The lower Miocene Scaphopoda of Chile

Scaphopods (Class Scaphopoda, Phylum Mollusca), commonly known as tusk shells, are univalve mollusks exclusively from marine environments that live buried within the substrate. Within this class there are two orders: Dentaliida (elongated shells with sculpture and ornamentation) and Gadilida (smaller, smooth shells). For the Miocene marine deposits (Burdigalian) of the Navidad Formation, Ranquil Formation, Lacui Formation and Ipún beds, the diagnostic characters of a total of 2,103 scaphopod specimens were studied in order to identify and define species, and to establish biogeographical patterns within the latitudinal transect from 33°S to 45°S, through the evaluation of the alpha, beta, gamma biodiversity and rarefaction indices. Eleven species of Scaphopoda were identified for the Lower Miocene of Chile. Of these species, seven belong to the order Dentaliida ( Dentalium sulcosum , Fissidentalium majus , Fissidentalium matanzasense comb. nov ., Fissidentalium subgiganteum , Fissidentalium taverai sp. nov ., Fissidentalium sp. 1, and Fissidentalium sp. 2) and four to the order Gadilida ( Gadila philippiana comb. nov ., Cadulus scarabinorum sp. nov ., Polyschides pichi sp. nov ., and Dischides nor sp. nov .), being the first Miocene gadilid species recognized from Chile. With the existing paleobathymetric information based on otolith associations, it was possible to determine the environment of the most abundant species of Scaphopoda from the Lower Miocene of Chile. The most abundant species are Gadila philippiana comb. nov. and Cadulus scarabinorum sp. nov., followed by Fissidentalium subgiganteum ; all three species are distributed in environments of 400–600 m water depth. The second most abundant Dentaliida species is Dentalium sulcosum , which is found in deeper environments (> 600 m). There are also species distributed in shallower environments (200–400 m), such as Fissidentalium matanzasense . Finally, there is no significant latitudinal species turnover, so the existence of only one paleobiogeographic province during this time range is suggested by the scaphopod fauna.