A new crinoid fauna has been discovered in the Upper Ordovician (Katian) Martinsburg Formation at a small shale quarry, locally known as the ‘Shale Bank,’ on the Shawangunk Ridge in Ulster County, NY. The assemblage, which is from a relatively low energy, offshore mud-bottom environment, includes four identified species, including a new species of glyptocrinid camerate, Pycnocrinus mohonkensis n. sp., described herein. Crinoid taxa in order of increasing branch density in the assemblage include (1) the dicyclic inadunate Merocrinus curtus with irregularly isotomous and heterotomous, non-pinnulate arms and a stout cylindrical column exceeding 700 mm; (2) the disparids Cincinnaticrinus varibrachialus, with heterotomous non pinnulate arms, and Ectenocrinus simplex, with extensively branched ramulate arms and meric columns of 460–500 mm; and (3) the camerate Pycnocrinus mohonkensis n. sp., with uniserial pinnulate arms and a somewhat shorter column. Some cylindrical stems with nodose and holomeric columnals are thought to belong to unknown camerate crinoids with pinnulate arms. Filtration theory is used to model food capture in the Martinsburg crinoids. Surprisingly, even densely pinnulate camerates were able to survive in this setting, suggesting that ambient currents attained velocities exceeding 25 cm/sec even in this offshore setting. Similar assemblages were widespread in eastern Laurentia during the Late Ordovician.

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A variety of pits representing symbiotic embedments, sometimes associated with pathological deformation in the host, are known from the skeletons of Paleozoic stalked echinoderms. These structures are well known from multiple genera of crinoids and a limited number of blastozoans but have not previously been described in detail from the skeletons of rhombiferans. This is surprising given the abundance of rhombiferans in certain deposits, the co-occurrence of rhombiferans with frequently infested taxa, including diploporitans, in multiple assemblages, and the morphological similarity between certain rhombiferan taxa and coeval infested crinoids. The common hemicosmitid rhombiferan Caryocrinites Say, 1825 is widespread throughout the middle Silurian of eastern North America and is herein reported to contain symbiotic (potentially parasitic) embedment structures. Specimens were collected from the lower portion of the mudstone lithofacies of the Massie Formation (Wenlock, Sheinwoodian) at the Napoleon quarry of southeastern Indiana, USA. Strong host specificity is indicated by the absence of pits in C. ornatus Say, 1825 and exclusive infestation of a smaller co-occurring species of Caryocrinites. Thecae with embedment structures are consistently smaller than thecae without such structures, with pitted specimens being restricted to a narrow range of thecal heights (20–24 mm). All embedment structures are present only on the proximal portion of thecae, with individual specimens containing between one and 30 pits. No elevated rims or significant swelling were observed on any specimens, and all pits are relatively small (~1 mm in diameter). The presence of symbiotic embedment structures represents an additional example of a crinoid-like aspect to the ecology of Caryocrinites.

Thirteen bryozoan species are described from the Brewer Dock (Hickory Corners) Member of the Reynales Formation (lower Silurian, Aeronian) at the locality Hickory Corners in western New York, USA. Three species are new: trepostomes Homotrypa niagarensis n. sp. and Leioclema adsuetum n. sp. and the rhabdomesine cryptostome Moyerella parva n. sp. Only one species, Hennigopora apta Perry and Hattin, 1960, developed obligatory encrusting colonies whereas the others produced erect ramose colonies of various thicknesses and shapes: cylindrical, branched, and lenticular. Bryozoans display high abundance and richness within the rock. This fauna is characteristic of a moderately agitated environment with a stable substrate. The identified species reveal paleobiogeographic connections to other Silurian localities of New York as well as Ohio and Indiana (USA) and Anticosti (Canada).

