Chapter 9 An Antarctic Mammalian Community 9.1 Introduction Until about 30–36 Ma ago, South America and Antarctica were in intimate contact via a wide connection of the Antarctic Peninsula to southern Patagonia (the Weddellian Isthmus), so that fauna was able to move freely back and forth between the two continents (Shen 1995, 1998). In the Late Cretaceous or very early Paleocene, South American marsupials were able to reach Australia, before 64 Ma when the South Tasmanian Rise became submerged and the last land bridge to Australia disappeared and the continent continued to rift away from Antarctica (Woodburne and Case 1996). During Cretaceous and Paleocene times, temperatures in Antarctica were much milder and did not begin to degenerate until mid-Eocene times when the world temperature began to decrease from the high point of Late Paleocene to Early Eocene world temperatures that for a time had produced a tropical world climate (Figs. 9.1, 9.2, 9.3, 9.4, and 9.5). 9.2 Peninsular Connection of South America to Antarctic The tip of South America was connected to Antarctica by an irregularly narrow land bridge (the Weddellian Isthmus), somewhat like the Isthmus of Panama of about 100–200 km in width and 700–900 km in length. This land bridge persisted from Early Cretaceous times to the end of the Eocene or the beginning of the Oligocene, lasting about 35 million years (Shen 1995, 1998) when a deep-sea rupture apparently occurred, allowing the establishment of the circumpolar current. The Weddellian Isthmus allowed a continuous flora and fauna to exist from southern South America to Antarctica and (in some cases) to Australia, although the istmus © Springer Nature Switzerland AG 2019 T. Defler, History of Terrestrial Mammals in South America, Topics in Geobiology 42, https://doi.org/10.1007/978-3-319-98449-0_9 185 186 9 An Antarctic Mammalian Community Fig. 9.1 Relationship of continents in the Early Paleocene 66 Ma showing Chicxulub (Chixulub on this map) zone, which impacted earth roughly 65.5 million years ago and caused the extinction of the nonavian dinosaurs among other groups. (By C. R. Scotese, Paleomap Project) Fig. 9.2 Middle Eocene and the existence of the La Meseta fauna in Antarctica. By this time the Antarctic-Australian land connection had been broken, although a connection continued between southern South America and Antarctica until around 30 Ma. (By C. R. Scotese, Paleomap Project) Fig. 9.3 The underwater topography that connects the southernmost point of South America with the Antarctic Peninsula. This topography was above water earlier than about 30 Ma and formed a barrier to ocean currents. (Image Lansat. Google Earth Image courtesy U.S. Geological Survey) Fig. 9.4 Location of Seymour (Marambio) Island in relation to the Antarctic Peninsula. (Based on Bond et al. 2011 and Google maps, by Diego Casallas, Applied Biodiversity Foundation) 188 9 An Antarctic Mammalian Community Fig. 9.5 Seymour-Marambio Island, Antarctica, and the location of the Argentinian base Antarctica-Marambio, Argentina’s largest Antarctic scientific and military base plus a good airstrip was possibly covered by a shallow sea from about 50 Ma, obstructing the entrance of notoungulates into the Antarctic and facilitating the development of endemism in the Antarctic metatheres (Reguero et al. 2014). 9.2.1 Vegetation of the Antarctic Peninsular Forest In the Early–Late Eocene, now tentatively dated at about 51.6–47.89 Ma, the fauna of the peninsula existed in a temperate climate as a result of the most extreme warming event known in the history of the planet (Shellito et al. 2003; Weijers et al. 2007; Krause et al. 2017)). At that time (Early to mid-Eocene), the peninsular forest was a biome equivalent to the present Valdivian rainforest of Chile, a mixed forest of neotropical angiosperms of at least 36 species growing alongside plants characteristic of cooler temperatures and including podocarp and araucarian conifers alongside southern beech, other gymnosperms, and at least three ferns (Romero 1986; Case 2006; Cantrill 2012; Poole and Cantrill 2006). There were also forests on the