Introduction

Subsequent to Norby (1976) restudying the type specimens of Lochriea montanaensis Scott, 1942 (Fig. 1) and describing newly collected bedding-plane assemblages of Lochriea commutatus (=Lochriea commutata [Branson and Mehl, 1941] [Branson and Mehl, 1941b]), several of which we refigure (Fig. 2), the conodont genus Lochriea Scott, 1942 was used to accommodate an increasing number of species and the biostratigraphic zones they define, with only minimal taxonomic and historical underpinnings that led to this usage ever having been presented. Despite assurances (Sweet, 1988, p. 111) that “species of . . . Lochriea . . . are represented by bedding-plane assemblages, hence there are few mysteries about [their] skeletal anatomy,” Lochriea and its apparatus were not nearly as well known then and in the intervening years as Sweet implied. Thus, we provide the foundations and justifications for accommodating certain Carboniferous carminiscaphate P₁ conodonts with unornamented or ornamented platforms, and the elements they were biologically associated with, in the genus Lochriea instead of in other genera, including Spathognathodus, Gnathodus, and Paragnathodus. We do so by tracing the generic assignments of the P₁ elements of Lochriea commutata and related species, and by re-examining and documenting the element composition, and the number of elements in the apparatus of the type species of the genus Lochriea, Lochriea commutata (Branson and Mehl, 1941) (Branson and Mehl, 1941b).

Range and biostratigraphic utility of Lochriea

The genus Lochriea occurs in, and is restricted to, strata of Carboniferous age. Atakul-Özdemir et al. (2012) concluded that the genus is monophyletic, biostratigraphically important, and that the first appearances of Lochriea species, and their transitions, are markers for global correlation (aspects of the latter were discussed by Somerville, 2008). Lochriea commutata and other species of Lochriea (some early listings were under the generic names Gnathodus and Paragnathodus) first appear at the base of the Viséan in Europe (Higgins, 1981), in the Arundian of England (Metcalfe, 1981; Stone, 1991), in the lower Meramecian of North America (Krumhardt et al., 1996), and in strata of equivalent age elsewhere in the world.

Figure 1.

Lochriea montanaensis Scott, 1942, holotype and paratype (= Lochriea commutata [Branson and Mehl, 1941] [Branson and Mehl, 1941b]). Scanning electron micrographs and outline drawing of bedding-plane assemblages on black shale, with interpretation of conodont elements present. Specimens reoriented relative to views shown by Scott (1942), and elements on parts and counterparts numbered sequentially from top down. Heath Formation, locality 2, Montana, USA. Scale bars = 0.5 mm. (1, 2) Fecal assemblage of 18 elements; holotype, part and counterpart (i.e., + and – of Scott [1942, pl. 37, figs. 2, 6], respectively), UI X-1318; (3, 4) fecal assemblage of 23 elements; paratype, part and counterpart (i.e., + and – of Scott [1942, pl. 37, figs. 4, 5]), respectively. Part (+) lost; outline drawing (3) based on Scott (1942, fig. 4), UI X-1319.

The earliest occurrences of a species of the genus are Lochriea cracoviensis (Belka, 1985), at the base of the Viséan in Poland (Belka, 1985, chart), and L. cracoviensis and L. saharae Nemyrovska, Perret-Mirouse, and Weyant, 2006, from the lower Viséan of Algeria (Nemyrovska et al., 2006), both species appearing slightly before L. commutata in the latter country. The upper limit of species of Lochriea, including that of L. commutata, is in the earliest Bashkirian (lowermost Morrowan) of Ukraine (Nemirovskaya et al., 1991), Uzbekistan (Nigmadganov and Nemirovskaya, 1992), south China (Wang et al., 1987b), southwest Japan (Mizuno, 1997), Spain (Sanz-López and Blanco-Ferrara, 2012), and the lower Namurian of Britain and Ireland (Higgins, 1985, table 7; Sweet, 1988, chart 6). The type species, L. commutata, is long ranging (Sweet, 1988, chart 6) and is of biostratigraphic utility only in a local context. Lochriea commutata and L. homopunctatus (Ziegler, 1960), were utilized by Metcalfe (1981) and Varker and Sevastopulo (1985) to define local-range zones. Other species, such as L. cracoviensis, L. mononodosa (Rhodes, Austin, and Druce, 1969), L. nodosa (Bischoff, 1957), L. multinodosa (Wirth, 1967), and others, have a more limited range and are therefore stratigraphically more useful (Higgins and Wagner-Gentis, 1982; Belka, 1985, chart; Sweet, 1988, chart 6). Atakul-Özdemir et al. (2012) suggested that Lochriea homopunctatus is globally important for marking and recognizing the base of the Viséan, and they indicated that the first appearance of Lochriea ziegleri Nemirovskaya, Perret, and Meischner, 1994, was under investigation as a marker for the Viséan/Serpukhovian boundary. Qi et al. (2018) provided occurrence data (fig. 2) for ten species of Lochriea at or near the Viséan/Serpukhovian boundary in south China; this data supports Sevastopulo and Barham (2014) and others in advocating for the use of the first appearance datum (FAD) of L. ziegleri as a definitive marker for the base of the Serpukhovian Stage. Qi et al. (2018, figs. 3, 4) also illustrated their interpretation of the evolutionary relationships among nine of the 10 Lochriea species recovered by them.

When Mizuno (1997) defined his new genus Neolochriea, he recognized four species, each of which was based solely on P₁ elements. He interpreted the four species of Neolochriea from Japan to be closely related to Lochriea spp., their morphology and stratigraphic distribution leading him to conclude that Neolochriea evolved from Lochriea. The first appearance of these Neolochriea species in southwest Japan is well within the Bashkirian (Morrowan), and it is above the occurrence of L. commutata in Japan and elsewhere in the world. In Japan, L. commutata ranges into the basal Bashkirian (i.e., into the Declinognathodus noduliferous Zone) (Mizuno, 1997). Although it is known to range higher into the basal Bashkirian of the Donets Basin of the Ukraine (Nemirovskaya et al., 1991) and south China (Wang et al., 1987b), the occurrence of L. commutata in Japan (Mizuno, 1997) is higher than has been recorded from Europe or North America.

Figure 2.

Lochriea commutata (Branson and Mehl, 1941) (Branson and Mehl, 1941b). Scanning electron micrographs (1A, 1B, 2), photomicrograph (4), and line drawings (3, 5) of bedding-plane assemblages on black shale surfaces. Solid lines (3, 5) represent elements and dashed lines, represent imprints of elements. Heath and Tyler formations, Montana, USA. Scale bars = 0.5 mm. (1A, 1B) Natural assemblage of 15 elements in lateral collapse with some rotation of P element complex, numbered diagonally from the upper left to lower right. Only part (i.e., of part and counterpart) is illustrated. Sample H-B-1-B, Tyler Formation, locality 3, ISGS 62P-207A. (2, 3) Natural assemblage of 15 elements in oblique lateral collapse pattern from the side (Purnell and Donoghue, 1998), numbered from the top down. Part and counterpart, respectively, with P₁ and P₂ element pairs in apposition mostly preserved on part (2), with anterior end of P₂^?d element preserved on counterpart (3), which was drawn rather than photographed. More detail of S elements is shown on counterpart (3), although some M and S elements are only imprints. Sample H-B-1-B-1, Tyler Formation, locality 3, ISGS 62P-216A and 62P-216B. (4) Natural assemblage of 13 elements in oblique collapse from behind, above, and to one side (Purnell and Donoghue, 1998), numbered from the top down. P₁, P₂, and M^d elements are imprints. S element array is tightly clustered, preventing specific identification of six S elements present; anterior ends of elements 11S–13S further revealed by excavation subsequent to photo. Probable topotype, of which only part is known. Sample H-A-1-1, Heath Formation, locality 2, ISGS 62P-210. (5) Natural assemblage of 13 elements in apparent lateral collapse, but with disrupted architectural pattern, numbered consecutively from the mirror image axis (horizontal dashed line) outward; part (lower) and counterpart (upper) show some scatter. Sample H-A-2-7-1, Heath Formation, locality 2, ISGS 62P-218A and 62P-218B.

Taxonomic notes

We conclude, as did Norby (1976), that Spathognathodus commutatus Branson and Mehl, 1941 (Branson and Mehl, 1941b) is the senior subjective synonym of Lochriea montanaensis Scott, 1942 and that the two are combined as L. commutata according to priority and availability. First and foremost, that conclusion is based on our detailed comparison and documentation (von Bitter and Norby, 1994a; Fig. 3) of the overall morphology of P₁ elements in the type specimens of L. montanaensis Scott, 1942 with the P₁ elements that are the type specimens of Spathognathodus commutatus Branson and Mehl, 1941 (Branson and Mehl, 1941b) (von Bitter and Norby, 1994a; Fig. 3), and of a wide range of P₁ elements from across North America and Europe (von Bitter and Norby, 1994a; Fig. 3). Our determination, based on this wide-ranging material, is that no apparent differences exist in overall P₁ morphology of the two taxa. Although the P₁ elements of the type specimens of Lochriea montanaensis tend to be longer than those of L. commutata, this observation has yet to be confirmed statistically. Discrete P₁ elements from the Heath Formation and from the overlying Tyler Formation of Montana, show considerable variation in morphological features such as the length and number of denticles, variation that we regard as normal phenotypic variation; however, further study may determine that this variation is ecophenotypic, and may be due to environmental differences during the deposition of the Heath and Tyler formations.

Second, our conclusion is based on our earlier determination (von Bitter and Norby, 1994b) that the well-developed microsculpture on the carinal denticles of P₁ elements of the type specimens of Lochriea montanaensis Scott, 1942, is not a defining characteristic of that taxon. Although this feature is obscured by diagenetic overgrowths on the lectotype and the paralectotypes of Spathognathodus commutatus Branson and Mehl, 1941 (Branson and Mehl, 1941b) (von Bitter and Norby, 1994a), that feature is present and was documented in the same study on more recently collected topotypes of S. commutatus. Additionally, P₁ elements of this morphology from a wide range of locations, including those from the Heath and Tyler formations of Montana, the Fayetteville Formation of Oklahoma, and the Herdringen Formation of Germany, exhibit this microsculpture (von Bitter and Norby, 1994a, b).

The weight of evidence supporting our conclusion that Lochriea montanaensis Scott, 1942 is a subjective junior synonym of Spathognathodus commutatus Branson and Mehl, 1941 (Branson and Mehl, 1941b), was based initially (von Bitter and Norby, 1994a) on our comparison of the characteristics, particularly the micromorphology, of their P₁ elements. Conodont P₁ elements had long been regarded as the most diagnostic and most quickly evolving elements, and S. commutatus was, when described and named by Branson and Mehl (1941b), based solely on P₁ elements. We (von Bitter and Norby, 1994a) determined that the macro- and micromorphology of the P₁ elements of the two species were identical, concluding that they were synonyms of each other, and with the genus name Lochriea and the species name commutatus each having priority, that its correct name was, after amending the species name ending, Lochriea commutata. We here extend our documentation of L. commutata P₁ elements by illustrating specimens from the United States, Canada, and Germany (Fig. 3), and re-illustrating the lectotype of Spathognathodus commutatus from its type stratum and type locality, the Hindsville Formation of Oklahoma at locality 4 (Fig. 3.7–3.10). We had previously illustrated both its lectotype and its three paralectotypes (von Bitter and Norby, 1994a, figs. 2.6–2.15, 3.1–3.12), as well as P₁ elements from the overlying Fayetteville Formation at locality 5 (Sutherland and Manger, 1979, fig. 2 correlation chart) (von Bitter and Norby, 1994a, fig. 5.1–5.12).

