THE MULTI-LINEAGE SAUROPOD RECORD FROM THE PORTEZUELO FORMATION (TURONIAN-CONIACIAN) OF SOUTHERN NEUQUÉN BASIN (PATAGONIA, ARGENTINA) AS EVIDENCE OF NICHE-PARTITIONING BETWEEN DERIVED TITANOSAURIFORMES

BELLARDINI, F.; WINDHOLZ, G.J.; FILIPPI, L.S.; GARRIDO ALBERTO CARLOS; BAIANO, M.A.

Salta

Jornada; Reunion de Comunicaciones de la Asociacion Paleontologica Argentina; 2022

APA IBIGEO IEBI UNSA IBIGEOP

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 theecological niches of Rebbachisauridae and broad-toothed Titanosauriformes. In the Neuquén Basin,the Turonian-Coniacian transition is represented by the Portezuelo Formation, a thick fluvialsuccession of middle-grained sandstones with intercalations of poorly-cemented siltstones and siltsandythin deposits. This unit yielded an abundant and diversified vertebrate fossil fauna, includingdifferent sauropod dinosaur specimens. In particular, two sauropod taxa are known: thesomphospondylian Malargueasaurus florenciae from the central of Neuquén Basin, andFutalognkosaurus dukei from the southern basin. However, isolated sauropod specimens fromSierra del Portezuelo, Los Bastos, and El Anfiteatro localities of Neuquén and Rio Negro provincessuggest a more diversified sauropod fauna during the Turonian-Coniacian transition. In thiscontribution we present a new sauropod record (MMS-PV-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 rightquadrate, 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 indeterminatefragments. 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 mediallyconvergent dentaries in dorsal view. The caudal vertebrae show strongly procoelic articulations,with trapezoidal and low neural spines in lateral view. The preliminary osteological analysis allowsus differ MMS-PV-34 from the two sauropod taxa known for Portezuelo Fm., suggesting closemorphological similarities with basal titanosaurians, such as Epachthosaurus and Sarmientosaurus.The record of a basal member of Titanosauria from Portezuelo Fm. together with thesomphospondylan Malarguesaurus and the longkosaurian Futalognkosaurus, could representevidence of a high-diversified sauropod fauna with different lineages of derivedTitanosauriformes. Although not direct evidence of co-existence are recorded, MMS-PV-34 haspaleoecological and paleoetological implications, supporting the hypothesis of a more complexdietary niche partitioning between different sauropod populations in Neuquén Basin than previouslyknown, at least during the Turonian-Coniacian transition.