Evolutionary tempo and mode of the inoceramid bivalves following the Cenomanian-Turonian boundary

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Evolutionary tempo and mode of the inoceramid bivalves following the Cenomanian-Turonian boundary

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Title:
Evolutionary tempo and mode of the inoceramid bivalves following the Cenomanian-Turonian boundary
Creator:
Boice, A. Erik.
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Tampa, Florida
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University of South Florida
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English
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viii, 85 leaves : ill. ; 29 cm.

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Inoceramidae ( lcsh )
Paleontology -- Cretaceous ( lcsh )
Geology, Stratigraphic -- Cretaceous ( lcsh )
Dissertations, Academic -- Geology -- Masters -- USF ( FTS )

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General Note:
Thesis (M.S.)--University of South Florida, 2000. Includes bibliographical references (leaves 65-70).

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University of South Florida
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Universtity of South Florida
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027778021 ( ALEPH )
47701980 ( OCLC )
F51-00148 ( USFLDC DOI )
f51.148 ( USFLDC Handle )

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Examining Committee : Office of Graduate Studies University of South Florida Tampa Florida CERTTFICA TE OF APPROVAL Master's Thesis This is to certify that the Master's Thesis of A ERIK BOICE with a major in Geology has been approved for the thesis requirement on July 3, 2000 for the Master of Science degree MajorMotessor: Peter J. Harries, Ph.D Member : Benjamin P. Flower Ph .P. Member: Terrence M Quinn, P'rl.o. Member : Eric A Oches, Ph D

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EVOLUTIONARY TEMPO AND MODE OF THE INOCERAMID BIV AL YES FOLLOWING THE CENOMANIAN-TURONIAN BOUNDARY by A. ERIK BOICE A thesis submitted in partial fulfillment of the requirements tor the degree of Master of Science Department of Geology College of Arts and Sciences University of South Florida August 2000 Major Professor : Peter J Harries Ph. D

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DEDICATION To my family who through all of the twists and turns in my life have steadfastly believed in me Their support cannot be overestimated or more appreciated Thanks

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ACKNOWLEDGEMENTS It is with the deepest gratitude that I wish to thank my advisor Dr. Peter J Harries for his support and guidance during my last two years at USF. But most of all I want to thank him for his belief in me and for profoundly changing the direction of m y life I believe this is the beginning of a long friendship I wish to thank the other members of my committee Dr Rick Oches Dr. Ben Flower and Dr Terry Quinn, each of whom have made inestimable contributions to my growth as a student of geology I give special thanks to my friends who have done so much for me The O Neill family especially Dan Maureen and Pat. Steve Hall and his family Greg Steve Sayer John and Shanna Coughlin Sarah, Toby, Steve Scrivner John Kantor and of course my friends in Pasadena who basically supported this little venture To Ralph Heath of the Suncoast Seabird Sanctuary. They have been the pillars upon which I leaned. All of my friends and colleagues at USF To Michelle I say thank you for bringing a smile to me every time I saw you and brightening even the worst of days. Funding and support for this project was provided by the Geological Society of America, The American Museum of Natural History in New York, the Tampa Bay Fossil Club Sigma Xi, and the Geology Department at the University of South Florida

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LIST OFT ABLES LIST OF FIGURES ABSTRACT INTRODUCTION Evolutionary Theory TABLE OF CONTENTS Mass Extinction and Evolution GEOLOGIC SETTING The Cretaceous Western Interior Seaway Regional Stratigraphy/Depositional Environment PALEOENVIRONMENTAL SETTING CenomanianTuronian Boundary CT Mass Extinction and the Inoceramid Bivalves STUDY AREA METHODS RESULTS Pueblo and Bunker Hill Sections Statistical Results Nipple Butte Section DISCUSSION Evolutionary tempo and Mode Patterns following the CenomanianTuronian Mass Extinction 111 l V V l I I 6 8 8 12 16 16 20 22 24 28 28 47 48 50 51 57

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CONCLUSIONS 63 REFERENCES 65 APPENDICES 71 Appendix I Measurement and Ratio Data from Study Sections 72 Appendix 2. Statistical Results 84 II

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Table 1 LIST OF TABLES Sampling intervals corresponding to lettered histograms for individual morphometric measurements at Bunker Hill (BHS) Pueblo ( PBS), and Nipple Butte (NBS) Ill 29

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LIST OF FIGURES Figure 1 Speciation by phyletic gradualism 2 Figure 2 Speciation by punctuated equilibrium 4 Figure 3 Polar view of the western interior Cretaceous seaway near peak transgression in the Early Turonian (after Eicher and Diner 1989). 9 Figure 4 Paleogeographic reconstruction of the Western Interior Basin of the United States during the CenomanianTuronian boundary interval (after Harries, 1993a) 11 Figure 5 Correlation of Pueblo Bunker Hill and Nipple Butte strata with European stages of the Cretaceous and time scale (modified after Olesen, 1991; Kauffman 1995). 13 Figure 6 Compilation of high-resolution sequence stratigraphic, cyclostratigraphic volcanic event-stratigraphic and geochemical data for the Cenomanian-Turonian boundary interval at the C-T boundary stratotype section west of Pueblo, Colorado (after Kauffman, 1995). 17 Figure 7 Map of reconstructed plate positions at -90 Ma. 19 Figure 8 Location map of study area with inset of the Western Interior Seaway in the Early Turonian. 23 Figure 9 Key external morphologic features shape descriptors and morphometric measurements for a hypothetical inoceramid left valve (modifie d from Hilbrecht and Harries, 1992). 27 Figure 10 PBS section-Height 30 Figure 11 PBS section-Length 31 Figure 12 BHS section Height 32 IV

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Figure 13 BHS section-Length 33 Figure 14 PBS section-Secondary Axis 34 Figure 15 PBS section-Axial Length 35 Figure 16 BHS section-Secondary Ax i s 36 Figure 17 BHS section-Axial Length 37 Figure I 8 PBS section-Axial Length/Secondary Axis 38 Figure 19 BHS section-Axial Length/Secondary Axis 40 Figure 20 PBS section-Hinge Line Length/Axial Length 41 Figure 2 I PBS section-Hinge Line Length/Secondary Axis 42 Figure 22 BHS section Hinge Line Length/Axial Length 43 Figure 23 BHS section-Hinge Line Length/Secondary Axis 44 Figure 24 PBS section-Height/Length 45 Figure 25 BHS section Height/Length 46 Figure 26 Correlation between PBS section and BHS section 49 Figure 27 Reticulate Speciation 56 Figure 28 Strat i graphic ranges on inocerarnids found in the Late Cenomanian through Early Turonian from six sections Spanning the Western Interior Basin of North America (modified from Harries and Little 1999). 59 v

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EVOLUTIONARY TEMPO AND MODE OF THE INOCERAMID BIVALVES FOLLOWING THE CENOMANIANTURONIAN BOUNDARY b y A. ERIK BOICE A n Ahstru c t of a thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Department of Geology College of Arts and Sciences University of South Florida August 2000 Major Professor : Peter J. Harries Ph D VI

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There is a continuing debate focused on the dominant pattern of evolution between two paradigms: phyletic gradualism and punctuated equilibrium. Evidence in support of both patterns has been gleaned from various intervals and groups from the fossil record. The inoceramids were dominant members of marine, epifaunal communities in the Mesozoic and represent an excellent group to investigate these two patterns During this period inoceramids were abundant, widespread and evolved rapidly allowirtg a detailed investigation into their evolution both geographically and temporally Evidence from Early Turonian strata outcropping in Pueblo, Colorado and Bunker Hill Kansas has revealed a pattern of higher variability with lower abundance and a restricted dead zone in the earliest Turonian (93 4-93 Ma). This is followed by a period of decreased variability or stasis in the middle of both sections (93-92.3 Ma) Toward the top of the sections there is period of highest variability and abundance Neither phyletic gradualism nor punctuated equilibrium evolutionary patterns correlate well with the evolutionary dynamics shown by these inoceramids. Instead, the reticulate speciation model of evolution most closely corresponds to the pattern seen. The first phase of variability is a response to the environmental distress of the mass extinction event and is not reflective of a specific evolutionary pattern. The period of stasis in the middle of the section corresponds with the stabilized interval of this model and the period of highest variability abundance diversification that follows represents the eruptive evolutionary interval of reticulate speciation. The post-extinction evolutionary dynamics revealed in this study follow the extinction-survival-recovery pattern put forth in previous literature. The lower abundance Vll

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and restricted dead zone on the lower sampling intervals is characteristic of the survival phase following a mass extinction. It represents a period of filtering during which various morphotypes are present due to changing environmental conditions The stable middle intervals is the lower recovery phase where conditions begin to ameliorate Also dufing this phase the progenitor species begins to emerge and will be the seed group for repopulation The period of highest variability diversification and abundance is the later part of the recovery interval where an eruptive phase of evolution takes place, vacated niches are filled and ecosytem stability is restored Abstract jor Professor : Peter J Harries, Ph D ofessor, Department of Geology Date Vlll

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INTRODUCTION Evolutionary Theory The mind cannot grasp the full meaning of the term of even a million years ; it cannot add up and perceive the full effects of many slight variations accumulated during an almost infinite number of generations . .. we see only that the forms of life are now different from what they formerly were. Charles Darwin On the Ori g in o[Species (1859) In his opus On the Origin o[Specie s Darwin (1859) hypothesized that new species evolve by phyletic evolution occurring over long periods of geologic time in a slow, gradual process that contains many intermediate steps Since his ideas on natural selection appeared there has been continued investigation, discussion, and debate of the variations in evolutionary rates and patterns found in the fossil record. Over the past two decades there has been an ongoing debate focused on two paradigms that adherents favor to explain evolution : phyletic gradualism and punctuated equilibrium The phyletic gradualism model of evolution which holds that species populations evolve differences gradually and sympatrically as they adapt to their local environments, has its roots in the Darwinian theory of natural selection (Figure 1). The premise of this model is that new species come about through the gradual metamorphosis of a population into modified descendant species and that this transformation occurs to most if not all of

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EPISODES Of MIGRATION 0 ISOlATION Geograph leal extent Figure I. Speciation by phyletic gradualism Both phylogenesis and cladogenesis occur The two branches show unequal rates of evolution Migration i s initiated at time level l. Geographic isolation is established at level 2 Ultimately, the two branches may become genetically incompatible Until they do they must be regarded as geographical subspecies. Each time-separated grade is a chronological subspecies (after Sylvester-Bradley 1977) 2

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the original population and over all of the original populations geographic range (Stanley 1979) This is also known as sympatric evolution (Mayr, 1963). Punctuated equilibrium (Figure 2) proposes a different pattern involving bursts of relatively rapid change before and after which there are long periods of evolutionary stasis (Eldredge and Gould, 1972). This evolutionary model stems from notions on possible speciation mechanisms such as quantwn evolution (Simpson, 1944) and allopatric speciation (Mayr, 1942). Quantum evolution provides a mechanism whereby small and isolated populations are in essence passing from one set of related ecologic niches (adaptive zones) to another through an unstable, inadaptive period of evolution (Simpson, 1944) It is during this period that evolutionary rates increase as adaptive thresholds are crossed. This idea contrasts sharply with the slow, steady process of evolution hypothesized by Darwin Allopatric speciation was proposed by Mayr ( 1942) and this model has become the favored mechanism of speciation. He focused on isolation as the key factor in this process This occurs when a small segment of the population is separated by a geographic barrier and diverges genetically. Eventually this new species will have diverged enough so that interbreeding with the original ancestral population is no longer possible (Mayr, 1953) The idea that periods of rapidly divergent speciation accelerate the rate of evolution is a critical component of punctuated equilibria Eldredge and Gould ( 1972) argued that because of this mechanism we should not expect to find gradual divergence in an ancestral descendent relationship in the fossil record because evolutionary change

