William I. Ausich

Tiering in Suspension-Feeding Communities on Soft Substrata Throughout the Phanerozoic

Tiering of benthic marine suspension-feeding communities on soft substrata has varied throughout the Phanerozoic. Epifaunal tiering was most developed during the middle and late Paleozoic and the Triassic to Jurassic, with large-scale reductions in tiering occurring during the Permian-Triassic extinctions and after the Jurassic. Infaunal tiering reached its highest level of organization after the Paleozoic.

Phanerozoic development of tiering in soft substrata suspension-feeding communities

Tiering is the vertical distribution of organisms within the benthic boundary layer. Primary tierers are suspension-feeding organisms with a body or burrow that intersects the seafloor. Secondary tierers are suspension-feeders that maintain positions above or below the sediment-water interface as either epizoans on primary tierers and plants or by living in the burrows of primary tierers. Different primary tierers from soft substrata, nonreef, shallow subtidal shelf and epicontinental sea settings have had different tiering histories, resulting largely from contrasting constructional and phylogenetic constraints. Primary colonial tierers generally occupied lower epifaunal tiers during the Paleozoic and Mesozoic, but since the Cretaceous they have been dominant in the highest tier (+ 20 to +50 cm). Primary echinoderm tierers have been almost exclusively epifaunal, and from the Paleozoic through the Jurassic they were present throughout the epifaunal tiered structure. Although primary bivalve tierers have been both epifaunal and infaunal, they have occupied only lower epifaunal tiers, whereas they have adapted to all levels of the infaunal tiering structure, particularly from the late Paleozoic through the Recent. Brachiopods have lived primarily in tiers directly above or below the water-sediment interface and have not contributed significantly to tiering complexity. Of the numerous physical and biotic processes and constraints that affect shallow marine benthos, a few have contributed more significantly to changes in tiering patterns. Trends for increasing body size could have accounted for most of the development of tiering complexity up to +50 cm and down to –12 cm. Development of tiering above +50 cm could have been due to processes which would have yielded greater feeding capability, such as competitive interactions for a place from which to feed or adaptations to velocity gradients in the hydrodynamic boundary layer. The most significant process for development of infauanl tiering below –12 cm appears to have been as an adaptive response for predator avoidance. Unlike infaunal tiering, which never declined after it developed, epifaunal tiering has undergone a general reduction twice. Reduction in epifaunal tiering at the end of the Paleozoic appears to have been the result of the mass extinction at this time, whereas long-term biotic processes seem to have been more important for the tiering decline at the end of the Mesozoic. Tiering structure through the Phanerozoic was thus produced through interactions of a number of physical and biotic factors, tempered by constructional and phylogenetic constraints of each primary tierer group.

Biotic Interactions among Recent and among Fossil Crinoids

Most previous reports on the biotic interactions of crinoids have treated either the living or the fossil forms exclusively. Major treatments of the biotic interactions of living crinoids are those of Clark (1921), Hyman (1955), Fell (1966), and Breimer (1978). Interactions of extinct crinoids have been summarized by N. G. Lane (1978). In the present review, we have compiled evidence for biotic interactions of both living and fossil crinoids in order to elucidate the role of biotic interactions in crinoid evolution. In Sections 2 through 6, we consider direct interactions of crinoids with other organisms and other crinoids. In Section 7, Habitat Modification, we consider ways by which crinoids modify their environment which will affect other organisms. The evolutionary history of biotic interactions of crinoids provides evidence that predation and competition have played significant roles in crinoid evolution.

Early phylogeny and subclass division of the Crinoidea (Phylum Echinodermata)

A stepwise approach is employed to determine the phylogeny of the initial crinoid radiation during the Arenig and Llanvirn series of the Ordovician. Parsimony-based character analysis is completed first on Arenig crinoids and then for Arenig and Llanvirn crinoids combined. The topology from well-resolved trees of this early crinoid radiation indicates that the Crinoidea should be subdivided into six subclasses. A new subclass and new order, Aethocrinea and Aethocrinida, respectively, are proposed for crinoids with four circlets of plates in the aboral cup: lintels, infrabasals, basals, and radials. This aboral cup construction is best displayed by Aethocrinus, one of the oldest known crinoids (?Tremadoc-Arenig). However, this primitive aboral cup construction is also present in two Llanvirn crinoids, Perittocrinus and Tetracionocrinus. The Aethocrinea was a small, short-lived radiation of crinoids with this design that was different from those of other crinoids. Two families in the Aethocrinida are the Aethocrinidae, which includes Aethocrinus, and the Perittocrinidae, which includes Perittocrinus and Tetracionocrinus. In addition to the Aethocrinea, the following crinoid subclasses are recognized based on character analyses of these earliest crinoids: Cladida, Camerata, Disparida, Flexibilia, and Articulata.

