Range and biostratigraphic utility of Lochriea

The genus Lochriea occurs in, and is restricted to, strata of Carboniferous age. Atakul-Özdemir et al. (Reference Atakul-Özdemir, Purnell and Riley2012) 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, Reference Somerville2008). 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, Reference Higgins, Neale and Brasier1981), in the Arundian of England (Metcalfe, Reference Metcalfe1981; Stone, Reference Stone1991), in the lower Meramecian of North America (Krumhardt et al., Reference Krumhardt, Harris and Watts1996), and in strata of equivalent age elsewhere in the world.

The earliest occurrences of a species of the genus are Lochriea cracoviensis (Belka, Reference Belka1985), at the base of the Viséan in Poland (Belka, Reference Belka1985, chart), and L. cracoviensis and L. saharae Nemyrovska, Perret-Mirouse, and Weyant, Reference Nemyrovska, Perret-Mirouse and Weyant2006, from the lower Viséan of Algeria (Nemyrovska et al., Reference Nemyrovska, Perret-Mirouse and Weyant2006), 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., Reference Nemirovskaya, Poletaev, Vdovenko, Brenckle and Manger1991), Uzbekistan (Nigmadganov and Nemirovskaya, Reference Nigmadganov and Nemirovskaya1992), south China (Wang et al., Reference Wang, Lane, Manger and Wang1987b), southwest Japan (Mizuno, Reference Mizuno1997), Spain (Sanz-López and Blanco-Ferrara, Reference Sanz-López and Blanco-Ferrera2012), and the lower Namurian of Britain and Ireland (Higgins, Reference Higgins, Higgins and Austin1985, table 7; Sweet, Reference Sweet1988, chart 6). The type species, L. commutata, is long ranging (Sweet, Reference Sweet1988, chart 6) and is of biostratigraphic utility only in a local context. Lochriea commutata and L. homopunctatus (Ziegler, Reference Ziegler1960), were utilized by Metcalfe (Reference Metcalfe1981) and Varker and Sevastopulo (Reference Varker, Sevastopulo, Higgins and Austin1985) to define local-range zones. Other species, such as L. cracoviensis, L. mononodosa (Rhodes, Austin, and Druce, Reference Rhodes, Austin and Druce1969), L. nodosa (Bischoff, Reference Bischoff1957), L. multinodosa (Wirth, Reference Wirth1967), and others, have a more limited range and are therefore stratigraphically more useful (Higgins and Wagner-Gentis, Reference Higgins and Wagner-Gentis1982; Belka, Reference Belka1985, chart; Sweet, Reference Sweet1988, chart 6). Atakul-Özdemir et al. (Reference Atakul-Özdemir, Purnell and Riley2012) 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, Reference Nemirovskaya, Perret and Meischner1994, was under investigation as a marker for the Viséan/Serpukhovian boundary. Qi et al. (Reference Qi, Nemyrovska, Wang, Hu, Wang and Lane2018) 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 (Reference Sevastopulo and Barham2014) 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. (Reference Qi, Nemyrovska, Wang, Hu, Wang and Lane2018, figs. 3, 4) also illustrated their interpretation of the evolutionary relationships among nine of the 10 Lochriea species recovered by them.

When Mizuno (Reference Mizuno1997) 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, Reference Mizuno1997). Although it is known to range higher into the basal Bashkirian of the Donets Basin of the Ukraine (Nemirovskaya et al., Reference Nemirovskaya, Poletaev, Vdovenko, Brenckle and Manger1991) and south China (Wang et al., Reference Wang, Lane, Manger and Wang1987b), the occurrence of L. commutata in Japan (Mizuno, Reference Mizuno1997) is higher than has been recorded from Europe or North America.

Taxonomic journey of Lochriea Scott, Reference Scott1942

Scott (Reference Scott1942, p. 298) defined the conodont genus Lochriea as “natural conodont assemblages made up of hindeodells, spathognaths, prioniods, and prioniodells.” With the discovery by Melton and Scott (Reference Melton, Scott and Rhodes1973, p. 58) of what they believed to be complete conodont animals containing in situ elements in functional position, they amended this definition slightly to “conodont-bearing animals in which conodonts are represented by hindeodellids, spathognathodids, neoprioniodids, and prioniodinids-ozarkodinids.”

Most conodont researchers have worked, and continue to work, on discrete elements recovered by breaking down sedimentary rock with acids and solvents. However, the preceding definitions of the apparatus composition of Lochriea species were based entirely on the study of rare bedding-plane assemblages and, 30 years later in the early 1970s, on conodontophages with elements of Lochriea and other conodont genera in their gut. This created a dichotomy between the taxonomy of ornamented and unornamented P₁ conodont elements now accepted to be the P₁ elements of Lochriea spp., and the taxonomy based on bedding-plane assemblages. Thus, starting in 1941, the year before Lochriea was first named, and continuing into the 1990s, those workers studying these ornamented and unornamented P₁ elements generally assigned P₁ elements that have a morphology similar or identical to those present in these rare bedding-plane assemblages to a variety of genera. The earliest of these assignments was by Branson and Mehl (Reference Branson and Mehl1941a, Reference Branson and Mehlb), who assigned their new species commutatus to Spathognathodus Branson and Mehl, 1941 (Branson and Mehl, Reference Branson and Mehl1941b). A year later, Scott (Reference Scott1942)—working at a time when neither a procedure nor an agreement had been established for how to reconcile taxonomies based on discrete isolated conodonts with the very same ones found in bedding-plane assemblages—bypassed Branson and Mehl's Spathognathodus commutatus in favor of his own Lochriea montanaensis.

