EARLY TRIASSIC FOSSIL COLLECTIONS REFLECT TRUE PALEOECOLOGICAL PATTERNS FOLLOWING THE END-PERMIAN MASS EXTINCTION

The Permian-Triassic transition was a significant interval: the end-Permian mass extinction was the largest of the Phanerozoic, and the Modern Fauna replaced the Paleozoic Fauna in the marine realm. Important evolutionary patterns, therefore, unfolded during the Early Triassic aftermath of the end-Permian mass extinction. Several studies propose that Early Triassic taphonomic processes obscured marine fossil signals, making it difficult to tease apart taphonomic artifacts from real ecological data. Through fieldwork and database analyses we tested two mainstays of the hypothesis that the Early Triassic fossil record is biased: 1) the Lazarus Effect is extensive during the Early Triassic, and 2) a lack of silicified Early Triassic faunas means paleoecological analyses are based on incomplete data.

Many Early Triassic taxa have been reported as Lazarus taxa, taxa that temporarily disappear from the fossil record and reappear later unchanged, but this phenomenon has not been rigorously tested for. We determined the number of Lazarus genera for Gastropoda, Bivalvia, Echinoidea, Strophomenata and Rhynchonellata for the Late Permian, Early Triassic, and Middle Triassic using Gastrobase and the Paleobiology Database (PBDB). A statistically significant Lazarus phenomenon during the Early Triassic exists only among gastropods (57% of gastropod genera are Lazarus taxa).

Because silicified faunas may have a higher fidelity of fossil preservation than nonsilicified ones, an absence of silicified Early Triassic invertebrate marine faunas has been proposed to skew paleoecological interpretations. Data from the PBDB indicate common silicified Early Triassic faunas: 58% of the collections of benthic invertebrate marine faunas with taphonomic data contained fossils that had been replaced by silica. Nonsilicified faunas are more diverse than silicified ones, but silicified collections record more individuals per taxon.

Results indicate that Early Triassic paleoecological data are largely unbiased, and reasons other than quality of the fossil record primarily caused observed patterns. The causes, characteristics, and evolutionary consequences of mass extinctions and their aftermaths can be more accurately determined and understood if the limits of the fossil record are quantified and acknowledged.