Quantitative analysis of conodont tooth wear and damage as a test of ecological and functional hypotheses

Mark A. Purnell and David Jones

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Paleobiology, 38(4), 2012, pp. 605–626

Quantitative analysis of conodont tooth wear and damage as a test of ecological and functional hypotheses

Mark A. Purnell and David Jones

Abstract.—Analysis of dental wear and damage is becoming an increasingly important tool in unraveling the trophic ecology of a wide range of vertebrates, and when applied to fossils it can provide evidence of both diet and feeding kinematics that is independent of morphological analysis. Conodonts have the best fossil record among vertebrates and their skeletal elements are known to exhibit surface wear and damage generated in vivo as a consequence of their function as teeth. We report the results of the first systematic survey and analysis of the frequency and extent of this wear and damage in conodonts (based on P1 elements from a range of Carboniferous genera). This has revealed that wear and damage are remarkably common, present in all conodont elements sampled. Multivariate analysis reveals that patterns of wear and damage differ significantly among different conodont taxa, and exploratory ANOVA and linear discriminant analyses show that wear and damage differ according to the position of taxa in an onshore-offshore gradient, and whether they are likely to have had a benthic or pelagic mode of life. The incidence of denticle tip spalling in particular is higher in more-offshore environments and in taxa likely to have had a pelagic mode of life. Aspects of the data also reflect the occlusal kinematics of the elements, providing a means of testing hypotheses of element function. Our results have wide-ranging implications for unlocking the fossil record of conodonts, by, for example, furnishing direct evidence of the diet-mediated processes that may have driven observed patterns of evolutionary change, and reducing the confounding effects of depth segregation when using conodonts in isotope-based paleotemperature studies.

Mark A. Purnell* and David Jones.** University of Leicester, Department of Geology, Leicester LE1 7RH, United Kingdom. E-mail: [email protected], [email protected]. *Corresponding author. **Present address: Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol BS8 1RJ, United Kingdom

Accepted: 11 April 2012

Introduction in large part upon understanding their ecolo- Conodonts are an important clade of early gy. Although conodonts were nektonic, pelag- vertebrates. The toothlike skeletal elements of ic taxa, particularly those occupying the their oropharyngeal feeding apparatus have a oceanic realm, are preferable for biostratigra- superb fossil record (Foote and Sepkoski 1999; phy because they are more likely to have wide Purnell and Donoghue 2005), and conodonts distributions and are less likely to be con- are consequently the paramount group for trolled by local environmental heterogeneity. biostratigraphic correlation and relative dat- Ecological factors are frequent drivers of ing through most of the Paleozoic and Triassic. evolutionary change. Interpretation of shifts The quality of their fossil record also makes in conodont oxygen isotope values in terms of them an invaluable resource for studying sea-surface temperature and/or sea-level evolutionary pattern and process. Additional- changes must exclude alternative explanations ly, conodonts are becoming increasingly im- that differences reflect variation in the depth, portant tools for paleotemperature studies and hence temperature, at which conodonts based on stable isotope analysis (e.g., Wenzel lived. et al. 2000; Joachimski and Buggisch 2002; Nonetheless, many fundamental aspects of Joachimski et al. 2006; Bassett et al. 2007; conodont ecology are poorly understood. Buggisch et al. 2008; Zigaite et al. 2010; Chen Facies distributions and patterns of taxon co- et al. 2011). occurrence have been documented and re- The biostratigraphic, evolutionary, and pa- viewed (e.g., Driese et al. 1984; Merrill and leoclimatological utility of conodonts depends von Bitter 1984; Pohler and Barnes 1990;

Ó 2012 The Paleontological Society. All rights reserved. 0094-8373/12/3804-0007/$1.00 606 MARK A. PURNELL AND DAVID JONES

Zhang and Barnes 2000), but determining the 2. Do patterns of surface wear and damage range of depths at which conodonts lived, and vary significantly among taxa? whether particular species occupied benthic or 3. Do patterns of surface wear and damage pelagic niches, is generally achieved using differ between conodonts that inhabited simplistic ecological models of spatial distri- different environments? bution and lateral segregation that are known In order to address these questions and test to be unreliable (Klapper and Barrick 1978). the associated null hypotheses, we have Similarly, understanding of conodont ele- developed the first rigorous protocols for ment functional morphology is rudimentary recording, quantifying, and analyzing the and limited to a few taxa (Purnell and von frequency and extent of wear/damage in Bitter 1992; Donoghue and Purnell 1999b), and conodont elements. knowledge of conodont dietary niches and how they differed between taxa is essentially Previous Observations of Surface Wear and non-existent. Consequently, evaluating the Damage in Conodonts selective pressures on conodont element mor- Despite some early observations of possible phology, and testing hypotheses that evolu- surface wear in some conodont elements, a tionary changes were adaptive, is currently strong consensus developed among cono- impossible. donts workers that elements generally do not Analysis of wear and damage in conodont show surface wear, and that it is certainly not elements may provide more robust constraints present at the levels that would be expected if on conodont ecology and element function. In elements had functioned as teeth (Huddle mammals, analysis of how tooth shape is 1934; Hass 1941; Rhodes 1954; Pierce and changed by wear from feeding (mesowear; Langenheim 1970; Nicoll 1987). Two of these Fortelius and Solounias 2000; Kaiser and studies were detailed SEM-based investiga- Solounias 2003), analysis of tooth breakage tions that failed to detect even microscopic (Van Valkenburgh 2009), and analysis of the evidence of wear (Pierce and Langenheim microscopic textures developed on tooth wear 1970; Nicoll 1987). Weddige’s (1990) work facets (microwear; e.g., Walker et al. 1978; documenting ‘‘pathologies’’ of conodont ele- Scott et al. 2005), furnishes direct information ments did include surface wear (his ‘‘abrasio’’ on diet and trophic niche. Previous studies of pathology) but the possible functional signif- dental wear and damage have focused pre- icance of this was not explored because dominantly on primates and ungulate mam- Weddige suspected it was postmortem in mals, but tooth wear studies are starting to be origin. Some of Weddige’s other classes of applied more widely, for example, to test ‘‘pathology’’ we would interpret, as he did, as hypotheses of feeding mechanics in non-avian damage resulting from in vivo toothlike dinosaurs (Williams et al. 2009) and to occlusion between elements. differentiate between fishes (living and fossil) More recent SEM-based work was able to occupying benthic and limnetic trophic niches go further, partly because of clearer under- (Purnell et al. 2006, 2007) and with different standing of P1 element occlusion (Fig. 1) diets (Purnell et al. 2012). Such studies suggest (Purnell 1995; Donoghue and Purnell 1999a). that analysis of dental damage and wear has This allowed interactive surfaces on which the potential to provide similar constraints on functional wear might develop to be differen- conodont ecology and function. Our aim here tiated from non-occlusal surfaces on which is to present a novel approach to interrogating damage was likely to be postmortem in origin the conodont fossil record, and to illustrate its (a key factor in studies of tooth wear in fossils potential, by testing null hypotheses linked to [Teaford 1988]). Thus Purnell (1995) docu- the following questions: mented wear patterns that provide direct evidence that elements functioned as teeth. 1. Do conodont elements commonly exhibit This was confirmed by subsequent analyses of surface wear and damage? surface wear and damage in occlusal pairs of TOOTH WEAR, FUNCTION, AND ECOLOGY OF CONODONTS 607

FIGURE 1. Diagram illustrating arrangement of elements within the conodont oropharyngeal skeleton, with biological orientation terms. Modified from Purnell et al. (2000) and Purnell (1995).