Ironically, subsequent workers did their own bypassing of Scott's conclusions regarding the bedding-plane assemblage-based Lochriea in favor of the better established, perhaps simpler, and (at the time) less controversial single-element taxonomy, thereby sending Spathognathodus commutatus and some other similar platform elements on a circuitous and complex taxonomic journey. Thus, Hass (Reference Hass1953, p. 80) assigned his new species inornatus, a junior subjective synonym of commutatus, to Gnathodus Pander, Reference Pander1856, and recognized its similarity to Gnathodus commutatus, with Bischoff (Reference Bischoff1957, p. 22) apparently being the first to assign Spathognathodus commutatus to Gnathodus. This was followed by Ziegler in Flügel and Ziegler (Reference Flügel and Ziegler1957, p. 39), Serre and Lys (Reference Serre and Lys1960, p. 39), Wirth (Reference Wirth1967, p. 206), Rhodes et al. (Reference Rhodes, Austin and Druce1969, p. 95), Thompson and Goebel (Reference Thompson and Goebel1969, p. 23–24), Marks and Wensink (Reference Marks and Wensink1970, p. 258), Aisenverg et al. (Reference Aisenverg, Brazhnikova, Vassilyuk, Reitlinger, Fomina, Einor, Wagner, Higgins and Meyen1979, p. 48), Metcalfe (Reference Metcalfe1981), and Dong and Ji (Reference Dong and Ji1988, p. 50) also assigning commutatus to Gnathodus. Bischoff (Reference Bischoff1957), and others who followed, generally did not provide reasons for removing the species commutatus from Spathognathodus, although good reasons for doing so are that: (1) Spathognathodus, a replacement name for the previously occupied Spathodus Branson and Mehl, Reference Branson and Mehl1933, had become a catch-all genus used for a very broad range of bladed P₁ conodont elements in animals that evolved over long periods of geologic time; (2) Lochriea commutata P₁ elements are morphologically distinct from most spathognathodid P₁ elements by having a blade with more uniform denticulation and a subcircular posteriorly-positioned basal cavity; and (3) Spathognathodus primus Branson and Mehl, Reference Branson and Mehl1933, the type species of Spathognathodus, is a middle Silurian multielement conodont species, with its own complex nomenclatural evolution from Spathognathodus primus to Hindeodella confluens (Jeppsson, Reference Jeppsson1969, p. 15), to Ozarkodina typica (Klapper and Philip, Reference Klapper and Philip1971, p. 441, 443), to O. confluens (Klapper, Reference Klapper and Ziegler1973, p. 211, 221), and back to O. typica (see Murphy et al., Reference Murphy, Valenzuela-Rios and Carls2004, for a revision of Silurian spathognathodids). Because the apparatus for O. typica is well known and restricted to the Silurian, neither Spathognathodus nor Ozarkodina can be used to accommodate the Carboniferous species Lochriea commutata.

Among the new conodont species and subspecies, based on P₁ elements with or without ornamentation that were being assigned to Gnathodus, were the subspecies Gnathodus commutatus nodosus Bischoff (Reference Bischoff1957, p. 23) and G. commutatus multinodosus Wirth (Reference Wirth1967, p. 208), as well as the species G. glaber Wirth (Reference Wirth1967, p. 210, 211) and G. mononodosus Rhodes et al. (Reference Rhodes, Austin and Druce1969, p. 103). However, by the late 1960s, some or all of these gnathodontids were increasingly understood to be morphologically and phylogenetically distinct from species with more complex ornamented P₁ elements, such as G. bilineatus (Roundy, Reference Roundy, Roundy, Girty and Goldman1926) and G. girtyi Hass, Reference Hass1953. The result was the informal (Meischner, Reference Meischner1970), and then the formal (Higgins, Reference Higgins1975), naming of the genus Paragnathodus for some of these conodont species. Paragnathodus was first used as a nomen nudum by Meischner (Reference Meischner1970, p. 1173, 1177, fig. 2); Higgins (Reference Higgins1975, p. 70) subsequently defined the genus, with Paragnathodus commutatus as the type species, as follows: “The unit consists of a subrectangular blade and carina and a low, subcircular to subquadrate posterior cup. The oral surface of the blade is denticulate and is not clearly distinguished from the carina; the denticles of the blade increase in width posteriorly when seen in oral view. The aboral side of the cup is excavated.”

