Cupulocrinid crinoids from the Middle Ordovician (Galena Group, Dunleith Formation) of northern Iowa and southern Minnesota

1992 ◽  
Vol 66 (1) ◽  
pp. 99-128 ◽  
Author(s):  
James C. Brower
Keyword(s):  
Niche Differentiation ◽  
Upper Ordovician ◽  
Average Width ◽  
Positive Allometry ◽  
Middle Ordovician ◽  
Surrogate Variable ◽  
Crown Volume ◽  
Food Particles ◽  
Anal Sac ◽  
Food Groove

Two cupulocrinids,Cupulocrinus crossmanin. sp. andPraecupulocrinus conjugans(Billings) n. gen., are known from the Middle Ordovician (Galena Group, Dunleith Formation) of northern Iowa and southern Minnesota. Various morphologic and ontogenetic features demonstrate thatPraecupulocrinusis more primitive thanCupulocrinus. The two species commonly occur together. In addition, both taxa coexisted at similar levels with stem lengths ranging from about 1.5 cm in juveniles to 15 cm in adults. Relatively complete growth sequences illustrate growth and variation and show how two related crinoids subdivided feeding niches. The crown volume provides a satisfactory surrogate variable for the size of the animal. The food-gathering system of the cupulocrinids is mainly augmented by the addition of new plates at the ends of the arms. The number of plates in the arms and the arm length exhibit positive allometry relative to crown volume, largely due to development of new branches at the arm tips. The food-gathering capacity equals the number of food-catching tube-feet multiplied by the average width of the food grooves. Food-gathering capacity is also positively allometric with respect to crown volume and the amount of tissue that must be supplied with food. Consequently, the ratio of food-gathering capacity:crown volume is either constant or declines slightly with increasing size and age. The food groove width increases throughout ontogeny so adult crinoids ate larger food particles than juveniles.Praecupulocrinus conjugans(Billings) n. gen. has more narrow food grooves thanCupulocrinus crossmanin. sp. of comparable size and age, which suggests niche differentiation based on food-particle size. The arm and tube-foot geometry indicates that both cupulocrinids utilized the same type of suspension feeding.The morphology of the anal sac and the lack of “patelloid” processes in the arms indicate thatCupulocrinus sepulchrumRamsbottom from the Upper Ordovician of Scotland belongs toDendrocrinus.

Eoparisocrinid crinoids from the Middle Ordovician (Galena Group) of northern Iowa and southern Minnesota

1995 ◽  
Vol 69 (2) ◽  
pp. 351-366 ◽  
Author(s):  
James C. Brower
Keyword(s):  
Growth Rates ◽  
Growth Curves ◽  
Groove Width ◽  
Stem Length ◽  
Middle Ordovician ◽  
Crown Volume ◽  
Food Particles ◽  
Food Groove ◽  
Branch Density ◽  
Tube Feet

Two species of eoparisocrinid crinoids from the Middle Ordovician Galena Group of northern Iowa and southern Minnesota are described, namely Eoparisocrinus crossmani n. sp. and E. grandei n. sp. The post-larval development of Eoparisocrinus crossmani is examined. Crinoid arms grow by addition of new plates at their distal tips in conjunction with calcite deposition on old plates. New branches appear where axillary plates are initiated. Consequently, the growth rates for number of brachials and length of food-gathering system compared to crown volume are much faster than if the animals were isometric. The number of food particles collected is related to the number of food-catching tube-feet, which can be estimated if the length of the arms and height of the covering plates are known. The size of the largest food item is constrained by the food groove width. Thus, food-gathering capacity is the number of food-catching tube-feet multiplied by food groove width. The food-gathering capacity increases more rapidly than if the animal grew isometrically, and the ratio of food-gathering capacity: crown volume only declines slightly over the known growth range. All Ordovician cladid crinoids examined follow nearly identical ontogenetic trajectories. The ecological niche of a stalked crinoid is related to four basic parameters: stem length, food groove width, tube-foot spacing, and branch density. Stem length limits the highest elevation above the seafloor. The column of E. crossmani becomes longer during ontogeny due to the formation of new columnals and height growth of old ones. Consequently, individuals gradually “move up” until the adult elevation of about 50 mm is reached. The growth rates of stem length relative to crown size are slow in the youngest and mature animals but rapid in juveniles. The food grooves become wider throughout growth so that older crinoids ate larger food particles than younger ones. The food groove width increases less rapidly than if the shape were constant, because distal plates and branches are more narrow and have more slender food grooves than proximal plates. Growth curves for food groove width versus stem length and elevation were generated for E. crossmani and other crinoids that commonly occur in the same beds. Together, elevation and food particle size define the main dimensions of the niche. The various taxa are more or less separated by different food groove widths at most comparable elevations. This pattern minimizes ecological overlap and probably competition between the different species. The tube-foot spacing of E. crossmani is constant regardless of size, which suggests that it employed the same type of feeding mechanism throughout post-larval ontogeny. The arm branches of adults gradually become less densely spaced relative to the area of water filtered than in juveniles.

