SYMPOSIUM CRETACEOUS-TERTIARY PALAEOBIOGEOGRAPHIC CONNECTIONS WITH ANTARCTICA

Transcription

SY M POSI U M
C RETAC EOUS -T E RT I A RY
PAL AEOBIOGEOGR A PH IC
CON N EC T IONS W I T H A N TA RC T IC A
ORGA N I Z E R S:
M A RC ELO A . R EGU E RO - EDUA R DO B. OLI V E RO
Cretaceous-Tertiary palaeobiogeographic connections with Antarctica / Oral
T H E L AT E C R E TAC EOUS F LOR A S F ROM
NORT H W EST E R N A N TA RC T IC P EN I NSU L A A N D T H EI R
EVOLU T IONA RY A N D PALEOGEOGR A P H IC ROLE
Tânia Lindner Dutra1, Bibiana Bastos1, Thièrs Wilberger1 and Cristine Trevisan1
1. Graduation Program in Geology, Vale do Rio dos Sinos University -UNISINOS
Av. Unisinos, 950, 93022-000, São Leopoldo, Rio Grande do Sul, Brazil. [email protected]
The end-Cretaceous floras from Antarctic Peninsula (AP) exhibit a distinctive composition,
including elements that will play an important role in the evolution of the Cenozoic and modern
floras from South Hemisphere. The partially continuous landmasses (Weddelian Province), the
wet and mild climates and the tectonic activity that created altitudinal gradients, stimulated the
appearance of some critical taxa in this region, allowing the survival of others, protecting them
against the drier climates of the tropical areas. Most of these processes have large-scale effects
on vegetation after the beginning of the Cretaceous when the typical early-middle Mesozoic
decreased in importance (ferns and primitive gymnosperm groups, like Pteridospermophyta,
Bennettitales, Cycadales, Gyngoales, Taxodiaceae and Palyssaceae), and opens space to the
evolution of a new kind of forested vegetation. Yet the “modern” South Hemisphere conifer
families (Araucariaceae, Podocarpaceae and Cupressaceae) and tree ferns are maintained, whereas
the first angiosperms appeared in the understory. Until the end of the period, putative Nothofagus,
Proteaceae, Elaeocarpaceae, Anacardiaceae and some laurophyllous flowering plants, occupy all
the landscape of the northwestern AP, with a marked altitudinal distribution near the volcanic
centers. Forms related to the modern Papuacedrus (Cupressaceae), Phyllocladus (Podocarpaceae),
dubious Melastomataceae and Aquifoliaceae make their first appearance. After this, guided by
the environmental changes resulting from the Gondwana fragmentation and consequent climate
changes, those forests will influence the composition of austral vegetation. Taking the opportunity
created by the subsequent favorable climates from the end of Paleocene - Early Eocene, they will
make part of a broad subtropical to warm temperate rainforest biome that dispersed to South
America and Australasia, only reduced with the arrival of the first cold conditions during the
Paleogene-Neogene transition. Today Papuacedrus is exclusive from Papua-New Guinea, yet other
Cupressaceae still lives in South America and the same genus is recorded there till the beginning of
Eocene. Phyllocladus grows only in New Zealand, Tasmania, Papua-New Guinea and other eastern
Pacific areas. The Melastomataceae are nowadays an important family of both mountainous and
lowland tropical areas of South America and other southern continents and the fossils here found,
if confirmed, could contradict the molecular clock approaches. The modern species of Nothofagus,
one of main taxa in attest the importance of AP in the evolution of austral floras, is only absent from
Africa and Madagascar. [CNPq, CAPES].
4th INTERNATIONAL PALAEONTOLOGICAL CONGRESS, Mendoza, Argentina. 2014
200
COM P R E H ENSI V E ST U DY OF A N TA RC T IC- PATAGON I A N
P L A N T DI V E R SI T Y DU R I NG T H E C R E TAC EOUS T E RT I A RY IS ESSEN T I AL FOR U N DE R STA N DI NG
MODE R N A M E R IC A N P L A N T DIST R I BU T ION
Maria A. Gandolfo1 and Maria C. Zamaloa2
1. L. H. Bailey Hortorium, Department of Plant Biology, Cornell University, Ithaca, NY 14853, USA. [email protected]
2. Departamento de Ecología, Genética y Evolución, Facultad de Ciencias Exactas y Naturales, Universidad de
Buenos Aires – IEGEBA (CONICET-UBA), Intendente Güiraldes 2620, C1428EHA Buenos Aires, Argentina.
In the Modern World the Northern Hemisphere (NH) is characterized by its continentality whereas
the Southern Hemisphere (SH) is characterized by its oceanicity. This results in completely different
scenarios for plant distributions, since the continentality of the north and oceanicity of the south have
considerable effects on the corresponding climates. Moreover, equatorial zones worldwide show
higher plant diversity that clearly decreases towards the poles indicating the presence of latitudinal
diversity gradients. Interestingly, the SH is more diverse than the NH, in particular Patagonia, which
is considered an area of high endemism. In general, peaks in diversity started with the beginning of
the fragmentation of Gondwana during the Jurassic followed by the appearance of the angiosperms
during the Cretaceous and increasing dramatically in the Tertiary (mostly during the Paleogene
- Miocene). The fossil record indicates 1- that equatorial peaks in species richness are typical of
terrestrial plants, 2- that diversity and equatorial peaks increased during the Cenozoic, and 3- that
several vicariant events that occurred during the Neogene were fundamental for the creation of high
diversity centers. Several biogeographical models and dispersion routes have been proposed for
explaining diversity centers and the Gondwana pathway is frequently recognized while the NorthSouth American connection is sometimes ignored. The main goal of this contribution is to present a
comprehensive analysis of plant diversity for Patagonia and the Antarctic Peninsula from the Late
Cretaceous to the Miocene. Although, the North-South America pathway is not strongly detected
in the plant fossil record at this point a route from the NH is emerging as boreotropical elements
(such as Ulmaceae, Juglandaceae, Azolla, Marsileaceae, and Nelumbo) were found in Cretaceous and
Paleocene sediments of Patagonia while the Antarctic route allowed the movement of Gondwanan
elements (such as Cunoniaceae, Myrtaceae, Nothofagaceae, Proteaceae, and Casuarinaceae) during
the Tertiary. As the climate changed, some elements became extinct but others survived and are
now members of the extant floras. Although today 98% of Antarctica is covered by ice, during the
Cretaceous – Oligocene the Antarctic Peninsula vegetation was similar to the one found today at
the Valdivian Forests of the west Patagonian Andes. The eastern vegetation of Patagonia is a typical
steppe or grassland. Undoubtedly, both routes influenced the composition of the extant floras and
are central for explaining modern austral vegetation and the high Patagonian endemism.
201
I M P LIC AT IONS OF T H E EVOLU T IONA RY STA SIS
OF NO T IOLOFOS A RQU I NO T I E NSI S (M A M M ALI A)
EOC EN E OF SE Y MOU R ISL A N D, A N TA RC T IC A
Javier N. Gelfo1
1. División Paleontología de Vertebrados, Museo de La Plata. Paseo del Bosque s/n
B1900FWA, La Plata, Argentina. [email protected]
The Sparnotheriodontidae litoptern Notiolofos arquinotiensis was the most abundant terrestrial
placental mammal in the Paleogene of Antarctica. This herbivorous mammal was a low-crowned
browser, with lophoselenodont and bicrescentic lower teeth and a strong lophoselenodont ectoloph
and bunoid lingual cusp in the upper molars. Phylogeny and paleobiogeographic evidence indicates
a South American origin of Sparnotheriodontidae, and an allopatric speciation event for the origin
of N. arquinotiensis. It was recorded exclusively in Seymour Island, through most of the La Meseta
Formation allomembers, including from base to top, Acantilados II, Campamento, Cucullaea I,
and Submeseta. Isotopic and paleomagnetic calibration of the La Meseta Formation suggests an
evolutionary stasis for Notiolofos of at least 17.5 Ma. The analysis of the morphological stability
displayed by paleospecies requires a profuse fossil sample through the stratigraphic succession.
