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Eocene land mammals from Seymour Island, Antarctica: Palaeobiogeographical implications

February 1994
Antarctic Science 6(01):3 - 15

February 1994
6(01):3 - 15

DOI:10.1017/S0954102094000027

Authors:

Sergio A. Marenssi

National Scientific and Technical Research Council

Marcelo A. Reguero

Universidad Nacional de La Plata

Sergio Nestor Santillana

Instituto Antártico Argentino

Sergio Fabián Vizcaíno

Facultad de Ciencias Naturales y Museo Universidad Nacional de La Plata

Middle Eocene land mammals from La Meseta Formation, Seymour (Marambio) Island are reviewed. A taxonomically diverse fossil land-vertebrate assemblage with small and medium-size mammals has been recovered from four localities. The depositional setting is shallow marine and most of the mammal-bearing beds are in reworked, moderate to high energy subtidal facies. The characteristics of these mammals not only confirm but also strengthen the biogeographical relationships between southern South America (Patagonian Province) and the Antarctic Peninsula during the Paleogene and rule out the possibility of a major barrier between these areas. The Antarctic ungulates (Astrapotheria and ?Litopterna) are plesiomorphics in retaining low crowned cheek teeth and are more similar to those from the Pancasamayoran local faunas of southern South America (Patagonia).

Map showing fossil localities at Seymour Island, Antarctic Peninsula, with the IAA and DPV mammal-bearing localities cited in the text.

…

Stratigraphic section of the La Meseta Formation, Seymour Island showing the mammal-bearing levels and localities.

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Taxonomic list for La Meseta terrestrial mammals, Seymour Island, Antarctica

…

Late Cretaceous ( V 75 Ma) paleogeographic reconstruction of southern continents showing the location of the Paleocene and Eocene units discussed in the text. Compiled from distributional data after Zinsmeister (1982); Woodburne and Zinsmeister (1984); Lawver et al. (1992). Abbreviations: NZ, New Zealand.

…

Taxonomic list for the Riochican mammals (Ernestokokenia faunal zone) from Patagonia, Argentina

…

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Antarctic Peninsula and South America (Patagonia)

Paleogene terrestrial faunas and environments:

biogeographic relationships

Marcelo A. Reguero a;, Sergio A. Marenssi b, Sergio N. Santillana b

aDepartamento Cient|

¤¢co de Paleontolog|

¤a Vertebrados, Museo de La Plata, Paseo del Bosque s/n, 1900 La Plata, Argentina

bInstituto Anta

¤rtico Argentino, Cerrito 1248, Buenos Aires 1010, Argentina

Received 25 January 2001; received in revised form 11 September 2001; accepted 21 September 2001

Abstract

The Eocene of Seymour Island contains the only association of Cenozoic plants and land vertebrates known from

anywhere in Antarctica and lies at about latitude 63‡ south. The late Early to latest Eocene La Meseta Formation fills

an incised valley and comprises sediments representing deltaic, estuarine and very shallow marine environments. The

Paleogene sequence in southern South America (Patagonia) and the Antarctic Peninsula reveals floristically distinct

periods (late Paleocene, early and middle Eocene and latest Eocene), based largely on leaf assemblages. The late

Paleocene Cross Valley flora (Seymour Island) contains ferns and other elements suggesting a much warmer climate

than at this latitude today. The Middle Eocene Fossil Hill (South Shetland Islands) and the R|

¤o Turbio (Santa Cruz

Province, southern Patagonia) floras have a mixture of both Neotropical and Antarctic elements. The La Meseta

paleoflora is distinctive in having a predominance of Antarctic taxa especially Nothofagus, podocarps, and araucarian

conifers in the Eocene deciduous and evergreen forests. This suggests a cooling trend during the Eocene of Antarctica

with mid- to late Eocene seasonal, cool-temperate, rainy climates and latitudinal and altitudinal gradients. The

Seymour Island La Meseta Fauna (Cucullaea Allomember, middle Eocene) contains at least 10 mammal taxa,

predominantly tiny marsupials (mostly endemic and new taxa). The endemism of these marsupials suggests the

existence of some form of isolating barrier (climatic and/or geographic) during the Eocene. Faunal similarity between

the La Meseta Fauna and the fauna assigned to the Riochican (late Paleocene) South American Land Mammal Age

of Patagonia strongly suggests that the former derived from the latter. The occurrence on Seymour Island of

sudamericids, that had become extinct in South America in the Paleocene, also indicates that isolation may have

allowed extended survival of this Gondwanan group in the Eocene of Antarctica and the factors that caused their

extinction did not affect this continent. Global warming and intercontinental dispersal have been major influences on

the timing and magnitude of terrestrial biotic change in the late Paleocene and early Eocene epochs. The faunistic

evidence indicates that the La Meseta mammalian fauna derived from late Paleocene/early Eocene Riochican/Vacan

PII: S0031-0182(01)00417-5

Abbreviations: DPV, Departamento Cient|

¤¢co de Paleontolog|

¤a Vertebrados, Museo de La Plata; IAA, Instituto Anta

¤rtico

Argentino, Buenos Aires; RV, University of California at Riverside, CA; SALMA, South American Land Mammal Age; LMF,

La Meseta Fauna

* Corresponding author. Fax: +54-21-425-7527.

E-mail addresses: regui@museo.fcnym.unlp.edu.ar (M.A. Reguero), smarenssi@dna.gov.ar (S.A. Marenssi),

ssantillana@dna.gov.ar (S.N. Santillana).

PALAEO 2776 14-5-02

Palaeogeography, Palaeoclimatology, Palaeoecology 179 (2002) 189^210

www.elsevier.com/locate/palaeo

faunas. The dispersal and vicariance events may have occurred during the onset of the climatic optimum of the

Cenozoic (late Paleocene^early Eocene) when major regressive events are recorded either in the northern Antarctic

Peninsula and southernmost Patagonia (between 58.5 and 56.5 Ma). The absence of notoungulates in the La Meseta

fauna is noteworthy. We speculate that the notoungulates could have passed into Antarctica during the latest part of

the Paleocene when the environmental conditions were warmer, and then became extinct at the onset of the climatic

Keywords: Cenozoic ; Eocene ; fauna ; £ora; Antarctica; Patagonia ; biogeography

1. Introduction

Reconstructing the sequence of terrestrial eco-

systems through time is frequently frustrated

mainly by the inadequacies of the fossil record.

Seymour (Marambio) Island (Fig. 1) contains

the only Cenozoic land vertebrate fauna known

in Antarctica, except for the avian tracks from

King George Island (Covacevich and Rich,

1982), and represents the southernmost part of

the distribution of some Paleogene South Ameri-

can land mammal lineages. The recovery of a

moderately varied, medial Eocene land vertebrate

fauna from the northern portion of the island re-

kindled interest in this area after the discovery of

the ¢rst land mammal in Antarctica (Woodburne

and Zinsmeister, 1982, 1984). This was especially

important because paleogeographic reconstruc-

tions (based on paleomagnetic data collected on

the continent itself) of the Antarctic Peninsula

during the Eocene indicate a paleolatitude as far

south as perhaps 63‡ (Lawver et al., 1992) (Fig. 2).

Concerted e¡orts between 1988 and 1996 resulted

in the discovery of terrestrial vertebrates and

plants from several di¡erent stratigraphic levels

(10 localities from four di¡erent stratigraphic ho-

rizons) within the Cross Valley and La Meseta

formations (Fig. 2); these range from upper Pa-

leocene to upper Eocene (Marenssi et al., 1994;

Dingle et al., 1998). This biota contains more than

30 taxa of terrestrial plants and vertebrates. Sur-

face prospecting and dry sieving of the sediment

during 5 yr of careful ¢eldwork recovered land

vertebrates at di¡erent localities and horizons.

Among these vertebrates, the mammals suggest

close biogeographic links with Paleogene faunas

of Patagonia (Bond et al., 1993; Marenssi et al.,

1994; Reguero et al., 1998 ; Goin et al., 2000).

The La Meseta Fauna (here termed LMF) from

the Cucullaea I Allomember of the La Meseta

Formation (Fig. 2) is unusual in being dominated

by large sparnotheriodontid ungulates and small

polydolopine marsupials (Reguero et al., 1998).

This is not the case in the Paleogene fossil record

of Patagonia. The high proportion of endemic

taxa (mainly tiny marsupials) within the Antarctic

fauna, together with relicts such as prepidolopid

and derorhynchid marsupials, gives it a very dis-

tinctive southern appearance, indicating that some

form of isolating barrier ^ climatic, geographic or

topographic ^ existed prior to the deposition of

the mammal-bearing horizon. Several types of en-

vironmental factors could result from the high

latitude, of which temperature may be the most

important. The relatively low temperatures of the

Antarctic regions during the early Paleocene and

again in the late Eocene (Dingle and Lavelle,

1998a,b; Dingle et al., 1998) (Fig. 4) seem to

have been matched by the development of a char-

acteristic biota (Marenssi et al., 1994).

In this paper we present paleo£oristic and faun-

istic data supporting the existence of a high-lati-

tude and -altitude land biota with di¡erences from

the contemporaneous faunas of Patagonia. The

latest possible time for mammal dispersal into

Antarctica is also suggested.

2. Paleogene Antarctic Peninsula

paleoenvironments: sources of evidence

2.1. Sedimentology

The Antarctic continent now consists of two

major parts: East Antarctica, a large stable block

that has existed relatively intact for hundreds of

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millions of years, and West Antarctica, an assem-

blage of smaller blocks that have been moving

relative to one another and to East Antarctica

during the last 230 Myr: Marie Byrd Land, Thur-

ston Island, Ellsworth-Whitmore Mountains, and

the Antarctic Peninsula

The Antarctic Peninsula is predominantly an

ensialic Mesozoic^Cenozoic magmatic arc related

to subduction of the proto-Paci¢c and Paci¢c

Ocean £oors (Pankhurst, 1982; Storey and Gar-

rett, 1985). The Transantarctic Mountains, which

separate the West Antarctic rift system from the

stable shield of East Antarctica, are the largest

mountains developed adjacent to the rift (3500

km long and 4500 m high).

