Friday, 30 December 2011

2011 Reviewed


2010 was an astonishingly busy year in the world of palaeontology and was often referred to as the year of the ceratopsians. 2011 has also been an amazing year and, looking back, it’s hard to think of declaring it as the year of anything in particular but, if I had to, I would declare 2011 the year of that most iconic of animals, Archaeopteryx. Here are some things that caught my eyes and ears during this most fascinating of years.

In January we were treated to the announcement of Teratophoneus curriei, yet another tyrannosaurid from the Carr and Williamson stable, presented as the most basal tyrannosaurine known from North America. “Currie’s monster murderer” provides further evidence of regional endemism in the American southwest.

Also, in January, there was another suggestion that dinosaurs may have survived the KT impact by as much as 700,000 years after a group of scientists, led by Larry Heaman of the University of Alberta, dated a hadrosaur femur using U-Pb (uranium lead) dating technology to 64.8 million years old. The researchers believe that if more recovered material is dated accordingly then the extinction date of the dinosaurs will almost certainly have to be revised.

February was fairly quiet although it was good to see Mike Taylor featuring in the New York Times, who briefly looked at his career in the wake of the announcement of Brontomerus mcintoshi. March, however, saw Greg Paul stir up the proverbial hornet’s nest by suggesting, albeit in a roundabout way, that his style of artistic restoration i.e. the “Greg Paul Look” is more or less his own copyrighted style and that permission should be sort before “his style” is utilised by other artists. He also appeared to criticise other artists for daring to sell images, in “his style”, at prices less than other well established artists would charge!

I am a huge admirer of Greg Paul, both as a palaeontologist and artist, but this did seem to be a little disingenuous and rightly provoked a huge response and outcry in the palaeoworld and the arguments that followed proved both fascinating and enduring. Just where this will end up in the future is anyone’s guess.
    
March also saw the announcement that a motion picture of Walking with Dinosaurs in 3D would be hitting the cinemas in 2013. With a budget in the region of 65 million dollars the film promises to use ground breaking 3D and LIDAR technology to make it the ultimate dinosaurian encounter. Of course, whether we can expect some science in the film is anyone’s guess but we all remain ever hopeful.

Another tyrannosaur made the news in March – this one being Zhuchengtyrannus magnus, brought to us by Dave Hone et al. Identified from an associated maxilla and dentary, Zhuchengtyrannus is yet another interesting tyrannosaurine and comparable in size to both Tarbosaurus and Tyrannosaurus.

April was a personal triumph for me as I found my first partially articulated plesiosaur in the Oxford Clay. The animal appears to be a juvenile and remains unidentified but it is slowly being prepared and this provides yet more detail as we proceed. We may be little closer to identifying the animal now after we compared some elements with multiple examples of plesiosaurs in the Leeds collection at the Natural History Museum in London last week – but  a degree of certainty remains elusive.

Back to tyrannosaurs and a superb paper describing the skull of a juvenile Tarbosaurus was published in May in the Journal of Vertebrate Palaeontology by Tsuihiji et al. I said at the time that I thought this was the paper of the year for me and I still do. The description of the cranial osteology of the specimen is an excellent and lucid account and the paper is set out spot on in my humble opinion. Read it now if you have not already done so.

Premiering in June, Dino Gangs was a documentary on the Discovery Channel featuring Phil Currie’s assertion that the tyrannosaurine, Tarbosaurus, hunted in packs. This was reviewed at multiple sites and blogs and met with a mixed reaction which, in the end, probably came out on the positive side of things. I felt that it was, overall, a good programme but that the assertion that tyrannosaurs hunted something akin to mammalian pack hunters of today was a little fanciful but at least the opposite view was fairly represented, albeit only briefly.

2011 was the 150th anniversary of the discovery of Archaeopteryx and the celebrations were launched, in earnest, during June. The Museum für Naturkunde in Berlin launched a special exhibition which not only displayed the Berlin specimen in all its glory, but also the counter slab for the first time, and also the original fossil feather that was first designated as Archaeopteryx.

The monograph describing Scipionyx samniticus was published to what appeared to be universal acclaim by the palaeoworld and huge praise was lavished upon the authors, Cristiano Dal Sasso and Simone Maganuco. It is unusual for such a monograph to be so well received and the authors are to be congratulated for producing such a fine (and important) publication and contribution.

July saw the news that Jurassic Park 4 was definitely going to be made – again. Steven Spielberg made the announcement in San Diego at Comic-Con 2011 and met with, yet again, a mixed reaction from fans and the palaeoworld alike. I suggest we wait until the film actually goes into production before anything else since there are no guarantees that it will ever get made in the first place.

Also during July was the assertion that Archaeopteryx was more likely to be a basal dromaeosaur as opposed to being a basal bird. A new paper by Xu et al describe a new theropod from China that suggests that features found in Archaeopteryx, thought to be diagnostic of Avialae, are actually characteristic of Paraves.  As you can imagine, this invoked huge discussion in the palaeoworld and was to take yet another direction later in the year.

In August it was announced that scientists had successfully created chicken embryos that grew crocodile-like snouts instead of beaks. By adjusting their DNA to resemble alligator genes, the beak development was halted and snouts developed instead. Genetic signalling such as this is becoming better understood with every passing year and Jack Horner’s “Chickenosaurus” is almost certainly just around the corner, if it has not already been done.

The suggestion that plesiosaurs may have given live birth is nothing new but evidence provided by F.R. O’Keefe and Luis Chiappe in August certainly was. Mentioned a couple of times in this blog, a specimen of Polycotylus latippinus clearly displays an embryo within the body cavity of the adult and suggests that these plesiosaurs may have given birth to a single well developed newborn that was possibly dependent on the adult for care.  

September was a bumper month for dinosaur television with Dinosaur Revolution, Planet Dinosaur and Terra Nova all premiering. Both Dinosaur Revolution and Planet Dinosaur were generally well received by the palaeoworld with both having strengths and weaknesses although, having seen both series, I feel that Planet Dinosaur was the more superior product from the scientific view point. They were both, however, a significant improvement on previous attempts at portraying the prehistoric world. After a slow start, Terra Nova slowly improved and it seems likely that a second series will now go ahead although we will probably have to wait until May for confirmation of that.

Also in September, Nick Longrich et al presented evidence that demonstrated that Late Maastrichtian birds were flourishing and diversifying right up to the moment that the K-T extinction occurred. The team identified 17 species that all failed to survive into the Paleogene and included birds of various sizes across a range of groups. This is the first evidence that contradicts the  suggestion that  archaic birds were gradually becoming extinct throughout the Late Cretaceous and then disappeared at the same time as the Chicxulub asteroid strike.

