Eyes and vision in the coeval Furongian trilobites Sphaerophthalmus alatus (Boeck, 1938) and Ctenopyge (Mesoctenopyge) tumida Westergård, 1922, from Bornholm,Denmark

The two olenid species Sphaerophthalmus alatus (Boeck, 1838) and Ctenopyge (Mesoctenopyge) tumida Westergård, 1922, occur together in the Ctenopyge tumida Zone (Zone 19) of the Furongian of Scandinavia. Material from Bornholm, Denmark, forms the basis of this study of the morphology and partial ontogeny of the eyes. The eyes of both species are directed laterally and have virtually panoramic vision, looking out sideways like those of a rabbit. The eye of S. alatus is comparatively smaller, with fewer lenses and a larger eye parameter; calculations show that this trilobite was adapted for dim light intensity, possibly suggesting a vagrant benthic habit. Ctenopyge (Mesoctenopyge) tumida, with a smaller eye parameter, was adapted for a higher light intensity, and this trilobite was most likely a pelagic swimmer. The two species, although preserved together, inhabited different levels in the water column.     

A tiny eye indicating a planktonic trilobite

Abstract: Cambrian trilobites mainly lived on the sea floor, and up till now few, if any, unequivocally planktonic trilobites have been reported from earlier than the Ordovician. The late Cambrian (Furongian) to late Ordovician olenids are a distinctive group of benthic (sea‐floor dwelling) or nekto‐benthic trilobites. Here we show, however, that one recently described, miniaturized and very spiny olenid species, Ctenopyge ceciliae must have been planktonic (passively drifting or feebly swimming in the upper waters of the sea). This interpretation is based not only upon body form but also on the analysis of its visual system and may be one of the earliest records of the planktonic realm being invaded by trilobites.     

Complete record of Furongian polymerid trilobites and agnostoids of Scandinavia – a biostratigraphical scheme

Terfelt, F., Ahlberg, P. & Eriksson, M.E. 2011: Complete record of Furongian polymerid trilobites and agnostoids of Scandinavia – a biostratigraphical scheme. Lethaia, Vol. 44, pp. 8–14. So far, 112 polymerid trilobite species/subspecies and 13 agnostoid species/subspecies have been recorded from the Furongian (upper Cambrian) of Scandinavia. For the first time, their zonal occurrences are summarized in a biostratigraphical scheme serving as a practical synopsis for students of this interval in time. Ninety‐six of the recorded polymerid trilobite species/subspecies belong to the family Olenidae whereas the remaining 16 are distributed across eight other families. Levels of increased speciation and low diversity (including stratigraphical range gaps) are conspicuous and these may be correlated with recorded physical and chemical anomalies. □Agnostoids, biostratigraphy, Cambrian, Furongian, polymerids, Scandinavia, trilobites.     

Ontogeny and Structure of a New, Miniaturised and Spiny Olenid Trilobite from Southern Sweden

Several hundred specimens of a tiny olenid trilobite, Ctenopyge ceciliae sp. nov., have been found in stinkstone nodules in the upper Cambrian Peltura scarabaeoides Zone in southern Sweden. This exceptionally spinose form is known only from disarticulated specimens, but is quite well preserved, and all growth stages are represented. The early ontogenetic stages are exceptionally small, the protaspis being only half the size of that of the associated Peltura species. There may have been no more than three thoracic segments. Thus the whole ontogeny was compressed, and this together with the very small size of the adult indicates a true miniaturisation. Whereas the likely control of the origin of the tiny C. ceciliae was basically progenesis, the extreme spinosity had a different origin; allometric growth or possibly peramorphosis. C. ceciliae is small enough for the spines to have appreciably retarded sinking through frictional effects, and this small trilobite is interpreted as a free-swimming or floating form.     

Faunal turnovers and trilobite morphologies in the upper Cambrian Leptoplastus Zone at Andrarum, southern Sweden

