TETRAPODS FROM THE SNOW HILL ISLAND FORMATION (LATE CAMPANIAN-EARLY MAASTRICHTIAN), JAMES ROSS ISLAND, ANTARCTICA: TAPHONOMIC AND DEPOSITIONAL SETTINGS

ZULMA GASPARINI; MARCELO REGUERO; MARTA FERNÁNDEZ; RODOLFO A. CORIA; EDUARDO OLIVERO; JOSÉ O´GORMAN; ARI IGLESIAS; JUAN J. MOLY

Mendoza

Congreso; 4th International Palaeontological Congress; 2014

IPA- CONICET Mendoza

The Snow Hill Island Formation (SHIF) constitutes the basal unit of the transgressive part of the NG Sequence (upper Campanian-lower Maastrichtian), which exposes extensively in the James Ross and Vega islands, James Ross Basin, northeast of the Antarctic Peninsula. The shallow marine sediments of the SHIF comprise two members: the upper Campanian Gamma Member and the lower Maastrichtian Cape Lamb Member. The SHIF yields mosasaurs, elasmosaurids, and dinosaurs, and contains the most diverse Mesozoic tetrapod assemblage recorded from Antarctica. At Santa Marta Cove (SM), James Ross Island the Gamma Member contains the holotype of the tylosaurine Taniwhasaurus antarcticus and a number of indeterminate elasmosaurid plesiosaurids. Additionally, three non-avian dinosaurs, represented by Antarctopelta oliveroi, Trinisaura santamartaensis, and an isolated sauropod vertebra, have been collected in this member. At The Naze (TN, James Ross Island) and Cape Lamb (CL, Vega Island) localities, from outcrops of the Cape Lamb Member, new non-aristonectine elasmosaurid and mosasaurids were recovered, identified as cf. T. antarticus, cf. Hainosaurus sp., and Tylosaurinae indet. (CL). Additionally, partial skeletons assigned to a hypsilophodontid (CL), a dromeosaurid (TN) and an ornithopod (TN) non-avian dinosaurs and few avian dinosaurs (CL, charadriiforms) were recovered from this member. Close scrutiny of the fossil assemblages and stratigraphic horizons indicates that at least two different subsets of articulated skeletons are present throughout the Gamma Member and have different taphonomic histories (including bone abrasion, scavenging, completeness, and sorting). Thus, allochthonous skeletons transported from continental fluvial systems are differentiated from autochthonous skeletons that were buried by the same bearer stratigraphic horizon. Taphonomic and depositional settings were analyzed in: 1) articulated skeletons of marine reptiles from SM, TN and CL (Taniwhasaurus; a new genus and species of elasmosaurid and several other elasmosaurid skeletons) with evidence of having been scavenged by hexanchid sharks and nautilods; and 2) dinosaurs recovered articulated from the same horizon of SM (Trinisaura santamartaensis and Antarctopelta oliveroi), associated to abundant plant debris share distinctive taphonomical history characterized by preservation of articulation and with no evidence of scavenging by hexanchid sharks on carcasses. Other isolated bones of dinosaurs (i.e. a sauropod vertebra), were found floating (not in situ) and from different stratigraphic horizons. Complete stratigraphic and taphonomic analyses of vertebrates are now available for the upper Campanian-lower Maastrichtian Snow Hill Island Formation, being possible better correlations through the Upper Cretaceous of West Antarctica with other Gondwanan area