Abstract

An ichthyosaur discovered in the Ultima Esperanza Province, southern Chile, is the southernmost specimen of this group yet discovered in South America. The incomplete fossil consists of 17 vertebrae and associated neural arches and ribs. Occurring within a large block in glacio-fluvial sediments adjacent to the Campo de Hielo Patagónico Sur, the remains cannot be given a species designation nor be dated with precision or tied to one specific formation at this time. However, the rock type, geologic occurrence of the block, and glaciology of the sector enable the material to be placed within the upper part of the Middle to Upper Jurassic Tobifera Formation or the Lower Cretaceous Zapata Formation. Although the fairly broad stratigraphic range and limited fossil material hamper careful stage-level paleobiogeographic analysis, this occurrence documents the existence of ichthyosaurs in the now closed Rocas Verdes back-arc basin. This occurrence extends the distribution of ichthyosaurs in South America some 1500 km south of previously reported fossil material. The fossil provides support for the existence of a possible migration seaway between southern South America and western Africa during the Late Jurassic associated with the breakup of the southern sector of Gondwana. This seaway would be the southern counterpart to the Hispanic Corridor that connected the Pacific to the west Tethys around the northern end of South America.

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