Hybocrinid and disparid crinoids from the Middle Ordovician (Galena Group, Dunleith Formation) of northern Iowa and southern Minnesota

1992 ◽  
Vol 66 (6) ◽  
pp. 973-993 ◽  
Author(s):  
James C. Brower
Keyword(s):  
Multivariate Statistics ◽  
Supply Rate ◽  
Middle Ordovician ◽  
Crown Volume ◽  
Food Particles ◽  
Attachment Device ◽  
Short Covering ◽  
Tube Feet

Four hybocrinid and disparid crinoids from the Middle Ordovician Dunleith Formation (Galena Group) of northern Iowa and southern Minnesota are described: Hybocrinus conicus Billings, Ohiocrinus levorsoni n. sp., Caleidocrinus (Huxleyocrinus) gerki n. sp., and Ectenocrinus simplex (Hall). The first three taxa are rare. Ectenocrinus simplex is an abundant and protean form ranging from the Shermanian to the Maysville and from the Appalachians to the Midcontinent. One Middle Ordovician specimen from the Dunleith is a complete small adult with stem and a lichenocrinid holdfast. The column was largely upright with the crown located about 25 cm above the seafloor. The Middle Ordovician crinoids differ somewhat from the later Cincinnatian material where only young E. simplex exhibit lichenocrinid holdfasts. Older crinoids became detached and were eleutherozoic well before the column was 25 cm long. Thus, the Cincinnatian individuals lost the attachment device earlier during ontogeny than their ancestors in the Middle Ordovician. Unlike most associated crinoids, E. simplex formed a roughly conical filtration net. The arms of E. simplex are extensively branched. Ten main arms bear unbranched ramules on alternate brachials, and the arm structure converges on the pinnulate pattern. Narrow food grooves and short covering plates are present. Analogies with living crinoids indicate that small food particles were caught by small and close-spaced tube-feet. The formation of new plates and ramules at the arm tips increases the size of the food-gathering system throughout ontogeny. The food-gathering capacity comprises the number of food-catching tube-feet times the width of the food grooves, and it measures the number and size of food particles that can be caught. Both size and capacity of the food-gathering system are positively allometric compared to crown volume and the amount of tissue that must be nourished. This is mainly caused by the addition of new ramules at the arm tips, which generates an exponentially increasing plate supply rate. Examination of numerous specimens from various geographic and stratigraphic horizons with multivariate statistics shows that the species was homogeneous throughout its range aside from the differences in living habits mentioned above.

Carabocrinid crinoids from the Ordovician of northern Iowa and southern Minnesota

1996 ◽  
Vol 70 (4) ◽  
pp. 614-631 ◽  
Author(s):  
James C. Brower
Keyword(s):  
Twin Cities ◽  
Upper Ordovician ◽  
Positive Allometry ◽  
Middle Ordovician ◽  
Length Increase

Four species of carabocrinids from the Ordovician of northern Iowa and southern Minnesota are described, namelyCarabocrinus radiatusE. Billings,C. vancortlandtiE. Billings,C. magnificusSardeson from the Middle Ordovician Dunleith Formation andC. slocomiFoerste from the Upper Ordovician Maquoketa Formation.Carabocrinus radiatusandC. vancortlandtiare also known from the Middle Ordovician of Ontario and Quebec. In addition,C. magnificusandC. vancortlandtiare recorded from the Decorah of the Twin Cities area and the Curdsville Limestone of Kentucky, respectively. Biogeographically, the Middle Ordovician carabocrinids from Iowa and Minnesota are most similar to those from rocks of similar age in the northern Appalachians.Development of the cup and its component plates inC. slocomiis almost entirely isometric so that the its shape is largely constant regardless of size. This species exhibits ridge canals on the shoulders of the radial plates in the cup. The ridge canals probably served for respiration. As expected, the number of ridge canals and their length increase with positive allometry compared to the size and volume of the cup. Growth of the ridge canals restricts the width of the radial facets.