Other items of interest in September include the first possible preservation of dinosaurian feathers preserved in 79 million year old amber from southern Alberta in Canada. Some of the preservation is outstanding and displays exquisite filaments and, amazingly, remains of pigment which has all sorts of implications as the search to reveal the colours of dinosaurs hots up.  A new troodontid was also announced in September, Talos sampsoni, and is the first troodontid to be named in North America for the best part of 75 years and the Hadrosaur Symposium took place at the Royal Tyrrell Museum in Alberta to much acclaim and there was some significant work presented regarding these wonderful animals. The volume of papers that will follow is sure to be in great demand and will greatly add to our knowledge of these fascinating creatures.

In October, a paper presented at the annual meeting of the Geological Society of America, lowered the bar for a so-called scientific paper by suggesting that not only did a giant kraken-sized squid prey on giant ichthyosaurs (for which there is no evidence) but also rearranged their bones in nice patterns to form a self-portrait! No need to say anymore about this really except that it has been universally condemned by all in the palaeoworld but it is unfortunate that it managed to get so much air time and press.

New images of a stunningly preserved theropod hit the wires in October and caused quite a stir. What a magnificent specimen it is and is 98% complete. Unusually, the paper and name of this animal are still to be released and, hopefully, Oliver Rauhut and his team won’t keep us in suspense for too much longer.

Earlier I mentioned how Archaeopteryx was now possibly a basal dromaeosaur but in October he was back to being a bird again as Michael Lee of the South Australian Museum performed a much more rigorous phylogenetic analysis using a superior and sophisticated statistical methodology. This dragged Archaeopteryx back from dromaeosaurs and nestled the animal quite happily back amongst the birds and highlights the fine line between what is a bird and what is a dinosaur – although, of course, they are one and the same thing. Still with Archaeopteryx and the London specimen (BMNH 37001) was finally designated the neotype by the ICZN since the original holotype was a feather and could not be designated to Archaeopteryx alone since there were almost certainly other feathered animals that shared the  same environment.

In November, it was suggested that the plumage of Archaeopteryx was likely to be black in colour after Ryan Carney and his co-authors discovered that the melanosomes identified on an Archaeopteryx feather were most likely to be black. These were identified using scanning electron microscopy and then comparing them with similar feathers from 87 extant bird species.

The Society of Vertebrate Paleontology annual meeting took place in Las Vegas and was one of the biggest meetings ever held. There were a multitude of presentations and posters that have been covered extensively on this blog and I covered only a fraction of the data that was presented. Finally, in November, tyrannosaur aficionados were interested by tyrannosaur remains reported from the Turonian of Uzbekistan. Authors Alexander Averianov and Hans-Dieter Sues suggest that the remains represent a non-tyrannosaurid tyrannosauroid more basal than the Campanian tyrannosaurids Bistahieversor and Appalachiosaurus.

There was still no let up in December as the new ceratopsian Spinops sternbergorum was announced, Alamosaurus was designated as the biggest North American sauropod – comparable to Argentinosaurus in size, and Nedoceratops became the latest casualty in the continuing synonymising of chasmosaurines, turning out to be an ontogenetic stage between Triceratops and the “Torosaurus” morphology. The mind boggles.....

This time last year, like the previous year, I was wondering if 2011 could possibly live up to the previous year but it has. As we go into 2012 I find myself wondering the same and yet the world of palaeontology has become a fast moving breathing object that has spread out across the globe and encompasses so many wonderful people who share the passion – some I am lucky to call both friend and colleague. I have no doubt that 2012 will be another fascinating year for all of us. Happy new year to you all.     



Friday, 23 December 2011

Crocs at Christmas


It occurred to me the other day that despite my extensive coverage of the Oxford Clay Formation and the abundant vertebrate fauna that inhabited these warm shallow tropical seas, I have actually not devoted any reasonable coverage to the marine crocodiles that shared the environment with the better known ichthyosaurs, plesiosaurs and pliosaurs.


There are currently two genera represented in the clay and these are Steneosaurus (the superb specimen above is from Holzmaden) and Metriorhynchus. These are both thalattosuchians that share their ancestry with the crocodiles and alligators of today and so belong to an ancient and very successful group whose origins can be traced back to the Latest Triassic – around 200 million years ago.
The early crocodiles were small and essentially land living animals. Eventually they evolved into water dwelling genera, the mesosuchians, which spread rapidly and became very successful, filling a variety of niches. These mesosuchians eventually gave way to more derived forms and some of these returned to the land while others went to sea.
Steneosaurus is a very familiar looking animal and could easily be mistaken for a gavial of today and it seems likely that it would have shared a very similar mode of life to its extant cousin. Approaching 4 metres in length, Steneosaurus was well adapted to a marine life. The skull was lightly constructed and the rostrum was elongate, narrow and there were over 40 teeth in both the upper and lower jaws. These teeth were conical, sharp and were ideal for catching fish and invertebrates that shared the environment although some specimens also display blunter teeth that may have been suited to dealing with more robust prey.
The limbs of Steneosaurus were typically crocodilian, as was the upper torso of the animal, which was covered with a layer of ornate protective osteoderms.  The tail, again, was extremely crocodilian, being long and powerful, and was clearly a significant propulsion unit for swimming.
Two species of Steneosaurus are generally accepted to have been part of the Oxford Clay fauna and these are S. leedsi and S. durobrivensis. The fact that their fossils are found in these marine sediments tends to confirm a gavial-like existence and Steneosaurus probably inhabited the coastal shores and the mouths of rivers that emptied into the sea.

The other crocodile that is found in the Oxford Clay is Metriorhynchus and this genus is much more robust than Steneosaurus, although not as long, and is fully adapted for life in the sea.  About 2 to 3 metres in length, the limbs of Metriorhynchus were fully developed flippers and were unsuitable for life on land. Of course, it would seem logical to assume that Metriorhynchus would have returned to shore to lay eggs but now, with evidence that plesiosaurs gave birth to live young, perhaps we should not so readily make such an assumption.


