Wednesday, 25 May 2011

The Great Unknowns

When walking through the great dinosaur halls of the big museums throughout the world, we are often treated to the sight of huge animals that are represented by complete skeletons. And we marvel – not only because of their size but also because we try to imagine these creatures as living, breathing animals.

There are often models, diagrams and paintings showing what these animals were like and information describing what they ate, how they may have reproduced, how they fought, how they moved and even how they may have migrated. To reach these conclusions has been the results of decades of field work, preparation and research and it is fair to say that today we have a pretty sound basis in our understanding of these long vanished animals with a high degree of confidence.

From the early days of vertebrate palaeontological research right through to the present day, the basis for most research has been to compare the fossilised remains of extinct animals with those of extant animals and perform comparative analyses supported by direct behavioural observation of the modern animal. This is known as comparative functional morphology.

When faced with reconstructing an extinct animal, possibly with no extant analogue, it’s normal to start with the basics and try to figure out its habits. Did it live on the land, in the air or in the sea? If a land animal, we should be able to determine whether it was quadrapedal or bipedal, whether it was fleet footed or slow and whether the limbs possessed any other adaptations that may be indicators to its lifestyle.

An aquatic animal may be a permanent inhabitant of the water or may show adaptations that indicate it came onto land on occasion. Wings, of course, are indicative of an inhabitant of the sky but was it a glider or could it sustain a powerful flapping flight?

What did the animal eat? Teeth are the clearest indicator of dietary preference and we can normally specify right away whether the animal is herbivorous or carnivorous. Further study determines what the diet may consist of such as meat, fish, coarse or soft vegetation. Teeth can reveal a lot, even specialist diets can be surmised such as insectivory or omnivory. And, of course, there are the toothless species to take into account.

These are fairly basic assumptions that we can make just by looking at the bones. But pretty soon we start approaching the great unknowns. How would you know if animals lived in herds or were whether they were loners? Did they lay eggs or give live birth? If eggs were laid, were they abandoned or brooded? Were they endothermic or ectothermic?

Fortunately, over the years, there has been more and more evidence to help clear up these matters although there is still much controversy regarding some and, despite the physical evidence, the arguments are not always persuasive. We have many bone beds of several taxa now that are indicative of herding. There are literally thousands of fossilised eggs, some in huge breeding sites that suggest social interaction, brooding and parental care. Significant research into bone histology reveals that dinosaurs were obviously more than ectothermic but whether they were full endotherms is still under the most intense of scrutiny.

Flesh and muscle can be put onto our fossil bones and, fortunately, the scars, lumps and depressions that show where the muscle attachments were fossilise well. Then we come to another great unknown. What was the texture of the skin or hide like? Was it furry, reptilian or were there feathers? Yet again we have been fortunate in some cases. Mummified skin and scale impressions have been found with some dinosaur remains, there are pterosaur specimens with outlines of fur, feather impressions have been revealed in the lithographic limestone from Solenhofen and most recently, and probably most spectacularly, the remains of small theropod dinosaurs from China revealing a wonderful outline of “fuzz” or proto-feathers.

But what about colour? This is virtually impossible to speculate about and remains a great unknown but it is likely that dinosaurs were indeed coloured to some degree since their closest living descendants, the birds, are often brightly coloured. But even here, research moves ever forward (Vinther 2008, 2010 and Zhang 2010) and perhaps we are moving ever closer to the truth.


Ultimately, there will always be an element of uncertainty and great unknowns will remain. For example, if it wasn’t for the exquisitely preserved ichthyosaur specimens from Holzmaden, then it is quite possible that these great marine reptiles would still be displayed in restorations without their dorsal fins and, indeed, the upper tail fluke since only the lower fluke has bone running through it.

For me, great unknowns are best summed up by an example that I recall seeing as a kid and which stuck with me all my life. If our extant elephants were already extinct and we had nothing to compare their bones with, then how on earth would we know that the animal had a long prehensile trunk? The nasal openings are high on the front of the skull and situated between the eyes and there is nothing to suggest the existence of such a trunk. And, when you think about it, the outer ears also leave no physical evidence although I do understand that this is singularly a mammalian trait. Can you imagine our restorations of elephants today if we did not have the modern analogy to compare with?



Yes, I know there are frozen mammoths that have been preserved displaying trunks and ears but the point is essentially correct. It’s an amazing thought that animals such as the dinosaurs, in some cases, may have been even weirder and more spectacular than they already are.

References

 
• Vinther, J., Briggs, D. E. G., Prum, R. O. & Saranathan, V. 2008. The colour of fossil feathers. Biology Letters 4, 522-525.