Notiolofos remains comprise neither complete dental series nor abundant teeth; its hypodigm joins
isolated teeth from different loci and from distinct stratigraphic levels. The stasis hypothesis is here
tested as opposite to the possibility of a wider and non-previously identified specific diversity of
the Antarctic sparnotheriodontids. The materials available for Notiolofos were compared in their
preservation, characters and dental occlusal areas to the more complete phylogenetic relative
Sparnotheriodon epsilonoides and the North American Meniscotherium chamense. Despite there is not a
direct phylogenetic relationship between Notiolofus and Meniscotherium, the morphological dental
similitude between both suggests they could be interpreted as ecologically equivalent taxa. The
analysis allows the reassignment of some Notiolofos teeth to other dental locus but not to consider a
higher variation than previously described. The temporal scale of Notiolofos is appropriate to consider
Court Jester hypothesis as the principal evolutionary force, so it could be expected that during this
span, environmental change triggered speciation events. The present analysis indicates that there
are no elements to justify the presence of different species through the stratigraphic sequence or to
refute the morphological stasis in Notiolofos. In a reductionist perspective, this suggests a stability
of the terrestrial physical conditions in West Antarctica during most of the Eocene, or at least, that
any environmental change, particularly in climate and vegetation, was not enough to generate an
evolutionary response.
202
N E W R ECOR DS OF C ENOZOIC BEN T H IC
FOR A M I N I F E R A F ROM A N TA RC T IC P EN I NSU L A
SEC TOR OF W EST A N TA RC T IC A
Wojciech Majewski1 and Andrzej Gaździcki1
1. Institute of Paleobiology, Polish Academy of Sciences, Twarda 51/55, 00-818 Warszawa, Poland.
[email protected]
Despite considerable efforts, our knowledge on pre-Quaternary foraminiferal communities from
the Antarctic Peninsula sector of West Antarctica remains far from satisfactory. Up to quite recently,
only a few reports have been published. Cretaceous-Paleocene foraminifera were described from
Seymour Island, Oligocene planktonic and Miocene benthic foraminiferal assemblages were
reported from King George Island (South Shetlands), and Miocene-Pliocene and Pliocene benthic
assemblages from James Ross and Cockburn islands west off Antarctic Peninsula. Here, we are
presenting foraminiferal finds from the lower Eocene La Meseta Fm. of Seymour Island, the lower
Oligocene Polonez Cove Fm. of King George Island, and the middle Miocene of Weddell Sea,
~150 km east off Joinville Island, which fill some gaps in foraminiferal Cenozoic record from the
Antarctic Peninsula region. At all three locations, calcareous, benthic foraminifera strongly dominate
the assemblages. The two Paleogene benthic foraminiferal assemblages from Seymour and King
George islands represent shallow-water biotas. They share a group of common species including
Gyroidina zealandica, sister species of Nonionella iridea and N. bradyi, Globocassidulina subglobosa,
Lobatula (Cibicides) lobatula, and Eilohedra (Epistominella) vitrea. These species belong to the most
morphologically conservative Antarctic foraminifera, which seem to be present continuously in
neritic Antarctic settings at least since the Eocene. The youngest (mid Miocene) assemblage from the
Weddell Sea is much different, probably not in situ. It is dominated by specimens similar to Recent
Elphidium macellum that is widespread in coastal Patagonia but absent in Antarctica. Also, some
important elements of the recently described Eocene and Oligocene foraminiferal communities
(e.g. abundant Eocene elphidiid foraminifera) show similarities to contemporaneous forms from
Patagonia, testifying for faunal links between Antarctic Peninsula and Patagonia through much of
Cenozoic.
203
GEODY NA M IC EVOLU T ION OF T H E SCOT I A A RC :
T H E F I NAL BR E A K U P OF GON DWA NAL A N D
A N D I TS GLOBAL I M P LIC AT IONS
Andrés Maldonado1 and SCAN GROUP
1. Instituto Andaluz de Ciencias de la Tierra, Consejo Superior de Investigaciones
Científicas and Universidad de Granada, Spain. [email protected]
The Scotia Arc, located between South America and the Antarctic Peninsula is a region of critical
importance because of its role as a developing ocean gateway during Eocene-Miocene times,
and because of its impact on global ocean circulation, with possible importance for PalaeogeneNeogene palaeoenvironmental change, early phases of development of Antarctic ice sheets, gene
flow, and resulting biodiversity. The Scotia Sea is embraced by the tectonic arc and reveals a host
of spreading ridges and small oceanic basins which allow reconstructing the growth patterns of
this sea and of Drake Passage, located in the western region. The opening of the Scotia Sea and
Drake Passage is a subject of considerable controversy. Drake Passage is widely recognized as key
gateway that controlled Cenozoic water-mass circulation and climate in the southern hemisphere.
The gateway permitted the gradual instauration of the Antarctic Circumpolar Current, which
isolated Antarctica from the influx of warm currents from the north and intensified its glaciation.
An initial interpretation attributed the climatic change and the development of the large Antarctic
ice sheets to the opening of Drake Passage, although additional hypothesis attributed the Eocene/
Oligocene climate change and the subsequent Cenozoic glaciation of Antarctica to variations in the
concentrations of greenhouse gases. A dense geophysical data set collected in the southwestern
Scotia Sea is presented and evidences for the occurrence of oceanic crust that is older than
previously reported are shown. The initial tectonic fragmentation of the South America-Antarctic
Bridge, followed by oceanic spreading, was characterized by jumping of the spreading centers.
An Eocene spreading center in the SW Scotia Sea was the precursor for the opening of the basin. A
model with four tectonic evolutionary phases is proposed: Phase I, Pacific subduction –Paleocene
to middle Eocene; Phase II, eastern Ona back-arc spreading –middle to late Eocene; Phase III, ridge
jumping and western Ona back-arc spreading –early Oligocene; and Phase IV, ridge jumping and
WSR spreading –early Oligocene to late Miocene. The development of shallow gateways allowed
an early connection between the Pacific and Atlantic oceans and initiated the thermal isolation of
the Antarctic during the Phase II. Deep gateways that enhanced the full isolation of the Antarctica
were developed in Drake Passage from the Eocene/Oligocene transition. A significant correlation is
observed between the tectonics, stratigraphic units and major climate events, thereby indicating the
influence of the local tectonic and paleoceanographic events of the southern oceans on the global
evolution.
204
FOSSI L F LOR A OF T H E C H AT H A M ISL A N DS, E A ST E R N
‘Z E AL A N DI A’: A W I N DOW I N TO T H E FOR EST BIOM E
OF T H E M I D -C R E TAC EOUS SOU T H POLE
Chris Mays1 and Jeffrey D. Stilwell1
Monash University, School of Geosciences, Monash University, Victoria, 3800, Australia.
