave had on hand. Factor in his enthusiastic feedback and that’s all the background you could ever need. At Dave’s request, I was depicting the animals without any filaments or other non-scale integument, so after familiarizing myself with the fine points of ceratopsian feet and beaks, all that remained was to design the color scheme.

I decided that the facial markings should be only part of the body with elaborate markings, as the frill and jugal bosses were proposed display structures. When designing markings for extinct animals, I like to thumbnail several different possibilities based closely on living creatures and remix them into something new. For Protoceratops, I mostly looked at antelope facial markings, and the final design features elements of bongo and sable. The jugal bosses are an eye-catching white, and the all-important frill is a splash of those ever-popular display colors, orange and red. I imagine that the animal would flush the frill with blood during an encounter with a potential mate or rival for flashier color. I used a camouflage-friendly beige for the animal’s base color, broken up by a line of darker splotches down each side that become bolder and more regular on the tail, another potential display structure. I used white again on the tip and ventral side of the tail to create a starker contrast, with more orange to draw attention to the ridge formed by the tall neural spines.

Dave asked for the piece to show two adult Protoceratops having a confrontation, while a group of less flashy subadults goes about its business in the background. I selected a pose that showed off the display structures: tail up, frill angled toward the other individual. I angled one adult’s head toward the viewer and one away to show that the display colors are limited to the front – no point wasting resources to color the side of your head that you can’t show off. I wanted the piece to be taller and narrower than your standard portrait orientation, so I raised the point of view above the two main animals and arranged the background players some distance away on another dune. Dave suggested adding the crisscrossing footprints in the staging area to suggest that this type of interaction has happened there before. I placed the animals in a particularly empty bit of desert, with just a few small, scrubby plants in the background.

I’d recently gotten good results from painting over a graphite drawing in Photoshop, so I was eager to try that again. There are different ways of doing this, but the technique I usually use is to set the graphite original to “multiply” and leave that layer on top, painting on a few different layers stacked underneath it. It’s an interesting change from using purely traditional media, and I’m looking forward to trying new things with it.

So there you have it: my process for making (definitely) accurate, (hopefully) interesting paleoart. If you’d like to see more of my work, I’m on all the usual sites under the name Near Bird Studios.

Preparation, predation and a missing quarry

I’ve already mentioned that my time in Canada involved a short trip to Dinosaur Provincial Park with Darren Tanke, but we were also out with Mark Graham, a preparator at the Natural History Museum in London. Mark has kindly written up a guest post on the trip and the hunt for the lost Spinops quarry.

Mark preparing Spinops

The recent  Fossil Preparation and Collections Symposium (FPCS) hosted by the Royal Tyrrell Museum in Drumheller, provided a great opportunity for me to give a talk about the recent conservation and mounting of a large skull of the ichthyosaur Temnodontosaurus platyodon and also to team up with Darren Tanke for some fieldwork in Dinosaur Provincial Park to try and find the location of a lost quarry.

The quarry we sought had contained, in 1916, a bonebed of material which the legendary Sternbergs had collected for the then Geological Museum in London (now the NHM). Among the specimens collected was the partial skull and parietal elements of a horned dinosaur – a centrosaurine ceratopsian – which I had the privilege of preparing in 2008. It was a new species named Spinops sternbergorum and it was through this work that I got to know Darren (we were co-authors on the descriptive paper). He suggested that I take along a sample of the Spinops matrix so that we could use it to try and match the distinctive ironstone to exposures in an area “3 miles upriver from Steveville”, which the Sternbergs had recorded as the location of the find in their field notes. Locating abandoned quarries in the badlands from clues left in old photographs, fieldnotes, quarry markers and litter is something of a speciality of Darren’s and so I tagged on three days holiday at the end of the symposium to do some sleuthing with him.

Spinops quarry material, replete with ironstone

Dave Hone was also at the Tyrrell, undertaking research with Darren into bite marks on fossil bones and he also attended the symposium and gave a very insightful presentation titled ‘Scientific Communication of Fossil Preparation in the Digital Realm’ [Dave adds: this should go online at some point]. This discussed how his blog had been used to communicate Darren’s prepwork on the tyrannosaurine Gorgosaurus to a wide audience of professionals and amateurs. Following the symposium, Dave joined in the expedition in search of the Spinops quarry.

First, we hired a small room in a ‘Hotel and BBQ Pit’ in a little place called Patricia, a few miles outside Dinosaur Provincial Park. It is an old haunt of Canadian palaeontologists and the accommodation could best be described as offering ‘substantial scope for improvement’. I experienced for the first time in many many years the joys of an upper bunk bed! But it all added to the fun and, as the name suggested, in the evening guests get to cook their own steaks, burgers and chicken on a big indoor barbeque.

