The loose, small zooecia of the cheilostome bryozoans have been discovered in the lowermost part of the La Meseta Formation on Seymour (Marambio) Island. They systematically include the representatives of Beanidae Canu et Bassler, Catenicellidae Busk, Savignyellidae Levinsen, and Calwelliidae MacGillivra y. The bryozoan assemblage is comprised of separate, small−sized internal moulds dominated by distinct, boat−shaped zooecia belonging to Beania , scarce, unizooidal internodes tentatively included into a ditaxiporine catenicellid ? Vasignyella , and representative of the family Savignyellidae. A few branched segments composed of multiserial zooecia arranged back to back were tentatively incorporated into ? Malakosaria . Beania , marks the oldest fossil record, whereas representatives of Savignyellidae along with ditaxiporine catenicellid and ? Malakosaria are for the first time reported from Antarctica. The relationship between the taxonomic composition, colony growth−patterns rep− resented by membraniporiform/petraliform, catenicelliform and cellariform, along with associated biota and sedimentary structures of the La Meseta Formation implies nearshore environment, with considerable wave action, and warm climatic conditions.
At the turn of October 1985, the abundance of breeding Adelie penguins was estimated at the Hope Bay oasis on the Antarctic Peninsula and on Seymour Island. In the Hope Bay rookery, 123850 pairs of penguins were recorded, beginning their breeding at the end of October. Data so far obtained indicate a continuous increase in the number of birds sat this rookery. On the other hand, the Seymour Island colony consisted of 21954 pairs of Adélie penguins. Clear differences in the geomorphological structure of areas occupied by penguins in those two places are discussed. No gentoo penguins were detected in either of the colonies.
Whale bones from the upper Eocene — ?lower Oligocene La Meseta Formation of Seymour (Marambio) Island, West Antarctica, are assigned to the Archaeoceti. They most probably belong to an undetermined genus of the family Basilosauridae Cope. 1867; subfamily Dorudontinae Barnes and Mitchel. 1978.
Fossil bird remains assignable to ratites (palaeognathous birds) are described from the Paleogene strata of the La Meseta Formation of Seymour Island, Antarctic Peninsula. This record sheds new light on Gondwana's avian history.
Mineral composition of bedrock is the main factor determining salt mineralization in the weathering zone of Seymour (Marambio) Island (maritime — Antarctic continent climatic boundary). Supply of salts by sea water spray can accelerate weathering process, modify chemical formula of salt minerals and give ephemeral efflorescences of easy soluble chlorides and partially longer lasting gypsum on the surface. Microbiologically mediated oxidation of sulphides and followed acid sulphate drainage formed K and Na jarosite, basic amorphous aluminium sulphate, gypsum, aluminium bearing ferrihydrite and ankerite in weathering zone of Paleogene sediments. Intense alteration of well-lithified, calcareous sandstones of unit 1 of the López de Bertodano Formation (Cretaceous) on old erosion surface led localy to surface mineralization comparable with that found in Antarctic Continent. Stones laying on the soil surface are covered by thin red film of ferrihydrite above the soil level and by light green crust of aragonite coloured by glauconite pigment on the underground side. Most of the Cretaceous sediment does not contain sulphides nor alteration susceptible silicates thus ephemeral sea salts efflorescences observed on its surface are more prominent than in another places.
Body size is an important measure in biology and especially in paleobiology. With respect to fossil penguins from the Eocene La Meseta Formation of Seymour Island (West Antarctica) the overall size has to be judged from the dimensions of single bones. The analysis based on selected measurements of hind limb bones from the Polish collection of Eocene Antarctic penguins yielded results supporting predictions published formerly. Estimated body masses and lengths indicate that mean interspecific body size of extinct Antarctic Spheniscidae exceeded that of Recent species.
Basing on isolated vertebrae, fossil fishes of the order Gadiformes have been first discovered in sediments of the La Meseta Formation (upper Eocene — ?lower Oligocene) on Seymour (Marambio) Island, West Antarctica. This is one of the oldest and the only locality with the Gadiformes skeletal remains in the Southern Hemisphere. Other poorly preserved centra have been determined as Teleostei (order incertae sedis).