[email protected]
1
The Chatham Islands, New Zealand, provide a unique perspective of the polar forest biome during
the mid-Cretaceous global greenhouse (palaeolatitude ~ 70–80° S), when eastern Zealandia was
attached to the West Antarctica sector of Gondwana. The palynological assemblage supports
a Cenomanian-Turonian (~ 98–90 Ma) age for the ~ 400 m thick succession. The examined
lithostratigraphic unit, the Tupuangi Formation, was deposited in a fluviodeltaic system; lithological
and palaeopedological evidences suggest that the local depositional environments associated with
the macrofloral remains were deltaic floodplains. Diverse macrofloral fossil assemblages were
found on numerous hydromorphic palaeosol horizons, often associated with well-established root
systems and in situ trunks, or entrained in overlying fine sandstone facies. This macroflora consisted
of prevalent conifers, locally abundant angiosperms and ginkgos (Ginkgoites), and uncommon freesporing plants, including non-vascular plants (marchantiophytes and bryophytes), herbaceous
lycopsids and ferns (Adiantites, Cladophlebis and Sphenopteris). The fern leaf and spore assemblage
comprised a lower diversity and abundance than coeval localities of the Southern Hemisphere,
including eastern Australia, the Antarctic Peninsula and mainland New Zealand. Quantitative
microfloral data reveal intermittent overabundances of monospecific fern spores, but these were
likely caused by the localised re-establishment of riparian fern taxa after disturbance of the
floodplain environment. In contrast to the relatively depauperate fern component, the high conifer
pollen diversity and abundance is unparalleled for mid-Cretaceous assemblages of the Southern
Hemisphere, and consists almost exclusively of Araucariaceae, Cupressaceae and Podocarpaceae.
The conifer-dominated assemblage is likely due to the relatively cooler, drier climate associated with
the extremely high palaeolatitude. Furthermore, the palynology hints at a previously unreported
microfloral subprovince, characterised by a very high abundance of cupressaceous pollen. A
combination of macro-, meso- and palynofloral fossil remains indicate a well-established coniferous
forest with a ginkgo-angiosperm understory, and subsidiary ferns, seed-ferns, lycophytes and nonvascular plants. This assemblage represents the highest southern latitude flora of the mid-Cretaceous
studied to date, and thus provides a crucial biogeographic and ecological end-member during one
of the most extreme global greenhouse regimes in geological history.
205
A N E W LOOK I N TO T H E A N TA RC T IC COOLI NG A N D T H E
DIST R I BU T ION OF SOU T H E R N M A R I N E BI VALV ES
Fernanda Quaglio1, Huw J. Griffiths2, Katrin Linse2,
Rowan J. Whittle2, Silvio S. Nihei3 and Marcello G. Simões4
1. Universidade Estadual Paulista, UNESPetro, Av. 24-A, 1515, Rio Claro, SP, 13506-900, Brazil. [email protected]
2. British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK.
3. Universidade de São Paulo, Instituto de Biociências, São Paulo, 05508-900, Brazil.
4. Universidade Estadual Paulista, Instituto de Biociências, Distrito de Rubião Júnior, Botucatu, 18618-000, Brazil.
The Antarctic cooling is associated to several environment-related changes occurred in the Cenozoic,
including: atmospheric CO2 drop during times of orbitally-induced decline in the polar seasonality,
tectonic isolation of Antarctica from Australia and South America, and reorganization of marine
and atmospheric currents. Major tectonic changes included the opening of the Tasmanian Gateway
(Late Eocene to Early Oligocene) and the Drake Passage (Late Eocene to Early Oligocene), which
are key Southern Ocean gateways, tied to the origin of the Antarctic Circumpolar Current. Both
cooling and opening of oceanic gateways are believed to have shaped the biotic evolution of the
southern regions throughout the Cenozoic to the Present-day. Previous studies link the origin of
modern Antarctic marine fauna to the geographic isolation of Antarctica, to the Cenozoic cooling,
or both. This study shows, by analyzing an extensive dataset of bivalve genera with an innovative
paleobiogeographic approach, that the main southern marine biogeographic provinces were
defined as early as the beginning of Paleogene because of tectonic causes. Along the Cenozoic, the
faunal differences were sharpened, probably due to climatic cooling, as indicated by the coupling of
the faunal similarity curve to the global temperature trend. Our results have important implications
for potential warmer marine environments.
206
U P P E R C R E TAC EOUS –?PALEOGEN E ST R AT IGR A P H Y
A N D V E RT EBR AT E PALEOECOLOGY OF V EGA ISL A N D,
A N TA RC T IC A : PALEOGEOGR A P H IC , PALEOC LI M AT IC ,
A N D SEQU ENC E ST R AT IGR A P H IC I M P LIC AT IONS
Eric M. Roberts1, Matthew C. Lamanna2, Julia A. Clarke3, Jin Meng4,
Eric Gorscak5, Joseph J. W. Sertich6, Patrick M. O’Connor5, Kerin M. Claeson7,
Nathan B. English1, Christa J. Placzek1, Jodie Kilpatrick1 and Ross D. E. MacPhee8
1. School of Earth and Environmental Sciences, James Cook University, Townsville, QLD 4811, Australia. [email protected]
2. Section of Vertebrate Paleontology, Carnegie Museum of Natural History, 4400 Forbes Ave., Pittsburgh, PA 15213, USA.
3. Department of Geological Sciences, University of Texas at Austin, 1 University Station, C1100, Austin, TX 78712, USA.
4. Department of Paleontology, American Museum of Natural History, Central Park West at 79th St., New York, NY 10024, USA.
5. Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, OH 45701, USA.
6. Department of Earth Sciences, Denver Museum of Nature and Science, 2001 Colorado Blvd., Denver, CO 80205, USA.
7. Department of Biomedical Sciences, Philadelphia College of Osteopathic Medicine, Philadelphia, PA 19131, USA.
8. Department of Mammalogy, American Museum of Natural History, Central Park West at 79th St., New York, NY 10024, USA.
In 2011, as part of a cruise sponsored by the U.S. National Science Foundation to the James Ross
Basin, Antarctica, our team carried out fieldwork on Vega Island during a two-week period of
mostly favorable weather. The project involved investigating the paleontology and sedimentology
of each of the Upper Cretaceous units exposed on the island, with a focus on the capping Sandwich
Bluff Member of the López de Bertodano Formation. Although this unit is one of the richest sources
of end-Cretaceous vertebrate fossils in Antarctica, it is also one of the least sedimentologically and
stratigraphically characterized units in the basin. Detailed facies and stratigraphic analyses of the
Sandwich Bluff Member were conducted alongside intensive prospecting for fossil vertebrates and
stratigraphic assessment of historic paleontological localities on Vega Island. This effort, coupled
with the acquisition of new strontium isotope data, have led to a revised stratigraphy for the
Sandwich Bluff Member and the precise stratigraphic placement of important terrestrial and marine
vertebrate fossil localities within it. Most significantly, this work resulted in the recognition of a new
sequence boundary near the top of the Sandwich Bluff Member, which is overlain by a 6 m-thick,
matrix-supported, pebble-cobble conglomerate of probable alluvial origin. A thin stratal package
above the conglomerate demonstrates a rapid return to marine conditions. A similar stratigraphic
pattern is well documented at the top of the López de Bertodano Formation and the base of the
overlying (Paleocene) Sobral Formation on Seymour Island in the southern part of the basin.