Figure 3.

Lochriea commutata (Branson and Mehl, 1941) (Branson and Mehl, 1941b) P₁ elements in bedding-plane assemblages on black shale (1–6), as acid residue-derived discrete elements (7–34), and in acid residue-derived fused assemblages (35). All are scanning electron micrographs except (3), which is a photomicrograph. Scale bars (1–6, 35) = 0.2 mm; for the remaining figures, actual specimen lengths are provided in descriptions below. (1) P₁^s,d element pair in functional apposition, lateral view along rostrocaudal axis of apparatus; element pair rotated ∼90° from original functional position in apparatus. Anterior ends of elements on right side of figure, posterior on left. See elements 1P₁^?s and 2P₁^?d (Fig. 2.2) for apparatus context of P₁^s,d element pair. Splotchy mottled surface attributable to uneven scanning electron micrograph coating, charging, or both. Sample H-B-1-B-1, Tyler Formation, locality 3, Montana, USA, ISGS 62P- 216A. (2) P₁^s,d element pair in ‘near’ functional position in lateral view along rostrocaudal axis of apparatus with anterior ends of elements on right, posterior ends on left. P₁^s element both ‘flipped’ and rotated ∼135° relative to its original functional apposition with P₁^d element. See elements 1P₁^s and 2P₁^d (Fig. 2.1A) for apparatus context of this element pair, and see element 4P₂^d (Fig. 2.1A) for apparatus context of anterior part of the P₂^d element on bottom left. Sample H-B-1-B, Tyler Formation, locality 3, Montana, USA, ISGS 62P-207A. (3) P₁^s,d element imprint pair in ‘near’ functional position, lateral view along rostrocaudal axis of apparatus, P₁^?s (upper) element rotated 180° relative to its original functional apposition with P₁^?d (lower) element. P₁^?d element a good imprint, P₁^?s element a partial imprint only. See elements 1P₁^?s and 2P₁^?d (Fig. 2.4) for apparatus context of the P₁^s,d element pair. Sample H-A-1-1, Heath Formation, locality 2, Montana, USA, ISGS 62P-210. (4) P₁^s element (in) Lochriea montanaensis Scott, 1942 holotype (= Lochriea commutata [Branson and Mehl, 1941] [Branson and Mehl, 1941b]), outer view. See element 2P₁^s (Fig. 1.1, 1.2) for apparatus context. Previously illustrated by von Bitter and Norby (1994a, fig. 2.1, counterpart). Heath Formation, locality 2, Montana, USA, UI X-1318. (5) P₁^?d element (in) Lochriea montanaensis Scott, 1942 holotype (= Lochriea commutata [Branson and Mehl, 1941] [Branson and Mehl, 1941b]), outer view. See element 11P₁^?d (Fig. 1.1, 1.2) for apparatus context. Previously illustrated by von Bitter and Norby (1994a, fig. 2.2). Heath Formation, locality 2, Montana, USA, UI X-1318. (6) P₁^?d element, (?) inner view. Heath Formation, locality 1, Montana, USA, CM 33965. (7–10) P₁^s element, upper, lower, outer, and inner views, respectively, of a syntype of Lochriea commutata (Branson and Mehl, 1941) (Branson and Mehl, 1941b). Designated as one of four cotypes and illustrated (with incorrect number UM C552-1) by Lane and Straka (1974, figs. 40.15, 40.16); catalogue no. UM C552-2 apparently applied by or at UM for series of four syntypes. Re-illustrated and designated lectotype (UM C552-2) of the species (other three specimens designated as paralectotypes and given new numbers) by von Bitter and Norby (1994a, fig. 2.6–2.9). Hindsville Formation, locality 4, Oklahoma, USA. Length = 0.91 mm. (11–18) P₁^s elements (14, 16–18) and P₁^d elements (11, ?12, 13, 15), upper views of approximate ontogenetic growth series from least to most mature. Sample H-B-1-A, Tyler Formation, locality 3, Montana, USA, ISGS 62P-1088 to 62P-1092, and 62P-1094 to 62P-1096. Lengths = 0.63, 0.89, 1.00, 0.82, 0.78, 0.62, 0.68, and 0.63 mm, respectively. (19–21) P₁^d (19), P₁^?d (20), P₁^?d (21) elements, upper views of three elements from most to least mature. Samples VS-1, VS-12, and VS-12, respectively, Ridenhower Formation, locality 7, Illinois, USA, ISGS 62P-1201, 62P-1202, and 62P-1093. Lengths = 0.55, 0.47, and 0.43 mm, respectively. (22–27) P₁^s (22, 23, 26) and P₁^d (24, 25, 27) elements, upper views of a potential ontogenetic growth series from most to least mature. USGS collection 34004-PC, Bluestone Formation, locality 8, West Virginia, USA, USNM 593924–593928 and 696950. Lengths = 0.61, 0.60, 0.55, 0.62, 0.61, and 0.43 mm, respectively. (28) P₁^d element, upper view. Sample Kenk-2-1, Kennetcook Member, Upper Windsor Group, locality 9, Colchester County, Nova Scotia, Canada, ROM 63699. Length = 0.75 mm. (29, 30) P₁^d elements, upper views. Sample Schälk 42, Herdringen Formation, locality 10, North-Rhine Westphalia, Germany, ISGS 82P-53 and ISGS 82P-54, respectively. Lengths = 0.54 and 0.37 mm, respectively. (31) P₁^d element, inner view. Sample H-B-1-A, Tyler Formation, locality 3, Montana, USA, ISGS 62P-1101. Length = 0.79 mm. (32, 34) P₁^d element, upper and inner (caudal) views, respectively. Illustrated by Lane and Straka (1974, fig. 37.1, 37.2), Goddard Formation, locality 6, Oklahoma, USA, SUI 33624. Length = 0.94 mm. (33) P₁^?d element, (?) inner view of immature element, Sample H-B-1-A, Tyler Formation, locality 3, Montana, USA, ISGS 62P-1097. Length = 0.44 mm. (35) P₁^?s element in ? upper view at posterior end of partial, fused S element array (see Fig. 9.21 for another view of this fused cluster). Apparatus showing several S elements of apparatus inclined toward one another. Collection USGS 34004-PC, Bluestone Formation, locality 8, West Virginia, USA, USNM 593966.

Because L. montanaensis Scott, 1942, was based on bedding-plane assemblages that contained elements other than P₁ elements, the key to confirming our earlier conclusion that L. montanaensis and S. commutatus Branson and Mehl, 1941 (Branson and Mehl, 1941b) were synonyms of one another, lay in demonstrating that their non-P₁ elements (i.e., their P₂, M, S₀, S₁, S₂, and S_3/4 elements) were also identical. Thus, we re-collected the type locality and type stratum of S. commutatus, the Hindsville Formation at locality 4 in Oklahoma, from which we recovered a few P₂, M, S₀, and S_3/4 elements that we identified as belonging to that species, as well as more than a dozen topotype P₁ elements, and compared the non-P₁ elements from there with the homologous elements in the type specimens of Lochriea montanaensis Scott, 1942 (Scott, 1942, pl. 37, figs. 2, 4–6; here re-illustrated in Fig. 1). We continued this process of comparing and documenting non-P₁ elements with those homologous elements in topotype specimens of that species collected by Norby (1976) from the Heath Formation, at locality 2, in Montana (Fig. 2). Finally, we examined and documented P₂, M, S₀, S₁, S₂, and S_3/4 elements, which we here identify and label as those of L. commutata, from a variety of localities in the United States, Canada, and Germany (Figs. 4–9). One of these localities, the Fayetteville Formation at locality 5 in Oklahoma (Sutherland and Manger, 1979, fig. 2), yielded characteristic and slightly better-preserved L. commutata P₂, M, S₀, and S_3/4 elements (Figs. 5.15, 6.12, 9.17, 9.18) than the non-P₁ elements we recovered from the Hindsville Formation at locality 4. We conclude, after examining and comparing lower Carboniferous conodont faunas from three countries on two continents, that the P₂, M, S₀, S₁, S₂, and S_3/4 elements, like the P₁ elements of the initially designated S. commutatus Branson and Mehl, 1941 (Branson and Mehl, 1941b), the subsequently named L. montanaensis Scott, 1942, and those of the final combination, L. commutata, show surprisingly little variation within each of the non-P₁ elements, confirming that L. montanaensis and L. commutata are indeed synonyms.

Previously, we (von Bitter and Norby, 1994a, b) regarded Branson and Mehl (1941b) as having provided the taxonomic foundation for the species Spathognathodus commutatus Branson and Mehl. We still do so, despite subsequently having become aware that E.B. Branson and M.G. Mehl had published an article a few months earlier (Branson and Mehl, 1941a) in which they used the name S. commutatus for illustrated specimens from the Caney Formation of Oklahoma, but without having fulfilled the requirements for naming a new species. In effect, the authors were using a nomen nudum, a condition they rectified a few months later in Branson and Mehl (1941b) when they described, named, and illustrated the species more adequately from material from the “Pitkin limestone” (now Hindsville Formation) of Oklahoma.

In addition to describing Lochriea montanaensis, Scott (1942, p. 299) also described a second species of the genus, L. bigsnowyensis. This description was also based on bedding-plane assemblages from the Heath Formation of Montana, the one specimen (the holotype) still available, being composed of a complement of 14 elements (Fig. 10). However, unlike L. commutata, it cannot contribute either to the generic concept of Lochriea or to our knowledge of the apparatus composition and structure of its species. Scott (1942, p. 299) described the defining P₁ elements (= his spathognaths) of L. bigsnowyensis as “blade wide, thin along aboral margin; denticles short, tips rounded, escutcheon moderately deep” adding (p. 299) that “only imprints and fragments of spathognaths have been found in assemblages of L. bigsnowyensis. As a result no sharp differences can be pointed out at this time.” Presumably, the “sharp differences” he alluded to referred to differences between the P₁ elements of this and related species, such as L. commutata.

Figure 4.

