A Titanosaur (Sauropoda) from the Gorro Frigio Fm. (Aptian, Lower Cretaceous), Chubut Province, Argentina

SEBASTIÁN APESTEGUÍA; OLGA GIMÉNEZ

Esquel

Jornada; XVII Jornadas Argentinas de Paleontologia de Vertebrados; 2001

Asociacion Paleontologica Argentina

The recognition of Titanosauriformes Salgado, Coria and Calvo, 1997 (Brachiosaurus, Saltasaurus, their most recent common ancestor and all descendants) gave new importance to the under represented South American Aptian taxa (e.g. Chubutisaurus). From the Cerro Barcino Formation, Bayo Overo Member, Chubut Province, an ‘E.Feruglio’ museum team discovered two series of three dorsal vertebrae each, a neural arch with attached rib, and a scapulocoracoid of a big titanosauriform. All dorsal centra are strongly opisthocoelous, as in Salgado et al.’s(1997) Camarasauromorpha, Upchurch’s(1999) Brachiosauria and Sanz’s(1999) node 2. Hyposphene-hypanthrum articulations are evident (although broken). Acuminate pleurocoels defines Upchurch’s(1999) Titanosauroidea and Salgado et al.’s(1997) Titanosauria, together with centroparapophyseal laminae and ventrally forked infradiapophyseal laminae. Short, unforked and flattened neural spines diagnoses Sereno & Wilson’s(1998) Macronaria. Althought prespinal laminae were not clearly preserved, postspinal laminae suggest their presence, allowing its inclusion in Salgado et al’s(1997) Titanosauriformes and Upchurch’s ‘N’ node. The large scapulo-coracoid has an ‘step-shaped’ and  posterodorsally directed articulation. The narrow blade  resembles BYU 9462 asigned by Curtice(1996) to Brachiosaurus sp. The posteroventral border is curved and the antero-dorsal is half straight. The transverse section is flat, unlike the externally convexe T-shape of Chubutisaurus. The coracoid is titanosaurian-shaped. Upchurch’s(1999) Titanosauridae or ‘P’ node is not defined by dorsal vertebrae features, but Salgado et al.’s(1997) Titanosauridae is diagnosed by the absence of hyposphene-hypanthrum, present in the new taxa. Although preliminary, the present evidence shows a non-Titanosauridae titanosaurian condition, closer to Andesaurus than to Chubutisaurus, thus probably confirming  the first argentinian Aptian titanosaurian.