Kowalewski, Michal1, Susan M. Kidwell2, Anna K.
Behrensmeyer3, John Alroy4, Franz T. Fursich5, Robert A.
Gastaldo6, Matthew A. Kosnik2, Roy E. Plotnick7, Raymond
(1) Virginia Tech, Blacksburg, VA
(2) University of Chicago, Chicago, IL
(3) Smithsonian Institution, Washington, DC
(4) National Center for Ecological Analysis and Synthesis, Santa Barbara, CA
(5) University of Wurzburg, D-97070 Wurzburg, Germany
(6) Colby College, Warterville, ME
(7) University of Illinois at Chicago, Chicago, IL
(8) Macalester College, Saint Paul, MN
Long-term patterns in the marine fossil record (e.g., Sepkoski’s and Alroy et al. 2001’s Phanerozoic diversity curves) may be subject to various taphonomic overprints. In particular, the record of durable vs. fragile organisms may be distorted if skeletal durability affects preservation potential. This study, conducted by the PDBD taphonomy working group using the Paleobiology Database [PBDB] (http://paleodb.org), tests the effect of durability on commonness of fossils. We focused on three major groups (bivalves, gastropods, and brachiopods) and restricted analyses to two time intervals best represented in PBDB (Ordovician-Carboniferous and Jurassic-Paleogene). For each group, 150 genera with the highest number of occurrences [collection records] in the PBDB were selected (450 genera total). To minimize monographic effects, the commonness of each genus was quantified as a total number of geological formations from which that genus was reported in the database (as of 09/2003). Seven taphonomic durability indices were estimated for each genus as average values computed for multiple species: mature specimens from collections or literature sources were scored in terms of body size, shell thickness, three reinforcement structures (folds, ribs, spines), shell mineralogy, and shell organic content. Results indicate that the frequency of formation occurrences of the most common genera in the PBDB is independent of durability-related characteristics. Thin-shelled and thick-shelled genera display occurrence-frequency distributions that are virtually identical in terms of shape and central tendency; results are similar for different shell mineralogies and body size classes. This pattern persists when data are analyzed separately for the Paleozoic and Meso-Cenozoic. The latter outcome is particularly notable considering substantial changes observed over time in body size, shell thickness, and the proportion of aragonitic fauna. Because a temperate-latitude bias in Meso-Cenozoic records should act against the observed secular changes in body size, shell thickness, and mineralogy, these trends likely reflect genuine biological patterns rather than taphonomic artifacts.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.