Lochriea commutata (Branson and Mehl, 1941) (Branson and Mehl, 1941b) P₂ elements in bedding-plane assemblages on black shale surfaces (1–7), in acid residue-derived fused assemblages (8, 17), and as acid residue-derived discrete elements (9–16, 18–23). All are scanning electron micrographs except (3), which is a photomicrograph. Scale bars (1–8, 17) = 0.2 mm. For the remaining figures, actual specimen lengths are provided in descriptions below. (1) P₂^s,d element pair in lateral view along rostrocaudal axis of apparatus, (upper) P₂^d element rotated ∼135° relative to (lower) P₂^s element ‘in apposition’ position. See elements 4P₂^d and 5P₂^s (Fig. 2.1A) for apparatus context of P₂^s,d element pair. Sample H-B-1-B, Tyler Formation, locality 3, Montana, USA, ISGS 62P-207A. (2) P₂^s,d element pair view along rostrocaudal axis of apparatus. Anterior part of P₂^?d element missing, but preserved on counterpart ISGS 62P-216B (Fig. 2.3). See elements 3P₂^?s and 4P₂^?d (Fig. 2.2, 2.3) for apparatus context of P₂^s,d element pair (however, P₂^s,d elements as shown in Fig. 2.2 are reversed relative to the position shown here). Sample H-B-1-B-1, Tyler Formation, locality 3, Montana, USA, ISGS 62P-216A. (3) P₂^s,d element pair in apposition in lateral view along rostrocaudal axis of apparatus. Lower P₂^?d element is imprint only. See elements 3P₂^?s and 4P₂^?d (Fig. 2.4) for apparatus context of P₂^s,d element pair. Sample H-A-1-1, locality 2, Heath Formation, Montana, USA, ISGS 62P-210. (4) P₂ element as (mostly) impression in ?inner view; only a few denticle tips of element preserved; posterior termination not preserved. See element 2P₂ (Fig. 2.5) for apparatus context. Sample H-A-2-7-1, Heath Formation, locality 2, Montana, USA, ISGS 62P-218B. (5) P₂^?d element (in) Lochriea montanaensis Scott, 1942 holotype (= Lochriea commutata [Branson and Mehl, 1941] [Branson and Mehl, 1941b]) in ?inner view. See element 17P₂^?d (Fig. 1.1, 1.2) for apparatus context of this element. Heath Formation, locality 2, Montana, USA, UI X-1318. (6) P₂ element in ?inner view, posterior tip broken and not present. See element 6P₂ (lower Fig. 2.5) for apparatus context. Sample H-A-2-7-1, Heath Formation, locality 2, Montana, USA, ISGS 62P-218A. (7) P₂^?d element, ?inner view. Heath Formation, locality 1, Montana, USA, CM 33965. (8) P₂^s,d element pair in approximate functional apposition in lateral view along rostrocaudal axis of nearly complete sinistral side of a fused apparatus (see Figs. 5.4, 7.7 for other views of this element pair in this apparatus). USGS collection 34004-PC, Bluestone Formation, locality 8, West Virginia, USA, USNM-593967. (9–16) P₂ elements, ?outer lateral views of two ontogenetic growth series (9–12) and (13–16) from smallest to largest. USGS collection 34004-PC, Bluestone Formation, locality 8, West Virginia, USA, USNM 593929–593936. Lengths = 0.28, 0.54, 0.60, 0.70, 0.45, 0.45, 0.53, and 0.55 mm, respectively. (17) P₂^s,d element pair fused in functional apposition, lateral view. USGS collection 34004-PC, Bluestone Formation, locality 8, West Virginia, USA, USNM 593968. (18) P₂^d element, inner view. Sample H-B-1-A, Tyler Formation, locality 3, Montana, USA, ISGS 62P-1102. Length = 0.50 mm. (19–22) P₂^s elements, inner views. Samples VS-12, VS-5, VS-1, and VS-5, Ridenhower Formation, locality 7, Illinois, USA, ISGS 62P-1117, 62P-1205, 62P-1116, and 62P-1206. Lengths = 0.47, 0.52, 0.44, and 0.61 mm, respectively. (23) P₂^d element, inner view. Sample HerbR-7-7, Herbert River Limestone, Upper Windsor Group, locality 9, Nova Scotia, Canada, ROM 63700. Length = 0.73 mm.

Scanning electron microscopy of the bedding-plane assemblage designated by Scott (1942) as the holotype of L. bigsnowyensis demonstrates (Fig. 10) that it contains one or more carminiscaphate P₁ elements, as well as P_2, M and S elements (Fig. 10) similar or identical to those present in apparatuses of Cavusgnathus spp. (von Bitter and Merrill, 1990, fig. 1B–D; Purnell and Donohue, 1998, text-fig. 15). The bedding-plane assemblage Scott (1942, p. 299) designated as the paratype, but did not illustrate, has been lost. We place the discrete L. bigsnowyensis prioniod element of Scott (1942, pl. 40, fig. 3) in synonymy with the L. commutata M element. The prioniodell elements illustrated by Scott (1942, pl. 40, figs. 4 and 5) may be L. commutata P₂ elements.

We conclude that L. bigsnowyensis was based primarily on a partial bedding-plane assemblage of an as yet unidentified species of Lewistownella Scott, 1942, which in turn is a junior synonym of an as yet unidentified species of Cavusgnathus Harris and Hollingsworth, 1933. Lochriea bigsnowyensis was also, but to a minor degree, based on a misidentified discrete M element that we place in L. commutata and on two P₂ elements that may have belonged to L. commutata.

Element composition of the Lochriea commutata apparatus

Scott (1942, p. 298, fig.1) concluded that the Lochriea montanaensis apparatus bore a minimum of 22 elements, comprising at least four each of “spathognaths,” “prioniodells,” and “prioniods,” and at least ten “hindeodells” (Fig. 11.1, 11.2), an element terminology that translates into four each of carminiscaphate, angulate_, and makellate elements, as well as ten bipennate elements, respectively (Fig. 11.1, 11.2).

Thirty-one years later, Melton and Scott (1973) named newly discovered fossils of a soft-bodied, cigar-shaped animal, Lochriea wellsi, because of conodont elements they recognized as those of a species of Lochriea, in the “deltaenteron,” or midgut, of the animal. Melton and Scott (1973) referred to these elements as “spathognathodids,” “prioniodinids/ozarkodinids,” “neoprioniodids,” and “hindeodellids” (Fig. 11.2). Scott (1973) in discussing this species, identified the “spathognathodids” as “a platform type” and suggested a possible ratio of the four element types present as 3:1:3:10 (Fig. 11.2), but admitted that the exact number of each was questionable. The species was subsequently assigned to a new genus by Conway Morris (1985), and was interpreted, as Typhloesus wellsi (Melton and Scott), to be a conodontophage (i.e., a conodont-eater) (Conway Morris, 1985, 1990), an interpretation supported by Sweet (1988) and by us. Reasons for our support for this conclusion are that: (1) elements of other conodont taxa, including those of Kladognathus Rexroad, 1958, have been found inside T. wellsi (Conway Morris, 1990; Purnell, 1993a); (2) elements of Lochriea observed and reported in T. wellsi are disorganized and jumbled; and (3) there is, notwithstanding the orderliness of the Kladognathus assemblage described by Purnell (1993a), a general uncertainty and inconsistency regarding the number and identity of Lochriea elements in T. wellsi. We conclude that the identity and apparatus composition of the species of Lochriea present in the gut of T. wellsi has yet to be determined and is presently of no help in elucidating the apparatus structure of L. commutata, or that of the genus Lochriea.

Scott (1942, p. 293) wrote that the bedding-plane assemblages he was studying “did not represent accidental accumulations or coprolite material.” Nevertheless, most of the elements in his illustrated bedding-plane assemblages show a definite lack of orientation and are best described as chaotic. The single exception (Scott, 1942, pl. 38, fig. 10; vide UI X-1385) is a symmetrical bundle of eight “hindeodells” (= S elements) with “four oriented with the denticles to the left and four to the right,” that he identified (p. 295) as L. montanaensis. This partial S-element assemblage may have been the one of the important clues, along with the presence of sinistral and dextral elements, that Scott (1942, fig. 1) used to arrive at his schematic diagram (Fig. 11.1) (although he did not specifically state that his assemblages represented bilaterally symmetrical apparatuses within the conodont animal, his diagram certainly implies that). Norby (1976) described Scott's apparatuses of Lochriea as having “a scattered arrangement,” and he regarded all but this single specimen as fecal. Proof that Scott's Lochriea assemblages were indeed fecal was provided by the numerous additional assemblages of L. commutata collected by Norby (1976) and the single bedding-plane assemblage collected by R. Lund in the Heath Formation of Montana, Scott's original collecting unit, as well those found by Norby (1976) in the overlying Tyler Formation. The best of Norby's bedding-plane assemblages are natural assemblages in which the elements show good parallel arrangement and pairing (Fig. 2).

Figure 5.

Lochriea commutata (Branson and Mehl, 1941) (Branson and Mehl, 1941b) M elements in bedding-plane assemblages (1–3), in acid residue-derived fused assemblages (4, 5), and as acid residue-derived discrete elements (6–22). Scale bars (1–5) = 0.2 mm. For the remaining specimens, actual lengths from cusp tip to anticusp are provided in descriptions below. (1) M^d element in Lochriea montanaensis Scott, 1942 holotype (= Lochriea commutata [Branson and Mehl, 1941] [Branson and Mehl, 1941b]) in outer (dorsal) view. See element 18M^d (Fig. 1.1, 1.2) for apparatus context. Heath Formation, locality 2, Montana, USA, UI X-1318. (2) M^d element imprint in outer view. See element 15M^d (Fig. 2.1B) for apparatus context. Sample H-B-1-B, Tyler Formation, locality 3, Montana, USA, ISGS 62P-207A. (3) M^s element in inner view, Heath Formation, locality 1, Montana, USA, CM 33965. (4) M^s,d elements in outer view of sinistral side of moderately complete apparatus (see Figs. 4.8, 7.7 for other views of this apparatus and element pair). USGS collection 34004-PC, Bluestone Formation, locality 8, West Virginia, USA, USNM 593967. (5) M^d element in outer view of moderately complete S–M element array (see Fig. 6.6, 6.7 for other views of this apparatus). USGS collection 34004-PC, Bluestone Formation, locality 8, West Virginia, USA, USNM 593969. (6–9) M^s elements, inner views of well-preserved ontogenetic growth series. USGS collection 34004-PC, Bluestone Formation, locality 8, West Virginia, USA, USNM 593937–593940. Cusp tip to anticusp = 0.69, 0.85, 0.81, and 0.57 mm, respectively. (10–13) M^d elements, inner views of well-preserved ontogenetic growth series. USGS collection 34004-PC, Bluestone Formation, locality 8, West Virginia, USNM 593941–593944. Cusp tip to anticusp = 0.49, 0.84, 0.76, and 0.76 mm, respectively. (14) M^d element, inner view. Sample Schälk 50, Herdringen Formation, locality 10, North-Rhine Westphalia, Germany, ISGS 82P-45. Cusp tip to anticusp = 0.43 mm. (15) M^s element, inner view. Sample 2, Fayetteville Formation, locality 5, Craig Co., Oklahoma, USA, ISGS 82P-46. Cusp tip to anticusp = 0.23 mm. (16, 17) M^s elements, inner views, showing crystal overgrowths and surface etching. Sample Kenk-2-1, Kennetcook Member, Upper Windsor Group, locality 9, Colchester Co., Nova Scotia, Canada, ROM 63701 and 63702, respectively. Cusp tip to anticusp = 0.44 and 0.49 mm, respectively. (18) M^s element, inner view. Sample Schälk 50, Herdringen Formation, locality 10, North-Rhine Westphalia, Germany, ISGS 82P-47. Cusp tip to anticusp = 0.82 mm. (19, 20) M^d elements, inner views. Sample H-B-1-A, Tyler Formation, locality 3, Montana, USA, ISGS 62P-1112 and 62P-1113, respectively. Cusp tip to anticusp = 0.43 and 0.65 mm, respectively. (21, 22) M^d elements, inner view. Samples VS-12 and VS-7, Ridenhower Formation, locality 7, Illinois, USA, ISGS 62P-1111 and 62P-1207, respectively. Cusp tip to anticusp = 0.37 and 0.84 mm, respectively.

