EARLIEST RECORDS OF THE GENUS SPITICERAS UHLIG IN THE NEUQUÉN BASIN, ARGENTINA: SYSTEMATIC AND BIOSTRATIGRAPHIC IMPLICATIONS

VENNARI, V.V.; AGUIRRE-URRETA, B.

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 2017 vol. 54 p. 83 - 106

0002-7014

The earliest records of the genus Spiticeras Uhlig in Western Gondwana occur in the Upper Jurassic?Lower Cretaceous deposits ofthe Vaca Muerta Formation in the Neuquén Basin, Argentina. Those records involve two species, Spiticeras acutum Gerth and Spiticeras hauthaliGerth, which were firstly described from Arroyo Durazno, Mendoza. A systematic revision and reconsideration of the biostratigraphic distributionof both species was performed based on the study of type material and new bed-by-bed collections in the type locality andother southern Mendoza sections. S. acutum and S. hauthali display a succession of ornamentation stages that, together with other morphological characters,sustain their assignation to the genus Spiticeras. Addidionally, macroconchiate and microconchiate specimens were identified in both taxa. Therecord of S. acutum from the lowermost beds assigned to the Late Tithonian?Early Berrisian Substeueroceras koeneni Assemblage Biozonesubstantiates the downwards extension of the known range of the species in the Neuquén Basin. Given that the basal portion of the S. koeneniBiozone can be correlated with the Late Tithonian Standard ?Durangites? Zone and that these early spiticeratins records have been found to beassociated with a Late Tithonian secondary nannofossil bioevent (Raghodiscus asper (Stradner) first occurrence) in two of the studied sections,a Late Tithonian age is suggested for the earliest records of Spiticeras in Gondwana.