Thursday, 30 June 2011

Whither Raptorex?


In my recent review of Tsuihiji et al's (2011) excellent recent paper on a juvenile Tarbosaurus, I made a reference to the taxanomic status of Raptorex kriegsteini and ended it with the phrase "watch this space" - and here's why:


Fowler DW, Woodward HN, Freedman EA, Larson PL, Horner JR (2011) Reanalysis of ‘‘Raptorex kriegsteini’’: A Juvenile Tyrannosaurid Dinosaur from Mongolia. PLoS ONE 6(6): e21376. doi:10.1371/journal.pone.0021376

Abstract

The carnivorous Tyrannosauridae are among the most iconic dinosaurs: typified by large body size, tiny forelimbs, and massive robust skulls with laterally thickened teeth. The recently described small-bodied tyrannosaurid Raptorex kreigsteini is exceptional as its discovery proposes that many of the distinctive anatomical traits of derived tyrannosaurids were acquired in the Early Cretaceous, before the evolution of large body size. This inference depends on two core interpretations: that the holotype (LH PV18) derives from the Lower Cretaceous of China, and that despite its small size, it is a subadult or young adult. Here we show that the published data is equivocal regarding stratigraphic position and that ontogenetic reanalysis shows there is no reason to conclude that LH PV18 has reached this level of maturity. The probable juvenile status of LH PV18 makes its use as a holotype unreliable, since diagnostic features of Raptorex may be symptomatic of its immature status, rather than its actual phylogenetic position. These findings are consistent with the original sale description of LH PV18 as a juvenile Tarbosaurus from the Upper Cretaceous of Mongolia. Consequently, we suggest that there is currently no evidence to support the conclusion that tyrannosaurid skeletal design first evolved in the Early Cretaceous at small body size.


Another paper of immense interest and freely available at PLoS One here. No doubt there will be further debate and response in the near future which we all look forward to. Now then - was it "Raptotyrannus" or "Nano rex"............?

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, 29 June 2011

Prep News

I finally managed to finish off the prep work on the pliosaur vertebra that I blogged about here. At that point I had more or less finished working on the centrum and had begun work on the neural arch and the remnants of the processes. I was aware just how rare this vertebra was since dorsal vertebrae of pliosaurs are hardly ever found uncrushed in the Oxford Clay and to have one in three dimensions with intact neural canal and processes is unheard of.


Preparation was, however, remarkably similar to working on the centrum. A painstakingly slow process removing matrix piece by piece, almost particle by particle, was followed. Only occasionally did I have the luxury of being able to mechanically remove one or two stubborn spots of matrix with no fear of damage to the specimen.

Although the bone was well mineralised and robust, the surface of the bone could be easily chipped in places if you were not careful. This was especially apparent when cleaning out all the nooks and crannies that were formed during fossilisation as extreme pressures distorted the bone and the cracks that resulted filled with matrix and slowly widened. Every pore of the bone had clay or other matrix in situ and this was prised out speck by speck. These areas were consolidated with Butvar B76 as I went along.

The neural canal itself was the longest job of all. The vertebra had been distorted so that the neural canal was not only compressed mediolaterally but also angled between 5° and 10° rostrocaudally, and this made cleaning out the canal particularly awkward. Removing the bulk matrix from the canal did not pose any particular problems but the finer preparation did, as I struggled to work in a tight enclosed canal with both magnification and light impaired.


Eventually, though, the canal was virtually clear of matrix and I was surprised at how big it was and how deep it ended up, as it plummeted ventrally into the centrum. The rest of the processes were more or less straightforward with only one or two areas of stubborn resistance. Once the prep had been finished, the specimen was gently cleaned and a final coating of consolidant finished the job.


To be honest, there are bound to be a few specks of matrix in situ, especially in the neural canal and I’m sure that I could probably keep on prepping the bone but I am happy that the vast majority of it is fully prepared and that the specimen is complete.



There are many projects still in the pipeline just now and I am particularly keen to start work on an impressive hadrosaur dentary but, the immediate plan is to start work on some associated plesiosaur material that I’ve already alluded to in earlier posts beginning with the stunning humerus pictured below.