Although no fossils were recovered to constrain the age of the upper 10–15 m of the succession on
Vega Island that preserves the newly recognized upper sequence boundary, strata below this level
can be confidently placed within the Manumiella bertodano interval zone, which extends to a short
distance below the K–Pg boundary on Seymour Island. Hence, based on sequence stratigraphic and
lithostratigraphic evidence, we propose that the uppermost 10–15 m of the succession on Vega Island
may encompass the Cretaceous–Paleogene boundary together with a few meters of the Paleocene
Sobral Formation. In addition, this presentation will briefly discuss the presence and implications of
‘dropstones’ in Upper Cretaceous strata of the James Ross Basin, as well as new strontium isotope
dating and preliminary taphonomic investigations of Antarctic Cretaceous fossil wood and bone
via synchrotron Fourier transform infrared (FTIR) analysis.
207
PALEOC EN E FOR ESTS A N D C LI M AT ES OF
A N TA RC T IC A : SIGNALS F ROM FOSSI L WOOD
Laura Tilley1, Jane Francis2, Vanessa Bowman2, Alistair J. Crame2 and Fiona Gill1
1. University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, United Kingdom. [email protected]
2. British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, United Kingdom.
During the greenhouse world of the Paleocene, Antarctica was covered in forests, even though
the continent was situated over the South Pole. Fossil wood is abundant in marine sequences of
Seymour Island, Antarctica. The wood originated from forests that once grew on a volcanic arc
now represented by the Antarctic Peninsula and then floated as driftwood on the ocean before
eventually sinking into the ocean sediments and becoming permineralised. Fossil wood has
been systematically collected from Paleocene marine sequences of Seymour Island and has been
studied in order to reconstruct the forest composition and evolution of the vegetation throughout
the Paleocene. The exact location of the wood was recorded on a measured stratigraphic section
so that preservation type, taxonomy and climate data derived from the wood could be put into
a stratigraphical and environmental context. Trees that lived in the forests included Nothofagus,
Myrtaceae, Weinmannia, Araucaria, Phyllocladus and podocarp conifers. These tree types can be
found in cool temperate forests in Chile and New Zealand today. Analysis of tree rings, angiosperm
vessels and specific gravity have been used to reconstruct climate in which forests grew during the
Paleocene. Mean growth ring analysis shows a trend towards narrow growth rings in the earlymid Paleocene, which suggests cooler climates. Mean sensitivity calculated from tree ring width
generally shows growth under an equable climate. Vulnerability Index (VI) and Mesomorphy
Index (MI) have been calculated using angiosperm vessels as an indicator of water availability,
and more precise MI values indicate sufficient water availability. Specific gravity has been linked
to a plants adaption to water availability in its environment as well as growth strategy. Most of the
fossil wood types show medium specific gravity (0.40–0.75) values, which is expected for temperate
forests. Podocarpaceae and Araucariaceae fossil wood shows high specific gravity values similar
to their modern relatives, suggesting that they had a similar life habit. Investigating these factors is
essential for understanding how sensitive vegetation was to climate change.
208
Cretaceous-Tertiary palaeobiogeographic connections with Antarctica / Poster
PALEOGEN E A N TA RT IC L A N D M A M M ALS:
T H EI R BIOGEOGR A P H IC R EL AT IONSH I PS A N D
T H E F I NAL BR E A K-U P OF GON DWA NA
M. Alejandra Abello1, Paula Posadas1, Edgardo Ortiz-Jaureguizar1,
Javier N. Gelfo2, Laura Chornogubsky3 and Marcelo Reguero2
1. CONICET, Laboratorio de Sistemática y Biología Evolutiva, Museo de La Plata, Paseo del
Bosque s/n, (B1900FWA) La Plata, Argentina. [email protected]
2. CONICET, División Paleontología Vertebrados, Museo de La Plata, Paseo del Bosque s/n,
(B1900FWA) La Plata, Argentina.
3. CONICET, Sección Paleontología de Vertebrados, Museo Argentino de Ciencias Naturales,
Av. Ángel Gallardo 470, Buenos Aires, C1405DRJ, and Departamento de Ciencias Básicas, Universidad
Nacional de Luján, Ruta 5 y Avenida Constitución, Luján, 6700, Buenos Aires, Argentina.
The Paleogene land fauna of Antarctica is exclusively known from outcrops of the La Meseta
Formation (Eocene to Oligocene) from Marambio/Seymour Island (Antarctic Peninsula). The
faunal association includes several mammalian groups as ungulates (Sparnotheriodontidae and
Astrapotheria), marsupials (Polydolopidae, Derorhynchidae and Microbiotheria) and non-therian
mammals (Sudamericidae and Dryolestoidea). This taxonomic composition is similar to that of
some Paleogene land mammal assemblages from the southernmost part of South America (i.e.
Patagonia), thereby, several hypotheses were proposed to account for the biogeographic history
of the Antarctic taxa, as well as for the timing of the paleogeographic events that could be implied
in the shaping of the Antarctic land mammal association. To identify the biogeographic events
(dispersion, vicariance) that could explain the observed distribution patterns of Antarctic land
mammals, we selected those groups for which a phylogenetic hypothesis was available. DispersalVicariance analyses were performed with RASP software for therian mammals (i.e. ungulates and
marsupials). The analysis of Astrapotheria and Sparnotheriodontidae yields a widespread ancestral
distribution, including South America and Antarctica, since the lower Paleocene up to middlelate Paleocene, when a vicariant event took place. In contrast, Polydolopidae marsupials show a
distribution restricted to Patagonia during the lower and middle Paleocene and a dispersal event
from Patagonia to Antarctica followed by a vicariance, both of them during the late Paleocene.
The three analyses resulted in a congruent vicariance during late Paleocene when the ancestral
distributions along Patagonia and West Antarctica were fragmented by the rise of a barrier leading
to the geographic isolation and differentiation of Patagonian and Antarctic lineages. In absence of
evidence of geographic barriers other than the emerging Drake Passage, the fragmentation of the
ancestral range could be explained by the earlier stages of rifting and stretching crustal thinning in
the opening of this seaway. From the results obtained we could conclude that the biogeographic
histories of sparnotheriodontids and astrapotherians were different from those of polydolopids,
but all of them support the hypothesis of an early stage (late Paleocene) in the paleogeogeographic
event leading to the development of a shallow epicontinetal sea which eventually led to the opening
of the Drake Passage.
209
N E W GI A N T P ENGU I N BON ES F ROM A N TA RC T IC A :
SYST EM AT IC A N D PALEOBIOLOGIC AL SIGN I F IC A NC E
Carolina Acosta Hospitaleche1
1. CONICET and División Paleontología Vertebrados, Museo de La Plata. Facultad de Ciencias Naturales y
Museo (UNLP), Paseo del Bosque s/n, B1900FWA, La Plata, Argentina. [email protected]
A tarsometatarsus (MLP 12-I-20-116) and a fragmented humerus (MLP 12-I-20-288) of striking
dimensions assigned to Palaeeudyptes klekowskii were collected in the DPV 13/84, Marambio
(Seymour) Island, Antarctica. They come from the middle Eocene- earliest Oligocene Submeseta
Formation, equivalent to the uppermost part of the former La Meseta Formation, according to
new stratigraphic proposal. Body mass and body length (maximum measurements from the tip
of the toes to the end of the bill, with the neck and legs outstretched) were calculated. The most
conservative values were used for diving duration estimations. The 91.3 mm long tarsometatarsus
is the most massive tarsometatarsus known for Palaeeudyptes (59- 82.4 mm), constituting the largest
one ever described. Subtle differences were obtained by using each measurements selected for
calculations. The tarsometatarsal width indicates a body mass of 114.38 kg and 2.01 m long, whereas
the anteroposterior width points toward a body mass of 116.21 kg and 2.02 m of total length. It
seems an extremely high value for both calculated parameters. Nevertheless, given that the living
Emperor penguin reaches 46 kg in weight and 136 cm in length –equivalent to near 116 cm in
height–, and its tarsometatarsus is only about 50 mm long, the estimated values based on an almost
double sized tarsometatarsus are not beyond the expected assessment. Assuming that the humerus
proportions are not sensitive to significant intraspecific variation, it seems possible to calculate an
approximate length of 259.2 mm for the MLP 12-I-20-288 on the basis of the measurements taken
in the co-specific MLP 11-II-20-07, and scaling its size from the width of the proximal epiphysis.
