Monday, 31 December 2012

2012 in Review


 
So another year in the palaeoworld draws to an end and, unlike the last couple of years, I found it to be relatively quiet by current standards. For example, 2010 was the year of the ceratopsians, last year I thought was the year of Archaeopteryx but this year there has been nothing that has really caught my eye to warrant such an epithet. Be that as it may, there was still plenty to keep us all occupied and here are some bits and bobs that caught my eye in 2012.
The year started on a very sad note with the passing of talented palaeoartist Dan Varner after a battle with a long illness. Dan was an accomplished landscape and wildlife painter but it was the prehistoric world that really fired his imagination and he produced copious amounts of paintings – in particular he was renowned for his depictions of the marine life in the Niobrara chalk seas of Kansas. Dan was also a noted field palaeontologist in his own right and had a solid knowledge of stratigraphy. For a superb gallery of some of Dan’s work, I urge you to head over to Mike Everhart’s superb Oceans of Kansas website and take a look. Dan will be sadly missed.
We also found out in January that Terra Nova had already been cancelled after only one series. I had mixed feelings about Terra Nova and would probably have liked the series to have been given the opportunity of a second series to see how it would have developed. But it was not to be and the series can be consigned to televisual history as an expensive failure. A shame.
One thing that came out of the blue was Jack Horner’s decision to marry 19 year old undergraduate Vanessa Shiann Weaver. This caused a little ripple throughout the paleontological world mainly due to the 46 year age difference between the two. In the end it is nobody else’s business whether we think it right or wrong or, indeed, question the ethics involved. It takes two to agree to get married and I hope that they are very happy together and have a long and successful marriage.
I confess that although I could not designate 2012 as the “year of” for anything in particular there was one subject that was perpetually in the headlines and that was the origins of Tyrannosauroidea. In February, Steve Brusatte and Roger Benson renamed some tyrannosauroid material from England as Juratyrant. They had been reassessing Late Jurassic elements and phylogenetic analysis revealed that this material, which had initially been diagnosed as Stokesosaurus sp., was sufficiently different to warrant the erection of a new taxon – Juratyrant. This places another cog in the continuingly turning wheels of the intricate understanding of tyrannosauroid evolution.
Also in February, and perhaps not totally unexpected, was the announcement by scientists from both the Universities of Liverpool and Manchester that Tyrannosaurus rex had the most powerful bite of any known land animal. I know that the team has actually put the science behind the statement but I could not help but think that this was proving something that was already generally accepted – Greg Erickson had proved this many years before. Still, as I say, the team has put the numbers in the column that reinforces the hypothesis some more and, in the end, it is still important.
Nick Longrich and Dan Field did their bit to keep the Torosaurus/Triceratops synonymy issue simmering along nicely. Using a combination of ontogenetic and taxonomic methods (amongst others) the authors state their belief that the two chasmosaurines are indeed separate taxa. This, of course, prompted yet more debate (some of it heated) on the issue but I am happy that there is always going to be scientists out there who challenge what can easily be perceived as a generally accepted hypothesis. There were further discussions on the issue at SVP so, if you have not already done so, go and check out the ceratopsian review.
Not a lot happened in March but the one stand out item, for me, was the publication of the Alioramus altai monograph by Brusatte and all. I wrote a pretty comprehensive review of this monograph but I will state again that, not only was this the paper of the year for me, but it raises the bar to a level for all other monographs to aim for. A superb descriptive narrative backed up by some of the best photographic images that you will see in any paper. I know that I am probably a little bias since it involves a tyrannosaurid but it really is that good and I learnt so much about tyrannosaurid anatomy. Read it now if you have not already done so but be warned – at nearly 200 pages long it is a BIG read but well worth it. Well done to the authors.
Probably the silliest story of the year appeared in April and involved a Professor Brian J. Ford and his aquatic dinosaur theory. If you did miss this (how?) Ford suggests that dinosaurs were so big that they could not possibly support their own body weight without the aid of water. He does not mean just sauropods either but all large dinosaurs. Unfortunately the story gained attention at a national level but there were enough of us to make sure that the story received the rebuttal it deserved. However, I understand we can expect further revelations from Ford about his aquatic dinosaurs in the not too distant future – I can hardly wait.
Yutyrannus arrived with a bang in April and the feathered tyrannosauroid ruffled more than a few feathers as it became apparent that 30 foot tyrannosaurs could indeed be feathered which of course led to yet more speculation that T. rex itself may have been feathered. My thoughts on this are well known and there is no need to go over them again and Yutyrannus is an awesome animal regardless but there is still a chance that it may not actually be a tyrannosauroid. I will know more in 2013 and, if I am permitted, then I will let you know.
In May, energy businessman David H. Koch of Koch Industries Inc. made a stunning $35 million donation to the Smithsonian NMNH to renovate its dinosaur hall. The new hall, on completion, will be named after Koch and I believe that this is only fair. Koch has made previous donations to the Smithsonian including one of $15 million to create its Hall of Human Origins. Other beneficiaries of Koch’s generosity also include the American Museum of Natural History where he donated $20 million to create the Koch Dinosaur Wing. Some people may question his ethics but you cannot question the fact that his donations and commitment are real and these institutions can consider themselves fortunate to be patronised by such an individual.
Another very popular paper was published in May and this was a phylogeny of Tetanurae by Messrs Carrano, Benson and Sampson. Another superb publication and an updated baseline for all those into their tetanurans. Great stuff.
It was also May that the ugly spectre of illegal smuggling form Mongolia was brought very much into the public eye with the now infamous Tyrannosaurus bataar skeleton that was auctioned at Heritage Auctions for over $1 million. Fortunately the sale was blocked and ever since then there has been a long drawn out process to return the specimen to Mongolia and see that justice is done. More on this later.  
In June came the announcement of a new theropod called Bicentenaria argentina. This 2.5 to 3 metre long animal is represented by 130 bones recovered from 90 million year old deposits in Rio Negro in Patagonia and is on display in the Museum of Natural Sciences in Buenos Aires. Unfortunately this is yet another taxon that has been released in public before the paper has been published and, as a result, very little is known about this enigmatic beast. I understand that sometimes sponsors or public events may dictate that a public announcement is required of some description but it would be nice if some reasonable data was made available at the same time – even if it was just an abstract or short communication.  Something would be better than nothing.
Another taxon that was similarly treated was the astonishingly well preserved Sciurimimus which was finally published in July by Rauhut et al. The “squirrel mimic” has turned out to be a juvenile megalosauroid and has yet further ramifications on the origins of feathers in dinosaurs and, indeed, about the distribution of feathers within Dinosauria as a whole.
Another story that tends to catch the eye, but for all the wrong reasons, is mindless vandalism of fossils in situ. This was brought home by the destruction of a hadrosaur specimen in Grand Prairie in Alberta which, incidentally, was one of several examples in Alberta this year. What on earth possesses these idiots to do such things? I cannot quite get my head around it and I urge you, wherever you are in the world, because this happens on a worldwide scale, to keep alert and inform the correct authorities if you know who may be responsible for such stupidity.
Dog Finds Dinosaur” is not a headline you expect to see but this actually happened during August. The dog did not locate the specimen of course and it is not a dinosaur but it is quite a remarkable specimen. The Keating family were out walking their dog in Nova Scotia when they stumbled across the remains of what was described as a sail-baked synapsid from the Late Carboniferous/Early Permian – circa 290 to 305 million years old. It turns out that the specimen is actually a temnospondyl – specifically Dendrerpeton arcadianum. There are certain characters that are particularly not found in synapsids. For example this specimen displays a sclerotic ring which is unknown in synapsids.
Another specimen of Mei long was announced in September and this specimen was also found in the “soundly sleeping dragon” position – just like the holotype. Whilst this in itself is not enough to confirm any behavioural implication, it does add to the growing belief that this is a stereotypical life position for these little dinosaurs.
SVP took place in October in Raleigh, North Carolina to universal acclaim that it was one of the best meetings in recent years. Being lucky enough to attend this year I can confirm that it was just brilliant and I look forward to the next meeting. Not such good news this month was that the Isle of Wight Council have decided to sell the building that constitutes the Dinosaur Isle Museum off to the highest bidder despite the fact it had been built using National Lottery funding. Backers of the museum have been trying to stop this and see the future of the building and museum as a trust and we wish them well in their endeavours.
Another big story broke in October and that was the discovery of ornithomimids with feathers. The fossils were recovered from Upper Cretaceous deposits in Alberta. These are superb specimens and again broaden the evolutionary scope of feathers within Dinosauria and are especially important since they reveal that this kind of plumage evolved relatively early in non-maniraptoran theropods.
Also in October, another new theropod taxon was announced by fellow blogger Andrea Cau and colleagues as they introduced us to Sauroniops pachytholus. This carcharodontosaurid looks a real bruiser with his heavily built and thickened skull and it will be fascinating to see more of this animal as and when more material is uncovered.    
There was still enough ceratopsian research throughout 2012 to keep us all on our toes and in November we welcomed Xenoceratops foremostensis to the fold. This interesting specimen came from Upper Cretaceous deposits of the Foremost Formation and is diagnosed as a new taxon due to characteristics in the squamosal and parietal. Xenoceratops comes out as the most basalmost centrosaurine known after an updated phylogenetic analysis.
And finally, in December, we see in the news that Eric Prokopi, the man responsible for smuggling in the illegally collected T. bataar specimen into the US, has indeed been found guilty of smuggling and other counts of misappropriation. The tyrannosaur skeleton will be returned to Mongolia whilst other substantial dinosaur remains have been forfeited to the court in an attempt to gain leniency from a sentence that could be as long as 17 years in jail.
Whilst I do not condone what Prokopi has done, I feel we must be very careful not to be jingoistic about the situation. Prokopi has got what he deserved for sure but there are many others who are equally as guilty and very likely on a much bigger scale. I prefer to be optimistic about the situation and hope that this is a landmark case which will lead to further prosecutions in the future and, ultimately, a change in the law which will see all illegally imported fossils returned to their country of origin, regardless of how they obtained entry into the US.
And Finally
2012 has been a big year for me in a number of ways. It is the year when I decided to make a mark in the world of palaeontology and I became proactive in establishing a research group which is slowly coming together and I hope will develop into something special. Certainly things have been going very well and we count in our small number a couple of established (and very well known) palaeontologists, three vertebrate preparators as well as other significant specialists.
It is regretful that I am presently unable to reveal any detail since the project is currently under a publicity embargo that prevents any disclosure until we are permitted. Whilst this may seem draconian I can assure you that this is absolutely necessary and we accept this restriction without question. Ultimately the groups’ aims are to the benefit of all students and palaeontologists worldwide and I assure you that any specimens involved will always end up in the correct accredited depositories and will always be available to researchers.
The palaeontological blogosphere has certainly blossomed in 2012 with several new blogs making their bow. We are quite the force for good these days and we all make a definite contribution to the promotion of our science. Social networking via Facebook, Twitter and others make the dissemination of information almost instant and the power we wield when we get together is not to be sniffed at – we can and do make a difference. Here’s to all my fellow bloggers and more power to you all.
At this point I would make a point of thanking a few names but there has been so many people this year who have helped that to single out a few would seem mean spirited but you know who you are – especially those of you at SVP who have offered help and advice with regards to the group. Thank you all.
And to you, my dear readers, my most humblest of thanks for continuing to peruse my blog. It really makes everything worthwhile and I really am very grateful for your presence.
All that remains to say is that I wish you all the happiest of New Year’s in 2013 and that all of your hopes and aspirations come true.

