Stephen Westrop

University of Oklahoma | ou · Sam Noble Museum

Appearance of the Cambrian Evolutionary Fauna is marked by a transition between the Terreneuvian Series (without known, or mineralized, trilobites) and Series 2 (commonly with trilobites) and appearance of more complex ecologic communities. Our new dates show the Terreneuvian–Series 2 (ca. 29 Ma) brackets two thirds of the Cambrian, with ca. 13 Ma...

The Cambrian dokimocephalid trilobite genus Deckera Frederickson, 1949 is a minor component of Steptoean (Jiangshanian) faunas of Laurentian North America. The original diagnosis emphasized strongly inflated palpebral areas of fixed cheeks and elevated palpebral lobes as important and novel characters. An appraisal of archival and new specimens fro...

Successions in Oklahoma and Nevada record trilobite extinction and replacement near the Steptoean–Sunwaptan boundary in inner-shelf and outer-shelf settings, respectively. Prior to the extinctions, different trilobite biofacies occupied these environments, but faunas became similar in composition across the environmental gradient in the overlying I...

High-precision U-Pb zircon ages on SE Newfoundland tuffs now bracket the Avalonian Lower–Middle Cambrian boundary. Upper Lower Cambrian Brigus Formation tuffs yield depositional ages of 507.91 ± 0.07 Ma ( Callavia broeggeri Zone) and 507.67 ± 0.08 Ma and 507.21 ± 0.13 Ma ( Morocconus-Condylopyge eli Assemblage interval). Lower Middle Cambrian Chamb...

Avalonia, the largest terrane of the Appalachian–Caledonian orogen, is best defined by a terminal Ediacaran–Ordovician sedimentary rock-dominated cover sequence (e.g., Rast et al., 1976) unconformable on a largely Mesoproterozoic–early Neoproterozoic basement (e.g., Murphy et al., 2018). Our concerns with Álvaro et al.’s (2022) depositional synthes...

Analysis of biostratigraphically dated boulders demonstrates that the Steptoean Positive Carbon Isotope Excursion (SPICE) is recorded in debris flow conglomerates of the Downes Point Member of the Shallow Bay Formation in western Newfoundland. Fifteen boulders composed of bioclastic carbonates were assigned to five faunas based on assemblages of ag...

Cambrian volcanic ashes are common in SE Newfoundland, and regional sampling has provided a zircon date sequence that brackets the Avalonian Lower-Middle Cambrian boundary interval faunal succession. The new U-Pb ages from the Brigus Fm. (upper-uppermost Lower Cambrian, Callavia broeggeri Zone-Morocconus-Condylopyge eli Assemblage) and lower Chambe...

Three shelf-derived boulders in debris flow conglomerates of the Downes Point Member of the Shallow Bay Formation of western Newfoundland yielded the first record of an Upper Cambrian shelf-margin trilobite fauna from the Elvinia Zone (Steptoean; Jiangshanian) in eastern North America. The fauna is dominated by the “catillicephalid” Buttsia Wilson,...

Non-technical summary A newly discovered trilobite fauna from the Cambrian Honey Creek Formation marks a distinct interval that follows an extinction event. Dominated by the genus Monocheilus in association with Ptychaspis , it resembles faunas from Alberta, Canada, and the Upper Mississippi Valley region of the United States. Ptychaspis bullasa Lo...

Earth's oldest cephalpods remain Late Cambrian in age. They appeared at the dawn of the Great Ordovician Diversification Interval as early nektic carnivores along with conodonts. A recent report of purported "cephalopods" 30 m.y. older in the Early Cambrian of eastern Newfoundland proves to be incorrect, as the tubular fossils are readily referable...

Earth's "oldest known" cephalopods from the Early Cambrian of SE Newfoundland are not cephalopods. They are best interpreted as post-mortem chimaers consisting of the open apertural chambers of several orthothecid hyoliths with invaginated narrow tubes of Coleoloides. The small tubes are misinterpreted as cephalopod siphuncles. The oldest known cep...