P1 elements from articulated skeletons that, of surface wear (Jeppsson 1979; Donoghue because they were articulated, could not have and Purnell 1999a) such that only those been subject to postmortem abrasion (Donog- elements from conodonts that died toward hue and Purnell 1999b). the end of a functional cycle will preserve Donoghue and Purnell (1999a) provided evidence of significant wear. further examples of functional damage in Despite the evidence that conodont ele- elements, preserved on the external surface ments do in fact preserve wear on occlusal (the functional surface at time of death) and as surfaces (i.e., in exactly the places where it internal discontinuities (former functional would be expected if elements functioned as surfaces subsumed by subsequent element teeth), and the lack of any subsequent pub- growth). These internal discontinuities reveal lished data or analysis that raises any signif- the relationship between element growth and icant doubts concerning this hypothesis, not function in conodonts. This relationship is all conodont workers agree that elements more complex than the situation in more functioned as teeth (e.g., Turner et al. 2010). derived gnathostome teeth, in which tooth A recent straw poll of conodont workers growth is followed by eruption, function, and subscribing to the conodont listserver ‘‘con- in some cases, shedding. Conodont elements nexus’’ suggests that the hypothesis that were not shed, but underwent repeated cycles elements display surface wear and damage of growth and function throughout the life of resulting from their use as teeth remains the conodont, with damage and wear from a controversial. Of 32 respondents, 16% agreed period of function being repaired or covered with the statement that such wear and by the deposition of multiple apatite lamellae damage are generally not present (with two during each subsequent phase of growth holding stronger views that such features (Donoghue and Purnell 1999a). It is possible, cannot develop because elements were not or even likely, that this mode of growth will teeth), 50% hold the view that wear and reduce the frequency of occurrence and extent damage resulting from element function are 608 MARK A. PURNELL AND DAVID JONES present but uncommon, and only 28% agreed analyzed (i.e., those with intact or largely that wear and damage on conodont elements intact blades and platforms, which retained is common. Thus, conodont workers clearly most of their denticles), and elements with have contrasting views on this matter, even evidence of significant abrasion and damage though the frequency of occurrence and extent on the non-functional aboral surfaces of the of surface wear and damage in conodont elements were also excluded. Such precau- elements, and their variation among taxa and tions may result in a slight bias in our results environments, have never been investigated. toward under-recording of in vivo wear and damage. All elements included had low Material and Methods thermal alteration (CAI) values, and so had Fossil Material.—This study focuses exclu- undergone little diagenesis. In order to avoid sively on P1 elements (Purnell et al. 2000) from possible ontogenetic differences in patterns of the feeding apparatus of conodonts assigned wear and damage, we also excluded the to Ozarkodinina (Donoghue et al. 2008). smaller immature elements, which have only Figure 1 illustrates the orientation of these a few denticles. Testing for differences be- elements within the feeding apparatus, their tween environments also requires samples anatomical terminology, and the nature of and taxa for which depositional setting is well bilateral occlusion of P1 elements (Purnell and constrained. Donoghue 1997; Donoghue and Purnell 1999b; On the basis of these criteria and the Purnell et al. 2000). Previous work has availability of material, we selected for anal- demonstrated that these elements exhibit wear ysis seven conodont species from 12 samples, and surface damage that reflect their role in all of Carboniferous age: Gnathodus pseudose- food processing (Purnell 1995; Donoghue and miglaber, Gondolella sublanceolata, Hindeodus Purnell 1999a,b). Ozarkodinin P1 elements minutus, Idiognathodus simulator, Mestognathus also provide the basis for much conodont beckmanni, Patrognathus capricornis, and Strep- taxonomy because they exhibit the clearest tognathodus pawhuskaensis. For brevity, hereaf- and best documented morphological differ- ter we refer to taxa by generic name only. The ences among taxa. As is the case with other species chosen all possess P1 elements with complex vertebrate teeth, these morphological expanded platforms and/or denticulated differences, in many cases, probably reflect blades (pectiniform elements), but provide a variation in the kinematics of food processing range of morphologies (Fig. 2), allowing us to and/or diet (Lucas 2004). develop protocols for scoring and analysis of Analysis of wear and damage in conodonts wear/damage with broad applicability to taxa requires material that meets certain criteria. with differently shaped elements. Sampling a Elements selected for analysis were well range of morphologies also allows us to preserved, with little or no diagenetic encrus- differentiate similarities in wear/damage aris- tation or acid etching (from laboratory recov- ing from similarities in function and occlusal ery methods). Postmortem breakage results kinematics from those that potentially reflect mainly from post-depositional compaction similarities in diet and niche (cf. mammalian (von Bitter and Purnell 2005). Postmortem mesowear analysis [see below]). abrasion resulting from transport and rework- P1 elements of Hindeodus are morphologi- ing is rare even in elements from shallow- cally simple and blade shaped. The Gondolella water deposits containing ‘‘conodont lags’’ P1 elements analyzed posses a ridged platform (e.g., Ellison 1987), and experimental evidence with a medial denticle row (carina), but lack a suggests that high-energy marine transport well-developed free blade. The P1 elements of conditions are unlikely to generate significant the remaining taxa all bear expanded dorsal postmortem breakage or wear on conodont platforms, differing in whether their ventral elements (Broadhead and Driese 1994). None- blades are developed in an axial or lateral theless, care was taken to exclude from our position. Mestognathus P1 elements have short, analysis elements exhibiting possible postmor- lateral blades with a prominent dorsal denti- tem damage: only complete elements were cle. In Mestognathus, the blade is always on the TOOTH WEAR, FUNCTION, AND ECOLOGY OF CONODONTS 609

FIGURE 2. Focus variation optical micrographs of conodont P1 elements analyzed in this study, illustrating their morphology and anatomical terminology. Terms shown for Idiognathodus are also applicable to Streptognathodus and Gnathodus. Terms shown for Mestognathus are also applicable to Patrognathus. Elements are figured in life orientation, so that ventral is toward the bottom of the figure, dorsal to the top. In Gondolella and Hindeodus, it is uncertain in isolated elements whether they are positioned sinistrally or dextrally within the skeleton, so the neutral term ‘‘lateral’’ is used. All elements are gold coated. Scale bar, 100 lm.

‘‘left’’ side of the platform (in oral view), located on the rostral margin, that on the right meaning that in life, with element pairs side of the body on the caudal margin [see opposed across the sagittal plane of the Purnell et al. 2000 for discussion of element animal, the ‘‘right’’ blade on one element orientation]). P1 elements of Idiognathodus, would have contacted the ‘‘left’’ margin Streptognathodus, and Gnathodus all have a (parapet sensu von Bitter et al. 1986) of the longer, ‘‘axial’’ blade, the morphology of other, rather than the blade (i.e., the blade on which is very similar in the three taxa, bearing the element on the left side of the body was numerous denticles of roughly equal size. 610 MARK A. PURNELL AND DAVID JONES

