A juvenile specimen of Neusticemys neuquina (Testudinata: Thalassochelydia) from the Upper Jurassic of Neuquén Basin (Neuquén Province, Argentina)

Abstract

Cranial and postcranial remains of a juvenile specimen from the lower section of the Vaca Muerta Formation (Lower Tithonian) recovered at Cerro Lotena (Neuquén Province, Argentina) are identified as Neusticemys neuquina. We contextualised this juvenile specimen inside the taxonomic and phylogenetic background of N. neuquina. The new information provided by the juvenile specimen indicates that relevant key features such as: a strong constriction of the horizontal pterygoid plate at the level of the basis of the quadrate process of the pterygoid, a round depression basisphenoidal, a well-developed parasagittal crest developed on the dorsal surface of the squamosal, a medial keel on the posterior part of the carapace, hyo and hypoplastra contacting each other by a tight suture, do not change along ontogeny and as so they are reliable characters for taxonomy and phylogenetic analysis. We also comment on some ontogenetic changes between juvenile and adult specimens (e.g., increase of fossa infratemporalis and parietal horizontal plate in the skull, reduction in the height at the surangular region in the lower jaw, and the reduction of costo-peripheral fenestrae on the carapace) of N. neuquina. In addition, we compare this species with other early stage juvenile eurysternids from the European Upper Jurassic.