The James Ross Basin (Del Valle et al., 1992) is

located in the Weddell Sea, adjacent to the north-

ern part of the Antarctic Peninsula. Paleogene

beds of the James Ross Basin are exclusively ma-

rine and are only exposed on Seymour and the

nearby Cockburn Islands (Fig. 1). They are com-

prised of shallow marine shelf deposits of the

uppermost Lo

¤pez de Bertodano and Sobral For-

mations (early Paleocene) and the incised valley

systems of the Cross Valley (late Paleocene) and

La Meseta (late Early to late Eocene) formations.

Main regressive periods are documented by the

unconformities at the base of the Cross Valley

and La Meseta Formations. They may be eustatic

or tectonic in origin, or a combination of the two

(Sadler, 1988; Marenssi, 1995 ; Marenssi et al.,

1998b).

The stratigraphic position of the land mammal

bearing localities are shown in Fig. 2. Herein we

follow the stratigraphic terminology used by Mar-

enssi et al. (1998b).

The La Meseta Formation (Elliot and Traut-

man, 1982; Marenssi et al., 1998b) ¢lls an incised

valley and is comprised of deltaic, estuarine, and

shallow marine deposits containing both marine

and terrestrial fossils (Marenssi, 1995; Marenssi

et al., 1998a). Paleoenvironmental reconstructions

indicate that the La Meseta Formation accumu-

lated at the seaward end of an incised valley dur-

ing an overall rise in sea level (Marenssi, 1995 ;

Marenssi et al., 1998a). Recent studies of the geo-

metric relationships in the La Meseta Formation

Fig. 1. Map showing fossil localities at Seymour Island, Ant-

arctic Peninsula, with the IAA and DPV mammal-bearing lo-

calities cited in the text.

Fig. 2. Stratigraphic section of the La Meseta Formation,

Seymour Island showing the mammal-bearing levels and lo-

calities.

PALAEO 2776 14-5-02

M.A. Reguero et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 179 (2002) 189^210 191

(Sadler, 1988; Marenssi, 1995 ; Marenssi et al.,

1998b) show that the steep erosional boundaries

are the margins of a large channel some 7 km in

width that originated farther west. The head of

the La Meseta incised valley was placed almost

60 km to the northwest, at the toe of the Antarc-

tic Peninsula (Stilwell and Zinsmeister, 1992).

Sedimentary environments such as tidal chan-

nels and £ats, an estuary mouth platform, and a

mid-estuary (Marenssi, 1995; Marenssi et al.,

1998a) formed a coastal area of low relief. In

contrast, far inland to the west, the Antarctic Pen-

insula was a highland, mountainous area charac-

terized by volcanoes sporadically active since the

Mesozoic.

Although paleogeographical interpretations in-

dicate that terrestrial facies had to be present

nearby to the west, they are not yet known from

Seymour Island; hence, all terrestrial fossils re-

ported to date were transported into marine set-

tings.

Land-derived fossils were concentrated in para-

lic and shallow marine environments after some

transport. However, the presence of leaves, tree

trunks, and a £ower suggest a nearby forested

terrain (Gandolfo et al., 1998a,b ; Torres et al.,

1994; Doktor et al., 1996).

Provenance studies on sandstones of the La

Meseta Formation demonstrate that the sedi-

ments came from the west^northwest, the source

rocks being those cropping out on the Antarctic

Peninsula (Marenssi, 1995; Marenssi et al., 1999 ;

Net and Marenssi, 1999). Additionally, paleocur-

rent measurements con¢rm the location of the

source area (Marenssi, 1995). Therefore, the

source area of the sediments, leaves and trunks

was the northern Antarctic Peninsula, a magmatic

arc that underwent uplift during the Cretaceous

and Cenozoic (Elliot, 1988). This cordillera sup-

ported forests in a range of habitats from coastal

to alpine. Seymour Island lies on the eastern

(back-arc) margin of the Antarctic Peninsula.

Leaves are associated with marine mollusks,

and tree trunks frequently are densely bored by

Teredolites, indicating extended submersion in the

water^sediment interface before burial. Also,

teeth and bones of land vertebrates are associated

with an abundant marine macrofauna. Conse-

quently, they are always recovered from a thana-

tocenosis (Marenssi, 1995), along with an abun-

dant marine fauna.

Geochemistry and clay mineralogy of sedimen-

tary rocks from Seymour Island were used to in-

terpret the climatic evolution of the northern Ant-

arctic Peninsula area since the Late Cretaceous

(Dingle and Lavelle, 1998a,b). A cool period is

indicated during the early Paleocene before the

climatic optimum of the Cenozoic (late Paleo-

cene^early Eocene) followed by a climatic deteri-

oration from very warm, non-seasonally wet con-

ditions (early middle Eocene) to a latest Eocene

cold, frost-prone and relatively dry stage (Dingle

et al., 1998).

In the marine realm, a cool-temperate sea was

proposed to exist based on the Paleogene inverte-

brate fauna (Zinsmeister, 1982). Meanwhile, sta-

ble isotope studies carried out on molluscan mac-

rofossils from the La Meseta Formation suggest a

cooling trend during the Eocene, with water tem-

peratures between 7.9 and 11.7‡C (Gazdzicki et

al., 1992; Ditch¢eld et al., 1994).

2.2. Plant fossils

Eocene £oras at di¡erent sites of the Antarctic

Peninsula (King George and Seymour islands)

suggest the presence of densely forested habitats

that were widely developed along the Peninsula at

that time (Case, 1988; Gandolfo et al., 1998a,b)

(Fig. 3).

On the Paci¢c side of the Antarctic Peninsula,

Haomin (1994) described a mixture of Antarctic

and Neotropical £oral elements in the Fossil Hill

Formation (King George Island ; Fig. 3), suggest-

ing mean temperatures between 10 and 14‡C for

the early^middle Eocene of the South Shetland

Islands.

The plant megafossils recovered from three Pa-

leogene localities on Seymour Island suggest that

the terrestrial environments changed drastically

from late Paleocene through late Eocene. The

late Paleocene £ora recovered from the Cross Val-

ley Formation (Gothan, 1908 ; Duse

¤n, 1908) has

been interpreted to represent a paratropical forest

growing in a warm, rainy climate (Gandolfo et al.,

1998a). Askin (1992, 1997) reported that the Late

PALAEO 2776 14-5-02

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Cretaceous and Paleocene plant communities

were dominated by conifer rainforest in the area

of Seymour Island.

The La Meseta Formation (late-early Eocene^

late Eocene) has yielded fossil plant material from

most of its stratigraphic column (Duse

¤n, 1908;

Cranwell, 1959; Askin and Fleming, 1982; Case,

1988; Torres et al., 1994; Brea, 1996; Brea and

Zuccol, 1996; Doktor et al., 1996; Askin, 1995,

1997; Gandolfo et al., 1998a,b). Mega£ora has

been collected from all but the lowest 120 m

(Case, 1988; Doktor et al., 1996; Gandolfo et

al., 1998a). The £ower (Gandolfo et al., 1998b),

some tree trunks (Torres et al., 1994 ; Brea, 1998),

and most of the leaves (Gandolfo et al., 1998a)

are preserved in ¢ne-grained heterolithic facies of

tidal origin, especially from the middle part of the

formation (middle Eocene). Some other tree

trunks and a few leaves come from coarse-grained

channel lags of the underlying late early Eocene

Acantilados and medial Eocene Campamento al-

lomembers. Carbonaceous detritus, spores, and

pollen are frequent throughout the ¢ne-grained

facies.

The late-early Eocene £ora of locality Univer-

sity of California at Riverside, CA, USA (RV)-

8425 (Acantilados Allomember) is dominated by a

large-leafed species of Nothofagus suggesting ‘‘Ta

Fig. 3. Late Cretaceous (V75 Ma) paleogeographic reconstruction of southern continents showing the location of the Paleocene

and Eocene units discussed in the text. Compiled from distributional data after Zinsmeister (1982); Woodburne and Zinsmeister

(1984); Lawver et al. (1992). Abbreviations: NZ, New Zealand.

PALAEO 2776 14-5-02

M.A. Reguero et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 179 (2002) 189^210 193

situation of ameliorating climatic conditionsT’’

(Case, 1988: 525). This paleo£ora also contains

two species of ferns. Doktor et al. (1996) also

described a late-early Eocene paleo£ora from the

La Meseta Formation. Podocarpaceous (Dacry-

carpus? tertiarius), Araucariaceae (Araucaria na-

thorsti), Nothofagaceae (Nothofagus sp.), Protea-

ceae (Knightiophyllum andreae), among others

leaves, were found at National Academy of Sci-

ence, Warsaw, Poland, ZPAL 9 locality (Fig. 2).

Case (1988) described the ¢rst mega£ora from

the La Meseta Formation, indicating a dominance

of the genus Nothofagus. Gandolfo et al.

(1998a,b) recognized this genus and reported the

presence of the families Dilleniaceae, Myricaceae,

Myrtaceae, Lauraceae, and Grossulariaceae, as

well. All but Lauraceae belong to the Antarctic

£ora of Romero (1986). Based on morphological

characters of 88 specimens collected from three

localities in the middle part of the La Meseta

Formation (Cucullaea I Allomember), Gandolfo

et al. (1998a) described the forests as mixed mes-

ophytic, indicating a seasonal cool-temperate

rainy climate. More than 300 samples represent-

ing fossil foliage referred to Tetracera patagonica

(Dilleniaceae), Hydrangeiphyllum a⁄ne (Hydran-

geaceae), and the families Nothofagaceae, Betula-

ceae, Myrtaceae, Myricaceae, Lauraceae, and

Grossulariaceae were recovered at locality Depar-

tamento Cient|

¤¢co de Paleontolog|

¤a Vertebrados,

Museo de La Plata (DPV) 3/84 (Gandolfo et al.,

1998a,b). Based on this £ora, the annual mean

paleotemperature was calculated to be 11^13‡C,

whereas the mean of the coldest month might

vary between 33 and 2‡C. The paleo£ora also

suggests that spring and summer were rainy, and

that the freezing season might last several months.

These data agree with the general climatic deteri-

oration that occurred in the rest of Antarctica at

the end of the Eocene (Dingle and Lavelle,

1998a,b; Dingle et al., 1998).

