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Master's Theses Graduate College

8-1978

Paleoecology of the Spiriferid Brachiopods of the Silica Shale Formation (Middle Devonian), S.E. Michigan and N.W. Ohio

Darioush T. Ghahremani

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Recommended Citation Ghahremani, Darioush T., "Paleoecology of the Spiriferid Brachiopods of the Silica Shale Formation (Middle Devonian), S.E. Michigan and N.W. Ohio" (1978). Master's Theses. 2093. https://scholarworks.wmich.edu/masters_theses/2093

This Masters Thesis-Open Access is brought to you for free and open access by the Graduate College at ScholarWorks at WMU. It has been accepted for inclusion in Master's Theses by an authorized administrator of ScholarWorks at WMU. For more information, please contact [email protected]. PALEOECOLDGY GF THE 5PIRIFERID BRACHIDPODS OF THE SILICA SHALE FORMATION (MIDDLE DEVONIAN), S.E, MICHIGAN AND N.W. OHIO

by Darioush T, Ghahremani

A Thesis Submitted to the Faculty of The Graduate College in partial fulfillment of the Degree of Master of Science

Western Michigan University Kalamazoo, Michigan August 1978

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. AB5TRACT

Spiriferid brachiopods of the Middle Devonian Silica

Formation in northwestern Ohio and southeastern Michigan

show many Features that are useful For paleoecologic in­

terpretation. This study is undertaken to examine and

interpret the paleoecology and paleobiology of six spiri­

ferid brachiopods Mucrospirifer prolificus, Mucrospirifer

grabaui, Mucrospirifer profundus, Mucrospirifer mucronatus,

Paraspirifer bownockeri and Spinocyrtia euryteines. All

are very abundant and can be easily collected from quarries

in the Silica Formation near Sylvania, Ohio.

Fourteen different morphologic characteristics have

been tabulated for all specimens used in this study. These

characteristics allow interpretations of the ontogenetic de

velopment and ecologic relationships of the six studied

species to their physical environment. In addition to mea­

surable morphologic characters, encrusting epizoans on the

shell surface during the brachiopods life and borings or

other trace of predators can be used to estimate the brachi

opod life orientations and substrate relations.

ii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS

The author wishes to express his gratitude to Dr,

William B, Harrison III for First introducing him to the

topic and for valuable assistance both in the field and

in research.

My appreciation also goes to Dr. W. David Kuenzi

and Dr, W, Thomas 5traw for their critical evaluation of

the manuscript.

Thanks are due to Dr, R. V, Kesling and R. Chilman

for the use of specimens and other facilities in the Uni­

versity of Michigan Museum of Paleontology, Ann Arbor,

Michigan, I would like to thank R, D, Havira for helpful

suggestions relevant to photographic techniques.

Lastly, I like to thank my wife Simin for all her

assistance, understanding and patience during this entire

project.

Darioush T. Ghahremani

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. MASTERS THESIS 13-11,965 GHAHREMANI, Darioush Tabrizi PALEOECOLOGY OF THE SPIRIFERID BRACHIOPODS OF THE SILICA SHALE FORMATION (MIDDLE DEVONIAN), S.E. MICHIGAN AND N.W. OHIO. Western Michigan University, M.S., 1978

University Microfilms International, Ann Arbor, Michigan 481C6

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS PAGE

INTRODUCTION ...... 1

SAMPLING LOCALITIES ...... 4

TECHNIQUES ...... 11

PREVIOUS WORK ...... 15

STRATIGRAPHY ...... 1?

MIDDLE DEVONIAN BRACHIOPOD COMMUNITIES ...... 21

PRINCIPLES OF PALEOECOLOGICAL ANALY5IS ...... 25

PALEOECOLOGICAL DESCRIPTIONS OF SPIRIFERIDAE IN

SILICA FORMATION ...... 29

CONCLUSIONS ...... 63

REFERENCES CITED ...... 70

APPENDIX I ...... 74

PLATES ...... 77

iv .

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF ILLUSTRATIONS

Page

Figure 1, Regional map of study a r e a ...... 3

Figure 2. Outcrop map of study a r e a ...... 5

Figure 3, Northwest wall of Medusa 5outh-5outh

quarry ..... 8

Figure 4, Medusa North quarry ...... 9

Figure 5. View looking southwest in Medusa South-South

quarry ...... 9

Figure 6. Medusa South-South quarry ...... 10

Figure 7. Molds of trails and burrows; bottom

surface of overturned slab, unit 14 ...... 10

Figure 8. Various morphologic characteristics of all

specimens used in this study ...... 14

Figure 9, Stratigraphic section of the Traverse

Group ...... 16

Figure 10. Correlation of the Devonian rocks of New

York, Northern Mich., S.E. Mich, and

N.Ul. Ohio ...... 18

Figure 12. Chart showing major faunal zones and correla­

tion of the Silica Formation with other rock

units in the Michigan basin ...... 22

Figure 13. Measurements of Mucrospirif er mucronatus

(Conrad) ...... 30, 31

v

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Figure 14, Relation of surface area and volume of

objects on substrate ...... 35

Figure 15. measurements of lYlucrospirifer profundus

(Grabau) ...... 37, 38

Figure 16, measurements of mucrospirifer qrabaui

(Stumm) ...... 41, 42

Figure 17. Orientation of mucrospirif er grabaui on

substrate in response to currents ...... 44

Figure 18. measurements of mucrospirifer prolifi-

cus (Stewart) ...... 46, 47

Figure 19. measurements of Paraspirifer bownockeri

(Stewart) ...... 50, 51

Figure 20. Growth characteristics of Paraspirifer

bownockeri (Stewart) ...... 53

Figure 21. Plot of length versus thickness in Para­

spirif er bownockeri (5tewart) ...... 55

Figure 22. Plot of volume versus length in Paras­

pirif er bownockeri (Stewart) ...... 56

Figure 23. measurements of Spinocyrtia euryteines

(Owen) ...... 60, 61

Figure 24, Alternative possible life orientations

for taxa studied herein ...... 66

Figure 25. measured sections in the Silica Forma­

tions ...... 75 Figure 26, Photo showing medusa South-South quarry. 75 vi

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Figure 27, Medusa 5outh-5outh quarry ...... 76

Figure 28. Medusa South-South quarry showing Ten Mile

Creek Dolomite overlying Silica Formation . 76

vii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. INTRODUCTION

During a Forty year period beginning with Dr. Grace A,

Stewart's work (1927) more than 200 invertebrate species

have been listed and described from the Silica Formation

in northwestern Ohio and southeastern Michigan, These

species represent a series of marine benthic communities

which existed on the Middle Devonian sea Floor during the

time oF Silica Formation deposition more than 350 million

years ago.

The 5ilica Formation has been a source oF remarkably

well preserved Fossils ever since it was exposed by the

quarrying operations oF the Sandusky (now Medusa) Portland

Cement Company at Silica, Lucas County, Ohio, about 1920,

Fossils From the Silica Formation have been extensively

sampled and described (Kesling & Chilman, 1975), This study

is undertaken to more careFully examine and interpret the

paleoecology and paleobiology oF one oF the abundantly repre­

sented Faunal constituents, the spiriFerid brachiopods.

Much work has been done using brachiopods as community

and ecological indicators (Ziegler, 19GB; Rolling and Dona­

hue, 1975; Richards, 1972; Anderson, 1971; Boucot, 1977),

Most oF this work has been done with ^rdovician, Silurian

and Early Devonian brachiopod Faunas, These have been

examined by Bowen, Rhoads and McAlester (1974), Copper (1966),

Thayer (1974), and Driscoll, Hall and Nussmann (1961);

1

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however, very little integrated analysis of biological com­

munities and their ecological relationships has been sug­

gested.

Because brachiopods are one of the most abundant groups

of fossils in the Silica Formation and because much previous

work exists on brachiopod communities and their ecology, a

selected group of brachiopods, the Spiriferida, was chosen

for this study in an attempt to characterize the communi­

ties and their ecological relationships to the Silica For­

mation, Thus, the spiriferid brachiopod faunal assemblages

in the Silica Formation along with their associated lithologies

(lithotopes) are described, and environmental conditions to

which such assemblages might have been adapted are suggested.

Variations in salinity, temperature, currents, depth, dis­

tance from shore, turbulence, sediment supply, rate of depo­

sition and availability of food are likely to have been major

factors which affected the survival and ecological develop­

ment of the described brachiopod taxa.

The Silica Formation is most extensively exposed in

limestone and shale quarries located near the town of Silica

(Lucas County) in northwestern Ohio (Fig. l). Other expo-

jures of this formation occur at Ten Mile Creek and at the

abandoned White House Quarry. Localities are also present

in southeastern Michigan,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3

ARBOR

Lenawee Co.

Sylvan W t

Lucas Co*

O tta w a

Scale in Miles

Figure 1. Map of study area showing quarries in vicinity of Sylvania.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5AIY1PLING LOCALITIES

The Silica Formation examined in this study is ex­

posed in Ohio and parts of IKlichigan. The entire region is

covered by glacial drift and all exposures are in quarries

(Fig. 2). Beloui are listed the quarries in the Silica For­

mation from which specimens were obtained.

