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Home , Astrapotheriidae, Loreto Formation, Microbiotheriidae, Riochican, Scaglia (mammal), Utaetus

Asociación Paleontológica Argentina. Publicación Especial 5 ISSN 0328-347X Paleógeno de América del Sur y de la Península Antártica: 185-198. Buenos Aires, 30-12-1998

EOCENE HIGH-LATITUDE TERRESTRIAL FROM AS BIOGEOGRAPHIC EVIDENCE

Marcelo A. REGUERO!, Sergio F VIZCAÍNO!, Francisco J. GOIN, Sergio A. MARENSSP and Sergio N. SANTlLLANN

A BSTRACT. A moderately di verse terrestrial biota is known from the - ?early Oligocene , , Antarctic Peninsula. The La Meseta Formation fills an incised valley and comprises sediments that represent deltaic, estua- rine and very shallow marine environments. Forests of both deciduous and evergreen trees were dominated by Nothofagus, podo- carps, and araucarian conifers. The La Meseta paleoflora is distinctive in having a predominance of Antarctic taxa; this suggests a seasonal, cold-temperate, rainy c1imate and a latitudinal gradient. Among the terrestrial vertebrates, there are at least nine rnammal taxa, predominantly tiny s (mostly endemic and new genera). The presence of these suggests the existence of some form of isolating barrier (c1imatic and/or geographic), which must have allowed development of this endemic fauna. Cornpa- risons with faunas assigned to the (late ), Riochican (late Paleocene), (early Eocene), and Mus- tcrsan (tentatively assigned to the middle Eocene) ages of were made. The assemblage of terrestrial vertebrates of the La Meseta Formation is unusual in the dominance of several endemic forms. The occurrence of protodidelphid and derorhynine marsu- pials, that had become extinct elsewhere in the Eocene of , on Seymour Island also indicates that isolation may have allowed extended survival ofthese taxa in theEocene of Antarctica. The nature, distribution, and composition ofthe La Meseta fauna firmly suggest a latitudinal differentiation in the middle Eocene. Paleogeographic evidence suggests that the terrestrial of the La Meseta Formation probably lived under crepuscular and even extended noctumal conditions (assuming that the angle of the earth's spin axis was relatively the same as it is now) during part of the year.

RESUMEN. VERTEBRADOS EOCENOS TERRESTRES DE ALTAS LATITUDES DE ANTÁRTIDA COMO EVIDENCIA BIO- GEOGRÁFICA. Una biota moderadamente diversa es conocida en la Formación La Meseta (Eoceno-Oligoceno temprano"), isla Seymour, Península Antártica. La Formación La Meseta rellena un valle incidido y comprende sedimentos que representan ambien- tes estuáricos y marinos muy someros. Bosques con árboles deciduos y perennes estuvieron dominados por Nothofagus, y coníferas podocarpáceas y araucarias. La paleoflora de la Formación La Meseta es distintiva y predominan taxones antártico s que sugieren un clima templado frío, lluvioso, estacional y un gradiente latitudinal. Dentro de los vertebrados terrestres hay 9 taxones de mamíferos, predominantemente pequeños marsupiales, mayormente endémicos y novedosos, que sugieren que alguna forma de barrera de ais- lamiento, c1imática y/o geográfica, debió haber permitido el desarrollo de esta fauna endémica. Se realizaron comparaciones con las Iaunas asignadas a las edades mamífero Itaboraiense (Paleoceno tardío), Riochiquense (Paleoceno tardío), Casamayorense (Eoceno temprano) y Mustersense (tentativamente asignada al Eoceno medio). La fauna de la Fm. La Meseta es particular por el predominio de varias formas endémicas. La presencia de marsupiales protodidélfidos y derorhinchinos, los cuales ya no se registran en ninguna de las faunas del Eoceno de América del Sur, indica que el aislamiento pudo haber permitido la supervivencia de estos taxones en el Eoceno de Antártida. La naturaleza, distribución y composición de la fauna de la Fm. La Meseta firmemente sugiere una diferencia- ción latitudinal en el Eoceno medio. Finalmente, las evidencias paleogeográficas sugieren que los mamíferos terrestres de la Forma- ción La Meseta probablemente vi vieron bajo condiciones crepusculares, aún nocturnas (asumiendo que la oblicuidad del eje de la Tierra fue relativamente la misma que la actual), durante parte del año.

KEY WORDS. Antarctic Peninsula. Eocene. High latitude fauna. Mammals. Palaeobiogeography.

PALABRAS CLAVE. Península Antártica. Eoceno. Fauna de alta latitud. Mamíferos. Paleobiogeografía.

INTRODUCTION a moderately varied, middle-late Eocene land fauna from the northern portion of the island rekindled Seymour (Marambio) Island (figure 1) contains the interest in this area. after the discovery of the first land only Eocene land vertebrate fauna known in Antarctica, in Antarctica (Woodburne and Zinsmeister, cxcept for the avian tracks from the King George Island 1984). This was especially true because paleogeographic (Covacevich and Rich, 1982), and represents the reconstructions (based on paleomagnetic data collected southernmost part of the distribution of so me on the itself) of the Antarctic Peninsula during South American land mammal lineages. The recovery of the Eocene indicate a paleolatitude as far south as perhaps 63° (Lawver el al., 1992; figure 2). Concerted effort between 1988 and 1996 produced terrestrial verte- 'Departamento Científico de Paleontología Vertebrados, Museo brates from several different stratigraphic levels (lO 10- de La Plata. Paseo del Bosque s/n, 1900 La Plata, Argentina. calities from 4 different stratigraphic horizons) within E-mail: [email protected] 'Instituto Antártico Argentino, Cerrito 1248, 1010 Buenos the La Meseta Formation (figure 3); these range from the Aires, Argentina. middle Eocene to the ?early Oligocene (Bond el al.,