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Evolving interactions between predators and prey constitute one of the major adaptive influences on marine animals during the Paleozoic. Crinoids and fish constitute a predator–prey system that may date back to at least the Silurian, as suggested by patterns of crinoid regeneration and spinosity in concert with changes in the predatory fauna. Here we present data on the frequency of breakage and regeneration in the spines of the Middle Devonian camerate Gennaeocrinus and late Paleozoic cladids, as well as an expanded survey of the prevalence of spinosity and infestation by platyceratid gastropods on crinoid genera during the Paleozoic. Spine regeneration frequency in the measured populations is comparable to arm regeneration frequencies from Mississippian Rhodocrinites and from modern deep-water crinoid populations. The prevalence of spinosity varies by taxon, time, and anatomy among Paleozoic crinoids; notably, spinosity in camerates increased from the Silurian through the Mississippian and decreased sharply during the Pennsylvanian, whereas spines were uncommon in cladids until their Late Mississippian diversification. Among camerates, tegmen spinosity is positively correlated with the presence of infesting platyceratid gastropods. These results allow us to evaluate several hypotheses for the effects of predation on morphological differences between early, middle, and late Paleozoic crinoid faunas. Our data corroborate the hypothesis that predators targeted epibionts on camerate crinoids and anal sacs on advanced cladids and suggest that the replacement of shearing predators by crushing predators after the Hangenberg extinction affected the locations of spines in Mississippian camerates.

Recent studies of eurypterid paleoecology suggest that formation of eurypterid Lagerstätten in the mid-Paleozoic of Laurentia was controlled by the presence of an ecological–taphonomic window that recurred predictably in nearshore, marginal environments during transgressions. We tested this hypothesis by performing a high-resolution taxonomic, environmental, and stratigraphic survey and quantitative analysis of all Silurian–Lower Devonian eurypterid-bearing intervals in the Appalachian basin, the most prolific region for eurypterid remains in the world. Canonical correspondence analysis of sedimentological and faunal associations revealed a strong lithologic gradient between groupings of eurypterid genera and associated taxa across the basin, and a significant association of eurypterids with microbialites (thrombolites, stromatolites) and evaporitic structures. Field observations confirmed that, stratigraphically, eurypterids in the basin frequently occur above the microbialite structures and beneath evaporites and other indicators of increased salinity or subaerial exposure. Following interpretation of these features within a sequence stratigraphic framework, we present a preservational model in which (1) eurypterids inhabited nearshore settings following freshening conditions concomitant with minor transgressions, (2) their remains were subsequently buried by storms or microbialite sediment baffling, and (3) subsequent long-term preservation of tissues was facilitated by regression and cyclical shallowing-up successions that promoted hypersalinity and anoxia. In the central and southern region of the basin, where microbial structures and evidence for hypersalinity are less common, a similar pattern of cyclical shallowing-upward deposition within eurypterid-bearing units holds. Thus, eurypterid preservation appears to reflect a combination of ecological preferences and abiotic conditions that promoted inhabitation and eventual preservation within the same setting. This study provides the first quantitative support for a sea level–based control on preservation of eurypterids and adds to the growing body of evidence that suggests that analysis of exceptional preservation in the fossil record benefits from interpretation within a sequence stratigraphic framework.

The Walcott-Rust Quarry, at Trenton Falls, New York, has yielded a large number of well-preserved, fully articulated fossils from the lower third of the Middle Ordovician Rust Formation, Trenton Group. Along with three species of the more common trilobites from the Trenton Group, fourteen species of rare and uncommon trilobites are found within a thin package of micritic limestones and shales. The first trilobites with preserved appendages, Ceraurus pleurexanthemus Green, 1832 and Flexicalymene senaria (Conrad, 1842), were described from one layer from this quarry. Unique specimens of Isotelus walcotti UIrich in Walcott, 1918, and Sphaerocorphe robusta Walcott, 1875, were found in the next higher bed. Re-excavation of the quarry yielded information about the taphonomy of the trilobites and stratigraphy of the trilobite layers. Nearly half of the beds surveyed (n = 50) yield direct evidence of obrution (i.e., rapid post-mortem or live burial) of benthic organisms. Unusual anaerobic microenvironments in partially enrolled trilobites of the Ceraurus layer facilitated very early calcification of appendages and other soft parts.