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I D B "* I A II' 11\ A huutl!l EPISODES Of __... MIGRATlON 0 ISOlATION + EXTINCTION r 1 111111111 c 5 Time t Geographical extent Figure 2. Speciation by punctuated equilibria. Species A in region X gives rise at time level 1 to a branch, which migrates to region Y; when it becomes i solated at level 2 it changes morphologically into species B This species migrates back to region X at level 3 replacing species A, which becomes extinct at leve14. Species B also migrates to region Z at level5 and changes to species C after isolation at level6 Similarly a branch of species C migrates back to region Y at level 7 and changes to species D, with i solation at level 8 and afterward invades region X, and replaces species B. Region X is thus characterized by three successive species, A, B D which abrubtly replace each other (after Sylvester-Bradley, 1977) 4

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occurs in a short period of time relative to the geologic range of species. Therefore after species have established themselves long periods of stasis would be present in the record until another phase of punctuated evolution begins. Proponents of punctuated equilibria believe that this model of evolution is in more agreement with the generally accepted processes of speciation than is phyletic gradualism and better reflects the fossil record It has been suggested that in addition to phyletic gradualism and punctuated equilibria a nwnber of intermediate patterns occur between these end members and that when the tempo of evolution is examined in the context of complex organism environment interactions a variety of patterns should be expected to emerge (Geary, 1995) Also, an important aspect of punctuated equilibrium is the ability of species to remain stable for long periods of geologic time and there are situations, other than stasis, where conditions of stability could result in a net directional morphological change that continues for millions of years (Geary, 1995) The important point here is that this does not necessarily mean change is occurring gradually from one generation to the next because rate is determined by the time interval in question and that quite probably if broken down we would see fluctuations in rate and direction of change (Geary, 1995) Examples of both punctuated equilibrium and phyletic gradualism have been gleaned from the fossil record In a study by Hallam (1982) he found that the punctuated equilibrium model fit the pattern of change he documented in Gryphaea. Sheldon ( 1987) however, found phyletic gradualism best fit the evolutionary pattern of the Ordovician trilobites he studied over a period of about three million years This debate remains unresolved and this study addresses this important question in a single though rapidly evolving group The inoceramid bivalves, epifaunal molluscs 5

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which first appeared in the Permian and eventually disappeared 67.5 Ma ( Kauffman et al. 199 3), represent an ideal group against which to test these competing evolutionary h y potheses During the Cretaceous, inoceramid diversity reached an acme, showing rapid evolutionary rates and they dominated marine benthic environments on a global scale (Harries and Crampton 1998). These environments were marked by high levels of extinction across the Cenomanian-Turonian boundary possibly caused by a global anoxic event (Kauffinan et al. 1992) The data collected in this stud y were used to examine whether the tempo and mode of inoceram i d evolution following the Late Cenomanian Early Turonian mass extinction is predicted by the punctuated equilibrium model of e v olution and study the post-extinction evolutionary dynamics of this dominant Mesozoic group. Mass Extinction and Evolution Another area of debate has been the role that mass extinction events have played in evolution Specifically what are the evolutionary dynamics associated with the period of recovery following mass extinction events and how different are these events from background extinction (Harries 1993) ? It is generally accepted that mass extinction events can change the direction evolution takes and not necessarily in the manner it might have taken with only background extinction (Jablonski, 1986) A pattern of extinction survival-recovery has been identified for the evolut i onary dynamics of mass extinctions (Harries and Kauffman 1990 ; Erwin 1996 ; Harries et al. 1996). After the mass extinction ends the surv i val period represents a pause before re covery begins Recovery begins as evolutionary rates begin to increase and niches v acated after the mass extinction are filled (Walliser, 1996 ) Eventually as competition 6

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and selection rise the rate of evolution begins to slow and the recovery phase is over (Erwin, 1996). The role mass extinctions play in evolution is a large one The opportunity for a chan g e in fauna is apparent with the removal of dominant species that allows other groups to engage in adaptive radiation. One obvious example is the extinction of the dinosaurs at the end of the Cretaceous that allowed the radiation of mammals Evolutionary experimentation and adaptive radiation are greatly increased and this repopulation is highlighted by rapid evolution (Harries 1993). The availability of niche space allows a rapid radiation of new forms before the recovery period comes to an end These forms may never have had an opportunity to become successful if the dominant groups had not changed and competition reduced It is therefore important to closely look at evolutionary dynamics in those intervals that follow mass extinctions 7

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GEOLOGIC SEmNG The Cretaceous Western Interior Seaway The Western Interior Seaway was a shallow, warm north-south oriented epicontinental sea that sporadically linked the subtropical Tethys Ocean with the temperate Boreal Ocean from Late Albian to Maastrichtian time (Figure 3) During peak transgressions the seaway attained a maximum width of 2000 km and depths of approximately 300m (Kauffman, 1985) The Western Interior Seaway occupied a complex foreland basin between the active Cordillera in the west and the stable craton to the east (Kauffman and 1993). The Cordillera, which included the Sevier orogenic belt was formed by collisions between the North American plate and the Kula and Farallon plates, and a compressional tectonic regimedomipated the western part of North America from the Jurassic through the Late Cretaceous (Kauffman and Calqwell, 1993) A subsiding asymmetrical basin that became shallower toward the east was the result of thrusting from the western orogenic belt. The history of the Western Interior Seaway records a number of alternating episodes of flooding and draining of the basin reflecting transgressive/regressive marine cycles that were the result of geodynamic controls such as local tectonic activity, subsidence due to sediment loading, and eustatic sea-level change (Kau.ffinan and Caldwell, 1993) Kauffinan (1977) divided the basin and seaway into four zones based on 8

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Figure 3 Polar view of the western interior Cretaceous seaway near peak transgression in the Early Turonian (after Eicher and Diner 1989) 9

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water-depth at periods near to or at maximum flooding (Figure 4 ) The western foreland zone, as stated earlier, had high subsidence rates as a result of isostatic loading due to eastward thrusting of the orogenic belt and also high sedimentation rates as a consequence of siliciclastic material shed offthe highlands of the Cordillera Because of the high rate of sedimentation the depth of the water in this zone probably did not exceed 50 m. The west central axial zone was also characterized by high subsidence rates but its distance :from the siliciclastic source area augmented by the presence of a foreland bulge resulted in lower sedimentation rates Sediments in this area are predominantly silt and interbedded clay and limestone Consequently this area represented the deepest part of the basin with depths of 200-300 m and potentially as much 500 min some places. The east-central hinge zone had low subs i dence rates and water depths were generally 100-200 m The fourth zone was the eastern stable cratonic zone constituting a broad shallow platfonn with very low sedimentation rates In this eastern part of the seaway comparatively thin deposits of marine shales and carbonates accumulated and water depths in this area were less than I 00 m. (Eicher and Diner 1989) The dominant pattern of flow wifuin the Western Interior Seaway during periods of lower sea level was southward. This pattern, along with residual topographic highs in the Texas panhandle area that resulted :from Paleozoic uplifts, worked to somewhat constrain inflow :from the Tethys Ocean to the south (Figure 3). The seaway tended to be dominated by lower salinity boreal waters :from the north as far south as Colorado for much of its history as foraminiferal faunas indicate (Eicher and Diner, 1989) These conditions led to generally lower salinities in the Western Interior Seaway than was found in the Tethys Ocean until the Late Cretaceous transgressions allowed Tethyan waters to overcome 10

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-Approx. shoreline position Figure 4 Paleogeographic reconstruction of the Western Interior basin of the United States during the CenomanianTuronian boundary interval (after Harries 1993a) II

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barriers to flow These waters made their way northward into Canada and during the Greenhorn transgressive / regressive cycle near-normal marine salinities were reached in the basinal areas of the western United States (Eicher and Diner, 1989) Regional Stratigraphy/Depositional Environment The Mancos Shale (Nipple Butte) and the Bridge Creek Limestone of the Greenhorn Formation (Bunker Hill and Pueblo) represent the major stratigraphic units in this study (Figure 5). These units are Late Cenomanian-Middle Turonian in age and the Lower Shale Member of the Mancos Shale is correlative with the Bridge Creek Limestone of the Greenhorn Formation (Olesen, Kirkland 1991) Kirkland ( 1991) delineated four members of the Mancos Shale : 1) a Lower Calcareous Shale Member, 2) a Middle Shale Member, 3) the Hopi Sandy Member, and 4) an Upper Shale Member (Figure 3). The Lower Calcareous Shale Member encompasses the unit for this study The lithology of this member is dominated by olive-gray calcareous shale Deposition of the lower member of the Mancos Shale began as sea level rose during the Greenhorn Cycle and water depth exceeded storm wave-base (Kirkland, 1991 ) The Greenhorn cycle probably the largest eustatic sea-level rise of the Cretaceous Period, began in the Cenomanian and reached peak transgression in the middle Early Turonian (Pratt, 1984 ; Elder 1987; Kirkland, 1991 ; Kauffman and Caldwell, 1993) The Bridge Creek Limestone Member of the Greenhorn Formation was also deposited during the Greenhorn Cycle (Figure 5) The lower and middle parts of this unit consist of bioturbated limestone and marlstone couplets (Pratt 1984) These interbedded units represent alternating and distinctly different benthic environments During the 12

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8 STAGE TIME PUEBLO BUNKER HILl. NIPPLE BUTTE SCALE SECTION SEC110N SECTlON ffi Q. FAIRPORT UPPER SHALE CHALKY < SHALE MEMBER :I: en MEMBER (/) 8 :J ::J a a: HOPI SANOY < 0 (.) MENSER 0 a: a: (/) MIDDLE (.) SHAlE t MEMBER ::> -92.10-MEMBER BRIDGE CREEl< LOWER a: UMESTONE CALCAREOUS 9 MEMBER JETMORE SHALE z MEMBER MEMBER -93.40a: m HARTlAND a: HARTl.ANO SHALE SHALE MEMBER t.EMBER Figure 5 Correlation of Pueblo, Bunker Hill and Nipple Butte strata with European stages of the Cretaceous and time scale (modified after Olesen 1991; Kauffman 1995) 13

