MACNBR   00242
MUSEO ARGENTINO DE CIENCIAS NATURALES "BERNARDINO RIVADAVIA"
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Rosellichnus patagonicus revisited: description, interpretation and paleoecological significance
Autor/es:
SARZETTI L.; GENISE J. F.; CANTIL, L.F.; BELLOSI E. S.
Lugar:
Colonia del Sacramento
Reunión:
Simposio; Tercer Simposio Latinoamericano de Icnologia; 2015
Institución organizadora:
Universidad de la Republica Uruguay
Resumen:
The ichnogenus Rosellichnus includes clusters of vertical cells with smooth inner surface and discrete wall, interpreted as constructions of bees. Rosellichnus patagonicus was described in 1996 based on two specimens from the Collón Curá Formation (Río Negro, Argentina) in the paleontological collection of the Museo de La Plata, and it was never found in the field again. The scarce material originally studied precluded a precise interpretation of its producer. Abundant new specimens of R. patagonicus with excellent preservation were collected in the La Pava and Collón Curá Formations (Miocene of NW Chubut), which also outcrop in SW Río Negro. These clusters are composed of 2 to 8 vertical cells arranged in one to two rows. The cells are 24?32 mm long and 14?17 mm in maximum diameter, and show a discrete wall 3?4 mm wide. Four specimens show cells with curved necks up to 9 mm long, although in most examined specimens cells lack their upper part. The paleosols with these clusters also include isolated cells showing the same discrete wall, passive filling, curved neck and measures as those of R. patagonicus. Similar characters (measures, discrete wall and curved neck) of isolated cells and cell clusters indicate that they would be constructed by the same producer. However, isolated cells cannot be included in R. patagonicus because it was created for clusters of cells, and cells having discrete walls and curved necks are not compatible with any Celliformidae described until now. The ichnospecies Celliforma curvata, recently defined for moulds of isolated cells with curved neck from the Collón Curá Formation, may correspond to the passive fillings of R. patagonicus and also of these new isolated cells. C. curvata was assigned to Diphaglossinae (Colletidae) bees which typically construct vertical cells with curved necks. Cells of the extant bee Cadeguala albopilosa (Diphaglossinae) from the Los Alerces National Park (Chubut) collected for a former study were re-examined as well as their tomographic images, showing that these curved cells have also discrete walls, and in some cases grouped in clusters. Cells and clusters of this species are comparable to the new material collected in the Miocene of Chubut. Cadeguala albopilosa nests in a xeric forest dominated by Austrocedrus chilensis (Cupressaceae) with a MAP of 700 mm 140 km westward of the outcrops with R. patagonicus. In accordance, Rosellichnus patagonicus would indicate the presence of xeric forests for the Miocene of NW Chubut.