Isolated and fragmented jaws, a single basioccipitale and vertebrae of the Gadiformes, indeterminate family and genus, are described from Eocene sediments of the La Meseta Formation, Seymour Island, Antarctic Peninsula. Based on the dentition and other characters of both jaws they are assigned an informal name of „Mesetaichthys". The remaining isolated bones belong probably to the same form.
The synsacrum is an important element of the axial skeleton in birds, both volant and flightless. Little is known about the maturation of this complex bone in penguins. In this work, the supposedly ontogenetically youngest known synsacrum of early penguins was described. The analysis of this specimen, collected within the Eocene La Meseta Formation of Seymour (Marambio) Island, Antarctic Peninsula, revealed that this bird had attained at least the fledging stage of growth. Studies of three mature synsacra recovered from the same formation focused on the synsacral canals and, using indirect reasoning, their contents. These analyses revealed that the lumbosacral intumescence of the spinal cord and its extensions, the transverse canals, had been developed roughly like those in extant penguins (and also swifts and cormorants). The neural spine extensions (a non−nervous tissue) tracing the transverse grooves of the dorsal wall of the synsacral canal are currently considered as involved in the control of walking. The presented data suggest that such a sense organ gained its current penguin configuration by the late Eocene.
The fossil record of the Antarctic penguins is dated to the late Paleocene of Seymour (Marambio) Island, but the largest sphenisciforms, genera Anthropornis and Palaeeudyptes , originate from the Eocene La Meseta Formation. Here, the most complete large−scale reconstruction of a limb skeleton (a whole wing and a partial hind leg) of a Paleogene Antarctic penguin is reported. All bones are attributable to a single individual identified as Anthropornis sp. The comparative and functional analyses of the material indicate that this bird was most probably well−adapted to land and sea while having a number of intriguing features. The modern−grade carpometacarpal morphology is unique among known Eocene Antarctic species and all but one more northerly taxa.
This report describes aims and preliminary results of geological fieldwork carried out by a joint Argentine-Polish party on Seymour (Marambio) and Cockburn islands. Antarctic Peninsula, during austral summer of 1987 88. Seymour Island exposes chiefly shallow-marine, fossiliferous siliciclastic sediments that form an upper, 2000 m thick part in the Mesozoic-Tertiary backarc basin-infill of the Antarctic Peninsula. The fieldwork centered on paleontology and sedimentology of the La Meseta Formation (upper Eocene- ?lower Oligocene), although some observations of older deposits were carried out also. Clupeoid fishes were discovered in the La Meseta Formation. This is the first record of such fish fossils on the Antarctic continent.
A sequence of glacial deposits up to 4 m thick unconformably overlies the Eocene La Meseta Formation on the Seymour Island plateau (meseta) and forms a lithostratigraphically distinct unit in the succession of the James Ross Basin, which is formally named here as the Weddell Sea Formation. The formation is thus far known only from Seymour Island. This is a terrestrial melt-out till which contains abundant erratics and also reworked Cretaceous–Tertiary micro- and macrofossils within a silty clay matrix. The terrestrial origin of this till is shown by glacial striations at the base of the unit. The largest erratics (up to 3 m in diameter) are composed of plutonic (granitoids) and metamorphic (gneiss and crystalline schist) rocks of the Antarctic Peninsula provenance. Smaller in size and much more numerous are erratics of volcanic rocks, represented by andesite, basalt and corresponding pyroclastics of the James Ross Island Volcanic Group. Less common are erratics of sedimentary rocks, sometimes bearing fossils derived from the underlying Tertiary and Cretaceous strata. A few erratics from the top of the studied sequence are conglomerates of the Cockburn Island Formation with a foraminifer fauna. These are the youngest clasts within the Weddell Sea Formation. The presence of the Pliocene index fossil Ammoelphidiella antarctica Conato et Segre, 1974 indicates a lower age limit of latest Pliocene or earliest Pleistocene age. The upper age limit of the formation has not been established. An encrusting, unilamellar, colony of the bryozoan Escharella Gray, 1848 has been found on the one of erratics from the Weddell Sea Formation. This is the first fossil record of this genus in Antarctica.