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| Bajadasaurus pronuspinax
Gallina, Apesteguía, Canale & Haluza, 2019
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Abstract
Dicraeosaurids are a group of sauropod dinosaurs characterized by a distinctive vertebral column with paired, long, neural spines, present in an extreme fashion in the South American form Amargasaurus cazaui. This distinctive morphology has been interpreted as a support structure for a thermoregulatory sail, a padded crest for display, a dorsal hump acting as fat reservoir, and even as inner cores for dorsal horns. Other inferred functions (if any) of this structure were related to sexual display and/or defense strategies. Here we describe a new dicraeosaurid sauropod, Bajadasaurus pronuspinax gen. et sp. nov., from Patagonia which preserves the most complete skull of the group and has extremely elongate bifid cervical neural spines that point permanently forward, irrespective of the neck position. Although much shorter versions of this neural spine configuration were already recorded for other dicraeosaurid taxa, the long, anteriorly bent spines of this new dinosaur support the hypothesis that these elongate spines of dicraeosaurid sauropods served as passive defense structures.
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| Figure 1 Skeletal reconstruction of Bajadasaurus pronuspinax gen. et sp. nov. (MMCh-PV 75), location and quarry map. (A) The neck and skull reconstruction in left lateral view, showing preserved bones in white. The complete anterior cervical vertebra is located tentatively in the fifth position (see Description). The total count of cervical elements, as well as the relative extension of the neural spines, is based in the complete series of the related taxon Amargasaurus, the other dicraeosaurid with extremely elongated bifid neural spines along the neck.
(B) A map of the surrounding area of the Ezequiel Ramos Mexía lake (Neuquén Province, Argentina) showing the type locality of Bajadasaurus (Bajada Colorada) indicated by a white star.
(C) A quarry map showing the association and location of the remains in the field. at, atlas; ax, axis; cv, cervical vertebra; d, dentary; f, frontal; m, maxilla; po, postorbital; pt, pterygoid; qj, quadratojugal.
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Illustration: Jorge A. González
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Systematic palaeontology
SAUROPODA Marsh 1878
DIPLODOCOIDEA Marsh 1884
FLAGELLICAUDATA Harris & Dodson 2004
DICRAEOSAURIDAE Huene 1927
Bajadasaurus pronuspinax gen. et sp. nov.
Etymology: Generic name from Bajada (Spanish for downhill, in reference to the locality Bajada Colorada) and saurus (Greek, lizard). Specific epithet from pronus (Latin, bent over forward) and spinax (Greek, spine), referring to the anteriorly pointed, curved, neural spines of the cervical vertebrae.
Pablo A. Gallina, Sebastián Apesteguía, Juan I. Canale and Alejandro Haluza. 2019. A New Long-spined Dinosaur from Patagonia sheds light on Sauropod Defense System. Scientific Reports. 9: 1392. DOI: 10.1038/s41598-018-37943-3
