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

Transcription

1 Western Michigan University ScholarWorks at WMU Master's Theses Graduate College Paleoecology of the Spiriferid Brachiopods of the Silica Shale Formation (Middle Devonian), S.E. Michigan and N.W. Ohio Darioush T. Ghahremani Western Michigan University Follow this and additional works at: Part of the Geology Commons 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 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

2 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

3 AB5TRACT Spiriferid brachiopods of the Middle Devonian Silica Formation in northwestern Ohio and southeastern Michigan show many Features that are useful For paleoecologic interpretation. This study is undertaken to examine and interpret the paleoecology and paleobiology of six spiriferid 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 measurable 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

4 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 University 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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6 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

7 TABLE OF CONTENTS PAGE INTRODUCTION... 1 SAMPLING LOCALITIES... 4 TECHNIQUES PREVIOUS WORK STRATIGRAPHY... 1? MIDDLE DEVONIAN BRACHIOPOD COMMUNITIES PRINCIPLES OF PALEOECOLOGICAL ANALY5IS PALEOECOLOGICAL DESCRIPTIONS OF SPIRIFERIDAE IN SILICA FORMATION CONCLUSIONS REFERENCES CITED APPENDIX I PLATES iv.

8 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 Figure 7. Molds of trails and burrows; bottom surface of overturned slab, unit Figure 8. Various morphologic characteristics of all specimens used in this study Figure 9, Stratigraphic section of the Traverse Group Figure 10. Correlation of the Devonian rocks of New York, Northern Mich., S.E. Mich, and N.Ul. Ohio Figure 12. Chart showing major faunal zones and correlation of the Silica Formation with other rock units in the Michigan basin Figure 13. Measurements of Mucrospirif er mucronatus (Conrad) , 31 v

9 Page Figure 14, Relation of surface area and volume of objects on substrate 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 Figure 18. measurements of mucrospirifer prolificus (Stewart)... 46, 47 Figure 19. measurements of Paraspirifer bownockeri (Stewart)... 50, Figure 20. Growth characteristics of Paraspirifer bownockeri (Stewart) Figure 21. Plot of length versus thickness in Paraspirif er bownockeri (5tewart) Figure 22. Plot of volume versus length in Paraspirif er bownockeri (Stewart) Figure 23. measurements of Spinocyrtia euryteines (Owen)... 60, 61 Figure 24, Alternative possible life orientations for taxa studied herein Figure 25. measured sections in the Silica Formations Figure 26, Photo showing medusa South-South quarry. 75 vi

10 Page Figure 27, Medusa 5outh-5outh quarry Figure 28. Medusa South-South quarry showing Ten Mile Creek Dolomite overlying Silica Formation. 76 vii

11 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 represented Faunal constituents, the spiriferid brachiopods. Much work has been done using brachiopods as community and ecological indicators (Ziegler, 19GB; Rolling and Donahue, 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

12 2 however, very little integrated analysis of biological communities and their ecological relationships has been suggested. 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 communities and their ecological relationships to the Silica Formation, 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, distance from shore, turbulence, sediment supply, rate of deposition and availability of food are likely to have been major factors which affected the survival and ecological development 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,

13 3 ARBOR Lenaw ee 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.

14 5AIY1PLING LOCALITIES The Silica Formation examined in this study is exposed 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 Formation 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 Sylvania 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

15 Dolomite Dundee ' Lucas Dol LJ Medusa S. S. Q u a rn M edusa S.Q u a rry YV-vv w,. '. '.» / - «, #* «* «.»*#*,* ^ V * G lass Q u a rry Ten M ile Creek! Dolomite ' Scale in Miles I M edusa Silica Fm. = 1 N. Q u a rry I N i c ^ J" Dundee n i h ti H k i K i n i j w t k n K r k r T j N M H j v r f r Centennial >l\sm\m\l\rul-uis~inkl»h t r v i - :». Figure 2. Outcrop of study area showing quarries near town of Silica, Ohio. m

16 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 Formation, 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 Formation 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,

17 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.