We were all up early the following morning and after a hot breakfast we set off for the field with pack lunches and plenty of water as the weather, which had been cold with snow flurries, had turned quite warm and windy. Darren had arranged access with a land owner and we drove across the prairie in search of a padlocked fence that we had been given the combination to. The terrain was incredibly flat and featureless but thanks to Darren’s knowledge and a bit of help from the GPS, we found our way. En-route we saw some great wildfowl and white tailed deer which gave Dave an opportunity to get busy with his telephoto lens.

Hoodoo

Soon enough we reached a point where the prairie fell suddenly away into coulees and down into the Red Deer River Valley with the great bluffs of the Upper Cretaceous rising all around. This landscape was formed after glaciers scraped away  great swathes of land during the last ice age 13,000 years ago and has been steadily eroding ever since, creating some wonderful capped pinnacles called hoodoos, where ironstone rich layers weather out atop columns of softer sandstone rocks, like giant mushrooms. The scene looked exactly like the old photos from the golden age of fossil hunting and we began working our way down the steep sides of the bluffs, stopping on platforms as we descended and jumping across the occasional water eroded crevice onto the next slope. Many of the surfaces were very slippery with weathered Bentonite clay shale, which mercifully was fairly dry. When wet the shale is treacherous and impossible to get a firm footing on.

Mark in the field. The area was cleared of cactus first.

Darren had warned us against nasty little cactuses which grew a few centimetres high and that left lots of needles in the hand if touched. It didn’t take me long to reach up for support climbing over a ledge and put my hand onto one, which resulted in some choice language. My right hand resembled a pin cushion and it took a while to remove the spines. Some of the broken ones stayed put and are still working their way out weeks later.

But we soon all started finding material – dinosaur, champsosaur and turtle was everywhere we looked, weathering out of the rocks all around us.  Hadrosaur and ceratopsian bones are commonplace and during our prospecting our finds included a row of articulated hadrosaur vertebrae, complete limb elements, a virtually intact ceratopsian vertebrae hanging off the edge of a slope, a perfect ankylosaur tooth and two large tyrannosaur teeth. We also found part of a hadrosaur limb with fantastic serration scars from predation. One area which demanded our attention was a steep slope at the bottom of which we were finding fragments of tyrannosaur bone and all three of us turned up several broken fragments across an area of a few feet, suggesting that a specimen was – or had been – weathering out.

Dave and Darren take out a tyrannosaur tooth

Under the provisions of the Alberta Historical Resources Act of 1978 all palaeotological, prehistoric and historic resources are protected on both crown and private lands. The DPP is a world heritage site and the law protecting its fossils is unambiguous – nothing may be removed.  Darren used a GPS to pinpoint our more significant finds and, because he represents the Royal Tyrrell, we were able to carefully remove, tag and bag the tyrannosaur teeth (which could be used in the museum’s excellent educational programme) and the predated specimen, which had an immediate research application. This material and the accompanying data were logged back at the museum. It was very satisfying for Dave and I to record our names on the specimen find tags alongside Darren, knowing that these would be associated with the specimens in the museum collections.

While no professional palaeontologist would argue against the need to protect fossils and guard against illegal collecting, it seemed very alien to leave behind really well preserved specimens to deteriorate in – and ultimately be lost to –  the elements. I couldn’t help thinking that, surely fossils like the perfect little ankylosaur tooth, the intact limb bones and phalanxes and unguals  and the  string of vertebrae could be loaned to schools and colleges  in the province and beyond to inspire students to study palaeontology; serving an important purpose and protecting the material for future generations?. While the scientific value of much of the isolated elements is limited, it could nevertheless spark passion in budding palaeontologists and who can argue that that is not in itself of scientific value?

We scoured a long stretch of the coulees – up and down each one – parallel to the river in the vicinity Darren had identified from the Sternberg field notes, paying particular attention to the boundary of the Dinosaur Park and Oldman formations. Dave found some rock closely matching the matrix sample but there was no sign of quarrying at that spot. On the second day, Darren found a metal quarry marker which he recorded on the GPS for further investigation, but he didn’t think it related to the missing quarry and he is now turning his attention (following some further intriguing clues)to the possibility that it might be located on the opposite side of the riverbank.

Spinops parietal frill: sadly still quarry-less.

My visit to the Royal Tyrrell collections, the symposium and the field trip were fantastic and I’d like to record my thanks to the organisers who did a fabulous job. In particular I know that Dave will join me in marking  our appreciation to  Darren, who spent a great deal of time with us even though he had other pressing demands, including his father’s hospitalization and a house purchase to deal with while we were with him.

Guest Post: Raptor Tails Declassified

Today Scott Persons returns to the Musings to talk more about theropod tails, their musculature and possible uses. This time around, it’s the oviraptorosaurs:

 

Previously on Archosaur Musings . . .

