Monte San Giorgio:
Remarkable Triassic Marine Vertebrates
THE MIDDLE TRIASSIC LAGERSTÄTTE OF MONTE SAN Giorgio, located in the southernmost part of Switzerland, is well known among vertebrate paleontologists and is considered the most important locality for Triassic marine fish and reptiles in the world (Bürgin et al. 1989). Its organic-rich black bituminous shales and gray laminated dolomites have yielded thousands of fully articulated and exquisitely preserved vertebrate fossils. However, because invertebrates other than ammonites and thin-shelled bivalves are virtually absent, this Lagerstätte is practically unknown among invertebrate paleontologists and taphonomists outside central Europe. Monte San Giorgio has consequently not been mentioned in any of the recent publications summarizing the stratigraphic and environmental occurrence of conservation deposits (Allison and Briggs 1991, 1993), even though some fish and reptiles show soft-part preservation. This is due mainly to the absence of a modern study integrating sedimentologic, paleontologic, and taphonomic features.
The orthodox view about the depositional environment holds that the fossiliferous layers of Monte San Giorgio formed in a stagnant basin with permanent anoxic bottom-water conditions (Rieber and Sorbini 1983; Bernasconi 1991, 1994; Furrer 1995). The richly fossiliferous units are finely laminated throughout, trace fossils are entirely absent, and the invertebrate fauna consists mainly of taxa traditionally believed to represent pseudoplankton and nekton. The very rare undisputed benthic invertebrates were probably washed into the basin from a nearshore environment. The same is certainly true for the rare land plants and terrestrial