As can be seen, this particular bone is virtually complete and is broken in two pieces but the join is excellent suggesting that the fracture has only occurred recently. Preparation would appear to be straightforward although both the proximal and distal ends are somewhat encrusted with shell debris and detritus.

The bone, again, is heavily mineralised and dense and the join will need to be exceptionally strong. To support the bone will require a small purpose built cradle which will needed to be constructed for the task and this will also serve the dual purpose of providing the permanent storage case for the specimen when it is finished.

After the humerus there will be a lot of the other bones from the same forelimb to work on including the radius, ulna, and a host of other associated bones. These too are all well preserved and there appear to be no obvious complications. I will detail these bones as I go along and post periodic updates.

The pliosaur vertebra - as found

Wednesday, 22 June 2011

More Tyrannosauridae


From Tsuihiji et al 2011

It cannot have escaped anybody’s attention that there have been a few new tyrannosaur papers this year, two of which I’ll discuss here. The first of these is Tsuihiji et als’ paper regarding a magnificent juvenile specimen of Tarbosaurus bataar from the Nemegt Formation in Mongolia.

I have to say that I really enjoyed this paper and I liked the way it was laid out. Firstly, the identification of the specimen as a juvenile Tarbosaurus had to be established and this was done by comparing it with two other skulls of Tarbosaurus that were adult animals. This direct observation was supplemented by state-of-the-art CT imaging that was overseen by the Witmer Lab.

It was obvious, from day one, that this was a tyrannosaurid and the specimen (Cat. No. MPC-D 107/7) clearly demonstrates numerous synapomorphies that support this affinity. But which tyrannosaur was it? The Nemegt appears to have three confirmed taxa – Tarbosaurus bataar (Maleev, 1955a), Alioramus remotus (Kurzanov, 1976) and A. altai (Brusatte et al, 2009). However, this specimen is from the Bugin Tsav locality and only Tarbosaurus is recovered from here.

Other features such as alveoli count in the juvenile are different from Alioramus and features, that are diagnostic of Tarbosaurus, such as a caudal surangular foramen that is smaller in relation to other tyrannosaurids, are present in the specimen. Combined with the fact that there are several autapomorphies found in Alioramus that are not found in MPC-D 107/7 more or less assures that the animal is indeed a juvenile Tarbosaurus. Estimation of age at death appears to be in the region of two to three years old.

A detailed description of the skull follows and, from a personal point of view, I found it to be one of the better descriptions I’ve read. The spotlight is on ontogenetic differences between MPC-D 107/7 and adult animals and comparisons made using previously described detail including Carr’s craniofacial ontogeny of Tyrannosauridae (1999).

This demonstrated immediately that Tarbosaurus and tyrannosaurids from North America shared a plethora of cranial morphologies during ontogeny. The only significant difference appears to be in the aspect of the antorbital fenestra which does not change greatly in shape in Tarbosaurus but does in their North American counterparts.

Interestingly, the skull lacks specific tyrannosaurid adaptations that allow for the bearing of great stress and torsional forces that are encountered during feeding. In addition, the teeth are much thinner labiolingually and are not as strong and this leads to the conclusion that dietary requirements for this juvenile were different from adults and that they progressively changed throughout ontogeny – not the first time this has been suggested and not just for tyrannosaurids either.

Taxanomic issues raised by the specimen again bring to the fore the status of Nanotyrannus lancensis – the feature this time being maxillary tooth counts and variability within taxa therein. Nanotyrannus has 14 or 15 maxillary teeth whilst Tyrannosaurus has 11 or 12 and here there is a clear difference of opinion as to whether tooth counts vary throughout ontogeny, which suggests Nanotyrannus is a juvenile T.rex (Carr 1999), or whether there is no clear pattern in tyrannosaurids, suggesting that Nanotyrannus is a valid taxon (Currie 2003a, 2003b).

Interestingly, I find both arguments neither correct nor incorrect since they both have merit but, for me, because of the likelihood that individual ontogenetic differences within taxa are highly likely, then maxillary tooth counts cannot be considered as taxonomically diagnostic within Tyrannosauridae – not yet anyway.

