A new chelid turtle, Prochelidella palomoi sp. nov., from campanian Anacleto Formation, Neuquén Basin, North-Western Patagonia, Argentina.

The new turtle remains were found in the Anacleto Formation (Campanian) exposed in the Aguada Grande site. This area is located 10 km from the south of the city of Rincón de Los Sauces, in the north of the province of Neuquén, Patagonia, Argentina. The specimen (MAU-Pv-AG-452) consists of a partially preserved skull, carapace remains, an almost complete plastron, and a left ilium. The skull shows some features (a developed retropterygoid foramen, and a big muscle attachment area over the basisphenoid) that allow us to refer this specimen to the genus Prochelidella. The visceral view of the first costal bone exhibits deeper axillary buttresses that extend 2/3 of the costal width. This condition is also observed in the costal bone of Prochelidella buitreraensis from the Candeleros Formation (Cenomanian). The scute pattern observed in the anterior lobe of the plastron shows a large gular that extends along the entoplastra length, and small extragulars over the epiplastra. In contrast with the scute scheme observed in Prochelidella cerrobarcinae and Prochelidella portezuelae where the gular does not extend beyond the first 1/3 of the entoplastron. The phylogenetic analyses performed recovered this new species as a member of Prochelidella. The material recovered from the Anacleto Formation represents the first undoubtedly finding of Prochelidella in the late Cretaceous (Campanian) and the second skull recognized for the genus.

A new large-sized species of Chelonoidis (Testudinidae) without gibbosities from the middle Miocene of Aguada Escondida (NW Chubut, Patagonia, Argentina).

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.

Tortoises and turtles from Huayquerías del Este (late Miocene-early Pliocene), Mendoza, Argentina.

We report new occurrences of Testudinidae and Chelidae from 11 different fossil sites in the Huayquerías and Tunuyán formations (late Miocene-Pliocene) in the Huayquerías del Este, Mendoza, Argentina. A total of 36 specimens were collected, representing at least three taxa from two different clades: 80.6% Testudinidae and 19.4% Chelidae. Testudinids are present throughout the stratigraphic succession, in alluvial, fluvial, and interdune sedimentary environments, represented by dorsal and plastron carapace plates, with some remains of the appendicular skeleton. A complete articulated plastron with some peripheral plates of the carapace was also recognized and is assigned to the extant species Chelonoidis chilensis, representing the oldest record for this taxon (late Miocene, Messinian). Another possible morphotype was recognized in the form of a large scapular girdle and femur that likely corresponded to an individual with a dorsal carapace of about 80 cm. This assemblage of small and large tortoise species is recognized for first time in the Messinian Age/Stage of Mendoza. Chelids are mostly restricted to fluvial deposits in the upper part of the Huayquerías Formation, except for two specimens which appear in the lower part. One specimen is represented by a right half plastron of an indeterminate Chelidae species which could correspond to a carapace of up to 24 cm in length with plastral lobes narrower than those observed in Phrynops species. Another specimen is characterized by a large costovertebral tunnel in the carapace, peripheral plates of the posterior margin of the carapace with ornamentation of fine grooves forming irregular polygons.

Shell bone histology of the long-necked chelid Yaminuechelys (Testudines: Pleurodira) from the late Cretaceous-early Palaeocene of Patagonia with comments on the histogenesis of bone ornamentation.

Yaminuechelys is a long-necked chelid turtle whose remains have been recovered from outcrops of the Santonian-Maastrichtian and Danian of South America. With the purpose of providing data about shell sculpturing origin and palaeoecology, the bone histology of several shell elements (including neural, costal, peripheral and plastral plates) of Yaminuechelys is described herein. Histological analysis reveals that Yaminuechelys shares with Chelidae the presence of interwoven structural fibre bundles in the external cortex, and parallel-fibred bone of the internal cortex. The presence of resorption lines in several samples indicates that the particular ornamentation of the external surfaces originated, at least in part, by focalized resorption and new bone deposition. This mechanism for ornamentation origin and maintenance is here described for the first time in a turtle. Compactness of the shell bones is consistent with an aquatic habitat, which supports previous hypothesis based on palaeoenvironmental and morphological data.