 

   

        

Monday, 24 December 2012

SVP 2012 - And finally . . . . .


 
With Christmas and the New Year upon us, it is time to wrap up my review of this year’s SVP despite the fact that there are so many other interesting topics to look at. So here is a brief look at some other presentations that we may, perhaps, look at in some detail in the future.
Greg Brown, of the University of Nebraska State Museum, is a top preparator and a nice guy to boot and his presentation looking at techniques and tools for the microfossil preparator was completely invaluable for those of us with an interest in preparing such intricate specimens. During the Preparators’ Session Greg presented a comprehensive guide to making things easier that was curtailed in its infancy primarily due to the constriction of the 15 minute time slot.
There was considerable emphasis on the preparator being comfortable at his work station and the need for stability, concentration and that the use of the right equipment is paramount. We touched on briefly about stereo microscopes, light sources and I found the part on the need for a stable work holding jig or vice, such as those ball vices used by engravers, to be particularly useful. The use of different lighting to highlight fossil from matrix was interesting as well and we will be seeing a lot more of this technology used at all levels in the future.
Far too much detail for the time slot and I hope Greg will consider providing all this information as a PowerPoint presentation at some point in the future or maybe even a paper. It really was essential listening for even the most accomplished preparators out there.  
Keeping with microfossils and Patrick Druckenmiller, of the University of Alaska Museum, and colleagues have been analysing dinosaur diversity in the Maastrichtian Prince Creek Formation of Northern Alaska. Despite being familiar with the fauna of this formation for some time now, the authors wanted to get a more comprehensive faunal make up which would enable more rigorous hypotheses about how these animals may have survived or perhaps even migrated during the colder periods. 
So a comprehensive analysis of teeth recovered from microvertebrate beds in the Prince Creek has revealed a much more diverse community than originally thought. Animals similar to the ornithischian Orodromeus, the theropod Richardoestesia as well as possible avialans and crocodilians have added to an already prolific palaeoenvironment. The authors hope these new taxa will enable further temporal comparison with similar fauna to those of formations such as the Horseshoe Canyon Formation in Alberta.
Evidence for predator-prey interaction has long been a favourite interest of mine since fossils that bear puncture, drag and serration scars make these animals come to life and we often find such bones in the Jurassic and Cretaceous. But Susan Drymala, of the University of Maryland, gave us a glimpse of the same interaction between taxa of the Upper Triassic Chinle Formation in the Petrified Forest National Park of Arizona.
An aetosaur osteoderm has been recovered displaying multiple tooth punctures, pits and scoring obviously as a result of feeding activity. To try and identify the possible maker of these marks the author compared the morphologies of the various marks with known carnivores that were contemporaneous with the aetosaur.
Phytosaurs, theropod dinosaurs and non-archosaurian archosauriforms were ruled out which left a raisuchian as the likely candidate and, indeed, the shape, striation density, spacing and curvature all point to an animal such as Postosuchus kirkpatricki as being responsible for the marks. This in itself does not seem all that spectacular but, speaking to Susan, she said that any evidence for species interaction in the Triassic is extremely rare and, as such, the specimen is relatively important.
Bone histology and growth rates have featured heavily in this blog and, again, at this year’s SVP and Carolyn Levitt, of the Natural History Museum of Utah, has been looking at the bones of Kosmoceratops richardsoni and Utahceratops gettyi from the Upper Cretaceous Kaiparowits Formation of southern Utah.
These are amongst the first chasmosaurines to be histologically studied and Levitt ran comparisons, not only with the centrosaurines of Alaska and Alberta, but with basal ceratopsids such as Psittacosaurus and Protoceratops.  This enabled the author to check out the various growth strategies amongst taxa and how their palaeogeographical position may have affected them.
 