After my first post on dinosaur tails (which was mostly focused on the rear-ends of tyrannosaurs), I was asked a seemingly innocent question in the comments section by archo muser “Lucy”. She wrote:

“So what about oviraptorids and their reduced tails – do we assume they went the same way as emus? And do we know anything about the other maniraptors (I’m particularly thinking of dromaeosaurs and their famously odd tail design)?”

I suspect no malice on the part of Lucy and her question, but her inquiry had inadvertently put me in a corner. She had asked a good question . . . so good that I had already devoted two chapters in my master’s thesis to thinking about it and had two papers addressing the question in the works. So, I had the wherewithal to answer it, and that was my dilemma.

I am of the opinion that science should not be a covert affair. New scientific discoveries should not be closely guarded secrets. By its very nature, science benefits from transparency and from the unobstructed flow of ideas. And yet, in the modern system of journal-based publish-or-perish scientific academia, a certain level of discretion and intrigue is prudent.

Otherwise, you might get scooped. You might prematurely tell one too many colleagues what you are researching and what your results are, and, next thing you know, those ideas wind up in someone else’s publication. Maybe that someone else was already thinking the same thing and, upon hearing that they are not the only one following that particular line of thought, they rush to publish first. That leaves you with an outdated thesis and nothing new to report (and the best academic journals don’t do reruns). Consider, as an extreme example, what Alfred Russel Wallace’s place in the history books would be if he had kept his ideas to himself until going to print and hadn’t sent a certain letter to a certain long-bearded British naturalist. And sometimes, of course, the scooping can be downright nefarious.

Not that dino tail research is a ticket into the history books (I am just happy when I get asked to do a guest blog), but what seems like your own quiet little corner of paleo research can get scooped out from under you. It has happened to some of my friends. So, I did not want to tip my hand and give Lucy the answer that her question deserved. Instead, with all the aggravating crypticness of a magic eight ball, I gave what I’m sure was a dissatisfactory answer. I said, in effect, “Why, yes, dromaeosaurid and oviraptorids do have unusual tails, and, yes, I do think they were specialized for unusual functions. I am going to publishing on those topics soon. Ask again later.”

Both raptor tail papers have come to academic fruition, and I am now free of my research paranoia. The paper on dromaeosaurids (coauthored with my graduate supervisor Dr. Phil Currie) has been published in a special volume of Acta Geologica Sinica, and the paper examining oviraptorid tails (coauthored with Dr. Phil Currie and Dr. Mark Norell) is now available for early view in Acta Palaeontologica Plonica. If you are interested in what I think was going on with dromaeosaurid tails (and I think a lot was going on), then you can checkout the guest post that Dave asked me to do over at Pterosaur.net. That leaves us with the tails of oviraptors . . .

“Do we assume they went the same way as emus?”

Oviraptors have short tails (both in terms of the total number of vertebrae in their tails and in terms of tail length relative to body length). It has been argued that such short tails are evidence that the group did go the way of the emu — i.e., the ancestors of oviraptors had reduced tails for the purpose of flight and that this reduced-tail condition was retained after the group had become secondarily flightless. In fact, it has been argued by various scientists that many groups of fully-terrestrial dinosaurs may have descended from flight-capable ancestors. It is my opinion (though many wise and respectable scientists would disagree) that some of these arguments for secondarily-flightless dinosaurs are probably valid. However, in the case of oviraptors, I don’t think that the tail lends much support to the secondarily flightless hypothesis. Let me tell you why.

The wonderfully preserved skeleton of the oviraptor Khaan mckennai.

Those readers who made it through my first tail post will recall that I am interested in the musculature of dinosaur tails (as inferred through digital reconstructions based on skeletal attachment sites and comparative dissections of modern animals). In particular, I am interested in the caudofemoral tail muscles. Caudofemoral muscles are part of the locomotive system. They attach via tendon to the femur, and their retractions helped to propel a dinosaur forwards when walking and running.

In birds, the caudofemoral muscles are tremendously reduced and sometimes completely absent. That makes sense. To fly, a bird benefits from weight reduction, and what better weight could a bird reduce than that of a big muscle dangling off the rear that functions in land-based locomotion. Emu’s have reduced caudofemoral muscles (they compensate for this, as many birds do, by placing less emphasis on femoral retraction when they walk and run), but there is every indication that oviraptors did not have reduced caudofemoral muscles.

Readers of my past post may also recall that caudofemoral muscles do not extend too far back towards the tip of the tail. Instead, most of their mass is located near the tail base (by the hips and legs). The shortening of oviraptor tails appears to have been restricted to the post-caudofemoral region of the tail – that is, vertebrae near the tip were lost — and I found no evidence that the caudofemoral muscles of oviraptors were reduced. Oviraptor tails were shortened, but not at the expense of muscles that helped them to move on the ground. Not like an emu.

