INVESTIGADORES
MARENSSI Sergio Alfredo
congresos y reuniones científicas
Título:
Antarctic Eocene loon (Gaviiformes): last refuge of survivor of a long lineage typically Holarctic?
Autor/es:
TAMBUSSI C,; DEGRANGE, F.J; REGUERO, M; MARENSSI, S.A; SANTILLANA, S
Lugar:
Portland
Reunión:
Conferencia; SCAR Open Science Conference; 2012
Institución organizadora:
SCAR
Resumen:
Extant loons (four species of the genus Gavia) are footpropelled divers found in North America and northern Eurasia. They breed at northern freshwater sites, but winter along sea costs in temperate
areas. Loons had a more
southerly distribution than today, and their fossils have been found in California, Florida, Italy, Austria,
Chile and Antarctica.
The earliest fossil gaviiform
that resembles the highly derived bone of modern loons had been described from
the Upper Cretaceous of Chile (Quiriquina
Formation) and Antarctica (López de
Bertodano Formation). It is likely that both records belong to the same
species, Neogaeornis wetzeli. A
near complete left coracoid (MLP 95-I-10-14) collected in the Cucullaea
I Allomember of the marine La Meseta Formation at Seymour (Marambio) Island (Early-Middle Eocene, Ypresian/Lutetian, ~49-52 Ma) can be assigned to a Gaviiformes. The coracoid
has a short and robust shaft; the cotyla scapularis is subtriangular and
deep; the facies articularis humeralis is flat, oval, and broad; the
procoracoid process is broken but the base is very broad; the processus
acrocoracoideus is partially broken but it was very well developed; the foramen
n. supracoracoidei is incospicuous; the facies articularis sternalis
is broad at the level of the angulus medialis; the impressio m.
stercoracoidei is shallow and the sulcus m. supracoracoidei is broad
and deep; the impressio lig. acrocoracohumeralis is conspicuous, deep
and situated proximad to the facies articularis humeralis. Although this
fossil cannot be distinguished in size and morphology from the living taxa (e.g
Gavia immer), the features of the only available specimen is
insufficient to determine the specific level at the moment.
Several mammalian terrestrial groups, mostly small-sized marsupials (e.g. polydolopids) of likely insectivorous
to frugivorous habits and larger-sized placental herbivores (litopterns and astrapotheres) are recovered
from Cucullaea I Allomember. Co-occurring penguin bones and mammals in the
same level indicates complex depositional environments. By the time of
deposition of this high productive mammalian
locality, a Nothofagus-dominated
megaflora is associated. The presence of a loon in the Eocene of La Meseta
Formation does not contradict this scenario. The fossil presented here
constitutes the earliest record of Gaviiformes in the southern hemisphere and,
also extends the permanence of this Holarctic lineage to the Eocene in the Southern
Hemisphere.