Endophyllum is described for the first time from North America. The occurrence of a single, large colony in Middle Devonian strata in New York is both biogeographically and environmentally anomalous: it belongs to an Old World Realm genus but was found in the Eastern Americas Realm, and it occurred in a gray, ambocoeliid-bearing mudstone, a facies in which morphologically complex corals are otherwise unknown. Available evidence suggests that the coral lived not far from where it was found, possibly on a hardground or bank a few km north of the outcrop. Endophyllum ciurcai new species is described.

Postibullinid edrioasteroids are a small clade of discoidal edrioasteroids that are locally common members of Devonian to Pennsylvanian, shallow marine, hard substrate faunas in North America and Europe. A small discoidal theca, narrow, highly elevated ambulacral cover plates, a highly elevated anal pyramid, and in many forms a posterior oral protuberance characterize this clade (Bell, 1976b; Sumrall et al., 2000). Here we describe the oldest known postibullinid, Pyrgopostibulla belli n. gen. and sp., a species that differs from other postibullinids by having a well-developed pedunculate zone and a complex, five-plate pattern of ambulacral cover plates. A dense population of these edrioasteroids preserved at a single stratigraphic horizon provides a census sample of individuals that were killed as a part of a final and abrupt burial pulse on this Lower Devonian hardground (Cornell et al., 2003). As such, this case study provides insight into the ontogeny and colonization strategies of isorophinid edrioasteroids.

Limestone beds in the Middle Ordovician (Trentonian) Bobcaygeon Formation, exposed near Kirkfield, Ontario, exhibit irregular, bored and encrusted surfaces indicative of early lithification. These hardgrounds were formed in extensively burrowed carbonate sediments and their hummocky surface topographies were inherited, in part, from a pre-existing pattern of burrow tunnels. A diverse community, including bryozoans, brachiopods, crinoids, edrioasteroids, and paracrinoids, colonized these hard substrates. In addition, most surfaces are riddled with small, cylindrical boreholes (Trypanites) which represent dwellings of soft-bodied organisms. Some hardground surfaces were inhabited by multiple generations of organisms. Remains of the older generations of encrusters were strongly abraded and nearly obliterated. Superimposed upon these worn remnants are well-preserved remains of rather fragile organisms, e.g. complete hybocystitid crinoids and edrioasteroids. Evidently, certain hardground surfaces were rapidly buried by muds, resulting in the in situ preservation of the last generation of attached organisms.

Slightly differing subcommunities of organisms inhabited various microhabitats provided by the irregular hardground surfaces. Thus, the relative abundance of bryozoans and echinoderms encrusting the roofs of small crevices differs from that on the exposed upper surfaces of the hardgrounds. This is the geologically oldest known hardground community in which microhabitat subdivision can be recognized. However, polarity between the subcommunities is not as pronounced as in geologically younger hard substrate faunas.

Previous observations about the stable nature of coral-rich assemblages from the Middle Devonian Hamilton Group have led some researchers to invoke the primacy of ecological controls in maintaining biofacies structure through time. However, few analyses have examined the degree to which recurring biofacies vary quantitatively, and none have assessed lateral variability as a benchmark for testing the significance of temporal variability. Thus, the extent to which Hamilton biofacies persist and the mechanism(s) responsible for their hypothesized stability remain contentious. In this study, recurring coral-rich biofacies were evaluated from two stratigraphic horizons within the Middle Devonian Appalachian Basin to examine (1) the extent to which species assemblages persisted within the basin through space and time, and (2) whether ecological interactions may be a plausible mechanism for generating the degree of stasis observed in this case.

Variations in species composition and abundance were examined across multiple spatial scales within both sampled coral-rich horizons. This permitted the establishment of a baseline against which temporal differences in biofacies composition and structure could be evaluated. Although successive coral-rich horizons remained taxonomically stable, their dominance structures changed significantly through the 1.5 Myr study interval. Moreover, additional comparisons among older Hamilton coral-rich horizons corroborate our primary results. These findings support a model in which species respond individually to fluctuations in the physical environment, as indicated by the fluidity of their relative abundances geographically and temporally.