The genus Lochriea Scott, Reference Scott1942, initially based on rare bedding-plane assemblages, was exhumed, in a sense by, Melton and Scott (Reference Melton, Scott and Rhodes1973) when they named conodontophages containing Lochriea sp. elements in their gut, Lochriea wellsi. Shortly thereafter, Norby (Reference Norby1976, p. 140) brought the genus into taxonomic play when, recognizing the priority of Spathognathodus commutatus Branson and Mehl, 1941 (Branson and Mehl, Reference Branson and Mehl1941b) over Lochriea montanaensis Scott, Reference Scott1942, he applied this priority to designate L. commutata (Branson and Mehl, 1941) (Branson and Mehl, Reference Branson and Mehl1941b) the type species of Lochriea. That conclusion, and the resulting action, required a conciliation of concepts based on bedding-plane assemblages and discrete platform elements—one more than three decades in the making.

Norby's work was not widely available and the generic designation Paragnathodus continued to be used, presumably by those who did not have access to, or who rejected Norby's conclusions. Thus, Higgins (Reference Higgins, Neale and Brasier1981, p. 39, fig. 4.3, 4.6) continued his earlier practice (Higgins, Reference Higgins1975, p. 70) of placing commutatus, nodosus, mononodosus, and cruciformis in Paragnathodus, and adding multinodosus and glaber, the latter species apparently only in Higgins (Reference Higgins, Neale and Brasier1981, fig. 4.6). In that study, he recognized and defined a Paragnathodus nodosus conodont zone in the Brigantian (early Carboniferous) of Britain. In subsequent work, Higgins (Reference Higgins, Higgins and Austin1985, pl. 6.1, figs. 7, 8, 11, 12) also placed commutatus and mononodosus in Paragnathodus.

By 1982, Higgins (in Higgins and Wagner-Gentis, Reference Higgins and Wagner-Gentis1982) recognized the probable synonymy of Paragnathodus and Lochriea and commented (p. 335) that “the composition of the multi-element genus [Paragnathodus] is unknown but it is likely to correspond to the natural assemblage Lochriea of Scott Reference Scott1942.” Higgins (Reference Higgins, Higgins and Austin1985, p. 214–215) subsequently assigned commutata and mononodosa to Lochriea; however, he continued to recognize Paragnathodus by placing nodosus in that genus while noting that Varker and Sevastopulo (Reference Varker, Sevastopulo, Higgins and Austin1985) assigned that species to Lochriea (Higgins, Reference Higgins, Higgins and Austin1985, p. 215, pl. 6.1, fig. 9 [caption under pl. 6.3, fig. 9]). In the same year, Grayson et al. (Reference Grayson, Davidson, Westergaard, Atchley, Hightower, Monoghan and Pollard1985, p. 169) assigned commutatus from southern Oklahoma to Paragnathodus. Belka (Reference Belka1985, p. 40) recognized and described a new species of Paragnathodus, P. cracoviensis, and the next year von Bitter et al. (Reference von Bitter, Sandberg and Orchard1986) referred “simple-cupped gnathodontiform” conodonts to that genus. Krumhardt et al. (Reference Krumhardt, Harris and Watts1996) documented that Ji (Reference Ji1987), Riley et al. (Reference Riley, Varker, Owens, Higgins and Ramsbottom1987), Wang et al. (Reference Wang, Lane, Manger, Brenckle and Lane1987a), Wang and Higgins (Reference Wang and Higgins1989), Nemirovskaya et al. (Reference Nemirovskaya, Poletaev, Vdovenko, Brenckle and Manger1991), Varker et al. (Reference Varker, Owens and Riley1991), Nigmadganov and Nemirovskaya (Reference Nigmadganov and Nemirovskaya1992), and Alekseev and Kononova (Reference Alekseev, Kononova and Tikhomirov1993), among others, continued to assign commutatus to Paragnathodus, and we here add Yanagida et al. (Reference Yanagida, Ota and Sano1992) to that list.

Those authors who did have access to the unpublished work of Norby (Reference Norby1976), and agreed with his conclusion that Lochriea was the earliest valid generic designation available, began to use Lochriea, but without full documentation regarding why the name applies. Horowitz and Rexroad (Reference Horowitz and Rexroad1982, p. 966) may have been the first to do so when they reconstructed a partial apparatus of L. commutata from the Chesterian of the Illinois Basin based on statistical analysis, and when they attempted to extrapolate those results to L. mononodosa Rhodes, Austin, and Druce, Reference Rhodes, Austin and Druce1969. By 1985, a number of authors had recognized either the utility, or the priority, of Lochriea. Varker and Sevastopulo (Reference Varker, Sevastopulo, Higgins and Austin1985, p. 174, 181–183, pl. 5.5, figs. 11–13, 16–18, 20) referred commutata, nodosa, and mononodosa to Lochriea, and applied each of the species names to a conodont zone. They also followed Rhodes et al. (Reference Rhodes, Austin and Druce1969, p. 160) and Marks and Wensink (Reference Marks and Wensink1970, p. 266) in their designation of some M elements as Neoprioniodus montanaensis, and acknowledged (p. 202, pl. 5.6, fig. 13) that Neoprioniodus singularis (Hass, Reference Hass1953), an M element, was “probably the Ne element of Lochriea commutata.”

