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.

Thursday, 10 November 2011

SVP 2011 - Sauropods

Sauropods continue to generate enormous interest and at this SVP meeting it was no different – and rightly so. They are the giants of the dinosaurian world but it is not always the biggest that is at the forefront of sauropod study and an ontogenetic series of the dwarf sauropod, Europasaurus holgeri, has provided new data on how dwarfism in dinosaurs evolved due to island isolation.

Oliver Wings of the Museum fr Naturkunde Berlin also revealed that the Langenberg Quarry in Northern Germany has provided an extensive vertebrate fauna that includes not only Europasaurus, but pterosaurs, crocodiles, turtles and fish. The focus of the study is to take into account the stratigraphy, taphonomy and palaeoecological considerations in combination with the taxanomic and palaeobiogeographic evidence to be able to identify what determined island dwarfing in dinosaurs.

Moving on to a “proper” sauropod and Kelli Trujillo et al reported on a specimen of Camarasaurus that may not be all that it seems. The specimen was recovered from a bonebed in the Upper Jurassic Morrison Formation of Albany County, Wyoming and took the team by surprise since, although the animal was quite large, it displayed characteristics that suggested it was actually a juvenile.

The specimen is made up of mainly caudal vertebrae, a few dorsals and the sacrum and since camarasaurid growth stages are recognised due to the degree of neurocentral suture fusion, this specimen can be recognised as a juvenile because a large proportion of the vertebrae are unfused. But the size of the bones are of an animal approaching 90% of a regulation sized adult Camarasaurus – and therein lays the dichotomy.

Another anomaly is the fact that this camarasaurid is perhaps one of the oldest known specimens of the genus. Perhaps the animal is one of those strange aberrant individuals that cause so much phylogenetic and taxanomic distortion when they are found. The authors will continue their research into the specimen and they also suggest that this animal may indeed be a new larger species of Camarasaurus, which would be really interesting.

Already mentioned in the blogosphere is the discovery of a partial titanosaur caudal vertebra that can be regarded as the first definitive record of sauropods from Antarctica. Ignacio Cerda et al reveal that the specimen was recovered from the Late Cretaceous (Campanian) of James Ross Island and extends the range of South American titanosaurs beyond the continent and represents the southernmost example of a sauropod ever found.

Back to the Morrison Formation and just how the vegetation that grew during the Late Jurassic managed to sustain such a vast population of giant sauropods, as well as other mega-herbivores, remains unclear. Until recently, it has remained a matter of uncertainty as to even what plants dominated the Morrison landscape but now Carole Gee, from the University of Bonn, may have provided a few of the answers.

Traditionally, the Morrison flora has been depicted as either fern dominated or something akin to the savannahs of Africa today, with a limited distribution of trees that were somewhat restricted and isolated in number. The fact that fossil wood and logs are commonplace in the formation seems to have been disregarded. But now a combination of the discovery of many new species of conifer cones, in tandem with pollen samples recovered throughout the Morrison, has shed new light on the true nature of the Late Jurassic flora.

The results suggest a landscape dominated by conifer forests that were interspersed with plants such as moisture loving ferns and these would have been able to provide a much greater quantity of fodder for the mega-herbivores as opposed to, for example, a savannah-like environment.

Nutritional analysis of similar extant analogies of the fossil plants suggests that they were also much more nutritious than previously thought and were well suited to the dietary needs of sauropods. When you consider the amount of fodder an adult sauropod would require on a daily basis, estimated to be in the region of between 1000 to 2000Kg, then this was just as well. It also supports the suggestion that sauropods were r-strategist breeders enabling juveniles to reach large sizes very quickly due to this extensive, and very nutritious, vegetation.

I mentioned during my post about Alamosaurus that there was more data in the pipeline regarding this enigmatic sauropod and Jeffrey Wilson and Michael D’emic of the University of Michigan provide it. They confirm that the holotype scapula is indeed diagnostic and that this enables several more specimens, that are much more complete, to be referred to Alamosaurus. This, in turn, expands the overall diagnosis for the taxon and new phylogenetic analysis recovers Alamosaurus as a derived titanosaur with either Asian or South American affinities. This appears to confirm that Alamosaurus was indeed an immigrant as opposed to being a member of Early Cretaceous North American sauropods that appear after surviving the so called 30 million year long sauropod hiatus.

References

Cerda, I., Paulina Carabajal, A., Salgado, L.,Coria, R. and Moly, J. 2011. The First Record of Sauropod Dinosaurs from Antarctica. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp86.