Some interesting points were highlighted of which one or two are worth a particular mention. There appears to be clear variation in lines of arrested growth (LAGS) ranging in taxa from the north to the south. Pachyrhinosaurus, a northern taxa, displays as many as 18 LAGS whilst there are only are two evident in the southern taxa such as Kosmoceratops. Centrosaurus, from Alberta, comes out somewhere in between, with around 7 LAGS.
You would expect this variation purely because of the obvious temperature variability from north to south but things are seldom as simple as that. The author highlights the variables that must be considered such as the fact that it was impossible to sample the same taxa over a wide range since most taxa appear restricted to their immediate endemic environment. This means that each taxon displays its own individual histological signal.
Temporal variation is another consideration but perhaps the biggest factor is the apparent amount of variation in the climate of Laramidia. As I have hypothesised in the past, Laramidia was likely composed of many pocket environments where the climate varied considerably and this would account for the variation in ontogenetic growth, rapidity and duration of growth. So this expected variation in latitudinal ceratopsids seems to be a genuine artefact and is further endorsed by similar histological evidence found in the hadrosaurid Edmontosaurus.
In Brief
A little closer to home now and Jeff Liston, of the National Museums Scotland (but now in China for a year I believe), has been looking at the growth, age and size of the pachychormid fish Leedsichthys problematicus. Some early estimates suggested sizes of up to 100 feet for this plankton feeder but we knew long ago that this was a clear overestimate. So how do you size up what is still a very large fish?
Well you gather up the five most complete available specimens, select those elements which provide the most consistency when trying to determine absolute size – in this case postcranial elements, section them and count the annuli to arrive at a best guestimate for age determination. The sizes of the specimens range from 8 to 16.5 metres and, when crossed referenced with the annuli counts, found the results compared favourably displaying rank by size and the specimens were found to be between 21 and 45 years of age.
Despite suffering from a lack of specimens (the bane of palaeontologists worldwide) Liston’s work provides a framework for further research and demonstrates that there is age and growth consistency within Leedsichthys and that this is entirely comparable with the big extant filter feeding chondrichthyans of today.
Jordan Mallon’s continuing work looking into the mega-herbivores of Dinosaur Provincial Park continues and looks at how so many different large taxa managed to co-habit with what would appear to be limited resources in the amazing continent of Laramidia.  We have mentioned this dichotomy many times in this blog and I have already mentioned about the possibility of multiple pocket environments within the continent each harbouring its own ecosystem featuring multiple taxa that are unique to that biosphere.
Mallon, of the University of Alberta, has been studying the possibility of dietary niche partitioning as a possible explanation to explain this conundrum and looked at feeding height, skull, beak and tooth morphology as well as jaw mechanics and dietary wear. Within each faunal composition the author was looking for comparisons (or lack of) which may indicate niche partitioning.
The results are encouraging and there is evidence that sympatric taxa, even those that are extremely closely related, do indeed exhibit tendencies that indicate dietary preference and speciality. The author quantifies this by highlighting the fact that it is likely that the large mega-herbivores of Laramidia were probably influenced to specialise because of direct competition from each other although whether these pressures were due to long term competition or driven by geographic separation remains unclear.
Apart from the usual presentations and posters there were other interesting projects on show and one that I am a huge admirer of is the Smithsonian’s attempt to gather the world’s field books together in a kind of super databank. The Field Book Project has been instigated to collect, integrate and digitise field books from around the world and make these unique sources of information available to academics and students worldwide.
Once the Field Book Registry has been created it will be made available to scientists of all capabilities and persuasions and will be a unique source of data to all. Field books have long been hidden from view and it is hoped that they will inspire further generations of aspiring palaeontologists. Keep a look out for this one as it develops – there is already a blog and website – and I cannot commend this project enough.
And, lastly, for this year’s SVP reports, comes the strange case of the pterosaur Scaphognathus crassirostris – did you know that these pterosaurs survived into the seventeenth century? No – nor did I but, according to some Young-Earth Creationists (YEC) they did and they have attempted to promote this strange theory in an attempt to discredit evolution.
But thankfully we have people around such as Pondanesa Wilkins and Phil Senter, both of Fayetteville State University, as our champions, ready to pour hot water on this puerile garbage. And yet, as the authors’ state, it is important to discredit such literature in an a constructive way that the true evidence cannot, and must not be denied.
According to the YEC, a skeleton of S. Crassirostris turned up in seventeenth century Italy that had apparently only recently been killed in the marshes near Rome. An anatomical drawing of the specimen was made and the YEC identified the specimen as S. crassirostris due its crest and long tail. However, when the authors checked out the specimen they found that, not only is it unlike S. crassirostris, but is actually unlike any known pterosaur whatsovever. In fact the “specimen” is actually a composite made up of dogs, bear and an eel tail – I kid you not. Even the skin has been faked and carefully manipulated to cover the joints where the bones articulate – or not as in this case. The wings are also, naturally enough, faked and do not even resemble those of pterosaurs.
So, thanks to the authors, this particular anti-evolutionary “evidence” can be completely and utterly refuted due to a combination of detective work and palaeontological and osteological research. Well done to Messrs Wilkins and Senter!
Er...this is what a pterosaur really looks like!
 
And Finally 
Well this wraps up my SVP reports for this year. It seems to have taken a long time to get through these reports since October and that is because it has. I have been very busy with different things over the last few months and have not blogged as regularly as I would have liked. I think it safe to say that I am going through a transitional stage just now and it really has taken up a lot of my time.
However, be that as it may, things are slowly coming back under control and I hope to blog a bit more frequently in the New Year. 2013 will also be busy – but I hope for all the right reasons and I have to admit to being VERY excited and, perhaps, a little nervous about a research project that I and a few colleagues started back in the winter of 2011 and that is slowly coming together right now.
More of this in time but until then, and to those of you who celebrate it, can I wish you all a very happy Christmas and hope you enjoy all the fun of the season. See you all soon!
References
Brown, G.W. 2012. Techniques and materials for microfossil preparation: maximizing success and minimizing stress. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp69.
Druckenmiller, P.S., Erickson, G.M., Brinkman, D.B. & Brown, C.M. 2012. Dinosaur diversity in the Arctic: new records of polar dinosaurs based on microvertebrate analysis from the Upper Cretaceous Prince Creek Formation, Northern Alaska.  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp88.
Drymala, S. & Bader, K. 2012. Assessing predator-prey interactions through the identification of bite marks on an aetosaur (Pseudosuchia) osteoderm from the Upper Triassic (Norian) Chinle Formation in Petrified Forest National Park (Arizona, USA). Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp89.
Levitt, C.G. 2012. Variation in ceratopsian histology and growth: new data from southern Laramidia and implications for paleoenvironmental differences. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp127.
Liston, J. 2012. Growth, age and size of Leedsichthys, the largest bony fish. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp128.
Mallon, J.C. 2012. Dietary niche partitioning as a means for the coexistence of megaherbivorous dinosaurs from the Dinosaur Park Formation (Upper Campanian) of Alberta, Canada.  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp134.
Nakasone, S. & Pyenson, N.D. 2012. The Field Book Project: connecting field books with the world. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp148.
Wilkins, P. & Senter, P. 2012. A paleontological and neontological investigation of the claim that the pterosaur Scaphognathus crassirostris survived into the seventeenth century. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp193.