The Avalonia microcontinent has diagnostic terminal Ediacaran–Ordovician lithostratigraphy, depositional sequence architecture, and igneous activity that extends for 2000+ km reflecting epeirogeny related to the Avalonian transform fault. Avalonia records an abrupt early Middle Cambrian (late Wuliuan) change from green, purple, or light grey to ove...

The Cambrian olenid trilobite Peltura Milne-Edwards, 1840 is widespread in the Furongian strata of the Cambrian continents of Baltica and Avalonia, and has played a significant role in biostratigraphic zonations for both regions. Despite this importance, the genus is poorly known in Avalonian Canada. New collections from the Chelsey Drive Group on...

Species of Catillicephala are known from sites around the mid-Cambrian margin of Laurentian North America, including Vermont, Quebec, Newfoundland and North Greenland. Catillicephala cifellii sp. nov. is from the Downes Point Member of the Shallow Bay Formation (Cow Head Group) in western Newfoundland. It occurs in three shelf margin-derived bou...

Distinctive uppermost Ediacaran–Ordovician rocks (Avalonian overstep sequence) were key in definition of Avalonia, which comprises large areas of the NE Appalachians and the Caledonian and Variscan mountains (Britain and western Europe). This siliciclastic-dominated cover succession unconformably overlies a Neoproterozoic pre-Avalonian basement col...

The Cambrian (Marjuman–Steptoean; Guzhangian–Paibian) kingstoniid trilobite Blountia Walcott, 1916 is distributed widely in shelf strata of Laurentian North America. Species known from Marjuman formations were lost at the mass extinction at the end of that stage. New species entered the succession during and after the extinction interval, only to d...

Reports on the Avalonia terrane in the Acadian-Caledonian (A-C) mountain belt often feature 1) an homage to a complex late Proterozoic basement and siliciclastic-dominated terminal Edicaran-Ordovician platform cover sequence (E-O cs) with distinctive macrobiotas; 2) sophisticated zircon/stable isotope work as a prelude to geologic history conclusio...

The dominant models for ancient and future global temperatures draw on Svante Arrhenius' 1896 insights. He concluded CO2 was a key temperature driver and anticipated the modern climate catastrophe by calculating the effect of rising industrial CO2 emissions. The link from the late-19 th century of rising temperature with ever higher pCO2 based on a...

Two species of the Middle Cambrian trilobite Eodiscus Hartt, in Walcott, 1884, E. punctatus (Salter, 1864) and E. scanicus (Linnarsson, 1883), have been reported from several paleocontinents. However, in their respective type areas of Avalonian Britain and Baltica (Sweden), both species are poorly documented from moulds preserved in siliciclastic m...

Holmdalia Robison, 1988 (Family Marjumiidae), was proposed as a monotypic taxon that occurred in mid-Cambrian outer shelf settings inNewYork and Greenland, with a subsequent report from northwestern Canada.Newcollections from the Shallow Bay Formation of western Newfoundland record a succession of at least seven species that spans most of the Drumi...

Taphonomic sorting can be assessed directly in fossil assemblages by comparing expected and observed proportions of elements of multielement skeletons. Trilobites are model organisms for this approach because each individual possesses one cranidium (head) and one pygidium (tail). Departures from an expected 1:1 cranidia:pygidia (C/P) ratio reflect...

New 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 for...

Study of type and new material of the pterygometopine Achatella Delo, 1935 demonstrates the presence of four species in Upper Ordovician (Katian) strata of Laurentian North America, A . achates (Billings, 1860) from the northeastern United States and the St. Lawrence lowlands of Canada, A . carleyi (Meek, 1872) from the Cincinnati region, Ohio and...

'Athabaskiella' and 'Bathyuriscidella' comprise a distinctive set of dolichometopid species that share a relatively short palpebral lobe and a bacula opposite the L1 glabellar lobe. Almost all of these species are known from allochthonous boulders in debris flow conglomerates that accumulated along the Quebec Embayment and the St. Lawrence Promonto...

