Abstract
AbstractLochriea commutata (Branson and Mehl, 1941), a senior subjective synonym of Lochriea montanaensis Scott, 1942, is the type species of Lochriea Scott, 1942, one of the first conodont genera named using bedding-plane assemblages. Lochriea commutata is both wide- and long-ranging, locally stratigraphically important, and a consistently recognized Carboniferous species, despite its taxonomic journey from Spathognathodus to Gnathodus to Paragnathodus to Lochriea.Lochriea commutata was, as Lochriea montanaensis, initially reported to contain 22+ elements, the apparatus composition of the genus being subsequently amended to 17+ elements based on Lochriea wellsi Melton and Scott, 1973, which is an untenable hypothesis because the latter was a conodontophage. Restudy of original and new bedding-plane assemblages in the mid 1970s established that the first assemblages studied were fecal, the initial reconstruction incorporated elements of two individuals, and Lochriea commutata possessed a feeding apparatus of 2P1, 2P2, 2M, 2S1, 2S2, 2S3, 2S4, and 1S0 elements. A Lochriea sp. bedding-plane assemblage was subsequently found to have the same element composition, and restudy of type material, available bedding-plane assemblages, and new fused clusters confirms that Lochriea commutata had a 15-element ozarkodinid apparatus.While species are still assigned to Lochriea using carminiscaphate P1 elements almost exclusively, those assignments must be considered tentative until their apparatuses are determined to be similar to that of L. commutata, and until characteristics of elements other than the P1 element, particularly the makellate M element and the bipennate S3/4 element, are also taken into account.Lochriea bigsnowyensis Scott, 1942 is reassigned to Cavusgnathus Harris and Hollingsworth, 1933.
Highlights
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
P1 element (Fig. 3).—Having previously 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
Microsculpture is absent on the denticles of these specimens, with the upper denticle surface being covered by secondary crystal overgrowths
Summary
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. 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 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 (= S3/4) 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. 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
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