THE SOUTHERNMOST OCCURRENCE OF THE AQUATIC SLOTH THALASSOCNUS (MAMMALIA, TARDIGRADA) FROM TWO NEW PLIOCENE LOCALITIES IN CHILE --- Preprint doi: 10.5710/AMGH.29.12.2016.3004

Saleta De Los Arcos, Diego Partarrieu, Jorge Carrillo-Briceño, Eli Amson

Abstract


Thalassocnus is a sloth (Mammalia, Tardigrada) adapted to an aquatic lifestyle. It was first described in the Neogene deposits of the Pisco Formation of Peru, from where most of the specimens come. The genus is represented by five species that extend from the upper Miocene to the upper Pliocene, occupying successive stratigraphic levels. Morpho-functional studies of the cranial and postcranial skeleton of Thalassocnus have demonstrated the progressive adaptation of these sloths to a marine environment, establishing gradual differences from the geologically oldest to the youngest species of the genus. The first records of Thalassocnus outside the Pisco Formation have been referred to the Neogene Bahía Inglesa Formation, in northern Chile, where older species were recovered. In this paper we describe materials from two new localities of the Pliocene of Chile: the Coquimbo and Horcón formations, in northern and central Chile respectively. The Coquimbo Formation material was collected in the Lomas del Sauce locality, and consists in a partial skeleton of a single individual. Detailed comparisons of the elements with diagnostic features allowed referral this specimen to T. carolomartini. The material from the Horcón Formation was collected at the Playa La Luna locality, and it consists in an isolated phalanx, which is attributed to one of the species of Thalassocnus younger than T. natans. Thus, we present the first record of younger species of Thalassocnus in Chile, and the southernmost occurrence of the genus.

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