Dimensions of the humerus are also huge, although these values are only estimates and cannot
be taken as absolute. The most conservative values were here taken for further paleobiological
calculations in order to prevent overestimations. The tarsometatarsus would belong to a penguin
with high diving skills, capable of making longer breath-hold dives than other heavy animals. It
was estimated that regular dives take 16.6 minutes duration (with potential and maximum dives
of 40 minutes). These approximations are consistent with the generalized idea that Antarctic large
penguins were piscivores. They had probably used pursuit diving techniques for the capture of
large fish. Gigantism would confer it certain advantages for survival within the colony, a more
effective defense against predators, and greater ability to catch prey.
210
C R E TAC EOUS EV I DENC E OF A ST E R ALE A N LI K E POLLEN I N A N TA RC T IC A
Viviana D. Barreda1, Luis Palazzesi1,2, Maria C. Tellería3, Eduardo Olivero4 and Felix Forest2
1. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” (MACN-CONICET),
Ángel Gallardo 470 (C1405DJR), Buenos Aires, Argentina. [email protected]
2. Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3DS, UK.
3. Laboratorio de Sistemática y Biología Evolutiva (LASBE), Museo de La Plata,
Paseo del Bosque s/n (1900) La Plata, Buenos Aires, Argentina.
4. Centro Austral de Investigaciones Cientíﬁcas (CADIC-CONICET), B. Houssay 200, 9410 Ushuaia,
Tierra del Fuego, Argentina.
Asterales is an order of flowering plants that includes the highly diverse Asteraceae —daisy family—
along with ten other phylogenetically related families. Asterales appear to have originated in the
Cretaceous, but no fossils from this period have been found to date to support this assumption
regarding the origin of this group. Here we report new Asteralean-like fossil pollen grains from
Antarctica that shed new light on the early evolution and diversification of Asterales. We recovered
these specimens from Campanian/Maastrichtian sediments of the Santa Marta, Snow Hill Island
and Lopez de Bertodano formations, on the James Ross and Vega islands, in Antarctica. We scored
75 binary pollen characters from 4 fossil forms and 55 extant species chosen to represent all families
and tribes in Asterales. We conducted parsimony analyses to assess the phylogenetic position
of each fossil using a highly supported molecular phylogenetic tree as backbone constraint. Our
phylogenetic analysis places the new fossils within the early-diverging branches of Asteraceae and
its sister Calyceraceae and Goodeniaceae. These fossils display some but not all the synapomorphies
of the crown group, and hence leading us to infer that these fossils might represent members of the
stem lineage. We reveal that some Asteralean lineages evolved in Antarctica during the Cretaceous,
survived the K–P global extinction event, and radiated into the world’s highest latitudes of
Gondwana by the Paleogene.
211
M IC ROPALEON TOLOGIC AL A SSE M BL AGES F ROM
E K ELÖF POI N T (U P P E R C R E TAC EOUS) OF SOU T H E A ST
JA M ES ROSS ISL A N D, A N TA RC T IC P EN I NSU L A
Andrea Caramés1, Cecilia R. Amenábar1,2, Alessandra Santos3 and Andrea Concheyro1,2
1. Instituto de Estudios Andinos Don Pablo Groeber-CONICET, Universidad de Buenos Aires, Departamento de Ciencias
Geológicas. Intendente Guiraldes 2160, C1428EGA, Ciudad Universitaria, Buenos Aires, Argentina. [email protected]
2. Instituto Antártico Argentino, Balcarce 290, C1064AAF, Buenos Aires, Argentina.
3. ITT FOSSIL, Instituto Tecnológico de Micropaleontologia, Universidade do Vale do Rio dos Sinos, Brazil.
A micropaleontological analysis of a sedimentary succession from the Rabot Formation (Upper
Cretaceous) at Ekelöf Point, southeast of James Ross Island, Antarctic Peninsula, is here presented.
This unit was dated as late Campanian-early Maastrichtian, based on ammonites and dinocysts. The
study is based on the analysis of foraminifera and palynomorphs from six fossiliferous samples of a
stratigraphic section (ca. 200 meters of thickness). This consists of dark grey siltstones and claystones
alternating with very thin indurated tuff levels and yellow claystones. At the top of the section a
condensed horizon with concretions containing trace fossils interpreted as a maximum transgressive
event is recognised. The foraminifera assemblage is characterised by benthic species. Except one
sample, with only five specimens of the calcareous Gavelinella sandidgei (Brotzen) and one indeterminate
fragment, the other ones are mainly composed of agglutinated species (70-80%). Bathysiphon, the
most common genus in the section is dominant in different samples. Reticulophragmoides aff. jarvisi
(Thalmann), Rzehakina minima (Cusman and Renz) and the calcareous species Gavelinella sandidgei
are also common. Furthermore, taxa from the following genera were recognised: Haplophragmoides,
Reophax, Ammodiscus, Karreriella?, Recurvoides, Dentalina, Lingulonodosaria and Lagena. Although
a few samples are suitable for suggesting only tentative conclusions, epibenthic foraminifera are
dominant and the agglutinated ones dominated by species with tubular morphology suggest a
tranquil bathyal palaeoenvironment. It is noteworthy the taxonomical change in a sample just
below the concretional level with a dominance of Spiroplectammina chicoana together with deeper
infauna (Reophax). Considering that Spiroplectammina is a genus characteristic of shelf and marginal
marine environments, a decrease in water-depth or a down-slope transport of shelf foraminifera
could be possible explanations of such change. Palynomorphs are abundant in all levels and consist
of dinocysts, pollen and spores in variable amounts. The continental palynomorphs represents 21
to 72% of the whole assemblage and indicate a continuous terrestrial influx to the marine basin.
The dinocyst assemblage is dominated by peridiniacean taxa including Isabelidinium cretaceum
(Lentin and Williams), Isabelidinium spp. and Isabelidinium/Manumiella complex, which are common
in proximal marine environments. Palaeoenvironmental interpretations based on foraminifera
are consistent with sedimentological studies which indicate an outer-shelf palaeoenvironment,
evidenced by a monotonous sedimentary succession produced by sediment fallout with occasional
ash fall from a volcanic arc. The dominance of peridinacean cysts and the continuous terrigenous
input can be explained by the existence of a short shelf where the material quickly runs down the
slope and would be deposited in the deep marine environment.
