THE ROLE OF PREDATION AND PARASITISM IN THE EXTINCTION
OF THE INOCERAMID BIVALVES: AN EVALUATION
by
COLIN R. OZANNE
A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Department of Geology University of South Florida
August 1999
Major Professor: Peter J. Harries, Ph.D. Graduate School University of South Florida Tampa, Florida
CERTIFICATE OF APPROVAL
Master's Thesis
This is to certify that the Masters' Thesis of
COLIN R. OZANNE
with a major in Geology has been approved by the Examining Committee on July 20, 1999 as satisfactory for the thesis requirement for the Master of Science degree
Examining Committee:
Major Prd*ssor: Peter J. Harries, Ph.D.
,. j '', v " ~ .....,,.- Member: Terrence M. Quinn, Ph.D.
~emberdisa L. Robbins, Ph.D. ACKNOWLEDGEMENTS
I would like to thank my advisor, Dr. Peter J. Harries, for his enthusiastic support,
knowledge and guidance during my two years at USF. I also wish to thank Dr. Terry
Quinn and Dr. Lisa Robbins, for their contributions as members of my committee and
their invaluable instruction throughout my graduate career.
I give special thanks to Dr. Donald Crowe, my stepfather and field assistant, for
putting up with my ignorance and irritability in the field and his steadfast support, both
financial and psychological throughout my studies. In addition, I would like to
acknowledge Neal Larson ofthe Black Hills Institute for Geologic Research for his help
and guidance in the field, without which this project would not have been completed. I
would also like to thank Donnely Darnell and his family for generously allowing me to
collect thousands of "useless" clams on their land in Wyoming. I am also indebted to Dr.
Irek Walaszczyk for his photography and helpful insights and Dr. Neil Landman for his
intellectual contributions.
I owe a great deal of thanks to my parents, grandparents and siblings for their
support and encouragement during the past two years and thanks to my friends and fellow graduate students who challenged me, prodded me, and suffered with me at times, through this endeavor.
Funding for this project was provided by the Geological Society of America, The
American Museum ofNatural History in New York and the Tampa Bay Fossil Club. It was essential for the completion of this project and I am very grateful for the support. TABLE OF CONTENTS
LIST OF TABLES lll
LIST OF FIGURES lV
ABSTRACT Vll
INTRODUCTION
GEOLOGIC SETTING 3 Paleogeography/Paleoceanograpy of CWIS 3 Stratigraphy 6
STUDY AREA 10
METHODS 12
RESULTS 14 Taphonomy and Preservation 14 Types of Deformities 17 "Awl Mark' 17 "Wedge" 18 "Vampire Bite" 18 "Squiggle" 20 "Bubbly" Nacre 20 Hohlkehle 20 Other 23 Distribution of Deformities 23 Statistical Results 26 Incidence of Deformities, Wyoming Sample 26 Incidence ofDeformities, Montana Sample 26 Species Composition and Percent Deformed for Wyoming Sample 28 B. eliasi zone 30 Lower B. baculus zone 31 Mid- B. baculus zone 31 Upper B. baculus zone 31 Transition zone 36 Lower B. grandis zone 36 B. grandis zone 39 DISCUSSION 41 Potential Predators 44 Marine Reptiles 45 Fishes 46 Mollusks 48 Decapod Crustaceans 49 Parasites 50 Evolutionary Implications of Predation/Parasitism 51 Why Only in the Western Interior? 60 Did This Increase in Predation, Parasitism and/or Disease Bring About the Demise of the Inoceramids? 61
CONCLUSIONS 68
REFERENCES CITED 70
APPENDICES 78 Appendix 1. Descriptions of Individual Deformed Specimens 79 Appendix 2. Statistical Results 86 Appendix 3. Species Descriptions and Plates 88
11 LIST OF TABLES
Table 1 Species present within each ammonite biozone from the Wyoming 42 sample.
Table 2 The occurrence of specific deformities among species of inoceramids 43 from the Wyoming sample.
Ill LIST OF FIGURES
Figure 1. Generalized map of the Western Interior showing likely extent of the Pierre Seaway during the Late Campanian and Early Maastrichtian (after Gill and Cobban, 1966). 5
Figure 2. Generalized stratigraphy of the Pierre Shale, its various members, contiguous formations and corresponding Stages and Sub-stages in the vicinity of the Black Hills Uplift (after Gill and Cobban, 1966). 7
Figure 3. Lithostratigraphic zonation and time-stratigraphic ammonite zonation of the Pierre Shale in the vicinity of the Black Hills Uplift (Wyoming, Montana, South Dakota). The study interval spans the ammonite zones of B. eliasi, B. baculus, B. grandis (after Gill and Cobban, 1966; Larson et al., 1997. 9
Figure 4. Location Map of Study Area. (A) An approximation of the extent ofthe Western Interior Seaway during Late Campanian/Early Maastrichtian (after Gill and Cobban, 1966). (B) Study localities identified by an asterisk(*). 11
Figure 5. Photograph of inoceramid specimen MBT: P-23 (Species F) with two "awl mark" deformities near the ventral margin of the right valve. Each depression is approximately 0.3 em deep. Specimen is actual size. 19
Figure 6. Photographs of inoceramid specimens exhibiting the common "wedge" deformity. A) The "wedge" in the right valve of specimen MBMB: P-1 (Species A) is approximately 1. 7 em long and 1.1 em wide at the margin. B) The "wedge" in right valve of specimen MBG: P-28 (Species I) is approximately 3.9 em long and 1.1 em wide at the margin. Specimens are actual size. 19
Figure 7. Photographs of inoceramid specimens exhibiting the "vampire bite" deformity. A) The "vampire bite" in the right valve of specimen MBT: P-25 (J aff. barabini) is approximately 1. 7 em long and 1.1 em at the margin. B) The "vampire bite" in the right valve of specimen MBT: P-4 (Species F) is approximately 1.3 em long and 1.0 em wide at the margin. Specimens are actual size. 21
Figure 8. Photographs of inoceramid specimens exhibiting the "squiggle" deformity. A) Specimen MBT: P-13 (Species F). B) Specimen MBT: P-6 (Species F). Specimens are actual size. 21
lV Figure 9. Photograph of inoceramid specimen exhibiting the "bubbles" or "bubbly" nacre. Specimen is actual size. 22
Figure 10. Photograph of inoceramid specimen SMB:Be Ps-2 (1. aff. barbini) exhibiting Hohlkehle. The characteristic U-shaped groove extends 6.0 em from the umbo, in a postero-ventral orientation, to the margin. Specimen is actual size. 22
Figure 11 . Photographs of irregular, "other" deformity in inoceramid specimens, A) MBG: P-18 ("I" subcircularis) and B) MBT: P-5 (Species F). Specimens are actual size. 24
Figure 12. The distribution of shell deformities showing the relative abundance of deformities for the entire sampled interval (B. eliasi - B. grandis) from populations of inoceramids from Wyoming. Note the relative abundance ofthe "wedge" and "vampire bite" deformities, comprising approximately 40% of the total deformities. 25
Figure 13. Incidence of shell deformities in populations of inoceramids from Wyoming. A general trend of increasing incidence is apparent between the ammonite zones of B. eliasi and B. grandis. 27
Figure 14. Incidence of shell deformities in populations of inoceramids from Montana. Like the Wyoming sample, a general trend of increasing incidence is apparent between the ammonite zones of B. eliasi and Transition. Units represent horizons sampled within each zone. 29
Figure 15. Species composition and the percent of each species deformed for the B. eliasi ammonite zone. The entire sample is composed of I. aff. barabini (assuming the unidentifiable specimens were also I. aff. barabini) and only 20% of the identifiable specimens showed evidence of deformity. 32
Figure 16. Species composition and the percent of each species deformed for the Lower B. baculus ammonite zone. Two species were identified, I. incurvus and I. subcircularis. Only I. incurvus showed evidence of deformity, approximately 4% of the population were deformed. 33
Figure 17. Species composition and percent of each species deformed from the Mid-B. baculus ammonite zone. Two species were identified, Species A and Species B. Species A made up the majority of the population sampled, yet had a lower percentage of deformed individuals than Species B. 34
v Figure 18. Species composition and the percent of each species deformed for the Upper B. baculus ammonite zone. Three new species were identified, Species C, D, and E, and a I aff. barabini morphotype reappeared. 20% or more of each species showed evidence of deformities. 35
Figure 19. Species composition and percent of each species deformed for the Transition ammonite zone. Five new species were identified within this zone, Species F, G, H, I, and Trochoceramus sp., as well as I aff. barabini morphotype from the previous zone. Note the high percentage of deformed individuals within each species and, although Trochoceramus sp. makes up over 20% of the total sample there is no evidence of deformity among T sp. individuals. 3 7
Figure 20. Species composition and percent of each species deformed for the Lower B. grandis ammonite zone. All species from the Transition zone persist into the Lower B. grandis except for Species G and a new species, Species J, appears. The percentage of deformed individuals for each species is consistently above 10% except forT sp., which again comprises a significant proportion of the total sample, but less than 10% ofT sp. individuals exhibit deformity. 38
Figure 21. Species composition and percent of each species deformed for the B. grandis ammonite zone. All species present within the Lower B. grandis zone persist into this zone except for Species J. An I aff. subcircularis morphotype reappears and a new species, I aff. vanuxemi, is present. This is the most speciose zone sampled and the zone with the highest percentage of deformed individuals per species. 40
Figure 22. Composite figure showing diachronous extinction of the inoceramids from global sections. Black lines represent evidence from body fossils. Gray lines represent evidence from inoceramid shell prisms (see MacLeod, 1993 for discussion of sampling). Regional correlations are based on magneto-, chemo, and biostratigraphy (Browler eta!., 1995; Chauris et al., 1998; Gradstein, 1995; Kauffman, 1993; Larson, 1997; MacLeod, 1994, 1996; McArthur et al., 1994). 62
VI THE ROLE OF PREDATION AND PARASITISM IN THE EXTINCTION
OF THE INOCERAMID BIVALVES: AN EVALUATION
by
COLIN R. OZANNE
An Abstract
Of a thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Department of Geology University of South Florida
August 1999
Major Professor: Peter J. Harries, Ph.D.
Vll The inoceramid bivalves were dominant constituents of marine, epifaunal communities throughout the Late Mesozoic. They experienced a rapid decline in the
Early Maastrichtian and virtually all taxa disappeared 1.5 Myr prior to the Cretaceous
Tertiary (K-T) boundary. The ultimate cause for their demise is still controversial. This study evaluates the role predation, parasitism and/or disease played in the evolution and extinction of Early Maastrichtian inoceramids from the Western Interior Seaway of North
America.
Escalation ("evolutionary arms race" between predators and prey) is said to be one of the most influential selective agents in evolution. Evidence of predation, parasitism and disease in inoceramids is virtually undocumented prior to the Turonian.
However, populations of inoceramids from the Late Cretaceous Pierre Shale show a marked increase in the number of individuals in which evidence for attempted predation and/or parasitism is preserved. The percentage of predation and or parasitism steadily increases between the B. baculus and the B. grandis ammonite biozones from 4.25% to
30.25%. The dramatic increase in shell deformities among inoceramids corresponds to a rapid radiation of shell crushing brachyuran crabs and may be related to their activity.
The introduction of a new, efficient predator, such as brachyuran crabs, combined with parasitism and disease could have stressed inoceramid populations. Thus, they may have been more susceptible to environmental perturbations that under normal
Vlll background conditions. The disappearance ofthe inoceramids may be one of the few cases in the history of life where virtually an entire family lost the "evolutionary arms race."