Gothan (1908), Torres et al. (1994), and Brea

(1996, 1998) studied fossil wood from the La Me-

seta Formation. Several coniferous and dicotyled-

onous (Nothofagus) woods were identi¢ed from

the middle part (Cucullaea I Allomember) of

this unit (Torres et al., 1994), dated as middle

Eocene (Marenssi et al., 1994). They have narrow,

but regularly spaced and well-marked growth

rings, typical of slow-growing trees with vegeta-

tive periods corresponding to seasonal climate

changes. Torres et al. (1994) described a total of

six taxa of fossil woods having a⁄nities with ex-

tant trees that grow in cold-temperate rainforest

areas of southern South America (the Valdivian

and Magellanic forests). Well-de¢ned growth

Fig. 4. Temperature and sea level at high southern latitudes during the Cenozoic. The temperature curve is for surface waters.

Time scale is according to Berggren et al. (1995). Sea-level pattern is after Haq et al. (1987).

PALAEO 2776 14-5-02

M.A. Reguero et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 179 (2002) 189^210194

rings within fossil wood samples from Seymour

Island indicate that this climate was markedly sea-

sonal.

Temperate to cool-temperate evergreen conifer/

broad-leaf forest exists today in southern South

America (between 37 and 55‡S). Rainfall in this

area is very high, mainly in summer and spring

seasons, with an average precipitation from 1000^

3000 mm/yr and freezing temperatures can prevail

during several months of the year. These forests

currently contain the richest biota of the sub-Ant-

arctic dominion.

In recent years, a growing body of information

has been accumulated about the Paleogene cli-

mate of the Antarctic Peninsula (see Dingle and

Lavelle, 1998b) (Fig. 4). Paleo£oral data sets

show that the middle^late Eocene was warmer

than present, but not as warm as the late Paleo-

cene (Cross Valley Formation) through early Eo-

cene (Acantilados Allomember, La Meseta For-

mation). Paleo£ora from the middle part of the

La Meseta Formation (RV-8200, Instituto Anta

¤r-

tico Argentino, Buenos Aires IAA 1/90, and DPV

3/84 = C/88, from Cucullaea I Allomember) indi-

cate a drop in temperature (Case, 1988 ; Gandolfo

et al., 1998a) with respect to lower levels of the

sequence.

Nothofagus is considered to be of critical im-

portance as an indicator of paleoclimate. Notho-

fagus is the predominant angiosperm taxon in

each of the three paleo£oras from the La Meseta

Formation mentioned above. Gandolfo et al.

(1998a) reported Nothofagus serrulata and two in-

determinate species of the same genus from the

late-early Eocene Acantilados Allomember (A/

88). The former species is now restricted to south-

ern South America, where it grows in a cool-tem-

perate climate. N. serrulata extends from southern

Chile (Carmen Silva, Loreto, and Brush Lake

Formations) and Argentina (R|

¤o Turbio, R|

¤o

Guillermo, and N

irihuau formations) to the

southern shores of Tierra del Fuego Province

(Cullen Formation), and thus represents a closer

geographical approach to Antarctica than is

achieved by other South American species (Fig. 3).

Romero (1986), based on a morphological anal-

ysis, determined the climate and phytogeography

of the Paleogene £oras of Patagonia. This author

stated that, during the Paleocene and early Eo-

cene, Patagonia’s forests were wet and paratrop-

ical, with mean temperatures between 20 and

25‡C, but in the middle Eocene (R|

¤o Turbio For-

mation) the forests were subtropical with a mix-

ture of Neotropical and Antarctic elements (‘Pa-

Table 1

Taxonomic list (families), stratigraphy, and references for the land vertebrates from the Eocene of Seymour Island, Antarctic Pen-

insula

Taxa Stratigraphy References

Marsupialia

Polydolopidae A. Cucullaea I Woodburne and Zinsmeister, 1984; Case et al., 1988; Goin et

al., 1995; Goin and Carlini, 1995; Goin et al., 1999

Microbiotheriidae A. Cucullaea I Goin et al., 1999

Derorhynchidae A. Cucullaea I Goin et al., 1999

Prepidolopidae A. Cucullaea I Goin et al., 1999

Gondwanatheria

Sudamericidae A. Cucullaea I This paper

Xenarthra

Tardigrada indet A. Cucullaea I Marenssi et al., 1994; Vizca|

¤no and Scillato Yane

¤, 1995

?Litopterna

Sparnotheriodontidae A.Cucullaea I and A. Submeseta Bond et al., 1990; Marenssi et al., 1994; Vizca|

¤no et al., 1997

Astrapotheria

Trigonostylopidae A. Cucullaea I Bond et al., 1990; Hooker, 1992 ; Marenssi et al., 1994

Ratitae A. Submeseta Tambussi et al., 1994

?Phorusrhacoid A. Submeseta Case et al., 1987

Falconidae A. Cucullaea I Tambussi et al., 1995

A. stands for Allomember

PALAEO 2776 14-5-02

M.A. Reguero et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 179 (2002) 189^210 195

leo£ora Mixta’). At the same time, the La Meseta

paleo£ora had a predominance of Antarctic ele-

ments, suggesting a colder climate and a latitudi-

nal gradient with respect to the paleo£ora of the

¤o Turbio Formation (51‡35PS, 72‡10PW, Santa

Cruz Province, Argentina). During the Eocene

gramineous phytoliths became more abundant

(Spalletti and Mazzoni, 1978), suggesting that

grassland environments began to be prominent

in middle latitudes (ca. 45‡S). The absence of

crocodiles and boid snakes after the Casamayoran

South American Land Mammal Age (SALMA)

suggests a climatic deterioration at that time in

Patagonia.

2.3. Mammal fossils

The known diversity of one of the mammal-

bearing horizons of the La Meseta Formation

(IAA 1/90) can be taken to represent essentially

a single fauna (Vizca|

¤no et al., 1998). There are 13

reported terrestrial vertebrate taxa, 11 of which

occur in a single level within the Cucullaea IAl-

lomember (IAA 1/90). A taxonomic analysis of

the LMF (Table 1) reveals a modest taxonomic

diversity that includes three avian and seven

mammalian ordinal groups (Table 2). This Eocene

mammalian assemblage was probably even more

diverse, because the documented diversity of the

La Meseta Formation’s mammals is, of course,

minimal, being derived from a few sites (Fig. 2)

and from small samples (less than 60 specimens).

Among the terrestrial mammals, the Sparno-

theriodontidae, an extinct South American ungu-

late group and the marsupial family Polydolopi-

dae were the dominant taxa. They were not

usually dominant elements in the much larger Pa-

leogene associations elsewhere in South America

(Reguero et al., 1998). The most abundant group

in the fauna is a suite of ‘opposum-like’ marsu-

pials (Goin et al., 1999).

The ungulates are represented by only two taxa

(one unnamed genus) in the LMF. The Antarctic

sparnotheriodontid (Fig. 5), previously referred to

Victorlemoinea (=Sparnotheriodon) (Bond et al.,

1990), is endemic at the generic level, and has

close a⁄nity with an undescribed new species

from Patagonia (Goin et al., 2000). Victorlemoi-

nea labyrinthica is a species relatively common in

the Riochican and the early Casamayoran (Vacan

‘subage’ sensu Cifelli, 1985) faunas. The oldest

known representative of the Sparnotheriodontidae

(Victorlemoinea prototypica) is from the medial

Table 2

Taxonomic list for La Meseta terrestrial mammals, Seymour

Island, Antarctica

Polydolopimorphia

Family Prepidolopidae

Perrodelphys coquinense

Family Polydolopidae

Polydolops dailyi

Polydolops seymouriensis

Polydolops sp. nov.

Didelphimorphia

Family Derorhynchidae

Derorhynchus minutus

Pauladelphys juanjoi

Xenostylus peninsularis

Microbiotheria

Family Microbiotheriidae

Marambiotherium glacialis

?Marsupialia

Family indet

Gondwanatheria

Family Sudamericidae

Gen. et sp. indet

Fig. 5. (A) Reconstruction of the environment and vertebrate assemblage from the middle-late Eocene of Antarctic Peninsula

based on the paleontologic evidence from La Meseta Formation (Cucullaea I Allomember), Seymour Island. Mammals depicted

here were analyzed during this study. In this reconstruction we are exercised a degree of artistic license to assemble these species

together. (B) Linear sketch showing the silhouettes of the following vertebrates, invertebrates, and plants: 1 : Sparnotheriodonti-

dae gen. et sp. nov., 2: Anthropornis nordenskjoeldi (penguin), 3 : Delphinornis larseni (penguin), 4 : Gondwanathere sudamericid,

5: Polydolops daily,6:Lyreidus antarcticus (crab), 7 : Cucullaea (bivalve), 8 : Eutrephoceras (nautiloid), 9: Ratitae bird, 10: Trigo-

nostylops sp., 11: Marambiotherium glacialis, 12: Sloth, 13: Polyborinae indet (falconid bird), 14: Araucaria, and 15 : Nothofagus

(Southern beech).

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Paleocene (Itaboraian SALMA) of Brazil, where-

as the youngest record in Patagonia is from the

Vacan ‘subage’ (late Paleocene^early Eocene ?).

The Antarctic edentate (Fig. 5) represents the

earliest unquestionable record of Pilosa in the

world (Vizca|

¤no and Scillato Yane

¤, 1995), and

shares plesiomorphic features with the most prim-

itive representative of the group, both Tardigrada

and Vermilingua. The earliest records of Tardi-

grada in South America come from the Deseadan

(middle Oligocene) of Patagonia and Bolivia

(Ho¡stetter, 1982; Engelmann, 1987). The oldest

South American vermilinguan was recovered from

the Miocene Colhuehuapian beds (Carlini et al.,

1992) of Patagonia.

The Antarctic sudamericid (Fig. 5) represents

the youngest record of the group and is very

closely related to Sudamerica ameghinoi from the

Paleocene of Punta Peligro in Patagonia, but is

more derived than the latter in the microstructure

of the enamel (Goin, personal communication,

2000). The Gondwanatheria is a peculiar mammal

order with a widespread Gondwanan distribution

in the Late Cretaceous of Patagonia (Bonaparte,

1986), Madagascar, and India (Krause et al.,

1998) and in the early Paleocene of Patagonia

(Scillato Yane

¤and Pascual, 1984). These mam-

mals bear gliriform incisors, and were the earliest

South American mammals to develop hypsodont

cheek teeth with thick cementum.