Friday, 14 December 2012

SVP 2012 - Tyrannosaurs


At last year’s SVP there was a symposium that focussed on many aspects of the unique continent of Laramidia and this year that other long lost land on the other side of the Western Interior Seaway, Appalachia, also came under close scrutiny. One of the presentations by Steve Brusatte, of the American Museum of Natural History, and colleagues looked at the theropods of Appalachia including ornithomimids but especially tyrannosaurs which we will look at now.
Compared to the wealth of fossils that are known from Laramidia, the record of Appalachian forms is sparse. This does not mean, however, that there are no specimens available and recent work has reinterpreted those fossils that were already held in collections as well as the new fossil discoveries of recent years. The rapid evolution of phylogenetic techniques has enabled these fossils to be classified with some degree of confidence and the tyrannosauroids Appalachiosaurus montgomeriensis and Dryptosaurus aquilunguis are extremely interesting specimens.
I recently blogged about these tyrannosaurs here and Brusatte et al are able to provide yet more detail that helps understand what was happening in Appalachia during the Late Cretaceous. The holotypes of these animals preserve both cranial and postcranial elements and the most recent phylogenetic analysis places them as intermediate forms between Asian taxa such as Guanlong and Dilong and the more derived tyrannosaurids of North America epitomised by such animals as Gorgosaurus and Daspletosaurus.
The authors suggest that these primitive forms in Appalachia remained isolated after the initial migration of basal tyrannosauroids from Asia was cut off by the Western Interior Seaway and that this particular landmass may have been a retreat from what was happening in the west during tyrannosauroid evolution. This backs up earlier work (Brusatte et al 2011) and suggests to me that there are probably many other primitive forms of dinosaur to be found and the authors point out that there is additional undiagnostic tyrannosauroid material that, although may be referable to either Appalachiosaurus or Dryptosaurus, may equally represent other taxa.  
Also featured on this blog here, and numerous other blogs and websites, is the continuing fascination with the forelimbs of tyrannosaurs and one presentation, that also received some publicity at the time, was a look at the forelimb musculature of these animals by Sara Burch of Stony Brook University.

Only the forelimb of Tyrannosaurus has been studied with any intensity but Burch looked at the forelimbs of eleven tyrannosauroids as well several other outgroup taxa for comparison. The purpose was to analyse any morphological change within the group as well as trying to identify any evolutionary traits that may indicate a reduction in forelimb use.
It appears that the most rapid change in forelimb musculature took place in the early evolution of Tyrannosauridae proper although a few basal tyrannosauroids were also identified as displaying change. The scapula and humerus both display enlarged muscle attachment sites. Various other muscle attachments also highlight the significant morphological change that took place as the forelimb reduced in size. Burch then identified the numerous functional changes that occur due to the reshaping of the muscles in tandem with the resulting changes in the various tendons.
The results show that there was an obvious reduction in some musculature whilst others became more robust.  What is fascinating here that, despite a superb analysis performed by the author, there appears be no clear functional evolutionary hypothesis for the forelimb. The arm in tyrannosauroids, as well as closely related taxa, was clearly capable of different functions and I suspect that the evolution of the theropod forelimb in general was fluid within taxa and did not neccesarily follow a common path. Even within tyrannosaurids proper there are obvious differences.
 Incidentally, I have skimmed over this presentation since, I must confess, musculature is not a strong point for me and is something I must address. But the presentation was much more lucid and made a lot of sense at the time. It was afterward when you are trying to take it all in that it starts to confuse......

 
Thomas Carr continues with his awesome work on tyrannosaurs and presented his research into the ontogeny and phylogeny of the cephalic ornamentation of these animals. There is a basic cephalic pattern that all tyrannosauroids conform to that includes processes on the jugal, lacrimal, postorbital and the rugosities of the nasal.
Carr used these characters as the base codings for a phylogenetic analysis of all derived tyrannosauroids ie Bistahieversor + Tyrannosauridae. Firstly the appearance of ornamentation appears in the same order through ontogeny. Firstly the ventral jugal horn appears, followed by the lacrimal process and then the postorbital process. Both the lacrimal and postorbital horns get larger throughout growth. Carr suggests that this is important since it signifies that these bony growths probably evolved to help recognise maturity and species recognition between taxa.
Interestingly, the same ontogenetic trend is followed in the early evolution of tyrannosauroids as a whole:  the early primitive form Dilong (the appearance of the corneal process of the jugal), the latter more derived Appalachiosaurus (the lacrimal process appears) and then in Bistahieversor, the appearance of the postorbital process.
There is also significant variety in the ornamentation throughout ontogeny. Most juvenile tyrannosauroids display as many three hornlet tips on the lacrimal horn but two of these are lost in adulthood. The one exception is Tyrannosaurus who loses the tip altogether at maturity.
Also of use is the fact that cephalic ornamentation can be used to diagnose taxa at the species level and there are certain characteristics, for example in Albertosaurus sarcophagus and Tyrannosaurus respectively, of the postorbital horn and the appearance of osteoderms that “cover” the lacrimal and postorbital that enable these identifications to be made.
Carr states that these species specific characteristics highlight the important of ornamentation in enabling species to recognise each other. He points to those formations that contain sympatric taxa such as Albertosaurus libratus and Daspletosaurus torosus in Laramidia and Alioramus altai and Tyrannosaurus bataar in Asia, as providing reasonable corroboration to back this hypothesis out.
Carr obviously looked at Alioramus in great detail due to his collaboration on the A. altai monograph and Alioramus obviously displays extreme ornamentation compared to other tyrannosaurids. Also of vast interest was his belief that he considers Raptorex to be a valid taxon since he was able to check out the fossils recently and characteristics in the lacrimal and horns have led him to this assertion.
Finally, I had the opportunity to talk to Thomas Carr at SVP and was very grateful that he spent some time with me chatting about all things tyrannosaur. Aside from discussing his presentation I asked him about his recent work on Daspletosaurus and was treated to a sneak preview of his upcoming monograph and it’s a big document – a VERY big document! I have been waiting for this to happen for a long long time and I was delighted that it was Thomas who was doing it. I cannot give too much away for obvious reasons but there will be, at last, details revealed about one of the new species of Daspletosaurus and maybe more…….

 
Following on from the aforementioned Alioramus monograph, the same team, this time led by Eugenia Gold of the Richard Gilder Graduate School, have been looking at the extreme pneumaticity of the skull of Alioramus.  Because the holotype of Alioramus altai is so complete the team were able to CT scan all of the pneumatic bones and the internal recesses of the skull including those of the face, palate and lower jaw and they were looking for clues into the origins of the coelurosaurian cranial sinuses as well as the morphological changes required to accommodate the evolution of the long snout in this taxon.
Results reveal that Alioramus displays a significant amount of derived coelurosaurian/avian characteristic recesses and vindicates the belief that this suite of characters evolved early in Theropoda.  This study also reveals that these very same cranial recesses suggest that cranial pneumaticity is stable in theropod evolutionary remodelling – even at the extreme snout lengthening stage of Alioramus.
The origins of tyrannosauroids remains one of the most interesting and vibrant aspects of our science. We have come to realise that the ancestors of the group probably evolved back in the Middle Jurassic and maybe even earlier. The absence of diagnostic remains has proved to be a stumbling block in our investigations but the new discoveries made in China and reappraisal of material from North America is now shedding light on this interesting aspect of the group.
Mark Loewen, of the University of Utah, and his colleagues have been looking at this in some detail and performed a phylogenetic analysis of 57 taxa and included neotheropod and coelurosaur outgroups to broaden the context of the analysis and then, in tandem with this, also re-examined the remains of the taxon Stokesosaurus clevelandi from the Cleveland-Lloyd Quarry in Central Utah.
Stokesosaurus not only retains its tyrannosauroid status and this is now reinforced by the identification of substantial new elements now assigned to the taxon. These include a premaxilla, maxilla, braincase and ilia. Bones from the craniofacial region are similar to those of Dilong, Guanlong and Proceratosaurus whilst the ilia are of particular interest and compare favourably to other recognised tyrannosauroids such as Eotyrannus and Juratyrant.
What this research helps to explain is the close relationship between Stokesosaurus and other early tyrannosauroids although we have to accept that there are still not that many specimens about that help fill the void between the Middle to Late Jurassic and the Early Cretaceous - a span of some 50 million years – so sampling remains an issue.  More derived tyrannosauroids such as Dilong, Eotyrannus and Yutyrannus appear closer to Tyrannosauridae although, again, there is a yawning gap of around 40 million years between these animals and Tyrannosauridae proper. As I continue to stipulate – sampling bias is an unavoidable element that must not be discounted and Roger Benson recently mentioned to me that such sampling issues are figuring high on his current agenda.
Never the less, this research emphasises my recent thoughts on tyrannosauroid evolution and the emergence of Tyrannosauridae – namely that it is most likely that there were many different dispersal and evolutionary events throughout the Jurassic and Cretaceous involving North America, Asia and Europe and I am very confident that there are many new tyrannosauroids still to be discovered.