IN OHIO:

West-southwest of 5ylvania, Sylvania Township, Lucus

County, Ohio.

1, Medusa North-North Quarry:

Operated in 1960 by the Medusa Portland Cement Co.,

abandoned around 1970, Located 1/8 to 1/4 mile west

of Centennial Road and 1/4 to 1/2 mile South of Syl­

vania Metamora Road.

2, Medusa South Quarry:

5tarted by Sandusky Cement Company in the 1920*s and

then operated by Medusa Cement Company, This quarry

is the first and the best collecting ground for Silica

Formation fossils and is still productive from the upper

units. Located 1/8 to 1/4 mile west of Centennial Road

and 1/2 mile south of Brint Road. (Fig, 3),

3, Medusa North Quarry:

Operated by Medusa Co. 1940's, Located 1/8 to 3/8 mile west of Centennial Road and from Brint Road to l/2 mile 4

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. m I Silica Fm. = __ c ' Scale in Miles Centennial J" Dundee M edusa ti ti HkiKinijwtknKrkrTjNM Hjvrfr Ten Ten Mile Creek ! Dolomite ------N. Quarry I N t r v i- : ».•■— n i h ^ >l\SM\M\l\rul-UIS~INkl»h 1 i i ■

M edusa S .Q u a rry YV-v v w v YV-v

Medusa Glass Quarry J • , .• '. ' . » / - « , # *•«*•«. ^ *•«*•«. »*#*,* # , - « / » . ' , '. .• • V • • * • S. S. QS. S. u a rn L Dolomite Dundee ' ' Lucas Dol Figure 2. Outcrop of study area showing quarries near town of Silica, Ohio.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6

north. (Fig. 4).

4, Medusa South-South Quarry:

Most of the materials collected for this study are

from this quarry. Located l/B to 3/8 mile west of

Centennial Road and from Sylvania Avenue to 1/2 mile

north. (Fig. 5, 6, ?).

IN MICHIGAN:

1, Martine-Marietta Quarry:

Opened by Martin-Marietta Corporation to obtain rock

from the Dundee Limestone in 1960, The Silica Forma­

tion, as well as the glacial cover, was stripped and

dumped as over-burden. As a result, no section of the

Silica Formation was ever developed as a clean face.

Not long after quarrying began, a well penetrated a

stratum bearing hydrogen-sulphide charged water and the

quarry rapidly flooded and was abandoned. Silica For­

mation fossils are available on weathered dump piles,

but their stratigraphic position can only be inferred

by the associated faunal assemblages. Located in Au-

gusto Township, Washtenaw County, South of Arkona Road

and 1 to 1/4 miles east of U.S. 23 (between Sanford

and Gadkins Roads and southeast of the Wabash railroad

right of way). Kesling, 1975,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7

Explanation of Fig. 3

Northwest wall of Medusa South-South Quarry, (See Fig, 2

for location)

Quarry floor is the top of the Dundee Limestone.

Units 1-9 of the Silica Formation on wall just above

Quarry's floor. Bench with drill is cut on top of

Unit 8,

Units 9-16 extend to the next bench.

Units 17-29, which are overlain by Ten Mile Creek

Dolomite and glacier drift, complete the section.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 5. View looking Southwest in Medusa south-south quarry.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 10

Figyre- Medui . units'9-

•. •■■■a n . - j ' . - i j a

Figure 7. Molds of ai~l£~and^t^ ^wsfr’bi>$^ . of overturfed slab unit 14, presenting record o£ . trails in? uppenftost layer of^uait '13v August , 1977r

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TECHNIQUES

The results presented in this paper are based on

collections and observations made at different localities

in the Silica Formation near Sylvania, Ohio. The majority

of the sampling was done in the South Quarry, South-South

Quarry and North Quarry of the IKledusa Cement Company (Fig.

2). Only the South-South Quarry exposes the entire thick­

ness of the Silica Formation.

After collecting samples in the Medusa South-South

Quarry, the best preserved specimens were prepared and

cleaned by chemical processes such as etching with dilute

acetic acid, or disaggregation of shale coatings with kero­

sene. Cleaning of some specimens by etching with airbrasive

equipment revealed fine details of the shell surface. Most

specimens have been photographed with a thin coating of

ammonium chloride, numbered and filed for future studies

in the Department of Geology, Western Michigan University,

Various morphologic characteristics were measured and

recorded (Fig. B). Results of these measurements are sum­

marized in a series of graphic comparisons presented with

the descriptive paleontology.

11

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The relationships between the measured parameters

have been analysed by statistical techniques using the

facilities and programs available in the Computer Center

at wmu.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Explanation of Fig. 8

A j Mucrospirifer

a- Length

B: Mucrospirifer

b- Width of the fold

b' - Height of the fold

C: Mucrosoirifer

c- Thickness

c'- Palintrope angle

D: Paraspirif er bownockeri

d- Number of grouithlines in each 5mm

d'- Point where the neui plica starts

d''- Width of the hingeline

E, Paraspirifer bownockeri

e- Number of plica in each 5mm

e'- Maximum thickness of inter area

F: Paraspirifer bownockeri

f- Total thickness

f' - Height of the fold

f " - Width of the fold

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 14

Figure 8. Measured parameters used in this study.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PREVIOUS WORK

(Diddle Devonian rocks, which are now known as the

Silica Formation were first described by Stauffer (1909),

who recognized their age and used the name "Traverse” for

them. Stewart (192?) first described many of the fossils

from these rocks. She called these beds the "Silica

Formation",

Ehlers, Stumm, & Kesling (1951) presented additional

information about the stratigraphy of the Silica Formation i along with some descriptive paleontology (Fig, 9), They

also extended the boundaries of the formation to include

the "blue limestone" below, which yielded a fauna similar

to that collected from the soft shales which Stewart had

called "Silica Formation," In addition, they noted that

the uppermost beds mentioned by Stewart were succeeded

by another thick sequence of shale which appeared to be the

base of a thick sequence of dolomitic rocks. The Ten Mile

Creek Dolomite is now thought to be a separate genetic unit

from the Silica Formation.

Several master thesis have been written on various as­

pects of the Silica Formation (Nussmann, 1961; Mitchell,

1967; Koch, 1973). They primarily consider general features

about the ecologic and community relationships, but lack

specific details that could help elucidate the paleoecology

of the formation, 15

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 16

Feet

Ten M ile Creek a. Dolomite

Units 19-25

UJ tn Q£ Silica Formation UJ 14-17 7 -13 CL I/I 1 -6

Dundee

Limestone

Anderdon Limestone

Lucas 8 4 Dolomite Ul u.

“ O

5 0 VI “0 TJ

Figure 9. Stratigraphy of lower and middle Devonian rocks in southeastern Michigan and northwestern Ohio(adapted from Ehler, Stumm, and Kesling,1951, Nussmann,1961 and Mitchell,1967) .

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. STRATIGRAPHY

Information about Middle Devonian Traverse Group stra­

tigraphy in the study area and adjacent areas has been accu­

mulating for more than 60 years (Cooper et al., 1942; Dris­

coll and Mitchell, 1969; Stewart, 1922, 1936, 1955; Ehlers

and Coolay, 1927; Stauffer, 1907, 1908, 1909, 1916; Ehlers,

and Kesling, 1970; Ehlers et al., 1951; Stumm, 1942;

Fritze, 1939; Grabau, 1917; Kier, 1952; Mitchell, 1967;

Tillman, 1970; Nussmann, 1961; Kesling and Chilman, 1975).

The Traverse Group is recognized here (Fig, 10) to in­

clude all Middle and Upper Devonian stratigraphic units di­

rectly above the Roger City and Dundee Limestones or rocks

of the Detroit River Group in the Southeastern Michigan

Basin (Cohee, 1947a, 1947b). It's upper boundary is at the

base of the Upper Devonian Antrim-Kettle Point-Ohio Shale

(Driscoll & Mitchell, 1969).

Lower Traverse strata are here considered to consist of

the Grabill Formation of Michell (1967), Silica Formation

(Roab, Berkey,and Brint Road Members), Plum Brook-Shale and

upper and lower Arkona Formation (Fig. 10).

Kesling (1975), divided the Traverse Group into five in­

formal litnoiogic units; Blue Limestone (3 feet), Silica

Formation (10 feet), Shaly limestone (4 feet), Blue lime­

stone (6 feet), Columbus Limestone,

17

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N E W YORK S.-E.MICH SERIES N.MICH. GENERALIZED N.-W.OHIO

ENFIELD SHALE AN TRIM SHALE

ITHACA SHALE ANTRIM SHALE O HIO SHALE

GENUNDEWA LIMESTONE SQUAW BAY Ls

GENESEO SHALE

THUNDER BAY Is . TUI IY Fm. POTTER FARM Fm.

MOSCOW Fm

NORW AY Pt Fm LUDLOWVILLE Fm

FOUR MILE TEN MILE CREEK DOLOMITE D AM Fm.

ALPENA Is.

NEW TON CREEK Is.

GENSHAW Fm. SKANEATELES Fm FERRON POINT Fm.