Species longevity as a function of niche breadth: Evidence from fossil crinoids

High-resolution stratigraphic and taxonomic data indicate that species longevities among Paleozoic (Mississippian) crinoids (Echinodermata) were affected by differences in niche breadth. A strong positive relationship exists between niche breadth, measured as the number of environments occupied by a species, and stratigraphic range. The robustness of this pattern is verified by a variety of rarefaction and statistical techniques confirming the long-held supposition that among animals ecological “generalists” have greater species longevities than ecological “specialists.” The results also support the hypothesis that specialist clades have higher species richness.

Aerosol suspension feeding and current velocities; distributional controls for late Osagean crinoids

Distributional patterns of late Osagean (Mississippian) crinoids from the east-central United States are examined using multivariate analysis of crinoid species diversity and species abundance data. We confirm previous hypotheses that three well-defined crinoid associations existed during the late Osagean. These associations were dominated, respectively, by 1) monobathrid camerates preserved in carbonate packstones; 2) poteriocrine inadunates in higher-energy siltstones and sandstones; and 3) disparid inadunates, cyathocrine inadunates, and flexibles in mudstones where neither monobathrids nor poteriocrines dominated. In conjunction with petrologic data on the enclosing sediments, the analyses suggest that these associations occurred along a spectrum of increasing current velocity at the seafloor. Camerates, poteriocrine inadunates, and flexibles are interpreted to display preferences for specific environmental conditions, whereas disparid and cyathocrine inadunates are inferred to be environmental generalists. The different environmental distributions of the major crinoid groups are interpreted to be a function of the mode or modes of aerosol filtration feeding used by each group. This inference is possible through functional morphologic and morphometric studies of crinoid arms, because the skeletal elements of the arms, which are commonly preserved, are directly involved in feeding.

Persistent predator–prey dynamics revealed by mass extinction

Predator–prey interactions are thought by many researchers to define both modern ecosystems and past macroevolutionary events. In modern ecosystems, experimental removal or addition of taxa is often used to determine trophic relationships and predator identity. Both characteristics are notoriously difficult to infer in the fossil record, where evidence of predation is usually limited to damage from failed attacks, individual stomach contents, one-sided escalation, or modern analogs. As a result, the role of predation in macroevolution is often dismissed in favor of competition and abiotic factors. Here we show that the end-Devonian Hangenberg event (359 Mya) was a natural experiment in which vertebrate predators were both removed and added to an otherwise stable prey fauna, revealing specific and persistent trophic interactions. Despite apparently favorable environmental conditions, crinoids diversified only after removal of their vertebrate consumers, exhibiting predatory release on a geological time scale. In contrast, later Mississippian (359–318 Mya) camerate crinoids declined precipitously in the face of increasing predation pressure from new durophagous fishes. Camerate failure is linked to the retention of obsolete defenses or “legacy adaptations” that prevented coevolutionary escalation. Our results suggest that major crinoid evolutionary phenomena, including rapid diversification, faunal turnover, and species selection, might be linked to vertebrate predation. Thus, interactions observed in small ecosystems, such as Lotka-Volterra cycles and trophic cascades, could operate at geologic time scales and higher taxonomic ranks. Both trophic knock-on effects and retention of obsolete traits might be common in the aftermath of predator extinction.

