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MIDDLE-UPPER CAMBRIAN TRILOBITE BIO STRATIGRAPHY OF SLOPE DEPOSITS, PAIBI, WESTERN HUNAN PROVINCE, CHINA
DISSERTATION
Presented in Partial Fulfillment of the Requirements for
the Degree Doctor of Philosophy
in the Graduate School of The Ohio State University
By
Gregory J. Wasserman
*****
The Ohio State University 1999
Dissertation Committee: Approved by Dr. Loren E. Babcock
Dr. William I. Ausich Adviser Dr. Lawrence A. Krissek Department of Geological Sciences
Dr. Douglas E. Pride X3MI N um b er: 9931696
UMI Microform 9931696 Copyright 1999, by UMI Company. All rights reserved.
This microform edition is protected against unauthorized copying under Title 17, United States Code.
UMI 300 North Zeeb Road Ann Arbor, MI 48103 ABSTRACT
A stratigraphie section through limestones and siliciclastic mudrocks near the village
o f Paibi, western Hunan Province, China, is under consideration as the international
stratotype for the Middle-Upper Cambrian boundary. This dissertation involves detailed
study of the biostratigraphy of non-agnostoid trilobites from the Paibi section, and
interpretation of biostratigraphic patterns.
The position of Middle-Upper Cambrian boundary is currently undecided, but is likely
to be placed at the first appearance worldwide of the agnostoid trilobite Glyptagnostus
reticulatus. In North America, the base of the Glyptagnostus reticulatus Interval-zone
corresponds to the base of the Pterochepaliid Biomere.
A biomere is a stratigraphie interval whose base is identified by an evolutionary
radiation and whose top is marked by a mass extinction event. Biomeres are assumed to have worldwide significance (although they are best studied in North America), and the bases of biomeres are assumed to represent post-extinction recoveries. The Paibi section,
China, records one of the most complete successions of Middle-Upper Cambrian strata known anywhere in the world. The section represents a slope environment adjacent to the Yangtze (South China) Platform. Because of its completeness, and its paleogeographic position, it offers an excellent opportunity to test for biomere patterns outside Laurentia (ancestral North America-Greenland), and in a shelf-margin environment. The characteristic “biomere” pattern of relatively slow evolutionary diversification followed by rapid mass extinction is not evident in the Piabi section. One possibility for this is that a rise in sea level or a rise in a thermocline and inundation of the shelf with cold or dysoxic water would have pronounced effects in a shelf environment but little effect in a slope environment. A more likely possibility involves downslope movement and resedimentation of trilobite sclerites through gravity displacement on the slope. Many species’ apparent ranges would have extended beyond their true ranges, effectively obscuring any sharp biostratigraphic boundary that may have existed and that may have been retained, in shallow, nearly horizontal, shelf strata.
Ill ACKNOWLEDGMENTS
Many people have helped or encouraged me in my Ph.D. work. I would like to thank my adviser, Dr. Loren E. Babcock, for taking a chance on me and allowing me to follow a dream I have always had. Without his help, encouragement, and support, I would not have finished. I cannot put into words how much I learned and grew both as a person and a scientist under him.
I would also like to thank my committee members, Drs. William I. Ausich, Lawrence
A. Krissek, and Douglas E. Pride. Their doors were always open to talk about my project and they always were willing to listen while I bounced ideas off of them.
Dr. Stephen Jacobson offered me not only a tremendous amount of encouragement, but he also helped me to organize my work load. He critiqued some of my earlier drafts and offered advice on writing style.
This project was funded in part by National Science Foundation grants to Richard A.
Robison (subcontract to Loren E. Babcock) and Margaret N. Rees. Additional funds in support of this work came from the China National Natural Science Foundation (awarded to Shanchi Peng and Wentang Zhang), and a Seed Grant from The Ohio State University
(awarded to Loren E. Babcock); and National Science Foundation grant EAR-9405990
(awarded to Loren E. Babcock).
IV Samples used in this study were collected by Loren E. Babcock, Margaret N. Rees,
Richard A. Robison, Shanchi Peng, Wenteng Zhang, Kunli Luo, and H. L. Lin.
I am indebted to Dr. Shanchi Peng. I was fortunate enough to work closely with him
for several months. He brought numerous rare publications to my attention and a wealth
of knowledge of trilobites from my study area.
Dr. Allison R. “Pete” Palmer was always willing to answer any questions I have had about biomeres, and provided much information by e-mail.
I would also like to thank James St. John. He was always willing to loan publications to me and to lend an ear to any ideas I may have had. We had long discussions on trilobites and paleontology in general, talks in which I learned a tremendous amount of information.
I need to mention my best friends, Jeff Rudnicki and Steve Macy, two individuals who provided encouragement when I needed it.
Finally, I must thank my parents, Jim and Connie Wasserman, and grandparents,
Leonard and Rita Matuszak, for their financial and emotional support, without which I could not have finished this work. VITA
May 16, 1967 ...... Bom -Toledo, Ohio
1990...... B.S., Geology, Bowling Green State University
1990-1992...... Graduate Teaching Assistant Michigan State University
1994...... M.S., Geology, Michigan State University
1993-1997...... Graduate Teaching and Research Assistant The Ohio State University
FIELDS OF STUDY
Major Field: Geological Sciences
VI TABLE OF CONTENTS
Page Abstract ...... ii
Acknowledgements ...... iv
Vita...... vi
List of Figures...... ix
List of Figures...... x
Chapters:
1. Introduction...... I
2. Study Area ...... 9
3. Regional Geologic Setting...... 10
Tectonic Blocks in China...... 10 Paleogeographic-Lithofacies Belts in South China...... 11 Relationship Between Paleogeographic-Lithofacies Belts and Trilobite Biogeography...... 13 Sea Level Trends ...... 14
4. Stratigraphy and Sedimentology...... 19
Lithostratigraphy and Sedimentology of the Paibi Section...... 19 Biostratigraphy...... 21 Depositional Environments...... 23 Modes of Occurrence of Trilobites in the Paibi Section...... 24
5. Trilobite Biogeography and Bio faces...... 28
6. History of Biomere Research...... 31
Definitionand Characterization of Biomeres...... 31 Proposed Causes of End-Biomere Extinctions...... 34
vii 7. Materials and Methods ...... 44
8. Test for Biomere Boundaries...... 46
Patterns within North American Biomeres...... 46 Patterns within the Paibi Section...... 47 Source of Trilobites...... 55 Effects of Resedimented Trilobites in Slope Environments...... 56
9. Suitability of the Paibi Section as a Global Stratotype for the Middle Cambrian-Upper Cambrian Boundary ...... 59
10. Systematic Paleontology...... 61
11. Conclusions...... 154
References...... 157
VIII LIST OF TABLES
Table Page
I. Comparison of extinction levels observed in the Paibi section and published data on Laurentian biomeres ......
IX LIST OF FIGURES
Figure Page
1. Map of western Hunan and adjacent areas showing the apporximate distribution of lithofacies belts...... 6
2. Stratigraphie ranges of non-agnostoid trilobites in collections from the Paibi section, Hunan Province, China...... 8
3. Map showing major tectonic blocks of China (generalized) indicating the relationships of the South China Block (Hunan Block) and other tectionic blocks ...... 15
4. Map of reconstructed Upper Camibrian paleogeography...... 16
5. Generalized diagram showing the relationships of trilobite assemblage- zones recognized in North America to differing interpretation of the positions of the four development stages of the Pterocehpaliid and Ptychaspid biomeres ...... 17
6. Chart showing the provisional biostratigraphic correlation of Laurentia, Australia, North China, Kazakhstan, and Baltica, and the relationships of established zonation and stage boundaries (far left column) as recognized in North America...... 18
7. Proposed mechanism of extinction where a rising thermocline inundates the shelf with cooler or less oxygenated water...... 40
9. Schematic diagram showing pattern of trilobite evolution and extinction within a biomere, compared with species ranges...... 41
9. Schematic diagram showing the distributica of biofacies and lithofacies across Laurentia during the Sun wap tan Stage ...... 42
10. Schematic diagram showing expected pattern of trilobite ranges on the shelf (left) and in slope or rise environments where downslope resedimentation of trilobites has occurred (right) in relationship to
X biomere boundaries (extinction events) ...... 43
11. Trilobites from Order Asaphida ...... 137
12. Trilobites from Order Corynexochida, Part 1...... 139
13. Trilobites from Order Corynexochida, Part II...... 141
14. Trilobites from Order Lichida ...... 143
15. Trilobites from Order Ptychopariida, Part 1 ...... 145
16. Trilobites from Order Ptychopariida, Part II ...... 147
17. Trilobites from Order Ptychopariida, Part III...... 149
18. Trilobites from Order Ptychopariida, Part IV...... 151
19. Trilobites of uncertain affinities...... 153
XI CHAPTER 1
INTRODUCTION
One fruitful topic of discussion in paleontology over the past two decades has been mass extinctions. Much of this interest was spurred by research on the end-Cretaceous event, which marked the demise of non-avian dinosaurs and other organisms and, more specifically, the hypothesis that a large bolide struck Earth and triggered extinctions
(Alvarez et al., 1980). While it is still argued whether or not such an event could trigger a mass extinction, the concept has stimulated research not only on the end-Cretaceous event, but on the larger record of pre-Holocene extinctions.
A mass extinction can be defined as a rapid decline in biologic diversity on a global scale over a short geologic interval. The Phanerozoic Eon is punctuated by at least five major mass extinctions: the end of the Ordovician, the Devonian Frasnian-Famennian boundary, the end of the Permian, the end of the Triassic, and the end of the Cretaceous
(Sepkoski, 1986). These events resulted in dramatic declines in the diversity of preserved fauna worldwide, and by implication, they also significantly altered contemporary biospheric composition. Other less significant mass extinctions (in terms of numbers or percentages of preserved taxa) occurred throughout the Phanerozoic. Among these less significant events were a series of declines in species richness that occurred during the
1 Cambrian Period. The evidence of these Cambrian extinctions is in the form of declines in shelly fossils such as trilobites, brachiopods, and paraconodonts. When viewed in strict numerical terms, such extinctions have the appearance of being relatively less significant than the Ordovician, Devonian, Permian, Triassic, and Cretaceous events.
However, if viewed in the larger framework of the historical development of life on
Earth, these events certainly could have played a substantial role in determining the composition of the post-Cambrian biosphere. Such extinctions early on the adaptive radiation of marine metazoans may have pruned evolutionary trees and helped to canalize evolutionary pathways at an early point in the Phanerozoic (Gould, 1989; but see
Conway-Morris, 1998). Thus it could be argued that the importance of Cambrian extinctions has been underestimated. Sepkoski (1981) noted a significant difference between the Cambrian faunas and later Phanerozoic biotas, differences that may be due partly to extinction events.
Mass extinctions during the Cambrian have been used to mark boundaries between evolutionary-extinction intervals known as biomeres (Palmer, 1965a). A biomere, as defined by Palmer (1965a), is a “regional biostratigraphic unit bounded by abrupt non-evolutionary changes in the dominant elements of a single phylum.” Palmer
(1965a) applied this term to turnovers in trilobite assemblages in North America.
However, faunal turnovers similar to those recorded in Laurentia (the ancestral North
America-Greenland continent) among trilobites, and among other organisms, seem to be present elsewhere in the world. In Australia, the Mindyallan-ldamean stage boundary is marked by an extinction event that correlates to the top of the Pterocephaliid Biomere of
North America (Opik, 1966; Henderson, 1976). A faunal turnover first reported by Walcott (1913, 1914) on the North China Platform also may coincide with the base of the
Glyptagnostus reticulatus Zone, which closely corresponds to the top of the
Pterocephaliid Biomere (Opik, 1976). Evidence has been gathered suggesting that the extinctions recognized among trilobites from Laurentia can be recognized from a variety of paleotectonic blocks (Taylor and Cook, 1990; Westrop, 1992; Table 1). Likewise, such evidence has been documented for brachiopods (Rowell and Brady, 1976) and paraconodonts (Miller, 1975, 1984. It is thus inferred that the extinctions were global in effect.
Mitigating against the notion that end-biomere extinctions during the Cambrian were global in effect is evidence from slope environments of Laurentia (Pratt, 1992; Westrop,
1995), where clear evidence of end-biomere extinctions has yet to be identified. The reason for the disparity in pattern between shelf lithofacies (where coinciding truncations of species ranges are present) and slope environments (where random truncations of species ranges are present) of the same paleotectonic block has yet to be clearly articulated. Using finely resolved biostratigraphic information, discussed in this dissertation, coupled with sedimentological evidence for the downslope transportation of shelly fossils, it is now possible to understand better this interesting paradox.
The purpose of this work is to provide documentation of biostratigraphic patterns across an inferred biomere boundary in an exceptionally complete stratigraphie section in
South China. The section, which is located near the village of Paibi, in western Hunan
Province, China (Figures 1, 2), is under consideration as a possible global stratotype for the Middle-Upper Cambrian boundary. In addition to having an unusually complete stratigraphie record through the Middle and Upper Cambrian, the section is also unusually rich in fossils, particularly trilobites. The section is in a key area paleogeographically: located midway between a low-latitude shelf (the Yangtze
Platform) and its adjacent slope and basin (the Jiangnan region), the section affords an opportunity to biostratigraphically tie end-biomere-type events recorded on the shelf with the record preserved in the slope-to-basin region. The section also offers an opportunity to further examine whether biomeres can be easily recognized outside of North America, and to examine the suitability of the Paibi section as the global stratotype for the Middle-
Upper Cambrian boundary. This work is related to work in progress by R. A. Robison
(University of Kansas) and Shanchi Peng (Nanjing Institute of Geology and
Palaeontology, Academics Sinica) on the agnostoid trilobites from the Paibi, China, section and to work in progress by Margaret N. Rees (University of Nevada, Las Vegas) on the sedimentology of the Paibi section. Taxonomic Level Family Genus Species Interval
PIB 115.6 0 29% 38% (2 of 7) (3 of 8)
PIE 282.75- 0 17% 38% 283.75 (2 of 12) (5 of 13)
36% 0 20% PIB 346.7 (2 of 10) (4 of 11)
PIB 361.5- 44% 0 50% 362.4 (4 of 8) (4 of 9)
Levels of Westrop and Longacre, 1970 extinction at Ludvigson, 1987 75% biomere 42% N/A boundaries (10 of 24) (15 of 20)
Table IrComparison of extinction levels observed in the Paibi section and published data of Laurentian biomeres. HUBEI \ O Hefeng CHINA O Xianfeng p o n Parjtazui Wa’argang^ V ) SICHUAN / O Baojing OHuaqtao Wangchun A Paibi O □ Jisbou Anhua GUIZHOU ^ Fenghuang / O HUNAN □ Huaihua
OYuoing
Provincial boundary □ O City and vülaga A Study area
Figure IrMap of western Hunan and adjacent areas showing the approximate distribution of lithofacies belts. Diagram is modified from Song (1989). Figure 2:Stratigraphic ranges of non-agnostoid trilobites in collections from the Paibi section, Hunan Province, China.
Positions of agnostoid zones are based on unpublished work by S. G. Peng and R. A. Robison. Position of the Middle-Upper Cambrian boundary is provisional, and subject to formal approval by the International Subcommission on the Cambrian System of the base of the Glyptagnostus reticulatus Zone as the base of the Upper Cambrian. Glyptagnostus reticulatus Zone Glyptagnostus stolidotus Z o n ^ *ci Uilii I I Linguagnostus reconditus Zone D
cE
Lejopyge laevigata Zone
I Goniagnostus nathorsti Zone -a
Ptychagnostiis punctiiosus Zone
!l Ptychagnostus atavus Zone
4 lt Silty Limestone •n Dolomite LEGEND Lenticular Carbonate ï t ô t ô ‘ Limestone Breccia
Figure 2 CHAPTER 2
STUDY AREA
The study area, a long section of moderately dipping strata near the village of Paibi, is located in northwestern Hunan Province, China (Figure 1). Strata are exposed through a series of active quarries along the road leading to Paibi, and in adjacent hillsides.
Paibi is one of several locations in western Hunan exposing a long section of Upper
Cambrian rocks. Detailed description of the Paibi section was chosen because, at the time of sampling, 1992, it appeared to be the most complete and the structurally least complicated section from Middle Cambrian to Upper Cambrian slope lithofacies in southern China. Additional work completed since 1992 reinforces that initial interpretation. CHAPTER 3
REGIONAL GEOLOGIC SETTING
Tectonic Blocks in China
Cambrian rocks from western Hunan represent part of the lower Paleozoic succession of the South China tectonic block. Present-day China is an amalgamation of at least seven tectonic blocks (Figure 3). During the Cambrian, major, separate blocks included the South China block (also known as the Hunan block), the North China block (also known as the Sino-Korean block), the Tarim block (western China), and the Lhasa block
(the region including Tibet). Paleogeographic positions of the blocks are not well determined, except in general terms. The South China block, which is replete with carbonate deposits, was probably located in or near the tropics during the Cambrian, similar to the position of Laurentia (Scotese and McKerrow, 1990, Yang, 1994). Scotese and McKerrow (1990) and Scotese and Denham (1988) placed the South China block approximately 30° south of the equator (Figure 5), whereas Yang (1994) placed the block
30° north of the equator. Scotese and McKerrow (1990) illustrated the North China block and the Tarim block as a single block during the Cambrian, whereas Yang (1994) depicted them as separate blocks. In both reconstructions (Scotese and McKerrow, 1990;
10 Yang, 1994), the South China, North China, and Tarim blocks were situated close to
Australia, an interpretation reinforced by faunal similarities (Jell, 1974). In the SWEAT model of Paleozoic paleogeography (Dalziel, 1992) and modifications of it (e.g., Grunow et al., 1994; Dalziel, 1997), the position of the South China block has been left undetermined.
Paleogeographic-Lithofacies Belts in South China
Middle and Upper Cambrian stratigraphie sections in western Hunan contain rocks representing three major paleogeographic-lithofacies belts: the Yangtze (South China)
Platform, the Jiangnan Region, and the Transitional Region (Figures 1). These rocks formed across a broad paleogeographic area, representing a shelf-to-basin setting.
However, individual sections typically represent only one lithofacies belt. By examining sections distributed from eastern Guizhou to northwestern Hunan, the paleogeographic pattern is more evident. Today, the three belts lie relatively close to each other as a result of compressional tectonics, so original width of the basin cannot be easily estimated, but it must have been in the range of hundreds of kilometers wide.
The Yangtze Platform occupies approximately the northwestern half of the South
China block. Rocks from the Yangtze Platform consist mainly o f carbonates and fine grained siliciclastics deposited on a marine continental shelf (Lu et al., 1974; Chang,
1980; Peng, 1992, Yang, 1994; Babcock and Zhang, 1997). Because of the abundance of dolostone and the presence of salt casts and gypsum, particularly in Lower Cambrian rocks (Yang, 1994), the climatic regime of the Yangtze Platform during the Cambrian has
11 been interpreted as having been warm and arid; the platform was hypersaline in places.
Fossils present in these shelf environments comprise a variety of shallow-shelf-dwelling trilobites (principally endemic polymeroids), brachiopods, and other shallow shelf taxa.
The Jiangnan Region, or Jiangnan Basin (Peng, 1992), is located in the southeastern part of the South China block. Rocks from the Jiangnan Region are principally dark- colored, thin-bedded mudrocks and are interpreted to have been deposited in slope to basinal environments (Peng, 1992; also compare Cook and Taylor, 1975). Turbidites are present in places. Inferred deep water organisms, such as pelagic agnostoid trilobites, comprise most of the biota except those remains judged to have been transported into this environment by turbidity currents.
Samples for this study were collected from the Transitional Region, or the Jiangnan
Slope Belt (Peng, 1992), in Hunan Province (Figure 1). The Jiangnan Slope Belt occupies a narrow strip between the Yangtze Platform and the Jiangnan Basin. The rocks have been interpreted to represent either deep-shelf to toe-of-slope environments intermediate between the Yangtze Platform and the Jiangnan Region (Yang, 1978, 1981;
Zhou et al., 1979; Song, 1989) or outer slope apron deposits (Rees et al., 1992). During times of sea level lowstands (such as the Early Cambrian), light-colored carbonate platform deposits were deposited, but during times of marine flooding or sea level highstand (such as much of the Middle and Upper Cambrian), dark-colored, deeper water carbonates, thin shale beds, and turbidites were deposited. Inferred short-term sea level falls are recorded by the deposition of breccias in the Jiangnan Slope Belt (Transitional
Region). Trilobites in the Transitional Region comprise autochthonous open-ocean species (mostly agnostoids) preserved in lime mudstones, and a mix of allochthonous or
12 parautochthonous shelf taxa and autochthonous open ocean agnostoids preserved in packstone beds (turbidites).
Relationship Between Paleogeographic-Lithofacies Belts and Trilobite Biogeography
Polymeroid trilobite assemblages from China have been grouped into two major faunal provinces, the North China Province and the South China Province (or Southeast
China Province; Yang, 1994; Peng, 1992; Lu et al., 1974). The North China trilobite fauna consists largely of shallow platform-dwelling taxa. The South China trilobite fauna consists of a mix of platform- and deeper-water dwelling taxa.
Yang (1994) subdivided the South China trilobite fauna into three biomes based on inferred paleoecologic factors. The positions of these biomes mirrors the positions of the major paleogeographic-lithofacies belts (Yangtze, Transitional, and Jiangnan belts). The
Yangtze biome, which occupied the Yangtze Platform, was interpreted to be a benthic community from an epicontinental sea. The Basinal biome, which occupied the lower slope, rise, and basin, consisted of inferred pelagic trilobites. The Platform Margin biome, which occupied the region between the other two biomes, was interpreted as a
“transitional” community, having a mixture of both benthic and planktonic trilobites.
This assemblage was the most diverse, and contained the greatest abundance of fossils.
Yang (1994) reasoned that the diversity was due to the presence of a more “advantageous environment” when compared to the other two settings. However, as explained later in this dissertation, many trilobite sclerites deposited in the Transitional Region have been transported from shallower water and mixed with those from deeper water, so the
13 apparent increase in diversity and abundance in the Transitional Region does not reflect original community composition and stmcture for that environment.
Sea Level Trends
During the Middle and Late Cambrian, sea level in South China was interpreted as having undergone a relative lowering, a trend that began during the Middle Cambrian and continued through the Early Ordovician (Peng, 1992). This interpretation was based on the increasing presence and thickness of allochthonous limestone breccias upsection in
Hunan (Peng, 1992). However, more recent work (Rees et al., 1992) indicates that the sea level history of the South China Platform is more complex. Using facies analysis and sequence stratigraphy, Rees et al. (1992) suggested that rocks from the Huaqiao
Formation (see discussion in Chapter 4) record three fairly relatively rapid sea-level rises followed by relatively slower sea level falls. The largest marine flooding events are recorded near the bases of the Ptychagnostus punctuosus, Lejopyge laevigata, and
Glyptagnostus reticidatus zones. These events are marked by dark lime mudstones showing increases in the abundance of agnostoid trilobites; turbidite beds containing polymeroid trilobites or breccia beds occur upsection from the inferred deepest point in each of the parasequences.
14 TARIM BLOCK
SINO-KOREAN BLOCK
HUNAN BLOCK
1000 KM
YANGTZE PLATFORM
Figure 3: Map showing major tectonic blocks of China (generalized) indicating the relationships of the South China Block (Hunan Block) to other tectonic regions; major lithofacies belts on the South China block are also indicated. Map modified from an unpublished diagram from S. A. Peng.
15 LAURENTIA
SOUTH CHINA
Figure 4: Map of reconstructed Upper Cambrian paleogeography (from Scotese and Denham, 1988).
Outlines of present-day geographic areas are included for reference. In this paleogeographic reconstuction, South China (including the Yangtze Platform) is hypothesized to have been located apporoximately 30°S latitude. In some other reconstuctions (for example, Yang, 1994), South China is hypothesized to have been located apporximately 30°N latitude, but in still other reconstuctions (e.g., Grunow et al., 1994; Dalziel, 1997), the postion is not addressed.
16 NORTH AMERICAN STITT PALMER TRILOBITE ASSEMBLAGE-ZONES (1971, 1975) (1979)
MISSISQUOIA ZONE Eurekia apopsis Subzone Slags 4_____
SAUKIA ZONE Stage 3 Stage 4
ELLIPSOCEPHALOIDES PTYCHASPID PTYCHASPID ZONE Stage 2 Stage 3 BIOMERE BIOMERE SARATOGIA ZONE
TAENICEPHALUS Stage 1 Stage 2 ZONE Irvingella inqjoi^S\^zone_ Stage_4 _____ Stase 1
ELVINIA ZONE
Stage 3 Stage 4 DUNDERBERGIA PTEROCEPHALIID PTEROCEPHALIID ZONE BIOMERE BIOMERE
PREHOUSIA ZONE Stage 2 Stage 3 DICANTHOPYGE ZONE
APHELASPIS ZONE Stage I Stage 2 Coosella perplexa Subzone Stase I CREPICEPHALUS MARJUMED MARJUMtlD ZONE BIOMERE BIOMERE
Figure 5: Generalized diagram showing the relationships of trilobite assemblage-zones recognized in North America to differing interpretations (Stitt, 1971, 1975; Palmer, 1977) of the positions of the four developmental stages of the Pterocephaliid and Ptychaspid biomeres (modified from Palmer, 1984).
