Ammonite shell shape covaries with facies and hydrodynamics: Iterative evolution as a response to changes in basinal environment

Research Article| October 01, 1994 Ammonite shell shape covaries with facies and hydrodynamics: Iterative evolution as a response to changes in basinal environment David K. Jacobs; David K. Jacobs 1Department of Invertebrates, American Museum of Natural History, New York 10024 Search for other works by this author on: GSW Google Scholar Neil H. Landman; Neil H. Landman 1Department of Invertebrates, American Museum of Natural History, New York 10024 Search for other works by this author on: GSW Google Scholar John A. Chamberlain, Jr. John A. Chamberlain, Jr. 2Department of Geology, Brooklyn College, Brooklyn, New York 11210 Search for other works by this author on: GSW Google Scholar Geology (1994) 22 (10): 905–908. https://doi.org/10.1130/0091-7613(1994)022<0905:ASSCWF>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation David K. Jacobs, Neil H. Landman, John A. Chamberlain; Ammonite shell shape covaries with facies and hydrodynamics: Iterative evolution as a response to changes in basinal environment. Geology 1994;; 22 (10): 905–908. doi: https://doi.org/10.1130/0091-7613(1994)022<0905:ASSCWF>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Shell shape varies within many ammonoid species, and some ammonoid lineages appear to have evolved in concert with changes in their environment. We report variation within an Upper Cretaceous ammonoid species that correlates with facies differences and is consistent with a hydrodynamic explanation. In the Turner Sandy Member of the Carlile Shale (Turonian) of South Dakota and Wyoming, more compressed morphs of Scaphites whitfieldi Cobban are found in nearshore sandy facies, whereas more depressed morphs occur in offshore muds. We measured drag forces on models of juvenile and adult shells that differed in lateral compression of the shell. Plots of drag coefficient as a function of Reynolds number indicate that thinner, more compressed morphs swam more efficiently at higher velocities and depressed morphs swam more efficiently at low velocities. Higher swimming velocities may be essential for life in nearshore sandy environments, which have higher ambient current velocities. Shelled cephalopods swim most efficiently at low swimming speeds; therefore, lower velocity, more energetically economical swimming should be preferred in more quiescent offshore settings. An analysis of power consumption supports this interpretation. Correlated changes in shell compression and environmental factors, here observed within a species, have been documented in numerous ammonite lineages. These iterative evolutionary changes within lineages may be similarly explained by selection for shell morphologies appropriate to environments that fluctuate cyclically with sea level. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.