HOW DIVERSIFIED WAS THE SAUROPOD FAUNA AT THE BASE OF THE NEUQUÉN GROUP? NEW EVIDENCE FROM CANDELEROS FORMATION (CENOMANIAN) OF SOUTHERN NEUQUÉN BASIN (PATAGONIA, ARGENTINA)

BELLARDINI, F.; WINDHOLZ, G.J.; BAIANO, M.A.; GARRIDO ALBERTO CARLOS; MANIEL, IGNACIO; HEREDIA, ARTURO; CIAFFI, A.; GUEVARA LUCERO, JAVIER; MESSINA, Y

Malargue

Jornada; IV Jornadas de Paleontologia de la Cuenca Neuquina; 2024

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The Neuquén Group represents a thick sequence of Upper Cretaceous terrestrial sediments that weredeposited over more than 20 million years in the Neuquén Basin, in northern Patagonia (Argentina).The Neuquén Group has yielded an abundant and diversified vertebrate fossil record, especially ofreptile fauna, allowing us to reconstruct part of the evolutionary history of different archosaurlineages, such as sauropod dinosaurs. In this contribution we report new sauropod findings from thelower section of the Candeleros Formation outcropping at El Sauce locality (Neuquén Province,Argentina), the earliest lithostratigraphic unit of the Neuquén Group, to explore the taxonomic andmorphological diversification of the sauropod fauna in southern Neuquén Basin during theCenomanian. The new fossil record is composed of: a middle-to-posterior incomplete cervicalvertebra (58-MES-PV-04), the anterior portion of a cervical vertebra (58-MES-PV-03), an incompleteanterior caudal vertebra (58-MES-PV-02), a proximal epiphysis of a radius (58-MES-PV-01), a distalepiphysis of a pubis (58-MES-PV-05), and an almost complete coracoid (58-MES-PV-07). Thecervical elements show opisthocoelic articulation, dorsoventrally low and transversely wide articularsurfaces, and camellate internal bone texture, as in derived Titanosauriformes. The anterior caudalcentrum has compact internal bone structure and amphicoelic articulation, with the posterior articularsurface more concave than the anterior one; moreover, the neural pedicels are tall and the incompletetransverse process, apparently dorsally directed, bears wide pneumatic fossae. The specimen 58-MES-PV-02 shares these conditions with most rebbachisaurids. The radius is triangular in proximalview, with the anterior margin slightly convex and the medial projection elongated and tapered, as inseveral Titanosauriformes. The distal pubis fragment is crescent in ventral view and anteriorlyprominent in lateral view, as in Ligabuesaurus. The coracoid is quadrangular, with the posterior marginslightly convex and the anterior one straight, as in Tapuiasaurus and Ligabuesaurus. The preliminarymorphological analysis of new findings from El Sauce locality suggests a diversified neosauropod fauna, composed of different specimens of both Diplodocoidea and Macronarialineages, such as Rebbachisauridae and Somphospondylii. This composition resembles the sauropodfauna recorded in the nearby Cerro de Los Leones locality, where the underlying Lohan CuraFormation (Albian) yielded the non-titanosaur somphospondylan Ligabuesaurus, the rebbachisauridAgustinia, and the indeterminate neosauropod MCF-PVPH-882. This new record suggests thepersistence of specific paleoecological conditions in the southern Neuquén Basin during the Early–Late Cretaceous transition, which allowed sustaining diversified sauropod faunae, probablysupported by a niche partitioning via feeding high stratification.