Figure 12 illustrates a two-dimensional exploded diagrammatic view of the relative position and arrangement of elements in the three-dimensional functional feeding apparatus of L. commutata. Aldridge et al. (1987) and Purnell and Donoghue (1997, 1998, text-fig. 1) proposed and reviewed possible three-dimensional arrangements of elements within the functioning ozarkodinid conodont apparatus, with Purnell and Donoghue (1998) concluding that their text-figure 1E best explained the position, arrangement, and functional morphology of elements in that apparatus.

Scott (1942, p. 299) recognized that the Lochriea montanaensis apparatus contained “at least ten hindeodells” (Fig. 11). This bundle of mostly parallel, elongated ramiform elements intergrade morphologically, and are characteristic of ozarkodinid conodont apparatuses (Aldridge et al., 1987; Sweet, 1988). Functionally, this group of elements was regarded by Hitchings and Ramsay (1978) to have served as a sieve basket, but was subsequently interpreted to have had a raptorial grasping function (Purnell, 1993b; Purnell and Donoghue, 1997). Norby (1976), using newly collected L. commutatus (= L. commutata) bedding-plane assemblages, recognized three distinct element types in Scott's “ten hindeodells,” one A₃ (= S₀), two A_1c (= S₁), and six A₁ (= S_2/3/4) elements (Fig. 11.2); he did not differentiate an S₂ element.

As well as differentiating three types of A (= S) elements in the newly collected bedding-plane assemblages of L. commutatus (= L. commutata), Norby (1976) also determined that the L. commutatus (= L. commutata) apparatus was composed of 15 elements, consisting of pairs of P (= P₁), O (= P₂), and N (= M) elements, as well as nine A (= S) elements. This conclusion was supported by Aldridge (1987) and Aldridge et al. (1987) when they determined that conodont apparatuses of the Polygnathacea Bassler, 1925, which includes Lochriea commutata, were composed of 15 elements. Each apparatus contained pairs of Pa (= P₁), Pb (= P₂), M, Sb, and Sd elements, two pairs of Sc elements, as well as an unpaired Sa (= S₀) element, which is an element plan that Purnell et al. (2000) determined to be plesiomorphic for complex conodonts. Purnell and Donoghue (1998) illustrated and described a bedding-plane assemblage of an unidentified species of Lochriea from the Namurian of Germany, the part and counterpart of which we re-illustrate in Figure 13.1 and 13.2, respectively. We also re-illustrate a camera lucida drawing of the same specimen (Fig. 14.1), first published by Purnell and Donoghue (1998), and subsequently amended by them to reflect topological element notation of Purnell et al. (2000). The three-dimensional apparatus architecture of the German Lochriea sp. specimen was illustrated by Purnell and Donoghue (1998, p. 76, figs. 11A, B) by juxtaposing a line drawing of Lochriea sp. with a photograph of a model of the apparatus architecture of another polygnathacaean, identified by M. Purnell (personal communication, 2019) as being Idiognathodus, both here re-illustrated as Figure 141 and 14.2., respectively.

Our identification of 18 and 23 elements in the holotype and paratype, respectively, of Lochriea montanaensis Scott, 1942 (Fig. 1; Table 1) is clearly at odds with the apparatus composition of Lochriea spp. as determined by Norby (1976), von Bitter and Norby (1998a, b), and Purnell and Donoghue (1998). The anomalously high numbers of elements in the two assemblage specimens chosen by Scott (1942) as the primary types of Lochriea montanaensis, the presence of three and four each of the P₁, P₂, and M elements, and the anomalously high number of each of S_3/4 and S elements in the holotype and paratype, respectively (Table 1), all suggest that the primary types consist of the elements of more than one individual. This, as well as their disorganized state (Fig. 1), suggests that both specimens are fecal composites, a conclusion at odds with those of Scott (1942, p. 293), who thought that the bedding-plane assemblages he was studying were not fecal, or accidental accumulations.

Figure 6.

Lochriea commutata (Branson and Mehl, 1941) (Branson and Mehl, 1941b) S₀ elements in bedding-plane assemblages (1, 2), as acid residue-derived discrete elements (3–5, 11–14), and in acid residue-derived fused assemblages (6–10). Scale bars (1, 2, 7–10) = 0.2 mm. For the remaining specimens, actual lengths are provided in descriptions below. (1) S₀ element, anterior view of anterolateral processes, with triangular bevel at base of cusp. Sample H-A-2-7-1, Heath Formation (not Tyler Formation as per Norby, 1976, pl. 11, fig. 15a), locality 2, Montana, USA, ISGS 62P-1103. (2) S₀ element, lateral dextral view of cusp and broken stubs of posterior and dextral anterolateral processes. See element 11S₀ (Fig. 2.1B) for the apparatus context of this element. Sample H-B-1-B, Tyler Formation, locality 3, Montana, USA, ISGS 62P-207A. (3–5) S₀ elements, lateral sinistral views of an ontogenetic series showing a rarely preserved, long posterior process, and shorter sinistral and dextral anterolateral processes. USGS collection 34004-PC, Bluestone Formation, locality 8, West Virginia, USA, USNM 593945–593947. Horizontal lengths = 0.65, 0.55, and 0.50 mm, respectively. (6–10) S₀ elements, USGS collection 34004-PC, Bluestone Formation, locality 8, West Virginia, USA. (6, 7) S₀ element in moderately complete sinistral and dextral fused S_0-4 element array, lateral sinistral and dorsal views, respectively (see Fig. 5.5 for another view of this fused assemblage and of its S₀ element), USNM 593969. (8, 9) S₀ element with short symmetrical anterolateral processes and long posterior process in fused S element array, oblique dextroventral and ventral views, respectively, of the mostly sinistral side of the rostral apparatus, USNM 593970. (10) S₀ element with short symmetrical anterolateral processes and long posterior process in fused S element array, ventral view. Arcuate indentation in upper left is the outline of the scanning electron microscopy mounting medium. USNM 593971. (11) S₀ element, dextral view of broken anterolateral lateral and posterior processes, sample H-B-1-A, Tyler Formation, locality 3, Montana, USA, ISGS 62P-1104. Horizontal length = 0.51 mm. (12) S₀ element, sinistral view of broken anterolateral and posterior processes. Sample 5, Fayetteville Formation, locality 5, Oklahoma, USA, ISGS 82P-48. Horizontal length = 0.16 mm. (13) S₀ element, posterior view of symmetrical anterolateral processes and central stub of broken posterior process. Sample Schälk 50, Herdringen Formation, locality 10, North-Rhine Westphalia, Germany, ISGS 82P-49. Vertical height = 0.35 mm. (14) S₀ element, sinistral view of broken anterolateral process and moderately complete, but relatively short posterior process. Sample VS-4, Ridenhower Formation, locality 7, Illinois, USA, ISGS 62P-1208. Horizontal length = 0.46 mm.

The best preserved eight bedding-plane assemblages of Lochriea commutata collected by Norby (1976), and presented here, show a maximum of 15 elements (Fig. 2; Table 1). The presence of two each of the P₁, P₂, and M elements in all but two of the eight specimens, are in agreement with the number of these elements that other authors, including Norby (1976), Aldridge (1987), Aldridge et al. (1987), and Purnell and Donoghue (1997, 1998), concluded were present in ozarkodinid conodont apparatuses. Remarkably, the rarely identified S₀ element, even though not identified in the type specimens of Lochriea montanaensis, was recognized in three and possibly an additional two of the apparatuses of Lochriea commutata (Table 1). The presence of only a single M element in ISGS 62P-210 and possibly 62P-211 (Table 1) is likely due to either preservational factors, or to our inability to recognize this element. Similarly, we attribute the underrepresentation of one or more of the categories of S₁, S₂, and S_3/4 elements in these eight specimens (Table 1) to the same preservational and human factors, a reality that forced us to place anomalously large numbers of elements into the more generalized and less specific category of S elements (Table 1). The more balanced element maximum of up to 15 elements in the eight assemblages (Table 1) and their less disturbed distribution suggest that they are ‘natural’ bedding-plane assemblages.

That the type species of Lochriea, L. commutata, possessed a food processing apparatus of 15 elements (Norby 1976; von Bitter and Norby, 1998a, b) (Figs. 11.2, 12; Table 1) has provided, and continues to provide, an element blueprint for the apparatus of other Lochriea species. That reconstruction was supported and strengthened when Purnell and Donoghue (1998) documented the element composition of a well-preserved, but unidentified, species of Lochriea from the Namurian of Germany—a bedding-plane assemblage that, in an outline drawing updated by Purnell and Donoghue (personal communication, 2019), shows paired P₁, P₂, S₁, S₂, S₃, and S₄ elements, as well as a single M element (a second M element was either not preserved, or was covered by other elements), and an S₀ element (Figs. 13.1, 13.2, 14.1).

The availability of an apparatus element blueprint for the type species Lochriea commutata resulted in others beginning to reconstruct the apparatuses of species of Lochriea, using a variety of approaches. The simplest approach was perhaps that of Stone (1991), who, using discrete collections, reconstructed a partial L. commutata apparatus by identifying its Pa (= P₁), Pb (= P₂), M, and Sc₁ (= S_3/4) elements, based on criteria presented by Norby (1976). Another more complicated approach was that of Horowitz and Rexroad (1982), Varker (1994), and Nemyrovska et al. (2006), who assumed that one or more species of Lochriea, while distinguished by their Pa (= P₁) elements, each bore morphologically identical non-platform elements in their apparatuses. Thus Horowitz and Rexroad (1982), in reconstructing a partial apparatus of L. commutata from discrete faunas, assumed (text-fig. 10) that L. mononodosa bore the ‘same’ (i.e., morphologically identical) Pb (= P₂), M, and Sc (= S_3/4) elements as L. commutata, doing so despite the fact that the rare L. mononodosa Pa (= P₁) element was grouped in their cluster analysis in the middle of mostly elements of Idioprioniodus healdi (Roundy, 1926) (Horowitz and Rexroad, 1982, text-fig. 3). Similarly, Varker (1994, p. 310) studying discrete elements and fused clusters, regarded L. commutata, L. mononodosa, and L. nodosa to “share” the same non-Pa elements (i.e., he interpreted the apparatuses of each of the three species to each have borne morphologically identical Pb [= P₂], M, Sa [= S₀], and Sc [= S_3/4] elements). Finally, Nemyrovska et al. (2006) concluded that the P₂, M, and S elements of three species of Lochriea (L. commutata, L. cracoviensis, and L. saharae) were morphologically the same.