• Vinther, J., Briggs, D. E. G., Clarke, J., Mayr, G. & Prum, R. O. 2010. Structural coloration in a fossil feather. Biology Letters 6, 128-131.

• Zhang, F., Kearns, S.L, Orr, P.J., Benton, M.J., Zhou, Z., Johnson, D., Xu, X., and Wang, X. 2010. Fossilized melanosomes and the colour of Cretaceous dinosaurs and birds. Nature 463, 1075-1078 .


Wednesday, 18 May 2011

Papers and Preparators

I recently blogged about the importance of keeping good records and documentation for all fossil specimens. Recently this has never been more highlighted since my involvement in the recent excavation of some significant vertebrate material which demonstrated that recording data from the first moment a specimen is found is absolutely essential.

Back in March there was a short but extremely interesting exchange on the Vertpaleo mail listings which came about because of a suggestion that perhaps it was time that scientific publications and papers actually acknowledged the preparator with a line of credit, perhaps attached to an image of the specimen. Although this has improved over the years, with preparators being acknowledged in papers and some also being named as co-author, there is also room for improvement.

And then Steve Jabo, researcher and vertebrate preparator at the Smithsonian Institution, came up with an excellent idea. He suggested that it was time that papers describing new specimens would benefit from an additional section that would include the preparation history of the specimen. This would include techniques, materials and which consolidants and adhesives were used, and the section could be used to aid further research or preparation in the future.

Steve suggested that the preparator could probably put the section together for the paper and that it would therefore always be associated with that particular specimen. This is so simple but the benefits are obvious. For example, if a specimen has had specific chemical treatment or handling, then this information may prevent an alternative form of investigation or conserving technique that may prove damaging.

Even short communications could have these details attached but they would be much more likely to have to be added into the supplementary detail that is normally available on line.

Steve also suggested that perhaps the Society of Vertebrate Palaeontology (SVP) could introduce a new standard to their “Best Practices......” guidelines, providing a basis for standardising such a practice as described. And, not only for new specimens, but also for those previously prepped and researched specimens that may require further conserving or preparation.

In many walks of life there are often sets of rules that we have to follow. Sometimes they are a pain in the backside but, in most cases, they are often sensible and, followed correctly, productive. These are standard operating procedures and they provide a formal set of guidelines for the worker to follow that formalise the same procedures again and again. Consistency being the key word.

It reminds me, in so many ways, of providing a full service history for a used car. Given the choice of a vehicle with such a history, or one with none, you would always go for the vehicle with history. We want to know that it’s been looked after, what repairs it has had and that it has been maintained alright. And this, for me, is the premise of formalising this excellent idea of attaching all the preparation data to the papers concerned.

During this discussion, no less a group including Scott Hartman, Tom Holtz, Andrew Heckert and Jean-Pierre Cavigelli all commented enthusiastically about Steve’s idea and I hope that the movement to introduce this process formally takes shape in the not too distant future.

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

Tuesday, 10 May 2011

A Stunning Juvenile Tyrannosaurid

This was the talk of the palaeoworld and blogosphere late last night. Published on line last night in the latest Journal of Vertebrate Paleontology is the long awaited paper by Tsuihiji et al describing a wonderful example of a juvenile Tarbosaurus bataar from the Nemegt Formation in Mongolia. Expect copious amounts of coverage over the next few days and weeks and no doubt expect me to comment in the not too distant future.

Awesome material backed up by stunning digital rendering by the Witmer Lab. Here’s the abstract:



Abstract

A juvenile skull of the tyrannosaurid Tarbosaurus bataar found in the Bugin Tsav locality in the Mongolian Gobi Desert is described. With a total length of 290 mm, the present specimen represents one of the smallest skulls known for this species. Not surprisingly, it shows various characteristics common to juvenile tyrannosaurids, such as the rostral margin of the maxillary fenestra not reaching that of the external antorbital fenestra and the postorbital lacking the cornual process. The nasal bears a small lacrimal process, which disappears in adults. Lacking some of the morphological characteristics that are adapted for bearing great feeding forces in adult individuals, this juvenile specimen suggests that T. bataar would have changed its dietary niches during ontogeny. The numbers of alveoli in the maxilla (13) and dentary (14 and 15) are the same as those in adults, suggesting that they do not change ontogenetically in T. bataar and thus are not consistent with the hypothesis that the numbers of alveoli decreases ontogenetically in tyrannosaurids.