The tail is a little similar to an ichthyosaur tail in as much as the caudals bend downward to create a proper fish-like tail and this animal was obviously a very efficient swimmer. Metriorhynchus completely lacks the dermal ossifications of Steneosaurus and this is always the best identifier when a crocodile skeleton is first revealed in the clay. The skull is still typically long but the rostrum is much broader than in Steneosaurus, and looks more crocodilian than gavialan, and is also much more rugose.
a) Metriorhynchus b) Steneosaurus
From Martill & Hudson 1991
Metriorhynchus was obviously a highly developed marine hunter that probably preyed on fish, belemnites and any other creature it could adequately despatch. Some specimens display contents in the stomach region and these often include belemnite hooklets and also, in one exceptional specimen, the remains of a pterosaur have been identified, probably a carcass that was floating on the sea that was snapped up by the passing croc. Two species of Metriorhynchus are currently recognised from the clay and these are M. brachyrhynchus and M. superciliosus.
Marine crocodiles are often passed over in favour of the more famous reptilian inhabitants of the Callovian Sea but they are as equally fascinating and not to be underrated. Indeed, I have just been very privileged to see two skulls from these animals undergoing conservation at the Natural History Museum in London – both from the Leeds collection and what big skulls they are! Steneosaurus may have been gavial-like in existence but this was a serious hunter and could obviously take quite large prey. Some of its teeth are much bigger than the ones I’ve seen from clay and this was an eye opener for me. The skull of Metriorhynchus is massively constructed and obviously powerful – indeed I was surprised how massive it was – and it appears that it too would be very capable of tackling large prey.
This is a very brief introduction to these superbly adapted animals and I would like to think that we will be able to extract another specimen of these superb crocodilians from the Oxford Clay at some point in the future.
Season’s Greetings!
I would just like to take the opportunity to wish all my friends, colleagues and all of you who have taken the time to read my blog this year a very happy Christmas and hope you all enjoy a wonderful festive season.
Reference
Martill, D.M & Hudson, J.D 1991. Fossils of the Oxford Clay. The Palaeontological Association, London, UK

Thursday, 15 December 2011

Uncovering Spinops

As most of you are all aware, there was yet another new ceratopsian announced last week and Spinops sternbergorum has now taken its place amongst a plethora of recently announced horned dinosaurs. I’ve known about Spinops’ existence for some time now, for reasons which will become apparent, and I was very pleased to finally see the official announcement last week. I love the way that news of newly announced dinosaurs travels across the globe almost instantly these days and the buzz created is palpable.

I first became aware that there was possibly a new ceratopsian in the vaults of the Natural History Museum in London (NHM) back in 2007. I’d met Mark Graham during the same year, whilst prospecting at Misty Bluff Quarry and we soon became good friends. Mark, at the time was a volunteer preparator at the NHM and told me that he hoped to be commissioned to prepare some “unusual” ceratopsian material that, although it looked initially a bit like Styracosaurus, could actually represent a new species.

I was intrigued and at the same time that Mark began looking at the material, a revision of the type specimen of Styracosaurus albertensis was published near the turn of the year (Ryan et al 2007) and thinking that it would be of help, I sent a copy off to Mark. I was too late – Mark had already received it and was already engrossed in it! Things started to move on.

In June 2008 Mark commenced work on the specimen and, in his own words:

The specimens (which were from a bone bed) were prepared by me in 2008/09 and the two large parietal elements were encased in extremely hard iron-rich matrix and heavy plaster of Paris jackets. The bone itself was significantly fractured - so much so that the combination of unyielding rock and fragile bone made for an interesting (not to say nerve-wracking at times!) project. The images show some of the preparation work and protective jacketing made for the specimens, together with a couple of images from the last day, in March 2009, when it was all completed.

A particular challenge was the removal of matrix from around the cores of the pro-curved parietal hooks, which actually displayed some lovely detail, and also from around the epiparietal, which was dangerously thin.

I’m thrilled that my first involvement with a scientific publication should be on such a significant specimen as Spinops.”


I am personally delighted for Mark, not only because he is a damned good preparator, but because he really is a nice guy and deserves his joint authorship. I hope it is the first of many for him. Incidentally, Mark is also involved in the instigation of a new volunteer programme at the NHM and the first workers have now begun preparation of sauropod material collected in the 1980’s and, as Mark points out:

“Another “new” dinosaur may soon see the light of day!”

Amen to that!

Note

The images here are reproduced with permission and are not to be used elsewhere without consent.

References

  A new centrosaurine from the Late Cretaceous of Alberta, Canada, and the evolution of parietal ornamentation in horned dinosaurs. Andrew A. Farke, Michael J. Ryan, Paul M. Barrett, Darren H. Tanke, Dennis R. Braman, Mark A. Loewen, and Mark R. Graham. Acta Palaeontologica Polonica 56 (4), 2011: 691-702 doi:10.4202/app.2010.0121

Ryan, M.J., Holmes, R., and Russel, A.P. 2007. A revision of the late Campanian centrosaurine ceratopsids genus Styracosaurus from the western Interior of North America. Journal of Vertebrate Paleontology 27: 944-962.

Thursday, 8 December 2011

A Pterosaur Revealed.....


As highlighted here previously and, as promised, here is the pterosaur Rhamphorhynchus muensteri in all its glory and what a spectacular specimen it is. This particular specimen, of course, is from the Upper Jurassic lithographic limestone of Solnhofen in Germany, around 155 million years old, and is arguably one of the finest examples of its kind ever recovered.

As I mentioned in my previous SVP report, the levels of preservation in the Solnhofen quarries are often spectacular. The limestones were laid down in lagoons that became cut off from the sea as coral reefs rose from the sea floor. It seems likely that salinity increased as a result and these isolated lagoons became toxic and depleted of oxygen which, although not very good for life at the time, proved to be excellent news for palaeontologists.

Any organism that ended up dead in the lagoons would have sunk softly into the muds and, because the isolated toxic environment prevented the carcasses being disturbed or dismembered, the preservation of many fossils is exquisite hence my previous comments regarding the somewhat problematic suggestion that R. muensteri may have displayed a sagittal cranial crest.
However, back to this fantastic specimen and some detail. The overall wingspan of this pterosaur is 725mm and the skull is 100mm long. Bone preservation is incredible and the vertebral processes remain intact – in fact all of the bone in this specimen is exactly as prepared and there are no composite pieces whatsoever. The preparator has done an excellent job.
However, there is a sting in the tail regarding this specimen and that is the fact that it is held in a private collection and I am not sure if it will ever be made available for study or public display. This is unfortunate and, as you are all aware, somewhat commonplace these days which is why I have kept these images for future reference.  That still doesn’t take away the fact that this is a quite wondrous and superb specimen.

Coming next – a Spinops exclusive!

Sunday, 4 December 2011

SVP 2011 - And Finally.....


This is the last of my SVP 2011 reports and I’m very grateful for the positive feedback that I’ve received from so many of you. This last batch of entries represents research across a variety of disciplines but are all equally interesting.

