Robert L. Anstey

Fourier Analysis of Zooecial Shapes in Fossil Tubular Bryozoans

Fourier harmonic amplitudes provide exact characterization of the cross-sectional morphology of fossil tubular bryozoans. The Fourier method resolves a complex zooecial shape into multiple shape components (harmonics), which can be treated as individual morphologic variables. Shape elongation caused by varying zooecial orientation affects only the value of the second harmonic. Fourier harmonic coefficients reveal small changes in model shapes involving different numbers of neighboring zooecia, thickening of zooecial walls, and acanthopore variation. The number (between three and six) of neighboring zooecia controls the gross zooecial shape, as reflected in the third to the sixth harmonic. The sixth harmonic reflects the closest packing of zooecia within a colony, and its mean correlates with the colonial growth form and number of mesopores. Monticules represent the budding centers of a colony: zooecial chambers decrease in maximum diameter and become more densely packed away from the monticules. Ontogenetic changes, from the budding of new zooids to the closest packing of mature individuals, involve variation in gross zooecial form, revealed in the amplitudes of the second to the sixth harmonic. Harmonics above the sixth reflect small-scale sculpturing of the zooecial margin. The mean harmonics of different taxa suggest that Fourier values can be used for multivariate phenetic differentiation. The mean spectra of different growth forms indicate that variation in the second and sixth harmonics results from ontogenetic differences and nonmutational response to external stresses. Comparison of intrageneric variability and intracolonial variability shows that the second and sixth harmonics vary more widely among genetically identical individuals than among evolving taxa, even though the morphologies they reflect have been used as major bio-characters in bryozoan systematics. The higher numbered harmonics, especially the seventh, carry evolutionary information.

Taxonomic survivorship and morphologic complexity in Paleozoic bryozoan genera

The shape of bryozoan taxonomic survivorship curves is strongly influenced both by grade of morphologic complexity and by mass extinction. Paleozoic bryozoan genera that are morphologically simple have linear taxonomic survivorship; morphologically intermediate taxa have slightly concave survivorship, and complex forms have very concave survivorship. Increasing morphologic complexity, and by inference, increasing specialization of adaptation appear to accompany a systematic departure from a stochastically constant extinction rate. However, the extinctions of the complex taxa are entirely concentrated during three mass extinction events, whereas the extinctions of the simple taxa are more uniformly distributed throughout the Paleozoic; the extinction pattern of the morphologically intermediate taxa is intermediate to those of the simple and complex groups. Exclusion of the genera affected by mass extinction increases the convexity of the survivorship curves, and reverses the apparent correlation of extinction rate with morphologic complexity. The macroevolutionary pattern of the complex genera resembles an r-strategy, whereas that of the simple taxa resembles a K-strategy.

Astogeny and phylogeny: evolutionary heterochrony in Paleozoic bryozoans

Astogenetic trajectories have constrained evolutionary changes in bryozoans. Rates and timing of astogenetic differentiation have been modified for characters defining the morphology of zooids, sub- colonies, and colonies. This paper catalogs 46 examples of bryozoan heterochrony, representing all five skeletonized orders. Heterochrony is inferred to have been a pervasive phenomenon in the evolution of Paleozoic stenolaemates, illustrated by 40 examples, 19 of which produced paedomorphosis and 21 peramorphosis. As a consequence, a restricted range of morphologic states has reappeared repetitively as homeomorphies and evolutionary reversals. Large-scale patterns developed across both geologic time and geographic space reflect variation in heterochronic products irrespective of the developmental processes by which they were achieved. Available evidence indicates that smaller, paedomorphic, and more plastic species inhabited onshore, low-diversity areas. Nonheritable plasticity is inferred to be a correlate of early growth stages and paedomorphosis. Taller, generally peramorphic species with damped plasticity are found in higher diversity, offshore regions. Seven key innovations, which first appeared during the early diver- sification of bryozoan clades, are peramorphic, and recapitulation was a predominant pattern during their Ordovician radiation. Trends in later phylogeny, on the other hand, have favored paedomorphic derived morphologies, as illustrated by 19 of the 32 examples. Recurrent reverse recapitulation suggests that offshore ancestors frequently gave rise to onshore paedomorphs.

