Late Cambrian Trilobites Research Articles

Morphology, variation, and systematics of the late Cambrian Laurentian dikelocephalid trilobiteWalcottaspis vanhornei(Walcott, 1914)

AbstractWalcottaspis vanhornei(Walcott, 1914) is a large, late Cambrian trilobite with a unique pygidial morphology known only from a narrow outcrop belt of the St. Lawrence Formation in the Upper Mississippi Valley. Found in carbonate-rich layers within heterolithic facies that represent the toesets of a prograding shoreface, it is restricted to a single or small number of parasequences. Only four specimens of any of its sclerites have been illustrated previously. Here holaspid examples of all its biomineralized sclerites are described and illustrated, along with a morphometric analysis of cranidial landmarks and landmarks plus semilandmarks for the pygidium. Ontogenetic allometry accounts for 29% of the variance among holaspid cranidia and includes a relative shortening and narrowing of the palpebral lobe and a reduction in the relative length and width of the frontal area. Notable pygidial phenotypic variation occurs in the extent of the postaxial region and in the proportion of the structure occupied by the axis. Phylogenetic analysis suggests thatW. vanhorneiis sister taxon toDikelocephalus minnesotensisOwen, 1852, which also occurs in the St. Lawrence Formation and has a broadly similar cephalon but distinctive trunk. The holaspid pygidium ofW. vanhorneiis uniquely characterized by the interpleural furrows of the first two segments becoming abruptly obsolete on approaching the axial furrow. Some pygidia show narrow, shallow, flat-bottomed grooves etched into the internal sides of the dorsal surface or doublure that apparently represent infestation of the live trilobite.

Cambrian correlation within the Perigondwana Faunal Realm

Stratigraphic positions of Redlichioidea trilobites found in the Lower Cambrian of Morocco, Spain, South France, Sardinia, Jordan, Doberlug and Gorlitz (both in Germany), and those from Central Asia, Himalayan region, Australia and Antarctica are correlated with that of the Chinese biostratigraphic scheme. During the Middle Cambrian, biostratigraphic correlation between the Mediterranean region (including Morocco and Central Europe) and China is very difficult because of the complete absence of Paradoxides-fauna in China. Based on shallow-shelf and open-shelf trilobite faunas, the Middle and Upper Cambrian biostratigraphy of the Near East, Central, South and Southeast Asia, Australia and Antarctica are correlated with that of both China's shallow-shelf and open-shelf biostratigraphic schemes. Late Cambrian trilobite faunas of eastern Asiatic affinities also occur in Morocco, Spain, South France and Turkey. So far, there is no trilobite fauna of the Late Cambrian Fengshanian Stage found in Europe.

The first systematic description of Cambrian fossils from Myanmar: Late Furongian trilobites from the southern part of the Shan State and the early Palaeozoic palaeogeographical affinities of Sibumasu

The existence of late Cambrian (Furongian) trilobites in Myanmar (Burma) has been acknowledged since the 1970s, but no formal systematic descriptions of such fossils have been published to date. Herein, we provide such descriptions of some trilobites from the Molohein Group’s Myet-Ye Formation from the Linwe area, Ye-Ngan Township of the southern Shan State. Three species from two genera are reported: Asioptychaspis (A. asiatica, previously known from the North China Block, and a new species, A. lata) and Eosaukia buravasi, also known from peninsular Thailand. The Molohein Group was initially assigned a late Cambrian age based on the reported, but unsubstantiated, occurrence of the Laurentian genera Saukiella and Drumaspis, and this age assessment is supported by the fauna we present, although Saukiella or Drumaspis remain unconfirmed from Myanmar. Asioptychaspis asiatica first appears in late Jiangshanian strata, and Eosaukia buravasi ranges up to the middle of Stage 10. Thus these ranges provide a more specific constraint on the age of the Molohein Group. Similarities are strong between upper Cambrian and Lower Ordovician successions in Sibumasu and northwestern Australia, particularly those from the Canning Basin succession. Regional geological data supports placement of Sibumasu adjacent to Western Australia during the Cambrian, without the Lhasa Block intervening between them, and Baoshan at the western end of Sibumasu during the early Paleozoic, towards the Himalayan margin. The new Burmese fauna is consistent with these suggestions, as they belong to the Sino-Australian faunal province.

