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WALL CALCIFICATION AND
RHYTHMIC GROWTH IN THE PERMIAN

STENOLAWTE BRYOZOAN W W
B?
John William Bartley

A DISSERTATION

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Geological Sciences

1988

ABSTRACT
HALL CALCIFICATION AND
RHYTHMIC onowwu IN THE PERMIAN
STENOLAEMATE BRYOZOAN IABQL;EQ§A,QA§§Q§A§L§
By

John William Hartley

The Early Permian stenolaemate bryozoan Tabulipora
gggbggizig is a good choice for growth rhythm analysis
because of its robust soarial growth habit, thick exozonal
walls with well-defined laminae, and exozonal wall segments
(monilae) which serve to partition the wall laminae into
natural higher-order growth increments. Fifty specimens of
1, 9312931111, selected from lithofacies likely to have been
influenced by tidal cycles, were obtained from 18 sampling
localities within the Lower Permian Nreford Megacyclothem of
Kansas and Oklahoma. Although wall laminae were counted for
571 monilae, discontinuities within monilae permitted
subdivision of the counts into 815 smaller units of growth,
herein termed wall clusters.

If wall growth was influenced by tidal cycles, subunits
should repeat with a frequency of 15, the number of days in
an Early Permian fortnight. Mean counts, averaged by
locality, range from 15.3 to 27.2 laminae per monila, and
from 12.8 to 16.7 laminae per wall cluster. Only 33% of the
wall cluster means differed significantly from the expected
frequency of 15, whereas 78% cf the monila sample means

showed significant differences. These results indicate that

wall clusters may have been modulated by fortnightly tidal
cycles, and that wall laminae represent daily growth
increments.

Both wall cluster cycles and monila cycles in I,
gggbggagii are comparable to polypide regression cycles in
living cheilostome bryozoans. An average wall cluster cycle
(15.0 days) is slightly less than half of the average
polypide longevity (33.2 days) reported for five extant
species, and an average monila cycle (20.8 days) is slightly
greater than half of the average polypide
degeneration-regeneration cycle (41.4 days) reported for
eight extant species. Based on this comparison, rhythmic
skeletal growth patterns may be a direct reflection of
polypide cycles in 1. gggbggigig and other extinct
stenoporids.

Laminae growth in 2, garbggigig was accomplished by
aborally-directed edgewise secretion of microcrystallite
layers. This is a new model for bryozoan wall
calcification, and represents the probable growth mode for

most of the stenoporid trepostomes. This model may have
broader application to other stenolaemate bryozoans,
particularly those taxa in which wall laminae are continuous

across zooecial boundaries.

ACKNOWLEDGMENTS

Most authors of theses or dissertations, if married,
generally extend thanks to their spouses for support and
encouragement at the end of an acknowledgments section.
These bland expressions of thanks generally give the reader
the impression that the spouse was remembered at the last
minute, as the writer was scrabbling around making sure no
one was left out. This has always seemed grossly unfair to
me, for the spouse is usually the first one to bear the
extra toll of stress, worry, and neglected feelings caused
by undertakings of this sort. I have chosen, instead, to
take this opportunity to put things in their proper
perspective, and to thank my spouse, Jacqueline Bartley, for
giving away that portion of her life that went to support my
work on this dissertation.

Dr. Robert L. Anstey served as major professor and
adviser for this dissertation; I am indebted to him for his
keen advice, patience, and innumerable helpful discussions
over the years. His insight and knowledge were invaluable
aids during the course of this research. To the members of
my advisory committee, Drs. J. Alan Holman, Chilton E.
Prouty, and Duncan F. Sibley, my thanks for their

encouragement and many helpful suggestions.

iv

Special thanks are due Dr. Roger J. Cuffey of the
Pennsylvania State University for generously loaning me the
collection of Hreford Tabglipora c rbonaria, for granting me
permission to thin section the specimens, and for providing
answers to my many questions.

Ms. Wendy Hunt provided assistance in the preparation
of acetate peels and thin sections, and Ms. Sally Davis
served as the unbiased observer for the test of increment
count reproducibility.

Financial support for this work was provided in part by
a research grant from the Geological Society of America, and
by a research fellowship under a Petroleum Research

Fund/American Chemical Society grant to Robert L. Anstey.

TABLE OF CONTENTS

LIST OF TABLES......................................... vii
LIST OF FIGURES....................................... viii
INTRODUCTION............................................. 1
Br or h ................................. 4
Review of Prior Studies Q; flgyggggg Growth Cyglgs.. 11
MATERIALS AND METHODS................................... 16
l P rat ................................. 16

S‘lsggion Of Sissim'niIIIIIIIIIIIIIIIIIIIIIIIIIIIII 18

Daf. .tiono G Wh IIIIIIIIIIIIIIIIIIII 24

Growth Increment Agglysig.......................... 35
RESULTS AND DISCUSSION.................................. 45

Growth Rhythm Analysis............................. 45

Implications of Tgbglipgra gggbongrig growth rhythms

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 62

flgl; Growth in Tabulipora carbonaria............... 64
CONCLUSIONSIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 72

APPENDIX AI I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 75
APPENDIX BI I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 84
APPENDIX CI I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I IIIIIII I I 107

LISTOFREFERENCESIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII126

vi

Table

Table

Table

Table
Table
Table
Table

4.
5.
6.

7.

LIST OF TABLES

Summary statistics, test of increment count
r.pr°du°ibilitYIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 42

Summary of results from monila growth increment

d.b.IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 46

Summary of results from wall cluster growth

increment data................................ 47
Schroyer Limestone (Hs) samples............... 86
Upper Havensville Shale (uuHh) samples........ 88
Lower Havensville Shale (llWh) samples........ 98
Lower Threemile Limestone (lwt) samples...... 106

vii

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

9.

10.

ll.

12.

13.

LIST OF FIGURES

Diagram of a portion of a stenolaemate bryozoan
soarium, illustrating the standard orientations
of sections used to study zoarial growth

patterns...................................... 7

Diagram of the general growth relationships
within stenolaemate soaria.................... 9

Map of sampled localities from beds of the

Nreford Megacyclothem........................ 20

Stratigraphic distribution of the 18 Tabulipora

gjgbggagig sample localities................. 23
General illustration of the spacing and size of
monilae in Igbglipgza carbonaria............. 26
Microstructure of a monila in Tabulipora
EizbonazieIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 30

Comparison of monilar microstructure using thin

section and acetate peel replica techniques.. 33
Delineation of wall laminae in Tabulipora

cazbonsziilIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 37
Intramonilar growth discontinuities.......... 41

Mean increment counts for the two samples from

the lower Threemile Limestone................ 50

Mean increment counts for the six samples from
the lower part of the lower Havensville Shale

52

Mean increment counts for the sir samples from
the upper part of the upper Havensville Shale

54

Mean increment counts for the three samples from
the lower part of the middle Schroyer
Limestone........

viii

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Distribution of Egbglipgga gagbonaria
samples and lithofacies pattern from the lower

part of the lower Havensville Shale.......... 61

Comparison of skeletal morphologies produced by
oral versus aboral edgewise laminar growth... 69

Growth increment distribution, locality KA01J

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 108

Growth increment distribution,

Growth increment distribution,

Growth increment distribution,

Growth increment distribution,

Growth increment distribution,

Growth increment distribution,

Growth increment distribution,

Growth increment distribution,

Growth increment distribution,

Growth increment distribution,

Growth increment distribution,

Growth increment distribution,

Growth increment distribution,

Growth increment distribution,

Growth increment distribution,
GE18(17)eaaeaeaaeeeeaeeaoaseae

ix

locality OSO4A
IIIIIIIIIIIIII109

locality ML03R
IIIIIIIIIIIIII11O

locality GEO7J
IIIIIIIIIIIIII111

locality GE13E
IIIIIIIIIIIIII112

locality GE16H
IIIIIIIIIIIIII113

locality GE17N
IIIIIIIIIIIIII114

locality GROlI
IIIIIIIIIIIIII 115

locality GEBOG
IIIIIIIIIIIIII116

locality MSOSE
IIIIIIIIIIIIII117

locality MSOSE
IIIIIIIIIIIIII118

locality CH19A
IIIIIIIIIIIIII119

locality CH24D
IIIIIIIIIIIIII 120

locality CH35H
IIIIIIIIIIIIII 121

locality GEOZC

locality

.. 122

Figure 32. Growth increment distribution, locality GE24D

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 124

Figure 33. Growth increment distribution, locality MSZIC

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 125

INTRODUCTION

The hypothesis that fossils with accretionary skeletons
might preserve records of physical cycles during earth
history was first proposed by Wells (1963). He counted the
number of finely spaced bands occurring between major growth
checks on the epitheca of Devonian rugose corals, and,
assuming that the major growth checks represented annual
increments of growth, concluded that the duration of the
Devonian year was approximately 400 days, and that each day
was approximately 22 hours in length. Bcrutton (1964), also
using Devonian corals, demonstrated that monthly tidal
cycles could be determined using presumed daily growth
increments, and concluded that the Devonian synodic month
(the period between successive identical phases of the Moon)
was 30.6 days in length, as contrasted with its present 29.5
day duration.

Interest in skeletal growth patterns has greatly
increased since these initial studies, largely because the
information contained in growth records has application to
problems in geophysics, stratigraphy, paleobiology, and
paleoecology. Studies of growth records in organisms other
than corals (principally bivalved molluscs, but also

including barnacles, brachiopods, fish, sclerosponges, and

stromatolites), have revealed that growth records cycles are
far more complex than initially assumed, and that rather
than simply acting as ”paleontological clocks,“ fossil
organisms modulated their growth according to a variety of
different cycles including fluctuations in reproductive
activity, temperature, salinity, dissolved oxygen, substrate
composition, nutrient levels, and turbidity, as well as
temporal effects (Bourget, 1980; Doemal and Brock, 1974;
Pannella, 1971; Rosenberg, 1962; Termier and Termier, 1977;
see also the review volumes of Rosenberg & Runcorn, 1975 and
Rhoads & Lutz, 1980).

Bryozoans are colonial, sessile invertebrates that
secrete accretionary skeletons, inhabit a variety of
environments, and have an abundant fossil record. Many
fossil bryozoans, particularly those from the Paleozoic
order Trepostomata, also possess a nested hierarchy of
repeated growth structures. Despite these characteristics,
studies explicitly addressing the issue of rhythmic growth
in bryozoans are virtually nonexistent.

This study is an investigation into the occurrence of
growth cycles in Paleozoic trepostome bryozoans. It
addresses four general questions regarding the growth of
stenolaemate bryozoans:

(1) What is the structural nature of bryozoan growth
increments and how did they form?

(2) Is it possible to reliably define and measure

growth increments in fossil bryozoans?

(3) Is it possible to quantitatively verify that
bryozoan growth increments are periodically repeated, and if
so, with what frequency?

(4) How useful are growth rhythm studies for
interpreting bryozoan paleobiology?

Many specimens from a number of different genera were
examined during the initial stages of this study in an
effort to resolve these questions. The results from a
series of preliminary tests indicated that the group most
likely to have preserved cyclic growth increments were
genera belonging to the family Stenoporidae. A case study
of the Permian stenoporid Ighglipgxg‘ggrbggigig was
conducted; the results of this study are interpreted to
suggest that daily increments of growth were recorded by
Igbglipgzg, and that these increments can be grouped into a
higher-order cycle with a fortnightly periodicity.

Developing and testing hypotheses about growth cycles
is dependent in part upon the measurement of the smallest
increments of growth. In bryozoans, the smallest increments
appear as microlaminae within the walls of the living
chambers housing the individuals of the colonies.
Measurement of increments at this level is no simple task,
due to the microscopic size of bryozoan living chambers
(wall thicknesses typically less than 0.05 mm), and high
variability in microlaminae discreteness, clarity, and
lateral continuity. A new model of trepostome wall growth

was developed from efforts directed toward identifying and

measuring these finest increments of growth. This model has
certain implications regarding future studies of growth
rhythms in bryozoans, and may have broader application to

interpreting the evolutionary history of the phylum as well.

