First record of dinosaurs in Antarctica (Upper Cretaceous, James Ross Island): paleogeographic implications

Abstract

During the austral summer of 1986,fieldwork on James Ross Island by the Instituto Antártico Argentino resulted in the discovery of the first remains of dinosaurs from the Antarctic continent. These consist of a partial skeleton and bony plates of an armoured ornithischian belonging to the Ankylosauria. The fossil material was found in marine sandy-facies of the Santa Mata Formation (Marambio Group) of Campanian age. The remains were associated with marine invertebrates. At a sligtly higher stratigraphic level, marine reptiles related to mosasaurs and plesiosaurs were also found. The occurrence of ankylosaurs on James Ross Island provides important new insight concerning hypothesis of land connections between South America and Antarctica during the Late Cretaceous. An earlier differentiation of the family Ankylosauridae and the distribution of these dinosaurs in Antactica during the Late Jurassic-Early Createous cannot be completerly ruled out. However, a late entrance of northern ankylosaurids into Antarctica, via South America, is considered more likely. Because it was not possible for these ankylosaurs to cross water barriers, their presence indicates that a continuous land connection must have existedd between Antarctica and South America for some period of time during the Late Cretaceous.

Full text

I
2
3
First record
of dinosaurs in Antarctica (Upper
Cretaceous,
James
Ross Island):
palaeogeographical
implications
E.B.
oLIvERo,'2. GASPARINI,2
C.A. RINALDI3
& R.
ScAsso'
Centro de Investigaciones en Recursos Geológicos, Ramirez de Velasco 847, 1414 Buenos Aires, Argentina
Museo La Plata, Paseo del Bosque, 1900 La Plata, Argentina
Instituto Antártico Argentino, Cerrito 1248, l0l0 Buenos Aires, Ar1entina
Abstract
During
the austral
summer of 1986,
fieldwork
on James Ross
Island by the Instituto
Antártico Argentino
resulted
in the
discovery
of the first remains
of dinosaurs from the
Antarctic
continent. These
consist
of a partial
skeleton
and
bony
plates
of an armoured
ornithischian belonging
to the Ankylosauria.
The
fossil
material
was
found
in marine
sandy-facies of the
Santa Marta Formation (Marambio
Group) of Campanian age.
The
remains were
associated
with marine invertebrates.
At a slightly
higher
stratigraphic
level, marine reptiles
related
to mosasaurs
and
plesiosaurs
were
also
found.
The
occurrence of ankylosaurs
on James Ross
Island
provides
important new insight
concerning hypotheses
of land
connections
between
South America and Antarctica
during the
Late
Cretaceous. An earlier
differentiation
of the family Ankylosauridae
and
the
distribution
of these dinosaurs in Antarctica
during
the Late Jurassic Early
cretaceous cannot
be completely
ruled
out. However,
alate entrance
of northern
ankylosaurids into Antarctica,
via South America,
is considered more
likely. Because
it
was not possible
for these
ankylosaurs to cross
water
barriers, their
presence
indicates
that a continuous
land
connection must
have
existed
between Antarctica
and
South
America for some
period
of time during
the Late
Cretaceous.
Introduction
In addition to its severe
present
climate, a distinctive
feature of Antarctica is
its complete
absence
of
permanent
land
vertebrates. Because Antarctica
is at present
an isolated land-
mass, encircled
by deep oceans,
the occurrence
of fossil
land
vertebrates is particularly
signiflcant
to the concept of con-
tinental drift and to our knowledge
of former land
connections
among the southern
continents. The
finding
of Triassic
terres-
trial reptiles and
amphibians
(Colbert,
1982),
ichnites
of large
Tertiary
ground
birds (Covacevich
& Rich, 1982)
and, par-
ticularly, Tertiary marsupials (Woodburne
& Zinsmeister,
1984), indicates that Antarctica
was faunally
an
integral part
of
Gondwana.
These
data
also suggested
the
probable
occurrence
of Cretaceous land vertebrates
in the Antarctic Peninsula
and
the
possibility
of a continental
connection between
this region
and South America.
During the austral
summer
of 1986, fieldwork
by the Insti-
tuto Antartico Argentino in James Ross Island (Fig. l)
resulted
in the discovery
of the first dinosaur from the Ant-
arctic continent. The occurrence
of these reptiles provides
important
new data concerning
hypotheses
of land connec-
tions
of the Antarctic
Peninsula
and supports
the idea
that a
continuous
land bridge
joined the Antarctic Peninsula
and
South America during Late Cretaceous
times. In this paper
we
will present
a
preliminary
description
of the dinosaur,
together
with a short explanation
of the stratigraphy
and geographic
location
of the fossil
locality.
