page_title: Bajadasaurus
section_title: Function of neural spines
hierarchical_section_title: Bajadasaurus / Palaeobiology / Function of neural spines
caption_attribution_description: Skeletal reconstruction of Bajadasaurus pronuspinax gen. et sp. nov (MMCh-PV 75). 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.
context_page_description: Bajadasaurus is a genus of sauropod dinosaur from the Early Cretaceous epoch of northern Patagonia, Argentina. It was first described in 2019 based on a single specimen found in 2010 that includes a largely complete skull and parts of the neck. The only species is Bajadasaurus pronuspinax. The genus is classified as a member of the Dicraeosauridae, a group of comparatively small and short-necked sauropods that lived from the Early or Middle Jurassic to the end of the Early Cretaceous.
  Bajadasaurus sported bifurcated, extremely elongated neural spines extending from the neck vertebrae. Similar elongated spines are known from the closely related and more completely known Amargasaurus. Various possible functions have been proposed for these spines in Amargasaurus, with the 2019 description of Bajadasaurus suggesting that they could have served as passive defense against predators in both genera. The skull was gracile and equipped with around 44 teeth that were pencil-shaped and restricted to the front of the jaws. The eye openings of Bajadasaurus were exposed in top view of the skull, possibly allowing the animal to look forwards while feeding.
context_section_description: Elongated and deeply bifurcated neural spines were common in dicraeosaurids. In Dicraeosaurus and Brachytrachelopan, they were inclined toward the front but remained much shorter than in Bajadasaurus. Only the spines of Amargasaurus were similarly elongated. The spines of Amargasaurus led to much speculation about their possible life appearance and function. As hypothesised by separate authors, they could have supported a sail or horny sheaths, and could have been used for display, defense, or thermoregulation. Daniela Schwarz and colleagues, in 2007, found that the double-row formed by the bifurcated neural spines along the spine of dicraeosaurids would have enclosed an air sac, the so-called supravertebral diverticulum, that would have been connected to the lungs as part of the respiratory system. In Dicraeosaurus, this air sac would have occupied the entire space between the left and right parts of the spines, while it would have been restricted to the lower third of the spines in Amargasaurus. The upper two thirds would likely have been covered by a horny sheath, as is indicated by longitudinal striations on their surface.
  Gallina and colleagues, in 2019, considered this the most reasonable interpretation that may likewise be applied to Bajadasaurus. These researchers further argued that horn is more resistant to impact-related fractures than bone, and that a horny sheath would therefore have protected the delicate spines from damage. Fracturing of the spines might have been a critical threat, as the bases of the spines roofed the spinal cord. The protection of the sheath would have been further enhanced if it would have extended past its bony core. Schwarz and colleagues reconstructed Amargasaurus with horny sheaths that did not reach far beyond their bony core; the same is true for most modern reptiles. In some modern even-toed ungulates, however, the horny sheath can be double the length of the horn core, and the exquisitely preserved ankylosaur Borealopelta was found with horny sheaths that extended the length of its spines by 25%, demonstrating that substantial horny extensions may occur in dinosaurs as well. Gallina and colleagues suggested that the spines of Amargasaurus and Bajadasaurus might have been 50% longer than indicated by their bony core. Their bending would have further increased their resistance, as is the case in modern bighorn sheep.
  Gallina and colleagues further speculated that the spines in both Amargasaurus and Bajadasaurus might have been used for defense. Due to its forward bent, the bifurcated neural spine of the supposed fifth neck vertebra would have reached past the head, acting as what was compared to a fence to deter predators. Similar, even larger spikes were postulated for the following neck vertebrae. Moderate damages would result in the break-off of the horny tips, leaving the bony spine intact. Amargasaurus lived around 15 million years later than Bajadasaurus, indicating that elongated neural spines were a long-lasting defense strategy.
caption: Speculative skeletal reconstruction by Gallina and colleagues, 2019,[2] showing known elements in white. The total number of neck vertebrae and length of the spines is based on Amargasaurus
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