Other implications from this study imply more variation in ontogenetic change in tyrannosaurines than previously thought suggesting that tyrannosaurids, as a whole, did not go through a “typical” morphological change as they grew. Also, similarities between Shanshanosaurus huoyanshanensis and MPC-D 107/7 reveal that the former is almost certainly another Tarbosaurus bataar. The status of Raptorex kriegsteini is also considered and after running a phylogenetic analysis, which included MPC-D 107/7, the authors are non-committal although it seems likely that R.kriegsteini is not a juvenile Tarbosaurus. Watch this space.

As I said earlier, I really enjoyed this paper and look forward to the description of the postcrania of this wonderful specimen at some time in the future.


From Tsuihiji et al 2011

 Perhaps not as spectacular, but just as fascinating, is the new tyrannosaurine Zhuchengtyrannus magnus, described by Dave Hone et al in Cretaceous Research. The material described is an associated right maxilla and left dentary from Campanian deposits exposed in the Zhucheng quarries of Shandong Province, China and represents a large theropod on a par with Tarbosaurus – perhaps even bigger.

The maxilla displays a maxillary fenestra that is diagnostic of tyrannosaurines but demonstrates sufficient morphological differences from other tyrannosaurines to warrant the raising of a new taxon and includes some unique characteristics.

Although the available material is of limited value to perform a phylogenetic analysis, the specimens, never the less, enable a few assumptions to be made. Firstly, this animal appears to be an adult based on the lack of juvenile characteristics and, of course, there is the size of the bones which are comparable to both Tyrannosaurus and Tarbosaurus. However, Zhuchengtyrannus can be clearly distinguished from Tarbosaurus due to several different characteristics.

As noted in the paper, perhaps the most interesting detail is the fact that there have been remains of a second tyrannosaurid recovered from the same quarry. When you add Tarbosaurus into the mix, then this demonstrates the presence of three large tyrannosaurid theropods living contemporaneously throughout the Campanian.

This is yet another example of an ancient ecosystem with multiple large predators coexisting and the authors highlight other formations that yield such animals such as the Morrison, Two Medicine, Dinosaur Park and Kem Kem Formations. This is what makes the latest Maastrichtian of North America so interesting if, indeed, Tyrannosaurus is the only large bodied theropod in residence.

The implications of this are continually fascinating. How did so many large theropods coexist at the same times? Niche partitioning maybe? Perhaps – and what are the physiological implications for all this, especially if you believe in endothermic dinosaurs? Bob Bakker (1972) postulated that predator-prey ratios were indicative of whether a specific ecosystem was endothermic or ectothermic ie low ratio of predatory animals to prey animals was typically an endothermic community whilst a high ratio of predators to prey animals was indicative of an ectothermic fauna.

Although predator-prey ratios have come under considerable scrutiny over the years and, in some circumstances, considered a flawed analytical tool, it would be interesting to see more research using them, taking into account the faunal increase and turnover in some formations, although sampling bias is often one of the biggest objections to predator-prey analysis. Perhaps it may support theories, such as Scott Sampson’s (2010), that dinosaurs may have been something in between cold blooded and warm blooded – mesothermic he described them.

Whatever the outcome, specimens such as the tyrannosaurids described above can, not only add to our understanding about these animals, but also may help in expanding our knowledge regarding Dinosauria as whole.

Footnote

Make a point of tuning into the Discovery Channel at 9 o’clock GMT on Sunday night for Phil Currie’s latest theories about gregarious tyrannosaurs in Dino Gangs. For a sneak preview, take a look here.

References

Bakker, R.T., 1972. Anatomical and ecological evidence of endothermy in dinosaurs. Nature 238:81-85.

Brusatte, S.L., Carr, T.D., Erickson, B.R., Bever, G.S., Norell, M.A., 2009. A longsnouted, multihorned tyrannosaurid from the late Cretaceous of Mongolia. 1Proceedings of the National Academy of Sciences 106, 17261:17266.

Carr, T.D., 1999. Craniofacial ontogeny in Tyrannosauridae (Dinosauria: Theropoda). Journal of Vertebrae Paleontology 19, 497:520.