Norby and Rexroad (Reference Norby and Rexroad1985) discussed similarities and associations of Lochriea with Vogelgnathus. And for the first time, Higgins (Reference Higgins, Higgins and Austin1985, p. 215, pls. 6.1, 6.3, and elsewhere) assigned commutata and mononodosa to Lochriea while, as noted earlier, continuing to place nodosus in Paragnathodus (Higgins, Reference Higgins, Higgins and Austin1985, p. 215, pl. 6.3, fig. 9). The next year, Mapes and Rexroad (Reference Mapes and Rexroad1986, p. 118) pointed out that the still widely used Paragnathodus was a junior synonym of Lochriea, an opinion subsequently shared by Stone (Reference Stone1991) and Skompski et al. (Reference Skompski, Alekseev, Meischner, Nemirovskaya, Perret and Varker1995). Mapes and Rexroad (Reference Mapes and Rexroad1986) described some elements of the L. commutata apparatus and noted the general agreement regarding the apparatus composition of the genus. Krumhardt et al. (Reference Krumhardt, Harris and Watts1996) supported the use of Lochriea and documented the gradual acceptance of the genus by numerous workers since 1986, including Armstrong and Purnell (Reference Armstrong and Purnell1987), Grayson (Reference Grayson and Ritter1990), Ramovš (Reference Ramovš1990a, Reference Ramovšb), Rexroad and Horowitz (Reference Rexroad and Horowitz1990), Whiteside and Grayson (Reference Whiteside, Grayson, Suneson, Campbell and Tilford1990), Weibel and Norby (Reference Weibel, Norby, Sutherland and Manger1992), Kolar-Jurkόvsek and Jurkόvsek (Reference Kolar-Jurkόvsek and Jurkόvsek1993), Nemirovskaya et al. (Reference Nemirovskaya, Perret and Meischner1994), and von Bitter and Norby (Reference von Bitter and Norby1994a, Reference von Bitter and Norbyb). We add Purnell (Reference Purnell1992) and Varker (Reference Varker1994) to this list, but make no claim that the citations before or after 1996 are either exhaustive or complete.

Lochriea commutata, parataxa, and a natural taxonomy governed by the International Code of Zoological Nomenclature

Lochriea commutata (Branson and Mehl, 1941) (Branson and Mehl, Reference Branson and Mehl1941b), the type species of the genus, remains one of the most consistently recognized Carboniferous conodont species, despite its generic journey from Spathognathodus to Gnathodus to Paragnathodus to Lochriea. The principal aspect that prevented placement of commutatus in Lochriea, and indeed its recognition as the type species of Lochriea prior to Norby (Reference Norby1976), was that most Carboniferous conodont workers were working with discrete conodont elements rather than with the much rarer bedding-plane assemblages. A second reason is that the diagnoses of Scott (Reference Scott1942, p. 298) and of Melton and Scott (Reference Melton, Scott and Rhodes1973, p. 58) failed to recognize and acknowledge that elements present in bedding-plane assemblages, or in the gut of conodontophages (Conway Morris, Reference Conway Morris1985, Reference Conway Morris1990; Sweet, Reference Sweet1988, p. 28), had previously been identified and named. Specifically, although Scott (Reference Scott1942, p. 300) was probably aware of Branson and Mehl's (Reference Branson and Mehl1941b) publication that included a description of Spathognathodus commutatus, he failed to recognize and acknowledge that the “spathognaths” present in Lochriea were both known and named. This resulted in the decades-long use of a dual nomenclature: one based on bedding-plane assemblages or similar uncommon material, and the other based on discrete elements.