They differ in platform morphology: in the (Gzhelian Stage) cyclothems of the midconti- Gnathodus species analyzed the platform is nental United States. The Heebner and Queen poorly developed, comprising two short par- Hill Shales are ‘‘core’’ shales, the former part apets either side of the carina; Streptognathodus of the Oread Cyclothem and the latter part of elements have a well-developed platform with the subsequent Lecompton Cyclothem. Both axial trough, whereas in Idiognathodus this units are fissile shales, ranging in color from trough is poorly developed or absent, the black to gray, largely lacking in situ macro- platform being covered by transverse ridges fossils (Malinky and Heckel 1998). The Platts- (see Barrick et al. 2008 for recent taxonomic mouth and Topeka Limestones are regressive revision). The P1 elements of Patrognathus sequences, representing the ‘‘upper’’ lime- capricornis have an ‘‘axial’’ blade and a stones of the Oread and Topeka Cyclothems platform ornamented with ridges and nodes. respectively. The Leavenworth Limestone is a In life, the P1 element pairs of Hindeodus, transgressive facies, constituting the ‘‘middle’’ Idiognathodus, Streptognathodus, Gnathodus, limestone of the Oread Cyclothem. All three and Patrognathus were opposed across the limestones are fossiliferous (von Bitter 1972). axis of the body; evidence from articulated Gnathodus, Mestognathus,andPatrognathus skeletal material and details of element asym- (sample 11040808) are from a horizon within metry indicate that elements were opposed the Rain Gill Limestone Member of the with the ‘‘left’’ sides of the blades in occlusal Hodder Mudstone Formation, of mid-Missis- contact (Purnell 1995; Purnell and Donoghue sippian age (Arundian Stage) from Lancashire, 1997; Donoghue and Purnell 1999b). Whether United Kingdom (Riley 1990). This argilla- the same is true of Gondolella is unknown. In ceous limestone includes several parallel elements with both blade and platform, the laminated beds and horizons of coarse shelly blade functioned to maintain element occlu- debris; it is interpreted as a turbidite deposit in sion during feeding (Jeppsson 1971; Weddige a deep-water hemipelagic setting (Riley 1990). 1990; Purnell 1995; Donoghue and Purnell Data Acquisition.—Elements were mounted 1999b), while the platform functioned as the on 12.7 mm SEM stubs using double-sided food-processing surface (Nicoll 1987; Weddige adhesive tape. Data were acquired from 1990; Purnell 1995; Donoghue and Purnell digital images captured using high-resolution 1999b). focus variation optical microscopy (Alicona Table 1 provides a summary of the taxa and Infinite Focus Microscope—IFM). This tech- samples included in our study. A total of 288 nique, which automatically captures an image elements were analyzed. Most of the elements stack from which a fully in-focus image is studied are from the late Pennsylvanian generated, has the advantages of being cheap-

TABLE 1. Summary details for P1 element samples analyzed for surface wear/damage; all Carboniferous in age. Sample size for Patrognathus was supplemented by additional material collected from the same unit (BGS samples MPA20677 and MPA20679).

Sample Taxon Unit Location Lithology P-13-4 Hindeodus minutus Plattsmouth Limestone Andrew Co., MO, USA Limestone He-2-2A Hindeodus minutus Heebner Shale Chautauqua Co., KS, USA Black shale He-16-1 Hindeodus minutus Heebner Shale Madison Co., IA, USA Gray shale He-5-1 Hindeodus minutus Heebner Shale Greenwood Co., KS, USA Brown shale He-5-1 Idiognathodus simulator Heebner Shale Greenwood Co., KS, USA Brown shale He-16-1 Idiognathodus simulator Heebner Shale Madison Co., IA, USA Gray shale He-14-1 Idiognathodus simulator Heebner Shale Cass Co., NE, USA Brown shale He-13-1 Idiognathodus simulator Heebner Shale Andrew Co., MO, USA Black-brown shale TOP-1-2 Streptognathodus pawhuskaensis Topeka Limestone Chautauqua Co., KS, USA Limestone Le-16-1 Streptognathodus pawhuskaensis Leavenworth Limestone Madison Co., IA, USA Limestone QH-2-4 Streptognathodus pawhuskaensis Queen Hill Shale Chautauqua Co., KS, USA Gray-brown shale He-15-2b Gondolella sublanceolata Heebner Shale Cass Co., NE, USA Black shale 11040808 Mestognathus beckmanni Rain Gill Limestone Lancashire, UK Limestone 11040808 Gnathodus pseudosemiglaber Rain Gill Limestone Lancashire, UK Limestone 11040808 Patrognathus capricornis Rain Gill Limestone Lancashire, UK Limestone TOOTH WEAR, FUNCTION, AND ECOLOGY OF CONODONTS 611 er and faster than SEM photomicrography, and Patrognathus,denticleswerecounted taking only a few minutes per element. This from, but did not include, the large dorsal approach to imaging can be applied to denticle of the blade. In Hindeodus, where uncoated specimens, but to maximize the several large ventral denticles are often pre- quality of surface imaging and remove noise sent, denticles were counted from, but did not arising from the translucency of conodont include, the dorsalmost large ventral denticle elements with low levels of thermal alteration (see Fig. 2). Scoring only the equal-sized (CAI), specimens were sputter-coated with denticles makes data from Hindeodus and gold prior to imaging. All images were Mestognathus more comparable to those de- acquired using fixed, co-axial illumination, rived from Idiognathodus, Streptognathodus, thus avoiding the problems of image variation and Gnathodus—the blades of which contain to which SEM-based wear work is prone only evenly sized denticles—because the (Gordon 1988; Scott et al. 2006). Comparable influence on wear/damage of differing denti- analyses could, however, be carried out using cle arrangements will be minimized. It should images acquired using SEM photomicrogra- be noted, however, that this approach to phy. Data were acquired from the blade enumerating denticles may overlook wear/ section of the element and, where present, damage on prominent denticles. Such infor- the platform region. Both the occlusal and mation may be significant for interpreting non-occlusal sides of blades were imaged, details of element function and occlusal together with the oral surface of platforms. All kinematics, but this is not the focus of the images were captured at constant magnifica- current work. tion such that a 1624 3 1218 pixel image Four types of in vivo wear/damage were captured a field of view approximately 0.25 3 recorded from the blade region of the element, 0.2 mm in size. Where elements were too large and a further three types from the platform for one field of view, several images were region (Table 2, Fig. 3). Figure 4 illustrates captured and auto-montaged within the IFM how the blade, platform and denticles were software. Scoring of wear and damage was divided into regions for wear/damage scor- carried out by a single user (D.J.) on-screen ing. using the GNU Image Manipulation Program The point in the conodont element growth- (version 2.6.4) to view images at approximate- function cycle at which the animal died will ly 1000 times actual size. Once captured, influence the extent and frequency of wear/ images were not adjusted or enhanced. damage on the element surface (see above), The protocol for recording surface wear/ which will inevitably create noise in the data. damage is designed to be straightforward and For example, two elements belonging to two generally applicable to conodont elements different taxa will seem to have comparably with different morphologies. The nature of low amounts of wear/damage if both are conodont element growth means that, unlike preserved at the start of a functional stage, mammal teeth, for example, where cusps can and have not had time to develop distinctive be homologized between individuals and patterns. In order to minimize this potential across taxa, it is difficult to recognize homol- bias and maximize the chances of detecting ogous landmarks on different elements (Jones associations or differences between samples, and Purnell 2007). Clearly, denticle numbering scores for wear/damage were summarized as must be standardized as far as possible to percentages for each sample, producing wear/ ensure repeatability and comparability be- damage ‘‘attributes’’ for the blade and plat- tween elements and across taxa, so we form (see Appendix for summary data). adopted a pragmatic approach and recorded This summary data set therefore captures the position of the denticles on which wear/ the frequency of occurrence of the different damage occurred by numbering the denticles wear/damage types among elements, i.e., the from dorsal to ventral (defined relative to the percentage of elements within each sample in vivo orientation of the elements within the that displayed a particular type of wear/ skeleton [Purnell et al. 2000]). In Mestognathus damage. The denominator for calculating 612 MARK A. PURNELL AND DAVID JONES

TABLE 2. Types of element surface wear/damage on conodont elements recorded, with details of scoring protocol. Figure 4 illustrates division of blade, platform, and denticle.

