The Great Canadian Dinosaur Hunt

Dino Hunt Canada is almost here! Starting this Friday, History Channel Canada will be airing a series of hour-long documentaries devoted to dinosaur expeditions all across Canada - and not just in the famous badlands of Alberta! The production crew visited field localities in Nova Scotia, Saskatchewan, multiple places around Alberta, and British Columbia. It's going to be a real who's who and where's where of Canadian palaeontology.

I'll be in the second episode featuring work in Dinosaur Provincial Park, which we filmed in 2013. It was a fun if somewhat unusual experience to have such a large film crew with us, and I'm looking forward to seeing the whole shebang!

What was the crew filming in DPP? Tune in to find out!

There's also a really excellent website to accompany the show. You can learn more about some of the dinosaurs featured in the series (including wonderful new artwork by Danielle Dufault!), see interviews with some of the palaeontologists, and submit ideas for a nickname for a new dinosaur excavated during the show by the Southern Alberta Dinosaur Project. You can even submit questions and maybe have my weirdo face answer them via Skype! All in all, it's looking really good so far and I'm so happy to see the huge variety of dinosaur research being conducted across Canada by so many talented and hardworking people.

Know Your Ankylosaurs: New Mexico Edition!

There's a new ankylosaur in town - meet Ziapelta sanjuanensis from the Cretaceous of New Mexico!

Hello, Ziapelta! Many thanks to new Currie Lab MSc student Sydney Mohr for this wonderful life restoration of Ziapelta.

Ziapelta is represented by the holotype skull, first cervical half ring, and assorted other osteoderms, AND a referred first cervical half ring! (What are the odds of finding two really nice cervical half rings in the same field season? Bonkers!) It's a wonderful find from an area that seems to keep producing interesting dinosaur fossils.

Surprisingly, Ziapelta doesn't seem to be particularly closely related to the other ankylosaurid from the Kirtland Formation, Nodocephalosaurus. Instead, it's a close relative of Euoplocephalus and friends from Alberta – it shares the same general shape and pattern of cranial ornamentation, with flat, hexagonal caputegulae rather than the round, conical caputegulae of Nodocephalosaurus. Ziapelta is distinct from all of the Albertan ankylosaurids though: it's squamosal horns are thick and curve slightly downwards laterally, and its median nasal caputegulum is huge and triangular, rather than hexagonal. Somewhat bizarrely, Ziapelta has slightly bulbous or 'inflated' looking cranial caputegulae, not to the same extent as some of the Mongolian ankylosaurids like Saichania, but definitely moreso than Euoplocephalus or Anodontosaurus.

Cervical half rings once again prove to be taxonomically useful. Ziapelta has taller, more rectangular keeled osteoderms compared to Euoplocephalus, Anodontosaurus, and Scolosaurus, but does share the interstitial osteoderms present in Anodontosaurus.

Although we don't have the rest of the postcrania, we can assume that Ziapelta would have had a tail club since it is deeply nested within the clade of clubbed ankylosaurids. Did it have huge, triangular osteoderms like Anodontosaurus, a round tail club like Euoplocephalus, or a narrow tail club like Dyoplosaurus?

Ziapelta isn't the first ankylosaur described from New Mexico - in fact, it's just the latest in a string of interesting armoured dinosaur discoveries from there. At present, Glyptodontopelta is the only nodosaurid from the state, from the Maastrichtian Ojo Alamo Formation. It's known only from osteoderms, and mostly those from the pelvic region, but they're pretty distinctive and have a unique dendritic surface texture.

Glyptodontopelta bits at the Smithsonian.

Nodocephalosaurus is known from a partial skull from the De-na-zin Member of the Kirtland Formation. Its nodular cranial ornamentation is totally unique among North American ankylosaurids and more closely resembles the Late Cretaceous Mongolian ankylosaurids - an intriguing biogeographical conundrum that remains unresolved.

Nodocephalosaurus holotype skull at the State Museum of Pennsylvania. Check out those conical caputegulae!

Lesser known but deserving of more attention, my fellow labmate Mike Burns and colleague Bob Sullivan recently named another ankylosaurid from the stratigraphically lower Hunter Wash member of the Kirtland Formation. Ahshislepelta has a weird scapula with a strongly folded-over acromion process, as well as various other bits and bobs of the postcrania. Although there is little overlapping material between Ahshislepelta and Ziapelta, Ahshislepelta's osteoderms have a smoother surface texture, and the stratigraphic separate suggests we're probably looking at two different species.