W

In order to clarify the following discussion, a number
of basic concepts regarding the morphology of bryozoans must
be introduced. Considerably more information is available
in Boardman (1983, p. 3-125) and Ryland (1970, p. 101-129).
All of the bryozoans discussed in this study are
representatives of the Btenolaemata, one of the three large
classes into which the phylum Bryozoa is subdivided. The
stenolaemates are defined as those bryozoans possessing
zooids with complete interior vertical walls forming
elongate tubular or conical living chambers (Boardman, 1983;
Borg, 1926).

The individual feeding organism of a bryozoan colony is
referred to as a polypide, and the skeletal chamber which
houses the polypide is referred to as the zooecium. A
zooecium and polypide together are termed a zooid; the
skeleton of an entire colony is referred to as a zoarium.
All of the many zooids that make up a bryozoan zoarium are

genetically identical because the entire colony is produced

by asexual budding from a single founder larva.

Stenolaemate bryozoans are generally studied through
the use of thin sections out along standard orientations.
These orientations are illustrated in Figure 1 and are
defined as follows: longitudinal sections are oriented so
that zooids are cut parallel to their entire length;
tangential sections are parallel to and just below the
surface of the colony so that the zooids are cut
perpendicular to their openings; transverse sections are
oriented so that the proximal ends of zooids are cut across
their diameters. The interpretation of growth patterns is
done primarily by using longitudinal sections, because
sections cut in this plane permit one to observe the
ontogenetic history of individual zooecia as well as the
ontogenetic history of the whole colony, referred to as the
astogeny of the zoarium.

Figure 2 illustrates the general relationship between
zooidal and zoarial growth directions as observed in
longitudinal section. The upper portion of the diagram
(Figs. 2A & 28) indicates the growth pattern observed in
ramose or branching colonies, while the lower portion of the
diagram (Figs. 2C & 2D) indicates the pattern observed in
unilamellar encrusting zoaria. The massive zoarial growth
habit is not illustrated, but can be approximated by a
vertically stacked series of encrusting layers. Growth
within a single zooecium proceeds from the aboral toward the
oral end of the zooecium by the accretion of new skeletal

material at the oral end of the tube. Each zooecium has a

Figure 1. Diagram of a portion of a stenolaemate bryozoan
zoarium, illustrating the standard orientations of sections
used to study zoarial growth patterns. Modified from
Boardman (1964).

endozone exozone
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Figure 2. Diagram of the general growth relationships
within stenolaemate zoaria. A, growth of a ramose (or
branching) colony at the zoarial level. B, growth of a
ramose colony at the zooecial level. C, growth of a
unilamellar encrusting colony at the zoarial level. D,
growth of an encrusting colony at the zooecial level. Arrows
indicate the growth direction at the various levels of
observation. Based on a diagram by Gautier (1970).

 

 

   

 

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10

proximal and distal side as well, the result of proximal to
distal growth of the zoarium by the budding of new zooids.
The zoarium is subdivided into an inner portion termed the
endozone and an outer region known as the exozone.
Characteristics of endozonal growth include thin vertical
walls growing parallel or at some low angle to zoarial
growth direction and a general absence of intrazooidal
skeletal structures. Exozonal characteristics include
thickened vertical walls growing at some high angle to the
zoarial growth direction with a variety of intrazooidal
skeletal structures; the growth rate of the exozone is
generally interpreted to be slower relative to that of the
endozone (Boardman, 1983; Tavener-Smith & Williams, 1972).
The zoaria of most stenolaemate bryozoans incorporate a
nested hierarchy of growth increments. At the level of the
individual zooid, many taxa exhibit microlaminae within
their zooecial walls, a pattern best developed in the
exozonal portion of the zoarium. At the intrazooidal level
of growth, the repeated emplacement of basal diaphragms,
cystiphragms, monilae, and other structures is quite common
in many stenolaemate genera, again usually best developed in
the exozone. Repeated zones of rejuvenation marked by
remnants of abandoned growing tips within the endozone
(Boardman, 1960, 1971; Borg, 1933; Cuffey, 1967) and
alternations of endozone and exozone layers (Anstey et al,
1976; Podell and Anstey, 1979) represent examples of growth

increments occurring on an intrazoarial level.

11

v' w P i Studi s o z a wth c

With the exception of Flor and Hillmer (1970) and
Rabbio and Regalbuto (1985), no prior published studies
explicitly document growth rhythms in fossil bryozoans. Flor
and Hillmer (1970) studied the Cretaceous cerioporid
cyclostome Multigggggig_tgbgggsg, a stenolaemate bryozoan
that built massive bulbous zoaria by accretion of zooecial
overgrowth layers. They measured the average thickness of
each overgrowth layer, plotted this information sequentially
in the form of a linear graph, and then visually inspected
the plot for patterns of repetition. Rhythmic growth was
determined to be of two types: one in which a thick layer
alternated with a thin layer, and one in which the repeated
sequence was a thick layer followed by two thin layers.
Based on the development of brood chambers at or near the

degeneration surfaces separating overgrowth layers, Flor and
Hillmer concluded that rhythmic growth in M. tuberosa was
related to internally directed reproductive cycles.
Arhythmia in a number of colonies was interpreted to be the
result of local fluctuations in turbidity, indicated by
sediment remnants preserved on degeneration surfaces. Flor
and Hillmer compared the overgrowth sequences in M. tuberosa
to those in living colonies of the cheilostome bryozoan
Schizoporella sanguinea, in which thick layers represent
long summer growth seasons, and thin layers represent a

short autumn growth season. Based on this comparison, the

12

couplet formed by a thin and thick layer in M. tugggggg can
be interpreted as an annual growth increment.

Rabbio and Regalbuto (1985) documented the occurrence
of growth cycles from counts of wall laminae within repeated
exozonal wall thickenings (monilae) in six zoaria of the
trepostome Tabulipggj from Lower Permian strata in Texas.
They reported peaks of 29, 44, and 122 increments per
monila, which they interpreted to represent a fundamental
growth frequency of 14.8 increments per monila, indicative
of growth modulated by a fortnightly tidal cycle.

Termier and Termier (1977) described three levels of
cyclic growth, which they termed megacycles, mesocycles, and
circadian cycles, in fossil sclerosponges. They
extrapolated their work on sclerosponges to some
Carboniferous ceramoporoid bryozoans, and recognized
megacycles in the layering of vesicles. They did not,
however, establish any periodicity or duration for these
megacycles.

In living bryozoans, Stebbing (1971) has documented
annual growth increments in living colonies of the
cheilostome Flustza Lgli;ggg. He observed that growth in E.
{gligggg occurs at a nearly constant rate of 15 mm per year,
irrespective of colony age. Stebbing reported finding
colonies as old as 12 years, with no apparent senescence in
growth. He also reported evidence of occasional brief
checks in growth occurring during August, corroborating the

work of Flor and Hillmer (1970).

13

Cycles of polypide degeneration and regeneration are
common among living bryozoans (Ryland, 1970, p. 59-60);
these cycles probably serve a rejuvenatory function for
bryozoan zooids (Gordon, 1977). Gordon provided measures of
polypide longevity and duration of regression for several
species of gymnolaemate and phylactolaemate bryozoans.

Polypide longevities as low as six days were reported for

Zogbotgygn gggtigillgtgg and Elggggg pilosg, and as high as
72 days in Cryptosglg pillagiggg, with regression durations
ranging from two days for 333311 ggligigg to 17 days in
We alumna (Gordon, 1977, p. 340).

Other bryozoan workers have inferred cycles from
repeated features of skeletal growth, without explicitly
attempting to establish any rhythm or periodicity in the
cycles. Tavener-Smith (1969), drawing on Williams's (1968)
work establishing diurnal periodicity in the shells of
brachiopods, suggested the possibility of diurnal layering
in the outer laminated wall of the reverse sides of branches
of the fenestrate bryozoan Fengstglla by comparison with the
Recent cyclostome Hgggerg. Newton (1971), following the
lead of Tavener-Smith, extended this suggestion to the
rhabdomesid cryptostome flggmggpggg lgpigggggdroidgs,
estimating the average longevity of colonies of this species
to fall somewhere between 325 to 380 days. Neither
Tavener-Smith nor Newton rigorously tested these hypotheses,
however; the speculations of both authors were based on

crude estimates of counts from only a few specimens. Gautier

14

(1970) and Malecki (1968) described cyclic alternations of
thin and thick-walled segments, producing a moniliform or
beaded appearance in longitudinal sections within the
exozone of Permian species of the trepostome ul 0 .
Nye (1976) reported similar patterns in the exozones of
cerioporid cyclostomes. Several authors have reported
cycles of rejuvenated growth surfaces, occurring as
abandoned tip remnants arching across endozones in Paleozoic
trepostomes (Boardman, 1960; Boardman et al, 1969; Cuffey,
1967), or as colony-wide regeneration surfaces in
post-Paleozoic heteroporid cyclostomes (Borg, 1933;
Henderson and Perry, 1981). Cyclic addition of layered
overgrowths of zoarial surfaces were reported by Nye and
Lemone (1978) in the Early Cretaceous cyclostome
3gpfigmgltig§ya.§g;ggg. Taylor (1976) reported the same
phenomenon in two species of Jurassic cyclostomes. Boardman
(1968), McKinney (1975), and Boardman and McKinney (1976)
reported the cyclic repetition of endozonal budding episodes
in six genera of Paleozoic trepostomes. Finally, Boardman
(1971) discussed the possibility that repeated sequences of
intrazooecial structures in trepostomes (such as hemiphragms
and cystiphragms), might have been related to polypide
degeneration-regeneration cycles.

-Although numerous authors have inferred hypotheses of
cyclic growth in fossil bryozoans, none of these hypotheses
have been tested rigorously by quantitative methods. Rabbio

and Regalbuto (1985) reported encouraging results based on a

15

systematic method of increment counts; however, their
conclusions were based on a relatively small sample which
included one misidentified specimen. Thus, suppositions
about cyclic growth in bryozoans prior to this study must be

regarded as inconclusive.

MATERIALS AND METHODS

5122;: Ezgpgration

One of the objectives of this study was to develop a
set of preparation techniques to enhance the optical clarity
of the zooecial wall laminae, thus improving the reliability
of counting and measuring the thickness of growth
increments. Conventional acetate peel replica techniques
(Boardman & Utgaard, 1964; Nye et al, 1972) do not produce
peels of sufficient quality for microstructural growth
rhythm analysis. Ultrathin polished sections yield
excellent preservation of skeletal microstructure, but
because these thin sections are difficult and time-consuming
to prepare, as well as being far more destructive of the
specimen than peel techniques, initial efforts were directed
toward refining the methods of acetate peel replication.

A lengthy series of tests were performed, using a
variety of different etching solutions, immersion periods,
and staining techniques; a complete list of these tests,
with procedural notes, is given in Appendix A. Bryozoans
used in these tests were selected on the basis of
morphological characteristics deemed favorable for

preserving rhythmic growth structures. These included taxa

16

17

with thick exozones of laminar skeletal material, multiple
intrazooidal partitions (such as diaphragms or
cystiphragms), and robust branching or massive zoarial
growth habit, to ensure zoarial longevities of several

seasons of growth. Genera meeting these criteria included

WV loor.flemnrm.£em_oma.h at .
Iggglipggg, and gtgggpggi. A total of 294 test peels and 19

polished thin sections were prepared from approximately 50
separate zoaria during this phase of the study. Although
some minor improvements in cptical clarity were achieved
(see Appendix A), none of the peel enhancement techniques
produced results comparable in quality to those obtainable
from polished thin sections (Bartley & Anstey, 1983).
Scanning electron microscopy (SEM) was used to study
details of skeletal ultrastructure in 11 zoaria of different
genera, including Pe o or , Mgggggtgypg, Rhombotr a, and
Tabulipgga. These included specimens prepared as
longitudinal sections by grinding, polishing, and etching,
as well as several specimens prepared as unetched fracture
surfaces. All specimens studied with SEM were
ultrasonically cleaned prior to coating with 20-30 nm of
gold using a sputter coater. Specimens were observed and
photographed using the ISI Super-III and JEOL-JSM 35C
scanning electron microscopes in the Center for Electron
Optics at Michigan State University. Additional
observations of some specimens were carried out using the

ISI Super-II SEM in the Biology Department at Hope College.

