Caught in fraganti: actual and Holocene, crowded Rosselia-like mud-lined tubes produced by spionid polychaetes

OLIVERO, E.B.,; LÓPEZ CABRERA, M.I.; ERCOLANO, BETTINA; PITALUGA SUSANA; LIZARRALDE ZULMA

General Roca

Encuentro; Reunión de Comunicaciones de la Asociación Paleontológica Argentina. Ciudad de General Roca, Provincia de Río Negro; 2012

Asociación Paleontológica Argentina

Based on studies in Japan, M. Nara has proposed terebellid polychaetes as the probable tracemaker of Rosselia socialis Dahmer. Our study on actual mud-lined tubes of Scolecolepidesuncinatus Blake (Polychaeta, Spionidae) from the Rio Gallegos estuary (Santa Cruz Province, Argentina) and similar biogenic structures found in raised Holocene deposits providesevidence that Rosselia can be produced by spionid polychaetes as well. The  tube-dwelling S. uncinatus occurs in crowded populations of 250 to 1500 individuals per square meter. The tubes, built in organic-rich, black or dark-gray silty-clay are mostly vertical and straight and rarely oblique, with curved segments, or forming wide U-tubes. The tubes, up to 20-25 cm long, have a central cylindrical lumen (4-5 mm wide) coated with mucus, which is surrounded by pale brown to orange, spindle-shaped muddy laminae produced by the polychaete by successive splitting of cylindrical laminae inside the lumen. The sediment laminae of the host muds are commonly deformed around the tube. The same biogenic structure is also present in upper intertidal, raised Holocene deposits exposed south of the Río Gallegos estuary. Here,crowded Rosselia are preserved in mudstones as concentrically laminated rings surrounding acentral lumen or as vertical, spindle-shaped chimneys, elevated over the surface. A polishedsection of a resin-impregnate specimen reveals the diagnostic, internal spindle shapelamination surrounding the central lumen typical of the trace fossil Rosselia.1Centro Austral de Investigaciones Científicas (CADIC-CONICET), B.A. Houssay 200, 9410 Ushuaia, Tierradel Fuego, Argentina. emolivero@gmail.com;2Universidad Nacional de la Patagonia Austral - Unidad Académica Río Gallegos. Lisandro de la Torre 1070 -9400 Río Gallegos, Santa Cruz, Argentina.