18 6

19 Figure 5. View looking Southwest in Medusa south-south quarry.

20 10 Figyre- Medui. units'9-. a n.-j'.-ija Figure 7. Molds of ai~l ~and^t^ ^ w sfr bi > $ ^. of overturfed slab unit 14, presenting record o. trails in? uppenftost layer of^uait '13v August,1977r

21 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 thickness 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 kerosene. 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 summarized in a series of graphic comparisons presented with the descriptive paleontology. 11

22 12 The relationships between the measured parameters have been analysed by statistical techniques using the facilities and programs available in the Computer Center at wmu.

23 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

24 14 Figure 8. Measured parameters used in this study.

25 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 i information about the stratigraphy of the Silica Formation 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 aspects 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

26 16 Feet a. Ten M ile Creek Dolomite Units U J tn Q U J Silica Formation CL I/I Dundee Limestone Anderdon Limestone Ul Lucas Dolomite 8 4 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).

27 STRATIGRAPHY Information about Middle Devonian Traverse Group stratigraphy in the study area and adjacent areas has been accumulating for more than 60 years (Cooper et al., 1942; Driscoll 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 include all Middle and Upper Devonian stratigraphic units directly 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 informal litnoiogic units; Blue Limestone (3 feet), Silica Formation (10 feet), Shaly limestone (4 feet), Blue limestone (6 feet), Columbus Limestone, 17

28 18 N E W YORK SERIES N.M IC H. G E N ER A LIZED S.-E.M IC H N.-W.O H IO ENFIELD SHALE AN TRIM SHALE ITHACA SHALE ANTRIM SHALE O HIO SHALE GENUNDEW A LIMESTONE SQUAW BAY Ls GENESEO SHALE TUI IY Fm. THUNDER BAY Is. POTTER FARM Fm. MOSCOW Fm LUDLOWVILLE Fm NORW AY Pt Fm FOUR MILE D AM Fm. TEN MILE CREEK DOLOMITE ALPENA Is. NEW TON CREEK Is. SKANEATELES Fm GENSHAW Fm. FERRON POINT Fm. ROCKPORT QUARRY Ls SILICA FORMATION MARCELLUS Fm BELL SHALE ROGER CITY Is OUNDEE Ls. DUNDEE Ls m 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>*

29 1 9 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 sequences of "ITflucrospiriferid Transition" zone, which in turn is overlain by shale (2, 3, 4), and an upper sequence consisting 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 adjacent 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 extensive Middle Devonian epicontinental sea.

30 20 Ten M ile Clc.Dol. Bioclastic Ls- Lithotope Norm al Argillaceous Ls. Lithotope ir B tnra Cryptostom ate Crinoid Ls. Lithotope Argillaceous mlulm m l f l m M ucrospirifer Transition Lithotope Shale Lithotope Proper «E.w» v o m Smothered Bottom Assem blage 03 O m m CO,m iw m im m m mi m fainflraifltowi units 1-27 from Nussmann,1975. units 1-5 from Kesling, \r * 5 A 4 1 n n E Z H 'TJ i " "i =a D u n d ee Ls. i ~ r Figure 11. Stratigraphic sequence of the Silica Formation.

31 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 Schizophoria ferronensis (Stewart) (imbrie) Locality: Michigan, S,E, Ontario 3. Aulocystis-Rhipidomella Echinocoelia sp, cf. ambocoeloides (Cooper) a Strophodonta sp, 0 Strophodonta sp. Locality: Ontario, Ohio, Z1

