THE MULTI-LINEAGE SAUROPOD RECORD FROM THE PORTEZUELO FORMATION (TURONIANCONIACIAN) OF SOUTHERN NEUQUÉN BASIN (PATAGONIA, ARGENTINA) AS EVIDENCE OF NICHEPARTITIONING BETWEEN DERIVED TITANOSAURIFO

BELLARDINI, F.; WINDHOLZ G.J.; FILIPPI, L.; GARRIDO, A.C.; BAIANO, M.A.

Congreso; RCAPA 2022; 2022

During the Turonian-Coniacian transition, the continental ecosystems of south-western Gondwanasuffered notably changes in their faunal compositions, which affected different tetrapod lineages,especially dinosaurs. Considering the sauropod faunae, with the post-Turonian faunistic turnover, the narrow-toothed titanosaurians arose as the only mega-herbivorous of all landmasses, holding the ecological niches of Rebbachisauridae and broad-toothed Titanosauriformes. In the Neuquén Basin, the Turonian-Coniacian transition is represented by the Portezuelo Formation, a thick fluvial succession of middle-grained sandstones with intercalations of poorly-cemented siltstones and silt-sandy thin deposits. This unit yielded an abundant and diversified vertebrate fossil fauna, including different sauropod dinosaur specimens. In particular, two sauropod taxa are known: the somphospondylian Malargueasaurus florenciae from the central of Neuquén Basin, and Futalognkosaurus dukei from the southern basin. However, isolated sauropod specimens from Sierra del Portezuelo, Los Bastos, and El Anfiteatro localities of Neuquén and Rio Negro provinces suggest a more diversified sauropod fauna during the Turonian-Coniacian transition. In this contribution we present a new sauropod record (MMSPV-34) from the Los Bastos locality (Neuquén Province, Patagonia, Argentina), where the upper section of Portezuelo Fm. outcrops. MMS-PV-34 is composed by cranial and post-cranial elements, including the basicraneum, the right quadrate, part of the right squamosal and right nasal, the left dentary with several unworned teeth, nine middle and one posterior caudal vertebrae, an ungueal phalanx, and several indeterminate fragments. The teeth are D-shaped and mesiodistally broad, without lingual grooves or crests, whereas the dentary is tall and anteriorly curved, suggesting a U-shaped mandible with medially convergent dentaries in dorsal view. The caudal vertebrae show strongly procoelic articulations, with trapezoidal and low neural spines in lateral view. The preliminary osteological analysisallows us differ MMS-PV-34 from the two sauropod taxa known for Portezuelo Fm., suggesting close morphological similarities with basal titanosaurians, such as Epachthosaurus and Sarmientosaurus. The record of a basal member of Titanosauria from Portezuelo Fm. together with the somphospondylan Malarguesaurus and the longkosaurian Futalognkosaurus, could represent evidence of a high-diversified sauropod fauna with different lineages of derived Titanosauriformes. Although not direct evidence of co-existence is recorded, MMS-PV-34 has paleoecological and paleoetological implications, supporting the hypothesis of a more complex dietary niche partitioning between different sauropod populations in Neuquén Basin than previously known, at least during the Turonian-Coniacian transition.