SILICA ROCKPORT QUARRY Ls FORMATION

BELL SHALE m ROGER CITY Is MARCELLUS Fm OUNDEE Ls. DUNDEE Ls

PARASPIRIFER ACUMINATUS

Figure 10.Correlation of the Devonian rocks of New York, northern

Michigan, southeastern Michigan, and northwestern Ohio#

Adapted from section by Mitchell( 196?) and Kesling(1975>*

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In the Silica Formation there are numerous disconformi-

ties which may record periods of non-deposition or erosion

by storms (Fig 9 and Appendix l), A graphic summary of the

stratigraphic sequence of biotopes of the Silica Formation

adapted from Nussman (1975), is presented in (Fig.11). He

proposed to divide the formation into five parts, A lower

bioclastic limestone sequence (l) is overlain by three se­

quences of "ITflucrospiriferid Transition" zone, which in turn

is overlain by shale (2, 3, 4), and an upper sequence con­

sisting largely of "normal" argillaceous limestone (5). All

these lithotopes are epineritic to infraneritic (Thorsen,

1957). Facies relations between these lithotopes produced

the interbedded appearance of most sections (Fig. 11),

Many species found in quarries near Silica also occur

in rocks exposed in the northern Lower Peninsula of Michigan,

especially in Alpena and Presque Isle Counties, and in adja­

cent Ontario, Canada. Similar faunal assemblages also are

found in the New York Hamilton Group (Cooper, 1937; Cooper,

et al., 1942), These widely separated but similar assemblages

apparently record similar environmental conditions in an ex­

tensive Middle Devonian epicontinental sea.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 20

Ten M ile Clc.Dol.

Bioclastic Ls- Lithotope

Normal Argillaceous Ls. Lithotope

ir®B tnra Cryptostomate — Crinoid Argillaceous Ls. Lithotope

mlUlm m l f l m Mucrospirifer Transition Lithotope

Shale Lithotope Proper

«

E .w » v o m Smothered Bottom Assemblage

03 O ,m iw m im m m mi m •m m CO fainflraifltowi

units 1-27 from Nussmann, 1975.

units 1-5 from Kesling,1975.

n n 5 A EZH 4 1 'TJ 1 i " "i=a \r *

D undee Ls. i ‘ ~ r

Figure 11. Stratigraphic sequence of the Silica Formation.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. MIDDLE DEVONIAN BRACHIOPOD COMMUNITIES

Mitchell (1967) recognized four distinctive brachio-

pod communities in the Silica Formation which appear to be

superimposed. They are characterized by restricted strati-

graphic ranges and wide geographic occurrence (see Fig, 12),

These communities and their diagnostic brachiopod faunas

are listed below,

1. T ropidoleptus-Hexagonaria

Devonochonetes coronatus (Hall) & Tropidoleptus carina-

tus (Conrad),

Locality: in Michigan, Ohio, Indiana Lower Traverse

Group,

2. Herocostrophia-Helopora

Hercostrophia robusta (Williams)

Muscrospirifer prolificus (Stewart)

Paraspirifer bownockeri (Stewart)

Schizophoria ferronensis (imbrie)

Locality: Michigan, S,E, Ontario

3. Aulocystis-Rhipidomella

Echinocoelia sp, cf. ambocoeloides (Cooper) a Strophodonta sp, 0 Strophodonta sp.

Locality: Ontario, Ohio,

Z1

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. M ro

Helopora Rhipidomela Aulocystis- Hexagonaria Leiorhynchus Hercostrophia Stereotoechus Tropidoleptus-

Plum Ohio Brook Fm. Prout Ls. Delaware Ls. N.-CENT.

N. S ilica Fm. Indiana Silica Fm. G ro u p Dolomite D et. River Ten M ile Ck.

Ohio Mich. )olom ite Lower Member Silica Fm. Silica Fm. Silica Fm. Ten Mile Ck. Dundee Ls. Middle Member N.W. UPPer Member S.E.

S.W. Fm. Rockport D undee H ungry Bell Sh, Q u a rry Ls. Ferron Pt. Ontario H o llo w Fm. Delaware Ls. A rko n a Fm.

Fm . N.E. Roger Fm. Rockport D am Fm. G en sh a w C ity Ls. Q u a rry Ls. Bell Sh. Ferron Pt. Four M ile Michigan A lp en a Ls. (Mitchell* 1967) . 1967) (Mitchell* N ew ton Ck. Ls. other rock units in the Mich, basin and adjacent midcontinent areas

Fm. N.W. Roger C ity Ls. Michigan Gravel Point Fm. Charlevoix Figure 12. Chart of major faunal zones and correlation of Silica Formation with

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 23

4. Leiorhynchus-Sterotoechus

Leiorhynchus kellogi (Hall)

lYlucrpspirifer arkonensis (Shimer & Grabau)

5chuchertella crossa (Imbrie)

Strophodonta extenuata (imbrie)

Locality: All others Ohio, Michigan, Ontario.

Mitchell (196?), also indicated that all four of these

communities are present in the Lower Traverse Group of Mi­

chigan, Indiana, Ohio and Ontario. The Tropidoleptus-

Hexaqonaria community is the only uiell developed community

in the basal portion of the Brint Road Member of the Silica

Formation of Ohio. Mitchell (1967), pointed out that this

assemblage is not found elsewhere in the Lower Traverse beds.

The Tropidoleptus-Hexaqonaria community occurs in dolo-

mitic limestone,and limestone. The Hercostrophia-Helopora

community is present in the shale and limestone lenses of

the lower portion of the lower Arkona Formation in Ontario

and is characteristic of the bulk of the Brint Road Member

of the Silica Formation (Fig. 12).

Dekeyser (1977) suggested four onshore to offshore com­

munities in the Lower Upper Devonian which are thought to

be primarily depth-dependent in their distribution.

Of these four communities only the Atrypid-Schizophoria

community seems to be widespread during the entire Devonian

(Dekeyser, 1977). Other Devonian communities have been

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 24

described byj Sutton et al, (1966), Allan (1935), Cooper

(1966), Laporte (196?), Beerbower & McDowell (i960), Bretsky

(1968), Boucot (1977), and Dekeyser (1977), The community

structure of the Silica Formation can be correlated with

the communities recognized elsewhere (Fig, 12),

In the Silica Formation, the Tropidoleptus-Hexaqonaria

community occurs in units 1-4 and the overlying riercostrophia-

nelopora community extends from units 5A to 12-13 (Fig, ll).

Aulocystls-Rhipidomella community starts at unit 14A and

ends above unit 18B, The Leiorynchus-Stereotoechus commu­

nity extends from unit 19 to unit 29 just under the Ten

Mile Creek Dolomite (Appendix I). These units are mostly

similar to the units presented in Fig, 9 adapted from Kesling

& Stumm & Ehlers (1975),

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PRINCIPLES OF PALEOECOLOGICAL

ANALYSIS

UniFormitarianism is the primary principle used by paleo-

ecologists to interpret the Fossil record. Analysis oF

modern Faunas and sediment types have given us many guide­

lines For interpretation oF the rock record. The key to

valid paleoecological interpretations is the preservation

oF Fossils in place, but Functional morphology analysis has

also been applied (Raup & Stanley, 1971),

The Silica Formation contains numerous examples oF

Fossils that have been disturbed very little since death.

Corals and bryozoans are preserved in liFe position in con­

trast to many oF the brachiopods uuhich appear to have been

transported From other areas and may be in diFFerent orien­

tations than their living positions. Although some brachio­

pods can be Found in liFe positions, most are probably not

and other criteria must be used to interpret their paleo-

ecology and liFe orientation. Observations oF positions

oF epizoans and traces oF boring or predatory organisms on

the brachiopod shells, along with quantitative measurements

oF shell shape, allow interpretation oF hydrodynamic sta­

bility and Functional orientation.

Fourteen diFFerent parameters were observed and care-

Fully measured For samples oF the six most abundant species

25

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of spiriferid brachiopods in the Silica Formation, These

measurements are based on the following characteristics

of the shells: thickness, length, width of the fold,

number of costae (plica) in each 5mm (before bifurcation

in Paraspirifer), number of growth lines (striations) in

each 5mm, volume, height/width ratio of the fold,thickness/

length ratio and the distance from the beak to where a new

plica starts (only on Paraspirifer bownockeri Stewart) Fig,

8), Additionally observations were made of general shell

shape and type and position of encrusting epifauna,

Epizoans encrusting on the shell surface during the

brachiopods life and borings or other traces of predators

may be used to estimate life orientations. Most encrustors

or predators will attack the exposed surface of the shell.

In the case of benthic marine invertebrates like brachio­

pods, this is the dorsal or upward direction in life. Even

if the brachiopods have been transported or disturbed from

their life orientation, the life orientation can be deter­

mined.

Many brachiopods from the Silica Formation are encrus­

ted and it is therefore commonly useful to take this approach

to paleoecological interpretations. The high percentage of

encrustations suggests that shells offered one of the few

suitable substrates for encrusting benthic invertebrates.

The orientation of epizoans is also indicative of whe­

ther the brachiopod was alive or dead when the encrustor

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came on the shell. For example when an encrusting bryozoan

encloses the brachiopod comissure line it means that the

brachiopod was dead when the bryozoan was growing in that

position.