 

Digital model of the tail skeleton and musculature of the oviraptor “Ingenia” yanshini. Three stages of reconstruction are shown: the tail skeleton modeled based on specimen measurements (A); the caudofemoral muscles (in red) modeled over the digital skeleton (B); and the full muscle reconstruction (C).

Curiouser and Curiouser

What about the other tail muscles, are they reduced? Yes, and no. The other muscles of an oviraptor tail are considerably reduced in relative length, but not in relative mass. Wide caudal ribs (transverse processes), among other features of the tail skeleton, affirm that oviraptors had unusually robust tail muscles. Oviraptor tails were short, but stocky.

In an oviraptor tail, the individual vertebrae were short and the vertebral articulations suggest a high degree of flexibility in between the vertebrae. So, oviraptors had a lot of flexor points crammed into their short stocky tails. Per unit of tail length, an oviraptor tail may have rivaled all other theropods in its flexibility.

Then, we come to the very tip of the tail, and that’s when things really get strange. Back in 2000, it was announced that the oviraptor Nomingia had a tail that terminated in a series of fused vertebrae. This fused terminal tip was termed a “pygostyle”. Pygostyles are found in the tails of modern birds and are thought to be associated with anchoring a bird’s fanning tail-feathers. Did Nomingia have a tail feather fan? It seems likely. Direct proof that some early oviraptors had tail-feather fans comes from exquisitely preserved specimens of Caudipteryx and Similicaudipteryx, which actually have fossilized feathers preserved.

The pygostyle of the oviraptor Nomingia, composed of five fused tail vertebrae.

In our oviraptor tail paper, my coauthors and I announced the discovery of three new oviraptor pygostyles. One of these was from a second specimen of Nomingia, one was from Citipati, and one (the smallest of the three) was from Conchoraptor. These new pygostyles suggest that Nomingia may have been the rule, not the exception, and that pygostyles along with their accompanying feather fans were probably common features of oviraptors.

 

If You’ve Got It, Flaunt It

Muscular, flexible, and ending in a feathered flourish, what were oviraptor tails doing? I think they were flirting.

What good are tail feathers if you cannot fly? A lot of modern birds make use of tail-feather fans when they are on the ground. Think about a tom turkey or a peacock. Such birds use flamboyant feather-fans as display structures, most commonly, as courtship display structures. Now, imagine if the avian ancestors of peafowl and turkeys had not been forced to abandon the longer and muscular dinosaurian tail for the sake of aeronautics. What sort of a tail might these birds “want” in order to best woo potential mates and to wield their feathery instruments of seduction? Flexible, strong, and muscularly dexterous tails.

Life reconstruction of “Ingenia” yanshini, depicting a male “peacocking” to a female. Painting by the exceptionally talented Canadian artist Sydney Mohr.

Lucy, I want you to know that this follow-up blog post was unsolicited. I trust that Dave humors me and posts it, and I hope you are satisfied with the answer. Sorry for the delay.

Guest Post: A phylogeny of ankylosaurian dinosaurs

At least a few parts of the dinosaurian family tree are still relatively little studied and are controversial. One of these is the ankylosaurian dinosaurs, though a new paper seeks to delve into this problem and produced a new and comprehensive analysis. Lead author Rick Thompson takes us through it:

In 1842 Richard Owen coined the term “dinosaur”, helping to imbue the world with a fascination for the gigantic ‘terrible lizards’ of the prehistoric world. Owen’s work was based on the fossil remains of three distinct archosaurs; Megalosaurus and Iguanadon have become fixed in our consciousness as archetypal dinosaurs, while the third, Hylaeosaurus, is very much the ‘ugly-duckling’ of the trio. Hylaeosaurus is a member of the Ankylosauria, a group of Middle Jurassic to the Late Cretaceous heavily armoured herbivorous dinosaurs, closely related to the stegosaurs in the clade Thyreophora. The story of Hylaeosaurus somewhat mirrors that of its ankylosaur relatives; fragmentary, difficult to study and lacking the popularity of its theropod, ornithopod and sauropod cousins. The ankylosaurs barely even worked their way into Jurassic Park (apparently Ankylosaurus does appear in Jurassic Park III – if you can stand it…)! The lasting image of the Ankylosauria in the public consciousness is the classic battle between Ankylosaurus and Tyrannosaurus, with the ankylosaur determinedly swinging its tail club towards the leg of its powerful foe. Indeed, it is the presence of the tail club, widely regarded as a defensive weapon that could shatter bone (Arbour et al. 2009), which has helped to raise the profile of this fascinating dinosaur group.