17 LAURENTIA AUSTRALIA NORTH CHINA KAZAKHSTAN BALTICA Missisquoia . Rhabdinopora Missisquoia Cordylodus proavus perpeus Paracerasopyge / 3 I nabelliforme Mictodaukia Microsaukia orierualis Euloma perplexa Acerocare Chaneia Eurekia apopsis Micragnostus quasibilobus / nomas Sinoeremoceras scarabaeoides Ouadraticephalus mutabilis Sinosaukta impayés Peltura minor Ptycbaspis / Tsmania Saukiella m axim us / papilio trisulcus praecursor hifnr / dennculattix ^rolatus^J^^eciath^^ scrobicularis patttlus / squamosa ElUpsocephaloides Kaolisliania Leptoplastus renia/guana auadrariformis II nvaliformis Taenicephalus secunda /glabella kazachstanicus pseudanvustilobus Parabolina. , iota / apsis spmulosa Elvinia Changsltania ivshini Irvingella tropica cunare scantcus / aneelm, Stiemaloa diloma dentatus~ Dunderbergia Ervcanium sentiim longiformis Olenus atjÉÜBBM. Prehousia Proceratopvge . Chuangia wahlenbergi ii Uicantftopyf*e cryptica Glyptagnostus Glyptagnostus Aphelaspis reticulatus reticulatus gibbosus Glyptagnostus Glyptagnostus Crepicepfialus Drepanura stolidotus stolidotus Agnostus pisiformis guasivespa Cedaria Blackwelderia simplex Damesella L laevigata & laevigata L laevigata L laevigata Taitzuia L armata S.brachymetopa p. Amphoton lundgreni / nathorsti noialibrae nathorsti II< punctuosus 5 — Crepicephalina Z Bolaspi- P. puncniosus P. punctuosus P. punctuosus optim us Uoparia ______della P. ataus P. atavus P, atavus Bailiella P. intermedius P. gibbus P. gibbus p. gibbus Poriagranulos uttimus II Sunaspis pinus praecurrens ii longingua
Figure 6: Chart showing provisional biostratigraphic correlation of Laurentia, Australia, North China, Kazakhstan, and Baltica, and the relationships of established zonation and stage boundaries to biomeres (far left column) as recognized in North America. The base of the Pterocephaliid biomere, within present biostratigraphic resolution, corresponds to the base of the Glyptognostus reticulatus Zone or equivalents.
18 CHAPTER 4
STRATIGRAPHY AND SEDIMENTOLOGY
Lithostratigraph V and Sedimentology of the Paibi Section
The Paibi section consists of about 390 meters of Middle and Upper Cambrian rocks belonging to the Huaqaio Formation (Figure 2) as revised by Peng and Robison (in review). Strata exposed through a series of roadside quarries and adjacent hillsides are moderately dipping (30 to 45 degrees), and as far as can be determined, are unfaulted except at a large valley marking the top of the section. Strata near Paibi include presumed light-colored Lower Cambrian dolostones overlain by predominantly dark- colored, thinly laminated Middle Cambrian to Lower Ordovician limestones. That part of the section that forms the basis of this work extends from the base of the exposed Middle
Cambrian (correlated with the Ptychagnostus atavus Zone) to the Upper Cambrian
(correlated with the Glyptagfxostus reticulatus Zone). Disconformities have not been identified in the Paibi section, although the bases of some carbonate packstones
(interpreted as turbidites) and breccia beds are erosional.
19 Formerly, two formations, the Huaqaio and the Chefli, were mapped at Paibi (e.g..
Song, 1989; Dong, 1991, and references therein). The Huaqaio Formation at Paibi overlies a dolostone unit of presumed Lower Cambrian position. The former Huaqaio
Formation-Chefu Formation contact, at about 290 meters in the measured section, is transitional and defined biostratigraphically (which is customary in this region) rather than lithostratigraphically (which is customary in North America). The base of the Chefu
Formation (as used previously) was located at the base of the Glyptagnostus reticulatus-
Chiiangia wulingensis Zone (an assemblage-zone).
The Paibi section is truncated at a deep valley, which is presumed to follow a fault line. Additional Upper Cambrian-Lower Ordovician strata continue beyond the valley, but the zonal indicators are displaced relative to the main section at Paibi. The fault is probably a thrust fault, which would be in accord with the compressional tectonic features that pervade the stratigraphy of northwestern Hunan. The amount of displacement along the inferred fault is unknown.
Lithologies present in the Paibi section include carbonates and minor terrigenous clay or siltstone interbeds. Carbonate lithofacies are dominated by dark gray to black, thinly laminated, virtually unbioturbated, lime mudstones that are weakly fossiliferous.
Agnostoid trilobites, which are commonly articulated, are the dominant macro fossils, although they tend to be uncommon, and diligent work is required to find specimens.
Numerous thin, medium to dark gray packstone lenses, grading laterally to wackestone lenses, occur sporadically through the lime mudstone beds. These lenses, which have thicknesses up to about 10 centimenters, and extend laterally on outcrop for at least a few tens of meters, are interpreted as Tc beds of carbonate turbidites (Boggs, 1987). Bases of
20 the packstone lenses are slightly erosional (on a millimeter scale), and the allochems contained in the packstones are commonly size-sorted. Allochems in the packstone
lenses include a mixture of disarticulated agnostoid and polymeroid trilobites. Carbonate breccia beds occur with increasing frequency toward the top of the section. The breccia beds have thicknesses up to four meters and are variously spaced; they extend laterally
for tens to hundreds of meters. Angular to subrounded clasts in the breccia beds include carbonate lithologies preserved in place at Paibi (such as reworked light-colored Lower
Cambrian dolostones similar to those preserved in place 200 m or lower in section), as well as more light-colored, carbonate lithologies that were probably reworked from shelf- margin sites, transported downslope, and resedimented.
Biostratigraphv
Correlation of the Paibi, China, section with sections elsewhere in the world is based principally on biostratigraphy of agnostoid trilobites (e.g., Robison, 1982, 1984, 1988,
1994; Peng and Robison, in review). Cosmopolitan agnostoids, many of which have relatively short stratigraphie ranges, provide for fine-scale biostratigraphic resolution through much of the Middle and Upper Cambrian. Over the last two decades, Robison
(1982, 1984, 1988, 1994) has been active in providing finely resolved biostratigraphic resolution of the Middle and Upper Cambrian in Laurentia, and elsewhere. That precision has been achieved in large part through application of the concept of interval- zones to strata. Interval-zones use the first appearances of stratigraphically significant species (preferably ones that are phyletically closely related), rather than using
21 assemblages of species (assemblage-zones), full ranges of species (range-zones), etc.
Most of the localities from which Robison was able to establish interval-zonation have been in open-shelf environments of Laurentia.
Despite its utility in shelf settings globally, application of the interval-zone concept to the Paibi section has proved to be inappropriate (Peng and Robison, in review) because of reworking and vertical mixing of agnostoid faunas (resulting in apparent upward range extensions), and because of the inability to always find eponymous zonal guide fossils, as opposed to just finding species that help to characterize zones. Of these two problems, the more significant is upward mixing of agnostoid sclerites because of the impact it has on the characterization of a zone using contained species. Specimens of most species occur where their first appearances would be expected based on global patterns (Robison,
1982, 1984, 1988, 1994), but specimens of some species continue to occur upsection from their expected last appearances based on global patterns. Although reworking of deposits during relative lowstands of sea level and subsequent redeposition of durable trilobite sclerites (reciprocal sedimentation) is the norm in slope settings (e.g., Wilson,
1954, 1967, 1975; Cook and Taylor, 1975, 1977; Taylor, 1976, 1977; Taylor and Cook,
1976; Babcock, 1998; Peng, 1998), this situation complicates biostratigraphic subdivision and correlation. Peng and Robison (in review), in subdividing the Paibi section, have applied zonal usage that is slightly modified from the inter\^al-zone concept. First appearances of stratigraphically useful species form the bases of zones, but because of unusual vertical range extensions of some species, last appearance information is not used in any way. Eponymous zonal guide fossils are not necessarily closely related
99 species. Zones are recognized not just by the presence of eponymous species, but also by an assemblage of characterizing species.
In the Paibi, China, section, the Huaqaio Formation consists of approximately 390 meters of strata. Using modified zonation based on first appearances of agnostoid species
(Peng and Robison, in review), the strata are inclusive from the upper Middle Cambrian
Ptychagnostus atavus Zone to the lower Upper CambrianGlyptagnostus reticulatus Zone
(Figure 2). Zones identified from the Paibi section are, in ascending order, the
Ptychagnostus atavus, Ptychagnostus gibbus, Goniagnostus nathorsti, Lejopyge laevigata, Proagttostus bulbous, Linguagfwstus reconditus, Glyptagnostus stolidotus, and
Glyptagnostus reticidatus zones (Peng and Robison, in review; Figure 2). The stratigraphie succession appears to be complete; that is, all expected agnostoid zones within that range are present, the thicknesses of strata assigned to each zone do not differ from the expected thicknesses based on equivalent strata globally, and significant disconformities and faults have not been discovered despite diligent searching by numerous geologists. In short, the Paibi section appears to be the most complete Middle
Cambrian to Upper Cambrian section known anywhere on Earth.
Depositional Environments
Three major marine environments have been recognized from lithofacies and biofacies in eastern northwestern Hunan Province and adjacent areas of eastern Guizhou Province,
China. From northwest to southeast (present coordinates), those environments are the
Yangtze Region (also known as the Yangtze Platform or South China Platform), a
23 shallow carbonate platform; the Transitional Region, comprising the shelf break, slope, and toe-of-slope or rise; and the Jiangnan Region, the ocean basin (Peng, 1992; Yang,
1994; Figure 1). These three environments correspond to the three paleogeographic- lithostratigraphic belts (the Yangtze, Transitional, and Jiangnan belts) described above.
The position of the Paibi section, during the Middle to Late Cambrian, was in the
Transitional Region (slope and toe-of-slope environments). Middle and Upper Cambrian shelf carbonates (principally light-colored dolostones) of the Yangtze Platform occur to the west and northwest of Paibi, and basinal deposits (principally dark-colored thinly laminated lime mudstones lacking trilobite-rich turbidites and breccia beds) occur to the southeast. Because of compressional tectonics in the region, original geographic distances across these regions are difficult to estimate with precision, but the width across the shelf, slope, and toe-of-slope environments must have exceeded 400 km. Water depth change over this distance is unknown.
Modes of Occurrence o f Trilobites in the Paibi Section
A bimodal distribution of trilobite sclerites is present in the Huaqaio Formation at
Paibi, China. Background sediments, the dark gray, thin-bedded lime mudstones, contain uncommon to rare agnostoid trilobites. Where present, they are often articulated and extended flat on bedding planes. Polymeroid trilobites are quite rare in thin-bedded lime mudstones. Trilobite taxa present in lime mudstone layers tend to be geographically widespread (most are cosmopolitan agnostoids) and are inferred to represent pelagic
24 species that lived in relatively deep, offshore environments that were oxygen-deficient or below a thermocline (e.g., Robison, 1988; Peng, 1992; Babcock, 1994a, 1998).
The other mode of occurrence of trilobite remains in the Paibi section is in thin (I- to
10-cm-thick) medium to dark gray packstone to wackestone lenses (inferred carbonate turbidites) that extend laterally over meters to decameters. The turbidites are tightly packed with disarticulated sclerites of polymeroids and agnostoids. Most polymeroid species are endemic to South China or occur both in North China and South China. They represent a mix of species from platform and slope environments (Yang, 1994; Zhang and Jell, 1987). Sclerites are generally randomly oriented relative to bedding, size- sorted, and to a certain extent, species-sorted or sclerite-type-sorted (see Figures 13.8,
15.2, 17.10, 18.13, 18.20). Occasionally sclerites appear to be current-aligned. Whereas the agnostoid trilobites preserved in the packstones are considered to have been pelagic inhabitants of slope and open-ocean environments, most of the polymeroid trilobites
(particularly representatives of the families Lisaniidae, Diceratocephalidae,
Anomocarellidae, Dorypygidae, Rhyssometopidae, and Catillicephalidae) were principally adapted to warm, well-oxygenated shelf environments (e.g.. Jell, 1974; Lu et al., 1974; Zhang and Jell, 1980; Peng, 1992; Yang, 1994); their disarticulated sclerites were evidently transported to deeper water (Peng, 1992) by sediment-gravity flows(resedimentation) in a shelf-margin setting (Figure 6). Resedimentation of sclerites can cause both a mixing of biofacies representatives and an upward stratigraphie mixing of sclerites (Wilson, 1975; Babcock, 1994a, 1998).
Interestingly, trilobite sclerites preserved in the carbonate turbidite beds show little or no evidence of transportation (such as abrasion marks) other than the occasional broken
25 margin spine. However, it has been repeatedly demonstrated that trilobite sclerites that have been transported considerable distances (at least tens of kilometers) and resedimented lack obvious outward evidence of abrasion (e.g., Rasetti, 1944, 1945a,
1945b, 1945c, I945d, 1946a, 1946b, 1948a, 19048b, 1948c, 1955, 1963; Wilson, 1954,
1967; Cook and Taylor, 1975, 1977; Taylor, 1976, 1977; Taylor and Cook, 1976;
Reinhardt, 1977; Babcock, 1994a, 1994b; Robison, 1994; Babcock and St. John, 1997).
In the classic example (the example most often cited in introductory textbooks), Wilson
(1954) described Late Cambrian polymeroids from the Marathon Uplift in Texas that were found stratigraphically higher than in situ Early Ordovician polymeroids. Wilson
(1954, 1967, 1975) referred to this phenomenon as "reciprocal sedimentation," and it is a fundamental aspect of the sedimentology of shelf-margin (particularly slope and toe-of- slope) carbonate environments (Wilson, 1975; Cook and Enos, 1977). In a more extreme example, Rasetti (1944, 1945a, 1945b, 1945c, 1945d, 1946a, 1946b, 1948a, 19048b,
1948c, 1955, 1963) documented Lower Cambrian, Middle Cambrian, and Upper
Cambrian trilobites that were mixed with Lower Ordovician trilobites from western
Newfoundland. An impressive analog to the well-documented examples of resedimented trilobites is that seemingly delicate Miocene calcareous nannofossils in deep sea environments have been buried, exhumed, transported, and resedimented in strata as young as Pleistocene in age, and also lack obvious outward evidence of their complicated taphonomic history (Aubry, 1993). In the cases of both trilobite sclerites and calcareous nannofossils, the most informative evidence of reworking and resedimentation of remains comes from detailing the vertical ranges of taxa and noting whether the fossils tend to be preserved in layers that are distinct from the normal background sedimentation. In the
26 case of transported arthropod fossils, it should be noted that Babcock and Chang (1997) demontrated empirically that modem arthropod exoskeletons can be transported more than 100 km and still show little disarticulation of sclerites or abrasion. By implication, exoskeletons of ancient arthropods also could have been transported considerable distances without showing much outward evidence of transport. When the effects of predators, scavengers, and bioturbators are excluded (Babcock, 1998), then time, rather than distance of transport, seems to be the most important factor governing the disarticulation of arthropod sclerites (Babcock and Chang, 1997; Babcock, 1998).
27 CHAPTER 5
TRILOBITE BIOGEOGRAPHY AND BIOFACIES
The Paibi section contains a rich trilobite fauna, with abundant agnostoid and polymeroid trilobites. The most diverse and numerous polymeroid trilobites are from the families Lisaniidae, Leiostegiidae, Damesellidae, Diceratocephalidae, Ordosiidea,
Anomocarellidae, and Ceratopygidae. Less diverse families represented are the
Dorypygidae, Rhyssometopidae, and Catillicephalidae, although numerically these forms are significant in terms of preserved specimens. Among the represented families, members of only one, the Damesellidae, seem to undergo a biomere-like pattern of radiation and extinction in the Paibi section. However the extinction is not abrupt as would be expected from terminal biomere positions on the Laurentian shelf.
The polymeroid trilobite fauna from the Paibi section is similar, at least at the generic level, with faunas from North China (Zhang and Jell, 1987), Australia (Opik, 1967),
Tasmania (Jago, 1987), Antarctica (Shergold et al., 1976; Jago and Webers, 1992), Iran
(S. C. Peng, personal communication, 1988), South Korea (Lee and Choi, 1995, 1996), and Kazakhstan (Ergaliev 1980). Some species are shared with these other regions; the greatest similarity (less than 25% shared species) is with North China. A few genera are present both in Laurentia and Paibi, but no species are shared between the two regions.
28 Segregation of biofacies near the shelf margin of the Yangtze Platform seems to have occurred during the Middle and Late Cambrian. Such segregation of trilobites in the
Yangtze Platform, which was located in the low paleolatitudes, appears to have been similar to the biofacies segregation near the shelf margin of Laurentia (which was also located in low paleolatitudes) during the same interval of time (see Cook and Taylor,
1975, 1976; Taylor, 1976; Taylor and Cook, 1976; Babcock, 1994a, 1994b; St. John and
Babcock, 1997). Polymeroid trilobites (many of which were endemic to the continent) and a few agnostoid trilobites inhabited relatively shallow, warm epicontinental seas, whereas a more widespread (cosmopolitan) assemblage of polymeroids and numerous agnostoids inhabited deeper waters below the shelf break. Models used to explain this disjunct distribution of trilobites near the shelf edge involve vertical temperature stratification of the marine water column (thermocline; Cook and Taylor, 1975, 1977;
Taylor, 1976, 1977; Taylor and Cook, 1976; Taylor and Forester, 1979; Theokritoff,
1979; Conway Morris and Rushton, 1988; Shergold, 1988; Babcock and Robison, 1989;
Babcock, 1994a; Babcock and St. John, 1997) or other factors that covary with depth
(Babcock, 1994a, 1998), such as an oxygen gradient (oxycline) or a density gradient
(pycnocline). In inferred slope or deep shelf lithofacies of Laurentia, mixing of trilobite sclerites from adjacent biofacies as the result of gravity displacement of sediment has been observed (e.g., Wilson, 1975; Taylor, 1976; Babcock, 1994a, 1994b, 1998). In some examples (particularly Wilson, 1975), resedimentation of trilobite sclerites near the shelf edge resulted in upward extension of the apparent stratigraphie ranges of species.
As reported in this dissertation, trilobites preserved in inferred turbidites from the
29 Transitional Region (Figure I) of the South China block show a similar pattern of mixing of biofacies, and upward range extension of some species.
30 CHAPTER 6
HISTORY OF BIOMERE RESEARCH
Definition and Characterization of Biomeres
Biomeres (Figure 5) were first described by Palmer (1965a), who defined them as regional biostratigraphic units bounded by abrupt non-evolutionary changes in the dominant elements of a single phylum. Biomeres, which were first recognized from
Cambrian strata but later (Stitt, 1977; Westrop and Ludvigsen, 1987; Brett and Baird,
1995; Jeppsen, 1998) recognized from post-Cambrian strata, can be recognized on a continental scale and are most easily recognized in shallow shelf lithofacies. Extinctions associated with biomeres appear to have been abrupt across continents. Recovery faunas seem to be distantly related to organisms that went extinct, so there is little continuance of “pre-extinction” genera and species as “post-extinction” genera and species across the boundaries (Stitt, 1975).
Palmer (1981) recognized five Cambrian biomeres from the Laurentian (North
American-Greenland) paleocontinent. They are the Lower Cambrian “Olenellid,” Middle
Cambrian “Corynexochid,” Middle to Upper Cambrian Maijumiid, Upper Cambrian
Pterocephaliid, and Upper Cambrian Ptychaspid biomeres. In North America, these
31 intervals are well-documented and widely recognized from shelf strata. In fact,
Ludvigsen and Westrop (1987) proposed these boundaries as formal stage boundaries for the Upper Cambrian of Laurentia. They replaced biomere terminology with new stage names, with the Marjumiid Biomere becoming the Marjumiid Stage, the Pterocephaliid
Biomere becoming the Steptoean Stage, and the Ptychaspid Biomere becoming the
Sunwaptan Stage. This substitution of terminology was not universally accepted by
North American Cambrian workers (Robison et al., 1985) at first, but Palmer (1998) has recently proposed that formal subdivision of the entire North American Cambrian into stages be parallel with the intervals represented by biomeres. In shelf-margin settings of
Laurentia, biomere boundaries are indistinct (Westrop and Ludvigsen, 1987).
In areas outside of Laurentia, biomere patterns have not been documented in as much detail as they have in Laurentia. However, major faunal turnovers such as those recognized at the base of the Glyptagnostus reticulatus Zone in North China (Walcott,
1913, 1914; Opik, 1966) and Australia (Opik, 1963, 1966), seem to correspond to biomere boundaries as recognized from Laurentia. Faunal turnovers at the base of the G. reticulatus Zone seem to correspond to the Marjumiid-Pterocephalid biomere boundary.
Cambrian biomeres, which are best interpreted from studies of trilobites, involve a characteristic pattern of evolution and extinction. The pattern began with invasion of the shelf by a group of slowly evolving, putatively deep-water-dwelling trilobites. Some of the invading trilobites became adapted to shallow water. After a period of increasing diversity, an abrupt extinction of the shelf-dwelling trilobites occurred. Biotic recovery following the extinction event involved another invasion of the shelf by phyletically related, putatively deep-water-dwelling trilobites.
32 Trilobite biomeres appear to consist of a four-stage evolutionary pattern (Stitt, 1971a,
1975; Palmer, 1979b; Figure 3). Stitt (1971a, 1975) outlined a pattern of increasing levels of spéciation and decreasing intraspecific morphologic variation in the first three stages. In the first stage, trilobite diversity was low and morphologic variability was high. Trilobite ranges were relatively short. In the next two stages, trilobite diversity and taxonomic ranges increased while morphologic variability decreased. At the end of stage
3, an abrupt extinction of trilobites occurred. Stage 4 is complex, containing a mixture of species related to those in the previous biomere and species not closely related to those in the previous biomere. Stage 4 ends with a second extinction event that eliminated remaining trilobites of the biomere. Palmer (1979) outlined a similar pattern of evolution and extinction, although he redefined the top of the biomere to coincide with the stage 3- stage 4 boundary of Stitt ( 1971 a, 1975; Figure 5).
Biomere boundaries appear to be isochronous within the limits of current biostratigraphic resolution (Palmer, 1982). It was originally thought that the boundaries were or could be diachronous (Palmer, 1965a), but subsequent work showed this to be incorrect (Opik, 1966; Henderson, 1976; Johnson, 1974; Ludvigsen, 1982). Biomere boundaries on the Laurentian shelf are not known to be associated with major lithologie changes (Palmer, 1965a, 1965b; Hood, 1989).
Currently, biomere terminology has been largely restricted to North America.
Whereas detailed data on polymeroid trilobite extinctions during the Cambrian is lacking, information on mass extinctions of other organisms exists. These extinctions appear to be coeval with biomere boundaries. An extinction of paraconodonts at the Pterocephalid-
Ptychaspid Biomere boundary, or at horizons equivalent to that position (Figure 6), has
33 been identified in western North America, Australia, China, and Kazakhstan (Miller,
1988). Studying general trends in faunal turnovers from Australia (Opik, 1963) and the
North China Platform (Walcott, 1913, 1914), Opik (1966) reasoned that turnovers in trilobite faunas in these regions were probably equivalent to the base of the
Pterocephaliid Biomere of North America. Other evidence has been presented suggesting that biomere extinctions occur outside North America (Taylor and Cook, 1990; Westrop,
1992) and were global phenomena. Moreover, Brett and Baird (1995) identified Silurian and Devonian evolution-extinction pulses as biomeres; Jeppson (1998) also identified
Silurian biomeres. Westrop (1996) disputed arguments favoring post-Cambrian biomeres, although supporting evidence for his view was not published. Furthermore,
Westrop (1996) suggested that the term biomere should be discontinued on the premise that biomeres represent stage-level intervals.