Abstract Approved: ---+1------=-
Maj Date Approved: ,_. -- • • • , 1 1 lX INTRODUCTION The inoceramid bivalves first appeared in the Permian and were the dominant epifaunal element of level-bottom communities by the Cretaceous. They had broad ecological tolerances and are known to have inhabited well-oxygenated, shallow-marine to poorly oxygenated, deep-marine settings (Kauffman and Harries, 1996). Despite their broad enviromnental tolerances and near ubiquitous presence within Cretaceous seas, the inoceramids experienced a rapid decline during the Early Maastrichtian. Nearly all species, except members of the enigmatic genus Tenuipteria, were extinct approximately 1.5 Myr prior to the Cretaceous- Tertiary boundary. The ultimate cause oftheir extinction is still unresolved. Numerous hypotheses have been put forth attempting to explain the inoceramids' demise. However, most of these have focused on global physical enviromnental changes such as overall cooling, changes in oceanic circulation patterns and ocean chemistry, and general enviromnental degradation (Kauffman, 1984; 1988; Kauffman et al., 1992; MacLeod, 1994; Fischer and Bottjer, 1995; MacLeod and Huber, 1996). Such hypotheses potentially explain the extinction of the group, yet the inoceramids had experienced similar periods of enviromnental instability and thrived during other mass extinctions attributed to similar global enviromnental changes (Harries, 1993). A hypothesis has yet to be proposed that incorporates biological factors such as predation or competition that potentially affected the evolution and extinction of the Late Cretaceous inoceramids. 1 Escalation ("evolutionary arms race") can be one of the most influential selective agents in the evolution of a group (Vermeij, 1977; 1982; 1987). Prior to the Turonian there is little documented evidence of predation on or parasitism in populations of inoceramids (Harries and Ozanne, 1998). However, Early Maastrichtian populations of inoceramids from the upper Pierre Shale of Wyoming and Montana show a dramatic increase in the incidence of shell deformities attributable to predation and parasitism. Interestingly, this rapid increase in the incidence of shell deformities corresponds to a rapid radiation of shell crushing brachyuran crabs. The data collected in this study were used to identify the potential shell-crushing predators, evaluate the effects of escalation on the Late Cretaceous inoceramid bivalves and determine the role it played in the extinction of the group. 2 GEOLOGIC SETTING Paleogeography/Paleoceanography of the CWIS From the Early Jurassic through the Late Cretaceous, Western North America was dominated by compressional tectonism. The successive plate collisions between the North American Plate with the Farallon and the Kula Plates resulted in the formation of the Cordillera (Kauffman and Caldwell, 1993). The major components of the Cordillera were emplaced by the Middle Jurassic and include: 1) a western coastal-belt subduction complex; 2) a central calc-alkaline magmatic arc; and 3) an eastern fold-and-thrust belt. Associated with the Cordillera's development was the formation of an asymmetric foreland basin to the east. This foreland basin was periodically inundated during eustatic highstands, creating epeiric seas (Kauffman and Caldwell, 1993). The depth of this Western Interior Seaway [WIS] varied spatially and temporally within the basin as a consequence of geodynamic controls, such as load-induced subsidence, tectono-subsidence and tectono-eustasy (Kauffman and Caldwell, 1993). Kauffman (1977; 1984) divided the basin and seaway into four tectono-sedimentologic and water-depth zones that developed during sea-level highstands: 1) a "foreland" zone; 2) a west-central "axial" zone; 3) an east-central "hinge" zone; and 4) an easternmost "stable cratonic" zone. High sedimentation rates and high subsidence rates characterized the westernmost "foreland" zone. Immediately adjacent to the Cordillera, the "foreland" zone received large amounts of siliciclastic material (primarily mud) shed off the highlands and water depths may not have exceeded 50 m. The west-central "axial" zone 3 also had high subsidence rates. However, being further away from the source and separated from the "foreland" zone by the foreland bulge, received less siliciclastic material than the "foreland" zone. This created the deepest portion of the basin, approximately 200-300 m deep and as much as 500 m deep in some areas. The deposits within this zone are predominantly fine-grained silt and clay interbedded with limestone. The east-central "hinge" zone was between 100-200 m deep, had low subsidence rates and the sediments were predominantly silts, clays and chalks. The easternmost "stable cratonic" zone was a shallow platform ( < 100 m deep) with only minor subsidence and low sedimentation rates. During most of the mid- and Late Cretaceous, a north-south trending seaway occupied the entire foreland basin and extended across much of the Western Interior of North America (Figure 1). From Late Albian through the Maastrichtian, the Cretaceous Western Interior Seaway [CWIS] periodically connected the tropical to subtropical Tethys Sea in the south with the temperate Boreal Sea in the north (Gill and Cobban, 1966; Kauffman; 1977; 1984). The circulation patterns within the CWIS during the Late Campanian and Maastrichtian were investigated by Wright (1987), Hay et al. ( 1993), Glancy et al. (1993) and Slingerland et al. (1996). Oxygen isotopic studies suggest Hay et al. 's (1993) second model and Glancy et al. 's (1993) model for oceanographic circulation patterns within the CWIS are the most probable during the deposition of the upper Pierre Shale (Schmidt, 1997). Both models suggest a stratified water column with a uniformly mixed bottom water mass influenced by warm, saline bottom waters from the Tethys, a uniformly 4 ~=land Figure 1. Generalized map of the Western Interior showing likely extent of the Pierre Seaway during the Late Campanian and Early Maastrichtian (after Gill and Cobban, 1966). 5 mixed, fresh to normal marine intermediate water mass and a fresh to brackish upper water mass influenced by precipitation and runoff. Based on 8 180 ratios from pristine baculitid specimens from the Pierre Shale (Lower Campanian-Lower Maastrichtian), Fatharree et al. (1998) estimated seasonal paleotemperature fluctuations to be 1ooc within the CWIS. This suggests conditions were fairly equable at mid-latitudes when compared with Recent oceans that have a 17° C seasonal temperature variation at similar latitudes (Fatheree et al., 1998). Stratigraphy The Pierre Shale represents sedimentation during the transgressive and regressive Claggett (late Early Campanian) and Bearpaw (latest Middle Campanian to Late Maastrichtian) Cyclothems. It is a thick, marine sequence of fossiliferous, dark gray to light gray, calcareous, clayey to silty shale containing numerous bentonitic layers (Robinson et al., 1964; Gill and Cobban, 1966). In the vicinity of the Black Hills Uplift, a region that encompasses the study area, it conformably overlies the Niobrara Formation and is conformably overlain by the Fox Hills Sandstone (Figure 2). The thickness of the Pierre Shale and its various members increases in a northwest-southeast trend from 625 min northern Campbell County, Wyoming to 957 m thick near the town of Red Bird, Niobrara County, Wyoming (Gill and Cobban, 1966). Gill and Cobban (1966) identified the following members (stratigraphically from bottom to top) of the Pierre Shale near the town of Red Bird, Wyoming: the Gammon Ferruginous Member, Sharon Springs Member, Mitten Black Shale Member, Red Bird· Silty Member, Lower Unnamed Shale Member, Kara Bentonitic Member, and the Upper 6 Sub- Stage stage FORMATION 3 Upper ~ Lance Formation u~ ~ ? - C/.)~ Fox Hills Sandstone ~ Lower Upper Unnamed Shale Member Kara Bentonitic Member Lower Unnamed Figure 2. Generalized Shale Member stratigraphy of the Pierre Shale, r.Ll its various members, contiguous Upper formations and corresponding C/)~ Stages and Sub-stages in the vicinity ofthe Black Hills Uplift ~ Red Bird r.Ll (after Gill and Cobban, 1966). ~ -p... Silty Member Mitten Black Shale u~ Member Sharon Springs Member Gammon Lower Ferruginous Member z < Upper .....z 0 zE- Middle <: C/) Niobrara Formation Lower f- ? z Upper ~ u Middle 0~ u Lower 7 Unnamed Shale Member (Figure 3). The samples collected for this study were found within the uppermost Kara Bentonitic Member and the Upper Unnamed Shale Member. The Kara Bentonitic Member is a gray, bentonitic shale with limestone concretions near the top of the unit and abundant swelling bentonite layers throughout. The lower Kara is a bentonite rich, light-olive gray shale that weathers to produce a soft, "popcom"-looking surface that is easily identifiable in outcrop. The middle portion is a bentonitic shale to silty or sandy shale and the upper portion is a bentonitic shale capped by brown, fossiliferous limestone concretions. The uppermost member of the Pierre Shale is the Upper Unnamed Shale Member (Gill and Cobban, 1966). This member consists of dark and light gray sandy and silty shale. Near the middle of this member, several dark, weathered bentonite beds can be recognized and numerous fossiliferous limestone concretions are found throughout. The Upper Unnamed Shale Member is conformably overlain by the Fox Hills Sandstone and the contact between the two is gradational (Gill and Cobban, 1966) 8 ] b Z' E..o Baculites c/inolobatus 1-t c: "'c 0E ~ 1-o ~ :5~ Baculites grandis .... 0 00 ~ ..,- - 0 o."'a,..C Study Interval ....:I ~CI) Baculites baculus "' . . ~ ~t:.E Baculites e/iasi ~~~ 8 ~ Baculites jenseni ...c:l...... 0 u Bacu/ites reesidei u>.. ~ ~ Baculites cuneatus ro ..c Cl)"' 1-o Q) e- -o ro 0 .... Baculites compressus ~ ~ E_g ~ o:l :::> "'c ..,E :5~ Didymoceras cheyennense ..,.... ~ 0 .....l Exite/oceras jenneyi Didymoceras stevensoni ~ Didymoceras nebrascense ~ Buculite:> :>cvlli ~ 0 Baculites gregoryensis u ~~ -o E v ·a:l~= Bacu/ites perplexus (late) 8 -o.., ~ ~ ~ ...c:l...... Baculites gi/berti -"d 0 "d (.) ->.. Baculites perplexus (early ~ u Mitte n ~ Black ~ Shale Baculites sp. (smooth) bO bOro Member u Baculites asperiformis Sharon Bacu/ites mclearni Springs Member Baculites obtusus Figure 3. Lithostratigraphic zonation and time-stratigraphic ammonite zonation of the Pierre Shale in the vicinity ofthe Black Hills Uplift (Wyoming, Montana, South Dakota). The study interval spans the ammonite biozones of B. eliasi, B. baculus, B. grandis (after Gill and Cobban, 1966; Larson et al., 1997). 9 STUDY AREA The study localities are situated along the western flank ofthe Black Hills Uplift near the towns ofNewcastle, Wyoming and Glendive, Montana (Figure 4). The inoceramids collected for this study are found within limestone concretions contained in the Kara Bentonitic Member and Upper Unnamed Shale Member of the Upper Cretaceous Pierre Shale (Robinson et al , 1964; Gill and Cobban, 1966). The specimens for this study were collected from Lower Maastrichtian ammonite zones of Baculites eliasi within the Kara Bentonitic Member and within Baculites baculus and Baculites grandis zones of the Upper Unnamed Shale Member of the Pierre Shale (Figure 3) (Gill and Cobban, 1966). 10 MONTANA Glend S. LJI""H"'-\.1.' Rfid City B A ~= land Figure 4. Location Map of Study Area. (A) An approximation of the extent of the Western Interior Seaway during Late Campanian/Early Maastrichtian (after Gill and Cobban, 1966). (B) Study localities identified by an asterisk(*). 11 METHODS Inoceramids were obtained from bulk-sampled, fossiliferous limestone concretions collected within the ammonite biozones of B. eliasi, B. baculus, B. grandis and B. clinolobatus from localities in eastern Wyoming and Montana. Concretions were carefully split in the field and in the laboratory to liberate the inoceramid specimens. Any other faunal elements were collected as well. Due to their biostratigraphic utility, ammonites of the genera Baculites and Scaphites were also sampled from the same concretions. Thin sections of the concretion matrix were made for detailed petrographic analysis (e.g., grain-size analysis, mineralogy etc.) in order to evaluate any changes in sedimentology and hence depositional environments between concretion horizons. Inoceramid specimens sampled from each ammonite zone were then classified based on their overall morphology. However, due to the inoceramids' problematic taxonomy, informal species designations were given to specimens based on identified morphotypes. Formal taxonomic designations are tentative where applied. All 1352 juvenile and adult inoceramid specimens sampled were investigated. The height and length of the deformed specimens was measured and their abnormalities were described, classified and reported in Appendix 1. The percent of deformed specimens was determined for each ammonite zone sampled (see Results). In addition, the percent deformed was also determined for each morphotype within each ammonite zone for the Wyoming samples (see Results). A two-sample Kolmogorov-Smimov test was then performed on the results from each ammonite zone to determine whether or not 12 the observed trends in the incidence of deformity were significant. It should be noted that the original sample interval was to include the Upper Campanian ammonite biozones of B. jenseni, B. reesidei, B. cuneatus and B. compressus. However, due to a lack of suitable concretions found within the field area, such sampling was not conducted. 