1993; Fordyce, 1989). This biota contains more than 30 marsupial s) within this fauna, together with relicts such taxa of terrestrial plants and vertebrates. Terrestrial verte- as protodidelphid and derorhinchine marsupials, give it a brates were recovered by surface prospecting and sieving very distinctive southern appearance, indicating that of the sediment after 5 years of careful fieldwork. These some form of isolating barrier (climatic, geographic or vertebrates, particularly the mammals, have close bioge- topographic) was in effect. Several types of environmen- ographical links with Paleogene faunas of Patagonia tal factors could result from the high latitude, of which (Bond et al., 1993). temperature may be the most important. The relatively The La Meseta land vertebrate fauna (here called low temperatures of the Antarctic regions during the LMF) is unusual in being dominated by large sparnothe- middle-Iate Eocene seem to have been matched by the riodontid ungulates and small polydolopine marsupials. development of a characteristic biota (Marenssi et al., This is not the case in the Patagonian record. Mo- 1994). reo ver, the high proportion of endemic taxa (mainly In this paper we present faunistic data, together with

____ Edge of shelf ice D Surficial deposits ~ La Meseta Fm. (Eocene) []]] Cross Valley Fm. (Paleocene) b Sobral Fm. (Paleocene) o D Lopez de Bertodano Fm. .~ 0" Seymour 1 E3 (-) ,- Dike 65°s James Ross I

CapeWiman IAA 2/95 DPV 6/84 Peninsula IAA 1/94 1M 1/90 250 Km IAA 1/95 DPV 16/84 Cape Bodman IAA 1/92 Seymour

Figure 1. Map showing the location of Seymour Island and the collecting sites. Mapa de ubicación de la Isla Seymour mostrando los sitios de coleccián.

A.P.A. Publicación Especial 5, 1998 EOCENE VERTEBRATES FROM ANTARCTICA 187

paleofloristic information, supporting the existence of a in the Eocene of Seymour Island. The stratigraphic posi- high latitude land biota with differences from the pene- tions of these localities are shown in figure 3. Herein we contemporaneous faunas of Patagonia. follow the stratigraphic terminology of Sadler (1988), be- cause the newest framework elaborated by Marenssi el ABBREVIATIONS al. (1998) is not widely accepted yet. The La Meseta Formation (ElIiot and Trautman, DPV: Departamento Científico de Paleontología Ver- 1982) fills an incised valley and comprises deltaic, estua- tebrados, Museo La Plata. IAA: Instituto Antártico Ar- rine, and shallow marine deposits containing both marine gentino, Buenos Aires. RV: University of California at and terrestrial (Marenssi, 1995; Marenssi el al., in Riverside, California. ZPAL: National Academy of press). Although paleogeographical interpretations indi- Science, Warsaw. TELM: Tertiary Eocene La Meseta cate that terrestrial facies had to be present nearby to the (Sadler's stratigraphic nomenclature). west, they are not yet known from Seymour Island; hence, all terrestrial fossils reported to date were trans- ported into marine settings. GEOLOGICAL OVERVIEW The location of the incised valley, its temporal persis- Ten terrestrial vertebrate-bearing localities are known tence, the lenticular nature of the internal units, the thick-

AFRICA

Figurez. Paleogeographic reconstruction of the southern at 50 Ma showing the distribution of the faunal and floristic units at high latitudes. Circles indicate 0", 30° and 60° S latitude after Lawver et al. (1992, fig. 11). Thick line denotes continents; thin lines show continental shelves 10 present day 200 In isobath. Reconstrucción paleogeográfica de los continentes del Hemisferio sur a los 50 Ma mostrando las [oruiaciones con elementos faunisticos y floristicas de altas latitudes. Los círculos de 0°, 3° Y 60° S esecí/1ilidicados. Modificadu de Lmvl'er er al. (1992, Jig. 11). La iinea gruesa indic« los conunentes, la 1(/1ea fina indica los bordes continentales actuales en la isobata de 200 m.

A.P.A. Publicación Especial 5, 1998 188 M.A. REGUERO, S.E VIZCAÍNO, EJ. GOIN, S.A. MARENSSI y S.N. SANTILLANA