Currie, P. J. 2003a. Cranial anatomy of tyrannosaurid dinosaurs from the Late Cretaceous of Alberta, Canada. Acta Palaeontologica Polonica 48:191–226.

Currie, P. J. 2003b. Allometric growth in tyrannosaurids (Dinosauria: Theropoda) from the Upper Cretaceous of North America and Asia. Canadian Journal of Earth Sciences 40:651–665.

Hone, D.W.E., et al., A new, large tyrannosaurine theropod from the Upper Cretaceous of China, Cretaceous Research (2011), doi:10.1016/j.cretres.2011.03.005

Kurzanov, S.M., 1976. A new late Cretaceous carnosaur from Nogon-Tsav Mongolia. Sovmestnaâ Sovetsko-Mongolskaâ Paleontologiceskaâ Ekspeditciâ. Trudy 3, 93e104 (in Russian).

Maleev, E. A. 1955a. [A gigantic carnivorous dinosaur of Mongolia]. Doklady Akademii Nauk SSSR 104:634–637. [Russian]

Sampson, S.D., 2009. The Goldilocks Hypothesis. In: Sampson, S.D., Dinosaur Odyssey. Fossil Threads in the Web of Life. University of California Press, pp. 175-191.

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, 15 June 2011

Plesiosaur Sp. - The Most Common Taxon of All

Plesiosaur limb morphology is a subject that I have been getting to grips with of late, and what an eye opener that has turned out to be. This has come about because of some recently recovered associated plesiosaur material that a few of us have been looking at and its identification is proving to be troublesome.



Plesiosaurs were a derived group of sauropterygians that used their flippers to, what is known today as, fly underwater. These limbs were used as their principal source of propulsion although it seems likely that there was also an additional tail fin in some cryptocleidoids to provide additional thrust and agility as required (Wilhelm 2010). The limbs were a wonderful design being rigid, paddle-like and elongate.

Unfortunately, this is about as simple as it gets since, as plesiosaurs evolved into more efficient swimmers, modifications to the limb structure, especially to the bones, has made identification of genera problematic. This is amplified when you realise the amount of bone remodelling that occurs throughout plesiosauromorph ontogeny.

Basal plesiosaurs from the Lower Jurassic, such as Plesiosaurus hawkinsi, reveal that the femur and humerus were approximately of similar size. The radius and ulna, in the case of the forelimb, and the tibia and fibula, in the rear limb, were much reduced in size. Postaxially, both the ulna and fibula were remodelled from the basal sauropterygian bone shape and became concave.

These basal plesiosaurs also increased the amount of phalanges throughout their limbs - this is known as hyperphalangy - and they retained this condition throughout their long existence.

More derived plesiosaurs, such as our recent example, display a number of characteristics. The humerus and femur are always less than half the length of the entire limb. Both the front and rear limbs are extremely long due to hyperphalangy as previously mentioned and also, as in basal plesiosaurs, the radius, ulna, tibia and fibula are also significantly reduced in size. Carpal and tarsal identification is somewhat problematic because of remodelling in their morphology.

Collectively, the mesopodials of both the rear limbs and forelimbs are well ossified and are firmly concentrated together. Likewise, the carpals and tarsals are also tightly compacted together. This made for a limb that was rigid and particularly strong and made for very effective swimming throughout the warm Mesozoic seas.

In cryptocleidoid plesiosaurs the fore limbs appear to have provided the majority of thrust since they are bigger than the rear limbs – the humerus is notably bigger than the femur. In pliosaurs it is the reverse and the rear limb appears to have been the main provider of forward thrust.

Although ontogenetic limb ossification is the primary driver of morphological change of bone within the limbs of plesiosaurs, the difference between juvenile and adult plesiosaur limb bones is never the less astounding. Cryptoclidus is the best known of the Oxford Clay plesiosaurs and is represented by multiple skeletons and yet, as with all vertebrate remains, juveniles are scarce. The lack of a decent ontogenetic series of complete specimens causes so many issues when it comes to identification. But the specimens that are available for study do demonstrate the problems faced by palaeontologists.

The Cryptoclidus growth series below from Caldwell (1997) gives an idea of the variability within species throughout ontogeny.


