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EXTINCTION OF THE ANTARCTIC TERRESTRIAL BIOTA
ALLAN C.
ASHWORTH1, DAVID J. CANTRILL2, GUILLERMO
KUSCHEL3, RICHARD C. PREECE4 F. CHRISTIAN
THOMPSON5 1. Department of Geosciences, North
Dakota State Univ, Stevens Hall, North Dakota
State University, Fargo, ND 58105-5517, 2.
Palaeobotany Section, Swedish Museum of Natural
History, Box 50007, Stockholm, SE 104 05, Sweden
3. Landcare Research, Private Bag 92 170,
Auckland, New Zealand, 4. Department of Zoology,
Univ of Cambridge, Downing Street, Cambridge, CB2
3EJ, U.K, United Kingdom, 5. Systematic
Entomology Laboratory, U.S. National Museum of
Nat History, NHB-169, Washington, DC 20560

INTRODUCTION Two species of
vascular plants and three species of flies
(chironomid midges) are the only terrestrial
organisms with complex life cycles that inhabit
Antarctica today. They are restricted to only
the most sheltered habitats along the northwest
coast of the Antarctic Peninsula. Further south,
the only vegetative cover is provided by
cryptogams (algae, mosses and lichens). The only
arthropods are springtails (Collembola) and
oribatid mites (Acari) (Convey, 1998). Coastal
species, like the vascular plants and chironomid
midges of the Antarctic Peninsula, are regarded
as postglacial immigrants but a few of the
species which inhabit nunataks on the continental
interior are considered to be relicts from the
Gondwana fauna (Marshall and Pugh, 1996 Starý
and Block, 1998). During the Cretaceous and
Paleogene Periods, temperate moist forests grew
in southern South America, Antarctica and
Australia (Askin, 1992). As Gondwana fragmented,
Antarctic organisms became isolated from the
larger gene pool, first from Australia 50
million years ago (Ma) and then South America
(30 Ma) (Lawver et al., 1992). In response to
climatic cooling, the forests became less diverse
and by the end of the Oligocene in the Ross Sea
region had been replaced by shrub
Nothofagus-herb-moss tundra that persisted into
the Miocene and maybe the Pliocene (Fleming and
Barron, 1996 Askin and Raine, 2000). The Meyer
Desert Formation fossils provide information
about the Neogene terrestrial life of Antarctica
before it mostly became extinct

PALEOCLIMATE The various
types of plants, insects and molluscs represented
by the Meyer Desert Formation fossils required at
least two summer months during which the average
temperature was about 5ºC. Francis and Hill
(1996) estimated a mean summer temperature of
about 5ºC based on an analysis of the width and
deformities in the growth rings of Nothofagus.
Ashworth and Preece (in press) estimated that a
minimum 5ºC air temperature would be the minimum
for freshwater molluscs to complete their
development. Ashworth and Kuschel (in press)
noted that the minimum summer temperature at
which listroderine weevils occur at treeline in
Tierra del Fuego is 4-5 ºC .

