Date of Graduation
Eberly College of Arts and Sciences
Geology and Geography
Thomas W Kammer
Kathleen C Benison
Timothy G Carr
A 2003 paper by Stanley and Powell reported depressed rates of origination and extinction in marine invertebrates during the Late Paleozoic Ice Age (LPIA) as compared to background rates during the Paleozoic. In their paper, trilobites were used as a specific example to support the hypothesis of sluggish evolutionary rates. Thus, can their hypothesis be tested using a different fossil group? Using an updated version of the crinoid database from Sepkoski's 2002 compendium of fossil marine genera, adding data from multiple sources, rates of origination, extinction, and genus duration were calculated at the stage level for the interval from the Early Devonian (419 Ma) to the Late Permian (254 Ma). This 165 m.y. time span includes non-glacial intervals before and after the LPIA, which spanned the Serpukhovian (331 Ma) to Sakmarian (290 Ma), providing background rates for comparison. The data generated on crinoid evolutionary rates during the Middle to Late Paleozoic were analyzed and compared to Stanley and Powell's data to determine if crinoid evolutionary patterns support their findings or suggest an alternative hypothesis.;The results of the analysis performed on the updated crinoid database support Stanley and Powell's hypothesis of depressed evolutionary rates in marine invertebrates during the LPIA. Rates of origination and extinction in all crinoid clades were reduced during the LPIA compared to the intervals examined before and after the LPIA. However, crinoid diversity was higher during the LPIA than the surrounding time intervals as origination rates exceeded extinction rates. This increased diversity does not follow Stanley and Powell's findings of reduced diversity in marine invertebrates during the LPIA. The increased diversity of crinoids through the LPIA indicates that taphonomic bias is not responsible for the depressed evolutionary rates. A lower diversity count would be expected during a glacial interval due to lower sea levels, which would result in reduced outcrop volume.;The difference in diversity trends between crinoids and other marine invertebrates is due to factors specific to the advanced cladids crinoid clade. Unstable, fluctuating environmental conditions during the LPIA created habitats suitable for opportunistic crinoid genera, which reduced both the probability of origination and extinction. Advanced cladids were solely responsible for the high diversity of crinoids during the LPIA because they represented the majority of crinoids. The increased diversity of the advanced cladids is due to their unique adaptation of muscular articulation, which allowed them to thrive in marine settings with increased siliciclastic influx. The advanced cladids responded opportunistically to the environmental change brought on by the Alleghenian orogeny, which caused an increase in siliciclastic dominated marine environments. Despite the advanced cladids' departure from the expected diversity count, the results of analyses performed on the updated crinoid database support Stanley and Powell's original hypothesis of depressed evolutionary rates in marine invertebrates during the LPIA.
Segessenman, Daniel C., "Did the Late Paleozoic Ice Age cause reduced evolutionary rates in marine invertebrates? : A test using the crinoid fossil record" (2016). Graduate Theses, Dissertations, and Problem Reports. 6597.