The differences from juvenile to adult are quite extreme. There are enough morphological changes in the humerus and femur alone to cause doubt when trying to establish taxanomic identification – especially when dealing with isolated elements. The other elements such as the mesopodials and metapodials also demonstrate extreme remodelling.

So this particular foray into the world of plesiosaur ontogeny and limb morphology has passed its first phase and we move on forward. Next up is preparation and comparative study of the new material and, if all goes well, the identity of this particular specimen will become apparent.

References

Caldwell, Michael W.(1997) 'Limb osteology and ossification patterns in Cryptoclidus (Reptilia: Plesiosauroidea) with a review of sauropterygian limbs', Journal of Vertebrate Paleontology, 17: 2, 295 - 307.

Wilhelm, B.C. 2010. Novel anatomy of cryptoclidid plesiosaurs with comments on axial locomotion. Ph.D thesis, Marshall University, Huntington, WV. USA

Wednesday, 8 June 2011

Uncertain Times Ahead

I’ve mentioned in the past how so many quarries have been lost over the last few years due to the continuous state of our fragile building economy. With so many projects shelved since the Government’s punitive austerity measures it should, perhaps, not be a surprise.

And yet when the current situation improves and we pull out of recession, will the investment and, just as important, the will be there to reopen some of these quarries or will it be seen to be prudent to import material from abroad, whether in its raw material form or, as seems likely, as a processed and finished product?




So many quarries have now shut that some of the most significant inland venues for vertebrate material have already been lost forever. This tragedy is magnified when coupled with the important geological exposures and successions that have also been lost. Simply put, within a very short period of time, the only vertebrate fossil localities that aren’t coastal may very well be a few survivors that are increasingly less inclined to permit access to both geologists and palaeontologists.

And now comes news that one of the last two brick works still operating in the Oxford Clay is to close with the loss of 56 jobs. In reality, the site is officially being mothballed but I fear that this particular works will not reopen. From our point of view, this is worrying since the clay for this works originally came from Quarry 4 and now from Quarry 5.

There have been brick works in the area since the 1800’s and this particular works was still making the famous Fletton brick which has seen a decline in demand for some years now. From a peak of 3,000 million in 1942, demand last year was less than half that figure and has continued to drop by 3% a year.

The Fletton brick is mainly used for repair and maintenance of existing buildings and not for new projects. Something called a flat set brick is now the building brick of choice and the last remaining brick works in the entire area is now due to have significant investment to set up flat set brick production. Quite where this leaves the mothballed site is uncertain at this time.

The fact that investment is being ploughed back into the remaining works is a positive since this should secure the jobs of the bulk of the 269 remaining employees although with proposed shift changes and other “adjustments”, there may yet be further job losses.

So what does this mean for Quarry 5 and the future Quarry 6? Obviously clay is still required for the one remaining brick works, so Quarry 5 will continue to be worked albeit, you would imagine, at a reduced capacity. The next few years are pivotal to the business and would dictate if and when Quarry 6 would need to be opened. If the mothballed works were to be reopened in the future then, all being well, demand for clay would almost certainly increase to levels previously required. At the moment, everything is up in the air so to speak.

From our point of view then, access is being curtailed with immediate effect and the future, instead of being filled with optimism, is now once more filled with not knowing. Indeed, our main champion and supporter of all things palaeontological is one of the casualties of the closure and we are bitterly saddened for him. One thing is certain, however, and that is gaining access to the quarries has just been made a hundred times more difficult than it ever was and I have to admit that denial of entry seems to be the most likely outcome. We will have to wait and see what happens in the short term before planning our next steps.

Wednesday, 1 June 2011

Learning Curves


Image from Wikipedia


Victoria Arbour, over at Pseudoplocephalus, recently highlighted a visit to the Smithsonian Museum of Natural History and reflected upon the fact that many people quite often visit a museum to, well, visit a museum, entertain the kids, take a few photos and generally have a good time.

There is nothing wrong with that, of course, but Victoria was questioning the role of museums and suggested that without stopping throughout a visit to take things in, to want to learn and ask questions, to explain things to children, then what does the museum experience actually provide?