Gee, C. 2011. Sauropod Herbivory During Late Jurassic Times: New Evidence for Conifer-Dominated Vegetation in the Morrison Formation in the Western Interior of North America. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp115.

Trujillo, K., Demar, D., Foster, J. and Bilbey, S.A. 2011. An Exceptionally Large Juvenile Camarasaurus from the Morrison Formation (Upper Jurassic) of Albany County, WY, USA. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp205.

Wilson, J and D’emic, M. 2011. The Validity and Paleobiogeographic History of the Titanosaur Sauropod Alamosaurus sanjuanensis from the Latest Cretaceous of North America. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp215.

Wings, O. 2011. Beyond Europasaurus: The Late Jurassic Vertebrate Assemblage of the Langenberg Quarry in Oker/Germany. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp215.

Sunday, 6 November 2011

SVP 2011 - Some Highlights

So SVP is over for another year and, embargoes now lifted, we can report on, and discuss, some of the excellent content that was presented in Las Vegas. Here I report on some of the highlights that, from a purely personal point of view, are amongst the most fascinating.

One of the most famous dinosaurs in recent years is a specimen of Thescelosaurus neglectus known as Willo who made worldwide headlines as possibly being the first dinosaur found with a fossilised four chambered heart. Naturally this has led to some controversial discussion as to whether the structure located within the thoracic cavity is actually what it appears to be.

But now, following on from his previous work (2011), Timothy Cleland of North Carolina State University has performed an extensive morphological examination of the specimen and has demonstrated that the “heart” of this dinosaur is almost certainly a geological artefact. However, there is also evidence of structures that are not conducive with being of geological origin and are actually similar to both plant and animal cells. Further examination using scanning electron microscopy suggest a biological origin for these structures which is somewhat intriguing although the overall evidence from this intense study overwhelmingly supports a geological origin for the structure.

Direct evidence of predator-prey relationships in the fossil record is always fascinating and brings the prehistoric world to life. Evidence of predation on fossil bone is more common than people realise and to see the serration and gouge marks, sometimes so clear on the surface of bone, is always a thrill. But now a specimen of Microraptor, from the Early Cretaceous of China, has taken this interaction to another level.


O’Connor, Zhou and Xu of the Institute of Vertebrate Palaeontology & Palaeoanthropology (IVPP) in Beijing reveal that the specimen appears to have the remains of an enantiornithine bird in its stomach. The authors  suggest that Microraptor did indeed hunt in the tree canopy since the birds were obviously arboreal. And, the authors also suggest, that this may be further evidence for a “tree down” origin for avian flight. Looking forward to the paper being published for this one.

The Morrison Formation is one of the most heavily sampled vertebrate bearing strata in the world and is rightly famous for providing a multitude of Late Jurassic dinosaurs. But there is also a varied mammalian community that is not so well known but is equally as fascinating and now Anthony Martin et al have revealed a wonderful discovery that captures one of those unique moments in time.

A quarry near Bluff in Utah has revealed an extensive network of burrows that have been dug by fossorial mammals probably weighing as much as 500gm – quite large for the time and represents an as yet unknown taxon. It is a typical burrowing system with main tunnels, side offshoots and various chambers and, amazingly, some of the smaller tunnels wind through and around the skeleton of a camarasaurid sauropod skeleton.

Palaeoenvironmental studies reveal that the sauropod had died millennia before in a waterhole environment and was buried in sediment and detritus. Eventually, the site was covered in newly formed soil as a result of pedogenesis. It was this soil that was tunnelled through by the mystery mammals who gradually penetrated through to the sauropod skeleton. The burrows within the skeleton actually change direction to get around the bones demonstrating how the mammals were affected by the obstruction. A wonderful and rare discovery capturing, indirectly, mammalian and dinosaurian interaction during the Jurassic.

Back in August, Robin O’Keefe and Luis Chiappe announced in Science that a specimen of Polycotylus latippinus, recovered from the Pierre Shale in Logan County, Kansas, was found in association with, what they describe as, embryonic remains of a juvenile. At SVP there was yet more detail displayed describing the specimen and shows that the bones of the juvenile are poorly ossified and are at an early ontogenetic stage.

The fact that the bones of the juvenile were found within the body cavity of the larger specimen and that they show no sign of being digested or chewed leads to the conclusion that this specimen of Polycotylus was a gravid female that died prior to giving birth. It is apparent that the embryo still had a period of significant development to undergo before coming to term and it appears likely that Polycotylus gave birth to single, very large new borns.