3. Discussion and conclusions

3.1. Comparison of LMF with Patagonian faunas

The LMF fauna shows greatest faunal resem-

blance with older Paleogene faunas of Patagonia

(Riochican SALMA and Vacan ‘subage’). The

oldest faunas of the Paleogene of Patagonia range

between (from the oldest to the youngest): early

Paleocene Peligran, medial Paleocene ‘Carodnia

faunal zone’ and ‘Kibenikhoria faunal zone’, late

Paleocene Riochican, and the late Paleocene^early

Eocene Vacan. These faunas in Patagonia are

mainly known from the Golfo de San Jorge Ba-

sin, Chubut Province at V45‡S (Fig. 6). A sum-

mary of the biostratigraphic, biochronologic and

faunistic data of these Patagonian faunas is pro-

vided below.

The Peligran SALMA (‘Banco Negro Inferior’,

Salamanca Formation, Hansen Member, Tiupam-

pian sensu Bond et al., 1995) (V61 Ma, Fig. 6) at

Punta Peligro, Chubut, contains only six mammal

taxa. Sudamericid gondwanatheres and derorhyn-

chid marsupials are known from these levels.

Simpson’s ‘Carodnia faunal zone’ (V57 Ma,

Fig. 6) is poorly represented and studied, and in-

cludes a ?borhyaenid indet, the polydolopid Seu-

madia yapa, the proterotheriid litoptern Wainka

tshotse, and the pyrothere Carodnia feruglioi.

Taxa from this horizon are apparently restricted

to the Pen‹as Coloradas Formation in the San

Jorge Basin (see Fig. 6), and they appear to rep-

resent a new biochronologic unit but present evi-

dence is meager and is not su⁄cient to warrant

erecting a new SALMA (Bond et al., 1995).

Simpson’s ‘Kibenikhoria faunal zone’ (V58.0

Ma, Itaboraian SALMA sensu; Bond et al.,

1995; Fig. 6) includes two polydolopines, Epido-

lops and ?Polydolops; a primitive ?didelphoid,

Derorhynchus; several protodidelphid marsupials,

and seven families placed in four orders of ungu-

lates. Trigonostylopidae are represented by a

primitive genus (Shecenia). Four families of No-

toungulata are recorded in this age.

The Riochican SALMA ( = ‘Ernestokokenia

faunal zone’ Simpson, 1935; V55.5 to V57.0

Ma; Table 3; and Fig. 6) records three families

of marsupials, the Polydolopidae being one of

them. Seven families of Notoungulata are re-

corded in this age. Sparnotheriodontidae are rep-

resented by the genus Victorlemoinea. The avail-

able record shows that this fauna underwent

Fig. 6. Paleocene time scale according Berggren et al. (1995), including early^middle Eocene epoch, showing chronology of South

American and Antarctic land biotas based on collective data and correlations made by Bond et al. (1995) and Marshall et al.

(1997) and discussions in text. Vertical black bars represent timing of fossil accumulation. Abbreviations: BNS, Banco Negro

Superior; BNI, Banco Negro Inferior. Sea-level pattern is after Haq et al. (1987).

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notable taxonomic reorganization beginning at

V58 Ma (Marshall et al., 1997). This fauna

shares four families (Polydolopidae, Prepidolopi-

dae, Sparnotheriodontidae, and Trigonostylopi-

dae) and two genera (Polydolops and Trigonosty-

lops) with the LMF. During the Riochican the

notoungulates became predominant, representing

44% of the taxonomic composition of the fauna

(Pascual et al., 1996).

The Vacan fauna (early Casamayoran, Table 4;

and Fig. 6) at Can‹ado

¤n Vaca, Chubut (Sarmiento

Formation) comprises archaic notoungulate fam-

ilies (Henricosborniidae, Isotemnidae), and the

relative primitiveness of this fauna document a

great faunal di¡erence from the subsequent Bar-

rancan ‘subage’ (Cifelli, 1985).

Concerning age, the Riochican contains species

which have been considered to be typically Vacan,

and several genera are shared (Victorlemoinea,As-

mithwoodwardia), suggesting that there is almost

no time between the latest Riochican (at Bajo

Palangana, Chubut) and the Vacan (at Can‹ado

¤n

Vaca, Chubut) faunas. Based on this evidence

Marshall et al. (1997) estimated the age of the

Riochican/Vacan boundary at V55.5 Ma (Fig.

6). So, the Vacan ‘subage’ possibly represents

part of the early Eocene. Available K/Ar data

from a new Vacan locality near Paso del Sapo,

in the west of Chubut Province, from levels

(ignimbrites) below and above the vertebrate-

bearing horizon shows a great temporal range

(V56 and V43 Ma) that spans the late Paleocene

and middle Eocene (Goin et al., 2000). On the

other hand, the Casamayoran SALMA (that in-

cludes Vacan and Barrancan ‘subages’) conven-

tionally was regarded as representing early Eocene

(55^50 Ma), but recently Kay et al. (1999), on the

basis of isotopic age determinations (Ar/Ar), re-

dated the younger Barrancan ‘subage’ at Gran

Barranca, Chubut, as late Eocene (V36 Ma.).

The Riochican and Vacan faunas (Tables 3 and

4, respectively) are characterized by the dominant

presence of browser types including extremely

low-crowned ungulates (83%) in several primitive

lineages such as henricosborniids (Notioprogonia)

and isotemnids (Toxodonta), although a few mes-

odont types (8%) occur in the Riochican (Pascual

and Ortiz Jaureguizar, 1990). This fact supports

Table 3

Taxonomic list for the Riochican mammals (Ernestokokenia

faunal zone) from Patagonia, Argentina

Polydolopimorphia

Family Polydolopidae

Polydolops

Family Prepidolopidae

a¡. Prepidolops

?Polydolopimorphia

Family incertae sedis

Palangania brandmayri

Sparassodonta

Family Borhyaenidae

?Nemolestes

Edentata

Family Dasypodidae

Gen. et sp. indet.

Condylarthra

Family Didolodontidae

Enneoconus

Ernestokokenia

Notoungulata

Family Henricosborniidae

Henricosbornia

?Othnielmarshia

Family Isotemnidae

Isotemnus

?Pleurostylodon

Family Interatheriidae

Notopithecus

Family Old¢eldthomasiidae

Old¢eldthomasia

Maxschlosseria

Family Notostylopidae

Notostylops

Family Archaeopithecidae

Archaeopithecus

Family Archaeohyracidae

Eohyrax

Gen. et sp. nov.

Notoungulata incertae sedis

Family indet

Brandmayria

Litopterna

Family Proterotheriidae

Ricardolyddekeria

Anisolambda

?Litopterna

Family Sparnotheriodontidae

Victorlemoinea

Astrapotheria

Family Trigonostylopidae

Trigonostylops

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the association of these mammals with warm and

humid forested habitats in the late Paleocene.

Frenguelli and Parodi (1941) reported the pres-

ence of Bambusoideae, the most primitive tribe

of Gramineae in the late Paleocene of Patagonia.

The paleo£oral record suggests that tropical to

subtropical coastal mangrove environments alter-

nated with inland sylvan and sclerophyllous forest

or savannas (Petriella and Archangelski, 1975).

3.2. Age of the La Meseta terrestrial

vertebrate-bearing horizons (Cucullaea I and

Submeseta allomembers)

Although the overall age of the La Meseta For-

mation may span much of the Eocene, the age of

the vertebrate-bearing horizons (Cucullaea I and

Submeseta allomembers) described here can be

more tightly constrained. The terrestrial verte-

brates recovered from the Cucullaea I Allomem-

ber, though numerically small, strongly suggest a

middle Eocene age (Bartonian, V37 to V41 Ma,

Woodburne and Case, 1996) or middle Eocene

(Goin et al., 1999). This temporal assignment is

consistent with the middle Eocene age assigned to

the ichthyofauna found in the same depositional

horizon (Cione and Reguero, 1994, 1998). Age

data from dino£agellates from the underlying lev-

els (Acantilados Allomember) are consistent with

a late-early Eocene age (Coccozza and Clarke,

1992). For our study, one biogenic carbonate

sample was collected from shells of Ostrea antarc-

tica from the lower part of the Acantilados Allo-

member (see Fig. 2). This sample with an 87 Sr/86Sr

ratio of 0.707709 yielded an age between 52.4 and

54.3 Ma. It yields an age consistent with its strati-

graphic position and associated fauna. Sr isotope

dating from the top of the La Meseta Formation

(Submeseta Allomember) yields an age of V34.2

Ma (Dingle and Lavelle, 1998a,b) and also is con-

sistent with the stratigraphy (see Fig. 2) and the

fauna. Based on this temporal determination, the

age of the LMF falls in the gap recognized be-

tween the Vacan and Barrancan ‘subages’ (Fig. 7).

Therefore, the LMF would partly ¢ll this consid-

erable temporal gap in the Eocene record of the

mammalian evolution in South America (con-

verted after Howarth and McArthur, 1997).

The new age assignment for the Barrancan (late

Casamayoran) in Patagonia (Kay et al., 1999) and

the re¢ned ages for the Paleocene faunas in the

San Jorge basin (Bond et al., 1995; Marshall et

al., 1997) seem to be more consistent with the

observed taxonomic similarities and di¡erences

between the land mammal fauna from Seymour

Island and those from the Paleocene and Eocene

of Patagonia. In summary, reassessment of the

age of the taxa from the middle levels of the La

Table 4

Taxonomic list for the Vacan (early Casamayoran) mammals

from Patagonia, Argentina

Didelphimorphia Notopterna

Family Didelphidae Family Indaleciidae

Coona Adiantoides

Microbiotheria Family Amilnedwarsidae

Family Microbiotheriidae Amilnedwardsia

Eomicrobiotherium Rutimeyeria

Sparassodonta Ernestohaeckelia

Family Proborhyaenidae Notoungulata

Arminiheringia Family Henricosborniidae

Polydolopimorphia Henricosbornia

Family Polydolopidae Othnielmarshia

Amphidolops Peripantostylops

Polydolops Family Notostylopidae

Edentata Eduardotrouessartia

Family Dasypodidae Homalostylops

Astegotherium Notostylops

Meteutatus Family Old¢eldthomasiidae

Prostegotherium Maxschlosseria

Utaetus Family Archaeopithecidae

Family Pampatheriidae Acropithecus

Machlydotherium Archaeopithecus

Condylarthra Family Isotemnidae

Family Didolodontidae Anisotemnus

Enneoconus Isotemnus

Ernestokokenia Pleurostylodon

Paulogervaisia Family Notohippidae

Litopterna Plexotemnus

Family Protolipternidae Astrapotheria

Asmithwoodwardia Family Trigonostylopidae

Family Proterotheriidae Trigonostylops

Anisolambda Family Astrapotheriidae

Guilielmo£oweria Albertogaudrya

Ricardolydekkeria Pyrotheria

Family Macraucheniidae Family Pyrotheriidae

Polymorphis Carolozittelia

Family Adianthidae

Proectocion

?Litopterna

Family Sparnotheriodontidae

Victorlemoinea

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Meseta Formation at Seymour Island shows that

they are middle Eocene and not late Eocene as

believed earlier by several authors (Zinsmeister,

1978; Wrenn and Hart, 1988 ; Woodburne and

Zinsmeister, 1982). Also, the revised late Eocene

age for the Barrancan of Patagonia (Kay et al.,

1999) provides indirect evidence for the antiquity

of the Seymour Island mammals and for its inser-

tion within a gap in the South American faunal

succession. Consequently the LMF from Cucul-

laea I Allomember is a unique fauna that may

document the evolution of mammals in the south-

ern area of South America in the Middle Eocene

(V49 and 37 Ma.).