18

Sglggtigg of Specimens

The preliminary work on sample preparation and the
report of Rabbio and Regalbuto (1985) resulted in the
selection of the stenoporid trepostome Tabulipora carbongrig
to serve as the basis for a case study of bryozoan growth
rhythms. A large collection of I. garbonaria from the Lower
Permian Wreford Megacyclothem of Kansas and Oklahoma was
obtained on loan from Roger J. Cuffey of the Pennsylvania
State University. The bryozoans are from 18 sample
localities distributed across the north-south outcrop belt
of the Wreford rocks (Figure 3). Most of the specimens
served as the basis for a systematic revision of the species
(Cuffey, 1967); others were added in the interim by Cuffey
during additional forays to the Wreford sites.

Detailed study of the stratigraphic relationships and
depositional environments of the Wreford Megacyclothem
(Cuffey, 1967; Hattin, 1957; Newton, 1971) has resulted in
subdivision of the Wreford into 22 successive stratigraphic
horizons, each of which is typically dominated by a single
lithofacies. The 18 samples are from six of these
subdivisions. Two of the samples are from the lower part of
the Threemile Limestone, six are from the lower beds of the
lower part of the Havensville Shale, six are from the upper
beds of the upper part of the Havensville Shale, one is from
the lower part of the Schroyer Limestone, and the remaining

three are from the lower beds of the middle part of the

19

Figure 3. Map of sampled localities from beds of the
Wreford Megacyclothem. Sample numbers and precise
geographic locations obtained from Cuffey (1967), Newton
(1971), and Lutz-Garihan (1976).

20

 

MARSHA“.

: ML03R

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

    

GEISE
GEIOH ——\ GEO7J
GEOZC
6E18(l7)— (3517“
GESOG GE24D
MSOSE
—— MSO6E 100
MSZIC L=—==j
CHASE KILOMETERS
/—— CH19A
.4.” CH24D
CHSSH l —a '——“
BUTLER
‘\\— CROII
GREENWOOD
COWLEY
KAY f OSAGE
KAO 1 J P— 0804A KANSAS

 

 

 

 

 

* l OKLAHOMA

 

 

21

Schroyer Limestone (Figure 4). The Threemile Limestone,
Havensville Shale, and Schroyer Limestone are the lower,
middle, and upper Members, respectively, of the Wreford
Limestone Formation. 16 of the samples are from beds of the
calcareous shale lithofacies (Cuffey, 1967), interpreted as
having been deposited in waters of normal marine salinity,
low turbulence, and ranging in depth from 3 to 15 meters,
although Newton (1971) suggested a range of only 3 to 9
meters. The remaining two samples (KAOlJ and OSO4A) are
from beds of the brachiopod-molluscan limestone facies,
interpreted as an intermediate facies between the calcareous
shale and the near-shore molluscan limestone, although of
similar water depth as the calcareous shale (Cuffey, 1967;
Newton, 1971).

The specimens of I, gggbgnigig were embedded in
transparent thermoplastic casting resin and sectioned
longitudinally, according to the grinding, polishing, and
mounting techniques described by Nye et al (1972), with one
modification. Heating the slides during application of the
epoxy cement and polished specimen apparently produced
stress within the glass slide, resulting in fracturing of
the slide as the mount cured. Because of this, mounting and
curing of the specimens was carried out at room temperature,
which eliminated the problem of fracturing. The thin
sections were then inspected for the presence of moniliform
wall sequences, which are regularly repeated swellings in

the zooecial walls that occur in the exozonal portion of the

22

Figure 4. Stratigraphic distribution of the 18 Tabulipora
carbonaria sample localities. Samples KAOlJ and 0504A are
from beds of the brachiopod-molluscan facies; all others are
from calcareous shale facies (Cuffey, 1967; Newton, 1971;
Lutz-Garihan, 1976).

 

23

 

 

 
  

 

 

  
    

 

   

 

 

 

 

 

GEOZC

GE18(17)

p-

CHlQA
CHZ4D
CHSSH
GESOG
MSOSE

@3065

GEl6H
GE17W

EEO7J
GElSE
GROlI
@0312

'KAOLI

 

 

LL}
(.9 z
< o
[— I—I
m I—
g 3
<1: o E
0 CI 0
z o u.
-o
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0H
.,—I (13
«4.. g m
p
(GU)
E I
Schroyer u
Limestone jg:
m@s___L_-
23, on
O o Havensville I
‘8 t;
.: a) Shale m
U s -—.—
-J Member 0
= W‘ E
{d
.H “O D —————————
2‘ 8 . "v
<6 ‘H Threemile
e 2 "W
3 3 L1mestone lo
2
Member at
I
on
g 0)
9-1
a ,2 m"
U m ulu
.—I H "I!
-r-4 a)
8 i3
:3 m m
o :2.
u m I

 

 

_pSO4A

24

zoarium (Figure 5). Not all monilae have clearly defined
growth increments (see following section); more often than
not the walls are quite granular and growth increments are
obscured. The thin sections were culled for specimens
containing monilae with clearly definable growth increments.
This resulted in the final selection of 50 specimens from
the 18 sampling localities. The number of zoaria in each
sample ranged from as few as one to as many as seven per
locality. Growth increment data from a total of 571 monilae

were obtained from these specimens.

9 [° '!I E 5 W!! I I

Rosenberg (1975) has thoroughly discussed the need for
precision when defining the terms used to describe growth
increments. The growth increments reported in this study
are structural features; that is, they are repetitive
textures visible as laminae in cross sections of the
zooecial walls. The tacit assumption of most bryozoan
workers is that these laminae represent increments of
skeletal accretion, although the precise nature of timing
and duration of lamina secretion, even among living
bryozoans, is poorly understood. This is essentially due to
the fact that unless one is interested in testing hypotheses
about daily, monthly, or other cycles of growth, such
precise estimates are unnecessary. Given the virtual

absence of growth rhythm studies on bryozoans, the lack of a

25

Figure 5. General illustration of the spacing and size of
monilae in Tabulipora carbonaria. Longitudinal thin
section, PSU GEBOG-bf-PR-4003. Scale bar 8 0.1 mm.

26

 

27

rigorously defined model of incremental growth in bryozoans
is not surprising.

Complicating matters is the indistinct quality of
lamination observable in the skeletal walls of most
stenolaemate bryozoans. Unlike the growth increments of
molluscs or brachiopods, whose boundaries are generally well
defined and laterally continuous, the laminae in bryozoans
are separated by poorly defined and laterally discontinuous
boundaries. This phenomenon of imprecision in increment
definition does not appear to be related to preservation
factors nor diagenetically induced, for it pervades the
phylum irrespective of geologic age or sedimentary
environment.

The criteria used in this study to define the smallest
growth increments are based on observations of wall
microstructure from thin sections, acetate peels, and SEM.
Although the following discussion deals with Iabulipoga
gargggggig, observations of the microstructure in other
trepostomes (including Stenopora, Mgterotgypa, Rhombotr a,
and Egrgggpggg), were incorporated in these criteria.

Observed using SEM, the microstructure of the monilae
in Tabulipora carbonaria appears to be a mosaic of calcite
microcrystallites, generally arranged in a sequence of
distally overlapping arc-shaped layers (Figure 6). This
pattern is the result of deposition by the inner zooecial
secretory epithelium at the growing surface of the vertical

wall; overall growth of the monila was from the lower right

28

toward the upper left of Figure 6A. The parallel arc-shaped
appearance of the layers reflects the distal (outward)
progression of this epithelium as growth of the wall took
place (Boardman & Cheetham, 1969; Borg, 1926; Brood, 1976;
Tavener-Smith & Williams, 1972).

Most of the microcrystallites are 2 - 5 times wider
than they are thick, averaging around 1 - 2 micrometers in
thickness and up to 10 micrometers in width when sectioned
longitudinally. The shape of individual microcrystallites
varies from those that are semi-tabular to others in the
shape of slightly curved pancakes or thin biscuits, with
irregular or undulatory surfaces. These surface
irregularities give rise to an interlocked structure, as
ridges or protuberances on a microcrystallite are
accomodated by grooves or pits on subjacent or superjacent
microcrystallites (Figure 6B). Bigey & Lafuste (1982)
described a similar crystallite morphology in the Devonian
trepostome Lgpggtglpgllg, a shape they termed
"pluricupular."

Although the microcrystallites are layered distally
within a monila, they do not form planar sheets like the
laminae illustrated by Armstrong (1970, pl. 115, fig. 6) in
the Permian trepostome Stenopora 9133;. Rather, the
crystallites tend to overlap one another, producing a
shingled pattern. This pattern is particularly prevalent
near the central portion of the wall (Figure 68). The

absence of any laterally continuous planar surfaces in SEM

29

Figure 6. Microstructure of a monila in Tabulipora
carbonaria. A, Scanning electron micrograph of a polished
and etched longitudinal section through a single monila of
specimen PSU GEBOG-bf-PR-4003. B, Detail of the central
portion of A. Scale bar for both micrographs 8 10.0
micrometers.

30

 

31

images of Ighglipgri_ggrpggggig would seem to preclude their

use for determining growth increment boundaries.

Figure 7 contains photomicrographs of an acetate peel
replica (Figure 7A) and a thin section (Figure 7B) of the
same monila illustrated by SEM in Figure 6. The pattern of
microcrystallite structure and laminae clarity in the
acetate peel replica is nearly identical to that of the SEM
image, as well it should be, since both images are formed by
the textural relief present on the etched surface of the
specimen. Lateral continuity of laminae bounding surfaces
is slightly improved in the peel replica; linear structures
are traceable across several areas of the image, but the
nature of lamination for the intervening skeletal material
is obscure. Ironically, this may be an indirect result of
the poorer resolving power of light microscopy when compared
to SEM. Every nuance of surface detail is precisely
recorded by the SEM image, which may in fact be providing
more information than is needed or desired. The light
microscope, on the other hand, fuses many of these
subtleties, and thus may actually become more useful because
of its limitations.

A thin section of the same monila (Figure 7B) preserves
the best indication of the presence of laminae bounded by
laterally continuous surfaces. These appear as thin linear
features formed by abrupt transitions from light to dark
regions of skeletal material. Although the quality of these

laterally continuous surfaces is nonuniformly distributed

32

Figure 7. Comparison of monilar microstructure using thin
section and acetate peel replica techniques. Photographs
are of the same monila illustrated in Figure 6. A, Acetate
peel replica. B, Polished thin section. Scale bar for both
= 0.05 mm.

33

 

34

across this photomicrograph, this can be remedied by
focusing the microscope up and down, bringing different
planes of the thin section into focus. This method of
“looking through the section“ reveals something about these
surfaces that is not obtainable from acetate peels or SEM
imagery. Essentially, these surfaces lie at some angle
other than perpendicular to the plane of the thin section.
This may be the result of fundamental differences between
the skeletal growth mode of bryozoans and those of other
invertebrates such as brachiopods and molluscs. Growth of
the stenolaemate zoarium is accomplished by the complex
process of adding new skeletal material to the outer ends of
closely-packed tubes and their interstices, rather than
along a simple linear front, as is the case for brachiopods
or clams. Although the biomineralization process in
bryozoans may be comparable to that of brachiopods
(Tavener-Smith & Williams, 1972), the resulting skeletal
geometries are constrained by the morphological differences
between the organisms, and corresponding differences between
their respective growth modes may be expected.

Thin sections appear to provide the most useful
information for defining the basic trepostome growth
increment. Laterally continuous surfaces separating
alternating zones of light and dark skeletal material are
more easily recognized in thin sections than in either
acetate peel replicas or SEM images. The etching process

required to produce the necessary surface relief for SEN

35

observation and acetate peel replication may be introducing
structural artifacts by artificially enhancing the
boundaries between microcrystallites, and, in so doing,
masking the growth increment boundaries. In order to be
consistent in defining growth increments, throughout this
study the boundary between adjacent growth increments shall
be defined as the interface between adjacent dark and light
laminae as observed in longitudinal thin sections. These
laminae vary from 3 - 6 micrometers in thickness and are
made up of semi-tabular to 'pluricupular' microcrystallites
of calcite arranged in overlapping or shingled layers. The
number of vertically stacked microcrystallites present
within each lamina can vary from as few as two to as many as
six, depending upon the thickness of the microcrystallites.
The thickness of the increments as well as the clarity of
their boundaries appears to be at least partly influenced by
the angle of intersection between the accretionary surface
and the plane of the thin section. Figure 8 provides an

illustration of this definition by means of a line overlay.

