James Sprinkle

Origin of echinoderms in the Paleozoic evolutionary fauna; the role of substrates

Comparison of echinoderm faunas from two partly coeval Early Ordovician units, the Fillmore Formation of western Utah and the Ninemile Shale of central and southern Nevada, indicates that the distribution of echinoderms during the initial radiation of the Paleozoic Evolutionary Fauna was substrate-controlled. Attached echinoderms, such as crinoids and edrioasteroids, are much more common on hard substrates in the shallow-water Fillmore, whereas vagile forms, such as rhombiferans and mitrate stylophorans, are found on soft substrates in both the shallow-water Fillmore and deeper-water Ninemile. We found few intermediates or holdovers among these new Early Ordovician echinoderms, implying that the Cambrian and Paleozoic Evolutionary Faunas were most likely discrete and real and that the Ordovician Radiation was already well under way by the middle of the Early Ordovician.

Rise of echinoderms in the Paleozoic evolutionary fauna: Significance of paleoenvironmental controls

Echinoderms were a major enduring component of Paleozoic marine faunas beginning with the rapid diversification of crinoids and other classes in the Early Ordovician. This diversification was triggered by increased availability of habitable areas accompanying sea-level rise and changed sedimentation styles. Newly collected Early Ordovician echinoderms facilitate determination in detail of life modes and important adaptations during this transition interval. Substrate consistency and stability were crucial spatial limiting factors that resulted in heterogeneous distribution patterns for echinoderm classes. Crinoids were overwhelmingly large-food-groove suspension feeders with relatively open filtration fans attached by small discs to hard-ground surfaces in shallow water. They were preadapted for this life mode. Rhombiferans were mobile small-food-groove suspension feeders; they lived on soft substrates at various depths. Several important crinoid clades underwent a second phase of diversification during the Middle Ordovician by developing holdfasts adapted to soft substrates and densely pinnulate arms with small food grooves, leading to dominance of this class among Paleozoic echinoderms. Our findings are in basic agreement with the overall onshore diversification pattern of most Paleozoic benthic invertebrates, but we argue for an extrinsic environmental control (substrate availability) for the observed echinoderm distribution.

Proterozoic stromatolites: The first marine evolutionary biota

Proterozoic stromatolites represent a Marine Evolutionary Biota, analogous to the three marine evolutionary faunas of the Phanerozoic that have been recognized on the basis of their characteristic benthic metazoans. The pattern of expansion and subsequent decline in morphological diversity of these earliest collectively mineralized benthic ecosystems is documented in this report. First known from the Archean, stromatolites began to radiate significantly in the Paleoproterozoic, beginning about 2500 million years ago. Throughout the Mesoproterozoic, they dominated marine shallow shelf environments as an ecologically simple, producer‐reducer ecosystem. Stromatolites declined drastically in diversity during the late Neoproterozoic and earliest Paleozoic as algae, other protistans, and metazoans diversified to form more complex, multilevel ecosystems. Remnants of this early evolutionary biota of the level sea floor survived through the Phanerozoic to the present day by retreating onshore, where they are now l...

Earliest crinoids: New evidence for the origin of the dominant Paleozoic echinoderms

The oldest crinoids have been discovered in Early Ordovician strata of the western United States. A set of emergent crinoid traits based on these and other early crinoids enables reinterpretation of crinoid origins and early history. The new fossils retain primitive echinoderm characteristics, including ambulacral floor plates and largely unorganized cup plating, a first for crinoids. They lack shared derived characteristics linking them to other stalked echinoderms, including blastozoans. Contrary to current widespread opinion, crinoids originated as an independent group during the Cambrian, apparently from an edrioasteroid ancestor. All four major Paleozoic crinoid clades had evolved by the early Ibexian (Tremadocian), and this initial diversification slightly preceded those of most other Paleozoic evolutionary fauna components. These earliest crinoids attached to carbonate hardgrounds developed on sponge-algal mounds, intraformational conglomerates, and grainstones.

Radiation of Echinodermata

Echinoderms underwent an initial radiation into marine shelf environments in the Early to Middle Cambrian. Within about 45 million years, nine new classes of echinoderms (as recognized in an evolutionary classification) appeared suddenly in the fossil record, many of these without obvious ancestors. This radiation then tapered off during the Late Cambrian, and no additional classes of echinoderms appeared in the record until the Early Ordovician, about 20 million years later, when a secondary radiation of echinoderms began.