3.3. LMF: interactions between plants and

plant-eating mammals

Based on the marine invertebrates from Sey-

mour Island, Zinsmeister and Feldmann (1984)

stated that high-latitude regions serve as ‘holding

tanks’ for taxa that remain isolated until they dis-

perse towards lower latitudes (heterochroneity).

The same authors recognized such high-latitude

regions as centers of origin of novel adaptations

leading to speciation. Case (1989) expanded the

concept of Zinsmeister and Feldmann (1984) to

the terrestrial fauna, especially the Seymour Is-

land marsupials (‘Weddellian marsupials’).

Various climatic and ecological factors in£u-

ence latitudinal gradients in mammalian diversity

and taxonomic composition, and they strongly

in£uence the formation of latitudinal faunal bar-

riers (Flessa, 1975; McCoy and Connor, 1980).

One of these factors could be the climatic cooling

that occurred in the Antarctic Peninsula during

the middle^late Eocene; many aspects of the £ora

and fauna may have been a¡ected if the temper-

atures had fallen below certain threshold levels.

Compositional di¡erences between Seymour and

King George Islands Eocene £oras indicate that

the climatic conditions were quite di¡erent on

each side of the Antarctic Peninsula.

Also, at high latitudes, a prolonged period (sev-

eral months?) of continuous darkness could have

had a signi¢cant e¡ect on the distribution of some

taxa in the fauna. In this regard, the paleolatitude

of Seymour Island during the Eocene was high

(nearly 63‡S), and the terrestrial biota would

have routinely experienced several months of al-

most complete winter darkness as now occurs at

these latitudes. Thus, some or all of the terrestrial

mammals of Seymour Island probably lived under

crepuscular and even extended nocturnal condi-

tions during part of the year (i.e. fall and winter

seasons). Direct evidence of crepuscular or noc-

turnal adaptations of the terrestrial vertebrates

from the Eocene of Antarctica is lacking.

Fossil mammalian diet can be inferred from

tooth morphology by using modern dental ana-

logues with known diet (Dodd and Stanton,

1990). We are here concerned with fossil plant-

eating mammals and thus with deducing frugivory

(diet of fruits and seeds) and herbivory (diet of

the green part of plants, including bark). In the

middle Eocene of Antarctica, the change from

podocarp- to Nothofagus-dominated closed for-

ests (Cucullaea I Allomember) would result in

an increase of arboreal habitats facilitating a

Fig. 7. Antarctic ungulates. Detailed scheme of upper M1.

(A) Sparnotheriodontidae gen. et sp. nov.; (B) Trigonostylops

sp.

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radiation of arboreal herbivorous/omnivorous

mammals. Most of the small-sized mammals re-

corded in the La Meseta Formation seem to be

adapted to this habitat. Marsupials and condy-

larths appear in South America near the K/T

boundary, but here they are divided into di¡erent

guilds, marsupials becoming frugivorous and in-

sectivorous and condylarths becoming the herbiv-

orous. The browsing guild from the LMF prob-

ably consisted of four taxa: sparnotheriodontids,

trigonostylopids, sloths, and sudamericids. Ant-

arctic marsupials probably were members of the

frugivorous/insectivorous guild (Goin et al., 1999).

The small-sized Antarctic sloth (ca. 10 kg) is

considered to have been semi-arboreal and mainly

folivorous (Vizca|

¤no et al., 1998). Also, we can

add that the trunk-climbing ability (scansoriality)

of this form is di⁄cult to ascertain, but the strong

laterally compressed claw recovered at RV-8200

locality (Cucullaea I Allomember) suggests this

ability.

For the sudamericids, Koenigswald et al. (1999)

inferred a semi-aquatic and perhaps a burrowing

way of life, similar to that of living beavers. Re-

garding this, the presence of two Antarctic taxa at

Seymour Island (Goin, personal communication,

2000) suggests an important paleoecological con-

straint related to the dietary preference of this

group.

Antarctic ungulates could browse, stripping o¡

twigs and saplings from evergreen trees even dur-

ing winter months (Vizca|

¤no et al., 1998). Sparno-

theriodontids and trigonostylopids share a num-

ber of dental characteristics that may be

adaptations to forested habitats (Reguero et al.,

1998). As Marenssi et al. (1994) pointed out, the

striking features of these mammals are brachyo-

donty and the particular structure of the enamel

(vertically oriented Hunter-Schreger bands). As

indicated by Janis (1984) brachyodonty is associ-

ated with browsing herbivores that are adapted to

forest habitats. No postcranial information is

available for the Antarctic ungulates, but infor-

mation from the nearest relatives (all of them fos-

sils) can be used to infer the locomotor adapta-

tion. Both astrapotheres and sparnotheriodontids

were medium to large ground mammals with re-

strictions in their mobility of limb articulations

(presence of wrist and ankle joints that restrict

lateral movement), presence of hooves and reduc-

tion of digits in related taxa.

Paleobotanical and geological evidence from

the Antarctic Peninsula indicates that at this

time (middle Eocene), the Antarctic Peninsula

was a densely forested high cordillera. These un-

gulates had a more bilophodont (Fig. 7), also

partly selenodont in the case of the sparnotherio-

dontids, than bunodont dentition and their teeth

had strong enamel ridges extending between the

cusps. These enamel ridges serve as surfaces of

shearing wear, and the formation of dentine

‘lakes’ along the ridges produces a double-edged

shearing blade. These performed mainly a shear-

ing action slicing up leaves into quite large pieces

like a modern tapir that feeds almost entirely on

leaves of forest trees. As Janis (1989) pointed out

the bulk food was processed rapidly and ine⁄-

ciently, a method typically used by perissodactyls

to exploit mainly cell contents. In addition, the

body size of the Antarctic sparnotheriodontid

(395^400 kg) indicates that it was the largest her-

bivore living in Antarctica at this time (Vizca|

¤no

et al., 1998). Evidently the large size of this her-

bivore favored the exploitation of leaves because

longer residence time in the gut for bacterial fer-

mentation is required to obtain su⁄cient nutrients

from leaves. Also, it is accepted that large herbi-

vores tend to feed more or less continuously on a

wide range of plant parts. Low metabolic rate

permits large herbivores to derive energy from

cellulose by retaining it in the gut for long periods

of microbial fermentation (Janis, 1976). Based on

dental morphology, astrapotheres and sparno-

theriodontids (Fig. 7) probably were hindgut fer-

menters like non-ruminant artiodactyls and peris-

sodactyls (Fortelius, 1985). Astrapotheres and

sparnotheriodontids also have teeth with vertical

Hunter-Schreger bands. Fortelius (1985) indicates

that a number of lophodont ungulates have

evolved vertically oriented Hunter-Schreger

bands, a modi¢cation that involves the mode of

prism decussation and three-dimensional arrange-

ment of the bands. This has been interpreted as

an adaptation to resist cracking when the enamel

edges are loaded in a direction away from the

supporting dentine (Boyde and Fortelius, 1986).

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Rensberger and Pfretzchner (1992) pointed out

that the molars of astrapotheres, especially the

uppers, strongly resemble those of rhinocerotoids.

In both groups the labial part of the upper molar

forms a thin, vertical, blade-like ectoloph (for

Sparnotheriodontidae see Fig. 5).

The record of Sparnotheriodontidae on Sey-

mour Island can be traced from the early-middle

Eocene to the latest Eocene La Meseta Forma-

tion. In the middle Eocene, when the climatic

conditions were cool-temperate, this group was

common. Its last record occurs in the highest ho-

rizon of the Submeseta Allomember, dated by

Dingle and Lavelle (1998a,b) at V34.2 Ma

(Fig. 2). This age coincides with the ¢rst well-

documented formation of the ¢rst major sea ice

and the initiation of the psychrosphere (Barron et

al., 1991).

3.4. Paleobiogeography: dispersal events

The dispersal of land mammals supposes sev-

eral prerequisites. One of them is the existence of

a physical link between the start and end points of

the route. Another is the availability of food and

shelter along with a non-aggressive environment

(e.g. climate, topography). Keast (1972) pointed

out that Antarctica acted as a ‘‘stepping stone’’

for the dispersal of land mammals between Aus-

tralia and South America. Simpson (1978) sug-

gested the term ‘‘intermediate area’’ for pen-

insular Antarctica. Cracraft (1973) envisioned

Antarctica ‘‘as a faunal dispersal route’’. Mid-

to high-latitude warming has been cited as the

key factor permitting interchange of fauna and

£ora between regions, e.g. Asia and North Amer-

ica, across high-latitude land connections (Wood-

burne and Swisher, 1995). Currently, Seymour

Island land vertebrate-bearing localities are sep-

arated from the bulk of the Patagonian local-

ities discussed herein by more than 15‡ of latitude

(i.e. approximately 1600 km). Considering that,

on the basis of geologic and paleogeographic

data (Lawver et al., 1992), the Drake Passage

(about 1000 km wide) started to open at about

36 Ma, then we can assume that, prior to that

time, the distance between the Antarctic Peninsula

and Patagonia ought to have been shorter (Fig.