Of course ankylosaurs are more than just a dinosaur with a weaponized tail. The Ankylosauria includes over 50 valid taxa, only a fraction of which possess this idiosyncratic armament. Fragmentary ankylosaur specimens have been recovered from every continent on Earth, though their record in North America and Asia is by far the best. It is their extensive covering of dermal armour, particularly that of the skull, that has proved to be both the blessing and bane of ankylosaur palaeontology. The high level of morphological diversity in the armour is probably responsible for the large number of ankylosaur taxa. The cranial ossifications completely cover the bony sutures of the skull, simultaneously providing a unique pattern to identify new species, while destroying a wealth of cranial characters that could help to resolve the interrelationships of the wider clade. Thus the evolution of the Ankylosauria is very poorly understood, and presents a tough challenge for systematic palaeontologists.

Traditionally the Ankylosauria is split into two families, the Ankylosauridae and Nodosauridae. The Ankylosauridae includes many of the more recognisable taxa including Ankylosaurus and Euoplocephalus. Ankylosaurids are generally identified by their short-broad skulls, which are ornamented with horn-like ossifications above (supraorbital), behind (squamosal) and below (quadratojugal) the eye, along with the presence of a tail club. The Nodosauridae generally have a more elongate skull, with a domed skull roof (parietal region) and boss-like rather than horn-like cranial ossifications. Their trunk armour often incorporates spike-like ossifications along their flanks, though no tail club is present. In recent years, a number of ankylosaurs, such Gastonia and the aptly named Gargoyleosaurus, have been found to possess combinations of these classic traits, thus blurring the distinction between ankylosaurids and nodosaurids. This has led some authors to erect a new group of ankylosaurs, the Polacanthidae, which includes many of these recent discoveries, along with a few older, fragmentary genera like Owen’s Hylaeosaurus.

 

A mounted skeleton of Gastonia burgei. Note the large shield over the pelvis, a character suggested to unite polacanthid taxa. Photo by Susie Maidment.

The validity of the polacanthid hypothesis has proved hard to test cladistically, as the majority of ankylosaur character sets are either heavily biased towards the skull, or include a limited number of taxa. As many of the potential polacanthid taxa are fragmentary, or predominantly postcranial, the incorporation of these taxa into ankylosaur phylogeny has been problematic. Studies including some polacanthid genera place them either towards the root of the Ankylosauridae, or as a new family (Polacanthidae), sister to the Ankylosauridae. During my Master’s Degree in Biosystematics at Imperial College, London, I was lucky enough to get the opportunity to try to resolve some of these issues in ankylosaur evolution. Paul Barrett and Susie Maidment offered me the chance to revise and update the unpublished PhD thesis of Jolyon Parish on ankylosaur phylogeny. My aim was to expand the taxon sample of Parish’s thesis, as well as modify his extensive character set. In this way I hoped to produce a ‘palaeontological total evidence’ phylogeny of the Ankylosauria, which included all valid taxa regardless of completeness, and a roughly even mix of cranial and postcranial characters.

The results of this project were recently published in the Journal of Systematic Palaeontology, and give some new insights into ankylosaur evolution. Encouragingly our data did support the traditional split between the nodosaurids and ankylosaurids; however, no polacanthid clade was recovered. Instead, all taxa that have been affiliated with the Polacanthidae by various authors (and Ankylosauridae by others) were resolved within the Nodosauridae. In the strict consensus tree (the tree which summarizes all of the information that each of the shortest possible evolutionary trees agree upon) the nodosaurid clade formed a polytomy – that is, we could say nothing about the internal relationships of the group. This poor resolution of the clade was in fact caused by a number of unstable taxa, whose position on the tree is highly variable. Unsurprisingly three of these unstable taxa have previously been attributed to the Polacanthidae. To counteract their influence we produced a derivative strict reduced consensus tree (shown in the figure). This tree prunes unstable taxa from the strict consensus tree, greatly increasing resolution. In this phylogeny it is clear that the ‘polacanthid’ taxa form a basal grade of nodosaurid dinosaurs, while the traditional nodosaurids (clade D) form a polytomy.

This result simultaneously highlights the strengths and weaknesses of the ‘palaeontological total evidence’ approach. By including all taxa (regardless of completeness) and a character set sampled from the whole skeleton, a large amount of missing data was guaranteed. This lowers the resolution of the tree, as seen in the traditional nodosaurid clade. However, it is the inclusion of such a broad sample of characters and taxa that has allowed completely new relationships to be revealed, placing ‘polacanthid’ taxa in the Nodosauridae. The problems have been further confounded by the extensive cranial ossification of the taxa. The variation in such complex ornamentation is exceptionally hard to capture using traditional discrete characters. This makes it very hard to test for presence of the evolutionary signal in the ornamentation. In the future, a study which incorporates extensive measurements of the cranial armour could better capture this variation, and more clearly reveal the relationships of the group. This is particularly important for the Nodosauridae, many of which are primarily distinguished by their cranial ornamentation.