And finally, Zhuchengtyrannus magnus is a large tyrannosaurine recovered from Upper Cretaceous deposits in Shandong Province, China and was brought to the world early in 2011 by Dave Hone et al. In that paper it was mentioned that it was likely that there was A secondary sympatric taxon from the same formation and now Corwin Sullivan, of the IVPP in Beijing, and colleagues have now revealed more detail about this tyrannosaurid.  
The quarries at Zhucheng have produced thousands of bones over the years from various dinosaurian taxa and amongst these remains were found tyrannosaurid teeth and the odd non diagnostic element. Eventually more diagnostic material came to light and Zhuchengtyrannus became the first named tyrannosaurid from the quarries.
Other material, however, including a maxilla and a dentary, are clearly different from the aforementioned taxon. The authors stress that this may not necessarily be a new taxon but may, indeed, be the remains of T. bataar despite the fact there are subtle morphological differences from that particular species. But as we know, and especially with Asian tyrannosaurids at the moment, morphological changes throughout ontogeny were rapid and apparently virtually continuous so these secondary remains are probably more likely to be from T. bataar.
Also of interest is that fact that the dentary from this animal displays a clear morphology which appears to be a dental abscess. The swollen area was CT scanned and appears to reveal evidence for osteomyelitic infection which has caused the deformation in the dentary. Although recognised in other dinosaurs eg hadrosaurs, this is an exceptionally rare example of this kind of infection in a theropod dinosaur. The authors speculate that that the condition would have impeded the tyrannosaurs feeding capabilities and, ultimately, led to a downturn in the animal’s wellbeing.

References

Brusatte, S.; Benson, R.; and Norell, M. (2011). The Anatomy of Dryptosaurus aquilunguis (Dinosauria: Theropoda) and a Review of Its Tyrannosauroid Affinities. American Museum Novitates, 3717, 1-53.
Brusatte, S.L.; Carr, T.D.; Norell, M.A. 2012: The osteology of Alioramus, a gracile and long-snouted tyrannosaurid (Dinosauria: Theropoda) from the Late Cretaceous of Mongolia. Bulletin of the American Museum of Natural History, (366)
Brusatte, S.L., Choiniere, J.N., Benson, R.B., Carr, T.D. & Norell, M.A. 2012. Theropod dinosaurs from the Late Cretaceous of Eastern North America: Anatomy, systematics, biogeography and new information from historic specimens.  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp70. 
Burch, S.A. 2012. Evolution of the forelimb musculature in Tyrannosauroidea (Dinosauria: Theropoda). Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp70. 
Carr, T.D. 2012. Ontogeny and phylogeny of cephalic ornamentation in Tyrannosauroidea (Dinosauria: Coelurosauria).  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp75. 
Gold, E., Brusatte, S.L. & Norell, M.A. 2012. Pneumaticity patterns in the skull of Alioramus altai, a long snouted tyrannosaurid (Dinosauria: Theropoda), from the Late Cretaceous of Mongolia. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp102. 
Hone, D.W., Wang, K.Z., Sullivan, C., Zhao, X., Chen, S., Li, D., Ji, S., Ji, Q. & Xu, X. 2011. A new large tyrannosaurine theropod from the Upper Cretaceous of China. Cretaceous Research 32 (4): 495 – 503.
Loewen, M.A., Sertich, J.J. & Irmis, R.B. 2012. The early evolution of tyrannosauroid dinosaurs: new anatomical, phylogenetic and biogeographic evidence. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp129.
Sullivan, C., Hone, D.W., Rothschild, B.M. & Wang, K.Z. 2012. Tyrannosaurid dinosaurs from the Upper Cretaceous Wangshi Group of Zhucheng, Shandong Province, China: coexisting giant carnivores and a tyrant with a toothache. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp181 - 182. 

 


 

 

 

 

Sunday, 2 December 2012

SVP 2012 - Theropods Part 2


 
The teeth of dinosaurs continue to fascinate. They are often well preserved, vary in shape and can be extremely large and impressive. They have also been intensely studied for function and morphology – I am fully aware of this fascination since I myself have been researching tyrannosaur teeth for a few years now.
But claws are another matter and, in particular, the manual unguals. But now Christopher Noto, of the University of Wisconsin-Parkside, has started to address this issue. Claws, like teeth, also show a huge variance in morphology but despite this it would appear that they were all universally utilised for predation. But is this actually the case?
The author analysed a total of 200 claws representing 80 taxa and a combination of methodologies including principal component analysis, reveal that nail curvature and nail size (relative to the ungual body) display the most morphological change and variance.  This analysis also reveals that digit 1 is nearly always the most morphologically different when compared with the other digits.  
Highlights include the fact that there is a significant difference in claw shape between coelurosaurs and non-coelurosaurs and the author suggests this demonstrates that coelurosaurs were ecologically more diverse. Non-coelurosaur claws are nearly always evolved with predation in mind. The diversification in coelurosaurian claws can be seen to evolve in stages as each clade moves to more derived forms. Examples include tyrannosaurid claws which are wickedly hooked and ornithomimids claws which became longer and straighter. Aviale and Deinonychosauria demonstrate a further extreme morphology which is likely to be indicative of a specialist climbing and/or grasping adaption.
This research into claw morphology and function further highlights the amazing variety within Theropoda and is a useful tool for determining their ecological differences and as an aide in establishing the mechanics of the theropod manus and, ultimately, will be useful for cladistics.
Oliver Rauhut, of the Bayerische Staatssammlung für Paläontologie und Geologie in Munich and Pol Diego, of the Museo Paleontológico Egidio Feruglio in Argentina, presented at SVP a quite bizarre looking new basal tetanuran. The specimen was found in the Middle Jurassic Cañadón Asfalto Formation in Chubut Province, Argentina. This formation has already revealed two other similar forms in the shape of Piatnitzkysaurus and Condorraptor.
The images presented revealed an unusual suite of characters that were readily apparent even though we were looking at the screen from distance. The specimen is fairly complete with elements of both the axial and appendicular skeleton present and, most importantly, a virtually complete skull. Any tetanuran from the Middle Jurassic is rare and to have one preserved this way is quite spectacular.
Firstly, it is a large animal with the skull around 0.8 metres in length. Secondly, it is clearly different from the aforementioned Piatnitzkysaurus and Condorraptor and was designated as a new taxon almost immediately. It does, however, demonstrate a suite of characters that are almost mongrel-like in their affinities.  There are the expected multiple tetanuran synapomorphies but there are also unexpected plesiomorphic characters, such as the short and distally expansive scapula, that are not usually seen in tetanurans.
To confuse matters more, the animal also shares derived characters that are found in both megalosauroids and allosauroids. For example, the maxillary fenestra is closed medially (a character found in megalosauroids) but the well developed lacrimal horn is clearly an allosauroid trait.  This specimen is SO weird but, since it is a basal tetanuran, incredibly important and the bizarre combination of characters lead the authors to believe that a monophyletic Carnosauria is a very real possibility or, on the other hand, may be evidence of homoplasy in early tetanuran evolution. My feel from the authors on this is that they favour the first option.
 
