Saturday, May 21, 2011

Ankylosaur tail pathologies.

My most recent paper with my coauthor and supervisor Phil Currie appeared online at Historical Biology this week. It is the last of the chapters from my MSc on ankylosaur tail club biomechanics (although I am still working on ankylosaurs, the focus is now on the phylogenetic relationships within the ankylosaurids and their biogeography). However, it contains very little about the biomechanics of tail clubs...

Most of my MSc thesis used a lot of math and fancy-dancy computer modeling to look at whether it is biologically feasible for ankylosaurids to have used their tail clubs for forceful impacts (and therefore as offensive or defensive weapons). But another way to look for evidence of behaviour is to look for injuries, which can sometimes, if you’re lucky, give you clues about some of the more dramatic moments in an animal’s life. So as I was looking at specimens for my MSc (and into my PhD), I always kept an eye open for anything unusual or abnormal that could be a pathology.

What I would love to tell you is that I found healing fractures in the handle vertebrae or knob of the tail club, because that would be pretty good evidence that ankylosaurids were smashing things with their tails. Sadly, I have not seen anything like that in any of the tail club specimens I’ve seen. There are several explanations for the absence of handle pathologies:
  1. Ankylosaurids did not use their tails for forceful impacts.
  2. Ankylosaurids did use their tails for forceful impacts, but the impact forces were never enough to cause the tail to break.
  3. Ankylosaurids did use their tails for forceful impacts, and the impact forces were so great that a fracture was probably catastrophic and unlikely to heal.
  4. Ankylosaurids did use their tails for forceful impacts, and injuries occurred sometimes, but we haven’t found any injured specimens yet.
Out of all of the above scenarios, I think #4 is the most likely. Ankylosaurids could pack a wallop with their tails, especially those with the largest knobs. I am quite sure injuries occurred sometimes, but I bet they were reasonably rare and the chances of finding a healed tail club are probably low.

What else did we find? Well, there’s a tail club knob that may have become infected – it’s on display at the Royal Tyrrell Museum Field Station if you happen to be visiting Dinosaur Provincial Park this summer, and you can check it out for yourself. There's a big hole on the right major osteoderm, and this osteoderm is also much taller in posterior view.


In two pelvis specimens, I saw large holes where some of the sacral vertebrae attach to the ilium. One of these is AMNH 5337, on display in the Hall of Ornithischian Dinosaurs at the American Museum of Natural History. I am unsure what exactly may be causing these holes, but in the paper we speculate that they may be similar to the extra fenestrae that sometimes occur in ceratopsian frills (see Tanke and Farke 2007). Perhaps these are areas of low mechanical stress and the bone is simply resorbed. They are certainly unusual, and it would be interesting to see if any other dinosaurs show evidence of lesions like these.


And finally, several specimens of anterior free caudal vertebrae had rough, rugose bone textures on the neural spines and sometimes on the transverse processes. In two specimens (a Euoplocephalus at the AMNH and the Talarurus mount at the Palaeontological Institute in Moscow) some of these anterior vertebrae are fused together. At first I thought these might be infections, but as it turns out, the anterior caudal vertebrae of whales and crocodiles can fuse as a mechanical response to stress from swimming motions (see Galatius et al. 2009 and Mulder 2001). It is conceivable that this was occurring in ankylosaurids either as a response to keeping the heavy tail club elevated off that ground, or as a result of tail club swinging.

I wasn’t able to draw any definitive conclusions about tail-clubbing in ankylosaurs based on my pathology survey, and trying to diagnose bone pathologies in fossils is EXTREMELY challenging. Perhaps it is something that gets easier with time. But I had a lot of fun with this project and I think it is worthwhile to look at palaeopathologies as potential sources of information, as long as you’re careful how you interpret them.

References!

Arbour VM, Currie PJ. 2011. Tail and pelvis pathologies of ankylosaurian dinosaurs. Historical Biology, online 19 May 2011.

Galatius A, Sonne C, Kinze CC, Dietz R, Beck Jensen J-E. 2009. Occurrence of vertebral osteophytosis in a museum sample of whitebeaked dolphins (Lagenorhynchus albirostris) from Danish waters. Journal of Wildlife Disease 45:19–28.

Mulder EWA. 2001. Co-ossified vertebrae of mosasaurs and cetaceans: implications for the mode of locomotion of extinct marine reptiles. Paleobiology 27:724–734.

Tanke DH, Farke AA. 2007. Bone resorption, bone lesions, and extracranial fenestrae in ceratopsid dinosaurs: a preliminary assessment. In: Carpenter K (ed). Horns and beaks. Bloomington (IN): Indiana University Press. p. 319–348.

