Wednesday, 11 May 2011

CJES Vol.47 - Albertosaurus Special Edition - a review.

Back in September of last year, the Canadian Journal of Earth Sciences produced a special volume devoted to Albertosaurus sarcophagus, specifically to celebrate the 100 year anniversary of the discovery, by Barnum Brown, of the now very famous Albertosaurus bone bed that he found near the Red Deer River in August 1910. Brown excavated the remains of at least nine individual tyrannosaurs and then, for one reason or another, the site got lost in the annals of time until it was famously rediscovered by Phil Currie in 1997.


This volume contains a number of papers that are exclusively devoted to the continual research and findings from this unique theropod bone bed. The volume has been specially edited by Currie and Eva Koppelhus with associate editing by Hans-Dieter Sues and they have amassed an impressive array of researchers to contribute to the volume.

The stratigraphy, sedimentology and taphonomy is looked at in considerable detail by Eberth and Currie and by combining the evidence from all three disciplines, they deduce that these tyrannosaurs were killed by a major storm event that was capable of uprooting trees and flooded much of the landscape, thus drowning these animals. Papers from Koppelhus and Braman and Larson et al also make significant contributions that enable us to successfully visualise in detail the palaeo-environment that these tyrannosaurs were part of.

These albertosaurs lived in a cool, dry climate that was becoming progressively warmer and wetter. Interestingly, Larson et al suggest that since the differences in fauna between the late Campanian and early Maastrichtian are so slight, that it is likely that environmental conditions were responsible for those that did occur as opposed to faunal turnover.

Tanke and Currie’s history of Albertosaurus discoveries is thorough, as you would imagine, and I particularly liked this paper since I do enjoy the history of dinosaurian discoveries. Indeed Darren’s work is always worthy of special mention and I am a huge admirer of his dedication and work ethic. I’ve blogged recently about Thomas Carr and am a confirmed follower and his contribution to the volume is his reassessment of the taxanomic affinities of Albertosaurus sarcophagus. Carr identifies the palatine and maxilla as diagnostic of the species and not only confirmed that the tyrannosaurids of the bone bed are indeed Albertosaurus sarcophagus but is also able to confirm that both the type (CMN 5600) and paratype (CMN 5601) are definitely referable to the taxon. Lots of detail including stratigraphic distribution and ontogeneric change make this paper a must read.

Some highly detailed work by Buckley et al look at tyrannosaurid tooth morphology using the multitude of specimens recovered from the bone bed that represent both adults and juveniles and conclude that variation in morphology occurs throughout ontogeny. Indeed, some of the tooth morphology is so extreme that specimens could be mistaken for either aberrant tooth morphologies or maybe even a new species. Only because the bone bed represents so many different individuals of different ages could these conclusions be made. Miriam Reichel also looks at teeth but this time looking at tyrannosaurid heterodonty using digital 3-D models. By comparing albertosaurine (A. sarcophagus) and tyrannosaurine (T.rex) teeth, Reichel confirms heterodonty and that tooth morphology and purpose is sensitive to the proportion of the jaw.

Phil Bell looks at a few of the bone bed elements that display paleopathologies and, whilst always fascinating, there are not enough elements to draw any satisfactory conclusions except, of course, that maybe this group of tyrannosaurs may have been in good health. Always hard to call, this sort of observation. Erickson et al look at the life expectancy curve of Albertosaurus sarcophagus since the number of recognised individuals in the quarry has now increased since 1997 and compared these details with results from earlier studies. These reveal that young albertosaurs had a (surprisingly) low mortality rate (3.47%) from ages two to thirteen but an increase in mortality rates to almost 20% from mid-life to death, which is postulated to be around 28 years of age. This may be due to animals becoming sexually mature and enduring all the rigours and challenges that reproduction represents. Also of interest is that if juveniles survived their first couple of years then they would invariably get to about 15 years of age and this appears to be the average life expectancy and it is expected that very few albertosaurs would make the maximum expected age of 28.

Finally, Currie and Eberth look at the possibility of gregarious behaviour in Albertosaurus and conclude that these tyrannosaurs were indeed gregarious to some degree. As we all know, and I continue to point out, any behavioural implication can only be inferred but I have to say that I do agree with the authors. A combination of osteology, ontogeny and sexual variation in skeletons, as well as evidence of intraspecific combat such as face biting, all suggest social interaction of some sort. The authors, however, maintain that the biggest pointer to gregariousness is the fact that the prey animals moved in herds and that it made good sense to hunt in numbers. How sophisticated this gathering may have been is impossible to quantify but there is sufficient implication from extant animals, such as birds and crocodiles that give some idea how this may have occurred.