The concept of coordinated stasis, manifest as a pattern of long intervals of concurrent taxonomic and ecologic persistence separated by comparatively abrupt periods of biotic change, has been challenged in recent studies that claim a lack of prolonged persistence of taxa and associations. A key problem has been the difficulty of distinguishing faunal change owing to localized, short-term environmental fluctuation or patchiness from that indicating regionally pervasive, long-term evolutionary or ecological change. Here, we use an extensive database from the Middle Devonian Hamilton Group of the Appalachian Basin to test for taxonomic and ecologic persistence within this ecological-evolutionary subunit, a succession of purported relative stability. Replicate samples collected from many localities and stratigraphic horizons over a wide geographic area allow us to address the effects of small-scale environmental variation and localized faunal patchiness while exploring basin-scale variation in faunal composition within and between the formations of the Hamilton Group.

Observed stratigraphic distributions of fossils are consistent with a scenario in which all taxa are present from bottom to top of the Hamilton Group, and absences result only from sampling failure. Although small-scale variation in faunal composition indeed does occur, there is no more variation among formations than occurs within them. Assemblages from different formations, whether they are defined by taxonomic or ecologic composition, are statistically indistinguishable according to several independent metrics, including ANOSIM and a maximum likelihood estimation that evaluates stratigraphic turnover using Bayesian “Information Criterion.” Simulated data sets indicate that test results are most consistent with species-level extinction of 2.6% per Myr within the Hamilton Group, far lower than the Givetian rate of 11.5% per Myr generic extinction derived from a global database. Such faunal persistence over the ~5.5 Myr encompassed by this unit is consistent with the pattern of coordinated stasis. Earlier studies showing greater amounts of temporal turnover in Hamilton Group faunas are likely influenced by their smaller geographic scale of analysis, suggesting that regional studies done elsewhere may yield similar results.

The mid-Paleozoic was punctuated by a rapid radiation of durophagous (shell-crushing) predators. These new predators were primarily placoderm and chondrichthyan fishes but probably also included phyllocarid and eumalacostracan arthropods. Coincident with the radiation of these durophages, beginning in the mid-Devonian, there was an increase in the frequency of predation-resistant morphologies in a variety of marine invertebrate taxa. Among bellerophontid molluscs, disjunct coiling disappeared and umbilici became less common while the frequency of genera with sculpture increased. The abundance of brachiopod genera with spines on one or both valves increased dramatically. Sculpture became more pronounced and common among genera of coiled nautiloids. Inadunate and camerate crinoids showed a marked increase in spinosity, and all three crinoid subclasses tended to develop thicker thecal plates.

Trends toward increasing relative frequencies of predation-resistant features were formed in different ways. Bellerophontid genera lacking predation-resistant features tended to go extinct, leaving the sculptured, tighdy coiled forms as the predominant forms. Among Brachiopoda, the radiation of productids provided the tremendous increase in numbers of spinose genera. Among crinoids, predation-resistant features were acquired through evolution within established clades.

These observations suggest that predation by shell-crushing predators has been an important control on the morphology and composition of the marine invertebrate fauna since at least the Middle Devonian. The mid-Paleozoic radiation of durophages and response of the marine fauna was in many respects similar to events of the Mesozoic Marine Revolution, in effect, the Paleozoic precursor to that event.

Interpretations of morphologic radiations and macroevolutionary patterns are dependent on a priori choices of taxonomic and geographic scales of study. The results of disparity analysis at varying taxonomic (species and genus) and geographic (regional, biofacies, and community) scales are examined in a study of Ordovician though Early Silurian crinoids. Using discrete morphologic characters, we examined the disparity of 421 crinoids from 65 Laurentian biofacies. Crinoid disparity differs when analyzed at the regional and biofacies levels. Regardless of fluctuations in regional crinoid disparity, average within-biofacies disparity was static throughout the Ordovician, deviating only during the Silurian because of the proliferation of the morphologically aberrant myelodactylid crinoids. The choice of taxonomic level does not have an effect at the biofacies level. However, at the regional level, the two taxonomic scales (genus and species) can produce different results because of variation in the number of species per genus through time and the amount of morphologic variation within individual genera. Weighting disparity by abundance provides a metric combining morphology and community structure. Average weighted disparity at the community level showed patterns similar to that of the biofacies-level disparity curve, but this metric has a greater degree of variation between biofacies. Biofacies with a low ratio of weighted to unweighted disparity display the distinctive community structure (based on aerosol filtration theory) that is often reported in crinoid assemblages.