Grgwth Increment Analysis

Two different types of data can be collected in the
analysis of growth increments: one can count the number of
increments occurring within a specified sequence of growth,
or one can measure the thickness of successive growth

increments and then analyze the variations in thickness for

36

Figure 8. Delineation of wall laminae in Tabulipora
carbonaria. A, Longitudinal thin section, PSU
CH19A-p-PC-4003. B, Same photograph as in A, with overlay
added to show increment boundaries. Scale bar 8 0.05 mm.

37

 

38

repeated frequencies (Dolman, 1975; Rosenberg, 1982).
Attempting to measure the variation in thickness of growth
increments along a continuous sequence in I, g;;bgg;;1§
would be a difficult task, for even under the best of
preservation circumstances, the increments lack complete
lateral continuity and one must offset the line of
measurement, much as one might use lateral offsets in
measuring stratigraphic sections containing covered
intervals. Unfortunately, this may introduce spurious
variation in the sequence of wall measurements, because the
laminae do not maintain uniform thickness across their
lateral extent. They are usually thickest in the axial
region of the zooecial wall, and thin toward the zooecial
living chamber (Figure 8). Because of this, only counts of
increments were used for the growth rhythm analysis.

During data acquisition, it was noted that many of the
monilae contained growth disruptions or discontinuities
(Figure 9A). Most of these discontinuities appeared to
represent the initiation of a new monilar growth cycle
(marked by the appearance of the thin-walled phase of
growth), which ended prematurely. The bryozoan then resumed
secreting thick walls, incorporating the incipient monila
within a single wall segment. Some large monilae contain as
many as three or four of these internal discontinuities. If
the discontinuities within the monilae represented true
cycles of wall growth, they were being masked by

incorporation within the larger monilae. To test this

39

hypothesis, two separate sets of data based on each of these
different levels of growth were compiled (Appendix B).
Monilae which contained internal growth discontinuities were
divided into segments termed 25;; clugtggg, and counts of
increments within each wall cluster were tabulated, as well
as a separate count of monila increments (Figure 98). For
monilae lacking internal discontinuities, the number of wall
cluster increments is equivalent to that of monila
increments. The number of monilae that contain growth
discontinuities is not insignificant; a comparison of the
two data sets discloses 571 monilae versus 815 wall
clusters.

It is possible that an observer who knows ; priori the
expected outcome of a series of observations may~
unintentionally bias those observations so that although the
expected results are achieved, their veracity may be
questioned. Given the degree to which Igbglipora carbonaria
wall laminae are poorly defined and laterally discontinuous,
the possibility for such a systematic bias in growth
increment counts is very real. One way to eliminate this
problem would be to use an unbiased observer to collect the
data. In the study at hand, this was not possible, given
the large number of monilae that were counted. As an
alternative, one can select a subset from the study sample,
obtain counts with an unbiased observer, and then compare
the mean of these counts to the mean of the same subset as

counted by the "biased“ observer with a simple two-tailed

40

Figure 9. Intramonilar growth discontinuities. A, PSU
CH19A-p64-PC-4002. Single monila containing two growth
discontinuities (arrows). Note that distal microlaminae
overlap and enclose proximal (earlier) increments of growth.
Scale bar = 0.05 mm. B, illustration of the method of
dividing a monila into counts of monila increments and wall
cluster increments.

41

—wall cluster A2

— wall cluster A1

 

 

 

 

monila A

 

42

t-test (Davis, 1986).

Fifty-three monilae were selected for this purpose from
the total counted sample of 571. The monilae chosen were
judged to have the best definition and clarity of wall
laminae present in the entire sample. Each monila was
photographed and printed individually at a magnification of
640x. The photographs were given to an undergraduate
student, who was instructed in the procedure for counting
the number of wall laminae in each monila (see p. 35-37),
but was not told the number of increments that could be
expected. Wall clusters were not counted separately for
this test; the counts obtained represent the total number of
laminae within each monila. After the same monilae were
counted by this author, summary statistics were calculated
for each data set (Table 1).

Table 1. Summary statistics, test of increment count

reproducibility. For both samples, n B 53, i = mean number
of increments per monila, S I sample standard deviation.

 

Unbiased observer This author
3 = 30.1 R I 29.3
S = 7.5 S = 6.9

 

A two-tailed tetest for equality of means (Davis, 1986)
yielded a 3 value of 0.512, indicating no significant

difference between the means (0.50 > P > 0.10). Thus it may

be assumed that the counts obtained by this author were not

43

biased with respect to g priori knowledge.

The length of the synodic month (the amount of time
required for the moon to pass through identical phases)
today is 29.54 solar days. Tidal cycles repeat with a
periodicity equal to a lunar fortnight, which is one-half of
the synodic month, or 14.77 solar days. Based on a 2
millisecond per century slowing of the Earth’s rotational
rate due to lunar tidal friction (Rosenberg, 1982), the
length of the Early Permian synodic month would have been
approximately 30 days. Panella et al (1968) published
estimates of the mean number of days per synodic month for
Upper Pennsylvanian (30.16 days) and Middle Triassic (29.68
days) rocks based upon growth increment counts from several
species of bivalved molluscs. These estimates support the
assumption of a 30-day Early Permian synodic month. The
Early Permian lunar fortnightly tidal cycle thus would have
repeated every 15 days. If the wall laminae of I.
ggngnigig were secreted on a daily basis, one may
hypothesize that skeletal structures repeating with a
periodicity of 15 days may have been tidally influenced. It
seems reasonable to assume that the Wreford specimens of I.
carbonaria were affected by tidal cycles, based on
paleoecological interpretations of the water depth in which
the organisms lived (Cuffey, 1967; Newton, 1971).

Standard statistical tests may be used to compare the
mean increment number to some expected standard, which in

this case would be 15 days (Sokal & Rohlf, 1981). In order

44

to use the more powerful parametric t-test to determine if
the increment means are significantly different from the
expected value of 15, one must assume that the sample data
are normally distributed. Because data in the form of
counts generally do not follow a normal distribution, but
usually are distributed according to a Poisson or similar
distribution (Gill, 1978), some form of data transformation
is necessary in order to assume normality. One generally
used method is to transform the data by taking the square
root of each observation and performing the statistical
tests on the transformed data (Sokal & Rohlf, 1981). Thus,
for each specimen, separate counts of monila increments and
wall cluster increments were tabulated for all monilae with
countable wall laminae. These observations were then
transformed to square roots, and, since it was assumed that
all zoaria at a single sample locality would be influenced
by the same tidal cycle, the data were pooled with means
calculated by sample locality. Frequency distribution
histograms comparing monila increment counts to wall cluster
increment counts were compiled from the pooled data for each

sample locality; these are given in Appendix C.

RESULTS AND DISCUSSION

W

The results from the monila increment and the wall
cluster increment data are summarized respectively in Tables
1 and 2. Because the raw counts were transformed using a
square root transformation, the sample means listed are
"back-transformed'I values which are calculated by squaring
the mean of the transformed observations. Due to the
asymmetry introduced by the square root transformation, 95%
confidence intervals are given for the sample means in lieu
of standard errors (Sokal & Rohlf, 1981, p. 423); these
values are similarly “back-transformed“ by squaring the
limits of the transformed means.

Sample means based on counts of monila increments
(Table 1) show considerable variability, ranging from 15.3
to 27.2 increments per monila. Only four of the sample
means are not significantly different from the predicted
tidally-influenced value of 15 increments; these samples
consist of colonies in which the monilae were generally
small and lacking internal discontinuities. The small size
of these four samples necessitates the use of caution in

interpreting these results; the hypothesis that sequences of

45

46

Table 2. Summary of results from monila growth increment
data. Sample numbers are from Cuffey (1967). N = number of
zoaria in each sample; n - pooled number of monilae counted
for each sample; 2 8 pooled sample mean. Means and 952
confidence interval limits are back-transformed values (see
text for explanation).

 

 

95x C.I.
Sample N n x L u no: P-15
63026 1 6 16.7 13.3 20.4 0.4;P>o.2
GE18(17) 1 20 19.3 17.3 21.9 xxx
GE24D 1 16 21.4 13.2 24.3 xxx
35216 1 9 25.6 21.7 29.9 xxx
63306 7 104 21.3 20.2 23.3 xxx
33053 1 10 27.2 13.4 37.7 xx
MSO6E 3 26 20.9 13.1 23.9 xxx
CH19A 5 53 21.2 19.3 23.2 xxx
CH24D 6 59 25.4 22.7 23.3 xxx
CH35H 2 20 19.2 16.3 22.3 xx
ML03R 2 20 15.3 14.0 17.6 0-42P>0-2
GE07J 3 23 22.6 19.5 26.0 xxx
63133 7 72 13.2 16.5 19.9 xxx
GE16H 1 13 23.2 17.3 29.4 xx
GE17W 4 62 24.1 21.3 26.5 xxx
GROlI 2 26 19.5 16.5 22.3 3*
KAOlJ 2 17 15.3 13.4 17.3 0.92P>0-5
OSO4A 1 10 17.1 13.3 20.7 0.2;P>0.1
0.05;P>0.o1 x; 0.01gp>o.001 = x; Pgo.oo1

Table 3.

sample mean.

47

Summary of results from wall cluster growth
increment data.

pooled number of wall clusters for each sample; 2 = pooled

back-transformed values.

N = number of zoaria in each sample; n =

Means and 95% confidence interval limits are

 

 

95X C.I.
Sample N n R L U HO8 P'15
GEOZC 1 6 16.7 13.3 20.4 0.42P>0.2
6316(17) 1 27 14.4 12.6 16.4 0.92P)0.5
GEZ4D 1 22 13.2 11.2 15.3 0.11P)0.05
MSZlC 1 14 16.3 13.5 19.3 0.42P>O.Z
GE3OG 7 146 15.5 14.6 16.2 O.22P)0.1
MSOSE 1 17 16.7 15.1 16.4 *
MSOSE 3 35 15.7 14.4 17.1 0.4ZP>O.Z
CH19A 5 70 16.1 15.0 17.3 *
CH24D 6 96 16.2 15.5 16.6 tit
CH35H 2 24 16.2 14.5 17.9 0.2;?)0.1
ML03R 2 22 14.4 13.1 15.6 0.4;?)0.2
GE07J 3 43 15.0 13.6 16.2 P)0.9
GE13E 7 97 13.7 12.6 14.6 **
GE16H 1 24 12.6 11.2 14.5 *
6317” 4 105 14.4 13.6 15.3 0.21P>0.1
GR01I 2 33 15.6 14.0 17.4 0.5;P>O.4
KAOIJ 2 20 13.0 11.6 14.5 *
0304A 1 12 14.4 12.6 16.2 0.52P>0.4
0.05_>_P>o.o1 x; 0.01_>_P>0.001 . xx; $0.001 = xxx

48

monilae represent growth modulated according to a 15-day
fortnightly tidal cycle is not supported by these data.

A marked difference is demonstrated by the summary
based on counts of wall cluster increments (Table 2). The
variability among the sample means is much lower, resulting
in narrower 952 confidence intervals, with 12 of the 18
samples showing no significant difference from the predicted
value of 15 increments per cycle. Especially encouraging is
the fact that the two largest samples (in terms of pooled
number of wall clusters counted) show no significant
variation from the 15-increment cycle. Although two-thirds
of the samples based on counts of wall cluster increments
are in agreement with the predicted number of increments one
might expect to find in an organism adding daily increments
to its skeleton under the influence of a 15-day tidal cycle,
a direct link of causality has not been established.
However, the pattern is generally consistent with the
results reported from similar investigations of other
invertebrates (e.g., Hughes, 1985; Panella, 1976; Rosenberg,
1982).

Comparison of the two different data sets within
stratigraphically equivalent units is presented graphically;
Figure 10 represents the two samples from the lower
Threemile Limestone, Figure 11 the lower part of the lower
Havensville Shale, Figure 12 the upper part of the upper
Havensville Shale, and Figure 13 the lower part of the

middle Schroyer Limestone. Within stratigraphically

49

Figure 10. Mean increment counts for the two samples from
the lower Threemile Limestone. Means are back-transformed
values plotted with their 95% confidence interval limits.
The dotted line = 15 increments.