Element Wear/damage component type Description Blade Breakage Denticles broken off cleanly Recorded as position of break on denticle (at tip, middle, or base of denticle) in dorsal, central, or ventral region of blade Spalling Upper layers of denticle enamel flaked/splayed off Recorded as position of spall on denticle (on occlusal, non-occlusal, ventral, or dorsal surface of denticle) in dorsal, central, or ventral region of blade Polishing Primary surface micro-ornament on denticles removed Recorded as typical extent of polishing for denticles in dorsal, central, or ventral region of blade (confined to tip or extending to middle or base of denticle) Rounding Denticle worn so that tip forms a markedly obtuse angle Recorded as presence/absence Platform Polishing on Primary surface micro-ornament removed on ridges, nodes, etc. topographic highs Recorded separately for dorsal and ventral regions of platform as presence/absence Polishing on Primary surface micro-ornament removed between ridges, nodes, etc. topographic lows Recorded separately for dorsal and ventral regions of platform as presence/absence Blunting Blunting of ridges, nodes, etc. as a consequence of breakage/wear Recorded separately for dorsal and ventral regions of platform as presence/absence these percentages was thus the total number A separate analysis, restricted to elements of elements in each sample. The data set with a platform, combined this data set with included six breakage attributes: the percent- six attributes capturing wear and damage on age of elements with broken denticles in the the platform: the percentage of elements with dorsal, central, and ventral regions of the polishing on topographic highs (ridges or blade (regardless of break position on the nodes) and lows, and percentage of elements denticle); and the percentage of denticles where topographic highs had been damaged broken at the base, middle, or tip (regardless (blunted). These were scored separately in of break position along the blade). Seven dorsal and ventral regions of the platform. spalling attributes were also calculated: the Clearly, there is a degree of non-indepen- percentage of elements with spalled denticles dence of data for breakage, spalling, and in the dorsal, central, and ventral regions of polishing: broken or spalled denticles within the blade (regardless of spall position on the a blade region may be impossible to score for polishing (although the extent of polishing denticle), and the percentage of elements with will remain clear if greater than the extent of denticles showing spalling on their occlusal, breakage). The typical extent of denticle non-occlusal, dorsal, and ventral surfaces polishing in that region can still be scored, (regardless of spall position along the blade). however, by summarizing data by blade For the rounding wear type, three attributes region. Moreover, elements generally display were included: the percentage of elements consistent patterns of polishing along the with rounded denticles in the dorsal, central, denticle row (see ‘‘Results’’), thus increasing and ventral regions of the blade. Nine confidence in the assessment of polishing on polishing attributes were calculated: the per- broken denticles. centage of elements in which polishing in each Scoring wear/damage on the platform was of the three blade regions was confined to the not possible in a few elements because exam- denticle tips or extended to the middle or base ination of captured images revealed the surface of the denticles. Previous work (Purnell 1995) to be partially obscured by postmortem encrus- and visual inspection indicate that polishing is tation or diagenetic recrystallization. As noted not consistently developed on non-occlusal above, post-depositional compressive forces surfaces; nevertheless non-occlusal wear was resulting from sediment compaction can cause evaluated qualitatively. Thus, the data set denticle breakage, with more breakage expect- comprised 25 attributes for the blade. ed in shales than limestones because of earlier TOOTH WEAR, FUNCTION, AND ECOLOGY OF CONODONTS 613

FIGURE 3. Focus variation optical micrographs (polarized light) of conodont P1 elements, illustrating the damage and wear types scored in this study. A, Denticle breakage, showing range of breakage points at tip, middle, and base of denticle (Hindeodus). B, Denticle rounding (Hindeodus). C, Denticle spalling (Gondolella). D, Denticle flattening at the dorsal end of the blade (Streptognathodus). E, Polishing away of primary striated micro-ornament on denticles, showing partial range of extent, from tip to middle (Idiognathodus). F, Blunting of topographic highs and polishing away of primary polygonal micro-ornament (on topographic highs and lows) on platform (Mestognathus). Insets in C–F show lower magnification image with higher magnification area boxed. Scale bars are 20 lm and refer to high-magnification images. cementation in the latter and greater compac- tween shales and limestones (Chi-squared test: tion in the former (von Bitter and Purnell 2005). v2 , 1.6, p . 0.05). Excluding broken elements and those that have Spalling has previously been recorded in lost all or most denticles should reduce this reptile and non-avian dinosaur teeth, and is potential bias, but to ensure that denticle interpreted as flaking of the upper enamel surface resulting from stresses produced dur- breakage scores still reflect in vivo processes, ing contact between tooth and food (Schubert we statistically compared the number of ele- and Ungar 2005). More recently it has been ments with broken denticles in limestone and observed in fossil whale teeth (Thewissen et shale samples of Hindeodus and Streptognatho- al. 2011). The cause of spalling in conodonts is dus. For both taxa, neither the number of difficult to determine but our knowledge of elements with broken denticles nor the total occlusal kinematics suggests that it is likely to number of breaks differed significantly be- result from direct contact between elements. 614 MARK A. PURNELL AND DAVID JONES

PCA to analyze percentages. However, our data differ from the percentage data usually analyzed in the literature (such as geochemical compositions), in that the rows in our summary data set s (i.e., all the damage and wear percentages for a given sample) do not always sum to 100%. Therefore, we analyze untrans- formed summary percentages using PCA based on a covariance matrix, because units and scale are the same for all variables. As a precaution, we checked our PCA results against a principal coordinate analysis (PCoor- FIGURE 4. Locational terms for wear and damage as dA), an ordination technique able to accom- recorded in this work. Left: division of blade into ventral, modate a wider variety of data types, including central and dorsal regions. Right: division of platform into dorsal and ventral areas. Inset: coding for position of untransformed percentages. This PCoordA was breaks on denticles (whether at base, middle, or tip) and based on a cosine-theta similarity index, known extent of polishing on denticles (whether confined to the to be effective at analyzing compositional/ tip, or extending to the middle or base). closed data (MacLeod 2006). The ordinations Although microscopic in scale, the wear produced by the PCA and PCoordA of the assessed in our study resembles the features same data were virtually identical, demonstrat- classified as mesowear on vertebrate teeth. As ing that the distribution of samples in principal originally defined (Fortelius and Solounias component space is not simply an artifact of 2000; Kaiser and Solounias 2003), mesowear the input data characteristics. One advantage analysis is based on scoring wear facet of principal components (PCs) is that they can be related back to the original input variables, development and differences in cusp relief through the loading values. These values caused by blunting and rounding of teeth. The indicate which of the original variables con- aims of our approach are comparable to those tribute the greatest share of variance to each of mesowear analysis: to characterize changes principal component. The greater the loading in morphology over the functional surfaces of value for a variable (regardless of sign), the teeth, rather than just specific facets. Meso- greater is its contribution to that PC axis. wear analysis has been applied extensively to Positive and negative loadings indicate wheth- mammals, and has been effective in constrain- er a variable’s magnitude increases or decreas- ing diet in many mammalian groups (see es in value along a PC axis. The loading values Croft and Weinstein 2008 and references for the PCs on which specimens are ordinated therein), suggesting that analysis of similar are provided in the Appendix. Missing data wear and damage features may likewise help (less than 2% of summary data set) was elucidate conodont diet. handled using iterative imputation. For be- Data Analysis.—Our primary goal is to tween-taxon comparisons, we selected a single explore the pattern of surface damage and sample per taxon; in all cases, to minimize wear within and between conodont taxa. environmental effects, the shallowest water Principal components analysis (PCA) is a sample was used. In order to explore the standard ordination technique for examining relationship between wear/damage and a data is this fashion. Compositional data, such priori hypotheses of ecology and life habits of as percentages, have characteristics that are taxa (deep to shallow-water environments; subtly different from those of the dimensional benthic vs. pelagic habits) we conducted data typically analyzed using PCA (i.e., data stepwise linear discriminant analysis (LDA) are usually ‘‘closed’’ at 100%). Hence, it is and analysis of variance (ANOVA). These were generally recommended that a transformation, carried out using JMP 8. All other data analysis such as Aitchison’s (1982, 1986) standard log- was conducted in PAST, version 1.89 (Hammer ratio transformation, be applied when using et al. 2001). TOOTH WEAR, FUNCTION, AND ECOLOGY OF CONODONTS 615