13 RESULTS Taphonomy and Preservation The inoceramids used in this study are exceptionally well preserved, often retaining much of the original shell material, within limestone concretions from the Pierre Shale. Siderite concretions are also present within the Pierre Shale. However, they are less fossiliferous, and the rare invertebrate shell remains they contain are poorly preserved and extremely flattened due to compaction (Tsujita, 1995). The formation of limestone concretions is an early diagenetic phenomenon that is thought to be associated with the anaerobic decomposition of organic matter either on or within the sediment (Berner, 1968). The initiation and continued growth of the concretion by precipitation of carbonate occurs directly from seawater and sediment pore-water and is believed to be caused by an increase in pH produced by bacterial decay (Berner, 1968). The limestone concretions of the Pierre are spherical to ovate in shape, range in size from several centimeters to over a meter in diameter and are irregularly distributed throughout individual horizons that are at least locally, and possibly regionally, persistent. Depending on the extent of weathering, the concretions can be dark gray (relatively fresh) to dull brown (more weathered) in color (Gill and Cobban, 1966; Tsuj ita, 1995). This, however, is primarily a function of the amount of sand and silt they contain. Those that are darker, even weathered, tend to be much finer grained; those that are lighter, as those from the Lower B. baculus ammonite zone, are coarser grained. This relationship between grain size and color is also clearly evident in thin section. Thin 14 sections made from a light-brown to tan concretions (TR-MS-1 , MBLB: MS-2, MBUB: MS-1 , MBUB: MS-2, MBT: MS-1, MBLG: MS-1, MBLG: MS-2, MBLG: MS-3) contained between 10% and 20% quartz silt and very fine sand whereas the darker concretions (SMB: Be MS 1, MBLB: MS-1 , MBLB: MS-3, MBMB: MS-1 , MBT: MS-2, MBG: MS-1, MBG: MS-2) contained less than 10% quartz silt and fine sand. The concentration and taxonomic diversity of the macro-fauna within the concretions varies temporally and sometimes geographically within a single concretion horizon. For example, the concretions sampled from the B. eliasi horizon contained only one species of inoceramid and baculite. Whereas the Mid- B. bacu/us through B. grandis concretions contained several species of inoceramids, two genera of ammonites, at least one genus of nautiloid, scaphopods, various gastropods other bivalves as well as numerous trace fossils. Gill and Cobban ( 1966) observed the same trend in their investigation of the Pierre Shale near Red Bird, Wyoming. However, they found a more diverse fauna (two ammonite species, a bivalve species and a gastropod species) within the B. eliasi sample horizon than obtained in this study. Yet, even the faunal diversity and fossil concentration they observed within the B. e/iasi concretions is low when compared to the diversity of the concretions sampled from the B. baculus and B. grandis ammonite zones in which they identified greater than fifteen species of mollusks. The condition of the macro-fauna preserved within the concretions is quite good and most of the fossils preserved have undergone little to no compaction. The majority of the inoceramid specimens within the concretions are preserved as internal molds and in many cases the nacreous layer is still retained. For reasons unknown, some inoceramid 15 specimens are often missing their outer prismatic calcite layer which has either been dissolved or delaminated from the underlying nacreous (laminated aragonite) layer. Several models have been proposed to explain the patchily distributed fossiliferous limestone concretions within the CWIS. Based on sedimentologic and taphonomic evidence, as well as the geometry of limestone concretions within the Bearpaw Shale (Canadian equivalent to lower portions of the Pierre Shale), Tsujita (1995) proposed that their distribution was the result of storm activity. He suggested invertebrate shells were concentrated in depressions (such as hummocks) produced by storm currents that were encased within the cemented limestone concretions shortly after deposition. However, no evidence was found in this study to support such a hypothesis. No sedimentologic evidence, such as rip-up clasts, hummocky cross stratification, or grain size changes, was found to indicate storm activity and analysis of the fossil assemblages did not yield any evidence of significant storm activity or storm influence. The individual fossils used in this study were randomly oriented throughout the concretions. They showed no signs of preferred alignment as would be caused by a dominant current direction or by gregarious life habit as has been suggested by Waage (1964) for certain inoceramid taxa. For the most part the fossils are well preserved and show little evidence of breakage or abrasion as might be expected if they experienced significant transport, especially under storm conditions. In fact, many of the thin-shelled Ampulella and Turritella gastropods found within concretions are pristine and still retain detailed ornamentation. Ammonites of the genus Scaphites also retain detailed ornamentation and are usually complete. 16 Moreover, ifTsujita's hypothesis is correct the shell clusters should only be found within the concretions that formed within the erosional depressions. But as Tsujita (1995) states, "shell clusters occur both outside and inside concretions. In some cases, shell material can be traced from the core of a concretion into the adjacent host sediment," (p. 409). Therefore, the preservation and distribution of fossils within the limestone concretions are interpreted to represent a concentrated horizon produced by either current winnowing of the surrounding sediment or ecological assemblages that experienced minimal transport and are not dependent on storm processes. Deformities The inoceramid shell deformities that occur between the B. eliasi and B. grandis ammonite zones are varied. However, five morphologically distinct deformities were recognized and present in almost every sample population. The names given to these deformities are purely descriptive and have no formal designation in the literature except for the Hohlkehle. Brief descriptions of each deformity are given below. "Awl Mark" In many of the inoceramid specimens a distinct pit or dent of varying size (0.1 - I em) can be seen on one or both valves (Figure 5). This "awl mark" can be a singular deformity occurring in only one location on the valve or in multiples scattered across the specimen. Often an "awl mark" co-occurs with other shell deformities such as the "wedge" or "vampire bite" (discussed below). 17 "Wedge" The most common shell deformity observed in these inoceramids is the "wedge" (Figure 6). The deformity appears as a wedge-shaped depression that increases in width and often depth in a postero-ventral orientation. This deformity begins at different times in the ontogenetic sequence of inoceramid specimens, but its characteristic shape and orientation remains fairly constant throughout the sampled individuals. Regardless of when in the ontogenetic sequence it is initiated, the "wedge" disrupts the rugae throughout the remainder of the inoceramids ontogeny and often becomes more irregular and disruptive in later stages of growth. "Vampire Bite" A deformity similar to the "wedge" in general character is the "vampire bite" (Figure 7). This deformity, like the "wedge", is initiated at different times in the ontogenetic sequence of the affected inoceramids and has a characteristic postero-ventral orientation. Unlike the "wedge", however, the "vampire bite" has two distinct grooves that are continuous throughout the length of the deformity. 18 Figure 5. Photograph of inoceramid specimen MBT: P-23 (Species F) with two "awl mark" deformities near the ventral margin of the right valve. Each depression is approximately 0.3 em deep. Specimen is actual size. A.) B.) Figure 6. Photographs of inoceramid specimens exhibiting the common "wedge" deformity. A) The "wedge" in the right valve of specimen MBMB: P-1 (Species A) is approximately 1.7 em long and 1.1 em wide at the margin. B) The "wedge" in right valve of specimen MBG: P-28 (Species I) is approximately 3.9 em long and 1.1 em wide at the margin. Specimens are actual size. 19 "Squiggle" The "squiggle" is an unusual deformity that appears as irregular shell growth that has a characteristic wrinkled or crumpled texture (Figure 8). This "squiggle" occurs at different stages of the inoceramids growth and appears to increase in intensity and breadth as growth continues. This deformity is restricted to the inoceramid species designated Species F. "Bubbly" Nacre "Bubbly" nacre is a feature found on the interior surface of the shell of the inoceramids and appear as small pimples in the nacreous layer (Figure 9). They can differ substantially in shape and size ranging from very small features confined to the nacreous layer to larger features that probably influenced the external, prismatic layer as well. Hohlkehle One of the common features found in Santonian through Maastrichtian inoceramids, and that may be present in Coniacian and potentially even in Jurassic inoceramids (Morris, 1995), is a pronounced internal rib or Hohlkehle that initiates behind the beak and is oriented towards the posterior margin (Figure 10). Whitfield (1880) used this feature as the critical character in identifying the subgenus (or genus of some authors) Endocostea. 20 A.) B.) Figure 7. Photographs of inoceramid specimens exhibiting the ··'vampire bite" deformity. A) The "'vampire bite" in the right valve of specimen MBT: P-25 (I. aff. barabini) is approximately 1.7 em .long and 1.1 cm.at the margin. B) The "vampire bite" in the right valve of specimen MBT: P-4 (Species F) is approximately 1.3 em long and 1.0 em wide at the margin. Specimens are actual SIZe. A.) B.) Figure 8. Photographs of inoceramid specimens exhibiting the ''squiggle" deformity. A) Specimen MBT: P-13 (Species F). B) Specimen MBT: P-6 (Species F). Specimens are actual size. 21 Figure 9. Photograph of inoceramid specimen exhibiting the "bubbles" or ''bubbly" nacre. Specimen is actual size. Figure 10. Photograph of inoceramid specimen SMB:Be Ps-2 (I. aff. barbini) exhibiting Hohlkehle: The characteristic U-shaped groove extends 6.0 cm.from the umbo, in a postero-ventral orientation, to the margin. Specimen is actual size. 22 The Hohlkehle is present in a very broad spectrum of inoceramids (i.e., including Platyceramus, Cladoceramus, Cordiceramus, Selenoceramus, and Endocostea species; Seitz, 1967) that, in the absence of the feature, would be grouped as separate genera. Therefore, it is not used for taxonomic differentiation in this study. Other Approximately 34% of the affected inoceramids have deformities that could not be classified in the above categories. Many of these "other" deformities are extremely varied and irregular, often occurring over much of the individual (Figure 11). Such deformities dominate the affected inoceramids appearance and makes species designations difficult. Distribution of Deformities The distribution of shell deformities appears in Figure 12. Besides "other" deformities (34% of the total of deformed specimens), the "wedge" and "vampire bite" are the most common, comprising approximately 21% and 19%, respectively. Over 10% ofthe deformed specimens exhibited the Hohlkehle, while the less common "awl mark", "squiggle" and "bubbles" appeared in less than 10% ofthe specimens exhibiting shell deformities. 23 A. B. Figure 11. Photographs of irregular, "other" deformity in inoceramid specimens, A) MBG: P-18 (''I" subcircularis) and B) MBT: P-5 (Species F). Specimens are actual size. 24 40 ,------~ n = 184 en 30 0 Cl) ·us Cl) 0. r/) "0 Cl) § t2 20 Cl) Cl c..-...... 0 0 Cl) u '""'Cl) 0.. 10 0 : -Q) -., ~ ... ~ Q) Q) -<:: Q) ... Cll) 2 "' (I) -o :0 Co :0 -5 "' Q) Cll) ~ E Q) .D } ... ·;; ;:I -<:: :0 ~ ·a. c:r -? :cu E ~ cu ="' ? Deformities Figure 12. The distribution of shell deformities showing the relative abundance of deformities for the entire sampled interval (B. eliasi- B. grandis) from populations of inoceramids from Wyoming. Note the relative abundance of the "wedge" and "vampire bite" deformities, comprising approximately 40% of the total deformities. 25 Statistical Results A two-sample Kolmogorov-Smirnov test was conducted at the 0.05 and 0.01 confidence intervals. The Kolmogorov-Smimov test determines whether or not the observed results between two samples could have been derived from a single sample population. The test was done on the Wyoming samples using the Lower B. baculus sample as the standard for comparison. The Lower B. baculus zone was chosen as the standard because it was the largest sample and therefore assumed to contain the least amount of sampling bias. All results were statistically significant at the 0.05 confidence interval and all results were statistically significant at the 0.01 confidence interval except the B. eliasi, Upper B. baculus and Lower B. grandis ammonite zones. The complete results are recorded in Appendix 2. Incidence of Deformities, Wyoming Sample The incidence of shell deformities within the Wyoming sample generally increases up section from the B. eliasi to B. grandis ammonite zones with some fluctuations between adjacent zones (Figure 13). The lowest number of individuals exhibiting some evidence of shell deformity was contained in the Lower B. baculus ammonite zone ( 4% of sample). The highest incidence of deformity was recorded from within the Transition zone (45% of the sample). The percentage of the population that display deformities for the other ammonite zones cluster around 20%, except for the B grandis zone. 26 50 n = 92 '"0 d) 40 § r.8 d) Q d) 30 0.. 8(13 \/) 4-< 0 ...... 20 ~ d) (.) 1-< d) p... 10 0 .., .., .., ·c:; ::s ::s s:: . ~ ::s ..:! ~ "'=' . ~ tJ ::s ::s s:: s:: - tJ tJ 1:3 - :~ 1:3 ~ 1:3 1:3 .., ~ ~ '- cci ~ !:>() t cci cci ~ .... cci .... ~ cci cci Q) -o Q) .... Q) ~ 0 ~ ~ .....l "" 0 ::::>"" .....l Ammonite Zone Figure 13. Incidence of shell deformities in populations of inoceramids from Wyoming. A general trend of increasing incidence is apparent between the ammonite zones of B. eliasi and B. grandis. 27 Incidence of Deformities, Montana Sample The Glendive, Montana samples were collected in distinct "units" that correspond to individual concretion horizons and span the ammonite zones of B. eliasi, Lower B. baculus, Mid- B. baculus, Upper B. baculus and the Transition zone of the Wyoming samples (Figure 14). Although the Montana sample does not extend into the B. grandis zone as the Wyoming sample due to the earlier initiation of the Fox Hills Sandstone in this area, and the total number of individuals investigated was substantially lower than the Wyoming sample, a similar trend is seen in the incidence of shell deformities between the two localities. As in the Wyoming sample, there is a general trend of increasing incidence of shell deformities up-section. The highest incidence of shell deformity occurred within the Upper B. baculus zone (37% ofthe sample). However, the number of individuals available for investigation of this zone was limited to eight. Hence, the fidelity of this sample's ability to represent a population ofUpperB. baculus inoceramids is questionable. The incidence of shell deformity for the Transition zone sample was 35%. This Transition zone sample also has the most comparable number of individuals between the two localities, with 110 individuals having been investigated. The incidence of deformity in Mid- B. baculus and Unit 4 of Lower B. baculus are both approximately 15%. The B. eliasi and Unit 3 of Lower B. baculus samples showed no evidence of deformity. 28 Jv ,------~ 40 '"0 0 § tS 0 Q 30 0 -0.. ao:s (/) '+-< 0 20 ...... l:::l 0 ~ 0 ~ 10 n =O =4 n = 2 0 0\ 0 -c ::::> ·a ..., ::::> :::. 1:: :::. -~ -u ~ ·;;; .<:) 1:: r:Q ~ .... ~ 0 P. Q. ::::> Ammonite Zone Figure 14. Incidence of shell deformities in populations of inoceramids from Montana. Like the Wyoming sample, a general trend of increasing incidence is apparent between the ammonite zones of B. eliasi and Transition. Units represent horizons sampled within each zone. 29 Species Composition and Percent Deformed, Wyoming Species composition and the percent of each species deformed were determined for each zone sampled at the Wyoming locality. This was done to determine any relationship between species and the number of individuals deformed. However, as discussed below, species were named based on identified morphotypes and formal taxonomic designations, where given, are tentative. It should also be noted that as a group, inoceramids are morphologically plastic and variable. Even a single species can display a wide a range of sizes and morphologies depending on the environmental conditions in the habitats of the individual (e.g., differences in substrate, salinity, energy of environment). Also, different species of inoceramids may appear to be a single taxon depending upon the ontogenetic stage the individual was in at the time of preservation. For example, juveniles of Inoceramus incurvus and Inoceramus aff. barabini are virtually identical. It is not until later in their ontogeny, when I incurvus' experiences a geniculation, that one can tell the two species apart. The ecophenotypic variation and homologous morphologies among inoceramid species further complicates taxonomic designations (Harries and Crampton, 1998). B. eliasi zone Only one morphotype was identified for this zone and given the formal taxonomic designation of Inoceramus aff. barabini. 163 specimens were examined, 26 of which were unidentifiable due to poor preservation or due to the extent of their deformities. Because only one species was found in this interval, no relationship between species and deformity can be determined. However, it should be noted that 55% of the deformities 30 within this zone were identified as Hohlkehle, and this was the highest percentage of Hohlkehle recorded from any zone (Figure 15). Lower B. baculus zone From the 343 specimens examined only two morphotypes were identified. The most dominant morphotype was given the formal taxonomic designation of Inoceramus incurvus. This morphotype comprised approximately 70% of the total population, 4% of which exhibited some shell deformity (Figure 16). The other morphotype was identified as Inoceramus subcircularis, none of which exhibited any deformity. Mid- B. baculus zone The 119 specimens examined from the Mid- B. baculus zone were divided into two distinct morphotypes, Species A and Species B. Approximately 82% of the population is composed of Species A, 14% are Species B and 4% are unidentifiable (Figure 17). 