Associated sediments have also been studied to under­

stand the nature of the substrate. The shales of the Silica

Formation are fine grained and homogenous suggesting a uni­

form soft muddy surface. In contrast, some of the lime­

stone in the Silica Formation shows more current activity,

as suggested by the great number of broken shells.

Size-frequency analysis and population dynamics of the

brachiopods can be used for recognizing life assemblages

(Thayer, 1975a), Interpretation of growth patterns may

suggest responses to different environments, however, an

interpretation of any size-frequency distribution requires

independent knowledge of growth rate (Thayer, 1975b).

There has been some work on population dynamics of liv­

ing articulate brachiopods (Thayer, 1975a). Life orientation

and mortality rates between these brachiopods are very dis­

tinctive factors controlling ecologic and paleoecologic

parameters.

Size-frequency and growth rate data have been used to

interpret trends in natural selection and evolution, Stanley

(1974) suggested that predators may have an important im­

pact on population numbers in young brachiopods, Paine

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 28

(1976) mentioned that many prey species grow rapidly in

early parts of life to minimize their susceptibility to

predators.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PALEOECOLOGICAL DESCRIPTIONS

OF SPIRIFERIDAE IN SILICA FORIY1ATION

Genus lYlucrospirifer mucronatus (Conrad), PI. 5, Fig, 9.

Locations Unit 17, lYledusa Quarries.

Figured Specimens UI1Y1U 2701, dorsal view of the specimen.

Descriptions Specimens are trigonal, compressed with nu­

merous ribs, crossed by prominent growth varices, hinge is

elongated and in some cases mucronate at the extremities.

In the 5ilica Formation, specimens of Hflucrospirifer mucrona­

tus (Conrad) found in Units 17-1B in the lYledusa Quarries,

generally have a well developed medial ridge in the sulcus

area and a medial groove on the fold. Width range from

2Q-50mm; thickness from 6-12mm, lYlean length is in the

15-17mm size class.

Discussion: lYleasurements of volume are compared to length,

thickness and width to get a better understanding of growth

of different body regions. lYleasurements of all specimens

(42) are presented in histogram form (Fig. 13). Nine dif­

ferent histograms have been prepared for each genus in the

lYlucrospiriferidae. The following characteristics are pre­

sented: height and width of the fold, width of the hinge-

line, thickness, length, volume, maximum thickness of inter-

area, number of growth lines in each 5mm, number of costae

(plica) in each 5mm, All measurements are in millimeters 29

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3D

Height of the fold Width of the fold

1 2 3 4 5 6 mm

Width of the hingeline

x = 11 X = 1A

5 10 15 20 mm o 5 10 15 20 25 mm

Thickness Length

n>42

Figure 13. Histograms showing distribution of physical parameters__measured on Mucrospirifer mucronatus (Conrad). X is the mean and n is the number of specimens measured.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 1

X = 4 X = 2

10 15 0 ml. 5 10 mm

Volume Max. thickness of inter area

3

2V X = 9

1

0 5 10 15 20

No. of growth in 5 mm No. of Plica in 5 mm

n=42

Figure 13. continued.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 32

except volume (ml). Ratios such as thickness/length and

height/width of the fold, uiere used for evaluating these

and other morphologic characteristics.

Examination of the growth lines indicate that the

specimens of lYlucrospirif er mucronatus studied were in the

same stage of development.

Tillman (1964) suggested an anterior upward life posi­

tion for lYlucrospirif er mucronatus collected from the other

formations of the Traverse Group of lYlichigan as that sug­

gested here (Fig. 17), Tillman (1964) pointed out that

the total number of costae on a given shell depends on the

age and size of the individual. This relationship is also

apparent on the specimens used in this study. There are

some specimens found in the Silica Formation in which the

number of plica in each 5mm varies with size, but it is

possible to find small specimens with a large number of

plica or some larger specimens with small number of plica

in each 5mm. This probably reflects more rapid growth in

some specimens than others.

Like other brachiopods, lYlucrospirif er mucronatus lived

in several orientations. Some specimens were attached by

their pedicle to other organisms such as bryozoans and other

brachiopods such as Paraspirif er (PI. 3, Figs.l, 2 and 3).

Some rested on the muddy substrate and, because of this

life orientation, it would be reasonable to assume that

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an increase in shell surface area aver the substrate would

keep them from sinking into the mud. As lYlucrospirif er

reached adult stages the "wings" were fully developed

for substrate support and the shell was quite thin and

light weight.

It has been suggested that articulate brachiopods are

excluded from turbulent environments by the weakness of

their pedicle attachment (Thayer, 1975b). However, some

evidence has been offered which does not support this

conclusion. Thayer (1975b) has experimented with the force

required to remove brachiopods from their substrate. Also

paleoecologists often assume that the size of the pedicle

foramen is directly proportional to attachment strength, a

relationship which is probably directly correlatable

(Thayer, 1975b),

Rudwick (197Q, p. 160) suggested that few living bra­

chiopods are able to initially colonize strongly current or

wave swept environments, probably because of the limited

strength of their pedicle attachment. Thus, brachiopods

with pedicles are probably confined to the more sheltered

parts of environments with continuous higher energy. How­

ever, if settlement can occur, the established brachiopod

may be able to withstand higher energies than was previous­

ly thought possible.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 34

Because of diagenetic processes, it is not possible to

determine the original weight of the brachiopod shells; how­

ever, measurements of volume can give relative relation­

ships (Fig, 14), Presuming that larger volumes reflect

heavier shells, interpretations can be made of the ecolo­

gical relationship between substrate consistency and shell

weight and form. Volume is not a direct measure of weight

but as volume increases weight will increase too (Fig, 14),

lYlucrospirif er mucronatus has a small volume and large sur­

face area, which may have kept it from sinking into the

soft sediment.

Genus lYlucrospirif er profundus (Grabau) PI. 5, Figs. 6,7

Location! Unit 7, South Quarry, lYledusa Cement Company;

lYlartin-IYlarietta Quarry,

Figured specimens IaIIYIU 2822 Ventral and dorsal views of

the specimen. This specimen is usually

very thick in contrast to the other

lYlucrospirif ers.

Descriptions lYlucronate but with delicate cardinal extremi­

ties; maximum width is along the hingeline, width about 1/3

greater on average than length. Lateral and anterolateral bor­

der are broadly convex, anterior border is straight or slightly

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 35

1

3320^738336284

Figure lif. Relation of surface area and volume of objects

on substrate. All objects of equal depth.

1- Large volume, large surface area

2- Large volume, small surface area

3- Small volume, large surface area

i+- Small volume, small surface area

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 36

concave. Number of plica in each 5mm ranges from 4-7mm

and averages shout 5, The number of growth lines in each

5mm ranges from 5-15mm. Costae and intercostal furrows

are V-shaped, and both valves are moderately convex in

lateral profile.

Surface length of pedicle valve is greater than bra­

chial valve. Sulcus is broadly U-shaped with subangular

edges, and is usually well preserved exclusive of cardinal

extremities (PI,5, Figs. 6,7). Thickness ranges from 7-16mm

and length ranges from 10-23mm with ranges of 17-lBmm for

length and 10-12mm for thickness. Volume ranges from 1.8-

7ml and the range in volume is 4-5ml, Thickness of inter-

area ranges from 0-5mm and width of the hingeline ranged

from 16-38mm (Fig, 15), Number of specimens 39,

Discussion: Seven different measurements were made on spe­

cimens of lYlucrospirif er profundus (Grabau) in order to

better understand the ecology and life position of the spe­

cies (Fig. 15),

Shells of this species are relatively thick in contrast

to lYlucrospirif er mucronatus which suggests that many indivi­

duals were probably supported by the substrate and the in­

flated shell elevated the free margin above the sediment sur­

face. However, some individuals lived attached to other

brachiopods or bryozoans (PI, 6, Fig. 1), and were well

preserved because of replacement of spiralia and other parts by pyrite.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3?

20 20

15 x=n 15 X = 17

10 10

2 0 2 5 5 10 15 20 25

Thicicnejs Length

20

15 X = 28 X = 2.5 F 10

5

0 3 4 5 1 0 -

Width of the hingeline Max* thickness

of inter area

n.39

Figure 15. Histograms showing distribution of physical parameters measured on Mucrospirifer profoundus (Grabaui). X is the mean and n is the number of specimens measured.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 38

Volum e No- of growthline in 5 mm

Figure 15. continued.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 9

A few specimens have broken tips that record injuries.

lYlucrospirif er profundus has the smallest width of

all the mucrospiriferids investigated and the ratio of

length to width is almost equal. The shape of the valves

gives a clue to understanding the way the species lived.

If they rested on the substrate with the pedicle valve

upward, they would have been subject to dislodging and

rolling by currents, but if they were lying on the sub­

strate with the brachial valve upward, they would present

a more streamlined surface to currents and thus be more

stable. Dn the other hand, if they were attached by their

pedicle, there would not be much difference between the

two valves.

Shell thickness is nearly equal to shell length, this

reinforces the subjective observations of high convexity in

this species. The pedicle opening is very small, compared

to those in other species of lYlucrospirif er, which suggests

that the relatively small pedicle muscle may not have been

sufficiently strong for attachment to the substrate or to

other organisms.