Dendrocrinid crinoids from the Ordovician of northern Iowa and southern Minnesota

1995 ◽  
Vol 69 (5) ◽  
pp. 939-960 ◽  
Author(s):  
James C. Brower
Keyword(s):  
Cladistic Analysis ◽  
Evolutionary Trends ◽  
Upper Ordovician ◽  
Middle Ordovician ◽  
Taxonomic Level ◽  
Stratigraphic Position ◽  
Anal Sac ◽  
Primitive Forms

Plicodendrocrinus n. gen. is erected for dendrocrinids with solid pentalobate columns, strong stellate ridges on the aboral cup plates, and highly plicate anal sac plates. Five species are assigned: Middle Ordovician; P. proboscidiatus (E. Billings, not W. R. Billings) n. comb., from the Trenton of Canada and the Dunleith of Iowa and Minnesota. Upper Ordovician; P. casei (Meek) n. comb., from the Richmond and Gamachian of the midcontinent; P. rugocyathus (Ramsbottom) n. comb., from the Ashgill of England; P. collapsus (Donovan) n. comb.; and P. granditubus (Ramsbottom) n. comb., from the Ashgill of Scotland.The Middle Ordovician dendrocrinids from the Dunleith Formation (Trentonian) of northern Iowa and southern Minnesota are P. proboscidiatus (E. Billings), Dendrocrinus acutidactylus E. Billings, and Quienquecaudex springeri (Kolata). All species are also known from the Middle Ordovician of Ontario and Quebec. In addition, O. springeri (Kolata) is recorded from the Platteville Group of Illinois. Biogeographically, the Dunleith dendrocrinids are most similar to those of the northern Appalachians.Plicodendrocrinus casei (Meek) ranges widely in the midcontinent and has been obtained from the Maysvillian and Richmondian Maquoketa Formation of Iowa and Minnesota, several Richmondian units in the Cincinnati area, and the Gamachian Girardeau Limestone of Illinois and Missouri.A quantitative cladistic analysis of Ordovician cladid and flexible crinoids produces five groups: primitive forms including Aethocrinus, Compagicrinus, Ottawacrinus, and Grenprisia; cyathocrinids with Carabocrinus, Palaeocrinus, Illemocrinus, and Porocrinus; merocrinids with Archaetaxocrinus, Merocrinus, Praecupulocrinus, Polycrinus, and Aithriocrinus; dendrocrinids with Esthonocrinus, Eoparisocrinus, Dendrocrinus, Quienquecaudex, Plicodendrocrinus and perhaps Eopinnacrinus; and Cupulocrinus and the flexibles, Protaxocrinus, Clidochirus, and Proanisocrinus. These groups are not consistent with the present taxonomy and several suggestions for restructuring are presented, notably grouping flexibles with cladids and adjusting the taxonomic level of cyathocrinids. The cladograms for early cladids and flexibles are poorly correlated with stratigraphic position because of numerous unfilled range zones for the taxa or their ancestors. Thus, the cladograms generate predictions that can be tested by later finds in the Lower and the lower part of the Middle Ordovician. The overall evolutionary trends are highly mosaic with numerous parallelisms and reversals.

Camerate and Cladid crinoids from the Upper Ordovician (Katian, Shermanian) Walcott-Rust Quarry of New York

2010 ◽  
Vol 84 (4) ◽  
pp. 626-645 ◽  
Author(s):  
James C. Brower
Keyword(s):  
New York ◽  
Upper Ordovician ◽  
Attachment Structures ◽  
Soft Objects ◽  
Food Particles ◽  
Anal Sac ◽  
Long Stem ◽  
Distal Stem ◽  
Attachment Devices ◽  
Stem Segments

The camerates, Pycnocrinus argutus (Walcott, 1883) and Rhaphanocrinus subnodosus (Walcott, 1883), are characterized by narrow food grooves. An open distal stem coil was present in P. argutus, and R. subnodosus may have possessed the same type of holdfast. Such holdfasts either lay loose on the seafloor or were wrapped around unknown soft objects. The rhaphanocrinids were located at elevations of at least 300 mm above the substrate. Conversely, the much smaller pycnocrinids lived close to the seafloor at levels of about 10 to 24 mm. The three cladids are Merocrinus curtus (Ulrich, 1879), M. retractilis (Walcott, 1883), and Dendrocrinus gregarius Billings, 1857a. Merocrinus typus Walcott, 1883 and M. corroboratus Walcott, 1883 are conspecific with M. curtus. The spiral anal sac of M. retractilis is unique. Embryocrinus problematicus Hudson, 1918 probably represents a juvenile of Dendrocrinus gregarius, which also occurs in Ottawa, Ontario. Complete columns and attachment structures have not been found for D. gregarius and Merocrinus retractilis. Merocrinus curtus ranges from New York into the Cincinnati, Ohio area of the midcontinent. Although attachment devices and long stem segments are not preserved in the New York specimens, individuals of Merocrinus curtus from Cincinnati either have a conical holdfast cemented to a bryozoan or a tight distal stem coil that was wrapped around the stem of another crinoid; adult merocrinids from the Cincinnati region were positioned high above the seafloor, and incomplete stem segments up to about 800 mm long are known. The Walcott-Rust Quarry cladids all possessed wider food grooves than the camerates, so they were able to catch larger food particles.