212
T E T R A PODS F ROM T H E SNOW H I LL ISL A N D
FOR M AT ION (L AT E C A M PA N I A N -E A R LY
M A A ST R IC H T I A N ), JA M ES ROSS ISL A N D, A N TA RC T IC A :
TA P HONOM IC A N D DE POSI T IONAL SE T T I NGS
Zulma Gasparini1, Marcelo Reguero1,2, Marta Fernández1, Rodolfo A. Coria3,
Eduardo Olivero4, José O´Gorman1, Ari Iglesias5 and Juan J. Moly1
1. Museo de La Plata, Universidad Nacional de La Plata, Paseo del Bosque s/n,
La Plata, B1900FWA, Argentina. [email protected]
2. Instituto Antártico Argentino, Balcarce 290, Buenos Aires, C1064AAF, Argentina.
3. CONICET / Museo Carmen Funes / Instituto de Investigación en Paleobiología y Geología,
Universidad de Río Negro, Isidro Lobo 516, General Roca, 8332, Argentina.
4. Centro Austral de Investigaciones Científicas CADIC-CONICET, B. Houssay 200, Ushuaia, 9410, Argentina.
5. Instituto de Investigaciones en Biodiversidad y Medioambiente
INIBIOMA-CONICET, Quintral 1250, San Carlos de Bariloche, 8400, Argentina.
The Snow Hill Island Formation (SHIF) constitutes the basal unit of the transgressive part of the
NG Sequence (upper Campanian-lower Maastrichtian), which exposes extensively in the James
Ross and Vega islands, James Ross Basin, northeast of the Antarctic Peninsula. The shallow marine
sediments of the SHIF comprise two members: the upper Campanian Gamma Member and the lower
Maastrichtian Cape Lamb Member. The SHIF yields mosasaurs, elasmosaurids, and dinosaurs,
and contains the most diverse Mesozoic tetrapod assemblage recorded from Antarctica. At Santa
Marta Cove (SM), James Ross Island the Gamma Member contains the holotype of the tylosaurine
Taniwhasaurus antarcticus and a number of indeterminate elasmosaurid plesiosaurids. Additionally,
three non-avian dinosaurs, represented by Antarctopelta oliveroi, Trinisaura santamartaensis, and
an isolated sauropod vertebra, have been collected in this member. At The Naze (TN, James Ross
Island) and Cape Lamb (CL, Vega Island) localities, from outcrops of the Cape Lamb Member,
new non-aristonectine elasmosaurid and mosasaurids were recovered, identified as cf. T. antarticus,
cf. Hainosaurus sp., and Tylosaurinae indet. (CL). Additionally, partial skeletons assigned to a
hypsilophodontid (CL), a dromeosaurid (TN) and an ornithopod (TN) non-avian dinosaurs and few
avian dinosaurs (CL, charadriiforms) were recovered from this member. Close scrutiny of the fossil
assemblages and stratigraphic horizons indicates that at least two different subsets of articulated
skeletons are present throughout the Gamma Member and have different taphonomic histories
(including bone abrasion, scavenging, completeness, and sorting). Thus, allochthonous skeletons
transported from continental fluvial systems are differentiated from autochthonous skeletons that
were buried by the same bearer stratigraphic horizon. Taphonomic and depositional settings were
analyzed in: 1) articulated skeletons of marine reptiles from SM, TN and CL (Taniwhasaurus; a new
genus and species of elasmosaurid and several other elasmosaurid skeletons) with evidence of
having been scavenged by hexanchid sharks and nautilods; and 2) dinosaurs recovered articulated
from the same horizon of SM (Trinisaura santamartaensis and Antarctopelta oliveroi), associated to
abundant plant debris share distinctive taphonomical history characterized by preservation of
articulation and with no evidence of scavenging by hexanchid sharks on carcasses. Other isolated
bones of dinosaurs (i.e. a sauropod vertebra), were found floating (not in situ) and from different
stratigraphic horizons. Complete stratigraphic and taphonomic analyses of vertebrates are now
available for the upper Campanian-lower Maastrichtian Snow Hill Island Formation, being possible
better correlations through the Upper Cretaceous of West Antarctica with other Gondwanan areas.
213
T H E FOR A M I N I F E R A A N TA RC T IC E L L A A N D C YC L A M M I NA
F ROM T H E M IOC EN E C A P E M ELV I LLE FOR M AT ION
OF K I NG GEORGE ISL A N D, W EST A N TA RC T IC A
Andrzej Gaździcki1 and Wojciech Majewski1
[email protected]
The Miocene (~22 Ma) Cape Melvile Formation consists of glaciomarine strata ~150 m thick that
are exposed on Melville Peninsula (King George Island, South Shetlands). They contain a rich,
predominantly invertebrate fauna that has a relatively deep-water, outer-shelf character, making it
one of the most significant Miocene biotas know from West Antarctica. Microfossils include benthic
calcareous and arenaceous foraminifera of at least 50 species. The most abundant agglutinated
species is Cyclammina cancelata Brady. It can be easily distinguished from other representatives
of this genus by its larger size and broadly rounded periphery with usually fourteen chambers
in the final whorl. Large population of this foraminifer of over 1000 well-preserved specimens
allowed for paleobathymetrical interpretation. According to recently observed water-depth related
variations in test width and diameter of C. cancelata living population, the Cape Melville Fm. was
likely deposited in a relatively deep sea ~1000 m water depth. In the studied strata, an intriguing
foraminifer, Antarcticella antarctica (Lackie and Webb), was recognized for the first time in the
Antarctic Peninsula area. This species was described from the late Oligocene to mid Miocene of the
Ross Sea as a planktonic form, but subsequently it has been interpreted as of benthic habitat. The
presence of Antarcticella antarctica in the South Shetlands adds to the dispersal reconstruction of this
biostratigraphically important taxon across the Southern Hemisphere.
214
U P P E R C R E TAC EOUS M AC ROF LOR A S, JA M ES
ROSS ISL A N D, A N TA RC T IC P EN I NSU L A
Ari Iglesias1, Marcelo A. Reguero2,3, Rodolfo A. Coria4 ,
Eduardo Olivero5 and José P. O´Gorman2
1. Instituto de Investigaciones en Biodiversidad y Medioambiente INIBIOMA-CONICET,
Quintral 1250, San Carlos de Bariloche, 8400, Argentina. [email protected]
2. Museo de La Plata, Universidad Nacional de La Plata, Paseo del Bosque s/n, La Plata, B1900FWA, Argentina.
3. Instituto Antártico Argentino, Balcarce 290, Buenos Aires, C1064AAF, Argentina.
4. CONICET; Museo Carmen Funes; Instituto de Investigación en Paleobiología y Geología,
Universidad de Río Negro, Isidro Lobo 516, General Roca, 8332, Argentina.
5. Centro Austral de Investigaciones Científicas CADIC-CONICET, B. Houssay 200, Ushuaia, 9410, Argentina.
We analyze macrofloras from the north part of the James Ross Island at the Santa Marta and Snow
Hill Island formations, Marambio Group, James Ross Basin. At the upper section of the Beta Member
of the Santa Marta Formation, well preserved petrified trunks, charcoalified wood, and twists, leaves
and seeds compression were collected. Leaves and seeds of angiosperms, podocarps and Araucaria
are preserved with other plant debris in large calcareous nodules within fine-grained sands, escaping
from bioturbation and taphonomical destruction. Some twists are preserved with attached large
leaves of podocarps and Araucaria. Woody angiosperm leaves are quite diverse, with medium sizes
(notophyll) and entire margins. Complete, small heteromorph ammonites in several orientations are
generally associated with the plants, whereas inner-shelf coquina beds with charcoal are observed at
the top of the unit. The ammonite assemblages indicate that this plant level is early-mid Campanian
in age. At the Santa Marta Cove, the Snow Hill Island Formation shows less abundant plant debris.