32 N.W. Michigan G ravel Point Fm. Charlevoix Fm. Roger C ity Ls. N.E. Michigan Four M ile D a m Fm. A lp en a Ls. N ew ton Ck. Ls. G en sh a w Fm. Ferron Pt. Fm. Rockport Q u a rry Ls. Bell Sh. Roger C ity Ls. S.W. Ontario H ungry H o llo w Fm. A rkona Ferron Pt. Fm. Fm. Rockport Q u a rry Ls. Bell Sh, D undee D e la w a re Ls. S.E. Mich. N.W. Ohio Ten M ile Ck. )olom ite Silica Fm. UPPer M em ber Silica Fm. M iddle Member Silica Fm. Lower M em ber Dundee Ls. N. Indiana Ten M ile Ck. Dolom ite S ilica Fm. Silica Fm. D et. River G ro u p N.-CENT. Ohio Prout Ls. Plum Brook Fm. D e la w a re Ls. Leiorhynchus Stereotoechus Aulocystis- Rhipidomela Hercostrophia Helopora Tropidoleptus- Hexagonaria Figure 12. Chart of major faunal zones and correlation of Silica Formation with other rock units in the Mich, basin and adjacent midcontinent areas (Mitchell* 1967). M ro

33 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 Michigan, 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 communities 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

34 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 riercostrophianelopora community extends from units 5A to (Fig, ll). Aulocystls-Rhipidomella community starts at unit 14A and ends above unit 18B, The Leiorynchus-Stereotoechus community 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),

35 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 guidelines 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 contrast to many of the brachiopods uuhich appear to have been transported From other areas and may be in different orientations than their living positions. Although some brachiopods 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 stability and Functional orientation. Fourteen different parameters were observed and care- Fully measured For samples of the six most abundant species 25

36 26 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 brachiopods, 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 determined. Many brachiopods from the Silica Formation are encrusted 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 whether the brachiopod was alive or dead when the encrustor

37 27 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 understand the nature of the substrate. The shales of the Silica Formation are fine grained and homogenous suggesting a uniform soft muddy surface. In contrast, some of the limestone 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 living articulate brachiopods (Thayer, 1975a). Life orientation and mortality rates between these brachiopods are very distinctive 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 impact on population numbers in young brachiopods, Paine

38 28 (1976) mentioned that many prey species grow rapidly in early parts of life to minimize their susceptibility to predators.

39 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 numerous ribs, crossed by prominent growth varices, hinge is elongated and in some cases mucronate at the extremities. In the 5ilica Formation, specimens of Hflucrospirifer mucronatus (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 different histograms have been prepared for each genus in the lylucrospiriferidae. The following characteristics are presented: height and width of the fold, width of the hingeline, 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

40 3D Height of the fold W idth of the fold mm W idth of the hingeline x = 11 X = 1A mm Thickness o mm 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.

41 3 1 X = 4 X = ml mm Volume M a x. thickness of inter area 3 2V X = No. of grow th in 5 mm No. of Plica in 5 mm n=42 Figure 13. continued.

42 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 position for lylucrospirif er mucronatus collected from the other formations of the Traverse Group of lylichigan as that suggested 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

43 33 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 brachiopods 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. However, if settlement can occur, the established brachiopod may be able to withstand higher energies than was previously thought possible.

44 34 Because of diagenetic processes, it is not possible to determine the original weight of the brachiopod shells; however, measurements of volume can give relative relationships (Fig, 14), Presuming that larger volumes reflect heavier shells, interpretations can be made of the ecological 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 surface 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 extremities; maximum width is along the hingeline, width about 1/3 greater on average than length. Lateral and anterolateral border are broadly convex, anterior border is straight or slightly

45 ^ 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

46 36 concave. Number of plica in each 5mm ranges from 4-7mm and averages shout 5, 5mm ranges from 5-15mm. The number of growth lines in each Costae and intercostal furrows are V-shaped, and both valves are moderately convex in lateral profile. Surface length of pedicle valve is greater than brachial 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 specimens of lylucrospirif er profundus (Grabau) in order to better understand the ecology and life position of the species (Fig. 15), Shells of this species are relatively thick in contrast to lylucrospirif er mucronatus which suggests that many individuals were probably supported by the substrate and the inflated shell elevated the free margin above the sediment surface. 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.

