James C. Brower

The relations between allometry, phylogeny, and functional morphology in some calceocrinid crinoids

Calceocrinids are unique crinoids with the crown movably hinged to a recumbent stem. The crown was raised for feeding by closing the hinge and bending the proximal stem. While resting, the crown lay parallel to the stem with the hinge opened. Allometric equations for four species reflect a combination of ontogeny, adult body size, phylogeny, habitat, and functional morphology. The hinge of most adult calceocrinids is extended into ear-like projections which made the crown more stable on the seafloor. For the hinge moment versus the effective weight of the crown, positive allometry characterized taxa that lived in agitated environments, whereas isometry was adequate for quiet-water species. The adult body size provides a secondary effect on the data for crinoids from the same type of environment. Here, the initial intercepts are transposed so that larger animals functioned like smaller ones. The equations are independent of phylogenetic position. All species exhibit positive allometry of the length and number of plates in the arms. The food-gathering capacity of a crinoid is estimated by the number of food-catching tube-feet multiplied by the width of the food grooves, whereas the soft parts that must be fed are proportional to the crown volume. The ratio of food-gathering capacity to crown volume is either fixed or decreases slightly in larger crinoids. Statistical tests reveal that all species follow a single developmental pattern for these two parameters. However, some of the evolutionary changes in the arms permitted calceocrinids to retain an adequate food-gathering capacity into larger adult body sizes.

Cupulocrinid crinoids from the Middle Ordovician (Galena Group, Dunleith Formation) of northern Iowa and southern Minnesota

ABSTRAcr-Five species of camerate crinoids from the Middle Ordovician Dunleith Formation (Galena Group) of northern Iowa and southern Minnesota are described: Cleiocrinus regius Billings, Cotylacrinna sandra n. gen. and n. sp., Euptychocrinus skopaios n. gen. and n. sp., Abludoglyptocrinus charltoni (Kolata), and Eopatelliocrinus ornatus (Billings) n. comb. Archaeocrinus desideratus Billings is assigned to Cotylacrinna, and Glyptocrinus fimbriatus Shumard and Ptychocrinus longibrachialis Brower are placed in Euptychocrinus. The geographical affinities of the Iowa and Minnesota crinoids lie with adjacent localities in the northern midcontinent and the Appalachian province of Canada and New York. Preservation of various specimens implies that Euptychocrinus skopaios, Abludoglyptocrinus charltoni, and Eopatelliocrinus ornatus utilized parabolic arm fans. Cotylacrinna sandra is a specialized rhodocrinitid which is perhaps the largest completely known Ordovician crinoid with a stem length of over 91 cm and a total volume of about 45,740 mm3. The root morphology indicates an upright column and this animal towered above the associated echinoderms, which ranged from the substrate level to a maximum of 25 cm above the seafloor. Euptychocrinus skopaios is marked by dwarfed morphology compared to the closely allied E. fimbriatus, and it exhibits accelerated development of fixed brachs, number of brachials in and length of the arms, and closely spaced pinnules. The dwarfism is interpreted as a specialization for small size and adults of E. skopaios were only located about five or six cm above the substrate. New brachials and pinnules form at the distal arm tips of E. skopaios throughout ontogeny. Consequently, the length of and the number of plates in the food-gathering system are positively allometric relative to the crown volume. Food gathering capacity equals the number of food-catching tube feet times width of the food grooves and it is also augmented more rapidly than expected for an isometric crinoid. Although distantly related to euptychocrinids, most other Dunleith camerates, namely Abludoglyptocrinus charltoni, Eopatelliocrinus ornatus, and Cotylacrinna sandra, follow the same developmental trends of the food-gathering system observed in Euptychocrinus skopaios. Comparison of the pinnulate camerates and three species of ramulate cladids and a disparid from the Dunleith reveals some striking contrasts. At equivalent crown volumes, the camerates are characterized by more numerous arm branches in the form of pinnules, more narrow food grooves, more closely spaced tube feet, and longer food-gathering systems with more plates and greater capacity. The Dunleith camerates were adapted for catching smaller food particles using more numerous and more closely spaced tube feet located on more extensively branched filtration nets than the associated cladids and disparid. The differences can be attributed to taxonomy and presumably phylogeny, that is camerates versus cladids and disparids, and/or morphology in the presence of pinnules versus ramules.