Genus lYlucrospirif er grabaui (Stumm) PI. 3, Fig. 7, PI,5,

Figs, 1-3 Ventral views of the specimen.

Locations Unit 15, lYledusa Quarries.

Figured specimens WIY1U 2698, 2687 Ventral view with sulcus

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is illustrated.

Description: Thickness of the shells ranges From l-15mm

but most between 10-15mm thick (Fig, 16). Shell width

ranges from 3-7mm.

Shells of this species have very fragile "wing-tips"

along the hingelines. Shells strongly mucronate by addi­

tion of shell material in the adult stage at the cardinal

extremities. Cardinal area fragile with less than 20 per­

cent preserved intact. Height and width of the fold averages

5mm and 6mm respectively. Number of plica ranges from 3-5

in each 5mm and averages 4. Number of growth lines ranges

from 4-8 in each 5mm interval, averaging 5.

Discussion: Units 15 and 17B (Fig, ll) are "mucrospiriferid

transition" units containing mostly lYlucrospirif er grabaui

(Stumm), whereas the sequence of units 7 through basal 9

constitutes a "mucrospiriferid transition" zone with an

abundance of individuals, and a much greater diversity of

species.

The absence of distorted or unequally developed shells

and the presence of a large uncovered pedicle opening sug­

gest that lYlucrospirif er grabaui possessed a functioning

pedicle of moderated length, that not only provided firm

attachment to the substrate but also permitted rapid change

of orientation. The broad wings probably prevented over­

turning and burial in the muddy substrate. Cooper (1937)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Thickness Width

length mm Volume ml

20 20

X = 4 15 X — 3 15

10 10 e 5 i 5 10 mm 5 10 15 20

M ax. thickness of inter area Height of the fold n* 14

Figure 16. Histograms showing distribution of physical para:; meters measured on Mucrospirifer grabaui(Stumm). X is the mean and n is the number of specimens measured.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 42

15

10 X=7.5 5 L o 5 10 15 20 25

W idth of the fold

10 X = 4.6 10 X=3.5

L f c 10 10

No- of growthline in 5 mm No- of Plica in 5 mm

n314

Figure 16. continued.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 43

suggested that the mucronate form acted as a "weather vane",

turning so that the long axis of the shell was parallel

to the current, presenting least resistance to the current

and preventing uprooting of the animal. Nussmann (1975)

pointed out that the two "wings" would have been in an opti­

mum position to prevent the shell from being overturned or

driven into the mud. Although such a position may have

been assumed during times of vigorous wave disturbances,

a more plausible orientation under calmer-water condition

would have been with anterior surface facing the current

(long axis perpendicular to the oncoming current).

By constantly maintaining this position lYlucrospirifer

qrabaui could have made maximum utilization of available

oxygen and nutrients in the water. Furthermore, in this po­

sition both the shell and circulation of water within it

would have been symmetric with respect to the oncoming cur­

rent. It is likely that water entered between the sulcus

and fold in the center of the anterior commissure and was

expelled via the two lateral wings (Fig. 17).

In any case, anchorage by a pedicle of moderate length

likely enabled lYlucrospirif er to change its position with

respect to the substrate and currents in response to changes

in oxygen, nutrients, turbidity, and wave agitation.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 44

"J and 2 • direction of current

1- parallel to axis of the wings

2- perpendicular to axis of the wings

Figure 17. Orientation of Mucrospirifer grabaui on substrate in

response to current. Orientation 1 represent higher energy

condition. Orientation 2 represent lower energy condition.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 45

Genus lYlucrospirif er prolif icus (Stewart) PI, 5, Figs,

4,5,8;

Location: Unit 1-9 especially in Unit 3, Medusa Quarries,

Figured specimen: U11Y1U 2745, WMU 2750, WIY1U 2751 Ventral

(sulcus or pedicle valve) views are

illustrated, also posteror (hinge)

views of complete specimen.

Description: lYlucrospirif er prolificus (Stewart) has fra­

gile cardinal extremities, slightly broken wing tips, both

valves attached. Cardinals sometimes are well preserved

or twisted slightly but the growth lines and plica still

can be seen all over the both valves. The number of plica

and growth lines are sometimes different in two valves.

Growth lines near the anterior margin are closer to each other

than those near the beak. This reflects changes in growth

rate in these parts of the shell.

Thickness ranges from 4-15mm and average 7.5mm. Width

ranges between 20-60mm with an average of 32mm, Shell length

ranges from l0-24mm and averages 17mm. Volume ranges from

l-8ml and the thickness of the interarea ranges from 2-3mm,

Number of plica ranges between 4-9 and averages 7, Height

and width measurements of the fold are summarized along with

the other measurements in (Fig, 18). Total number of speci­

mens measured was 77 (Fig. 18),

Discussion: lYlucrospirifer prolificus (Stewart) is one of

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 46

Growthline in 5m m

Figure 18. Histograms showing distribution of physical para­ meters measured on Mucrospirifer prolificus(Stewart). X is the mean and n is the number of specimens measured.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4?

X=I7 X = 8 2 F

10 o 5 10 15 20 25

Thickness Length

X=35

0 1 2 3 4 5 6

W idth of the hinge line

3

2 X=4.8 X=2.6

1

0 5 10 10

Volume M ax. thickness of inter area

na77

Figure 18. continued.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 48

the most studied species of Mucrospirifer mainly because

of their abundance in Units 1-9, Specimens are very well

preserved and easily measured, Rudwicfe (1962) suggested

that fossil articulate brachiopods are often abundant in

rocks that appear to have accumulated as soft sediment. In

some species there is evidence (e.g. a diminutive or plugged

foramen) that the pedicle atrophied during ontogeny and that

the adult shells were free-living. Most articulate brachio­

pods living today seem to require some hard and firm sub­

stratum (for example, rock or shell) for attachment (Plate

6), but enough exceptions are known to show that it is possi­

ble for the pedicle to obtain satisfactory anchorage in soft

materials and this type of attachment may have been much

more common in the past (Rudwick, 1962), Mucrospirifer

prolificus has a large pedicle opening indicating a thick

pedicle muscle which could have provided attachment or anchor­

age on soft substrate.

Genus Paraspirifer bownockeri (Stewart) PI, 1, Figs, 1-6;

PI. 2, Figs, 1-6; PI.3, Figs. 1-3; PI.4, Figs. 1-3;

PI.6, Fig. 1.

Location: Unit 7-11, especially Unit 9, Medusa Quarries.

Figured specimen: WMU 2632, WMU 2633, WMU 2634, WMU 2637,

WMU 2639, WMU 2642, UIMU 2650, WMU 2660

Ventral, dorsal, anterior, posterior views of Paraspirifer

bownockeri.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 9

Description: The volume of the shells ranges from 15-45ml;

the distribution of the values is bimodal and suggests that

two separate populations may be represented in the collec­

ted specimens (Fig. 19). Shell width ranges between 30-65mm

and averages 54mm,

Plicae range from 3-6 per each 5mm (Fig, 19), Growth

lines range From 10-16 and average 12, Width of the hinge-

line ranges from 26-56mm while the maximum thickness of

interarea ranges between 1.5-5mm and averages 3.5mm.

A histogram was also made for Paraspirifer bownockeri

to show the different distances from the beak where new

plicae start (Fig, 19). This distance ranged from 10-20mm

and averaged 15mm, Total number of specimens used for this

study was 37.

Discussion: Paraspirifer bownockeri (Stewart) life orienta­

tions are perhaps the best documented of any in this study.

The well-preserved specimens with abundant epizoans provide

ample data for interpretation (Fig. 20). Comparison of

shell volume to surface area suggests that the larger shells

sank more deeply into the mud, therefore a mechanism was

required to keep muddy sediment from clogging the lophophore

during later growth stages. Paraspirifer must have selec­

tively increased its thickness 18-43mm more than its width

to keep itself out of the mud (Fig. 20), Some specimens

of Paraspirifer compensated for their increased weight by

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 50

X=l-9 X=3.6

1

0Ln1 2 3 4

Total w idth Thickness / Length

X=3.8 3 3 X=15 2 I 2 1 1 _L 0 10 0

N o - of Plica in 5 n Distant of the new p|;ca from the beak

3 X=12 X = 21.4

2

1 1

0 5 10 15 20 0 10 20 30 40 50 »i

No- of growthline Volum e n» 37 111 5n

Figure 19. Histograms showing distribution of physical parameters measured on Paraspirifer bownockeri (Stewart). X is the mean and n is the number of specimens measured.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 51

X=2.4

0 1 2 3 4 5 mm

Height / Width of the fold

X = 1 .6

1

L l 0" 1 2 3 4 5 "

Width of the hingeline

0 5 10

Max. Thickness of inter area

"= 3 7

Figure 19. continued.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 2

EXPLANATION OF FIG. 20

1, Paraspirifer bownockeri (Steuiart): brachial valve

upward (life position).

