Ronald D. Lewis

Character and Genesis of the Ingersoll Shale, A Compact Continental Fossil-Lagerstätte, Upper Cretaceous Eutaw Formation, Eastern Alabama

Abstract The Ingersoll shale, a thin (<1 m) clay-dominated lens within the Upper Cretaceous Eutaw Formation in eastern Alabama, contains a well-preserved, primarily continental biota that includes a diverse, carbonized, and variably pyritized flora, abundant amber with fossil inclusions, and common feathers. Geometry of the Ingersoll shale lens and its position between high-energy tidal deposits below and estuarine central bay deposits above indicate deposition in a shallow, narrow channel in the lower reaches of a bayhead delta in response to estuarine transgression. Tidal rhythmites and textural trends indicate that the channel filled very rapidly (55–80 cm per yr), under progressively waning energy regimes. Ichnofabrics, high organic carbon contents, and abundant pyrite indicate highly fluid and reducing sediments. Marine palynomorphs, sulfide contents, and δ34S values of pyrite sulfur indicate normal to near-normal marine salinities. Environmental factors and sedimentary processes contributing to preservation of the Ingersoll shale biota include (1) rapid deposition and burial (obrution); (2) reducing pore waters (stagnation), which limited bioturbation and scavenging, promoted pyritization of some fossils (diagenetic mineralization), and facilitated bacterial replacement of others (i.e., feathers); and (3) concentration of allochthonous or para-autochthonous amber clasts (preservation traps) by tidal currents. Lessons from the Ingersoll shale may help prospect for similar, isolated yet fossil-rich marginal marine deposits.

Feathers of the Ingersoll shale, Eutaw Formation (Upper Cretaceous), eastern Alabama: The largest collection of feathers from North American Mesozoic rocks

Abstract The Ingersoll shale (Santonian) is a small mudstone lens in eastern Alabama, interpreted as an abandoned tidal-channel fill that accumulated rapidly within the lower reaches of a bayhead delta. The diverse biota found in this fossil Lagerstätte includes 14 individual feather specimens, the largest collection known from the Mesozoic of North America. Occurring separately throughout nearly the entire thickness of the clay lens and with a range of sizes and morphologies, the feathers most likely represent a number of theropod species. Based on known taxa in the region, the largest specimen (16.5 cm) may be a rectrix (tail feather) from a dromaeosaurid dinosaur or from a hesperornithid. Smaller feathers may have belonged to a range of shore birds. The best-preserved specimens were found in the finest grained intervals. SEM examination reveals very well preserved microstructure consisting of carbonized rod-shaped bodies ∼1 µm in length, preserved in three dimensions and solid internally. Although identical in size and shape to modern feather-degrading bacilliform bacteria and displaying some bacteria-like features, their alignment along the axis of feather structures indicates that they are more likely the fossil remains of melanosomes, melanin bodies used for color production during life. No three-dimensional arrays or patterned differences of morphotypes have been seen thus far; almost all elements are elongate (apparently eumelanin). Inferred colors for four of the feathers, based on differences in melanosome morphologies, range from gray and brownish gray to black. Whereas the majority of feather-bearing deposits represent inland lakes, the estuarine setting adds a view of coastal feathered theropods preserved in detail by rapid deposition of fine-grained sediment.

Mandalacystis, a new rhipidocystid eocrinoid from the Whiterockian Stage (Ordovician) in Oklahoma and Nevada

Mandalacystis dockeryi n. gen. and sp. is known from seven complete or nearly com- plete thecae, six partial thecae, and numerous separate plates from the Oil Creek Formation in south-central Oklahoma, and a single thecal plate from the Antelope Valley Limestone in Nevada. Details of skeletal microstructure (stereom) are well preserved, permitting scanning electron mi- croscopy for the first time in the Eocrinoidea, and demonstrating that plate thickness on thecal faces is only 60-70 clm. Mandalacystis is characterized by labyrinthine ridges on both faces of the theca, relatively short brachioles, and a normal stem with holdfast (at least in juvenile stages). Based on the normal biserial arrangement of brachiolar plates in the brachioles and the possession of a normal stem, Mandalacystis appears to be one of the most primitive rhipidocystids, closely related to Petalocystites. Mandalacystis dockeryi lived in a storm-dominated, shallow-water offshore habitat on patches of skeletal debris surrounded by soft, terrigenous mud. This setting may have been conducive to the transition from an erect, attached mode of life to the prone, unattached lifestyle of later rhipidocystids.