Further consideration of placoderm evolution

ABSTRACT The flight performances of Pteranodon ingens and Nyctosaurus gracilis from the Upper Cretaceous of Kansas were modeled using data from a Sailvane hang-glider which has an airfoil similar to that of a pterosaur. The aerodynamics of large pterosaurs were mainly dictated by three parameters: low wing loadings, wings with high aspect ratios, and the performance of the thin cambered airfoil. Given maximum muscular efforts, Nyctosaurus and Pteranodon could have taken off at airspeeds of 1.5 and 4 m/sec, respectively. These airspeeds included windspeed, running speed, and a flapping component, so takeoff presented no problems. Landing speeds were also slow. The sustained power output of Pteranodon was not enough for continuous level flapping flight. A maximum burst of power allowed level flapping or climbing flight. However, this required anaerobic muscle operation and was only maintained briefly. The power profile shows that Pteranodon was a soarer. On the other hand, the sustained power output of Nyct...

Statistical testing of community patterns: Uppermost Hamilton Group, Middle Devonian (New York State: USA)

Abstract We present an extensive and rigorously controlled quantitative paleoecological study within an interval of inferred coordinated stasis. This Middle Devonian Hamilton Group study completes a 20-yr project by providing data within the unresolved upper Hamilton Group section. Together with other rigorously controlled studies, these data sets have the potential to address the larger question of coordinated stasis in the fossil record. We collected data from the Windom Member, Moscow Formation (uppermost Hamilton Group), to test different statistical approaches to define paleocommunities. We evaluate various techniques, including non-parametric multidimensional scaling and agglomerative hierarchical clustering to decipher community patterns. Additionally, we advocate regular use of cluster significance testing along with ANOSIM (i.e. analysis of similarities) when examining ecological data. Together these techniques test the significance of sample groups more rigorously than conventional testing (e.g. discriminant analysis or analysis of variance (ANOVA)). Our results indicate that communities within this upper Hamilton Group interval exhibit variable taxonomic membership within a relatively stable ecological structure.

Does coordinated stasis yield taxonomic and ecologic stability?: Middle Devonian Hamilton Group of central New York

Statistical tests of coordinated stasis within the Middle Devonian Hamilton Group demonstrate significant temporal changes in taxonomic composition and ecological structure of the macrofauna throughout a 5‐6 m.y. time span. The analysis, based upon a collection of .38,000 specimens obtained over a 20 yr period from the Hamilton Group of central New York, used highly controlled sampling techniques, applied within a single, well-defined lithofacies. Assemblages were tested for stability through time, as would be predicted by the model of coordinated stasis. Our results reveal that within at least one major Hamilton environment, taxonomic and ecological stability are not statistically significant and therefore do not support the hypothesis of coordinated stasis.

Hybocrinid and disparid crinoids from the Middle Ordovician (Galena Group, Dunleith Formation) of northern Iowa and southern Minnesota

Four hybocrinid and disparid crinoids from the Middle Ordovician Dunleith Formation (Galena Group) of northern Iowa and southern Minnesota are described: Hybocrinus conicus Billings, Ohiocrinus levorsoni n. sp., Caleidocrinus (Huxleyocrinus) gerki n. sp., and Ectenocrinus simplex (Hall). The first three taxa are rare. Ectenocrinus simplex is an abundant and protean form ranging from the Shermanian to the Maysville and from the Appalachians to the Midcontinent. One Middle Ordovician specimen from the Dunleith is a complete small adult with stem and a lichenocrinid holdfast. The column was largely upright with the crown located about 25 cm above the seafloor. The Middle Ordovician crinoids differ somewhat from the later Cincinnatian material where only young E. simplex exhibit lichenocrinid holdfasts. Older crinoids became detached and were eleutherozoic well before the column was 25 cm long. Thus, the Cincinnatian individuals lost the attachment device earlier during ontogeny than their ancestors in the Middle Ordovician. Unlike most associated crinoids, E. simplex formed a roughly conical filtration net. The arms of E. simplex are extensively branched. Ten main arms bear unbranched ramules on alternate brachials, and the arm structure converges on the pinnulate pattern. Narrow food grooves and short covering plates are present. Analogies with living crinoids indicate that small food particles were caught by small and close-spaced tube-feet. The formation of new plates and ramules at the arm tips increases the size of the food-gathering system throughout ontogeny. The food-gathering capacity comprises the number of food-catching tube-feet times the width of the food grooves, and it measures the number and size of food particles that can be caught. Both size and capacity of the food-gathering system are positively allometric compared to crown volume and the amount of tissue that must be nourished. This is mainly caused by the addition of new ramules at the arm tips, which generates an exponentially increasing plate supply rate. Examination of numerous specimens from various geographic and stratigraphic horizons with multivariate statistics shows that the species was homogeneous throughout its range aside from the differences in living habits mentioned above.

