UPPER MIDDLE TRIASSIC “SMALL SHELLIES” FROM THE KLEINE TERREBRATELBANK OF THE MUSCHELKALK, BAVARIA, GERMANY: THE ROLE OF “ATTENTION BIAS” IN UNDERESTIMATING THE DISTRIBUTION OF PHOSPHATIC MICROSTEINKERNS

“Small shelly fossils” (SSFs) are largely preserved as phosphatic microsteinkerns and often thought to be exclusive to the Cambrian. The sparsity of post-Cambrian reports has been interpreted as evidence of rarity, thus signifying taphonomic conditions unique to the Cambrian. Our literature review found many reports of similar preservation throughout the Phanerozoic, although unevenly distributed in time, with a notable gap between the lower Triassic and the Upper Jurassic. We suspect that the scattered reporting stems from a lack of attention, not just a lack of occurrences. This “attention bias” may arise stratigraphically as reports consider economic phosphorites rather than marine paleontology, as larger marine fossils increase in abundance, as conodonts (accidental SSF discovery in acid residues) disappear from the record, and as terrestrial faunas draw attention away from marine faunas.

Recent work in the Upper Ordovician around Cincinnati (SE Indiana, SW Ohio, and N Kentucky) suggests SSFs are concentrated in slowly deposited and reworked sediments. We hypothesized that there are unreported occurrences in strata deposited under similar conditions. Given the likely causes of attention bias in the Mesozoic and the gap in reported occurrences, we decided to test this hypothesis by searching the Triassic Muschelkalk of the Schwäbisch region of Germany, a storm-influenced succession of interbedded limestones and mudstones with similar depositional environments to the Cincinnatian of the USA.

After examining thin sections (Munnecke collection in Erlangen), analyzing small molluscan steinkerns in fossil collections (Muschelkalkmuseum Hagdorn in Ingelfingen), inquiring about small molluscan steinkerns in acid residues (from the Kramm collection), and collecting samples from the Jagst River Valley, we found abundant SSFs from at least 4 localities from the uppermost Muschelkalk in approximately coeval sediments of the Kleine Terrebratelbank. That these occurrences have not been reported (despite being “known”, and despite the abundance of literature concerning the Muschelkalk) reinforces the idea that temporal patterns of taphonomic bias may be strongly overprinted with stratigraphically uneven attention bias.