Those of us who frequent museums on a regular basis know exactly what Victoria is referring to and I bet that all of us have similar experiences to hers. Firstly, I suggest that this is simply how museums are visited today. A lot of the time, they are simply a place to tick off the list and say “been there, done that”. And this is the same for all museums and not just those that house our beloved dinosaur skeletons.

For instance, we recently visited the RAF museum at Hendon and came across the same apathetic attitude to the exhibits there. The planes on display are, indeed, wonderful and exciting and the exhibits excellent, but there was seldom any discourse between parents and their children. Most of the time, the parents were walking around, taking photos while the kids ran around – no discussion about anything, no parents explaining anything. Of course, not everyone is the same and I delight in listening to parents taking the time and patience to explain things to their children and of course, more often than not, the children respond in kind.

School visits have always been a decent learning tool in my opinion and I have fond memories of my own museum trips. However, the problem today is that, quite often, the amount of children involved on a trip is considerable and they are often only managed by a couple of teachers. Sometimes there may be a couple of volunteers who help with the overall control of the group but controlled education and interaction in such situations is difficult and some children can sometimes feel left out of things , since teachers are so concerned with health and safety issues these days that education suffers as a result. And I am not blaming the teachers for this – the situation simply exists.

And yet throughout all of this, the willingness of both adults and children to learn often shines through. I’ve been approached a couple of times to do a couple of talks on dinosaurs and vertebrate palaeontology for a couple of local societies. This is small potatoes compared to my more esteemed colleagues but I still prepared thoroughly, providing samples and casts of fossils, as well as images and diagrams and, of course, notes for me to refer to throughout.

I was nervous at first but, after the initial early stages had passed, everything became a lot easier and the meetings passed off really well. On both occasions, the question and answer sessions were most entertaining and I was really pleased and, I have to say, pleasantly surprised with the depth of knowledge displayed by some in the audience – and over a broad range of subjects as well.

I hope I’m not sounding too condescending here, it’s just that I wasn’t expecting to be discussing the physiology and metabolism of dinosaurs in such detail and I certainly did not expect to face questions regarding the biomechanics of dromaeosaurid claws. Not my strongest subject so, after some pretty intense discussion, I referred them to Manning (2009) and got out of it that way!

Children have been a delight to work with on the odd occasion that I have done so. Once a year, the local county has an open day that publicises the virtues of different clubs and societies and there are many different exhibits and demonstrations that are all designed to get people involved.

I’ve represented a local geological society a couple of times with a group of colleagues who engage the public to get them interested in geology and palaeontology and to join the society. With stands displaying images of field trips and various meetings backed up with specimens of both minerals and fossils on show, the day always proves to be stimulating and rewarding.

The kids are always great though. We provided a sand pit and hid various fossils in the sand so that they could “excavate” their own fossil. These were all fossils provided by members of the society and were mainly scrappy non-diagnostic bits and pieces that we all picked up over the years, along with the odd sharks tooth.

But the children loved them! They were fascinated by the fossils and quite often asked about what they had found, what part of the animal it was and how old it was. You could see that they were absolutely delighted with their bit of ammonite or belemnite and we genuinely felt that they really had got something out of the experience.

Some older children engaged in questioning us about the fossils and minerals on display and it was again encouraging that they displayed a terrific understanding of the prehistoric past and were thirsty for more. A couple of them were with us for a couple of hours and you could tell that they had reached, without doubt, their happy place. Future geologists and palaeontologists perhaps? I would like to think so.

In the end I suppose we should be grateful that there are both adults and children alike who do indeed want to quench their thirst for knowledge. And if that quick trip to a museum, or maybe that visit to an open day such as I’ve described above, does indeed inspire one person to perhaps become a scientist of the future, then that can only be a good thing.

Reference

Biomechanics of Dromaeosaurid Dinosaur Claws: Application of X-Ray Microtomography, Nanoindentation, and Finite Element Analysis Phillip L. Manning, Lee Margetts, Mark R. Johnson, Philip J. Withers, William I. Sellers, Peter L. Falkingham, Paul M. Mummery, Paul M. Barrett and David R. Raymont Anatomical Record Hoboken NJ 2007 (2009) Volume: 292, Issue: 9, Pages: 1397-405 DOI: 10.1002/ar.20986