Proposed Causes of End-Biomere Extinctions
Several hypotheses have been put forward to explain extinctions at biomere boundaries. The first hypothesis, proposed by Palmer (1965a, 1965b; 1984) and later championed by other authors (Stitt, 1971 a, 1971b, 1975, 1977, 1983; Taylor, 1971,
1985; Stanley, 1984a, 1984b; Hood, 1989), involved a marine cooling event (Figure 8) or multiple cooling events (Taylor, 1984). In this hypothesis, the Cambrian oceans were temperature stratified (e.g.. Cook and Taylor, 1975; Babcock 1994a, 1994b). Warm water was present in shallow seas that covered continents located in low paleolatitudes, and cool water was present in high paleolatitudes and in deep-water regions located in
34 low paleolatitudes. Trilobites were either warm-water adapted or cool-water adapted. If a sudden marine cooling event (rise in the thermocline) occurred, it would bring cool waters into previously warm-water, shallow-shelf environments of low-latitude continents. This cooling event is inferred to have driven warm-water-adapted trilobites to extinction. The shelf environment was then invaded by cool-water-adapted trilobites that later adapted to warm-water conditions when warm-water conditions returned to the shelf
(Figure 7, 8).
The second major hypothesis for end-biomere extinction involves a biofacies shift
(Hardy, 1985; Westrop and Ludvigsen, 1987; Westrop, 1989a, 1989b, 1991, 1992; Figure
9) due to marine transgression (Ludvigsen, 1982; Conway Morris and Rushton, 1988;
Ludvigsen et al., 1988). After examining many stratigraphie sections throughout North
America, Westrop and Ludvigsen (1987) identified five trilobite biofacies with an inferred associated immigration of off-shelf trilobites due to a rise in sea level. In this idea, deeper water facies replaced shallower water facies of inner-shelf environments, causing environmental shifts and “telescoping” of biofacies. Displacement (and extinction) of shallow water trilobites by deeper water trilobites (Ludvigsen, 1982;
Westrop and Ludvigsen, 1987; Westrop, 1989a, 1989b, 1991, 1992) would occur. This would result in an increased number of eurytopic trilobite taxa in the remaining biofacies.
The cause of such biofacies shifts, if in fact they were a driving mechanism of extinction, has been challenged. Rather than a sea level rise near the top of a biomere, evidence in the form of shallow-water carbonates, including oolites and stromatolites, has been presented to suggest a sea level fall at the top of a biomere (Miller, 1978, 1984; Fortey,
35 1984; Hallam, 1984). Westrop and Ludvigsen (1987) challenged without explanation the interpretations that biomere tops are associated with sea level falls.
Several other hypotheses for extinction during the Cambrian have been proposed but have not received as much attention as those previously discussed. For example, some authors invoked a sea-level fall (Lockman-Balk, 1970; Johnson, 1974; Miller, 1978,
1984; Erdtmann and Miller, 1981; Fortey, 1984; Hallam, 1984) as a mechanism for extinction. This would cause the geographic ranges of shallow-water, shelf-dwelling organisms to be restricted. Other authors suspected that a marine anoxic event led to the extinction of shallow-water, shelf-dwelling trilobites (Palmer, 1984; Wright et al., 1984;
Taylor, 1985). Similar to the marine-cooling hypothesis, the Cambrian oceans may have been strongly stratified with respect to oxygen. If anoxic water inundated shallow-water shelf regions, shallow-water trilobites would have suffered extinction. Deeper water trilobites, adapted to oxygen-poor environments, would have invaded the shelf later and undergone adaptive radiation.
Other extinction hypotheses center around extraterrestrial causes. Palmer (1982) invoked the hypothesis of impact by an extraterrestrial body (compare Alvarez et al.,
1980). In the case of a bolide impact on Earth, mass extinction would be triggered by a variety of proximal causes, including acid rain, worldwide drop in temperatures, and lethal doses of radiation. However, no iridium anomalies have been discovered in subsequent searches (Orth et al., 1984). Finally, Opik (1966) thought that an extraterrestrial heating event could have caused extinction through sterilization of animals.
36 Chatterton and Speyer (1989) examined the role that larval ecology played in the extinction and survival of trilobites after the end-Ordovician mass extinction. Working with silicified trilobite larvae (protaspides). Chatterton and Speyer (1989) classified the modes of life of juvenile trilobites based on morphology, degree of spinosity, and general body plan. Using these criteria, they placed the larvae into four groups, or “life history strategies:” benthic protaspides/benthic adults; benthic or planktonic protaspides/pelagic adults; planktonic protaspides/benthic adults; and planktonic, then benthic protaspids/benthic adults. They found that the trilobites having a planktonic protaspid stage went completely extinct at the end of the Ordovician; those having a benthic protaspid stage suffered a large drop in diversity but were the ancestral stock for post-
Ordovician trilobites; and those having a two-stage larval stage suffered the least. They attributed this pattern to a lowering of sea level and global climatic changes associated with glaciation at the end of the Ordovician.
The Chatterton and Speyer (1989) hypothesis is difficult to apply to the recurring pattern of evolution and extinction in Cambrian biomeres. First, it is difficult to infer the mode of life of the protaspid stage of a trilobite based solely on external morphological characters. Second, there are virtually no protaspids preserved in the Piabi collections, and most of the juveniles, which are mostly meraspids, cannot be assigned to a species.
The mechanisms proposed for Cambrian end-biomere extinctions and the end-Ordovician extinction are different. Biomere extinctions are generally thought to have been caused by either a rise in sea level or a rise in the thermocline, whereas the end-Ordovician extinction is thought to have been caused by a drop in sea level due to Gondwanan glaciation. If trilobites in a biomere were subjected to differential survivorship during the
37 protaspid stage, then certain life histories would likely be eliminated and would not be factors in subsequent biomeres. This would mean that each end-biomere event would potentially have different driving mechanisms to produce the same pattern of evolution, extinction, and radiation, which is unlikely. If this hypothesis held true for Cambrian biomere extinctions, then certain larval life histories certainly would have been eliminated by the Ordovician. If there were some holdover taxa for a given larval life history that survived each biomere and if they were the ancestral stock for subsequent trilobites for that life history, then it is reasonable to assume that this process also would have taken place in the Ordovician, and certain animals having mass extinction-resistant life history strategies would have survived. If this hypothesis does not hold true for
Cambrian biomere extinctions, then the question as to why it operated in the Ordovician and not the Cambrian needs to be addressed.
Chatterton and Speyer (1989) also discussed the role of phytoplankton productivity in the end-Ordovician mass extinction. The end-Ordovician mass extinction generally is thought to have been caused by environmental changes due to widespread glaciation and associated global cooling. In modem oceanic ecosystems, organisms with planktotrophic larvae are numerically much rarer in cool-water, high-latitude environments than they are in warm-water, low-latitude environments. Thus, during period of global cooling, many planktotrophic larvae living in warm-water, low-latitude environments might be adversely affected. If biomere extinctions were caused by a rise in the themiocline such that cool water inundated shelf environments, then planktotrophic larvae may have been adversely affected. If biomeres were restricted to tropical settings, and trilobites with planktotrophic larvae were eliminated from this setting, then it is possible that trilobites
38 having a life history that included planktotrophic larvae could have reinvaded the shelf from other, perhaps deeper water, environments and adapted to subsequent warm-water shelf conditions. Organisms that fed on planktotrophic larvae would have been similarly affected in this scenario.
Biomeres may represent the effects of adaptive radiation more than the effects of mass extinction per se (Stitt, 1971a, 1971b, 1975, 1977; Palmer, 1979b). An adaptive radiation results in “a divergent cluster of taxa of monophyletic origin whose proliferation is due primarily to the opening of a new ecospace” (Hardy, 1985; see also Valentine, 1973;
Eldredge and Cracraft, 1980). The invaded ecospace can represent a new “adaptive zone” or a habitat that was previously unoccupied (Simpson, 1944, 1953; Valentine,
1973; Eldredge and Cracraft, 1980; Hardy, 1985). At the beginning of an adaptive radiation, spéciation rates must exceed extinction rates (Simpson, 1944, 1953; Sepkoski,
1978, 1979; Stanley, 1979; Hardy, 1985) with extinction rates either exceeding spéciation or equilibrating with it as the radiation proceeds. However, biomeres do not appear to fit this pattern precisely. Hardy (1985) noted several pulses of spéciation and extinction throughout a biomere. Hardy (1985) identified three intervals where species diversity increased in the Ptychaspiid Biomere. A period of gradual decline followed the first two, but after the third increase, in which species diversity reached a maximum, an extinction event occurred and diversity dropped off markedly (Hardy, 1985).
39 UNSTRATIFIED OCEAN EXTINCTION
STRATIFIED OCEAN
STRATIFIED OCEAN
SLOPE SHELF
Figure 7: Proposed mechanism of extinction where a risisng thermocline inundates the shelf with cooler or less oxygenated water; shaded portion represents cooler or oxygen- poor water (modified from Palmer, 1989).
40 BIOSTRATIGRAPHIC EVOLUTIONARY PATTERN RANGES SHELF Ocean i L
Invasion EXTINCTION i i
Slowly evolving basic stock Biomere Invasion
EXTINCTION
Time
Figure 8: Schematic diagram showing pattern of trilobite evolution and extinction within a biomere, compared with species ranges (modified from Stitt, 1975).
41 TRILOBITE ZONES
Missisquoia typicalis
Missisquoia depressa
Eurekia apopsis
Saukiella serotina
DISTRICT OF a l b e r t a OKLAHOMA NEW YORK QUEBEC. NEWFOUNDLAND MACKENZIE NEWFOUNDLAND
Outer detrital belt
Light colored grainstones and packstones in shallow carbonate bank settings
Light colored wackestones in deep subtidal ramp and shelf margin settings
Algal buildups in outer shelf and shelf margin settings
BIOFACIES: Par, Parabolinella; Apo, Apoplanies; PI, Plethopeltis; Lar, Larifiiguia; Cor, Corbinia; Ka-Yu, Kathleenella-Yitkonaspis; Eup-Eur, Eiiprychaspis-Eurekia; Ble, Blenvillia; Log, Loganellid; Pl-Ca, Plethopeltid-Catillicephalid
Figure 9: Schematic diagram showing the distribution of biofacies and lithofacies across Laurentia during the Sunwaptan Stage (modified from Westrop, 1989); time is approximated by trilobite zones.
42 SLOPE - RISE SHELF
JJ_ TT
I I
Figure 10: Schematic diagram showing expected pattern of trilobite ranges on the shelf (left) and in slope or rise environments where downslope resedimentation of trilobites has occurred (right) in relationship to biomere boundaries (extinction events).
43 CHAPTER 7
MATERIAL AND METHODS
A total of 390 meters of the Piabi section was measured, and collections of polymeroid trilobites were taken at 82 levels, surface exposure permitting (Figure 2).
The section was measured by M. N. Rees and L. E. Babcock. PIE numbers were assigned in the field to specimens from the Paibi section. Each number reflects how many meters above the base of the Paibi section the sample was collected. Rocks were sampled on a centimeter-by-centimeter basis where practical. However, not all intervals were productive, so samples that were collected are only from the productive intervals.
The samples were collected from limestones. The only siliciclastics present in the section were thin shale partings. Trilobites were not found in the shaly partings. Additional samples were taken for isotopic analysis by M. D. Brasier (University of Oxford).
Intervals that were determined in the field to be close to the recognizable biostrati graphic boundaries, or where trilobites were numerous, were sampled more closely than were other intervals. Samples were labeled according to the number of meters above the base of the measured section. A portion of the section, between samples PIB 130.95 and PIB
230.95, was not sampled because it was covered by recently slumped material.
44 In the laboratory, samples were split by R. A. Robison using a hydraulic jack in an effort to separate fossils from their matrix. Trilobites specimens then were coated with magnesium oxide to make features on the sclerites more conspicuous and to aid in identification. Trilobites were identified to species level, when possible, and their positions in the stratigraphie section were plotted.
Stratigraphie sections from central Texas that contain appropriate biomere boundaries were also studied in the field for comparative reasons. These sections have been well described previously (e.g., Longacre, 1970; Hood; 1989), and this work did not yield new information.
45 CHAPTER 8
TEST FOR BIOMERE BOUNDARIES
Patterns within North American Biomeres
Previous workers examined levels of trilobite extinction at the family, genus, and species level in North America. Palmer (1965a, 1982, 1984), Longacre (1970), and Stitt
(1971a, 1975) examined species-level extinction at the microstratigraphic scale. The extinctions of polymeroid trilobites are abrupt and occur within several centimeters
(Palmer, 1984). Longacre (1970) reported the extinction of 75 percent (15 of 20 species) of the polymeroid trilobites from the Ptychaspid Biomere in central Texas within several centimeters (see Longacre, 1970, text-fig. 2; Table 1). Palmer (1982, 1984) found a high turnover among trilobite genera at biomere boundaries in western North America. His data included agnostoid genera as well as polymeroid genera, and he noted that agnostoid trilobites suffered a high level of extinction as well. In the House Range, Utah, 78 percent of the trilobite genera disappeared within one meter of the biomere boundary (7 of 9), with the remaining two genera becoming very rare above the boundary before going extinct less than one meter above the boundary (Palmer, 1982, 1984). In the
Highland Range, Nevada, all genera present one meter below the boundary became
46 extinct (Palmer, 1982, 1984). In the Desert Range, Nevada, all but one genus present within one meter of the boundary became extinct. Interestingly, the surviving genus is very rare below the boundary, but becomes extremely common just above the boundary
(Palmer, 1982, 1984).
Westrop and Ludvigsen (1987) recorded family-level extinctions in western Canada.
Family-level extinctions are relevant to this discussion because Briggs et al. (1988) argued that the only true extinctions are those that eliminate a clade. Such terminations, they stated, should be considered at the generic level or higher. They reasoned that the true extinction of a species in the fossil record is very difficult to separate from a
“taphonomic event.” Extinction at the family level at the top of the Ptychaspid Biomere of North America (or the Sunwaptan Stage of Westrop and Ludvigsen, 1985) is 42 percent (10 of 24). Unlike the data collected at the species level (Palmer, 1965a, 1982,
1984; Longacre, 1970; Stitt, 197la, 1975), where the extinction interval occurred within one centimeter of stratigraphie thickness, family-level extinctions recorded by Westrop and Ludvigsen took place over a larger stratigraphie interval, up to 26 meters (Westrop,
1989a, 1989b; Ludvigsen and Westrop, 1983; Westrop and Ludvigsen, 1987).
Patterns within the Paibi Section
For the purposes of this discussion, range tops of taxa in the Paibi, China, section will be treated a priori as extinction points. This assumption involves certain drawbacks, such as drawing equivalence between local disappearance of a species for environmental
47 reasons and a global extinction. Because other age-equivalent stratigraphie sections in
China have not been resolved to the same level of detail as the Paibi section, it is difficult to ascertain at present whether range tops of all taxa represented in the Paibi section do, in fact, correspond to true extinctions. However, general trends established from the examination of numerous published sections in China indicate that many of the longest ranging trilobites in the Paibi section are unusually long-ranging (and probably anomalously extended) compared to the regional pattern.
Polymeroid trilobite taxa identified from the Paibi, China, section are described in the section on Systematic Paleontology (below), and stratigraphie ranges of taxa are plotted in Figure 2. The section contains strata assigned to thePtychagnostus atavus Zone, the
Ptychagnostus gibbus Zone, the Goniagnostus nathorsti Zone, the Lejopyge laevigata
Zone, the Proagnostus bulbous Zone, the Lingiiagnostus reconditus Zone, the
Glyptagnostus stolidoius Zone, and the Glyptagnostus reticidatus Zone (Peng and
Robison, in review).
Based upon the ranges of identified family-, genus-, and species-level taxa, sharp biomere-type extinction horizons cannot be identified from slope deposits of the Huaqiao
Formation in the Paibi section. The base of the Pterocephaliid Biomere in North America is marked by the first appearance o f the agnostoid trilobite Glyptagnostus reticidatus.
The base of the Glyptagnostus reticidatus Zone, which is equivalent to the base of the
Pterocephaliid Biomere (Figure 6), occurs in sample PIB 367 in the Paibi section. Unlike the sharp truncation of trilobite ranges observed in shelf strata of western North America at the Ptychaspid-Pterochephaliid biomere boundary (Palmer, 1965a, 1965b; Stitt, 1975;
Hood, 1989), faunal turnover at the equivalent horizon at Paibi appears to be gradual. In
48 fact, faunal turnover throughout the section appears to be gradual. The levels of extinctions in the Paibi section are much lower at both the species and family level than are the levels of extinction in the biomeres of North America (Palmer, 1965a, 1982,
1984; Longacre, 1970; Stitt, 1971, 1975; Westrop and Ludvigson, 1987; Table 1).
Although biomeres in North America have been examined at different scales, there is still no apparent mass extinction at either the microstratigraphic level, as examined by Palmer
(1965a, 1982, 1984), or at the macrostrati graphic level, as examined by Westrop and
Ludvigson (1987). Further, the pattern of evolution and extinction in the Paibi Section does not fit the four- stage pattern of evolution and extinction within a biomere as outlined by Palmer (1979a) and Stitt (1971a, 1975).
Percentages of species turnover at various levels within the Paibi section are summarized in Table 1. Single occurrence taxa are not included in the statistical data because it is possible that their remains were transported in from a different biofacies.
Alternatively, the observed ranges of the rare taxa may be explained by the Signor-Lipps effect. The Signor-Lipps effect is a phenomenon by which rare taxa became underrepresented in the fossil record. Their actual ranges may be significantly longer, but, because they are rare, the chance of finding them is quite low at any given sample interval. Finally, the question would arise that, if these rare taxa are included in the statistical data, should they be included as the first occurrence or the last occurrence of the taxa? Thus, they are omitted from the statistical data.
There is no bed in the Paibi section in which mass extinction is evident at the species level (Figure 2; Table 1). Extinction rates were calculated for beds where numerous species were present above and below a given sample. There are samples in the section
49 that have elevated levels of extinction (Table I), although they are about the same magnitude as the presumed background levels of extinction within the Ptychaspid
Biomere in central Texas (see Longacre, 1970). There is an interval just below the base of the Glyptagnostus reticidatus Zone that has an elevated level of species turnover (PIB
361.5 to PIB 362.4). Here, 44 percent of the species disappear (4 of 9). However, the truncation of species ranges occurs over an interval of nearly one meter, a much larger interval than the one centimeter interval within which the Marjumiid/Pterocephaliid biomere extinction event occurs (Palmer, 1984). The truncation is unlikely to be related to a difference in the sedimentation rate of the Paibi section because lime mudstones of slope environments were probably deposited at a slower rate than the platform carbonates and siliciclastics of the studied Laurentian sections. Further, the range tops have a stepwise pattern, with two of the four species disappearing at a different sample interval than the other two species. This particular interval occurs close to the top of the measured section.
Just as a horizon showing a high level of species-level extinction is not evident in the
Paibi, China, section, an inter\^al of elevated family-level extinction is also not evident.
Families do not appear to have gone extinct at the base of theGlyptagnostus reticidatus
Zone in the Paibi, China, section. No families go extinct in the interval between PIB
361.5 and PIB 362.4, just below the base of the Glyptagnostus reticidatus Zone, an interval representing an elevated level of species extinction. If a 26-meter interval is used above and below this horizon (the maximum interval outlined by Westrop and
Ludvigsen, 1987), there are still no extinctions at the family level. Thus, if Briggs et al.
(1988; see also Westrop, 1989a, 1989b) are correct, and the only true extinctions are
50 among clades above the species level, then there is no evident mass extinction represented in any sample interval in the Paibi section. It is important to note that Palmer
(1982) found a marked turnover in trilobite families at the base of a biomere. He also noted that almost all families below a biomere boundary disappear within one meter of the boundary. Throughout the Paibi section, family turnover is very low, with many families having extremely long ranges.
No genera go extinct at the base of theGlyptagnostus reticidatus Zone in the Paibi section. The highest level of extinction occurs between sample interval PIB 361.5 and
PIB 362.4, just below the base of the Glyptagnostus reticidatus Zone, where 50 percent
(4 of 8) of the genera disappear. The last occurrence of genera in this sample interval may not reflect true extinctions, as apparent ranges may have been truncated by the top of the section, and the genera may occur in overlying rocks elsewhere.
The four-stage pattern of evolution that occurs within biomeres in North America
(Palmer, 1979b, 1984; see also Stitt, 1971a, 1975) is not evident in the Paibi section.
Palmer’s (1979b, 1984) four stages began with the abrupt extinction of a diverse fauna; a period of rapid diversification (attributed to open niche space), where trilobites have short ranges; a drop in diversity in which species have longer ranges; and finally, the domination of the assemblage by a single taxon. This pattern cannot be identified in the
Paibi section. There is no identifiable phase of domination by one taxon just below the
Glyptagnostus reticulatus Zone. Palmer (1982) noted that numerical domination by a single taxon continues for several meters above the bases of biomeres in North America, a feature not observed in the Paibi section. For the most part, there seems to be the gradual evolution and extinction of taxa throughout the Paibi section.
51 Despite having a richly fossiliferous, continuous section from the Middle to Upper
Cambrian, the Paibi section, western Hunan, does not display the expected pattern of evolution and extinction present in biomeres of western North America as defined by
Palmer (1965a, 1982, 1984). However, there are significant differences between the
North American sections and the Paibi section that may account for the lack of biomeres in the Paibi section. Perhaps the most important difference between classic North
American biomere sections and the Paibi, China, section is a lithofacies difference. The
Paibi section apparently represents a slope environment, whereas described biomere- bearing sections in North America represent shelf settings. Sections in shelf settings are likely to be less continuous than sections in the slope settings.
Characteristics that support the interpretation that the Paibi section represents a slope environment includes the section’s paleogeographic position, the presence of dark colored lime mudstones, the presence of turbidites that include a mixed fauna from shelf and inferred deep-water settings, the presence of carbonate breccia beds containing transported clasts, the high organic content o f the lime mudstones, and a predominantly pelagic fauna in the lime mudstones. As yet, biomeres have not been identified from slope environments of North America (Pratt, 1992; Westrop, 1995). In fact, Westrop
(1989a) noted that extinctions of shelf-dwelling trilobite families whose ranges extended onto the slope were much lower in terms of percent of families that went extinct than were extinctions of trilobite families whose ranges were restricted to the shelf. Further,
Westrop (1989a) found that trilobite families with slope-dwelling species found outside
North America were more widespread. Shelf-dwelling trilobites collected from North
America tend to be endemic to Laurentia. Westrop and Ludvigsen (1987) also showed
52 that during periods of sea-level rise, slope environments could expand onto the shelf, perhaps acting as a source for subsequent immigration of slope-dwelling trilobites onto the shelf. This would increase the probability of survival of slope-dwelling families because of biofacies expansion (Westrop, 1989a; Westrop and Ludvigsen, 1987).
Because the Paibi section was deposited in a slope environment, it is possible that the trilobites dwelling in this environment did not suffer extinction at the same rapid rate as those dwelling in a shelf environment. Indeed, they would be likely to immigrate onto the shelf following the extinction of shelf-dwelling species. Thus, it is possible that biomere-type patterns exist outside North America (see Miller, 1988; Opik, 1963;
Walcott, 1913, 1914) but are essentially restricted to shelf lithofacies.
A second major difference between Laurentia and South China is in the geographic extent of their trilobite biotas. It has long been recognized that many of the shelf- dwelling trilobites of Laurentia are endemic (Jell, 1974; Westrop, 1989a; Babcock,
1994a, 1994b; Palmer, 1998). The trilobite families that were restricted to shelf facies suffered higher extinction rates at biomere boundaries than those families whose ranges extended onto the slope (Westrop, 1989a). Westrop (1989a) argued that families of slope-dwelling trilobites could also be found outside of North America. Those families suffered much lower extinction rates than did shelf-dwelling trilobites (Westrop and
Ludvigsen, 1987). In fact, as an extinction proceeded, species endemic to the shelf were replaced by more widespread slope-dwelling species (Westrop and Ludvigsen, 1987).
The slope-dwelling trilobites were merely filling niche spaces left empty by the extinction of shelf-dwelling trilobites. In the model proposed by Westrop and Ludvigsen
(1987), the telescoping of biofacies during a sea level rise caused the extinction of the
53 shelf-dwelling organisms. Because there would be no niche space available to be occupied, the endemic, shelf-dwelling trilobites suffered extinction. This contrasts with the inferred extinctions recorded in the Paibi section of South China. In this slope setting, the known trilobites were more widespread than were the coeval taxa from shelf environments of Laurentia. Many of the genera and species present at the Paibi area are also present in North China (Zhang and Jell, 1987), Australia (Opik, 1967), Tasmania
(Jago, 1987), Antarctica (Shergold et al., 1976; Jago and Webers, 1992), Iran (S. C. Peng, personal communication, 1988), South Korea (Lee and Choi, 1995, 1996) and
Kazakhstan (Ergaliev, 1980). Based upon the work of Westrop and Ludvigsen (1987) from North America, one would expect Paibi section taxa to have longer ranges than
Laurentian shelf-dwellers. Moreover, end-biomere-inducing phenomena probably had a greater effect in shallow water, so it is possible that many slope-dwelling taxa from South
China could survive extinction events at biomere boundaries. It is possible that many of the species that did go extinct during this interval were quickly replaced by related taxa from deeper water environments that could readily adapt to the conditions of the shelf environment.