It appears to me that ichthyosaurs are undergoing something of resurgence in popularity and those of the Cretaceous are proving to be not quite as elusive as they were once thought to be. Valentin Fischer has been actively studying these fascinating animals and following on from his recent paper in the Journal of Paleontology, where he announced the new taxonSveltonectes insolitus, he presented more data detailing that ichthyosaurs were still very diverse throughout the Early Cretaceous.
In particular ophthalmosaurids continued to be a very successful group right through the Early Cretaceous. It was initially thought that they had rapidly declined after their initial radiation during the Middle Jurassic but new fossils from Europe and Russia (including Sveltonectes) clearly dispel this theory. It is now apparent that typical Late Jurassic ophthalmosaurs shared the seas of the Eurasian archipelago with typically more derived ichthyosaurs from the same clade such as Platypterygius and that these taxa also appear to be well adapted to fill different niches in the ecosystem.
Staying with marine reptiles, only this time plesiosaurs, and some interesting morphological study of the plesiosaurian body shape by Courtney Richards et al. Comparative studies of three cryptoclidid plesiosaurs– Tatenectes, Cryptoclidus and Muraenosaurus – were performed using a combination of measurements and photographs to correctly position the various bones, such as the vertebrae and ribs etc, which enabled the accurate structural depth and width shape to be attained.

A.Muraenosaurus B. Cryptoclidus
C. Tatenectes (from O'Keefe et al 2011)
To supplement this detail, the vertebrae were also analysed to see if the morphology of the centrum is relevant to the curvature of the spine. Those vertebrae that are most rhomboidal correlate with those areas of the spine that curve the most while those that are less rhomboidal correlate with sections of the spine that are flatter and/or curve less.
Running this data through the computer and subjecting the various structures to lateral rolling suggests that the shallow draft plesiosaurs such as Tatenectes and Cryptoclidus were well suited to shallow waters while those with a deeper draft, like Muraenosaurus, were far more adapted to an open ocean deep water existence.
This is interesting because of its relevance to the Oxford Clay Formation, which has featured heavily in this blog throughout. The sea where the Oxford Clay was deposited was both warm and shallow and conditions were such that vertebrate remains fossilised well and are relatively abundant. Muraenosaurus is a very common genus from these deposits and this does not tie in with the above findings so it will be interesting when this data is formally published. I wonder what the author’s interpretation of deep water is in relation to the Oxford Clay Sea? 

One of the symposia this year featured the evolution and ecology of terrestrial ecosystems of Campanian Laramidia. Currently, research in this particular field is incredibly popular and there is enough data around to fill a series of volumes on its own. There are a couple of presentations that I have opted to highlight and one was presented by Mark Loewen et al and discussed the evolution of theropods and how it was affected by geographical boundaries.
In recent years there have been more fossil discoveries from southern Laramidia to complement the already heavily sampled northern fossil fields. Because theropods are less likely to be affected by climatic differences and any change in flora, they were chosen to see if they provide evidence of faunal endemism. Despite the fact that all major groups of theropods are represented from north to south there is no doubt that there were different species represented in different isolated endemic faunas. Tyrannosaurids, as an example, were used to explain that, although they were all large predators that hunted, more or less, the same prey, they still evolved into distinct clades.
Add to this the fact that all these animals all display patterns of diversification and dispersal that are characteristic of those that exist in isolation. These findings seem to confirm what has been suspected for some time now, namely that there was some form of geophysical dividing barrier between north and south Laramidia restricting any obvious faunal exchange. However, just what this barrier was still has to be determined.
From Sampson et al 2010
The second presentation came from, more or less, the same research team – this time with Scott Sampson as lead author. At the time that the Western Interior Seaway split the North American continent into two, Laramidia was isolated for around 25 million years. It has always been assumed, more often than not, that because Laramidia and the corresponding formations of Asia display the same clades of dinosaur, the origins of these clades in North America are as a result of a dispersal event from Asia.
Timing of such an event has been problematic since the Asian formations still have to be satisfactorily radioisotopically dated and now new fossil evidence from the Campanian rocks of the Wahweap and Kaiparowits Formations of southern Utah throws the original dispersal theory into doubt. Specimens of both tyrannosaurid and ceratopsids have been recovered that have been established as the earliest representatives of their kind and this, in addition to stratigraphic, phylogenetic and biogeographic analysis, suggests that it was, indeed, the landmass of Laramidia that was probably responsible for the origins of many taxa in Asia.
The authors suggest that this is unusual since most dispersal events are usually biased in as much that the bigger landmass normally provides the greater faunal exchange and this is particularly true of Cenozoic events. However, Laramidia was a comparatively small landmass compared to the Asian continent and this stands out as being a truly unusual event. There are so many unanswered questions regarding Laramidia that it will continue to attract increased attention and research.
Another symposia this year was devoted to vertebrate diversity patterns and sampling bias and Matthew Carrano and Matthew Oreska, both of the Smithsonian Institute, demonstrated the importance of vertebrate microfossil bone beds. I’m a big fan of these extremely interesting fossil hot spots and the data they provide and, if you have never looked at microfossil sites, then you are missing out – I recommend Julia Sankeys’ work if you are looking for somewhere to start.
The Cloverly Formation of Wyoming and Montana has been worked for around 75 years now and since collecting techniques tend to concentrate on macrovertebrate remains it appears that the overall diversity of the this formation has been overlooked. Reassessment and analysis of the microfossil sites have now added considerably to our knowledge of the animals that once lived in this area during the Early Cretaceous.
The authors report that freshwater sharks, crocodilians and mammals have all been identified with, as is the norm with this kind of analysis, bony fish and crocodilians dominant. But there are significant remains of dinosaurs, amphibians and turtles as well and even after taking proportional representation and other sorting biases into consideration, the results stand up to scrutiny. This is reminiscent of later Hell Creek microsites and is indicative of a wet, aquatic and semi-aquatic environment.
Microfossil bone beds continue to add to our understanding of many palaeoenvironments and, provided the sampling technique is consistent and of sufficient quantity, they are very effective indicators of the different kinds of vertebrate taxa that can be identified in various formations throughout the world.
Now you may remember my teaser image of a rhamphorynchid pterosaur a little while back which will be featuring in my very next blog post and S. Christopher Bennett, of Fort Hays University, has suggested that Rhamphorynchus muensteri may have actually displayed a cranial crest. Although crests for non-pterodactyloid pterosaurs are known, no specimen of Rhamphorynchus has been found with structures preserved that are indicative of a sagittal cranial crest– until now.
A large adult specimen appears to display a series of features on the skull roof that may have formed the base of a soft tissue crest that covers an area measuring about 25% of the skull. Interestingly the author suggests that the majority of R. muensteri fossils are juveniles since there are over 100 specimens in depositories all over the world and not one fossil displays the same features or, indeed, evidence of a crest. 
Image by Ryan Somma
This is a very strange and problematic. Preservation of these pterosaurs from the fine grained limestones of such places as Solenhofen is spectacular and specimens of both invertebrates and vertebrates often display the fleshy outlines of wings and body shapes and yet there is not one fossil of R. muensteri that displays any signs of a crest. Even if all the specimens were juveniles, surely there would be one specimen that was at least starting to develop a sagittal crest?
This lack of evidence, for me, is troubling but then the author may correct in his assertion that all the specimens are indeed juvenile. But what would cause such a preservational bias? I’m not too sure but it will be interesting to read the paper on this one and I will look forward to its publication in the future.
And now for my final piece from this year’s SVP and features the ankylosaur Pinacosaurus. Victoria Arbour (of Pseudoplocephalus fame) and Phil Currie, both from the University of Alberta, report on bone beds in Bayan Mandahu, China and Alag Teeg in Mongolia and describe how multiple skeletons that were more or less aligned in close proximity and preserved upright in a miring situation may be indicative of a social group.
Both sites mainly contain the remains of juveniles but at Alag Teeg there is also one large specimen that is certainly an adult. The preservation of the remains is good and taphonomic analysis suggests that this was not groups of animals perhaps gathering together around a dwindling pool in a drought situation. The remains in drought assemblages tend to have their remains scattered and are often badly trampled.
The authors suggest that the ankylosaurs at both bone beds were probably mired in a fairly short space of time by sandstorms or even an alluvial fan. It is possible that the juveniles were accompanied by an adult or adult animals to provide some protection from predators since their osteoderms were yet to develop as well as their tail clubs, which had only partially developed. This scenario suggests that the adult animal(s) were able to pull themselves out of the sand whilst the juveniles could not although obviously, at Alag Teeg, one adult did not escape. It will be interesting when other bone beds are found to see if further evidence and analysis can also suggest the possibility of a social structure in ankylosaurs.