2, Paraspirifer bownockeri (Stewart): several Cornultes

along commissure of the brachiopod, causing consi­

derable displacement of the line of closure. Also

right and left side of the brachial valve is encrusted

with bryozoa of Genus Hederella and sponge boring along

the commissure line,

3, Paraspirifer bownockeri (5tewart): valves are marked

with Aulopora microbuccinota (Watkins) as well as

previously mentioned epibionts.

Drawn from specimens collected from Unit 9, Medusa

Quarries.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ul LA Width = Height and Thickness Height and Thickness larger than Width

of growth. and Thickness Width larger than Height Figure 20. Comparison of the height and thickness to the widthat different stages

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 54

increasing their surface area (Fig. 20).

The length/thickness ratio of the shells also reflects

growth designed to survive on soft substrates, A plot of

length versus thickness suggests that most of the growth

after a certain size was as an increase in thickness rather

than length (Fig, 21). This relationship also holds for

volume/length ratios (Fig. 22).

A reasonable interpretation is that the growth pattern

of Paraspirifer bownockeri was an adaptation for life on

a soft substrate. The predominantly upward growth during

later growth stages compensated for sinking into the soft

sediment due to increased weight during growth. Growth

was accentuated in one direction to keep its margin above

the sediment-water interface, Anisometric growth of this

type allowed the brachiopod to increase its size with age

while maintaining a relatively constant position on the

sediment surface.

Encrusting organisms associated with Paraspirifer show

how other species (like IKlucrospirifer & Sphenophraqmus)

lived during early ontogeny (Plate 6), After settling on

the brachial valve of Paraspirifer, they produced shells

with beak directions oriented towards the anterior part of

the Paraspirifer (Specimen IaINIU 2560 Plate 5, Fig, 1; PI,

1, Fig. 6; PI, 3, Figs. 2,4, & 6; PI. 5, Fig, 5). The

life orientation of these small attached brachiopods

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. without prohibited reproduction Further owner. copyright the of permission with Reproduced

Figure 21. Length bownockerishowing thegrowth modification at aparticular stage 5 3 inlarger specimens. of shelllength diminishes while thickness continuesto increase substratum* (point 0 3 5 2 10 15 5 A ) ) A Thickness A , , A to foradjust continual sinking into the soft muddy plot ofplotlength compared to thickness in Paraspirifer B» is shellis thickness and L , , L s shellis length. Growth GROWTH *< ----

1 STAGE 55 >B -> AGE

o 10

Length

Fiffiirs 22. plot of volume compared to length in Paraspirifer

bownockeri showing the growth modification at a particular

stage {point 3; to adjust for continual sinking into the

soft muddy substratum .

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 57

PI. 3, Figs. 2,4, & 6; PI. 5, Fig. 5). The life orientation

of these small attached brachiopods indicate that while the

Paraspirifer was living the other brachiopods were attaching

to its brachial valve (upward in its life time) and their

beak direction, which is towards the commissure line, sug­

gests that they were collecting food from the currents

created by the Paraspirifer (Plate 6, Fig, l). Bryozoans

are the other major group of encrusting organisms on the

Paraspirifer and other spiriferid species; however, encrust­

ing corals and worms are locally common on the brachiopods

(PI, 1, Figs. 2-5; PI, 2, Figs. 1-4; PI. 3, Figs. 1-4;

PI. 4, Figs. 3 & 5). The restriction of some attached bryo­

zoans, corals, worms and sponges to brachiopod brachial

valves suggests that they grew while the brachiopod was

alive. However, some encrustors did extend from the brachial

valve onto the pedicle valve, suggesting habitation after the

brachiopods death (PI. 2, Fig, 4),

The surfaces of both valves have grooves which are

areas of reduced shell deposition because of parasitic worms

attached to the mantle edge. Normal shell deposition will

occur after the parasite is gone (PI, 2, Figs. 1-6; PI. 3,

Figs, 1 & 5 and Kesling, 1975).

The size distribution of Paraspirifer bownockeri (Stewart)

presents some confusion as to their ecological distribution.

No specimens smaller than 30mm wide are known. Although cir-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 58

cumstantial, this may suggest some current sorting of Para­

spirifer in these units. The abundance of larger specimens

may also suggest rapid growth during immaturity, which in

turn would reduce the fraction of life-span during which

shell size was small and thus the proportion of small indi­

viduals found in the death assemblages. Also selective pre­

servation of the large thicker shell has undoubtedly had

some effect as well.

Life orientation of Paraspirifer seems to differ from

smaller sizes to larger ones. Adult Paraspirifer has no

functioning pedicle because the delthyrium is closed by in­

curved beaks while, the young have an open delthyrium sug­

gesting a functional pedicle. The adults were resting on

the substrate and therefore must have had mechanisms for

stability. With regard to this principle, the adult Para­

spirifer was not capable of locomotion and only the smaller

individuals could have moved slightly over the substrate

by their pedicle anchorage (Cooper, 1937),

Genus Spinocyrtia euryteines (Owen) PI. 3, Figs, 4-6; PI,

A, Fig. 5,

Locations Unit 7 & 9 Silica Formation Medusa Quarries,

Figured specimens WMU 2686, 286D, 2861, 2864,

Descriptions The number of specimens studied was 71. In

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 9

general Spinocyrtia has a larger size range than Paraspiri­

fer. Their width ranges from 10-75mm. They also show ani-

sometric growth increases, but to a lesser extent than

Paraspirifer.

Their length ranges from 5mm-35mm and averages 27,5mm.

Thickness ranges from 5-35mm and averages 22.5, Number of

plica ranges from 3-11 in each 5mm and number of growth

lines ranges from 5-30 in each 5mm (Fig, 23).

The shells collected are of a wide size range, bi­

convex in profile, have slightly mucronate cardinal extre­

mities, and have broadly rounded anterolateral and anterior

margins. Their convexity increases toward the posterior

part of specimen. The sulcus is wider toward the anterior

part. Spinocyrtia* s beak is slightly pointed and dis­

tinctly incurved. The fold is low and generally has a

medium depression (or medial fold groove). The interarea

is very low and their micro-ornamentation is distinctive

and separates them from Hflediospirif er and other orthospiri-

fers. Their micro-ornamentations are very fine textured

and consist of radial capillae which are subordinate to the

granular ornamentation which distinctly look like tear­

drops, Their spines are fairly distinct, rising at inter­

vals from the crests of the capillae.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 60

M ax. thickness of inter area (1)

M ax. thickness of inter area (2 )

Figur*' 23. Histograms showing distribution of physical parameters measured on Spinocyrtia euryteines (Owen). X is the mean and n is tne number of specimens measured.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 61 Figure Figure 23. continued.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 62

Discussion; Spinocyrtia euryteines (Owen) is as not abun­

dant as Paraspirifer, but it does provide more information

about general paleoecology. Spinocyrtia euryteines (Owen)

is one of the rare species of spiriferid brrachiopods in

units 7 & 9. These species are well-preserved, mostly by

pyritization. Their growth lines and plica are very well-

preserved (PI. 3, Fig. 4-6).

Spinocyrtia had a functioning pedicle (G. A, Cooper,

1937, Nussmann, 1967), which held the shell firmly to the

substate. The pedicle opening in the shell is the largest

of the species investigated in this study. In Units 6 and

7 (Fig. 11), some specimens of 5pinocyrtia euryteines are

found with pedicle opening downward and compressed in an

anterior-posterior direction as a result of sedimentary

compaction. In Unit 9, Spinocyrtia euryteines specimens

are seldom crushed and are preserved mostly in an inflated

form. However, small individuals are very rare and again

it would be possible for them to be poorly preserved or

sorted out by sedimentary processes.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CONCLUSIONS

The fallowing general palenecological principles can

be used for interpretation of Middle Devonian Silica For­

mation spiriferid brachiopods,

1, Substrate Relations:

Associated sediments have been studied to understand

the nature of the substrate. The shales of the Silica are

fine grained and homogenous suggesting a uniform soft

muddy surface. In contrast some of the limestone in the

5ilica Formation show more current activity,

2, Growth Through Ontogeny:

Ontogeny can be determined by measurements of thickness,

length, width of the fold, number of costae (plica) in each

5mm, number of growth lines (striations) in each 5mm,

volume, height/width ratios of the fold, thickness/length

ratio, general shape of the individuals, and by encrusting

epifauna. Interpretation of growth patterns may suggest

responses to different environments (particularly soft

bottom), however, an interpretation of any size-frequency

distribution requires independent knowledge of growth rate,

3, Encrusting Epizoans:

Encrusting epizoans on the shell surface during the

brachiopods life and borings or other traces Df predators

may be used to estimate life orientations. The orientation

63

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 64

of epizoans is also indicative of whether the brachiopod

was alive or dead when the encrustor came on the shell.

Life orientation and mortality rates between the brachiopods

are very distinctive factors controlling ecologic and paleo-

ecologic parameters.

4, Life Position and Their Orientation in Response to

Currents:

It has been suggested that articulate brachiopods are

excluded from turbulent environments by the weakness of their

pedile attachment. However, some evidence has been offered

in this study which does not support this conclusion. The

orientation of lYlucrospirif er on the substrate in response

to the local current shows that these brachiopods can filter

the water through their body by entering between the fold

and sulcus in the center of the anterior suture and expell­

ing via their two wings,

5, Anchorage and Functioning Pedicle:

Life orientation of some spiriferids seems to change

during life. Adult Paraspirifers have no functioning pedi­

cle because the delthyrium is closed; however, the young

have an open delthyrium suggesting a functional pedicle.