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51

Figure 11. Mean increment counts for the six samples from
the lower part of the lower Havensville Shale. Means are
back-transformed values plotted with their 95% confidence
interval limits. The dotted line 8 15 increments.

52

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53

Figure 12. Mean increment counts for the six samples from
the upper part of the upper Havensville Shale. Means are

back-transformed values plotted with their 95% confidence

interval limits. The dotted line = 15 increments.

54

ImmIO

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6:66 \mscOEOBE Id

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55

Figure 13. Mean increment counts for the three samples from
the lower part of the middle Schroyer Limestone. Means are
back-transformed values plotted with their 95% confidence
interval limits. The dotted line = 15 increments.

56

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57

equivalent units, the counts of wall cluster increments
consistently show stronger correlation to the predicted
15-increment cycle than do the counts of monila increments.
In addition, the 95% confidence interval limits of the six
samples for which the null hypothesis is rejected are quite
close to the 15-increment value; a less conservative
approach might result in acceptance of the null hypothesis
for most of these samples.

Rosenberg and Hughes (1983) compared samples of
brachiopods from deep and shallow water environments for
amplitude and frequency, distinctness, and lateral
continuity of their growth increments. In both living and
fossil forms, they found that specimens from shallow,
turbulent water had well-defined growth increments grouped
in “tidal” clusters, whereas those from deeper, quieter
water specimens were poorly defined. If Ighgiipggg
gggpgngzig modulated its growth according to a tidal cycle,
one might expect to find a similar depth-related pattern
expressed in its growth records.

Cuffey (1967) has described the paleogeographic setting
during Wreford deposition as one in which panhandle and
northern Texas, northern Oklahoma, Kansas, and southern
Nebraska formed a carbonate shelf, with tectonically active
areas to the west (central Colorado) and south (southern
Oklahoma). These tectonically active areas were of
sufficient relief to produce significant deposits of

terrigenous clastic sediments which grade laterally into the

58

Wreford carbonates. On the basis of the distribution
pattern of the various lithofacies into which the Wreford
rocks have been subdivided, Cuffey (1967) has described a
slight depth gradient extending from north to south across
the sample area, with a shoreline farther south of the
southernmost Oklahoma sampling localities (although its
precise location is not specified). Other paleogeographic
reconstructions (Hills, 1972; Peterson, 1980) indicate a
shoreline during the time of Wreford deposition running from
north-northeast to south-southwest, and located
approximately 130 km east of the boundary between Kay and
Osage counties in Oklahoma. Because the distribution of
samples is controlled by the outcrop pattern of Wreford
rocks, the depth gradient along a line connecting the
sampling localities must have been extremely slight, as the
trend of this line is only gently convergent to the
shoreline rather than perpendicular to it. Nevertheless,
samples from northern Kansas localities generally represent
deeper (or at least quieter), depositional settings than do
those from southern Kansas and northern Oklahoma. Thus if
samples can be obtained from a single stratigraphic interval
spanning all or part of this gradient (no matter how
slight), they should be examined for evidence that tests the
hypothesis of Rosenberg and Hughes (1983).

Only the samples from the lower part of the lower
Havensville Shale can be considered to show any geographic

variation across this depth gradient, although none of the

59

samples are from the shallower water algal limestone or
algal-molluscan limestone facies (Figure 14). An
examination of Figure 11 reveals no apparent depth-related
improvement in the recording of tidal cycles by I.
gaghggggig. In addition, there is no apparent qualitative
improvement in the clarity, distinctness, or lateral
continuity of growth increments in specimens from northern
localities versus those from southern localities. Certainly
a major contributing factor to this pattern must be that the
distribution of localities represents an incomplete sampling
of the depth gradient, since the shallowest environments are
unsampled. In addition, the depth gradient across the
region may have been so slight that no pattern of
improvement may have been evident even with a more complete
sampling design. A third explanation might be that colonies
of I. cggbgnarig were only mildly influenced by tidal cycles
during skeletal accretion, with the external effects of
changing water depth being damped out by internally
regulated growth factors. Whatever the case, the evidence
from the Wreford T. carbonaria specimens at present is
insufficient to either support or dispute the argument of
Rosenberg and Hughes (1983) regarding the effects of water

depth on invertebrate growth records.

60

Figure 14. Distribution of Tabulipora carbonaria samples
and lithofacies pattern from the lower part of the lower
Havensville Shale. Cuffey (1967) has assigned a water depth
of 0-15 m to the algal limestone facies, and 0-3 m to the
algal-molluscan limestone facies. Map based on Cuffey
(1967, Fig. 25) and Lutz-Garihan (1976).

 

61

      
     
     
  
   

     

GEIOH {III

III IIIIII"IIIII||||

”I”

Pi:

‘J’H: IIII

L 1100

KILOMETERS

     
 

  

—GR01I

 

“HHMHH = Calcareous shale

g = Algal limestone

 
  

Algal—molluscan
limestone

 

 

 

 

KAY ‘ OSAGE

 

62

lic t'ons of Tab 1' a carb nari rowth rh th

If wall clusters in I. carbonari; were initiated on a
15-day cycle, one might inquire as to the biological
significance of such a cycle. In living bryozoans, the most
comparable short term cycle would be the periodic
degeneration and regeneration of the polypides. In many
species, the regression products of the polypide gut form
small, dark spherical masses termed ”brown bodies” which
often are retained within the zooecial tube even after
regeneration of a new polypide (Gordon, 1977; Ryland, 1970).
Similar organic remnants reported in fossil trepostomes
(Boardman, 1971; Cumings & Galloway, 1915; Morrison &
Anstey, 1979), including one species of Iapglipora
(McKinney, 1969), have been interpreted as fossilized brown
bodies. This evidence suggests that polypide replacement
was a phenomenon of Paleozoic stenolaemates as well as
Recent ones.

Several of the Wreford T, carbogggig specimens contain
masses of material similar in size, composition, and
distribution to those described as brown bodies by the
aforementioned authors. They range in color from dark
reddish-brown to pale orange-brown; although irregular in
shape, they range from 0.13 - 0.20 mm across their largest
dimension, and are made up of many subspherical grains
between 0.003 - 0.016 mm in diameter. They most commonly

occur in the exozonal portion of the zooecial tubes, but are

63

present in endozonal zooecia as well in some specimens. If
these masses represent fossilized brown bodies, they are

indicative of polypide degeneration-regeneration cycles in

I, Qagpggggig. They also represent the first report of
their occurrence in Wreford I, ggggggggii, their absence

having been specifically noted previously (Cuffey, 1967, p.
53).

The best data available on the duration of polypide
regression cycles in living bryozoans is that published by
Gordon (1977, p. 340) for eight cheilostome species. The
average duration of regression for these eight species is
8.2 days, with a range from 2 to 17 days. Figures for
polypide longevity (the amount of time between periods of
regression), for five of these species are also provided by
Gordon (1977); these range from 6 to 72 days, with an
average longevity of 33.2 days.

If the data from I. gaggggglig are examined with
respect to these living bryozoans, some interesting
comparisons result. The grand mean for monila increments in
I. carbgngria is 20.8 laminae, and the grand mean for wall
clusters is 15.0 laminae. If these laminae were added to
the zoarial skeleton on a daily basis, then an average wall
cluster cycle is slightly less than half of the average
polypide longevity in living bryozoans. The average
duration for one complete polypide degeneration-regeneration
cycle in living bryozoans can be estimated by adding the

average polypide longevity to the average regression

64

duration; the result is 41.4 days. An average monila cycle
in 2..g§;Qgg§;;§ is slightly greater than half of a complete
polypide degeneration-regeneration cycle in living
bryozoans. Based on this comparison, it is possible to
infer that the average polypide longevity in 1. carbonaria
is represented by two wall clusters, and that a complete
polypide degeneration-regeneration cycle is the equivalent
of two monilae. The incremental difference between wall
clusters and monilae must then represent additional skeletal
accretion that took place during regression of the polypide.
If this is true, then skeletal growth in I, carpoggrig was
slightly decoupled from the polypide growth cycle, to the
extent that skeletal accretion continued even though a
functional polypide was absent.

This interpretation linking monila and wall cluster
cycles with polypide degeneration-regeneration cycles must
be regarded as somewhat speculative, considering the
significant morphologic and geologic age differences
separating T, carbonaria from living cheilostomes.
Nevertheless, the similarity in cycle durations is

interesting and warrants further study.

Wall Growth in Tabulipora carbogaria

Three general models of wall calcification have been
proposed for stenolaemate bryozoans (Boardman, 1983;

Boardman & Cheetham, 1969), based on the orientation of

65

laminae within the zooecial walls. In the first of these,
wall growth is accomplished by the simultaneous thickening
of single laminae added in succession at the oral ends of
the zooecial tubes. The laminae are convexly arched in the
oral direction, and are assumed to have been deposited by
and parallel to the zooecial lining epidermis. Each lamina
was essentially complete before the growth of the succeeding
lamina, thus the laminae boundaries represent both inception
and accretion surfaces (Boardman & Cheetham, 1969, Text-fig.
2a, p. 211).

The second model is similar to the first in that it
also produces orally convex laminae. Unlike the first,
however, in which growth is assumed to take place by simple
outward thickening of the laminae, growth in the second mode
occurs by edgewise accretion of either single or multiple
laminae. In this case, inception occurs at the zooecial
chamber lining, with edgewise growth of the laminae directed
orally toward the zooecial boundary (Boardman & Cheetham,
1969, Text-fig. 2c, p. 211). Because both of these growth
modes produce orally convex laminae in sequence parallel to
the presumed secretory epithelium, the laminae bounding
surfaces can be interpreted as growth lines.

The third conventional model is also characterized by
multiple edgewise growth of laminae; however, in this case
the inception surface and the laminae orientation are the
reverse of those in the second mode. Growth begins at the

zooecial boundary (the axial region of the wall), and is

directed orally and toward the zooecial chamber lining
(Boardman & Cheetham, 1969, Text-fig. 2b, p. 211). This
produces laminae that diverge orally; because of this, the
laminae boundaries are perpendicular to the growth surface,
and thus cannot be interpreted as growth lines.

gigglipora and most other Paleozoic stenolaemates by
convention have been assumed to fall under either the first
or second growth modes, because they possess compound
zooecial walls with orally convex laminae (Armstrong, 1970;
Boardman, 1983; Boardman & Cheetham, 1969; Brood, 1976;
Tavener-Smith & Williams, 1972). The vast majority of
post-Paleozoic stenolaemates, including all Recent forms,
are of the third type and possess orally divergent wall
laminae (Brood, 1976). Thus, no good modern analogues are
available to aid in deciphering the skeletal growth
processes of Tabulipora. The task is not insurmountable,
however, and is simply made more interesting by these
circumstances.

Careful observation and reconstruction of the nature of

wall lamination in I. Qgghggggig, specifically directed
toward resolving questions of rhythmic growth, has turned up
several features that are not in accordance with the
conventionally accepted models of growth. As a result, a
new model of wall calcification is herein proposed for
Tabulipora and related stenoporids.

SEM observation of the monilae in 1. carbonaria (Figure

6) reveals that the laminae are a mosaic of tabular

67

microcrystallites, generally in parallel alignment with the
presumed former position of the secreting epithelium. These
microcrystallites are arranged in a shingled fashion, with
zones of truncation commonly occurring along the flanks of
monilae. If the laminae grew by simple outward thickening
of single layers of microcrystallites, they should consist
of uniform layers without shingling or truncation (Boardman,
pers. comm. 1986). Since this is not observed, it seems
unlikely that this growth mode was utilized by Tabglipora.

Although the remaining conventional model (orally
directed edgewise growth of single or multiple laminae), can
account for the shingled and truncated microcrystallites, it
also predicts the development of a structural feature not
observed in Tabulipgrg or related stenoporids. That is, as
the laminae grow orally toward the zooecial boundary in the
center of the wall, a terminus or boundary line should be
produced, marking the junction of laminae growing from
opposite sides of the zooecial wall (Figure 15A). This
structure can be observed, for example, in Heterotr a,
Maplexgporg, and other trepostomes, but it does not occur in
Eagulipoga.