47 3? x=n 15 X = Thicicnejs Length F 10 X = 2 8 X = W idth of th e hingeline M a x * thickness o f 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.

48 38 Volum e No- of growthline in 5 mm Figure 15. continued.

49 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 substrate 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

50 4 0 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 addition of shell material in the adult stage at the cardinal extremities. Cardinal area fragile with less than 20 percent 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 suggest 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 overturning and burial in the muddy substrate. Cooper (1937)

51 Thickness W idth length mm Volume ml X 3 15 X = e 5 i mm Max. 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.

52 X=7.5 L o W idth of the fold 10 X = X= L f c 10 No- of growthline in 5 mm No- of Plica in 5 mm n314 Figure 16. continued.

53 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 optimum 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 position both the shell and circulation of water within it would have been symmetric with respect to the oncoming current. 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.

54 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.

55 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 fragile 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 specimens measured was 77 (Fig. 18), Discussion: lylucrospirifer prolificus (Stewart) is one of

56 46 Growthline in 5m m Figure 18. Histograms showing distribution of physical parameters measured on Mucrospirifer prolificus(stewart). X is the mean and n is the number of specimens measured.

57 4? X = 8 2 F X=I7 10 o Thickness Length X= Width of the hinge line X=4.8 X= Volume M ax. thickness of inter area na77 Figure 18. continued.

58 48 the most studied species of Mucrospirifer mainly because of their abundance in Units 1-9, preserved and easily measured, Specimens are very well 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 brachiopods living today seem to require some hard and firm substratum (for example, rock or shell) for attachment (Plate 6), but enough exceptions are known to show that it is possible 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 anchorage 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.

59 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 collected 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 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 orientations 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 selectively 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

60 Ln X=l-9 X=3.6 Total w idth Thickness / Length 3 2 I X= X= _ L N o - of Plica in 5 n Distant of the n e w p ;ca from the beak 3 2 X=12 X = No- o f grow thline 111 5n »i Volum e n» 37 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.

61 5 1 X= mm Height / W id th of the fold X = " L l " W id th o f the hingeline M a x. Thickness of inter a re a "= 3 7 Figure 19. continued.

62 5 2 E X P L A N A T I O N OF FIG. 20 1, Paraspirifer bownockeri (Steuiart): brachial valve upward (life position). 2, Paraspirifer bownockeri (Stewart): several Cornultes along commissure of the brachiopod, causing considerable 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.

63 W id th larger than H eight W id th = H eight and Thickness an d Thickness H e ig h t and Thickness larger than W id th Figure 20. Comparison of the height and thickness to the width at different stages of growth. Ul LA

64 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

65 55 GROWTH STAGE *<---- -> B Length Thickness Figure 21. A, plot of length compared to thickness in Paraspirifer bownockeri showing the growth modification at a particular stage (point A ) to adjust for continual sinking into the soft muddy substratum* B» is shell thickness and L, is shell length. Growth of shell length diminishes while thickness continues to increase in larger specimens.

66 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.

67 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, suggests 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, encrusting 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 bryozoans, 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-

68 58 cumstantial, this may suggest some current sorting of Paraspirifer 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 individuals found in the death assemblages. Also selective preservation 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 incurved beaks while, the young have an open delthyrium suggesting 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 Paraspirifer 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

69 5 9 general Spinocyrtia has a larger size range than Paraspirifer. Their width ranges from 10-75mm. They also show anisometric 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, biconvex in profile, have slightly mucronate cardinal extremities, 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 distinctly 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 teardrops, Their spines are fairly distinct, rising at intervals from the crests of the capillae.

70 60 Max. 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.

71 6 1 Figure 23. continued.

72 62 Discussion; Spinocyrtia euryteines (Owen) is as not abundant 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. pyritization. These species are well-preserved, mostly by 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.