References

Arbour, V. and Currie, P. 2011.Taphonomic filters of age groups on the ankylosaurid dinosaur Pinacosaurus. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp64.
Bennett, S.C. 2011. First evidence of a cranial crest in the pterosaur Rhamphorynchus muensteri. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp69.
Carrano, M. and Oreska, M. 2011. The importance of vertebrate microfossil bonebeds in understanding the fossil record: examples from the Cloverly Formation. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp84.
Valentin Fischer, Edwige Masure, Maxim S. Arkhangelsky & Pascal Godefroit (2011): A new Barremian (Early Cretaceous) ichthyosaur from western Russia, Journal of Vertebrate Paleontology, 31:5, 1010-1025.
Fischer, V. 2011. New ophthalmosaurids from Europe and Russia broaden the biodiversity of Early Cretaceous ichthyosaurs. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp110.
Loewen, M., Zanno, L., Irmis, R., Sertich, J. and Sampson, S. 2011. Campanian theropod evolution and intracontinental endemism on Laramidia. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp146.
O'Keefe, F. Robin, Street, Hallie P., Wilhelm, Benjamin C., Richards, Courtney D. and Zhu, Helen (2011) . A new skeleton of the cryptoclidid plesiosaur Tatenectes laramiensis reveals a novel body shape among plesiosaurs. Journal of Vertebrate Paleontology 31:2, 330-339.
Richards, C., O’Keefe, R. and Henderson, D. 2011. Plesiosaur body shape and its impact on stability. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp178.
Sampson SD, Loewen MA, Farke AA, Roberts EM, Forster CA, et al. (2010) New Horned Dinosaurs from Utah Provide Evidence for Intracontinental Dinosaur Endemism. PLoS ONE 5(9): e12292. doi:10.1371/journal.pone.0012292

Sampson, S., Loewen, M., Irmis, R., Sertich, J. and Evans, D. 2011. Laurasian faunal interchange in the Late Cretaceous: the out of Laramidia hypothesis. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp185.



Friday, 25 November 2011

SVP 2011 - Hadrosaurs & Ceratopsians

Research into hadrosaurs and ceratopsians continues to be popular and vibrant and there was some fascinating data discussed at SVP. Prosaurolophus maximus is an understated hadrosaurine from the Campanian of the Dinosaur Park Formation in Alberta but despite being represented by multiple articulated specimens, the taxon has received little attention in the way of both morphological and phylogenetic analysis.

But Christopher McGarrity of the University of Toronto has looked at the cranial characteristics and ontogenetic features closely and found some interesting detail. P. maximus displays an allometric solid nasal crest that, as appears to be so often the case these days, is probably a deirved feature for sexual selection and recognition.   
P. maximus, as well as a second species,  P.blackfeetensis from the Two Medicine Formation of Montana, were included in a new phylogenetic analysis which recovered the two species  as sister taxa and the author states that the morphological differences between the two are hard to quantify and is indicative that P. blackfeetensis is a junior synonym of  P.maximus.  This suggests that Prosaurolophus has an extended chronological range of 1.6 million years and that is actually a long time when you consider species longevity.
I’ve already mentioned one poster regarding unusual skin preservation in a specimen of Gryposaurus but just why does hadrosaur skin appear to preserve more readily than other dinosaurian taxa? Matt Davis, of Yale University, has provided some detail. Hadrosaurs have been, and continue to be, heavily sampled due to the fact that many Upper Cretaceous Formations are exceptionally well known and it is also the peak period when hadrosaurs were incredibly numerous and diverse. The early 20th century saw an abundance of hadrosaur skin fossils recovered, especially from the extensive fossil fields of the Cretaceous Western Interior.