main part of the Antarctic continent. Assumedly these forests also sheltered a fauna similar to what we know about the Eocene Antarctic Peninsula and afterward. As the high temperatures began to decrease, the continental vegetation degenerated, becoming scarce, and then extinct. Forests 9.2 Peninsular Connection of South America to Antarctic 189 Fig. 9.6 The land bridge Isthmus of Scotia (based on Shen 1995) or Weddellian Isthmus (Reguero et al. 2014) that connected South America to Antarctica from Early Cretaceous times to the end of the Eocene (Shen 1998). (a) Early Cretaceous; (b) Late Cretaceous; (F) Tierra del Fuego Island; (G) South Georgia Island; (S) South Shetland Islands: (AP) Antarctic Peninsula; (A) Alexander Island. (By Diego Casallas, Applied Biodiversity Foundation) existing after the Middle Eocene, when temperatures had begun to cool, were dominated by ferns Nothofagus, Podocarpus, and Araucaria in a mesophytic mixed forest (Barrett 1999; Case 1988, 2006; Gandolfo et al. 1998; Jamieson and Sugden 2008). These are the forests where we have some fossil knowledge of the fauna that included marsupials, ratite birds, ornithorhynchus (platypus), gondwanatherians, primitive xenarthrans, astrapotheres, litopterns (or condylarthras), and other groups (Fig. 9.6). We know a lot about this southern temperate Antarctic forest (after the Middle Eocene) especially because of the discovery and analysis of fossils on Seymour Island. A rich Eocene fauna and flora has been recovered from fossils of La Meseta Formation (49–51 Ma) and from various subunits of the La Meseta Formation. These corresponded to the Middle Eocene age for the majority of the fossil recoveries, when temperatures had begun to decline in the world from the Early Eocene climatic optimum. This is the only Cenozoic land vertebrate fauna known for the Antarctic. During early mid-Eocene, the world temperatures had reached the highest point in the entire Cenozoic (the Eocene Optimum). Argentina was subtropical (Fig. 9.7). In the Middle–Late Eocene, the climate was beginning to cool, and the forest was dominated by Nothofagus and three species of fern. 190 9 An Antarctic Mammalian Community Fig. 9.7 The course of temperature change during the Cenozoic which allowed a rich fauna and flora to flourish in Antarctica during the Eocene. Temperature changes (green line) are based on a compilation of oxygen isotope measurements (δ18O) on benthic foraminifera published by Zachos et al. (2001). This can be converted into temperature changes (left axis). Temperature changes have been standardized by the observation that the oxygen isotope measurements of Lisiecki and Raymo (2005) are tightly correlated to temperature changes at Vostok as established by Petit et al. (1999). Present day is indicated by 0. (By R. A. Rohde for Global Warming Art) Other flora was Podocarpaceous (Dacrycarpus, Araucariaceae (Araucaria nathrosti), Proteaceae (Knightliophyllum andreae), and the families Dilleniaceae, Myricaceae, Myrtaceae, Lauraceae, and Grossulariaceae). This was a mixed mesophytic forest, a seasonal cool-temperate rainy climate (Case 1988, 2006; Gandolfo et al. 1998) not dissimilar to some Eocene floras sampled in southern Patagonia. Based on this flora, the paleotemperature was probably about 11–13 °C, and the mean of the coldest month was probably between −3 °C and 2 °C (Dingle and Lavelle 1998a, b, 2000; Dingle et al. 1998). It will be very exciting to find evidence of the mammalian fauna corresponding to the height of the Pliocene-Eocene climatic optimum and the Early Eocene climatic optimum which existed before the cool temperate Nothofagus dominated rain forest that was the habitat of the only known ancient mammalian community of La Meseta. 