Lissodus sardiniensis, Fischer & Schneider & Ronchi, 2010

Fischer, Jan, Schneider, Jörg W. & Ronchi, Ausonio, 2010, New hybondontoid shark from the Permocarboniferous (Gzhelian-Asselian) of Guardia Pisano (Sardinia, Italy), Acta Palaeontologica Polonica 55 (2), pp. 241-264 : 255-256

Synecology of Lissodus sardiniensis sp. nov. in lake Guardia Pisano

In a hypothetical food chain for the lakes of the Permian Saar−Nahe Basin Boy and Schindler (2000: fig. 1) considered Lissodus as a small durophagous−omnivorous bottom dwelling fish in the third trophic level as a secondary consumer. In the case of the lake ecosystem of Guardia Pisano, a food chain with five trophic levels seems to be plausible so far ( Fig. 9 ) based on indirect evidence derived from functional−morphological interpretations. The first trophic level with phytoplankton as primary producers is generally not preserved but assumed as a food base for higher trophic levels, sensu Boy (1998) and Kriwet et al. (2007). The second level with zooplankton and hard shelly benthos is documented by the rare and badly preserved ostracods and small gastropods. The third level is composed of the durophagous−omnivorous Lissodus , the nectonic planctivorous Acanthodes and the branchiosaur−like amphibians as secondary consumers. One or two different predatory xenacanthid sharks ( Xenacanthus ,? Bohemiacanthus ) form the fourth level as tertiary consumers. It is commonly assumed that diplodoselachid piscivorous sharks, such as Orthacanthus , were the top predators in Late Carboniferous and Permian lakes. In this case, Orthacanthus −like tooth fragments indicate a fourth consumer in the fifth level of that food chain. However, we have doubts concerning the role of Orthacanthus in this and other lake ecosystems, because remains of juveniles and subadults are generally missing in the lakes and the occurrence of skeletons of adults is mostly restricted to single bedding planes in the lake deposits (e.g., Lake Heimkirchen in the Saar−Nahe Basin, Buxières lake in the Aumance Basin of the French Massif Central; personal observations by JWS). Possibly, large diplodoselachid sharks such as Orthacanthus and Orthacanthus (Lebachacanthus) were river dwellers and appeared sporadically only in the lakes, most possibly during drought periods with low water doi:10.4202/app.2009.0019

levels in the rivers. This assumption is supported by the discovery of gastroliths of exotic rock pebbles in Orthacanthus (Lebachacanthus) skeletons. These pebbles were probably swallowed in the catchment area of the Early Permian Saar−Nahe river systems and are interpreted as ballast countering buoyancy ( Boy 1994).

Figures

Fig. 9. Hypothetical food chain for the Early Permian Guardia Pisano lake environment based on indirect evidence (dashed lines) derived from functional−morphological interpretations (following Boy and Schindler 2000 and Kriwet et al. 2007). The producers are presupposed for the existence of the 1st (gastropods, ostracods) and 2nd consumers (undetermined branchiosaur, Acanthodes sp., and Lissodus sardiniensis sp. nov.), the 3rd consumer are xenacanthid sharks (Xenacanthus sp.,?Bohemiacanthus sp.), and a diplodoselachid−like shark forms the top predator.