Study of a Sauropod Dinosaur Vertebra Found in the Kimmeridgian of Cricqueboeuf (Normandy, France)

Detta är en Master-uppsats från Uppsala universitet/Institutionen för geovetenskaper

Sammanfattning: In 1999 a Kimmeridgian age vertebra of a sauropod dinosaur was discovered directly in a layer of clays from Cricqueboeuf in Normandy, France. The vertebra is now located at the Paleospace museum and was part of an inventory in 2015 as well as the subject of this Master thesis. Two shells of the oyster Deltoideum delta typical of the upper Jurassic, sits on the vertebra making it easy to identify the original stratigraphic position of the vertebra. The origin of the vertebra, found in situ in a bed of clays, and the presence of these oysters assure that the vertebra belongs to the Kimmeridgian (between 157,3 ± 1 and 152,1 ± 0.9 millions of years). No reworking is possible in this environment of low energy and with a such weight (2,430 kg). The position of the vertebra in the skeleton of a sauropoda has been ascertained in this study. It belongs to the caudal part of the skeleton, but the position in the tail was more difficult to find. Fortunately, with some literary review, the vertebra is identified as a middle caudal vertebra essentially based on its dimension and based on the presence of the articulation facets for a typical bone in the tail, the chevron. The goal of this study was also to find a clade of dinosaur to which we can link this vertebra. Based on its morphology, the base of the neural arch is located on the anterior two thirds of the centrum; this is a particularity of the Titanosauriform dinosaurs. After reviewing the sauropod fauna present during the Kimmeridgian in Europe, the two titanosauriforms to which this vertebra can be referred are Europasaurus holgeri from Germany and Lusotitan atalaiensis from Portugal. Arguments are established to compare with these two taxa. Cricqueboeuf’s vertebra seems to have some morphological characteristics of Lusotitan atalaiensis. It should be considered that the comparisons could have been done with closest fauna like sauropods of England but unfortunately, they stay very poorly known. The paleogeography of the Kimmeridgian indicates that France was composed of few European islands and lithology confirms that Cricqueboeuf was located underwater (200 m maximum). Finding a sauropod vertebra in marine sediments indicates drifting after death and taphonomy is also discussed in this article. The vertebra may have come to the Armorican massif (western France) because it is the closest island to Normandy in the Kimmeridgian. Because European and Norman sauropods are not well known, and a lot of fossils are in private collection without no description, only future discoveries and studies may allow us to confirm or reject this hypothesis that the vertebra of Cricqueboeuf could be a vertebra of Lusotitan atalaiensis. In the future it will be necessary to clarify the faunal relations between the different European islands of the Kimmeridgian.

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