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limestone intervals bottom water tended to be moderate-towell oxygenated while being PQOrly oxygenated to anoxic during the marlstone intervals (Pratt 1984). The carbonate cyclicity found in the Western Interior Seaway in general and the Bridge Creek Limestone in particular is thought to be forced by Milankovitch cyclicity and that these rythmic bedding sequences are the result of orbital forcing of climate (Barron et al., 1985 ; Elder 1987 ; Sageman et al. 1997) There is, however some discussion as to which orbital cycles are represented in the Bridge Creek Limestone Estimates have ranged from 0.02-0 1 Ma (Sageman et al., 1997). Elder (1987) proposed that the deposition of the madstone beds corresponded to the 0 02 Ma processional cycle and deposition of the limestone beds reflected the 0 1 eccentricity cycle Barron et al. (1985) put forth that bundling of beds in sets of four to five would produce an eccentricity signal (0 1 Ma) and that the overall average periodicity of the Greenhorn Cyclothem matches the obliquity cycle (0 04 Ma) Regardless of the exact periodicity, it appears that Milankovitch orbital forcing has had a significant influence on bedding cycles found in the Western Interior Seaway If these beds are driven by a rythmic process it allows for a refined timescale against which e v olutionary rates can be temporally calibrated The question of how this bedding cyclic i ty developed has resulted in two models being proposed. The Pratt (1984) model called for a brackish cap during periods of high precipitation that stratified the Western Interior Seaway This resulted in reduced ox y genation of bottom waters and shale deposition Conversely during dry periods low runoff and therefore decreased amounts of terrigenous sediment were transported to the seaway resulting in relatively pure pelagic carbonate accumulating No lid of brackish water allowed vertical mixing and the bottom waters were well-oxygenated and supporting 14

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benthic organisms A second model was proposed by Eicher and Diner (I 989) and put fqrth that the limestone-madstone rhythms represented productivity cycles caused by alternations in vertica l circulation Limestone beds were produced during times of high levels of production of calcareous planktonic skeletons with the marlstones being produced during low productivity periods. 15

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PALEOENVIRONMENTAL SETTING CenomanianTuronian Boundary The CenomanianTuronian boundary records a period of worldwide environmental perturbations This interval is characterized by increased volcanism, a major sea-level transgression widespread oceanic anoxia, and a significant extinction event (Kerr, 1998). An understanding of the interrelationship of the environmental factors that existed at this time is important in evaluating the subsequent evolutionary dynamics of the inoceramid bivalves. A greenhouse world with warm, stable climates characterized this period (Kauffman, 1985) This situation reduced circulation and amplified stratification of marine waters increasing the potential for anoxic conditions Jenkyns (1980) identified three Cretaceous oceanic anoxic events one of these occurred at the Cenomanian Turonian boundary and the other developed during the Late Barremian-Albian and, to a lesser extent the Coniacian-Santonian These events are identified by the occurrence of black-shale sedimentary facies interpreted as recording low-oxygen concentrations They also correlate closely with transgressions suggesting a potential causal linlc In addition they are typically associated with pronounced fluctuations of 813C 8180, Corg, as well as minor trace elements as shown in Figure 6 for the CenomanianTuronian boundary These fluctuations have been interpreted as indicators of perturbations in the ocean climate system (Kauffman, 1995). As was stated earlier, a major transgression, which in 16

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I J'ii } ilol! J ; .1 ::> >= > ,; > s J! s c .!:'I. It 2 za J t > a H a: 0 :n :! w .... !_ (.) 0 r w iii cs oo ':' .a. 'I' !'m-: I 8f .. ., > ., > a. ., 1YIIOIDJII II CJ !i 1!: en jl !J 0 il 5 !if lf -E Figure 6. Compi lation o f high-res o l u tio n sequence strat i graphic, cyclostratigraphic volcanic eve n t st rati gra phi c, a nd geo c h e mical d ata f o r the CenomanianT uronian boundary interval at the C T boundary s t r at otyp e section west of Pueblo, Colorado (afte r K auffman, 199 5). 1 7 i

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the Western Interior is recorded by the Greenhorn cyclothem peaked in the Early .Turonian (Kauffman and Hancock 1979). This worldwide, eustatic sea-level rise is recorded in Europe, although there was a brief episode of shallowing at or slightly before the CenomanianTuronian boundary not apparent in the Western Interior of North America (Kauffman and Hancock, 1979; Tyson and Funnel, 1990). Corresponding with the transgression and oceanic anoxia at the CenomanianTuronian boundary was a period of increased volcanism Abundant widespread, and relatively thick bentonite beds are common in the stratigraphy of the Late Cretaceous Western Interior Basin of North America (Elder, 1988). Also, there was a significant increase in oceanic crustal production caused by the eruption oflarge plume-related volcanic provinces 1991; Sinton and Duncan, 1997; Kerr, 1998). It has been hypothesized that this large-scale submarine magmatism directly contributed to the . oceanic anoxic conditions present at the Cenomanian Turonian boundary (Sinton and Duncan, 1997 ; Kerr, i998)'and may have played a considerable role in the extinction event of this time period (Kerr 1998) Three mechanisms for plume-related volcanism producing oceanic anoxia at the CenomanianTuronian boundary have been proposed The first involves the CaribbeanColumbian plateau (Figure 7) that formed close to the only major opening between the Pacific and proto-Atlantic Oceans. Kerr (1998) speculates that this plateau could have erupted close to the surface of the ocean and disrupted oceanic circulation in the Pacific to such a degree that cool oxygenated polar waters did not circulate to lower latitudes This would have resulted in increased oceanic anoxia because most oxygenated water came to the Atlantic from the Pacific. A second mechanism proposes that vented 18

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\0 Western Interior U.S. Arens of unoxic or dysoxic waters Land nreus Ontong-Java Plnteau 180 90W. oo 90E Figure 7 Map of reconstructed plate positions at 90 Ma. Land areas are shown by a stipple pattern and present continental margins are outlined The approximate area of anoxic or dysoxic conditions (shaded areas) and the approximate paleopositions of the Ontong-Java and Caribbean plateaus and the Madagascar flood basalts are shown (after Sinton and Duncan, 1997).

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hydrothennal material that was oxidized during these plateau eruptions reduced the levels of dissolved 02 (Sinton and Duncan, 1997). Finally, the introduction ofbiolimiting nutrients such as Fe into ocean surface waters by hydrothermal plwnes would have significantly increased primary productivity and the phytoplankton blooms that resulted reduced 02 in the oceans (Sinton and Duncan, 1997). The CenomanianTuronian Mass Extinction and the Inoceramid Bivalves The CenomanianTuronian mass extinction was a second-order event with 7% of marine families and 26% of marine genera becoming extinct during this time (Raup and Sepkoski, 1986). The pattern of this event was gradual to stepwise with a higher incidence of extinction at lower latitudes than at higher latitudes (Raup and Sepkoski 1986). The duration of the event was approximately 0.42 m y signifying a long-tenn cause such as anoxia and not-a single short-tenn catastrophic event (Harries and Little 1999). The limestone-marlstone couplets found in the Western Interior Basin and the stratigraphic position of extinction horizons imply that short-tenn Milankovitch forced climate changes were an important factor in driving this extinction event by varying the rates of water mass turnover and therefore the oxygen levels of deep water (Harries, 1999). Epifaunal bivalves in general and the inoceramids in particular became a dominant faunal component as the extinction progressed. The inoceramids are pterioid bivalves (scallop group) that have no modern analogs which to study and their taxonomy is not well resolved (Harries and Crampton, 1998). This group expanded rapidly approximately 110 million years ago and were a dominant Late Cretaceous group until their virtual extinction approximately 1.5 Myr prior to the CretaceousTertiary boundary 20

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Inoceramids inhabited a wide range of marine environments from the nearshore to deepocean and were found at high and low latitudes This group flourished in oxygen-poor environments and is commonly found in the black shales of the Cretaceous (Harries and Crampton, 1998) The anoxic conditions that pervaded the Western Interior Seaway at the CenomanianTuronian boundary may well have enhanced extinction among the benthic community and allowed the inoceramids to thrive Indeed, based on the literature and provided the taxonomy applied is correct, in the Cenomanian evolutionary rates were approximately 5 1 species / m.y. with a slight decrease to 4 7 species / m.y. in the Late Cenomanian. This evolutionary rate increased dramatically in the Early Turonian and can be attributed to Mytiloides lineage which survived a major inoceramid extinction in the latest part of the Cenomanian and radiated into the open niches that resulted (Harries, 1993 b) The interelationship of environmental factors occurring during this period undoubtedly had a significant impact on the rate and pattern of evolution following the CenomanianTuronian mass extinction event. 21

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STUDY AREA The study localities are situated in a transect across the Western Interior Basin ( Figure 8). Sampling took place at three main locations with different environmental settings First is Bunker Hill Kansas approximately 7 miles east of Russell Kansas, in the eastern stable platform The second is Pueblo Colorado located in the axial basin which is also the reference section for the CenomanianTuronian boundary and the third location is the Nipple Butte section in the western foreland province located 4 miles west of Lake Powell Arizona 22

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J Analyzed Section COLORADO PBS BHS KANSAS Fig ur e 8 Location map of Study Area with inset of the Western Interior Seaway in the Early Turonian (In set after Eicher and Diner 1989 ) 2 3

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METHODS The inoceramid specimens used in this study were collected from the Bridge Creek Limestone Member at Pueblo, Colorado (PBS), the Greenhorn Formation at the Bunker Hill, Kansas section (BHS) and from the Mancos Shale at the Nipple Butte section in Utah (NBS) Samples from the Pueblo site were augmented with specimens from the PhD collection of Dr. Peter Harries as was the Nipple Butte Section. The collecting and sampling at these localities was performed at 20 em intervals Furthermore, the sections were analyzed using high-resolution stratigraphic analysis sensu Kauffman (1986). The application of this technique is important in determining evolutionary rates and patterns in the fossil record In addition, this type of analysis the use of geographically extensive marker beds that allow the investigator to correlate between sections at a high level of resolution (Kauffman, 1986). This also provides a tool to analyze temporally synchronous events on a geographically widespread scale. As discussed earlier, large-scale volcanism during the CenomanianTuronian boundary interval resulted in numerous bentonite beds in the Western Interior Basin that can be traced over wide areas. This, along with extensive previous work on this period by Hattin (1985; 1987), Barron et al. (1985), Elder (1987; 1988), Harries (1993a), Kauffman (1985; 1993) Kirkland (1991) and Olesen (1991) allow a high level of resolution in the correlation between the sections in this study 24

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The three sections in this study were selected because of their completeness and due to the fact they represent major depositional environments along an east-west transect within the Western Interior Seaway including the foreland basin (NBS) the axial basin (PBS) and the eastern stable platform (BHS) The sections under study were trenched to identify the bentonite marker beds needed to locate stratigraphically the Cenomanian Turonian boundary. Sampling was initiated just below the CenomanianTuronian boundary and the sampling intervals were kept as uniform as possible. In some instances slight alteration of the sampling intervals was necessaty to allow a limestone or shale bed to be sampled as a distinct unit. The PBS section had 39 sample intervals and yielded I 98 samples The BHS section also had 39 sample intervals that generated I I 0 samples and the NBS section contained 36 sample intervals with 38 total samples. All specimens of inoceramids sampled were investigated for their utility in the analysis As samples were prepared some proved unsuitable for the study A detailed morphometric analysis was undertaken to determine their evolutionary rate and pattern Measurements of morphometric parameters such as height (H), length (L ) secondary axis (SA) hinge line length (HLL), and axial length (AL) were taken and observations of ornamental elements made (Figure 9). Height is the maximum distance between the beak and the ventral margin of the shell being measured, perpendicular to the hinge line Length is the perpendicular distance between two lines that are perpendicular to the hinge line one intersecting the anteriormost projection of the shell, and another intersecting the posteriormost projection of the shell. The secondary axis is the maximum diameter of the s hell measured perpendicular to the axial length Axial length is the greatest linear dimension of a valve approximately equivalent to the growth axis extending from the 25