In conclusion then, I have only scratched the wealth of information that is enclosed in this unique volume and, if like me, you are a follower of tyrannosaur research, then I can heartily recommend the volume. The amount of data provided is astonishing and it is only when you read a unique publication, such as this one, that you can appreciate the amount of work, research, time and effort that goes into the study of a bone bed such as this. All this and an awesome Michael Skrepnick cover as well. Recommended.

References

Phil R. Bell. Palaeopathological changes in a population of Albertosaurus sarcophagus from the Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada. Canadian Journal of Earth Sciences, 2010, 47:1263-1268, 10.1139/E10-030

Lisa G. Buckley, Derek W. Larson, Miriam Reichel, Tanya Samman. Quantifying tooth variation within a single population of Albertosaurus sarcophagus (Theropoda: Tyrannosauridae) and implications for identifying isolated teeth of tyrannosaurids. Canadian Journal of Earth Sciences, 2010, 47:1227-1251, 10.1139/E10-029

Thomas D. Carr. A taxonomic assessment of the type series of Albertosaurus sarcophagus and the identity of Tyrannosauridae (Dinosauria, Coelurosauria) in the Albertosaurus bonebed from the Horseshoe Canyon Formation (Campanian–Maastrichtian, Late Cretaceous. Canadian Journal of Earth Sciences, 2010, 47:1213-1226, 10.1139/E10-035

Philip J. Currie, David A. Eberth. On gregarious behavior in Albertosaurus. Canadian Journal of Earth Sciences, 2010, 47:1277-1289, 10.1139/E10-072

David A. Eberth, Philip J. Currie. Stratigraphy, sedimentology, and taphonomy of the Albertosaurus bonebed (upper Horseshoe Canyon Formation; Maastrichtian), southern Alberta, Canada. Canadian Journal of Earth Sciences, 2010, 47:1119-1143, 10.1139/E10-045

Gregory M. Erickson, Philip J. Currie, Brian D. Inouye, Alice A. Winn. A revised life table and survivorship curve for Albertosaurus sarcophagus based on the Dry Island mass death assemblage. Canadian Journal of Earth Sciences, 2010, 47:1269-1275, 10.1139/E10-051

E. B. Koppelhus, D. R. Braman. Upper Cretaceous palynostratigraphy of the Dry Island area. Canadian Journal of Earth Sciences, 2010, 47:1145-1158, 10.1139/E10-068

Derek W. Larson, Donald B. Brinkman, Phil R. Bell. Faunal assemblages from the upper Horseshoe Canyon Formation, an early Maastrichtian cool-climate assemblage from Alberta, with special reference to the Albertosaurus sarcophagus bonebed . Canadian Journal of Earth Sciences, 2010, 47:1159-1181, 10.1139/E10-005

Miriam Reichel. The heterodonty of Albertosaurus sarcophagus and Tyrannosaurus rex: biomechanical implications inferred through 3-D models. Canadian Journal of Earth Sciences, 2010, 47:1253-1261, 10.1139/E10-063

Darren H. Tanke, Philip J. Currie. A history of Albertosaurus discoveries in Alberta, Canada. Canadian Journal of Earth Sciences, 2010, 47:1197-1211, 10.1139/E10-057

7 comments:

Hadiaz said...
This comment has been removed by the author.
Hadiaz said...

I know this is an old blog post, but I have some questions about the Albertosaurus papers.

"Some highly detailed work by Buckley et al look at tyrannosaurid tooth morphology using the multitude of specimens recovered from the bone bed that represent both adults and juveniles and conclude that variation in morphology occurs throughout ontogeny."

Are you saying that young albertosaurines (like young tyrannosaurines) have different teeth & thus ate different things from the adults? I ask b/c, last I checked (See "Tyrannosauridae": http://books.google.com/books?id=6ZV1KcVNM18C&pg=PA119&dq=%22tyrannosauridae+in%22&hl=en&ei=VPPPTq6XLuff0QHf9rHsDw&sa=X&oi=book_result&ct=result&resnum=4&ved=0CD8Q6AEwAw#v=onepage&q=%22tyrannosauridae%20in%22&f=false ), young albertosaurine teeth "are simply scaled down versions of" adult albertosaurine teeth. What exactly changed since then? Just making sure I follow.

"Finally, Currie and Eberth look at the possibility of gregarious behaviour in Albertosaurus and conclude that these tyrannosaurs were indeed gregarious to some degree. As we all know, and I continue to point out, any behavioural implication can only be inferred but I have to say that I do agree with the authors. A combination of osteology, ontogeny and sexual variation in skeletons, as well as evidence of intraspecific combat such as face biting, all suggest social interaction of some sort."