The Furongian (upper Cambrian) Leptoplastus Zone marks a time of critical changes in the evolution of olenid trilobites. This zone, unexposed at Andrarum in Skåne, southern Sweden, has been re-excavated and the sequence of faunas and sediments logged in detail. The faunal succession accords with that previously described from borehole cores by Westergård, and the subzones of L. paucisegmentatus, L. raphidophorus, L. crassicornis, L. ovatus, L. angustatus, and L. stenotus have been recognized. In the first two subzones the olenid assemblages are monospecific. At the base of the L. crassicornis Subzone more than one species is present and morphotypes with long genal spines appear for the first time. Faunal turnover is rapid, but the incoming of new species is invariably linked to an abrupt change in sedimentation, or follows an unfossiliferous interval; species either arose or migrated in after a time of environmental perturbation. Particular faunal associations are often confined to discrete sedimentary packages though some species may range through a succession of sedimentary changes. Leptoplastus crassicornis has very long genal spines, adapted for resting on the sea floor; it may have competed with the coeval, and very similar, L. angustatus. Subsequently, L. angustatus is accompanied by the stout-bodied, short-spined L. ovatus, which presumably occupied a different niche within the same environment. Leptoplastus stenotus is convergent on the much earlier L. paucisegmentatus, and likewise is found as a monospecific assemblage, presumably being adapted to a similar niche.     

Cambrian high-resolution biostratigraphy and carbon isotope chemostratigraphy in Scania, Sweden: first record of the SPICE and DICE excursions in Scandinavia

A core drilling (Andrarum‐3), from the classical locality at Andrarum, Scania, southernmost Sweden, penetrated a 28.90‐m‐thick Cambrian succession. The core comprises dark grey to black, finely laminated mudstones and shales with early concretionary carbonate lenses (stinkstones or orsten) and a few primary carbonate beds. The middle Cambrian (provisional Series 3) part of the core comprises 17.35 m, whereas the Furongian Series (upper Cambrian) part covers the remaining 11.55 m. Nineteen trilobite and two phosphatocopine genera are present in the middle Cambrian, whereas the less diverse Furongian interval yielded four trilobite and three phosphatocopine genera. Other, less frequent, faunal elements include conodonts (s. l.), brachiopods, sponge spicules, bradoriids, and coprolites. Trilobites and phosphatocopines were used to subdivide the core into seven biozones ranging from the Ptychagnostus atavus Zone to the Parabolina spinulosa Zone (P. spinulosa Subzone). Carbon isotopic analyses (δ¹³C_org) through the core show two important excursions, the negative DrumIan Carbon isotope Excursion (DICE) in the Pt. atavus Zone, and the Steptoean Positive Carbon Isotope Excursion (SPICE) beginning near the first appearance of Glyptagnostus reticulatus and extending upward into the Olenus and Agnostus (Homagnostus) obesus Zone. The DICE displays a peak value, in the samples at hand, of –30.45‰δ¹³C_org in the lower part of the P. atavus Zone. The δ¹³C_org values increase through the overlying L. laevigata and A. pisiformis zones and display peak values of c. –28.00‰δ¹³C_org in the lowermost Furongian Olenus wahlenbergi and O. attenuatus subzones. Thereafter the values decrease significantly through the O. scanicus Subzone. Both isotopic excursions have been documented from several palaeocontinents, but never before from Baltica. Moreover, for the first time these excursions are recorded from organic matter in an alum shale setting. The recorded shift of +1.50–2.00‰δ¹³C_org is approximately half the magnitude of the SPICE documented from other regions. This discrepancy may be related to temporal variations in the type, origin, or diagenesis of the organic fraction analysed.     

Aligned trace fossils from the Utica Shale: implications for mode of life and feeding in the trilobite Triarthrus beckii

The olenid trilobite Triarthrus commonly occurs in nearly monospecific assemblages within otherwise relatively barren black shales. As such, it has been proposed that these trilobites preferred dysoxic or even anoxic habitats and suggested feeding habits range from predation and particle feeding to chemoautotrophism. A unique bedding‐plane assemblage of aligned traces that grade from Rusophycus to Cruziana, with associated Triarthrus beckii carcasses, are described from three localities in the Indian Castle Formation (upper Utica Shale) just below a K‐bentonite bed. Although few body fossils are preserved, it is clear that the 15‐cm‐thick, laterally extensive Thruway K‐bentonite created a unique taphonomic window that preserved the activities of numerous olenid trilobites. Rusophycus and Cruziana, consistently observed in densities above 100 trackways/m², were excavated by the trilobites into the upper surface of a micro‐graded bed, likely a distal turbidite deposit. Sedimentological and trace metal data (Mo, Mn, V and U) support dysoxic but not persistently anoxic conditions through this interval. Measurements from over 500 individual trackways have mean orientations of 259.1° (WSW) at the Myers Rd. locality and 224.59° (SW) at the Dolgeville Dam locality. These orientations are closely similar to independent sedimentological indicators of current transport direction at these sites, which indicates that the trilobites preferentially faced into the prevailing current. The trackways provide compelling evidence that Triarthrus beckii individuals were engaged in feeding, probably assisted by current transport of particles. These results do not support previous suggestions that Triarthrus may have relied upon a chemoautotrophic life habit, but are consistent with suggestions of predation or scavenging from the sediment.     