Paleoenvironmental Constraints on Conodont The lithological and environmental context Taxa of our samples is broadly consistent with these Conodont ecology is generally understood hypotheses of conodont ecology (see above through analysis of element distributions with and Table 2). Our samples of Hindeodus derive respect to depositional facies or paleogeogra- from a range of different lithologies, all from phy. The prevalence of Hindeodus in lime- the Pennsylvanian midcontinental United stones, for example, suggests that this taxon States (see above). The fossiliferous limestone (sample P-13-4) was deposited in a shallow- occupied predominantly nearshore, shallow- water shelf environment of 30–100 m depth water habitats (Merrill and von Bitter 1976, (Malinky and Heckel 1998). Gray shales (He- 1984; Driese et al. 1984; Krumhardt et al. 16-1) record a slightly deeper facies and, based 1996). Recent analysis of oxygen isotopes in on the spatiotemporally sporadic occurrence Permian Hindeodus supports this hypothesis of benthic fauna, varied from oxic to dysoxic (Chen et al. 2011), but Hindeodus is also found (Malinky and Heckel 1998). The range of in lithologies deposited in more offshore brown to black shales (He-5-1, He-2-2A) settings (Merrill and von Bitter 1984; Krum- represents deep-water environments of 100– hardt et al. 1996). Patrognathus has previously 150 m depth, which were predominantly been interpreted as living in nearshore peri- anoxic or dysoxic, and from which all but tidal environments (Sandberg and Ziegler the most tolerant benthic organisms were 1979; Austin and Davies 1984) but most of excluded (Malinky and Heckel 1998). Cono- these interpretations concern the slightly older donts recovered from these black shale lithol- species, P. variabilis. Similar environmental ogies are unlikely to have inhabited the preferences have been inferred for Mestogna- seafloor and are thus probably not benthic thus (von Bitter et al. 1986). Streptognathodus (see Idiognathodus and Streptognathodus be- and Idiognathodus occur in abundance in shale low). It is possible that the Hindeodus elements lithologies but are also commonly found in in the brown and black shales were transport- limestones; they probably occupied more ed from oxygenated shallower settings, but offshore environments but also ranged into the euxinic nature of the shales, with their nearshore settings (Heckel and Baesemann well-developed laminated fabric (Algeo and 1975; Heckel 1977; Merrill and von Bitter 1984; Heckel 2008), argues against this possibility. Brown et al. 1991; Krumhardt et al. 1996). Transport of elements from nearshore to Perhaps the most precise interpretation of offshore through deposition of fecal matter Gnathodus species ecology during Early to by conodont predators offers another possible Middle Mississippian time is that they ‘‘were explanation for the presence of elements from these taxa in black shales, but it seems benthic slope dwellers, whose habitats bot- unlikely that this mechanism could have tomed out seaward against the dysaerobic introduced elements in the abundance at zone’’ (Sandberg and Gutschick 1984: p.150). which they occur in these samples. Other authors have made similar interpreta- Three other taxa were sampled from the tions: Krumhardt et al. (1996) concluded that Pennsylvanian midcontinental United States. Gnathodus occupied below-wave-base open- Idiognathodus and Streptognathodus elements marine settings. Gondolella is found predomi- derive from a variety of lithologies (see above) nantly in deeper-water lithologies and is including fossiliferous limestones (TOP-1-2, considered an offshore taxon (Heckel and Le-16-1) and gray shales (He-16-1) deposited Baesemann 1975; Heckel 1977; Merrill and in shelf settings, and brown shales and black von Bitter 1984; Driese et al. 1984). Recent shales lacking macrofossils (He-5-1, He-14-1, analysis of oxygen isotopes in the Permian He-13-1, and QH-2-4). The variety of litholo- gondolellid genera Jinogondolella and Clarkina gies suggests that these taxa ranged through is consistent with this (Chen et al. 2011), but environments with different bottom conditions the degree to which these results are applica- and, probably, depths. This in itself is sugges- ble to older Gondolella is uncertain. tive of pelagic habits, and, as noted by Klapper 616 MARK A. PURNELL AND DAVID JONES and Barrick (1978), we can be fairly confident Ideally, the paleoenvironmental constraints that the elements recovered from black shale on the samples from which our elements were samples are not from conodonts occupying obtained would be based on detailed analysis benthic niches. Our sample of Gondolella (He- of characteristics such as faunal content, but 15-2b) is from fissile black shale deposited in such data were unavailable to us. For our deep water, and we interpret these elements, purposes, however—to test the hypothesis too, as the remains of pelagic animals. that element damage and wear differ between Sample 11040808 is a limestone turbidite conodonts that inhabited different environ- (see above) that mixes conodonts from differ- ments—categorization by color, lithology, and ent contemporaneous environments. Restrict- faunal abundance is enough to place samples ed nearshore shallow-water and peritidal along a broad facies gradient; differences in sequences of the same Arundian age in the these lithological characteristics clearly reflect Northumberland Basin to the north contain a environmental differences. For exploration range of taxa generally considered to inhabit (using ANOVA and LDA) of how wear/ shallow-water settings, and detailed analysis damage varies according to environment, we of the distribution of Mestognathus and Pa- assigned the samples of Hindeodus, Idiognatho- trognathus, relative to an environmental gra- dus, and Streptognathodus to relative depth dient of increasing restriction, supports this categories of nearshore, intermediate, and interpretation for these taxa. The distribution offshore respectively. For exploration (LDA) of Patrognathus is significantly correlated of how wear/damage varies with mode of (Spearman’s rank correlation, p , 0.05) with life, we classified Patrognathus, Mestognathus, an environmental gradient defined on the Gnathodus,andHindeodus as benthic, and basis of sediment components, providing Idiognathodus, Streptognathodus, and Gondolella strong evidence that it occupied benthic niches as pelagic. Future applications of our ap- (Purnell 1989). The distribution of Mestogna- proach could investigate how element damage thus in the same sequence is comparable, and and wear differ among samples defined more it, too, is likely to have been benthic (Purnell precisely in terms of paleoenvironment. 1989). Consequently, we interpret the Mestog- nathus and Patrognathus in sample 11040808 as Results being shallow-water benthic taxa, carried into Overall Patterns.—Figure 5 summarizes the the deeper-water settings by turbidity currents percentage of P1 elements in each of the seven originating on the shelf (von Bitter et al. [1986] taxa that display breaks, spalls, rounding, and reached similar conclusions regarding Mestog- polishing. Every element included in the nathus occurrences in other sections in the analysis was found to display wear, with the same depositional basin as our samples). primary micro-ornament on the denticles Gnathodus is entirely lacking from Arundian polished away to some degree on the occlusal sequences in the Northumberland Basin (Pur- surface of the blade. Wear facets (flattened nell 1989), and its presence in sample 11040808 areas of polishing oblique to the denticle reflects its preference for deeper, more open surface, often displaying some within-facet marine environments. This does not in itself pitting/chipping) are occasionally developed, address the question of whether it was benthic but polishing without faceting is more typical. or pelagic, but comparison of oxygen isotope Within most taxa examined, the extent of ratios derived from elements of Gnathodus and polishing across the denticles exhibited a Mestognathus in this sample indicates that consistent pattern, decreasing gradually from Gnathodus (d18O 20.9 6 0.2% V-SMOW dorsal to ventral along the denticle row, or ¼ [unpublished data]) occupied waters approx- developing to a similar extent along the entire imately 48C cooler than Mestognathus (19.8 6 row (Patrognathus and Gondolella). All samples 0.4% V-SMOW [unpublished data]). This is analyzed also contained elements exhibiting in consistent with hypotheses that Gnathodus vivo damage. Breakage and rounding of occupied deeper-water benthic habitats (Sand- denticles was often apparent in elements berg and Gutschick 1984), or was mesopelagic. where the largest denticles were intact and TOOTH WEAR, FUNCTION, AND ECOLOGY OF CONODONTS 617