Allosaurus
 
The Witmer Lab of Ohio University was well represented at this year’s SVP and one study, led by Eric Snively, looked at feeding motions in that well known Late Jurassic theropod Allosaurus. Despite numerous studies that have analysed the biomechanics of the skull, very little research has looked at the overall motion of the head and neck. In this case, the authors used one well preserved specimen to use for their template.
Typically, the authors utilised the very latest in digital technology to bring these motions to life in Allosaurus. A combination of CT scanning of the skull and soft tissue reconstruction enabled three dimensional modelling that was highly detailed and included reconstructing sinuses, airways and bone density. Multi-body dynamics allowed that their attention to detail and allowance for every single known permutation and/or variation enabled them to come up with the most vigorous reconstruction yet of Allosaurus.
This specimen of Allosaurus has demonstrated that lateral angular acceleration was rapid – twice as fast as those calculated for Tyrannosaurus although dorsiflexive acceleration was comparable. Powerful coordination of lateroflexive muscles enabled rapid flexion of the cervical spine allowing the head to move down fast. However, due to the narrow build of the skull and a low ability in being able to power the head in a side to side motion suggests that Allosaurus pulled its head right back when feeding – a motion reinforced by the high sagittal mobility of the neck.
This combination of evidence suggests that Allosaurus dismembered and fed on their carcasses very much like raptors of today and are therefore very different from tyrannosaurids and crocodiles.
The Lower Cretaceous Cedar Mountain Formation of Central Utah is clearly an important formation and no doubt harbours many interesting fossils from this crucial period in dinosaurian evolution. There are many clues and I (amongst many) have been waiting for more remains of the elusive Cedar Mountain tyrannosauroid to come to life – so far only represented by teeth. But whilst waiting for that, another large theropod has appeared and Lindsay Zanno, of the North Carolina Museum of Natural Sciences, and colleagues have brought this important new animal to light.
Firstly, not only does this animal represent another new taxon, but, more importantly, represents the latest surviving allosauroid yet known from North America. Although there is no skull material available, there is enough of the skeleton to be able to refer the specimen to Carcharodontosauria and particularly displays high axial pneumaticity. This animal shares morphologies with the Neovenatoridae but the most anteriorly positioned centra of the dorsal vertebrae are relatively elongate which neovenatorids do not have. The posterior placed dorsals are similar to those of Neovenator and Aerosteon whilst other details share characteristics with neither carcharodontosaurids nor, indeed, Acrocanthosaurus.
This specimen extends the temporal overlap between carcharodontosaurians and advanced tyrannosauroids in the Early Cretaceous of Western North America although we must accept that there is still so much we do not know about this time period and that sampling remains an issue and, by implication, there remains a huge disparity in the phylogenetic make up of these groups that were coeval at the time.
Next up and worth the wait - tyrannosaurs.
References
Noto, C.R. 2012. What big claws you have: implications of morphological variation in theropod manual unguals. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp 150.
Rauhut, O.W. and Diego, P. 2012. A new basal tetanuran theropod from the Early Middle Jurassic of Patagonia, Argentina.  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp 160.
Snively, E., Cotton, J.T., Ridgeley, R.C. & Witmer, L.M. 2012. Feeding motions in Allosaurus (Dinosauria: Theropoda): multibody dynamics of the cervicocephalic apparatus suggest rapid lateral strikes but sagittal prey dismemberment.  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp 175.
Zanno, L.E., Makovicky, P.J. & Gates T.A. 2012. A new giant carcharodontosaurian allosauroid form the Lower Cretaceous Cedar mountain formation of Central Utah.  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp 199.

Sunday, 25 November 2012

SVP 2012 - Theropods Part 1


 
There is no doubt that theropods are probably the most popular dinosaur group of all and, knowing most of you like I do, then it is the theropods that are of the greatest interest whenever there is new research and information revealed. So without further ado, we can proceed. I always feel that ornithomimosaurs do not get as much attention as they deserve but they are bang in the news at the moment because of the newly revealed feathered ornithomimosaurs from Alberta and they also received some attention at SVP this year.
Ornithomimosaurs have long be known as “ostrich mimics” but how true a comparison is this with today’s extant palaeognaths – especially when it comes to the crania? By digitally reconstructing three ornithomimosaur skulls (Garudimimus, Struthiomimus and Ornithomimus), Andrew Cuff and Emily Rayfield, both of the University of Bristol, have produced some interesting results.
By utilising a combination of techniques including virtual muscle attachment data, adding hypothetical beaks to the rostra and studying finite element models and then, by comparing them to both ostrich and other theropods, has indicated that the sutures of the skull were key in minimising pressure to the skull. The beaks too also help in reducing strain and the different morphologies, especially of those beaks that are more extensive, help compensate for the loads.
More derived ornithomimosaurs reveal lesser muscle loads but still strain similarly to more basal forms. Compared on a like for like basis, the skulls of the advanced forms buckle quicker than the more primitive forms. The authors take this as indication that derived ornithomimosaurs may have been changing or varying their diets.
Not surprisingly, the skulls of ornithomimosaurs differ greatly from other theropods – in this study with Allosaurus and Coelophysis. The authors speculate that this may simply be a feature of herbivory evolving in ornithomimosaurs and in other theropods and the repeated evolution of beaks in Theropoda would simply have been a natural progression.
I mentioned earlier the feathered ornithomimosaurs from Alberta and a bone bed from the Upper Cretaceous Horseshoe Canyon Formation in the same province has been providing interesting histological data to Thomas Cullen, of Carleton University in Ottawa, and colleagues. The bone bed, the first of its kind in North America, contained the remains of three individuals and multiple leg elements from these specimens were histologically examined.
As is often the case with histological studies of non avian dinosaurs, indications are that growth was rapid, lines of arrested growth are equispaced and there is fibrolamellar tissue present.  At time of death, however, the larger individual reveals growth to be slowing up thus indicating the onset of maturity. Age for the two smaller individuals is estimated to be between two and three years old whilst the older specimen may be approaching four years of age.
Because the lines of arrested growth are constant throughout growth the authors suggest that postcranial long bones may be used as good indication of age – particularly in smaller theropods and, if they are correct in their hypothesis, then we may already have a wealth of information in our collections that enables us to determine growth patterns in different taxa - especially if the overall body size of a specimen can be ascertained.
Now I have mentioned on this blog on more than one or two occasions that the Upper Jurassic Morrison Formation of North America has many surprises still left up its sleeve and that there were many new taxa still to be described. However, this next one may seem surprising since it appears that we have yet another large bodied allosauroid in residence in what already appears to be an ecosystem already well represented in that department.
The specimen was recovered from McElmo Canyon in Montezuma County, Colorado and is late Tithonian in age. There are multiple elements represented including cranial, axial and appendicular and these have been examined by Sebastian Dalman, of Fort Hays State University, and colleagues with particular attention made to the cranial bones which were CT scanned and then digitally reconstructed three dimensionally.
This has enabled the authors to highlight characters in the premaxilla, maxilla and quadratojugal that warrant the erection of a new taxon. This animal is a large allosauroid comparable with other sympatric theropods in the same formation such as Allosaurus and Saurophaganax although, when compared with elements of similar sized Allosaurus specimens, is clearly a more massive animal.
Early phylogenetic analysis indicates the specimen is well placed within Allosauroidea and is closely related to Allosaurus, Fukuiraptor and Neovenator.   
 