Integrated biostratigraphy and carbon isotopes from the Cambrian Tangwangzhai section,North China

The Tangwangzhai section, western Shandong Province, North China, the type section for the Cambrian Kushan and Chaomitian formations, yielded a diverse and relatively well-preserved conodont fauna, in which we recognize the Westergaardodina orygma, Westergaardodina matsushitai, Muellerodus? erectus, and Westergaardodina aff. fossa–Prooneotodus rotundatus zones of the North China conodont zonation. The Tangwangzhai conodont succession can be correlated not only with the polymerid trilobites occurring in the section but also with the conodont zones established for South China. The first occurrence of Furnishina longibasis and Furnishina quadrata in the upper part of the Westergaardodina matsushitai Zone allows the recognition of the base of the Paibian Stage and Furongian Series in the upper part of the Kushan Formation. The base of the Jiangshanian Stage, in the uppermost Muellerodus? erectus Zone, can be recognized by the presence of Westergaardodina cf. calix close to the base of the Chaomitian Formation. Chemostratigraphic analyses of the Tangwangzhai section show the onset of a positive carbon isotope excursion, referred to the SPICE event, in the upper part of the Kushan Formation at a level corresponding to the first occurrence of F. longibasis and F. quadrata. The base of the Jiangshanian Stage in the section is close to the demise of the SPICE positive excursion.     

Trilobite faunal successions across the base of the Furongian Series in the Taebaek Group, Taebaeksan Basin, Korea

The base of the Furongian Series in the Sino-Korean Block has not been clearly defined due to the lack of the index taxon, Glyptagnostus reticulatus. The Sesong Formation of the Taebaek Group, Taebaeksan Basin, Korea, has been known to range from the Guzhangian Stage of the Cambrian Series 3 to the middle Furongian Series, hence embracing the base of the Furongian Series. Silicified polymerid trilobites were recovered from the middle part of the Sesong Formation. Described are a total of 18 polymerid species of 13 genera: Neodrepanura sp. 1, Teinistion sp. 1, Huzhuia sp. 1, Huzhuia sp. 2, Liostracina simesi, Liostracina sp. 1, Parachangshania monkei, Parachangshania rectangularis nov. sp., Placosema bigranulosum, Fenghuangella laevis nov. sp., Baikadamaspis jikdongensis nov. sp., Baikadamaspis sp. 1, Prochuangia mansuyi, Maladioides coreanicus, Alataspis sesongensis nov. gen., nov. sp., Chuangia sp. 1, and ceratopygids genus and species indeterminate 1 and 2. The stratigraphic occurrence of these trilobites provides a basis for recognition of five zones across the base of the Furongian Series (in ascending order): the Neodrepanura, Liostracina simesi, Fenghuangella laevis, Prochuangia mansuyi, and Chuangia zones. The Neodrepanura and Chuangia zones are provisionally adopted from the previous biostratigraphic scheme, while the three other ones are newly proposed. The recommended base of the Furongian Series in the Taebaek Group of Korea coincides with the base of the Fenghuangella laevis Zone, which appears to represent an episode of profound trilobite faunal turnover.     

Why barren intervals? A taphonomic case study of the Scandinavian Alum Shale and its faunas

The Scandinavian Alum Shale Formation (Middle Cambrian to Lower Ordovician) accumulated under generally low oxygen concentrations. Syndepositional changes in the oxygen concentrations of the bottom water are reconstructed on the basis of the fossil fauna. Under relatively high oxygen concentrations, brachiopods and non-olenid polymerid trilobites inhabited the sea floor. Under lower oxygen concentrations the fauna was dominated by agnostids and at lowest oxygen levels by olenid trilobites. The enrichments of vanadium relative to nickel, as well as the enrichment of sulphur, match these faunal changes. A geochemical classification of the dysoxic environment is presented. The abundance of calcareous fossils decreases with increasing bottom water oxygen concentrations, indicating that the preservation of calcareous hard parts is most likely at the lowest oxygen concentrations. The poor preservation of calcareous fossils at relatively high oxygen concentrations is explained by the generation of corrosive pore waters during the reoxidation of sulphide compounds. Trilobitic and non-trilobitic intervals alternate up through the shale. Non-trilobitic intervals are either barren or contain non-calcareous fossils (phosphatic brachiopods, phosphatic 'ostracodes' and graptolites). The stratigraphical variation of trilobitic and non-trilobitic intervals is interpreted to reflect major changes in oxygen levels that might be linked to sea-level and climatic fluctuations.     