Patterns of bryozoan endemism through the Ordovician-Silurian transition

Abstract Area cladograms produced by parsimony analysis of endemicity illustrate historically developed biogeographical associations among Caradocian, Ashgillian, Llandoverian, and Wenlockian bryozoans. Areas in North America, Siberia, and Baltica were organized into three provinces and 12 biomes over a time interval of 35 million years. Six of these biomes belonged to the North American-Siberian Province and became extinct during the Ashgillian. Three biomes represent a successional series of biogeographical associations in the Late Ordovician of Baltica, and the middle biome of this succession is most closely related to that of the Wenlockian platform in North America. All four Silurian biomes are represented in Late Ordovician local areas, indicating that the associations important in the recovery radiation were already in existence prior to the extinction events. Three of these four biomes expanded their geographic extent in the wake of the Late Ordovician extinctions. Several biome extinction and replacement events took place during lowstands of sea level, suggesting that biogeographic reorganizations took place as a consequence of habitat loss in epeiric seas. Biome development largely depended on the extent of major lithotopes and their intersections with deep ocean and climatic barriers. The loss of regional habitats, associated with marine regression, was a key factor in biome extinction and reorganization, and indicates that biogeography played a significant role in the Late Ordovician mass extinctions and Silurian recovery radiations. Vicariance hypotheses are needed to account for the development of barriers subdividing ancestral areas, whereas hypotheses of congruent dispersal are required to explain the appearance of biomes in geographically disjunct areas.

Genetic Meaning of Zooecial Chamber Shapes in Fossil Bryozoans: Fourier Analysis

Fourier harmonic amplitudes quantitatively characterize chamber shapes of fossil tubular bryozoans. The odd-numbered harmonics, particularly the seventh, carry evolutionary information. The phenotypically plastic second and sixth harmonics measure zooecial orientation and packing, respectively. As a measure of crowding, the sixth harmonic reflects mechanistic growth response to paleoenvironmental conditions.

Harmonic analysis of cephalopod suture patterns

Harmonic (Fourier) analysis provides a series of multivariate descriptors that exactly quantifies the shapes of cephalopod suture patterns in the Subclasses Nautiloidea and Bactritoidea, and in four of the eight orders of the Ammonoidea. The method allows the calculation and graphic display of the mean suture patterns of the subclasses and orders studied, and exactly measures the morphological differences between groups. Discriminant analysis provides significant differentiation of the four ammonoid orders using only the harmonic amplitudes of the sutures. Discriminant analysis also indicates significant differences between the two symmetric halves of sutures in Acanthoclymenia neapolitana, and thereby measures the withingenotype norm of reaction in that species. Twelve sutural harmonic amplitudes are significantly correlated with ontogenetic changes in apertural size and shape in Koenenites cooperi. Specific harmonic amplitudes increase monotonically in the ontogeny of K. cooperi, but do not change within the phylogeny of its family, the Gephuroceratidae. This method permits statistical testing of assumptions of heterochronous evolution in cephalopod lineages.

Regional bryozoan biostratigraphy and taphonomy of the Edenian stratotype (Kope Formation, Cincinnati area); graphic correlation and gradient analysis

A regionally correlated biostratigraphic gradient divides the Kope Fm. (Late Ordovician, Indiana-Kentucky-Ohio) into twelve bryozoan concurrent range zones averaging 7.6 m in thickness. Stratigraphic (temporal) resolution has been enhanced by post-mortem lateral dispersal of bryozoans by storm processes. Abundance patterns reflect a bathymetric gradient in the original benthic communities. The presence and absence of short-ranging genera define a temporal gradient of faunal replacement within these communities. Both gradient analysis and graphic correlation indicate significant regional correlations between sections, and a robust biostratigraphic zonation. Gradient analysis also indicates regionally consistent variation in sedimentation rates and key horizons (isochrons) probably generated by taphonomic processes.

The concepts of astogeny and ontogeny in stenolaemate bryozoans, and their illustration in colonies of Tabulipora carbonaria from the Lower Permian of Kansas

JOSEPH F. PACHUT, ROGER J. CUFFEY, AND ROBERT L. ANSTEY Department of Geology (Cavanaugh Hall), Indiana University-Purdue University at Indianapolis, 425 University Boulevard, Indianapolis 46202, Department of Geosciences (Deike Building), Pennsylvania State University, University Park 16802, and Department of Geological Sciences (Natural Science Building), Michigan State University, East Lansing 48224