 
Now we are all familiar with the great nest sites of sauropods and oviraptorids but those of other saurischians, particularly large theropods, whilst not unknown, remain relatively rare. The great nest sites of Portugal are an exception and a talk by Octávio Mateus, of the Universidade Nova de Lisboa, and colleagues have brought some amazing insights.
The nest, from the Upper Jurassic Lourinhã Formation in Paimago, Portugal contains the remains of approximately 100 eggs although erosion and the amount of eggshell present indicates the nest held many  more. Also of interest is that the nest also contains crocodile eggs but we can only speculate as to their presence here.
There appears to be no clear structure to the nest but the best preserved eggs and embryonic bones are preserved in the centre suggesting that these were the first laid and were at a more advanced ontogenetic stage than those on the exterior of the nest.  There are around 300 bones that have been recovered so far and this is despite the fact that the vast majority of the eggs are crushed.
The authors tentatively assign these embryos to Lourinhanosaurus antunesi since, although the bones are very similar to those of this theropod, the autapomorphies required to confirm identification were not preserved. However, there are sufficient differences in the remains to confirm that they are neither Allosaurus, Ceratosaurus nor Aviatyrannis. Nor does it seem that these eggs were laid by Torvosaurus, since the known nest, from the same formation, that was designated as belonging to this taxon are dissimilar in as much as the egg shell ornamentation is completely different and the embryonic remains are larger.
The authors point out that these embryos are very much fully loaded miniature versions of the adults and appear ready to become active predators from the moment they hatched. One other point of interest is that there are some very small patches of skin preserved in the nest and that these particular baby theropods display no evidence whatsoever of feathers or fuzz – only clearly defined scales -  again highlighting the danger of assuming that all theropods were feathered to some degree.
Scott Persons and Phil Currie, both of the University of Alberta, have been continuing their research into the cursorial ability in theropods and this time looked at the relative length of limb bones measured against the enormous variance in overall theropod body size as well as the effects of allometry on limb proportions.
Sixty one different theropod taxa were studied that all had complete hind limbs. The authors confirm that distal limb bones are unaffected by allometry and compensate for this fact. This allowed them to recognise adaptions in limb proportions and, as a result, they were able compare theropods despite the extreme differences in size.
The essential result of this is that there is no evidence that limb proportions in theropods that change throughout ontogeny are different in any way from those that would be predicted by simply observing body size. Highlights of this study include that the relative limb proportions of Nanotyrannus, when compared to other tyrannosaurids including Tyrannosaurus, are so extreme that the authors suggest that Nanotyrannus is indeed a valid taxon (here we go again). There is also evidence that there was continuous adaptivity in improving cursorial ability in many theropod groups including troodontids and tyrannosauroids.
 Of particular surprise, however, is that dromaeosaurids actually demonstrate a reduced ability to run which is quite the shock when you consider how we have all assumed them to be amongst the quickest and most agile of all the theropod dinosaurs.

More in Part Two.

References  
Cuff, A.R. & Rayfield, E.J. 2012. Functional Mechanics of ornithomimosaur crania compared to other theropods. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp 82.
Cullen, T.M., Ryan, M.J., Evans, D.C., Currie, P.J. & Kobayashi, Y. 2012. Multi-element histological analysis of an ornithomimid (Dinosauria) bone bed from the Horseshoe Canyon Formation, Alberta. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp 82- 83.
Dalman, S., Paulina Carabajal, A. & Currie, P.J. 2012. A new large-bodied theropod dinosaur from the Upper Morrison Formation (Late Jurassic, Tithonian) of Colorado. . Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp 84.
Mateus, O., Carrano, M.T. & Taquet, P. 2012. Osteology of the embryonic theropods from the Late Jurassic of Paimago, Portugal.  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp 137.
Persons, W.S. & Currie, P.J. 2012. Adaptive cursorial trends among theropod dinosaurs and an attempt to look beyond allometry. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp 156 - 157.

 

 

      

Monday, 19 November 2012

SVP 2012 - Some Tasty Morsels


 
Evidence of interaction and behaviour between extinct animals is always fascinating since it brings the prehistoric world to life. And, in this section, such evidence features heavily. David Burnham, of the University of Kansas, and colleagues presented a poster said to demonstrate evidence of predation by a plesiosaur on a specimen of Hesperornis.
Hesperornis is a well known Late Cretaceous ornithurine that was an abundant component of the Niobrara chalk sea in Kansas. A left forelimb of this bird demonstrates a series of small conical holes that suggest this specimen was attacked but survived since radiological examination reveals osteomyelitis infection had developed in the distal tibiotarsus.
Comparing the depressions and spacing of the tooth holes suggests that the attacker was most likely to be a small polycotylid plesiosaur. The authors interpret this as evidence that the plesiosaur attacked the bird from behind but was unable to maintain a grip on its intended victim and, thus, was able to make its escape. There appears, on the face of it, a little uncertainty about this since there were so many other predatory fish in the oceans with similar teeth that to be certain that a plesiosaur was responsible for the attack seems a little premature.
 But Bruce Rothschild was present and defending the poster and he was adamant that they were correct and since he knows more about bone pathologies than most people I think we can give him the benefit of the doubt for now. Even so, this is a very cool specimen that highlights the dangers that these large flightless birds must have faced every time they took to the ocean.
Sigilmassasaurus brevicollis was another theropod found in Late Cretaceous rocks (Cenomanian?) of North Africa. Known as Spinosaurus “B” by Ernst Stromer, the taxon was formally named Sigilmassasaurus by Dale Russell in 1996. And now Serjoscha Evers, of Ludwig-Maximilians-University, and colleagues have taken on the task of identifying this mystery taxon. The validity of this animal has always been in doubt since the remains are limited to vertebrae but now new vertebrae, consisting of one dorsal and several cervicals, found in museums in both London and Munich, have presented new data.
Firstly there several characters in line with the original descriptions that demonstrate that they are definitely from Sigilmassasaurus. Secondly the cervicals also demonstrate morphological differences that clearly show that they are not from Carcharodontosaurus – which some authors have considered that these remains belong to. Under CT-scanning, they also have internal arched pneumatic chambers whilst those of carcharodontosaurids are the familiar honeycomb-like small chambers.
What they are similar to, however, are the vertebrae of megalosauroids – especially spinosaurids. This suggests that Stromer may have been right (not for the first time) and that Sigilmassasaurus may represent a new spinosaurid taxon. The authors take this is a further indication that spinosaurids were a more diverse clade of dinosaurs than originally thought.
The small ornithopod Oryctodromeus cubicularis first came to our attention back in 2007 as the first dinosaur that potentially could be described as a possible burrowing or denning dinosaur (Varrichio et al 2007). The remains were found in the Mid-Cretaceous Blackleaf Formation in Montana and were found disarticulated in a partially preserved chamber at the end of a tunnel. Further research into the burrowing hypothesis has continued but has proven hard to quantify.
Now Jamie Fearon and David Varrichio, both of Montana State University, have been examining the forelimb morphology of Oryctodromeus to see if there are any specific adaptions for a burrowing lifestyle. This is problematic in as much that there are no extant analogues around to be able to compare the specimens with. 
But by using a combination of traditional and other geometric statistical analyses, including principal components analysis (PCA), of various ornithopods (including Oryctodromeus) the authors have been able to demonstrate some interesting results.   Iguanodontians and hypsilophodontids share similar basic forelimb morphologies but are distinct from hadrosaurids due to the shape of the deltopectoral crest. However, the PCA reveals that hypsilophodontids are distinct from both iguanodontids and hadrosaurids mainly due to the variance in the morphology of the scapula which is broader at both the proximal and distal ends.
So where does Oryctodromeus figure in all this? Well surprisingly not that close to any of the other groups mainly due to a ventral expansion along the posterior border of the scapula blade. The authors hypothesise that since this is the attachment site for the deltoideus muscle there is a chance that this can be seen as an adaption for digging since extant mammals that burrow today use that very same muscle. I asked the other question that has bugged the burrowing dinosaur theory – was there enough flexibility in the tail for the animal to be able to turn in such a tight area? Jamie Fearon believes that there probably was although she took great pains to point out they were only looking at the forelimb in this current study.
Serration scars are vivid on this example
A very popular poster, and another that has received good publicity, was titled “How to eat a Triceratops….” – a title guaranteed to generate interest. Denver Fowler, of the Museum of the Rockies, and colleagues have been looking at traces of tyrannosaurid carnivory by studying trace marks on numerous bones of Triceratops.
As noted here before, the Hell Creek Formation Project (1999-2011) has yielded 100 specimens of Triceratops and, of this number, there are eight individuals displaying tooth marks with another six that may possibly show evidence of carnivory. The real interesting thing here is that all the bones bar an ilium are from partially articulated or disarticulated skulls.
All bones display typical tyrannosaurid predation marks including puncture wounds and the classic puncture /pull drag marks. Such marks and analysis of the tooth spacing clearly indicate tyrannosaurid predation – in this case Tyrannosaurus rex since it was (and still is) the only known tyrannosaurid from the Late Maastrichtian rocks of Hell Creek.
Closer scrutiny of these marks reveal interesting, indeed, surprising feeding techniques. It appears that these carnivores were actually quite partial to the head of Triceratops. There are several drag marks on the parietosquamosal frills of a few specimens which, on the face of it, is surprising since there is apparently very little flesh there. The authors suggest that this may be indicative of the tyrannosaur manoeuvring the head to get to the succulent neck muscles and they quantify this suggestion by highlighting the fact that there are two occipital condyles displaying deep predatory gouges on them.
At the same time there are lighter feeding traces on bones such as a nasal and premaxilla suggesting that tyrannosaurs could be quite delicate in their feeding. This is not surprising since the premaxillaries of tyrannosaurids have often been described as “nibbling” teeth and now we have the evidence to back that up. But big tyrannosaurids, and Tyrannosaurus in particular, were well suited to large volume dismemberment of a carcass, whether killed or scavenged, and this new research highlights their various abilities in processing their prey to maximise the calorific intake.
What you cannot appreciate reading this, and unless you were at SVP, is the attached images with the poster showing these bones with the signs of carnivory. They are awesome and, in particular, the gauges on the occipital condyles are amazing. I am not sure how far away this paper is from publication but the images will be even better. When it is published take a look and be impressed – great work.
Yet more tyrannosaurid scars
 