Assumptions of sharing non-platform elements in apparatuses of Lochriea spp., while possibly true, remain unproven, and there has been little success in reconstructing the apparatuses of Lochriea species, other than L. commutata (see Skompski et al., [1995] for a key to the up to 10 species of Lochriea, and to which additional species, such as L. saharae have since been added). The major reason for that lack of success is the relative rarity of bedding-plane assemblages and fused clusters of Lochriea spp., and that the reconstruction of conodont apparatuses from discrete collections is largely dependent on the availability of conodont faunas that are composed, if not of the elements of a single conodont species, then of the elements of several species, the components of which can readily be disentangled and identified.

The sole exception to our generalization that there have been few successful attempts to reconstruct the apparatuses of species other than that of L. commutata, involved five samples studied by Atakul-Özdemir et al. (2012, p. 1281) that contained “P₁ elements of L. homopunctatus along with morphologically distinctive P₂, M and S elements that could not be assigned to any of the 11 other co-occurring species.” These authors, in reconstructing most of the apparatus of L. homopunctatus, also concluded that the characteristics of P₂, M, and S elements may be as, or more, important in determining and defining Lochriea spp. than those of the traditionally used P₁ elements. We concur and contend that the current practice of assigning species to Lochriea almost entirely on the basis of ornamented or unornamented P₁ elements leaves those assignments in doubt, at least until the rest of their apparatuses are determined, and found to be similar to that of the type species. Relying solely on P₁ elements to carry the taxonomy ignores important taxonomic and phylogenetic information that almost certainly resides in the other elements of their apparatuses. Of interest in this context, and a step forward, was the interpretation by Atakul-Özdemir et al. (2012) of an M element, illustrated by Nemyrovska et al. (2006) from a sample from Algeria containing P₁ elements of only a single Lochriea species, L. saharae, as the M element of that species.

Figure 7.

Lochriea commutata (Branson and Mehl, 1941) (Branson and Mehl, 1941b) S₁ elements in bedding-plane assemblages (1–4), in acid residue-derived fused assemblages (5–8), and as acid residue-derived discrete elements (9–18). Scale bars (1–8) = 0.2 mm. For the remaining specimens, actual lengths are provided in descriptions below. (1, 2) S₁^s element with long posterior process in outer lateral view (1, right), and broken-off anterior process in outer lateral view (1, left, and 2). Sample H-A-2-2, Heath Formation, locality 2, Montana, USA, ISGS 62P-1114. (3) S₁^s element in outer lateral view, with an unidentified S element, a remnant of a possible M element crossing the posterior process and a possible P₂ element in upper left. See element 5S₁^s (bottom of Fig. 2.5) for apparatus context of this element. Sample H-A-2-7-1, Heath Formation, locality 2, Montana, USA, ISGS 62P-218A. (4) S₁^d element stub in inner lateral view. See element 11S₁^d (upper Fig. 2.5) for apparatus context of this element. Sample H-A-2-7-1, Heath Formation, locality 2, Montana, USA, ISGS 62P-218B. (5–8) S₁ elements in fused assemblages. USGS collection 34004-PC, Bluestone Formation, locality 8, West Virginia, USA. (5, 6) S₁^d,s element pair in upper and lateral sinistral views, respectively; (6) is rotated around the rostrocaudal axis ∼90° from (5), USNM 593972. (7) S₁^s,d element pair in lower (ventral) view in moderately complete fused apparatus (see Figs. 4.8, 5.4 for other views of this element pair and of this fused cluster), USNM 593967. (8) S₁^s element in lower (ventral) view with its posterior process fused in functional position against posterior process of S₂^s element. Partially complete but disrupted apparatus, USNM 593973. (9–18) S₁ elements, acid residue-derived discrete elements. USGS collection 34004-PC, Bluestone Formation, location 8, West Virginia, USA. (9–11) S₁^s element in inner views (9, 10) and in upper view (11), USNM 593948. Length = 1.18 mm. (12) S₁^s element in upper view, USNM 593949. Length = 0.76 mm. (13, 14) S₁^d element in inner views, USNM 593950. Length = 0.90 mm. (15–18) S₁^d element tilted to varying degrees in inner views (15–17) and in upper view (18), USNM 593951. Length = 0.93 mm.

Materials and methods

We studied three kinds of conodont fossils, the first, and the most commonly recovered, being individual discrete elements that collectively functioned in the feeding apparatuses of conodonts. Isolated discrete elements were recovered from carbonates or carbonate-rich sediments by standard acid digestion techniques, using either dilute acetic or formic acid (Collinson, 1963, 1965; Stone, 1987) and from organic-rich black shales using a sodium hypochlorite and sodium hydroxide solution (Norby, 1976; Duffield and Warshauer, 1979; Stone, 1987) and Stoddard Solvent, a kerosene-derivative, used to process soft clay-rich shales (Collinson, 1963, 1965; Norby, 1976). Gentle boiling in water with Quaternary O, a deflocculating agent, was used for all shales and some carbonates (Norby, 1976; Duffield and Warshauer, 1979; Stone, 1987). Discrete elements were concentrated using heavy liquids such as tetrabromoethane (Collinson, 1963, 1965; Stone, 1987), then the heavy fractions, occasionally magnetically separated, were subsequently hand-picked for conodont elements using binocular microscopes.

The second, much less common material collected and studied, are bedding-plane assemblages, most commonly preserved on black shale surfaces as groups of conodont elements preserved in close proximity to one another, that are either classified as fecal assemblages, or as natural assemblages, depending on whether or not they had been ingested and gone through the gut of a conodontophage. In rare situations, a conodont assemblage inside the body of a conodontophage is both sufficiently well preserved, and retains enough of its original structure, to be classified as a natural assemblage, one such example being the apparatus of the conodont Kladognathus Rexroad, 1958, in the midgut of the conodontophage Typhloesus wellsi (Melton and Scott, 1973), and another is the apparatus of the conodont Bispathodus Müller, 1962 in the gut of a Devonian shark (Purnell and Donoghue, 1998).

In this study, bedding-plane assemblages were recovered by hand splitting organic-rich black fissile shales with a thin sharp knife or a cleaver, and then using the naked eye and a hand-lens or a low-powered microscope to locate them; the latter procedure was best accomplished by taking advantage of the reflectivity of the conodont elements in the sun in the field, or of artificial light in the laboratory. The most useful natural assemblages were, and are, those that had not been disturbed, or had only been minimally disturbed, by sedimentologic, taphonomic, or biologic processes, and that preserved important information regarding the number, morphological types, and arrangement of conodont elements in the feeding apparatus of conodonts. Conversely, feeding apparatuses that had been ingested, digested, and excreted, generally preserved a minimum of such information.

The third, and the rarest kind of conodont material studied, were fused clusters, which, depending on their history and on their preservation, may be considered more three-dimensional categories of bedding-plane assemblages, also theoretically being divisible into both ‘natural’ and ‘fecal’ categories. In fused clusters, typically just the elongated bipennate elements are compacted and fused together, and are preserved in their original relative position and orientation within the feeding apparatus. The fused clusters of Lochriea commutata recovered and studied by us are only the second reported occurrence, after Varker (1994), of fused clusters of Lochriea spp. The fused clusters were recovered from carbonate concretions by the standard acid digestion and heavy liquid techniques described above.

Our examination of Scott's (1942) Lochriea montanaensis bedding-plane assemblages suggests that although some represent the feeding apparatus of a single individual and provide information regarding the element composition of the L. commutata feeding apparatus, all appear to be of fecal origin (Fig. 1; Table 1). In contrast, we subjectively categorize the 34 bedding-plane assemblages of L. commutatus (= L. commutata) collected by Norby (1976) from the Heath Formation of Montana, as three natural, two ?natural, 23 fecal, and six ?fecal. Similarly, of the 81 assemblages collected by Norby (1976) from the Tyler Formation of Montana, we categorize five as natural, 29 as ?natural, 19 as fecal, and 28 as ?fecal. Several of the Montana natural assemblages of L. commutata are shown on Figure 2. Those considered natural consist of up to 15 elements, although some elements may be hidden beneath other elements. Natural assemblages typically exhibit a recognizable recurring pattern of element positions; however, element positions may be disrupted by postmortem changes. Those assemblages termed ?natural are probably natural, but show varying degrees of element disturbance; these two categories provide the most useful information regarding original element composition and position. Fecal assemblages are associations of two or more elements, but typically of 15 or more elements of varying maturities, sometimes including elements belonging to different conodont species, that are jumbled, show no discernible element pattern, and occur with black bituminous material. Assemblages termed ?fecal are most likely fecal, however, they typically may represent one, or sometimes two or more relatively complete individuals, that show moderate to significant disruption. They occasionally provide information regarding element composition and position in an apparatus. Conodonts in the fecal and ?fecal categories were either regurgitated, excreted, or even brought together by bottom currents.

Figure 8.

Lochriea commutata (Branson and Mehl, 1941) (Branson and Mehl, 1941b) S₂ elements in bedding-plane assemblages (1–4), as acid residue-derived discrete elements (5–11), and in an acid residue-derived fused assemblage (12). Scale bars (1–4, 12) = 0.2 mm. For the remaining specimens, actual lengths are provided in descriptions below. (1, 2) ?S₂^d element in inner lateral view of anterior end of part and counterpart, respectively. See element 10?S₂^d (lower and upper Fig. 2.5, respectively), for apparatus context of this element. Sample H-A-2-7-1, Heath Formation, locality 2, Montana, USA, ISGS 62P-218A and 62P-218B. (3) ?S₂^s element in inner view; see element 9?S₂^s (lower Fig. 2.5) for apparatus context of this element. Sample H-A-2-7-1, Heath Formation, locality 2, Montana, USA, ISGS 62P-218A. (4) ?S₂^d element, Lochriea montanaensis Scott, holotype (= Lochriea commutata [Branson and Mehl, 1941] [Branson and Mehl, 1941b]) in outer view of anterior end; see element 6?S₂^d (Fig. 1.1, 1.2) for apparatus context of this element. Heath Formation, locality 2, Montana, USA, UI X-1318. (5–11) S₂^s elements (5–7) and S₂^d elements (8–11) in inner views of two partial ontogenetic series. USGS collection 34004-PC, Bluestone Formation, locality 8, West Virginia, USA, USNM 593952–593958. Lengths = 1.13, 1.01, 0.86, 1.05, 1.02, 0.74, and 0.76 mm, respectively. (12) S₂^d element in inner view, fused against the inner surface of an S₃^d element, which is, in turn, fused against the inner surface of an S₄^d element. USGS collection 34004-PC, Bluestone Formation, locality 8, West Virginia, USA, USNM 593974.

Figure 9.