The new model of wall growth accomodates these
deficiencies in existing growth models. Wall laminae in
Tabulipora were secreted in an edgewise fashion, but with
growth directed aborally (Figure 158). New laminae are
initiated at or near the zooecial boundary, and grow

aborally outward as either single or multiple laminae. This

68

Figure 15. Comparison of skeletal morphologies produced by
oral versus aboral edgewise laminar growth. A, orally
directed growth, in which inception occurs along the
zooecial wall flanks and proceeds toward the zooecial
boundary, producing an axial terminus. B, aborally directed
growth, in which inception occurs at the zooecial boundary
and proceeds toward the flanks.

69

oral growth

(l l I l l m

1 2 3 4
A

aboral growth

70

model accounts for the shingled arrangement and truncation
of older layers by younger layers of microcrystallites, as
well as the absence of a zooecial boundary terminus in the
walls of Tabuli ra, gtgggpggg, and related genera.
Additional evidence to support this growth model comes from
the internal growth discontinuities used to subdivide the
monilae into wall clusters (Figure 9). Because they are
initiated in the axial regions of the monilae, it is
difficult to conceive of a simple mechanism to produce these
discontinuities, unless new growth begins at the zooecial
boundary. Confirmation of aborally directed edgewise growth
should be possible by examination of fracture sections of
laminae edges for the presence of chevron-shaped
microcrystallite growth surfaces, an approach that was
employed by Armstrong (1970). Repeated attempts to observe
such features in T. carbonaria have not succeeded. Perhaps
diagenesis has removed all traces of microcrystallite growth
from the Wreford specimens. Although edgewise laminar growth
was established by Armstrong (1970) in the related genus
Stengpora, the directional polarity of this growth was not.
Despite this lack of direct confirming evidence for aborally
directed edgewise growth, the previously cited
circumstantial evidence is robust, and is at least as strong
as the evidence that forms the basis for the conventional
growth models.

This new model of aborally directed edgewise laminar

growth is based on observations of the wall structure in

71

Tabulipgrg and the related genus Sggggpggg. Its extent of
applicability to other stenolaemates is unknown at this
time, although the model may have broad application among
Paleozoic taxa, particularly those in which wall laminae are

continuous across zooecial boundaries.

CONCLUSIONS

At the beginning of this study, several major questions
were identified with respect to various aspects of growth
cycles in Paleozoic stenolaemate bryozoans. The major
findings of this study are presented hereinafter in a
summary review of those questions.

(1) ”What is the structural nature of bryozoan growth
increments and how did they form'?‘I Zooecial wall laminae in
I§22112211,2§12223;1§_(and related stenoporid genera) are
made up of semi-tabular to pluricupular calcite
microcrystallites arranged in orally,convex overlapping
layers. The laminae vary from 3 to 6 micrometers in
thickness; they are thickest in the axial portion of the
wall and thin toward the zooecial interior. Each lamina can
contain as few as two to as many as six vertically stacked
microcrystallites. Shingling of microcrystallites and
truncation of older layers by younger layers of
microcrystallites are commonly observed patterns in the
walls of I. carbonaria.

The shingling and truncation of microcrystallite
layers, the absence of a zooecial boundary terminus, and the
initiation of wall cluster formation in the axial portion of

the zooecial walls of T. carbonaria are all characteristics

72

73

that cannot be accomodated by existing models of
stenolaemate wall growth. A new model of wall growth is
proposed for I. ggrhggggig and related stenoporid bryozoans
in which new laminae are inititiated at or near the zooecial
boundary and grow by aborally directed edgewise accretion of
either single or multiple laminae.

(2) “Is it possible to reliably define and measure
skeletal growth increments in fossil bryozoans?“ The
smallest increments of growth in I. 931293;;13 are defined
as adjacent dark and light laminae observed in longitudinal
thin sections of exozonal zooecial walls. Thin sections
afford better definition and reliability in counting and
measuring growth increments than either acetate peel
replicas or SEM images.

Although not as well defined as the growth increments
in clams and some other invertebrates, wall laminae in T.
Qgghgggzig are sufficiently distinct to assure
reproducibility in data acquisition. A test based on counts
of wall laminae in 53 monilae revealed no significant
difference in mean counts of increments per monila obtained
by two different observers.

(3) “Is it possible to quantitatively verify that
bryozoan growth increments are periodically repeated, and if
so, with what frequency?“ The monilae of T. carbonaria
contain discontinuities which define subunits of growth
herein termed wall clusters. Statistical analysis of

increment counts within monilae and wall clusters suggests

74

that wall clusters are the next higher order of incremental
growth above wall laminae. In 67% of tested samples, the
number of increments within individual wall clusters was not
significantly different (P50.05) from 15, the number
expected for shallow water marine invertebrates modulating
their growth under the influence of fortnightly tidal cycles
and accreting daily increments to their skeletons.

(4) “How useful are growth rhythm studies for
interpreting bryozoan paleobiology?" 'The average duration
of wall cluster cycles in I. ggrhggggig is slightly less
than half of the average polypide longevity of living
gymnolaemate bryozoans. In addition, the average duration
of monila cycles in I. ggghgngxi; is slightly greater than
half of the polypide degeneration-regeneration cycle in
living gymnolaemates. The average life-span of the
polypides in I. garbonaria may thus have been approximately
30 days, or the amount of time required for the accretion of
two wall clusters. Likewise, a complete polypide
degeneration-regeneration cycle in 1. carbonaria can be
estimated to have been approximately 41.6 days in duration,
or the amount of time required for the accretion of two
monilae. These estimates, although speculative, provide
additional insight into questions of polypide-skeletal
relationships in Paleozoic stenolaemates, and invite

additional research.

APPEN DI CES

APPENDIX A

The following is a complete listing of etching and
staining solutions tested during the development of specimen
preparation techniques used in this study. Notes on
procedure are given for each solution. In order to ensure
continuous contact of the specimen surface with fresh
solution during immersion, each solution was agitated by
stirring the solution with a magnetic stirrer. All tests
were conducted at normal room temperature (21° C) unless

otherwise indicated.

E!°I° 5 J !’

1. 8:100 aqueous dilution of concentrated (38%)
hydrochloric acid (Wolf, Easton & Warne, 1967): Test
specimens were immersed for intervals of 5 and 60

seconds.

2. 8:500 aqueous dilution of concentrated hydrochloric

acid: Tested with immersions of 1 and 10 seconds.

3. 1.0% aqueous hydrochloric acid: Tested for immersion

intervals of 5 and 10 seconds.

4. 1:500 aqueous dilution of concentrated hydrochloric

acid: Tested at l-minute increments of immersion times

75

10.

11.

76

ranging from 1 to 14 minutes.

1:1000 aqueous dilution of concentrated hydrochloric
acid: Tested at 30-second increments ranging from 30

seconds to 10 minutes, and at 1-minute increments from

10 to 19 minutes.

1.0% acetic acid: Test immersions of 5 and 10 seconds.

1:1000 aqueous dilution of glacial acetic acid: Tested

at 1-minute increments ranging from 1 to 4 minutes.

1:40 aqueous dilution of concentrated (88%) formic acid:

Test immersions of 15, 30, 60, and 120 seconds.

1:100 aqueous dilution of concentrated formic acid:

Test immersions of 5 and 10 seconds.

1:1000 aqueous dilution of concentrated formic acid:

Test immersions of 60 and 70 seconds; also tested at

1-minute increments ranging from 1 to 15 minutes.

0.5% aqueous solution of disodium ethylenediamine
tetraacetate (EDTA): Tested at 10-minute increments
ranging from 20 to 60 minutes, and at 20-minute

increments from 60 to 120 minutes.

77

12. 1.0% aqueous EDTA: Test immersions of 15, 20, 30, 40,

55, and 85 minutes.

13. 1.5% aqueous EDTA: Test immersions of 5, 10, 15, and

20 minutes, at 600 C.

14. 9.0% aqueous EDTA (Glover, 1961): Test immersions of

30 and 60 seconds.

15. 2.0% aqueous ammonium chloride (NH Cl) (Honjo,

4
1963): Tested at 1-minute increments ranging from 1 to
10 minutes, and at 5-minute increments from 10 to 20

minutes.

mm

Although hydrochloric acid (HCl) is not commonly used
for etching bryozoans, various concentrations of this acid
were tested on the basis of results reported by Wolf et al
(1967). These authors reported that etching with HCl
produced enhanced clarity in distinguishing compositional
differences in texture and structure. To a certain extent,
this was true for the bryozoans tested, particularly at
extremely low concentrations. Peels made from HCl-etched
bryozoans are characterized by sharply-defined crystal
boundaries producing uniformly good contrast over the slide.

Unfortunately, the strong activity of HCl produces

76

effervescence and other damaging effects that obscures the
structure of the microcrystallites of the zooecial wall
laminae. The depth of etch (affecting the relief and,
hence, the contrast of the peel), is extreme in HCl-treated
specimens, even at very low concentrations and short
immersion times. For these reasons, HCl appears to be a
poor choice for studying the growth of wall laminae in
bryozoans.

Acetic and formic acid have both been conventionally
used in acetate peel preparations of bryozoans (Boardman &
Utgaard, 1964; Nye et al, 1972). At the concentrations
tested, both produce a gentle reaction, with no visible
effervescence. The reaction of both of these acids with the
bryozoan skeletal calcium carbonate is apparently less
uniform than that of HCl (Wolf et al, 1967), producing a
rougher surface texture with concomitant loss of boundary
clarity. The rate of etching of these acids also appears to
vary with respect to crystal size, with the
microcrystallites of the wall laminae being attacked more
readily than the larger crystals of diagenetic calcite
infilling the zooecial tubes. This produces a problematic
contrast gradient - peels in which the etching time is kept
to a minimum in order to preserve microstructural detail
lack sufficient contrast for general observation and
photomicrography at lower magnifications. Conversely, peels
with sufficient overall contrast are over-etched at the

microstructural level and thus useless for observing wall

79

laminae.

Glover (1961), Morrison & Anstey (1979), and Rosenberg
(1982) reported the use of ethylenediamine tetraacetate
(EDTA) for etching carbonate specimens. The advantage of
using low-strength solutions of EDTA with long immersion
intervals is that the complexing rate of the calcium ions by
the EDTA can be greatly reduced, resulting in little or no
damage to the skeletal microstructure (Rosenberg, pers.
comm. 1983). The principal disadvantage, of course, is the
amount of immersion time required to produce an etch of
sufficient quality. Rosenberg (1982) reported good results
on Ordovician brachiopods using an 18 minute immersion in 1%
EDTA. Immersion durations of up to an hour in 0.5% EDTA
have also yielded good results with brachiopods (Hughes,
Rosenberg, personal communications). Unfortunately, this
does not appear to be true for bryozoans. Experiments in
which several different dilutions of EDTA were tested on a
number of different bryozoan taxa produced inconclusive
results. The uniformity of depth of etch, peel contrast,
and microstructural integrity varied widely across taxa,
specimens, and, in several instances, within a single
specimen. Attempts to repeat experiments using identical
solution strengths and immersion times usually were
unsuccessful, hampering efforts to establish a preparation
protocol.

Honjo (1963) reported the use of a 2% aqueous solution

of ammonium chloride for overcoming the problems of variable

80

pH and effervescent damage effects associated with acid
solution etching. Tests of this solution on a number of
different bryozoan taxa produced the best results of all
tested etching solutions. Results are somewhat variable
across taxa, but generally an immersion time of 5 to 7
minutes produced peels of uniform depth, adequate contrast,
and excellent preservation of wall laminae
microcrystallites. One additional advantage to using
ammonium chloride is that it is self-buffering, maintaining
a fairly constant pH during the etching process, allowing
one to use a single batch to etch a large number of

specimens without altering the immersion times over the run.

Staiging solgtiogg

1. Trypan blue - 0.1 gm trypan blue dissolved in 100 ml of

1:40 aqueous formic acid.

2. Methylene blue 1 - dissolve 1.0 gm of methylene blue
chloride in 100 ml distilled water; to this solution,

add 5 drops glacial acetic acid (Clark, 1973).

3. Methylene blue 2 - dissolve 0.5 gm of methylene blue
chloride in 100 ml distilled water; add 5 drops glacial

acetic acid.

4. Methylene blue 3 - dissolve 1.0 gm of methylene blue

10.

11.

12.

61

chloride in 100 ml of 1.25% aqueous EDTA.