Solving the Mystery of Crinoid Ancestry: New Fossil Evidence of Arm Origin and Development

Abstract Apektocrinus ubaghsi new genus and species is a monospecific taxon assigned to the new family Apektocrinidae based on additional preparation of a single previously studied specimen. Apektocrinus is among the oldest known crinoids (Early Tremadoc, Early Ordovician). Although expressing crinoid apomorphies, it is interpreted as retaining plesiomorphies in its arms reflecting early edrioasteroid rather than blastozoan (eocrinoid) ancestry. Apomorphies represent basal crinoid and cladid (crownward) levels of phylogeny. Restudy fortifies previous reports of the presence of a basal echinoderm plesiomorphy; floor plates above brachials in the arms of Apektocrinus, as well as in other approximately contemporary crinoids. Apektocrinus furnishes the first record of podial basins in crinoid arms. Arms and calyx of Apektocrinus merge gradually, facilitated by continuations of interbrachials (extraxial body plates) extending onto the arms and separating floor plates from brachials. These arm interbrachials, which diminish and pinch out distally as floor plates nestle into the brachial (adoral) groove, have not been recognized as such in crinoids.

New echinoderms from the Early Ordovician of west Texas

ABsTRAcr-Four specimens of blastozoan and crinozoan echinoderms are described from the Lower Ordovician El Paso Group in the southern Franklin Mountains just north of El Paso, west Texas. Cuniculocystis floweri n. gen. and sp., based on two partial specimens, appears to be a typical rhombiferan in most of its morphologic features except that it lacks pectinirhombs and instead has covered epispires (otherwise known only from Middle Ordovician eocrinoids) opening on most of the thecal plate sutures. The covered epispires in Cuniculocystis indicate that some early rhombiferans had alternate respiratory structures and had not yet standardized on pectinirhombs, a feature previously used as diagnostic for the class Rhombifera. Bockia? elpasoensis n. sp. is a new eocrinoid based on one poorly preserved specimen that has a small ellipsoidal theca and unbranched brachioles attached to a flattopped spoutlike summit. It is the earliest known questionable representative of this genus and the only one that has been described from North America. Elpasocrinus radiatus n. gen. and sp. is an early cladid inadunate crinoid based on a single well-preserved calyx. It fits into a lineage of early cladids leading to the dendrocrinids and to Carabocrinus. Several additional separate plates, stem segments, and a holdfast of these and other echinoderms are also described.

Ponticulocarpus, a new cornute-grade stylophoran from the Middle Cambrian Spence Shale of Utah

Four specimens of a new cornute-grade stylophoran Ponticulocarpus robisoni new genus and species are described from the Spence Shale of northern Utah. Ponticulocarpus has wide and thin spinal and glossal processes interpreted as a mechanism for snowshoeing in a soft substrate. The presence of a posterior bar across the inferior posterior lobe, and two small bridges connecting the left adoral to M92 on the superior face and connecting M1 to M3 on the inferior face are unique in cornute-grade stylophorans. The posterior bar may be homologous with the posterior marginals M95 and M6 of other cornute-grade stylophorans, and an opening of the most posterior portion of the theca may have resulted in the development of the digital and glossal processes from marginals.

AN EDRIOASTEROID-DOMINATED ECHINODERM ASSEMBLAGE FROM A LOWER PENNSYLVANIAN MARINE CONGLOMERATE IN OKLAHOMA

Abstract Four species of isorophinid edrioasteroids, Ulrichidiscus forbesi n. sp., Neoisorophusella whitesidei n. sp., Postibulla westergaardi n. sp., and Parapostibulla graysoni n. sp., are described from unnamed unit 1 of the Golf Course Formation, Dornick Hills Group, Lower Pennsylvanian (Morrowan), at Forbes Ranch, north of Marietta, southern Oklahoma. This locality is the first report of edrioasteroids attached to extraformational clasts, and they exhibit extremely high specimen density and the highest taxonomic diversity known from the post-Ordovician. The associated fauna consists of the stemless crinoid Paragassizocrinus tarri, serpulid worm tubes, and the acrothoracic barnacle boring, Rogerella, along with a few brachiopods, rugose corals, and other open marine organisms. Edrioasteroids show no preference for clast type, size, or shape. Intraspecific spatial competition is shown by polygonal specimen outlines in highly crowded conditions, whereas interspecific competition results in specimen overgrowth in a predictable manner.

Revision of lyracystid eocrinoids from the Middle Cambrian of South China and Western Laurentia

Abstract The Middle Cambrian eocrinoid genera Lyracystis Sprinkle and Collins, 2006, from western Laurentia and Balangicystis Parsley and Zhao, 2006, from South China, described in the same year, have turned out to be closely related genera assigned to the Family Lyracystidae. Both have erect, lyre-shaped, arm-like, brachiole-bearing, feeding appendages, here termed exothecal ambulacra, that are not homologous to crinoid arms. They also have a long, multiplated stalk to elevate the theca and feeding appendages well above the sea floor, making them among the highest tiered echinoderm suspension feeders known from the Middle Cambrian. The long stalk was either inserted a short distance into the muddy sediment, or attached to rare skeletal fragments lying on the sea floor. Both genera seem well adapted to quiet-water or slow-current conditions in deeper water (150–200 m) on the outer shelf or upper slope of their respective continents.