Small calcareous nodules in different levels have preserved diverse angiosperm and conifer woods.
In some cases, the specimens conserved the external cortex of branches and twists with 3D leaf scar
arrangement. Some large podocarp leaves were collected preserving stomata arrangement on the
surface. The ammonite assemblages indicate a lateCampanian – early Maastrichtian age for these
plant levels. Facies analysis suggests the evolution of a progradational deep-water delta system.
Plant remains may be transported seawards by deltaic currents from the continental areas of the
Antarctic Peninsula. Systematic and taphonomic studies of these plants and other transported
fossils (i.e. vertebrates) give evidence about how high-latitude continental environments were in
Antarctica in places that today are permanently covered by ice.
215
A R EV I E W OF T H E L AT E C R E TAC EOUS MOSA SAU R
FAU NA OF NORT H E A ST BR A Z I L
Isabela Lima¹, Tatiane Silva¹, Iru Iakovisky¹, Adelino A. Carvalho¹ and Roberto Candeiro¹
1. Universidade Federal de Uberlândia - Campus Pontal, Laboratório de Geologia,
Rua 20 n° 1600, Ituiutaba, 38304-402, Brazil. [email protected]
The Late Cretaceous of northeast Brazil is among one of the few South American places that
preserve a rock record that documents mosasaur remains. This is a critical period for distribution of
mosasaur related to final opening of South Atlantic Ocean. In post-Cenomanian time, Mosasaurinae
and Plioplatecarpinae have been recorded in the marine deposit exposed along the northeast Brazil
coastline. The oldest-known specimen of a Brazilian mosasaur has been assigned to Mosasaurinae
indet. and is from the Cenomanian Alcântara Formation (São Luís Basin). Two isolated teeth
originally assigned to Platecarpus sp. come from the late Turonian and Turonian-Coniacian Sergipe
Basin (the Cotinguiba Formation?). While they exhibit general plioplatecarpine traits such as lateral
fluting and/or medial striation of the crown, marginal tooth morphology is strongly conserved
within the subfamily, and recent studies also indicated the range of Platecarpus to be no older than 85
Ma. These teeth therefore can be referred at best to Plioplatecarpinae gen. et sp. indet. Plioplatecarpus
sp. is known from the Campanian Calumbi Formation (Sergipe Basin). The Maastrichtian Gramane
Formation, which yielded the most representative Brazilian mosasaurid record, is represented
by Carinodens belgicus Woodward 1891, Plioplatecarpinae gen. et sp. indet., and Mosasaurinae
gen. et sp. indet. These mosasaur-bearing units ranging in duration approximately from 100 Ma
(Cenomanian) to 65 Ma (Maastrichtian) serve as a unique and important reference point to further
our understanding of mosasaur diversity and distribution patterns both in time and space, in the
ancient South Atlantic Ocean in particular and in the Southern Hemisphere in general.
216
OLIGOC EN E BEN T H IC FOR A M I N I F E R A F ROM
T H E POLON E Z COV E FOR M AT ION OF K I NG
GEORGE ISL A N D, W EST A N TA RC T IC A
Wojciech Majewski1 and Andrzej Gaździcki1
[email protected]
Abundant benthic foraminifera are described for the first time from Oligocene strata of the Antarctic
Peninsula sector of West Antarctica. They come from deposits of prograding fan-delta front of the
lower Oligocene Low Head Member of the Polonez Cove Formation, which are exposed in some
cliffs and nunataks of King George Island. Despite being collected from eight different sites, the
foraminifera reported constitute a single diverse assemblage strongly dominated by calcareous
species, belonging to Cibicides along with Globocassidulina, Ammoelphidiella, Discorbis, Melonis,
Lobatula, Gyroidina, and Pullenia, as well as miliolids and unilocular calcareous foraminifera,
enriched in foraminifera with robust tests. This assemblage does not correspond with any known
modern Antarctic foraminiferal community, but it shows some links with Patagonian assemblages,
suggesting different environments during the early Oligocene than in Recent Antarctica. Its
general taxonomic composition and the enrichment in robust tests fit well into the shallow-water
environment interpreted from geological data. Despite presence of some characteristic Antarctic
taxa, for example species of the extinct Ammoelphidiella, the assemblage from the Polonez Cove
Fm. is difficult to correlate biostratigraphically with a particular part of the foraminiferal record
from the Ross Sea. Apparently, a strong environmental imprint on the shallow-water foraminiferal
assemblage from the Oligocene of King George Island overshadows long-term evolutionary changes.
217
N E W NON -T H E R I A N M A M M AL F ROM M A R A M BIO
(SE Y MOU R) ISL A N D I N W EST A N TA RC T IC A : F I R ST
M E R I DIOLEST I D OU TSI DE SOU T H A M E R IC A
Agustín G. Martinelli1, Laura Chornogubsky2,
M. Alejandra Abello3, Francisco J. Goin3 and Marcelo A. Reguero3,4
1. Departamento de Paleontologia e Estratigrafia, Universidade Federal do Rio Grande do Sul. Ave. Bento Gonçalves
9500, Agronomia, 91501-970, Porto Alegre, RS, and Centro de Pesquisas Paleontológicas L.I. Price, CCCP/UFTM,
BR-262, Km 784, Bairro Peirópolis, 38001-970, Uberaba, MG, Brazil. [email protected]
2. CONICET-Sección Paleontología de Vertebrados, Museo Argentino de Ciencias Naturales “Bernardino
Rivadavia”. Av. Ángel Gallardo 470, C1405DJR, Buenos Aires, and Departamento de Ciencias Básicas,
Universidad Nacional de Luján. Ruta 5 y Av. Constitución, 6700, Luján, Buenos Aires, Argentina.
3. CONICET-División Paleontología Vertebrados, Museo de La Plata, Paseo del Bosque s/n (B1900FWA) La Plata, Argentina.
4. Instituto Antártico Argentino, Balcarce 290, C1064AAF Buenos Aires, Argentina.
The Cucullaea I Allomember of La Meseta Formation (Early Eocene to ?early Oligocene), Marambio
(Seymour) Island, Antarctic Peninsula contains most of the terrestrial mammals, including nontherian gondwanatheres, metatherians, and eutherians recorded in Antarctica. This composition
reflects a strong paleogeographical link between the Paleogene faunas of Patagonia and West
Antarctica. A small isolated tooth (MLP 91-II-4-3) was found in locality IAA 1/90 from Cucullaea
I Allomember and was originally interpreted as a possible third upper molar from a bat or an
“insectivore” because of its zalambdodont appearance, and then more broadly assigned to Mammalia
Incertae sedis. We present here an alternative interpretation, considering MLP 91-II-4-3 as a right
lower molar of a non-therian Dryolestoidea, possibly being a member of the clade Meridiolestida.