Quantifying the middle–late Cambrian trilobite diversity pattern in South China

The middle–late Cambrian is a key interval between the Cambrian Explosion and the Great Ordovician Biodiversification Event (GOBE) that marks a major biologic evolutionary transition in the geologic record. Diversity (i.e. richness) patterns in this interval show that macro-biota experienced evolutionary setbacks for the first time. However, relatively little attention has been paid to this interval in previous macroevolutionary studies and very different conclusions about the diversity patterns in coarse time-resolution have been documented. As a dominate group of marine benthic organisms in the Cambrian, trilobites provide insightful information to understand the history of biodiversity in the Cambrian marine ecosystem from the Cambrian Explosion to the GOBE. South China is a region with relatively good preservation of Cambrian fossil materials and sections, and 4 out of 6 Cambrian GSSPs were established in South China. In this paper, we use constrained optimization (CONOP) to correlate 19 sections from South China to reduce the Signor-Lipps effect and integrate the results with high-resolution chronostratigraphic data to evaluate the middle–late Cambrian trilobite diversity pattern in South China. This study, for the first time, constructs a high time-resolution (about 60 kyr) trilobite species-level richness curve with estimated time from Age 4 to the Paibian. A double-peaked species diversification is separated by a minor extinction in Stage 4; this is followed by a gradual decline of species diversity over the entire Wuliuan Age. A radiation of three times increase of species diversity in the Drumian and Guzhangian is exhibited and the diversity remains high for most of the Guzhangian Stage; this is followed by a great extinction at the end of the Guzhangian with around 50% species lost. Detailed comparison with previous composite studies and fossil material from single sections revealed that the Signor-Lipps effect could produce large biases in diversity pattern. In addition, a precise analysis of species evolution features compared with environmental indices provides a perspective about trilobite evolutionary mechanisms associated with environmental changes related to the carbon cycle and biotic competition.

Satunarcus, a new late Cambrian trilobite genus from southernmost Thailand and a reevaluation of the subfamily Mansuyiinae Hupé, 1955

AbstractThe Ao Mo Lae Formation of the Tarutao Group crops out on Thailand's Tarutao Island and contains a diverse assemblage of late Furongian trilobite taxa, including several endemic forms. This study presents a new genus and species, Satunarcus molaensis, discovered at two locations on the island. A cladistic analysis of the kaolishaniid subfamily Mansuyiinae in light of Satunarcus and similar genera known from across upper Cambrian equatorial Gondwanan rocks suggests that the subfamily is polyphyletic in its current definition, and thus is not a natural group. Separating Mansuyia Sun, 1924 from the other taxa conventionally placed in Mansuyiinae permits recognition of a previously unrecognized monophyletic subfamily Ceronocarinae new subfamily. As established herein, this kaolishaniid subfamily contains Satunarcus n. gen. and all genera previously recognized as Mansuyiinae. with the exception of Mansuyia itself. Ceronocarinae n. subfam. occur in middle Jiangshanian to middle Cambrian Stage 10 sedimentary rocks from Australia, South China, North China, and Sibumasu, with most genera endemic to Australia.UUID: http://zoobank.org/618c5136-73f0-4912-a7d3-e56559d2a76c

Late Cambrian (Iverian, Jiangshanian) fossils from the Professor Range area, Western Tasmania

Late Cambrian (Iverian, Jiangshanian) agnostoids and trilobites are described from two localities in the Professor Range area of western Tasmania. The fossils occur within a thick folded flysch succession of siltstone, mudstone, quartzwacke sandstone and siliceous conglomerate that forms the lower part of the Owen Group correlatives in this area. The flysch succession has a conformable and probable gradational contact with the underlying Mt Read Volcanics and is abruptly overlain by the siliceous pebble-cobble conglomerate correlated with the Middle Owen Conglomerate of the West Coast Range. The stratigraphically lower southern locality contains the agnostoids Pseudagnostus sp. and Agnostinae gen. et sp. indet. plus the polymerid trilobites Parabolina sp., Hedinaspis sp. cf. H. regalis and Eugonocare sp. The northern locality contains the agnostoids Rhaptagnostus sp. and Pseudagnostus sp. plus the polymerid trilobites Hedinaspis sp. cf. H. regalis, Ketyna? sp. 1, Ketyna? sp. 2, and Cermatops sp. It is possible that most specimens of the cosmopolitan genus Hedinaspis belong in the type species, H. regalis.Christopher J. Bentley [bigfossil@bigpond.com], 30 Albert Street, Clare SA 5453; James B. Jago [jim.jago@unisa.edu.au], University of South Australia, School of Natural and Built Environment, Mawson Lakes, SA 5095; Keith D. Corbett [keith.corbett@bigpond.com], 35 Pillinger Drive, Fern Tree Tas 7054, Australia.