They are also nearly always found in sandstone exposures which tend to preserve more hadrosaur skin impressions than other facies. And although hadrosaurs were more abundant than other clades in these exposures, there is still an obvious bias towards hadrosaurian skin preservation. And yet despite these quantative statistics there is still no obvious reason to explain this unusual bias.
Just because hadrosaurs were abundant and the formations they are found in are extremely well known there is still no physical evidence to theorise and account for this unusual skin preservation. One can see that it is not easily explained but the one theory that cannot be ruled out is that hadrosaurs did indeed have some form of morphological skin condition or unusual behaviour that aided this unusual preservational bias.
Everybody is aware that the hadrosaur dental battery was a miracle of evolution and produced one of the most efficient plant processing machines that ever evolved. Greg Erickson and Mark Norell have conducted an extensive histological study of hadrosaur cheek teeth and have found that they were truly complex and even more specialised than mammal teeth. One particular tissue identified on the teeth was coronal cementum and this has actually been proposed as evidence for superior advancement in mammalian dentition. The study provides further evidence and enhances the fact that hadrosaurs possessed a truly remarkable and innovational dental arrangement.
Moving on to ceratopsians and the following focusses, again, on the on going research into dinosaurian synonymy. To begin with is a study of two large “Triceratops” skulls at Brigham Young University by Andrew Beach who re-evaluated the specimens after the very high profile synonymizing of Triceratops and Torosaurus last year. The first specimen, BYU 12183, was unfortunately shown to have extensive restoration and this covered much of the original skull morphology. But the second skull, BYU 19974, has suffered no such remodelling and this turned out to be very much more interesting indeed.
The specimen, which essentially comprises the frill, displays all the ontogenetic markers of an adult Triceratops and yet the parietal is actually thinning down where you would expect to find the parietal fenestrae in Torosaurus. This appears to provide yet more powerful evidence that Triceratops and Torosaurus are the same taxa and the author describes BYU 19974 as an ontogentically transitional form.

Triceratops fossils are remarkably abundant in the Hell Creek Formation and this provides ample opportunity to research gross morphology, ontogeny and phylogeny in this taxon taking into account stratigraphic variability. John Scanella et al have performed just such an analysis focussing on cranial variation in multiple specimens of Triceratops and the results are illuminating and indeed reinforce current thinking and thus open new doors which may affect dinosaur taxonomy as a whole.
It is apparent that ontogenetically identical specimens of Triceratops, even from the same stratigraphic level, can demonstrate astonishing variation. As expected, there is always variation in cranial ornamentation and there are significant morphological differences within individual animals. More surprising is that suture fusion, both within the skull and epi-ossifications, is not necessarily a sign of a mature animal and also that some sub-adult animals are actually bigger than adults. This makes such features unreliable as indication of adulthood. The implications of this are obvious when you consider something like Nanotyrannus where the sutres of the type skull (CMNH 7541) are fully fused and was one of the principle reasons why the taxon was raised in the first place instead of being identified as a juvenile Tyrannosaurus – which is the general consensus today.
Furthermore, histological evidence indicates that even the larger, more mature animals were still undergoing morphological change even at an advanced ontogenetic stage. Many other morphologic variations were revealed by the study and suggest that if other dinosaurs were also subject to the same rapid morphological change then a rapid rethink is necessary when quantifying the amount of dinosaurian taxa in any given formation. Incidentally, the authors report no evidence for sexual dimorphism in Triceratops and suggest that gender recognition was a much more subtle affair and may have been indicated by a visual signal, perhaps even coloration.
From the same stable, and featuring three of the same authors, comes yet more data indicating that it is not just Triceratops and Torosaurus that need to be synonymized. Denver Fowler et al introduce us to unified frames of reference which is a combination of methodologies combining, not only morphology and ontogeny, but stratigraphy, phylogeny, geography and tapohistory.
Not only has Triceratops displayed multiple morphologies at different ontogenetic stages, the same can be said for other chasmosaurines and it appears that both Mojoceratops and Kosmoceratops may both be juvenile morphs of Chasmosaurus sp. and Chasmosaurus irvensis respectively. Similarly, but at the other end of the ontogenetic stage, Titanoceratops displays morphologies that you would expect to find in older specimens of Pentaceratops.
A blast from the past
There are further implications from this research that focusses on biogeographical distribution and faunal endemism and that is currently a very heavily researched and debated subject in the palaeoworld, especially where Laramidia is concerned, and this on-going and important work will make a valuable contribution to our understanding of the diversification of dinosaurs and the environments they inhabited.
References
Beach, A. 2011. Triceratops and Torosaurus synonymy: an evaluation of two large specimens from Brigham Young University. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp68.
Davis, M. 2011. Complete census of published fossil dinosaur integument quantifies taphonomic bias towards prevalence of hadrosaurid skin. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp96.
Erickson, G. and Norell, M. 2011. The histology of hadrosaurid dinosaur teeth – reptiles that exceeded mammals in dental complexity?   Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp105.
Fowler, D., Scanella, J. and Horner, J. 2011. Reassessing ceratopsid diversity using unified frames of reference.  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp111.
McGarrity, C. 2011. Cranial morphology and variation in Prosaurolophus maximus with implications for hadrosaurid diversity and evolution.  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp155.
Scanella, J., Fowler, D., Trevethan, I., Roberts, D. and Horner, J. 2011. Individual variation in Triceratops from the Hell Creek Formation, Montana: implications for dinosaur taxonomy.    Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp187.

Saturday, 19 November 2011

SVP 2011 - Theropods

Time for theropods and about time too I hear you say. No matter whoever tries to convince you otherwise, theropods are without doubt the coolest animals ever to walk the planet and, of course, they were strongly represented at SVP.

Did change in theropod skull morphology occur due to the type of prey animals that shared their environment? Richard Bykowski of Indiana University has attempted to answer this question by combining the morphological data taken from the maxillary bones of multiple theropod specimens with the estimated relative abundance of other dinosaurs - including multiple prey animals as well as other theropods.
It appears that there is slight variation in maxilla morphology when the abundance of coexisting animals varies. However, faunas dominated by sauropods display the greatest change whereby the skull becomes more elongate, displays a flatter ventral border and a thickened ramus of the maxilla where it ascends. Other results indicate a lengthening of the snout where there are increased populations of marginocephalians and thyreophorans, and theropods, that shared their environment with larger populations of both ornithopods and other theropods, developed deeper and stronger skulls.
The sauropod result is interesting bearing my recent post about titanosaurs and carcharodontosaurs and Bykowski suggests that the typical carcharodontosaur skull layout is well suited to “slash and run” techniques which, again, I alluded to in the same post. Nice work by the author and I must point out that I have only skimmed the surface of what is obviously an intense and thorough study but I have to say that I would have thought that a sampling bias, in either direction, would probably affect results.
Any material from the mid-Cretaceous that transcends the early to late Cretaceous faunal changeover is rare and when it consists of new theropod material as well then it is doubly important. Derek Main et al have revealed new theropod specimens from the Arlington Archosaur Site in north Texas which comprises of a fauna that inhabited the Cenomanian coastal delta plains and comprise of multi-sized taxa, from the small to the large.
What makes this fauna so special is that it includes both basal tetanurans and dromaeosaurids which are representative of both early and late Cretaceous communities - transitional. Why were basal tetanurans, which originated from Gondwana, still around at this point? It seems that there was a global semi-arid climate that extended from Texas right through to Morocco and Niger and is indicative that these tetanurans preferred this drier environment   and this also explains their presence in this transitional mid-Cretaceous fauna.
Study of this unique fauna continues and it is hoped that it will shed more light on both palaeogeographic and palaeoclimatic questions during this crucial period in the Cretaceous. Of particular interest is how Gondwanan land faunas made the dispersal across the Berentsian land bridge and when this occurred since the Arlington fauna suggests an earlier crossing than initially thought.
Ornithomimus is one of best known ostrich-like dinosaurs and it is good to know that the holotype, Ornithomimus velox, is indeed a confirmed and valid taxon. Leon Claessons et al have reappraised the type material, which comprised of a distal tibia, partial pes and a partial manus, and performed a detailed examination which was enhanced by the fact that the material had been properly prepared and freed from matrix for the first time in over one hundred years.