More than 5000 measurements were taken on over 1000 specimens of two species of brachiopods, Mediospirifer audaculus and Athyris spiriferoides, from the Middle Devonian Hamilton Group of New York state. Statistical analyses were performed on these data, with specimens partitioned by their occurrence in one of many paleoenvironments and stratigraphic horizons. Neither species showed substantial morphological departures between first appearance and extinction (the range of the Hamilton Group, roughly 5 m.y.). However, oscillations in morphology were discovered in both taxa.

For the two species we studied, groups of organisms occurring in a single paleoenvironment undergo moderate morphological change through time; however, the net sum of changes through time in all paleoenvironments in which these species occur is essentially zero. Therefore, stasis may be partly a property of the organization of species into different environmental populations. Different “environmental populations” may evolve, but they will typically do so in several different “directions,” generally producing no net change. The difference between the morphology of species in different environments over the whole interval of the Hamilton Group is also nil, thereby ruling out any major role that ecophenotypic effects could play in the patterns recognized herein.

Substrata for numerous epizoans in the Silurian Waldron Shale were provided by the toppled and overturned calyces of camerate crinoids. These were inhabited by a skeletonized fauna consisting of at least 25 species; including several bryozoans, tabulates, inarticulate brachiopods, worms, and echinoderms.

Many of the encrusting bryozoans exhibit skeletal overgrowths which appear to reflect competitive interactions for space. Coexistence of certain of the bryozoans involved in such interactions is suggested by skeletal features such as inflated growth forms and upturned margins at junctions between colonies (both representing attempts to avoid being overgrown). In addition, the occurrence of overgrowth reversals within individual encounters indicates contemporaneity of that pair. Species may be ranked according to their relative overgrowth success; however, this ranking is far from rigid as lower ranked species may on occasion overgrow more highly ranked species. Such nontransitive patterns appear similar to those described from Recent cryptic bryozoan faunas.

Northern Appalachian Basin deposits and associated fossils have served as exemplars for ecological-evolutionary investigations, and as the reference interval for the concept of coordinated stasis. Here, we examine faunal and environmental changes within the uppermost Hamilton and lowermost Genesee Groups of the late Middle Devonian succession of New York State. Dramatic diversity loss, faunal migrations, and ecological restructuring recognized in these strata have been used previously to define the end of the Hamilton ecological-evolutionary subunit, and, furthermore, these strata and corresponding faunal changes represent the type region for the global Taghanic Biocrisis. We present and analyze a new, high-resolution data set of post-Taghanic Genesee fossil assemblages, in which we recognize 11 biofacies corresponding to an onshore-offshore (depth) gradient. The Genesee Fauna shows an unexpectedly high taxonomic similarity to nearshore biofacies of the pre-Taghanic Hamilton Fauna, related to the persistence of siliciclastic-dominated nearshore settings through the Taghanic Biocrisis, whereas the onset of anoxic/dysoxic conditions typified offshore portions of the environmental gradient. The “Nearshore Refugium Model” of Erwin offers a possible explanation for the persistence of taxa through the biocrisis in nearshore settings. This constriction was followed by subsequent expansion of these residual taxa to offshore environments in relatively similar associations, as increased Acadian orogenic activity and resultant delta progradation increased habitable space offshore by decreasing the extent of deeper-water, oxygen-poor settings. Although taxonomic similarity was high between the Hamilton and Genesee Faunas, biofacies structure differed primarily because of tectonically driven physical transformations to the basin and associated biotic turnover. Nevertheless, the combination of high taxonomic persistence of Hamilton nearshore taxa and the introduction of relatively few new taxa in the Genesee Fauna resulted in a taxonomic holdover that was much higher than observed in the original formulation of coordinated stasis.