A discussion
of the palaeogeo-
graphic
implications
of the
discovery
will also
be included.
Description
of the fossil material
The
dinosaur
from James
Ross Island
is an ankylosaur
(Ornithischia)
of small
size,
perhaps
a
juvenile
specimen.
Most
of the recovered
bones are fragmented,
but the material is
sufficient to warrant identiflcation. The skull of these arm-
oured dinosaurs was protected by thick dermal co-ossifl-
cations. In the ank¡rlosaurids
the postero-lateral
co-ossifi-
cations of the skull
bear marked lateral projections (Coombs,
1978).
Several
of these
plates
are
preserved
in the Antarctic
ankylosaur. A fragment
of left dentary is the only preserved
part ofthe mandible. It bears a double
row ofalveoli and
one
lingual tooth (Fig. 2a). This tooth has the characteristic
low,
leaf-shaped
crown, with apical cusps and lacks a distinct
cingulum. The root of the tooth forms a cylindrical stem
(Fis.2b).
Other
preserved
parts
of the skeleton
consist of vertebrae
and ribs, lragments of the limbs, dermal
plates
and part of the
617
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lce or Debris
a: Moraine
Cenozoic
Volcanics
a: Dykes
Santa
Marta
Fm.
(Campanian)
Geological
Section
@
o
o
lE6';ll Foss¡l
l,)-*l Locality 14-S1
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200
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DfÁ-l
Gamma
Mbr.
Cenozoic
palaeoenvironments
Fig, l. Location map of the James Ross Island Group and geological sketch of Santa Marta Cove area showing
Cretaceous outcrops. The dinosaur site (D6-t) and location of the cross-section of the Santa Marta Formation are also
indicated.
618
tail club. The vertebrae are amphiplatyan
and those corres-
ponding to the sacrum are fused.
In transverse section
the ribs
are T-shaped.
In dorsal view, the ribs show ossified tendons
which are
very coÍrmon in ornithischians.
Several
bony plates and dermal ossicles
that shielded the
body of ankylosaurs
were also recovered
in the specimen
from
James
Ross Island. Some of these
plates
are oval, thickened
and show
á longitudinal crest;
others are
flat, subcircular and
enclosed
by smaller
polygonal plates. The dermal ossicles are
of very small
size.
The
marked lateral
projections
of the dermal
co-ossiflcations
of the skull (Fig.2c), the tooth without a distinct cingulum
(Fie.2b) and the tail club (Fie.2A allow assignation of this
specimen
to the family
Ankylosauridae
(Coombs,
1978; Car-
penter
& Breithaup,
1986). A more detailed
analysis of the
anatomy of this dinosaur
is given by Gasparini et al. (1987).
The material
MLP 86-X-28-l
is deposited at Museo
La Plata,
Division Paleontologia
de Vertebrados
(La Plata, Argentina).
Stratigraphy
The Cretaceous
deposits on James
Ross Island comprise
two main stratigraphic units: the Gustav Group ((?)Bar-
remian Santonian)
and the Marambio Group ((?)Santonian-
Campanian)
(Ineson, Crame & Thomson, 1986; Olivero,
Scasso
& Rinaldi, 1986).
The first group
crops
out along the
coast of Prince Gustav Channel and comprises a thick
sequence
of more than
2000 m of marine conglomerates,
brec-
cias, sandstones
and
mudstones, arranged
in a complex
succes-
sion of coarse-
and fine-grained units (Ineson
et al., 1986).
Most clasts
of the conglomerates are composed of low-grade
schists,
volcanic and granitic rocks, and marine marls and
I

E.B. Olivero e¡
a/. 619
(ot R
Fig. 2. Specimen MLP 86-X-28-1, Campanian ankylosaurid from Santa Marta Formation, James Ross Island, Antarctica: ao
left dentary with a lingual tooth; ó, a lingual tooth without a distinct cingulum; c, dermal plate of the skull roof; d, part of the tail
club. Length of bar is I cm.
mudstones of Late Jurassic Early Cretaceous age (Malagnino
et al., 19781- Medina et al., 7982; Ineson et a/., 1986). This
clearly indicates that the source of the clastic material of the
Gustav Group was the Antarctic Peninsula
to the west.