Strangely, you would think that there would have been other specimens of pregnant plesiosaurs found by now, especially when you consider how many plesiosaurs have been collected over the years. Perhaps the most interesting part of this discovery is the hypothesis, because a single birth by implication suggests as much, that plesiosaurs may have demonstrated parental care for their young which in turn leads to suggestions that they also engaged in a form of social structure and interaction. This leads to all sorts of new conjecture and may redefine how we interpret reproductive and behavioural patterns in other marine reptiles.

Finally, here’s one for you palaeoartists out there and is amazing in its own right. A hadrosaur, tentatively referred to Gryposaurus, recovered from the Upper Cretaceous Kaiparowits Formation of southern Utah has revealed some unique and illuminating skin impressions displaying previously unknown morphologies.

Katherine Clayton et al have demonstrated that there is a single line of large scutes that sit proud along the dorsal ridge of the tail - totally unknown before now. On the flank of the tail, it is apparent that the skin tubercles are bigger dorsally at the proximal end whilst distally the largest tubercles are situated ventrally. The tubercles themselves are polygonal and irregular in size and display various lines of ridges that terminate in a scalloped edge that are non-uniform. This find is comparable to other skin impressions found in this and other similar formations but is quite distinct from other hadrosaurs such as Edmontosaurus.

References


Clayton, K., Irmis, R., Getty, M., Lund, E. and Nicholls, W. 2011. An Exceptionally Preserved Hadrosaurid Dinosaur Skeleton with Integument Impressions From The Upper Cretaceous Kaiparowits Formation of Utah. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011,pp90.

Cleland, T., Stoskopf, M.K. and Schweitzer, M.H. 2011. Histological, Chemical, and Morphological Reexamination of the “Heart” of a Small Late Cretaceous Thescelosaurus. Naturwissenschaften 98: 203-211.

Cleland, T. 2011. Chemical and Morphological Reinvestigation of the Dinosaur Heart. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011 pp90.

Martin, A., Noto, C. and Chiappe, L. 2011. A Burrow Runs Through It: Unusual Co-occurrence of a Large Mammal Burrow System and Dinosaur Skeleton in the Morrison Formation of Utah. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011 pp152.

O’Connor, J., Zhou, Z. and Xu, X. 2011. Small Theropod with Bird in Stomach Indicates Both Lived in Trees. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011 pp168.

O’Keefe, F.R. and Chiappe, L. 2011. Viviparity and K-Selected Life History in a Mesozoic Marine Plesiosaur (Reptilia: Sauroppterygia). Science 333, 870-873.

O’Keefe, F.R. and Chiappe, L. 2011 Viviparity and Cetacean-Like Life History in a Mesozoic Marine Plesiosaur (Reptilia: Sauropterygia). Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011 pp 168.

Thursday, 3 November 2011

How Big a Bite is Big?

So Planet Dinosaur has now finished its six episode run and I think it fair to say that the series has been generally well received by both the general public and the palaeoworld as a whole. It was my intention to review the series but I think Marc Vincent has done an excellent job of that over at Love in the Time of Chasmosaurs and presents a reasonable and balanced view. Head over there and take a look if you haven’t already done so.

In one episode, New Giants, there is a sequence depicting a group of Mapusaurus attacking a group of Argentinosaurus and at a one point we witness one of the theropods removing great slices of flesh from the flanks of a distressed, what appears to be, sub-adult sauropod. The theropods withdraw leaving the unfortunate beast with great wounds that bleed profusely and it is intimated in the narration that the sauropod is slowly being reduced to a moving feast as the attackers return again and again to take yet more flesh from the slowly dying animal. But how possible or realistic is this?

Carcharodontosaurid teeth are flat, blade-like and heavily serrated making them ideal cutting tools and are well suited, it would appear, of removing significant amounts of flesh from prey animals. Mapusaurus was a big theropod, comparable with Tyrannosaurus, with a massive skull and powered with significant jaw muscles and it is likely that Mapusaurus was very capable of taking huge bites out of sauropods. Or was it?


From Coria & Currie 2006
Just how thick the skin of sauropods was must remain a matter of conjecture but it is safe to state that it was considerable. The hide of an elephant maybe up to 100 to 125mm thick in some places so it seems reasonable to assume that a sauropods’ skin would have been thicker by an undetermined amount but, for the sake of argument, lets imagine it to be in the region of 150 to 200mm thick which does not appear to me to be unreasonable.