ness of the sedimentary facies and geometric relation- unless they are rapidly buried. Heavy minerals also may ships 01' the bedding and synsedimentary faults (Sadler, be informarive about of climate. Sandstones of the La 1988; Marenssi, 1995; Marenssi el al., in press) indicate Meseta Formation are mainly feldspathic and lithic-feld- that sedimentation was strongly controlled by subsidence spathic arenites and wackes, containing unstable and me- and tectonics. tastable heavy minerals (anphiboles, pyroxenes, epidote, Paleoenvironmental restorations indicate that the La garnet); thus, either rapid burial or a low degree of weat- Meseta Formation accumulated at the seaward end of an hering is indicated (Marenssi, 1995). Detrital grains in incised valley during an overall rise in sea level (Ma- samples of the La Meseta Formation usually are unalte- renssi, 1995; Marenssi el al., in press). Recent studies of red, although occasional clasts of feldspars and volcanic the geometric relationships in the La Meseta Formation rock fragments do exhibit minor to moderate alteration. (Sadler, 1988; Marenssi, 1995; Marenssi et al., 1998) Historically, feldspars have been considered to be indica- show that the steep erosional boundaries are the margins tive of a humid source area (Folk, 1980) although James of a large channel some 7 km in width that originated et al. (1981) determined that the amount of feldspar alte- farther west. Outcrops of the La Meseta Formation on ration is similar in wet and arid c1imates. Furthermore, Cockburn Island, about 10 km west, and the meandering stable isotope studies of molluscan macrofossils from the character of Herbert Sound between James Ross and La Meseta Formation suggest a cooling trend during the Vega islands have prompted Stilwell and Zinsmeister Eocene with water temperatures between 7.90 and 11.70 C (1992) to place the head of the La Meseta incised valley (Gadzicki el al., 1992; Ditchfield et al., 1994). almost 60 km to the northwest, at the toe of the Antarctic To sum up, sediments of the La Meseta Formation ac- Peninsula. cumulated in marine to paralic environments. The source Although the plant remains were concentrated in pa- of sediments was located to the west-northwest along the ralic environments after some transport, the presence of present-day Antarctic Peninsula. The c1imate of the sour- leaves, tree trunks, and a flower suggest a forested nearby ce area can not be unequivocally interpreted from petro- terrain (Gandolfo et al., 1998a, 1998b; Torres el al., logic studies but, based on paleobotanical evidence (dis- 1994). Leaves are associated with marine mollusks, and cussed below), it was not warm. At the time of deposition tree trunks frequently are densely bored tTeredolites¡ in- of the middle part of the La Meseta Formation, Seymour dicating extended submersion in the water-sedirnent in- Island was a low-relief coastal area but a mountainous terface before burial. Also teeth and bones of land verte- highland region was located a few kilometers to the west. brates are associated with the abundant marine macrofau- The altitudinal differences between both areas must have nao They are always recovered from a thanatocoenosis produced a climatic and biological gradient in the terres- (Marenssi, 1995), along with an abundant marine fauna. trial environments. The provenance of these vertebrate remains supports the existence of a terrestrial environment nearby. EOCENE ANTARCTIC PENINSULA FLORA Sedimentary environments such as tidal channels and AND ENVIRONMENT flats, an estuary mouth platforrn, and a mid-estuary (Marenssi, 1995; Marenssi el al., in press) formed a coas- Eocene floras at different sites of the Antarctic Penin- tal area of low relief. In contrast, far inland to the west, sula (King George and Seymour islands) suggest the pre- the Antarctic Peninsula was a highland, mountainous sence of densely forested habitats that were widely deve- area characterized by volcanoes since the . loped along the Peninsula at that time. The La Meseta The sedimentary structures, the thicknesses of the fa- Formation has yielded fossil plant material from most of cies, the preservation potential of the fossils, and the lack its stratigraphical column (Dusén, 1916; Cranwell, 1959; of change in the marine invertebrate fauna throughout the Askin and Fleming, 1982; Sadler, 1988; Torres el al., formation point to a rapid sedimentation rate (Marenssi, 1994; Brea, 1998; Brea and Zuccol, 1996; Gandolfo el 1995). The heterolithic lithofacies have the highest net al., 1998a). Megaflora has been collected from all but the accumulation rate, whereas the shell beds have the lowest 120 m. The flower (Gandolfo et al., 1998a), some lowest. tree trunks (Torres el al., 1994), and most of the leaves Provenance studies on sandstones of the La Meseta (Gandolfo el al., 1998b) are preserved in fine-grained he- Formation demonstrated that the sediments come from terolithic facies 01' tidal origin, especially from the midd- the west-northwest, the source rocks being those crop- le part of the formation. Some other tree trunks and a few ping out on the Antarctic Peninsula (Marenssi, 1995). lea ves come from coarse-grained channel-lags. Carbo- Additionally, paleocurrent measurements confirm the 10- naceous detritus, spores, and pollen are frequent throug- cation of the source are a (Marenssi, 1995). The detrital hout the fine grained facies. Askin (1992, 1995) reported modes of sandstone often are considered to have been in- that the Late Cretaceous and Paleocene plant community fluenced by the c1imate of a source area. Based on the was dominated by conifer rainforest in the area of light mineral suite, rock fragments and feldspars are the Seymour Island. most sensitive indicators of climate (Suttner and Dutta, Gothan (1908) and Torres el al. (1994), studied fossil 1986), these are quickly destroyed in a warm, humid climate, wood from the La Meseta Formation. Several coniferous

A.P.A. Publicación Especial 5, 1998 EOCENE YERTEBRATES FROM ANTARCTICA 189 and dicotyledoneous tNothofagusy woods were identified reported the presence of the families Dilleniaceae, Myri- from the middle part of this unit (Torres el al., 1994), da- caceae, Myrtaceae, Lauraceae, and Grossulareaceae, as ted as middle Eocene (Marenssi el al., 1994). They have well. All but Lauraceae belong to the Antarctic Flora of narrow, but regularly spaced and well-rnarked, growth Romero (1986). Based on morphological characters of 88 rings, typical of slow-growing trees with vegetative pe- specimens collected from three localities of the middle riods corresponding to seasonal elimate changes. Torres part of the La Meseta Formation, Gandolfo el al. (l998a) el al. (1994) described six taxa of fossil woods having af- described the forests as mixed mesofitic indicative of a finities with extant trees that grow in cold-temperate rain- sea son al cold-ternperate rainy climate. In one of these 10- forest areas of southern South America (the Valdivian calities, DPV 3/84 (GPS data: 64°13'58" S, 56°39' 15" and Magellanic forests). Well-defined growth rings W), more than 300 samples were recovered and represent within fossil wood samples frorn Seymour Island indica- fossil foliage referred to Tetracera patagonica (Dille- te that this climate was markedly seasonal. Temperate to niaceae), Hydrangeiphvlum affine (Hydrangeaceae) and cool-temperate evergreen coni fer/broad-leavcd forests the families Nothofagaceae, Betulaceae, Myrtaceae, My- exist today in southern South America. Rainfall in these ricaceae, Lauraceae, and Grossulariaceae (represented by areas is very high, mainly in summer and spring seasons, a flower, Gandolfo el al., 1998b; 1998a). Based on this with an average precipitation frorn 1000-3000 mm/y. flora, the annual mean paleotemperature was calculated These are as currently contain the richest biota of the sub- to be 11°-13°C whereas the mean of the coldest month Antarctic dominion. Freezing temperatures can prevail might vary between _30 and 2°C. The paleoflora also sug- during several months of the year. gests that spring and summer were rainy, and that the fre- Case (1988) described the first megaflora from La ezing season might have lasted several months. Meseta Formation, indicating a dominance of the genus Based on a morphological analysis, Romero (1986) Nothofagus. Gandolfo el al. (1998a) recognized this genus and determined the climate and phytogeography of the flora

Sadler (m) (1988) 750

DPY 16/84 TELM 7

...... TELM 6/7 TELM 6

DPY 6/84 550 TELM 5 Q lo~ <:::) C~> Do I Breccia 1M 1/90, 1M 1/95, IM2/95 1M 1/96, 1M 2/96 - -- Mudstone DPV 2/84, 1M 1/92 TELM 4 ~

- -- Muddy-Sandstone C=

v/\(;. Shell bed TELM 2 ~

~ Covered

TELM 1 C=

...... o

Figure 3. Stratigraphic section of La Meseta Fonnation (Eocene to ?early Oligocene) showing the land-vertebrate horizons and 10- calities. SecciólI eSlf(/ligrc{{ica de 1(/FUnll(/ciúll L(/ Meseta (Eaceuo-í Oligoceuo temprano] mostrando los horizontes y las localida- des COI/ vertebrados terrestres.