Ahshislepelta holotype scapula at the State Museum of Pennsylvania.

Ziapelta is also neat because it (and Nodocephalosaurus) occur in a slice of time where we don't have very good ankylosaurid material in Alberta. In Alberta, we're in the lower part of the Horseshoe Canyon Formation – probably Anodontosaurus was found here around that time, but we don't have too many good specimens. Was it possible that Ziapelta roamed through the lower HCF? Or, are Ziapelta and Nodocephalosaurus characteristic of a southern Laramidian dinosaur fauna, like we seem to be seeing with some of the slightly older formations in Alberta (Dinosaur Park Formation) and Utah (Kaiparowits Formation)? Only more specimens will help us answer those questions.

I'm very grateful to Bob Sullivan, who found these specimens, for inviting me to help out with this paper, and to Spencer Lucas at the New Mexico Museum of Natural History and Science for his hospitality during my visit in 2012 to study the specimen. I hope one day I can have a chance to do some fieldwork in New Mexico, although I fear my thick Canadian blood would not serve me well and I would pretty much immediately die from the heat. Mike Burns and I had a great visit to Albuquerque in June 2012 to study the specimen, but boy howdy was it hot there. Ziapelta is housed at the New Mexico Museum and will be on display there, so if you're in the neighbourhood go say hi for me!

You can read all about Ziapelta in our open access paper in PLOS ONE!

Arbour VM, Burns ME, Sullivan RM, Lucas SG, Cantrell AK, Fry J, Suazo TL. 2014. A new ankylosaurid dinosaur from the Upper Cretaceous (Kirtlandian) of New Mexico with implications for ankylosaurid diversity in the Upper Cretaceous of western North America. PLOS ONE 9:e108804.

Ninja-edit! I would be severely remiss in not linking to some of the thoughtful news coverage we were very lucky to receive for this paper!
* Brian Switek covers our research at Laelaps: "Ziapelta - New Mexico's newest dinosaur."
* Hear my weirdo voice on the CBC's Edmonton AM!
* And via the University of Alberta, "New dinosaur from New Mexico has relatives in Alberta."

More papers!

Burns ME, Sullivan RM. 2011. A new ankylosaurid from the Upper Cretaceous Kirtland Formation, San Juan Basin, with comments on the diversity of ankylosaurids in New Mexico. New Mexico Museum of Natural History and Science Bulletin 53:169-178.

Ford TL. 2000. A review of ankylosaur osteoderms from New Mexico and a preliminary review of ankylosaur armor. New Mexico Museum of Natural History and Science Bulletin 17:157-176.

Sullivan RM. 1999. Nodocephalosaurus kirtlandensis, gen. et sp. nov., a new ankylosaurid dinosaur (Ornithischia: Ankylosauria) from the Upper Cretaceous Kirtland Formation (Upper Campanian), San Juan Basin, New Mexico. Journal of Vertebrate Paleontology 19:126-139.

Dinosaur Provincial Park fieldwork 2013

Last week I returned to Happy Jack's at Dinosaur Provincial Park for a brief stint of fieldwork. This has been the University of Alberta's base camp since 2008, and the area has been very productive for us.

Just north of our campground is the old homestead Old Mexico Ranch, where Happy Jack lived from 1903 to 1942.

A few weeks before we arrived in camp, a huge fire burnt away most of the sage bushes and other scrub at ground level. You can see scorch marks on the cottonwood trees in this photo. Windy days meant we all got pretty dirty from blowing ash.

We have a pretty nice setup in camp - two large canvas tents are our supply tent and kitchen tent (and also work as a shelter during rainy days). A fire pit and grill are available for cooking when there aren't fire bans, and the river is our bathtub (although a bit silty). 

We headed across the river from Happy Jack's to check out some possible locations for the Scolosaurus quarry. I was very grateful to be out with Darren Tanke, who has been researching the location of the quarry for quite some time, and Phil Currie. Both of them know Dinosaur Provincial Park like the back of their hands (well, their own hands). 

We weren't able to pinpoint the exact location of the quarry just yet, but tantalizing clues continue to be unearthed. I am hopeful that one day we will be able to relocate the quarry and determine once and for all if Scolosaurus is from the Oldman or Dinosaur Park formation.