Pattern of some Silurian bioevents

The best‐known Silurian bioevent occurred at the end of the Wenlock: the lundgreni event, together with the nassa‐ludensis crisis, was established among planktic graptolites. The East Baltic data show several peaks of high diversity (especially triangulatus, turriculatus, scanicus zones) and three levels of low diversity of graptolites (antennularius, radians, ludensis zones). These are more or less coincident with sea‐level changes. Energetic innovation of the shallow shelf corals started in the early Silurian. The late Wenlock regression seems not to affect them seriously but the late Silurian decline coincides with the aridization of the climate and a regression of the shelf seas. The Agnatha had strong radiations in the Wenlock (ludensis Zone) and Ludlow (leintwardinensis Zone), the fishes in the Pridoli. Many Silurian vertebrates were long‐ranging and extinction rate was relatively low; only at the late leintwardinensis level and in the latest Ludlow did considerable extinctions occur.     

Tremadocian (Ordovician) biostratigraphy and graptolites at Dayangcha (Baishan,Jilin, NE China)

Based on a systematic study of Tremadocian graptolites from the Early Ordovician Yehli Formation at Dayangcha, Baishan of Jilin, NE China, a revised graptolite zonation is proposed for the Tremadocian rocks in the area. In ascending order, the graptolite zones include theRhabdinopora flabelliformis parabola Zone, theAnisograptus matanensis Zone, thePsigraptus jacksoni Zone and theAorograptus victoriae Zone. The first three zones are discussed with their definitions and durations clarified, whereas the last zone is introduced for the first time as a replacement of the formerAdelograptus-Clonograptus Zone. The entire Yehli Formation is considered to be older than the late Tremadocian Hunneberg Substage of Scandinavia, the latter being represented by the carbonate-dominated basal part of the overlying Liangchiashan Formation where no graptolites have so far been discovered. The Tremadocian succession in the Dayangcha area is regarded as being representative of the North China (Sino-Korea) Palaeoplate, and a correlation of the Tremadocian graptolite sequence with those of other continents is suggested. Nine species belonging toDendrograptus, Aspidograptus, Callograptus andAirograptus of the family Dendroidae, and eight species ofPsigraptus, Adelograptus, Aorograptus andKiaerograptus of the family Anisograptidae are described and some are revised in the present paper. Among the important revisions are the reconstructed proximal development ofPsigraptus jacksoni based on partially three-dimensional specimens from the area, and the complex thecal structures ofAspidograptus.      

Lower-Middle Cambrian boundary in open shelf facies of the Siberian Platform

In the Early and Middle Cambrian (of traditional usage), three broad facies belts were developed over the Siberian Platform. The lithofacies belts comprise evaporitic-carbonate, reef-shoal, and open-marine environments.Trilobites assemblages are most diverse in the open-marine lithofacies (Judoma-Olenek facies), represented especially by the Kuonamka Formation, in the eastern part of the platform. Species, genera and families of trilobites gradually increased through the Middle-Cambrian boundary interval in the Kuonamka Formation. Protolenidae dominated in the time represented by the Lermontovia Zone. In strata assigned to the Anabaraspis Zone, the protolenids disappear, the paradoxidids appear, and the diversity of dorypygids increases. The number of trilobite families increases in the Oryctocara and Kounamkites zones.Well represented in the Kuonamka formation of the eastern Siberian Platform are three levels of trilobites that have potential for global correlation. They are the Oryctocephalus reticulatus (=O. indicus latus), Oryctocephalus indicus, and Ovatoryctocara granulatus levels. The Lower-Middle Cambrian boundary in the South China correlates to the lower part of the Kounamkites Zone of the Siberian Platform.     

Biotic zonation on rocky shores of Heard Island

Summary The zonation of rocky shore biota on Heard Island is described for the first time, related to a universal zonation scheme and compared with that recorded for other sub-Antarctic localities. The Kelp Zone of holdfasts of the giant kelp, Durvillea antarctica (Chamisso) Hariot (one of the characteristic features of these regions) is confirmed as a sublittoral fringe. The occurrence of a Bare Zone within the littoral zone on sub-Antarctic shores is discussed. The possible roles of submersion, spray, freezing and predation by gulls in influencing the extent and composition of zones are discussed.     