A.P.A. Publicación Especial 5, 1998 190 M.A. REGUERO, S.E VIZCAÍNO, EJ. GOIN, S.A. MARENSSI y S.N. SANTILLANA of the middle Eocene. He stated that the forests in Pata- 1995) was added to a second polydolopid taxon (Case el gonia were wet subtropical with a mixture of Neotropical al., 1988), and the first terrestrial placental, a Tardigrada and Antarctic elements ("Paleoflora Mixta"). At the same or Vermilingua edentate (Carlini el al., 1990). Between time, the La Meseta paleoflora has a predominance of 1990 and 1996, new discoveries of cursoríal and flying Antarctic elements, this suggests a colder climate and a birds (Tambussi el al., 1994, 1995), marsupia1s (Goin el latitudinal gradient with respect to the paleoflora of the al., 1995; Candela and Goin, 1995), edentates (Vizcaíno Río Turbio Formation (51°35' S, 72°10' W, Santa Cruz, and Scillato Yané, 1995), and South American ungulates Argentina). (Hooker, 1992; Bond el al., 1990; Vizcaíno el al., 1997) In recent years, a growing body of information has notably increased our knowledge ofthe Eocene terrestrial been accumulated about the Eocene climate of the Antarctic fauna. The known diversity of one of the mam- Antarctic Peninsula. Paleofloral data sets show that the rnal-bearing horizons of the La Meseta Formation middle-Iate Eocene was warmer than present, but not as (TELM 5) can be taken to represent essentially a single warm as the Late Cretaceous through early-rniddle Paleo- fauna (Vizcaíno el al., 1998) and can be compared with cene. Seymour Island paleofloras RV-8200, IAA 1/90, Patagonian faunas. There are 12 reported terrestria1 ver- and DPV 3/84 from TELM 5 seem to indicate a climatic tebrate taxa, 10 of which occur in a single level (TabJe 1). drop that apparently correlates with the general climatic This land-vertebrate fauna, though numerically small, deterioration that occurred in the rest of the world at the strongly suggests a middle Eocene age based on cladistic re- end of the Eocene (Case, 1988). The compositions of lationships ofthe spamotheriodontids and po1ydolopids (Wo- these paleofloras indicate a cool, humid climate. A diffe- odburne and Zinsmeister, 1984; Bond el al., 1993). This age rent situation characterizes the lower levels of the se- assignment correlates well with the middle Eocene age ofthc quence, where the early-late Eocene flora of the locality ichtiofauna found in the same depositional horízon (Cione RV-8425 (TELM 2) that was dominated by a large-leafed and Reguero, 1994, 1998) and with age data from marine mi- species of Nothofagus suggests " ... a situation of amelio- crofossils (Coccozza and Clarke, 1992). rating climatic conditions ..." (Case, 1988: 525). This pa- A taxonomic analysis of the La Meseta fauna (Table leoflora also contains two species of ferns. 1) reveals a modest diversity that includes three avian Nothofagus, now known from macrofossils (Case, and six mammalian ordinal groups (Table 2). The most 1988; Gandolfo, 1998a), is considered to be of critical abundant element of the fauna is a suite of marsupials importance as an indicator of paleoclimate. Notliofagus is comprising approximately six taxa (4 new genera). The the predominant angiosperm taxon in each of the three South American ungulates are less diverse with two taxa paleofloras from Seymour Island mentioned above. Gan- (one new genus) being represented. This Eocene rnarn- dolfo el al. (1998a) reported N. serrulata and two inde- malian assemblage was probably even more diverse, be- terminate species of the same genus from this unit cause the documented di versity of the La Meseta Forma- (TELM 5, IAA 3/84). The former species is now restric- tion mammals is, of course, minimal, being derived from ted to southern South America, where they grow in a cool a few sites (9) and from small samples (less than 60 spe- temperate climate. Nothofagus serrulata extends from cimens). Among the terrestrial mammals, the dominant southern (Carmen Silva, Loreto, and Brush Lake taxa are the South American ungulates (Sparnotheriodon- Formations) and Argentina (Río Turbio, Río Guillermo, tidae) and the marsupial s (Polydolopidae). They are not and Ñirihuau Formations) to the southern shores of Tierra usually dominant elements in much larger thanatocoeno- del Fuego (Cullen Formation), and thus represents a clo- ses elsewhere in South America. ser geographical approach to Antarctica than do other The endemic polydolopines are closely related to the South American species (figure 2). Casamayoran genus Polydolops. Relict taxa in the LMF, protodidelphid and derorhynine marsupials, indicate that ANTARCTIC AND PATAGONIAN EOCENE whatever factor led to their elsewhere did not LAND-VERTEBRATE FAUNAS: affect the Antarctic Peninsula at this time. If these factors A BRIEF FAUNAL COMPARISON were biological, isolation is suggested, in that these factors could not reach the Antarctic Peninsula. LA MESETAFAUNA(Tables 1, 2) The tardigrade edentate represents the earliest un- questionable record of this group in the world (Vizcaíno In Antarctica, the first terrestrial mammal was reco- and Scillato Yané, 1995). The earliest records in South vered from the La Meseta Formation (Woodburne and America of Tardigrada come from the (Oligo- Zinsmeister, 1984). It was referred to the Polydolopidae, cene) of Patagonia and Bolivia. a fami1y of extinct marsupia1s previously known from The Antarctic sparnotheriodontid taxon is endemic at strata of middle Paleocene to late Eocene age in Patago- the generic level, and has a close affinity with one undes- nia, southern Argentina, Chile, and Brazil. Later work cribed Casamayoran taxon of Chubut Province (M. within the same unit recorded the first running bird (Case Bond, pers. comm., 1996). el al., 1987), and, subsequently, new terrestrial mammal Among the terrestrial birds, two flightless taxa were remains were reported. A microbiotheriid (Goin and Carlini, reported (a ?phororhacoid and a ratite). The ratite was

A.P.A. Publicación Especial 5, 1998 EOCENE VERTEBRATES FROM ANTARCTlCA 191

Table 1. Taxonomic list, stratigraphy, and references for the land vertebrates from the Eocene of Seymour Island, Antarctic Penin- sula.Lisra raxonólllica, estratigrafía y referencias de los vertebrados terrestres del Eoceno de la isla Seymoll/; Península Antártica.