Alizarine

100 ml of

Alizarine

100 ml of

Malachite

in 100 ml

Malachite

in 100 ml

Toluidine
100 ml of

Safranin

red S 1 - dissolve 0.1 gm of alizarine red in

0.2% hydrochloric acid (Friedman, 1959).

red S 2 - dissolve 0.5 gm of alizarine red in

1.25% aqueous EDTA.

green 1 - dissolve 1.0 gm of malachite green

of 2.0% aqueous EDTA.

green 2 - dissolve 2.0 gm of malachite green

distilled water.

blue - dissolve 1.0 gm of toluidine blue in

2.5% aqueous EDTA.

0 - dissolve 1.0 gm of safranin O in 100 ml

distilled water.

Orange G

- dissolve 1.0 gm of orange G in 100 ml

distilled water.

Flemmings triple stain - 1% safranin O in 50% ethanol,

1% aqueous crystal violet, and 1% aqueous orange G (Nye

et al, 1372).

62

Results

Organic membranes have been suggested as having acted
as templates for the seeding of sheets of bladelike crystals
of calcite during accretion of the bryozoan skeleton
(Tavener-Smith & Williams, 1972). If remnants of these
membranes were preserved along growth increment interfaces,
and if they could be stained to enhance their appearance,
they would be useful in delineating and improving the
clarity of growth increments within zooecial wall laminae.
Morrison and Anstey (1979) reported partial success with
toluidine blue and safranin-O in attempts to stain
fossilized “brown bodies“ in Ordovician trepostomes. Soft
tissues in living taxa can be stained using methylene blue
hydrochloride, toluidine blue, and Flemmings triple stain
(Nye et al, 1972).

Tests of various stains were conducted on specimens of
several different fossil bryozoan taxa to determine if
traces of the organic components of the skeletal walls were
preserved during fossilization. These tests were largely
unsuccessful; if organic membranes were present during the
secretion of calcium carbonate, they were either not
preserved during fossilization, or were preserved in such
small amounts as to remain undetectable via this means.
Limited enhancement of growth increments was obtained with

the methylene blue chloride and malachite green

preparations; however, this enhancement occurred only by

63

accumulation of the staining agent in low sites of surface

relief produced by prior or concurrent etching of the
specimen in acid solution. While this collection of stain
by surface relief may seem fortuitously advantageous, it is
negated by the fact that the stains are also soluble in
acetone, and are essentially washed off the specimen during

the peeling process.

APPENDIX B

The following is a complete listing of the growth
increment data obtained from each specimen of Tabulipgga
‘ggggggggig. Each monila is indexed alphabetically for each
specimen; wall clusters are indexed numerically within
monilae. The specimen numbering system used here is the
same as that used in previously published studies of Wreford
bryozoans (see Cuffey, 1967; Newton, 1971; Lutz-Garihan,
1976): the first four characters designate a locality, with
the following letter(s) or number(s) referring to a specific
bed within the exposure at that locality. This is followed
by a hyphen, which separates the locality information from a
series of letter symbols which refer to various collection
methods and/or sorting procedures: fl I sample picked from
float within the bed, fp 8 float sample picked from the
surface of the bed, p a sample picked in place from the
surface of the bed, bf I bulk fresh sample, bsf = a mixture
of surface and bulk fresh, PC 8 sample picked completely for
bryozoans, PR = sample picked randomly for bryozoans, and PL
= picked for large bryozoans only. The final number is a
unique identifier assigned to each individual specimen.

Detailed geographic information for each sample
locality has been published elsewhere and will not be
repeated here (see Cuffey, 1967; Newton, 1971; and

Lutz-Garihan, 1976). As an example, GEOZC-fl-p-PC-4021

refers to specimen number 4021 from locality 02 in Geary

84

65

County, Kansas. The specimen was float picked from the
surface of bed C at locality 02, and the surface was picked
completely for bryozoans. All specimens, thin sections, and
peels are housed in the Paleobryozoological Research
Collection, Department of Geosciences of the Pennsylvania
State University.

In the following tables, these column headings are
used: M I monila index, which may be a single letter
indicating that the counts came from one monila, or may be
two letters separated by a hyphen (e.g., B-D), indicating
the end member monilae in a growth sequence within a single
wall segment, with the first letter representing the
proximal monila and the second letter the distal monila in
the sequence; MI I total number of increments within the
monila; NC I wall cluster, indexed numerically within the
alphabetic index of the containing monila; WCI = number of
increments within the wall cluster. Monilae which lack
internal growth discontinuities contain by definition a
single wall cluster, and in these instances the number of

monila increments and wall cluster increments will be

identical.

Table 4. Schroyer Limestone (Ws)

W393

86

 

GEOZC-fl-p-PC-4021

GElB(17)-bf—PR-4003

GE24D-bf-PR-4002

samples.
M, M; WC. W9;
A-B
A 14 A1 14
B 15 Bl 15
C-D
C 23 C1 23
D 16 D1 16
E-F
E 14 El 14
F 19 F1 19
A 25 A1 13
A2 6
A3 6
B 27 81 17
82 10
C 24 C1 16
C2 8
D-E
D 15 D1 15
E 17 E1 17
F-H
F 16 F1 16
G 16 61 16
H 18 H1 18
I 19 I1 19
J-M
J 19 01 19
K 16 K1 16
L 22 L1 6
L2 16
M 16 M1 16
N 27 N1 11
N2 16
O 22 01 22
P-R
P 16 P1 16
Q 20 01 20
R 15 R1 15
S-T
S 20 81 20
T 30 T1 14
T2 16
A-B
A 25 A1 15
A2 10
B 18 Bl 7
82 11
C-E
C 19 C1 19

Table 4, cont.

c' mbe

67

 

MSZlC-bf-PR-4003

M 31 we 131
D 20 D1 20
E 13 E1 13
F-I
F 14 F1 14
G 24 61 13
62 11
H 14 H1 14
I 16 I1 18
J-L
J 27 31 14
J2 13
K 16 K1 16
L 19 L1 19
M-P
M 16 M1 16
N 16 N1 12
N2 4
O 23 01 17
02 6
P 17 P1 17
A-B
A 30 A1 18
A2 12
B 30 Bl 13
62 17
C-F
C 17 Cl 17
D 25 D1 25
E 22 E1 22
F 28 F1 15
F2 13
G-I
G 20 61 20
H 31 H1 7
H2 24
I 30 I1 15
12 15

Table 5. Upper Havensville Shale (uuWh) samples.

W

 

GE3OG-bf-PR-4003

GEBOG-bf-PR-4004

M MI; W91 W
A-C
A 30 A1 18
A2 12
8 25 81 16
82 9
C 22 C1 22
D-I
D 35 D1 18
D2 17
E 21 E1 21
F 24 F1 14
F2 10
G 24 61 24
H 27 H1 18
H2 9
I 35 I1 16
IZ 19
J-N
J 8 31 8
K 40 K1 22
K2 18
L 17 L1 17
M 28 M1 15
M2 13
N 20 N1 20
O-R
O 29 01 16
02 13
P 36 P1 19
P2 17
Q 10 01 10
R 30 R1 16
R2 14
S-W
S 35 Si 18
82 17
T 12 T1 12
U 35 U1 17
U2 18
V 32 V1 17
V2 15
W 38 W1 12
W2 11
W3 15
A-G
A 30 A1 15
A2 15
B 24 61 13
62 11

Table 5, cont.

finesiees_esshsre

89

 

GE3OG-bf-PR-4013

GE3OG-bf-PR-4022

GE3OG-bf-PR-4024

M MI, BE. 891
c 23 c1 13
C2 10
0 15 01 15
3 11 31 11
3 21 31 21
6 13 61 13
A-B
A 23 A1 23
3 41 31 22
32 19
C-E
c 31 C1 19
C2 12
D 19 01 19
3 36 31 19
32 17
F-G
3 21 31 21
6 20 61 20
A-B
A 24 A1 24
3 12 31 12
C-D
c 24 c1 13
62 11
0 14 01 14
3-6
3 15 31 15
3 15 31 15
G 22 61 22
A-C
A 13 11 13
B 24 31 24
c 11 c1 11
0-3
0 23 D1 23
3 22 31 22
F-H
3 20 31 20
G 24 61 24
H 15 H1 15
I-K
I 13 11 13
J 24 51 24
K 20 K1 20
L-N
L 21 L1 21

Table 5, cont.

W

90

 

GE3OG-bf-PR-4031

GE3OG-bf-PR-4036

M Ml "Ce £91
M 17 M1 17
N 17 N1 17
O-P
O 20 01 20
P 16 P1 16
Q-R
Q 20 01 20
R 24 R1 24
A-C
A 24 A1 12
A2 12
6 24 B1 14
82 10
C 33 C1 12
C2 21
D-F
D 23 D1 23
E 16 E1 16
F 16 F1 16
G-K
6 36 61 20
62 16
H 26 H1 14
H2 12
I 16 I1 16
J 15 31 15
K 19 K1 19
L-O
L 32 L1 21
L2 11
M 21 M1 21
N 6 N1 8
O 34 01 18
02 16
A-B
A 26 A1 14
A2 14
B 33 61 14
82 19
C-E
C 13 C1 13
D 28 D1 15
D2 13
E 31 E1 18
E2 13
F-M
F 21 F1 13
F2 8

Table 5, cont.

53323393_323291e

91

 

MSOSE-fl-p-PC-4002

3, 3; 39_1. 39;
6 19 61 19
3 16 31 16
I 23 I1 13
12 10
J 6 01 6
K 19 K1 19
L 12 L1 12
3 25 M1 12
32 13
N-T
3 16 31 3
32 3
o 17 01 17
P 34 P1 14
32 20
0 10 01 10
3 16 31 16
s 15 31 15
T 21 T1 12
T2 9
u-x
u 19 01 19
v 21 V1 21
3 36 31 12
32 14
33 10
x 29 x1 19
32 10
Y-AA
v 23 v1 16
Y2 12
z 11 21 11
AA 15 311 15
A 15 A1 15
B-C
3 35 31 16
32 19
c 26 c1 12
62 14
0 64 01 22
02 12
03 14
04 16
3 39 31 22
32 17
3-1
3 23 31 23
6 33 G1 16
62 17

Table 5, cont.

§eseissn_snshere

 

MSOSE-fl-p-PC-4017

MSOSE-fl-p-PC-4021

MSOEE-fl-p-PC-4031

CH19A-p64-PC-4001

3’ 0110

I
O

3 311 3g 3g;
3 17 H1 17
I 16 I1 16
J 19 01 19
A 3
A 14 A1 14
3 17 31 17
c F
c 46 c1 24
C2 22
0 32 01 16
02 16
3 16 31 16
3 13 31 13
A
A 17 A1 17
3 14 31 14
c 35 c1 16
c2 19
A-C
A 23 A1 17
A2 11
3 30 31 17
32 13
c 13 c1 12
62 6
0-3
0 20 01 20
3 17 31 17
3 13 F1 13
6 19 61 19
3 25 31 14
32 11
I 16 I1 16
J 13 J1 13
K
K 20 K1 20
L 12 L1 12
3 23 M1 13
32 10
N-Q
3 23 N1 14
32 14
19 01 19
17 P1 17
22 01 22

Table 5, cont.

im m e

93

 

CH19A-p64-PC-4002

CH19A-p-PC-4002

M M1 39 £91
A 16 A1 16
B 24 81 24
C 20 C1 20
D-G
D 24 D1 16
D2 8
E 19 E1 19
F 6 F1 6
G 15 61 15
A-C
A 22 A1 22
8 19 81 19
C 37 C1 19
C2 18
D-G
D 14 D1 14
E 16 E1 13
E2 5
F 16 F1 16
6 24 61 15
62 9
H-J
H 15 H1 15
I 23 11 23
J 16 J1 16
K-P
K 31 K1 16
K2 15
L 16 L1 16
M 12 M1 12
N 18 N1 16
O 32 Ol 12
02 7
03 13
P 35 P1 16
P2 19
A-B
A 31 A1 17
A2 14
B 14 61 14
C-D
C 16 Cl 18
D 19 D1 6
D2 13
E-F
E 22 E1 22
F 17 F1 17

Table 5, cont.