A new high-resolution planktic foraminiferal zonation and subzonation for the lower Danian

A new planktic foraminiferal zonation has been established for the lower Danian, based on some of most expanded and continuous pelagic sections known to date (from Spain, Tunisia and Mexico). This biozonation is considered valid for low and middle latitudes. The maximum stratigraphical distribution of the index-species approximately coincides in all the studied sections. The index-species are abundant and easily recognizable. We propose the following biozones and subzones: Guembelitria cretacea Zone and the Hedbergella holmdelensis and Parvularugoglobigerina longiapertura subzones; the Parvularugoglobigerina eugubina Zone, which is subdivided into the Parvularugoglobigerina sabina and Eoglobigerina simplicissima subzones and the Parasubbotina pseudobulloides Zone with the Eoglobigerina trivialis and Subbotina triloculinoides subzones. A biomagnetostratigraphic correlation and calibration of the stratigraphical ranges of these species suggest that the biohorizons used to define the new biozonation are very isochronous, at least in the geographical areas analysed.     

Extreme protomeric development in a burlingiid trilobite from Cambrian glacial erratics of Denmark

Pengia Geyer & Corbacho is a Cambrian burlingiid trilobite with fused trunk segments devoid of any articulation in the anamorphic and epimorphic phases of development. The type species is Pengia fusilis (Peng et al.) from the Wanshania wanshanensis Zone of China. Here we describe a second species, Pengia palsgaardia sp. nov., from the Lejopyge laevigata Zone of the Paradoxides forchhammeri Superzone. It comes from a glacial erratic in Denmark which probably originated in the Alum Shale Formation of Västergötland, Sweden. Pengia palsgaardia is a large burlingiid (~10 mm in length), with 14 fused segments in the trunk whose boundaries are marked by ridges. The axis is narrow, with the axial furrows faintly indicated or effaced across the median. Laterally along the axis and the tapering glabella, symmetrical globular lobes are developed that are pinched at their base. During ontogeny the glabellar furrows are pit‐like adaxially but shallow towards the axial furrow as the globular lobes develop. Their pit‐like appearance in Pengia palsgaardia and some other burlingiid species is not considered similar to the condition seen in oryctocephalid trilobites. A median preglabellar ridge resembling that of Schmalenseeia Moberg develops late in ontogeny but in early ontogeny the preglabellar field resembles that of Burlingia Walcott, Alumenella Geyer & Corbacho and Niordilobites Geyer & Corbacho. This gives Pengia a more basal position in the schmalenseeid lineage, outside the derived Schmalenseeia. In mature specimens the facial sutures in P. palsgaardia are fused, but an ocular suture may have been present. During ontogeny Pengia would have gone through the anamorphic and protomeric protaspid segmental conditions, but articulation between either the cephalon and pygidium, or pygidium and thoracic segments of the trunk never developed so it did not progress beyond the protaspid phase. This extreme protomeric development is considered to be a derived feature in Pengia.     

Biostratigraphic distribution of ammonites and calpionellids in the Tithonian of the internal Prerif (Msila area,Morocco)

Because of the relatively thick succession exposed in the Msila area, new bed-by-bed sampling has been carried out in order to investigate late Tithonian ammonites and the correlation between biostratigraphic scales based on ammonites and calpionellids. The outcrop begins with Lower Tithonian beds assigned to the Fallauxi Zone. Ammonites have been found that allow recognition in the same section both Fallauxi and Ponti Zones. The most significant species are: Simoceras admirandum Zittel, which is the marker of the upper subzone of the Fallauxi Zone, i.e. the Admirandum/Biruncinatum Subzone, and several species of the genus Lemencia and Burckhardticeras peroni (Roman), that characterize the Ponti Zone. Ammonites that belong to the Microcanthum Zone appear in bed 18. This zone is usually subdivided into two subzones, of which only the lower one, the Simplisphinctes Subzone, has been recognized. The upper Transitorius Subzone has been recognized on the basis of the occurrence of Moravisphinctes fischeri (Kilian). The last ammonite unit, the Durangites Zone, is easily recognizable because of the occurrence of species of the genera Durangites and Protacanthodiscus. The section ends with the beginning of the Berriasian, which is characterized by a well-exposed, ammonite-rich bed of the Jacobi Zone. Correlation of the ammonite zones with calpionellid zones has been investigated. The Chitinoidella Zone is characterized by calpionellids with microgranular tests that appear in the ammonite Admirandum/Biruncinatum Subzone with species of the Dobeni Subzone, which extends up to the Ponti Zone. Representatives of the Boneti Sub-Zone appear in bed 16, which probably correlates with the base of the ammonite Upper Tithonian Microcanthum Zone. Two horizons have been distinguished within the calpionellid Subzone A3.     