TAXA STRATI GRAPHY REFERENCES

MARSUPIALlA

Polydolopidae TELM 5 Woodburne and Zinsmeister, 1984; Case el al., 1988; Goin el al., 1995

Microbiotheriidae TELM 5 Goin and Carlini, 1995; Goin el al., 1995 Protodidel phidae TELM 5 Goin el al., 1995

Derorhynchid-like TELM 5 Goin el al., 1995 Dasyurid-like TELM 5 Goin el al., 1995

Tardigrada indet. TELM 4-5 Marenssi el al., 1994; Vizcaíno and Scillato Yané, 1995 ?L1TOPTERNA

Spranotheriodontidae TELM 4-5-7 Bond el al., 1990; Marenssi el al., 1994; Vizcaíno el al., 1997

Trigonostylopidae TELM 5 Bond el al., 1990; Hooker, 1992; Marenssi el al., 1994 RATITAE Family indet. TELM7 Tambussi el al., 1994

?PHORUSRHACOID TELM7 Case el al., 1987 FALCONID TELM 5 Tambussi et al., 1995 found in the upper levels of the unit (ZPAL 4, TELM 7). the existence of a forested habitat in the middle to late Pa- Ratites are mainly distributed in the southern continents leocene. AdditionalIy, the presence of crocodiles, alliga- and probably have a Gondwanan origin (e.g. Cracraft, tors, boid snakes, and ?pelomedusid turtles indicate at 1975). The record of a ?phororhacoid bird is consistent least warm temperatures. The paleofloral record suggests with the previous discovery of avian ichnites (Covace- that tropical to subtropical coastal mangrove environ- vich and Rich, 1982) on Fildes Peninsula, King George ments alternated with inland sylvan and sclerophylic fo- Island. Several of these footprints may belong to pho- rest or savannahs (Petriella and Archangelski, 1975). rorhacoids. The mammal faunas of the Eocene of Patagonia in- elude the earIy Eocene Casamayoran, the relatively poorly known middle Eocene (both known PATAGONIAN FAUNAS (Tables 3, 6) almost exclusively from Argentine Patagonia), the ?Iate Paleocene continental Patagonian mammal faunas in- Eocene (very incompletely known), and the elude the middle Paleocene Tiupampian, the middle Pa- late Eocene "" from central Chile. Only the leocene Itaboraian and the late Paleocene Riochican (see Casamayoran and Mustersan (included in the Panca- tables 3 and 4). Only the ltaboraian and Riochican faunas samayoran Subcycle of Pascual and Jaureguizar, 1990) share familial and generic taxa with LME Two polydolo- have taxonomic similarities (in age and taxonomic com- pines, Eudolops and ?Polydolops, a primitive ?didel- position) with LME The Patagonian rnammal-bearing phoid, Derorhynchus, and several protodidelphid rnarsu- horizons are included in the Sarmiento Formation com- pials (table 3) are present in the Itaboraian Fauna. Within posed of pyroclastic-derived sediments (Spalletti and the ungulates, Trigonostylopidae is present with one ge- Mazzoni, 1978). The Casamayoran (earIy Eocene) is per- nus, Shecenia. The South American ungulates are repre- haps the best known and best sampled of the South sented by seven families placed in four orders. Four fa- American ages (Simpson, 1967). The best re- milies of Notoungulata are recorded in this age. The Rio- presentative localities yielding Casamayoran mammals chican Fauna record s three families of marsupials, the cluster around 45", 48° S (Gran Barranca -45°42' S, Polydolopidae being one of them. Polydolops is the only 68°42' W-, Cañadón Vaca, Cañadón Hondo, and Valle genus of this family present in the Riochican Age (Bond Hermoso from Chubut Province). Mammals from these el al., 1995). localities are listed in table 5. A striking feature of the These ages are characterized by the dominant presen- Casamayoran fauna is its domination by extremely low- ce of brachyodont ungulates (92% of the fauna), although crowned ungulates (83%), including severa1 primitive li- a few mesodont types (8%) occur in the Riochican neages such as henricosborniids and isotemnids. The (Pascual and Ortiz Jaureguizar, 1990). This fact suggests South American ungulates are represented by 20 families

A.P.A. Publicación Especial 5, 1998 192 M.A. REGUERO, S.E VIZCAÍNO, EJ. GOIN, S.A. MARENSSI y S.N. SANTILLANA