The phylogeny of the Ankylosauridae was much better resolved, and broadly in agreement with existing studies, if the ‘polacanthid’ taxa are discounted. Again in this clade we see that the basal lineages do not conform to the traditional view of the Ankylosauridae, often having elongate skulls. The tip of the tail has not been recovered in many of these taxa, so the presence of a tail club is uncertain. However, our tree is the first cladistic analysis to place an ankylosaur that clearly lacks a tail club within the Ankylosauridae. Zhongyaunsaurus was originally described as a nodosaurid, though this assignment was subsequently corrected by Ken Carpenter (Carpenter et al. 2008). Our phylogeny confirms that Zhongyaunsaurus was indeed an ankylosaurid, and suggests that the most characteristic trait of the Ankylosauria is only present in the most derived ankylosaurids.

Unfortunately our study has done little to help the plight of the earliest known ankylosaur, Hylaeosaurus. Our analysis suggests that it is a member of the Nodosauridae, but its removal from the reduced consensus tree feels like a sad continuation of its rather anonymous history. Never the less, our study has helped to reveal a new perspective on the Ankylosauria. Although the ankylosaurid-nodosaurid dichotomy has been maintained, it appears that the classical characters of these groups only apply to the most derived of their forms. The earliest lineages of each family show greater levels of diversity in their armour and body form. This has made their classification difficult, and without more fossils, or newer forms of character, it is likely to remain so. There is still much work to do in order to understand the evolution of this extraordinary group of animals, but hopefully our study can serve to trigger a new wave of research in the coming years.

 

 

Guest Post: Yurgovuchia doellingi

Those keeping up with the scientific literature will know that a new dromaeosaur was described just the other day. One of the authors, Jim Kirkland, has been kind enough to pen a few lines about the discovery and has included some nice photos of the excavation too. Enjoy:

Extra final bonus Gorgosaurus preparation post

Well, it has been a while since the last post where we finally rounded up and summarised Darren’s massive series of posts on preparing a Gorgosaurus specimen. Here Darren summarises the prep work done since and provides new photos of the skull now seen from the others side.

After a long hiatus, I update the Gorgosaurus preparation series, with this, the final installment. Since the last posting, the entire specimen, and select parts thereof were moulded in a high-quality silicone rubber compound so detailed casts of the specimen can be made in the future. After the moulds were removed, the entire specimen was covered in a separating layer of wet tissue paper, and then plastered over and flipped over.

The side now facing up is that which faced up in the field. As this is the upward-facing side, and there was only low rock overburden in the field, this side of the skeleton was more exposed to the effects of rain, frost, rock fracturing and rock expansion/contraction from summer heat (up to +40C) and cold winter temperatures (down to – 40C). Because of this, this side of the specimen is less well preserved, in fact I’d say in many places it is poorly preserved- in some areas the bone is like the consistency compressed hot chocolate powder. Bones are also badly crushed in many places. If I can remove the equivalent of a sugar-cube sized piece of rock per day, that is pretty good going as I super detail the many bones preserved. The skull, being better ossified, was in better shape, but the bone quite splintery in places. This means the work has proceeded very, very slowly. The tools and techniques were much the same as in earlier postings, though much of the work is being done with a head-mounted magnifying lens and later, probably microscope work. Also the work has to go much slowly. It can be seen that the posterior right side of the face is missing. This is because as the carcass rotted, the side of the head, exposed to water currents, was disarticulated and piece by piece the bones were washed away. We have a couple of them, but are missing 6-7 to make a full skull. However, we get a beautiful side view of the braincase which is important for researchers. We had the whole skull CT scanned recently and really nice images resulted for study by one of the Royal Tyrrell Museum scientists.

Preparation work on this side has also revealed some anatomical details that are important to future scientific study and eventual publication(s) that cannot be shared here or at this time and therefore, this series must end with this posting. I have been happy to share the preparation of this gorgeous little specimen with you all and hope you learned something about the intricacies of fossil preparation.

Best, Darren Tanke, Senior Technician II, Royal Tyrrell Museum, Drumheller, Alberta, Canada.

As usual all images are copyright to Darren / the Tyrrell Museum.

Guest post: Rhamphorhynchus…again: Superprecocial “flaplings” or defenseless hatchlings?