22% of Species A and 30% of Species B were deformed. All four unidentifiable specimens were deformed in some manner and, if more complete, would likely have been classified as Species A or B. Upper B. baculus zone Within this zone, three different morphotypes were identified as well as the reappearance of the l aff. barabini morpho type. Species C, D, and E each comprise less than 25% of the total population while l aff. barabini is the most abundant (30% of the population) (Figure 18). However, Species C and E have a higher percentage of 31 Species Composition Percent Deformed 100 100 90 90 80 80 70 70 C1) 0.. 60 60 § 00 50 ~ 50 t+-. 0 40 40 ~ 30 30 20 20 10 I 0 0 0 C"-· C"-• ., ~ .D ::0 ·.s- ~ :§ ~ ..() t;:; ..() t;:; ~ <:l <:l c ..<:l c ..() ., ..() ., ~ ~ t:: c:: !::::: c:: ~ :::l ~ :::l .....; .....; Figure 15. Species composition and the percent of each species deformed for the B. eliasi ammonite zone. The entire sample is composed of I. aff. barabini (assuming the unidentifiable specimens were also/. aff. barabini) and only 20% of the identifiable specimens showed evidence of deformity. w N Species Composition Percent Deformed 100 100 90 90 80 80 70 70 Q) 60 60 -0.. ~ 50 50 r:/) ~ <+-< 0 40 40 ~ 30 30 20 20 I 0 I 0 -1 n = 249 I IW/¢4 n = 94 0 0 I .., -~ .., ::: .... -~.... ~ ::: c ::: ~ :::c ::: ~ - ~ <.l <.l !:: <.l .!:; -!:: <.l ....; ~ -<:) <::; ....; ..,::: ....; ....; Figure 16. Species composition and the percent of each species deformed for the Lower B. baculus ammonite zone. Two species were identified, I. incurvus and I. subcircularis. Only I. incurvus showed evidence of deformity, approximately 4% of the population were deformed. w w Species Composition Percent Deformed n=4 100 100 90 90 80 80 70 70 20 20 10 10 0 .;, 0 < al ::0 < al 0 0 ::0 0 "' II) 0 "' ·o 1.::"" "' "' t;:; ·o II) ·o ·o "" 0 0 0 0.. 0.. c: II) 0.. 0.. c: C/l C/l II) -o C/l C/l -o c ;:I c ;:I Figure 17. Species composition and percent of each species deformed from the Mid-B. baculus ammonite zone. Two species were identified, Species A and Species B. Species A made up the majority of the population sampled, yet had a lower percentage of deformed individuals than Species B. \.;.) ~ Species Composition Percent Deformed 100 n = 2 100 90 90 80 80 70 70 0 0 u Q t.tl 0 ::0 C'· u Q t.tl :s od ::0 ..&::> 0 0 0 od "' "' "' :s 0 <:::: "(3 "(3 "(3 5 ..&::> "'0 "'0 "' .... (/) (/) (/) 0 c <::1 0. 0. 0. 0 tt:: ..&::> (/) (/) (/) «l "c :"S! ::l tt:: c .....; od ::l .....; Figure 18. Species composition and the percent of each species deformed for the Upper B. baculus ammonite zone. Three new species were identified, Species C, D, and E, and a I. aff. barabini morpho type reappeared. 20% or more of each species showed evidence of deformities. w VI deformed individuals than the more abundant I aff. barabini and Species D. In an · unusually large number of specimens, shell deformity was so prevalent and severe that species identification was impossible. Transition zone Six morphotypes were identified within the Transition zone: Species F, G, H, I, I aff. barabini and Trochoceramus sp. Species F was the most abundant, comprising almost 30% of the population (Figure 19). Trochoceramus sp. and I aff. barabini were fairly abundant comprising 24% and 18% ofthe population, respectively. Species G (5%), H (12%) and I (2%) were less common. Approximately 50% ofthe specimens of Species F were deformed. All the specimens of Species G and I displayed a deformity while the second most abundant morphotype, Trochoceramus sp., did not have any specimens with evidence of deformity. Finally, 20% of Species H and 31% of I aff. barabini were also deformed. Lower B. grandis zone All the morphotypes represented in the Transition zone were present, along with a new morphotype, Species J. Trochoceramus sp. was the most abundant (30%) with Species H and F comprising 20% and 15% of the population, respectively (Figure 20). I aff. barabini, Species I and J each made up less than 15% of the sampled population. Trochoceramus sp. had the lowest percentage of deformed individuals despite being the most common morphotype in the sample. Approximately 15% of Species F, H 36 Species Composition Percent Deformed n=6 n=2 100 n = 118 100 90 90 80 80 70 70 tU 60 -1 60 len <+-< t( 50 0 50J t( 40 40 30 30 20 20 10 10 0 0 C"-· 0 ~ ~ ~ ~ t.L.o 0 ::r: ci. 30 30 20 20 I 0 10 0 0 II I I~ (..L., C'· ::c ci. (..L., C'• -. v (/) (/) .0 ::c ci. (/) (/) ·;: - (/) -(/) (/) (/) v (/) :0 v v v :§ v v ·o ·o ~ ·o ~ ·o t.::"' ·"'o ·o ·o t.:: v (:I v v ·o "'::s 0 "' v 0. ... 0. !:: v v (:I v 0. C/) (:I (:I 0. c 0. ""' 0. !:: 0. C/) C/) C/) 0. C/) ...(:I (:I C/) ... v C/) C/) c0 :3 ... "0 ~ (J ""' "'0 c ""'~ (J "-' ;::l "' c ~ 'a 0 ;::l .....; (J ~ "' 0 .....; (J 0 ~ ~ Figure 20. Species composition and percent of each species deformed for the Lower B. grandis ammonite zone. All species from the Transition zone persist into the Lower B. grandis except for Species G and a new species, Species J, appears. The percentage of deformed individuals for each species is consistently above 10% except forT sp., which again comprises a significant proportion of the total sample, but less than 10% ofT sp. individuals exhibit deformity. w 00 and I were deformed while I. aff. barabini, and Species J had a rather larger percentage ·of deformed individuals, 85% and 42%, respectively. B. grandis zone Seven morphotypes were identified within this zone: Species F, H, I, I. aff. barabini, Trochoceramus sp., I. aff. vanuxemi and the reappearance of a morphotype similar to I. subcircularis of the Lower B. baculus ammonite zone (Figure 21 ). This morphotype has been designated I. aff. subcircularis rather than I. subcircularis because it is unclear whether this is truly the same species or just a repeated morphotype. Species I and Trochoceramus sp. comprised 28% and 18% ofthe sample population, respectively, while the remaining morphotypes cluster around 10%. Similar to the Lower B. grandis sample, Trochoceramus sp. was an abundant morphotype but had the second lowest percentage of deformed individuals. Species F had the highest percentage of deformed individuals (54%) and Species H, I, I. aff. barabini, and I. aff. subcircularis have between 30% and 35% deformed. 39 Species Composition Percent Deformed 100 100 90 90 80 80 70 70 -aQ) 60 60 ~ 50 rJJ ~ 50 <+-< 0 0 40 40 0~ 30 30 20 20 10 I 0 0 0 t.L.. C'• ci.. C'· C'• 0 Ill ~ t.L.. ci.. C'• ::t .., "jg :t Ill Ill -Ill .D Ill Ill .E Ill ·;:: Ill - :0 0 0 ·;:: 0 0 0 :s 0 .., - ~ .:c; ~ ..(;) >.. ·u ·u ~ ~ t:::"' ·u ·u :::: c::s t::: 0 ·u 0 !:: 0 ·u "'~ "' 0 c. 1::: 0 0 !:: ::; c. c. ~ c::s c c. ~ c. c::s s::: C/l c::s C/l >.. ~ 0 C/l c. c::s C/l <.> c::s c C/l ..(;) . ~ C/l ..(;) >.. >.. ;. 0 <.> <.> ·c:; ..(;) tt:: <.> 1::; 0 "·c: tt:: 0 ..(;) 1t:: "r:: ...::: :; ::l :::: ::l <.> ....:"' ...::: .., "' ....:"' 0 ....:"' <.> ....: tt:: 0 1t:: ~ ~ ....:"' ....:"' Figure 21. Species composition and percent of each species deformed for the B. grandis ammonite zone. All species present within the Lower B. grandis zone persist into this zone except for Species J. An I. aff. subcircularis morphotype reappears and a new species, I. aff. vanuxemi, is present. This is the most speciose zone sampled and the zone with the highest percentage of deformed individuals per species . .f:>. 0 DISCUSSION The fossil record provides at least three types of evidence that can be utilized in evaluating the evolutionary and ecological importance of predation: 1) presence of identifiable remains in fossil feces, 2) fossils that have been attacked and killed in a specific way by predators (i.e., boring by gastropods), and 3) scars or repaired shell as result ofunsuccessful attack (Vermeij, 1983). In this study, the incidence of predation was evaluated using the presence of scars on individual inoceramids from the sampled populations. Because it is impossible or at least extremely difficult to differentiate physical and biotic fragmentation, the actual efficiency of the predation and, therefore, the effects upon these Cretaceous inoceramid communities remains elusive. Although these scarred individuals do not represent the actual predatory efficiency, they at least provide a proxy for the predation intensity and allow several important conclusions to be drawn. The data presented here display three distinctive trends that are consistent at both study localities: 1) an increase in the incidence of shell deformities among Early Maastrichtian inoceramid populations from the ammonite zones of B. eliasi through B. grandis in the Wyoming material and B. eliasi through the Transition in the Montana material (Figure 13 and 14); 2) a general trend of increasing species diversity among inoceramid populations from B. eliasi through B. grandis (Table 1); and 3) a pattern of deformity that is not species specific in all cases except for the "squiggle" (Table 2). 41 Table 1 Species present within each ammonite biozone from the Wyoming sample. SPECIES ci. Ammonite ·;::"' ·~.... "' ·- ~ ~ ~ !:; "' ~ ..::;,:s !:; ~ <.> ~ (.j c:s c:s .... "'~ . ~ .... ( .... s:: <.> c:s ·;:; c:s --< co u Q t.Ll l:.t.. 0 :I: ....., ..::;, Biozones ..::;, <:; <.> ..() ;:. ~ "'0 - ....; .s ..,"' ..,"' ..,"' .., ..,"' ..,"' .., ..,"' ..,"' .., ...... £:: tl:i ·c; ·c; ·c; ·c;"' ·c; "' ·c; ·c; ·c;"' ....;"' .....; <.> "' .., .., .., .., .., ·..,o ·..,o .., .., .., ...... ;"' 0 .....;"' p. p. p. p. p. p. p. p. p. p. ~ - V) V) V) V) V) V) V) V) V) V) .....;"' B. grandis Lower B. grandis ' ' ' ' ' ' ' Transition ' ' ' ' ' ' Upper B. baculus ' ' ' ' ' ' Mid- B. baculus ' ' ' ' Lower B. baculus ' ' B. eliasi I ' ' ~~- -- -- ~ ' N Table 2 The occurence of specific deformities among species of inoceramids from the Wyoming sample. SPECIES TYPE ci. .~ Ill .~...... <::! ~ OF :s ::"' :: :: ·~ IJ -t:l :: t: IJ "';>. <::! -... .!: ~ ...... s:: IJ DEFORMITY <::! :: ~ 'i:i < co u 0 U.l LL. 0 :r: ....., -t:l -t:l IJ IJ -t:l ~ Ill Ill Ill Ill Ill Ill Ill Ill -Ill Ill :: 0 1M .s :: v 0 0 v v v v 0 0 v -s:: '(j '(j · c::; '(j · c::; · c::; · c::; ' (j ·c::; · c::; ..... IJ c ...,;"' ....; "' v 0 0 0 v v v v 0 v ...... ;"' !=> ....;"' p, p, p, p, a. a. a. a. a. a. ~ - C'/) C'/) C'/) C'/) C'/) {/) C'/) C'/) C'/) {/) ....;"' Wedge Vampire Bite ' ' ' ' ' ' ' ' ' ' ' ' ' ' Awl Mark ' ' ' ' ' ' ' ' ' ' ' Squiggle ' ' ' ' ' ' ' ' ' Bubbles ' Holkehle ' ' ' ' Other ' ' ' ' ' ' ' ' ' ' ' ' I =Presence of Deformity 43 The increase in shell deformities is interpreted as an increase in predation on, ·parasitism in and potentially disease within Early Maastrichtian inoceramid populations from the WIS. The non-species specific nature, consistent character and diachronous appearance of the "wedge", "vampire bite" and "awl mark" in the ontogenetic sequences of individuals of the same species suggests these types of deformities are the result of unsuccessful predation. More specifically, they are interpreted as evidence of a crushing predation style that did not kill the individuals, but severely disrupted the mantle causing irregular growth in the affected region throughout the remainder of the individual's ontogeny. The "bubbles" and Hohlkehle deformities, following Toots (1964) and Seitz (1967), are interpreted as evidence of parasitism. The "other" type deformities are difficult to classify based on morphology, and therefore their origin is not speculated upon. The abrupt appearance and rapid increase in the incidence of repaired inoceramids between the B. eliasi and B. grandis zones generates several questions: 1) what was preying on or parasitizing these populations of inoceramids?; 2) what evolutionary influence, if any, did this increase in predation and parasitism or disease have on the inoceramids?; 3) why is it only evident in the Early Maastrichtian of the Western Interior?; and 4) could this increase in predation on and parasitism/disease in the inoceramids have caused their demise? 1) Potential Predators A definitive answer to the first question may never be attained. However, with the evidence presented in this study and the knowledge of the numerous predators known 44 to have inhabited Late Cretaceous seas, an attempt to determine a cause and effect · relationship between inoceramid shell deformities and potential predators/parasites is warranted. The following are considered potential predators capable of inflicting the crushing-type damage identified on the Late Cretaceous inoceramids: marine reptiles, bony fish, cartilaginous fish, mollusks and decapod crustaceans. Marine Reptiles One of the dominant predators of Late Cretaceous seas, whose abundant remains are found throughout the Pierre Shale, especially in the Sharon Springs Member, were the mosasaurs (Robinson et al., 1964; Gill and Cobban, 1966; Kauffman, 1990). It is generally believed that mosasaurs were highly specialized, pelagic marine predators that inhabited shallow epicontinental and shelfal seas and preyed upon pelagic organisms such as fish, squid, belemnites, ammonites and other marine reptiles (Kauffman, 1990). Unlike the Triassic placodonts, however, these marine reptiles show no aptations, such as a grinding palate or blunt teeth, that would suggest a bivalve diet. Furthermore, despite the co-occurrence of mosasaur and inoceramid remains, there is no indication that these reptiles had the capabilities to dive to depths inhabited by Pierre inoceramids or were significant harvesters of the epifuanal clams. Marine chelonians are another possible predator of Late Cretaceous inoceramids. Modern loggerhead turtles are known to crush and consume the giant clam Tridacna (Vermeij, 1987). However, there is no evidence that Cretaceous sea turtles were preying upon inoceramids despite being found within the Sharon Springs member of the Pierre Shale (Larson et al., 1997). Moreover, the turtles had coexisted with the inoceramids 45 since at least the Albian and possibly earlier, during which little to no documented ·evidence of injured inoceramids exists (Colbert and Morales, 1993; Hirayama, 1998). Fishes Molluscivory is common among modem Pisces and was a dominant feeding behavior in the Cretaceous. The fishes (including some sharks and rays) adapted to a diet of shelled prey have high-crowned, blunt teeth or a grinding palate specifically designed for shell crushing (Carter, 1968). There is ample evidence that both types of fishes inhabited the CWIS as evident by preserved scales, dermal denticles, teeth and bones (Dunkle, 1962; Robinson et al., 1964; Gill and Cobban, 1966; Kauffman, 1972; MacLeod, 1982; Kauffman, 1990). However, direct evidence of fish predation upon inocerarnids anywhere in the Cretaceous is rare. Kauffman (1972) has suggested that the depressions in the type specimen of Inoceramus tenuis were the result of an attack by a species of the durophagus shark Ptychodus, possibly P. decurrens. Speden (1971) also documented the occurrence of inoceramid prism and shell fragment aggregates in the Cretaceous strata of the Clarence Series in New Zealand. He concluded that these patchy aggregates of inoceramid material represent regurgitated gastric residues and fecal material produced by vertebrates such as teleosts, sharks or rays. However, to date no vertebrate remains have been found within the strata to further support his conclusions. Hattin (1975) has also suggested shark predation upon inoceramids was prevalent. He suggested that the inoceramid-rich