MEYER DESERT FORMATION
PALEONTOLOGY Fossils of several types of
organisms occur in the siltstones, marlstone and
indurated peat. Wood (Carlquist, 1987 Francis
and Hill, 1996), leaves (Hill et al., 1996), and
pollen and spores (Askin and Markgraf, 1986 Hill
and Truswell, 1993) have been previously
reported. Nothofagus wood and leaves have been
described as a new species, Nothofagus
beardmorensis . Other fossils in the process of
being described are moss stems and leaves, tissue
and seeds of vascular plants, skeletal parts of
insects, the shells of a freshwater molluscs and
an ostracod species, and the tooth of a fish.
The fossils are representative of a low-diversity
community that inhabited a glacial margin.
The Meyer Desert Formation at Oliver Bluffs is
about 75 m thick and the base of it is at 1760 m
above sea level. The Mill Glacier and the
Supporters Range are in the background.
Agglutinated foraminifera from near the base of
the section a few hundred meters southward,
suggest that the sequence was deposited near sea
level and has undergone about 1500 m of
post-depositional uplift.
The branching tissue of a cushion plant.
The scale bar is in centimeters. The plant was
buried in its growth position by outwash.
A sea level mean annual temperature (MAT) curve
is reconstructed based on climatological data
from stations in South America, islands in the
Southern Ocean, and Antarctica. Restoring the
Oliver Bluffs fossil site to its pre-uplift
position near sea level provides an estimate of
MAT of about -25ºC. The closest site to
Antarctica where listroderine weevils and
Nothofagus are found today is Tierra del Fuego
where the MAT is about 7ºC. This would imply a
difference of 32º C between the MATs of today
and the Neogene for the interior of Antarctica.
This difference, however, is exaggerated because
of the comparison of oceanic with continental
climates. Ashworth and Kuschel (in press)
estimated a MAT of -8ºC based on weevil fossils
and Francis and Hill (1996) estimated a MAT of
-12ºC based on Nothofagus wood . This suggests
that the paleoclimate had a MAT 13-17º C warmer
than the climate of today.
A leaf of Nothofagus beardmorensis.
Achenes and fruits of vascular plants. The
majority of the achenes are assigned to
Ranunculus species (buttercups)
setae
15 microns
B.
The interbedded diamictites, fluvioglacial and
glaciolacustrine deposits represent a series of
glacials and interglacials. The thickness of the
diamictites, the stratification and sedimentary
structures of the fluvial and lacustrine beds are
evidence of deposition from temperate or
wet-based glaciers. Water in the liquid phase
does not exist at the site today.
1 micron
1 mm
C.
A.
Various skeletal parts of Curculionidae (weevils)
belonging to the Southern Hemisphere group
Listroderina. A. head with orbit, scrobe and
mandible visible, B. pronotum with central median
ridge visible, C. femur. The fossil head is
broader than in any of the known Rhytirhinini
species, which suggests that the fossil species
is extinct and only distantly related to any
extant species.
LOCATION The
fossil site is located on the Beardmore Glacier
about 150 km inland from where it joins the Ross
Ice Shelf. The site is on the edge of the Meyer
Desert in the Dominion Range of the
Transantarctic Mountains, about 500 km from the
South Pole at latitude 85º S.
STRATIGRAPHIC AND AGE RELATIONSHIPS Sirius
Group deposits occur throughout the
Transantarctic Mountains in discontinuous
outcrops. In the Beardmore valley, the Sirius
is divided into a lower, glaciomarine sequence,
the Cloudmaker Formation, and an upper
terrigenous glacial and interglacial sequence,
the Meyer Desert Formation (Mercer, 1972
McKelvey et al., 1991 Webb et al., 1996). A
Pliocene age assigned on the basis of recycled
marine diatoms is controversial because the
source would require open marine conditions in
the interior of Antarctica ( Harwood, 1986 Webb
et al., 1996). The degree of pedogenesis in the
paleosols in the sections is also taken to
indicate a younger Pliocene, rather than a
Miocene age (Retallack et al., 2001). Counter
hypotheses for the deposits being pre-Pliocene in
age have been advanced. They are based on the
diatoms being later introductions to the Sirius
deposits either by being windblown from an
unknown source (Burckle and Potter, 1996 Kellogg
and Kellogg, 1996 Stroeven et al., 1996 Barrett
et al., 1997) or by being ejected from the deep
ocean floor by the impact of the Eltanin Asteroid
(Gersonde et al., 1997).
The posterior segment of the puparium (case for
the last larval instar) of a cyclorraphan Diptera
(higher fly). The maggot indicates that the
species was breeding at the site and is not a
blow in.
A. A leg of a cyclorraphan fly in which the coxa,
trochanter, femur, tibia, and tarsus are still
connected. The specimen is preserved inside of a
Ranunculus achene. The specimen has distinctive
cabled setae which are adaptive to clinging to
plant stems in wind-swept locations.
The stratigraphy and paleontology of the
fossiliferous bed in the Meyer Desert Formation
indicates a tundra-like vegetation that
colonized a moraine on the margins of the Neogene
Beardmore Glacier. The habitat may have been
very similar to glacial margins in Patagonia
today.
Summary of the climatic and vegetational history
of Antarctica during the Cenozoic Era


CONCLUSIONS I am inclined to look ... to a
former and warmer period, before the commencement
of the Glacial period, when the antarctic lands,
now covered with ice, supported a highly peculiar
and isolated flora Charles Darwin The Origin
of Species The Meyer Desert Formation organisms
are believed to be the descendants of an ancient
Gondwana fauna . Cooling of the climate and the
growth of ice sheets, associated with the opening
of the Drake Passage and the formation of the
Circumpolar Current between 34 to 22 Ma, caused
the initial decline in species diversity of
plants and animals. The East Antarctic Ice Sheet
was fully formed by 14 Ma and the West Antarctic
Ice Sheet by 5 Ma (Hansom and Gordon, 1998).
Increasingly the climate became more arid, and
after 7.5 Ma in the Dry Valleys, a shift from
wet-based to cold-based glaciations occurred. We
speculate that ice-free areas, starved of
moisture, became polar deserts resulting in the
extinction of vascular plants, most cryptograms,
arthropods other than a few species of mites and
collembolla, and all aquatic organisms of the
Neogene tundra biota.
Looking southward on the Beardmore Glacier
towards Mount Mills and the edge of the Polar
Plateau. The Sirius Group deposits are
unconformable on Mesozoic-aged igneous and
sedimentary strata. Passchier (2001) proposed a
long complex glacial history during which there
was an overriding of the higher ranges of the
Transantarctic Mountains during the late
Oligocene and/or early Miocene. This was
followed by a shift in the late Miocene early
Pliocene to the development of overdeepened
glacial troughs due to uplift and structural
segmentation of the Transantarctic Mountains
The tooth of a fish. The specimen does not
possess any characters which enable it to be
identified to a particular species. It could be
from a freshwater fish or a marine fish that
spawned in a river or freshwater lake. A fish in
the Southern Hemisphere family Galaxiidae, which
occur in South America, Tasmania and New Zealand
, is a candidate.
Shells of freshwater molluscs. A. fragment of
the shell of the fingernail clam Pisidium. B.
and C. An adult and juvenile specimens of an
unidentified lymnaeid gastropod (Ashworth and
Preece, in press)
Different views of the carapace of an ostracod.
The specimen is similar in morphology to
Xestoleberis, a brackish water species occurring
in fiords, estuaries, and shallow marine shelves
(Patrick DeDecker, pers. comm.)
The brown coloration is from a deformed peat bed.
The bed was deformed during the till
deposition.
REFERENCES
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Barrett, P. J., Bleakley, N. L., Dickinson, W.
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McKelvey, B. C., Webb, P. N., Harwood, D. M., and
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Resources, Addison Wesley Longman, Singapore
File of poster is available at
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