Table 2. Taxonomic list for La Meseta terrestrial mammals, age. The lower diversity among Mustersan ungulates (4 Seymour lsland, AntarcticaLisllI taxonúniicn de los mllmíferos orders and 10 families) almost certainly reflects the rela- terrestres de la Formucián La Meseta, Isla Seymoui; Antáriida. tively short duration of the Mustersan and the fact that it is poorly sampled. No sparnotheriodontids are recorded Polydolopimorphia in this fauna. The diversity of the marsupials is low, con- Family Polydolopidae sisting of two families with two genera. Polydolops dailyi Environmental and climatic data are provided by the Polydolops seymouriensis "Paleoflora Mixta" ("cold temperate flora" + subtropical Polydolops sp. nov. flora") of Romero (1978) from Río Turbio Formation Didelphimorphia Family Protodidelphidae (Eocene), Santa Cruz Province. Throughout the Casama- gen. et sp. nov. yoran and Mustersan gramineous phytoliths became Family indet. more abundant (Spalletti and Mazzoni, 1978) suggesting gen. etsp. nov. 2 rhat grassland environments began to be prominent in middle latitudes (ea. 45°S). In addition, the dental featu- Family Microbiotheriidae res of some marsupials with "plagiaulacoid" specializa- gen. et sp. nov. 3 tions (e.g. Polydolopidae) suggest the presence of sean- gen. et sp. indet. sorial and probably arboreal types that one would expect ?Dasyurida to occupy forested habitats (Pascual, 1980). The absence Farnily indet. gen. et sp. nov. 4 of crocodiles and boid snakes after the Casamayoran age Order indet. suggests a climatic deterioration at that time. Family incertae sedis gen. et sp. nov. 5 HIGH LATITUDE EFFECT Edentata Tardigrada or Vennilingua Increasing latitudinal separation yields decreases in Tardigrada indet. faunal similarities between localities (Flyn, 1984). Today, ?Litopterna the Seymour Island land vertebrate-bearing localities are Family Sparnotheriodontidae gen. et sp. nov. separated frorn the bulk of the Casamayoran-Mustersan Astrapotheria localities by more than 15°. If we consider, on the basis Family Trigonostylopidae of geologic and paleogeographic data (Lawver el al., Trigonostylops 1992; Shen, 1995), that the Drake Passage (about 1000 Mammalia incertae sedis km wide) started to open at about 36 Ma, we can assume Family indet. that, prior that time, the distance between Antarctic Pe- ninsula and Patagonia ought to have been shorter. placed in four orders. Notoungulates dominate, with Highly distinctive Late Cretaceous and Eocene high seven families present in this age. In contrast, litoptern latitude terrestrial vertebrate faunas have been described diversity during the Casamayoran is surprisingly low in (Brouwers el al., 1987; McKenna, 1980; Hickey el al., view of the earlier diversity of the group. Sparnotherio- 1983; Rich el al., 1988) and each is characterized by spe- dontids and trigonostylopids were part of this fauna. cial attributes related to the highly distinctive paleoenvi- Within the Sparnotheriodontidae, Victorlemoinea (= ronment in which each fauna developed at different Spamotheriodon, junior synonym) is the best represented times. It is accepted that several types of environmental genus. A modest radiation of trigonostylopids occurred factors could effect latitudinal zonation (Hallam, 1984). during the Casamayoran. Only seven marsupial families Based on the marine invertebrates from Seymour Island, with nine genera are present in the Casamayoran. The Zinsmeister and Feldmann (1984) stated that high-Iatitu- polydolopines had a southern distribution and in the Ca- de regions serve as "holding tanks" for taxa that remain samayoran, three genera were present, including isolated until they disperse from the region C'high latitu- Polydolops. The polydolopines were small, rodent-like de heterochroneity" = differential appearance of taxa bet- marsupial s that appeared last in the "Tinguirirican" (late ween high and mid- to low latitudes). The same authors Eocene) of Chile (Wyss el al., 1990). Coincidently, recognized such high-Iatitude regions as centers of origin Tinguiririca (34°59' S, 70°26' W) represents the nort- of novel adaptations leading to speciation. Case (I989) hernmost distribution of this subfamily. The Mustersan expanded Zinsmeister and Feldmann 's (1984) concept Age (tentatively assigned to the middle Eocene) is known to the terrestrial fauna, especialIy the marsupials almost exclusively from Patagonia. The best representa- ("Weddellian marsupials"), from Seymour Island. tive localities yielding Mustersan mammals are Gran Lewin (1983) hypothesized that the high-Iatitude re- Barranca, Cerro del Humo and La Gran Hondonada frorn gions seem more suitable for the origin of new taxa than Chubut Province. Mammals from these localities are lis- areas of low latitude, such as the tropics. AIso, it is appa- ted in table 6. Notoungulates are the dominant group rent that many austral biotas (high-Iatitude biotas) have among the ungulates, with six families present in this demonstrably lower taxonornic diversities than their lower-

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TabIe 3. Taxonomic list for the Itaboraian mammals from Pata- Table 4. Taxonornic list for the Riochican mamrnals from Pata- gonia, Argentina. Lista taxonomica de los mamíferos gcnia, Argentina. iraboraianos de Patagonia, Argentina.

Polydolopimorphia Polydolopirnorphia Family Polydolopidae Family Polydolopidae Epidolops Polydolops ?Polydolops Family Prepidolopidae Didelphimorphia aff. Prepidolops Family Protodidelphidae Sparassodonta Bobbscaefferia Family Borhyacnidae Guggenheituia TNemolestes Protodidelphis Edentata ?Didelphoidea Family aff. Itaboraidelphys gen. et sp. indet. arf. Didelphopsis Condylarthra Derorliynchus Family Didolodontidae Minusculodelphis Enneoconus Marniosopsis Ernestokokenia Monodelphopsis Notoungulata Peradectida Family Henricosborniidae Family Caroloameghiniidae Henricosbornia Procaroloaineghinia ?Ot/1I1ielmarshia Microbiotheria Family Isotemnidae Family Microbiotheriidae Isotemnus Mirandatherium "Pleurostylodon Sparassodonta Family Interatheriidae Family Borhyaenidae Notopithecus Patene Family Oldfieldthomasiidae ? Oldfieldthomasia Family indet. Maxschlosseria Gashternia Family Notostylopidae Condylarthra Notostylops Family Didilodontidae Family Archaeopithecidae Ernestokokenia Archaeopithecus Notoungulata Family Archaeohyracidae Family Henricosborniidae Eohyrax Hcnricosbornia gen. et sp. nov. ?Pcripantostylops Notoungulata incertae sedis Family Isotemnidae Family indet. Ylsoternnus Brandmayria Family Interatheriidae Litopterna "Transpithecus Family Proterotheriidae Family Oldfielthornasiidae Ricardolyddekeria Kibenikhoria Anisolambda Colbertia ?Litopterna Camargomendesia Family Sparnotheriodontidae Itaboraitherium Victorlemoinea ?Litopterna Astrapotheria gen. indet. Family Trigonostylopidae Astrapotheria Trigonostylops Family Trigonostylopidae Shecenia levels. AIso, at high latitudes, a prolonged period (seve- latitude counterparts (Sheehan, 1986). Various climatic ral months?) of continuous darkness (assuming that the and ecological factors int1uence latitudinal gradients in position of the earth's rotational pol e with regard to Sey- mammalian diversity and taxonomic composition, and mour Island was not signicantly different than at present) they strongly int1uence the formation of latitudinal faunal could have had an important effect on the distribution of barriers, as well (Simpson, 1964; Flessa, 1975; McCoy some taxa of the fauna. In this regard, the paleolatitude of and Connor, 1980). One of these factors could be a coo- the Antarctic Peninsula during the Eocene was high (ne- ling of the climate in the Antarctic Peninsula during the arly 630 S). Although the terrestrial biota was living far Eocene; many aspects of the flora and fauna may have from the Polar Circ\e (850 S), it could have routinely ex- been affected ifthe temperatures fell below certain threshold perienced 1 to 3 months of complete winter darkness as

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Table 5. Taxonomic list for the Casamayoran mammals from Patagonia, Argentina. Lista taxonómica de los mamíferos casamayorel1ses de Putogonia, Argentina.

