title: From success to persistence: Identifying an evolutionary regime shift in the diverse Paleozoic aquatic arthropod group Eurypterida, driven by the Devonian biotic crisis.
abstract: Mass extinctions have altered the trajectory of evolution a number of times over the Phanerozoic. During these periods of biotic upheaval a different selective regime appears to operate, although it is still unclear whether consistent survivorship rules apply across different extinction events. We compare variations in diversity and disparity across the evolutionary history of a major Paleozoic arthropod group, the Eurypterida. Using these data, we explore the group's transition from a successful, dynamic clade to a stagnant persistent lineage, pinpointing the Devonian as the period during which this evolutionary regime shift occurred. The late Devonian biotic crisis is potentially unique among the "Big Five" mass extinctions in exhibiting a drop in speciation rates rather than an increase in extinction. Our study reveals eurypterids show depressed speciation rates throughout the Devonian but no abnormal peaks in extinction. Loss of morphospace occupation is random across all Paleozoic extinction events; however, differential origination during the Devonian results in a migration and subsequent stagnation of occupied morphospace. This shift appears linked to an ecological transition from euryhaline taxa to freshwater species with low morphological diversity alongside a decrease in endemism. These results demonstrate the importance of the Devonian biotic crisis in reshaping Paleozoic ecosystems.
authors: Division of Paleontology, American Museum of Natural History, Central Park West at 79th Street, New York, New York, 10024.|Department of Geology and Geography, West Virginia University, 98 Beechurst Avenue, Brooks Hall, Morgantown, West Virginia, 26506.
authors: James C
authors: JC
authors: Lamsdell
authors: Paleontological Institute and Department of Geology, University of Kansas, 1475 Jayhawk Boulevard, Lawrence, Kansas, 66045.|Natural History Museum, Cromwell Road, London, SW7 5BD, United Kingdom.
authors: Paul A
authors: PA
authors: Selden
mesh_terms: D000818:Animals; D001181:Arthropods / Q000502:physiology*; D044822:Biodiversity; D005075:Biological Evolution; D053476:Extinction, Biological; D005580:Fossils
keywords: Biotic crises; macroecology; macroevolution; mass extinction; morphological disparity; phylogeny