73 CONCLUSIONS The fallowing general palenecological principles can be used for interpretation of Middle Devonian Silica Formation 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

74 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 paleoecologic 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 expelling via their two wings, 5, Anchorage and Functioning Pedicle: Life orientation of some spiriferids seems to change during life. Adult Paraspirifers have no functioning pedicle because the delthyrium is closed; however, the young have an open delthyrium suggesting a functional pedicle. Adults rested on the substrate and therefore needed mechanisms 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

75 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 Formation (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 ornamentation 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 sediment surface. Cardinal area not expanded for

76 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 Spiriferids.

77 6? s u b s t r a t e support. Epizoans: Very few because of coarse ornamentation. Life position: Some were attached to other brachiopods 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.

78 68 G r o w t h ontogeny: Cardinal a r e a s are of m o d e r a t e length in adults but not extended in young forms, Epizoans: Very few. Life position: The pedicle is able to obtain satisfactory anchorage in soft materials, but the broad area of the shell and cardinal areas could support 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.

79 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 suggested by a very large pedicle opening.

80 R E F E R E N C E S CITED Ager, D, V, 1963, Principles of Paleocology. McGraw-Hill Book Co. 371 p. New York, Anderson, E, J. 1971, Environmental models for Paleozoic communities. Lethaia, v, 4, p Basset, C. F. 1935, Stratigraphy and paleontology of the Dundee Limestone of southeastern Michigan, Bull. Geol. Soc, Amer. v. 46, p Bertsky, P. W. 1969, Evolution of Paleozoic benthic marine invertebrate communities, Paleogeog,, Palaeoclimatol, and Palaeoecology, v. 6, p Bowen, Z. P., Rhoads, D. C, & lylcalester, A, L. 1974, Marine benthic communities in the Upper Devonian of New York. Lethaia, v. 7 p Cloud, P. E. 1948, Assemblages of diminutive brachiopods and their paleoecological significance. Jour. Sed. Petrology, v. IB, p Cooper, G. A, 1937, Collecting fossils in Michigan, Pennsylvania, New York, and Canada. Smithsonian Inst. Explor, and field work 1938, Pub p Cooper, G. A, 1942, Correlation of the Devonian sedimentary formations of North American. Geol. 5oc, Am. Bull, v. 53, p 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 Copper, p. 1967, Adaptations and life habits of Devonian atrypid brachiopods. Paleogeog,, Palaeoclimatol., Palaeoecology, v. 3 p Craig, G. Y. 1953, Fossil communities and assemblages. Jour. Soc., v. 251 p , Am. Craig, G. Y. & Hallam, A, 1963, Size-frequency and growthring analysis of Mytilus edulis & Cardium edulis and their paleoecological significance Paleontology, v. 6 p

81 71 Dekeyser, T. L, 1977, Late Devonian (Frasnian) brachiopod community patterns in western Canada and Iowa. Jour. Paleontology, v. 51, No. 1, p , 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 , 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 Fagerstrom, J. A. 1964, Fossil communities in Paleoecoiogy: Their recognition and significance. Geol, Soc, Am, Bull., v. 75, p, Fenton, C, L, & Fenton, M.A, 1928, Ecologic interpretation of some biostratigraphic terms. Am, Midland Naturalist, v. 11, p Fox, W, T. 1962, Stratigraphy and paleoecoiogy of the Richmond Group in southeastern Indiana. Geol. Soc. Am. Bull., v. 73, p Hoare, R, D, & Stellar, D. L, 1969, Inarticulate brachiopods of the Silica Formation (Devonian) of Ohio and Michigan. Contrib, Mus. Paleontology Univ. Mich., v. 22, p Kesling, R, V. & Chilman, R, 1975, Strata and megafossils of the Middle Devonian 5ilica Formation. Papers on Paleo. No. 8 p Mitchell, 1967, Stratigraphy of the Silica Formation of Ohio S. and Hungry Hollow Formation of Ontario, with paleogeographic interpretations: Papers, Mich. Acad, Sci., Art, Letters, v. 52, p , Nussman, D. G. 1975, In Kesling & Chilman. Paleoecoiogy and pyritization of the Silica Formation, strata and megafossils. Pitrate, C. W. 1975, Orthospirifer, New Genus of Devonian Spinocyrtid Brachiopods. Jour. Paleontology v. 49, p