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beak to the most distal point on the ventroposterior margin The hinge line length is the distance from the anterior edge of the hinge line, below or anterior to the umbo, to the posterionnost projection of the hinge line (Hilbrecht and Harries 1992). Additionally, ratios between important morphometric parameters including HLLIAL, HLL/ SA, and AL/SA were also calculated Results of these analyses are reported in Appendix 1 26

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EXTERNAL VIEW (left valve} beak {B) DORSAL lnge line lenth (Hll)r----if---1-hinge fine (HL) an tenor auricle Dorsoanlerlor margin anterior face (AF) Ventroanterlor margin disc (0} Dorsoposterlor margin r:r (I) 0 tiS" ;r !U 0 :u '-l. _______ ,englh (L),----_.., Ventroposlerfor margin VENTRAL Figure 9. Key external morphologic features, shape descriptors, and morphometric measurements for a hypothetical inoceramid left valve (modified from Hilbrecht and Harries, 1992). 27

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RESULTS Pueblo and Bunker Hill Sections These two sections show remarkable similarity in pattern and therefore will be discussed together. Preservation of the inoceramid specimens collected from these sections is good (little or no fragmentation) to poor (extensive fragmentation) Both sections show a similarity in that the specimens collected from shale horizons are less well preserved than those obtained from limestone intervals Those from the shale horizons are also flattened due to compaction. Numerous partial specimens were recovered but only those specimens that could reasonably yield the necessary measurements were used Extensively fragmented samples were not included in this study When height and length are investigated individually for the PBS section (Figures 10 and II respectively), a period of variability near the top of the section can be seen, as is an extended period of lower variability below this zone Absent, however, is a more variable zone at the bottom of the section following the Turonian boundary that was seen in most of the ratios. BHS height and length plots (Figures 12 and 13 respectively) have almost identical patterns Of note is a slight, but definite, reduction in values for both height and length from the lower intervals toward the middle of the section beginning at interval G in both the PBS and BHS sections This pattern is mirrored in Figures 14I 7 for SA and AL for both sections 28

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Bar Graph Intervals Sample Intervals BHS PBS s n/a 37-39 R 38-39 36 Q 37 35 p 36 33-34 0 35 31-32 N 34 28-30 M 33 26-27 L 32 25 K 31 24 J 29-30 23 I 28 21-22 H 24-27 18-20 G 22-23 )6-17 F 19-21 15 E 16-18 14 D 12-15 13 c 6-11 7-12 B 5 4-6 A 1-4 1-3 Table 1. Sampling intervals corresponding to lettered histograms for individual morphometric measurements at Bunker Hill (BHS) and Pueblo (PBS) 29

PAGE 42

92.1 s.i. (Ma) ,...."'\-1-r-,-r-,r""T""lr""T""l.......-1"1 3 .. 4 6 ...l PBS Section Ulf10LOG!CAL KEY l". =--'I$..._ [1} 1Jin6SiriM -= tr:D==: \_-.:1 s--. [)3} MarlslOM Celclslll (]3] f::'.:: S snoa '*' 0 Sll ... Figure 10 PBS Section-Height. s.i =sarnple interval m=meter s R nO Q p 0 cJ I h N M JJ c [b,______,l B A 2 3 4 5 6 7 8 9 10 11 em 30

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3 4 6 g L$ ,.j s. i. PBS Section Figure II. PBS Section-Length 31 s R Q p 0 N M L K J H G F E D c 8 A c=D CJ c=CJ dl JJ II[]__, cfJ=J I I I J b dlh 2 3 4 5 6 7 8 9 10 em

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R o D I I I I 1-92.1s.i (Ma) I Q I I I I I 1--co R I t--: p p I I I I I I I 0 D I I J2 E. IN N I I I I 1 1-1-I IK M ,--[]......,
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s.i. (Ma) I I I leo f-IR I I I R D D I I Q I I I I I I I p D D IP 0 r=CJ TI I II 1<0. -= IJ 1 I ....... N I lltll. M I I I I L I I I K I I liT I 1[25 J I I I I I ....... h D I I 1-.:t TTT F H I I b ---E c:: C':l ....... a G CJ F I I I 8 .\1 f-ID :>... ....... 1-1 L....-"--C':l IJ,:I I (\I E I I I I I 0 I I c I I I I 8 I I ] l 1-A I I :J 2 3 4 5 6 7 8 9 10 T T em ""93.4-p e C-T Boundary 0 c: 0 0 u ...j BHS Section Figure 13. BHS Section Length 33

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92.1 s i (M a) 3 4 6 g .. u ..j PBS Section Figure 14. PBS Section-Secondary Axis 34 s R a p 0 N M L Kr{b. J d I I 1 H b H cCh-, G n-il C? F JJ I h E c-rlJ_, D Jb c s[L 8 r=;C[J A D D 2 3 4 56 78 em

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s 92 1 s i. r-"-1 0 R (Ma) ,..._ c=CJ Q p 0 c=J I I ,--, 0 0 I I I I I I I I .. .. .. .. .. . .. .. N I I I I I I M SL L I I I t:: K D ...., a I I 8 J r:=r=[1=J !-< I I I I n ... ...., I 1-tl H I I I I I G I I I I I I F I I I I I : E I I I I I 0 I I I I I I 3.4 6 0 c n 0 u ,_j I I B dJ PBS Section A ; I I l 2 3 4 5 6 7 8 9 10 II 12 em 0 Figure 15. PBS Section-Axial Length 35

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r92. -S .l. (M a ) I I I co D I I ,, [ p TI = -1 ---1 I I I (DJ J I 1--,,, r 1-r. I F -s:: -E 1':1 s I :I D >. a:: 1':1 Jl.l C\1 -c ----1 -A 1-93.4-b e lm ;ary 0 c t.l u ...i BHS Section Figure 16. BHS SectionS e condary Axis 36 R Q p 0 N M L K J H G F E D c B A CJ n CJ --o OCJ d 0 CJ 2 3 4 5 6 7 8 9 em

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s:: tO a 0 E-o >. -.:::: tO 93.4 e 0 c ., u BHS Section R Q p 0 D : 0 N C? r-Ch:d:J M [J_..., r==J L K r=D D J o H D 0 I I G CJ I I F I I I I E 1 I I r D r=D I I c r=D ,...., B A I I I 3 4 5 6 7 8 9 10 0 Figure 17 BHS Section-Axial Length 37 11 12

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(Ma) ,,.._ ., ... c: co c: 0 ... ::s E-< co N 0 6 0 m c u u .J 40 s 1 1111111111 I--1111111111 f-1-1-..... ........... r-1--" r-I I I I ,__ 1--" .................... 1--" r-I I I I I I I I I I I I I I I I I I I I 1--" r--1--" I Ill I I I I I I r-1--" r--liiiiiiiiJ r-r-r---CT Boundary 1 1"'1"'1-1"'1"'1-13 J..!l .. ll"'l"'l"'!..! 1 .. 1 1: 13 PBS Sect i on -35 35 30 25 25 20 -I 15 5 15 10 5 0 0.85 .. .. ... ... ....... \ ,. ... ..... - .... ... ... ... ... .. ...... -... ..... .... . 1.05 qs 1.45 1.65 Ratio Value Figure 18. PBS Section-Axial Length/Secondary Axis 38 .... ,. .. 1.85 2.05

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Figure 18 shows the ALISA ratio for the PBS section and is characterized by some variability for sample intervals 1-15 representing the period immediately following the Cenomanian-Turonian boundary In sample intervals 16-31 there is a marked decrease in variability with ratios generally ranging between 0.95 and 1 .45 indicating less elongate samples This changes again to a period of high variability at the top of the PBS section from sample intervals 32-35 with values ranging from 1.05-2.05. Intervals 36-39 show a reduction in variability similar to the middle part of the section although the average has shifted to an increased ratio value. Figure 19 showing the same AL/SA ratio from the BHS section reveals that although the top of the section mirrors closely that in the PBS section the lower intervals (1-15) do not contain as much variability The ratios HLLI AL and HLL/SA for PBS shown in Figures 20 and 2 I show a very similar pattern with that of the AL/SA ratios Again, the lower sampling intervals ( 1-15) and the intervals at the top of the section (32-35) have a higher variability than do those toward the middle of the section (16-31) Intervals 36-39 show a reduction in variability seen in the ratios mentioned earlier There is however some difference between the patterns of these ratios at PBS and those at BHS shown in figures 22 and 23. The period of! ower variability appears but is not as pronounced in the BHS section, and the differences between the zones of higher and lower are also not as evident. Additionally, there is a general trend toward increasing ratio values upsection for both HLL/SA and HLLI AL that does not appear in the PBS section. The HIL ratio for PBS (Figure 24) has a similar pattern to the other ratios at this section although in the lowermost intervals (2-6) there is a cluster pattern not apparent in the other ratios BHS section HIL ratio (Figure 25) shows no similarity to the PBS section 39

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BHS Section 0 0.75 0 .95 .. H f4 ... ... Hf .. .. .. .... ... t 1.15 1.35 1.55 Ratio Value Figure 19. BHS Section-Axial Length/Secondary Axis 40 1.75 us 2.15

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t-92.1 (Ma) -'. i:: co :'oL. 0 e 0 m c: Ill u ...j 1111111111 1111111111 .. u I . 00 II I I I I I 1 1 I I I I I I I I I I I II I I I I I II I 1111111111 C-T B o und a ry N N N N N N N N N N ..... s. 1 r-1-35 1--1-1--1--135 30 r-1-1--1-1-1-1--1-1---1--1--1------125 2 5 20 1-' 15 15 5 tO ..; 1..; 1 .; 1 .; 1 .; 1..; 1..; 1""1"" HNI PB S S e cti o n 5 0 0.1 ... tt t p ... t t t t tt tf .... 0.2 0.3 G.4 Ratio Value F igure 2 0 P BS Sec ti on-Hi n ge L in e L e n gth/ Axia l Le n gth 4 1 0.5 0 6 0.7

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1-92.1 (Ma) lr-.. --v r:: a 0 =' f-< >. -lo e 0 m c u (.) ,_j s i. r--1--II LLIJ Ill ...._ 11 I I I I Ill 1--1--1-.................... 1--1-1--I I I 1-.......... ............ 1--1--II I I I I I II II I I I I I I II 1--1-1-11 IIIIITf 1-1--1-35 35 l) 2S 25 20 15 15 11 lllllll 1--1-1--1-C-T Boundary N N N N N N N N ...., N N N PBS Section 1-' 5 10 5 0 0.10 0.20 t++. .. --t--+ ... ... .. ... 0 .30 0 .40 0 .50 Ratio Value Figure 21. PBS Section-Hinge Line Length/Secondary A xis 42 T 0 .60 0 .70

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s:: C':S a e >. C':S 93.4 e 0 c ., u BHS Section 20 15 0 _0.10 0.20 .. .. - .. i- . 0.30 .40 'Ratio Value Figure 22. BHS Section-Hinge Line Length/ Axial Length 43 .. 0 .50 0.60

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f-92 1 -(Ma) I I I IX) I I I <0I I I I l v I co a e ;::3 E->. -.::: co Ul I N f-93.4-p t-T Bou ndary e m 0 c u u .J BHS S ec t ion 1--I--1--I-I--1--......_ 1--1-1---1-1-1-1-1--1--r-r--1--1-3 -l 35 5 )J 5 20 5 15 -5 10 5 0 0.10 0.20 .. ,.. .. ,. y ... .. .. ... . ... ... 0 .30 0 .40 0 .50 Ratio Value Figure 23 BHS Section-Hinge Li n e Length/Secondary Axis 44 ; 0 .60 0.70 0.80