calcarenites found within the mid-Cretaceous WIS are the result of shark predation. Based on the lithologic and stratigraphic context of these beds, Sagemann 46 (1996), however, proposed the formation ofthese deposits was related to sea-level ·fluctuations rather through biologic action. Another line of indirect evidence comes from examining the feeding behavior of modem sharks and rays. Many studies have shown that sharks and rays are very efficient predators of epifaunal and shallow-infaunal bivalve communities (e.g., Bigelow and Schroeder, 1953; Herald, 1967; Orth, 1975). Orth (1975) documented the destruction of community structure and shallow-infaunal clam populations caused by the feeding habits of cow-nosed rays. Herald (1967) has also reported that bat rays and other eagle rays decimated cultivated clam beds within San Francisco Bay following the uprooting of clam fences (predator prevention) after major storms. The common occurrence of fish scales, dermal denticles and Ptychodus teeth within the Upper Unnamed Shale and Kara Bentonitic Members of the Pierre Shale, the epifaunal life habit of the inoceramids, and the morphologic similarity between the depressions described by Kauffman's ( 1972) specimen of I tenuis and the "awl marks" described on inoceramids from this study suggest fish, shark or ray predation upon inoceramids probably occurred. However, the extent to which these fishes preyed upon inoceramids is unclear. The "awl marks" may have been produced by such shell crushing fishes as Ptychodus. Even so, the "awl marks" account for only 8% of the total deformed specimens. Yet, if the feeding behavior of modem durophagus sharks and rays is similar to that of Late Cretaceous molluscivorous fishes and if Speden's ( 1971) interpretations of the inoceramid-prism, shell-fragment aggregates is correct, it may have been substantially more common than indicated by this study. However, fishes probably did not influence 47 inoceramid communities as much as the invertebrate predators present within the CWIS. · Thorson (1958) concluded that only 1-2% of the benthic invertebrates are taken by fishes, sharks and rays, while modern invertebrate predators likely consume four times as much food per day or unit weight as bottom-dwelling fishes. Mollusks Although modern mollusk groups such as the gastropods and cephalopods (specifically the octopods) are principal predators of bivalves, neither group employs crushing as the method of eviscerating their prey. Gastropods utilize their radula accompanied, in most cases, with the secretion of a chemical to drill a hole in the valve to gain access to the bivalve's viscera. This type of predation leaves a characteristic hole in the valve that has a very high preservation potential (i.e., Carter, 1968; Vermeij, 1983; Wayne, 1987). Octopods also gain access to the insides of the bivalve by drilling a hole with the radula and salivary papilla or by prying the valves open using their suckers (Carter, 1968; Vermeij, 1987). However, no such evidence of drilling-type predation was observed on the 1352 inoceramid specimens examined in this study despite the co occurrence of boring gastropods, such as Euspira obliquata (Naticea), and inoceramids in some of the concretions (Sohl, 1967). The Pierre Shale is probably best known for the abundant and diverse ammonite assemblages it contains. Numerous ammonite species, including those of the genera Baculites and Scaphites as well as several nautiloids, are found within the same concretion horizons as the inoceramids from this study (i.e., Gill and Cobban, 1966; Kauffman et al., 1993; Larson et al., 1997). The jaws of the ammonites and nautiloids, 48 however, were composed of chitin and would not have withstood the rigors of a bivalved ·diet (Carter, 1968). Moreover, like the fishes and marine reptiles, ammonites and nautiloids had co-existed with inoceramids since the inoceramids appearance in the Permian. Therefore, if ammonites and nautiloids were significant predators of the group, it is unlikely that evidence of their attacks upon inoceramids prior to the Late Cretaceous would not previously have been documented. Yet, there is no documentation of deformities similar to those seen in the Early Maastrichtian populations of inoceramids from this study. Therefore, because of the immense numbers of nautiloids and especially ammonites found within numerous Mesozoic units and the lack of abundant deformities on inoceramids until the Early Maastrichtian, ammonites and nautiloids are not considered to have been substantial predators of the Late Cretaceous inoceramids. Decapod Crustaceans Decapod crustaceans, such as crabs and clawed lobsters, are well known as indiscriminant scavengers, but they are also devastating harvesters of epifaunal and shallow-infaunal bivalves (i.e., Lunz, 1947; Carter, 1968; Vimstein, 1977). The brachyuran crabs and the lobsters differ, however, in their methods of attacking bivalves. The crabs' common method of attack is to break away the margins of the valve (Carter, 1968). Most molluscivorous crabs possess a large master claw that both shears and crushes as it closes on the margin of the valves, and a smaller cutter claw, used to tear away flesh, to hold or to manipulate prey. Clawed lobsters, however, simply crush the entire shell in their pincers (Carter, 1968). 49 Although no fossil crabs or lobsters were found in this study, both lobsters and · brachyuran crabs are known to have inhabited the CWIS during the Early Maastrichtian (Bishop, 1973; 1982; 1985; Larson et al., 1997). Several horizons within the Pierre Shale yield abundant lobsters and crabs, both within the shale and within concretions (Larson et al., 1997). Unlike the mollusks, the exoskeleton of crabs and lobsters is made of a chitinous material that is susceptible to rapid bacterial decomposition (Allison, 1990). Therefore, localized abundances of these predators within the Pierre Shale suggest that unique preservational conditions, such as unusual chemical conditions, prevailed at the time these organisms expired allowing for their preservation. This selective preservation is thought to be responsible for the lack of crab and lobster remains found within the study interval and therefore their absence is mediated by taphonomic overprinting rather than their absence from such Early Maastrichtian environments. Parasites Speculating on the parasites and pathogens that could have affected the inoceramids is problematic due to the lack of fossil evidence of such small, often microscopic, soft-bodied organisms. Therefore, the discussion of potential parasites is limited to parasites that could have elicited the observed morphological responses ("bubbly" nacre and Hohlkeh/e) in the individual inoceramids. The "bubbles" observed on some inoceramid specimens are morphologically variable and appear to be randomly spaced throughout the affected individuals. It is believed these "bubbles" are the result of the mantle secreting calcium carbonate in response to parasites or pathogens living between the mantle and the interior of the shell. 50 The nature of these parasites is elusive. However, there is abundant evidence that larval ·trematodes infest modem bivalves, and it is possible that such infestations result in the secretion of additional nacre by the bivalve (Sannia et al., 1978; Jonsson and Andre, 1992). The Hohlkehle observed in numerous inoceramid specimens is believed to represent infestation of the inoceramid by a worm, possibly a polychaete. A modem analog to this type of parasitism was documented by Cocker et al. ( 1921) in freshwater mussels. Although the deformity they described was not identical to the Hohlkehle, the consistency of form and position of the scar was interpreted as the result of an unknown parasite, possibly a worm. Another case of parasitism documented on one of the inocerarnids closest Cenozoic analogs, Isognomon maxi/latus, resembled the Hohlkeh/e. The hollow, U-shaped tube observed within Pliocene /sognomon was attributed to a polychaete, possibly closely related to the serpulids (Savazzi, 1995). However, the exact nature of the relationship between the bivalve and worm is unclear, yet the position and character of the U-shaped tubes suggests the organism was ideally situated to exploit the digestive tract of the Isognomon maxi/latus. Toots (1964) suggested a similar hypothesis to explain the position of the Hohlkehle in the inoceramids. The consistent location of the Hohlkehle along the oral-anal axis of the inoceramids led Toots (1964) to suggest the parasite was feeding on the waste effluent from the exhalent siphon of the inoceramids. 2) Evolutionary Implications of Predation/Parasitism All the predators previously discussed could have preyed upon inoceramids and likely did to some extent. However, bony fishes, cartilaginous fishes, and cephalopods 51 had coexisted with inoceramids since the appearance of the first inoceramids in the ·Permian and marine reptiles since at least the Triassic. But prior to the latest Turonian, evidence of predation on or parasitism in inoceramids is rare to undocumented (Harries and Ozanne, 1998). In the case of predation, this may reflect very high predatory efficiencies, but the fact that most predators are substantially less than 100% efficient (Vermeij, 1987) makes this interpretation tenuous. If predators were a significant factor in cropping inoceramid populations, there should be some indication of unsuccessful attacks. For the majority of the inoceramids stratigraphic range, this evidence is, for the most part, strikingly rare. Moreover, for parasitism, tracks and traces of parasitic activity should also be preserved, but prior to the Coniacian there is no documented case in the inoceramids (Harries and Ozanne, 1998). Vermeij (1976, 1983, 1987) has extensively documented the role of escalation in evolution and suggests predation can be the most influential selective agent in the evolution of a group. The increased incidence of repaired individuals from the Early Maastrichtian populations of inoceramids suggests there was either an increase in the abundance of shell-crushing predators within the CWIS or the ability of inoceramids to resist breakage increased, or perhaps both. In an attempt to determine whether there was an increase in predation upon the inoceramids (via an increase in the number or efficiency of predators) or an increase in resistance to predation by the inoceramids, it is crucial to identify the defensive strategies the inoceramids already possessed (Ricklefs, 1979; Vermeij, 1982). By the Late Cretaceous, the inoceramids had evolved two main anti-predatory strategies. First, being epifaunal and possibly byssally attached in some cases, the 52 inoceramids primary anti-predatory defense was avoidance (Harries and Crampton, · 1998). Although they are known to have inhabited a variety of environments, including well-oxygenated shore-face sands, their primary habitat was the widespread anoxic mud bottom environments represented by the numerous, Cretaceous black shales (Harries and Crampton, 1998). The anoxia of these habitats would have excluded many potential predators allowing the inoceramids to flourish and exist relatively unmolested. The inocerarnids second anti-predatory defense was resistance. The inoceramids, like some other pteriomorphs, such as the pinnacean bivalves, had a prismato-nacreous shell that was extremely flexible. Although thin, this flexible shell provided a tight fitting margin and some resistance against breakage associated with crushing (Carter, 1968). The tightly fitting margin not only prevented entry by predators, but also aided in avoiding predators, because when the mantle of the bivalve was retracted and the valves closed, the tight-fitting margin decreased the chemical signature emitted from the bivalve. This in turn prevents detection by predators that utilize chemo-sensory as the primary method oflocating prey (i.e., sharks, rays, gastropods) (Carter, 1968; Vermeij, 1983). One anti-predatory strategy not employed by the inoceramids was escape. Although escape is a common form of anti-predatory defense among certain modem groups of bivalves there is no indication that inoceramids could escape a predator by "swimming", like the modem scallop, or hopping like Clinocardium nuttali (Conrad) (Carter, 1968; Vermeij, 1987; Harries and Ozanne, 1998). It appears that, if detected, an individual inoceramid would not have been able to escape, and would have relied on its flexible shell for resistance against the predator. 53 If the increase in the incidence of shell repair is indicative of an increase in · capacity to resist predation, then certain adaptive characteristics other than the two aforementioned, should also be apparent in Late Cretaceous inoceramids. However, no new adaptations related specifically to margin-crushing type predation such as thickening of the margins, overlapping of the valves or development of spines are apparent in Early Maastrichtian populations of inoceramids. Neither is there any evidence to indicate evolutionary innovations for general resistance to overall shell-crushing such as thickening of the shell, increasing convexity of the valves or presence of deterrent ornamentation. This fact, along with coeval radiation of the margin-crushing brachyuran crabs suggest that the increase in shell repair observed in Early Maastrichtian populations of inoceramids inhabiting the CWIS was likely the result of an increase abundance of predators rather than a significant increase in the inoceramids ability to resist attack. The most common deformities described from these populations of Early Maastrichtian inoceramids are indicative of margin-crushing type predation ("wedge", "vampire bite" to a lesser extent the "squiggle"), comprising over 40% of the total deformed specimens (Figure 11). The brachyuran crabs appear to be the only predators capable of inflicting the observed margin-crushing type deformities. They are also the only group of potential predators that experienced a rapid evolutionary radiation at end of the Cretaceous (i.e., Bishop, 1973, 1983, 1985) which could account for the increased incidence of deformed inoceramids in the Early Maastrichtian. Intriguingly, this radiation and the increase incidence of deformities among inoceramids occur at approximately the same time. 54 In addition, the abrupt increase in the incidence of the Hohlkehle and "bubbly" ·nacre among inoceramids is suggestive of an increase in parasitism. What evolutionary and biological implication this may have had for inoceramids is difficult to determine. Because of the complex life cycle and biology of parasites, as well as the nature of their relationship to the host, it is difficult to evaluate their effect on modem populations and virtually impossible in the fossil record. However, some parasites are known to weaken their host and often make their hosts more susceptible to predation, competition and environmental fluctuations (Ricklefs, 1979). Therefore, the invasion by the brachyuran crabs into the black-shale environments and the apparent increased parasitism appears to have had a significant effect on the inoceramids. The effects such an invasion might have had on the inoceramids can be likened to the biological invasions that have occurred on and are best documented from isolated islands (Elton, 1958; Ehrlich, 1988; Noble, 1988). On many of the Pacific and Caribbean islands, native species of plants and animals have been eradicated by the introduction of predators and ecological analogs from the continents. Restricting the discussion to animals, the large success that these continentally derived invaders have on remote islands can be attributed to two main factors. First, island communities, having been colonized by relatively few species of animals, evolve under "relaxed" selective pressures and sometimes even in the absence of certain selective agents such as predation (Elton, 1958; Moulton and Pimm, 1986; Simberloff, 1986a; Ehrlich, 1988). Therefore, the island species are less adept at combating and competing with the invasive continental species that have experienced greater escalation having evolved with constant interaction of numerous competitors and predators (Rand, 55 1954). Second, as well as having experienced greater escalation on the continents, the · successful invaders have certain characteristics that allow them to monopolize resources and thrive in their new habitat (Ehrlich, 1988; Noble, 1988; Rand, 1954). Generally these are eurytopic characteristics and include broad environmental tolerances, a broad diet and short generation times (Newsome and Noble, 1986). These characteristics allow the invaders to out-compete the island biota for resources and monopolize prey. The result of which is extreme reduction in the native populations, forcing the remainder of the populations to inhabit less than ideal "fringe" environments. Ultimately, this can lead to the extinction of the native groups. In the case of predation, the introduction of a new predator on these islands often does result in the extinction of one or more endemic prey species. If the exotic predator(s) has a varied diet and is not significantly affected by the reduction in prey population, this may occur directly from the over-harvesting of the prey species. This situation is typified by the decimation of the native avifauna ofNew Zealand. The introduction of the "native" Maori people and the predatory mammals that accompanied them resulted in over-hunting and extinction of 34 species of non-marine birds (Diamond and Veitch, 1981 ). With the arrival of Europeans and their associated predatory mammals (mustelids, cats and rats), eight out of the 77 native non-marine species of bird have become extinct and 13 species have become endangered (Diamond and Veitch, 1981). Diamond and Veitch's (1981) study showed predation by the introduced mammals was the primary factor in the avifauna's decimation, competition and habitat destruction being less significant. 