Scott (Reference Scott1942, Reference Scott1973) and Melton and Scott (Reference Melton, Scott and Rhodes1973), studying what they thought were whole taxa, were undoubtedly aware of earlier publications, but, in the thinking of the times, they bypassed the priority of previously named discrete conodonts. Considerable debate had arisen before (e.g., Croneis, Reference Croneis1939) and after (e.g., Moore, Reference Moore, Hass, Häntzschel, Fisher, Howell, Rhodes, Müller and Moore1962), but little agreement was found in how to deal taxonomically with fragmentary versus whole fossil material. One of the proposed solutions was to create and use parataxa (i.e., to maintain a parallel but taxonomically separate classification system independent of the International Code of Zoological Nomenclature [ICZN]) for fragmentary fossils such as crinoid ossicles, holothuroid spicules, fish remains, and conodonts. With conodonts the problem was twofold. The first was how to name discrete, individual elements, whether that was according to their shape, denticulation, or other criteria. And second, after conodont bedding-plane assemblages were discovered and named first by Hinde (Reference Hinde1879), and subsequently by Scott (Reference Scott1934) and Schmidt (Reference Schmidt1934b), the question arose of whether the names of previously named discrete conodonts should have nomenclatural priority, when several different kinds of already named conodont elements were present in bedding-plane assemblages. Scott (Reference Scott1942) and fellow conodont workers before and after him were undoubtedly aware of this dilemma and gave it much thought; however, being unable to untie this particular taxonomic Gordian knot, they bypassed previously named taxa based on discrete conodont elements and created new taxonomic categories based on bedding-plane assemblages. Thus, Scott (Reference Scott1942) named Lewistownella for bedding-plane assemblages that contained the earlier-named diagnostic platform element Cavusgnathus Harris and Hollingsworth, Reference Harris and Hollingsworth1933, also bypassing the earlier-named species Spathognathodus commutatus when he named Lochriea montanaensis. As late as a decade later, Rhodes (Reference Rhodes1953) named Scottognathus on the basis of bedding-plane assemblages from the Pennsylvanian of Illinois, bypassing the Law of Priority set by the ICZN, even though Gunnell (Reference Gunnell1931) and Stauffer and Plummer (Reference Stauffer and Plummer1932) had previously named the diagnostic platform elements present in these assemblages Idiognathodus and Streptognathodus, respectively. Much the same situation prevailed with the recognition and naming of Illinella and Duboisella based on bedding-plane assemblages, while avoiding the available and earlier-named Gondolella Stauffer and Plummer, Reference Stauffer and Plummer1932 and Idioprioniodus Gunnell, Reference Gunnell1933, respectively (Rhodes, Reference Rhodes1952).

Conodont workers and other paleontologists of the time continued to wrestle with the paleontological angst created by the question of how to deal taxonomically with isolated fragmentary fossil remains. One result was the proposal to the ICZN by Moore and Sylvester Bradley (Reference Moore and Sylvester-Bradley1957a, p. 5) for the recognition and use of parataxa “as a special category for the classification and nomenclature of discrete fragments or of life-stages of animals which are inadequate for identification of whole-animal taxa, with proposals of procedure for the nomenclature of Parataxa” (see Moore and Sylvester Bradley, Reference Moore and Sylvester-Bradley1957b, regarding the application of parataxa to conodonts). Rhodes (Reference Rhodes, Hass, Häntzschel, Fisher, Howell, Rhodes, Müller and Moore1962, p. W82) described the rather hasty rejection of this proposal by the ICZN in 1958, noting that the body “offered no alternative solution” and that “this action leaves conodont nomenclature in a confused and unstable position.” In discussing the taxonomic problems of a dual nomenclature, Rhodes (Reference Rhodes, Hass, Häntzschel, Fisher, Howell, Rhodes, Müller and Moore1962, p. W81) favored giving “new names to natural conodont assemblages and to retain the existing system of nomenclature for isolated conodonts.” Moore (Reference Moore, Hass, Häntzschel, Fisher, Howell, Rhodes, Müller and Moore1962, p. W92–W97) discussed the illegality of a dual classification and suggested adopting a conservative course such that “species, genera and families distinguished on the basis of discrete conodonts . . . are to be regarded as “natural” taxa, and the species and genera defined on the basis of conodont assemblages likewise.”

The summary refusal of the ICZN may, however, have had the beneficial effect of forcing conodont workers to try harder to reconstruct apparatuses from collections of discrete conodont elements, and to name them according to the priority of the most characteristic named element, generally, but not always, the P₁ element. Simultaneous with the debates for and against the use and legality of parataxa, the stirrings of a revolution in conodont taxonomy were taking place in Germany. Here, Tatge (Reference Tatge1956) and Huckriede (Reference Huckriede1958), studying Triassic conodonts, and Walliser (Reference Walliser1964), working on Silurian conodonts, grouped discrete conodonts into tentative apparatuses, but without formally naming them.

By the mid-1960s, American Ordovician conodont workers Webers (Reference Webers1966) and Bergström and Sweet (Reference Bergström and Sweet1966) not only reconstructed apparatuses from discrete conodont collections, but also named them in conformity with the ICZN Law of Priority. Clearly, the revolution in conodont taxonomy was taking hold, and at the 1971 Symposium on Conodont Taxonomy, the Marburg Proposal (Aldridge and von Bitter, Reference Aldridge, von Bitter and Over2009, appendix II), with F.H.T. Rhodes as its prime mover, and its strong emphasis on strict application of the ICZN Code, passed with no further mention of parataxa. Some of the younger Carboniferous conodont workers who participated in the Marburg Symposium, or whose better-financed PhD advisors were there to later pass the ideas and recommendations of that meeting on to their students, correctly read the taxonomic winds that were blowing in conodont taxonomy. They did this by taking up the challenges of multielement taxonomy, and in quick succession (von Bitter, Reference von Bitter1972; Baesemann, Reference Baesemann1973; Perlmutter, Reference Perlmutter1975; Norby, Reference Norby1976) began to reconstruct conodont apparatuses, and gave priority to the earliest validly named genus name, such as Streptognathodus, Idiognathodus, Cavusgnathus, and Gondolella, irrespective of how whole or fragmentary the original material used to describe these genera had been. Subsequent to 1971, even though students of some other fossil groups decided to continue to use parataxa, conodont workers overwhelmingly distanced themselves from parataxa and agreed to use a natural taxonomy governed by the International Code of Zoological Nomenclature. This group decision by members of the Pander Society was subsequently recognized by the ICZN (Melville, Reference Melville1981).