The Utility of Isolated Crinoid Ossicles and Fragmentary Crinoid Remains in Taphonomic and Paleoenvironmental Analysis: An Example from the Upper Pennsylvanian of Oklahoma, United States

Abstract The crinoid fossil record is dominated by isolated ossicles, pluricolumnals, arm segments, and other fragmentary remains resulting from postmortem skeletal disarticulation; however, few studies to date have focused on dissociated crinoid elements in taphonomic and/or paleoenvironmental analysis. A diverse, abundant, and taphonomically variable crinoid fauna recovered from a thin mudstone interval within the Upper Pennsylvanian Barnsdall Formation in northeastern Oklahoma presents a unique opportunity to test the value of incomplete crinoid remains in reconstructing paleoenvironmental conditions and understanding taphonomic patterns. Isolated radial plates were identified to the most precise level possible, commonly genus or species, and used to calculate the minimum number of completely disarticulated individuals; this value was then compared to the number of articulated specimens representing that same taxon to determine the proportion of individuals with cups that have undergone disarticulation into separate ossicles. Cladid taxa are shown to be particularly prone to total disarticulation, with disparid microcrinoids and, somewhat surprisingly, flexibles demonstrating more resistance to disarticulation. Genus-level taphonomic trends among cladid taxa indicate that genera with large but thin cup plates, short anal sacs, and arms capable of adopting a trauma posture are less prone to total disarticulation. Analysis of fragmentary crinoid material recovered from disaggregation of bulk mudstone slabs reveals that thin horizons containing abundant articulated crinoid crowns are enriched in skeletal material and encrusted ossicles relative to thicker subjacent and superjacent intervals, providing further evidence that such horizons represent periods of sediment starvation on the distal shelf that were episodically punctuated by storm events.

Genus-level taphonomic variation within cladid crinoids from the Upper Pennsylvanian Barnsdall Formation, northeastern Oklahoma

Abstract Previous comparative taphonomic studies have convincingly demonstrated that the taphonomic state of crinoid fossils is controlled largely by paleoenvironmental processes and constructional morphology. While taphonomic variability among depositional facies has a long history of investigation, the degree to which preservational heterogeneity is controlled by crinoid morphology has only recently been addressed and only at relatively coarse levels. Most studies to date have focused on taphonomic variability at the subclass or ordinal level, with little documentation of lower level taphonomic variation within a single crinoid subclass. A remarkably diverse, abundant, and well-preserved crinoid fauna, recovered from a single mudstone interval within the Upper Pennsylvanian (Missourian) Barnsdall Formation in northeastern Oklahoma, midcontinent North America, provides a unique opportunity to examine taphonomic trends among poteriocrine cladid crinoids at refined taxonomic levels. Genus-level variations in specimen completeness, axis of compaction, arm position, and features attributed to decay and scavenging are observed within this assemblage and taphonomic trends related primarily to the size of individuals are detected. These results indicate that taphonomic variability extends at least to genus level within the subclass Cladida. Understanding this variability is important in interpreting the genesis and nature of crinoid-bearing units, as minor variations in morphology, ethology, and scavenger preferences impart unexpected biostratinomic heterogeneity to Copan crinoid fauna that would otherwise be difficult to explain. Taphonomic variability at low taxonomic levels and the influence of preferential scavenging should be accounted for in future crinoid taphonomic grade studies, particularly in Pennsylvanian and younger deposits, in order to avoid taphonomic assumptions that may be overly broad.

