A sauropod from the Lower Jurassic La Quinta Formation (Dept. Cesar, Colombia) and the initial diversification of eusauropods at low latitudes

The northern-most occurrence of Sauropoda in South America was collected in the 1940s from Early–Middle Jurassic-aged continental sediments on the western flank of the Serranía del Perijá in Colombia. Relocation of the site and re-preparation of the specimen, a well-preserved dorsal vertebra, provide important information about the initial diversification of sauropods at low latitudes. The specimen possesses autapomorphies and a unique combination of character states (e.g., divided centropostzygapophyseal lamina, strongly dorsally arched postzygapophyseal facets) that diagnose it as the new genus and species <i>Perijasaurus lapaz</i>. A medium-sized early eusauropod, <i>Perijasaurus</i> inhabited tropical lowland forested areas around the Toarcian–Aalenian boundary. Our phylogenetic analysis recovers <i>Perijasaurus</i> near the base of Eusauropoda, in an unresolved position near <i>Cetiosaurus</i>, <i>Patagosaurus</i> and kin (<i>Bagualia</i>, <i>Spinophorosaurus</i>, <i>Nebulasaurus</i>), and more deeply nested eusauropods. The phylogenetic position of <i>Perijasaurus</i> bolsters the idea that eusauropods achieved a broad geographic distribution during the Early–Middle Jurassic, before the deeper fragmentation of Pangea and after the Toarcian faunal turnover documented at high southern latitudes. <i>Perijasaurus</i> and other basally diverging sauropods display an intermediate level of bone weight reduction in the axial column that represents an antecedent to the more highly developed pneumatic system characterizing Neosauropoda.