This next one is a belter of a fossil. Finding dinosaurs with associated eggs is always fascinating but a partial oviraptorid recovered from the Upper Cretaceous Nanxiong Formation of Jiangzi in China appears to give us truly remarkable insights into the origins of avian reproduction. Tao He, of the Zhejiang Museum of Natural History in China, and colleagues have been looking at this specimen and made some interesting observations.
First of all, only the posterior half of the animal is preserved but it is well articulated. There are two eggs in association and they are both long and asymmetric and are designated as belonging to the Elongatoolithidae. One is located posterior to the sacrum (below caudals 4 – 7) and the other between the ischia. They are both covered in shell which is 1.0mm thick and is streaked by lineated ridges that run the length of the egg. The egg situated between the ischia also displays its blunt end in an apparent caudal direction.
The authors postulate that the relative position of the eggs suggests that they were partially expelled as the animal decayed – something that has been observed in extant drowned pregnant cattle as the calves were expelled after some decomposition(and there were some graphic images to show this). A blunt ended caudally facing egg suggests that theropods did not lay eggs in bound pairs as originally postulated and is actually opposite to what is found today in extant birds.
Two other points of note. Maniraptora have often been described as being monoautochronic – that is the simultaneous production of a single egg by each of a pair of oviducts -  and this specimen is clearly indicative of this. It is also suggestive that laying eggs two by two in a clutch enabled eggs to be proportionally larger and more robust when compared to the overall body size of the adult. This was a great presentation and the displayed images of the specimen were superb.
 
A typical dromaeosaurid
 
Richardoestesia is an enigmatic theropod taxon of uncertain phylogenetic affinities from the Maastrichtian of North America. It has been referred to dromaeosaurids, troodontids and aves but until more definitive remains are found is best left as status to be determined. However, we may be closer to understanding how this taxa eked out a living – by taking a closer look at its teeth.
Microvertebrate fossil specialist Julia Sankey, of the California State University Stanislaus, has been looking at abundant quantities of teeth belonging to Richardoestesia isosceles – a species she named herself back in 2001. Sankey has recognised that the straight tooth morphology is perhaps indicative that the taxon was a fish eater and quantifies this by highlighting that the teeth are much more prevalent in coastal as opposed to inland deposits. Richardoestesia, therefore, could be the first recognised fish eating theropod on the continent of North America.
And finally, in this post, we look at another fascinating case of interaction between taxa but perhaps not quite the animals that you might have expected. Jason Schein, of the New Jersey State Museum, and colleagues have been looking at a hadrosaurid femur recovered from the Main Fossiliferous Layer (MFL) of the lower Hornerstown Formation in New Jersey. The bone displays multiple straight to slightly curved grooves that are typical predation marks of oceanic sharks and the dinosaur was likely a typical bloat-and-float carcass that had been swept out to sea.
This femur, however, may be quite unique. The MFL has proven difficult to age correctly but it does appear likely that these sediments were deposited almost exactly at the contact point between the Maastrichtian and Danian – in fact the MFL has virtually one leg in each stage. Regardless of the complex taphonomic and depositional permutations, the femur represents what may potentially be the youngest non avian dinosaur fossil ever discovered.

References  

Burnham, D.A., Martin, L.D. & Rothschild, B.M. 2012 Plesiosaurs had a taste for birds.  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp 71.
Evers, S.J., Rauhut, O.W. & Milner, A.C. 2012. Was Stromer right? The affinities of Sigilmassasaurus brevicollis (Theropoda, Tetanurae).  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp 91.
Fearon, J.L. & Varricchio, D.J. 2012. Comparative pectoral and forelimb morphology of Ornithopoda: does Oryctodromeus cubicularis exhibit specialization for digging? Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp 92 - 93.
He, T., Varricchio, D.J., Jackson, F.D., Jin, X. & Poust, A.W. 2012. An oviraptorid adult-egg association and the origin of avialan reproductive strategies.   Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp 108.
Sankey, J.T. 2012. Something’s fishy: was one of the most abundant Late Cretaceous theropods a fish eater? Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp 165.
J.T. Sankey, 2001, "Late Campanian southern dinosaurs, Aguja Formation, Big Bend, Texas", Journal of Paleontology 75(1): 208-215 
Schein, J.P., Poole, J.C. & Lacovara, K.J. 2012. A shark-bitten hadrosaurid femur from the basal Hornerstown Formation, New Jersey, USA.: one of the youngest non-avian dinosaur remains known.  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2012, pp 166. – 167.
D. J. Varricchio, A. J. Martin, and Y. Katsura. 2007. First trace and body fossil evidence of a burrowing, denning dinosaur. Proceedings of the Royal Society of London B 274:1361-1368.