Lochriea commutata (Branson and Mehl, 1941) (Branson and Mehl, 1941b) S_3/4 elements in bedding-plane assemblages on shale surfaces (1–5), as acid residue-derived discrete elements (6–10, 12–20), and in acid residue-derived fused assemblages (11, 21). Scale bars (1–5, 21) = 0.2 mm. For the remaining specimens, actual lengths are provided in descriptions below. (1, 5) S₃^s and S₄^s element pair in inner views of part and counterpart, respectively. S₃^s element closest to viewer lacks most of posterior process, whereas S₄^s element behind S₃^s element is only an impression; see elements 7S₄^s and 8S₃^s (Fig. 2.5) for apparatus context of this element pair; sample H-A-2-7-1, Heath Formation, locality 2, Montana, USA, ISGS 62P-218A and 62P-218B. (2) S_3/4^d element, Lochriea montanaensis Scott, paratype (= Lochriea commutata [Branson and Mehl, 1941] [Branson and Mehl, 1941b]) in outer lateral view of anterior end; see element 1S_3/4^d (Fig. 1.3, 1.4) for apparatus context of this element. Heath Formation, locality 2, Montana, USA, UI X-1319. (3, 4) S_3/4^d element in outer view in S element array. Anterior end of S_3/4^d element in upper right, posterior end in lower left of (3); close-up of anterior end of S_3/4^d element in (4) (see element 12S_3/4^d in Fig. 2.1B for apparatus context of this and associated elements 11S₀ and 13?S₁^s). Sample H-B-1-B, Tyler Formation, locality 3, Montana, USA, ISGS 62P-207A. (6–10) S_3/4^s elements in inner lateral views, forming a partial ontogenetic growth series. USGS collection 34004-PC, Bluestone Formation, locality 8, West Virginia, USA, USNM 593959–593961, 696951, 593962. Lengths = 1.44, 1.45, 1.21, 1.28, and 0.49 mm, respectively. (11) S₃^d and S₄^d element pair in inner view in partial fused assemblage; outer surface of S₃^d element fused in functional position against inner surface of S₄^d element (see Fig. 8.12 for an almost identical S₃^d and S₄^d element pair, except for the additional presence of an S₂^d element). USGS collection 34004-PC, Bluestone Formation, locality 8, West Virginia, USA, USNM 696952. Length = 1.16 mm. (12–14) S_3/4^d elements in inner views, that together with USNM 696952 (11) form a partial ontogenetic growth series. USGS collection 34004-PC, Bluestone Formation, locality 8, West Virginia, USA, USNM 593963–593965. Lengths = 1.31, 1.00, and 0.45 mm, respectively. (15–20) S_3/4 elements in inner views of anterior ends. (15) S_3/4^s element. Sample H-B-1-A, Tyler Formation, locality 3, Montana, USA, ISGS 62P-1109. Length = 0.48 mm. (16) S_3/4^d element. Sample H-B-1-A, Tyler Formation, locality 3, Montana, USA, ISGS 62P-1107. Length = 0.29 mm. (17) S_3/4^s element. Sample 5, Fayetteville Formation, locality 5, Afton, Oklahoma, USA, ISGS 82P-50. Height = 0.21 mm. (18) S_3/4^s element. Sample 5, Fayetteville Formation, locality 5, Afton, Oklahoma, USA, ISGS 82P-51. Height = 0.24 mm. (19) S_3/4^s element. Sample Schälk 50, Herdringen Formation, locality 10, North-Rhine Westphalia, Germany, ISGS 82P-52. Height = 0.25 mm. (20) S_3/4^s element. Sample VS-7, Ridenhower Formation, locality 7, Illinois, USA, ISGS 62P-1209. Length = 0.38 mm. (21) S_3/4^s pair in ?upper (?dorsal) view of partial S element array (see Fig. 3.35 for another view of this fused cluster). USGS collection 34004-PC, Bluestone Formation, locality 8, West Virginia, USNM 593966.

We list the material studied by locality in the section that follows. Abbreviations for the institutions at which specimens are reposited are provided at the end of the section, and locality data are provided in the Appendix.

Figure 10.

Lochriea bigsnowyensis Scott, 1942, holotype (= an undetermined species of Cavusgnathus Harris and Hollingsworth, 1933), illustrated by Scott (1942, pl. 38, fig. 8); paratype UI X-1321 lost. No counterpart known. Scanning electron micrographs of bedding-plane assemblage on black shale, with interpretation of conodont elements present. All elements, notably the P₁^d element (9P₁^d), are characteristic of species of Cavusgnathus Harris and Hollingsworth, 1933. Heath Formation, locality 2, Montana, USA, UI X-1320. Scale bars = 0.5 mm. (1) Fecal assemblage of 14 elements numbered clockwise commencing in upper right. (2) The carminiscaphate P₁^d element and parts of associated M and S elements. (3) M and S elements below P₁^d element.

Figure 11.

(1) Twenty-two (22⁺) element apparatus reconstructions of Lochriea montanaensis Scott, a subjective junior synonym of L. commutata (Branson and Mehl, 1941) (Branson and Mehl, 1941b); after Scott (1942) and labeled with his terminology for the four element types recognized by him; shape categories used (in parentheses) are those of Sweet (1981, 1988). (2) Interpretations of the apparatus composition of Lochriea spp. since 1942, based on bedding-plane assemblages. Lochriea wellsi was named for a conodontophage containing elements of species of Lochriea and other conodont taxa in its gut. The identity of Lochriea sp. of Purnell and Donoghue (1998) is indeterminate, and the reconstruction of L. homopunctatus (Ziegler, 1960) by Atakul-Özdemir et al. (2012), based on discrete elements, is not included.

Figure 12.

The 15 element apparatus of Lochriea commutata (Branson and Mehl, 1941) (Branson and Mehl, 1941b) in exploded view using the topological element notation of Purnell et al. (2000; cf., their fig. 3). This two-dimensional diagrammatic representation of the three-dimensional apparatus shows the apparatus in dorsal view, but does not show the downward (ventrally) sloping anterior (rostral) ends of the S elements or the vertical (dorsoventral) orientation of the P element pairs, whose anterior ends point downward (ventrally). Morphologically, P₁ elements are carminiscaphate, P₂ elements are angulate, M elements are makellate, the S₀ element is alate, and S₁–S₄ elements are bipennate with three different morphologic types.

Notes on conodont element notation.—Lochriea commutata Scott, 1942, Lochriea sp. of Purnell and Donoghue (1998), and Lochriea bigsnowyensis Scott, 1942, the latter here re-assigned to Cavusgnathus Harris and Hollingsworth, 1933, possessed 15-element apparatuses of paired P₁, P₂, M, S₁, S₂, S₃, and S₄ elements, and an unpaired S₀ element. Many of the illustrated elements of these taxa have a superscript notation d, ?d, s, or ?s after the element type, indicating whether that element was positioned on the right (dextral) or the left (sinistral) side of the plane of bilateral symmetry of the skeletal apparatus (Sweet, 1981), with the question mark indicating uncertainty (e.g., a P₂^d element is a dextral P₂ angulate element positioned on the right side of the feeding apparatus, and a S₂^?s element is a questionable sinistral S₂ bipennate element on the left side of the apparatus).

Figure 13.

Lochriea sp. bedding-plane assemblage, counterpart (1) and part (2), as designated by Purnell and Donoghue (1998, pl. 2). Lüsenberg Formation, locality 11, North-Rhine Westphalia, Germany, IMGP Gö 600-36. From the collection of Schmidt and Müller (1964); after Purnell and Donoghue (1998, pl. 2), and reproduced with permission of the Palaeontological Association. Scale bars = 1 mm.

Repositories and institutional abbreviations.—Specimens examined in this study are deposited in the following institutions: Carnegie Museum of Natural History (CM), Pittsburg, Pennsylvania, USA; University of Göttingen (IMGP Gö), Göttingen, Germany; Illinois State Geological Survey (ISGS), Champaign-Urbana, Illinois, USA; Royal Ontario Museum (ROM), Toronto, Ontario, Canada; State University of Iowa (SUI), Iowa City, Iowa, USA; University of Illinois (UI), Champaign-Urbana, Illinois, USA; University of Missouri (UM), Columbia, Missouri, USA; University of Montana (UM), Missoula, Montana, USA; U.S. Geological Survey (USGS), Reston, Virginia, USA; U.S. National Museum (USNM), Washington, D.C., USA.

Figure 14.

(1) Lochriea sp., bedding-plane assemblage, composite camera lucida drawing of IMGP Gö 600-36 (counterpart) shown in Figure 13.1. After Purnell and Donoghue (1998, text-fig. 11A), and reproduced with permission the Palaeontological Association. Positional element notation shown was modified and provided by M. Purnell subsequent to the publication of Purnell and Donoghue (1998), and is used with their permission. (2) Photograph of a model, identified by M. Purnell (personal communication, 2019) as of Idiognathodus sp., taken from right side and slightly in front to simulate the collapse pattern of Lochriea sp. shown in Figures 13 and 14.1. After Purnell and Donoghue (1998, text-fig. 11B), and reproduced with permission of the Palaeontological Association.

Table 1.

Conodont elements on the holotype and paratype of Lochriea montanaensis Scott, 1942 (= Lochriea commutata [Branson and Mehl, 1941] [Branson and Mehl, 1941b]) from the Heath Formation, and on three and five specimens of Lochriea commutata (Branson and Mehl, 1941) (Branson and Mehl, 1941b) from the Heath and Tyler formations, respectively. All 10 specimens are bedding-plane assemblages from Montana, USA. Underlined element designations (i.e., , etc.) are the number of each those elements identified on that assemblage. The parenthetical designations below them—(2P₁^s, 3?P₁, 11P₁^?d), (4P₂, 13P₂^?s, 17P₂^?d), and so forth—represent the position of that element in that assemblage, as labeled on Figures 1 and 2, followed by our determination of the identity of that element, preceded or followed by question marks indicating the degree of certainty of our identification. An asterisk (*) indicates only the part is present; other conodont elements may have been present on the counterpart.

Systematic paleontology

Discussion

P₁ element (Fig. 3).—Having previously (von Bitter and Norby, 1994a, b) correlated the changes in the width of carinal nodes and their microsculpture fields with an increase in element size, we agree with Rhodes et al. (1969, p. 96) and Metcalfe (1981, p. 21) that the morphology of the Lochriea commutata P₁ element is variable. The length to height ratio typically increases with ontogeny by becoming more elongated (greater length to height), as noted in the lectotype and paralectotypes of the species (von Bitter and Norby, 1994a, figs. 2.6–2.15, 3.1–3.6), but particularly for specimens from the Heath and Tyler formations of Montana (von Bitter and Norby, 1994a, figs. 6, 7), and reaches a maximum length to height ratio in specimens from the Heath Formation (von Bitter and Norby, 1994a, fig. 7).

Blade denticulation of P₁ elements is also variable, with the lectotypes and paralectotypes of the species, for example, not being particularly denticulate (von Bitter and Norby, 1994a, figs. 2, 3), which Branson and Mehl (1941b, p. 98) described as having a tendency “to fuse.” Microsculpture is absent on the denticles of these specimens, with the upper denticle surface being covered by secondary crystal overgrowths (von Bitter and Norby, 1994a, fig. 3.9–3.12). We conclude that Lochriea commutata P₁ elements vary from being relatively short with stubby, commonly fused blade denticles and carinal nodes to more elongate with better-defined blade denticles and carinal nodes (Fig. 3).

Variation in P₁ element morphology has been the most frequently applied criterion for recognizing and defining conodont species. Among Lochriea species with unornamented P₁ elements, recognition of such variation has led to the definition of species such as Spathognathodus pellaensis Youngquist and Miller, 1949, Gnathodus inornatus Hass, 1953, G. commutatus nagatoensis Igo and Koike, 1965 (the latter included by Mizuno, 1997, in Neolochriea), G. scotiaensis Globensky, 1967, and G. simplicatus Rhodes et al., 1969, the latter species recently placed in Pseudognathodus by Sanz-López et al., 2018. Confirmation that these species with unornamented P₁ elements are valid species related, or unrelated, to Lochriea commutata must await monographic and biometric study. Increasingly, it will also be necessary to determine the element composition of their apparatuses to confirm or refute these relationships.