3). In fact, they must have been neighbors. We

can follow the overland connection between these

two major areas at least since the Late Creta-

ceous. The width of the land connection between

South America and West Antarctica is unknown,

but it might be assumed that a fairly narrow cor-

ridor would have functioned (Fig. 3). The disper-

sal of dinosaurs into Antarctica from South

America in the Late Cretaceous (Gasparini et

al., 1987; Olivero et al., 1990 ; Molnar et al.,

1996; Hooker et al., 1991 ; Case et al., 2000),

and monotremes into South America from Aus-

tralia via Antarctica in the Paleocene (Pascual et

al., 1992), implies a connection, either as an island

chain or as an isthmus, between Patagonia and

the Antarctic Peninsula. By the Late Cretaceous

or early Tertiary the Antarctic Peninsula^Andean

Cordillera was being fragmented and pushed east-

ward, and it can be expected that vertebrate dis-

persal became more of a ‘‘sweepstakes’’ type. Sev-

eral authors (Macellari, 1988; Askin, 1988)

postulated that the regression through the K/T

transition might have been largely responsible

for changes in marine faunas and £oras. This re-

gressive event may also have directly a¡ected land

£oras by providing newly created lowland areas

for new plant species.

The terrestrial mammals of Seymour Island

greatly strengthen the hypothesis that the LMF

had its origin in times that pre-date the middle

Eocene. Various lines of evidence suggesting this

are summarized in the following points :

(1) The Antarctic sudamericid probably derived

from the Peligran species Sudamerica ameghinoi

(Goin, personal communication, 2000).

(2) The Antarctic derorhynchids Derorhynchus

minutus and Pauladelphys juanjoi show close sim-

ilarities with two new, unpublished, species of

Derorhynchus from the Las Flores locality (Chu-

but) of Itaboraian age (Goin et al., 1999).

(3) The Antarctic microbiotheriid Marambio-

therium glacialis closely resembles the Itaboraian

species, Mirandatherium alipioi of Patagonia

(Goin et al., 1999).

(4) The new Antarctic sparnotheriodontid is

very close (perhaps representing the same species)

to an unpublished new Vacan species from Paso

del Sapo (Goin et al., 2000). Some dental features

PALAEO 2776 14-5-02

M.A. Reguero et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 179 (2002) 189^210204

of the Antarctic species seem to be more advanced

than the Riochican and Vacan genus Victorlemoi-

nea.

(5) The Antarctic astrapothere belongs to the

family Trigonostylopidae and tentatively was re-

ferred to the genus Trigonostylops by Bond et al.

(1990). This genus is recorded in the Riochican,

Vacan and Barrancan faunas of Patagonia.

(6) The Antarctic Pilosa shares plesiomorphic

features with primitive Tardigrada and Vermilin-

gua. Despite some dubious Eocene records (Simp-

son, 1948) the Antarctic form represents the ear-

liest unquestionable record of Pilosa (Vizca|

¤no

and Scillato Yane

¤, 1995).

(7) The case of the endemic polydolopine Poly-

dolops dailyi, a species closely related to the spe-

cies Polydolops thomasi (Woodburne and Zins-

meister, 1984; Candela and Goin, 1995) present

in the Vacan and Barrancan ‘subages’, is very

interesting because their close relationships sug-

gest a short term of di¡erentiation between both

species.

The above evidence indicates that the La Me-

seta mammalian fauna derived from Paleocene,

probably Riochican or Vacan faunas.

Put in the simplest terms, we might expect taxa

to immigrate into the Antarctic Peninsula during

a global warming phase. The late Paleocene^early

Eocene was the apogee of Cenozoic warmth. Dur-

ing this interval, the tropics extended between 10

and 15‡ poleward, and both polar regions were

populated with temperate forests (Frakes et al.,

1992). The late Paleocene subtropical Cross Val-

ley Flora on Seymour Island documents the

warmest climatic conditions in the Paleogene of

Antarctica. Based on the record of South Ameri-

can ungulates, one of the most probable dispersal

events between Patagonia and the Antarctic Pen-

insula could have occurred during the late Paleo-

cene and it was probably enhanced by the begin-

ning of the ‘climatic optimum’ period (late

Paleocene/early Eocene) and with the sea-level

lowstand identi¢ed between 58.5 and 56.5 Ma

(Haq et al., 1987). Lowering of the sea level might

have increased the extension of low-lying coastal

areas, providing an easier route than crossing

rough mountainous terrain (Antarctic Peninsula)

by leaving a long, continuous coastal region bor-

dered by shallow seas and high mountains. The

actual placement of the coastline during the latest

Paleocene remains speculative (Fig. 3), but the

overall physical consequences are not. The geo-

logical record shows a decrease in marine rocks

(Cross Valley Formation) before the Paleocene/

Eocene boundary.

Some non-mammal groups that may have used

the same route at this time include £ightless phor-

usrhacoid and ratite birds. This hypothesis ex-

plains the close a⁄nity of the LMF with Paleo-

cene faunas of Patagonia as well as the relict

character of some Antarctic taxa, even though a

still earlier (Late Cretaceous ?) dispersal of Gond-

wanan vertebrates (gondwanatheres, ratites and

monotremes) cannot be ruled out. However, the

Gondwanan origin of these groups ¢ts better with

vicariance events than with dispersal events. We

consider the presence of the family Sudamericidae

in Antarctica as re£ecting an artifact of a Gond-

wanan distribution. The ¢rst representatives of

the family are recorded in the early Paleocene

Peligran fauna. The known distribution of gond-

wanatheres (Argentina, India, Madagascar, and

Antarctica) is consistent with at least two major

biogeographic hypotheses: (1) the group origi-

nated before the major continental fragmentations

of the Early Cretaceous, and spread throughout

most of Gondwana (the absence of gondwana-

theres in Africa is attributable to poor sampling,

di¡erential extinction, or both), or (2) the group

originated sometime in the Early Cretaceous after

the tectonic isolation of Africa.

The most unexpected circumstance in the LMF

is the apparent lack of notoungulates and other

ungulate groups such as Condylarthra and non-

sparnotheriodontid Litopterna. Notoungulata

were the most diverse (morphologically as well

as taxonomically) and successful of the South

American ungulate groups. One of the most im-

portant radiations of notoungulates in Patagonia

occurred during the late Paleocene^early Eocene.

As we suppose that no barrier to dispersal existed

between Patagonia and Antarctic Peninsula dur-

ing the Paleocene, the absence of this group in

Antarctica could be explained by suggesting that

the LMF is composed only of those taxa that

were able to adapt to cooler conditions. However,

PALAEO 2776 14-5-02

M.A. Reguero et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 179 (2002) 189^210 205

the evidence of the presence of a high cordillera

along the peninsular isthmus could have acted as

a strong geographical barrier for the dispersal of

terrestrial vertebrates in the late Paleocene. Per-

haps only vertebrates adapted to high altitudes

were able to migrate further southward. The un-

gulates so far recorded at Punta Peligro (Peligran

SALMA) are the enigmatic Peligrotherium tropi-

calis (?condylarth), the mioclaenid condylarths,

and the notonychopid Requisia vidmari (?Litopt-

terna) (Bonaparte et al., 1993 ; Bonaparte and

Morales, 1997). They document the existence of

primitive ungulate lineages at this time. The most

probable progenitors of the notoungulates, the

mioclaenid condylarths, are present in this fauna.

The ¢rst record of representatives of Notoungu-

lata in Patagonia occurs in the late Paleocene ‘Ki-

benikhoria faunal zone’ (Itaboraian SALMA sensu

Bond et al., 1995) showing a discrete radiation of

four families (Henricosborniidae, Isotemnidae, In-

teratheriidae, Old¢eldthomasiidae). However, the

earliest record of this group in South America is

in the older Tiupampian beds of Bolivia (Muizon,

1991). Additionally but interestingly, Bond (1999)

remarks the noteworthy di¡erence in the geo-

graphic distribution between Notoungulata and

Litopterna in the late Pleistocene (Lujanian) in

Patagonia; whereas the litoptern Macrauchenia

patachonica has a wide range of distribution

southward (Santa Cruz Province) in this age,

the notoungulate Toxodon reached only Bahia

Blanca (38‡ 45PS). This fact suggests that some

factor (geographic or environmental) a¡ected

the dispersal of notoungulates to southern lati-

tudes.

If the notoungulates migrated southward into

the Antarctic Peninsula during the late Paleocene,

they presumably became extinct prior the deposi-

tion of the La Meseta Formation (late-early Eo-

cene^late Eocene). In sum, the most plausible hy-

potheses for the absence of Notoungulata, and

other groups, in the LMF are (1) the record of

this group is taphonomically biased, or (2) this

group could have passed into Antarctica during

the latest part of the Paleocene when the environ-

mental conditions were warmer, and then became

extinct at the onset of the climatic deterioration

(early Eocene), (3) the topography of the Antarc-

tic Peninsula cordillera prevented the dispersal of

this group into Antarctica, or (4) the presence of

some sort of ecological barrier that prevented the

dispersal of this group. Based on the evidence

presented above we favor the second choice.

We agree that Seymour Island and the sur-

rounding region (Antarctic Peninsula) started its

faunal isolation from South America from the

early Eocene and this might suggest that geo-

graphic isolation by a physical barrier (seaway)

would be among the possible hypotheses avail-

able to explain the extinctions and the endemism

of the fauna. Although a physical barrier (seaway)

might not have developed until the end of the

Eocene, the cooling trend that began during the

middle Eocene might have acted as an earlier

barrier, discouraging new mammal immigrations.

Therefore we suggest that regional cooling is the

most reliable hypothesis to explain the extinc-

tions, endemism, and relict character of the Eo-

cene LMF. Isolation, that began through temper-

ature decrease during the cooling trend from the

middle Eocene onwards, became physical with

the development of the seaway between the Ant-

arctic Peninsula and Patagonia at the end of the

Eocene.

Acknowledgements

We especially acknowledge the Instituto Anta

¤r-

tico Argentino and Fuerza Ae

¤rea Argentina, which

provided logistical support for our participation in

the Antarctic fieldwork. We also have benefited

from collaborative effort in the field (prospecting

and picking) of Juan Jose

¤Moly, Sergio F.

Vizca|

¤no, Cecilia Besendjak, Laura Net, Hugo

Devido, Andrea Concheyro and Rolando Maida-

na. Part of this study was funded by the National

Geographic Society (Grant 6615-99 to S.A.M.).

Reviews by Richard Cifelli and Jeremy Hooker

allowed significant improvement of the original

manuscript. A. Vin‹as skillfully prepared Figs. 3

and 7. The manuscript benefited from comments

offered by F.J. Goin and A.L. Cione (Museo de La

Plata).