A comparison of methods for the quantification of assemblage zones

Abstract Several methods of quantitative biostratigraphy that are based on assemblage zones are examined utilizing three sets of faunal distribution data. Two of the data sets are structured simply and one is complex. Various types of cluster analysis and multidimensional scaling are applied to weighted and unweighted binary (presence/absence) data. For weighted data, the presences are multiplied by the relative biostratigraphic values (RBV) of the taxa. There are two options for calculating the RBVs. One method (RBV2) emphasizes timestratigraphic correlation, whereas the other is a compromise between time-stratigraphic correlation and biofacies correlation (RBV1). Results from lateral tracing also are examined. The case studies allow the formulation of a general strategy. Weighting is not appropriate if paleoecological groupings are sought. If biostratigraphic zonation is required, weighted data may produce clusters that are stratigraphically more homogeneous than those based on unweighted data. Also the RBVs can point out species that can be deleted from the analysis without losing significant biostratigraphic information. Range through data should be employed in most situations. Similarity matrices between samples can be calculated from various coefficients based on presences. Biostratigraphic zones are extracted from the similarity matrix by cluster analysis, multidimensional scaling and lateral tracing to produce an overall view of the data structure. Lines of correlation and fence diagrams can be constructed between the samples in adjacent stratigraphic sections using the same techniques.

Eoparisocrinid crinoids from the Middle Ordovician (Galena Group) of northern Iowa and southern Minnesota

Two species of eoparisocrinid crinoids from the Middle Ordovician Galena Group of northern Iowa and southern Minnesota are described, namely Eoparisocrinus crossmani n. sp. and E. grandei n. sp. The post-larval development of Eoparisocrinus crossmani is examined. Crinoid arms grow by addition of new plates at their distal tips in conjunction with calcite deposition on old plates. New branches appear where axillary plates are initiated. Consequently, the growth rates for number of brachials and length of food-gathering system compared to crown volume are much faster than if the animals were isometric. The number of food particles collected is related to the number of food-catching tube-feet, which can be estimated if the length of the arms and height of the covering plates are known. The size of the largest food item is constrained by the food groove width. Thus, food-gathering capacity is the number of food-catching tube-feet multiplied by food groove width. The food-gathering capacity increases more rapidly than if the animal grew isometrically, and the ratio of food-gathering capacity: crown volume only declines slightly over the known growth range. All Ordovician cladid crinoids examined follow nearly identical ontogenetic trajectories. The ecological niche of a stalked crinoid is related to four basic parameters: stem length, food groove width, tube-foot spacing, and branch density. Stem length limits the highest elevation above the seafloor. The column of E. crossmani becomes longer during ontogeny due to the formation of new columnals and height growth of old ones. Consequently, individuals gradually “move up” until the adult elevation of about 50 mm is reached. The growth rates of stem length relative to crown size are slow in the youngest and mature animals but rapid in juveniles. The food grooves become wider throughout growth so that older crinoids ate larger food particles than younger ones. The food groove width increases less rapidly than if the shape were constant, because distal plates and branches are more narrow and have more slender food grooves than proximal plates. Growth curves for food groove width versus stem length and elevation were generated for E. crossmani and other crinoids that commonly occur in the same beds. Together, elevation and food particle size define the main dimensions of the niche. The various taxa are more or less separated by different food groove widths at most comparable elevations. This pattern minimizes ecological overlap and probably competition between the different species. The tube-foot spacing of E. crossmani is constant regardless of size, which suggests that it employed the same type of feeding mechanism throughout post-larval ontogeny. The arm branches of adults gradually become less densely spaced relative to the area of water filtered than in juveniles.