Some middle and late Cambrian trilobites and brachiopods from the Adamsfield Trough, Tasmania

Jago, J.B., Bentley, C.J., Laurie, J.R. & Corbett, K.B., 26 June 2018. Some middle and late Cambrian trilobites and brachiopods from the Adamsfield Trough, Tasmania. Alcheringa 43, 1-17. ISSN 0311-5518.Cambrian Series 3 and Furongian trilobites and brachiopods are described from the Adamsfield Trough in southwestern Tasmania. The oldest fossils are very poorly preserved trilobites, assigned to Asaphiscidae gen. et sp. indet. from within the Island Road Formation a short distance above the unconformity with the underlying Proterozoic Wedge River Beds. A trilobite species from within the isolated Boyd River Formation is referred to Lioparia sp. The Island Road Formation and the Boyd River Formation are stratigraphically equivalent to the Trial Ridge Beds which have previously been dated as belonging to the Lejopyge laevigata Zone. The Trial Ridge Beds are overlain unconformably by the Singing Creek Formation. In the Adamsfield, Clear Hill and Stepped Hills areas, stratigraphic equivalents of the Singing Creek Formation collectively contain the trilobites Pseudaphelaspis sp., Pseudaphelaspis? sp., Prochuangia sp., Mindycrusta sp., Nepeidae gen. et sp. indet., and Olenidae gen. et sp. indet. plus the brachiopods described herein as Billingsella sp. aff. costata, Billingsella sp. A, Billingsella sp. B and a possible member of the Billingselloidea. The Singing Creek Formation has been previously correlated with the Stigmatoa diloma Zone. The genus Lotosoides Shergold 1975 is placed in synonymy with Prochuangia Kobayashi 1935.James B. Jago* [jim.jago@unisa.edu.au] University of South Australia, School of Natural and Built Environment, Mawson Lakes, SA 5095, Australia; Christopher J. Bentley [bigfossil@bigpond.com] 30 Albert Street, Clare, SA 5453, Australia; John R. Laurie [john.r.laurie@gmail.com] Department of Biological Sciences, Macquarie University, NSW 2109, Australia; Keith D. Corbett [keith.corbett@bigpond.com] 35 Pillinger Drive, Fern Tree, Tas 7054, Australia.

The agnostoid arthropod Lotagnostus Whitehouse, 1936 (late Cambrian; Furongian) from Avalonian Cape Breton Island (Nova Scotia, Canada) and its significance for international correlation

AbstractNew and archival collections from the Chelsey Drive Group of the Avalon terrane of Cape Breton Island, Nova Scotia, Canada, yield late Cambrian trilobites and agnostoid arthropods with full convexity that contrast with compacted, often deformed material from shale and slate typical of Avalonian Britain. Four species of the agnostoid Lotagnostus form a stratigraphic succession in the upper Furongian (Ctenopyge tumida–Parabolina lobata zones). Two species, L. ponepunctus (Matthew, 1901) and L. germanus (Matthew, 1901) are previously named; L. salteri and L. matthewi are new. Lotagnostus trisectus (Salter, 1864), the type species of the genus, is restricted to compacted material from its type area in Malvern, England. Lotagnostus americanus (Billings, 1860) has been proposed as a globally appropriate index for the base of ‘Stage 10’ of the Cambrian. All four species from Avalonian Canada are differentiated clearly from L. americanus in its type area in Laurentian North America (i.e., from debris flow blocks in Taconian Quebec). In our view, putative occurrences of L. americanus from other Cambrian continents record very different species. Lotagnostus americanus cannot be recognized worldwide, and other taxa should be sought to define the base of Stage 10, such as the conodont Eoconodontus notchhpeakensis.