Tuesday, May 17, 2011

The World's Largest Dinosaurs!

After my visit to the Smithsonian I popped over to New York to spend some time at the AMNH. As luck would have it, the special exhibit The World’s Largest Dinosaurs had just opened a few weeks ago.



The AMNH already has a pretty big claim to fame sauropod-wise in their dynamic, rearing Barosaurus mount. In the Hall of Saurischian Dinosaurs, there’s also an Apatosaurus and the excellent Glen Rose sauropod tracks from Texas. But there was still plenty to see and learn from the new exhibit.



For all that the name implies, the World’s Largest Dinosaurs actually does not overwhelm with large sauropodiness. There are two very large pieces in the room, the Mamenchisaurus model and accompanying projection show, and a large mock-up of the lungs. The lungs were pretty cool and quite a clever way to convey how unidirectional airflow works for us tidal-flow mammals, and also did a great job emphasizing the great distances involved in just getting air to the lungs. Blue and red coloured lights tracked the progress of oxygenated and deoxygenated air into and out of the lungs. It was kind of abstract and it was beautiful, and I could see that this was catching people's attention. It was just so darn weird that people had to find out what it was supposed to be.



However, many of the displays were smaller and at kid-height and focused on individual bits of anatomy – in this station, we see a braincase and brain, and there was a nice labelled diagram on the panel below. Other stations let you look in a microscope to see the pores in chicken eggs, through special glasses to see the different colour patterns a sauropod might have had, and a comparison of a sauropod vertebra to a giraffe vertebra. There was lots of hands-on stuff.



I also liked the emphasis on the diversity of sauropods. Although they all have the same basic bodyplan, there are really a great deal of variations on the long-neck-long-tail theme. I’m curious if the models above were maquettes for the large mural accompanying the exhibit. Featured sauropods include (from the back and then left to right): Argentinosaurus, Apatosaurus, Camarasaurus, Sauroposeidon, Europasaurus, Mamenchisaurus, and Amargasaurus. If I could have added a few more, I would have put in the short-necked Brachytrachelopan, the thagomizer-having Spinophorosaurus, and the tail-clubbed Shunosaurus. But perhaps I reflect a tail-bias in that previous sentence...



And finally, as a thyreophoran worker I would be sorely remiss if I did not feature this tremendous osteoderm...even though it’s not from an ankylosaur. It’s a titanosaur osteoderm from India. The responses to this station by the visitors included “What’s that? ....uh, what?” and “No really, what’s that?” Oh well. I liked you, shapeless osteoderm.


You can read another review of The World's Largest Dinosaurs at SV-POW!

Monday, May 9, 2011

Name That Specimen, Smithsonian Edition

The fossil halls at the Smithsonian were great fun, but do you know what might have been my next most favourite hall? The Hall of Bones! I am not sure I have ever seen so many non-mammal skeletons on display. I also liked how a lot of the displays highlighted anatomy and functional morphology. The whole thing was just deliciously old-school museum in all the best ways: detailed, focused, and elegantly presented. In a way it was like stepping into a 3-dimensional anatomy textbook, but more fun because here are the bones right in front of you that you can see from all kinds of different angles, and compare easily.


I'm not sure a hall like this would be built nowadays - detailed anatomy guides may not seem as relevant as ideas about ecology, conservation, and evolution. It was also extremely low-tech, with not a single touch-screen, TV, or projection to be seen. But I was glad it was there, and I think it complemented the taxidermy dioramas and multimedia-intensive galleries.

Here are some close-ups from some of the photos I took – can you guess what animal each belongs to? Answers below!


1.

2.

3.

4.

5.

6.

7.





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1. Look closely – you’ll see the tiny arms of the brown kiwi (Apterix australis) alongside it’s egg-shaped body. I also had no idea kiwi ribs were so broad!

2. Quill knobs are prominent on the humerus of the brown pelican (Pelecanus occidentalis).

3. The powerful shoulders and large olecranon process should give you a clue: this is the arm of the giant anteater (Myrmecophaga tridactyla).

4. That fang looks like it should belong to a sabre-toothed cat, but it’s actually an Indian muntjac, Muntiacus muntjak, a small deer (amusingly labelled as a barking deer in the exhibit, which I suppose must be an older name).

5. The casque of the cassowary (Casuarius casuarius) is surprisingly spongy.

6. Those unusual rodent-life incisors belong to the aye-aye (Daubentonia madagascariensis).

7. This strangely bent neck belongs to the anhinga, Anhinga anhinga (anhinga anhinga anhinga...).

Saturday, May 7, 2011

Look at that...whatever it is.