The Marambio Group comprises a mainly fine-grained
and
highly fossiliferous sequence,
> 3000 m in thickness,
exposed
on James Ross, Vega, Cockburn, Snow Hill and Seymour
(Marambio) islands.
The lower part of the sequence is (?)San-
tonian-Campanian in age
(Olivero et a1.,1986). The upper part
of the Marambio Group is considered to be Maastrichtian
early Tertiary in age
(Macellari, 1986).
The dinosaur remains were found in the basal beds of the
Marambio Group in James Ross Island. This section has been
differentiated recently as a new stratigraphic unit named the
Santa
Marta Formation (Olivero et al.,1986). This unit is well
exposed
in northern James
Ross Island, between the head of
Brandy Bay and Santa Marta Cove (Fig. 1). It consists of
about 1100 m of marine clastic sediments, divided into three
members: Alpha, Beta and Gamma. The basal Alpha Member,
- 480 m in thickness,
consists
of unconsolidated fine coarse-
grained sandstones and mudstones with occasional layers of
conglomerates and coquinas. Marine invertebrate fossils are
abundant and diverse only in the middle and the top, with
leaves, carbonaceous debris and large trunks occasionally
found throughout the Alpha Member.
The Beta Member consists of - 350 m of a rhythmic
sequence of conglomerates with large clasts up to 40 cm in
diameter in a silty or sandy matrix, pebbly sandstones
and
mudstones. The most common lithologies of clasts in the
conglomerates are low-grade schists, volcanic and plutonic
rocks, and reworked sandy
or silty concretions.
Marine fossils,
particularly ammonites, are common and more diverse at the
base of the member. In the upper part, coquina lenses and beds
with trigoniids, baculitids and belemnites
are common. Inter-
calated with these beds are mudstones and sandy siltstones
with abundant carbonaceous material and large silicified or
carbonized logs up to 1 m in diameter.
The Gamma Member consists of about 280 m of friable
fine medium-grained silty sandstones,
frequently with glau-
conite, and carbonaceous mudstones with occasional layers
or lenses of pebbly sandstones or medium conglomerates.
Only in the upper two-thirds of this member is the marine
invertebrate fauna abundant and diverse, comprising serpu-
lids, corals, gastropods, bivalves, ammonites and echinoids.
At locality QF (Fig. 1) a partial skeleton of a plesiosaur
and
vertebrae of a mosasaur were found associated with this
fauna. In the lower third of the Gamma Member, marine
invertebrate fossils are rare; no ammonites were recorded,
4nd gastropods and bivalves are scarce and restricted to a
few horizons. The ankylosaur skeleton was recovered at
locality D6-1 about 90 m above the base of the member
(Fig. 1). At this locality the lithology consists of massive
strongly bioturbated silty sandstones
devoid of glauconite, or
with < 5% of this mineral. Trace fossils are abundant with
most of them consisting of the ichnogenera Ophiomorpha,
Thalassinoides
and Skolithos. These sandstones
are interca-
lated with thin layers of carbonaceous mudstones
with abun-
dant remains of silicified or carbonized wood. Also associ-
ated with the dinosaur skeleton were fish vertebrae and
nautilid phragmocones.

Cenozoic
palaeoenvironments
Age of Santa Marta Formation
Except for the section with dinosaur bones, the rest of
Santa Marta Formation contains a rich assemblage of marine
invertebrates. The top of the Alpha Member and the Beta
Member bear an abundant and relatively diverse ammonite
fauna. On the basis of the presence
of species of Anapachydi-
scus,
Eupachydiscu's and Baculites, which are common or show
strong affinities with species
widely distributed in Patagonia,
Madagascar, South Africa, Japan and the west coast of North
America, Olivero (1984) assigned
a Campanian age to this
fauna. Recent finds ofwell preserved
nostoceratids and diplo-
moceratids (consisting of species of Ainoceras, Eubos*y-
choceras, Ryugasella and Pseudoxybeloceras) provide
additional support for an Early Campanian age for this
section.
Above the stratigraphic interval with the dinosaur bones,
marine fossils are again abundant in the upper third of the
Gamma Member. Although the ammonite assemblage is less
diverse,
it is characterized
by abundant specimens
of Gunna-
rites afl. antarc
ticus.
The evidence derived from ammonite assemblages
occurring
both below and above the lower third of Gamma Member
indicates a Campanian age, most probably Late Campanian,
for the beds
with dinosaur bones.