CLADISTIC AND PHENETIC RECOGNITION OF SPECIES IN THE ORDOVICIAN BRYOZOAN GENUS PERONOPORA

Abstract We compare cladistic, phenetic, stratophenetic, and typological methods of recognizing species within a single well-sampled, long-lived Ordovician bryozoan genus, Peronopora Nicholson, 1881. A consensus of 11 methods recognizes 14 species within Peronopora, each of which has both cladistic and phenetic support, and support by at least four different methods. Comparison of methods was based on: 1) the number of species recognized; 2) the degree of splitting of consensus groups; 3) consistency in determining first and last appearance datums, and stratigraphic ranges; 4) consistency in the number of specimens assigned to species; 5) stability in recognizing geographic distributions; and 6) correlations with character heritability. The five methods most closely approaching consensus were: 1) Ward clustering on Euclidean distance; 2) K-means splitting; 3) Ward clustering on correlation coefficients; 4) cladistic parsimony; and 5) cladistic parsimony plus iterative discriminant analysis. The three methods farthest from consensus were: 1) stratophenetics; 2) average linkage on Euclidean distance; and 3) conventional typology. Cladistic parsimony is the only method that can recognize all 14 consensus clusters. We argue that the overall advantages of parsimony analysis outweigh the merits of the various phenetic approaches in recognizing paleontological species. We also argue that given sufficient allochrony in sampling, cladistic structure is detectable both within and among species. Recognizing species based on fixed character states would require at least 72 species in our material. The crown groups of Pachut and Anstey (2002) are herein recognized as monophyletic species in the sense of Mishler and Theriot (2000), one of which we designate as a new species, P. browni. Six of our eight nonmonophyletic stem groups are recognized in this paper as metaspecies in the sense of Donoghue (1985) and Gauthier et al. (1988). Two of our stem groups are phenetically indistinguishable from phyletically contiguous crown groups, and we attribute the failure of parsimony analysis to recognize the monophyly of these groups to homoplasy.

PHYLOGENY, SYSTEMATICS, AND BIOSTRATIGRAPHY OF THE ORDOVICIAN BRYOZOAN GENUS PERONOPORA

Abstract Specimens of Peronopora Nicholson, 1881, are abundant in Upper Ordovician rocks of the North American Midcontinent. Based on the positions of units in the Composite Conodont Standard Section, we have sampled 211 specimens over a stratigraphic interval of 9.1 million years. The average duration of sample spacing is 61,664 years but is commonly as small as 32,800 yr. Thirty-four morphometric characters were measured in each specimen and were converted into multistate characters; character-state breaks were established based upon each characters ability to discriminate between phenetic groupings. Each character was subsequently weighted based on the number of derived states, degree of independence from other attributes, and estimated heritability. Cladistic analysis of these data indicate that there are eight species in Peronopora each consisting of an optimally defined crown group and a basal stem group (or paraclade). Character states shared by stem and crown groups define species but, within species, stem and crown groups also differ in some character states. The species are, in ascending order from the base of the tree, Peronopora decipiens (Rominger, 1886), P. compressa (Ulrich, 1979), P. pauca Utgaard and Perry, 1964, P. milleri Nickles, 1905, P. horowitzi new species, P. vera Ulrich, 1888, P. sparsa Brown and Daly, 1985, and finally P. dubia (Cumings and Galloway, 1913). Diagnostic keys permit the unique assignment of each specimen to a species and the separation of members of stem groups from those of crown groups. Thirty-one characters are required to discriminate between all 211 specimens. This contrasts with previous studies of Peronopora where eight or fewer characteristics were used. Of the ten characters most useful in discrimination, only three had been used in the conventional species literature. This accounts, largely, for only 29.8 percent (51 of 171) of previously identified specimens being classified as members of the same species in this analysis. Discriminant function analysis of original measurements, using species identity as the grouping criterion, produces statistically significant separation of species. It appears that stratigraphic position had an explicit and undue effect on previous concepts of species many of which could not be recognized independently of stratigraphic position. All species of Peronopora appear, or are inferred to have appeared, within the Lexington Limestone between the base of the Grier Member and the top of the Millersburg Member. The cladogram indicates that species evolved in a sequential order, but their first appearance datums have been stratigraphically punctuated. Three species have ranges terminating in the Early to Middle Maysvillian, one in the Middle Richmondian, and four in the Late Richmondian. The latter four (or five) of these species died out in the extinction associated with the unconformity at the top of the Richmondian.