page_title: Bajadasaurus
section_title: Classification
hierarchical_section_title: Bajadasaurus / Classification
caption_attribution_description: English: Isolated upper tooth row of Bajadasaurus pronuspinax (MMCh-PV 75), showing premaxillary teeth (pm1–5) and maxillary teeth (m1–m8).
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: Dicraeosaurids are one of the three principal families comprising the Diplodocoidea, a major subdivision of sauropod dinosaurs. Within Diplodocoidea, dicraeosaurids form the sister group of the Diplodocidae, while the third family, the Rebbachisauridae, is more distantly related. Dicraeosaurids and diplodocids are united within the group Flagellicaudata, which is named after the whip-like tail characteristic for the group. In their 2019 description of Bajadasaurus, Gallina and colleagues recognised seven additional dicraeosaurid genera. The earliest is Lingwulong from the late Early to early Middle Jurassic of China, while three genera are known from the Late Jurassic—Brachytrachelopan from Argentina; Suuwassea from the US; and the eponymous Dicraeosaurus from Tanzania. Early Cretaceous dicraeosaurids include Bajadasaurus as well as Amargatitanis, Pilmatueia, and Amargasaurus, all from Argentina. An unnamed specimen from the Itapecuru Formation of Brazil indicates that the group persisted at least until the end of the Early Cretaceous.
  In their phylogenetic analysis, Gallina and colleagues recovered Bajadasaurus as an intermediate member of Dicraeosauridae, more derived (advanced) than Suuwassea and Lingwulong, but less so than Pilmatueia, Amargasaurus, Dicraeosaurus, and Brachytrachelopan. Amargatitanis was removed from the analysis due to its unstable position. The referral of Bajadasaurus to the Dicraeosauridae was supported by six synapomorphies (anatomical features shared with other members of the group). Bajadasaurus itself can be differentiated from other dicraeosaurids by a unique combination of features, which includes four autapomorphies (a medially extended posttemporal fenestra; slender and long basipterygoid processes; vertically oriented neural spine of second neck vertebra; and elongated, forward curved neural spines in the neck).
  The following cladogram by Gallina and colleagues (2019) shows the possible relationships between members of the Dicraeosauridae:
caption: Isolated tooth row showing the premaxillary (pm1–4) and maxillary teeth (m1–8)
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