I had an unsettling moment today when it occurred to me that, perhaps, people don’t learn anything from museums.

I sincerely hope this is not true. I say this after having visited the marvellous Smithsonian Museum of Natural History, spending about 5 hours today perusing the galleries and shamelessly eavesdropping on people’s reactions to the exhibits. Kids were certainly excited about the exhibits and eagerly pointed things out to their parents. But what sorts of things did I overhear parents saying to their children?

In reference to a very nice mosasaur skeleton, with accompanying illustration: “That’s neat sweetie, look. It looks kind of like a crocodile I guess. It must be a crocodile fish.”


By that logic, I guess the early whale Zygorhiza is probably a crocodile fish, too.


Looking at Pteranodon: “Look at that...whatever it is.”


That is a Pteranodon, good sir, as the label clearly states. This comment particularly stung because of all the things I remember from my visit to the Smithsonian when I was 10, it was this Pteranodon keeping watch over the dinosaur hall that was most burned into my memory. Also, holy mackerel! Look at the wing below it!


In front of Ceratosaurus: “Look kiddo, T. rex!”

Ceratosaurus does not equal Tyrannosaurus.


I was heartened to see some parents slowing down, reading things to their children and asking them questions about the exhibits. But for the most part, most folks simply went ‘Wow! A dinosaur!’, snapped a photo, and kept going. The same was largely true for a lot of the other exhibits as well, particularly in the ocean gallery (although in that case, the comment was ‘Wow! A giant squid!’).


In other galleries, I was a bit surprised by reactions to the unknown or new.

At the binturong: “What kind of cat is that?” followed by immediately walking away.



At the Chinese pangolin: “What the hell is that? GROSS!” followed by immediately walking away.



I will not fault people for not knowing that Ceratosaurus is different than Tyrannosaurus, or not having any idea what a pangolin is. What I find distressing is the lack of desire to KNOW reflected by some of these comments. The reactions were not “What kind of cat is that? A binturong? Oh, it’s not a cat? Why? That’s neat!” or “Look at that...whatever that is...oh, it’s a Pteranodon!” The reactions were “I don’t know what that is and I’m not going to do anything to change that.”

These comments got me thinking about the role of natural history museums (and museums of any sort, I suppose), once again. I love museums. I think I learn when I visit museums, especially for topics I know little about. I may not get a lot out of most dinosaur exhibits, but I almost always find something new (e.g., the Smithsonian’s small but very good exhibit on the dinosaurs from Maryland, and I will talk about this more in a later post). But how do other people approach museums? Perhaps not everyone shares the same enthusiasm for all topics, and will breeze through the exhibits – and that’s ok. Perhaps museums are most effective at teaching when they are visited by school groups; school visits are probably more focused on a single gallery, may have the students filling out worksheets or booklets and therefore LOOKING at things for more than 5 seconds, and teachers may have access to curriculum guides and other resources not available to tourists or parents. Follow-up activities may help the students reflect on what they saw. For most regular tourists though, what are they getting out of the museum? I don’t mean this flippantly – I would be genuinely interested to know if there has been any research done on what people retain from museum visits, and how to deliver information in a museum setting most effectively. The museum was busy and bopping and full of energy, and everyone seemed to be enjoying themselves immensely. But if you aren’t pausing, reflecting, asking questions and seeking answers, what are you getting out of the museum experience?

Tuesday, May 3, 2011

Congratulations Phil Bell!

Some congratulations are in order for my fellow grad student Phil Bell, who successfully defended his PhD thesis today!


Phil's thesis is titled "Systematics and palaeobiology of the crested hadrosaurine Saurolophus, from Canada and Mongolia." He's been working for the Philip J. Currie Dinosaur Museum (previously the River of Death and Discovery Dinosaur Museum) since last fall.

You can read more about his work on Saurolophus in these papers; I'm sure there will be several more to come:

Bell PR, Evans DC. 2010. Revision of the status of Saurolophus (Hadrosauridae) from California, USA. Canadian Journal of Earth Sciences 47:1417-1426.

Bell PR. 2011. Redescription of the skull of Saurolophus osborni Brown 1912 (Ornithischia: Hadrosauridae). Cretaceous Research 32:30-44.

Bell PR. In press. Cranial osteology and ontogeny of Saurolophus angustirostris from the Late Cretaceous of Mongolia with comments on Saurolophus osborni from Canada. Acta Palaeontologica Polonica.