The area around Happy Jack's, on the north side of the Red Deer River, has steeper badlands compared to the 'core' area of Dinosaur Provincial Park where the camping and visitor facilities are located. This means there's slightly less accessible exposure and you have to do a lot of climbing. But, it also meant it had been prospected much less for several decades until we began working there in 2008. We've found several interesting and scientifically significant specimens over the last few years that are still undergoing preparation and awaiting publication, but I'm looking forward to sharing them here once they're published!

Traversing the steep slopes sometimes requires more courage than I think I am naturally equipped with, but I enjoy the challenge of navigating around this landscape. You have to watch out for sinkholes and steep dropoffs. Ironstone pebbles and dry bentonite can roll under your feet and cause you to fall and slide, so you have to be relatively surefooted. 

The bentonite is surprisingly sharp on your hands when it's dry, and it isn't pleasant to put your hands on it while climbing. (But still preferable to sticking your hand on a cactus, which I stupidly did a couple of times when I started to slide. Ouch!) When it rains, the bentonite swells up and becomes incredibly greasy. It's impossible to get your footing, and it gloms on to your boots. When it rains it is too treacherous for us to go hiking, but even as the bentonite is drying it can be very slippery.

But the rewards of hiking around this terrain are well, well worth it. It is almost impossible to walk around Dinosaur Provincial Park without finding at least some bone. The trick is finding stuff that is worth collecting - the volume of bone is so high that we cannot possibly collect all of it, so we need to be somewhat choosy in what we bring back to the university. (No hadrosaur caudal centra allowed, unless they are pathological!) The bones in this picture are the weathered remains of a hadrosaur. They were too far gone to collect, but we recorded their location with a GPS. We keep a database of uncollected dinosaur skeletons in the park, for understanding relative dinosaur diversity geographically and stratigraphically.

I was happy to find this nicely preserved ?fibula on the second day of fieldwork. Just a little piece of one end was showing, but it was obviously still going into the ground, so I decided to pick a little bit at it. I'm glad I did!

On my last afternoon in the park, we spent an hour or so prospecting in the marine Bearpaw Formation, which overlies the terrestrial Dinosaur Park Formation. I don't usually spend a lot of time looking in the Bearpaw, so this was neat for me. The Bearpaw is usually a dark grey shale, but at this spot in the prairie it is weathering out a bit reddish. You can see a couple of white chert nodules in the bottom left corner - these often had chunks of large ammonites, or sometimes clams or bryozoans!

Who-oplocephalus: Everything old is new again.

Over the last few posts, I've talked about why Euoplocephalus tutus is a valid genus and species, how the Horseshoe Canyon Formation ankylosaurid is really Anodontosaurus lambei, and how the headless and clubless holotype of Scolosaurus cutleri is most likely the same species as the ankylosaurid from the Two Medicine Formation. Here's a diagram summarizing some of the key points from the paper.

One ankylosaur I didn't talk about in the previous posts was Dyoplosaurus acutosquameus, an ankylosaurid long synonymized with Euoplocephalus tutus but resurrected by me and my colleagues Michael Burns andRobin Sissons back in 2009. 

ROM 784, holotype of Dyoplosaurus acutosquameus, from Arbour et al. (2009).

The holotype of Dyoplosaurus, ROM 784, is another really nice specimen, consisting mostly of the back half of the animal (although a fragmentary skull is also preserved). Dyoplosaurus differs from Euoplocephalus in the shape of the hooves on the hind foot (which are more triangular than in other ankylosaurs), and in some aspects of the pelvis. The tail club knob is very narrow compared to almost all other tail clubs from the Dinosaur Park Formation, although it's not entirely clear how much of this is related to ontogeny versus taxonomy. Do tail clubs start off narrow and become increasingly wider as the animal grows? Or do they maintain approximately the same proportions and just increase in size? The sole tail club knob for Scolosaurus is about the same width as in ROM 784, but the knob is round and about as long as wide. If knob proportions changed as they got bigger, we'd expect knobs of the same width to have about the same length:width ratio, but that isn't the case between TMP 2001.42.9 and ROM 784. We'll need more specimens in order to really test this hypothesis, but for now I'm tentatively considering the narrow tail club knob of Dyoplosaurus to be a characteristic of that genus. And because of that, there is one other isolated tail club that may be referable to Dyoplosaurus – UALVP 47273, a specimen I CT scanned and used in my biomechanics of tail clubbing project.

Digital model of UALVP 47273 from CT scans, made using Mimics. 

