Previously, only one small-sized species of Testudinidae (Chelonoidis gringorum) was named from Lower-Middle Miocene of Central Patagonia. In this short article, we describe a new large Testudinidae, here named Chelonoidis meridiana sp. nov. This large new species (carapace up to 80 cm) differs from other large species of the southern South American fossil record by the absence of gibbosities on neural and costal carapacial bones, a short and wide entoplastron with a humeropectoral sulcus that was placed well behind its posterior end, and pectoral scutes that are medially longer, approximately one-third of the medial length of the hyoplastra. The discovery of this new species in the Middle Miocene increases the raw turtle diversity in Chubut, permitting to reduce the gap between the raw and phylogenetic diversity previously proposed. This occurrence is also important from both a temporal and geographic point of view. It permits fixing the presence of large-sized tortoises in the continent since ~15 million years ago (Middle Miocene). This occurrence predates all other large and giant tortoises from Argentina and South America and it is older than the giant Chelonoidis from the Langhian-Tortonian of Colombia. This is also the southernmost occurrence of a large-sized testudinid in the world.
Keywords: Collón Curá Formation; Neogene; new large tortoise; pyramiding; southern South America.
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