The possibility of a pycnocline effecting control over trilobite distribution during the
Cambrian has not been discussed much in the literature. However, good comparative examples of pycnoclines (oxyclines) and their effects on sedimentation patterns and biofacies have been suggested for the Devonian (e.g., Broadhead et al., 1982; Potter et al., 1982; Brett and Baird, 1985; Ettensohn, 1985a, 1985b) and the Pennsylvanian
(Heckel, 1985, 1977) of Laurentia. Rise of a pycnocline, causing anoxic or dysoxic water to inundate the shelf, could have driven trilobite extinctions during the Cambrian.
54 Source of Trilobites
One major unanswered question pertaining to biomeres is the source of the post extinction trilobites. Cook and Taylor (1975) indicated that there was some faunal overlap among trilobites between China and Laurentia. However, few polymeroid genera are shared between South China (or even North China) and Laurentia. Examples of shared genera between South China and Laurentia are Proceratopyge, Charchaqiiia, and
Pianaspis. These genera seem to have appeared earlier in South China and migrated later to Laurentia. Proceratopyge is present in the Middle Cambrian in South China (herein), and is also found later in the Upper Cambrian of Laurentia (Pratt, 1997). However, it is not involved in end-biomere extinction events because it never invaded the shelf. This seems to rule out the possibility that trilobites that invaded the shelf following extinction came from deeper water areas such as those exemplified by slope areas of South China.
Endemism of Laurentian trilobite faunas may have been stronger than previously acknowledged. Palmer (1998) suggested that one of the reasons biomeres are more evident in North America than elsewhere is because of the relative isolation of Laurentia compared to other paleocontinents, and because of endemism of its trilobite faunas (i.e., the trilobites were restricted to Laurentia). Where, then, did the invading trilobites in
Laurentia come from? Perhaps there were small réfugia (areas that retained environmental characteristics necessary for the survival of a given species) for eurytopic taxa during biomere extinction events . Trilobites in such shelf or slope réfugia of
55 Laurentia could have been better able to cope with changes in the thermocline or
pycnocline thanmost of those on the shelf. This would help explain the apparent
morphologic similarity among trilobite families in adjacent biomere intervals.
Effects of Resedimented Trilobites in Slope Environments
Most polymeroid trilobite sclerites in the Paibi, China, section evidently were
resedimented but are parautochthonous. Resedimentation in this slope setting could
extend the local stratigraphie ranges of species and effectively spread out the evidence of
any sharp extinction event. It is important in this regard to distinguish between the
stratigraphie range of a species and the time range of a species. The time range of a
species is the interval of time between the evolution and the extinction of a species. The
stratigraphie range of a species is the stratigraphie interval between the first appearance
and the last appearance of a species in the fossil record. The first appearance depends on
factors such as species evolution, migration of species to a local area, and taphonomy.
The last appearance depends on true extinction (elimination of the species from the
planet), migration from the local area, and taphonomy. Body fossils, particularly strongly
calcified sclerites such as those of trilobites, can remain in the sedimentary record long
after the species disappears. Resedimentation of trilobite sclerites has been shown in
certain carbonate-rich environments (e.g., Wilson, 1967, 1975) to extensively extend the stratigraphie ranges of species.
56 In the Paibi section, both the bottoms and the tops of the stratigraphie ranges of polymeroid trilobites seem to have been affected by resedimentation to some extent, but the tops of ranges are probably more severely affected. The bases o f carbonate turbidites can scour existing beds to some extent, resulting in minor truncation of beds and thus affecting apparent range. Resedimentation of stratigraphically low specimens could yield a local “first appearance” that underestimates the true first appearance. In many samples, sclerites are size sorted (Figures 13.8, 15.2, 17.10, 18.13, 18.20). There also are numerous examples where only certain sclerites of a given species are present in a sample. For example, there are dozens of cranidia of the speciesPianaspis sinensis in the
Paibi collections, but no pygidia. Similarly, there are many cranidia of Fenghuangella in the Paibi collections (Figure 13.10), but pygidia are extremely rare. The ranges of species represented by abundant material in the Paibi section are longest at the bottom of the section and get progressively shorter closer to the top. This resembles a biomere in reverse, where the longest ranges of a species in a biomere are at the top and the shortest ranges are at the bottom. Such a pattern is expected if the ranges of early-appearing species are extended through most of the section, but the ranges of late-appearing species are extended only through the upper part of the section. This "reverse biomere" pattern is precisely the pattern expected if reciprocal sedimentation (Wilson, 1967, 1974, 1975) had occurred. The tops of many species’ stratigraphie ranges at Paibi probably are extended beyond the extinction of the species. When the ranges of numerous species are considered, any sharp extinction, if it occurred in this environment, would likely be
“smeared out” by resedimentation (Figure 10).
57 There are hints of a biomere-type succession in the Paibi section, although the clades from South China are different from those in Laurentia. In Laurentia, the Pterocephaliid trilobites are the clade involved in the Pterocephaliid Biomere, but pterocephaliids are absent from China. In South China, the drepanurid trilobites (comprising ofMeringaspis,
Paradamasella, Prodamasella, Protaitzehoia, Teinistion, and Palaeodotes) undergo a radiation similar to that of the pterocephaliids in Laurentia, but they did not go extinct abruptly at the position of the inferred biomere boundary. The base of the
Pterocephaliid-Ptychaspid Biomere boundary in Laurentia corresponds to the base of the
Glyptagnostus reticulatus Zone, which is recognized through much of the rest of the world.
The first stratigraphie appearances of species in the Paibi section are inferred to be close to their appearances in time (evolution-based or migration-based positions) because sclerites in the Paibi section are inferred to be parautochthonous. Downslope movement should not have altered first appearance positions as much as it should have altered last appearance positions. The first appearance is a function largely of evolution and migration; remains of any given species cannot ordinarily be present in strata underlying those representing the time that the species evolved. In contrast, a species’ apparent stratigraphie range can be extended long after the species has become extinct by exhumation and redeposition of remains.
58 CHAPTER 9
SUITABILITY OF THE PAIBI SECTION AS A GLOBAL STRATOTYPE FOR THE
MIDDLE CAMBRIAN-UPPER CAMBRIAN BOUNDARY
The Paibi section, Hunan, China, records one of the most complete, uninterrupted successions of Middle-Upper Cambrian strata known anywhere in the world, based on a lack of truncation of the finely resolved record of agnostoid trilobite zones (Peng and
Robison, in review) and the lack of substantial truncation at any stratigraphie interval.
The section represents a slope environment with slow background sedimentation punctuated by downslope movement of sediment (including trilobite sclerites), leading to a mixing of biofacies. Thus, it should be possible to tie the open-ocean trilobite record to the trilobite record for shallower shelf and shelf-edge environments in South China.
Also, many South China polymeroid trilobites are widespread through Gondwana and peri-Gondwanan terranes, making near-global correlation between shelf and ocean environments possible. The likely Middle Cambrian-Upper Cambrian boundary, the base of the Glyptagnostus reticulatus Zone, is exposed and accessible at the Paibi, China, section.
The major drawback to using the Paibi section as the international stratotype for the
Middle-Upper Cambrian boundary is that upward range extensions of trilobites appear to
59 have occurred because of resedimentation. However, this problem is largely negated by the use of first appearance data of common, widespread, species, particularly agnostoids.
Assemblage-zones, range-zones, Oppel Zones, concurrent range-zones, etc. are of little usefulness in this setting. This is important to recognize, as several possible international stratotype sections under consideration for Cambrian stages record shelf-margin to slope environments. The isotope record of the Paibi, China, section accords with the global pattern (M. Saltzman, personal communication, 1998); a positive ^^C excursion occurs across the base of the Glyptagnostus reticulatus Zone, just as it does elsewhere in the world (Saltzman et al., 1995).
60 CHAPTER 10
SYSTEMATIC PALEONTOLOGY
Terminology.-MorpholQgic terms used here are defined in the Treatise of Invertebrate
Paleontology (Whittington and Kelly, 1997). Collection numbers (PIB numbers) record the distance about the base of the measured section in Paibi, Hunan, China.
Repository.-Illustrated specimens and other specimens examined in this study are deposited in the Nanjiang Institute of Geology and Palaeontology, Academia Sinica,
Nanjiang, China (NIGP).
Phylum ARTHROPOD A Siebold in Seibold and Stannius, 1845
Class TRILOBITA Walch, 1771
Order AS APHID A Salter, 1864
Family CERATOPYGIDAE Linnarsson, 1869
Subfamily PROCERATOPYGINAE Wallerius, 1895
Genus PROCERATOPYGE Wallerius, 1895
Type species.-Proceratopyge conifrons Wallerius, 1895.
61 Discussion.-T\iQ generic concept ofProceratopyge is problematic. Some authors subdivided it into three subgenera, Proceratopyge (Proceratopyge) Wallerius, P.
(Sinoproceratopyge) Lu and Lin, and P. (Lopnorites) Troedsson, based on differences in the cranidium. The three subgenera are from in progressively higher stratigraphie levels in western Hunan (Peng, 1992). However, Lu and Lin (1989) contended that subgeneric differences do not exist in the thorax or pygidia. Peng (1992) stated that early proceratopygids have pygidia that are more transverse, are shorter, are wider, and have fewer segments in the axes than later species. In this report, the genus will be used sensu lato, without the subgenus, until a consistent nomenclature is devised.
PROCERATOPYGE FENGHWANGENSIS Hsiang, 1963
Figure 11.1-11.3
Proceratopyge fenghwangensis HSIANG, 1963, p. 47, PI. 10, figs. 1-9; LU, CHANG,
CHU, CHIEN, and HSIANG, 1965. p. 548, PI. 114, figs. 10-13; YANG, 1978, p. 65.
New material.-Move than twenty sclerites, the majority being cranidia, in PIB 367,
368.8, 371.2, 375, 375.9, and 378.25.
Remarks.-New material from the Huaqaio Formation, western Hunan, resembles the type material from western Hunan and eastern Guizhou. Key characters that warrant placing the new material into the species include a cephalon with a long, conical glabella and a pygidium that is longer and more rounded posteriorly than other species of
Proceratopyge.
62 Occurrence. -MQàxViVn. to dark gray wackestones and packstones of the Huaqaio
Formation, western Hunan. In the Paibi section, this species occurs in rocks correlated with the Glyptagnostus stolidotus and Glyptagnostus reticulatus Zones.
PROCERATOPYGE FUYANGENSIS Lu and Lin in Peng, 1987
Figure 11.14-II. 15
Proceratopyge fiiyangensis LU and LIN in PENG, 1987, p. 114, PI. 2, figs. 7-10.
New material.-M.OXQ than thirty sclerites, including both cranidia and pygidia, in PEB
296.54, 298.54, 301.9, 3 16.1, 317.2, and 326.9.
Remarks.-'New material from the Huaqaio Formation, western Hunan, resembles the type material from western Hunan. This species has a glabella that tapers forward slightly and a very short, wide pygidium. The pygidium is wider than it is long. In other species ofProceratopyge, the pygidium is longer than wide.
Occurrence.-Medixxm. to dark gray wackestones and packstones of the Huaqaio
Formation, western Hunan. In the Paibi section, this species occurs in rocks correlated with the Lejopyge laevigata, Proagnostus bulbus, and Lingiiagnostus reconditus Zones.
Subfamily MACROPYGINAE Kobayashi, 1937
Genus PSEUDOYUEPINGIA Chien, 1961
Type species.-Pseiidoyiiepingia modesta Ch\Qn, 1961, p. 106.
Discussion.-A review of the generic concept was done by Jago (1987), and this concept is followed here.
63 PSEUDO YUEPINGIA MODESTA Chien, 1961
Figure 11.9-11.10
Pseiidoyuepingia modesta CHIEN, 1961, p. 106, PI. 5, figs. 5-7; LU, CHANG, CHU,
CHIEN, and HSIANG, 1963, p. 506, PI. 103, figs. 1-3.
Pseudoyiiepingia laochatianensis YANG in ZHOU, LIU, MENG, AND SUN, 1977, p.
216, PI. 63, figs. 14-15; YANG, 1978, p. 69, PI. 3, figs. 5-17.
New material.-NI ovq the twenty sclerites, including both cranidia and pygidia, in PIB
353.64, 353.7, 361.5, and 362.35.
Remarks.-'New material from the Huaqaio Formation, western Hunan, resembles the
type material from western Hunan. Key characters that warrant placing the new
specimens in this species include a cephalon with narrow fixagena, a gently tapering
glabella, and an elongate, semi-elliptical pygidium that lacks marginal spines. The first
segment of the pygidium reaches the border.
Pseiidoyuepingia laochatianensis is here synonymized with P. modesta because both
have identical morphologies, are of similar age, and are from the same localities.
Pseudoyiiepingia laochatianensis is from a more shale-rich facies and many of the
perceived differences between the two species appear to be preservational.
Occurrence.-Nledmva to dark gray wackestone and packstones of the Huaqaio
Formation, western Hunan. In the Paibi section, this species occurs in rocks correlated with the Lingiiagnostus reconditus Zone.
64 Family LIOSTRACINIDAE Raymond, 1937
Subfamily LIOSTRACININAE Raymond, 1937
Genus LIOSTRACINA Monke, 1903
Type species.-Liostracina krausei Monke (1903, p. 114).
Disciission.-Th.e. generic concept of Opik (1967, p. 352) is followed here.
LIOSTRACINA BELLA Lin and Zhou, 1983
Figure 11.13
Liostracina bella LIN and ZHOU, 1983, p. 407, PI. 3, figs. 7-10; PENG, 1987, p. 110.
PI. 12, Figure 7.
New material.-M.OÏO. than ten cranidia in PIB 308, 316.1, 331.8, 341.7, and 361.5.
Remarks.-The. new material from the Huaqaio Formation, western Hunan, resembles the type material from western Hunan. Key characters that warrant placement of the new material into this species include a cephalon with a complete preglabellar furrow, a paradoublure ridge with a central node, and an eye ridge that is more prominant than in the type species.
Occnrrence.-Medium to dark gray wackestones and packstones of the Huaqaio
Formation, western Hunan. In the Paibi section, this species occurs in rocks correalted with the Lingiiagnostus reconditus and Glyptagnostus stolidotus Zones .
Family MONKASPDDAE Kobayashi, 1935
Genus MONKASPIS Kobayashi, 1935
65 Type species.-Anomocare (?) daulis Walcott (1905, p. 50).
Discussion.-Va& generic concept of Zhang and Jell (1987, p. 191) is followed here.
MONKASPIS QUADRATUS Yang, 1978
Figure 11.4-11.5
Monkaspis quadratus YANG in ZHOU, LIU, MENG, and SUN, 1977, p. 150, PI. 46, figs. 19-22; YANG, 1978, p. 37, PI. 5, figs. 9-11.
New material.-M.ovc than ten pygidia and a single cranidium in PIB 298.54, 316.1,
319.6, and 341.7.
Remarks .-New material from the Huaqaio Formation, western Hunan, resembles the type material from western Hunan and eastern Guizhou. Key characters that warrant placement of the new material into this species include a short quadrate glahella, a flat, slightly rounded anterior border, and plueral furrows that extend nearly to the tip of the border spines.
Occurrence.-Mcdiom to dark gray wackstones and packstones of the Huaqaio
Formation, western Hunan. In the Paibi section, this species occurs in rocks correlated with the Lingiiagnostus reconditus Zone.
Family RJHYSSOMETOPIDAE Opik, 1967
Genus RHYSSOMETOPUS Opik, 1967
Type species.-Rhyssometopus (Rhyssometopus) rhyssometopus, Opik (1963, p. 273).
Discussion.-The generic concept of Peng (1987, p. 100) is followed here.
66 RHYSSOMETOPUS ZHONGGUOENSIS Zhou in Zhou, Liu, Meng, and Sun, 1977
Figure II.8, 19.3
Rhyssometopus (Rhyssometopus) zhongguoensis ZHOU in ZHOU, LIU, MENG, and
SUN, 1977, p. 209, PI. 61, figs. 19-20.
New material.-Aboni ten cranidia in PLB 341.7, 353.7, 361.5, 363.7, and 374.9..
Remarks.-How material from the Huaqaio Formation, western Hunan, resembles the type material from western Hunan. This species has a cephalon with a wide preglabellar field, a narrow anterior border, wide fixigena, relatively small eye lobes, and a wide occipital ring with a small medial node.
Occurrence.-M.e6.mm to dark gray wackestones and packstones of the Huaqaio
Formation, western Hunan. In the Paibi section, this species occurs in rocks correlated with the Linguagnostus reconditus, Glyptagnostus stolidotus, and Glyptagnostus reticulatus Zones.
RHYSSOMETOPUS cf. R. SINENSIS Peng, 1987
Figure 11.11
Rhyssometopus sinensis ?ENG, 1987, p. 100, PI. 8, Figure 12, text-Figure 13.
New material.-bess than ten cranidia in PIB 273.8, 278.1, 296.4, 298.54, and 341.7.
Remarks.-blew material from the Huaqaio Formation, western Hunan, is similar to the type material from western Hunan. The new material is similar to the type material in
67 having a long, wide glabella, distinct lateral glabellar furrows, a narrow preglabellar field, and narrow fixigena. There are a few characters in the new specimens that differ somewhat from the type material. The new material does not always have a well developed notch in the anterior portion of the glabella; the posterolateral limbs of the fixagena appear to be a bit larger; and there are also fine granules on the cranidium.
Since the type material is, like the new material, from the Huaqaio Formation in western
Hunan, the species concept may need to be expanded to accommodate the variations found in the new material.
Occurrence.-Medium to dark gray wackestones and packstones of the Huaqaio
Formation, western Hunan. In the Paibi section, this species occurs in rocks correlated with the Lejopyge laevigata Zone.
RHYSSOMETOPUS? sp. 1
Figure 11.12
Material.-A. single cranidium in PEB 115.6.
R e m a r k s material from the Huaqaio Formation, western Hunan, is questionably assigned to the genus Rhyssometopus. The new material possesses several features common to the genus, including a convex glabella, a small preglabellar field, a wide, deep occipital furrow, an occipital ring that is widest in the middle, and narrow posterolateral lobes of the fixigena.
There are several characters that are not in other species o f this genus including narrow fixigenae and small palpebral lobes located in the midline of the glabella.
68 Additionally, the glabella is parallel-sided. Species of Rhyssometopus usually have a glabella that is gently curved and widest in the middle.
Occurrence.-Axg\W?LCQO\xs limestone in the Lejopyge laevigata Zone of the Huaqaio
Formation, western Hunan.
Order CORYNEXOCHIDA Kobayashi, 1935
Family CORYNEXOCHIDAE Angelin, 1854
Genus CHATIANIA Yang, 1978
Type species.-Chatania chatianensis Yang, 1978.
Discussion.-The. generic concept of Yang (1978, p. 36) is followed here.
CHATIANIA CHATIANENSIS Yang, 1978
Figure 13.6
Chatiania chatianensis YANG in ZHOU, LIU, MENG, and SUN, 1977, p. 377, PI. 43,
figs. 14-15; YANG, 1978, p. 36, PI. 5, figs. 5-7; LIU, 1982, p. 886, PI. 217, figs. 9-12;
PENG, 1987, p. 92, PI. 5, Figure 18; DONG, 1990, p. 79, PI. 3, Figure 13; DONG,
1991, p. 457, PI. lU, Figure 10.
New material.-M.oiQ than ten cranidia in PIB 331.8, 341.7, 353.7, 361.5, and 362.4.
Remarks.-Now material from the Huaqaio Formation resembles the type material from the same area in western Hunan. A relatively large, low convexity, forwardly expanding glabella; a narrow, flat, preglabellar field; and moderately large palpebral lobes characterize this species.
69 Occurrence.-Axg\W?iceous limestone in theAmmognostus integriceps-Chatiania Zone of
the “Paotaishan” Formation, western Hunan. In the Paibi Section, Hunan, this species
occurs in dark gray wackestones and packstones of the Huaqaio Formation that are
correlated with the Linguagnostus reconditus Zone.
CHATANIA sp. I
Figure 13.5
Material.-ÉK. single cranidium in PIB 308.
Diagnosis.-Species ofChatania with a short, wide glabella, three faint pairs of lateral
glabellar furrows, and large palpebral lobes in which the posterior end is close to the
axial furrow.
Description.-Cvanidium longer than wide, having low convexity. Anterior border flat,
moderately wide, uniformily curved. Glabella moderately convex, wide, expanding
forward slightly, nearly parallel-sided, extending to anterior border, with anteromedial
notch. Lateral glabellar furrows faint, S1 and 82 posteromedially directed; S3 anteromedially directed. Fixigena narrow. Palpebral lobes long, posterior end extending close to the axial furrow. Occipital furrow moderately deep, transverse. Occipital ring wide, bearing small median node. Surface smooth.
Remarks.-This species resembles Chatania chatianensis in most cranidial characters.
However, it differs from that species in having a more nearly straight-sided glabella, and palpebral lobes of different shape (longer, extending closer to the axis at the posterior end).
70 Occurrence.-bAeàhxm to dark gray packstone of the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated with theLinguagnostus reconditus Zone.
Family DORYPYGIDAE Kobayshi, 1935
Genus DORYPYGE Dames, 1883
Type species.-Dorypyge richthofeni Dames (1883, p. 24).
Discussion.-Th.e. genus concept of Zhang and Jell (1987, p. 56) is followed here.
DORYPYGE RICHTHOFENI Dames, 1883
Figure 12.3, 12.7
Dorypyge richthofeni DAMES, 1883, p. 24, PI. 1, figs. 1-6; WAI.COTT, 1913, p. 108,
Pi. 8, figs. 1, la-f; KOBAYASHI, 1937, p. 434, PL 17, figs. 13a, b; SCHRANK, 1977,
p. 145, PI. 1, figs. 1-6; PI. 2, figs. 1-5; ZHANG and JELL, 1987, p. 58, PI. 12, figs. 4-7;
PI. 13, figs. 1-10; PI. 15, Figure 7.
Dorypyge (Olenoides) richthofeni LORENZ, 1906, p. 81, PI. 4, figs. 1-5.
Dorypyge lorenzi RESSER, 1942, p. 18.
Dorypyge suni RESSER, 1942, p. 19.
Dorypyge shantungensis KES'SEK, 1942, p. 19.
Dorypyge chihliensis RESSER 1942, p. 19.
New material. Numerous sclerites, including both cranidia and pygidia, in PEB 7.25,
42.5, 81, 108, 121.48, and 126.
71 iîe/wûrÆs.-Specimens from the Huaqiao Formation in western Hunan are quite similar to the type material from in Shandong, North China (Dames, 1883). The key points of comparison are six pairs of marginal spines on the pygidium, four axial rings and a terminal piece on the pygidial axis, and coarse, widely-spaced granules on the cranidium.
The species has been redescribed numerous times by Walcott (1913), Schrank (1977), and Zhang and Jell (1987) using Dames’s original specimens. Resser (1942) erected numerous new species using Dames’s original material, although he did not figure any of the specimens. Zhang and Jell (1987) reviewed this material and synonymized all of
Resser’s species into D. richthofeni.
Occwrence.-Thc type material occurs in oolitic limestone and interbedded limestone and shale in the Amphoton Zone of the Changhia Formation, Shandong, China. The species has a wide distribution through China, where it occurs in Middle Cambrian strata.
In the Paibi section, Hunan, it occurs in dark gray wackestones and packstones of the
Huaqaio Formation that are correlated with thePtychagnostus atavus, Ptychagnostus punctuosus, and Goniagnostus nathorsti Zones.
DORYPYGE BISPINOSA Walcott, 1905
Figure 12.4, 12.8
Dorypyge bispinosa WALCOTT, 1905, p. 28; WALCOTT, 1913, p. 107, PI. 8, Figure 3;
CHANG in LU, CHANG, CHU, CHIEN, HSIANG, 1965, p. 99, PI. 15, Figure 1;
ZHANG and JELL, 1987, p. 60, PI. I4,Figure 12.
New material.-One cranidium and two partial pygidia in PIB 130.25 and 130.95.
72 R e m a r k s . specimens from the Huaqiao Formation of western Hunan fall within the species concept ofD. spinosa (Walcott, 1905, 1913; Chang, 1965; Zhang and Jell, 1987) from regions south of Yanzhuang, Xintai district, Shandong in North China. The character that distinguishes this species from all others is the presence of two pairs of long marginal spines on the pygidium.
Occurrence.-Oolitic limestone and interbedded limestone and shale in the Amphoton zone of the Changhia Formation, Shandong. In the Paibi section, Hunan, this species occurs in dark gray wackestones and packstones of the Huaqaio Formation that are correlated with the Goniagnostus nathorsti, Lejopyge laevigata, and Proagnostus bulbous Zones.