Going from one to four species is a big increase in diversity. Is this a reasonable conclusion based on the patterns of diversity in other dinosaurs? I think so. Euoplocephalus was already kind of weird for dinosaurs from Alberta because it occurred in the Oldman Formation, throughout the Dinosaur Park Formation, and throughout the Horseshoe Canyon Formation. Few dinosaur species are found in all three formations, and even within the Dinosaur Park Formation there are three faunal zones with distinct sets of species. Based on my research, there is now good evidence to suggest that Euoplocephalus tutus was primarily found in Megaherbivore Assemblage Zone 1 (sensu Mallon et al. 2012), which represents about the lower 30 m of the formation. Anodontosaurus lambei is almost exclusively found in the Horseshoe Canyon, with only one specimen, TMP 1997.132.1, found in the upper part of the Dinosaur Park Formation. Scolosaurus is mostly present in the Two Medicine Formation, and the holotype is either from the lowest Dinosaur Park Formation, or perhaps from the Oldman Formation. Finally, Dyoplosaurus is from the lowest Dinosaur Park Formation as well.

Campanian-Maastrichtian ankylosaurids from Alberta and Montana, from Arbour and Currie (2013).

So, where do I go from here? Well, for my PhD dissertation I'm trying to better understand the evolution of ankylosaurid dinosaurs, and so knowing who all of the players are is really essential for constructing a revised phylogenetic tree. Understanding variation in cranial ornamentation in Euoplocephalus will also help me understand which other ankylosaur species are valid or need to be synonymized, or maybe even identify some new species. I also now know that tail club shapes are at least somewhat taxonomically informative, and this leads to questions about function and behaviour. If there really are three ankylosaurid species in the lower Dinosaur Park Formation, what does that mean for niche partitioning among similar large herbivore species? Why does Scolosaurus appear in the geologically older Oldman Formation, disappear, and then reappear in the younger upper Two Medicine Formation? Does this reflect habitat preferences in ankylosaurid species? As usual in science, answering one question leads to many more.

I've also had some people asking if there's anything going on with the Albertan nodosaurid ankylosaurs. My fellow grad student Mike Burns is currently working on the nightmare of taxonomy that is Edmontonia longiceps, Edmontonia rugosidens, Panoplosaurus mirus, and various combinations thereof. I'm looking forward to seeing what he comes up with! And of course, don't forget that the Royal Tyrrell Museum collected an astonishingly good nodosaurid (probably) fossil from Early Cretaceous marine sediments near Fort McMurray, Alberta, in spring 2011. If you're visiting the Tyrrell this summer, you can see parts of it being prepared in the lab.

Tomorrow I am off to Dinosaur Provincial Park for a brief bit of fieldwork, including, hopefully, a search for the Scolosaurus quarry. Wish me luck, and hopefully there will be even more ankylosaur news over the next couple of months.

Papers!

Arbour VM. 2009. Estimating impact forces of tail club strikes by ankylosaurid dinosaurs. PLOS ONE 4:e6738.

Arbour VM, Snively E. 2009. Finite element analyses of ankylosaurid dinosaur tail club impacts. Anatomical Record 292:1412-1426.

Arbour VM, Currie PJ. 2013. Euoplocephalus tutus and the diversity of ankylosaurid dinosaurs in the Late Cretaceous of Alberta, Canada, and Montana, USA. PLOS ONE 8:e62421.

Hill SR. 2012. An unconvential discovery from an unconventional resource: recovery of an Early Cretaceous ankylosaur fossil from an oil sands mining operation, Fort McMurray, Alberta, Canada. Search and Discovery Article #70121, adapted from poster and extended abstract presented at AAPG Annual Convention and Exhibition, Long Beach, California, April 22-25, 2012.

Mallon JC, Evans DC, Ryan MJ, Anderson JS. 2012. Megaherbivorous dinosaur turnover in the Dinosaur Park Formation (upper Campanian) of Alberta, Canada. Palaeogeography, Palaeoclimatology, Palaeoecology 350-352:124-138.

Who-oplocephalus?

Today I published a revision of the North American ankylosaurid genus Euoplocephalus. I'd like to take some time to go through some of the major points of the paper over the next few days here, but today I will give a brief introduction to the motivation behind this study.

Euoplocephalus is one of those 'classic' dinosaurs. Named in 1902 (as Stereocephalus, which was preoccupied by...a beetle! of course), it wasn't known from very much material. All that Lambe had was a chunk of the snout/forehead region, and an unusual structure called a cervical half ring. Cervical half rings are totally bizarre structures that seem to be unique to ankylosaurids. They're made of an underlying yoke of fused bone segments, and topped by fused osteoderms like you see on the rest of an ankylosaur's body. 