Mollusk-­rich assemblages with Watsonella crosbyi with or without Aldanella spp. represent a temporally problematical, earliest Cambrian interval. Although frequently regarded as Tommotian-­equivalents (upper Terreneuvian), new biotic and carbon isotope data demonstrate a pre­-Tommotian (middle Terreneuvian) age for early W. crosby-i­A. spp. assemb...

Recurrent mass extinction events (at "biomere"-a biostratigraphic unit-boundaries) characterize the middle Cambrian to Early Ordovician (Tremadocian) time interval that is between the major Cambrian and Ordovician radiations of animal life. A role for anoxia in maintaining elevated extinction rates in the late Cambrian has been proposed based on co...

12th International Symposium on the Ordovician System Field Trip Guide

The common belief that organic-rich mudstones formed in quiescent, distal settings is further weakened by study of an upper Cambrian (Leptoplastus - lower Peltura superzones) succession in the Chesley Drive Group in Avalonian Cape Breton Island that is comparable to Alum Shale successions in Baltica. Dramatic sea-level (likely eustatic) changes are...

The Upper Ordovician (Sandbian-Katian) bathyurid trilobite Raymondites Sinclair is revised using new collections from Missouri and Ontario, and archival material from Illinois, Wisconsin, New York, and Ontario. Phylogenetic analysis supports monophyly of Raymondites, but recognition of this genus renders Bathyurus Billings paraphyletic. We treat Ra...

Classification and relationships of the Ordovician encrinurines Frencrinoides Lespérance and Desbiens and Walencrinoides Lespérance and Desbiens are poorly understood, with little evidence for monophyly of either genus. We revise the type species of both genera, F. capitonis (Frederickson) and W. rarus (Walcott), using new and archival material. We...

The Upper Ordovician (Sandbian; late Whiterockian to Mohawkian) Bromide Formation of south-central Oklahoma was deposited along a distally steepened ramp that descended into the Southern Oklahoma Aulacogen (SOA). It provides an unparalleled opportunity to examine a spectrum of marine facies that extended from back ramp peritidal settings to the cen...

Species of Deiracephalus Resser, 1935, are rare elements in most Guzhangian (upper Marjuman) trilobite faunas of Laurentian North America, and are characterized by striking cephalic spinosity that includes very long genal and occipital or preoccipital glabellar spines. Almost all previous reports of the genus have assigned sclerites to two species,...

Species of Catillicephala Raymond, 1938 from eastern Canada are revised from restudy of types, including a number of previously unfigured specimens, from the Grosses-Roches Formation, Quebec, and undescribed material from the Shallow Bay Formation (Cow Head Group), western Newfoundland. In both regions, sclerites are from allochthonous, shelf-deriv...

Pioneering work by Christian Poulsen on Early Ordovician Laurentian faunas from Greenland established several genera which have been used often in the literature. Poulsen's original material has not previously been fully revised, and the content and identity of some genera have depended upon interpretations of his tiny photographs. We revise the ty...

The Early Ordovician genus Pseudohystricurus Ross has been treated as a minor taxonomic wastebasket for poorly known species featuring small, dorsally convex cranidia and tuberculate sculpture. No previously assigned species apart from the type species appear to belong to the genus. The type species, P. obesus Ross, has been known in its type area...

Missisquoiid trilobites are widespread in Laurentian North America but most occurrences have been reported under a single name, Missisquoia typicalis Shaw 1951 (now = Parakoldinioidia stitti Fortey 1983). The base of the Parakoldinioidia Zone (= Missisquoia typicalis Subzone of older publications) is usually defined by the first appearance of the e...

New field collections from sections in western Utah and southeastern Idaho permit the development of a high resolution trilobite biostratigraphy for the northern Laurentian Lower Ordovician (upper Tremadocian) Stairsian Stage similar to that proposed previously for the overlying Tulean and Blackhillsian stages. Four zones recognised previously are...