P₂ element (Fig. 4).—We recognize three main morphotypes of Lochriea commutata P₂ elements in North America, two of which appear to intergrade, based on the degree of arching of the posterior process, on the degree of denticle separation or fusion, and on the overall length/height ratio. The first, the montanaensis morphotype, is the classic one illustrated by Scott (1942, pl. 40, figs. 9, 10), and is often found in bedding-plane assemblages from Montana (Fig. 4.1, 4.2, 4.5, 4.7, 4.19, 4.22). It is recognized as possessing a strong upward-arching posterior process and generally distinct denticle separation, particularly on the posterior process.

Some montanaensis morphotype P₂ elements illustrated in the literature are Prioniodina montanaensis (Scott, 1942), Stanley, 1958, p. 474, pl. 64, fig. 5 (lower left specimen), pl. 65, fig. 1; ?Prioniodina sp. A Stanley, 1958, p. 474, pl. 65, fig. 3; Prioniodina sp. B Stanley, 1958, p. 474, pl. 65, fig. 7; ?Prioniodina sp. C Stanley, 1958, p. 474, pl. 65, fig. 2; and ?Ozarkodina deflecta Stanley, 1958, p. 472, pl. 65, figs. 4, 5.

The second, the recta morphotype, is characterized by Ozarkodina recta of Rexroad, (1957, pl. 2, figs. 5, 6) and is recognized by its less-pronounced arching of the posterior process and denticles that tend to be somewhat shorter and fused along part of their length (Fig. ?4.3, 4.21, 4.23). Intergradations between the montanaensis and recta morphotypes are shown in Figure 4.18 and 4.20. Those shown in Figure 4.4 and 4.6 do not fit either of the two end-member morphotypes precisely; however, the specimen illustrated in Figure 4.4 is probably closer to the montanaensis morphotype. Both examples show some downward arching of the tip of the anterior process, which is seen in only a few examples of the recta morphotype (e.g., Fig. 4.22).

Some recta morphotype P₂ elements illustrated in the literature are Ozarkodina recta Rexroad, 1957, p. 36, pl. 2, figs. 5, 6; ? Rexroad and Furnish, 1964, p. 674, pl. 111, fig. 8; Thompson and Goebel, 1969, p. 41, pl. 3, fig. 22; and Ozarkodina cf. O. recta Rexroad, Dunn, 1970, p. 338, pl. 62, figs. 25, 26.

The Bluestone morphotype (Fig. 4.9–4.17), based on P₂ elements from the Bluestone Formation of West Virginia, is recognized as a third morphotype; it is similar to the montanaensis morphotype, but the length/height ratios differentiate the Bluestone and montanaensis morphotypes. The Bluestone morphotype P₂ elements show shorter anterior and posterior processes that possess exceptionally long, non-fused, comb-like denticles whose lengths are commonly two to three times that of the supporting process bar. Further study of the Bluestone morphotype may lead to the recognition and definition of a new subspecies of Lochriea commutata. Bluestone morphotype P₂ elements have not been described previously and are illustrated in Figure 4.9–4.17.

The fourth morphotype, the subaequalis morphotype, is based on Subbryantodus subaequalis of Higgins (1961, pl. 12, fig. 15), and is likely the Lochriea commutata P₂ element most common in Europe. It shows similarities to both the montanaensis and recta morphotypes, exhibits some arching of the posterior process, and often shows alternation of slightly smaller denticles with larger denticles on the anterior process. Although we did not recover or recognize the subaequalis morphotype in North American collections, Scott (1942, pl. 40, figs. 4, 5) illustrated examples that are similar.

Some subaequalis morphotype P₂ elements in the literature are Subbryantodus subaequalis Higgins, 1961, p. 218, pl. 12, fig. 15, text-fig. 6; Higgins and Bouckaert, 1968, p. 47, pl. 3, figs. 1, 2; Higgins, 1975, p. 74, pl. 5, fig. 17; Metcalfe, 1981, pl. 19, fig. 17; Prioniodina subaequalis (Higgins), Rhodes et al., 1969, p. 198, pl. 28, figs. 1a–4; Ozarkodina subaequalis (Higgins), Marks and Wensink, 1970, p. 267, pl. 1, fig. 13 only; ?Subbryantodus stipans Rexroad, 1957, Higgins, 1961, p. 219, pl. 12, fig. 14, text-fig. 6; Higgins, 1962a, p. 13, pl. 1, fig. 9, text-fig. 2; ?Prioniodina stipans (Rexroad), Rhodes et al., 1969, p. 198, pl. 28, figs. 7a–10c; Ozarkodina plana (Huddle), Reynolds, 1970, p. 2, pl. 2, fig. 12; Lochriea commutata Pb element, Stone, 1991, p. 34, pl. 4, fig.14; Lochriea sp. Pb element, Varker, 1994, pl. 4, figs. 11, 12.

Most Montana P₂ elements are of the montanaensis morphotype, although some mature elements from the Tyler Formation of Montana that tend to be larger and have more completely fused denticles are of the recta morphotype. Most Illinois P₂ elements are of the recta morphotype; however, they are generally smaller than Montana specimens, and conversely, a few Illinois P₂ elements are of the montanaensis morphotype. The Bluestone morphotype has been recovered from only a single locality in West Virginia and presently appears to be restricted to eastern North America.

Although all elements exhibit breakage, many more elements, particularly the P₁, M, and S_3/4 elements, can be recognized from fragmented or smaller remains than can the P₂ elements. The thin, blade-like nature of the anterior and posterior processes of P₂ morphotypes and the fragility of their discrete denticles lead to breakage, which makes it difficult to identify discrete P₂ elements.

The co-occurrence of L. commutata P₁ elements and P₂ recta morphotypes in the Renault and Ridenhower formations of Illinois (Rexroad, 1957, table 1), as well as in our own collections from the Ridenhower Formation of Illinois, suggests that they were part of the same apparatus. However, the cluster analysis applied by Horowitz and Rexroad (1982, p. 966, text-fig. 3) to Chesterian conodont collections from the Beech Creek, Haney, and Glen Dean formations of Indiana failed to group the recta element with the P₁, M, and S elements they hypothesized to be parts of the Lochriea commutata apparatus. The authors nevertheless included the recta element in the statistical reconstruction of the species (text-fig.10), attributing the failure of the clustering procedure to low element occurrences and difficulties in identifying broken elements, also noting that current sorting and breakage also affects the presence and abundance of conodonts. Subsequently, Rexroad and Horowitz (1990, p. 509) did include Ozarkodina recta and O. subaequalis in their extensive synonymy of the Pb (= P₂) element of Lochriea commutata.

M element (Fig. 5).—This large pick-shaped element is, along with the P₁ element and perhaps the S_3/4 elements, the most distinctive element of the L. commutata apparatus. Variation in this element includes differences in denticle spacing, the angle of the posterior bar to the apical denticle, and the length of the anticusp. Many mature specimens from the Heath and Tyler formations of Montana and the Bluestone Formation of West Virginia show well-developed attachment scars (Fig. 5.7, 5.8, 5.12, 5.14), whereas this feature is less well developed in immature specimens, such as in those from the Ridenhower Formation of Illinois (Fig. 5.21, 5.22). Examination of the two associated M elements illustrated by Scott (1942, p. 298, pl. 39, fig. 9) show them to be outer lateral views of sinistral and dextral M elements of similar maturity. This is probably a fortuitous association because no other elements occur in the vicinity of these two elements, and we know of no other L. commutata M elements in such direct association with each other.

Some M elements of Lochriea commutata, or of related Lochriea spp., illustrated in the literature are Prioniodus singularis Hass, 1953, p. 88, pl. 16, fig. 4; Prioniodus roundyi var. dividen Elias, 1956, p. 110, pl. 2, figs. 39–41; Prioniodus cf. P. singularis, Elias, 1956, p. 112, pl. 2, fig. 45; Prioniodus roundyi var. parviden Elias, 1956, p. 112, pl. 2, figs. 42, 43; Prioniodina alatoidea (Cooper), Bischoff, 1957, p. 45, pl. 5, figs. 33, 34, 36; Prioniodus sp. A Ziegler in Flügel and Ziegler, 1957, p. 50, pl. 4, fig. 3; Neoprioniodus singularis (Hass), Stanley, 1958, p. 471, pl. 66, figs. 2, 3; Higgins, 1961, pl. 11, fig. 5; Higgins, 1962a, pl. 1, fig. 8; Higgins, 1962b, p. 68, pl. 3, fig.11; Rexroad and Furnish, 1964, p. 674, pl. 111, fig. 32 (listed as fig. 33 in text); Higgins and Bouckaert, 1968, p. 45, pl. 1, fig. 8; Webster, 1969, p. 40, pl. 7, fig. 14; Dunn, 1970, p. 337, pl. 64, figs. 32, 33; Thompson, 1972, p. 37, pl. 1, figs. 21, 22; Lane and Straka, 1974, fig. 34.1; Higgins, 1975, p. 68, pl. 3, fig. 11 (not Higgins and Varker, 1982, pl. 19, fig. 15); Metcalfe, 1981, pl. 18, figs. 1–3; Neoprioniodus sp. A Stanley, 1958, p. 472, pl. 66, figs. 4, 5; ?Neoprioniodus miser Elias, 1959, p. 154, pl. 2, figs. 23, 24; Elias, 1966, p. 26, pl. 2, figs. 23, 24; Neoprioniodus aff. N. alatoideus Elias, 1959, p. 155, pl. 2, fig. 3 (only); Elias, 1966, p. 27, pl. 2, fig. 3 (only); ?Neoprioniodus singularis (Hass), Globensky, 1967, p. 444, pl. 55, figs. 23, 24; Koike, 1967, p. 307, pl. 4, fig. 30; Neoprioniodus montanaensis (Scott), Rhodes et al., 1969, p. 160, pl. 22, figs. 5a–8b; Marks and Wensink, 1970, p. 266, pl. 1, figs. 9, 10; Igo, 1973, p. 195, pl. 29, fig. 32; Lochriea commutata M element, Stone, 1991, p. 34, pl. 4, fig. 13; Lochriea sp. element, Varker, 1994, pl. 1, fig. 5, 6 (both clusters contain the characteristic Lochriea commutata M element); Lochriea sp. M element, Varker, 1994, pl. 4, figs. 13, 14.

S₀ element (Fig. 6).—The S₀ element of L. commutata is rare because it is only one of 15 elements in the apparatus and because of its susceptibility to breakage, being exceeded in rarity only by the S₁ and S₂ elements. This alate element is, like most elements of this general morphology, particularly susceptible to breakage when compressed laterally, the result being that its two anterolateral processes, and or its posterior process, are generally broken. The posterior process (Fig. 6.3–6.5, 6.14) has prominent terminating denticles at its posterior end, making it unlikely to be confused with those of any of the other S elements. Although an uncommon feature, a few specimens exhibit an everted lower surface (Fig. 6.11).