56 Although the effects of introduced predators are best documented on isolated · islands, such effects are not limited to such ecosystems. Similar effects have been observed within continental ecosystems (Elton, 1958). One such example is documented from the fossil record and is associated with the great American faunal interchange that occurred following the connection ofNorth and South America during the Middle Pleistocene. Numerous species ( 10 of 13) of South American ungulates became extinct shortly after the formation of the Central American isthmus (Webb, 1976). The disappearance of so many taxa coincides with the arrival of the North American ungulates and their predators, primarily dogs and cats, into South America. It is unclear whether competition by the new ungulates or predation by the introduced predators was responsible for their demise, but it seems likely that both factors contributed significantly to the observed decrease in nativeS. American ungulate diversity. Parasites are also known to have detrimental effects on host populations. There are some examples in which parasites decimate populations of host organisms. Jonsson and Andre (1992) documented the mass mortality ofthe bivalve Cerastoderma edule by the parasitic trematode Cercaria cerastoderma I. In a population of C. edule on the west coast of Sweden, 70% of the individuals on the surface of the sediment were infested with the C. cerastoderma I trematode. The infestation was so intense that much of the C. edule's tissue, reproductive organs, and other anatomy, including the foot, were damaged and rendered useless. Eventually, infestation and consumption by the parasitic trematodes resulted in mass mortality of the bivalves. In other cases, parasites have been known to alter their intermediate host's behavior to ensure the parasites transmission to another host via ingestion of the 57 intermediate host by the primary host (Huxham et al., 1995). It has been shown that · infaunal bivalves and gastropods usually do not attempt to burrow while infested with certain fish parasites. It is believed this behavioral alteration in the intermediate host is produced by several parasitic trematodes, and it ensures the passage of the parasite from its intermediary molluscan host to the fish which prey on the exposed mollusks (Jonsson and Andres, 1992; Huxham et al., 1995). Another potentially devastating effect of trematode infestation among mollusks is castration (Sousa, 1983). Sousa (1983) documented the effects of larval trematodes in the mud snail Cerithida californica. He showed that castration of the snail occurred following infestation by several trematode larvae and thus inhibited the snails reproductive capabilities. Such infestations, if prevalent enough, can significantly reduce the size of populations. Often the most severe infestations occur when parasites and other pathogens are introduced to a new host. Previously unexposed populations have no immunities to new pathogens and parasites (De Vos et al., 1956). The introduced pathogens may easily become established in native species and often prove impossible to eradicate. Unfortunately, human history is replete with such devastating outbreaks. Global colonization by people of European descent resulted in the complete destruction of numerous Caribbean and Pacific island peoples due to epidemics of small pox, measles, influenza, typhus, yellow fever and malaria carried by the explorers and colonists (Bianchine and Russo, 1995; Navanjo, 1995). Nearly 90% ofthe natives on the island of Hispaniola succumbed to disease after Christopher Columbus's first trip to the New World (Navanjo, 1995). Bianchine and Russo (1995) suggest the introduction of new 58 diseases and epidemics, not the horse or superior European military technology, that ·allowed the displacement and conquest of the Native American peoples such as the Aztecs, Mayans, and Incas. This phenomenon is also not unique to Homo sapiens. For instance, introduction of avian malaria and bird pox (via mosquitoes) to Hawaii quickly destroyed highly susceptible, virgin, bird populations and as a result several species went extinct (Warner, 1968). Extinction of endemic island groups may be indirectly related to new predators. If new predators reduce populations significantly there is a reduction in the genetic variation of that species. This genetic variation is essential in combating new pathogens, parasites and environmental changes via natural selection. Hence, in certain instances this genetic "bottle neck", created by limiting the number of individuals and the genetic variability of a population, can ultimately lead to the extinction of the endemic species Interestingly, besides having a rapid radiation during the Late Cretaceous the Brachyura, as a group, have all the characteristics associated with the successful invaders discussed above and had acquired such features early in their evolutionary history (Cretaceous) (Stevcic, 1971 ). Besides being evolutionarily plastic, which allows them to exploit new habitats such as the deep-sea, fresh-water, and even terrestrial environments, they are also extremely mobile. This mobility affords them great hunting and foraging efficiency (Carter, 1968; Stevcic, 1971). Another feature of the Brachyura that likely played a large role in their success and that could have been the most detrimental to the Early Maastrichtian inocerarnids, was their ability to subsist on a varied diet. They are known to be highly efficient, indiscriminant scavengers and omnivores, taking advantage and exploiting any food 59 resource available (Carter, 1968; Stevcic, 1971; Vermeij, 1987). This ability to exploit · numerous food resources may have devastating affects on prey species (Thortonson, 1958). Not being limited to a single prey species or food source allows the Brachyura to be opportunistic and permits over-harvesting of prey species without reciprocating negative effects on the Brachyura. When one food resource has expired, they simply move to a new location and feed on whatever may be existing in the new area (Vimstein, 1977). There is no doubt that the introduction of new, efficient predators, parasites or disease can have profound and sometimes catastrophic affects on previously unexposed populations of organisms. In this instance it appears that such may have been the case. But then why is this phenomenon only evident within the WIS? 3) Why only in the Western Interior? Intriguingly, the time of the inoceramids' disappearance also corresponds with a time of increased diversity within the Maastrichtian deposits of the WIS. At approximately the time of their demise within the B. grandis ammonite zone, the inoceramids reach their peak diversity in the Maastrichtian with seven species (Figure 20). From a broader biogeographic perspective, other authors have documented inoceramids from slightly younger strata within the Maastrichtian from S. Europe. These are often based on single taxon preserved as sparse specimens in stark comparison to the diversity and abundance within the WIS (Figure 22). Moreover, the Italian, French and Spanish specimens are from strata suggestive of slope deposition or turbidity flows which could well be older reworked remains. However, in most Maastrichtian sections 60 inoceramids are already absent by this time (Dhondt, pers. comm., 1998) or are only preserved as calcitic prisms (Huber, 1991; MacLeod, 1994; MacLeod et al., 1996; Chauris et al., 1998). The reliability of these single specimens and prisms as last appearance data is suspect and are clearly unsuitable for evaluating the role of predation, parasitism and disease. 4) Did this increase in predation, parasitism and/or disease bring about the demise of the inoceramids? The ultimate cause of the inoceramids decline is still debatable. A number of hypotheses exist attempting to explain their extinction. These include: 1) poisoning of the inoceramids by the influx of oxygen-rich Antarctic bottom waters (MacLeod, 1994; MacLeod and Huber, 1996; Barrera et al., 1997); 2) the loss oftheir primary habitat (Kauffman et al., 1992; Fischer and Bottjer, 1995) and; 3) potentially related to 1 and 2, the inoceramids, along with the rudistid bivalves, were the first step of the K-T mass extinction (Kauffman, 1988). Such hypotheses could potentially explain the disappearance of the inoceramids, yet the group survived similar environmental perturbations throughout its long evolutionary history (Kauffman, 1988; Harries, 1993 ). In addition, as previously mentioned, some inoceramids inhabited well-oxygenated, shallow-water environments and the timing, duration, effects and extent of changes in ocean chemistry and circulation, especially in these shallow-water settings are still unresolved (i.e., Barrera, 1997; Fatherree et al., 1998). 61 TIME 0 I CD v•n.vnc. • vvnr\.vnv runnnmucrdtl Ammonite Zone INOCERAMID RANGES (Myr) ~ STRATIGRAPHY Cal~onellid Western Interior I ~ N. America Spain Tuni. Italy Abyssal n <'• :a ~ r .g .."' 8 c: -.. .::: c: ...., ~ u c 0 .!! u .., ...... u " c " "' .. u .. x"" "(; ... 0 - 0. t: ..."' ~ 0. > c E .. .., E 0 ~ ...u -" u .. (/) CD .. ... " .. ~ > ;: '<; (/) iii :X: N" u <= N .. c C31n I t--'H. nebrascensis'-I ~ (/).. "'..... - 1>. < CD 0 .::: '() 0 :; ..... 0 (/) 1>. C31r I I B. Prandi.t I I "T' 0 CD 0 ~ ~~~r Q G. gansscri I B. eliasi I I I I I II !_ ; T "&, ? ...() ? I; ? ? , ? ? ·;:: ? :§ ~ ? g. ~ ...: "2.4 ? l: () () ? c I; T? G. r B. compressus ~ I; ? aegyptico .. I; ci. ~ , ci. , D. cheyennense ""'~I:'- "'c gr:::_ ~ ~ ~ ...: ....: G. E. jenneyi !:! ~.....: ...:"'" havonaensis § !:l D. stevensoni -G. ~~ co/carlo D. nebrascense il"·- O(j ~~ .!}OJ) - · ---··· C33n I I B. gregoryensis I G. ventricoso G. C33r (part) eleva/a R3 (part) Figure 22. Composite figure showing diachronous extinction of the inoceramids from global sections. Black lines represent evidence from body fossils. Gray lines represent evidence from inoceramid shell prisms (see MacLeod, 1993 for discussion of sampling). Regional correlations are based on magneto-, chemo-, and biostratigraphy (Browler et al., 1995; Chauris et al., 1998; Gradstein et al., 1995; Kauffinan, 1993; Larson et al., 1997; MacLeod, 1994, 1996). 0'1 w The data presented here suggest that the influence of a predator and/or parasite (s) · and disease had a profound affect on Early Maastrichtian populations of inoceramids. The brachyuran crabs appear to be responsible for the dramatic increase in shell margin crushing deformities and repairs seen in the Early Maastrichtian inoceramids of the WIS. A new, efficient predator that had a significant evolutionary advantage over the inoceramids, such as the Brachyura, could have decimated their populations. This may be one of the only documented cases from the fossil record in which a group was out escalated by a predator. Although the introduction of the Brachyura may not have directly brought about the extinction of the inoceramids, its seems plausible that the increase in predation, accompanied with the increase in parasitism and/or disease could have reduced populations of inoceramids. Such a dramatic reduction in the populations could make them more susceptible to the environmental perturbations hypothesized by other authors that were previously not detrimental. Isolating the causes for the extinction of a group and the role each played in the extinction is extremely difficult. In many instances the phenomenon responsible for the disappearance of the last individual or population is not the only or necessarily the primary cause for the extinction of an entire group. Ziswiler ( 1967) states that the extinction of the heath hen from the eastern United States was due to anthropogenic reasons such as over-hunting. However, Simberloff(1986b) attributes the final demise of the bird to two harsh winters and a poultry disease that further reduced the population to a critical number in which extinction came as a result of inbreeding and genetic drift. Therefore, a distinction must be made between proximate and ultimate causes of 64 extinction. Simberloff(l986b) suggests the cause(s) for the extinction of the last few individuals of a species or sub-population is not the ultimate cause of the extinction but, rather, the proximate causes of extinction. It is a classic case of the straw that broke the camel's back. In the case of the inoceramids it would appear that the oxygenation of their habitat or reorganization of the circulation patterns, that have been suggested as the primary causes oftheir demise (MacLeod, 1994; MacLeod and Huber, 1996; Barrera et al., 1997), may simply have exacerbated things for the inoceramids who appear to already have been under duress from predation, parasitism and/or disease. Interestingly, immediately preceding their disappearance from the WIS, inoceramids reached their peak Maastrichtian diversity within the B. grandis ammonite zone. The inoceramids, however, are not the only group to show a marked increase in diversity with the WIS at this time. The concretion fauna within the Lower B. grandis and B. grandis ammonite zones increases dramatically with numerous gastropods, scaphopods, ammonites, and other bivalves becoming increasingly abundant. Prior to the Transition zone there were few taxa other than the inoceramids and ammonites of the genus Baculites found within concretions. This increase in diversity of the benthic fauna may suggest that conditions during this time were becoming more hospitable to other taxa and may have been due to increased oxygen levels within the bottom waters ofthe WIS. Several authors (i.e., Barrera et al., 1997; Macleod and Huber, 1996) have documented an oxygen isotope excursion at approximately this time and suggest that the amount of oxygen reaching the bottom of the oceans was increasing. If this oxygenation of the suboxic to anoxic benthic 65 habitats took place in the WIS, it could have had a substantial impact on the benthic biota and significantly altered the structure of the WIS benthic ecosystem. In the case of the inoceramids this may have been ruinous. As previously discussed the inoceramids relied on avoidance as their primary anti-predatory defense. The incidence of injuries attributed to predation had been increasing throughout the Early Maastrichtian and oxygenation of their habitat would have allowed more, previously excluded predators to invade their benthic refuge. The result would have been a smorgasbourg of epifaunal inoceramids for any predator suited to a diet of bivalves at the expense of the already stressed inoceramid populations. This may have directly resulted in the extinction of the group, or further reduced populations below the size of a minimum viable population, thereby indirectly bringing about their extinction. This does not, however, account for the continued existence of the enigmatic Tenuipteria. By the B. clinolobatus ammonite zone the inoceramids had disappeared except for members ofthe genus Tenuipteria. Tenuipteria was rare to absent from the populations of inoceramids sampled in this study prior to the B. grandis ammonite zone. The 33 specimens of Tenuipteria that were obtained from this zone show no evidence of deformities. The increase in the abundance of Tenuipteria and their persistence until the terminal Cretaceous event is difficult to reconcile with the other data from this study. However, it seems likely that Tenuipteria had different environmental tolerances than the other genera of inoceramids and were possibly more suited to resist shell-crushing predation as evidenced by the distinct radial ribs in some species. These attributes may have allowed the group to thrive and radiate into the epifaunal niche left open by the 66 extinction of the other inoceramid taxa until the terminal Cretaceous event (Kauffman, 1988). 