DORYPYGE PERGRANOSA? Resser and Endo, 1937
Figure 13.1
Dorypyge pergranosa RESSER and ENDO, 1937, p. 210, PI. 31, figs. 6-13; CHANG in
LU, CHANG, CHU, CHIEN, HSIANG, 1965, p. 103, PI. 15, figs. 13-14; ZHANG and
JELL, 1987, p. 59, PI. 14, figs. 1-11; PI. 15, figs. 1-5, 8-9, 12.
Dorypyge matsushitai RESSER and ENDO, 1937, p. 210, PL 43, figs. 22-24; CHANG in
LU, CHANG, CHU, CHIEN, HSIANG, 1965, p. 102, PI. 15, Figure 12.
Dorypyge bigranosa RESSER and ENDO, 1937, p. 212, PI. 44, figs. 15-20.
Dorypyge pergranosa bilobata CHANG in LU, CHANG, CHU, CHIEN, HSIANG,
1965, p. 103, PL 15, Figure 15.
New material.-S>ing\e broken cranidium from PIB 97.25.
73 Remarks.-A single broken cranidium is questionably assigned to this species. Whereas it is similar to D. pergranosa in having a broad, subquadrate glabella, it differs from typical D. pergranosa having coarser granulation. Zhang and Jell (1987) also stated that this species is small for the genus, but the this cranidium from PIB 97.25 is as large as many ofD. richthofeni. With no pygidium to compare to the type material, the cranidium cannot be positively assigned to this species.
Occurrence.-ThQ type material is found in oolitic limestone and shale of the
Crepicephalina Zone of the Changhia Formation, Liaoning, North China. In the Paibi section, Hunan, this species occurs in dark gray wackestone of the Huaqaio Formation that is correlated with the Ptypcagnostiis atavus Zone.
DORYPYGE sp. 1
Figure 12.9, 12.10
Material.-One cranidium and one pygidium in PIB 81.
Z)/ag7zo5/5.-Species of Doipyge lacking granules, having a wide parallel sided glabella with a deep notch at the antennal pits and a pygidium that posseses five axial rings and a long terminal piece in the axis and five pairs of marginal spines.
D escription. convex. Anterior border narrow, broadly rounded. Glabella wide, nearly parallel sided, with a deep notch at the antennal pit. Occipital furrow shallow, deepening at sides. Occipital ring wide. Eye ridge wide. Posterior border furrow moderately well defined.
74 Pygidium wider than long, with an axis that has four rings and a long terminal piece.
Marginal spines consist of five pairs. Surface granulation absent from the cranidium and pygidium.
Remarks.-This species, apparently new, is represented by few incomplete sclerites. In cranidial characters, it seems to most closely resemble D. pergranosa. However, it differs from D. pergranosa in having a less rounded glabella anteriorly, and in lacking granules.
Occurrence.-M.Qhi\xm to dark gray packstone of the Huaqaio Formation, Paibi, China where is occurs in rocks correlated with thePtychagnostus atavus interval-zone.
DORYPYGE sp. 2
Figure 12.2
Material.-One. cranidium in PIB 81.
Dmg770^/5.-Species ofDorypyge with a wide, bulbous, anteriorly expanding, glabella, large, closely spaced granules cover the surface.
Description.-Crzmdhxm wider than long. Anterior border narrow, broadly curved.
Axial furrow deep. Glabella wide, bulbous, anteriorly expanding, with small notch at antennal pit. Fixagena narrow. Eye ridge faint. Palpebral lobes short, located near middle of the glabella. Posterior border furrow deep, wide.
Remarks .-This species is known from incomplete sclerties that are too poorly preserved to allow detailed comparison to most described species in this genus. However, this species has one of the widest glabellas known in the genus.
75 This species has a disjunct stratigraphie distribution, occuring in rocks correlated with the Ptychagnostus punctuosus and Lejopyge laevigata Zones, but not in the Goniagnostus nathorsti Zone. Because this species is known from few specimens, it is uncertain whether this punctuated distributional pattern is the result of ecological factors or the reappearance upsection of resedimented sclerties.
Occurrence.-M&à\\xm to dark gray packstone of the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated with thePtychagnostus punctuosus and Lejopyge laevigata Zones.
DORYPYGE sp. 3
Figure 12.6
Material. -M.OVQ than ten sclerites, including both cranidia and pygidia, in PIB 249,
273.52, 273.8, 282.75(7), 283.47(7), and 283.75.
Z)/ag7205zr.-Species of Dorypyge with a glabella that expands forward and is covered with finer granules than the fixagena, lacking an anterior border, an angular anterior portion of the cranidium, and a stout, very long, last pair of pygidial spines.
Description.- Cranidium wider than long, with finer granules on the glabella than on the fixagena. Front of the cranidium angular. Axial furrow moderately shallow with deep antennal pits. Glabella convex, with weak furrows. Occipital furrow well defined.
Occipital ring curved, widest medially. Palpebral lobe weakly expressed, short. Anterior border and preglabellar field absent. Anterior sections of the facial sutures converge forward; posterior sections long. Posterior border furrow well defined.
76 Pygidium rounded, with five pairs of spines, the last pair being very long and stout.
Three axial rings and a rounded terminal piece. Well developed interplueral furrows
with almost no border furrow.
Occw/re/zce.-Axgillaceous limestone in theLejopyge laevigata Zone of the Huaqaio
Formation, western Hunan.
DORYPYGE? sp.
Figure 12.1
Material.-On. 0. pygidium from PIB 290.5.
Remarks.-A. single pygidium is tentatively placed in the genus Dorypyge. The pygidium
resembles some other pygidia ofDorypyge in having five pairs of marginal spines, six
axial rings and a short terminal piece, weak interpleural furrows, strong pleural furrows,
and coarse granules. However, it differs in being narrow, and having a postaxial ridge
extending to the posterior margin.
Occurrence.-Medium to dark gray packstone of the Huaqaio Formation, Paibi, China,
where it occurs in rocks correlated with theLejopyge laevigata Zone.
Family DOLICHOMETOPIDAE Walcott, 1916
Genus AMPHOTON Lorenz, 1906
Type species .-Amphoton steinmanni Lorenz, 1906, p. 89 (subjective junior synonym of
Dolichometopus deois Walcott, 1905).
77 Remarks.-The generic concept of Zhang and Jell (1987, p. 62) is followed here. Yang
(1978) erected the subgenus Paramphoton, although no additional subgenera have been
erected. It is considered to be a junior synonym in this project.
AMPHOTON DEOIS (Walcott, 1905)
Figures 13.3,13.4
Dolichometopus deois WALCOTT, 1906, p. 94; WALCOTT, 1913, p. 216, PI. 21, figs.
13, 13a-d; PI. 22, figs. 1, la-g, 2, 2a, 2b; SUN, 1924, p. 81, PI. 5, Figure 9.
Dolichometopus (?) deois WALCOTT, 1916, p. 365, PI. 54, figs. 1, la-b, 2.
Dolichometopus dirce WALCOTT, 1905, p. 96 (cephalon only); WALCOTT, 1913, p.
218, PL 22, Figure 5 (not PI. 22, figs. 5a-b).
Amphoton steinmanni LORENZ, 1906, p. 89, PI. 4, figs. 15-17.
Bathyuriscus asiaticus LORENZ, 1906, p. 87, PI. 5, figs. 1-5.
Amphoton deois KOBAYASHI, 1935, p. 138, PL 22, Figure 12; RESSER and ENDO,
1937, p. 205, PL 38, Figures 1, 9; KODAYASHI, 1942, PL 1, Figure 10; LU, 1957, p.
263,
PL 140, Figure 5; CHANG in LU, CHANG, CHU, CHEN, and HSIANG, 1965, p. 113,
PL 17, Figure 16; SHRANK, 1977, p. 148, pi. 2, Figures 6-7; PL 3, Figure 1; ZHANG and
JELL, 1987, p. 63, PL 17, Figures 2-14; Pis. 18-20, 23; PL 22, Figures 1-7; PL 122,
Figure
5.
Dorypyge manchuriensis RESSER and ENDO, 1937, p. 208, PL 31, Figure 3.
78 Amphoton parallela RESSER and ENDO, 1937, p. 206, PI. 38, figs. 2-8, 10-13; PI. 39,
figs. 19-20.
Amphoton alia RESSER and ENDO, 1937, p. 207, PI. 38, figs. 14-18.
Amphoton divergens RESSER and ENDO, 1937, p. 208, PI. 48, figs. 31-32 (not PI. 48,
Figure 33).
Amphoton blackwelderi RESSER, 1942, p. 5.
Amphoton kaipingense RESSER, 1942, p. 5.
Eurodeois deois ÔPIK, 1982, p. 58, PI. 20, Figure 5.
New material.-Mor& than ten sclerites, including both cranidia and pygidia, in PIB 115.6 and 130.
Remarks.AA qw material from the Huaqaio Formation, western Hunan, resembles described material from North China and Australia in all respects.
Occurrence.-OoXilic limestone and shale of theAmphoton Zone of the Changhia
Formation, Shandong, north China, limestone in thePtychagnostus punctuosus Zone of the Currant Bush Limestone, Australia. In the Paibi section, Htman, this species occurs in dark gray wackestones and packstones of the Huaqaio Formation that are correlated with the PtychagJtostus punctuosus Zone.
AMPHOTON XIANGXIENSIS Yang, 1978
Amphoton xiangxiensis YANG, 1978, p. 34, PI. 4, figs. 9-10.
79 New material. - M o x q than ten sclerites, including both cranidia and pygidia, in PIB 42.5,
108, and 108.5.
Remarks.-New material from the Huaqaio Formation, western Hunan, closely resembles
the type material which is also from the Huaqaio Formation of western Hunan.
Occurrence.-In the Paibi section, Hunan, this species occurs in dark gray wackestones
and packstones of the Huaqaio Formation that are correlated with thePtychagnostus
atavus, Ptychagnostus punctuosus, and Goniagnosuts nathosrsti Zones.
Genus FUCHOUIA Resser and Endo in Kobayashi, 1935
Type species.-Bathyuriscus manchuriensis Walcott, 1911, p. 49.
£>frcî<55io«.-The generic concept of Zhang and Jell (1987, p. 66) is followed here.
FUCHOUIA CHIAI
Figure 12.11, 13.2, 13.10, 13.12-13.13
Fuchouia chiai LU, 1957, p. 264; ERGORAVA, XIANG, LI, NAN, GUO, HSIANG,
LEE, NAN, and KUO, p. 31, PI. 4, figs. 3-6.
Mater/a/.-More than thirty sclerites, including both cranidia and pygidia, in PIB
112.42, 115.6, 121.48, 126, 130, 130.25, and 130.95.
Diagnosis . o fFuchouia with an anteriorly expanded, proportionately large
glabella and a rounded margin.
Description.-Cxdimàinm widest at posteriolateral limbs. Glabella expands anteriorly, proportionately large. Axial furrows moderately deep, expanding forward. Preglabellar
80 field short to absent. Palpebral lobe moderately strong, located near the midline of the glabella. Fixagena narrow. Posteriolateral limbs blade-like.
Pygidium semicircular, poorly segmented. Interpleural furrows weak to absent.
Occurrence.-AxgiWzLCQOxxs, limestone in the Goniagnostus nathorsti Zone to theLejopyge laevigata Zone of the Huaqaio Formation, western Hunan.
FUCHOUIA ORATOLIMBA Yang, 1978
Figure 13.7
Fuchouia oratolimba YANG, 1978, p. 33, PI. 4, figs. 5-7; LU and LIN, 1983, p. 241,
PI. 17, figs. 1-8.
New material.-Maze, than thrity sclerites, including both cranidia and pygidia, in PIB
0.25, 7.25, 71.35, 80.5, 82, 82.8, 84.85, 85.52, 90, 93.7, 97.25(7), 98, and 108.
R e m a r k s material from the Huaqaio Formation, western Hunan, closely resembles the type material, which is from the Huaqaio Formation and equivalent strata of western
Hunan and eastern Guizhou.
Occurrence.-M&dinm to dark gray packstones of the Huaqaio Formation, western
Hunan, where it occurs in rocks correlated with the Ptychagnostus atavus Zone.
FUCHOUIA sp. I
Figure 13.8-13.9, 13.11 Material. -M oxq than forty sclerites, including cranidia, pygidia, and thoracic segments,
in PIB 237.25, 260.08, 273.46(7), 273.52, 273.6, 273.66, 273.8, 278.04, 278.1, 279.7,
282.95, 283.47, and 283.75(7).
Diagnosis . o fFuchouia with a long, slender, parallel-sided glabella, short
preglabellar field, and strong S1, S2, and S3. Pygidium having seven axial rings, eight
pleural furrows, and seven interpleural furrows.
Description.-Cvzmdhxm wider than long. Anterior border convex, weakly bowed
forward. Preglabellar field short. Glabella long, slender, nearly parallel-sided, with three
pairs of lateral glabellar furrows, 81 distinct, strongly postero laterally diverted; 82
distinct, weakly posterolaterally diverted; 83 distinct, weakly anterolaterally diverted.
Anterior part of the fixigena narrow, posterior branch wide. Eye ridge short, distinct.
Palpebral lobe moderately long for genus. Occipital furrow distinct, deepest at sides.
Occipital ring wide medially, narrow at sides; having small medial node.
Thorax having eight segments. Pleural area flat, with strong interpleural furrow;
termination blunt.
Pygidium semicircular, much wider than long. Axis narrow, having seven rings and
terminal piece. Plural area flat, having eight pleural furrows and seven interpleural
furrows.
8urface smooth.
Remarks .-This, species, which is apparently new, is unique to this genus in possessing
the combination of strong 81, 82, 83 lateral glabellar lobes, and in having a pygidium with seven axial rings, eight pleural furrows, and seven interpleural furrows.
82 Occzfrre/zce.-Medium to dark gray packstone of the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated with theLejopyge laevigata and Proagnostus bulbous
Zones.
Order LICHIDA Moore, 1959
Family DAMESLLIDEA Kobayashi, 1935
Subfamily DAMESELLINAE Kobayashi, 1935
Genus BLACKWELDERIA Walcott, 1906
Type species.-Calymene? sinensis Bergeron, 1899.
Discussion.-T\iQ generic concept of Walcott (1905, p. 35) is followed here.
BLACKWELDERIA n. sp.
Figure 14.3-14.4
Mdrerza/.-Single cranidium and single pygidium in PIB 298.54.
Diagnosis.Sptcits ofBlach,velderia having a wide glabella, deeply incised S1 and 82 lateral glabellar furrows, narrow fixagena, wide anterior border, and seven pairs of marginal spines, plus a medial spine, on the pygidium.
Description.- Cranidium about twice as wide as long, moderately convex. Granules large, bimodal in size, and covering the surface except for marginal areas, extending to anterior border. Anterior border wide, upturned. Glabella wide, slightly tapering forward 81 deep, posteromedially directed, isolating a small lateral lobe; 82 shallow, nearly transverse, intersecting 81 at axial furrow; S3 deep, posteromedially deirected.
Palpebral lobe weak, posteriorly directed. Palpebral lobe short.
8 3 Pygidium wider than long. Axis narrow, slightly tapering posteriorly, with six rings and a short terminal piece. Pleural field containing five deep pleural furrows and four shallow interpleural furrows. Marginal spines consist of seven pairs of long, narrow spines plus a medial spine.
Surface area, except for marginal areas, covered with large but bimodally sized granules.
/2emarÂ::s.-This species, apparently new, is similar to Blackwelderia sinensis. However,
Balckwelderia n. sp. differs from Blackwelderia sinensis in having a medial spine on the pygidium and longer, thinner marginal spines. Blackwelderia paronai posseses similar long, thin marginal spines on the pygidium but lacks the medial spine and also has a different granulation pattern.
Occurrence.-Mtàmm to dark gray packstone of the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated with theLinguagnostus reconditus Zone.
Genus MERINGASPIS Opik, 1967
Type species.-Meringaspis meringaspis Opik (1967, p. 323).
Discussion.-Th& generic concept of Opik (1967, p. 323) is followed here. The genus
Paradamesops (Yang, 1974) is apparently a junior synonymo ïMeringaspis. Type material ofParadamesops jiamaensis, the type species from western Hunan, is similar to the type material ofMeringaspis (particularly Meringaspis meringaspis, the type species from Queensland, Australia), in all respects except the posterior of the pygidium. InM. meringaspis, Opik (1963) interpreted the posterior portion of the pygidium to be pointed, or triangular. However, upon further examination of the photographs of the type material
84 (Opik, 1963, PI. 45, figure 2), this part of the pygidium is broken, and the shape cannot be positively identified. In Paradamesops jiamaensis, the posterior of the pygidium is rounded. The difference between these two forms, if substantiated, is interpreted to be a specific rather than a generic difference.
MERINGASPIS JIAMAENSIS Yang, 1978
Figure I4.I-I4.2
Genus and species indeterminate, EGOROVA, XIANG, LI, NAN, and KUO, 1963, p.
43, PI. 7, figs. 7-8.
Paradamesops Jiamaensis YANG in LU, CHU, CHIEN, LIN, ZHOU, and YUAN, 1974,
p. 86, PI. I, figs. 15-16; PI. 2, Figure 11; YANG in ZHOU, LIU, MONG, and SUN,
1977, p. 199, PI. 58, figs. 9-11; YANG, 1978, p. 58, sp. 13, figs. 1-2; YIN and LI,
1978, p. 511, PI. 170, Figure lO-II.
Me\v material.-hAort than twenty pygidia, a single cranidia, and a hypostome, in PIB
237.25, 259.85, 260.08, 273.66, 273.8, 278.1, 279.7, 282.75, 283.47, 283.67, 283.75
290.5, 293.21, 295.13, and 298.54.
R e m a r k s material form the Huaqaio Formation, western Hunan, resembles the type material from western Hunan. Key features of this species include a cranidium having a strongly convergent anterior of the facial suture, an eye ridge that is obliquely forwardly directed, an eye lobe that is anteriorly located, a narrow posterolateral limb of the fixigena, and a short, wide pygidium that is rounded posteriorly.
85 Herein, a hypostome that apparently belongs to this species is illustrated (Figure
13.21). The central body is wide, with a narrow anteriorly bowed ring anteriorly and a large, bulbous, posteriorly expanding lobe posteriorly. The anterior rings are wide and strongly curved anteriorly.
Occurrence . t o dark gray packstone of the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated to theLejopyge laevigate, Proagnostus bulbus,
Linguagnostus reconditus Zones.
Genus FARADAMASELLA Yang, 1978
Type species.-Paradamesella typica Yang, 1978, p. 55.
Discussion.-T\ lIQ genus concept of Yang (1978, p. 55) is followed here.
PARADAMESELLA TYPICA Yang, 1978
Figure 14.5-14.6
Paradamasella typica YANG, 1978, p. 56, PI. 12, figs. 1-8.
New material.-Ltss than ten sclerites, but including both cranidia and pygidea, from
PIB 353.7.
Remarks.-N q-w material from the Huaqaio Formation, western Hunan, resembles the type material from western Hunan and eastern Guizhou. Key characters that warrant placement of the new material into this species include a cephalon with a wide pleural field and long, thin spines on the pygidium.
86 Occurre«ce.-The Paradamesops jimaensis-Cyclolorenzella tuma Zone of the Huaqiao
Formation, western Hunan and eastern Guizhou. In the Paibi section, Hunan, this species occurs in dark gray wackestones and packstones of the Huaqaio Formation that are correlated with the Lingiiagnostus reconditus Zone.
PARADAMESELLA NOVEMOSPINOSA Yang, 1978
Figure 14.8-14.10
Paradamasella paratypica YANG, 1978, p. 56, PI. 7, Fig. 9.
Paradamasella novemospinosa YANG, 1978, p. 57, PI. 12, Fig. 10.
Paradamasella decemosplnosa YANG, 1978, p. 57, PI. 12, Fig. 11.
Paradamasella septemispinosa YANG, 1978, p. 57, PI. 12, Fig. 12.
New material.-Move than ten sclerites, including cranidia, pygidea, and fixagena, in PIB
283.47, 293.21, and 317.2.
Remarks.-Based upon new material from the Huaqaio Formation and Chefu Formation, western Hunan, Paradamasella novemospinosa, P. decemosplnosa, and P. septemispinosa are synonymized with P. paratypica as the new specimens have a spectrum of characters indicating that these four Yang (1978) species are gradational.
Key characters in the expanded species description include a cephalon with a narrow pleural field, a pygidium with an axis that is relatively thicker than in P. typica and nine to eleven pairs of wide, triangular spines.
Occurrence.-A.vg\\\aceous limestone in the Lejopyge laevigata Zone of the Huaqiao
Formation in western Hunan and eastern Guizhou. In the Paibi section, Hunan, this
87 species occurs in dark gray wackestones and packstones of the Huaqaio Formation that
are correlated with the Lingiiagnostus reconditus Zone.
Genus PRODAMESELLA Chang, 1957
Type species.-Prodamesella convexa Chang (1959, p. 196).
Discussion.-Tht generic concept of Chang (1959, p. 218) is followed here. The type
species was illustrated by Chang (1957) but not described until later (Chang, 1959).
PRODAMESELLA BISERRATA Jell in Jell and Robison, 1978
Figure 14.18
Prodamesella biserrata JELL in JELL and ROBISON, 1978, p. 17, PI. 1, Figure 9; PI. 4,
figs. 1-6.
New material.-Less than ten cranidia in PIB 115.6, 130.25, and 273.8(?).
Remarks.-'blew material from the Huaqaio Formation, western Hunan, closely resembles the type material from northwestern Queensland, Australia. Important characters in the new material include a semicircular, convex, nearly smooth cranidium with a short, curved anterior border and a glabella having an anteromedial notch.
Occurrence.-Livaestone in the Peronopsis opimus Zone of the Current Bush Limestone,
northwestern Queensland, Australia. In the Paibi section, Hunan, this species occurs in
dark gray wackestones and packstones of the Huaqaio FormationGoniagnostus nathorsti
and Lejopyge laevigata Zones.
88 PRODAMESELLA SUBTRIANGULATA Peng, 1987
Figure 14. II
Prodamasella subtriangiilata PENG, 1987, p. 105, PI. 8, Figure 13.
New material.-N single cranidia in PIB 319.6.
Remarks.-N qw topotypic material from the Huaqaio Formation, western Hunan, closely resembles the type material. Key characters that warrant placement of the new material into this species include a long, somewhat narrow cranidium, with a curved anterior margin, a short eyeridge, and glabella having an anteromedial notch.
Gccurre«ce.-Medium to dark gar>' packstone of the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated with theLingiiagnostus reconditus Zone.
Genus PROTAITZEHOIA Yang, 1978
Type species.-Protaitzehoia granifera Yang, 1978, p.59.
Discussion.-T )\q genus concept of Yang (1978, p. 59) is followed here.
PROTAITZEHOIA GRANIFERA Yang, 1978
Figure 14.15
Blackwelderia sp. HSIANG in ERGOROVA, HSIANAG, LI, NAN, and, KUO, 1963, p.
40, PI. 8, Figure 4; LU, CHANG, CHU, CHIEN, and HSIANG, 1965, p. 383, PI. 72,
Figure 4.
Protaitzehoia granifera YANG, 1978, p. 60, PI. 13, Fig. 8, PENG, 1987, p. 100, PI. IX,
Fig. 4.
89 New material.-NhovX ten sclerites, mostly broken cranidia, from PIB 249, 282.75,
298.54, and 331.8.
R e m a r k s . material from the Huaqiao Formation, western Hunan, resembles the type material from western Hunan. Key characters that warrant placement of the new material into this species include a long cranidium; a narrow, long glabella that is constricted in the middle; and a narrow fixigena.
Occurrence.-M.Q6.mm to dark gray packstone of the Hauqaio Formation, Paibi, China, where it occurs in rocks correlated with theLejopyge laevigata Zone.
PROTAITZEHOIA SUBQUADRATA Peng, 1987
Figure 14.7
Protatzehoia subquadrata PENG, 1987, p. 101, PI. IX, figs. 5-6.
New material.-'L qs',s than ten sclerites in PIB 319.6, 326.9, and 341.7.
Remarks.-'N qw material from the Huaqaio Formation, western Hunan, is closely similar to the type material from western Hunan. Characters that warrant placement of the new material into this species include a relatively wide cranidium, a wide, short glabella that is weakly constricted in the middle and a wide fixigena.
Occurrence.-MQ6mm to dark gray packstone of the Huaqaio Fomation, Paibi, China, where it occurs in rocks correlated with the Lingiiagnostus reconditus Zone.
90 PROTAITZEHOIA YUEPINGENSIS Yang, 1978
Protaitzehoiayiiepingensis YANG, 1978, p. 60, PI. 13, Figure 4.
New material. - L q s s than ten sclerites in PIB 308 and 316.1.
Remarks.-Now material from the Huaqaio Formation, western Hunan, resembles the
type material from the same area. Key characters of this speices include a cephalon
having a shallow anterior border furrow and lacking granules.