We have some skin impressions of sauropods which display a conventional scale covered surface and, in the case of some titanosauriformes, is supplemented by raised and not insignificant osteoderms (e.g. Bonaparte 1999). Just how durable all this makes the skin is conjecture but this appears to me to represent one hell of a tough mouthful for an attacking Mapusaurus to contend with. The skin alone is probably thicker than the teeth are long and you have to remember that carcharodontosaurid teeth are essentially flat and narrow, even if the crowns are approaching 125mm in length, and do not have the power or durability of, for example, tyrannosaurid teeth. Although theropod teeth were constantly being replaced throughout their lifetime, it seems likely that any theropod would prefer not to lose too many at any one time.

Even if there were no osteoderms, obtaining a mouthful of flesh for the theropod is problematic. The sauropod is certainly not standing around allowing the carnivores to attack at will and will be a moving target, albeit a slow one, and has the added bonus of a significant mass and tonnage which the attacker would do well to avoid.

Looking at other possibilities, maybe there were more vulnerable areas to attack such as the neck but this would be a constantly moving target and it would also be capable of generating significant force that may inflict substantial damage on any attacker. However, as already stated, the teeth of carcharodontosaurids are excellent cutting tools and maybe they were used simply to cut the skin, perhaps supplemented by claws from both the manus and pes, to get the sauropod bleeding as much as possible. Constant hit and run attacks in this way would be an efficient and safer option for any attacking theropod as opposed to trying to tear out great chunks of flesh - slash-and-dash as it is often referred to.

The other tool in the theropods tool box is the fact that they were much faster and agile than any sauropod could possibly be and should be capable of side stepping any flailing neck or tail (remember that we are discussing titanosaurs – not diplodocoids). Having said that, if sauropods moved in herds then it seems possible that they may have defended themselves as a collective group and then the problem is amplified for the attacker and they would need every ounce of agility to avoid injury.


Image from Planet Dinosaur © BBC
All of this assumes that large theropods such as Mapusaurus actively targeted sub-adult and adult animals but this was almost certainly not the case unless one such animal was sick or injured. In such cases as these, the hunters could probably take their time with their assault since the unfortunate beast was almost certainly on its way out anyway. It appears obvious to me that even the largest of theropods would take the easier options of softer targets such as the weak, the sick, the young and, of course, any carrion that they came across.

One thing this particular episode of Planet Dinosaur probably got right were the high mortality rates of young sauropods at the nesting grounds. Using the famous titanosaur nesting ground of Auca Mahuevo as the setting, the episode showed pterosaurs and the abelisaurid Skorpiovenator plundering the nests of the young hatchlings and it seems obvious that the annual? sauropod nesting season would have attracted every predator for miles to join in on the feast and I would include the giant carcharodontosaurs in on this.

Nesting sites such as Auca Mahuevo suggest that sauropods were almost certainly what are known as r-strategists (Chiappe 2003). That is that they laid vast quantities of eggs producing young sauropods that, although tiny in comparison to the adults, were able to survive on their own – if they lived long enough to do so. Mortality rates would have been enormous but those that survived would have grown rapidly and got relatively big very quickly although it would still have taken several years to become a giant. This would have meant that there would have been many different generations of sauropod in circulation at any one time and these animals were likely to be those favoured by theropods – including the giants such as Mapusaurus.

Of course, all of this still has to be considered speculation and it seems likely that very few sauropods would attain their full adult size due to predation but if sauropods were herding animals that grouped together for protection then there may have been an element of sanctuary within the herd for some juveniles at least.

References

Bonaparte, J. F., 1999. An armoured sauropod dinosaur from the Aptian of northern Patagonia, Argentina, pp. 1–12 in Tomida, Y., Rich, T.H., and Vickers-Rich, P. (eds.), Proceedings of the Second Gondwana Dinosaur Symposium.

Coria R. A. & Currie P. J. 2006. — A new carcharodontosaurid (Dinosauria, Theropoda) from the Upper Cretaceous of Argentina. Geodiversitas 28 (1) : 71-118.
 
Chiappe, L.M., Coria, R.A., Jackson, F. & Dingus, L. 2003. The Late Cretaceous Nesting Site of Auca Mahuevo (Patagonia, Argentina): Eggs, Nests & Embryos of Titanosaurian Sauropods. Palaeovertebrata, Montpellier, 32 (2-4): 97-108.