82 72 Pitrate, C, W. 1977, Spiriferid Brachiopods from the Traverse Group of Michigan: Orthospirifer Jour. Paleontology, No. 2 p Richards, R. P. 1972, Autecology of Richmondian brachiopods (Late Ordovician of Indiana & Ohio) Jour. Paleontology, v. 46 p Rollins, H, B, & Donahue, J, 1975, Towards a theoretical basis of Paleoecoiogy concepts of community dynamics. Scientific Contribution No Lethaia, v. B, p Rudwick, M. J, , Notes on the ecology of brachiopods in New Zealand, R. 5oc. New Zealand Trans., v. 88, p Hutchin Rudwick, 1TI, J S. 1970, Living fossil brachiopods. son and Lompany f London. 199 p. Shimer, H, Ul., Grabau, A. Ul. 1902, Hamilton Group of Thedford, Ontario. Bull, Geol. Soc. Am., v. 13, p Stanley, S. ffl, 1974, What has happened to the articulate brachiopods? Geol, 5oc, Am, Ann, Mtgs. Abstr, with Programs, v, 6, p Stanley, S, IY1, 1975, A theory of evolution above the species level. Proc. Nat. Acad, Sci, U.S.A., v, 72, p 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 Formation of Lucas County, Ohio. Bull. Geol. Surv. Ohio, v, 30,p Stumm, E. C. 1951, Check list of fossil invertebrates described 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 invertebrates described from Traverse Group of mich. Contrib. mus. Paleontol. Univ. mich. v. 17, p

83 73 Stuum, E, C. & Chilman, R. B. 1967, Check list of fossil invertebrates described From the Middle Devonian Silica Formation of Northwestern Ohio and Southeastern Michigan, Contribution from the Museum of Paleontology, Univ. of Mich, v. 21, p , 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 , Thayer, C, W. 1974, Marine paleoecoiogy in the Upper Devonian of New York. Lethaia, v, 7, p , Thayer, C, W, 1975a, Size-frequency and population structure of brachiopods, Palaeogeog., Palaeoclimatol and Paleoecoiogy, v, 17, , Thayer, C, IaJ. 1975b, Strength of pedicle attachment in articulate brachiopods: ecologic and paleoecologic significance. Paleobiology, v, 1, p, , Thayer, C, W, & Steele-Petrovic, H, 1975, Burrowing of the lingulid brachiopod Glottidia pyramidate: its ecologic and paleoecologic significance, Lethaia, v. 8, p Thayer, C, W, 1977, Recruitment, growth and mortality of a living Articulate brachiopod, with implication for the interpretation of survivorship curves. Paleobiology, v. 3, p , Thorson, G, 1957, Bottom communities, p, in Hedgpeth, J. W., Editor. Treaties on marine ecology and pajeoecology, 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 Veevers, J, J. 1959, Size and shape variation in the brachiopod Schizophoria from the Devonian of Western Australia, Jour. Paleontology, v. 33, Zeigler, A, M., 1968, The composition and structure of lower Silurian marine communities: Lethaia, v. 1, p. 1-27,

84 APPENDIX I 74

85 75 I Figure 25. measuring the section looking to the west units 11-16, slabs are from 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,

86 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,

87 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

88 PLATE

89 ?B P late Two Figure 1-6. Paraspirifer bownockeri (Stewart): Units 7 and Page 49 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

90 PLATE 2

91 79 P late Three Figure Page 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 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.

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

93 P l a t e F o u r F igure 1-3, Paraspirif er bouunockeri (Stewart): Units 7 and P a g e 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).

94 PLATE 4