67 CONCLUSIONS • There is a marked increase in the percentage of individuals with shell deformities in Lower Maastrichtian (- 15% B. eliasi- - 32% B. grandis) populations of inoceramidsfrom the Western Interior of North America (Wyoming and Montana). • Species diversity of inoceramids increases from one to seven from the B. eliasi through the B. grandis ammonite zones. Overall faunal diversity within the concretions sampled also increases from B. eliasi to B. grandis. • Deformities such as the "awl mark", "wedge", "vampire bite" and possibly many "other" deformities are interpreted as evidence of unsuccessful predation attempts on the inoceramids. Such deformities as the "bubbles" and Hohlkehle are interpreted as evidence of parasitism on inoceramids. • Deformities do not appear to be species specific except for the characteristic "squiggle" of informal Species F of the Transition, Lower B. grandis and B. grandis ammonite zones. The "squiggle" may be a genetic response unique to Species F brought about by events similar to those which caused "wedge" and "vampire bite" deformities in other species. 68 • The hypotheses presented by other authors to explain the inoceramids' demise do not seem convincing in that the group had survived similar environmental, climatic, and paleoceanographic changes earlier in their history. This fact, combined with the quantitative data presented here and the known appearance of predatory decapods during the Late Campanian, suggests that predation and parasitism may have played a significant role in their disappearance, at least within the Western Interior Seaway of North America. 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New York, Springer Verlag. 77 APPENDICES 78 Infested, Injured or Irregular inos from D. eliasi: SMD Road Unidentifiable H. em Valve ~ Specimen L.cm Irregularity Location Type u T ""0 26 26 ztTl I. a ff. bnrabini ...... t:l ~ SMO:De U-7 3.2 4.4 LV "wedge", .?em 1.3 em umbo o-a ax is Predation Ill 137 ...... SMD:De U-8 2.1 3.2 LV "awl mark" .6 em d, .2 em deep 1.6 em umbo o-a ax is Predation SMD:Oe Ps-4 2.3 3.2 DV "bubbles" ubiquitous Parasitism t:l 0 SMO:Oe Ps·l 3.6 5.2 nv 1/ohlkl!hle. 2.1 em L, .19-.29 em 2.2 em umbo o-a ax is Parasitism (I) 0 SMO:OeU-1 4.1 6.4 nv depression along rugae 1.2 em umbo o-a ax is Parasitism -o·~ SMG:Oe P-1 3.3 5.2 LV irregular depressions 2.7 em umbo o-a ax is Predation o·...... SMO:Ile P-2 ID 6.3 LV "vampire bite", .7 em long, toward hi. anterodorsal margin Predation ::s SMIJ:De Ps-2 4.8 8.2 LV llohkl!hle. 6.0 em L. or. n-o ax is umbo-shell termination Parasitism (I) 0 SMB:Ile U-5 3.2 5.3 LV "bubbles" ubiquitous Parasitism ....., ...... Total of 12 spcci. SMB: Be-Ps-12 all-2.5 -4.0 BY 1/oh/keh/e umbo-shell termination Parasitism ::s 0.. SMIJ:De U-2 2.7 3.7 LV deep groove, flallened margin Predation :t SMil:Oe U-6 4.7 6 LV "awl mark", overlapping, 3x 3 area 1/3 ofv, along anl.mar Predation 0: SMD:De U-3 3.7 5 LV .. ~wl mark" leflofumbo Predation c SMD: De Ps-6 4 5 RV irregular depressions total area= 1.9 em x 2.1 2.2 em from hinge Predation e?.. SMD:OeU-4 10 10 ID depressions ID Predation t:l :y0 s(1) Infested, Injured or lrrcgul:lr inos from Lower B. baculus: MilAR Ranch 0.. I. inc11n11s Specimen II. em L. em Valve lrrcgul:arily Location Type u T C/) Possibly some MOLO: C-P-1 3.45 5.1 LV "awl mark" .3 em x .3 em 2.4 em umbo o-a nx is Predation 240 249 "0 0 I. aff. hnrnhini MOLB:C-P-2 2.7 4 LV 2 "wedgc"s //, 1.7 em L@gn., 1.2 em L@subgn. Predation 0 MllUl: C-1'-3 II) ID II) 4 "wedgc''s, each .8 em L&wide toward term. Predation §' 0 MllLil: C-1'-4 2.4 4.1 LV ritsldimrlets. 8 aprarent truncating rugae ubiquitous Parasitism ::s (I) MOLB: C-P-5 1.8 2.8 RV "bubbles" ubiquitous Parasitism MOLD: C-P-6 3.2 4.5 RV 1/oh/kehlt:, 1.2 em L, .25 em W@ margin/term. 3.0 em umbo o-a ax is Parasitism MOLD: C-P-7 3 4.8 LV 1/ohkehlt!. 1.7 em L, afler 1.1 em trunc more ventral 2.2 em umbo o-a ax is Parasitism MOLD: C-P-8 2.6 4.2 LV 1/ohlkehle. .8 em L terminates before margin/term. 2.6 em umbo 0-a ax is Parasitism MOLD: C-P-9 10 10 10 scverly pined:"bubbles"? ubiquitous Parasitism "Inoceramus" n. sp. cf. 94 94 "l"s11bcirC1tlaris Infested, Injured or Irregular inos from Mid D. baculus: 1\tDAR Ranch Unidentifiable Specimen H. em L.cm Valve Irregularily Location Type u T MBMB:U-6 10 ID ID "squiggle" 10 Predation .....J \0 MOMO: U-4 ID 10 10 depression truncating rugae 10 Predation MOMO: Ps-I ID ID 10 Hohlkeltle 2 em L mid-valve, tenn. Parasitism MOMB: U-13 10 ID LV "awl mark".) em x .3 em near umbo Predation Species A 76 98 Morphotype I MBMB: P-1 3.7 6.8 ov "wedge", 1.1 em W, .4 em depth 2.8 em umbo o-a ax is Predation MBMO: P-2 2.8 4.2 RV "wedge", 2.3 em L, 1.4 em W, .3 em depth 2.6 em umbo o-a ax is Predation MBMO: P-3 2 4 RV "vampire bite", 2.2 em L, 1.0 em W, .2 em depth 2.1 em umbo o-a ax is Pedation MBMB: P-4 3.7 5.5 LV 3.0 em x 1.9 em area distorted and elevated 2.5 em umbo o-a ax ix Predation MOMO: P-12 2.6 4.2 LV "vampire bite", 1.4 em L 2.7 em umbo o-a ax is Predation MBMB: P-6 3.4 5.4 LV pits eventually fonn "vampire bite", 1.7 em L 3.7 umbo o-a ax is Predation MBMB: P-5 2.7 3.9 LV "vampire bite", .8 em L, .4 em W, 2.1 em umbo Predation MBMB: U-5 2.8 4.7 LV "wedge", .8 em L, .6 em W, .4 depth 2.5 em umbo Predation MBMB: U-7 2.6 5.4 LV defonned, some resemblance of"vamp bite" 2.6 em umbo o-a ax is Predation MBMO:P-7 2.5 3.4 LV indentations across rugae at margin margin ??? MBMO: P-8 2.4 5 LV "vampire bite"/wedge, 2.0 em L, 1.3 em W 1.9 cm umbo Predation MBMO: P-9 2 8 RV "wedge", ?L, I em W, .4 depth 10 Predation MBMO: P-10 ID 10 10 "awl mark" ID Predation MBMO: U-11 3.7 5.1 RV depression in middle of shell 1.1 em x 1.9 em middle of valve Predation MOMO: U-6 3.2 5.9 LV defonned, defonnity posteroventralldorsal post/vent dorsal Predation MBMB: U-15 3 5.5 LV circular depression . I cmd, . 7 em umbo o-a ax is Predation MIJMB: U-10 JD M ID "vampire bite", 1.5 em L ventral margin Predation MOMO: U-14 4.6 7.7 RV 2 1.0 em depressions x ing 3-4 rugae postero-ventral margin Predation MOMO: U-8 2.7 4 LV defonned, rugae truncated or irregular most of shell ??? MBMB:U-12 3.4 5.8 RV .7 em x 1.7 em elevated rectangle, !rune. rugae 2.5 em umbo toward ven ??? MOMO: U-9 3.2 3.5 ov "vampire bite", 2 em W on Both Valves mid-valve to margin Predation MflMB: Ps-2 ID ID nv I folrlkehh:, 1.9 em L begins at mid-valve Parasitism Species n 12 17 Morphotype 2 MOMO: P-15 ID 5.5 RV depressions across rugae, 1.7 em x 2.8 em postero-dorsal margin Predation MflMO: U-2 3.9 8.8 ov "wedge" 1.7 em L, .2 em W, 1.6 em o-a ax is Predation MOMB: P-11 3.4 5.4 RV depression and irregular, I.7 em x 2.4 em ventral margin ??? MBMO: PS-3 fD ID ID crcacc in shell as if fold ed mid-valve? ??? MflMO: U-1 3.1 7.7 LV 3.2 em x 4.0 em area of defonnity, "wedge" type 3.3 em umbo Predation lnfestrd, Injured or lrregul2r inos from Upper B. b2culus: MBAR R2nch Unidentifi2ble Specimen II. em L.cm V2lve Irregularity Location Type u T MBUO: U-3 ID L ID 2 "vampire bite"s crossing 2 rugae and stop toward ventral margin Predation 40 42 00 0 MOUO: P-4 ID M 10 "vampire bite" , .5 em L 1.7 em umbo post-vent Predation I. aff. barahini 20 25 MOUO: P-11 3.2 4.8 LV 2 areas of deformation, 2 em x 2 em, .3 cmdep 2.8 em umbo Predation MOUO: P-12 1.5 2.6 RV "awl mark" 2.6cm umob Predation MllUD: PS- I 2.5 5.1 OV 1/oh/ke/tle, 1.6 em L, 2.3 em umbo o-a ax is Parasitism MOUO: P-7 3 5.2 ov depression/"groove " parallel to ribs, 1.5 em L 2.1 em umbo ??? MOUil: P-6 3.6 5 nv distorted margin, 114 of shell post-ventral margin Predation Species C 4 9 Morpltorype 3 MOUO: P-8 3.7 4.8 ov "wedge" with adjacent linear depres. 2x 2 area, Predation MBUO: P-2 ID M 10 "wedge", > I em 10 Predation MBUB: U-1 4 5.1 LV depression 1.5 cmd 4.6 em umbo post-vent Predation MDUD : U-2 5.2 7.3 LV "wedge" 1.3 em L 3.1 em umbo ant-vent Predation MOUO : P-5 4.2 5 LV depression 1.5 cmd, crosses 3 rugae 1.9 em umbo post-vent Predation Species 0 7 9 Morpltotype 4 MOUO: U-4 5.5 L ID deformed, knuckles imprint carried throughout ubiquitous Predation MOUO: P-3 ID L ov irregular "L" shaped depression 1.8 em x 2.0 em post-ventral margin Predation MOUO: P-1 ID L ID "vampire bite" 2.4 em L, 1.6 em W, towards post margin Predation MOUn: P-9 >7.0 >9.0 LV many pits and two "wedges"s 2.7,1.5 em 2.3 em umbo post-vent Predation Species E 2 2 Morpltotype 5 MOUn: PS-12 3.9 8 nv Hohlkehle, 3.0 em L 1.0 em umbo-?loss shell Parasitism MllUO: P-10 3.2 4.8 LV "vampire bite" 3 em L 1.9 em umbo post-vent Predation Infested, Injured or lrregul:~r inos from the Transition Zone between Upper 0 . Daculus and Lower B. grand is Un identifiahle Specimen H. em L.em Valve lr regularily Location Type u T MOT: P -7, 8, 9 ID M 10 deformed, "squiggles", "vampire bite" ID Predation 10 19 MBT: P-15 ID L RV "wedge" 1.1 em L, postero-ventral direct. ?mid-valve Predation MOT: P-21 3.2 5.5 ID "wedge" 2.2 em L, 1.5 em at termination 2.9 em post-vent Predation MDT: P-38 ID M ID irregular depressions, 2.3 em x 2.3 em ?? Predation MOT: P-24 ID M ID "vampire bite", depression 1.5 em x 1.2 em ID Predation MOT: P-22 ID M ID deformed ID Predation MDT: P-20 ID L ID "vampire bite" .4 em b. groov ID Predation Species F 16 32 Morphorype 6 MOT: P-13 2.8 3.9 LV Crease, 2"squiggles" 2.3 em L, 2.0 em W 1.9 em umbo o-a ax is Predation 00...... MOT: P-23 2.5 4 LV 2 "awl mark" .3 cmdep 1.8 cm2.3 em umbo o-a Predation MBT: Pl7 ID L ID blunt depression 1.5 em x 1.2 em ID Predation MBT: U-1 2.4 3.1 LV ·~wl m~rk" 2.3 em umbo o-a ax is Predation MOT: P-39 2.6 3.8 RV "v~mpire bite" 1.4 em x 1.0 em ~nd irregular 1.5 em umbo o-a ax is Predation MBT: P-18 10 L ID numerous "awl m~rk", -6 ID Predation MOT: U-4 ID M ID deformed 10 Predation MOT: P-35 2.6 3.7 LV bulb like structre, elev~ted shell 3.7 umbo o-a ax is ??? MOT: P-36 2.1 2.7 RV crescent depression 2.5 em umbo o-a ax is Predation MOT: P-37 1.9 M LV "awl mark" becomes irregular toward margin 1.6cmumbo Predation MOT: U-3 ID M ID bulb like structre, elevated shell 10 ??? MOT: P-1 2.8 4.6 BY "wedge" 2.6 em L, 1.5 em W margin/term. 2.0 em umbo o-a ax is Predation MOT: P-29 2.8 3.1 LV "vampire bite" 1.0 em L, ends in .4 emdep pit 2.0 em umbo postvent Predation MOT: P-4 1.9 2.9 RV "wedge" 1.2 em L terminates&"vampire bite" I.) em L 1.1 em, 2.2 em, umbo Predation MBT: P-5 3.2 4.8 BY multiple "vampire bite", 3/4 shell, 1.3 em umbo Predation MOT: P-6 2.7 4.5 LV 2 "squiggle" increase toward postvent 1.7 em umbo Predation MOT: P-7' 2.6 3.8 RV "squiggle" 1. 1 em L, 2. 1 em umbo o-a ax is Predation Species G 0 6 Morphotypc 7 MOT: P-C 3.4 5.2 LV "wedge", 3.6 em L 3.5 em umbo o-a ax is Predation MOT: PS-I 2.6 ID LV · ~wl m~rk" ubiquotous Predation MOT: P-16 4.9 5.5 LV "vampire bite" 2.1 em W margin 2.8 em umbo anterovent Predation MOT: P-3 10 M ov truncated rugae merge with irregular depress. mid-valve Predation MOT: P-34 3.2 4.5 BY "vampire bite" 1.4 em L 3.2c, umbo o-a ax . Pstv Predation MOT: P- It 4.7 6.1 BY "wedge" 2.5 em W&"V" on LV 3.0 em umbo o-a ax is Predation Species II II 14 MorphOI)1'1! 8 MOT: U-2 ID 6.9 truncated and elevated rugae 1.5 em x 1.3 em near marin/term. ??? MBT:P-27-28 4.4 6 BY "vampire bite" 1.1 em L, .8 em W, .4 em b.groov 4.5 em umbo o-a ax is Predation I. aff. bllrahini 13 19 MBT: P-31 5.2 6.8 LV "wedge" 2.4 em L, 1.9 em W 5.6 em umbo o-a ax is Predation MflT: P-32 8. 1 II LV displaced rugae at 45 degrees to other rugae anterior face of valve ??? MOT: P-33 5.5 L RV deformed, pits, depressions, deformed begins -1.0 em umbo Predation MOT: P-30 10 L ID "wedge" 1.2 em at margin/term. 10 Predation MOT: P-14 3.9 5.9 RV deformed, 113 of shell, widens toward post-ven 2.0 em umbo o-a ax is Predation MOT: P-25 3.8 5.9 RV "vampire bite" I. 7 em L, 1.1 em W margin/term. 3.7 em umbo o-a ax is Predation Sprcirs I 0 2 Morphotype 9 MBT: P-10 6 7.5 ov "wedge", 3.9 em W at margin/term. 4.5 em umbo o-a ax is Predation MOT: P-26 ID L RV "wedge" 3.2 em L, 2. 1 em \Vat termination 10 Predation 00 N 26 26 Troclrocernnws sp. Infested, Injured or lrregul:~r inos from Lower n. gr:~ndis from MIJAR R:~nch Unidentiri:~ble Specimen II. em L.cm Valve lrrtgularity Location Type u T MOLG: U·2 ID ID ID "vampire bite• impressions .4 cmH, .6 em apart NA Predation 22 26 MOLG: P·l ID ID ID deformed NA Predation MllLG: P-16 ID ID ID deformed NA Predation MOLG: P-18 ID ID ID depression truncating 4 rugae NA Predation Species F 16 19 Morplroi)'PI' 6 MOLG: P·3 3.6 S.l nv "vampire bite" 1.2 em L toward venter Predation MBLG: P-20 2.2 3.2 RV "wedge• 1.6 em L, I .3 em \Vat termination anterovenl. Margin Predation MBLG: P-13 2 2.8 LV "wedge" .6 em L, terminating before shell term. .S em umbo o-a ax is Predation Troclroct:ranrus sp. 31 34 MOLG: 1'·9 4.7 6.3 LV depression 1.0 em x 1.0 em, trune.#l2·1 S rugae anteroventrnlly loc. Predation MllLG: 1'·10 3 4.6 LV "vampire bite" iner. to deformed, 2.7 em L, 2 em \V anteroventrnlly Joe. Predation MllLG: P·IS 6.4 6.5 LV 2 depressions, .S em x .S em, I em x I em anterodorsally loc. Predation Species II 18 21 MurplrOI)p<: S MOLG: P-4 S.8 8.2 LV "wedge" 3.8 em L, 1.1 em \V margin/term. Predation MOLG: 1'· 12 4.2 7.1 RV "wedge" 2.1 em:, . 7 em W at term. 4.6 em umbo o·a ax is Predation Species I 13 IS Morphoi)'PI! 9 MOLG: P· ll 3.2 4.6 RV irregular depressions and "awl mark"2.3 em x 1.7 em 2.3 umbo o·a ax is Predation MOLG: P·S 4.1 6.4 nv "wedge" 3.0 em L, I,S em \Vat mnrginltcrm. 2. 