Although Scott (1942) did not recognize an S₀ element to have been a part of the L. commutata apparatus, he illustrated (Scott, 1942, pl. 40, fig. 16) and recognized (p. 299 in pl. 40 explanation) an S₀ element as “the only specimen of its kind found in the Heath shales.” Some S₀ elements of Lochriea commutata, or of related Lochriea spp., illustrated in the literature are Hibbardella pennata Higgins, 1961, p. 213, pl. 12, figs. 5, 6; Reynolds, 1970, p. 2, pl. 2, figs. 8, 9; Higgins, 1975, p. 36, pl. 1, fig. 6 (only); Metcalfe, 1981, pl. 14, figs. 1a, 1b, 4a, 4b; Riley et al., 1987, pl. 2, fig. 15; ?Higgins and Bouckaert, 1968, p. 36, pl. 1, fig. 10; ?Hibbardella (Hibbardella) parva Rhodes et al., 1969, p. 114, pl. 25, fig. 21a, 21b.

Other than Norby (1976, p. 157, pl. 11, figs. 15a, 15b, 17a–18), who described this as the A₃ element of L. commutatus, only Mapes and Rexroad (1986, p. 115, pl. 1, fig. 21) and Rexroad and Horowitz (1990, p. 510, pl. 2, fig. 25) referred to this element, describing it as the Sa element of this species. Varker (1994, pl. 4, fig. 7) referred a well-preserved S₀ element to Lochriea sp., which we would include in L. commutata.

This element can be confused with S₀ elements belonging to species of other genera, particularly those of Gnathodus. S₀ elements of G. bilineatus have a much more acute angle, <60°, between the lower edges of the two anterolateral processes (e.g., Varker, 1994, pl. 3, fig. 8), whereas that same angle is 145° or greater in Lochriea commutata S₀ elements (cf., Varker, 1994, pl. 4, fig. 7).

S₁ element (Fig. 7).—Scott (1942) illustrated an S₁ element as a “hindeodell” element of Lochriea montanaensis (Scott, 1942, pl. 39, fig. 1, subhorizontal element). The S₁ element has a characteristic scythe-shaped or shepherd's crook morphology, with an angle of ∼70° (Fig. 7.8–7.10, 7.13–7.17) to 90° (Fig. 7.3, 7.12, 7.18) between the anterior and posterior processes. The S₁ element (Fig. 7.1, 7.2) was described and figured by Norby (1976, text-fig. 21, pl. 12, fig. 5c, 5d) as the Lochriea commutatus A_1c element, and by Purnell and Donoghue (1998, text-fig. 11A) as the Sb₁ element of Lochriea sp.

The juncture between the anterior and the posterior processes of Lochriea commutata S₁ elements is broadly curved and expanded laterally (Fig. 7), resulting in the characteristic shepherd's crook shape of their anterior ends. Discrete S₁ elements are generally broken (e.g., those from bleach-processed residues from the Heath Formation), and are reported and illustrated only infrequently. Similarly, S₁ elements are rarely identified in bedding-plane assemblages, and the anterior ends needed to identify them are generally preserved only as short broken stubs, (e.g., in bedding-plane assemblages from Montana; Fig. 7.1–7.4). The best-preserved, complete, discrete S₁ elements (Fig. 7.9–7.18) and S₁ element pairs (Fig. 7.5–7.8) were those recovered with, or in, fused clusters from West Virginia. One remarkable S₁ element pair (Fig. 7.7) shows the anterior process of the dextral S₁ element closely interlocked with the anterior process of the sinistral S₁ element, and preserving the two elements in a tight embrace with their anterior processes facing one another (Figs. 4.8, 5.4, 7.5–7.7), and in another (Fig. 7.5, 7.6) the element embrace not being as tight (i.e., the elements having moved relative to one another). The interlocked S₁ elements of Lochriea commutata (Figs. 4.8, 5.4, 7.5–7.7), like those illustrated by Varker (1994, pl. 1.4) in a fused cluster of Gnathodus bilineatus from England, are positioned over the posterior ends of the long posterior process of the central S₀ element (Figs. 4.8, 5.5, 7.7), S₁^d and S₂^d are preserved farther posteriorly than the other S elements. Because S elements were located and functioned at the anterior end of the feeding apparatus (Aldridge et al., 1987; Purnell and Donoghue, 1998, text-fig.1e) (Fig. 12), and are not known to have functioned in apposition to one another, both the position and the interlocking nature of the S₁ elements in fused clusters of both species are presently best accounted for by postmortem contraction.

Ramiform elements with a scythe or shepherd's crook shape, similar to those of Lochriea commutata S₁ elements, have been illustrated in the Carboniferous conodont literature. These include upper views of Hindeodina uncata Hass, 1959, p. 383, pl. 47, fig. 6; Hindeodella uncata (Hass), Metcalfe, 1981, pl. 15, ?fig. 2; Hindeodella brevis Branson and Mehl, Higgins, 1961, pl. 10, fig. 14; and Hindeodella croka Rhodes et al., 1969, p. 121, pl. 28, figs. 15, 17. Hindeodina uncata occurs in early Carboniferous strata and is probably the S₁ element of a species of Gnathodus or of a related gnathodontid, a likelihood Varker (1994, p. 309) recognized when he identified this element, Hindeodella uncata (Hass), as the Gnathodus bilineatus Sd element. Higgins (1975, p. 44, pl. 4, figs. 1–3) illustrated upper and lateral views of Hindeodella uncata that possesses a gently downward-arching anterior process.

S₁ elements of gnathodontids, particularly those of Gnathodus bilineatus, as illustrated in Norby, 1976, pl. 7, figs. 6, 8, 9, 11 (A_1c element), Aldridge et al., 1987, fig. 4.1 (Sd element), polygnathacean apparatuses and reconstructions, Aldridge et al., 1987, fig. 4.7–4.12 (unlabeled Sd elements), Varker, 1994, pl. 1, figs. 3, 4, 7, pl. 2, fig. 1 in fused clusters of G. bilineatus and in pl. 3, figs. 13, 15 as discrete G. bilineatus Sd elements, and of Streptognathodus/Idiognathodus von Bitter, 1972, pl. 11, fig. 4a–d (Hindeodella parva), are similar to Lochriea commutata S₁ elements; however, they can generally be differentiated from Lochriea spp. S₁ elements by the characteristic sharp downturn, or anticusp-like extension, of the distal end of their anterior process, their more robust denticles, and the robustness and arching of their posterior process.

S₂ element (Fig. 8).—The S₂ element is approximately the same length as an S₁ element of similar maturity, and slightly shorter than S_3/4 elements. Like S₁ elements, the S₂ element is very rarely preserved intact, and has been difficult to recognize and characterize in bedding-plane assemblages from the Heath and Tyler formations (Fig. 8.1–8.4). The exceptionally preserved specimens associated with fused clusters in the Bluestone Formation of West Virginia (Fig. 8.5–8.12) have provided the basis for much of the foregoing description.

Because S₂ elements lack strong morphological features and tend to break easily during compaction, it has been difficult to recognize them among the thousands of pieces of disjunct S elements recovered from Montana. Similarly, we have been able to identify and illustrate only a few S₂ elements in bedding-plane assemblages of Lochriea commutata, generally only with a question mark (Fig. 8.4; Table 1). As with the other exceptionally preserved S elements in the Bluestone Formation of West Virginia, the S₂ elements recovered with fused clusters (Fig. 8.5–8.12) have provided the basis for most of our understanding and description of S₂ elements.

Scott (1942, pl. 39, fig. 1, nearly vertical element) illustrated a possible S₂^d element that crosses an S₁^d element and is the only such element that we identified among his illustrated material of Lochriea montanaensis. Higgins (1975, p. 43, pl. 6, figs. 1–3, 5) named Hindeodella sinuosa on the basis of elements from Great Britain that are morphologically similar to Lochriea commutata S₂ elements (Fig. 8). Hindeodella sinuosa Higgins has the same range as P₁ elements of Lochriea commutata and other Lochriea species illustrated by Higgins (1975, p. 70–72) as species of Paragnathodus: P. commutatus (pl. 7, figs. 7–9, 11, 13, 16, 20, 21), P. cruciformis (pl. 7, fig. 10), P. mononodosus (pl. 7, fig. 14), and P. nodosus (pl. 7, figs. 12, 15, 17–19, 22, 23). More recently, Varker (1994, p. 310, pl. 1, fig. 6) illustrated Hindeodella sinuosa in a fused cluster of Lochriea sp., and two discrete S elements, as the “probable” Sb elements of Lochriea sp. (Varker, 1994, p. 310, pl. 4, figs. 16, 18), here regarded as S₂ elements.

S_3/4 element (Fig. 9).—The S_3/4 element is the most commonly recognized S element of the Lochriea commutata apparatus, and is abundant in collections of discrete elements, bedding-plane assemblages, and fused clusters of the species. This abundance is primarily due to the relative robustness of the anterior process, which is a structure that does not appear to break as easily as that of S₁ and S₂ elements, making it easier to recognize the element. S_3/4 elements are the only elements in the L. commutata apparatus that we are unable to distinguish from one another on purely morphological grounds (i.e., we are able to differentiate them only by their position within the apparatus). Thus, the S elements in the dextral nested S_3/4^d element pair (Figs. 8.12, 9.11) and the sinistral S_3/4^s element pair (Fig. 9.1, 9.5) exhibit no morphologic differences that presently allow us to distinguish them from one another in discrete element collections. The S_3/4 elements are among the three most morphologically diagnostic elements of the species. One prominent feature is the large cusp with its anterior process, which is about one-third the height of the cusp and two or three times the height of the posterior process. The anterior denticles increase in height anteriorly giving the process an upswept appearance, which is an atypical feature in ozarkodinid S_3/4 elements.

Some examples of S_3/4 elements of Lochriea commutata, or of related Lochriea species, illustrated in the literature are ?Hindeodella bigeniculata Elias, 1956, p. 106, pl. 1, figs. 20, 21, (non pl. 1, fig. 16), line drawings only; Hindeodella mehli Elias, 1956, p. 108, pl. 1, fig. 24 (?figs. 22, 23), line drawings only; Metcalfe, 1981, p. 29, pl. 15, fig. 3; Hindeodella germana Holmes, 1928; Bischoff, 1957, p. 27, pl. 6, fig. 32 (non pl. 6, fig. 34); Higgins, 1961, pl. 10, fig. 12 (?fig. 13); Higgins and Bouckaert, 1968, p. 36, pl. 1, fig. 12; Higgins, 1975, p. 38, pl. 5, fig. 6; Hindeodella montanaensis (Scott), Stanley, 1958, p. 465, pl. 64, figs. 1–4, 5 (upper specimen); Rhodes et al., 1969, p. 123, pl. 28, figs. 21, 26; Lochriea commutata Sc element, Rexroad and Horowitz, 1990, p. 510, pl. 2, fig. 24; Lochriea commutata Sc₁ element, Stone, 1991, p. 34, pl. 4, fig. 12; Lochriea sp. Sc element, Varker, 1994, p. 310, pl. 4, figs. 15, 17; possibly present as an S element in a fused cluster identified as Lochriea sp. (Varker, 1994, pl. 1, fig. 5).