Occurrence.-Mtàxvim. to dark gray packstone of the Huaqaio Formation, Paibi, China,
where it occurs in rocks correlated with theLinjuagnostus reconditus Zone.
Subfamily DORYPYGELLINAE Kobayashi, 1935
Genus TEINISTION Monke, 1903
Type species.-Teinistion lansi Monke (1903, p. 117).
Discussion.-T\iQ generic concept of Zhang and Jell (1987, p. 218) is followed here.
TEINISTION POSTEROCOSTUM (Yang, 1977)
Figure 14.16-14.17
Dorypygella posterocosta YANG in ZHOU, LIU, MENG, and SUN, 1977, p. 200, PI. 59,
figs. 15-16; YANG, 1978, p. 63, PI. 11, figs. 7-11.
Teinistion sp. LU and LIN, 1989, p. 254, PI. 22, fig. 8.
91 New material.-NI ovq than twenty sclerites, including both cranidia and pygidia, in PIB
273.46, 317.2, 319.6, 326.9, 341.7, 353.64, and 361.5.
Discussion.-N qw material from the Huaqaio Formation, western Hunan, resembles the type material from western Hunan and eastern Guizhou. Key characters of this species include a glabella that is moderately tapered forward and truncated anteriorly; occipital furrows that curve forward at sides, and a distinct broad, long, triangulate pygidium that possesses long, flat marginal spines and deep pleural furrows.
The specific name has been modified to P. posterocostum from P. posterocosta in order to agree with the neuter gender of the generic name.
Occurrence.-Medium to dary gray limestone from the Huaqaio Formation of western
Hunan and eastern Guizhou. In the Paibi section, this species occurs in dark gray wackestones and packstones of the Huaqaio Formation that are correlated with the
Linguagnostus reconditus Zone.
Subfamily DREPANURINAE Hupé, 1953
Genus PALAEADOTES Opik, 1967
Type species.-Palaeadotes dissidens Opik (1967, p. 341).
Discussion.-T\ve genus Palaeadotes has commonly been considered a subgenus of
Bergeronites. Significant differences between Bergeronits {Palaeodotes) and
Bergeronites {Bergeronites) support using Palaeadotes as a separate genus. In
Bergeronites, the cranidium does not taper forward like it does in Palaeadotes-, rather, it is curved, or drum-shaped. Bergeronites has smaller eye lobes than Palaeadotes. In
92 Palaeadotes, the first pair of lateral glabellar furrows bifurcates, whereas in Bergeronites it does not. Palaeadotes also possesses a weakly defined posterolateral lateral glabellar lobe. The pygidia of the two genera are also different. Palaeadotes possesses incomplete interpleural and pleural fLirrows. The interpleural furrows are effaced near the axial furrows and then become very deep. The first pair of marginal spines is stronger in Palaeadotes than in Bergeronites. Palaeadotes possesses a complete border and border furrow. The axis of Palaeadotes is generally larger than in Bergeronites.
PALAEADOTES HUNANENSIS Yang, 1977
Figure 14.12-14.14
Drepanura sp. EGOROVA, HSIANG, LI, NAN, and KUO, 1963, p. 39, PI. 13, Figure 2.
Bergeronites himanensis YANG in ZHOU, LIU, MENG, and SUN, 1977, p. 199, PI. 59,
figs. 6-8; YANG, 1978, p. 61, PI. 10, figs. 6-10.
Bergeronites austriacus YANG, 1978, p. 62, PI. 11, figs. 3-4 (not 1-2).
Bergeronites (Palaeadotes) hunanensis PENG, 1987, p. 106, PI. 11, figs. 1-5, 14.
New material.-Moro. than thirty sclerites, including cranidia, pygidia, and fixagena in
PIB 279.7, 282.75, 290.5,293.21, 295.13, 298.54, 308, 316.1, 317.2, 326.9, 331.8, 341.7,
353.64, and 353.7.
Remarks.-'Now material from the Huaqaio Formation, western Hunan, resembles the type material from the western Hunan. This species is distinguished by a short, wide glabella, a narrow and upturned anterior border, a very thick axis on the pygidium, and shallow pleural and interpleural furrows on the pygidium.
93 Occurrence.-Medium to dark gray packstone o f the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated with theLejopyge laevigata, Proagnostus bulbus, and
Lingiiagnostus reconditus Zones.
Order PTYCHOPARIIDA Swinnerton, 1915
Family ANOMOCARELLIDAE Hupè, 1953
Genus ANOMOCARELLA Walcott, 1905
Type species.-Anomocarella chinensis Walcott, 1905.
Dzjcz(j.ymM.-The generic concept of Zhang and Jell (1987, p. 176) is followed here.
ANOMOCARELLA CONCAVA Resser and Endo, 1937
Figure 15.14
Anomocarella concava RESSER and ENDO, 1937, p. 167, PI. 35, fig. 8; ZHANG in LU,
CHANG, CHU, CHIEN, and HSIANG, 1965, p. 318, PI. 58, fig. 18; ZHANG and JELL,
1987, p. 181, PI. 78, figs. 8-9.
Manchuriella nodai RESSER and ENDO, 1937, p. 243, PI. 36, figs. 9-10; CHANG in
ZHOU, CHANG, CHU, CHIEN, and HSIANG, 1965, p. 300, PI. 54, figs. 5-6.
New material.-A single cranidia from PIB 7.25.
Remarks.-New material from the Huaqaio Formation, western Hunan is similar to the type material from southwest Liaoning in northeastern China. Key characters that
94 warrant placing the new material into this genus include a cephalon with a well developed, strong plectrum, a wide preglabellar field, and a short glabella.
Occurrence.-OoWiic limestone and shales in the Crepicephalina Zone to theAmphoton
Zone of the Changhia Formation, Liaoning. In the Paibi section, Hunan, this species occurs in dark gray wackestones and packstones of the Huaqaio Formation that are correlated with the Ptychagnostus atavus Zone.
ANOMOCARELLA? sp. 1
Figure 16.1
Material.-One cranidium from PIB 34.3.
Remarks.-A. single, broken cranidium from the Huaqaio Formation, western Hunan, is questionably assigned to the genus Anomocarella. The cranidium has a wide glabella with nearly straight axial furrows that taper forward, a slightly rounded anterior margin; and a glabella with faint lateral glabellar furrows and a carina. Most species of
Anomocarella lack distinct glabellar furrows and have a curved, or rounded, anterior margin of the glabella. Because this single specimen is broken, it can be only questionably assigned to Anomocarella.
Occurrence.-Wlç.é\\xm to dark gray packstone of the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated with the Ptychagnostus atavus Zone.
ANOMOCARELLA? sp. 2
Figure 16.4
Material.-One cranidium from PIB 34.3.
95 Remarks.-K single, incomplete cranidium from the Huaqaio Formation, western Hunan is questionably assigned to the genus Anomocarella. The cranidium has a wide, slightly constricted glabella with three pairs of faint glabellar furrows and a slightly rounded anterior margin; SI biffcates; carina. The preglabellar field seems to lack a plectrum.
Until more material is collected, this cranidium can only be questionably assigned to
Anomocarella.
Occiirrence.-M.cd{\xm to dark gray packstone of the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated with the Ptychagnostus atavus Zone.
ANOMOCARELLA sp. 3
Figure 16.5-16.6
Material.-K sclerites in PIB 80.5 and 108.
Remarks.-An incompletely known species ofAnomocarella having a narrow, slightly tapering, moderately convex, glabella; faint lateral glabellar furrows; a distinct weak eye ridge; and a short palpebral lobe.
The pygidium is wider than long, with a smooth margin, and nearly effaced. This axis is narrow and contains six rings and a terminal piece. The pleural areas contain at least four faint pleural furrows and three faint interpleural furrows. A wide, concave border is present.
The surface is smooth.
O ccurrence. to dark gray packstone of the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated with the Ptychagnostus punctuosus Zone.
96 Genus HUNANASPIS Zhou, 1977
Type species.-Hunanaspis gracilis Zhou, 1977
Discussion.-Tho. generic concept of Zhou (1977, p. 123) is followed here.
HUNANASPIS? TRUNCATUS Peng, 1987
Figure 15.13
Hunanaspis? tnincatus PENG, 1987, p. 98, PI. 7, Figure 4.
New material.-K single cranidia in PIB 319.6.
R e m a r k s . topotypic material from the Chefu Formation, western Hunan, is indistinguishable from the type material from Hunan. Key characters of this species include a cephalon with a slightly tapering, anteriorly truncated glabella and a cranidium that lacks row of pits in the anterior border furrow.
This species is questionably placed into the genus Hunanaspis because it lacks a row of pits in the anterior border furrow. The cranidium of the type species,H. gi-acilis, does possesses such pits.
O ccurrence. to dark gray packstone of the Huaqaio Formation, western Hunan.
In the Paibi section, this species occurs in rocks correlated with theLinguagnostus reconditus Zone.
Genus NEOANOMOCARELLA Hsiang, 1963
Type species.-Neoanomocarella asiatica Hsiang, 1963.
Discussion.-The generic concept of Hsiang (1963, p. 55) is followed here.
97 NEOANOMOCARELLA ASIATICA Hsiang, 1963
Figure 16.I0-I6.Il
Neoanomocarella asiatica HSIANG, 1963, p. 55, PI. 8, figs. 1-3; LU, CHANG, CHU,
CHIEN, and HSIANG, 1965, p. 255, PI. 12, figs. 9-11; ZHOU, LIU, MENG, and SUN,
1977, p. 183, Pl. 54, figs. 3-4; YANG, 1978, p. 52, PI. 8, figs. 15-17; ERGALIEV,
1980,
PI. 5, figs. 17-18; PENG, 1987, p. 99, PI. 7, figs. 13-14, PI. 8, figs. 1-3.
New material.-M.OÏQ than twenty sclerites, including both cranidia and pygidia, in PIB
295.13, 296.4, 298.54, 301.9, 305.05, 308, 331.8, and 341.7.
Diagnosis-New material from the Hauqiao Formation strongly resembles the type material from western Hunan. Characters that warrant placement of the new material in this species include a cephalon with a strong plectmm, a nearly straight-sided glabella with furrows that taper slightly forward, and a wide anterior border.
Occiirrence.-M.td\\xm to dark gray wackestones and packstones of the Huaqaio
Formation, western Hunan and eastem Guizhou, China. In the Paibi section, this species occurs in rocks correlated with theLejopyge laevigata, Proagnostus bulbous, and
Linguagnostus reconditus Zones.
Genus PARANOMOCARELLA Yang, 1977
Type species.-Paranomocarella parallela Yang, 1977.
Discussion.-The generic concept of Yang (1978, p. 53) is followed here.
98 PARANOMOCARELLA FORTIS Peng, 1995
Figure 16.9
P aranomocarella fortis PENG in PENG, LIN, and CHEN, 1995, p. 294, PL 1, fig. 12a;
PL
2, Figure 4-13; PL 4, figs. 1-4.
New marerfa/.-About ten sclerties, including both cranidia and pygidia, in PIB 130(7),
130.25, and 130.95.
Remarks .material from the Huaquiao Formation is closely similar to the type
material from the same locality. Key features that warrant placing the new material into
this species includes a cephalon with a strong plectrum, a transverse pygidium with a flat
and elevated anterior border.
Occurrence.-M.eà.i\xm to dark gray packstone of the Huaqaio Formation, Paibi, China,
where it occurs in rocks correlated with thePtychagnostus atavus, Ptychagnostus punctuosus, Goniagnostus nathorsti, and Lejopyge laevigata Zones.
PARANOMOCARELLA PARAPOLITA Yang, 1978
Figure 16.2
Paranomocarella parapolita YANG, 1978, p. 54, PL 9, figs. 4-6.
New material.-Less than ten sclerites in PIB 121.48, 126, and 130.
99 Remarks.-'Hew material from the Hauqiao Formation, western Hunan, resembles the type material from western Hunan and eastem Guizhou. Key characters that warrant placing the new material into this species include a cephalon with well developed palpebral lobes, a weak plectrum, a wide and short glabella, and wide fixigenae.
Occurrence . t o dark gray packstone of the Huaqaio Formation, western Hunan,
China. In the Paibi section, this species occurs in rocks correlated with the Goniagtxostiis nathorsti Zone.
Family ASAPHISCIDAE Raymond, 1924
Genus ZFTUJIA Ju, 1983
Type species.-Zhujia liibrica Ju in Qiu, Lu, Zhu, Bi, Lin, Zhang, Qian, Ju, Han, and
Wei, 1983.
Disciission.-VaQ generic concept of Peng (1995, p. 297) is followed here.
ZHUJIA HUNANENSIS Peng, 1995
Figure 17.1-17.2
Zhujia hunanensis PENG in PENG, LIN, and CHEN, 1995, p. 297, PI. V, figs. 7-10.
New material.-LtS5 than ten sclerties, including both cranidia and pygidia in PIB 108,
108.5, 115.6.
Remarks.-Hew, topotypic material from western Hunan is closely similar to the type material
100 Occurrence.-M&6x\xm to dark gray packstone of the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated with thePtychagnostus punctuosus Zone.
Family CATILLICEPHALIDEA Raymond, 1938
Genus BUTTSIA Wilson, 1951
Type species.-Buttsia drabensis Wilson (1951, p. 627).
Discussion.-Vaç. generic concept of Lu and Lin (1987, p. 251) is followed here.
BUTTSIA GLOBOSA Lu and Lin in Peng, 1987
Figure 18.5-18.6
Buttsia globosa LU and LIN in PENG, 1987, p. 94, PI. 6, figs. 1-5; LU and LIN, 1989,
p. 251, PI. 21, figs. 7-10.
Buttsia (Waergangia) globosa LIN, 1991, p. 372, PI. 2, Figure 6
Buttsia (Waergangia) spectabilis LIN, 1991, p. 372, PI. 2, figs. 4-5, 7.
New material.-A single cranidia and pygidia in PIB 282.75 and 283.67.
Remarks.-Thc new material from the Huaqaio Formation, western Hunan, resembles the type material from western Hunan. This species has a large, nearly spherical glabella with two pairs of lateral glabellar furrows (81 turning backward), a median spine on the occipital ring, a flat preglabellar field, and a pygidium with short pairs of marginal spines.
There appears to be a high degree of variability in amount of expression in certain characters in this species. Lin (1991) erected a new subgenus and a new species based
lOI upon the width of the preglabellar field, the depth of glabellar furrows, and the amount of constriction in the posterior portion of the glabella. However, specimens from the Paibi collections show a range of variation in these characters. The depth of the lateral glabellar furrows shows a gradation in expression, ranging from deep and well defined to shallow and almost absent. Exfoliated specimens tend to have more distinct glabellar furrows. The preglabellar field ranges from narrow and wide. In some specimens, the glabella is constricted posteriorly.
Occnrre«ce.-Argillaceous limestone in theLejopyge laevigata Zone of the the Huayansi
Formation, western Zhejiang. In the Paibi section, Hunan, this species occurs in dark gray wackestones and packstones of the Huaqaio Formation that are correlated with the
Lejopyge laevigata Zone.
Genus DISTAZERIS Raymond, 1937
Type species.-Distazeris acuta Raymond (1937, p. 1095).
D iscussion. generic concept of Raymond (1937, p. 1095) is followed here.
DISTAZERIS HUBEIENSIS, Zhu, 1980
Figure 18.16
Distazeris hubeiensis ZHU, 1980, p. 380, PI. 132, figs. 13-15; PENG, 1987, p. 92,
PI. 6, figs. 10-11.
New material.Single cranidium in PIB 319.6.
102 Remarks.-New material from the Huaqaio Formation, western Hunan, resembles the type material from western Hunan. This species has a narrow, straight-sided glabella, two distinct pairs of lateral glabellar furrows, a narrow fixagena, and a long median spine on the occipital ring.
Occurrence.-Medmm to dark gray wackestones and packstones of the Huaqaio
Formation, western Hunan. In the Paibi section, this species occurs in rocks correlated with the Lingiiagnostus reconditus Zone.
DISTAZERIS HUNANENSIS, Peng, 1987
Figure 18.2
Distazeris hunanensis PENG, 1987, p. 93, PI. 6, figs. 7-9.
New material.-LQSS than five cranidia in PIB 301.9, 362.4(7), and 364.5(7).
Remarks.-Ntw material from the Huaqaio Formation, western Hunan, resembles the type material from western Hunan. This species is distinguished by a bulbous glabella and relatively narrow fixigenae.
Occurrence.-Medmm to dark gray packstone of the Huaqaio Formation, western Hunan.
In the Paibi section, this species occurs in rocks correlated with theLinguagnostus reconditus Zone.
Genus MADAROCEPHALUS Resser, 1938
Type species.-Medarocephalus laetus Resser (1938, p. 87).
Discussion.-Th& generic concept of Rasetti (1946, p. 457) is followed here.
103 MEDAROCEPHALUS sp. 1
Figure 18.14
Material.-M.OV& than ten cranidia in PIB 249, 273.16, 273.52, 273.66, 273.8, 282.75, and
283.47.
R e m a r k s from the Huaqaio Formation, western Hunan, resembles
Medarocephalus from other localities. The new material has a smooth, forwardly expanded glabella, a uniformly curved anterior margin, and a strong median spine on the occipital ring. Three pairs of shallow lateral glabellar furrows are present; S 1 bifurcates.
This is the only knownMedarocephalus species to have a bifurcation S 1.
Occurrence.-Mcdhxm to dark gray packstone of the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated with the Lejopyge laevigata Zone.
Genus ONCHONOTELLUS Lermontova, 1956
Type species.-Solenopleura subcincta Lermontova (1951, p. 22).
Discussion.-Tht generic concept of Peng (1992, p. 65) is followed here.
ONCHONOTELLUS sp. 1
Figure 17.4
Material.-Less than ten cranidia in PIB 375, 375.15, and 383.5.
DmgMO.yfj.-Species ofOnchonotellus with a bulbous glabella and widely spaced, large granules.
104 Description.-Ctzmdmm wider than long, convex. Anterior border narrow. Glabella bulbous, extending to anterior border, with three pairs of faint lateral glabellar furrows.
Eye ridges distinct. Palperbral lobe small. Occipital furrow curved, moderately well defined.
Surface of cranidium with two sizes of granules; finer, densely spaced granules cover entire cranidium, coarse granules found in a regular pattern, with three pairs of coarse granules on the glabella and five pairs on the fixigena.
Remarks.-Vaxs species, although incompletely known, is distinguished from all other species assigned to the genus by its distinct granulation pattern.
Occurrence.-yitdhxm to dark gray packstone of the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated with theLejopyge laevigata Zone.
Family DICERATOCEPFIALIDAE Lu, 1954
Genus CYCLOLORENZELLA Kobayashi, 1960
Type species.-Larenzella quadrata Kobayashi (1935, p. 210).
Discussion.-The. generic concept of Zhang and Jell (1987, p. 131) is followed here.
CYCLOLORENZELLA TUMA Yang, 1978
Figure 17.17
Cyclolorenzella tuma YANG in ZHOU, LIU, MENG, and SUN, 1977, p. 170, PI. 50,
figs. 17-18; YANG, 1978, p. 43, PI. 7, figs. 9-11.
New material.-A.ho\xi ten cranidia in PIB 273.8, 278.01, 278.04, 278.1, and 282.75.
105 Remarks.-New material from Huaqaio Formation, western Hunan, resembles the type
material from western Hunan. Key characters that warrant placement of the new material
into this species include a semicircular, densely granulated, cephalon with a pair of
preglabellar furrows, a narrow border, and distinct, transverse eye ridges situated near the
anterior end of the glabella.
Generic placement of this species has been problematic. It shares many characters
with the genus Xiangia (Peng, 1987), the type material of which is also from the Huaqaio
Formation. Shared characters include a granulated surface, distinct eye ridges, and
preglabellar furrows. Most species ofCyclolorenzella lack distinct eye ridges and C.
tuma. Except for the presence of eye ridges, this species most closely resembles
Cyclolorenzella. The most parsimonious solution to generic placement of this species is
to expand the definition ofCyclolorenzella to include species with eye ridges.
Occurrence.-Medium to dary gray packstone of the Huaqaio Formation, Paibi, China, where it occurs in the Lejopyge laevigata Zone.
Genus FENGHUANGELLA Yang, 1978
Type species.-Fenghuangella laochatianensis Yang, 1978.
Discussion.-T\\e generic concept of Yang (1978, p. 44) is followed here.
FENGHUANGELLA LAOCHATIANENSIS Yang, 1978
Fenghuangella laochatianensis YANG, 1978, p. 44, PI. 7, figs. 12-13; PENG, 1987, p.
97, PI. VII, figs. 6-9.
106 New materiaL-MovQ than ten cranidia in PEB 298.54,326.9, 331.8, 341.7, and 375.
Remarks.-'New material from the Huaqaio Formation, western Hunan, resembles the type material from the same area. This species lacks surfaces granules on the sclerites.
Occurrence-MQdmm to dark gray packstone of the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated with theLejopyge laevigata Zone.
FENGHUANGELLA CONIFORMA Yang, 1978
Figure 17.6
Fenghuangella cotiiforma YANG, 1978, p. 45, PI. 7, figs. 15-16.
New material .cranidium in PIB 317.2.
Remarks.-'Now material from the Huaqaio Formation, western Hunan, resembles the type material from western Hunan. This species has a semicircular cranidium, strong eye ridges that project anterolaterally and a small palpebral lobe located on the anterolateral area of the cranidium, a conical glabella; a narrow preglabellar field, fine granules on the posterolateral area of the fixigena, and a genal spine on the librigena. New material also shows that the ring bears a small medial spine and a prominent preglabellar node.
Occurrence . t o dark gray packstone of the Huaqaio Formation from western
Hunan. In the Paibi section, in occurs in rocks correlated with the Linguagnostus reconditus Zone.
107 FENGHUANGELLA LIOSTRACINAIA Yang, 1978
Fenghuangella liostracinaia YANG, 1978, p. 44, PL 7, Figure 14.
New material-NhonX. ten cranidia in PIB 363.7 and 353.7.
Remarks-N&w material from the Huaqaio Formation, western Hunan, resembles material previously described from western Hunan (Yang, 1978). This speices has just one preglabellar furrow.
Occurrence.-M&dium to dary gray packstone of the Huaqaio Formation, western Hunan.
In the Paibi section, it occurs in rocks correlated with the Linguagnostus reconditus,
Glyptagnostus stolidotus, and Glyptagnostus reticulatus Zones.
FENGHUANGELLA MAGNISPINA Lin in Lin, Lin, and Zhou, 1983
Figure 17.10, 1712
Fenghuangella magnispina LIN in LIN, LIN, and ZHOU, 1983, p. 407, PI. II, figs. 3-5;
PENG, 1987, p. 98, PI. VII, figs. 10-11.
New material.-M.QIQ than ten cranidia in PIB 308, 3 16.1, 317, and 319.6.
Remarks.-New material from the Hauquio Formation resembles the type material from western Hunan. The key character that warrants placing the new material into this species it the presence of a distinct occipital spine.
Occurrence.-Medxam to dark gray packstone of the Huaqaio Formation, western Hunan.
In the Paibi section, it occurs in rocks correlated with the Lejopyge laevigata,
108 Proagnostus bulbous, Linguagnosuts reconditus, Glyptagnosuts stolidotus, and
Glyptagnostus reticulatus Zones.
FENGHUANGELLA PARACONIFORMA Yang, 1978
Figure 17. II
Fenghuangella paraconiforma YANG, 1978, p. 45, PI. 7, Figure 17-18.
New material.-S'mglQ cranidium in PIB 326.9.
Remarks-FI qw material from the Huaqaio Formation, western Hunan, resembles the type material from the same area. Key characters that warrant placing the new material into this species include a long glabella that expands forward, a cranidium in which the anterior portion is not gently curved downward, but ramp-like, a flat preglabellar area that slopes downward sharply, an effaced anterior end of the axial furrow, and an occipital ring with a posteriorly located median node.
Occu/7'e«ce.-Medium to dark gray packstone of the Huaqaio Formation, western Hunan.
In the Paibi section, it occurs in rocks correlated with theLinguagnostus reconditus
Zone.
FENGHUANGELLA sp. I
Figure 17.13
Material.-LQSS than five cranidia in PIB 378.25.
Diagnosis.S^QCXQS ofFenghuangella having relatively wide fixigena, a relatively short, conical glabella, and large, closely spaced granules.
109 Description.-CtzmàÎMm semicircular, longer than wide. Glabella relatively short, conical. Closely spaced, double preglabellar furrows located in anteromedial area.
Fixigena relatively wide. Eye ridge faint extending anterolaterally. Occipital ring with small, slender median spine. Genal spines lacking.
Surface covered with large, closely spaced granules.
Occurrence.-M.tdi\xm to dark gray packstone of the Huaqaio Formation, western Hunan.
In the Paibi section, it occurs in rocks correlated with the Glyptagnostus reticulatus Zone.