Specimen pgmbgr

94

 

CH19A-p-PC-4003

CH19A-p64-PC-4009

CH24D-fl-p-PC-4004

M 11L "L I191
A-D
A 26 A1 26
8 17 81 17
C 26 C1 26
D 30 D1 16
D2 12
E-I
E 16 E1 16
F 25 F1 25
G 24 61 24
H 17 H1 17
I 18 I1 18
J-L
J 16 J1 16
K 14 K1 14
L 21 L1 21
M-O
M 16 M1 16
N 16 N1 16
O 21 01 21
P-Q
P 24 P1 24
Q 34 01 16
02 18
A-8
A 14 A1 14
8 26 81 15
82 13
C-D
C 32 C1 14
C2 18
D 35 D1 16
D2 19
E-G
E 17 E1 17
F 33 F1 17
F2 16
G 34 61 16
G2 18
A-D
A 18 Al 18
8 24 81 24
C 15 C1 15
D 13 D1 13
E-G
E 21 E1 21
F 23 F1 23
G 42 G1 16

Table 5, cont.

Speciggn nugbg;

95

 

CH24D-fl-p-PC-4005

CH24D-fl-p-PC-4009

CH24D-fl-p-PC-4025

M, 13;. 39 391
62 13
63 13
A 44 A1 16
A2 16
A3 12
3-6
3 32 31 17
32 15
c 24 c1 12
62 12
A-c
A 16 A1 16
3 25 31 12
82 13
c 23 c1 12
62 16
0-3
0 13 01 13
3 11 31 11
3 35 31 17
32 13
G 22 61 22
3-1
3 13 31 13
I 13 11 13
A-B
A 27 A1 14
A2 13
3 20 31 20
C-F
c 35 c1 13
62 17
0 25 01 15
02 1o
3 30 31 15
32 15
F 27 F1 14
32 13
G-J
6 39 61 13
62 21
3 15 31 15
I 34 11 13
12 16
J 20 J1 20
K-L
K 16 K1 16

Table 5, cont.

3 cim

 

CH24D-fl-p-PC-4015

CH24D-fl-p-PC-4024

31 M;, mg mg;
L 30 L1 15
L2 15
A-c
A 40 A1 23
A2 17
3 37 31 19
32 13
c 63 c1 15
C2 16
C3 16
64 21
D-G
3 19 31 13
3 33 31 17
32 16
3 1o 31 1o
6 45 61 17
62 16
63 12
H-K
H 19 H1 19
I 14 I1 14
J 24 31 24
K 34 K1 17
32 17
L 37 L1 14
L2 11
L3 12
M-N
M 42 M1 20
32 22
u 39 N1 19
32 20
A-3
A 21 A1 21
3 16 31 16
c 45 c1 17
62 17
C3 11
3 35 D1 13
32 17
3 17 31 17
F-K
F 17 31 17
6 32 61 19
62 13
H 18 H1 18
I 15 11 15

Table 5, cont.

C.

CH35H-f1-1

CHSSH-fl-Z

be

97

 

M 9M;39 HQ 39;
J 15 J1 15
K 14 K1 14
L-N
L 19 L1 19
M 46 M1 17
M2 16
M3 13
M 30 M1 16
32 14
A-3
A 13 A1 13
3 21 31 21
c 23 c1 23
3-3
D 22 D1 22
3 9 31 9
3 21 31 21
A-3
A 35 A1 22
A2 13
3 31 31 15
32 16
C-D
c 23 c1 15
62 13
D 19 D1 19
3-6
3 19 31 19
3 16 31 16
6 13 61 13
H-K
H 14 H1 14
I 16 I1 16
J 24 J1 12
J2 12
K 20 K1 20
L-N
L 20 L1 20
M 10 M1 10
N 15 N1 15

Table 6. Lower Havensville Shaln (1133) samples.

5322;333_3332239

SB

 

MLOBR-Sd-bf—PR-4005

MLOSR-Sd-bf-PR-4017

GEO7J(baSE)-b5f-PL-4003

1M Mli 391 M
A-c ‘
A 17 A1 17
3 22 31 22
c 27 c1 15
62 12
A 15 A1 15
3 13 31 13
C-D
c 14 c1 14
D 16 31 16
3-6
3 15 31 15
3 14 31 14
6 21 61 11
62 1o
H-I
H 15 H1 15
I 16 I1 16
J-M
J 13 J1 13
K 12 K1 12
L 16 L1 16
M 11 M1 11
M 14 M1 14
O-Q
o 13 01 13
P 9 P1 9
Q 17 01 17
A-3
A 27 A1 14
A2 13
3 14 31 14
6—3
C 29 C1 12
C2 17
D 22 31 22
3 34 31 20
32 14
3-3
3 22 31 22
6 55 61 9
62 14
63 15
64 17
H 23 H1 23
I-J
I 23 I1 14
I2 14

Table 6, cont.

Speggmgg nugbg;

99

 

GEO7J(base)-bsf-PL-4004

GEO7J(b350)-bsf-PL-4005

GElaE-bf-PL-4003

GElBE-bsf-PR-4001

M ng, wg Mg;
J 16 J1 16
A-c
A 25 A1 14
A2 11
3 13 31 13
6 43 61 20
62 12
63 11
3-3
3 31 31 16
32 15
3 19 31 19
3 22 31 22
6-I
6 23 61 13
62 10
H 17 H1 17
I 30 I1 15
12 15
A-6
A 14 A1 14
3 22 31 11
32 11
6 17 61 17
3-6
3 23 31 23
3 21 31 21
3 13 31 13
6 19 61 11
62 3
H-I
H 19 H1 19
I 14 I1 14
A 53 A1 22
A2 17
A3 14
3 33 31 13
32 20
6 50 C1 15
62 13
63 17
3 30 31 12
32 13
3 17 31 17
A-c
A 15 A1 15

Table 6, cont.

§392£393_33333£

100

 

GElSE-bsf-PR-40ll

GEl3E-bsf—PR-4014

M M; 3; Mg;
3 20 31 13
32 7
6 14 61 14
3-3
3 17 31 17
3 13 31 13
3 16 31 12
32 4
A-6
A 23 A1 20
3 12 31 12
6 12 61 12
3 13 31 13
3 14 31 14
3 16 31 16
6 22 61 11
62 11
H-I
H 21 H1 11
32 13
I 20 I1 20
J 13 J1 13
K-o
K 11 K1 11
L 10 L1 13
M 16 M1 16
M 13 M1 13
o 12 31 12
P-R
P 17 P1 17
Q 14 61 14
3 17 R1 17
S-T
9 13 91 13
T 20 T1 12
32 3
A-3
A 16 A1 16
3 20 31 12
32 3
6 23 61 23
3 23 31 13
32 7
33 3
3-3
3 19 31 15
32 4
3 17 31 17

Table 6, cent.

8 1m mb

101

 

GE13E-bsf—PR-4017

GE13E-bsf-PR-4019

M NJ ”9 ”5.1
G 20 81 20
H 10 H1 10
I-L
I 22 11 22
J 18 31 18
K 19 K1 10
K2 9
L 23 L1 15
L2 8
“-0
N 30 M1 17
M2 13
N 21 N1 21
O 28 01 14
02 7
03 7
A-B
A 18 A1 18
8 21 81 15
82 6
C-D
C 13 C1 13
D 17 D1 17
E-I
E 19 E1 19
F 17 F1 17
G 16 61 16
H 17 H1 17
I 17 11 17
J-O
J 21 31 21
K 14 K1 14
L 10 L1 10
M 14 M1 14
N 8 N1 8
O 20 01 20
A-C
A 32 A1 14
A2 18
8 18 81 18
C 20 C1 20
D-G
D 14 D1 14
E 30 E1 16
E2 14
F 17 F1 17
G 27 61 13
82 14

Table 6, cont.

§3993323_99399£9

102

 

GElSH-bsf—PL-4005

GE17N-bsf—PL-4004

M 3111* W93 36;
A-3
A 24 A1 15
A2 9
3 13 31 13
6 25 61 11
62 14
3 14 31 14
3 16 31 16
3-J
3 15 31 15
6 25 61 15
62 1o
3 47 31 17
32 21
33 9
I 15 I1 15
J 25 J1 12
J2 13
K-M
K 33 K1 13
K2 7
K3 13
L 25 L1 1o
32 5
L3 10
M 32 M1 14
32 13
A-6
A 13 A1 9
A2 9
3 20 31 12
32 3
6 16 61 16
3-3
3 23 31 19
32 9
3 21 31 21
3 34 31 17
32 17
6—J
6 22 61 22
3 19 31 19
I 26 I1 13
12 13
J 21 J1 21
K—M
K 22 K1 22
L 23 L1 13
L2 7

103

Table 6, cont.

 

§2991393_993393_, M M; "9: "91
L3 3
M 19 MI 19
N-P
M 25 MI 16
32 9
3 15 31 15
P 21 P1 21
GEl7N-bf—PL-4003 A-3
A 16 A1 16
3 9 31 9
c 13 61 13
3 26 31 19
32 7
3 22 31 22
GEl7N-bsf-PL-4013 A-6
A 23 A1 20
3 46 31 1o
32 19
33 17
3 13 31 13
3-3
3 35 31 15
32 23
3 20 31 20
6 39 61 15
62 14
63 1o
3 25 31 6
32 1o
33 9
I-J
I 23 I1 13
I2 13
J 32 J1 15
J2 17
K-M
K 57 K1 9
K2 15
K3 14
K4 19
L 25 L1 13
L2 12
M 15 M1 15
3 45 31 14
32 12
33 19
o 37 31 12
oz 14

Table 6, cont.

Specimeg gumbe;

104

 

GE17N-bsf-PL-4014

M M;;f 36 36;
33 11
P-Q
P 23 P1 12
32 16
Q 46 Q1 17
02 13
03 11
3 33 31 19
32 14
S-T
3 45 91 11
32 13
93 21
T 29 31 16
32 13
u—v
u 36 U1 17
32 19
v 23 v1 15
V2 13
3-x
3 44 31 15
32 16
33 13
x 33 x1 16
32 14
Y-Z
Y 24 Y1 24
z 19 21 19
A-3
A 31 A1 23
A2 3
3 19 31 19
6 20 61 20
3-3
3 19 31 14
32 5
3 13 31 13
3 20 31 12
32 3
G-I
6 15 61 15
3 14 31 14
I 16 I1 16
J-L
J 19 J1 19
K 16 K1 16
L 21 L1 21
M-o

Table 6, cont.

§2991333.33399141

105

 

GROlI-p-PC-4001

GROlI-p-PC-4006

M AM: 36 361
M 11 M1 11
M 27 31 23
32 7
3 27 31 11
32 16
A-c
A 19 A1 14
A2 5
3 13 31 13
6 21 61 13
62 11
A-3
A 53 A1 26
A2 27
3 23 31 23
6 23 61 23
3 24 31 24
3 11 31 11
3 13 31 13
6-L
6 16 61 16
3 12 31 12
I 14 Ii 14
J 13 J1 13
K 16 K1 16
L 17 L1 17
M 27 M1 16
M2 11
N-P
3 32 31 16
32 16
3 16 31 16
F 14 P1 14
3-3
3 16 31 16
3 13 R1 13
9-3
8 15 51 15
T 17 T1 17
U 28 U1 16
32 12
V-N
V 32 V1 17
v2 15
N 12 W1 12

Table 7. Lower Threemile Limestone (lWT) samples.

Spgcimeg gumber

 

106

 

KAOlJ-fp-4501

KA01J-fp-4503

OSO4A-p+fp-4501

M 3119 "93 36I
A-D
A 15 A1 15
3 27 31 14
32 13
6 23 61 12
62 3
3 14 31 14
3-3
3 15 31 15
3 14 31 14
6 19 61 19
3 14 31 14
I-J
I 16 II 16
J 17 JI 17
A-3
A 13 A1 13
3 13 31 13
6 13 61 13
3 13 31 13
3-6
3 19 31 13
32 6
3 14 31 14
6 I4 61 14
A-3
A 16 A1 16
3 13 31 13
6-3
6 15 61 15
3 26 31 14
32 12
3 13 31 13
3-J
3 17 31 17
6 25 61 15
62 13
3 13 31 13
I 13 II 13
J 16 J1 16

APPENDIX C

On the following pages are histograms comparing monila
increment counts to wall cluster increment counts for each
of the 18 Nreford Megacyclothem sampling localities. Pooled
counts for all specimens from each locality are represented
by black bars for counts of increments per monila, and by

white bars for counts of increments per wall cluster.

107

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