The oldest theropods from the Neuquen Basin: Predator dinosaur diversity in the Bajada Colorada Formation (Berriasian - Valanginian), Neuquén, Argentina.

CANALE, JUAN I.; APESTEGUÍA, SEBASTIÁN; GALLINA, PABLO A.; ALEJANDRO HALUZA; GIANECHINI, FEDERICO A.; LEONARDO JAVIER PAZO

buenos aires

Jornada; XXX Jornadas Argentinas de Paleontología de Vertebrados; 2016

museo argentino de ciencias naturales

In this contribution an updated summary of the theropod materials collected from the Bajada Colorada Formation (Lower Cretaceous, BerriasianeValanginian). Although fragmentary, the recovered material shows a diverse association of meat-eatingdinosaurs for this poorly understood period of time. Three techniques were used to assess the phylogeneticposition of the isolated teeth: multivariate (PCA), discriminant and phylogenetic analyses. Themorphotypes 1, 2 and 3 (small non-recurved isolated crowns) were regarded as Theropoda indet., as ouranalyses failed to support a more precise classification. Two large almost complete ziphodont crowns,considered morphotype 4, were identified as belonging to megalosaurid tetanurans by phylogenetic,discriminant and multivariate analyses, thus likely representing the first record of this ancient family inSouth America, and the youngest worldwide. We refer the axis to a small abelisauroid ceratosaurianbased on the following suite of characters; long and pointed epipophyses, a pneumatic foramen in thecentrum, the invaginated spinopostzygapophyseal lamina, and the anteroposteriorly long, dorsallyconvex, and dorsally/posteriorly unexpanded neural spine. The caudal centra can be referred to atheropod, and tentatively to Abelisauroidea, suggesting that they may belong to the same taxon than thatrepresented by the axis. The tibia lacks the incisura tibialis, presents a low, sharp and proximally positionedfibular crest, and has a deep lateral fossa, which is limited dorsally by a coarse, rounded in sectionand anteriorly directed crest. This combination of features allows to refer it to a large abelisaurid. TheBajada Colorada dinosaur record includes so far a small abelisauroid, a large abelisaurid, a probablymedium to large megalosaurid tetanuran, diplodocid and dicraeosaurid sauropods. It shows some similaritieswith Middle and Upper Jurassic units in central Patagonia, Africa and Portugal, suggesting that nosignificant dinosaur faunal turnover took place through the Jurassic-Cretaceous event in the southernpart of South America.