Comparing the type material with specimens of Ornithomimus edmontonicus has shown the two genera to be similar but O. velox has slightly longer metacarpals although the pes of O. edmontonicus are longer overall but not a as robust. There is also an unusual development in the metatarsals and that is metatarsal II is longer than metatarsal IV which no other ornithomimid displays.
But the authors point out that a specimen from the Campanian Kaiparowits Formation of Utah has a similar condition and since there is a ten million year age gap between it and the purely Maastrichtian O. velox then it is apparent that O. velox is valid. Incidentally, the fossils from the Kaiparowits display morphological differences that infer that there are at least two as yet unnamed taxa from this formation.
Michael D’emic has featured a few times in recent posts and this time, with lead author Keegan Melstrom, both from the University of Michigan, have reported on a partial skeleton of a juvenile Acrocanthosaurus atokensis that has been recovered from the Cloverly Formation of Wyoming – the first time that this allosauroid has been identified in this formation.
The specimen has provided further data revealing that these theropods also grew fast at similar rates to tyrannosaurids and would reach adult size somewhere between 20 – 30 years old. Acrocanthosaurus represents one of the basal Gondwanan forms that was referred to earlier in the post and appears to have been widespread leading up to the early/late Cretaceous transitional stage.
A few years ago I was privy to some research being carried out on spinosaurids and baryonychinines and was told, in no uncertain terms, that it was certain that Suchomimus would be sunk into Baryonyx because they were irrefutably the same taxon. Well in 2011, that appears to no longer be the case. Nizar Ibrahim and Paul Sereno have revealed detail s of some new Suchomimus material which appears to contradict that theory.
The material was recovered from Middle Cretaceous exposures in Niger and includes a complete snout and, for the first time, some braincase material. There are several features, both cranial and postcranial that, according to the authors, settles the argument once and for all that Suchomimus and Baryonyx are, in fact, distinct genera – now where have I heard that one before?
It will be interesting to hear the response from the opposition camp and, as usual, we will all have to wait for the paper. Somehow, I suspect that this is not the end of this saga just yet. On the same poster the authors report on new spinosaur material from the early Upper Cretaceous deposits of Morocco and by comparing this new material with some “original” material from Egypt, they suggest it is likely that there was only one species of Spinosaurus that existed throughout the Cenomanian of Africa.
The quotation marks on “original” are my additions since, according to the abstract, the comparison was with “........the type material of Spinosaurus from Egypt.” And yet it is generally accepted that all of this material was destroyed by allied bombing during the war – so where did this material come from? It will be interesting to find out what this compared material actually is and again we must wait for the paper – the devil is in the detail.

A very popular talk, and discussed already in the palaeoworld by Brian Switek at Dinosaur Tracking and Stu Pond over at Paleo Illustrata, Alicia Cutler et al looked at why and how the classic theropod death pose occurred whereby the head and neck are stretched and arched back almost over the sacrum and the tail stretches cranially over the head and neck.
 Since most fossils discovered this way are found in sediments laid down in an aqueous environment, the authors decided to test the theory that submersion would inflate the elongate muscles that lie along the long axis which would shorten them thus creating the familiar contraction. Utilising some novel controlled experiments by submerging plucked chickens in water have provided the authors with startling results.

Astonishingly, once submerged, there is an almost instantaneous reaction by the head and neck muscles that pulls the head back – in some cases almost identically to the positions found in theropod dinosaurs. To make sure of their findings, controlled experiments with chicken carcasses in a dry environment were performed but with no noticeable distortion in over three months.
The team were both surprised and delighted by the results and suggest that movement was also helped by the fact that skull pneumaticity was a contributing factor due its relative lightness. Contraction continues after the initial submersion but only to a slight degree. For me, this is science at its best and I love the nature of these experiments and its simplicity and the team are to be highly commended.

Tyrannosaurs did not feature too much this year – indeed only there were only three technical sessions and one poster this year - of which three refer to T.rex, but the one of most interest, to me, is Thomas Carr’s continued work within Tyrannosauridae. This time Carr focussed on the sequence of development (heterochrony) that led to evolved features (synapomorphies and autapomorphies within tyrannosaurid phylogeny.
Because several species of tyrannosaurids are represented by almost complete ontogenetic life histories it was possible, by using cladistic analysis, to compare these stages and look for evidence of heterochrony. The author did indeed identify heterochrony, especially within tyrannosaurines, highlighting the maxillary fenestra as evidence and suggests that this kind of study is indeed ideal for identifying the morphological processes arrived at via heterochrony.

References

Bykowski, R. 2011. Biting Off More Than They Can Chew: A Geometric Morphometric Approach to Theropod Feeding Ecology. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp81. 

Carr, T. 2011. A Comparative Study of Ontogeny Between Derived Tyrannosauroids: Evidence for Heterochrony. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp84.

Claessens, L., Loewen, M. and Lavender, Z. 2011. A Reevaluation of the Genus Ornithomimus Based on New Preparation of the Holotype of O.velox and New Fossil Discoveries. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp90.

Cutler, A., Britt, B., Scheetz, R. and Cotton, J. 2011. The Opisthotonic Death Pose as a Function of Muscle Tone and Aqueous Immersion. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp95.

Ibrahim, N and Sereno, P. 2011.New Data on Spinosaurids (Dinosauria: Theropoda) from Africa. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp130.

