Lanea carlsi (Boersma, 1973)

Slavík, Ladislav, 2011, Lanea carlsi conodont apparatus reconstruction and its significance for subdivision of the Lochkovian, Acta Palaeontologica Polonica 56 (2), pp. 313-327 : 316-318

Lanea carlsi apparatus position and its generic classification

Reconstruction of a spathognathodontid apparatus based on a natural assemblage from the Lochkovian of Podolia was presented by Mashkova (1972). Although two elements were lacking in her apparatus, this reconstruction and later discovered natural assemblages were the basis for the completed model of skeletal apparatus of ozarkodinid conodonts. It was presented by Purnell and Donoghue (1998) as a sexmembrate apparatus having 15 elements that includes seven mirror image pairs and one symmetrical element. Similarly like in the other spathognathodontid taxa, the reconstruction of Lanea carlsi apparatus is based on this concept.

The apparatus has been found in the sample 4Po22 ( Fig. 2 ) in the Požár−3 section. Apart from some elements of Belodella the sample contains only two spathognathodontid taxa. These are strikingly different. The first taxon is represented by 4 juvenile elements: 1x Pa, 1x Pb, 1x Sa and 1x M. Considering the size proportionality and common morphological features, all these elements probably belong to the same apparatus and possibly even to the same organism. The denticulation of the spathognathodontid Pa element with prominent cusp and cockscomb at the anterior end of the blade resemble Zieglerodina remscheidensis , but it slightly differs from Z. remscheidensis by stronger inclination of denticles towards the posterior. The other elements of the apparatus show typical characters of the Zieglerodina apparatus that was described in Murphy et al. (2004). The Pb element is very short, the Sa element shows a very sharp angle between lateral processes which are rather high. Almost regular alternation of denticle size is seen also in the M element.

The second taxon in the sample is L. carlsi which is represented by 12 Pa, 7 Pb, 5 M, 5 Sa, 4 Sb, 7 Sc, and 28 fragments of diverse elements. The complete material of the taxon is 68 complete or fragmentary elements in total showing various stages of maturity. L. carlsi was also found in sample 4Po32 (only 2 Pa elements were identified) in the same section in association with fragments of Lanea sp. , Wurmiella cf. wurmi ( Bischoff and Sannemann, 1958) , and Zieglerodina sp. More specific determination of platform and ramiform elements of Lanea is difficult because these have siliceous grains fused to their surfaces.

At the same stratigraphic level as the appearance of Lanea carlsi (22 m above the base of the section) but in a different sample (4Po22a) taken during previous sampling has been detected one characteristic Pa element of Lanea omoalpha Murphy and Valenzuela−Ríos, 1999 . This is accompanied by a few fragments of ramiform elements which belong to the apparatus of Lanea and resemble very much the ramiforms of the apparatus described in this paper. The range of L. carlsi in the Požár−3 section is only 10 m (i.e., the interval between samples 4Po22 and 4Po32). The taxon occurs also in the parallel section Požár−1–2 at about the same stratigraphic position with roughly corresponding range (four succeeding samples in 8 m interval). The total number exceeds 80 Pa elements in this section. In association with the Pa elements of L. carlsi in the samples co−occur also other taxa of Lanea ( L. omoalpha , L. eoeleanorae , L. cf. omoalpha ), “ Pandorinellina ?” boucoti Klapper, 1969, and Wurmiella wurmi . The ramiform elements are thus mixed in samples, but assignation to the genus is possible.