A new subdivision of the Albian spore-pollen zonation of Australia

The Albian spore-pollen zonation of Australia is used to date terrestrial sequences from Antarctica to New Zealand. A detailed qualitative and quantitative study of the Albian Crybelosporites striatus and Coptospora paradoxa Zones in the Gippsland Basin confirms many of the published zone indicator taxa are reliable. The first and last appearance datums can be further refined quantitatively based on the upward reduction in the abundance of seed fern produced pollen. Three subzones are defined in the C. paradoxa Zone using a combination of presence/absence range and abundance data. These are (from oldest to youngest): the Trilobosporites trioreticulosus, Pilosisporites grandis and Cicatricosisporites cuneiformis Subzones. This latter subzone presents a new subdivision of this zone in the Gippsland Basin in southeast Australia. All these subzonal divisions have sufficient resolution to facilitate reservoir-scale correlation of fluvial strata confined to the C. paradoxa Zone in the Gippsland Basin. This study has the first record of Taxodiaceaepollenites hiatus in the Early Cretaceous of Australia and a new species Aequitriradites burgerii is described. A re-examination of the chronology of the zones in the Cretaceous marine basins confirms a 103.5 Ma age for the top of the C. paradoxa Zone, however the chronology of the base of this zone is unclear in the Albian.     

Anomalous facies and ancient faeces in the latest middle Cambrian of Sweden

The middle Cambrian–Furongian transitional interval was a time of significant biotic and environmental changes. Strata of this age in Scania, southern Sweden, contain two interlayered biofacies, a normal one dominated by trilobites and an anomalous one dominated by phosphatocopines (small bivalved arthropods). In places these biofacies are separated by intervals barren of fossils. In a phosphatocopine facies without trilobites in the upper Agnostus pisiformis Zone at Andrarum we recovered scattered fossil aggregates with a homogeneous composition of tightly packed and stacked phosphatocopines. These aggregates are interpreted as coprolites produced by an undetermined predator, possibly the chaetognath-like protoconodont animal or some other soft-bodied metazoan. The so-called barren intervals of Scania are not necessarily barren of fossils, but only trilobites, brachiopods, and other skeletal elements with a calcium-carbonate composition. The phosphatocopine facies with coprolites in the uppermost part of the A. pisiformis Zone correlates with the trilobite mass extinction at the top of the Marjumiid Biomere in Laurentia and immediately prior to the onset of the Steptoean Positive Carbon Isotope Excursion (SPICE), inferring a global shift in the oceanic chemistry that in Scania favoured phosphatocopines over the more common, trilobite-dominated faunas.     

THE EARLY JURASSIC AMMONITE BADOUXIA FROM BRITISH COLUMBIA, CANADA

Abstract:  Most species of the Lower Jurassic ammonite genus Badouxia are restricted to the eastern Pacific where they are of fundamental importance to the Hettangian/Sinemurian ammonite zonation of North America. The fauna from the type area for the genus has been restudied and four species and two transitional forms are now recognized. Badouxia forticostata and Badouxia castlensis are new. Badouxia occidentalis (Frebold) and Badouxia oregonensis Taylor are placed in synonymy with Badouxia canadensis (Frebold). These major taxonomic changes and subsequent modification to the range of B . canadensis require revisions to the current zonation for the Western Cordillera of North America. The Oregonensis Zone is re-named the Mineralense Zone. The Canadensis Zone is abandoned and its previously defined Rursicostatum and Columbiae subzones are elevated to the level of full zones. Large samples indicate that most species of Badouxia display a remarkable range of continuously variable morphology. In addition, the genus shows some of the best-documented evidence of sexual dimorphism in Early Jurassic ammonites. Badouxia spans the Hettangian/Sinemurian boundary and based on the range of different species, five stratigraphic intervals are recognized. Intervals 1–3 correlate with the north-west European Angulata Zone. The majority of interval 4 and the whole of interval 5 correlate with the north-west European Bucklandi Zone. The age of the base of interval 4 is uncertain.