MORPHOLOGICAL VARIABILITY IN THE GASTROPOD PERISSODONTA MARTENS (=STRUTHIOLARELLA) FROM THE EARLY MIOCENE OF TIERRA DEL FUEGO

LOPEZ CABRERA, M.I; E.B. OLIVERO

PUERTO MADRYN

Otro; RCAPA 2018; 2018

IPGP-CENPAT CONICET

High morphological variability in Neogene struthiolarid gastropods from Patagonia and Tierra del Fuego has been recognized since earliest studies by Ihering, Steinmann, Wilckens, and Ortmann. In particular, when Steinmann and Wilckens erected the genus Struthiolarella, which is now interpreted as a junior synonym of Perisodonta Martens, they remarks the difficulty of differentiating S. ameghinoi (Ihering) -the type species of Struthiolarella? of other species or varieties recognized in the Cenozoic of Patagonia, Chile, and Tierra del Fuego. Nonetheless, in Tierra del Fuego four species-subspecies of the struthiolarid gastropod Perissodonta have been recognized, including: Struthiolaria chilensis fueguina Ihering, Struthiolarella fueguina (Ihering), Struthiolarella ameghinoi (Ihering), and Struthiolarella densestriata (Ihering). These species/subspecies of Struthiolarella were mainly differentiated on the basis of sculptural features of the shell, including differences in the axial and spiral ornamentation, density and number of fine spiral threads and strong spiral cords in the body whorl, and axial tubercles or nodes on the periphery of the whorl. A preliminary study of more than 100 specimens referred to Perissodonta from the classical localities of The Sierra de Carmen Silva and new localities included Punta Basílica, Cabo Viamonte, and Río Irigoyen indicates that all these specimens have slightly globose to fusiform medium-size shell, with thick inductura. However, axial and spiral ornamentation of the shell vary markedly between specimens, supporting the conclusions of earlier researchers. Accordingly, we interpret that the studied material correspond to a single highly variable species that can be accommodate in Perissodonta ameghinoi (Ihering), of probably Early Miocene age.