Family EOACIDASPIDAE Poletaeva, 1956
Genus PARAACIDASPIS Poletaeva, 1956
Type species.-Paraacidaspis sibirica Poletaeva, 1956.
Discussion.-Vas. generic concept of Yang (1978, p. 71) is followed here.
PARAACIDASPIS HUNANTCA Egorova in Egorova, Hsiang, Li, Nan, and Kuo, 1963
Figure 17.14-17.16
Paraacidaspis hunanica EGOROVA in EGOROVA, HSIANG, LI, NAN, and KUO,
1963, p. 53, PI.12, figs.6-8; YANG, 1978, p. 71, PI.13, igs. 12-14, text-Figure 9a-b.
New material.-Less than ten sclerites, including cranidia, pygidia, and fixagena, in PIB
316.1 and 383.5.
Remarks.-New material from the Huaqaio Formation, western Hunan, closely resembles the type material from western Hunan. Key characters that warrant placement of the new
110 material into this species includes a cephalon with a glabella that is initially convergent then expands anteriorly, small eye lobes, and a wide preglabellar area.
O ccurrence. to dary gray packstone of the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated with the Glyptagnostus reticulatus Zone.
Family EULOMIDAE Kobayashi, 1955
Subfamily EULOMINAE Kobayashi, 1955
Genus STIGMATOA Opik, 1963
Type species.-Stigmatoa diloma Opik (1963, p. 87).
Discussion.-Th& generic concept of Opik (1963, p. 87) is followed here.
STIGMATOA YANGZIENSIS Yang, 1978
Figure 17.3
Stigmatoa yangziensis YANG, 1978, P. 36, PL 5, Figure 8; PENG, 1982, p. 40, Figure
I8A-C.
New material.-K single cranidia in PIB 370.6.
Remarks.-'Hew material from the Huaqaio Formation, western Hunan, resembles the type materiant from the Bitiao Formation, western Hunan. This species has a cranidium with a pitted anterior border furrow, strong eye ridges, and a nearly straight-sided glabella that tapers forward.
Occurrence.-Innitagnostus inexpectans-Proceratopyge protracta Zone to Agnostus
(Pseudoglyptagnostus) clavatus-Ii'vingella angustilimbata Zone of the Bitiao Formation.
Ill In the Paibi section, Hunan, this species occurs in dark gray wackestones and packstones of the Huaqaio Formation that are correlated with theGlyptagnostus reticulatus Zone.
Family KINGSTONIIDAE Kobayashi, 1935
Genus BCINGSTONIA Walcott, 1924
Type species.-Kingstonia apion Walcott (1924, p. 58).
Disciission.-Ths generic concept of Walcott (1924, p. 58) is followed here.
KINGSTONIA sp. 1
Figure 15.12
Material.-h^ss than five sclerites in FIB 7.25.
Remarks.-A. species ofKingstonia, with effaced cephalon and pygidium, is present in
Paibi collections. The cranidium and pygidium are much wider than long. A proparian facial suture pattern seems to be present. At present, this species is left in open nomenclature because of difficulty of assigning effaced forms without large collections that offer some details of segmentation, etc. However, this is the only known species having a proparian facial suture.
Occurrence.-M.e(i\\xm to dark gray wackestones and packstones of the Huaqaio
Formation, Paibi, China, where it occurs in rocks correlated with thePtchagjiostus atavus
Zone.
Family HARPIDIDAE Whittington, 1950
Genus LOGANOPELTOIDES Rasetti, 1945
112 Type species.-Conocephalites zenkeri Billings, 1860, p. 305.
Discussion.-ThQ generic concept of Rasetti (1945, p. 46) is followed here.
LOGANOPELTOIDES SINENSIS Yang, 1978
Figure 17.5
Loganopeltoides sinensis YANG, 1978, p. 70, PL 13, figs. 11-12.
New material.-Abonl ten cranidia in PIE 316.1, 367, 370.6, 371.2, 375, 375.15, and
383.5.
Remarks.-'Ne.w material from the Huaqaio Formation, western Hunan, resembles material from the same area. Key character that warrant placing the new material into this species include a densely granulose cranidium, a shorter glabella than the type species, and distinct facial sutures.
Occurrence.-M&dium to dark gray packstone of the Huaqaio Formation, western Hunan.
In the Paibi section, it occurs in rocks correlated with theLinguagnostus reconditus,
Glyptagnostus stolidotus, and Glyptagnostus reticidatus Zones.
Family LISANIIDEA Chang, 1963
Genus LISANIA Walcott, 1911
Type species.-Anomocarella (?) bura Walcott, 1905, p. 56.
Discussion.-The. generic concept of Zhang and Jell (1987, p. 134) is followed here.
Zhang and Jell synonymized Aojia with Lisania and that practice is followed here.
113 LISANIA PLACIDO Yang, 1978
Lisania placido YANG, 1978, p. 46, Pl. 6, fîgs. 14-15.
New material.-M ovq than twenty sclerites, including cranidia and pygidia, in PIB 108.5,
112.42, 115.6, 121.48, 126, 130, 130.25, 130.95, and 273.46(7).
Remarks.-'Hew material from the Huaqaio Formation, western Hunan, show a range of characters that appear to fall within the species concept ofLisania placido Yang, 1978.
The new material displays some or all of the following characters: a cranidium with a narrow fixigena, four pairs of distinct lateral glabellar furrows ; S1 bifurcating; a short, narrow anterior border; an eye ridge that is close to the axial furrow; a short, narrow, blade-like posteriolateral limb of the fixagena, and a narrow occipital ring with a median node. Although not all of these characters have been previously reported in ths species, large collections from Paibi, China, indicate that all of them are present in the species.
Occiin-ence.- The type material is from slightly older rocks in theParamphoton Zone of the Aoxi Formation, western Hunan. In the Paibi section, Hunan, this species occurs in dark gray wackestones and packstones of the Huaqaio Formation that are correlated with the Ptychagnostus punctuosus and Goniagnostus nathorsti Zones.
LISANIA YUANJIANGENSIS (Yang, 1978)
Figure 15.4, 15.6
Aojia yuanjiangensis YANG in ZHOU, LIU, MENG, and SUN, 1977, p. 172, PI. 51,
114 figs. 5-7; YANG, 1978, p. 47, PI. 6, figs. 10-11.
New material.-Less than ten sclerites in FIB 80.5 and 121.48.
Remarks.-New material from the Huaqaio Formation, western Hunan, closely resembles the type material from western Hunan and eastern Guizhou. Key characters that warrant placing the new material into this species includes a cephalon having a shallow occipital furrow and shallow lateral glabellar furrows; a wide fixagena; a long, narrow, triangular posterolateral limb; and an occipital ring that is wider in the middle than that of the type species Lisania bura.
Occurrence.-Medium to dark gray packstone of the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated with theLejopyge laevigata Zone.
Genus SHENGIA Hsiang in Egorova, Hsiang, Li, Nan, and Kuo, 1963
Type species.-Shengia quadrata Hsiang in Egorova, Hsiang, Li, Nan, and Kuo, 1963, from the Hunan.
Discussion.-TLe genus concept of Hsiang (1963, p. 55) is followed here.
SHENGIA QUADRATA Hsiang in Egorova, Hsiang, Li, Nan, and Kuo, 1963
Figure 18.1
Shengia quadrata HSIANG in EGOROVA, HSIANG, LI, NAN, and KUO, 1963, p. 57,
PI. 13, figs. 1-11; LU, CHANG, CHU, CHIEN, and HSIANG, 1965, p. 275, PI. 47, figs.
12-15; ZHOU, LIU, MENG, and SUN, 1977, p. 175, PI. 51, figs. 21-24; YANG, 1978
p. 80, PI. 8, fig. 12; PENG, 1992, p. 76, figs. 40A-E, L-O, 43.
115 Shengia wannanensis QIU in QIU, LU, ZHU, BI, LIN, ZHANG, QIAN, JU, HAN, and
WEI, 1983, p. 134, Pl. 37, fîgs. 15-16.
Shengia mina QIU in QIU, LU, ZHU, BI, LIN, ZHANG, QIAN, JU, HAN, and WEI,
1983, p. 134, Pl. 43, fig. 4.
Shengia convexa QIU in QIU, LU, ZHU, BI, LIN, ZHANG, QIAN, JU, HAN, and WEI,
1983, p. 133, Pl. 43, fîgs. 6-8.
New material.-A.hoMi ten sclerites in PIB 370.6 and 371.2.
R e m a r k s material from the Huaqaio Formation, western Hunan, is closely similar to type material western Hunan.
Occnr/-e«ce.-Argillaceous limestone in theChuangia-Prochuangia Zone of the
Tingziguan Formation in western Hunan and Southern Anhui, argillaceous limestone in the Glyptagnostus reticulatiis-Chuangia wulingensis Zone of the Bitiao Formation. In the Paibi section, Hunan, this species occurs in dark gray wackestones and packstones of the Huaqaio Formation that are correlated with theGlyptagnostus reticulatus Zone.
SHENGIA sp. 1
Figure 15.8
Material.-Nloto than twenty sclerites, including both cranidia and pygidia, in PIB 371.2,
375, 375.15, 378.25, and 383.5.
/?emarfo.-Material collected from the Huaqaio Formation, western Hunan, strongly resembles Shengia quadrata. However, it appears to have a finer granulation pattern
116 than S. quadrata. The species concept ofS. quadrata may need to be expanded to accommodate this. Until this is resolved, this form will remain in open nomenclature.
Occurrence.-bAtdiwm to dark gray packstone of the Huaqaio Formation, western Hunan, where it occurs in rocks correlated with the Glyptagnostus reticidatus Zone.
Family LEIOSTEGIIDAE Bradley, 1925
Subfamily LEIOSTEGIINAE Bradley, 1925
Genus CHUANGIA Walcott, 1911
Type species.-Ptychoparia? batia Walcott (1905, p. 75).
Discussion.-The. generic concept of Zhang and Jell (1987, p. 199) is followed here.
CHU ANGIA SUBQUADRANGULATA Sun, 1935
Figure 18.7, 18.13, 18.17-18.18
Chuangia subquadrangidata SUN, 1935, p. 24, PI. I, Figure 12; LU, CHANG, CHU,
CHIEN, and HSIANG, 1965, p. 369, PI. 68, figs. 17-18; QIU, LU, ZHU, BI, LIN,
ZHOU, ZHANG, QIAN, JU, HAN, WEI, and LIU, 1983, p. 171, PI. 56, Figure 11.
New material.-M.ovQ than ten sclerites in PIB 370.6, 374.9, 375.15, and 383.5.
Remarks .-'How material from the Huaqaio Formation, western Hunan, is similar to the type material from Shandong, North China. The new material resembles the type material in having a subrectangular glabella with three pairs of short, shallow lateral glabellar furrows. However, the glabella in the new material is not straight-sided like the
117 type material but, instead, is somewhat constricted in the center. The new material also looks similar to Cbatia, but the glabella is not as long and narrow as in C. batia.
Occiirrence.-M.Qdmm to dark gray packstone of the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated with the Glyptagnostus reticulatus Zone.
Subfamily PAGODIINAE Kobayashi, 1935
Genus PROCHUANGIA Kobayashi, 1935
Type species.-Prochungia mansuyi Kobayashi, 1935.
Discussion.-T\iQ generic concept of Shegold, 1982, is followed here.
PROCHU ANGIA LINICISPINATA Peng, 1992
Figure 18.3-18.4
Prochuangia linicispinata PENG, 1992, p. 75, Figiure 41B-I.
New material.-More, than ten sclerites in PIB 374.9, 375, 375.15, and 378.25.
Remarks.-New material the Huaqaio Formation, western Hunan, resembles the type material from the Bitiao Formation, western Hunan. The key characters of the new material that require assignment to this species include scattered granules on the cephalon and a slighty tapered glabella that is constricted laterally.
Occurrence.-Med\\xm to dark gray packstone of the Huaqaio and Bitiao Formations, where it occurs in rocks correlated with the Glyptagnostus reticulatus Zone.
118 Family OLENIDAE Burmeister, 1843
Genus HUZHUIA Chu, 1965
Type species.-Huzhuia typica Chu (1965, p. 141).
Dîscussion.-T\iQ generic concept of Chu (1965, p. 141) is followed here.
HUZHUIA PARATYPICA Yang, 1978
Figure 18.8
Solenoparial sp. EGOROVA, HSIANG, LI, NAN, and KUO, 1963, p. 37, PI. VI, Figure
15.
Huzhuia paratypica YANG, 1978, p. 40, PI. 6, Figure 5.
New material.-NI oxq than twenty cranidia in PIB 273.8 and 316.1.
Remarks.-Nçw material from the Huaqaio Formation, western Hunan, resembles the type material from western Hunan. Key characters that warrant placing the new material into this species include a smooth cranidium and a cecal system on the fixigena, preglabellar field and border.
O ccurrence. to dark gray wackestones and packstones of the Huaqaio
Formation, western Hunan. In the Paibi section, this species occurs in rocks correlated with the Lejopyge laevigata Interval-zone.
HUZHOUIA sp. 1
Figure 18.9
Material.-X. sclerites in PIB 316.1.
119 Diagnosis.-Species ofHuzhouia having granules covering the cranidium.
Description.-Cv 2iaidi\im wider than long, covered with granules. Anterior border narrow. Preglabellar field narrow. Glabella long, convex, straight sided, rounded anteriorly. Axial furrow moderately deep. Fixigena wide. Eye ridge distinct. Palpebral lobes small, located anterior of the glabellar midline.
Remarks .-This species most closely resembles Huzhouia paratypica. However, it differs in having granules covering the cranidium, whereas H. paratypica has a smooth cranidium.
Occurrence.-Medi\xm to dark gray packstone of the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated with theLejopyge laevigata Zone.
Family ORDOSIIDAE Lu, 1954
Genus EOSFIENGIA Yang, 1978
Type species.-Eoshengia subquadrata Yang, 1978.
Discussion.-The generic concept of Yang (1978, p. 49) is followed here.
EOSHENGIA SUBQUADRATA Yang, 1978
Figure 15.1-15.3
Eoshengia subquadrata YANG, 1978, p. 49, PI. 8, figs. 1-2.
Eoshengia quadrata YANG, 1978, p. 50, PI. 8, figs. 4-5.
EoshengiaJiudiantangensis YANG, 1978, p. 50, PL 8, fig. 3.
Eoshengiaparagenalata YANG, 1978, p. 51, PI. 8, figs. 9-11.
120 New material.-NI oxq than thirty sclerites from PIB 237.25, 249, 250, 251, 260.08, 264.2,
273.66, and 273.8..
Remarks.-New material from the Hauqiao Formation, western Hunan warrants synonymizing E. quadrata, E.Jiudiangensis, and E. paragenalata with E. subquadrata because it shows that a range of character states exists in this species. Whereas some specimens lack spines and other possess them, type specimens of these species seem to be identical to each other in all other respects. All four of these species are in the same localités in western Hunan and in the same horizons. Specimens from the Paibi collections possess a less convex glabella than other species ofEoshengia and either have a short occipital spine or lack such a spine.
Occurrence.-M.edmm to dark gray packstone of the Huaqaio Formation, western Hunan.
In the Paibi section, this species is found in rocks correlated with the Lejopyge laevigata
Zone.
EOSHENGIA SPINOSA Yang, 1978
Figure 15.7
Eoshengia spinosa YANG, 1978, p. 50, PI. 8, figs. 6-8.
New material.-Move than ten sclerites in PIB 278.1, 279.7, 282.25, and 283.75
Remarks.-New material from the Hauqaio Formation, western Hunan, closely resembles the type material from the same area. Key features of this species are a very long spine on the occipital ring and a lack of surface granulation.
121 Occurrence.-lAQiium to dark gray packstone of the Huaqaio Formation, western Hunan.
In the Paibi section, this species occurs in rocks correlated with theLejopyge laevigate
Zone.
EOSHENGIA sp. 1
Figure 15.9
Mctena/.-About ten sclerites in PIB 249 and 251.
D/ag/zo^/s’.-Species ofEoshengia with deep lateral glabellar furrows, a distinct eye ridge, amd coarse surface granulation.
Description.-Cxzmàixim wider than long. Anterior border wide. Glabella straight sided, tapering forward moderately, moderately convex, rounded anteriorly. Lateral glabellar furrows deep; SI posterolaterally directed; S2 slightly posterolaterally directed; S3 slightly anterolaterally directed. Medial carina present on glabella. Fixigena moderately wide. Eye ridge distinct. Occipital ring narrow at sides, wide medially, with small medial node. Occipital furrow deep.
Surface covered with coarse, closely spaced granules.
Remarks.-T\i\s species, which is possibly new, has a granulation pattern that seems to be previously undescribed in this genus. However, too little of this species is known at present to warrant formal erection of a new species name.
Occurrence.-M.tdivivn. to dark gray packstone of the Huaqaio Formation, western Hunan.
In the Paibi section, this species occurs in rocks correlated with the Lejopyge laevigata
Zone.
122 EOSHENGIA sp. 2
Figure 15.10-15.11
Material.-M.OV& than thirty sclerites in PIB 273.8, 282.75, 295.13, 296.2, 296.4, 296.54,
298.54, 301.9, 316.1, 317.2, 319.6, and 326.9.
D i a g n o s i s . ofEoshengia having a straight, parallel-sided glabella, an anterior notch in the glabella, and densely spaced granules.
Description.-Cv 2imà.mm wider than long. Anterior border wide, moderately rounded forward. Glabella wide, long, straight-sided, with anteriolateral notch. Preglabellar furrow slightly curved forward. Fixigena moderately wide. Eye ridges strong. Palpebral lobes long. Anterior branch of facial suture straight, parallel to glabella. Posterolateral branch extends laterally then posterolaterally. Occipital ring wide. Occipital furrow deep, transverse.
Surface covered with closely spaced, variably sized granules.
Remarks.-Thxs species resembles E. quadrata in many respects, including having a shallow preglabellar furrow and strong eye ridges and palpebral lobes. However, it is easily distinguished from E. quadrata in being covered with dense granules.
Occun-ence.-lAQdixxm to dark gray wackestone and packstone of the Huaqaio
Formation, Paibi, China, where it occurs in rocks correlated with theLejopyge laevigata,
Proagnostus bulbous, and Linguagnostus reconditus Zones.
Genus WANSHANIA Rong and Yang, 1978
Type species.-Wanshania wanshanensis Rong and Yang (1978, p. 41).
Discussion.-Ths genus concept of Rong and Yang (1978, p. 40) is followed here.
123 WANSHANIA WANSHANENSIS Rong and Yang, 1978
Figure 18.15, 18.19-18.20
Wanshania wanshanensis RONG and YANG in YANG, 1978, p. 41, Pl. 7, fîgs. 1-2.
New material.-M.Oïe than fifty sclerites in PIB 273.46, 273.52, 273.66, 273.8, 273.85,
278.01, 278.1, 279.1, 282.75, 283.47, 283.75, 290.5, 293.21, 295.13, 296.2, 296.54,
298.54, 301.9, 305.05, and 308.
Remarks-Tht new material from the Huaqaio Formation, western Hunan resembles the type material from western Hunan. The key character that warrants placement of the new material into this species is a distinct plectrum that is widest medially, varies in width, and a long narrow glabella. The thorax possesses eight segments; the thoracic axis is moderately convex and lacks nodes or spines. Thoracic segments have moderately expressed pleural furrows and falcate pleural tips.
Occiirrence.-M.ed\\xm to dark gray wackestones and packstones of the Huaqaio
Formation, western Hunan. In the Paibi section, this species occurs in rocks correlated with the Lejopyge laevigata, Proagnostus bidbus, and Linguagnostus reconditus Zones.
Family PAPYRIASPEDIDAE Whitehouse, 1939
Genus PIANASPIS Saito and Sakakura, 1936
Type species.-Pianaspis sinensis Saito and Sakakura (1936, p. 114).
Discussion.-The generic concept of Lu and Lin (1989, p. 248) is followed here.
124 PIANASPIS SINENSIS (Yang, 1978)
Figure 16.12
Prohedinia sinensis YANG, 1978, p. 39, PI. 6, fig. 6.
Pianaspis sinensis LU and LIN in PENG, 1987, p. 248, Pi. 20, figs. 1-5.
New marena/.-More than thirty cranidia in PIB 115.6, 117.25(7), 121.48, 126, 130,
130.25, 130.95, 259.85, and 260.08.
Remarks.-New material from the Huaqaio Formation, western Hunan, resembles the type material from western Hunan and eastern Guizhou. Key characters that warrant placement of the new material into this species includes a cranidium with long palpebral lobes, narrow fixigena, and narrow (tr.) posterolateral limbs of the fixigena.
Occurrence.-Medium to dark gray wackestones and packstones of the Huaqaio
Formation, western Hunan and eastern Guizhou. In the Paibi section, this species occurs in rocks correlated with the Lejopyge laevigata Zone.
Family SOLENOPLEURIDAE Angelin, 1854
Genus CHANGQINGIA Lu and Zhu in Qiu, Lu, Zhu, Bi, Lin, Zhou, Zhang, Qian, Ju,
Han, Wei, and Liu, 1983
Type species.-Changqingia shandongensis Lu and Zhu in Qiu, Lu, Zhu, Bi, Lin, Zhou,
Zhang, Qian, Ju, Han, Wei, and Liu, 1983, p. 104.
Disciission.-The generic concept of Lu and Zhu in Qiu, Lu, Zhu, Bi, Lin, Zhou, Zhang,
Qian, Ju, Han, Wei, and Liu (1983, p. 104) is followed here.
125 CHANGQINGIA INTERMEDIA (Walcott, 1906)
Figure 17.8
Ptychoparia (Liostraciis) intermedia WALCOTT, 1906, p. 592.
Solenopleura intermedia WALCOTT, 1913, p. 169, PI. 17, fig. 16.
Shumardia sp. undt. WALCOTT, 1913, PI. 7, fig. 9.
Solenoparia hemicycla RESSER and ENDO, 1937, p. 290, PI. 47, fig. 23.
Solenoparia intermedia RESSER, 1942, p. 51; CHANG in LU, CHANG, ZHU, CHIEN,
and HSIANG, 1965, p. 201, PI. 34, figs. 28-29.
Aiistrosinia intermedia ZHANG and JELL, 1987, p.94, PI. 39, figs. 5-8; PI. 40, fig. 9.
New material.~S>mg\e cranidium in PIB 81.
Remarks.S'^ec.ies o ïAustrocinia were reassigned to Changqingia by Peng et al. (1995).
New material from the Huaqaio Formation, western Hunan, resemble the type material form Shandong, North China. Key features that warrant placing the new material into this species include a cephalon with a narrow, conical glabella with fine granules and a lesser amount of scattered coarser granules, narrow eye ridges, and small palpebral lobes.
Occurrence.-OoWiic limestone and shale in the Amphoton Zone (?) o f the Changhia
Formation, Shandong, north China. In the Paibi section, Hunan, this species occurs in dark gray wackestones and packstones of the Huaqaio Formation that are correlated with the Pychagtjostus atavus Zone.
126 CHANGQINGIA LAEVIS Peng, Lin, and Chen, 1995
Figure 17.9
Changqingia laevis PENG, LIN, AND CHEN, 1995, p. 292, Pl. II, fîgs. 1-4.
New material.SivigXç. cranidium in PIB 112.42.
Remarks.-'Ne.w material from the Huaqiao Formation, western Hunan, is closely similar to the type material from the same locality. The character that warrants placement of the new material into this species is the lack of granules on the cephalon and pygidium.
Occurrence.-NiQàmva to dark gray packstone of the Huaqaio Formation, western Hunan.
In the Paibi section, this species occurs in rocks correlated with the Goniagnostus nathorsti Zone.
CHANGQINGIA sp. 1
Figure 17.7
Material.-A. single cranidia in PIB 34.3.
D i a g n o s i s . ofChangqingia with a long, straight glabella, strong eye ridge, and a straight preoccipital furrow directed inward and downward diagonally.
Description.- Cranidium moderately convex, with granules. Axial furrow deep, rounded anteriorly. Long, straight glabella with three pairs of weakly developed furrows; first pair straight, directed inward and downward diagonally. Occipital ring with a small medial node. Palpebral lobe lying posterior to middle of cranidium. Strong ocular ridge, curved obliquely rearward. Anterior border narrow and convex. Preglabellar field
127 impressed with a faint median furrow. Anterior sections of the facial sutures slightly
convergent forward; posterior sections nearly straight, divergent rearward.
Pygidium semicircular, wider than it is long; granulose. Possess three axial rings and
a terminal piece; end of the axis nearly to the border furrow. Pleural field contains four
segments. Moderately wide, concave border. Border furrow wide and shallow.
Occurrence.-Axgi\\3.c&o\xs limestone in the Ptychagnostus atavus Zone of the Huaqaio
Formation, western Hunan.
Family uncertain
Genus ADELOGONUS Opik, 1967
Type species.-Adelogonus solus Opik (1967, p. 203).