Biostratigraphy of the Peri-Gondwana Cambrian trilobite fauna (northern Kerman, Iran) and correlation with other countries

Polymeroid trilobite fauna from two stratigraphic sections (Godbondar and Kuhbanan) of the Kuhbanan Formation in northern Kerman (central Iran) were studied and subjected to biostratigraphic analysis. Eleven genera and species are recognised from the latest Early Cambrian and Middle Cambrian Peri-Gondwanian successions of the study sections. The recognised fauna includes Afghanocare lategenatum, Blountia blountia, Iranoleesia sp., Iranoleesia pisiformis, Kermanella kuhbananensis, Kermanella lata lata, Kermanella lata minuta, Kermanella sp., Redlichia chinensis, Redlichia noetlingi and Redlichia sp. Based on trilobite distribution, three trilobite biozones were recognised in the study sections, namely Redlichia noetlingi biozone, Kermanella kuhbananensis biozone and Iranoleesia pisiformis biozone. The age of the study sections is late Early Cambrian to late Middle Cambrian based on the recognised trilobite biozones. The recognised late Early Cambrian trilobite assemblages (especially Redlichia and Kermanella) from northern Kerman are similar to those found from some other parts of Gondwana or Peri-Gondwana terrains (north India, Pakistan, northwestern Kashmir, Tajikistan, South Australia, South China and Afghanistan) and show affinities with fauna found in some other parts of Iran (Alborz, northern Iran; Tabas, eastern Iran; southeast Karman).

Furongian (late Cambrian) trilobites from the Asioptychaspis subglobosa Zone of the Hwajeol Formation, Korea

Park, T.-Y.S. & Kihm, J.-H., 3.10.2014. Furongian (late Cambrian) trilobites from the Asioptychaspis subglobosa Zone of the Hwajeol Formation, Korea. Alcheringa 39, xxx–xxx. ISSN 0311-5518The Hwajeol Formation of the Taebaek Group, Korea extends from the Jiangshanian Stage to Cambrian Stage 10. The lower part of the formation incorporates the Asioptychaspis Zone, which is closely correlated to the Asioptychaspis–Tsinania Zone of North China. This study documents silicified trilobites from the lower part of the Hwajeol Formation in the Sagundari section. Asioptychaspis subglobosa occurs throughout the interval; hence the biozone is renamed as the Asioptychaspis subglobosa Zone in this study. The Asioptychaspis subglobosa Zone of the Hwajeol Formation yields 14 polymerid species belonging to 14 genera. Of these, 11 species including three new species are documented for the first time in Korea. Among other taxa, the occurrence of Caznaia is stratigraphically significant because two biozones were established in Australia based on representatives of this genus: i.e., the Rhaptagnostus clarki patulus–Caznaia squamosa–Hapsidocare lilyensis and Rhaptagnostus clarki prolatus–Caznaia sectatrix zones in ascending order. Owing to the lack of cosmopolitan trilobites, the international correlation of these Iverian biozones has been equivocal. The occurrence of Caznaia from the Asioptychaspis subglobosa Zone of Korea indicates that the Rhaptagnostus clarki patulus–Caznaia squamosa–Hapsidocare lilyensis and Rhaptagnostus clarki prolatus–Caznaia sectatrix zones of Australia are correlated with the Asioptychaspis subglobosa Zone of Korea and the Asioptychaspis–Tsinania Zone of North China.Tae-Yoon S. Park [typark@kopri.re.kr] and Ji-Hoon Kihm [jhkihm@kopri.re.kr] (corresponding author), Division of Polar Earth-System Sciences, Korea Polar Research Institute, Incheon 406-840, Korea.