Depositional environment
Deposition in slope apron-basin plain and submarine
fan settings was proposed for the Gustav Group (lneson,
1985).
It seems likely that most of the Cretaceous
sequence
of
western James
Ross Island consists of a thick wedge
of marine
sediments
deposited
at the foot of a fault-controlled scarp, with
intermittent synsedimentary
tectonic activity. At least part of
Santa Marta Formation, e.g. the Beta Member, appears to be
related to this depositional setting. This is supported by the
occurrence
ofthe coarse conglomerates which display a chaotic
internal structure suggesting a debris flow type of transport.
Despite the above mentioned features, other data suggest
that part of the Santa Marta Formation was deposited in
shallow water. This is indicated by the widespread
distribution
of large fossil tree trunks and plant debris, often occurring
within lenses or as thin beds of coal or carbonaceous mud-
stones.
In particular, the uppermost
part of the Beta Member is
characterized
by coquinas and pebbly shell banks composed
almost exclusively of trigoniid shells. These are intercalated
with fine sandstones and mudstones rich in plant debris. Such
beds could represent longshore bars and lagoonal facies,
respectively. The succeeding lower section of the Gamma
Member, composed of similar fine-grained, strongly biotur-
bated carbonaceous sediments,
could also represent lagoonal
and littoral deposits.
All the recovered dinosaur bones belong to a single speci-
men. Because they were found in a small area of about
2 m x 3 m it seems that the material was not reworked. It was
not possible
to recover
part of the skeleton because the bones
were broken into small fragments by the action of ice. These
facts, together with the evidence for a shallow-water environ-
620
ment of deposition, indicate that the lower section of Gamma
Member has the potential for further dinosaur finds.
An unusual feature of the locality where the ankylosaur
bones were discovered is the presence
of a relatively large
number of nautilid phragmocones, which are assigned tenta-
tively to Cymatoceras sp. Nautilid shells are generally very
scarce in the Cretaceous and Tertiary deposits of the James
Ross Island group and it is interesting to note that the first
discovered
mammal bones from Antarctica were also associ-
ated with a relatively large number of them (Woodburne &
Zinsmeister, 1984). This unusualiy large number of Tertiary
nautilids, associated with marsupial bones, was interpreted as
the result of the stranding of shells along a beach. It seems
likely that the large concentration of nautilid shells at the
dinosaur locality could be explained by the same
process.
Palaeogeographical implications
The discovery of a Late Cretaceous
ankylosaur in Ant-
arctica provides important new data concerning hypotheses of
past land connections of the Antarctic Peninsula. In order to
explain the occurrence
of these reptiles
in Antarctica, two main
hypotheses can be considered
(Gasparini
et al.,1987).
Firstly,
the ankylosaurs
were already differentiated at the family level
in the Late Jurassic Early Cretaceous. By this time they were
distributed in both Laurasia and Gondwana, and the Antarctic
species would be the result of some form of vicariance. The
oldest known ankylosaurids are from the Upper Cretaceous
(Coniacian) of Asia (cf. Gasparini et al., 1981
, and the biblio-
graphy therein) and consequently their fossil record does not
support this flrst hypothesis. However, an older non-documen-
ted fossil record for this family cannot be completely ruled out.
In the second hypothesis it is considered that Late Cre-
taceous
northern ankylosaurids entereci Antarctica via South
America; such a derivation is considered to be much more
likely. Previous records of ankylosaurs from Patagonia have
been questioned and this group of dinosaurs is not yet docu-
mented in South America (Bonaparte, 1986).
Nevertheless, the
family Ankylosauridae is well represented
in the Upper Cre-
taceous of North America and Asia (Coombs, 1978) and other
data indicate the possibility of a land vertebrate interchange
between North and South America during part of the Late
Cretaceous
(Bonaparte, 1
986). Concerning the problem of how
the ankylosaurs were able to get onto the Antarctic Peninsula
from South America, a number of independent data strongly
suggest a close proximity of these two areas during Late
Cretaceous times (Dalziel & Elliot, 1913, 1982:
Zinsmeister,
1982, 1987). The finding on Seymour Island of marsupials with
South American affinities leaves
no doubt about the proximity
of these continents during the latest Cretaceous or earliest
Tertiary, and strongly suggests a continuous land connection
between South America and Antarctica (Woodburne & Zins-
meister, 1984). Such a connection for these continents is also
indicated by the distribution of two families of Cretaceous
continental turtles (meiolaniids and cheliids)
which occur only
in Australia and South America (Baez & Gasparini, 1979;
Gasparini, De la Fuente & Donadio, 1986).