Homocrinid crinoids from the Upper Ordovician of northern Iowa and southern Minnesota

1997 ◽  
Vol 71 (3) ◽  
pp. 442-458 ◽  
Author(s):  
James C. Brower
Keyword(s):  
New Species ◽  
North America ◽  
Larval Development ◽  
Proximal Part ◽  
Upper Ordovician ◽  
Positive Allometry ◽  
Middle Ordovician

Three homocrinid crinoids from the Upper Ordovician Maquoketa Formation of northern Iowa and southern Minnesota are described: Ectenocrinus simplex (Hall), Drymocrinus strimplei new species, and Sygcaulocrinus typus Ulrich. Ectenocrinus simplex is relatively abundant, geographically widespread in the Appalachians and midcontinent of North America, and long-ranging in time (Middle Ordovician Shermanian to Upper Ordovician Maysvillian). The aboral cup of ectenocrinids underwent transpositional allometry during its evolution so that juvenile cups from the Upper Ordovician Maquoketa Formation resemble the adult cups of ancestral individuals from the Middle Ordovician. Sygcaulocrinus typus exhibits a unique expanded proximal stem consisting of three-to-five large columnals throughout its post-larval development. These columnals are rigidly joined to the aboral cup. Consequently, the proximal generative zone for new columnals is displaced below the proximal part of the stem. In addition, the columnals in the proximal stem of S. typus mainly grow with stong positive allometry with respect to the aboral cup. Essentially, the growth vectors of the proximal columnals converge on those of the aboral cup plates.

Some disparid crinoids from the Upper Ordovician (Shermanian) Walcott-Rust quarry of New York

2008 ◽  
Vol 82 (1) ◽  
pp. 57-77 ◽  
Author(s):  
James C. Brower
Keyword(s):  
New York ◽  
Deep Water ◽  
Upper Ordovician ◽  
Food Items ◽  
Wide Range ◽  
Food Particles ◽  
Anal Sac ◽  
Long Stem ◽  
Distal Stem

locrinus trentonensis Walcott, 1883 is characterized by the widest food grooves and the largest covering plates of any of the Walcott-Rust Quarry crinoids, which indicates that the animal captured relatively large food particles with large and widely separated tubefeet. Although iocrinids are generally considered as primitive disparids, their anal sac is unique. the holdfasts of I. trentonensis consist of distal stem coils that are tightly wrapped around the columns of other crinoids. the relatively long column of Ectenocrinus simplex (Hall, 1847) was attached to a wide range of shelly substrates by a small irregular and somewhat lobate holdfast. Ectenocrinids ate much smaller food items that were collected by smaller and more tightly packed tubefeet. the ontogeny of E. simplex illustrates the differences between the food gathering systems of conspecific crinoids from shallow and deep water habitats. the calceocrinid Calceocrinus barrandii Walcott, 1883 lived with its long stem forming a runner along the seafloor. the crown was movably hinged to the basal circlet and the stem. Moderately wide food grooves were probably present.

scholarly journals Ontogeny and functional morphology of Eoparisocrinus crossmani, a cladid crinoid from the Middle Ordovician

1992 ◽  
Vol 6 ◽  
pp. 39-39
Author(s):  
James C. Brower
Keyword(s):  
Functional Morphology ◽  
Growth Rates ◽  
Feeding Habits ◽  
Groove Width ◽  
Stem Length ◽  
Food Particle ◽  
Crown Volume ◽  
Food Particles ◽  
Food Groove ◽  
Tube Feet