Adults rested on the substrate and therefore needed mecha­

nisms for stability. Some Spinocyrtia species also did not

have a functioning pedicle and good anchorage during life,

because of their narrow pedicle opening, they had a weaker

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 65

pedicle and probably lived in a lower energy environment.

Those species with larger pedicle openings may have anchored

around boulders or other hard objects to withstand higher

energy conditions.

Specific interpretation of ecological relationships can

be made For the brachiopod genera found in the Silica Forma­

tion (Fig, 24).

1, lYlucrospirif er mucronatus (Conrad)

5ubstrates Soft lime mud or clayey mud units 17 & 18,

Growth ontogeny* Rapid growth (larger specimens with

small number of plica in each 5mm,

Epizoanss Very few, probably because coarse ornamen­

tation prevented easy attachment to shell surface.

Life position: Increased surface area to keep from

sinking in the mud, most obviously by non-

isometric growth of the cardinal areas.

Anchorage: 5ome were attached by pedicle and their

small pedicle opening suggests they had a weak

anchorage.

2, lYlucrospirif er prof undus (Grabau) Unit 7

Substrate: Lime or clayey mud, often slightly silty.

Growth ontogeny* Adults usually very thick; inflated

shell elevated the free margin above the sedi­

ment surface. Cardinal area not expanded for

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 24. Alternative possible life orientations for taxa studied herein.

1. Mucrospirifer has large surface area to keep from sinking in to the mud. 2. Spinocyrtia, their wide pedicle opening allows for stableattachment. 3. Paraspirifer with encrusting of other brachiopods like Mucrospirifer S Sphenophragmus and other taxa 4. Mucrospirifer attaching on bryozoans. 5. Crinoid could be an attachment site for young brachiopods. 6. Strophodonta has large surface area to keep from sinking in to the mud. Although not studied in this work, this genus shows adaptations to soft substrates which are very-similar to the Spiri- ferids.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6?

substrate support.

Epizoans: Very few because of coarse ornamentation.

Life position: Some were attached to other brachio­

pods or bryozoans and some were lying on the

muddy surface with their brachial valve upward.

Anchorage: Some were attached by pedicle and the

strength of attachment is proportional to the

size of the pedicle opening.

3. Hflucrospirifer grabaui (Stumm) Unit 15

Substrate: Clayey muds, some shell pavements, silty

muds.

Growth ontogeny: Strongly mucronate and very fragile

cardinals which developed at later growth stages;

young individuals (less than 12mm) are not

strongly slate,

Epizoans: Very few.

Life position: Functioning pedicle that provided firm

attachment to the substrate and ability tD change

orientation.

Anchorage: Pedicle of moderate length enabled them to

change position with respect to the substrate

and currents.

4, mucrospirifer prolificus (Stewart) Unit 7

Substrate: Soft clayey mud, some lime muds, occasionally

silty.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 68

Growth ontogeny: Cardinal areas are of moderate length

in adults but not extended in young forms,

Epizoans: Very few.

Life position: The pedicle is able to obtain satisfac­

tory anchorage in soft materials, but the broad

area of the shell and cardinal areas could sup­

port the free living shell.

Anchorage: Specimens of this species have a large pedicle

opening indicating a thick pedicle muscle which

could help them maintain their anchorage on soft

or hard substrate.

5. Paraspirifer bownockeri (Stewart) Units 7 & 9

Substrate: 51ightly silty, clayey and lime mud.

Growth ontogeny: Thickness of shell is accentuated in

large forms to keep its margin above the sedi-

ment-water interface. Rapid growth during their

immaturity.

Epizoans: Abundant on dorsal valve suggesting a dorsal

upward life orientation.

Life position: Brachial valve upward and exaggerated

thickness to keep from sinking into the mud,

free living on the muddy surface.

Anchorage: No functioning pedicle in adult

stage indicated by delthyrium and incurved beak growth.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 69

6. Spinocyrtia euryteines (Owen) Units 7 & 9

Substrate: Slightly silty, calcareous muds, shell

pavements.

Growth ontogeny: Rapid growth during immaturity,

little difference between the growth of the

two valves. Nearly isometric growth through

ontogeny,

Epizoans: Common, near anterior margin.

Life position: They are found with their beak area

downward on the substrate, large pedicle opening

suggests strong attachment to substratum.

Anchorage: They had a strong functioning pedicle sug­

gested by a very large pedicle opening.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. REFERENCES CITED

Ager, D, V, 1963, Principles of Paleocology. New York, McGraw-Hill Book Co. 371 p.

Anderson, E, J. 1971, Environmental models for Paleozoic communities. Lethaia, v, 4, p. 287-302.

Basset, C. F. 1935, Stratigraphy and paleontology of the Dundee Limestone of southeastern Michigan, Bull. Geol. Soc, Amer. v. 46, p. 425-462.

Bertsky, P. W. 1969, Evolution of Paleozoic benthic marine invertebrate communities, Paleogeog,, Palaeoclima- tol, and Palaeoecology, v. 6, p. 45-59.

Bowen, Z. P., Rhoads, D. C, & lYlcAlester, A, L. 1974, Marine benthic communities in the Upper Devonian of New York. Lethaia, v. 7 p. 93-120.

Cloud, P. E. 1948, Assemblages of diminutive brachiopods and their paleoecological significance. Jour. Sed. Petrology, v. IB, p. 56-60.

Cooper, G. A, 1937, Collecting fossils in Michigan, Pennsyl­ vania, New York, and Canada. Smithsonian Inst. Explor, and field work 1938, Pub. 3525 p. 29-32.

Cooper, G. A, 1942, Correlation of the Devonian sedimentary formations of North American. Geol. 5oc, Am. Bull, v. 53, p. 1729-1794.

Cooper, G. A. 1967, Age and correlation of the Tully and Cedar Valiev Formations in the United States. In D. H. Oswald (ed.J International symposium on the Devonian system. Alberta Soc. Pet, Geol. v. 2 p. 701-709.

Copper, p. 1967, Adaptations and life habits of Devonian atrypid brachiopods. Paleogeog,, Palaeoclimatol., Palaeoecology, v. 3 p. 363-379.

Craig, G. Y. 1953, Fossil communities and assemblages. Am. Jour. Soc., v. 251 p. 547-548,

Craig, G. Y. & Hallam, A, 1963, Size-frequency and growth- ring analysis of Mytilus edulis & Cardium edulis and their paleoecological significance” Paleontology, v. 6 p. 731-750.

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Dekeyser, T. L, 1977, Late Devonian (Frasnian) brachiopod community patterns in western Canada and Iowa. Jour. Paleontology, v. 51, No. 1, p. 181-196,

Driscoll, E. G., Hall, D., Nussmann, D, G. 1965, Morphology & Paleoecoiogy of the brachiopod Leiorhynchus kelloggi (Hall), Middle Devonian. Ohio and Michigan and Dnfcario. Jour. Paleontology, v. 39, p. 916-1100,

Ehlers, E t, Stumm, E, C, & Kesling, R, V, 1951, Devonian rocks of southeastern Michigan and northwestern Ohio, 40 p., illus. ind, geol. sketch map, Ann Arbor, Edwards Bros.

Elliott, G, F. 1956, Post-Paleozoic brachiopod ecology a reassessment. Geol. Mag., v. 93, p. 196-200.

Fagerstrom, J. A. 1964, Fossil communities in Paleoecoiogy: Their recognition and significance. Geol, Soc, Am, Bull., v. 75, p, 1197-1217.

Fenton, C, L, & Fenton, M.A, 1928, Ecologic interpretation of some biostratigraphic terms. Am, Midland Naturalist, v. 11, p. 1-23.

Fox, W, T. 1962, Stratigraphy and paleoecoiogy of the Rich­ mond Group in southeastern Indiana. Geol. Soc. Am. Bull., v. 73, p. 621-642.

Hoare, R, D, & Stellar, D. L, 1969, Inarticulate brachiopods of the Silica Formation (Devonian) of Ohio and Michi­ gan. Contrib, Mus. Paleontology Univ. Mich., v. 22, p. 263-272.

Kesling, R, V. & Chilman, R, 1975, Strata and megafossils of the Middle Devonian 5ilica Formation. Papers on Paleo. No. 8 p. 1-408.

Mitchell, 1967, Stratigraphy of the Silica Formation of Ohio S. and Hungry Hollow Formation of Ontario, with paleo- geographic interpretations: Papers, Mich. Acad, Sci., Art, Letters, v. 52, p. 175-196,

Nussman, D. G. 1975, In Kesling & Chilman. Paleoecoiogy and pyritization of the Silica Formation, strata and mega­ fossils.

Pitrate, C. W. 1975, Orthospirifer, New Genus of Devonian Spinocyrtid Brachiopods. Jour. Paleontology v. 49, p. 387-394.

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Pitrate, C, W. 1977, Spiriferid Brachiopods from the Traverse Group of Michigan: Orthospirifer Jour. Paleontology, No. 2 p. 330-342.

