MACNBR   00242
MUSEO ARGENTINO DE CIENCIAS NATURALES "BERNARDINO RIVADAVIA"
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Redescription and palaeoecological significance of the bryozoan Hippoporidra patagonica (Pallaroni, 1920) in the San Julián Formation (late Oligocene) of Santa Cruz province, Argentina
Autor/es:
PEREZ, L.M.; GRIFFIN, M.; PASTORINO, G.; LÓPEZ-GAPPA , J.; MANCEÑIDO, M.O.
Lugar:
Valdivia
Reunión:
Simposio; IV Simposio Paleontología en Chile; 2014
Institución organizadora:
Universidad Austral de Chile y Asociación Chilena de Paleontología
Resumen:
The relationship between bryozoans and pagurids takes place when the bryozoan begins to bud an encrusting colony on a gastropod shell to suitable a benthic island. Hippoporidra is a cheilostome bryozoan that predominantly encrusts gastropod shells inhabited by hermit crabs. Upon lying on the bottom, the shells become available for the settlement of bryozoan larvae, which later develop an encrusting colony. This abstract aims to record the presence of Hippoporidra in the Gran Bajo Member of the San Julián Formation and to describe for the first time the morphology of its autozooids and polymorphs based on SEM. The faunal context of this genus and its palaeobiogeographic distribution in the Southern Hemisphere are also discussed. The specimens were recorded at the locality known as 'Conito Colmena' in Santa Cruz Province, Argentina. The species Cellepora patagonica Pallaroni, 1920 is here transferred to Hippoporidra. Leanza (1956) described the morphology of gastropod-like specimens heavily encrusted by bryozoans and endorsing Pallaroni´s ideas, he interpreted the process generating the structures and also analyzed palaeoecological aspects of a colony which was found surrounding a pagurized shell of Turritella ambulacrum, and considered the relationship to be a case of mutualism. The colonies of H. patagonica are robust, multilamellar, very thick, covering the whole external surface of gastropod shells. Autozooids chaotically arranged, without distinguishable boundaries, their convex frontal wall pierced by areolae only. Orifice semicircular, with straight proximal border. A pair of small condyles separating the small poster from the anter. Monticules scattered over the colony surface in a quincuncial pattern, composed of several cortical zooids with protruding frontal walls and orifices slightly smaller than those of autozooids. Peristomial avicularia small, ovate, with complete pivotal bar, close to the proximal margin of the orifice, usually on a peristomial suboral umbo. Interzooidal avicularia large, protruding, ovate, with blunt, triangular rostrum and a complete pivotal bar. Ovicells unknown. This species can be distinguished from the remaining species of the genus by the peculiar shape of its interzooidal avicularia and the morphology of its orifice. The record of Hippoporidra patagonica (Pallaroni, 1920) confirms the presence of this genus at the southern tip of South America and indicates a Pan-Atlantic distribution during the Eocene to Holocene in the Cenozoic.