9.3 Seymour Island (La Meseta) Fauna The La Meseta fauna was intimately associated with the southern parts of South America. It included 16 or more taxa of terrestrial mammals. These included ten species of metatherians, including the families Polydolopidae, Microbiotheriidae 9.3 Seymour Island (La Meseta) Fauna 191 (the group that gave rise to Australian marsupials), Derorhynchidae, and Prepidolopidae. It also included one species of gondwanatheria, one primitive xenarthran, and perhaps two species of astrapotheres (Hooker 1992; Goin et al. 1999, 2006; Case 2006) and one litoptern ungulate (Vizcaíno et al. 1997). Of course there were many birds and sea mammals as well; the birds included ratites (relatives of rheas and ostrich) as well as primitive penguins. The quality of the fossils is not good and except for the birds the majority are teeth that have been reworked by shallow seas. All of these animals must have been adapted to a climatic regimen that included several months of darkness and crepuscular conditions because of the high latitude involved (Seymour island is located at 64°14′S, 56°37′W). A reconstruction of the environment and a vertebrate assemblage from the Middle to Late Eocene of Antarctic Peninsula, Seymour Island would include the following animals and plants: (1) Sparnotheriodontidae gen. et sp. nov. (condylarth-litoptern), (2) Anthropornis nordenskjoeldi (penguin), (3) Delphinornis larseni (penguin), (4) Gondwanathere sudamericid, (5) Polydolops (metatherian-marsupiales) (6) Lyreidus antarcticus (crab), (7) Cucullaea (bivalve), (8) Eutrephoceras (nautiloid), (9) Ratitae bird, (10) Trigonostylops sp. (astrapothere), (11) Marambiotherium glacialis (marsupial - Microbiotheriidae), (12) Didelphimorphia - marsupiales (12) Sloth, (13) Polyborinae indet (falconid bird), (14) Araucaria, and (15) Nothofagus (Southern beech) (Reguero et al. 2002; Reguero 2016). 9.3.1 The Metatherians So far there have been five families of metatherians described, all of which were probably frugivorous/insectivorous. These eight species of mammals represent the most diverse group of mammals so far found from La Meseta. They include two species of Polydolopidae (common during the Early and mid-Eocene of Patagonia), Polydolops dailyi and P. seymouriensis), Microbiotheriidae? (1 species, Marambiotherium glacialis), Woodburnodontidae, Woodburnodon casei, Derorhynchidae (3 species, Derorhynchus minutus, Pauladelphys juanjoi), and an undetermined genus and species, an indeterminate family, sp. Xenostylus peninsularis, Prepidolopidae (1 species) Perrodelphys coquinense, and a possible marsupial whose taxonomic status is indeterminate (Goin et al. 1999; Chornogubsky et al. 2009; Reguero et al. 2013; Vizcaíno et al. 1988; Woodburne and Zinsmeister 1982). Finally a new species of marsupial of what is perhaps Glasbiidae has been reported (Reguero et al. 2016) (Fig. 9.8). The endemism of several of these marsupials (prepidolopid and one derorhynchid marsupials) suggest there was some sort of isolating barrier, probably climatic, between La Meseta and Patagonia (Reguero et al. 2002, 2013). Others show close affinity to Patagonian fauna. In fact the polydolopid marsupials may have evolved as part of the Nothofagus flora (Reguero et al. 1998). Medium- to large-sized carnivore marsupials are lacking on the Antarctic Peninsula. These La Meseta marsupials were likely insectivores, frugivorous, and omnivores (Goin et al. 1999). 192 9 An Antarctic Mammalian Community Fig. 9.8 Polydolops sp. Two species of these marsupials are known from La Meseta fauna, and they are the most abundant mammal from the Eocene of the Antarctic. (By William Stout, Frozen in Time) 9.3.2 Gondwanatheria The gondwanatherian belongs in the family Sudamericidae and is closely related to Sudamerica ameghinoi, although it is more derived. Gondwanatherians are known for the Cretaceous and Early Paleocene of Patagonia, Madagascar, and India. This is the last (and most recent) gondwanatherian to be found, and since they had disappeared in Patagonia by this time, it seems to be evident for some sort of isolating barrier during the Eocene, probably some sort of water barrier (Reguero et al. 2002; Goin et al. 2007). 9.3.3 Xenarthra? A supposed xenarthran fossilized caniform tooth was first considered to be a primitive sloth/anteater; they had not yet separated into distinctive lineages. This is the earliest record for a known Pilosa (anteaters and sloths (Tardigrada)) (Carlini et al. 1990; Vizcaíno and Scintilato-Yané 1995). However, MacPhee and Reguero (2010) have recently disagreed that it may or may not be xenarthran and state that this fossil is best considered to be a mammal incertae sedis (Reguero 2016). 