Morphological variability in the gastropod Perissodonta Martens (=Struthiolarella) from the Early Miocene of Tierra del Fuego

LOPEZ CABRERA MI; OLIVERO, E. B.

Puerto Madryn

Congreso; RCAPA 2018; 2018

APA

High morphological variability in Neogene struthiolarid gastropods from Patagonia and Tierra del Fuego has been recognized since earliest studies byIhering, Steinmann, Wilckens and Ortmann. In particular, when Steinmann and Wilckens erected the genus Struthiolarella, which is nowinterpreted as a junior synonym of Perissodonta, they remark the difficulty of differentiating S. ameghinoi (Ihering) -the typespecies of Struthiolarella? from 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: Struthiolariachilensis 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, includingdifferences in the axial and spiral ornamentation, density and number of fine spiral threads and strong spiral cords in the body whorl, and axialtubercles or nodes on the periphery of the whorl. A preliminary study of more than 100 specimens referred to Perissodonta from the classicallocalities of The Sierra de Carmen Silva and new localities including Punta Basílica, Cabo Viamonte, and Río Irigoyen indicates that all thesespecimens have slightly globose to fusiform medium-size shell, with thick inductura. However, axial and spiral ornamentation of the shell varymarkedly between specimens, supporting the conclusions of earlier researchers. Accordingly, we interpret that the studied material corresponds toa single highly variable species that can be accommodate in Perissodonta ameghinoi (Ihering), of probably Early Miocene age