Among bedding-plane assemblage-based generic names, such as Scottognathus, Duboisella, and Illinella, practically none are now used or invoked by Carboniferous conodont workers. All three are junior synonyms of earlier named taxa and are now mostly of historical interest. Lochriea, however, is the exception and survives because, unlike these three named bedding-plane assemblages, no previously assigned competing Carboniferous generic name based on discrete element taxonomy was, and is, available.

Taxonomic notes

We conclude, as did Norby (Reference Norby1976), that Spathognathodus commutatus Branson and Mehl, 1941 (Branson and Mehl, Reference Branson and Mehl1941b) is the senior subjective synonym of Lochriea montanaensis Scott, Reference Scott1942 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, Reference von Bitter and Norby1994a; Fig. 3) of the overall morphology of P₁ elements in the type specimens of L. montanaensis Scott, Reference Scott1942 with the P₁ elements that are the type specimens of Spathognathodus commutatus Branson and Mehl, 1941 (Branson and Mehl, Reference Branson and Mehl1941b) (von Bitter and Norby, Reference von Bitter and Norby1994a; Fig. 3), and of a wide range of P₁ elements from across North America and Europe (von Bitter and Norby, Reference von Bitter and Norby1994a; 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.

Figure 3. Lochriea commutata (Branson and Mehl, 1941) (Branson and Mehl, Reference Branson and Mehl1941b) 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, Reference Scott1942 holotype (= Lochriea commutata [Branson and Mehl, 1941] [Branson and Mehl, Reference Branson and Mehl1941b]), outer view. See element 2P₁^s (Fig. 1.1, 1.2) for apparatus context. Previously illustrated by von Bitter and Norby (Reference von Bitter and Norby1994a, fig. 2.1, counterpart). Heath Formation, locality 2, Montana, USA, UI X-1318. (5) P₁^?d element (in) Lochriea montanaensis Scott, Reference Scott1942 holotype (= Lochriea commutata [Branson and Mehl, 1941] [Branson and Mehl, Reference Branson and Mehl1941b]), outer view. See element 11P₁^?d (Fig. 1.1, 1.2) for apparatus context. Previously illustrated by von Bitter and Norby (Reference von Bitter and Norby1994a, 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, Reference Branson and Mehl1941b). Designated as one of four cotypes and illustrated (with incorrect number UM C552-1) by Lane and Straka (Reference Lane and Straka1974, 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 (Reference von Bitter and Norby1994a, 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 (Reference Lane and Straka1974, 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.

Second, our conclusion is based on our earlier determination (von Bitter and Norby, Reference von Bitter and Norby1994b) that the well-developed microsculpture on the carinal denticles of P₁ elements of the type specimens of Lochriea montanaensis Scott, Reference Scott1942, 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, Reference Branson and Mehl1941b) (von Bitter and Norby, Reference von Bitter and Norby1994a), 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, Reference von Bitter and Norby1994a, Reference von Bitter and Norbyb).

The weight of evidence supporting our conclusion that Lochriea montanaensis Scott, Reference Scott1942 is a subjective junior synonym of Spathognathodus commutatus Branson and Mehl, 1941 (Branson and Mehl, Reference Branson and Mehl1941b), was based initially (von Bitter and Norby, Reference von Bitter and Norby1994a) 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 (Reference Branson and Mehl1941b), based solely on P₁ elements. We (von Bitter and Norby, Reference von Bitter and Norby1994a) 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, Reference von Bitter and Norby1994a, 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, Reference Sutherland, Manger, Sutherland and Manger1979, fig. 2 correlation chart) (von Bitter and Norby, Reference von Bitter and Norby1994a, fig. 5.1–5.12).

Because L. montanaensis Scott, Reference Scott1942, 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, Reference Branson and Mehl1941b) 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, Reference Scott1942 (Scott, Reference Scott1942, 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 (Reference Norby1976) 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, Reference Sutherland, Manger, Sutherland and Manger1979, 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, Reference Branson and Mehl1941b), the subsequently named L. montanaensis Scott, Reference Scott1942, 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.

Figure 4. Lochriea commutata (Branson and Mehl, 1941) (Branson and Mehl, Reference Branson and Mehl1941b) 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, Reference Scott1942 holotype (= Lochriea commutata [Branson and Mehl, 1941] [Branson and Mehl, Reference Branson and Mehl1941b]) 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.