Didelphimorphia Family Didelphidae Adiantoides Coolla Family Amilnedwarsidae Microbiotheria Amilnedwarsia Family Microbiotheriidae Rutimeyeria Eomicrobiotherium Ernestohaeckelia Peradectida ?Litopterna Family Caroloameghiniidae Family Sparnotheriodontidae Caroloameghinia victorlemoinea Sparassodonta Sparnotheriodon Family Proborhyanidae Notoungulata Arnuniheringia Family Henricosbomiidae Family Borhyaenidae Henricosbornia Nemo/estes Othnielmarshia Family Hathliacynidae Peripantostylops Patene Family Notostylopidae Polydolopimorphia Eduardotrouessartia Family Polydolopidae Homalostylops Aniphidolops Notostylops Eudolops Family Oldfieldthomasiidae Polydolops Maxschlosseria Edentata Oldfieldthomasia Family Dasypodidae Paginula Astegotlierium Ultrapithecus Meteutatus Family Archaeopithecidae Prostegotherium Acropithecus Utaetus Archaeopithecus Family Pampatheriidae Family Interatheriidae Muchlydotherium Antepithecus Condylarthra Notopithecus Family Didolodontidae Transpithecus Didoiodus Family Archaeohyracidae Elllleocollus Eohyrax Ernestokok enia Family Isotemnidae Paulogervaisia Anisotemnus Proectocion Isotemnus Litopterna Pleurostylodon Family Protolipternidae Thomashuxleya Asmithwoodwardia Family Notohippidae Family Proterotheriidae Plexotemnus Anisolambda Astrapotheria Guilielmofloweria Family Trigonostylopidae Josepholeidya Trigonostylops Ricardotvdekkeria Family Family Macraucheniidae Albertogaudrya Polymorphis Family Adianthidae Pyrotheria Proectocion Family Pyrotheriidae Notopterna Caroloziuelia Family Indaleciidae now occurs. Thus, the terrestrial mammals of Seymour trees (Vizcaíno et al., 1998). Unfortunately, there is no di- Island probably lived under crepuscular and even exten- rect evidence that the terrestrial vertebrates from the Eo- ded nocturnal conditions during part of the year (i.e. fall cene of Antarctica were adapted to crepuscular or noctur- and winter seasons). Most forest trees, such as some nal conditions. We could speculate that seasonal migra- Nothofagus spp. and araucarians, are evergreen; therefo- tion of mediurn- and large-sized mammals (trigonostylo- re, they would have retained green foliage even during pids and sparnotheriodontids) might have occurred, as it several months of darkness, as is evident in extant taiga does in many modern, large, polar mammals, which mo- floras. Hence, Antarctic ungulates could continue to ve over great distances annually. Nevertheless, by the Eo- browse, stripping off twigs and saplings frorn evergreen cene, the Antarctic Peninsula was separated from the

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Table 6. Taxonomic list for the Mustersan marnrnals from Pata- al. (I 994) pointed out, the striking features ofthese mam- gonia, Argentina. Lista taxonániica de los mamíferos mal s are brachyodoncy and the particular structure of the ntustersenses de Patagonia, Argentina. enameI. Brachyodoncy is associated with browsing her- bivores that are adaptated to forest habitats (Janis, 1984). Sparassodonta Family Borhyaenidae In Patagonia, the latest community dominated by low- Plesiofelis crowned (brachyodont) is the middle Eocene Procladosictis Mustersan fauna. The appearance of hypsodoncy is docu- Polydolopimorphia mented in the late Eocene (Wyss et al., Family Polydolopidae 1994), and the fauna from the presumably coeval Iocali- Polydolops ties of Cañadón Blanco and Lomas Blancas (Reguero, Edentata 1993) in Chubut Province. Hypsodoncy probably is rela- Family Dasypodidae ted to cIimatic changes, the establishment of seasonally Meteutatus Condylarthra drier, more open habitats, and more abrasive diets (Janis, Family Didolodontidae 1984). The numerical dominance of the sparnotheriodon- Xesinodon sp. tids among the ungulates on Seymour Island could reflect Litopterna adaptation of these to high-latitude climates. Family Proterotheriidae Our interpretation of the structure of the La Meseta Heteroglyphis land-vertebrate cornmunity (Vizcaíno et al., 1995a, Polyacrodon 1995b, 1998) is in accordance with presumably analo- Notoungulata gous, present-day environments, such as those at the aus- Family Notostylopidae Otronia tral end of Patagonia (Tierra del Fuego Province). Family Oldfieldthomasiidae Tsamnichoria SUMMARY OF SIGNIFICANCE OF lERRESTRIAL Family Interatheriidae FAUNA OF SEYMOUR ISLAND Guilielmoscottia YNotopíthecus l. The far south was occupied during the Eocene by Family Archaeohyracidae a terrestrial biota composed of plants and vertebrates ha- Pseudhyrax ving at least ternperate climatic adaptations. During a pe- "Eohyrax riod of global cooling, such as the one that occurred du- Family Isotemnidae Distylophorus ring the middle-Iate Eocene, a distinctive, high-Iatitude Periphragnis flora was present on Seyrnour lsland, Antarctica. Striking Rh)1Jodo/l differences in the composition of this flora with respect to Family Notohippidae other paleofIoras of southem distribution are evident. The Puelia Eocene Seymour Island flora was dominated by An- Astrapotheria tarctic taxa, whereas the Eocene Patagonian paleofloras Family Trigonostylopidae were dominated by a mixture of Neotropical and Antarc- Trigonostylops tic taxa (Río Turbio Formation). Family Astrapotheriidae Astraponotus 2. The LMF shares important similarities with the Riochican, Casamayoran, and Mustersan faunas; howe- ver, this does not necessarily indicate an assignment of southernmost part of South America; therefore, it was not this fauna to one ofthese ages. The phylogenetic relation- possible for large mammals to migrate to the distant ships of the Antarctic sparnotheriodontid and polydolopi- north. At present, we cannot resolve whether these mam- ne taxa suggest that they could have been derived from mals (mainly the large ones) occupied the area only sea- Casamayoran taxa, and thus, suggest a younger age for sonally or whether they were permanent residents of the- the La Meseta Formation. se high latitudes. Small marsupials might have survived 3. The numerical dominance of the sparnotheriodon- such a regime by seeking natural shelters (e.g., by burro- tids among the ungulates and the polydolopids among the wing). Extant South American marsupial s have several marsupials in the LMF could have resulted from adapta- adaptations (e.g. incrassated tail, daily torpor andJor hi- tions of these groups to high-latitude paleoenvironments bernation) that may have been present in the Antarctic ta- in cornbination with isolation in Antarctica. xa. 4. In Patagonia, the notoungulates were the most di- The LMF is important paleoecologically because it verse (morphologicaIly as weIl as taxonomicalIy) and documents the coexistence of two ecologicaIly similar, successful South American ungulate group. Four families primitive groups of South American ungulates. are represented in the Itaboraian, seven in the Riochican sparnotheriodontids and trigonostylopids share a nurnber and the Casamayoran, and 10 in the Mustersan of Patago- of dental characteristics that may be adaptations ro nia. Nevertheless, this group is notably absent in the La Antarctic habitats (NolllOfagus forests). As Marenssi el Meseta fauna.