9.3 Seymour Island (La Meseta) Fauna 9.3.4 193 Astrapotheria Two astrapotherians were identified in the La Meseta fauna, one in the Trigonostylopidae family, according to Bond et al. (2011) but not belonging to the genus Trigonostylops (Marenssi et al. 1994; Case 2006; Bond et al. 2011). Another astrapothere has been identified as a new genus and species (Antarctodon sobrali) from the Astrapotheriidae, but the description of the new astrapothere and comparisons to all other previously collected materials concluded that Antarctodon is a non-trigonostylopid astrapothere (Bond et al. 2011) (Fig. 9.9). 9.3.5 Youngest and Oldest Record of Ungulate from Eocene The M3 molar from the La Meseta is the oldest evidence of mammals from the Late Eocene (also proposed as Early Oligocene). It has been analyzed as a liptotern ungulate Notiolofos arquinotiensis of the family Sparnotheriodontidae (Vizcaíno et al. 1997; Bond et al. 1990, 2006, 2014; Gelfo et al. 2015).The ungulate’s presence Fig. 9.9 Antarctodon sobrali, La Meseta astrapothere, needed to be adapted to temporal winter conditions, which would have included sunless and crepuscular weeks and some seasonal freezing temperatures. (By Zimices or Julián Bayona). In contrast to this image, because of the climate, it probably had a hairy body 194 9 An Antarctic Mammalian Community was accompanied by the beginning of glaciation in Antarctica and a cool-temperate Nothofagus-dominated forest on the Antarctic Peninsula (Case 1988). The tooth of the sparnotheriodontid ungulate Notiolofos was from the most recent subunit of La Meseta which was probably Late Eocene (37.8 Ma) or even Early Oligocene (34.2 Ma) and was a forest-adapted browser. It probably weighed about 395–400 kg and was the largest (and most common) Antarctic herbivore at the time. Corresponding plant fossils indicate that there was still a Nothofagus-dominated forest as during the Middle Eocene community. The tooth suggests a browsing herbivore (Vizcaíno et al. 1997). A lower right molar was found of apparently the same species of litoptern, Notiolofos arquinotiensis, from Early Eocene deposits of Seymour Island, making it and an accompanying eutherian fossil phalanx (unidentified as to group) the oldest mammalian material found from Antarctica at about 55.3 Ma. If this fossil specimen is truly N. arquinotiensis, it indicates a very broad time range spanning as it does the oldest La Meseta to the youngest material for the species at 37.8 Ma (at least spanning 17.5 Ma, much longer than most mammalian species) and suggests a considerable evolutionary stasis for the species. So it is appropriate to consider that the physical conditions in West Antarctica remained the same during most of the Eocene (Gelfo 2014) despite evidence that this time frame represented a considerable ecological change from warm times around 55 Ma to a cool, Nothofagus forest at 37.4 Ma (Gelfo 2016) (Fig. 9.10). A second species of Notiolofos, N. regueroi, has recently been described, smaller than N. arquinotiensis; it possibly massed at around 25–58 kg. This litoptern was also a browser in the local forests and existed sympatrically with the larger species at least from about 53 to 49 Ma during the Early and mid-Eocene (Gelfo et al. 2017). Fig. 9.10 Notiolofos arquinotiensis, the archaic litoptern from Las Mesetas, the largest and one of the most common mammals in the La Meseta fauna. (Based on Bond et al. 2006, by Marie GiraudLópez, Grupo EEMN Universidad Nacional de Colombia) References 9.4 195 Comparison to Early Eocene Southern Patagonian Fauna Case (2006) compares the Seymour Island La Meseta vertebrate fauna with Early Eocene Patagonian fauna (Casamayoran) and finds that the body size distribution in the two is quite different. On the one hand, the paleofauna of La Meseta is U-shaped with several small and several large species with an absence of medium-sized animals. On the other hand, the