First Furongian (late Cambrian) trilobites from the Cantabrian Zone (north-western Spain)

Guillermo F. Acenolaza, Roberto Albani, Enruque Bernardez, Diego C. Garcia-Bellido, Juan Carlos Gutierrez-Marco, Isabel Rabano & Artur A. Sa

The Late Cambrian (Furongian) trilobiteTangshanaspisZhou and Zhang, 1978, in North America

Tangshanaspis Zhou and Zhang, 1978 (Family Missisquoiidae), has been reported widely from western North America and has been assigned invariably to a single species, T. depressa (Stitt, 1971b). The base of the T. depressa Subzone as defined in Oklahoma is an important biostratigraphic datum for inter-regional correlation of uppermost Cambrian strata. Study of previously undescribed material in collections from Oklahoma shows that T. depressa is, in fact, a composite of cranidia and pygidia that belong to two stratigraphically segregated species in the Signal Mountain Formation. Tangshanaspis silveri n. sp. includes the pygidial morph originally attributed to T. depressa. Revision of the species from Oklahoma allows definition of a new biostratigraphic unit, the Tangshanaspis Zone, which is divided into a lower T. silveri Fauna and an overlying T. depressa Fauna; in addition to the eponymous species, the T. depressa Fauna includes pygidia that represent two additional species of Tangshanaspis that are placed in open nomenclature. Correlation with other areas suggests that the “Missisquoia” mackenziensis Fauna of northern Canada may be equivalent to the T. silveri Fauna of Oklahoma, rather than a pre-Tangshanaspis interval that is unrepresented elsewhere in Laurentian North America.

Species-level phylogenetic analysis of pterocephaliids (Trilobita, Cambrian) from the Great Basin, western USA

Considerable systematic work devoted to late Cambrian trilobites includes very little species-level phylogenetic analysis. This paper presents the phylogenetic analysis of 36 species representing eight genera assigned to the Family Pterocephaliidae that occur in the Great Basin of the western United States during the Steptoean stage (Furongian). Continuous characters are treated in four different ways: discretization using finite mixture coding, discretization using gap-weighting, “as such” using ranges of values as implemented in the phylogeny program TNT, and exclusion altogether. Results indicate that even the inclusion of only a few continuous characters dramatically increases the resolution of nodes. Despite the different treatments of continuous characters, major features of the trees are shared across all results. The subfamily Pterocephaliinae is restricted to genera which possess a concave anterior border. Relative stratigraphic placement was estimated using a composite section built in CONOP and used to scale the tree topologies and to assess stratigraphic consistency. Although previously hypothesized multispecies evolutionary series are not supported by the results, tree topology, stratigraphic distribution, and optimized character state transformation support the interpretation of several sister taxa as direct ancestor-descendent pairs.

HOW SPECIES LONGEVITY, INTRASPECIFIC MORPHOLOGICAL VARIATION, AND GEOGRAPHIC RANGE SIZE ARE RELATED: A COMPARISON USING LATE CAMBRIAN TRILOBITES

Phenotypic variation is fundamental to evolutionary change. Variation not only evinces the connectivity of populations but it is also associated with the adaptability and evolvability of taxa. Despite the potential importance of morphological variation in structuring evolutionary patterns, little is known about how relative differences in intraspecific morphological variation and its geographic structure are linked to differences in species longevity. This study offers a novel combination of analyses that reveal the quantitative relationships among intraspecific variation, geographic range size and duration in the fossil record using late Cambrian trilobites. Results show that geographic range size and duration are positively correlated. Surprisingly, longer lived species tend to have less intraspecific variation. Phylogenetic effects were also explored and found not to determine the association between these variables. However, the distribution of geographic range sizes shows strong phylogenetic signal. In light of previous work, one possible explanation for these results is that species with shorter durations have comparatively higher rates of morphological evolution, reflected in higher phenotypic variation overall.

A review of the Late Cambrian (Furongian) palaeogeography in the western Mediterranean region, NW Gondwana