The “Age of Crinoids”: A Mississippian Biodiversity Spike Coincident with Widespread Carbonate Ramps

Abstract Crinoids reached their highest generic richness and overall abundance during the Mississippian, which thus has been dubbed the Age of Crinoids. The causes are hypothesized to be from the coincidence of two factors. First, in the wake of the Late Devonian mass-extinction event, the five major crinoid groups recovered and radiated in the Early Mississippian. The advanced cladids continued to radiate from their origin in the Early Devonian and reached a peak in the Middle Mississippian (Visean) that was not exceeded again until the Middle Pennsylvanian (Moscovian). Second, the Late Devonian mass-extinction event destroyed the extensive coral-stromatoporoid platform-edge reefs that had restricted circulation on carbonate platforms and limited the abundance of crinoids, which are stenohaline. The resulting carbonate ramps during the Mississippian had improved circulation, producing stenohaline conditions that resulted in an abundance peak for crinoids, recorded by widespread regional encrinites on multiple continents. This increased habitat space was ideal for camerate crinoids and resulted in a new radiation of camerate crinoids. The simultaneous radiation of pinnulate cladids and the short resurgence of camerates were responsible for the biodiversity spike in the Mississippian. The Age of Crinoids ended with a major drop in sea level at the end of the Mississippian as massive glaciers formed on Gondwana and epicontinental seas were drained.

Demise of the middle Paleozoic crinoid fauna: a single extinction event or rapid faunal turnover?

Macroevolutionary change from the Middle to the Late Paleozoic crinoid fauna was not the result of mass extinction. The presumption that the decline of the middle Paleozoic crinoid fauna was from a single mass extinction event was tested using seriation, multidimensional scaling (MDS), binomial analysis, and bootstrapping simulations on a data set which is a comprehensive revision of old faunal lists. The data for these analyses were based on temporal distributions of 214 species from 69 late Osagean and early Meramecian localities from the midcontinental United States. The time under consideration is subdivided into seven informal intervals using MDS in conjunction with biostratigraphy. Seriation of species ranges into these intervals results in a gradual pattern of faunal turnover, and sampling bias can be eliminated as a cause for this more gradual pattern. MDS analysis of the crinoid range data is similar to MDS simulations using data with continuous, mono- tonic species turnover and dissimilar to a simulated mass extinction. Binomial analysis and boot- strapping demonstrate that the observed number of extinctions at the putative extinction boundary were not unusually high. All methods agree that extinctions throughout this time were high but spanned several time intervals and that rapid, monotonic faunal turnover describes the data better than mass extinction. Macroevolutionary processes other than mass extinction and microevolution- ary processes must have dictated the character and composition of this remarkable faunal transition among the Crinoidea.

Comparative taphonomy of echinoderms in carbonate facies; Fort Payne Formation (Lower Mississippian) of Kentucky and Tennessee

Taphonomic analysis of more than 3000 specimens of crinoids and blastoids from 14 localities from south-central Kentucky and north-central Tennessee reveals differences in preservational style among five carbonate and associated clastic facies. Collections from each locality were sorted on the basis of a 9-point taphonomic scale ranging from fully articulated specimens with arms and column to isolated plates. Degree of skeletal articulation is used as a relative measure of burial rate and autochthony. Preservational style of a pelmatozoan assemblage is the product of both depositional processes and differential taphonomic behavior of different morphotypes. The taphonomic profile for an assemblage is strongly influenced by the preservational style of its dominant pelmatozoan taxa. Taking this taxonomic and morphologic bias into account, both autochthonous and allochthonous pelmatozoan-rich facies are recognized in the Fort Payne Formation. Carbonate facies judged to be chiefly autochthonous are 1) crinoidal packstone buildups showing a full range of preservation including articulated specimens, and 2) wackestone buildups dominated by complete calyxes lacking arms and column. Green shales associated with carbonate buildups are dominated by disarticulated specimens but include complete calyxes and arm segments, suggesting slow background deposition punctuated by periodic rapid influxes. Allochthonous carbonates include 1) sheetlike packstones dominated by complete and partial calyxes, and 2) channelform packstones dominated by disarticulated skeletal debris with occasional fully articulated crinoids. Fort Payne carbonate facies in north-central Tennessee are exclusively allochthonous, sheetlike packstones, whereas both allochthonous and autochthonous facies occur in Kentucky proximal to the Borden Front. The taphonomic character and distribution of pelmatozoan-rich facies in the Fort Payne in Kentucky and Tennessee are consistent with a progradational, basin-filling depositional model.