Canadian Museum of Nature 0210, holotype of Euoplocephalus tutus. On the left, the skull chunk. On the right, the first cervical half ring. Images modified from Arbour and Currie (2013).

Over the next couple of decades, three more ankylosaurid species would be identified from Alberta (besides Ankylosaurus): Anodontosaurus, Dyoplosaurus, and Scolosaurus. Anodontosaurus is known from a complete but somewhat squished skull and a half ring, Dyoplosaurus is known from an articulated pelvis and tail, plus hindlimb and other assorted bits, and Scolosaurus is known from an exquisitely preserved skeleton with in situ osteoderms and skin impressions, but without a skull or tail club.

In the 1970s, Walter Coombs, Jr. undertook a large and important study of the ankylosaurian dinosaurs, which formed the foundation for many subsequent studies of ankylosaur anatomy and systematics. More specimens had been collected by that point, and subtle variations in the skull ornamentation among these specimens led Coombs to conclude that either every specimen must be its own distinct species, or they all represented the same species: Euoplocephalus (because it was named first). That's a pretty reasonable conclusion to have drawn with the available evidence at the time.

For my MSc thesis at the University of Alberta, I studied the biomechanics of tail clubbing in ankylosaurids, and specimens referred to Euoplocephalus formed an important part of that research. This is where I became interested in the variation that I saw in tail clubs referred to Euoplocephalus – some were small, some were large, some were skinny, some were round, some were pointy. What did it all mean? Were all of these the same species? Was I looking at ontogenetic changes? Were tail clubs just really variable in Euoplocephalus? What would this mean for how the tail clubs were used?

Wow, 2007 was a long time ago. Anyway, here's me at the Royal Ontario Museum holding the smallest tail club referred to Euoplocephalus, ROM 7761, and standing next to the largest, ROM 788. I CT scanned ROM 788 for my finite element analysis research, and you can now see it on display in the ROM's dinosaur gallery.

This was ultimately what led me to pursue my current line of research into ankylosaur systematics and evolution. I hoped that by understanding variation within Euoplocephalus, I would be better able to assess the validity of other ankylosaurid species, and perhaps identify new species. Over the next couple of posts, I'll talk about how I did this study, and what makes a Euoplocephalus a Euoplocephalus. Stay tuned!

The title for this post was shamelessly stolen from Collin Vanburen, because it is hilarious and perfect.

(But you don't have to take my word for it...: Arbour VM, Currie PJ. 2013. Euoplocephalus tutus and the diversity of ankylosaurid dinosaurs from the Late Cretaceous of Alberta, Canada, and Montana, USA. PLOS ONE 8: e62421.)

What I Did on My Summer Vacation: Happy Campers

 

This is Happy Jack's (or as it used to be called, Old Mexico Ranch), an old homestead occupied by Happy Jack Jackson from 1903 to 1942. There are a couple of log cabins, some with cacti growing on the roof. Happy Jack's is found on the north side of the Red Deer River in Dinosaur Provincial Park, and is the home base for the Currie Lab when we do fieldwork in DPP.

 

 

The cabins are full of rattlesnakes, so rather than camping right out in the field, we have a really nice spot in the cottonwood grove near the river. The night I took this photo there were 18 people in camp, but most of the time our crew is around 10 people. 

 

 

The badlands around Happy Jack's have been very productive for the last five years, and we've collected several very nice skeletons that unfortunately I can't say anything about yet (but I promise they're good). This year we didn't have any major finds, but we did a lot of prospecting and collected lots of interesting small things. In the photo above, a bunch of us are checking out an articulated hadrosaur, that was unfortunately too far gone to be salvageable or worth collecting. It was a nice spot on a sunny day, however, so nobody minded too much. There are always more bones in Dinosaur Provincial Park.

 

 

And when I say there are always more bones, I mean it. Dinosaur Park is kind of a ridiculous place. There are so many bones that we only collect things that are complete and well-preserved, so I didn't bring back the vertebra you can see in the lower left of this picture (although I did get a hadrosaur frontal from this spot). There are many places where you can't help but walk all over bone fragments, because they are just so numerous.

 

 

And then there are bones that look like they're straight out of a 'How to be a Palaeontologist' book, like this femur my friend Scott found.  

 

 

We have some awfully nice scenery in camp.