The Cambrian–Ordovician transition of the western Mediterranean region (NW Gondwana) is characterized by the record of major erosive unconformities with gaps that range from a chronostratigraphic stage to a series. The hiatii are diachronous and involved progressively younger strata along the Gondwanan margin, from SW (Morocco) to NE (Montagne Noire). They can be related to development of a multi-stage rifting (further North), currently connected to the opening of the Rheic Ocean, and concomitant erosion on southern rift shoulders. The platforms of this margin of Gondwana occupied temperate-water, mid latitudes and were dominated by siliciclastic sedimentation, while carbonate factories were only episodically active in the Montagne-Noire platform. The Upper Cambrian is devoid of significant gaps in the southern Montagne Noire and the Iberian Chains. There, the sedimentation took place in a transgressive-dominated depositional system, with common offshore deposits and clayey substrates, and was bracketed by two major regressive trends. The Late Cambrian is also associated with the record of volcanic activity ( e.g., in the Cantabrian and Ossa-Morena zones, and the northern Montagne Noire), and widespread development of a tectonic instability that led to the episodic establishment of palaeotopographies and record of slope-related facies associations. Several immigration events are recognized throughout the latest Middle Cambrian, Late Cambrian and Tremadocian. The trilobites show a stepwise replacement of Acado-Baltic-type families ( e.g., the conocoryphid–paradoxidid–solenopleurid assemblage) characterized by: (i) a late Languedocian (latest Middle Cambrian) co-occurrence of Middle Cambrian trilobite families with the first anomocarid, dorypygid and proasaphiscid invaders; (ii) a Late Cambrian immigration replacing previous faunas, composed of trilobites (aphelaspidids, catillicephalids, ceratopygids, damesellids, eulomids, idahoiids, linchakephalids, lisariids, onchonotinids, and pagodiids), linguliformean brachiopods (acrotretids, obolids, scaphelasmatids, siphonotretids, and zhanatellids), echinoderms (mitrates, glyptocystitid cystoids, and stromatocystoids), and conodonts belonging to the lower Peltura Zone; and (iii) the subsequent input of new trilobites (asaphids, calymenids, catillicephalids, nileids and remopleurids), which marks the base of the Proteuloma geinitzi Zone, associated with pelmatozoan holdfasts ( Oryctoconus), and a distinct input of late Tremadocian conodonts ( Paltodus deltifer Zone). The biogeographic distribution of latest Middle and Late Cambrian trilobites supports brachiopod data indicating strong affinities between the western Mediterranean region, East Gondwana (North China/Korea, South China, Australia, and Antarctica) and Kazakhstania during the late Languedocian, which became significantly stronger during the Late Cambrian. This major shift may suggest modification in oceanic circulation patterns throughout Gondwana across the Middle–Late Cambrian transition.

Stratigraphic Implications of Lower Ordovician Conodonts from the Munising and Au Train Formations at Pictured Rocks National Lakeshore, Upper Peninsula of Michigan

Early Ordovician conodonts have been recovered from the upper Munising Formation and the lower part of the Au Train Formation at Pictured Rock National Lakeshore in the Upper Peninsula of Michigan. Two trilobites from the lower Au Train probably represent the Symphysurina Zone ( S. woosteri Subzone) and confirm the Early Ordovician age of the Au Train. The presence of middle Late Cambrian (Franconian) trilobites in the underlying Munising Formation led to traditional assumption of a major hiatus between the Munising and the Au Train. An unconformity between these formations has been difficult to recognize in outcrops because upper Munising sandstones grade upward into weathered, reworked beach sands deposited during Ordovician transgression. The reworked sands traditionally have been assigned to the Munising, with the base of the Au Train placed at the lowest occurrence of carbonate rocks in the sequence. Conodonts from the uppermost Munising and lower Au Train are characteristic of the Rossodus manitouensis Zone (upper Skullrockian Stage, Millardan Series, Lower Ordovician). The conodont and trilobite data permit correlation of the rocks of this interval with sequence stratigraphic units in the Burnout Canyon Member of the House Limestone in the Ibex area of Utah and with equivalent strata in other parts of Laurentia.

THE UPPER CAMBRIAN TRILOBITE OLENUS AT ANDRARUM, SWEDEN: A CASE OF ITERATIVE EVOLUTION?

Abstract: The morphological changes in four species-level lineages of the Late Cambrian trilobite Olenus from the Alum Shale at Andrarum, south-east Scania, Sweden, have been analysed with the aim of re-examining the classical study of iterative evolution by Kaufmann (1933a). New material comprising 647 pygidia was collected for a restudy of Olenus, and for comparison the skeletal development of 918 cephala and 568 pygidia from the associated Homagnostus obesus were included. The re-examination shows that (1) only pygidia of the O. transversus – O. truncatus – O. wahlenbergi lineage display a statistically significant directional change towards a narrower shape; (2) all other lineages, including the agnostids, show net morphological stasis; (3) hence iterative directional evolution cannot be confirmed. Based on morphological investigations it is tempting to conclude that the lineage O. transversus – O. truncatus – O. wahlenbergi represents just one species displaying gradual morphological changes. Whether this is an evolutionary or an ecophenotypic phenomenon remains uncertain. The vertical distributions of olenids and agnostids are compared by using vanadium/(vanadium + nickel) ratios from the Olenus Zone of the nearby Gislövshammar-2 drill-core. It appears that incursions of olenids were linked to increases in bottom-water oxygen levels and that Homagnostus obesus was tolerant of lower dysoxia than olenids.