7 em umbo o·a ax is Predation I . aff. bnrbini ? I 6? MBLG: P-2 5.4 8.3 RV "awl marl:" .4 em x .4 em, groove I.) em L, .4 em W 3.1 umbo o·a ax is Predation MULG: 1'·14 6.1 8 nv numerous "awl marl:" on LV, "wedge" on RV, 3.3 em awls"Ubiquitous, V vent Predation MOLG: 1'·8 5 8 RV irregular depressions and "wedge"l.4 em L "wedge" at termination Predation MOLG: U·l ID ID ID two ridges, 2.2 em L, .2 em W, .S em apart /I anteroventrnlly loc. Parnsitism MOLG: 1'·7 6.1 10.2 LV "awl mark" .S em x .S em, 2depressions, - 1 em x I em 2.9 em umbo o·a ax is Parnsitism Species J 4 7 Morphotypl' /0 MOLG: 1'·17 2.9 5.2 LV "wedge• .2 em 2.8 em umbo o-a ax is Predation MBLG: P·6 ID ID ID "vampire bite" I .I em L, .3 em W at margin/term. mid·valve Predation 00 VJ MBLO: P-19 1.9 2.9 LV "awl mark" .3 em x .3 em&depression .3 em x .2 em anteroventrally locJter Predation Infested, Injured or Irregular inos from B. gr:mdis Unidentifiable Specimen II. em L.cm Valve Irregularity Location Type u T MOO: P-C ID ID 10 "vampire bites" .8 emd, .6 cmd, .6 cmapart&deformed 10 Predation 9 17 MDG : P-27 ID ID ID "vampire bite".7 emd,.4 cmdep, .5 emd,.2 emdep,l em apart 10 Predation MDG: U-2 ID 10 10 "awl mark" and other minor irregularity depress. 10 Predation MDG: P-3 ID L 10 rectangular "awl mark" I . em x I .7 em, .4 cmdep term. before margin Predation MBG: P-16 ID M 10 "awl mark" .5 emd,.2 cmdep&other minor depress. 10 Predation MDG: P-25 ID s ID "wedge" .7 em L, .3 em W at term. 10 Predation MDG: P-23 ID L ID irregular depressions truncate rugae everywhere ID Parasitism MOO: P-5 ID L ID "vampire bite" .6 emd, .3 cmdep., 2 em apart 10 Predation I. off. van"T emi MOO: P-15 8.9 > II LV "awl mark" 1.3 cmd, .4 cmdep@irreg. "VB"3.4 em L 3.4 em umbo supra o-a Predation 12 14 MBG: P- 17 10 10 DV "vampire bite" 2.3 em L, 2.2 em W, I .3 em L, 1.1 em W 10 Predation I. aff. barhini MOG: P-14 ID 10 LV very deformed everywhere Predation 7 10 MOO 1'-4 ID ID RV 3.4 em L, 1.0 em W, .7 cmdep groove@"V"2.3 em x 1.1 2.3 em umbo o-a ax is Predation MOO: 1'-30 6 >8.0 RV "wedge"2.5 em L, 1.3 em W at margin/term. 3.2 em umbo o-a ax is Predation Species F Morphotype 6 MDG: U-1 2.1 2.8 RV "vampire bite".2 emd, .4 em apart 1.1 em umbo o-a ax is Predation 5 II MOG: U-6 2.7 3.7 RV "squiggle", "awls mark" and small "V", deformed everywhere Predation MOG: U-3 2.6 4.3 LV "squiggle" everywhere Predation MBG: 1'-13 2.1 3.7 LV 2 "awl mark", .3 cmd, .2 cmd & deformed posteroventrally Predation MOG: 1'-24 ID ID RV "vampire bite" 2.4 em L, .4 em, .5 em apart mid-valve? Predation MBG: 1'-31 1.1 2.8 LV "vampire bite". 7 em L, .I cmd, .2 em apart, posteroventrally Predation Species I Morphotype 9 MOG: 1'-28 4.3 10 LV "wedge" 3.9 em L, 1.1 em W@terrn. 2.3 em umbo o-a ax is Predation 21 30 MOG: P-20 3.6 4.9 RV "wedge" 1.5 em L, 1.1 em W@terrn. 3.2 em umbo o-a ax is Predation MBG: I'-1 1.5 3.7 LV "vampire bite" 1.6 em L, 2.0 em W@terrn. 1.8 em umbo o-a ax is Predation MBG: P-9 2.5 4.2 LV irreg. pits anter.&2"V" .7 em L, .9 em, 1.1 em apart posteroventrally Predation MOG: 1'- 10 2.3 3.5 RV "buck tooth" .8 em W 1.2 em umbo o-a ax is Predation MOG: P-5 5.8 >1.0 LV very deformed everywhere Predation MOO: P-19 5.3 >7.0 RV very deformed begins 3.1 em umbo o-a Predation 00 ~ MllG: P-8 5.3 >8.0 LV "wedge" 9.4 em 1.., orient Change 3.2 em 3. 7 em umbo o-a ax is Predation MOG: P-26 4.8 7.6 RV "wedge" 1.4 em L, 1.0 em W 6.2 em umbo o-a ax is Predation Species H Morphotype 8 MOG : P-11 3.6 5.7 BV "vampire bite" 2.2 em 1.., .5 em, .7 em W,.4 em apart 4 em umbo o-a ax is Predation 5 8 MOG: P-6 3.8 6.6 RV "vampire bite" 1.9 em L, .5 em W, .6 em apart 3.7 em umbo o-a ax is Predation MOG: P-7 ID ID ID "wedge" 5 em L, .3 em W ID Predation Trochoceranms sp. MOG: 1'-21 ID ID ov irregular "wedge" 2.0 em L, 1.5 em W ID Predation 14 17 MOG: 1'-12 3.8 >S ov "vampire bite".4 em apart, .4 em W, .7 em W@"V" 4 em umbo o-a ax is Predation MOG: P-22 4.7 6.6 ov inflated, irreg. Area, 2.4 em x 1.6 em, rugae weaken near margin Parasitism "Inoceramus" n. sp. cf. "I" subcircularis MOG: U-5 1.3 2.9 LV "wedge" .6 em L, .3 em W 1.9 em umbo o-a ax is Predation 6 9 MOG: P-29 3.4 10 LV "bubbles" anterior Parasitism MOG: P-18 >5.5 >7.0 LV "wedge" 7.3 em L, becomes lumpy, 2.3 em@ term 1.9 em umbo o-a ax is Predation 00 Vl Ammonite zone Total # of Specimens # Deformed % Defonned N' D Two tail test at the: '"0> 0.01 (99%) 0.05 (95%) '"0 ~ Lower B. baculus 343 9 0.026239067 0.095332531 0.13425476 0.155392025 0.12965224:1 0 B. diasi 162 26 0.160493827 Significant ~ N .....C/) Lower B. baculus 343 9 0.055555556 0.120731938 0.204948646 0.196793059 0.16419543l ;;;·s...... Mid B. baculus 119 31 0.260504202 Significant Significant c:;· e. g' (/) Lower B. baculus 343 9 0.026239067 0.12004043 0.180657485 0.1956659 0.163254984 c ~pper B. baculus 87 18 0.206896552 ~ificant ~ Lower B. baculus 343 9 0.026239067 0.117409613 0.430282672 0.191377668 0.159677073 Transistion 92 42 0.456521739 Si~ificant Significant Lower B. bacrtlus 343 9 0.026239067 0.103575827 0. 145635933 0.1 68828598 0.140863124 Lower B. grand}! 128 22 0.171875 Shmificant ·--- --·-·------· Lower B. baculus 343 9 0.026239067 0.10919918 0.307094266 0.177994663 0.148510885 B.:.. grandis Ill 37 0.333333333 Sig_!!ificant ~ificant Ammonite zone Total II of Specimens # Deformed %Deformed N' D Two tail test at the: (-) Holrlkelr/e d.at~ Lower B. baculus 343 6 0.017492711 0.09533253 I 0.056581363 0.1 55392025 0.129652242 B. eliasi -- 162 12 0.074074074 ------_ _ j 00 0\ Lower B. baculus 343 6 0.01749271 I 0.106389911 0.217801406 0.173415556 0.144690279 - ·~- --··-·· - ---- ·------· ------· Mid /J. /){lCIIIIIS ---·-- -·· ... -·-- 119 2R ---0.235294118------·- ~gnificant Significant Lower B. baculus 343 6 0.017492711 0.12004043 0.166415335 0.1956659 0.163254984 ~pper B. bac1!lus 87 16 0.183908046 Significant Lower B. baculus 343 6 0.01749271 I 0. 117409613 0.439029028 0.191377668 0.159677073 Transistion 92 42 0.45652 I 739 Significant Significant Lower----- B. baculus- 343 6--- 0.017492711-·-- - 0.103575827 0.154382289 0. I 68828598 0.140863124 Lower B. grant/is 128 22 0.171875 Significant - Lower B. ba-c-ulu· s 343 6 - 0-.0174- 9271 I- 0.10919918 0.315840622 0.177994663 0.148510885 B. gram/is Ill 37 0.333333333 Significant Significant 00 -.....! APPENDIX 3. Species Descriptions and Plates "Inoceramus" aff. barabini Morton, 1834 (Pl.l, n. 1, 2, 3) MATERIAL: 218 specimens from the B. eliasi, Lower B. baculus, Upper B. baculus, Transition, Lower B. grandis and B. grandis ammonite zones of collected within the Kara Bentonitic and Upper Unnamed Shale Members of the Pierre Shale near Newcastle, Wyoming. Specimens are housed at the University of South Florida Department of Geology. DESCRITPTION: Medium to large, inequilateral, equivalve, anterior margin steep, hinge line medium long and straight. Ornamentation consisting of strong, sharply edged, relatively closely spaced concentric, subcircular rugae. "Inoceramus" incurvus Meek and Hayden, 1856 (Pl. 1, n. 4) MATERIAL: 249 specimens collected from the Lower B. baculus ammonite zone within the Upper Unnamed Shale Member of the Pierre Shale near Newcastle, Wyoming. Specimens are housed at the University of South Florida Department of Geology. DESCRIPTION: Small to medium, inequilateral, equivalve, anterior margin very steep, two distinct geniculations, hinge line straight and short to medium long, extremely inflated and convex. Ornamentation consisting of weak to strong concentric subcircular rugae. Two forms appear to exist, a smaller more spherical morphotype with closely spaced, weak concentric rugae and a larger more square morphotype with a developed in a postero-ventral orientation and stronger concentric rugae. REMARKS: These two different morphotypes could be different species but were classified together for this study based on the presence of the geniculations. "Inoceramus" aff. vanuxemi Meek and Hayden, 1860 (Pl.l , n. 5) MATERIAL: 14 specimens were collected from within the B. grandis ammonite zone from the Upper Unnamed Shale Member of the Pierre Shale near Newcastle Wyoming. Specimens are housed at the University of South Florida Department of Geology. DESCRIPTION: Medium to large, inequilateral, valves longer then high, ?equivalve, moderately convex. Ornamentation consists of strong, closely spaced almost circular concentric rugae that gradually increase in width apart away from umbo and decrease in sharpness. 88 "Inoceramus" subcircularis Meek, 1860 (Pl.2, n. 6, 7) MATERIAL: 94 specimens collected from the Lower B. baculus ammonite zone within the Upper Unnamed Shale Member of the Pierre Shale near Newcastle, Wyoming. Specimens are housed at the University of South Florida Department of Geology. DESCRIPTION: Small to medium, inequilateral, equivalve, anterior margin steep, one geniculation, hinge line straight and long, weakly convex to flat. Ornamentation consisting of sharp, prominent, almost circular regular concentric rugae. Trochoceramus sp. (Pl. 2, n. 8) MATERIAL: 77 specimens collected from the Transition and B. grandis ammonite zones within the Upper Unnamed Shale Member of the Pierre Shale near Newcastle, Wyoming. Specimens are housed at the University of South Florida Department of Geology. DESCRIPTION: Moderate to very large, slightly oblique, moderately inequilateral, equivalved, distinct geniculations, hinge line short to moderately long and straight, somewhat flattened. Ornamentation consisting of very prominent, sharp, widely spaced concentric rugae. Species A (Pl. 2, n. 9) MATERIAL: 98 specimens collected from the Mid-B. baculus ammonite zone within the Upper Unnamed Shale Member of the Pierre Shale near Newcastle, Wyoming. Specimens are housed at the University of South Florida Department of Geology. DESCRIPTION: Medium to moderately large, inequilateral, equivalve, anterior margin steep, hinge line straight and long, moderately inflated and convex. Ornamentation consisting of large, subcircular concentric rugae that are relatively widely spaced at an early stage of ontogeny. REMARKS: This form appears very similar to I aff. barabini in size and form. However, the rugae appear to be more broadly spaced than most I aff. barbini specimens from other ammonite zones. 89 Species B (Pl. 2, n. 10) MATERlAL: 17 specimens collected from the Mid-B. baculus ammonite zone within the Upper Unnamed Shale Member of the Pierre Shale near Newcastle, Wyoming. Specimens are housed at the University of South Florida Department of Geology. DESCRlPTION: Small to medium, inequilateral, equivalve, anterior margin very steep, hinge line short to moderately long and straight, extremely inflated and convex. Ornamentation consisting of weak, closely spaced, subcircular concentric rugae. Species C (Pl. 3, n. 11) MATERlAL: 9 specimens collected from the Upper B. baculus ammonite zone within the Upper Unnamed Shale Member of the Pierre Shale near Newcastle, Wyoming. Specimens are housed at the University of South Florida Department of Geology. DESCRlPTION: Small to medium, inequilateral, equivalve, anterior steep, hinge line short to moderately long and straight, slightly inflated and "rectangular" shaped valves. Ornamentation consisting ofbroad, subcircular, relatively widely spaced concentric rugae. Species D (Pl. 3, n. 12) MATERlAL: 9 specimens collected from the Upper B. baculus ammonite zone within the Upper Unnamed Shale Member of the Pierre Shale near Newcastle, Wyoming. Specimens are housed at the University of South Florida Department of Geology. DESCRlPTION: Medium to large, robust, ovate to circular, inequiiateral, equivalve ?, short to moderately long straight hinge line, slightly convex, one geniculation. Ornamentation consists of prominent, broad, circular to subcircular, widely and regularly spaced concentric rugae. Species E (Pl.3, n.13) MATERlAL: 2 specimens collected from the Upper B. baculus ammonite zone within the Upper Unnamed Shale Member of the Pierre Shale near Newcastle, Wyoming. Specimens are housed at the University of South Florida Department of Geology. 90 DESCRIPTION: Medium to large, ovate, inequilateral, equivalve, long straight hinge line, very inflated and extremely convex. Ornamentation consists of sharp, regularly spaced, subcircular concentric rugae that become more widely space later in the individuals ontogeny. Species F (Pl. 3, n. 14) MATERIAL: 62 specimens collected from the Transition and B. grandis ammonite zones within the Upper Unnamed Shale Member of the Pierre Shale near Newcastle, Wyoming. Specimens are housed at the University of South Florida Department of Geology. DESCRIPTION: Small to medium, inequilateral, equivalve, moderately long, straight hinge line, anterior very steep, very inflated and convex. Ornamentation consists of fine, sharp, subcircular, relatively closely spaced concentric rugae. A secondary, less prominent rugae are often found between more robust rugae. REMARKS: Besides having the above morphologic traits, the specimens of this species usually have a distinct, almost plastic appearing, brown nacreous layer present. Species G (Pl. 3, n. 15) MATERIAL: 6 specimens collected from the Transition ammonite zone within the Upper Unnamed Shale Member of the Pierre Shale near Newcastle, Wyoming. Specimens are housed at the University of South Florida Department of Geology. DESCRIPTION: Small to medium, inequilateral, equivalve, moderately long, straight hinge line, anterior steep, moderately inflated and convex. Ornamentation consists of weak, closely spaced, subcircular concentric rugae. Species H (Pl. 4, n. 16) MATERIAL: 43 specimens collected from the Transition and B. grandis ammonite zones within the Upper Unnamed Shale Member of the Pierre Shale near Newcastle, Wyoming. Specimens are housed at the University of South Florida Department of Geology. DESCRIPTION: Medium, inequilateral, equivalve, moderately long straight hinge line, anterior very steep, slightly inflated and convex with one geniculation. Ornamentation consists of sharp, virtually circular, regularly spaced concentric rugae that become more widely separated after the geniculation. 91 REMARKS: This species resembles the "/." subcircularis of the Lower B. baculus ammonite zone but was not classified as such based on it's generally larger size and unique spacing and size of it's rugae. Species I (Pl. 4, n. 17) MATERJAL: 47 specimens collected from the Transition and B. grandis ammonite zones within the Upper Unnamed Shale Member of the Pierre Shale near Newcastle, Wyoming. Specimens are housed at the University of South Florida Department of Geology. DESCRJPTION: Medium to large, inequilateral, equivalve, very long straight hinge line, ovate to subquadrate, moderately inflated and convex. Ornamentation consists of widely, regular spaced, subcircular concentric rugae. Species J (Pl. 4, n. 18) MATERJAL: 7 specimens collected from the B. grandis ammonite zones within the Upper Unnamed Shale Member of the Pierre Shale near Newcastle, Wyoming. Specimens are housed at the University of South Florida Department of Geology. DESCRJPTION: Small to medium, inequilateral, equivalve, moderately long straight hinge line, anterior steep, slightly inflated and slightly convex with one geniculation. Ornamentation consists of weak, closely spaced circular to subcircular concentric rugae. A secondary, less prominent rugae are often found between more robust rugae. 92 ~ ---;- / . •. J,. e.. ~- ~· - -- -~ 1 3 4 5 93 Description of Plate 1. Specimens 1 - 3 "Inoceramus" aff. barabini Morton, 1834, actual size, Glendive, Montana. Specimen 4 "Inoceramus "incurvus Morton, 1834, X 0.8, Newcastle, Wyoming. Specimen 5 "Inoceramus" aff. vanuxemi Meek and Hayden, 1860, actual size, Newcastle, Wyoming. 94 6 7 / / -L( ~ '>. ./ -1''. • ' r; ' . ' 8 9 10 95 Description of Plate 2. Specimens 6, 7 "Inoceramus" subcircularis Meek, 1860, actual size, Glendive, Montana. Specimen 8 Trochoceramus sp., X 0.9, Newcastle, Wyoming. Specimen 9 Species A, X 0.7, Newcastle, Wyoming. Specimen 10 Species B, X 0.75 , Newcastle, Wyoming. 96 11 12 13 14 15 97 Description of Plate 3. Specimen 11 Species C, X 1.5, Newcastle Wyoming. Specimen 12 Species D, actual size, Newcastle, Wyoming. Specimen 13 Species E, X 0.8, Newcastle, Wyoming. Specimen 14 Species F, X 0.8, Newcastle, Wyoming. Specimen 15 Species G, X .9, Newcastle, Wyoming. 98 16 17 18 99 Description of Plate 4. Specimen 16 Species H, X 0.925, Newcastle, Wyoming. Specimen 17 Species I, X 0.8, Newcastle, Wyoming. Specimen 18 Species J, X 0.8, . Newcastle, Wyoming. 100