PALAEO 2776 14-5-02

M.A. Reguero et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 179 (2002) 189^210206

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Earliest fossils of giant-sized bony-toothed birds (Aves: Pelagornithidae) from the Eocene of Seymour Island, Antarctica

Article

Full-text available

Oct 2020

While pelagornithid or ‘bony-toothed’ bird fossils representing multiple species are known from Antarctica, a new dentary fragment of a pelagornithid bird from the middle Eocene Submeseta Formation on Seymour Island, Antarctica represents a species with a body size on par with the largest known species in the clade. Measurements from the partial ‘toothed’ dentary point to a giant body size for the species, although the spacing among the pseudoteeth difers from that published for other pelagornithids. The discrepancy might suggest that previous techniques are not adequate for examination of incomplete material or that another factor such as phylogeny might impact size estimates and comparisons. Combined with a revised stratigraphic position in the early Eocene La Meseta Formation on Seymour Island for the largest pelagornithid tarsometatarsus known, these Antarctic fossils demonstrate the early evolution of giant body size in the clade (by~ 50 Ma), and they likely represent not only the largest fying birds of the Eocene but also some of the largest volant birds that ever lived (with an estimated 5–6 m wingspan). Furthermore, the distribution of giantsized pelagornithid fossils across more than 10 million years of Antarctic geological deposits points to a prolonged survival of giant-sized pelagornithids within the southern seas, and their success as a pelagic predatory component of marine and coastal ecosystems alongside early penguins.

Marine and terrestrial invertebrate borings and fungal damage in Paleogene fossil woods from Seymour Island, Antarctica

Article

Full-text available

Aug 2020

Stephen Mcloughlin

An assemblage of permineralized conifer and angiosperm woods collected from Paleogene marine strata on Seymour Island during the Swedish Antarctic expedition of 1901–1903 includes many specimens with internal damage caused by an array of xylophagous organisms. Short, broad, clavate borings referable to Gastrochaenolites clavatus are attributed to pholadid bivalves. Elongate borings with carbonate linings referable to Apectoichnus longissimus were produced by teredinid bivalves. Slender, cylindrical tunnels cross-cutting growth rings and backfilled in meniscoid fashion by frass composed of angular tracheid fragments were probably produced by a terrestrial beetle borer. They are most similar to tunnels generated by modern cerambycid and ptinid coleopterans. Less regular, spindle-shaped cavities and degraded zones flanking growth rings are similar to fungi-generated modern white pocket rot. Larger chambers in the heartwood referable to the ichnotaxon Asthenopodichnium lignorum were produced by an alternative mode of fungal degradation. The biological interactions evident in the fossil woods illustrate additional terrestrial trophic levels enhancing the known complexity of ecosystems on and around the Antarctic Peninsula shortly before the initial pulse of mid-Cenozoic glaciation in Antarctica that caused extirpation of the majority of plants and animals in that region.

Late middle Miocene Metatheria (Mammalia: Didelphimorphia and Paucituberculata) from Juan Guerra, San Martín Department, Peruvian Amazonia

Article

Jul 2022
J S AM EARTH SCI

Currently, marsupials (modern members of the Metatheria clade) are widely distributed in tropical and subtropical areas of South America, but poorly represented in the fossil record of these regions. Except for the species-rich fossiliferous localities of La Venta in Colombia, additional Miocene metatherians from tropical, equatorial South America are sparsely reported in Bolivia, Brazil, Peru, and Venezuela. Here, we introduce new metatherian remains recovered from the late middle Miocene locality of TAR-31, San Martín Department, Peru, which has been assigned to the Laventan South American Land Mammal Age (∼13 Ma) by mammalian biostratigraphy. Three metatherian taxa are recognized at TAR-31: the didelphid didelphimorph ‘Thylamys’ cf. ‘T.’ colombianus, and the paucituberculatans aff. Palaeothentes and Pitheculites ipururensis sp. nov. This assemblage and the presence of a cebid primate at TAR-31 suggests predominantly humid and warm tropical conditions, with the occurrence of both forests and drier habitats in the surroundings. Comparisons with other Miocene metatherian assemblages at low and mid latitudes of South America clearly confirm close relationships between TAR-31 and La Venta (agreeing with observations based on monkeys and rodents), as well as, to a lesser extent, with Acre River local faunas and Madre de Dios (MD-67) in Brazil and Peru, respectively. The current results support the hypothesis that Western Amazonia was a single and consistent biogeographical region for land mammals over middle Miocene times, at the western edge of the Pebas Mega-Wetland System, and highlight the role of the Amazonian region concerning marsupial Neogene radiation. U–Pb analysis made on detrital zircon grains from TAR-31 gave a maximum depositional age of 17.4 ± 0.12 Ma (i.e., 4 Ma older than the biostratigraphical age), with a mixed detrital source likely comprising Precambrian (Western Amazon Craton), Neoproterozoic (Neoproterozoic mobile belts), and Phanerozoic rocks (Andes).

The South American Mesozoic Record and Early Evolution of Mammals

Chapter

Feb 2021

The sparse record of archaic Mesozoic South American mammals extends from the latest Early Jurassic to the latest Cretaceous, involving about 115 Ma, which can be further extended to about 160 Ma, including the post-K/Pg evidence. We review here the distribution, predicted time of origin, and likely place of origin for the lineages covered in the preceding chapters during that span of time and against the evolving geological backdrop of continental drift and paleogeography. Size, dental diversity, and likely dietary specializations of the Mesozoic South American mammals are discussed in the context of Mesozoic mammals in general. A few of the many surprising advances in comparative genetic and molecular evolution are discussed as part of a holistic view of early mammalian evolution to which fossils can, and should, be integrated. Social, financial, and geographical issues affecting paleontological research in South America, early mammals, in particular, are highlighted. We recognize that we are still in the early stages of development and that much of what we know about Mesozoic South American mammals is likely to be drastically altered by finds in the continent or underrepresented areas from formely Gondwanan landmasses such as Antarctica or Africa. Their scarce mammalian fossil record has hampered their full incorporation into an integrated view of early mammalian evolution. The relatively robust paleontological community present in several South American countries, relatively inexpensive nature of the discipline, and extensive outcrops are likely to ensure continuity of a synergistic research agenda. The potential for novel data, regional strengths in systematics, and the global resurgent importance of time as integral to model-based phylogenies are auspicious signs for the future of Mesozoic mammal research in South America.

Dryolestoids

Chapter

Feb 2021

Dryolestoids are iconic members of the Mesozoic mammalian associations in South America. They achieved a large taxonomic diversity in this region with disparate dental and cranial morphotypes ranging from the classical role of sharp-toothed insectivores to bunodont, complex dentitions reflecting omnivore/herbivore adaptations. The South American radiation of dryolestoids, the meridiolestidans, are among the most abundant Cretaceous mammals, surviving the K/Pg mass extinction and continuing until the Miocene as minor members of the South American biotas. New specimens have been recently discovered, some of them including associated upper and lower jaws, and exceptionally preserved skulls. These high-quality fossils provide crucial intraspecific dental variation, both along the tooth row and from upper to lower, allowing critical re-interpretation of some taxa originally named on the basis of isolated teeth or very incomplete material. The Cretaceous diversity of meridiolestidans has been grossly overestimated, with taxa based on different dental positions of what was later determinied to be a single taxon. One relatively poorly known Late Cretaceous taxon, Groebertherium, shares many features with the classical Holartic dryolestoids and may represent a Late Jurassic/Early Cretaceous foundational morphology expected for meridiolestidans.

The Origin and the Radiation of Early Mammals: A Southern Perspective

Chapter

Feb 2021

Non-mammaliaform cynodonts, formerly called “mammal-like reptiles,” illustrate earlier states of the morphological architecture in the mammalian lineage. These mammalian forerunners show unique character combinations without direct counterparts among living vertebrates reflecting adaptations long lost along the millions of years of cynodont history. The fossil record from South America, originating mostly from the Middle to Late Triassic of Argentina and Brazil, is one of the most prolific worldwide. SA non-mammalian cynodonts are systematically diverse, including approximately 40 species that present great morphological disparity in skull shape, tooth morphology, pattern of tooth replacement, masticatory mechanisms, and locomotory architectures. In this chapter, we summarize the record of SA non-mammaliaform cynodonts.

Primer mamífero Mesozoico de Chile: el registro más austral de un gondwanaterio del Cretácico tardío

Article

Full-text available

Jun 2020

Se describe a Magallanodon baikashkenke gen. et. sp. nov., un nuevo mamífero gondwanaterio del Cretácico tardío de la Región de Magallanes, en el sur de Chile (Valle del Río de Las Chinas, Estancia Cerro Guido, norte de Puerto Natales, Provincia de Última Esperanza). Las capas portadoras se ubican entre los niveles del Campaniano tardío-Maastrichtiano temprano de la Formación Dorotea (Cuenca de Magallanes/Austral). Los nuevos restos constituyen el registro más austral de un mamífero gondwanaterio del Mesozoico, como así también el primer mamífero Mesozoico conocido para Chile. El nuevo taxón es comparable en tamaño a las formas hipsodontes Gondwanatherium (Cretácico tardío) y Sudamerica (Paleoceno temprano), pero con molares notoriamente braquidontes soportados por cuatro a cinco raíces. Como en otros gondwanaterios, posee al menos un incisivo superior rodentiforme en la serie superior. Se diagnostica y describe brevemente el nuevo taxón, considerado tentativamente como un ferugliotérido (Ferugliotheriidae). De confirmarse esta asignación, este nuevo taxón representaría el miembro de mayor tamaño para la familia. El patrón oclusal de los molariformes, con el desgaste, se semeja también al de otros gondwanaterios, en particular al de los ferugliotéridos y al del sudamerícido Gondwanatherium, agregando en consecuencia más evidencias en favor de la proximidad filogenética entre ambas familias. Se llevó a cabo un análisis de la microestructura del esmalte del incisivo superior de Magallanodon; como resultado, se encontraron varias similitudes importantes con el patrón existente en Gondwanatherium (Sudamericidae). Se discute la significación de Magallanodon en la adquisición, entre los gondwanaterios, de un patrón molariforme caracterizado por la presencia de lofos transversos. Finalmente, se discute la significación del nuevo hallazgo en el contexto de las biotas australes, incluyendo aquellas de Patagonia y Antártica.