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92. 1 (Ma) 3 4 e 0 c:: OJ u ,...j s i. m CT Boundary PBS Section 35 35 A 25 15 6 0 . .. .. "' . ....... ... ... .. .... .... ... .... .. _... ... . .. ... ... ...... .. f ... .. .. ...... ....... -. ........... ....... .. ..... .. .. ...... .... ... ... .. Q.60 OJO Q.8) Q.IJ : 1J . UO 1JJ Ul 1.40 Ratio Value Figure 24. PBS Sect i on-He i gh t/L ength 4 5

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f-92. -( Ma) leo I I leo_,_ I I I = ell a e ::I E->. -.: ell IJ.l I N c.;; I e lm C -T Bound ary 0 c u u ,_j BHS S e ction f--1'-!-35 f--r--f-25 --r--1-15 -----r--f-1-1--: 3S 25 15 10 5 0 o.m Figu r e 25 B H S S eqti onHeig h t/Le ngth 4 6 ....... ... ... ... & ..... ... ... .... ... ... ... .. ... .... OJO tOO uo 1SI 1bl Ratio Value

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or any of the other ratios The values here tend to be grouped between 0.80 and 1.20 for almost the entire section with a slightly increased variability toward the top of the section Through all of the measurements taken there is no evidence that changes in lithology control the size and shape of the inoceramid specimens studied Figure 11, for example which shows the length measurements for the PBS section the patterns remain similar through the three main zones that are present. There is no discemable difference between the limestone and calcareous shale/marl stone beds in terms of size and shape This holds true for all ratios also. As stated earlier there is an increased tendency for compaction in the shale beds but since width is not considered in this study any bias due to this is not applicable In summary, the results of the PBS and BHS sections together show seven of the eight ratio pattern figures and all eight individual attribute figures show a high degree of variability in sampling intervals at the top of the sections (32-39) The same number show a zone of low variability in the sampling intervals located toward the middle of the sections ( 16-31 ). The intervals at the bottom of the sections ( 1-15) show high variability in five of the eight ratios and two of eight individual attributes. Correlation between these two sections is shown in Figure 26. Statistical Results A two-sample student s t-test was conducted at the 0 .05 confidence interval. The t-test determines whether the means of the two samples are equal and therefore whether they are two statistically different populations. The test was done between the lower (intervals 1-15) and middle zones (intervals 16-31) identified in this study and also the 47

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middle and upper zones (intervals 32-39) The test was performed for all individual morphometric measurements for the PBS and BHS sections All results were statistically significant at the 0.05 confidence interval for all measurements at both the PBS and BHS sections except for BHS secondary axis (intervals 16-31 vs. 32-39). The conclusion is that there is statistical evidence to suggest that the samples in these three zones came from populations having different means. In addition a two-sample F-test was performed at the 0.05 confidence level and to the same interval zones as the t-test. The F-test compares the variance of two populations. All results for the comparison of intervals I -15 and 16-31 for every morphometric measurement at both PBS and BHS were statistically significant. None of the results for the comparison of intervals 16-31 and 32-39 at both sections were significant. The complete results for both statistical tests are recorded in Appendix 2 Nipple Butte Section Poor preservation due to the fissile nature of the Mancos Shale at Nipple Butte and the low number of samples from this location make analysis of the NBS section problematic at best. Due to this lack of usable data analysis of this section was omitted The data, such as it is, is included in Appendix 1 however. 48

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s. i f.-1--s i. r-3 '-I--.._ II II 111111 !--.._ I--.._ 1111111111 1--<0 f-f.-f5 1--<0 r-.................... 1-25-I .._ .._ .._ 1-- 00 .. .. .. .. . . . .. .. .. -1111111111 '--f-2 5 .. .. .. .. . .. .. .. .. --f-I I I I I I I I I I 15 .._ .._ f--I I I I I I I I I I f--1-'--.__ 1111111111 -.__ C\1 -------5 1111111111 --5 1-1--1--r--.._ 0 0 CT Boundary ,_,_,_,_ ,_,_,_,_,_,_,_ m ,., N ,., N ,., ,., ,., ,., ,., "'INI m N N I N I N 1 ,; H.; 1 .; 1 .; 1.; l;;j PBS Se ct ion BHS S ect ion Fig ure 26 Co rr e l a tion b e t wee n P BS sec ti on a n d BHS s ection 49

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DISCUSSION One of the most important pieces of evidence the fossil record can provide in any study of evolution is the pattern that it reveals This can also be its most subtle and elusive component due to the incompleteness of the record and the interpretive nature of these patterns The ability to hypothesize a verifiable evolutionary pattern that is universally accepted has proven to be impossible. But does this have to be the end goal of every investigation? A critical element in any evolutionary study is to identify the hypothesis that has the greatest probability of explaining the pattern that has been gleaned from the record. In so doing, another piece of documentation is added to the body of knowledge and perhaps a larger pattern will begin to emerge. In this study the pattern of evolution following the Cenomanian-Turonian mass extinction was evaluated using measurements of key morphometric features from sample populations at three locations. The data presented here reveal three distinctive phases that are consistent at the two main study localities of PBS and BHS: I) instability and variability immediately following the CenomanianTuronian boundary ; 2) a period of lower variability following this initial zone; and 3) a phase of higher variability in the upper portion of the study sections Results from statistical analysis supports the presence of three distinct populations The initial zone of variability is interpreted as being an unstable period following the CenomanianTuronian mass extinction The zone of stability and relatively low 50

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variability is interpreted as a period of evolutionary stasis and the highly variable upper part of the sections is thought to be an eruptive evolutionary period. This very pronounced and consistent pattern raises two questions : I) what do these three phases represent in terms of the evolutionary dynamics of the inoceramid bivalves following the Cenomanian-Turonian mass extinction?; and 2) what evolutionary pattern best explains what is seen in the record ? Evolutionary Tempo and Mode The fossil record provides us with a historical perspective that is not possible solely from the study of living organisms It is this perspective that allows the investigation of the potential patterns evolution produces through time. However there are inherent biases that can alter how these patterns are perceived and also whether there is such a thing as a pattern It is convenient to think in terms of patterns because this implies a broader applicability but maybe they don' t exist. The imperfection of the geological record is a problem but singularly as important are preconceived ideas as to what the record will show. It is critical in any evolutionary study to remove these preconceptions because the rock record being what it is, the problem of seeing a pattern that has been predicted is a very real one This study attempted to remove this bias by just looking at the pattern that the measurements and ratios produce and not identifying species Therefore just a determination of the number of different species present was done. 51

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It is important to note how critical fine-scale temporal resolution is to evolutionary studies It is incumbent on the investigator to make every effort to provide as full a picture as possible with regard to the progression of morphological change within species and high-resolution stratigraphic is the best tool yet known to do this Low-resolution studies leave too much of an already incomplete fossil record out of the analysis For example, in a study by Nehm and Geary (1994) an almost 300m section at Rio Gurabo in the Dominican Republic was subdivided into 8 sampling intervals with less than 250 total specimens and the other intervals included in the analysis were more sparse than this. Nehm and Geary (1994 ) after conceding the presence of gaps in the sampling intervals was a problem, concluded that stasis had occurred in the section Studies over this scale fail to provide the necessary resolution to make determinations as to evolutionary tempo and mode If, for example, a number of the sample intervals in this study were omitted how different would the pattern look and would important attributes such as the restricted dead zone and the distinct differences in the three phases of the study sections appear in the data lbis study has endeavored to provide as full a picture as possible and still more detail would be of inestimable value to the analysis. So the primary question becomes what patterns can be seen in the data provided in this study? The lower intervals contain higher variability but low abundance This pattern seems to be a response to the environmental chaos of the mass extinction event and does not fit any evolutionary model. The evidence at both PBS and BHS show a distinctive period of stasis occupying the middle portions of both sections This pattern 52

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shows up both in the ratios of calculated and the individual morphometric parameters, such as length, of the inoceramids that were measured This stable period also has a gradual reduction initially which is interpreted as chance variation or what is termed "random walk". The level of variability declines from the lower intervals and is markedly lower than that found in upsection at both main localities Kauffman ( 1977b) documented this same period of stasis in studying the growth ridges in inoceramids of this time at the Pueblo section. Eldredge and Gould (1972) proposed that stasis should be the dominant pattern seen in the fossil record since the evolutionary events occur rapidly over relatively short periods of time. There is no question that a period of stasis is present at these locations but does this by itself lead to the conclusion that punctuated equilibrium is the overall pattern of evolution in this sequence? In a study ofNeogene bryozoans Cheetham (1987) investigated individual characteristics in nine species and documented overwhelming evidence of stasis His conclusion, by inference was that punctuated equilibrium was the mechanism of speciation He found that although there were some departures from the generally static pattern in morphology they were so few in number and so poorly related to the distinguishing morphology between an ancestor-descendant relationship that these departures were simply chance variation. His conclusion of punctuated equilibrium was based on the presence of a long period of stasis and not any documentation of the pattern of speciation The difficulty with this type of interpretation is that it presupposes a pattern of punctuated equilibrium based only on the presence of stasis This essentially limits the debate of the pattern of evolution to a choice between the end members phyletic 53

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gradualism and punctuated equilibrium. This exclusion of possible intermediate patterns is an unfortunate collateral effect of this debate and again points out the pitfalls of preconceived ideas Williamson (1981) provides a more definitive documentation of punctuated equilibrium. In his study of Cenozoic molluscs in east Africa, there is evidence of both stasis and punctuated speciation Long-term stasis in all of the lineages studied is punctuated by periods of rapid and significant phenotypic change and no gradualistic trends were observed (Williamson, 1981) The rapid speciation events of these molluscs were on the order of 5 ka to 50 ka which are much shorter than the periods of evolutionary stability in these lineages (Williamson, 1981) The presence of stasis alone cannot lead to the conclusion of punctuated equilibrium It must be accompanied by a pattern of rapid punctuated speciation Looking at the upper sampling intervals of the BHS and PBS sections another d i stinctive pattern is apparent. Here an eruptive evolutionary phase occurs and is characterized by increased variability of both the individual morphometric characteristics and the ratios being used in this study This eruptive phase following a long period of stasis does not follow the pattern of slow phyletic change prescribed by gradualism. In so far as punctuated equilibrium is concerned the period of stasis followed by rapid evolutionary change is indeed similar to what the model predicts however the pattern of speciation is best described by another mechanism The phylogenetic model of reticulate speciation ( Figure 32) proposed b y S yl vester-Bradley (1977 ) is a synthesis of phyletic gradualism and punctuated equilibrium and represents one of the intermediate patterns mentioned earlier This 54