The crown is dominated by three cusps and a distolingual talonid cusp. The protoconid is flanked
mesially by the paracristid and distally by the metacristid, which reach the paraconid and metaconid,
respectively. Both crests form an acute angle, without a clear notch at mid-way. The labial wall of
the protoconid is convex whereas the lingual face is slightly concave. The paraconid is worn out and
lower than the metaconid. The flexid is notorious and forms a “v” shaped notch between paraconid
and metaconid. The protoconid and metaconid are similar in height. The metaconid connects by
a crest with the talonid. The talonid has a hook-like disto-lingual projection with a large cusp,
slightly bent lingually, and an accesory more labially placed cuspule. The mesial cingulum starts
as a thin ridge below the paraconid and becomes wider on its ventrolabial trajectory. It is unknown
if the cingulum continues on the labial slope of the protoconid. A portion of a root is preserved
below the paraconid-protoconid and it seems to be transversely wide. The crown morphology of
MLP 91-II-4-3 closely resembles that of the meridiolestidans Barberenia and Brandonia from the Late
Cretaceous of Patagonia (Los Alamitos and Allen formations). Meridiolestida is a diverse group of
dryolestoids recorded mostly from Patagonian Cretaceous outcrops, which survived the Cretaceous/
Paleocene boundary with the youngest representative of the clade (Necrolestes) from early Miocene.
If proven correct, our hypothesis would expand the distribution of the Meridiolestida to West
Antarctica, representing the second non-therian mammal from this continent. Thus, it would agree
with previous inferred scenarios that show West Antarctic faunas more closely related to those of
Patagonian Paleogene than to any other one from the Southern Hemisphere.
218
OR IGI N OF MODE R N A N TA RC T IC IC E -F ISH ES (T ELEOST EI,
NOTOT H EN IOI DEI ) A N D T H E I DEN T I T Y OF EOC EN E F ISH
R E M A I NS F ROM SE Y MOU R ISL A N D, A N TA RC T IC A
Thomas Mörs1, Andrea Engelbrecht2, Jürgen Kriwet2,
Cathrin Schwarz2 and Marcelo Reguero3
1. Department of Palaeobiology, Swedish Museum of Natural History, P.O. Box
50007, SE-104 05 Stockholm, Sweden. [email protected]
2. Department of Palaeontology, University of Vienna, Althanstr. 14, 1090 Vienna, Austria.
3. CONICET; División Paleontología de Vertebrados, Museo de La Plata, Paseo del Bosque s/n, B1900FWA La Plata, Argentina.
The modern Antarctic fish fauna is highly endemic and well-adapted to the polar conditions and
geographic peculiarities of the Southern Ocean, which is geologically the youngest ocean and forms
about 10% of the world’s ocean surfaces. Continental ice sheets, cold polar waters delimited by the
Antarctic Polar Frontal Zone (45-60°), the circum-Antarctic current, as well as shelf and upper slopes
that are isolated from other shelf areas are characteristics of modern Antarctica. The development of
the circum-Antarctic current is generally related to the opening of the Tasmanian Gateway between
Australia and Antarctica during the Palaeogene, with deep-water circulation being established
at about 31 Ma ago. The Drake Passage between South America and Antarctica opened perhaps
as early as 33 Ma ago; it was certainly open to deep-water flow, deeper than 2000 m, by 29 Ma
and the thermal isolation of Antarctica was complete. A benthic association that lacks skeletonbreaking (durophageous) forms but also epipelagic predators (this niche is filled by cephalopods
today) characterizes the fish fauna inhabiting this extreme habitat today. Notothenioid teleosts that
dominate the modern Antarctic fish fauna have evolved special features to cope with the extreme
environmental conditions. Generally, the evolution of these fishes is linked to the development
of the powerful Antarctic Circumpolar Current. However, recent analyses show that major high
latitude cooling and the onset of Cenozoic glaciation predate the development of this current
suggesting that adaptive traits in notothenioids probably started earlier then the development of
glaciation, if the attribution of a single Eocene fossil skull to notothenioids, which was used to
calibrate molecular clocks, is correct. The transition from a typical open marine fish fauna including
diverse chondrichthyan associations to the modern, mostly benthic notothenioid-dominated fish
fauna thus must have occurred in the Palaeogene after the K/T boundary event. However, more
recent molecular analyses suggest that adaptation of fishes to polar conditions and subsequent
evolution of notothenioids occurred prior to 24 Ma by directional selection and geographic isolation.
Nevertheless, isolated fish remains from Eocene strata of Seymour Island recently were interpreted
as relicts of notothenioids reiterating previous hypotheses. Here, we present a re-evaluation of
Eocene Antarctic fossil teleost remains including abundant jaw elements and otoliths based on
morphological comparisons of selected extant Antarctic fishes employing non-invasive micro-CT
techniques for 3D visualization of skeletal and otolith structures. Our results are discordant with
previous interpretations indicating that evolution of notothenioids must have occurred later.
219
T WO N E W SP EC I ES OF NON -A R ISTON EC T I N E
EL A SMOSAU R I DS (P LESIOSAU R I A ; SAU ROP T E RYGI A)
F ROM T H E W EDDELLI A N P ROV I NC E A N D T H E
OR IGI N OF T H E A R ISTON EC T I NAE
José P. O’Gorman1,2
1. División Paleontología Vertebrados, Museo de La Plata, Universidad Nacional de La Plata, Paseo del Bosque s/n., B1900FWA,
La Plata, and CONICET, Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina. [email protected]
The elasmosaurids from the Weddellian province (Patagonia, Western Antarctica and New Zealand)
comprises the distinctive large skulled aristonectine (Aristonectes, Kaiwhekea) and the more typical
small skulled non-aristonectine elasmosaurids. Here two new non-aristonectine elasmosaurids
from the Weddellian Province are commented. The nov. sp. 1 (MLP 93-I-5-1, Museo de La Plata,
Argentina) comes from Vega Island, James Ross Archipelago, Antarctica, lower Maastrichtian Cape
Lamb Member of the Snow Hill Island Formation. The nov. sp. 2 (MLP 71-II-13-1) comes from
Lago Pellegrini, Río Negro, Patagonia (upper Campanian-lower Maastrichtian Allen Formation).
The nov. sp. 1 is one of the few Late Cretaceous elasmosaurids from the South Hemisphere whose
postcranial anatomy is well-known. The nov. sp. 1 is distinguished from other elasmosaurids by
the following combination of characters: cervical region with 54 vertebrae with elongated centra,
dumbbell shaped articular faces and lateral ridge present in the anterior and middle part of the neck
but absent in the posteriormost cervical vertebrae; scapula with ventral ramus bearing a strong ridge
in the anteromedial corner of its dorsal surface; ilium shaft, with expanded distal end, divided in
two parts forming an angle of 140° opening anteriorly; humerus with anterior knee and prominent
posterior projection with accessory posterior articular facet. The nov. sp. 2 shares with the nov. sp.
1 the humeral morphology (humerus with anterior knee and prominent posterior projection with
accessory posterior articular facet) but differs from the nov, sp. 1 in its distinctive small body size
(about 3.7 m long), more elongated cervical centra, caudal parapophysis laterally projected and
presence of pelvic bar. Preliminary phylogenetic analysis places the nov. sp. 1 and nov. sp. 2 within
a clade that includes the Late Cretaceous Weddellian aristonectine elasmosaurids, Aristonectes and
Kaiwhekea. This indicates a close relationship between Aristonectinae and non-Aristonectinae Late
Cretaceous Weddellian elasmosaurids and reinforces the hypothesis of the Weddellian origin for
the Aristonectinae.
220

SYMPOSIUM CRETACEOUS-TERTIARY PALAEOBIOGEOGRAPHIC CONNECTIONS WITH ANTARCTICA

Transcription

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