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.

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