Eocene palaeoenvironments and palaeoceanography of areas adjacent to the Drake Passage: insights from dinoflagellate cyst analysis

Article

May 2022

A proper understanding of the palaeoceanographic evolution of the Drake Passage during the Palaeogene is hampered by the lack of precise tools to date and correlate the sedimentary units of areas adjacent to the region. In this work, considering recently published radiometric U–Pb dates, we revised the age of a previous dinoflagellate zones for the middle to upper Eocene units of the Austral–Magallanes Basin. The quantitative analysis of middle to late Eocene dinoflagellate cyst assemblages from different localities close to the Drake Passage allowed us to reconstruct the palaeoenvironmental conditions and the possible surface ocean currents during this time in the area. Assemblages dated between 41.3 and 38.1 Ma represent relatively warm waters in inner shelf settings, while those ranged between 36 and 35 Ma reflect coastal areas with cool, nutrient‐rich surface waters. The proposed surface ocean circulation pattern, based on dinoflagellate cysts distribution between 41.3 and 38.1 Ma, agrees with the results of a palaeoclimatic numerical model simulation performed with a Drake Passage shallow opening of 100 m depth. At c. 36 Ma, several Antarctic gonyaulacacean taxa tolerant to relatively warmer waters were replaced by some Antarctic peridinacean species better adapted to colder conditions. This change could be linked to a progressive deepening of the Drake Passage that is estimated to have reached 1000 m depth promoting a cooling in the South Atlantic. Such passage depth would have enabled stronger flows from the Pacific to the Atlantic Ocean, which is reflected by the increase of cosmopolitan species.

Allotheria: Gondwanatherians and Multituberculates

Chapter

Feb 2021

The enigmatic Gondwanatheria includes mammals with a mosaic of plesiomorphic and apomorphic cranial and dental features challenging our attempts to reconstruct their phylogenetic affiliation. They are generally perceived as sharing a closer ancestor with multituberculates than with therians in a variably conceived Allotheria. Two major groups are classically recognized among the South American Gondwanatheria: the brachyodont-toothed Ferugliotheriidae and the hypsodont-toothed Sudamericidae, although not all taxa fall easily in these categories. The affinities of the Ferugliotheriidae are, however, unsettled, with some authors favoring the hypothesis that they are indeed a derived branch of multituberculates. The original foundational Patagonian finds of gondwanatherians have recently been much improved by spectacular Late Cretaceous Malagasy materials, which increase dental diversity of the group, provide detailed cranial/postcranial morphology, and support allotherian affinities for the group.

First Mesozoic mammal from Chile: the southernmost record of late Cretaceous gondwanatherian

Article

Full-text available

Jun 2020

We describe Magallanodon baikashkenke gen. et. sp. nov., a new gondwanatherian mammal from the Late Cretaceous of the Magallanes Region in southern Chile (Río de Las Chinas Valley, Estancia Cerro Guido, north of Puerto Natales city, Última Esperanza Province). The mammal-bearing layer is placed within the Late Campanian-Early Maastrichtian levels of the Dorotea Formation (Magallanes/Austral Basin). The new remains constitute the southernmost record of a Mesozoic gondwanatherian mammal, as well as the frst Mesozoic mammal from Chile. This taxon is comparable in size to the hypsodont-toothed Gondwanatherium (Late Cretaceous) and Sudamerica (Early Paleocene) but with noticeably brachyodont molariforms supported by four to fve roots. As in other gondwanatherians, it has at least one hypertrophied, rodent-like incisor in the upper jaw. The new taxon is here diagnosed and described, and is regarded as a possible ferugliotheriid (?Ferugliotheriidae). If confrmed, it would represent the largest known taxon for this family. Its molariform occlusal crown pattern, after wear, resembles that of other gondwanatherians, particularly ferugliotheriids and that of the sudamericid Gondwanatherium. This adds new evidence on the phylogenetic proximity of ferugliotheriid and sudamericid gondwanatherians. An analysis of the enamel microstructure of the upper incisor of Magallanodon was performed demonstrating several crucial similarities with the pattern shown by Gondwanatherium (Sudamericidae). We discuss the signifcance of Magallanodon for understanding the acquisition, within gondwanatherians, of a lophed molariform pattern. Finally, we discuss the signifcance of the new fnding in the context of southern biotas, including those of Patagonia and Antarctica.

Maderas fósiles de la isla Seymour, Formación La Meseta, Antartica

Article

Full-text available

Jan 1994

Se determinan maderas fósiles terciarías provenientes de la Formación La Meseta, en la isla Seymour (64° 1.5' S.. 56°40' W.). La mega/lora se compone de cinco coniferas: Araucarioxylon novaezelandae Stopes, A. pseudoparenchymatosum Goihan, A. seymourense sp. nov., Cupressinoxylon seymourense sp. nov,, Phyllocladoxylon antarcücum Gytnan y la dicotiledónea Noihofagoxylon scalanforme Goihan. Las seis especies identificadas, tres de las cuales son citadas por vez primera, tienen afinidades con especies arbóreas que crecen actualmente en zonas boscosas de climas lluviosos, temperados-fríos, con estaciones diferencii-ias. Sobre la base de este conjunto florístico, se infieren condiciones paleocü.náticas similares para los depósitos de la isla Seymour durante el Eoceno-Oligoceno. Se discute las condiciones de depositación y se concluye que las maderas se petrificaron en un medio rico er. carbonatas. Las maderas habríanflotado en el mar, siendo depositadas en una zona protegida, probablememe una bahía. Estos fósiles, bien situados en ¡os niveles eocénico-oligocénicos de la Formación La Meseta, pueden ser utilizados como indicadores en correlaciones estratigráficas entre el extremo sur de Sudamérica y otras localidades de la Antartica (isla Rey Jorge), en donde se han encontrado maderas fósiles similares.

Land mammals: Paradigm of Cenozoic South American geobiotic evolution

Article

Full-text available

Apr 1996

Cenozoic South American land mammals demonstrated to be the richest and most eloquent known testimonies to infer the geobiotic evolution of the continent throughout the geological span. The concept and practice followed to recognize by them the South American Land Mammal Ages (SALMAs) are explained. Likewise, it is explained the analytical method used to recognize four hierarchical ranks of organization of the 16 SALMAs, which are distinguished as “faunal cycles” (from higher to lower, Megacycles, Supercycles, Cycles and Subcycles). Each of these cycles is defined by an unique association of mammal families, and on the whole are apparently correlated to a hierarchy of world-wide and regional changes in environmental conditions. The Faunistic Cycles are used as “standard units” because they appear to be more closely related to physical and biological regional phenomena. The long-standing autochthonism showed by the South American Late Cretaceous-Cenozoic mammals, as well as the peculiar South American biogeographical history, is briefly analyzed as associated to the climatic shifts related to eustatic falls and geodynamic processes. The successive Late Cretaceous-Cenozoic range pattern and facies of land mammal-bearing deposits is also analyzed in association to eustatic falls and geodynamic processes. Finally, using this background, and as base for the seven Faunistic Cycles so far recognized, the general pattern of evolution of land mammals is chronologically and synthetically analyzed, and particularly, the trends and features of each of the Faunistic Cycles. Key Words: Land mammals, Cenozoic, South America. geobiotic evolution.

Un ankylosaurio (Reptilia, Ornithischia) Campaniano en el continente Antartico

Article

Full-text available

Jan 1987

Ungulate cheek teeth: Developmental, functional, and evolutionary interrelations

Article

Full-text available

Jan 1985

Mikael Fortelius

Addresses problems of coronal morphogenesis, amelogenesis, food comminution and digestion, amastication, tooth eruption and wear, in order to identify functional intrrelations and developmental constraints in the evolution of cheek tooth morphology. Many aptive features probably or certainly did not arise for their current functions, but are one-time constraints which have become incorporated into functional systems (exaptations rather than adaptations).-from Author

Heavy mineral suites as provenance indicators: La Meseta Formation (Eocene), Marambio (Seymour) Island, Antarctic Peninsula

Article

Jun 1998

Resultados de los trabajos de campo en una localidad del Eoceno de la Isla Marambio (Seymour), Península Antártica.

Article

Jan 1993

Geology and paleontology of Seymour Island, Antarctic peninsula.

Article

Jan 1984

William J. Zinsmeister

Results of NSF expeditions to Seymour Island since 1981 are outlined. The eminent suitability of the geologic setting of the island for uncovering the Late Cretaceous and Early Tertiary discoveries include jaw fragments of the extinct marsupial Polydolops, remains of large Late Cretaceous marine reptiles, well preserved marine invertebrates (molluscs, starfish, crinoids, crabs, and corals), pre-glacial microfloras, the partial skull of a giant penguin (six feet tall) and other fossil remains. The significant of these finds is pointed out.-from Current Antarctic Literature

Late Cretaceous-Cenozoic climatic variations of the northern Antarctic Peninsula: New geochemical evidence and review

Article

Jan 1998
PALAEOGEOGR PALAEOCL

A gigantic phororhacoid(?) bird from Antarctica

Article

Nov 1987

The anterior portion of a fossilised beak from a gigantic, (?) flightless, predaceous bird was recovered from the late Eocene La Meseta Fm., on Seymour Island, Antarctic Peninsula. It appears to have belonged to a phororhacoid, a group of carnivorous birds of large size, which occupied a primary carnivore niche in South America from the early Oligocene to the medial Pliocene. The Antarctic find is aged at approximately 40 Ma, based on associated mega- and microfossils and so predates the oldest geologic occurrence described from South America. -after Authors

Area, Continental Drift and Mammalian Diversity

Article

Jan 1975

Karl W. Flessa

Mammalian generic, familial, and ordinal diversities correlate significantly with continental area. The area effect is similar in form to that shown for true islands: S = kA z , where S is the diversity, A is the area, and k and z are fitted constants. For mammalian genera and continental area, z equals 0.33, for families, z equals 0.23, and for orders, z equals 0.13. The area effect permits quantitative modeling of extinction due to biotic competition between previously isolated faunas. The Late Cenozoic extinction of North and South American mammalian faunas following the rise of the Panamanian land bridge is overestimated by seven families. The overestimate may result from assumptions of complete biotic interchange and universal competition. The role of plate tectonics in regulating diversity may be extensively modified by regional environmental conditions.

Eocene land mammals from Seymour Island, Antarctica: Palaeobiogeographical implications

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