Richards, R. P. 1972, Autecology of Richmondian brachiopods (Late Ordovician of Indiana & Ohio) Jour. Paleontology, v. 46 p. 386-405.

Rollins, H, B, & Donahue, J, 1975, Towards a theoretical basis of Paleoecoiogy concepts of community dynamics. Scientific Contribution No. 74-237 Lethaia, v. B, p. 255-270.

Rudwick, M. J, 5. 1962, Notes on the ecology of brachiopods in New Zealand, R. 5oc. New Zealand Trans., v. 88, p. 327-355.

Rudwick, 1TI, J S. 1970, Living fossil brachiopods. Hutchin­ son and Lompanyf London. 199 p.

Shimer, H, Ul., Grabau, A. Ul. 1902, Hamilton Group of Thed- ford, Ontario. Bull, Geol. Soc. Am., v. 13, p. 149- 186.

Stanley, S. ffl, 1974, What has happened to the articulate brachiopods? Geol, 5oc, Am, Ann, Mtgs. Abstr, with Programs, v, 6, p. 966-967.

Stanley, S, IY1, 1975, A theory of evolution above the species level. Proc. Nat. Acad, Sci, U.S.A., v, 72, p. 646- 650.

Stewart, G, A, 1927, Fauna of the Silica Formation of Lucas Co., Ohio, Ohio Geol. Surv, Bull., Surv. 4, v, 32, 76 p.

Stewart, G, A. 1930, Additional species from the Silica For­ mation of Lucas County, Ohio. Bull. Geol. Surv. Ohio, v, 30,p. 52-58.

Stumm, E. C. 1951, Check list of fossil invertebrates des­ cribed from Traverse Group of Mich, Contrib, Mus. Paleontol, Univ. mich. v. 9, p. 1-44,

Stumm, E, C, 1961, Addenda to check list of fossil inver­ tebrates described from Traverse Group of mich. Con­ trib. mus. Paleontol. Univ. mich. v. 17, p. 149-171.

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Stuum, E, C. & Chilman, R. B. 1967, Check list of fossil invertebrates described From the Middle Devonian Silica Formation of Northwestern Ohio and South­ eastern Michigan, Contribution from the Museum of Paleontology, Univ. of Mich, v. 21, p. 123-137,

Sutton, R. G., Bowen, Z. P. & McAlester, A, L, 1970, Marine environments of the Upper Devonian Sonyea Group of New York, Bull. Geol, Soc, Am., v, 81, p. 2975-2992,

Thayer, C, W. 1974, Marine paleoecoiogy in the Upper Devonian of New York. Lethaia, v, 7, p. 121-155,

Thayer, C, W, 1975a, Size-frequency and population struc­ ture of brachiopods, Palaeogeog., Palaeoclimatol and Paleoecoiogy, v, 17, 139-148,

Thayer, C, IaJ. 1975b, Strength of pedicle attachment in articulate brachiopods: ecologic and paleoecologic significance. Paleobiology, v, 1, p, 388-399,

Thayer, C, W, & Steele-Petrovic, H, 1975, Burrowing of the lingulid brachiopod Glottidia pyramidate: its ecologic and paleoecologic significance, Lethaia, v. 8, p. 209-221.

Thayer, C, W, 1977, Recruitment, growth and mortality of a living Articulate brachiopod, with implication for the interpretation of survivorship curves. Paleo­ biology, v. 3, p. 98-109,

Thorson, G, 1957, Bottom communities, p, 461-534 in Hedgpeth, J. W., Editor. Treaties on marine ecology and paJeo- ecology, V. 1 Ecology Geol. Soc, Am. Mem. 67, 1296 p.

Tillman, J, R. 1964, Variation in species Mucrospirifer from Middle Devonian rocks of Michigan"! Ontario and Ohio. Jour, Paleontology, v. 38, p. 952-964.

Veevers, J, J. 1959, Size and shape variation in the brachi­ opod Schizophoria from the Devonian of Western Austra­ lia, Jour. Paleontology, v. 33,

Zeigler, A, M., 1968, The composition and structure of lower Silurian marine communities: Lethaia, v. 1, p. 1-27,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX I

74

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I

Figure 25. measuring the section looking to the west units 11-16, slabs are from 13-14 with molds of burrows & trails, South-South Quarry,

:...... r

Figure 26. Medusa south-south Quarry looking at west units 9-17, the person is standing in front of units 10-14, August, 1977,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. F igure 27, Medusa south-south quarry, looking uiest, person is standing on approximately units 9 & 10, the rest of the section is from

F igure 28, Medusa south-south quarry e southwest corner of the quarry as seen from the upper bench. Ten Mile Creek Dolomite over unit 29, August, 1977,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PLATES

Plate One

Figure Page

1-6 Paraspirifer bouinockeri (5tewart): Units 7 and ^

9 Medusa south-south quarry, UlfYlL) 2634, XI UIIY1U 2639,

XI. 3, LUIY1U 266D, XI.

1, Anterior view with sponge borings along commissure

line. IA1IY1U 2859 XI.3.

2, Dorsal view with encrusting bryozoans, WIY1U 2634,

XI.

4, Dorsal view with encrusting bryozoans.

WIY1U 2639, XI.1.

6, Dorsal view with encrusting brachiopods lYlucrospiri-

fer profundus (Grabau) and 5phenophragmus sp. U1IYILJ

2660, XI.

3&5, Anterior views. UIIY1U 2639, XI.1 WMU 2634, XI.3

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PLATE

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ?B

Pla t e Two

Figure Page 49 1-6. Paraspirifer bownockeri (Stewart): Units 7 and

9 Medusa south-south quarry.

1, Ventral view infested with Cornulites sp, causing

considerable displacement of the line of closure. UJIY1U

2637, XI.1.

2, Ventral view infested with Cornulites sp. causing

considerable displacement of the line of closure. U1IYIU

2642, XI.1.

3, Dorsal view with marks of injuries. WHflU 2642, XI

5, Dorsal view with marks of injuries, WIY1U 2633, XI

4, Lateral view of Paraspirif er with four Cornulites

along its edge. U1WU 2642, XI

6, Ventral view with marks of injuries. UJMU 2632, XI

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PLATE 2

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 79

Plate Three

Pag e Figure

1-3. Paraspirif er bownockeri (Stewart)s Units 7 and 5 49

medusa south-south quarry. WMU 2660, XI.2

1, Dorsal view with encrusting of Hflucrospirifer

profundus (Grabau) and Sphenophragmus sp. WMU 2660,

XI.2

2&3, Lateral views. WMU 2660, XI.2

4-6. Spinocyrtia euryteines (Owen): Unit 7, Medusa south- 59

south quarry,

4, Ventral view with attached Mediospirifer audaculus

near the sulcus area. WMU 2686, XI

5, Ventral view with encrusting of bryozoans. WMU

2860, XI.2

6, Dorsal view with encrusting of bryozoans. WMU 2661, XI

7, Mucrospirifer grabaui 5ttJmm: Unit 15, Medusa south- 39

south quarry, WMU 2862, XI,1

Ventral view with preservation of the fragile "wing

tips" along the hinge.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PLATE 3

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission P la te F o u r

F igure Pag e

1-3, Paraspirif er bouunockeri (Stewart): Units 7 and 49

9 Medusa south-south quarry.

1, Posterior view with heavy pyritization WMU

2636, XI.3

2» Dorsal view with heavy pyritization, WMU

2636, XI.2

3, Anterior view with sponge borings along the

commissure line. WMU 2863, XI.2

4, .Paraspirifer bownockeri (Stewart): Units 7 49

and 9 Medusa south-south quarry. WMU 2650,

XI.2

Lateral view with interior calcite crystal

growth,

5, Spinocyrtia euryteines (Owen): Unit 7 59

Medusa south-south quarry. WMU 2864, XI,1

Posterior view with pedicle opening.

6, Close up of Mucrospirifer profundus (Grabau) 35

encrusting on the Paraspirif er bownockeri

(Stewart).

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P la te Five

Figure Page 1-3. Hflucrospirifer grabaui (Stumm): Unit 15 39

lYIedusa south-south quarry.

1, Ventral vieui LUIY1U 2693, XI.7

2, Ventral view WMU 2692, XI

3, Ventral view WMU 2751, XI.1

4,5,8, Mucrospirifer prolificus (Stewart): Unit 7 45

Medusa quarries, WMU 2745, XI.2 WMU 2758, XI.4

WMU 2750, XI.2

6,7 Mucrospirifer profundus (Grabau): Unit 7 35

Medusa south-south quarry WMU 2822, XI,2

Ventral and dorsal views

9, Mucrospirifer mucronatus (Conrad): Unit 17 28

Medusa quarries, WMU 2880, XI,3

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P l a t e Six

F igure Page 49 1, Paraspirifer bownockeri (Stewart)j Units ? and

9, IAIIY1U 2660, X2.9

Medusa south-south quarry, dorsal view with en­

crusting Mucrospirifer profundus (Grabau) and

Sphenophragmus sp., arrows indicate the direction

of the fold-beak axis.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PLATE 6

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.