Cool Stuff

"Cool Stuff: The University of Alberta Museums Do Winter" is a winter-themed exhibit that opened last week at the U of A's Enterprise Square location. I checked it out last weekend and was pleased to see so many different types of objects on display. We have 28 different collections on campus, and most (maybe all?) were represented in the exhibit - butterflies, moss, picked parasites, textiles, and more. 

The University of Alberta Laboratory for Vertebrate Paleontology contributed fossils from our Grande Prairie and Edmonton dinosaur bonebed excavations. Although we usually collect stuff in the summer, we've had snow during our Edmonton fieldwork, even in May.

We showed off some field jackets, too. The Monoclonius and ornithomimid are pretty self-explanatory, and if I recall correctly, "Skull B" is from the Wapiti bonebed in Grande Prairie. There were also photos from our December tyrannosaur helicopter lift in Dinosaur Provincial Park, including a photo taken by me!

Last spring we purchased a cast of the Cryolophosaurus original non-reconstructed skull for both teaching and research, but it fit in perfectly with the exhibition theme! The grey slab behind the skull is the Wonder Block from the MOTH locality, which has a variety of 'jawless fish'. Phil will be giving a talk about his 2011 Antarctic expedition on March 1, as part of the exhibition's speaker series.

The exhibition also features specimens from our zoology collections, including these Arctic and sub-Arctic mammals (caribou, deer, and walrus).

"Cool Stuff" mixes natural history objects with cultural heritage objects, and in particular I was pleased to see so many Inuit and Inuvaliut art pieces. I am always astounded by whalebone sculptures like this one.

Another display had Inuit dolls, musical instruments, hunting tools, and boots. The beautiful paintings in the background are the original art from Ted Harrison's "A Northern Alphabet". Click the photo to make it bigger, and see if you can figure out what letter each painting represents.

"Cool Stuff" is open until March 4, and admission is free. It was cool, go check it out. 

5 Questions for Caleb Brown

I'm very pleased to present another UALVP-related study today, this time by Caleb Brown (formerly at the University of Calgary and now at the University of Toronto). Caleb recently published a paper in PLoS ONE featuring one of my favourite UALVP specimens, our Stegoceras partial skeleton, UALVP 2.


1. What inspired you to conduct this study?

I was initially interested in pachycephalosaur postcranial anatomy for the purpose of differentiating between isolated pachycephalosaur postcranial material and those of basal ornithopods (like Thescelosaurus and Parksosaurus), on which I was doing my Masters research at the University of Calgary with Anthony Russell. In order to get a better understanding of the postcranial anatomy of these animals I went to the source, Stegoceras - UALVP 002, one of the best (if not the best) pachycephalosaur skeletons known, and the first postcranial skeleton discovered. In addition to other things, I was initially struck by the presence of large numbers of bony elements that I could not identify and that did not match the morphology of other ornithischians.

 

 

These elements looked superficially like gastralia, and indeed that is what they were identified in Gilmore’s 1924 description. But ornithischians were not supposed to have gastralia, so my interest was peeked. Investigation into the literature revealed that others had worked on these enigmatic elements; Marya´nska and Osmólska (1974) found similar elements in the tail of Homalocephale in Mongolia, illustrating they were not gastralia, and Sues and Galton (1987) correlated the structures between Homalocephale and Stegoceras. Particularly interesting was the articulated series found in the tail of Homalocephale. These showed a distinctive pattern that matched myomeres and myosepta, the sideways “w” shaped muscles and tendons, seen in fish.

Fortunately, with funding from Lubrizol Corp. and Montessori High School (University Circle, Cleveland, OH) I was able to accompany Michael Ryan (Cleveland Museum of Natural History) and David Evans (Royal Ontario Museum) to Mongolia to do fieldwork in the summer of 2009. I was also fortunate enough to be able to examine the Homalocephale specimen while I was there. This allowed me to test my ideas about the deep homology of these interesting structures.

2. What’s so special about pachycephalosaur tails, anyway?

First off, pachycephalosaur tails, like the rest of their postcranial skeletons, are rare. Often with dinosaurs you find the rest of the skeleton but are missing the most important part, the head. This is not true for pachycephalosaurs, which we know almost everything about based on the skull. You can count on one hand the number of partial skeletons known (and these are partial skeletons). What we know about pachycephalosaur skeletons is limited to these few specimens. They are special in that when preserved they show a unique morphology of having a halo of superficial “W” shaped elements forming a cylinder around the entire circumference of the tail. This is not seen in other dinosaur groups, or any other tetrapod. That is not the only odd thing though; they lack the deep longitudinal or paraxial tendons seen in most other ornithischian groups and they have elongated and highly bowed caudal ribs.  These three things may be related, but that is not yet clear.