Reference

Tsuihiji, Takanobu , Watabe, Mahito , Tsogtbaatar, Khishigjav , Tsubamoto, Takehisa , Barsbold, Rinchen , Suzuki, Shigeru , Lee, Andrew H. , Ridgely, Ryan C. , Kawahara, Yasuhiro and Witmer, Lawrence M.(2011) 'Cranial osteology of a juvenile specimen of Tarbosaurus bataar (Theropoda, Tyrannosauridae) from the Nemegt Formation (Upper Cretaceous) of Bugin Tsav, Mongolia', Journal of Vertebrate Paleontology, 31: 3, 497 — 517 DOI: 10.1080/02724634.2011.557116

Wednesday, 4 May 2011

Harley Garbani - A Few Thoughts

I was saddened to hear about the death of Harley Garbani a couple of weeks ago. He was 88 and died from natural causes. It was good to see that his passing was marked by a number of publications and that the palaeo-world was universal in its appreciation of his amazing talents.

Harley was a man who inspired others and is another example of someone who applied himself after graduating from high school and did what so many of us aspire to, namely to become a self-taught palaeontologist. Harley’s discoveries over the years are legion and many of his discoveries are on display in such repositories such as the Museum of the Rockies, the University Of California Museum Of Palaeontology and, the institution he was mostly associated with, the Natural History Museum of Los Angeles County.

I first became aware of Harley during yet more tyrannosaur research. I was particularly looking at a specimen of Tyrannosaurus rex (LACM 23844) which was of considerable interest since the quarry had also produced a second tyrannosaur and theropod bone beds are exceptionally rare. Although I didn’t know at the time, this was actually Harley’s most memorable find.

During 1966, Harley set out to specifically locate a T.rex specimen, if it were possible, and decided very wisely, not only to go blindly prospecting in the Missouri Breaks of eastern Montana, but also to cultivate the knowledge of the local ranchers and the people of Jordan. He became a temporary “Jordanian” and got to know the locals, enjoying both a drink and their company, all the while listening out for any clues that would help in his quest.

Harley met rancher Lester Engdahl and it was this meeting that was to lead to his fist T.rex. Engdahl’s ranch was around 20 miles northwest of Jordan and Engdahl had commented that he had seen some strange bones on his land. Harley knew that this could be the break he was looking for and was soon scouring the area. On July 27th he spotted what appeared to be a massive toe bone eroding out of some mudstone. In his journal Harley recorded:

About 3 p.m. over north of the dam, I ran into what I believe is limb and tarsal and two toes of the hard to find rex”

The remains did indeed turn out to be T.rex - only the third specimen recovered from the Hell Creek Formation and was an important specimen. The remains were excavated over several field seasons and amount to about 25% of a skeleton although the skull was fairly complete and there are casts of the skull in museums all over the world.

Although LACM 23844 is Harley’s most famous find he has been instrumental in locating many other significant and important discoveries. A skull of Edmontosaurus annectens (LACM 23502) is unique because it preserves evidence of the horny sheath that covered the beak. Thescelosaurus garbanii was named after Harley and became the second named species of this dinosaur although this animals taxanomic affinities have often been subject to intense scrutiny. The specimen (LACM 33542) represents an animal some 15 feet long which is somewhat large for a hypsolophodontid.

In 1997 he discovered the disassociated remains of what appeared to be a pachycephalosaurid but when pieced together they proved to be from the smallest Triceratops skull ever discovered, about a foot long and only missing the nose and beak. A further two Tyrannosaurus specimens can be added to his impressive tally and this includes LACM 2841 which is estimated to represent an individual of only two years of age. All of these specimens and more are testimony to Harley Garbani’s astonishing ability at finding unique and important fossils.

Harley was also an accomplished preparator and was renowned for his eye to detail and his astonishing technique. He also collected mammals and other fossils as diverse as clams, snails and plants. He was a recognised expert in Native American archaeology and amassed a significant collection of artefacts.

Harley had several specimens named after him such as the aforementioned Thescelosaurus garbanii and others such as Geomys garbanii (a type of gopher) and Elomeryx garbanii – a kind of hippopotamus. In all, there are seven species that bear his name. Never was tribute more deserved. But he will always be remembered for his dinosaur discoveries and the world of palaeontology is worse off for his passing.

Footnote

LACM 23845 was also discovered by Harley Garbani from the same quarry as the previously mentioned LACM 23844 and was actually discovered in the overburden that was covering the original specimen. This was the holotype of Albertosaurus megagracilis but is generally accepted to be a juvenile Tyrannosaurus rex.