size distribution in Patagonia in the Early Eocene is normally distributed and much less diverse than further to the south. The La Meseta fauna existed in a temperate climate that was highly seasonal and mean winter temperatures of between −3° and −2 °C. The fauna reflects high latitude faunas where both small and large mammals have evolutionary tactics of either physiological adaptation or small surface area-to-volume ratios to cope with the cold, neither of which is available to medium-sized mammals. In contrast, the southern parts of Patagonia were subtropical in the Late Paleocene and Early Eocene with temperatures 10°– 15.6 °C, permitting higher diversity and an equitable size distribution. Curiously, although notoungulates were very common in the Eocene mammalian fauna of Patagonia, none have been found in La Meseta, although a litoptern was common. Also, although small- to medium-sized carnivores (Sparassodonta) were common in Patagonia, none have been discovered in La Meseta (Vizcaíno et al. 1998). 9.5 Connection to South America, Disconnection Southern Patagonian flora was a rich mixture of over 100 species identified with 88 species of dicots (flowering plants) and the rest monocots (angiosperms, ferns, conifers, cycads, and ginkgoes) (Wilf et al. 2003). In contrast the flora of La Meseta on Seymour Island was dominated by Nothofagus, podocarps, and araucarian conifers (Reguero et al. 2002), and this forest persisted after the climate had begun to cool. The land bridge between South America and Antarctica lasted until about 30–35 Ma until it became interrupted, allowing a circumpolar current to become established. This circumpolar current locked in the ever colder temperatures, allowing Antarctica to begin developing glaciers around 34 Ma, which persisted throughout most of the Oligocene. By the end of the Eocene or the beginning of the Oligocene, the La Meseta fauna probably no longer existed because of the increasing cold. References Barrett P (1999) Antarctic climate history over the last 100 million years. Terra Ant Rep 3:53–72 Bond M, Pascual R, Reguero MA, Santillana SN, Marenssi SA (1990) Los primeros “ungulados” extinguidos sudamericanos de la Antártida. Ameghiniana 26:240 Bond M, Reguero MA, Vizcaino SF, Marenssi SA (2006) A new “South American ungulate” (Mammalia: Litopterna) from the Eocene of the Antarctic Peninsula. In: Francis JE, Pirrie 196 9 An Antarctic Mammalian Community D, Crame JA (eds) Cretaceous-Tertiary high-latitude palaeoenvironments: James Ross basin, Antarctica. Geol Soc SP, London 258: 177–186 Bond M, Kramarz A, MacPhee RDE, Reguero M (2011) A new astrapothere (Mammalia, Meridiungulata) from La Meseta Formation, Seymour (Marambio) Island, and a reassessment of previous records of Antarctic astrapotheres. Am Mus Novit 3718:1–16 Bond M, Reguero MA, Vizcaíno SF, Marenssi SA (2014) A new “South American ungulate” (Mammalia: Litopterna) from the Eocene of the Antarctic Peninsula. In: Francis JE, Pirrie D, Crame JA (eds) Cretaceous-Tertiary high-latitude palaeoenvironments, James Ross basin, Antarctica. Geol Soc SP, London 258:163–176 Cantrill DJ (2012) The vegetation of Antarctica through geological time. Cambridge University Press, New York Carlini, AA, Pascual R, Reguero MA, Scillato Yané GJ, Tonni EP, Vizcaíno SF (1990) The first paleogene land placental mammal from Antarctica: its paleoclimatic and paleobiogeographic bearings. In: IV international congress of systematic and evolutionary biology, Maryland, Abstracts, p 325 Case JA (1988) Paleogene floras from Seymour island, Antarctica Peninsula. In: Feldmann RM, Woodburne MO (eds) Geology and palaeontology of Seymour island, Antarctic peninusula. Geol Soc Am Mem 198:523–530 Case JA (2006) The late middle Eocene terrestrial vertebrate fauna from Seymour Island: the tails of the Eocene Patagonian size distribution. In: Francis JE, Pirrie D, Crame JA (eds) CretaceousTertiary high-latitude palaeoenvironments: James Ross basin, Antarctica. Geol Soc SP, London 258: 177–186 Chornogubsky L, Goin FJ, Reguero M (2009) A reassessment of Antarctic polydolopid marsupials (Middle Eocene, La