3. What is the difference between gastralia, ossified tendons, and ossified myorhabdoi?

This is an interesting question with a bit of a complex answer. All of these structures are similar in that they are not endochondral bones, that is they do not develop from a cartilaginous precursor, which is the case with the majority of the postcranial bones in most taxa.

Gastralia are dermal or intramembranous bones that are associated with the abdominal musculature, and can be associated with respiration. They were likely the primitive condition for tetrapods but today are restricted to Crocodylia, Sphenodon, and possible the plastron of turtles (Classens, 2004).

The term ‘ossified tendons’ describes a variety of structures including ossified myorhabdoi. Although this term would include any ossification of the connective tissues articulating muscles to bones, its usage in dinosaurs, particularly ornithischians, usually refers to longitudinal paraxial structures along the dorsal or caudal vertebral series. These tendons often have the pattern of either a trellis or longitudinal bundles, can be epaxial or hypaxial, and are usually closely associated with the vertebrae (Organ 2006). Ossified myorhabdoi are restricted to the caudal musculature, and are essentially ossified myosepta. Unlike the majority of the paraxial tendons, these are superficial, forming a halo around the circumference of the tail where the transverse skeletogenous septum intersects with the integument, and preserve a morphology reminiscent of the undifferentiated myoseptal musculature of fish. They are also different in their histological structure (Organ and Adams, 2005). We still know very little about ossified myorhabdoi and hopefully discovery of additional specimens and more research on extant taxa will reveal more regarding their significance.

4. Why don’t other dinosaurs have a caudal basket?

It is often hard to answer why some groups have a structure while other don’t, and this becomes particularly difficult when the function of the structure is not fully understood. If the function of the ‘caudal basket’ is to rigidify the tail of pachycephalosaurs, then the reason that other groups don’t have it is because many have found a different solution to the same problem.  Many other ornithischians have longitudinal or paraxial tendons (usually called “ossified tendons”) in the form of a trellis or bundles. Some theropods stiffen their tail by extending the zygapophyses across numerous vertebrae. Until the function of these structures can be better established, we may not know the full significance of their occurrence.

 

5. Does the presence of a caudal basket tell us anything about head-butting behaviour in pachycephalosaurs?

The caudal basket likely had significant implications for the posture and locomotion of pachycephalosaurs. It has been suggested by previous authors that it helped the tail to act as a tripodal prop, potentially during intraspecific behaviour. It would also have greatly stiffened the tail. Our analysis is consistent with these interpretations, and in that manner is consistent with the idea of head-butting behaviour in pachycephalosaurs. 

The presence of the caudal basket has also been used to support the idea of agonistic flank butting behaviour in pachycephalosaurs (Goodwin et al., 1998), with the caudal basket acting as armor. We suggest that the morphology of the myorhabdoi is not consistent with armor seen in other groups, and this function in pachycephalosaurs seems unlikely.

Thanks very much Caleb! You can read more about pachycephalosaur tails in:

Brown CM, Russell AP. 2012. Homology and architecture of the caudal basket of Pachycephalosauria (Dinosauria: Ornithischia): the first occurrence of myorhabdoi in tetrapoda. PLoS ONE 7(1): e30212.

Old Man Winter

A diversion today before I finish my Argentina posts, since we did something really cool (cool! get it? ha!) yesterday.

We headed to Dinosaur Provincial Park to finish collecting a tyrannosaur that had been discovered in 2010 and largely excavated this summer. The specimen has a complete pelvis, but it was just too large a jacket to take out with people power alone. We enlisted the help of a helicopter to bring the jacket up to prairie level, and although we were a bit concerned about fog when we arrived it cleared up in plenty of time and the lift went off without a hitch.

The helicopter was able to set the jacket right into the flatbed truck and the pelvis is now at the university waiting to get prepped.

December in Alberta can be pretty chilly but it was a beautiful snowy day with hoarfrost coating all of the trees and grasses. The snow wasn't very deep but it did make it a bit challenging to descend into the badlands, as there were some steep and slippery spots and we had to watch out for semi-covered sinkholes. In the end it was a lovely crisp day to be outside, and very fine indeed to come home to a hot chocolate (with maybe a dash of Baileys for good measure).

You can pick your friends, and you can pick your nose...and you can definitely pick your ankylosaur's nose.