An Early Cambrian caliche on the St Non's Formation (emended) is the base of the Caerfai Bay Formation (unit-term changed) at Caerfai Bay, South Wales. Subaerial exposure and the caliche mean the two formations were not genetically related units. The St Non's is an older sand sheet (likely tidalitic, not delta-related) referred to Avalonian deposit...

The first records of the upper Cambrian agnostoid genera Kormagnostella, E. Romanenko, in Romanenko and Romanenko, 1967, and Biciragnostus F. Ergaliev, in Eraliev and Ergaliev, 2001, in Laurentian North America are from a narrow stratigraphic interval in the Steptoean-Sunwaptan boundary interval (Furongian, Jiangshanian) of Nevada and Utah. In Neva...

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 strat...

2012): A systematic revision of the Upper Ordovician trilobite genus Bumastoides (Illaenidae), with new species from Oklahoma, Virginia and Missouri, Journal of Systematic Palaeontology, 10:4, 679-723 This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, l...

Nine agnostoid species from late Cambrian (Paibian: Steptoean) boulders from the Cow Head Group in western Newfoundland fall into three biostratigraphically distinct faunas. The Glyptagnostus reticulatus Fauna contains only the eponymous species and correlates with the lower part of the Paibian and the basal Steptoean of North America. The "Innitag...

Slow subsidence and tectonic quiescence along the New York Promontory margin of Laurentia mean that the carbonate-dominated Tribes Hill and overlying Rochdale formations serve as proxies for the magnitude and timing of Tremadocian eustatic changes. Both formations are unconformity-bound, deepening–shoaling, depositional sequences that double in thi...

Macropyge gladiator Ross, 1951a, is the type species of the previously monotypic Gladiatoria Hupé, 1955. It has been regarded as the only known post-Tremadocian macropygine ceratopygid, and the only known ceratopygid from the Ordovician of Laurentia. Well preserved new material from western Utah and southern Idaho includes the first positively iden...

Eodiscoids form a significant component of the Lower Cambrian (Branchian) trilobite fauna of the St. Mary's and lower Jigging Cove members of the Brigus Formation exposed along Conception and Trinity bays, northern Avalon Peninsula, Newfoundland. Two species of Serrodiscus Richter & Richter, four species of Hebediscus Whitehouse, and rare sclerites...

Psalikilopsis Ross, 1953, has been known from a single species and interpreted as a " hystricurine" ancestral to some, but not all, " bathyurids" . Comprehensive revision of the type species and the description of three new species demonstrate that the taxon is ingroup Bathyuridae. The unusual morphology of its more derived species is associated wi...

Restudy of type and other material shows that the Cambrian (Sunwaptan, Furongian) agnostoid arthropod Lotagnostus americanus (Billings, 1860), far from being distributed globally, can be identified with confidence only at its type locality of Quebec. As such, it is ill-suited as an index for international correlation. Lotagnostus obscurus Palmer, 1...

Two completely dissimilar faunal changes occur between the Sunwaptan and Skullrockian Stages (Ptychaspid and Symphysurid ‘Biomeres’) in the uppermost Cambrian on the east Laurentian craton. An undolomitized section in the Little Falls Formation in Washington County, New York, shows a typical ‘biomere’ extinction, with highest Sunwaptan trilobites f...

The best definition for the base of the terminal Cambrian (Stage 10) is the conodont Eoconodontus notchpeakensis FAD ± onset of the HERB carbon isotope excursion. These horizons allow precise intercontinental correlations in deep ma-rine to peritidal facies. The agnostoid Lotagnostus americanus (Billings, 1860) FAD has been suggested as a Stage 10...

A limestone boulder in the Triassic Lepreau Formation near Saint John, New Brunswick, has yielded the first diverse marine fauna from the sub-Caradoc Ordovician of the western Avalon continent. This fauna includes the first Arenig conodonts recovered from Avalon and represents an unexposed interval in southern New Brunswick. Association of the cono...