New fossil remains from the Lago Colhué Huapi Formation (Coniacian-Maastricthian): Increasing the record of vertebrate diversity and the paleoecological knowledge for the Late Cretaceous of Patagonia

BECERRA, MARCOS G; CASAL, GABRIEL A.; STERLI, JULIANA; IBIRICU, LUCIO M.; ONORATO, A.M

Puerto Madryn

Jornada; Reunión de Comunicaciones de la Asociación Paleontológica Argentina 2018; 2018

In this communication we present a fossil association found in a new locality of the Lago Colhué Huapi Formation of Chubut,Central Patagonia. This site is located 16.65 km south-eastern of the origin of the Chico River and 3.65 km south of the stratotype locality of the Formation. The fossils were recovered about 1.5 m below the erosive contact with the base of the Salamanca Formation. This association mainly includes postcranial remains of Hadrosauridae and Testudinata found in successive layers of green-greyish to reddish mudstones with carbonized logs, interpreted as distal floodplains. The hadrosaurid remains comprise vertebrae representing all regions, fragments from the pectoral and pelvic girdles and fragmentary fore and hind limb bones. Several limb bone fragments, although lacking of overlapping morphology, show a marked difference in size, supporting the coexistence of different ontogenetic stages of a Hadrosauridae representative. The turtle remains are fragmentary but can be identified belonging to two different groups, supporting the coexistence of different sized Testudinata in this association. A large, undecorated peripheral plate is identified as Testudinata indet. In addition, a small, decorated peripheral plate is identified as Chelidae indet., however its size and ornamentation resembles Hydromedusa sp. and Yaminuechelys sp. This fossil association increases the knowledge of the vertebrate diversity and paleoecology of the formation, resulting in the first record of different ontogenetic stages of Hadrosauridae, and the first evidence of different fresh-water turtles with contrasting sizes interacting at the same environment.