ONTOGENY OF THE FOOD-GATHERING SYSTEM IN ORDOVICIAN CRINOIDS

Abstract The growth of the food-gathering systems of Ordovician crinoids illustrates the solutions evolved to avoid or minimize problems of suspension feeding and maintenance. The column has low metabolic requirements and may even be self-sufficient; little or no food need be diverted from the crown to the column. The tissue that the food-gathering system supplies with food is all or mostly in the crown. The volume of tissue in the crown is isometric with its volume. Distal arm branches, ramules, or pinnules form throughout growth of most taxa. The number of arm branches is constant in hybocrinids and porocrinids. The length and number of plates in the food-gathering system show marked positive allometry relative to crown volume. Food grooves become wider in larger crinoids but growth rates vary greatly. Branch density declines in all species studied. The tubefoot spacing can be constant, increase, or decrease in larger crinoids. Food-gathering capacity is the number of food-catching tubefeet multiplied by the average food-groove width, and it is positively allometric in terms of crown volume. The food-gathering ratio (food-gathering capacity: crown volume) declines somewhat, remains the same, or increases slightly during growth. The food-gathering parameters are correlated with arm structure. Crinoids with pinnulate arms exhibit the highest food-gathering ratios, high values of tubefoot spacing and branch density, and narrow food grooves, and they catch small food particles with small and closely spaced tubefeet. The lowest food-gathering ratios are seen in crinoids with unbranched and nonpinnulate arms which possess low tubefoot spacings and branch densities and wide food grooves. On average these organisms ate larger food items collected by larger and more widely spaced tubefeet. Larger food-gathering ratios are associated with greater resistance to fluid flow through the arms and tubefeet. The allometry of the food-gathering systems of Ordovician crinoids suggests that their metabolic rates could be proportional to body mass0.75 as in many living animals and plants.

Methods for the quantification of assemblage zones based on multivariate analysis of weighted and unweighted data

Abstract A general strategy for the quantification of assemblage zones is outlined. The data represent presences and absences of different species for numerous samples in n stratigraphic sections, and can be applied in raw form or converted to range through form. Next, the attributes of an index fossil, vertical range, geographic persistence, and degree of facies independence are quantified for each species. With this information, relative biostratigraphic values (RBVs) can be calculated for the taxa. The RBVs measure the amount of biostratigraphic information conveyed by the presence of a particular species. Numerous RBVs are available and the appropriate one can be selected which incorporates the required properties. Depending on the distribution of the RBVs, some or all of the taxa with low RBVs may be omitted from later stages of the analysis. The presences can be weighted by the RBVs of the species. Absences remain absences regardless of the RBV of the taxon concerned. The advantage of this technique is that each species contributes an amount of information that is proportional to its RBV. With either weighted or unweighted data, the next step is the computation of a similarity matrix between all pairs of samples. Inasmuch as a species can be absent from a sample for various reasons, absences cannot be evaluated completely for biostratigraphic data. Consequently only similarity coefficients based on mutual presences or positive matches are recommended. Various similarity coefficients, such as Jaccard, Dice, or Simpson can be employed although we prefer middle-of-the-road types such as the Dice coefficient. The last step in the analysis is to extract the main themes from the similarity matrix with methods such as cluster analysis, principal components, factor analysis, principal coordinates, multidimensional scaling, or lateral tracing. For our case studies, the best results have been obtained by cluster analysis, multidimensional scaling, and lateral tracing. A two-fold approach is adopted. First, the entire data set is treated in order to gain an overall picture and the desired correlations or zones are extracted from the clusters or ordinations. Second, the analysis focuses on pairs of adjacent sections to prepare a line of sections or a fence diagram yowing more detailed correlations. The data matrix can be transposed and an R-Mode analysis can be performed on the species with the same techniques.