A.P.A. Publicación Especial 5, 1998 196 M.A. REGUERO, S.E VIZCAÍNO, FJ. GOIN, S.A. MARENSSI y S.N. SANTILLANA

5. No species are shared berween Antarctic and Pata- Bond, M., Carlini, A. A., Goin, E J., Legarreta, L., Ortiz Jaure- gonian assemblages in the middle Eocene. Only two ge- guizar, E., Pascual, R. and Uliane, M. A., 1995. Episodes in nera, Polydolops and Trigonostylops, are common taxa South American land marnrnal evolution and sedimenta- between the LMF and the Casamayoran, and Mustersan tion: testing their apparent concurrence in a PaIeocene suc- cession frorn central Patagonia. 6° Congreso de Paleontolo- faunas of Patagonia. This supports differentation of two gia y Bioestratigrafta. Actas: 47-58. Trelew. distinct biogeographic regions. Brea, M., 1998. Análisis de los anillos de crecimiento de leños 6. Arnong marsupials, six species only known from fósiles de coníferas de la Formación La Meseta, isla Sey- the LMF fauna dernonstrate significant endemism. The mour (Mararnbio), Antártida. Asociación Paleontolágia diversity of the tiny Antarctic marsupials is greater than Argentina, Publicación Especial 5. Paleágeno de América those of the Pancasamayoran. del Sur)' de la Peninsula Antártica: 163-175. Buenos Aires. 7. The occurrences of protodidel phids and de- Brea, M. and Zuccol, A. F., 1996. Estructura reproductiva feme- rorhynchines are thought to represent temporal relicts nina de una conífera de la Formación La Meseta, isla Sey- mour, Antártida. Resúmenes Congreso Paleágeno de Amé- and to indicate isolation of this part of Antarctica during rica del SU/; p. 28 Santa Rosa. the early Eocene. Brouwers, E. M., Clemens, W. A., Spicer, R. A., Ager, T. A., 8. The presence of hoofed, mediurn-sized Carter, L. D. and Sliter, W. v., 1987. Dinosaur on the North taxa having low-crowned teeth in peninsular Antarctica Slope, Alaska: High latirude, latest Cretaceous environ- during the Eocene to ?eariy Oligocene suggests a persis- ments. Science, 237: 1608-1610. Washington. tence of archaic forms that lived in Patagonia prior to the Candela, A. and Goin, F. J., 1995. Revisión de las especies an- climatic deterioration in this region. tárticas de marsupiales polidolopinos (Polydolopimorphia, Polydolopidae). 3" Jornadas de Comunicaciones sobre 111- 9. The geological and biological evidence discussed vestigaciones Antárticas, Resúmenes, Buenos Aires. here suggests that peninsular Antarctica was located at a Carlini, A. A., Pascual, R., Reguero, M. A., Scillato Yané, G. J., high latitude during the eariy-middle Eocene, just as it is Tonni, E. P. and Vizcaíno, S. F., 1990. The first Paleogene today. Peninsular Antarctica contained a distinctive te- land placental marnrnal from Antarctica: its paleoclirnaiic rrestrial fauna, the high-Iatitude position of this fauna and paleobiogeographical bearings. 4° International COI1- suggests that climate and isolation were the rnost impor- gtess of Systeniatic and Evolutionary Biology, Abstracts: tant factors affecting the distribution of these mammals. 325. Maryland. Case, J. A., 1988. Paleogene floras from Seymour Island, Antarctic Peninsula. In: Feldmann, R. M. and Woodburne, ACKNOWLEDGEMENTS M. O. (Eds.), Geology and Paleontology of Seymour Island, Antarctic Peninsula. Geological Society of America, Me- We especially acknowledge the Instituto Antártico ntoir 169: 523-530. Boulder, Argentino, which provided logistical support for our par- Case, J. A., 1989. Antarctica: the effect of high latitude heterochro- ticipation (S.A.M., S.N.S., S.F.Y., and M.A.R.) in An- neuy on the origin of the Australian marsupials, In: Crarne, J. tarctic field work. We also have benefited frorn collabo- A. (Ed.), Otigins and Evolution of the Antarctic Biota, Geo!o- rative effort in the field of J. J. Moly (Museo de La Pla- gical Society Special Publication 47: 217-226. Cambridge. ta). We thank M. O. Woodburne and R. L. Cifelli for Case, J. A., Woodburne, M. O. and Chaney, D. S., 1987. A gi- gantic phororhacoid(?) bird frorn Antarctica. Journal of comments on an early version of this manuscript. IIlustra- Paleontology, 61 (6): 1280-1284. Tulsa. tions were rendered by A. Iglesias. Case, J. A., Woodburne, M. O. and Chaney, D. S., 1988. A new genus and species of polydolopid marsupial from the La REFERENCES Meseta Formation, late Eocene, Seymour Island, Antarctic Peninsula. In: Feldmann, R. M. and Woodburne, M. O. Askin, R. A., 1992. 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