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 wellpreserved 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.A mmonites have constituted a primary data source for the fields of evolution, paleoceanography, biostratigraphy, and paleoecology for more than a century; their ubiquity, diversity, occurrence in a wide variety of marine environments, and readily preservable shell account for their utility in both paleontological and geological studies. Ammonites have been used extensively in studies of heterochrony because their shells preserve distinct ontogenetic changes that can be tracked in evolving lineages (1, 2); they are valued in paleoceanographic research because, like most mollusks, they are inferred to have precipitated their aragonitic shells in isotopic equilibrium with the surrounding seawater (3, 4). Thus, shell chemistry may record temperature, via oxygen isotopes (δ 18 O) (5), and water mass properties, such as strontium isotopes ( 87 Sr/ 86 Sr), which are used to estimate numerical age (6). Ammonites are also a textbook example of an index fossil; besides being abundant and widespread, they evolved rapidly, making them the dominant Mesozoic tool for relative dating and correlation of shallow water strata. For example, the 35-My-long stratigraphic record of Upper Cretaceous deposits in the US Western Interior Seaway (WIS) has been partitioned into 66 ammonite zones (7). Finally, ammonites underwent a spectacular extinction at the close of the Mesozoic. Explanations for why the ammonites, which were flourishing immediately before the Cretaceous-P...
2,6‐Dicyano‐4,8‐diphenylbarbaralane[1] Conjugate addition of the phenylcuprate reagent, obtained from phenyllithium, copper(I) cyanide, and boron trifluoride–diethylether, to the bicyclo[3.3.1]nonadienedione 3 affords the diphenylbicyclo[3.3.1]nonanedione 4 in high yield. Catalyzed by the potassium cyanide/18‐crown‐6 complex, addition of trimethylsilyl cyanide produces a mixture of the diastereomeric bis[O‐(trimethylsilyl)cyanohydrins] exo,exo‐, exo,endo‐ and endo,endo‐5. The hydrogen fluoride – pyridine complex in phosphorus oxychloride as solvent and, subsequently, an excess of pyridine convert the diastereomers 5 into the unsaturated γ,γ′1‐diphenyldinirile 6. This is brominated by N1‐bromosuccinimide to yield the γ,γ′1‐dibromodinitriles exo‐ and endo‐ 7 (6:1). The predominant diastereomer exo‐7 is debrominated by the zinc‐copper couple to afford the orange‐red title compound 2 in 78% yield. More conveniently, the unsaturated dinitrile 6 is converted to 2 in a single step by treatment with hexachloroethane and concentrated aqueous sodium hydroxide in the presence of tetrabutylammonium hydroxide as phase‐transfer catalyst. Surprisingly, low yields of 2 are also obtained when the bis[O‐(trimethylsilyl)cyanohydrins] 5 or the unsaturated dinitrile 6 are treated with phosphorus oxychloride in boiling pyridine. – The structures of the new compounds are based on spectroscopic evidence and X‐ray diffraction analyses of 2, 4, and endo,endo‐5. The conformations of 4 and endo,endo‐5 in solution are inferred on the basis of vicinal proton coupling constants and a comparison with coupling constants calculated with the aid of the Karplus equation and torsional angles obtained by X‐ray diffraction analyses. – While the barbaralane 2 exists as a pair of very rapidly rearranging degenerate valence tautomers in solution, the degeneracy is lifted in the crystal lattice. As a result, the crystal consists of two rapidly rearranging but non‐equivalent valence tautomers in a ratio of 9:1 as estimated from the apparent atomic distance C2–C8 of 2 and the C2–C8 bond length of non‐rearranging barbaralanes. – The colour of 2 in the crystal and in solution results from a maximum at 436 nm which increases on heating of the solution to 450 K. Cooling to 77 K results in reversible fading and the disappearance of the maximum. Thus, 2 is a barbaralane like 1 which exhibits colour though it is lacking a classical long‐wavelength chromophore.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.