Testing hypothesis of skeletal unity using bone histology: The case of the sauropod remains from the Howe-Stephens and Howe Scott quarries (Morrison Formation, Wyoming, USA)

Abstract

Specimens of sauropod dinosaurs from the Upper Jurassic Morrison Formation of the Western Interior of the USA are mostly found as partial and partially articulated skeletons or as isolated bones, as seen in, e.g., the Dinosaur National Monument quarry. This mode of preservation sometimes makes an assignment of specific bones to individuals difficult, especially if other partial skeletons or scattered bones of the same taxon are found nearby. In this study, a detailed assessment of skeletal unity is provided by means of paleohistology for several sauropod partial skeletons and isolated long bones from the Howe-Stephens and the Howe Scott quarries, Wyoming, USA. Using histological characters such as histological ontogenetic stages, cyclicity of growth marks, and remodeling rate, an assignment of bones to individuals was made and compared with previous hypotheses of skeletal unity that were based on field observations only. Our study indicates, based on these characters, it is possible to assign isolated bones to an existing individual, recognize isolated bones as belonging to a new individual, and test whether a specific bone belongs to the assigned individual. The histological evidence should be combined with other sources of data such as morphology and taphonomy to reassess previous hypotheses of skeletal unit. The method presented in this study can be used not only for Morrison Formation sauropods, but to test skeletal unity for other fossil tetrapod taxa as well. Kayleigh Wiersma-Weyand. Abteilung Paläontologie, Institut für Geowissenschaften, Universität Bonn, Nussallee 8, 53115 Bonn, Germany. kayleigh.wiersma@uni-bonn.de Aurore Canoville. Paleontology, North Carolina Museum of Natural Sciences / Department of Biological Sciences, North Carolina State University, 11 W Jones Street, 27601 Raleigh, North Carolina, USA, and Abteilung Paläontologie, Institut für Geowissenschaften, Universität Bonn, Nussallee 8, 53115 Bonn, Germany. canoville.aurore08@gmail.com Hans-Jakob Siber. Sauriermuseum Aathal, Zürichstrasse 69, 8607 Aathal, Switzerland. aathal@sibersiber.ch P. Martin Sander. Abteilung Paläontologie, Institut für Geowissenschaften, Universität Bonn, Nussallee 8, 53115 Bonn, Germany. martin.sander@uni-bonn.de WIERSMA-WEYAND ET AL.: BONE HISTOLOGY SAUROPODS 2