Meseta formation). Antarct Sci 21(3):285–297 Dingle R, Lavelle M (1998a) Antarctic Peninsula cryosphere: early Oligocene (c. 30 Ma) initiation and a revised glacial chronology. J Geol Soc Lond 155:433–437 Dingle R, Lavelle M (1998b) Late Cretaceous-Cenozoic climatic variations of the northern Antarctic Peninsula: new geochemical evidence and review. Palaeogeogr Palaeoclimatol Palaeoecol 107:79–101 Dingle RV, Lavelle M (2000) Antarctic peninsula Late Cretaceous-Early Cenozoic palaeoenvironments and Gondwana palaeogeographies. J Afr Earth Sci 31(1):91–105 Dingle R, Marenssi S, Lavelle M (1998) High latitude Eocene climate deterioration: evidence from the northern Antarctic Peninsula. J S Am Earth Sci 11:571–579 Gandolfo MA, Marenssi SA, Santillana SN (1998) Flora y paleoclima de la Formación La Meseta (Eocene medio), isla Marambio (Seymour), Antártida. In: Casado S (ed) Paleógeno de América del sur y de la península Antártica. Asoc Pal Argent Publ 5:155–162 Gelfo JN (2014) Implicatieons of the evolutionary statis of Notiolofos arquinotiensis (Mammalia) Eocene of Seymour Island, Antarctica. Symposium: cretaceous-tertiary palaeobiogeographic connections with Antarctica. 4th international palaeontological congress, Mendoza Gelfo JN (2016) Considerations about the evolutionary stasis of Notiolofos arquinotiensis (Mammalia: Sparnotheriodontidae), Eocene of Seymour Island, Antarctica. Ameghiniana 53(3):316–332 Gelfo JN, Mörs T, Lorente M, López GM, Reguero M (2015) The oldest mammals from the Antarctic, early Eocene of the La Meseta Formation, Seymour Island. Palaeontology 58(1):101–110 Gelfo JN, López GM, Santillana SN (2017) Eocene ungulate mammals from West Antarctica: implications from their fossil record and a new species. Antarct Sci 29(5):445–455 Goin FJ, Case JA, Woodburne MO, Vizcaino SF, Reguero MA (1999) New discoveries of “opossum-like” marsupials from Antarctica (Seymour Island, Middle Eocene). J Mamm Evol 6(4):335–365 Goin FJ, Reguero MA, Pascual R, Von Koenigswald W, Woodburne MO, Case JA, Marenssi SA, Vieytes C, Vizcainso SF (2006) First gondwanatherian mammal from Antarctica. In: Francis JE, Pirrie D, Crame JA (eds) Cretaceous-Tertiary high-latitude palaeoenvironments: James Ross basin, Antarctica. J Geol Soc Lond 258:135–162 References 197 Goin FJ, Zimicz N, Reguero MA, Santillana SN, Marenssi SA, Moly JJ (2007) New marsupial (Mammalia) from the Eocene of Antarctica, and the origins and affinities of the Microbiotheria. Rev Asoc Geológ Argent 62(4):597–603 Hooker JJ (1992) An additional record of a placental mammal (Order Astrapotheria) from the Eocene of West Antarctica. Antarct Sci 4(1):107–108 Jamieson SSR, Sugden DE (2008) Landscape evolution of Antarctica. In: Cooper AK, Barrett PJ, Stagg H, Storey B, Stump E, Wise W (eds) Antarctica: a keystone in a changing world. Proceedings of the 10th International Symposium on Antarctic Earth Sciences. The National Academies Press, Washington, DC, pp 39–54 Krause JM, Clyde WC, Ibañez-Mejía M, Schmitz MD, Barnum T, Bellosi ES, Wilf P (2017) New age constraints for early Paleogene strata of Central Patagonia, Argentina: implications for the timing of South American Land Mammal Age. Geol Soc Am Bull 129(7/8):886–903 Lisiecki LE, Raymo ME (2005) A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records (PDF). Paleoceanography 20; 1003. https://doi.org/10.1029/2004Ä001071 MacPhee RDE, Reguero MA (2010) Reinterpretation of a middle Eocene record of Tardigrada (Pilosa, Xenarthra, Mammalia) from La Meseta formation, Seymour Island, West Antarctica. Am Mus Novit 3698:1–21 Marenssi SA, Reguero MA, Santillana SN, Vizcaino SF (1994) Eocene land mammals from Seymour Island, Antarctica: palaeobiogeographical implications. Antarct Sci 6(1):3–15 Petit JR, Jouzel J, Raynaud D, Barkov NI, Barnola JM, Basile I, Bender M, Chappellaz J, Davis J, Delaygue G, Delmotte M, Kotlyakov VM, Legrand M, Lipenkov V, Lorium C, Pépin L, Ritz C, Saltzman E, Stieveard M (1999) Climate and atmospheric history of the past 420,000 years from the Vostok Ice Core, Antarctica. Nature 399:429–436 Poole I, Cantrill DJ (2006) Cretaceous and Cenozoic vegetation