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

ABSTRACT

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 Perijasaurus lapaz. A medium-sized early eusauropod, Perijasaurus inhabited tropical lowland forested areas around the Toarcian–Aalenian boundary. Our phylogenetic analysis recovers Perijasaurus near the base of Eusauropoda, in an unresolved position near Cetiosaurus, Patagosaurus and kin (Bagualia, Spinophorosaurus, Nebulasaurus), and more deeply nested eusauropods. The phylogenetic position of Perijasaurus 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. Perijasaurus 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.

RESUMEN

La ocurrencia más septentrional de Sauropoda en América del Sur se recolectó en la década del 1940 en sedimentos continentales del Jurásico Inferior a Medio, en el flanco occidental de la Serranía del Perijá en Colombia. La relocalización del sitio y una nueva preparación del espécimen, correspondiente a una vértebra dorsal bien conservada, brindan información importante acerca de la diversificación inicial de los saurópodos en paleolatitudes bajas. El espécimen tiene autapomorfías y una combinación única de caracteres morfológicos (por ejemplo, lámina centropostzigoapofiseal dividida, facetas postzigoapofiseales fuertemente arqueadas dorsalmente) que lo diagnostican como un nuevo género y especie, Perijasaurus lapaz. Perijasaurus es un eusaurópodo de tamaño mediano, que habitó en áreas boscosas en tierras bajas tropicales alrededor del límite Toarciano-Aaleniano. Nuestro análisis filogenético muestra a Perijasaurus cerca de la base de Eusauropoda, en una posición ambigua cercana a Cetiosaurus, Patagosaurus y sus parientes (Bagualia, Spinophorosaurus, Nebulasaurus), y eusaurópodos anidados más profundamente. La posición filogenética de Perijasaurus refuerza la idea de que los eusaurópodos alcanzaron una amplia distribución geográfica durante el Jurásico Temprano-Medio, antes de la fragmentación completa de Pangea y posterior al recambio faunístico del Toarciano documentado en las altas latitudes del sur. Perijasaurus y otros miembros basales de saurópodos muestran un nivel intermedio de reducción de la masa ósea en la columna vertebral que representa un precursor del sistema neumático más desarrollado que caracteriza a Neosauropoda.

http://zoobank.org/urn:lsid:zoobank.org:pub:7409E4E7-8BED-4AF5-814A-FEDAE7FC4596

ACKNOWLEDGMENTS

Field reconnaissance in the La Paz–Manaure area (Depto. Cesar) was conducted thanks to the assistance of E. Gómez-Díaz, C. Montes, A. Reyes-Céspedes, J. D. Atencio (Uninorte), P. P. Contreras, J. Angarita, and the Tierra Grata Territorial Training and Reincorporation Space (Espacio Territorial de Capacitación y Reincorporación, ETCR) in Manaure, Cesar. We thank P. Holroyd (UCMP) for access to collections (J.A.W.M., M.D.E.) and loan of specimen to the UMMP for preparation, which was carried out by Chief Preparator W. J. Sanders. We are grateful to UMMP Collection Manager A. Rountrey for the three-dimensional models and virtual slices and T. Abdul Kareem assisted in lighting and orienting the three-dimensional surface models featured in Figures 3–5. R. T. Figueroa generously loaned us a WACOM tablet for line work. Color scheme in Figures 3 and 4 was developed by C. Abraczinskas. We thank C. Woodruff (Great Plains Dinosaur Museum) for discussion and assistance with literature. We wish to thank J. M. M. Ferrer and A. Aberasturi of the Museo Paleontológico de Elche (Spain) for access to Spinophorosaurus, and F. Ortega and P. Mocho for the opportunity to examine material presently under description. We are indebted to those who contributed sauropod occurrence data to The Paleobiology Database, especially M. Carrano; these data were used to highlight the paleolatitudinal and temporal uniqueness of Perijasaurus. We thank editor M. D’Emic and reviewers J. Carballido, F. Holwerda, and P. Mannion for their helpful comments on this manuscript. Access to the free version of TNT 1.5 was possible due to the Willi Hennig Society. Field research and museum visits in Colombia by J.A.W.M. were supported by a Fulbright Award. Field research by A.F.R. and D.A.R. was supported by UniNorte internal research fund (CC FOFICO 32101 PE0031:2018-10, Paleobiogeography of the Caribbean). Visit of M.D.E. to the UCMP was funded by the Samuel Welles Fund Grant and his research is currently funded by Agencia Nacional de Promoción Científica y Técnica (PICT 2018–01186).