D7ycr(.9jzoM.-The generic concept of Opik (1967, p. 203) is followed here.
ADELOGONUS cf. A. SOLUS Opik, 1967
Figure 19.8
Adelogonus solus OPIK, 1967, p. 204, PI. 8, fig. 3, text-fig. 70.
New material.Single pygidium and possible cranidium in PIB 331.8 and 341.7.
Remarks.-lAew material from the Huaqaio Formation, western Hunan, resembles the type material of the species from Queensland, Australia. The Hunan material differs in having more granulation, a pair of nodes near the anterolateral comers, and distinct
lateral glabellar furrows.
128 The pygidium is semi-elliptical, densely granulose with deep, wide, poorly defined
border furrows, an upward curved margin, three pairs of plueral furrows, four axial rings
and a terminal piece.
Occurrence.Sha.\o. in the Glyptagnostus stolidotus Zone of the O’Hara Shale,
Queensland, Australia. In the Paibi section, Hunan, this species occurs in dark gray packstones of the Huaqaio Formation that are correlated with theLinguagnostus
reconditus Zone.
Genus CERMATASPIS Opik, 1967
Type species.-Cermataspis abundans Opik (1967, p. 204).
Discussion.-ThQ generic concept of Opik (1967, p. 204) is followed here.
CERMATASPIS sp. 1
Figure 19.4, 19.9
Material.-Less than ten sclerites in PIB 273.8, 278.1, and 378.25.
Diagnosis.-StT^eexes ofCermataspis with three shallow pairs of lateral glabellar furrows, weak eye ridges, and a weak median node.
Description.-CxdLrâàmva longer than wide. Anterior border narrow. Preglabellar area narrow, concave. Glabella long, narrow, slightly tapering forward; with three pairs of shallow, transverse lateral glabellar furrows. Fixagena narrow. Eye ridge weak.
Palpebral lobe moderately large.
129 Pygidium semielliptical, wider than long. Axis two-thirds the pygidial length, weakly segmented with five or six rings and a terminal piece. Plural field weakly segmented.
Three plural furrows present. Border wide, concave.
Surface smooth.
Remarks.-This species is similar to Paranomacare in having a short preglabellar field, short palpebral lobes, proportionately large glabella, wide, more divergent preoccular suture, and a relatively efaced pygidium with a short axis.
Occurrence.-M&àium to dark gray packstone of the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated with the Glyptagnostus reticulatus Zone.
Genus “LUASPIS” Peng, 1995
Type species.- "Luaspis " decorosa Peng, 1995, p. 298.
Discussion.-Vtic generic concept of Peng (1995, p. 298) is followed here.
“LUASPIS” DECOROSA Peng, 1995
Figure 19.5-19.6
Luaspis decorosa PENG, 1995, p. 298, PI. 6, figs. 1-9.
New material.-Nooui twenty sclerites in PIB 273.8, 282.75, 290.5, 296.54, 301.9, and
3196.
Remarks.-Now material from the Huaqiao Formation, western Hunan, is closely similar to the type material from the same locality. This species has a cranidium with bulbous
130 glabella, a wide anterior border that is horizontal to slightly downsloping forward, and a small median node on the occipital ring. The pygidium is mostly effaced.
The genus name Luaspis is currently occupied by another organism and a new genus name will have to be erected.
Occi/rrence.-Medium to dark gray wackestones and packstones of the Huaqaio
Formation, western Hunan, were it occurs in rocks correlated with thePtychagnostus atavus, Ptychagnostus punctuosus, Goniagnostus nathorsti, and Lejopyge laevigata
Zones.
“LUASPIS” sp. 1
Figure 19.12-19.13
Material.-S>mg\Q cranidium and single pygidium from PIB 296.54; other pygidia assigned to this species but without associated cranidia are in PIB 296.54 and 298.54.
Remarks-K broken cranidium having a bulbous glabella apparently represents an undescribed species LuaspisP The specimen is too fragmentary for a meaningful description.
Occurrence.-M.Qdi\ixa. to dark gray packstone of the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated with theLejopyge laevigata Zone.
Genus PARACOOSIA Kobayashi, 1936
Type species.-Paracoosia mansuyi Kobayashi (1936, p. 172).
131 Discussion.-T\xQ generic concept of Opik (1967, p. 225) is followed here. Additionally, see Opik (1967, p.226) for explanation of the family placement of this genus.
PARACOOSIA sp. I
Figure 19.10-19.11
Coosia sp. EGOROVA in EGOROVA, HSIANG, LI, NAN, and KUO, 1963, p. 49, PI.
11, Figure 15.
Metanomocare ? sp. YANG, 1978, p. 38, p. 5, figs. 12-14.
Material-M oxq than ten sclerites in PIB 278.1, 295.13, 308, 316.1, and 331.8.
Remarks.-This species has been well decribed by Ergorova (1963) and Yang (1978), although neither author erected a species name for it. Ergorova’s material was based on the pygidium only. Yang worked with framentary material but figured one partial pygidium and two fragmentary cranidium.
The new material is also fragmentary. The cranidium is smooth and nearly flat, with a distinctive long, wide preglabellar field. The glabella is weakly convex, wide posteriorly, tapering rapidly forward; the lateral glabellar furrows are distinct. The eye
132 ridge moderately strong. The fixigena is wide. The occipital ring is moderately narrow, and the occipital furrow is moderately deep and transverse.
The pygidium is incomplete but inferred to be semicircular. The axis is short, slender, with at least eleven axial rings and a terminal piece. The pleural field is wide, with seven pleural furrows. A wide, concave border is present.
The surface is smooth
O ccurrence. to dark gray packstone of the Huaqaio Formation, western Hunan.
In the Paibi section, this species occurs in. rocks correlated with theLejopyge laevigata,
Proagnostus bidbus, and Linguagnostus reconditus Zones.
PARACOOSIA sp. 2
Figure 19.7
Material.-More, than five pygidia in PIB 326.9, 375, 375.15, 375.25, and 378.25.
D i a g n o s i s . ofParacoosia having 10 axial rings and six pleural furrows in the pygidium.
Description.- Pygidium wider than long. Axis long, narrow, convex, contaning 10 rings and a short terminal piece; furrows weak. Pleural field containing six weak pleural furrows. Border moderately wide, concave. Margin smooth.
133 Surface smooth.
Occiirrence.-Mtéium to dark gray packstone of the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated with the Glyptagnostus reticulatus Zone.
PARACOOSIA sp. 3
Figures 119.1-19.2
Material.-S\ng\e cranidium and single pygidium in PIB 378.25.
Diagnosis.-St'pecies ofParacoosia having a relatively short glabella, and a relatively narrow border on the pygidium.
Description.-Cmmdixxvn. long. Anterior border wide. Preglabellar wide, concave.
Glabella moderately short, straight sided, tapering forward, and convex. Axial furrows deep. Eye ridge weak. Palpebral lobe moderately long.
Pygidium semicircular, wider than long. Axis long, narrow, slightly tapering, containing about nine rings, furrows faint. Pleural field moderately convex, with five weak pleural furrows. Border moderately wide, concave. Margin smooth.
Surface covered with fine granules.
134 Occiirrence.-M&di\xm. to dark gray packstone of the Huaqaio Formation, Paibi, China, where it occurs in rocks correlated with theLejopyge laevigata Zone.
135 Figure 11 : Trilobites from Order Asaphida.
1-3. Proceratopygefenghuanensis. I. Cranidiun, X7.5, NIGP 000000 from PIB 317.2. 2. Librigena, X4.5, NIGP 000000 from PIB2 4.38. 3. Pygidium, X7.5, NIGP 000000 from PIB 367. 4-5. Monkaspis quadrata. 4. Broken cranidium, X4.5, NIGP 000000 from PIB 289.54. 5. Pygidium, X4.5, NIGP 000000 from PIB 298.54. 6-7. Proceratopyge tnincata. 6. Cranidium, X7.5, NIGP 000000 from PIB2 60.15. 7. Broken pygidium, X3, NIGP 000000 from PEB2 60.15. 8. Rhyssometopus zhongguensis. Cranidium, X7.5, NIGP 000000 from PIB 361.5. 9-10. Pseudoyuipingia modesta. 9. Cranidium, X7.5, NIGP 000000 from PIB353.64. 10. Pygidium, X4.5, NIGP 000000 from PIB 361.5. 11. Rhyssometopus cf. R. sinensis. Cranidium, X7.5, NIGP 000000 from PIB 278.1. 12. Rhyssometopusl sp. Cranidium, X7.5, NIGP 000000 from PIB 121.48. 13. Liostracina bella. Cranidium, X7.5, NIGP 000000 from PIB 308. 14-15. Proceratopyge fuyangensis. 14. Cranidium, X7.5, NIGP 000000 from PLB 317.2. 15. Broken pygidium, X7.5, NIGP 000000 from PIB 317.2
136 Figure 11 137 Figure 12: Trilobites from Order Corynexochida, Part I.
1. Dorypyge? sç>. Broken pygidium, X4.5, NIGP 000000 from PEB 290.5. 2. Dorypyge sp. 2. Cranidium, X2.25, NIGP 000000 from PIB 108. 2,1. Dorypygerichthofeni. 3. Small cranidium, X7.5, NIGP 000000 from PIB 81. 7. Broken pygidium, X2.25, NIGP 000000 from PEB 42.5. 4,8. Dorypyge bispinosa. 4. Broken pygidium, X4.5, NIGP 000000 from PIB 130.95. 8. Broken pygidium, X4.5, NIGP 000000 from PEB 130.95. 5. Lisania yiianjiangensis. Pygidium, X7.5, NIGP 000000 from PIB 80.5. 6. Dorypyge s^. 2. Cranidium, X7.5, NIGP 000000 from PEB 273.8. 9-10. Dorypyge sp. 1. 9. Broken pygidium and broken cranidium, X4.5, NEGP 000000 from PEB 81. 10. Broken cranidium, X4.5, NEGP 000000 from PIB 81. 11. Fuchouia chiai. Small pygidium, X7.5, NIGP 000000 from PEB 80.
138 Figure 12 Figure 13: Trilobites from Order Corynexochida, Part II
1. Dorypygepergranosal. Broken cranidium, X4.5, NIGP 000000 from PIB 97.25. 2. Fuchouia chiai. Small pygidium, X4.5, NIGP 000000 from PIB 130.95. 3-4. Amphoton deios. 3. Cranidium, X2.25, NIGP 000000 from PEB 108. 4. Librigena, X4.5, NIGP 000000 from PIB 115.6 5. Chatiania sp. 1. Small cranidium, X7.5, NIGP 000000 from PEB 308. 6. Chatiania chatianensis. Small cranidium, X7.5, NIGP 000000 from PEB 331.8. 7. Fuchouia orotolimba. 7. Small cranidium, X7.5, NIGP 000000 from PEB 98. 8-9,11. Fuchoida sp. 8. Three cranidium, X3, NEGP 000000 from PEB 273.52. 9. Pygidium, thoracic segments, and broken cranidium, X2.25, NEGP 000000 from PIB 273.8. 11. Thoracic segments, X2.25, NEGP 000000 from PEB 273.8. 10, 12-13. Fuchouia chiai. Broken cranidium, X2.25, NIGP 000000 from PEB 130.95. 12. Librigena, X3, NIGP 000000 from PEB 130.95. 13. Small pygidium, X7.5, NIGP 000000 from PIB 130.
140 m
Figure 13 Figure 14: Trilobites from Order Lichida.
1-2. Meringaspis jiamaensis. I. Hypostome, X2.25, NIGP 000000 from PIB 298.54. 2. Broken pygidium, X2.25, NIGP 000000 from PIB 273.8. 3-4. Blackwelderia n. sp. 3. Broken cranidium, X2.25, NIGP 000000 from PIB 294.51. 2. Pygidium, X2.25, NIGP 000000 from PIB 294.51. 5-6. Paradamasella typîca. 5. Broken cranidium, X7.5, NIGP 000000 from PIB 353.1. 6. Thoracic segments, X I.5, NIGP 000000 from PIB 353.9. 7. Protaitzehoia subquadrata. Broken cranidium, X7.5, NIGP 000000 from PIB 331.8. 8-10. Paradamasella novemospinosa. 8. Broken cranidium, X4.5, NIGP 000000 from PIB 317.2. 9. Pygidium, X3, NIGP 000000 from PIB 317.2. 10. Librigena, X3, NIGP 000000 from PIB 317.2. 11. Prodamasella siibtriangidata. Small crandium, XIO, NIGP 000000 from PIB319.6. 12-14. Palaeodotes hunanensis. 12. Broken cranidium, X7.5, NIGP 000000 from PIB 298.54. 13. Hypostom, X4.5, NIGP 000000 from PIB 298.54. 14. Pygidium, X3, NIGP 000000 from PIB 293.21. 15. Protaitzehoia granifera. Broken cranidium, X 7.5, NIGP 000000 from PIB 331.8. 16-17. Teinistium posterocostum. 16. Broken cranidium, X4.5, NIGP 000000 from PIB 319.6. 17. Pygidium, X4.5, NIGP 000000 from PIB319.6. 18. Prodamasella biserrata. Cranidium, XIO, NIGP 000000 from PIB 319.6.
142 Figure 14 Figure 15: Trilobites from Order Ptychopariida, Part I
1-3. Eoshengia subquadrata. I. Cranidium, X7.5, NIGP 000000 from PIB 264.2. 2. Two librigena, X4.5, NIGP 000000 from PIB 264.2. 3. Broken pygidium, X4.5, NIGP 000000 from PIB 260.08. 4,6. Lisania yuanjîangensis. 4. Cranidium, X4.5, NIGP 000000 from PIB 121.48. 6. Small cranidium, X7.5, NIGP 000000 from PIB 115.6. 5. Shengia trapizia. Cranidium, X2.25, NIGP 000000 from PEB 60.15. 7. Eoshengia spinosa. Broken cranidium, X2.25, NIGP 000000 from PEB 278.1. 8. Shengia s^.l. Cranidium, X2.25, NEGP 000000 from PEB 378.25. 9. Eoshengia s^. \. Broken cranidium, X4.5, NIGP 000000 from PIB 249. 10-11. Eoshengia sp. 2. 10. Cranidium, X4.5, NIGP 000000 from PEB 301.9. 11. Librigena, XI.5, NEGP 000000 from PIB 316.1. 12. Kingstonia n. sp. Pygidium, XIO, NIGP 000000 from PEB 7.25. 13. Hunanaspis tnmcatus. Cranidium, X7.5, NEGP 000000 from PEB 319.6. 14. Anomocarella concava. Cranidium, X7.5, NEGP 000000 from PEB 7.25.
144 Figure 15 145 Figure 16: Trilobites from Order Ptychopariida, Part II
1. AnomocarellaP. sp. 1. Broken cranidium, X7.5, NIGP 000000 from PIB 34.3. 2. Paranomocarella parapolita. Broken pygidium, X2.25, NIGP 000000 from PIB 130. 3. Paranomocarella parallela. Broken pygidium, X7.5, NIGP 000000 from PEB 81. 4 Anomocarellal sp. 2. Broken cranidium, X7.5, NIGP 000000 from PIB 34.3. 5-6. Anomocarella sp. 2. 3. Broken cranidium, X4.5, NIGP 000000 from PIB 108. 6. Pygidium, X4.5, NIGP 000000 from PEB 108. 7-8. Paranomocarella cf. P. fortis. 7. Broken cranidium, X4.5, NIGP 000000 from PIB 130. 8. Pygidium, XI.5, NIGP 000000 from PEB 130. 9. Paranomocarella fortis. Pygidium, X2, NIGP 000000 from PEB 130.25. 10-11. Neoanomocarella asiatica. 10. Cranidium, X7.5, NIGP 000000 from PIB 331.8. 11. Pygidium, XI.5, NIGP 000000 from PIB 331.8. 12. Pianaspis sinensis. Cranidium, X7.5, NIGP 000000 from PEB 130.95.
146 Figure 16 1^7 Figure 17: Trilobites from Order Ptychopariida, Part III
1-2. Zhujia hunanensis. I. Cranidium, X4.5, NIGP 000000 from PEB 108. 2. Pygidium, X4.5, NIGP 000000 from PIB 108. 3. Stigmatoayangziensis. Broken cranidium, X4.5, NIGP 000000 from PEB2 (-2.1). 4. Onchonotellus sp. I. Cranidium, X4.5, NIGP 000000 from PIB 375. 5. Loganopeltoides sinensis. Cranidium, X7.5, NIGP 000000 from PEB 316.1. 6. Fenghuangella coniforma. Cranidium, X 10, NEGP 000000 from PEB 317.2. 7. Changqingia sp. I. Cranidium, X7.5, NEGP 000000 from PEB 81. 8. Changqingia intermedia. Cranidium, X7.5, NIGP 000000 from PEB 81. 9. Changqingia laevis. Cranidium, X7.5, NIGP 000000 from PEB 112.42. 10,12. Fenghuangella magnispina. 10. Four cranidium, XIO, NIGP 000000 from PEB 308. 12. Cranidium, XIO, NEGP 000000 from PIB 308. 11. Fenghuangellaparaconiforma. Cranidium, XIO, NIGP 000000 from PEB 326.9. 13. Fenghuangella sp. I. Cranidium, XIO, NIGP 000000 from PEB 378.25. 14-16. Paraacidaspis hunanica. 14. Broken cranidium, X4.5, NIGP 000000 from PIB 3I6.I. 15. Pygidium, X4.5, NIGP 000000 from PIB2 55.5. 16. Librigena, X4.5, NIGP 000000 from PIB2 55.5. 17. Cyclolorenzella tuma. Small cranidium, XIO, NIGP 000000 from PIB 282.75.
148 Figure 17 149 Figure 18: Trilobites from Order Ptychopariida, Part IV
1. Shengia quadrata?. Librigena, X4.5, NIGP 000000 from PIB 378.25. 2. Distazeris hunanensis. Broken cranidium, X7.5, NIGP 000000 from PIB 301.9. 3-4. Prochuangia lincinispinata. 3. Cranidium, X7.5, NIGP 000000 from PIB 378.28. 4. Pygidium, X7.5, NIGP 000000 from PEB 378.25. 5-6. Biittsia globosa. 5. Broken cranidium, XIO, NIGP 000000 from PEB 283.67. 6. Small broken pygidium, XIO, NIGP 000000 from PIB 282.75. 7. 13 Chuangia subtriangulata. 7. Cranidium, X4.5, NIGP 000000 from PBB2 55.5. 12. Two cranidium, X7.5, NIGP 000000 from PIB 2 26.5. 8. Huzhouia paratypica. Small cranidium, XIO, NIGP 000000 from PIB 316.1. 9. Huzhouia sp. 1. Small cranidium, XIO, NIGP 000000 from PIB 316.1. 10-11. Prochuangia cf. P. granulosa. 10. Cranidium, X7.5, NIGP 000000 from PEB 375.15. 11. Pygidium, X7.5, NIGP 000000 from PEB 374.9. 12. Prochuangia granulosa. Cranidium, X2.25, NIGP 000000 from PEB2 55.5. 14. Medarocephalus sp. 1. Cranidium, XIO, NIGP 000000 from PIB 273.8. 15. 19-20. Wanshania wanshanensis. 15. Pygidium, X2.25, NIGP 000000 from PIB 273.8. 19. Librigena, X3, NIGP 000000 from PEB 273.8. 20. Two cranidium, X3, NIGP 000000 from PEB 273.8. 16. Distazeris hubeiensis. Cranidium, XIO, NIGP 000000 from PEB 319.6. 17-18. Chuangia subquadrangulata. 17. Cranidium, X4.5, NIGP 000000 from PEB 370.6. 18. Pygidium, XI.5, NIGP 000000 from PIB 374.9.
150 Figure 18 Figure 19: Trilobites o f uncertain affinities.
1-2. Paracoosia sp. 3. 13. Broken cranidium, X4.5, NIGP 000000 from FIB 378.25. 14. Broken pygidium, X4.5, NIGP 000000 from PEB 378.25. 3. Rhyssomtopus zhongguensis. Librigana, X7.5, NIGP 000000 from PIB 363.7. 4,9. Cermataspis sp. I. 4. Cranidium, X7.5, NIGP 000000 from PIB2 4.28. 9. Broken pygidium, X7.5, NIGP 000000 from PIB 273.8. 5-6. “Luaspis” decorosa. 5. Cranidium, X7.5, NIGP 000000 from PIB 290.5. 6. Pygidium, X4.5, NIGP 000000 from PIB 301.9. 7. Paracoosia sp. 2. Broken pygidium, X4.5, NIGP 000000 from PIB 375.25. 8. Adelogomus C Î . A. solus. Pygidium, X2.25, NIGP 000000 from PIB 331.8. 10-11. Paracoosia sp. 1. 10. Broken cranidium, X4.5, NIGP 000000 from PIB 295.13. 11. Broken pygidium, X2.25, NIGP 000000 from PIB 316.1. 12-13. “Luaspis" s^. 12. Broken cranidium, X7.5, NIGP 000000 from PIB 298.54. 13. Pygidium, X4.5, NIGP 000000 from PEB 298.54.
152 ÿÀV s
Figure 19 CHAPTER 11
CONCLUSIONS
Based upon ranges of non-agnostoid trilobites, putative biomere extinction boundaries cannot be identified with certainty in the Paibi section of south China. Although one interval near the inferred position of the biomere boundary, PIB 361.5-362.4, shows extinction levels that are higher than the rest of the section, the levels of extinction are much lower than those observed at biomere boundaries in North America (Palmer, 1965a,
1982, 1984; Longacre, 1970; Stitt, 1971, 1975, 1983; Westrop and Ludvigsen, 1987;
Westrop, 1989). In the interval between PIB 361.5-362.4, taxonomic ranges also may have been artificially truncated due the termination of sampling at the top of the section.
There are several possible explanations for the absence of biomere boundary-type extinctions in the Paibi section. Perhaps the most significant factor is the difference in the depositional settings between the two regions. The biomeres of North America have been identified in shelf deposits. However, the Paibi section was deposited in a slope settings. Documented accounts of biomeres in North America show that extinction levels fall off dramatically when moving from shelf to slope facies, with shelf-dwelling families whose ranges extend onto the slope suffering lower extinction levels (Westrop, 1989).
Thus, since the Paibi section consists of slope deposits, biomere extinction events may
154 not be observable. Trilobite sclerites found in slope deposits have been resedimented, and the tops of trilobite ranges may not represent the true extinction point of the organisms. The record of potential biomere events may have been “smeared” out because resedimentation of sclerites extended trilobite ranges. As a result of this process, only interval-zones, marked by the first appearances of common species should be used when choosing an international stratotype in such a slope environment. Use of assemblage-zone, etc., is not recommended, for the tops of a species ranges may not be the same worldwide because of resedimentation. It is possible that biomeres can be
found outside North America, but that they are restricted to shelf settings.
The second factor that may explain the apparent lack of biomeres in the Paibi section
is the amount of endemic taxa that exist in North American sections. Shelf-dwelling trilobites of Laurentia tend to be endemic, while slope-dwelling trilobites of Laurentia are more widespread (Westrop, 1989). The taxa that were endemic suffered much higher extinction rates than did the cosmopolitan taxa (Westrop, 1989). Trilobite taxa identified
in the slope deposits of the Paibi section tend to be widespread, similar to slope-dwelling trilobites in Laurentia. It stands to reason that these trilobites would have suffered lower extinction rates.
Future research should focus on sampling sections in South China representing shelf
facies, as well as sampling additional sections in slope settings. Sampling shelf facies is
important as this appears to be the most likely setting to find biomeres. Ideally, a series of sections representing a shelf-to-slope progression should be sampled. This could confirm the idea that cold/deep-water-dwelling trilobites invaded the shelf after a
155 biomere-type extinction event to fill available niche space left open by the extinction of warm-water, shelf-dwelling trilobites. Additionally, changes in the marine biosphere associated with “El Nino” or “La Nina”-type events should be examined. Since “El
Nifio” or “La Nifia”-type events involve a shift of warmer or colder water into normally cool-water or warm-water regions, similar to proposed mechanisms driving biomere extinctions (i.e., a rise in the thermo dine), such events, and the changes in the biosphere associated with them, may serve as a corollary to biomere extinctions. Research should be undertaken to determine the potential influence of a rising pycnocline on biomere extinctions. Clearly, something was causing biofacies differentiation during the
Cambrian, and the presence of a well developed pycnocline, similar to that found during the Devonian and Pennsylvanian, may have been a major factor involved in this differentiation.
Finally, the Piabi section, western Hunan, China, seems to be a suitable location for the Middle-Upper Cambrian boundary stratotype. The base of the Glyptagnostus reticulatus Interval-zone is present and well exposed as Paibi, and its stratigraphie context is well understood. The base of the G. reticulatus Interval-zone is globally identifiable, and would make an excellent horizon for the Middle-Upper Cambrian boundary;
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