of Antarctica integrating the fossil wood record. In: Francis JE, Pirrie D, Crame JA (eds) Cretaceous-Tertiary high-latitude palaeoenvironments; James Ross basin, Antarctica. J Geol Soc Lond 258:63–81 Reguero MA (2016) Evolution of the Cenozoic mammals from Antarctica. In: Agnolin FL, Lio GL, Brissón Egli F, Chimento NR, Novas FE (eds) Historia evolutiva y paleobiogeográfica de los vertebrados de América del Sur. MACN-Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” e Instituto Nacional de Investigación de las Ciencias Naturales, Buenos Aires, pp 403–412 Reguero MA, Vizcaíno SF, Goin FJ, Marenssi SA, Santillana SN (1998) Eocene high-latitude terrestrial vertebrates from Antarctica as biogeographic evidence In: Casadio S (ed) Paleógeno de América del Sur y de la península Antártica. Asoc Pal Argent Publ, 5:185–198 (cited in Chornobubsky et al. 2009) Reguero MA, Marenssi A, Santillana SN (2002) Antarctic Peninsula and South America (Patagonia) Paleogene terrestrial faunas and environments: biogeographic relationships. Palaeogeogr Palaeoclimatol Palaeoecol 179:189–210 Reguero MA, Goin F, Acosta Hopitaleche C, Dutra T, Marenessi S (2013) Late Cretaceous/ Paleogene West Antarctica terrestrial biota and its intercontinental affinities. Springer, New York Reguero MA, Gelfo JN, López GM, Bond M et al (2014) Final Gondwana breakup: The Paleogene South American native ungulates and the demise of the South America-Antarctica land connection. Glob Planet Chang 123:400–413 Reguero MA, Goin FJ, Abello MA, Chornogubsky L, Gelfo JN (2016) New metatherian mammal from early Eocene levels of the la Meseta Formation, Antarctic Peninsula. Open Science Conference SCAR 2016, Kuala Lumpur, Malaysia. Abstracts Romero EJ (1986) Paleogene phytogeography and climatology of South America. Ann Mo Bot Gard 73:449–461 Shen Y (1995) A paleoisthmus between southern South America with the Antarctic Peninsula during Late Cretaceous and Early Tertiary. VII International Symposium on Antarctic Earth Sciences, Abstracts. Siena Shen Y (1998) A paleoisthmus linking southern South America with the Antarctic Peninsula during Late Cretaceous and Early Tertiary. Sci China Ser D Earth Sci 41(3):225–229 198 9 An Antarctic Mammalian Community Shellito CJ, Sloan LC, Huber M (2003) Climate model sensitivity to atmospheric CO2 levels in the Early-Middle Paleogene. Palaeogeogr Palaeoclimatol Palaeoecol 193:113–123 Vizcaíno SF, Carlini AA, Reguero MA (1988) Primer registro de un marsupial Didelphimorphia en Antártida. Su implicancia biogeográfica. In: Quiroga JC, Cione AL (eds) 5th Jornadas Argentinas de Paleontología Vertebrados, Abstracts. Universidad de La Plata, La Plata, pp 30–31 Vizcaíno SF, Scintilato-Yané GJ (1995) An Eocene tardigrade (Mammalia, Xenarthra) from Seymour Island, West Antarctica. Antarct Sci 7:407–408 Vizcaíno SF, Bond M, Reguero MA, Pascual R (1997) The youngest record of fossil land mammals from Antarctica; its significance on the evolution of the terrestrial environment of the Antarctic Peninsula during the late Eocene. J Paleontol 71(2):348–350 Vizcaíno SF, Reguero MA, Goin FJ, Tambussi CP, Noriega JI (1998) Community structure of Eocene terrestrial vertebrates from Antarctic Peninsula. In: Casadio S (ed) Paleóg Amér Sur Peníns Antártida, Asociación Paleontológica Argentina. Publicación Especial, vol 5, pp 177–183 Weijers JWH, Schouten S, Sluijs A, Brinkhuis H, Damste JSS (2007) Warm arctic continents during the Paleocene-Eocene thermal maximum. Earth Planet Sci Lett 261:230–238 Wilf P, Cuneo NR, Johnson KR, Hicks JF, Wing SL, Obradovich JD (2003) High plant diversity in Eocene South America: evidence from Patagonia. Science 300:122–125 Woodburne MO, Zinsmeister WJ (1982) Fossil land mammal from Antarctica. Science 218:284–286 Woodburne MO, Case JA (1996) Dispersal, vicariance, and the Late Cretaceous to Early Tertiary land mammal biogeography from South America to Australia. J Mamm Evol 3(2):121–161 Zachos J, Pagani M, Sloan L, Thomas E et al (2001) Trends, rhythms, and aberrations in global climate 65 Ma to present. Science 292(5517):686–693. https://doi.org/10.1126/science.1059412