#ardetosaurus

Results from the #paleostream

A new diplodocine sauropod from the Morrison Formation, Wyoming, USA

Tom T.P. van der Linden, Emanuel Tschopp, Roland B. Sookias, Jonathan J.W. Wallaard, Femke M. Holwerda, and Anne S. Schulp

ABSTRACT

The Morrison Formation of the western United States is well-known for its high diversity of sauropod dinosaurs. The Howe-Stephens Quarry in northern Wyoming is one of several quarries which has yielded several associated to completely articulated dinosaur specimens, among which a semi-articulated diplodocid specimen, MAB011899, which was excavated in 1993. This diplodocid specimen is represented by posterior cervical, dorsal, sacral, and anterior caudal vertebrae, multiple thoracic ribs, two chevrons, a left coracoid, a left ilium, both pubes and ischia, a left femur, a left tibia, and a left fibula. Through comparative anatomy, we interpret this specimen as a new species of diplodocine sauropod, Ardetosaurus viator gen. et sp. nov. Unambiguous autapomorphies include paired accessory laminae in the spinoprezygapophyseal fossae of posterior cervical and anterior dorsal vertebrae, bifurcating anterior centrodiapophyseal laminae in the anterior dorsal vertebrae, fossae present in the centropost zygapophyseal laminae of the second dorsal vertebra, a low vertebral height/centrum length ratio of the posterior dorsal vertebrae and reduced to absent centroprezygapophyseal laminae in the anterior caudal vertebrae. Local autapomorphic features include single centroprezygapophyseal laminae in the posterior cervical vertebrae and a highly elliptical cross-section of the femoral midshaft. Ardetosaurus viator is the first skeletally mature sauropod specimen described from the Howe-Stephens Quarry. This specimen provides insight into serial variation of vertebral laminae and laminar transitions. Finally, the peculiar morphology of the—often not preserved—first chevron is described in detail, and its possible use in studying sexual dimorphism in sauropods is discussed.

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(Neck vertebra of Ardetosaurus viator, with reconstructed portions shaded in white, from van der Linden et al., 2024)

Meaning of name: Ardetosaurus = burnt [in Latin] lizard [in Greek]; viator = traveler [in Latin, referring to the original specimen having been transported from the United States to Switzerland, Germany, and the Netherlands]

Age: Late Jurassic (Kimmeridgian), between 149.21–150.44 million years ago

Where found: Morrison Formation, Wyoming, U.S.A.

How much is known: Partial skeleton of one individual including multiple vertebrae, part of the hips, and some limb bones.

Notes: Ardetosaurus was a diplodocid sauropod, making it a close relative of Diplodocus and Apatosaurus. Given that the type specimen preserves a large portion of the spinal column, it provides valuable information on how the anatomy of the vertebrae varied across different parts of the spine in sauropods. It also exhibits features of the vertebrae that distinguish it from all other known diplodocids.

The type specimen of Ardetosaurus was dug up in 1993–1994 and has been nicknamed "Brösmeli" (meaning "crumbly" in Swiss German). In 2003, part of the specimen, including several of its neck vertebrae, were destroyed by a fire at the Dinosaurier Freilichtmuseum in Germany (hence the name Ardetosaurus), in a case of malicious arson. Based on microscopic examination of its bone structure, the type specimen was an adult at the time of its death, probably about 22 years old.

(Schematic skeletal of Ardetosaurus viator by Ole Zant [scale bar = 1 m], with preserved bones in white and bones that were preserved but subsequently lost in light gray, from van der Linden et al., 2024)