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model is unlike punctuated equilibrium (Figure 2) where a changing environmental landscape or migration cause species become isolated, then new species arise and the old species are replaced as they become extinct (Eldredge and Gould, 1972). Also a pattern seen from punctuated equilibrium is a morphologic jump unless the isolated allopatric center is sampled but that is highly unlikely and in this study the same trend is apparent in two geographically disparate areas so this jump should be seen if this is the correct model. In reticulate speciation, as an ancestral species increases in abundance and migrates into new areas gene flow is maintained through this increasingly variable population (Sylvester-Bradley, 1977) This period of increasing variability is the eruptive phase after which, during the reticulate phase, there is alternating isolation and hybridization while the populations are still genetically compatible until finally when isolated long enough divergence occurs and genetic incompatibility prevents any further hybridization (Sylvester-Bradley, 1977) Isolation, although still an important overall factor, is not as key to this mechanism in the early phases as it is to punctuated equilibrium. Analysis of the patterns from the PBS and BHS sections suggests the period of stasis is the stabilized period at the base of the model for reticulate speciation (Figure 27) Meanwhile the period of variability in the upper portions of both is interpreted as being the eruptive phase of the model. This pattern seems to have a much higher probability of being reticulate speciation than punctuated equilibrium due to this eruptive phase being present. Reticulate speciation is a workable hypothesis worthy of consideration in future 55

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7 Geographical eJittent EPISODES Of -.. MIGRATIOH 0 I SOLATION + EXTINCTION "2 "' .0 (/) c: .. 01 > 0 Gi a: .:: a. :::J ... w Figure 27. Reticulate speciation Four phases succeed each other In the eruptive phase the ancestral species increases in numb ers and variety. and extends its area of occupation (levels I to 2) During the ret iculate phase isolation and h ybri dization alternate (levels 3 to 6) Of the five phyletic lines that survive th is phase. two become extinct during the divergent phase ( l evels 6 to 7) The three s urvivors persist into a stabilized phase without further modification 56

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evolutionary studies. After analysis of the data there is no question that this study would have benefited from being able to sample further upsection than the localities allowed The patterns from intervals above those in this study would have provided further resolution and documentation Perhaps the debate between punctuated equilibrium and phyletic gradualism needs to be opened up to include other patterns more readily or the risk of looking at evolutionary tempo and mode myopically will remain Patterns Following the CenomanianTuronian Mass Extinction Data for the CenomanianTuronian mass extinction suggest a step-wise pattern of extinction occurring over several million years{Hanies and Kauffinan, 1990). It has been hypothesized that periods following step-wise mass extinction events have a restricted or absent, fossil poor, dead zone and a reduced chance of explosive radiation because more niches remain filled This may differ from the period following a catastrophic extinction where it has been suggested that the biot.a is decimated and an extensive dead zone resides and free niche space is more abundant (Harries et al 1996). Although recently this hypothesis has been brought into question based on data from the catastrophic CretaceousTertiary mass extinction (Harries, 1999) The evidence presented in this study warrant an investigation as to whether the phases present mirror hypothesized repopulation patterns following step-wise mass extinctions and what these individual phases can tell about evolutionary dynamics during this period Evidence from ratios of the inoceramids measured in this investigation shows the initial phase following this event is one of high variability reflecting the instability of a post-extinction environment. Indeed, the lower intervals from the BHS and PBS sections show a generally lower abundance, also docwnented by Harries (1999), and a somewhat 57

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restricted dead zone. This lower interval seems to correlate with the survival interval documented by Harries (1999) (Figure 28) The survival interval in the PBS section of Harries (1999) is about 1m in length from the base ofthe Cenomanian-Turonian boundary whereas it is thicker i n the PBS section in this study (approx. 2.5-3 m) This could be a function of the transition between the survival and lower recovery intervals being reflecting the biota as a whole and not just the inoceramids The survival interval fo11owing a step-wise mass extinction event is characterized during the earliest stage by the population bloom of disaster species that usually have short life cycles and become almost absent as the next group the ecological opportunists begin to flourish later in the survival interval and environmental equilibrium is reestablished (Kauffinan and Harries 1996) During the late part of the survival interval the first radiation of the crisis progenitor taxa occurs and sets the stage for the recovery interval. Kauffman and Harries ( 1996) defined progenitor taxa as species that arise during the extinction and survival intervals are adapted to the environmental perturbations asociated with the mass extinction interval and therefore are a seed group for the recovery interval. A study of benthic foraminiferal assemblages across the CenomanianTuronian boundary by Peryt and Lamolda (1996) clearly shows the presence of the "' components in the survival interval laid out by Kauffinan and Harries (1996) They docwnent the presence of progenitor species a short dead zone interval early in the survival period, and the appearance of disaster and opportunistic taxa and species In addition there was also lower abundance in the survival period. In the case of the Cenomanian-Turonian mass extinction Mytiloides (Family Inoceramidae) has been identified as a crisis progenitor genus (Kauffinan and Harries 58

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Vl '-0 I! ... l .: I a 1: 1 INOCERAMIOS -I : :s: f% :' r::11 H1.;1 : .:! .. J::: Jia: !d:di;!ll z -i :nniiHH! I '}pH!I'f:i; i ,::,iiif iii! = l:il I ,p;qp!iH .; i i ;; r1,li!!!I::!.J . :; Gt i >-a! I -4 w -e -c: 0 .s i : l z 'a i j .: ; N..l :1 ::: 0 z IU u elj :;; i ... ;:. j:! :e l!iiiHif: ,:.. ,..; i;; if j .:. ----'IHHi:. lt:rf '':'"' din== .... n:: I j i ;_ I : ;c 4 !! I .., ... I ILUS EX"nNCTlC.H tm!RVW t..ue z ,.. c a:: 5 c u :I w L = 0 ... 11.1 c;: SURVIVAL INT!IIVA1. L__ Extinct spec1es Survivors ..... Crisis Progenitors ............. New Species from Surviving Genus ---New Species from New Genus Uthologles: D Shale/Marlsione []] Umestone/Calcarenite Bentonite Figure 28. Stratigraphic ranges on inoceramids found in the Late Cenomanian through Early Turonian from six sections spanning the Western Interior Basin ofNorth America (modified from Harries and Little, 1999).

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1996). This group arose in the lastest Cenomanian, rapidly diversified and was very abundant after the boundary extinction (Kauffman and Harries 1996). What does this initially variable survival phase reveal ? It appears that this is a period of filtering for the inoceramid bivalves in response to the environmental perturbations causing the mass extinction and results in a variable mix of morphotypes within the population. This initial phase present at both major sampling localities, appears to be occupied by a community indicative of a highly stressed environment. The inoceramid bivalves are known to have flourished in oxygen-deficient and otherwise difficult environmental conditions (Harries and Crampton, 1998). The presence of a variable population that has survived the CenomanianTuronian mass extinction event suggests some adaptation to environmental stresses during the extinction and survival intervals. The lower variability middle phase (phase II) and the higher variable upper phase (phase III) are interpreted as being the recovery interval from the CenomanianTuronian mass extinction The middle phase shows a generally more stable environment and may represent the beginning of a return to environmental equilibrium Indeed it has been postulated that conditions ameliorated quickly and this allowed an expansion of diversity and abundance (Harries and Little, 1999) Harries ( 1999) documents the emergence of a morphologically diverse group of ammonites in the early Turonian as evidence of a significant improvement of environmental conditions After the major environmental perturbations it seems that this stable interval represents a pause after the filtering of species in the survival phase. Based on the morphological data in this study it appears that one species is present during the period of 60

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lower variability. Specimens sampled at both BHS and PBS during this low variability phase have generally lower values for the measurements of individual attributes such as height length axial length and secondary axis This indicates a population of smaller sized inoceramid bivalves perhaps in response to competition during the extinction and s urvival intervals Again statistical results support these observations Data as to whether there is a positive relationship between shell size and species duration/extinction risk is i nconclusive (Jablonski 1996) The recovery interval is characterized by a return to envirorunental stability and a period of enhanced diversification as niches are filled. Early in the interval new species predominantly evolve from lineages that survive the mass extinction and later a major radiation of new lineages ensues (Harries and Kauffman, 1990 ; Harries et al. 1996 ; Harries and Little 1999) Tur ( 1996) showed a pattern similar to this in a study of planktonic foraminifera recovery from the CenomanianTuronian mass extinction During the later part of the recovery phase there was a strong increase in morphological diversity from the survival and lower recovery phases (Tur, 1996). The upper variable phase is interpreted as an eruptive diversification period indicative of the later part of the recovery phase The pattern is similar to that in the Harries ( 1999) study of repopulation after the CenomanianTuronian mass extinction (Figure 28). It appears from analysis of the morphological data that three to four species begin emerging toward the later part of the early recovery interval. It is suggested that the upper variable phase in this study represents this period of repopulation Additionally there is an increase in the instances of larger measurement values for individual 61

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morphometric attributes of the inocerarnids measured This increase may be attributed to a return of ecosystem stability and favorable environmental conditions. It seems that the three distinct phases documented in this study are reflective of the survival and recovery intervals put forth by Harries and Kauffinan (1990). The inoceramid bivalves show high variability and low abundance with a restricted dead zone during the initial phase indicative of the surv i val interval sensu Harries and Kauffman ( 1990) Following this there is a period of stability and followed by variability leading to diversification that would be expected in the recovery interval. 6 2

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CONCLUSIONS There is a period of high variability and low abundance observed in the lower intervals of the PBS and BHS sections. This phase is a response to the environmental perturbations experienced during the CenomanianTuronian mass extinction event and does not fit any of the evolutionary models put forth The significance of this phase in terms of evolution seems to be more in its setting of the table for the succeeding phases A distinct period of stasis is documented in the middle portions of these sections along with smaller overall inoceramid body size. The slight gradual decline in body size in the initial part of this phase is attributed to genetic random walk and not to any evolutionary pattem Stasis is followed by a marked increase in variability toward the top of both sections indicating an eruptive phase of evolution Investigation of the morphological data indicates the presence of one species of inoceramid during the stasis phase and increasing to three or four species during this eruptive period Results from a Student's t-test support the presence of three statistically distinct populations in these three zones. F-test results suggest a statistically significant difference in variance between the lower and middle zones but no such results were found when the middle and upper zones were compared. The evolutionary pattern observed is not readily explained by either phyletic gradualism or punctuated equilibrium There is no evidence of gradualism other than that attributed to chance variation. Also, although a period of stasis is present at the BHS and PBS sections there is no pattern of morphologic jumps recorded by the data which is a 63

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characteristic that is expected of punctuated equilibriwn Since these morphological jumps are a critical component of this model the presence of punctuated equilibrium is not present in the data analyzed Reticulate speciation is the evolutionary model that best fits the pattern fmmd in this study The period of stasis apparent in these sections represents the stabilized phase of this model. Additionally, there is a pronounced period of eruptive evolution above this stabilized period and this fits the hypothesized pattern developed for reticulate speciation extremely well The evolutionary dynamics of the inoceramid bivalves in the Western Interios Seaway following the CenomanianTuronian boundary confonn to the model extinction survival-recovery The lower intervals in the sections studied represent the survival phase grading into the recovery phase This period has a restricted dead zone lower abundance and higher variability characteristic of the survival interval These are all responses to the environmental distress of the mass extinction event and represent a filtering phase due to this stress The recovery interval is marked initially b y lower variability and the presence of one species probably the progenitor taxa upon which evolutionary radiation will be based later in the recovery phase. The smaller body sizes that are observed are the result of increased competition as the environment begins to stabilize In the upper portions of the sections an increase in diversity and abundance, typical of the later part of the recovery interval, is apparent. The emergence of three to four species during this eruptive phase is an expected component of this interval as niches vacated during the mass extinction are filled and environmental stability is reestablished 64