Sciadiocrinus, convergence on the family Pirasocrinidae (Crinoidea: Echinodermata)

Sciadiocrinus Moore and Plummer is synonymized with Schistocrinus Moore and Plummer, with the name Sciadiocrinus retained by the Law of Priority. This synonymy is based on a reexamination of the type material, study of a previously undescribed ontogenetic sequence in S. tegillum Strimple and Moore, and close inspection of separate radial plates and anal-sac spines. The holotype specimen of the type species of Sciadiocrinus was incorrectly illustrated in the original description of the genus, and appears to be immature. The basal plates of this specimen are shown to be separated from each other by the junction of the radial plates with the infrabasals—a principal character in the original concept of Schistocrinus. The Sciadiocrinus tegillum hypodigm now includes specimens which also have relatively large radial–infrabasal sutures as well as individuals with little or no contact between these plates. Examination of this collection and previously described material shows that mode of arm branching, details of radial-plate articular facets, and some features of the anal-sac spines are also equivalent in the two genera. Sciadiocrinus , presently classified in the family Pirasocrinidae, is distinct from all known pirasocrinid taxa in a number of morphological characters. We believe the genus should be removed from the Pirasocrinidae, and recommend its assignment to the family Anobasicrinidae based primarily on similarities in arm structure. The remarkable convergence between Sciadiocrinus and the Pirasocrinidae emphasizes the adaptive significance of the spinose, umbrella-like anal-sac roof, which apparently served as a deterrent to predators.

Grain morphologies and surface textures of Recent and Pleistocene crinoid ossicles, San Salvador, Bahamas

The comatulid crinoids Davidaster rubiginosa and D. discoidea live in shallow (5 m) patch reefs off the western coast of the island of San Salvador (Bahamas) and at the shelf edge along the western and southern sides of the island. Their ossicles (plates) occurs as rare, but recoverable, elements in the seafloor sediment. Living specimens of Davidaster were collected, and their arm plates (brachials) and pinnule plates (pinnulars) were subjected to laboratory tests of abrasion and dissolution in order to identify the effects of these processes on the echinoderms stereom. Ossicles from a Pleistocene reef exposed on the island are rare, but demonstrate the potential for future studies of both biostratinomy and diagenesis

SIDERITE CONCRETIONS IN THE COPAN CRINOID LAGERSTÄTTE (UPPER PENNSYLVANIAN, OKLAHOMA): IMPLICATIONS FOR INTERPRETING TAPHONOMIC AND DEPOSITIONAL PROCESSES IN MUDSTONE SUCCESSIONS

ABSTRACT A thin interval of bioturbated, fossiliferous mudstone within the middle portion of the Upper Pennsylvanian Barnsdall Formation crops out near Copan, northeastern Oklahoma. Representing slow background sedimentation in an oxygenated distal shelf setting, this exposure has yielded an exceptionally diverse and well-preserved crinoid fauna consisting of over 1200 articulated or partially articulated specimens. The interval is also characterized by abundant siderite concretions, present as four morphologies. Large concretions without a distinct skeletal nucleus are located in thin horizons containing abundant articulated crinoids; these indicate sediment starvation on the shelf. Also in these thin, crinoid-bearing units are extremely localized siderite concretions precipitated around sites where soft tissues would have been volumetrically more abundant within large macrofossils, notably tegmina and proximal arms of articulated crinoids, indicating extremely rapid burial events that episodically punctuated the sediment-starved conditions. Small concretions, generally <60 mm in diameter and commonly precipitated around endobenthic-fossil nuclei, are located in thicker units with few articulated crinoids. These indicate higher sedimentation rates and thicker individual burial events. Sideritized large-diameter burrows with sharply defined walls indicate firmer substrates created by minor erosive events. These are located in the thicker units alongside the smaller concretions and indicate higher-energy storm events than those represented in the thinner, crinoid-bearing units. Collectively, the evidence provided by siderite concretion morphologies and their relationships to macrofossil preservation demonstrate that the Copan crinoid Lagerstätte formed through periods of sediment starvation occasionally interrupted by distal storm events. These periods alternated with intervals of increased sedimentation and more violent storms.