FIGURE 5. Summary percentages of P1 elements in each of the seven taxa displaying breaks, spalls, rounding, and polishing, in each blade region. For multi-sample taxa (Hindeodus, Idiognathodus, Streptognathodus) the shallowest-water samples are plotted. Black lines in diagrams indicate portion of element blade included in analysis. 618 MARK A. PURNELL AND DAVID JONES retained an acute angle at their tips (see Fig. 2A,D); this is additional evidence for in vivo origin of such damage and wear, because the most prominent denticles would probably be the first to break or wear down during extensive postmortem compaction or trans- port. Spalls on the denticles have a similar configuration to those on the teeth of other vertebrates, generally extending from the denticle tip, the most likely point of initial contact during spall generation. Between-Taxon and Mode of Life Comparisons FIGURE 7. Analysis of blade and platform wear/damage Based on Blade Attributes.—Figure 6A shows attributes among taxa in conodont P1 elements. A, Principal component analysis, showing taxa (letters) the results of the principal components anal- plotted on first principal component axis. Axis label gives yses (PCA) based on the summary data set of percentage variance explained by each component. B, wear/damage attributes for the blade. Here Distribution of taxa according to percentage of elements with damage to the ventral part of the platform. LDA and in Figure 7 we show only the distribution based on this variable assigns all taxa to correct mode of of taxa along PC axis 1 because PC axis 2 (25% life categories; gray bars show 95% confidence intervals on of the variance) seems to be dominated by means for mode of life categories: dark gray, benthic; light gray, pelagic. noise, and does not reflect systematic variation in occlusal kinematics, environment, or habi- variation with mode of life based on a priori tat. The attributes that contribute the greatest assignment of taxa to benthic or pelagic variance to PC-1 relate to polishing: this axis is categories reveals that five attributes differ a contrast between the percentage of elements significantly (ANOVA; n 7). The percentage where polishing on the dorsal blade extends to ¼ of elements with central spalling (F 18.23; p the denticle bases and the percentage of ¼ ¼ 0.008), ventral spalling (F 7.34; p 0.04), elements where polishing on the central blade ¼ ¼ non-occlusal spalling (F 22.06; p 0.005), is confined to the denticle tips. The denticle ¼ ¼ row tends to develop the most extensive and polishing that extends to the base of denticles in the dorsal blade (Welch F 13.32; polishing in Gondolella and the least in ¼ Patrognathus.Explorationofwear/damage p 0.02) are all higher in pelagic taxa ¼ (Idiognathodus, Streptognathodus, and Gondolel- la). The percentage of elements with dorsal blade polishing that extends to the middle of denticles (F 9.72; p 0.03) is higher in ¼ ¼ benthic taxa (Patrognathus, Mestognathus, Gna- thodus, Hindeodus). That some of these p- values are well below 0.05 indicates that our results are not Type I errors arising from multiple testing. Any of these variables alone is sufficient to correctly assign taxa to benthic and pelagic categories using stepwise linear discriminant analysis. Figure 6B shows the FIGURE 6. Analysis of blade wear/damage attributes among taxa in conodont P1 elements. A, Principal distribution of benthic and pelagic taxa component analysis, showing taxa (letters) plotted on according to the percentage of elements with the first principal component axis. Axis label gives percentage variance explained by PC1. B, Distribution of non-occlusal spalling. We are least confident taxa according to percentage of elements with non- in our ecological assessment of Hindeodus, as occlusal spalling. LDA based on this variable assigns all the broader range of facies in which it is found taxa to correct mode of life categories; gray bars show 95% confidence intervals on means for mode of life categories: suggests it may be more pelagic. Interestingly, dark gray, benthic; light gray, pelagic. for three of the five variables, Hindeodus has TOOTH WEAR, FUNCTION, AND ECOLOGY OF CONODONTS 619 values that among benthic taxa are the closest where polishing in the ventral blade is confined to the pelagic values. to the denticle tips and the percentage of Between-Taxon and Mode of Life Comparisons elements where polishing on dorsal blade is Based on Blade and Platform Attributes.—Figure confined to the denticle tips. Although no clear 7A shows the results from the PCA that ecological signal emerges from the PCA results, incorporated wear/damage types relating to it is noteworthy that samples form nonover- both platform and blade by including plat- lapping taxon-specific rather than facies-specific form data as additional attributes to the blade clusters. Exploration through ANOVA of how data set. This PCA included all taxa except wear/damage varies with environment— Hindeodus (which lacks a platform). Polishing based on a priori assignment of the 11 samples attributes relating to the blade again had of Hindeodus, Idiognathodus, and Streptognatho- maximum loading values: PC-1 is a contrast dus to environmental categories (nearshore, between the percentage of elements where intermediate, and offshore)—reveals that none polishing in the central region of the blade of the variables differ significantly. Stepwise was confined to the tip and the percentage of linear discriminant analysis, however, reveals elements where polishing in the ventral region that only two variables are required to correctly of the blade extended to the base. Exploration assign all samples to categories: percentage of of how wear/damage varies with mode of life elements with occlusal spalls, and percentage based on a priori assignment of taxa to benthic of elements with non-occlusal spalls (Fig. 8B). or pelagic categories reveals that three attri- Canonical axis 1 corresponds to a gradient butes differ significantly (ANOVA; n 6). The ¼ from offshore (negative values) through inter- percentages of elements with central spalling mediate to nearshore environments (positive (F 21.60; p 0.01) and non-occlusal spalling ¼ ¼ values), with occlusal spalling showing a (F 34.62; p 0.004) are higher in pelagic taxa ¼ ¼ general trend of increase toward offshore (Idiognathodus, Streptognathodus, and Gondolel- environments. la), whereas the percentage of elements with damage to the ventral part of the platform (F ¼ Discussion and Conclusions 67.14; p 0.001) is higher in benthic taxa ¼ Our three null hypotheses—that conodont (Patrognathus, Mestognathus, Gnathodus). elements do not commonly exhibit surface Again, low p-values suggest that our results are not Type I errors. Any of these variables wear and damage; that wear/damage does alone is sufficient to correctly assign taxa to not vary among taxa; and that wear/damage benthic and pelagic categories using stepwise does not vary with environment—are clearly linear discriminant analysis. Figure 7B shows and unequivocally rejected. We consider each the distribution of benthic and pelagic taxa of our associated questions below. according to percentage of elements with Do Conodont Elements Commonly Exhibit damage to the ventral part of the platform. Surface Wear and Damage?—Perhaps the most Between-Environment Comparison Based on significant finding of our work is that every Blade Attributes.—The results of analysis de- conodont element included in our analysis signed to explore how wear/damage varies exhibited in vivo wear, in which the primary with environment within taxa is shown in surface micro-ornament on the denticles had Figure 8. Figure 8A shows the results from the been polished away on the occlusal side of the PCA including multiple samples from three blade, with occasional formation of wear taxa—Hindeodus, Idiognathodus, and Streptogna- facets. All the samples we analyzed also thodus—each sample from a different facies. contain elements displaying in vivo damage, PC-1 is a contrast between the percentage of in the form of broken denticles and spalls. elements where polishing in the dorsal blade Systematic observation and recording has extends to the denticle bases and the percent- therefore demonstrated that surface wear/ age of elements where polishing in the central damage is generally present on P1 elements blade is confined to the denticle tips. PC-2 is a in ozarkodinin conodonts. This would be contrast between the percentage of elements expected in elements functioning as teeth. 620 MARK A. PURNELL AND DAVID JONES