Today a guest post by Edina Prondvai. Edina and her work group have a new paper out looking at the growth rates of specimens of the ubiquitous Solnhofen pterosaur Rhamphorhynchus which has important implications for the ecology of young animals. Here she takes us through the work (which is in PloS ONE and so available to all right here):

Guest Post: Dinosaurs and the latitudinal biodiversity gradient

Today Phil Mannion returns to the Musings with a guest post on his recent paper on dinosaur diversity patterns and their relationships to latitude. Take it away Phil:

The presence of a latitudinal biodiversity gradient (LBG), whereby species richness is highest in the tropics and declines polewards, is a pervasive pattern affecting the majority of life on Earth today, and was recognised by early naturalists such as Charles Darwin and Alexander von Humboldt (whose foundation coincidentally partly supported the research outlined below). Despite its near ubiquity (on both land and in the sea), the causes of the gradient are less well established, with numerous hypotheses proposed over the last fifty or so years. Most of these have been refuted, leaving climate and the distribution of area as the two most likely causes. Understanding the cause and evolution of the gradient is vital to predicting biodiversity loss driven by present-day climate change and explaining geographical variation in biodiversity; as such the fossil record offers a unique perspective on this issue.

Previous work investigating the deep time LBG focused on marine invertebrates – these studies tended to find support for a modern type pattern throughout the Phanerozoic (approximately the last 530 million years). Little prior work has been carried out on terrestrial species, but the few studies to look at the deep time LBG on land found no evidence for a modern pattern until after the Eocene (approximately 30 mya).

Along with colleagues from the UK (Roger Benson, Paul Upchurch, Richard Butler and Paul Barrett) and USA (Matt Carrano), we looked at the LBG in Mesozoic dinosaurs (including birds). Using a number of different methods to mediate for sampling biases in the fossil record, we found no evidence for a modern type pattern at any point in the 160 million year evolutionary history of Mesozoic dinosaurs; instead we found dinosaur diversity to peak at palaeotemperate latitudes (30-60° North and South). The consistency of this result across analyses for different time slices indicates that this pattern is not controlled by climatic fluctuations – evidence suggests that the climatic gradient was “flatter” in the Mesozoic than today (i.e. there was less of a difference in temperature between tropical and temperate regions) – but was instead driven by the amount of available land area in latitudinal belts.

Residual dinosaur diversity after controlling for sampling, plotted against non-marine area (NM area) and palaeogeographical reconstructions for the Late Triassic (bottom), Jurassic (middle) and Cretaceous (top). From Mannion et al., 2012

Given that living birds conform to the modern day pattern, a significant change must have occurred at some point in the last 65 million years. Evidence from molecular phylogeny (and work on fossil insects) suggests that this change occurred at the end of the Eocene (34 mya), following the strengthening of the climatic gradient and an increase in seasonality. As such, there is no evidence for a modern type LBG on land before the last 30 million years.

Mannion, P. D., Benson, R. J. B., Upchurch, P., Butler, R. J., Carrano, M. T. and Barrett, P. M. 2012 (Published online). A temperate palaeodiversity peak in Mesozoic dinosaurs and evidence for Late Cretaceous geographical partitioning. Global Ecology and Biogeography, doi: 10.1111/j.1466-8238.2011.00735.x

Guest Post: Dysalotosaurus histology

Today Tom Hübner takes us through his recent paper on the bone histology of Dysalotosaurs. This little ornithopod is a close relative of Dryosaurus (pictured here) but unlike the US Dryosaurus, comes from the famous Tendaguru beds of Tanzania. This is a great piece of work to see for me as Tom started this work for this PhD thesis in Munich while I was there and so I know the long hours and hard work Tom put into this and it’s great to see it come to fruition.

Many of you might know it already that I finally got a rather long paper on the bone histology of a small ornithopod dinosaur (Dysalotosaurus) published in PLoS ONE. 29 pages sounds like a lot but I wanted to break with tradition a bit to publish only as brief a paper as possible. This had something to do with the beginnings of my studies on bone histology because most papers at that time restricted the information to the most necessary facts which was quite difficult to follow and reconstruct. Without the personal help of ‘experts’ I never would have understood all that. Another reason for the length of the paper is the enormous variation in the microstructure of the bone. Many times I was struck by a completely different type of tissue and it needed some time to identify them and sort them out. That’s because ‘variation’ is also one of the three main topics of the paper.

Anyway, for everyone interested in bone histology, I think it is worth reading [seconded, it’s a great review as well as providing new information and analyses]. The most important aspect is the usage of a new type of growth cycles for life history reconstructions which might be applicable for other vertebrates as well, especially when they lack lines of arrested growth (LAGs).

From Hubner, 2012. Thin sections of Dysolotosaurs bone in normal and polarised light

Some might wonder why such a small animal delayed sexual maturity until about its 10th year of life because it should suffer many losses by all types of predators. Well, that’s a good question and difficult to answer. One strategy is definitely the precocial breeding strategy, but the predators could also be the reason for delayed sexual maturity. The animals would not start breeding until they were large and strong enough to withstand the additional stress of mating and breeding, and they still had at least 5 years for reproduction because, according to the size-frequency distribution, only after about 15 years of age decreased their abundance within the herd significantly. Large ornithopods, on the other hand, had the opposite strategy (see Cooper et al. 2008) by outgrowing predators in a short time. Most of them also had altricial breeding behavior. This, and other arguments presented in the paper, could be a good non-phylogenetic difference between small and large ornithopods in general, but there is still much do to before this can be a strongly supported theory. As always: “More fossils and more studies …”.

