Alan Stanley Horowitz

Lyellian bryozoan percentages and the fossil record of the Recent Bryozoan fauna

Although general percentages for Recent species of bryozoans in Cenozoic faunas have been published by several authors and were reviewed by Stanley (1979), we present percentages calculated from a number of post-1950 faunal studies of Cenozoic bryozoans. Variability among faunas of the same age is not great and the increase through the Cenozoic in the percentage of bryozoan species currently in the modern fauna is monotonic when calculated per million years of each Cenozoic epoch. The 12.5 % of the Recent bryozoan fauna with a fossil record is the same as recorded by Jelly (1889) over a century ago. This contrasts greatly with Valentines (1989) data (77%) for the fossil record of recent molluscs from the Californian biogeographic province. The average duration of Recent species having a fossil record is 12.2 MY calculated from the midpoint of the earliest Cenozoic epoch in which each species occurs. INTRODUCTION

ABNORMALITIES IN PENTREMITES SAY (BLASTOIDEA) FROM THE PELLA FORMATION (UPPER MISSISSIPPIAN) OF IOWA

Approximately 10,000 determinable specimens of Pentremites pulchellus Ulrich (Blas- toidea, Echinodermata) from a single quarry in the Pella Formation near Oskaloosa, Mahaska County, Iowa, have been examined for abnormal morphologic characters. The total frequency (2.7%) and the frequency among different types of abnormalities (ambulacral 29%; basal 46%; symmetrical 12%) are significantly different in the Pella material than in previously published studies (Wanner, 1932; Macurda, 1980). The greater frequency of abnormalities in the Pella For- mation than in previous studies may reflect higher environmental stress because of variable tem- peratures or salinities or both. The kinds of abnormalities are the same among published studies, which suggest that the underlying biological causes of abnormalities were similar throughout the geologic history of the blastoids. Ambulacral abnormalities are symmetrically distributed, but the division and inversion of basal plates show an asymmetrical distribution as previously recorded by Macurda (1980). The Pella Formation is of Genevievian age (Upper Mississippian) based on the occurrence of Pugnoides ottumwa (White) and convex ambulacra in Pentremites pulchellus. Other unequivocal guide fossils are unknown in the Pella Formation.

Polyphyly in the Pentremitidae (Blastoidea, Echinodermata)

In order to maintain a phyletic classification within the Blastoidea, the polyphyletic order Spiraculata will require revision or replacement. Previously created familial and subfamilial names suffice for most of the independent pentremitid lineages, but the new family Ambolostomatidae and the new subfamily Belocrininae are created for the genera Amobolostoma and Belocrinus , respectively. The genera placed in the spiraculate blastoid family Pentremitidae apparently had at least six independent origins from fissiculate and spiraculate incestors. The late Siegenian pentremitid Belocrinus appears before the well-documented lineage of Pentremitidea - Conuloblastus - Hyperoblastus , which contains the transition from a fissiculate to a spiraculate blastoid and is not clearly related to other pentremitids. The Middle Devonian genera Devonoblastus and Eleutherocrinus are related hyperoblastids and probably developed from an unknown early hyperoblastid. The Famennian Petaloblastus could be derived from Hyperoblastus (Emsian-Givetian) by exposing the lancet plates and lengthening the deltoid crest so that it became visible in lateral view. The Early Mississippian (Kinderhookian, Tournaisian) fissiculate genus Pentremoblastus could have become a new spiraculate genus morphologically similar to Pentremites by bridging its open fissiculate slit to create spiracular pores and reducing the anal deltoids to two; the new spiraculate genus retains deltoid crests. The presence of a conspicuous spiracular septum (a presumed primitive character) in the earliest species heretofore assigned to Pentremites and undescribed intermediate forms from the Kinderhookian (Tournaisian) Lodgepole Formation of Montana suggest that Pentremites could have arisen by merging the 10 spiracles found in Strongyloblastus . Ambolostoma has morphologic features which suggest that it is unrelated to other genera presently placed in the Pentremitidae. The Permian genera Calycoblastus and Rhopaloblastus , although placed in the family Pentremitidae, were regarded by Fay (1968) as derived from the spiraculate troosticrinid genus Metablastus .

The H. A. Nicholson Collection of Paleozoic stenolaemate bryozoans: comparison of cladistic and phenetic classifications

Until the late 1960s, most of Nicholsons types of Paleozoic bryozoans were not available for study. We present a set of coded characters of many of Nicholsons types, which should assist in bringing his species into conformity with current taxonomic standards so that his species can be consistently recognized and used in biostratigraphic, paleobiogeographic, and evolutionary studies. Cladistic and phenetic analyses of these species permit comparisons between inferred phylogenies of Nicholson specimens, adaptive morphospace, and treatise-based systematic relationships. Specimen-based cladistic and phenetic analyses of Nicholsons species both produce clusters that are congruent with existing family-level taxonomic assignments of species in the collection. However, cladistic analysis more fully retrieves the pattern of branching, or degree of relatedness, among higher taxa. Phenetic clusters represent adaptive peaks in morphospace for these specimens, but higher level “phenons” are strongly affected by multiple evolution of the same character states.

Cladistic Assignment of Specimens to Species of the Cystoporate Bryozoan Genera Strotopora Ulrich and Cliotrypa Ulrich and Bassler Using Gap-Coded Characters

Abstract Gap-coding permits the use of continuous metric characters in cladistic analyses. Character means are converted to integer equivalents by placing character state divisions in the locations of phenetic breaks between specimen clusters, under the assumption that these breaks represent the locations of bottlenecks in character distributions. Similarities and differences between specimens from closely related species of cystoporate bryozoans were evaluated for the first time by converting continuous morphometric measurements into gap-coded binary and multistate characters and analyzing them cladistically, rather than just phenetically, across multiple species of Strotopora, Cliotrypa ramosa and Fistulipora compressa. Our results demonstrate that cladistic analysis of gap-coded morphological characters can be effective in resolving phylogenetic relationships at low taxonomic levels (within and among genera) while objectively highlighting both the morphological features that specimens (taxa) share and ...

Identification of Biotic Constituents

We have endeavored to provide a brief, elementary summary of the groups of fossils one is likely to encounter and recognize in thin sections at magnifications of 10 to 100 and to indicate where additional information is available. Our coverage includes 18 major fossil groups.

Getting Started in Carbonate Petrography: Methodology and Applications

An introductory text on the petrography of fossils would be incomplete without mention of its uses as well as informing the reader how to begin the study of carbonate rocks in thin section.