we have studied may reflect either differences between the occlusal kinematics of different taxa or differences in trophic niche, or both. Trophic niche differences include dietary effects, where different taxa fed on different foods, and substrate effects, where abrasive sediment is ingested with food and so comes into contact with elements during feeding, and both are known to affect tooth microwear in fishes (Purnell et al. 2006). Do Patterns of Surface Wear and Damage Vary among Conodont Taxa?—Patterns of wear and damage do vary among the conodont taxa we have analyzed. The attributes that displayed the greatest between-taxon variance related to polishing of denticles, rather than breakage. The general absence of systematic patterns in breakage attributes among taxa may reflect the fact that, despite our precautionary exclusion of elements exhibiting numerous broken denticles (see method), inevitably some of the features we recorded as in vivo breaks may have been postmortem. The noise introduced to the data as a result may have obscured signals in the breakage data. Alternatively or additionally, FIGURE 8. Analysis of blade wear/damage attributes in denticle breakage may simply occur randomly. conodont P1 elements among facies, with sample lithology indicated. A, Principal component analysis, showing taxa Similarities in depth distribution and mode of plotted on the first two principal component axes. B, life may also be more important than taxon- Linear discriminant analysis based on percentages of elements with occlusal spalls and with non-occlusal spalls, specific differences (see below). showing taxa plotted on the first and second canonical The occurrence of spalling provides a test of axis. All taxa are correctly assigned to environmental hypotheses of element occlusion and the categories; circles show 95% confidence intervals for environmental categories: offshore (dark gray), mid- kinematics of food processing. Spalling is (mid gray), and nearshore (light gray). most likely to result from element malocclu- sion, which causes denticles to be misaligned The relative rarity of faceting suggests that when coming together during the occlusal blade occlusion was imprecise compared to cycle. Opposed denticles must be separated mammal tooth occlusion. Thus wear would for spalls to form, so the distribution of have been dominated by abrasion (element- spalls—along the entire length of the denticle row in all taxa—demonstrates that during the food contact) rather than attrition (element- occlusal cycle the blades separated completely. element contact). The paucity of faceting also This verifies the occlusal model of Donoghue means that wear and damage themselves may and Purnell (1999b) for these taxa. Qualitative introduce some noise into the data: because it observations revealed that polishing on the reduces denticle tip sharpness (Jones et al. 2012), non-occlusal surface of the free blade is much wear may progressively limit the range of food less frequent and is generally restricted to the that the elements are able to process, changing denticle tips. The non-occlusal polishing prob- diet subtly through the period of time when the ably results from a combination of element element surface is functioning in feeding (anal- misalignment and contact with food. ogous to the functional life of a tooth). A unique pattern of surface damage and The variation in patterns of in vivo surface wear is present in Gondolella, compared to the wear and damage in the conodont elements other taxa: it developed extensive polishing TOOTH WEAR, FUNCTION, AND ECOLOGY OF CONODONTS 621 along the entire denticle row, and across the vary significantly according to mode of life platform, and has a high percentage of and environment. The incidence of spalling is elements with both occlusal and non-occlusal higher in more offshore environments and in spalls. This probably reflects the pelagic mode taxa likely to have had a pelagic mode of life, of life of Gondolella and its preference for whereas dorsal blade polishing and ventral offshore environments (see discussion below), platform damage are higher in benthic taxa. but there may also be a functional component. Given the exploratory nature of this first The P1 elements of Gondolella are quite systematic analysis of wear and damage in different from most of the other taxa in this conodonts, it is difficult to be certain about the analysis (e.g., absence of a free blade to guide underlying causes of the variation between occlusal alignment [Donoghue and Purnell taxa with different modes of life. The marked 1999b], prominent carina running the length difference in morphology between some of the of the platform; see Fig. 2). The pattern of elements in the same mode-of-life category wear and damage in Gondolella may therefore demonstrates that the differences between be a consequence of the occlusal and process- benthic and pelagic taxa are unlikely to be ing components of its P1 elements being less caused by systematic differences in occlusal functionally and spatially differentiated than kinematics. Similarly, because denticle spall- in the other taxa: because there is no free blade ing is more frequent in pelagic taxa it cannot to guide occlusion in Gondolella, occlusion may be a consequence of benthic taxa in shallow be less well constrained, resulting in more water having a greater likelihood of ingesting denticle misalignment and occlusal spalling. extraneous particles of substrate (cf. stickle- The denticle row also forms an integral part of backs, the teeth of which have more surface the food processing platform surface in wear when they feed benthically [Purnell et al. Gondolella, which could explain the extensive 2006, 2007], although spalling in sticklebacks polishing along its entire length. has not been analyzed). Although there is no Do Patterns of Surface Wear and Damage Differ direct evidence, the most likely remaining between Conodonts That Inhabited Different possibility is that the differences in wear and Environments?—Patterns of wear and damage damage between benthic and pelagic cono- differ between congeneric samples from differ- donts reflect differences in diet. ent environments, but the results of PCA reveal Directions for Future Research.—The results little systematic variation in these attributes presented here demonstrate that analysis of with facies. Moreover, clustering of samples in surface wear and damage in conodonts is multivariate space reflects taxon-specific informative, and has implications for releasing wear/damage. The differences in wear and the paleobiological potential of the fossil damage between Idiognathodus and Streptogna- record of this clade. Clearly, wear and damage thodus, despite their morphological similarity, can be used to test and further refine may reflect trophic differentiation, although hypotheses of element occlusion, and perhaps subtle differences in occlusal kinematics be- provide evidence of the diet-mediated chang- tween these taxa cannot be excluded as an es in element function that have driven alternative explanation. The between-taxa observed patterns of evolutionary change. comparison also suggests a depth and habitat More functional studies of conodont elements signal in the data, with ordination along PC-1 are also required to complement the informa- from low to high scores possibly reflecting an tion gleaned from the wear and damage ecological gradient from shallow, benthic patterns. The evidence that wear and damage Patrognathus to deep, pelagic Gondolella. differ according to mode of life and environ- This possible ecological signal in the PCA ment should be further tested through analy- ordination is more clearly evident in the sis of more conodont taxa for which results of ANOVA and linear discriminant environmental range is well constrained. Our analysis. These analyses indicate that several analysis suggests that, like other vertebrates, spalling and blade polishing attributes and patterns of tooth wear and damage reflect damage to the ventral part of the platform feeding kinematics and other aspects of trophic 622 MARK A. PURNELL AND DAVID JONES

Buggisch, W., M. M. Joachimski, G. Sevastopulo, and J. R. Morrow. niche. Although the confidence that can be 13 18 2008. Mississippian ] Ccarb and conodont apatite ] O: their placed in hypotheses regarding the depth at relation to the Late Palaeozoic glaciation. Palaeogeography, which a given species lived varies among taxa, Palaeoclimatology, Palaeoecology 268:273–292. the relationships between wear/damage and Chen, B., M. M. Joachimski, Y. D. Sun, S. Z. Shen, and X. L. Lai. 2011. Carbon and conodont apatite oxygen isotope records of environment—and whether a particular cono- Guadalupian-Lopingian boundary sections: climatic or sea-level dont species was likely to have had benthic or signal? Palaeogeography, Palaeoclimatology, Palaeoecology pelagic habits—suggest that analysis of wear 311:145–153. Clark, D. L., ed. Conodont biofacies and provincialism. 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Appendix

Summary percentage data for wear/damage attributes scored for sixteen samples of P1 elements from Carboniferous conodont taxa. N/A: Hindeodus elements lack platforms, so wear/damage attributes relating to the platform are non- applicable. N/D: Encrustation on some elements prevented certain wear/damage attributes from being scored, resulting in no data. See Table 2 for definition of wear/damage types.