From Hubner, 2012: Comparative growth rates of Dysolotosaurs with other dinosaurs and mammals

Constructive criticism is always welcome, so don’t hesitate to post them. I’m still not at all too old to change my mind. Well, this is science – nobody can learn something new without knowing where the mistakes are.

As this is in PLoS ONE, the paper is freely available here.

Hübner TR (2012) Bone Histology in Dysalotosaurus lettowvorbecki (Ornithischia: Iguanodontia) – Variation, Growth, and Implications. PLoS ONE 7(1): e29958. doi:10.1371/journal.pone.0029958

Guest Post: Scarfe’s snout

After a week of pterosaur posts, it’s time for Dave Martill to pitch in with this guest effort. Dave and Steve Etches have just described a new pterosaur and Dave has been kind enough to pen this little effort on the critter:

Cuspicephalus scarfi from the Late Jurassic Kimmeridge Clay Formation of Dorset is one of those irritating fossils. It was clearly a beautiful animal, with long, slender jaws and fine teeth that would have made it look impressive. It is without doubt a cracking fossil, displaying a near perfect right lateral outline, with only a little bit of the dorsal rest missing. OK, it is sad that the lower jaw and rest of skeleton is missing, but in the UK, this specimen is the best thing since the second specimen of Dimorphodon was discovered in the Lower Jurassic in the mid 1800s. But despite its near completeness for a British pterosaur skull, it is not entirely clear where it belongs in the grand scheme (or schemes), of pterosaur phylogeny. It appears to be a pterodactyloid similar to Germanodactylus on the basis of its single NAOF and straight dorsal border, but when compared with Darwinopterus, its affinities become less clear cut. Sure, it isn’t Darwinopterus, but it isn’t Germanodactylus in the strictest sense either. Dave Unwin thinks it might lie close to the base of Dsungaripteroidea, and I am inclined to agree, but caution that this is based mainly on the nature of its crest… not a good criterion given the distribution of elongate fibrous-looking crests in Pterosauria.

Cuspicephalus skull. From Martill & Etches, in press

Cuspicephalus was discovered by Steve Etches. Known to most UK vertebrate palaeontologists, Steve collects fossils exclusively from the Kimmeridge Clay of Dorset and has built up a renowned collection housed in the Museum of Jurassic Marine Life (MJML) in Kimmeridge, Dorset. Steve discovered Cuspi on the wave cut platform in Kimmerdge Bay and reckons that one more tide would have destroyed it. Steve has found several other pterosaurs in the Kimmeridge Clay, some of which are represented by associated remains attributable to an animal close to Rhamphorhynhcus, and currently being examined by PhD student Michael O’Sullivan. A few specimens in Steve’s MJML have been identified as representing a germanodactylid by DMU, and it is possible that these elements are from the same animal as Cuspicephalus: clearly Steve needs to get out and find the complete skeleton. (Late edit: bonus images courtesy of Dave).

The name Cuspicephalus is derived from the sharp pointed nature of the skull in lateral view, and I suspect in dorsal view too, but Kimmeridge Clay fossils are rather 2D to tell. The specific epithet honours Gerald Scarfe CBE. Scarfe is known to most UK citizens as the artist who provided the caricatures for the intro to the extremely popular satirical TV series Yes Minister and follow up Yes Prime Minister. Both were excellent lampoons of the UKs higher civil servants and mainly incompetent elected politicians. Globally Scarfe is known to several generations of Pink Floyd fans as the artist behind The Wall (album, film and more).

Margret Thatcher as drawn by Gerald Scarfe. Courtesy Dave Martill

To readers of certain newspapers and periodicals Scarfe is loved or laothed for hard hitting political caricatures, and in particular those of British Prime Ministers and other notorious world leaders. Many were reproducible in daily newspapers, but others remained within the underground literature for reasons of decency (check out Rupert bear ****ing Mary Whitehosue with the Pope watching on). One cartoon of Scarfe’s that stands out is a caricature of Margaret Thatcher, an ex British Prime Minister who Scarfe Portrayed as a Tory blue, saggy-breasted pterodactyle, and therefore it seemed only fair that he should be honoured. Scarfe’s cartoon might have the number of fingers wrong, and he might have followed the Frey and Riess model for the orientation of the pteroid, but we all know he got the colour right.

Pip pip
Martill