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REFERENCES Barron E. J., Arthur, M .A., and Kauffman E. G., 1985. Cretaceous rythmic bedding Sequences : a plausible link between orbital variations and climate : Earth and Planetary Science Letters v 72: 327-340 Cheetham A. H., 1987 Tempo of evolution in a Neogene bryozoan : are trends in single morphological characters misleading? : Paleobiology, v 13: 286-296 Darwin C 1859. On the Origin of Species : University of Pennsylvania Press Philadelphia 816 pp Eicher D L. and Diner R., 1985. Foraminifera as indicators of water mass in the Cretaceous Greenhorn Sea Western Interior In Pratt L. M., Kauffman, E. G., and Zeit, F B eds ., Fine-grained deposits and biofacies of the Cretaceous Western Interior Seaway : Evidence of cyclic sedimentary processes : SEPM Field Trip Guidbook no 4 Golden Colorado : 60-71. Eicher D. L. and Diner, R., 1989.-0rigin ofthe Cretaceous Bridge Creek Cycles in the Western Interior, United States: Palaeogeography Palaeoclimatology Palaeoecology, v 74: 127-146 Elder W P ., 1987. The Paleoecology of the Cenomanian-Turonian (Cretaceous) Stage Boundary Extinctions at Black Mesa Arizona : Palaios v. 2 : 24-40 E lder W P ., 1988. Geometry of Upper Cretaceous bentonite beds : Implications about Volcanic source areas and paleowind patterns western interior United States : Geology v 16: 835-838 Eldredge, N and Gould, S. J., 1972. Punctuated Equilibria : An alternative to phyletic gradualism In Schopf, T. J. M ed., Models in Paleobiology San Francisco Freeman-Cooper : 83-115. Erwin, D. H., 1996. Understanding Biotic Recoveries : Extinction Survival and Preservation during the End-Permian Mass Extinction In Jablonski, D Erwin D H., and Lipps, J. H eds Evolutionary Paleobiology. Chicago The University of Chicago Press : 398-418. Geary D., 1995. The importance of gradual change in species level transitions In Erwin D. H. and Anstey R. L. eds., New Approaches to Speciation in the Fossil Record 65

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Hallam A, 1982 Patterns of speciation in Jurassic Gryphaea: Paleobiology v 8 : 354366 Hancock, J. M and Kauffman, E. G 1979 The great transgressions of the Late Cretaceous: Journal of the Geological Society of London, v 136 : 175-186 Harries P. J ., 1993a. Patterns of repopulation following the CenomanianTuronian (Upper Cretaceous) mass extinction : Unpublished PhD dissertation, University of Colorado, Boulder Harries P J., 1993b. Dynamics of survival following the CenomanianTuronian (Upper Cretaceous) mass extinction event: Cretaceous Research, v. 14: 563-583 Harries P. J., 1999 Repopulation s from Cretaceous mass extinctions : Environmental and/or evolutionary controls? In Barrera E. and Johnson, C C ., eds Evolution of the Cretaceous Ocean-Climate System: Geological Society of America Special Paper 332. Boulder, Colorado: 345-363 Harries P J. and Crampton, J. S 1 998 The Inoceramids: American Paleontologist v. 6 no. 4 : p 2-6 Harries, P J. and Kauffman, E. J., 1990. Patterns of survival and recovery following the Cenomanian-Turonian (Late Cretaceous) mass extinction in the Western Interior Basin, United States. In Kauffman E. G. and Walliser, 0. H., eds. Extinction events in Earth history : Springer-Verlag. Berlin: 277-298. Harries, P J., Kauffman, E G and Hansen T. A 1996 Models for biotic survival following mass extinction In Hart M B ed. Biotic Recovery from Mass Extinction Events : Geological Society Special Publication No. 102 London : 4160. Harries P J., and Little C T. S ., 1999 The early Toarcian (Early Jurassic ) and the CenomanianTuronian (Late Cretaceous) mass extinctions : similarities and contrasts : Paleogeography Paleoclimatology, Paleoecology v. 154: 39 66 Hattin, D E ., 1985. Distribution and significance of widespread, time parallel pelagic Limestone beds in Greenhorn Limestone (Upper Cretaceous) of the central Great Plains and southern Rocky Mountains In Pratt, L. M., Kauffman E. G and Zeit, F. B eds., Fine-grained deposits and biofacies of the Cretaceous Western Interior Seaway : Evidence of cyclic sedimentary processes: SEPM Field Trip Guidbook no. 4 Golden, Colorado : iv-xi 66

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Hattin, D E. 1987 Pelagic/Hemipelagic rhythmites of the Greenhorn Limestone (Upper Cretaceous) of northeastern New Mexico and southeastern Colorado: New Mexico Geological Society Handbook 38th Field Conference : 237-247. Hilbrecht H. and Harries P. J., 1992 Lower Turonian Euramerican Inoceramidae : a morphologic taxonomic, and biostratigraphic overview: A report from the First Workshop on Early Turonian Inoceramids (Oct. 5-8 1992) in Hamburg, Germany : 641-671. Jablonski D., 1986 Background and Mass Exti nctions : The alternation of Macroevolutionary Regimes: Science v 231 : 129-133. Jablonski D., 1996 Body size and Macroevolution In Jablonski, D., Erwin, D H. and Lipps J. H. eds. Evolutionary Paleobiology Chicago The University of Chicago Press : 256-289 Jenkyns, H C., 1980. Creatceous anoxic events: from continents to oceans : Journal of the Geological SocietyofLondon, v 137 : 171-188 Kauffman, E. G., 1977a. Geological and biological overview: Western Interior CretaceousBasin Geologist v 14 : 75-99 Kauffman E G 1977b Evolut i onary rates and Biostratigraphy In Kauffman, E G and Hazel J. E. eds., Concepts and Methods of Biostratigraphy : 109-141 Kauffman E. G ., 1985. Cretaceous evolution of the Western Interior Basin of the United States In Pratt L. M Kauffman, E G ., and Zeit, F B. eds. Fine-grained deposits and biofacies of the Cretaceous Western Interior Seaway : Evidence of c y clic sedimentary processes : SEPM Field Trip Guidbook no. 4, Golden, Colorado : iv-xi. Kauffman E. G ., 1995. Global Change Leading to Biodiversity Crisis in a Greenhouse World : The Cenomanian-Turonian (Cretaceous) Mass Extinction. In Effects of Past Global Change on Life : 47-71. Kauffman, E. G ., 1995 Global Change Leading to Biodiversity Crisis in a Greenhouse World : The Cenomanian-Turonian (Cretaceous) Mass Extinction In Effects of Past Global Change on Life : 47-71. Kauffman E. G ., Villamil, T. Harries P J ., Meyer C A and Sageman, B B. 1992 The flat-clam controversy : Where did they come from ? Where did they go ? In Fifth North American Paleontological Convention Chicago II: I 57. 67

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Kauffman E G and Caldwell W G E., 1993. The western interior basin in space and time In Caldwell, W G E. and Kauffman, E. G. eds., Evolution of the Western Interior Basin, Geological Association of Canada Special Paper 39 : 397-434. Kauffman, E G ., Sageman B B., Kirkland J. I. Elder W. P ., Harries P J., and Villamil T., 1993. Molluscan biostratigraphy of the Cretaceous Western Interior Basin : Special Paper, Geological Association of Canada : 397-434 Kauffman E. G. and Harries, P J., 1996. The importance of crisis progenitors in recovery from mass extinction In Hart, M B ed ., Biotic Recovery from Mass Extinction Events : Geological Society Special Publication No. 102. London : 15-39 Kerr, A C., 1998. Oceanic plateau fonnation : a cause of mass extinction and black shale Deposition around the Cenomanian-Turonian boundary? : Journal of the Geological Society of London, v 155: 619-626 Kirkland J I. 1991. Lithostratigraphic and biostratigraphic framework for the Mancos Shale (Late Cenomanian to Middle Turonian) at Black Mesa northeastern Arizona In Nations, D J. and Eaton, J. G eds Stratigraphy, depositional environments and sedimentary tectonics of the western margin Cretaceous Western Interior Seaway : Geological Society of America Special Paper 260: 85-111. Larson R. L., 1991. Latest pulse ofEarth : Evidence for a mid-Cretaceous superplume : Geology v 19: 547 -550. Mayr E ., 1942 Systematics and the Origin of Species : Columbia University Press New York 334 pp Mayr E.,1954. The Major Features ofEvolution : Columbia University Press New York 434 pp Mayr E., 1963. Animal Species and Evolution : Harvard University Press Cambridge 797 pp. Nehm R. H and Geary D H., 1994 A gradual morphologic transition during a rapid speciation event in marginellid gastropods (Neogene: Dominican Republic) : Journal ofPaleontology v. 68 : 787-795 68

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Olesen J. 1991 Foraminiferal biostratigraphy and paleoecology of the Mancos Shale ( Upper Cretaceous) southwestern Black Mesa, Arizona In Nations D J. and Eaton J G eds. Stratigraphy depositional environments and sedimentary tectonics of the western margin Cretaceous Western Interior S e away : Geological Society of America Special Paper 260 : 153-166 Peryt D and Lamolda M ., 1996 Benthonic foraminiferal mass extinction and surviva l Assemblages from the CenomanianTuronian Boundary Event in the Menoy o Section northern Spain I n Hart M B ed., Biotic Recovery from Mass Extinction Events: Geological Society Special Publication No. 102 London: 2 45258 Pratt, L. M. 1984 Influence ofPaleoenvironmental Factors on Preservation of Organic Matter in Middle Cretaceous Greenhorn Formation, Pueblo, Colorado American Association of Petroleum Geologists Bulletin, v 68 : 1146-1159 Raup D M and Sepkoski J. J. 1986 Periodic Extinction ofFarni1ies and Genera : Science v. 231: 833-836 Sageman, B. B., Rich, J. Arthur, M A Birchfield, G E. and Dean, W E. 1997 Evidence for Milankovitch periodicities in CenomanianTuronian Lithologic and Geochemical Cylces Western Interior U.S .A.: Journal of Sedimentary Research, v. 67: 2 86-302 Sheldon P.R., 1987. Parallel gradualistic evolution of Ordovician trilobites : Nature v. 330 : 561-563 Simp s on, G G ., 1944 Tempo and Mode in Evolution : Columbia University Press New York. Sinton C. W and Duncan R. A 1997 Potential Links between Ocean Plateau Volcanism and Global Ocean Anoxia at the CenomanianTuronian Boundary : Economic Geology v 92 : 836-842 Stanley S M ., 1979. Macroevolution : Pattern and Process : The Johns Hopkins University Press Baltimore and London Sylvester-Bradley P C., 1977 Biostratigraphical Tests of Evolutionary Theory. I n Kauffman, E. G., and Hazel J. E eds., Concepts and Methods of Biostratigraphy: 4 1 -63 69

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Tur N A. 1996 Planktonic foraminifera recovery from the Cenomanian Turonian mass extinction event northeastern Caucasus In Hart, M B. ed., Biot i c Recovery from MassExtinction Events : Geological Society Special Publ i cation No. 1 02. London : 259-264 Walliser 0 H., 1996. Patterns and causes of global events In Walliser 0 H ., ed., G l obal events and event stratigraphy: 225 250 Williamson, P. G ., 1981. Palaeontologi cal documentation of speciation i n Cenozoic Molluscs from Turkana Basin : Nature v 2 93 : 437-443 70

