title: Ammonite habitat revealed via isotopic composition and comparisons with co-occurring benthic and planktonic organisms.
abstract: Ammonites are among the best-known fossils of the Phanerozoic, yet their habitat is poorly understood. Three common ammonite families (Baculitidae, Scaphitidae, and Sphenodiscidae) co-occur with well-preserved planktonic and benthic organisms at the type locality of the upper Maastrichtian Owl Creek Formation, offering an excellent opportunity to constrain their depth habitats through isotopic comparisons among taxa. Based on sedimentary evidence and the micro- and macrofauna at this site, we infer that the 9-m-thick sequence was deposited at a paleodepth of 70-150 m. Taxa present throughout the sequence include a diverse assemblage of ammonites, bivalves, and gastropods, abundant benthic foraminifera, and rare planktonic foraminifera. No stratigraphic trends are observed in the isotopic data of any taxon, and thus all of the data from each taxon are considered as replicates. Oxygen isotope-based temperature estimates from the baculites and scaphites overlap with those of the benthos and are distinct from those of the plankton. In contrast, sphenodiscid temperature estimates span a range that includes estimates of the planktonic foraminifera and of the warmer half of the benthic values. These results suggest baculites and scaphites lived close to the seafloor, whereas sphenodiscids sometimes inhabited the upper water column and/or lived closer to shore. In fact, the rarity and poorer preservation of the sphenodiscids relative to the baculites and scaphites suggests that the sphenodiscid shells may have only reached the Owl Creek locality by drifting seaward after death.
authors.affiliation: Division of Paleontology, American Museum of Natural History, New York, NY 10024; jsessa@amnh.org.
authors.forename: Jocelyn Anne
authors.initials: JA
authors.lastname: Sessa
authors.affiliation: Division of Paleontology, American Museum of Natural History, New York, NY 10024; Department of Earth and Environmental Sciences, Brooklyn College, Brooklyn, NY 11210; Department of Earth Sciences, University of Southern California, Los Angeles, CA 90018;
authors.forename: Ekaterina
authors.initials: E
authors.lastname: Larina
authors.affiliation: Division of Paleontology, American Museum of Natural History, New York, NY 10024; Department of Earth and Environmental Sciences, Brooklyn College, Brooklyn, NY 11210;
authors.forename: Katja
authors.initials: K
authors.lastname: Knoll
authors.affiliation: Department of Earth and Environmental Sciences, Brooklyn College, Brooklyn, NY 11210;
authors.forename: Matthew
authors.initials: M
authors.lastname: Garb
authors.affiliation: School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY 11794;
authors.forename: J Kirk
authors.initials: JK
authors.lastname: Cochran
authors.affiliation: Department of Paleobiology, National Museum of Natural History, Washington, DC 20013;
authors.forename: Brian T
authors.initials: BT
authors.lastname: Huber
authors.affiliation: Department of Geological Sciences, University of Missouri, Columbia, MO 65211.
authors.forename: Kenneth G
authors.initials: KG
authors.lastname: MacLeod
authors.affiliation: Division of Paleontology, American Museum of Natural History, New York, NY 10024;
authors.forename: Neil H
authors.initials: NH
authors.lastname: Landman
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002247:Carbon Isotopes / Q000032:analysis; D049830:Cephalopoda / Q000737:chemistry* / Q000145:classification; D017753:Ecosystem; D056908:Foraminifera / Q000737:chemistry / Q000145:classification; D005580:Fossils; D008974:Mollusca / Q000737:chemistry / Q000145:classification; D010103:Oxygen Isotopes / Q000032:analysis; D010163:Paleontology; D010933:Plankton / Q000737:chemistry; D013696:Temperature
chemical_list: D002247:Carbon Isotopes; D010103:Oxygen Isotopes
keywords: Late Maastrichtian; ammonite; habitat reconstruction; mollusk; paleoecology