Vertebrate assemblage and depositional environment of the Fayetteville Shale (Upper Mississippian, middle Chesterian)

The Upper Mississippian (Middle Chesterian) Fayetteville Shale has long yielded exceptionally preserved plant and invertebrate fossils, but its vertebrate fossils have only recently been investigated in earnest. These investigations have yielded numerous three-dimensionally preserved chondrichthyan remains, capturing key features for reconstructing early chondrichthyan relationships. Over the last several decades, paleobotanists and invertebrate paleontologists have collected vast numbers of phosphatic concretions from this formation. For this investigation, dozens of these concretions housed at the American Museum of Natural History were split open or µCT-scanned, revealing a diversity of vertebrate fossils previously unknown from these deposits. We provide an account of the vertebrate diversity, as well as a summary overview of previous hypotheses of Fayetteville Shale paleoecology and depositional environment. Synchronous synchrotron X-ray fluorescence and X-ray diffraction mapping, combined with powder diffraction, were used to characterize the elemental and mineralogical composition of a concretion and its fossil content. The obtained data support reconstructions of the depositional environment and explain the exceptional preservation of calcified cartilage but limited preservation of bone and shell.