Have you read Cau's blog post about that paper (See the last paragraph: http://translate.google.com/translate?hl=en&sl=it&u=http://theropoda.blogspot.com/2010/09/albertosaurus-2010-numero-speciale-del.html&ei=9a_BT8DDAYbK6gGmnNXGCg&sa=X&oi=translate&ct=result&resnum=8&ved=0CGQQ7gEwBw&prev=/search%3Fq%3Dtheropoda%2Balbertosaurus%2Bcau%26hl%3Den%26biw%3D1366%26bih%3D706%26prmd%3Dimvns )? I ask b/c, as you can see, he basically said the opposite of what you said about Currie & Eberth's conclusions & the evidence for gregariousness. If what you said is true (While I haven't been able to read the paper myself, you've proven yourself trustworthy IMO), then that means he blatantly misconstrued what Currie & Eberth said. I knew he had a tendency to ignore relevant evidence based on his other blog posts, but this is a new low. Just making sure I'm not the only 1 who noticed if this is the case.

Many thanks in advance.

-Herman Diaz

Mark Wildman said...

Interesting comments. Bear with me for a week or so since I am currently away from the archives and I'll respond on my return.

Mark Wildman said...

Dinosaur Systematics was published in 1990 and, although it is still a worthy contribution to the literature and worthy of reference,understanding the morphology of teeth has improved no end.

The paper mentioned from that volume (Currie et al 1990) examines multiple theropod crowns from throughout the Judith River Formation. Reichel's work, however, is from what appears to be a single population of albertosaurs represented by individuals at different ontogenetic stages.

My interpretation of Reichel's work is that tyrannosaurid teeth, in general (hence the comaprison with the tyrannosaurine Tyrannosaurus),naturally changed their shape and thickness throughout ontogeny to reach the standard incrassate shape in the adult stage.

Whether this meant a different feeding strategy in younger animals is uncertain but the well publicised juvenile Tarbosaurus from last year (Tsuihiji et al 2011)displays characters that suggest this may have been the case.

However, looking at Tarbosaurus recently leads me to believe that it is not the best analogue to describe tyrannosaurine characteristics. It displays some very odd, almost basal, traits for such an advanced theropod.

With reference to gregarious behaviour in albertosaurs, I have now looked at Andrea's post and compared it with mine and I think you are a little harsh in your assessment. In effect we are both stating the same thing but in different ways although Andrea is indeed a critic of anything that implies behaviour in extinct organisms simply because it is untestable.Google's translation leaves a little to be desired as well.

My post does indeed highlight the facts and as Currie and Eberth state and they do believe that these animals were gregarious to some extent but obviously cannot determine why and for how long - except for the usual speculation. I do too incidentally.

Perhaps I should have used the word "infer" as opposed to "conclude" since, as I have only recently blogged about, such words can cause consternation and confusion amongst the palaeo-community.

Hadiaz said...

"The paper mentioned from that volume (Currie et al 1990) examines multiple theropod crowns from throughout the Judith River Formation. Reichel's work, however, is from what appears to be a single population of albertosaurs represented by individuals at different ontogenetic stages."

That helps explain what's changed since Currie et al. 1990. 1 of said paper's conclusions is that young theropod teeth "are simply scaled down versions of" adult theropod teeth. IIRC, this is still the general rule, but now w/tyrannosaurids as the possible exception, right?

"With reference to gregarious behaviour in albertosaurs, I have now looked at Andrea's post and compared it with mine and I think you are a little harsh in your assessment. In effect we are both stating the same thing but in different ways although Andrea is indeed a critic of anything that implies behaviour in extinct organisms simply because it is untestable.Google's translation leaves a little to be desired as well."

Again, sorry if I came across too strongly/harshly. It's just that, after noticing Cau's aforementioned tendency, I got used to assuming the worst from him. In this case, though, it was just a matter of you & him using different wording (& Google's translation being weird), right?

-Herman Diaz

Mark Wildman said...

I believe that most theropod teeth display some form of morphological change throughout ontogeny but only to a limited extent. Certainly a juvenile allosauroid tooth is the same, more or less, as the adult version although some carcharodontosaurid teeth can also look tyrannosaurid on occasion when they inflate.

But tyrannosaurid teeth certainly go through a somewhat significant change as they get older and bigger.

Andrea has very clear views on what he perceives and believes in. I believe a lot of what he writes on his blog suffers through the translation although he writes excellent english. In my experience, he knows what he's talking about - it's just that it might not always fall into line with other people's perceptions and Andrea is not afraid to say so. He's alright is Andrea - trust me on this!

Hadiaz said...

In reference to teeth, that's more-or-less what I thought based on what I've read (E.g. http://discovermagazine.com/2003/jun/cover ). Thanks for confirming my thoughts.

In reference to Cau, don't get me wrong: My problem isn't w/him having different views, but w/him not accounting for relevant evidences that contradict his views. However, I trust you in that he probably does mean well & just didn't know about said evidences when he posted his views. Again, sorry if I came across too strongly/harshly. It's just a pet peeve of mine.

-Herman Diaz

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