A post-larval development sequence of complete specimens of Eoparisocrinus crossmani provides a unique opportunity to examine growth and functional morphology. Food particles are caught by the tube-feet in the arms which must provide enough material to nourish a volume of tissue. Tissue volume is assumed to be proportional to crown volume. Ignoring the stem is justified inasmuch as most soft parts are housed in the crown. Crinoid arms grow by terminal addition of new plates at their distal tips in conjunction with calcite deposition on old plates. New branches appear where axillary plates are initiated. Consequently, the growth rates for number of brachials and length of food-gathering system compared to crown volume are much faster than if the data were isometric. The number of food particles collected is related to the number of food-catching tube-feet which can be estimated if the length of the arms and height of the covering plates are known. The size of the largest food item is constrained by the food groove width. Thus, food-gathering capacity is defined as the number of food-catching tube-feet multiplied by food groove width. Food-gathering capacity is the product of two linear dimensions so the expected exponent for food-gathering capacity and crown volume comprises 0.67. The computed exponent is significantly larger than the isometric value so the food-gathering capacity increases much more rapidly than if E. crossmani retained the same shape at all ages, and the ratio of food-gathering capacity:crown volume only declines slightly over the known growth range. Student's t tests indicate that all Ordovician inadunate crinoids examined follow nearly identical ontogenetic trajectories. Conversely, Ordovician camerates are characterized by larger food gathering capacities at equivalent crown volumes. This suggests that the feeding habits of Ordovician inadunates and camerates were quite different.The ecological niche of a stalked crinoid is at least partially categorized by three parameters. Stem length limits the highest elevation above the seafloor. The column of E. crossmani becomes longer during ontogeny due to the formation of new columnals and height growth of old ones. Consequently, individuals gradually “move up” through various levels until the adult elevation of about 50 mm is reached. The growth rates of stem length relative to crown size are slow in the youngest and mature animals but quite rapid in juveniles. The food groove width defines the size of the largest food particle that can be trapped and transported down the arms to the mouth. The exponents for the average food groove width versus cup height or crown volume are slightly less than the corresponding isometric values. The food groove width is augmented less rapidly than if the shape were constant, because distal plates and branches are more narrow and have more slender food grooves than proximal plates. Growth curves for food groove width versus stem length and elevation were generated for E. crossmani and its common associates. Together, elevation and food particle size define the main dimensions of the niche. The various taxa are more or less separated by different food groove widths at most comparable elevations with two exceptions. One deals with adults of Eoparisocrinus crossmani and juveniles of Cupulocrinus crossmani which sometimes occur together. This overlap would have been of short duration if the juveniles were growing rapidly. The youngest crinoids of all species probably intergraded. This pattern minimizes ecological overlap and probably competition between the different species. Tube-foot spacing is correlated with feeding habits and environment. The tube-foot spacing of E. crossmani is constant regardless of size which suggests that it employed the same type of feeding mechanism throughout post-larval ontogeny.

Camerate crinoids from the Middle Ordovician (Galena Group, Dunleith Formation) of northern Iowa and southern Minnesota

1994 ◽  
Vol 68 (3) ◽  
pp. 570-599 ◽  
Author(s):  
James C. Brower
Keyword(s):  
New York ◽  
Root Morphology ◽  
Stem Length ◽  
Middle Ordovician ◽  
Developmental Trends ◽  
Crown Volume ◽  
Substrate Level ◽  
Food Particles ◽  
Tube Feet