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APPENDICES 7 1

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-.....) N 1 BHS _J_Section l 1 +----+ .. 1------Interval HLUSA AUSA L_!-i LUAL H/L HLL __ __ AL [ SA Length 2 0.49 1.08 0.45 1 05 3 0 6 6 6 1 6 0 5 7 4 -= --1 .29 0 16 0 95 0 9 __ 4:5 t4 2 = 4.4 . 4__1_0 32.__ 1 .07 0 34 0 95 0 9 __ 65 I 0.24 1 07 ti.5 _ __ _t _ _.?.:i_ 2 -J-.-2:.?..L ______ 1.06 _____ =t 0 .51 0 .90 ___ __ _?_-t 1 .35 1 o.19 o.87 ____ g__ :ri: t=-H 1--H :---ti--L = __: : 11 :: t_! L : __ ; --= 11.__: _ _E4 _J_ 1.33 0 .18 I 1 25 __7.3 5 5 ____ j_ _ __ ....:.!___ o.36 _j ____ __!1? _____ o 32_L_ o.89 1 3 3--1-____ 14 0.32 I 1 15 : 0 28 I 1 00 1 5 : 5.4 4 7 I 4 6 4 6 ---__ _ _: __ ...Q;_4_9__i---_g3 _____ : 0.33 0 88 : __ : _ __..:_6__ _ 1.18 ______ +o 36-+ o .81 _: _ 2.i__! ____ 5 6 ___ ___ __;_ __ 0 25 __ _! ______ 1.40 ____ .;.... ___ 0 18 1-0 95 _: _ ..12__ ; __ .2i_ ___ j ___ 5 3 ___ __ o 36 ____ o 97 _____ : _ Q 38 i o 88 ; 2.1 : ___ _1 __ 4 6 _____ .?2_. 16 : 0 34 ; 1.40 l 0 24 : 0 .98 i 1 8 7.4 l 5 3 6 0 6 1 1 6 _;_-=. --I 1 01 : . .. ___ 16 0 35 1.12 0 .31 0.84 1.5 4 8 I 4 3 : 3 7 l 4.4 -----:;"? ___ -D.3s--.. -"1.04-----0.34 -:s_s_ .. !----s 4 --:---4 6 ... -4 : a. -... .... -----.. ...... ----------------.................... ..... ---. ------. I-.------17 0.4 7 1 1 34 0 35 1 .1() 1.8 5 1 3 8 4.4 : 4 0 1 -------.,--- ... .................. ------ ........... "'........... - -....... I -17 0 29 1 32 0 22 0 89 1 2 5.4 4 1 4 1 4 6 -------------------------........ -----------,--------.... -------------I ---_ ___ J.? -. : ....... 1.4_?. .. .. .. ... . ____ 1..:_6__ _ ---.. 5 8__ .. j .. 17 0 16 1 33 0 12 0 89 0 8 6 5 4.9 4 8 I 5.4 .. -=---= 4 I ... r 18 0 39 1 22 0 32 1 07 1 6 5 0 4 1 4 6 4 3 19 ----o.47 _______ -------1 24 - "'0 "'0 (1) ::s 9-: X 3::: (1) (I) c: @ 3 (1) ::s 0.. :;10 g S" -..,. c :3 C/.) -c: C/.) n (") .... o ::s (I)

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;j 0.41 ___ 1 22 I 0 .33 ___ 1 ____ 231 0 .50 1 29 0 .39 1.12 6 2 4 8 5 6 5 0 K=l-0 53 _1.01-1 --.:. 1 2s o .51 1 36 o 38 1 28 3 6 9 5 1 o r 8 3 6 5 26 0 32 0 .20 .!J..!_ I=B _J __ ..:__ 4 :-:;-r 5.(--__ 4 6 26 I 0 52 1 26 0.41 1 02 I 2.4 I 5 8 : 4 6 I 5 2 5 1 ------------------------1-----,-------14. -__ L_Q;_53 __ J. ___ 4 0 _ ,_.!Q__ _J.:__1 __ 4 5 ----f--3 9 .. 0.44 1 1 22 ---+-0 36 4 0 98 : 1 _._ _ _!_!_ __ -.. -... _ --... _L __ 0 .29 -_ 1 07 _[ _ ___ 2 6 ... i. ... .... -?.:!_ __ +=. 0.49 1 04 I ... .. ___E. __ _:_ _ 1 .23 ___ j_ _ 0.45i 1 09 6.4 : ___g_ __ 0.41 -----1.05 : 0 39 __ + __ _2.:95 __ .. 1 : 1 ----1 05 ___ .. __ ... 1 : 05 ___ : ___ _______ 4_:!, _ t, __ .... --! 2 28 0 43 1 .11 0 39 i 0 90 1 2 : 3 1 : 2 8 i 2 7 3 0 !----=-:----_ ;_ -----.. ----------------.. __ _______ ------------------: ; ; : f---;------------. ----_,_Q}2 ____ ___ 0 .28 _____ .... .. .. 1-----4 0 -. 0.40 : _____ .;...... _2.38 ______ 3.4 ____ 1 -3 0 29 0.40 : 1 30 0 .31 ; 0 93 1 6 5 2 ; 4 0 4 2 i 4 5 : 1 .oo 4 2 c=Is --:-_ .. __ .. .... .... .......... ___ _9. 3o __ .. :.... .oo_ ....... J 1 __ .. .. ] : ? ... ... .......... .. L 30 0.36 1 .31 0 27 0 80 1.6 5 9 4 5 4 5 5 6 --36 --.. -0.43 .. : .... -----f21"--------a 35 _ .. ------:;-.-o2 .............. ..... ------4 2 .... .. .. r--4.4 --31'-----6':-46-----.. ........ 0 38-.. o .ss ......... 2:1 ........ --4 : 6 --4.9:-.. s o-.. I'?)_ ....... --_ . 1_.4 --.:: ---5) .. .. .. ii_ ... 31 0 34 1 09 0.31 0 92 1 1 3 5 3 2 3 3 3 6 --3 1 ...... _0.54 ______ ..... --f25--------o :43 --To1---1 : 5 ....... 3.5 ... ---2 : 8 ...... 3 2 i .... '3.o _ . -----.. ... ------------ .. --. ---. . .. 1'"''''' ---... 31_ ... --Q .g_ .......... ___ 1 00 .. .. .. ....... ; 32 0.37 1 28 0 29 0 96 1 6 5 5 4 3 4 5 4 7 --32-........ o 4 s----1:2i ............ o:Js ........ -3:3 ...... 2 6 ------2 8 -2 6-----32 ----o:-44.. .......... --1 .33--.. 6 .33 .. .. 1 6........ 4 a 3.6 .. 3 9 ...... 3 5---32 o :4o ...... ... .. {o9 ........ ----0 .37 o :9s .. ... 1 . 4 ... .. i e........ "3.5 3.6 --3 : 8 32 ........ --a.51.... ... 1 :12 ----.. ......... o.'8a ....... 2 ".'6 ....... 5.'7 ... .. 5 : 1 ... ... 4 6 5.2 .. 33 ------o.s1 _____ .... -f32..... ... ____ .. o.3a -----o :96 -----3 :i3" .. --9 : 4--i:; ....... 4 7 ... s o )> "'0 "'0 (i) ;:;, :>< -() 0 ;:;, .-;:;, c: (i) 0.. -

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-....) 1-33 I 0 .5 3 _ 0 95 0 .56 1 06 2 .0 33 0 52 1.45 0 36 1 .06 1.6 3 1 I 0 .56 1 .37 0.41 1 .03 1 .5 3 7 2 7 E 33 -o.4_ 4 ___ 1':30 ___ -0 34 -i-1.'10 -12' --3 5 ---E. 34 0 36 1 39 0 26 1 .00 2 0 7 8 5 6 --------1 55 0 26 __ 1 14 2 2 _ 8 5 5 5 34 I 0 52 1 26 0.4 1 1 .12 1 2 2 9 2 3 2 8 2 5 ---'-----!------,------!-----+--------------I 34 r_QJ.Q ___ _ .. s ___ o .34 E'94 __ _ r __ 4 s ____ __ 4 1 .38 0 34 0.92 __ 7 _ ::i--+ -j : : "' .. 0 23 _ _ __QJ1 0 37 .. 1 .17 .. g=t_ 4 2._ ----3 6 _ _2:?0 _J 1 43 0.42 0 94 .. ___ 6.9 __ __ o 59 0 98 tj}-+--i---t: -f---1: : ; : : }35 I=-0.46 _ : .-__ 1 ___ 1 1 3 o .28 _-y-0.89 __ 4 7 _E.:L_ o 58 _j 1 .18 ---!...-._._!2_. _ 6 5 _ 36 : 0.48 I 1 98 I 0 24 I 0 84 I 3.2 I 13.1 6 6 I 8 7 10 3 --. -----1------r--------: 0. 75 J_ __ : __ _2J_ ___ 5 5 _ _ _QJ_ 3 _ __ _!_ ... ... _L_ 9 6 ___ 36 : 0 .40 : 1 35 i 0 30 : 0 98 : 3 3 : 11. 1 : 8 2 I 8.8 1 9 0 ------. -----. --------------------r-----... -.. ------. r .......... 36 o 53 1 30 o.4o o .8e 2 1 5.2 4 0 4 5 1 5.1 ----... __________ .. ______ .. -----------------------------.. ---------... _ ... .. _________ -r --36 0 27 1.42 : 0 .19 : 1 05 2 3 : 12. 1 8 5 10 1 9 6 3 6 029 -------.. ___ -........ o.-22----1.10-.. -s.o .... _ .. 3.8 -4 5 .. ;f:;----36 ____ -o.eo--:-----u 4 .. ... --o 53 .. -:--Toe-.. ... .. ..... ---3 5 -4.o! -3.::;------------------------------------------.... ----------. 1-. ----37 0 52 1 .12 0.46 0.90 4.2 : 9 1 8.1 8 3 9 2 .. ... l.lb= : .. _ ... 37 0 39 1.45 0 27 0 85 1 5 5 5 3 8 3 9 4 6 -. :-r.. 38 0 .66 1.13 0 58 1 00 2 1 3 6 3 2 3 2 : 3 2 ""'38 ----0.51-------'1.47 ____ -.. :--"(f35 .. : .. 1.55 ... -.... 2 .. 5 ___ ____ 7 2 .. 4:9 .... .. "5:f3" 5.5" ... 3 8 ..... : -.... ...... a 5 f a .93------is ...... -.. 6 .'3---s i -: 5.3 s.i ---39--" "0'.49 -1.17"-.. :--0.42 .. ----1.13 .. -4 -.3.. -.. 1 0 3-.. 8 8 -:-9.6 -.. 8 5 )> "0 "0 Cl> ::s 9-: X ..-.. (') 0 ::s ::!' ::s c: &. ""-"

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---l-----1.44 ___ -'--5..: 1_L_ _g._? ___ __ _ 39 : 0 54 i 1 .28 I 0.42 1 .07 3 1 7 3 ; 5 7 ; 5.9 ; 5.5 ,____ ------------t-----.. --"----------------------__ .--t-0 36 0 98 _: 5 8 -39 ; 0 .38 1 22 I 0.31 I 1 03 I 1 2 3 9 i 3 2 ; 3.4 3 3 )> "0 "0 ::s & X ,..-,. (") 0 ::s -::s a.

PAGE 88

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PAGE 89

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PAGE 90

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PAGE 91

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PAGE 92

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PAGE 94

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PAGE 95

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PAGE 96

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PAGE 97

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