Late Campanian-Early Maastrichtian Vertebrates From The James Ross Basin, West Antarctica: Updated Synthesis, Biostratigraphy, And Paleobiogeography.

The Snow Hill Island Formation (SHIF; late Campanian - early Maastrichtian) crops out in the northeast of the Antarctic Peninsula and constitutes the basal part of the late Campanian-early Maastrichtian sedimentary succession of the James Ross Basin (NG Sequence). Its major exposures occur at the James Ross and Vega islands. Several fossil-bearing localities have been identified in the SHIF providing a valuable fauna of invertebrates and vertebrates, and flora. Our study focuses on the vertebrate fauna recovered at Gamma and Cape Lamb members of the SHIF. The marine vertebrate assemblages include chondrichthyans, actinopterygians, and marine reptiles (elasmosaurid plesiosaurs and mosasaurs). A diverse terrestrial vertebrate assemblage has been reported being characterized by dinosaurs (sauropod, elasmarian ornithopods, nodosaurid ankylosaur, and a paravian theropod), pterosaurs and birds. Most SHIF dinosaurs share close affinities with penecontemporaneous taxa from southern South America, indicating that at least some continental vertebrates could disperse between southern South America and Antarctica during the Late Cretaceous. The Snow Hill Island Formation provides the most diverse Late Cretaceous marine and continental faunas from Antarctica. The present study summarizes previous and new vertebrate findings with the best actualized stratigraphical framework, providing a more complete fauna association and analyzing further perspectives.

New pycnodontiform fishes (Actinopterygii, Neopterygii) from the Early Cretaceous of the Argentinian Patagonia.

Here we describe new pycnodontiform fish material recovered from the marine Agrio Formation (lower Valanginian-lower Hauterivian) of the Neuquén Province in the south-western of Patagonia, Argentina. The new material include an incomplete skull and an incomplete prearticular dentition. The incomplete skull consists of some dermal and endochondral elements as well as dental remains and represents a new large-sized gyrodontid that is referred to a new species, Gyrodus huiliches. Gyrodus huiliches sp. nov. is characterized by a unique combination of tooth crown ornamentations and tooth shape separating it easily from all known Gyrodus species. The incomplete prearticular dentition shows a tooth arrangement and sculpture that resembles that of "Macromesodon" agrioensis -the previously only known pycnodontiform in the area. This allows revising this species, which was based on an isolated vomerine dentition and which we refer to a new genus, Tranawuen. The new Patagonian fishes reported here expand the knowledge of South American pycnodontiforms. We hypothesize that meanwhile the new Patagonian genus - Tranawuen- diverged from Gyrodus after it migrated into the eastern Pacific through the Hispanic Corridor during the Late Jurassic, the new species -Gyrodus huiliches- most likely diverged from a Central or South American species of Gyrodus. Both represent the youngest gyrodontid records and simultaneously the southernmost Early Cretaceous occurrences of pycnodontiform fishes.