Bajada Colorada (Valanginian) dinosaurs from Neuquén: note on the oldest Cretaceous dinosaurs from the Neuquén basin

SEBASTIÁN APESTEGUÍA; JOSÉ F. BONAPARTE

La Plata

Jornada; XX Jornadas Argentinas de Paleontologia de Vertebrados; 2004

Museo de La Plata

Here we report the first dinosaur remains from the Bajada Colorada Formation (Valanginian), which outcrops close to El Marucho Hill, Neuquén. The material comprises an incomplete sauropod dorsal vertebra and a fragmentary theropod femur. The sauropod vertebra has a high neural spine, about six times the centrum height. The tetralaminar pattern, with a wide spinodiapophyseal lamina, plus a complicated and diverging postspinal lamina gives to the vertebra an axial organization which resembles those of basal diplodocoids (e.g. Rebbachisaurus). The theropod femur differs from those of abelisaurs in the well developed fourth trochanter and the deep anterior supracondylar groove. It differs from those of Ceratosauria and Allosauroidea in lacking a large mediodistal crest and from the latter in the large fourth trochanter, gracile tibial condyle and shallower anterior intercondylar groove, the latter being typical of basal tetanurans. It differs from those of Coelurosauria in the slight development of mediodistal crest, laterally compressed tibial condyle and shallow anterior intercondylar groove. It shares with Streptospondylus cuvieri,  a Jurassic basal tetanuran from Europe, a medially projected tibial condyle, and wide posterior and shallow anterior intercondylar grooves. This evidence suggests its position as a basal tetanuran (“megalosaur”). The possible basal diplodocoid and basal tetanuran are in accord with the Valanginian age proposed for the bearing unit. This evidence from Neuquén extends the dinosaur record for most of the Cretaceous of Patagonia.