Late Cambrian ptychaspidid trilobites from western Utah: implications for trilobite systematics and biostratigraphy

The Notch Peak Formation (Late Cambrian, Sunwaptan) of western Utah yields diverse silicified trilobite faunas that provide new information on the anatomy of many taxa. The family Ptychaspididae Raymond, 1924, is represented by species of Keithiella Rasetti, 1944; Idiomesus Raymond, 1924; Euptychaspis Ulrich in Bridge, 1931; and Macronoda Lochman, 1964. At least four species are new, of which E. lawsonensis and M. notchpeakensis are named formally. Much previous work on Late Cambrian trilobites has emphasized biostratigraphic utility and the recognition of geographically widespread species. Data from new silicified collections indicate that this approach is difficult to justify because many putative ‘index species’ actually represent a plexus of closely related species whose biostratigraphic significance has yet to be determined. One such plexus is represented by E. kirki Kobayashi, 1935, whose previously reported occurrences in Texas, Oklahoma, Utah, Nevada and northern Canada record at least four distinct species. Similarly, Macronoda can now be shown to consist of at least five late Sunwaptan species in south-central and western North America.

Heterochrony of the Late Cambrian olenid trilobites from the Machari Formation, Yeongwol, Korea: implications for biostratigraphy and intercontinental correlation

This study deals with the heterochrony of two Late Cambrian olenid trilobites,Olenus asiaticus Kobayashi, 1944 from theGlyptagnostus reticulatus Zone andHancrania brevilimbata Kobayashi, 1962 from theHancrania brevilimbata Zone, recovered from the Machari Formation in Yeongwol, Korea. Comparison of ontogenetic developments ofOlenus asiaticus andHancrania brevilimbata led to consider that the two species are phylogenetically related: viz.,Hanerania brevilimbata is a probable descendant ofOlenus asiaticus. The ontogenetic trajectories of the two species are closely comparable in the protaspid and early meraspid stages, but deviate in the late meraspid and holaspid stages. The morphological changes with growth in theOlenus asiaticus-Hancrania brevilimbata lineage may have resulted from combined heterochronic processes: i.e., the reduction of preglabellar field in the descendant is attained by paedomorphic progenesis, whereas the expansion of glabella is a consequence of peramorphic acceleration. Of these, the progressive reduction of preglabellar field has been known to occur in other parts of the world and thus is assumed to be useful in improving the biostratigraphic correlation among widely separated paleogeographic provinces, such as Baltica and Avalonia. TheGlyptagnostus reticulatus Zone of the Paleozoic Gondwana can be correlated with theOlenus gibbosus Subzone of Avalonia and Baltica, while theHancrania brevilimbata Zone of Korea with theO. attenuatus andO. dentatus subzones of Baltica and the lower part of theO. cataractes Subzone of Avalonia.

The Late Cambrian trilobite Hamashania from Korea

The Late Cambrian trilobite genus Hamashania Kobayashi, 1942a has hitherto been poorly understood and is herein revised based on well-preserved specimens from Korea. Platysaukia Kobayashi, 1960 and Goumenzia Guo & Duan, 1978 are treated as junior synonyms of Hamashania. Hamashania comprises only two species, H. pulchera Kobayashi, 1942a and Pterocephalus busiris Walcott, 1905, and is restricted to North Chinaand Korea. The new genus Pacootasaukia is proposed to accommodate the Australian species Platysaukia jokliki Shergold, 1991 as type species, and Platysaukia tomichi Shergold, 1991, which are so distinct that they cannot be included within Hamashania. The generic concept of Mareda Kobayashi, 1942b, which was often confused with Hamashania, is confined to the type material.