Say hello to Euoplocephalus, the best known ankylosaur you've never heard of. Besides Pinacosaurus from Mongolia and China, there are more specimens referred to Euoplocephalus than to any other ankylosaurid, and it is certainly the most well represented ankylosaurid from North America. Yet Euoplocephalus often gets overlooked because its younger cousin is THAT ankylosaur, the one that starred at the World's Fair and was in Jurassic Park III and Clash of the Dinosaurs and Dinosaur Revolution and gets all the cool toys and, you know, is the namesake of the group. You know, Ankylosaurus. Well, hopefully you'll be hearing more from me about Euoplocephalus over the coming months. Today we'll be picking its nose.

Ankylosaurs are kind of weird as dinosaurs goes, because they get rid of things like the antorbital and supraorbital fenestrae, and tuck the laterotemporal fenestrae back behind the squamosals and quadratojugals. In a sense, the windows to the skull are all closed, and so it's hard to see some of the internal features that are more visible on other dinosaur skulls. Our new paper describes UALVP 47977, a busted up Euoplocephalus skull from Dinosaur Provincial Park. Normally, busted skulls don't appear very exciting, as important pieces might be missing, and they don't make very good display specimens. In this case however, UALVP 47977 gives us more information because it is broken! This specimen shows off details of the braincase and nasal passages that we don't typically get to see, including impressions of blood vessels.

I am trying (slowly but surely) to sort out the mess that is the genus Euoplocephalus, and so I was interested in comparing UALVP 47977 with other skulls to see if any of its features were present in other skulls. The only other skull that is naturally broken in a similar way is AMNH 5238, and it looks pretty similar - it even has blood vessel impressions in the same place (this specimen is also super cool because it has ciliary osteoderms, or, bony eyelids!). I was delighted when Dr. Larry Witmer made the CT scans of AMNH 5405 available on his website following the Witmer and Ridgely (2008) publication on paranasal sinuses. I also made arrangments to CT scan UALVP 31, one of our 'classic' University of Alberta specimens.

With CT scans in hand, I went through the process of eliminating matrix from the inside of the nasal passages (in essence, picking their noses), so I could examine the skull roof of these two specimens. This process is called segmentation, which means that you place a 'mask' over the parts of the CT scan that you want to appear in the 3D model, and remove the mask where you don't want something in the model. Although the software we use, Mimics, has lots of tools to help speed up the segmentation process, with fossils sometimes the contrast between bone and stone is not very great. As a result, sometimes you just have to go through the CT scans slice by slice and trace out by hand what you want to keep. This is super tedious work at times and I have the utmost respect for the amazing 3D visualizations that come out of Dr. Witmer's lab. Eventually we invited Dr. Witmer to collaborate on the paper with us, but I think it was good that we were able to independently test their 3D model using different software and fresh eyes, a sentiment echoed over on the WitmerLab blog.

The segmentation process begins! All of that uniformly-dense stuff in the palatal area has to go. The green 'mask' will be eliminated wherever there is matrix instead of bone, leaving only the bone in the 3D model.

I won't go into too much detail on the paper here, but I will say that this was a tough but very interesting project to work on. I've learned a lot about braincases and brains and noses over the course of writing this manuscript, but I'm sure I've still got more to learn. I've definitely had a lot of moments where I felt pretty stupid for not knowing certain things, but I think perhaps part of science is getting outside of your comfort zone. Ankylosaur tails are good, but skulls are pretty fun too, and I hope I can share some more skull papers with you soon! 

Here's a video we put together for the press release accompanying the paper, featuring the ever lovely UALVP 31.

Literature!

Miyashita T, Arbour VM, Witmer LM, Currie PJ. 2011. The internal cranial morphology of an armoured dinosaur Euoplocephalus corroborated by X-ray computed tomographic reconstruction. Journal of Anatomy, first published 29 Sept 2011, doi:10.111/j.1469.-7580.2011.01427.x.

Witmer LM, Ridgely RC. 2008. The paranasal air sinuses of predatory and armored dinosaurs (Archosauria: Theropoda and Ankylosauria) and their contribution to cephalic architecture. Anatomical Record 291:1362-1388.

And check out the post over at Pick & Scalpel, which has more information and some great images!

An armored dinosaur gets a second opinion—and the crazy-straw nasal passage survives!

...and finally, because this has certainly helped me sometimes:

Schwartz MA. 2008. The importance of stupidity in scientific research. Journal of Cell science 121:1771.