In previous reconstructions
ofGondwana, the area between

E.B. Olivero et al.
Fig.3. Palaeogeographic sketch map of the Antarctic Peninsula and
southern South America during the Late Cretaceous. Features shown are:
inferred continuous land connection (stippled area) between
the Antarctic
Peninsula and South America; the marine Upper Cretaceous deposifs of
the Austral Basin (AB) and James Ross basin (JRB); New Zealand (NZ)
and the inferred seaway between East ¿nd West Antarctica. Data in part
from Norton (1982), Riccardi (1987) and Zinsmeister (1987).
Tierra del Fuego and the Antarctic Peninsula is generally
depicted
as an archipelago
(cf. Dalzie\
& Elliot, 1982). The
occurrence of dinosaurs in James Ross Island
provides
new
insight
concerning the nature
of the
land
connection
between
these
regions. Because
ankylosaurs were large, heavy,
arm-
oured dinosaurs, their passive
transportation
across water
barriers
(e.g.
on natural rafts)
seems unlikely. Consequently, if
the hypothesis
ofa late
entrance ofankylosaurs into Antarctica
is correct, their
presence
in James Ross Island indicates
that a
continuous
land connection must have existed
between Ant-
arctica
and South America for some
period
of time
durine the
Late Cretaceous.
During the
Late
Cretaceous in the Austral
(or Magallanes)
Basin of southern
Patagonia
marine
conditions
prevailed
south
of Deseado Massif. Geological
data indicate
that this basin
opened
to the
Antarctic
with elevated terranes situated
along
the
present
axis of the Cordillera
(Riccardi,
1987). A compara-
ble palaeogeographical
setting can be interpreted for the Cre-
taceous
sediments of the Gustav and Marambio groups
in
Antarctica. Distribution of coarse
clastic facies
and com-
position
of clasts clearly indicate that this basin was confined
621
to the west by elevated
terranes
situated along the axis of the
Antarctic Peninsula.
In the palaeogeographical
scheme
of Fig.3, a continuous
land connection, required for the migration of land verte-
brates, is shown along the Pacific margin of the Antarctic
Peninsula and South America. In this scheme
the Late Cre-
taceous
position
of the
southern Gondwana
continents
is that
of Norton (1982).
The location of the seaway between
the base
of the Antarctic Peninsula
and East Antarctica was adopted
from Dalziel & Elliot (1982)
and Woodburne
& Zinsmeister
11984).
If the idea of a continuous land connection as
explained above
is accepted,
then this seaway
is necessary to
justify the affinities between the Late Cretaceous marine
invertebrate faunas of Antarctica-Patasonia
and New Zealand
(Zinsmeister,
1982).
There is independent evidence suggesting
a relatively warm
climate during the Late Cretaceous, with the presence, par-
ticularly in the peninsula region, of an abundant flora
(Woodburne
& Zinsmeister,
1984; Francis,
1986). The occur-
rence
of trunks,
leaves
and
plant fragments
in the Santa Marrta
Formation clearly
indicates
that the land situated to the west
of
James
Ross Island was
densely vegetated. According
to palae-
omagnetic data, the Antarctic Peninsula
was situated near its
present position by the Late Cretaceous
(Codignotto et al.,
1978; Dalziel & Elliot, 1982), indicating that this forest was
able to grow at the palaeolatitude
of James Ross Island
(i.e.
about
64'S).
Acknowledgements
We would like to thank the Instituto Antártico Argen-
tino, Fuerza Aérea Argentina and the Centro de Investiga-
ciones en Recursos Geológicos
(CIRGEO) for providing
the
means and logistic support. Alejandro
López Angriman
and
Ricardo Roura
(University
of Buenos
Aires)
and Mario Buirás
and Jorge
Amat (Comando
Antártico de Ejército) were active
collaborators during the fieldwork. We are indebted to Dr
William J. Zinsmeister
(Purdue University) for the critical
reading
ofpart ofthis study.
The
elaboration
of this
study has
been made in part by one
of the authors (EBO) at Purdue University (Indiana, USA)
during the tenure of a Fellowship of Consejo Nacional de
Investigaciones
Científicas y Técnicas (Argentina). All the
assistance
and support provided by the Geosciences
Depart-
ment and Interlibrary Loan Office of Purdue University is
greatly
appreciated.
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