Five species of camerate crinoids from the Middle Ordovician Dunleith Formation (Galena Group) of northern Iowa and southern Minnesota are described:Cleiocrinus regiusBillings,Cotylacrinna sandran. gen. and n. sp.,Euptychocrinus skopaiosn. gen. and n. sp.,Abludoglyptocrinus charltoni(Kolata), andEopatelliocrinus ornatus(Billings) n. comb.Archaeocrinus desideratusBillings is assigned toCotylacrinna, andGlyptocrinus fimbriatusShumard andPtychocrinus longibrachialisBrower are placed inEuptychocrinus.The geographical affinities of the Iowa and Minnesota crinoids lie with adjacent localities in the northern midcontinent and the Appalachian province of Canada and New York. Preservation of various specimens implies thatEuptychocrinus skopaios, Abludoglyptocrinus charltoni, andEopatelliocrinus ornatusutilized parabolic arm fans.Cotylacrinna sandrais a specialized rhodocrinitid which is perhaps the largest completely known Ordovician crinoid with a stem length of over 91 cm and a total volume of about 45,740 mm3. The root morphology indicates an upright column and this animal towered above the associated echinoderms, which ranged from the substrate level to a maximum of 25 cm above the seafloor.Euptychocrinus skopaiosis marked by dwarfed morphology compared to the closely alliedE. fimbriatus, and it exhibits accelerated development of fixed brachs, number of brachials in and length of the arms, and closely spaced pinnules. The dwarfism is interpreted as a specialization for small size and adults ofE. skopaioswere only located about five or six cm above the substrate. New brachials and pinnules form at the distal arm tips ofE. skopaiosthroughout ontogeny. Consequently, the length of and the number of plates in the food-gathering system are positively allometric relative to the crown volume. Food gathering capacity equals the number of food-catching tube feet times width of the food grooves and it is also augmented more rapidly than expected for an isometric crinoid. Although distantly related to euptychocrinids, most other Dunleith camerates, namelyAbludoglyptocrinus charltoni, Eopatelliocrinus ornatus, andCotylacrinna sandra, follow the same developmental trends of the food-gathering system observed inEuptychocrinus skopaios.Comparison of the pinnulate camerates and three species of ramulate cladids and a disparid from the Dunleith reveals some striking contrasts. At equivalent crown volumes, the camerates are characterized by more numerous arm branches in the form of pinnules, more narrow food grooves, more closely spaced tube feet, and longer food-gathering systems with more plates and greater capacity. The Dunleith camerates were adapted for catching smaller food particles using more numerous and more closely spaced tube feet located on more extensively branched filtration nets than the associated cladids and disparid. The differences can be attributed to taxonomy and presumably phylogeny, that is camerates versus cladids and disparids, and/or morphology in the presence of pinnules versus ramules.

Oxygen isotope (δ18O) trends measured from Ordovician conodont apatite using secondary ion mass spectrometry (SIMS): Implications for paleo-thermometry studies

2021 ◽  
Author(s):  
Cole T. Edwards ◽  
Clive M. Jones ◽  
Page C. Quinton ◽  
David A. Fike
Keyword(s):  
Mass Spectrometry ◽  
Secondary Ion Mass Spectrometry ◽  
Matrix Effects ◽  
Analytical Techniques ◽  
Upper Ordovician ◽  
Bulk Analysis ◽  
Middle Ordovician ◽  
Ion Mass Spectrometry ◽  
Oxygen Isotopic ◽  
Secondary Ion

The oxygen isotopic compositions (δ18O) of minimally altered phosphate minerals and fossils, such as conodont elements, are used as a proxy for past ocean temperature. Phosphate is thermally stable under low to moderate burial conditions and is ideal for reconstructing seawater temperatures because the P-O bonds are highly resistant to isotopic exchange during diagenesis. Traditional bulk methods used to measure conodont δ18O include multiple conodont elements, which can reflect different environments and potentially yield an aggregate δ18O value derived from a mixture of different water masses. In situ spot analyses of individual elements using micro-analytical techniques, such as secondary ion mass spectrometry (SIMS), can address these issues. Here we present 108 new δ18O values using SIMS from conodont apatite collected from four Lower to Upper Ordovician stratigraphic successions from North America (Nevada, Oklahoma, and the Cincinnati Arch region of Kentucky and Indiana, USA). The available elements measured had a range of thermal alteration regimes that are categorized based on their conodont alteration index (CAI) as either low (CAI = 1−2) or high (CAI = 3−4). Though individual spot analyses of the same element yield δ18O values that vary by several per mil (‰), most form a normal distribution around a mean value. Isotopic variability of individual spots can be minimized by avoiding surficial heterogeneities like cracks, pits, or near the edge of the element and the precision can be improved with multiple (≥4) spot analyses of the same element. Mean δ18O values from multiple conodonts from the same bed range between 0.0 and 4.3‰ (median 1.0‰), regardless of low or high CAI values. Oxygen isotopic values measured using SIMS in this study reproduce values similar to published trends, namely, δ18O values increase during the Early−Middle Ordovician and plateau by the mid Darriwilian (late Middle Ordovician). Twenty-two of the measured conodonts were from ten sampled beds that had been previously measured using bulk analysis. SIMS-based δ18O values from these samples are more positive by an average of 1.7‰ compared to bulk values, consistent with observations by others who attribute the shift to carbonate- and hydroxyl-related SIMS matrix effects. This offset has implications for paleo-temperature model estimates, which indicate that a 4 °C temperature change corresponds to a 1‰ shift in δ18O (‰). Although this uncertainty precludes precise paleo-temperature reconstructions by SIMS, it is valuable for identifying spatial and stratigraphic trends in temperature that might not have been previously possible with bulk approaches.

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