Main, D., Noto, C. and Scotese, C. 2011. New Theropod Material from the Cretaceous (Cenomanian) Woodbine Formation of North Central Texas: Paleobiogeographic and Paleoecological Implications. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp150.

Melstrom, K. and D’emic, M. 2011. Acrocanthosaurus atokensis (Dinosauria: Theropoda) from the Cloverly Formation of Wyoming: Implications for Early Cretaceous North American Ecosystems. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp157.








Sunday, 13 November 2011

SVP 2011 - Lungs, Legs & Rapid Growth

Contributions on dinosaur physiology were well represented at SVP and here are a few that I found interesting. How dinosaurs managed to regulate their body temperature has been debated ad infinitum and this will no doubt continue to be so and, regardless of whether they were endothermic or not, the problem of overheating and how they managed to avoid it has proven difficult to explain.

William Porter and Larry Witmer of Ohio University hypothesised that dinosaurs must have used a form of vascular physiology as a method for heat control. Using a combination of CT scanning and the Extant Phylogenetic Bracket whilst studying dinosaur fossils, and then running the data in a 3D environment, has provided some interesting preliminary results. By comparing these results with similar studies of extant animals, such as birds and reptiles, a vascular anatomical profile of three dinosaurs (Majungasaurus, Edmontosaurus and Diplodocus) was established.

In simple terms, similar osteological correlates were identified in these dinosaurs that are present in the extant taxa examined. This study is at an early stage but further investigatitive techniques, new methodologies and expanding the results by utilising more dinosaurian taxa may provide a more robust and demonstrable dataset.

Today’s birds and crocodiles are in possession of lungs that allow unidirectional airflow but what are the origins of this physiological adaption in archosaurs and is there evidence for it in Triassic and Jurassic archosaurs? Physical evidence of postcranial skeletal pneumaticity (PSP) does not fossilize but traces remain and can suggest the extent of any air sacs that were present which, in turn, may indicate an avian-like respiratory system. Paul Barrett et al used micro-CT scanning on multiple archosaur specimens from the Triassic and Jurassic to search for evidence of PSP - and the results were encouraging.

It seems likely that non-avian saurischians and pterosaurs did indeed possess advanced respiratory systems but the results are less conclusive for ornithischians and other archosaurs. In these specimens there are other features, however, that may be indicative of a somewhat less advanced form of respiratory system and the authors suggest this may also be indicative of an earlier origin for the system, not only in dinosaurs, but throughout the entire archosaurian lineage. Interestingly, it seems, like so many other evolutionary convergences, that different groups of archosaur evolved their own form of respiratory systems and these, in turn, were probably variations on a theme that developed unidirectional airflow, as well as specialised air sacs.

A quick mention now about Heinrich Mallison’s contribution that looks again at how dinosaur speed is calculated and discusses how our original perception of speed that was calculated by using Alexander’s froude number, is outdated and is compromised by far too many inconsistencies. Instead, Mallison uses modern digital models combining SIMM and computer aided design to reach some interesting conclusions. Already discussed at national level at Nature, Mallison is currently explaining his work at his own blog, dinosaurpaleo, and I strongly advise you to visit – great stuff.

Of course, one of the pre-requisites in working out speed and locomotion in dinosaurs is being sure that your limb posture is correct in the first place but things are seldom that easy in vertebrate palaeontology. Forelimb posture in quadrapedal dinosaurs continues to stimulate debate with ceratopsians often at the forefront of discussion but the problems are much broader than that. Where and how do you start to sort this problem out?

Well you need radii, lots of them, 380 in fact and then you have to perform a painstaking morphological study and quantify them before comparisons can be made – and this is what Collin Vanburen and Matt Bonnan of Western Illinois University have done. The sample included radii from mammals and sauropsids, as well as dinosaurs, and this provided the ability to test the theory that, if dinosaurs had an erect limb posture similar to mammals, then it should follow that the shape of the radius would be similar as well.

However, the results suggest that dinosaurs and mammals are not alike at all – in fact they are actually more similar to non-erect sauropsids. And ceratopsians were hugely different from mammals, which substantially challenges the suggestion that they were able to run and charge like extant rhinos. The radii of sauropodomorphs, typically of the group, resemble neither radii from both mammals and sauropsids and have their own distinct morphology which suggests that they may have held their forelimbs erect but in a very specialised manner.

The authors conclude by stating that it seems likely that the majority of quadrapedal dinosaurs held their forelimbs in a non-erect posture and that it is best not use the mammal analogy as a basis for further study, whether assessing dinosaurian speed, gait or posture.

The study of bone histology was at the very forefront of the dinosaur revolution back in the seventies and continues to yield yet more data in support of active, high metabolic dinosaurs. Some of the latest information is provided by Koen Stein and Martin Sander of the Steinmann Institut fr Geologie in Bonn, Germany and concerns different cellular density in fibrolamellar bone.

Cellular density is measured by studying something known as osteocytes and these exhibit distinct patterns and morphologies that allow them to be quantified. By comparing the osteocytes of mammals and saurischians dinosaurs, including both sauropods and large theropods, it was possible to compare the two and then expand the analysis by also including extant poikilotherm ectotherms.

Saurischian dinosaurs have a much higher osteocyte density than mammals of comparable size and, likewise, mammals have a much greater density than ectotherms. Since mammals are high metabolic endotherms then the study suggests that dinosaurs had different ways of building fibrolamellar bone. High osteocyte density that is so much greater than ectotherms also provides powerful evidence for sustained active, high metabolic saurischians dinosaurs.

I have merely skimmed the detail of the top of this fascinating work and it provides the foundation for further studies of osteocyte density within the greater framework that is bone histology and physiology. And, of course, yet more evidence that supports the already huge amount of data that tells us that dinosaur were fast growing, high metabolic animals.

References

Barrett, A., Butler, R., Gower, D. And Abel, R. 2011. Postcranial Skeletal Pneumaticity and the Evolution of Archosaur Respiratory Systems. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp66.

Mallison, H. 2011. Fast Moving Dinosaurs: Why Our Basic Tenet is Wrong. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp150.

Porter, W. and Witmer, L. 2011. Vascular Anatomy and it Physiological Implications in Extant and Extinct Dinosaurs and Other Diapsids. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp176.

Stein, K. And Sander, P.M. 2011. Osteocyte Lacuna Density in Saurischian Dinosaurs and the Convergence of Fibrolamellar Bone in Mammals and Dinosaurs: Different Strategies to Grow Fast. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp199.

Vanburen, C. and Bonnan, M. 2011. Quantifying the Posture of Quadrapedal Dinosaurs: A Morphometric Approach. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp208.