Wednesday, 11 May 2011
CJES Vol.47 - Albertosaurus Special Edition - a review.
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.
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