Abstract Shell beds, or coquinas, have a complex origin, limiting their utility in paleoecology. However, such accumulations can serve as crucial paleoenvironmental indicators, since their bioestratinomic and diagenetic properties explain the physical-chemical and biological processes of their formation, as well as the ancient environments linked to their development. In 2016, the PALEOANTAR Project sampled coquinas from the James Ross Island (Antarctic Peninsula) in Passo São José (PSJ – San José Way) and Muro do Castelo (MDC – Castle Wall), two new localities with outcrops of the lower Lachman Crags Member, Santa Marta Formation, Marambio Group, Cretaceous of Larsen Basin. The paleontological content and sedimentary structures indicate a shallow marine depositional system. The PSJ coquina are composed by gastropods bioclasts, with predominantly dense/loose packing. The MDC presents a larger variety of bioclasts with bivalve dominance on a loose packing and conglomeratic horizons, that varies from granule to pebble. Sedimentary and biostratinomic features observed in samples from both localities indicate their genesis from high-energy events, characterized as a proximal tempestite. These descriptions allow a more accurate reconstruction of the depositional environments, highlighting the importance of these rocks in the geological record during the Cretaceous of Antarctica. beds origin paleoecology However indicators physicalchemical physical chemical formation development 2016 Antarctic Peninsula Way Wall, Wall , Wall) Member Formation Group Basin system denseloose dense horizons pebble highenergy high energy events tempestite Antarctica 201 20 2

Abstract This study investigates ichnoassemblages characterized by spreite trace fossils from the Upper Cretaceous Snow Hill Island Formation on Vega Island, Antarctica. The succession reveals alternating heterolithic beds of sandy siltstones to very fine- to fine-grained sandstones, suggestive of a deltaic depositional setting influenced by fluctuating energy conditions. The dominance of spreite structures, such as Paradictyodora antarctica and Euflabella, suggests the prevalence of a colonization window for deposit- or detritus-feeding activity. Notably, the prevalence of Euflabella towards the upper levels of the succession, in more proximal and impacted depositional setting, suggests an adaptive strategy for coping with varying food resources, corroborating its role as a trophic generalist. Additionally, the absence of distinct shifts between fully marine and stressed ichnofauna challenges a clear assignation to the Phycosiphon or Rosselia ichnofacies, although in vertical succession the Euflabella dominance in upper levels is related to a lower diverse ichnoassemblage than Paradictyodora in lower levels, suggesting some freshwater impact in the top. The occurrence of horizontal and vertical sessile deposit feeding structures would align with the Rosselia ichnofacies definition, but the presence of spreite burrows and high ichnodisparity better fits into the Cruziana ichnofacies. These spreite-dominated ichonoassemblages are here attributed to Cruziana ichnofacies. Antarctica fine finegrained grained sandstones conditions detritusfeeding detritus activity Notably resources generalist Additionally top definition spreitedominated dominated

Abstract A worldwide revision of the Cretaceous record of Neornithes (crown birds) revealed that unambiguous neornithine taxa are extremely scarce, with only a few showing diagnostic features to be confidently assigned to that group. Here we report two new neornithine specimens from Vega Island (López de Bertodano Formation). The first is a synsacrum (MN 7832-V) that shows a complex pattern of transversal diverticula intercepting the canalis synsacri, as in extant neornithines. Micro-CT scanning revealed a camerate pattern of trabeculae typical of neornithines. It further shows the oldest occurrence of lumbosacral canals in Neornithes, which are related to a balance sensing system acting in the control of walking and perching. The second specimen (MN 7833-V) is a distal portion of a tarsometatarsus sharing with Vegavis iaai a straight apical border of the crista plantaris lateralis. Osteohistologically the tarsometatarsus shows a thick and highly vascularized cortex that lacks any growth marks, resembling Polarornis gregorii. The cortex is osteosclerotic as in other extinct and extant diving neornithines. These new specimens increase the occurrences of the Cretaceous avian material recovered from the Upper Cretaceous strata of the James Ross Sub-Basin, suggesting that a Vegaviidae-dominated avian assemblage was present in the Antarctic Peninsula during the upper Maastrichtian. crown birds scarce group López Formation. Formation . Formation) MN 7832V V 7832 7832-V synsacri neornithines MicroCT Micro CT perching 7833V 7833 7833-V lateralis marks gregorii SubBasin, SubBasin Sub Basin, Basin Sub-Basin Vegaviidaedominated Vegaviidae dominated Maastrichtian 783 78 7

Abstract Despite the enormous paleobotanical record on different islands of the Antarctic Peninsula, the evidence of insect activity associated with fossilized plants is scarce. Here we report the first evidence of insect-plant interaction from Cretaceous deposits, more precisely from a new locality at the Rip Point area, Nelson Island (Antarctic Peninsula). The macrofossil assemblage includes isolated Nothofagus sp. leaf impressions, a common component of the Antarctic paleoflora. Two hundred leaves were examined, of which 15 showed evidence of insect activity, displaying variations in size, shape, and preservation. Two types of interaction damage, galls and mines, were identified. A single specimen retained a circular scar recognized as galling scar, while meandering tracks were considered mines. These traces of herbivore insect activity, correspond to the oldest known record of this type of interaction of West Antarctica and the oldest record of insect-plant interaction in Nothofagus sp. reported so far. Peninsula scarce insectplant plant deposits area Peninsula. . Peninsula) sp impressions paleoflora examined 1 size shape preservation damage mines identified far

Abstract Notosuchian crocodyliforms were major components of the South American Cretaceous biota and, for over 125 years, paleontological fieldwork in this continent recovered several well-preserved fossils of these animals. They are largely recognized for terrestrial life and specialized feeding habits, frequently presenting bizarre taxa such as Comahuesuchus. A new species, Comahuesuchus bonapartei n. sp. (MUCPv 597; cast MN), is described from geological strata of Sierra Barrosa Formation (Upper Turonian) and Portezuelo Formation (Lower Coniacian) of Lake Barreales, Patagonia, Argentina. The new fossil comprises a right dentary bone that shares important and unique anatomical features with specimens of Comahuesuchus brachybuccalis, such as the presence of a well-marked shelf on the lateral surface of the bone; a flat, low, and wide mandibular symphysis; an enlarged, labiolingually compressed caniniform tooth at caudal position in the dentary; the presence of serrated mesial and distal carinae in the caniniform with a faceted labial surface, and the absence or extremely reduction in number of the postcaniniform dentition. C. bonapartei differs from C. brachybuccalis in having individual dentary alveoli, rather a dentition set in groove. Phylogenetic analyses support a sister-relationship between both species, which are well nested within notosuchians. 12 years wellpreserved preserved animals habits species n sp MUCPv 597 MN, MN , MN) Upper Turonian Lower Coniacian Barreales Patagonia Argentina wellmarked marked flat low symphysis enlarged C alveoli groove sisterrelationship sister relationship notosuchians 1 59 5