Compound Asterosoma ludwigae Schlirf, 2000 from the Jurassic of the Lusitanian Basin (Portugal): conditional strategies in the behaviour of Crustacea

Resumen

Asterosoma ludwigae Schlirf, 2000 is described in two sections of different age and palaeoenvironment in the Jurassic of the Lusitanian Basin. The scarce and low diversity of palaeoichnocoenoses associated with these trace fossil, as well as body fossils, indicate low oxygenation of sediment levels close to substrate-water interface. Thus, the palaeoecological signifi cance of Chondrites in lithofacies preceding those with Thalassinoides suevicus and Asterosoma ludwigae (Upper Jurassic of Guincho) or in direct association with similar morphotypes (Lower Jurassic of Peniche) is emphasized. In the syn-rift, fore-reef calciturbidites of the Kimmeridgian-to-Tithonian Mem Martins Formation, an exotic palaeoichnocoenosis dominated by Asterosoma ludwigae in three morpho-ethological gradational stages suggests a forced opportunistic, conditional strategy for the trace maker population. However, in the “Calcários e margas de Peniche” Formation, that is coeval with the post-rifting depositional setting, Asterosoma is found in palaeoichnocoenoses representing equilibrium conditions. A close spatial relationship exists, in both cases, between Asterosoma ludwigae and the “S-O-T group” burrow networks referring to fodinichnia of possible decapod crustaceans.