Figure 5. Lochriea commutata (Branson and Mehl, 1941) (Branson and Mehl, Reference Branson and Mehl1941b) 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, Reference Scott1942 holotype (= Lochriea commutata [Branson and Mehl, 1941] [Branson and Mehl, Reference Branson and Mehl1941b]) 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 6. Lochriea commutata (Branson and Mehl, 1941) (Branson and Mehl, Reference Branson and Mehl1941b) 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, Reference Norby1976, 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.

Figure 7. Lochriea commutata (Branson and Mehl, 1941) (Branson and Mehl, Reference Branson and Mehl1941b) 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.

Figure 8. Lochriea commutata (Branson and Mehl, 1941) (Branson and Mehl, Reference Branson and Mehl1941b) 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, Reference Branson and Mehl1941b]) 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, Reference Branson and Mehl1941b) 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, Reference Branson and Mehl1941b]) 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.

Previously, we (von Bitter and Norby, Reference von Bitter and Norby1994a, Reference von Bitter and Norbyb) regarded Branson and Mehl (Reference Branson and Mehl1941b) 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, Reference Branson and Mehl1941a) 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 (Reference Branson and Mehl1941b) 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 (Reference Scott1942, 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 (Reference Scott1942, 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 10. Lochriea bigsnowyensis Scott, Reference Scott1942, holotype (= an undetermined species of Cavusgnathus Harris and Hollingsworth, Reference Harris and Hollingsworth1933), illustrated by Scott (Reference Scott1942, 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, Reference Harris and Hollingsworth1933. 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.

Scanning electron microscopy of the bedding-plane assemblage designated by Scott (Reference Scott1942) 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, Reference von Bitter and Merrill1990, fig. 1B–D; Purnell and Donohue, Reference Purnell and Donoghue1998, text-fig. 15). The bedding-plane assemblage Scott (Reference Scott1942, p. 299) designated as the paratype, but did not illustrate, has been lost. We place the discrete L. bigsnowyensis prioniod element of Scott (Reference Scott1942, pl. 40, fig. 3) in synonymy with the L. commutata M element. The prioniodell elements illustrated by Scott (Reference Scott1942, 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, Reference Scott1942, which in turn is a junior synonym of an as yet unidentified species of Cavusgnathus Harris and Hollingsworth, Reference Harris and Hollingsworth1933. 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 (Reference Scott1942, 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).

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, Reference Branson and Mehl1941b); after Scott (Reference Scott1942) and labeled with his terminology for the four element types recognized by him; shape categories used (in parentheses) are those of Sweet (Reference Sweet, Clark, Sweet, Bergström, Klapper, Austin, Rhodes, Müller, Ziegler, Lindström, Miller and Harris1981, Reference Sweet1988). (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 (Reference Purnell and Donoghue1998) is indeterminate, and the reconstruction of L. homopunctatus (Ziegler, Reference Ziegler1960) by Atakul-Özdemir et al. (Reference Atakul-Özdemir, Purnell and Riley2012), based on discrete elements, is not included.

Thirty-one years later, Melton and Scott (Reference Melton, Scott and Rhodes1973) 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 (Reference Melton, Scott and Rhodes1973) referred to these elements as “spathognathodids,” “prioniodinids/ozarkodinids,” “neoprioniodids,” and “hindeodellids” (Fig. 11.2). Scott (Reference Scott1973) 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 (Reference Conway Morris1985), and was interpreted, as Typhloesus wellsi (Melton and Scott), to be a conodontophage (i.e., a conodont-eater) (Conway Morris, Reference Conway Morris1985, Reference Conway Morris1990), an interpretation supported by Sweet (Reference Sweet1988) and by us. Reasons for our support for this conclusion are that: (1) elements of other conodont taxa, including those of Kladognathus Rexroad, Reference Rexroad1958, have been found inside T. wellsi (Conway Morris, Reference Conway Morris1990; Purnell, Reference Purnell1993a); (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 (Reference Purnell1993a), 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 (Reference Scott1942, 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, Reference Scott1942, 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 (Reference Scott1942, 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 (Reference Norby1976) 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 (Reference Norby1976) 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 (Reference Norby1976) 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 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. (Reference Aldridge, Smith, Norby, Briggs and Aldridge1987) and Purnell and Donoghue (Reference Purnell and Donoghue1997, Reference Purnell and Donoghue1998, text-fig. 1) proposed and reviewed possible three-dimensional arrangements of elements within the functioning ozarkodinid conodont apparatus, with Purnell and Donoghue (Reference Purnell and Donoghue1998) concluding that their text-figure 1E best explained the position, arrangement, and functional morphology of elements in that apparatus.

Figure 12. The 15 element apparatus of Lochriea commutata (Branson and Mehl, 1941) (Branson and Mehl, Reference Branson and Mehl1941b) in exploded view using the topological element notation of Purnell et al. (Reference Purnell, Donoghue and Aldridge2000; 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.