Damage attributes Position of break on blade Position of break on denticle Sample Taxon n % Dorsal % Central % Ventral % Base % Middle % Tip P-13-4 Hindeodus minutus 19 0 27.3 27.3 27.3 0 18.2 He-2-2A Hindeodus minutus 11 25 35 35 20 40 25 He-16-1 Hindeodus minutus 20 20 35 50 50 20 35 He-5-1 Hindeodus minutus 20 5.3 5.3 15.8 15.8 5.3 5.3 He-5-1 Idiognathodus simulator 20 20.0 20.0 40.0 35.0 15.0 20.0 He-16-1 Idiognathodus simulator 20 5.0 10.0 35.0 25.0 20.0 5.0 He-14-1 Idiognathodus simulator 20 15.0 10.0 20.0 15.0 15.0 10.0 He-13-1 Idiognathodus simulator 20 10.0 15.0 40.0 35.0 5.0 35.0 TOP-1-2 Streptognathodus pawhuskaensis 20 35.0 25.0 40.0 30.0 25.0 40.0 Le-16-1 Streptognathodus pawhuskaensis 20 0.0 10.0 30.0 15.0 15.0 15.0 QH-2-4 Streptognathodus pawhuskaensis 20 20.0 15.0 35.0 10.0 30.0 35.0 He-15-2b Gondolella sublanceolata 14 14.3 21.4 64.3 64.3 7.1 21.4 11040808 Mestognathus beckmanni 17 23.5 11.8 11.8 23.5 17.6 0.0 11040808 Gnathodus pseudosemiglaber 20 10.5 0.0 21.1 31.6 0.0 0.0 11040808 Patrognathus capricornis 12 18.2 9.1 27.3 27.3 0.0 27.3

Wear attributes Extent of polishing on Extent of polishing on denticles of dorsal blade denticles of central blade % to % to % to % to % to % to Sample Taxon n Base Middle Tip Base Middle Tip P-13-4 Hindeodus minutus 19 54.5 27.3 18.2 9.1 45.5 45.5 He-2-2A Hindeodus minutus 11 5.3 52.6 42.1 0 26.3 73.7 He-16-1 Hindeodus minutus 20 70 25 5.0 20 45 35 He-5-1 Hindeodus minutus 20 0 33.3 66.7 0 33.3 66.7 He-5-1 Idiognathodus simulator 20 60.0 40.0 0.0 0.0 30.0 70.0 He-16-1 Idiognathodus simulator 20 85.0 15.0 0.0 0.0 40.0 60.0 He-14-1 Idiognathodus simulator 20 55.0 40.0 5.0 0.0 5.0 95.0 He-13-1 Idiognathodus simulator 20 80.0 20.0 0.0 5.0 50.0 45.0 TOP-1-2 Streptognathodus pawhuskaensis 20 100.0 0.0 0.0 10.0 70.0 20.0 Le-16-1 Streptognathodus pawhuskaensis 20 89.5 10.5 0.0 0.0 78.9 21.1 QH-2-4 Streptognathodus pawhuskaensis 20 90.0 10.0 0.0 15.0 75.0 10.0 He-15-2b Gondolella sublanceolata 14 71 14 14 86 7 7 11040808 Mestognathus beckmanni 17 52.9 41.2 5.9 5.9 76.5 17.6 11040808 Gnathodus pseudosemiglaber 20 47.4 47.4 5.3 0.0 26.3 73.7 11040808 Patrognathus capricornis 12 0 20.00 80 0 0 100

Platform damage and wear attributes % Elements with % Elements with % Elements with polishing on highs polishing on lows polishing on highs Sample Taxon n of ventral platform of ventral platform of dorsal platform He-5-1 Idiognathodus simulator 20 19 47 0 He-16-1 Idiognathodus simulator 20 32 72 11 He-14-1 Idiognathodus simulator 20 0 88 0 He-13-1 Idiognathodus simulator 20 5 61 0 TOP-1-2 Streptognathodus pawhuskaensis 20 N/D N/D N/D Le-16-1 Streptognathodus pawhuskaensis 20 5 61 0 QH-2-4 Streptognathodus pawhuskaensis 20 N/D N/D 0 He-15-2b Gondolella sublanceolata 14 71 100 93 11040808 Mestognathus beckmanni 17 81 83 31 11040808 Gnathodus pseudosemiglaber 20 100 100 N/D 11040808 Patrognathus capricornis 12 0 77.8 0 TOOTH WEAR, FUNCTION, AND ECOLOGY OF CONODONTS 625

Appendix. Extended.

Damage attributes Position of spall on blade Position of spall on denticle % Dorsal % Central % Ventral % Occlusal % Non-occlusal % Dorsal % Ventral 9.1 18.2 18.2 27.3 9.1 0 0 20 30 5 35 20 0 0 35 30 30 40 40 0 0 10.5 26.3 15.8 15.8 31.6 0 0 50.0 50.0 35.0 70.0 45.0 10.0 5.0 30.0 40.0 35.0 45.0 50.0 15.0 0.0 55.0 35.0 35.0 60.0 40.0 20.0 15.0 50.0 45.0 25.0 65.0 40.0 15.0 5.0 40.0 45.0 25.0 50.0 20.0 25.0 15.0 35.0 45.0 20.0 25.0 55.0 0.0 0.0 10.0 70.0 20.0 35.0 15.0 15.0 25.0 71.4 64.3 35.7 85.7 71.4 7.1 0.0 5.9 5.9 0.0 0.0 5.9 0.0 5.9 15.8 10.5 21.1 21.1 21.1 0.0 5.3 0.0 18.2 9.1 18.2 9.1 9.1 0.0

Wear attributes Extent of polishing on denticles of ventral blade Rounding % to % to % to % % % Base Middle Tip Dorsal Central Ventral 0 9.1 90.9 0 0 0 0 10.5 89.5 5 0 0 0 20 80 15 10 0 0 33.3 66.7 5.3 42.1 15.8 0.0 10.0 90.0 50.0 0.0 0.0 0.0 0.0 100.0 65.0 5.0 0.0 0.0 0.0 100.0 45.0 0.0 0.0 0.0 30.0 70.0 55.0 15.0 0.0 5.0 60.0 35.0 70.0 20.0 0.0 0.0 21.1 78.9 65.0 0.0 0.0 15.0 60.0 25.0 75.0 15.0 5.0 62 23 15 35.7 14.3 0.0 0.0 29.4 70.6 17.6 0.0 0.0 0.0 5.3 94.7 52.6 10.5 0.0 0 0 100 18.2 0.0 0.0

Platform damage and wear attributes % Elements with % Elements with % Elements with polishing on lows blunting on blunting on % Elements with of dorsal platform ventral platform dorsal platform flattening 0 21 0 65 33 40 10 65 0 50 0 65 5 45 4 85 N/D 95 15 80 5 45 5 100 0 50 0 90 100 29 29 N/A 25 94 29 N/A N/D 83 88 30 9.1 83.3 41.7 N/A 626 MARK A. PURNELL AND DAVID JONES

APPENDIX FIGURE. Loading values from principal components analysis of wear/damage attributes scored for 16 samples of P1 elements from Carboniferous conodont taxa, for each data set. Variables are in the same order as listed in Appendix tables. Asterisks indicate attributes with heaviest loading on each axis.