Scott (Reference Scott1942, 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., Reference Aldridge, Smith, Norby, Briggs and Aldridge1987; Sweet, Reference Sweet1988). Functionally, this group of elements was regarded by Hitchings and Ramsay (Reference Hitchings and Ramsay1978) to have served as a sieve basket, but was subsequently interpreted to have had a raptorial grasping function (Purnell, Reference Purnell1993b; Purnell and Donoghue, Reference Purnell and Donoghue1997). Norby (Reference Norby1976), 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 (Reference Norby1976) 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 (Reference Aldridge and Aldridge1987) and Aldridge et al. (Reference Aldridge, Smith, Norby, Briggs and Aldridge1987) when they determined that conodont apparatuses of the Polygnathacea Bassler, Reference Bassler1925, 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. (Reference Purnell, Donoghue and Aldridge2000) determined to be plesiomorphic for complex conodonts. Purnell and Donoghue (Reference Purnell and Donoghue1998) 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 (Reference Purnell and Donoghue1998), and subsequently amended by them to reflect topological element notation of Purnell et al. (Reference Purnell, Donoghue and Aldridge2000). The three-dimensional apparatus architecture of the German Lochriea sp. specimen was illustrated by Purnell and Donoghue (Reference Purnell and Donoghue1998, 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 14.1 and 14.2, respectively.

Figure 13. Lochriea sp. bedding-plane assemblage, counterpart (1) and part (2), as designated by Purnell and Donoghue (Reference Purnell and Donoghue1998, pl. 2). Lüsenberg Formation, locality 11, North-Rhine Westphalia, Germany, IMGP Gö 600-36. From the collection of Schmidt and Müller (Reference Schmidt and Müller1964); after Purnell and Donoghue (Reference Purnell and Donoghue1998, pl. 2), and reproduced with permission of the Palaeontological Association. Scale bars = 1 mm.

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 (Reference Purnell and Donoghue1998, 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 (Reference Purnell and Donoghue1998), 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 (Reference Purnell and Donoghue1998, text-fig. 11B), and reproduced with permission of the Palaeontological Association.

Our identification of 18 and 23 elements in the holotype and paratype, respectively, of Lochriea montanaensis Scott, Reference Scott1942 (Fig. 1; Table 1) is clearly at odds with the apparatus composition of Lochriea spp. as determined by Norby (Reference Norby1976), von Bitter and Norby (Reference von Bitter and Norby1998a, Reference von Bitter and Norbyb), and Purnell and Donoghue (Reference Purnell and Donoghue1998). The anomalously high numbers of elements in the two assemblage specimens chosen by Scott (Reference Scott1942) 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 (Reference Scott1942, p. 293), who thought that the bedding-plane assemblages he was studying were not fecal, or accidental accumulations.

Table 1. Conodont elements on the holotype and paratype of Lochriea montanaensis Scott, Reference Scott1942 (= Lochriea commutata [Branson and Mehl, 1941] [Branson and Mehl, Reference Branson and Mehl1941b]) from the Heath Formation, and on three and five specimens of Lochriea commutata (Branson and Mehl, 1941) (Branson and Mehl, Reference Branson and Mehl1941b) from the Heath and Tyler formations, respectively. All 10 specimens are bedding-plane assemblages from Montana, USA. Underlined element designations (i.e., 3P₁, 3P₂, 3M, 2S₁, 1S₂, 6S_3/4, 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.

The best preserved eight bedding-plane assemblages of Lochriea commutata collected by Norby (Reference Norby1976), 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 (Reference Norby1976), Aldridge (Reference Aldridge and Aldridge1987), Aldridge et al. (Reference Aldridge, Smith, Norby, Briggs and Aldridge1987), and Purnell and Donoghue (Reference Purnell and Donoghue1997, Reference Purnell and Donoghue1998), 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 Reference Norby1976; von Bitter and Norby, Reference von Bitter and Norby1998a, Reference von Bitter and Norbyb) (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 (Reference Purnell and Donoghue1998) 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 (Reference Stone1991), 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 (Reference Norby1976). Another more complicated approach was that of Horowitz and Rexroad (Reference Horowitz and Rexroad1982), Varker (Reference Varker1994), and Nemyrovska et al. (Reference Nemyrovska, Perret-Mirouse and Weyant2006), 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 (Reference Horowitz and Rexroad1982), 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, Reference Roundy, Roundy, Girty and Goldman1926) (Horowitz and Rexroad, Reference Horowitz and Rexroad1982, text-fig. 3). Similarly, Varker (Reference Varker1994, 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. (Reference Nemyrovska, Perret-Mirouse and Weyant2006) 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., [Reference Skompski, Alekseev, Meischner, Nemirovskaya, Perret and Varker1995] 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. (Reference Atakul-Özdemir, Purnell and Riley2012, 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. (Reference Atakul-Özdemir, Purnell and Riley2012) of an M element, illustrated by Nemyrovska et al. (Reference Nemyrovska, Perret-Mirouse and Weyant2006) from a sample from Algeria containing P₁ elements of only a single Lochriea species, L. saharae, as the M element of that species.

Systematic paleontology