Regarding the history, the taxon originally named as “ Spathognathodus carlsi ” has been coined by Boersma (1973) who studied condonts from the Spanish Central Pyrenees. He collected 41 specimens from “ Orthoceras limestones” at Bahent locality and established a new spathognathodontid taxon for these Pa elements with a widely open and asymmetrical basal cavity with one ornamented lobe. The associated conodonts found by Boersma (1973) in the Pyrenees together with Lanea carlsi are icriodids of the Icriodus woschmidti group ( I. woschmidti postwoschmidti Mashkova, 1968 ), I. angustoides bidentatus Carls and Gandl, 1969 , I. rectangularis Carls and Gandl, 1969 , and the taxa “ Spathognathodus remscheidensis ” ( Ziegler, 1960) and “ Spathognathodus steinhornensis repetitor ” ( Carls and Gandl, 1969) . The platform elements of L. carlsi were previously described from the Lochkovian of Frankenwald ( Bischoff and Sannemann 1958) and from Aragón ( Carls and Gandl 1969). In accordance with the past nomenclature, the L. carlsi was assigned originally to Spathognathodus and later was also transferred to Ozarkodina as was the case of most spathognathodontid taxa in the eighties and early nineties of the last century. Klapper et al. (1991) assigned the L. carlsi to the genus Ancyrodelloides Bischoff and Sannemann, 1958 mainly due to the presence of distinct ornamentation on the platform lobes, and provided a complete synomymy. A relatively large number (50 of Pa elements) of “ Ozarkodina carlsi ” were found by Valenzuela−Ríos (1994) in the section Geri 1.1 (Pyrenees) where its range is well controlled stratigraphically by the succession of diagnostic taxa. It appears below morphotypes of “ Ancyrodelloides omus ” including Lanea omoalpha (= A. omus delta morph Valenzuela−Ríos, 1994, according to Murphy and Valenzuela−Ríos 1999) which are well below Ancncyrodelloides transitans and A. trigonicus . Valenzuela−Ríos and Murphy (1997) in their zonation of the middle Lochkovian kept some diagnostic taxa with Ancyrodelloides (including A. omus alpha Murphy and Matti, 1983 and A. eleanorae Lane and Ormiston, 1979 ). Later, Murphy and Valenzuela−Ríos (1999) proposed a new genus Lanea for several rather robust species of the middle Lochkovian Spathognathodontidae sharing numerous morphological characters. The authors presented the hypothesis of a separate history for the two stratigraphically closely related genera— Lanea and Ancyrodelloides . Lanea was separated from the latter genus mostly on the basis of “normally unornamented basal platform lobes” equipped with terraces. According to Murphy and Valenzuela−Ríos (1999), in more derived members of Lanea (i.e., L. eleanorae and L. telleri ( Schulze, 1968) , and Ancyrodelloides (i.e., A. transitans ) the basal grooves and basal cavities are already restricted to some extent. Although the overall characteristic of the new genus is robust, the authors remarked that at the dawn of the Lanea clade, its early members show similarities to coeval taxa. An example of such a strong similarity can be the identically developed basal cavity in the taxa L. carlsi and L. omoalpha . The authors included in the new genus Lanea several distinct taxa— L. omoalpha Murphy and Valenzuela−Ríos, 1999 , L. eoeleanorae Murphy and Valenzuela−Ríos, 1999 , L. eleanorae Lane and Ormiston, 1979 , and L. telleri ( Schulze, 1968) . L. carlsi was not discussed in that paper and in their interpretation remained it within Ancyrodelloides ( Murphy and Valenzuela−Ríos 1999: table 1). Their concept also left L. omus Murphy and Matti, 1983 within Ancyrodelloides mainly because of ornamentation of the platform lobes (see Murphy and Matti 1983: pl. 2: 21–29). To sum up, the interpretation by Murphy and Valenzuela−Ríos (1999) supposes stratigraphically close or almost corresponding origin of both genera and the branching point should be expected close to the lower/middle Lochkovian boundary (cf. the ranges of taxa carlsi and L. omus in Pyrenees: section Gerri 1.1., Valenzuela−Ríos 1994 and Segre 1, Valenzuela−Ríos 2002, and ranges of taxa omus alpha, L. omus beta and “ A. omus sp. nov. — A. transitans ” ( Murphy and Matti 1983: table 2, pl. 2: 13, 15, 17) =? L. carlsi (this paper). The figured Nevadan specimen that might probably be L. carlsi in the Simpson Park Range Section VII coexists with L. omoalpha Murphy and Valenzuela−Ríos, 1999 , Amydrotaxis johnsoni Klapper, 1969 , and L. eleanorae , and is well below A. transitans . The faunal succession in the sections of the Požáry Quarries that were obtained by relatively dense sampling in the Lochkovian (almost 100 conodont samples) also confirms the stratigraphic succession of these important members of Lanea and Ancyrodelloides .

The main reason for re−allocation of L. carlsi to the genus Lanea in this paper is the strong similarity to representatives of Lanea clade and faunal successions that may point to modified concept of Ancyrodelloides and Lanea lineage. The striking similarity does not apply to the platform elements only, but is also observed in the entire apparatus, which is probably almost undistinguishable from Lanea omoalpha and its immediate doi:10.4202/app.2009.0046

descendants within the Lanea clade. Moreover, it is possible to distinguish certain elements of the apparatus from those of Ancyrodelloides ( A. trigonicus , A. kutscheri , and especially, A. transitans ). Murphy and Valenzuela−Ríos (1999) remarked that the entire apparatus of Lanea , Ancyrodelloides , and Kimognathus have not been reconstructed yet mostly because of their common co−occurrence, element mixing, and scarcity of certain ramiforms. The apparatus of early Lanea member— L. carlsi reconstructed in this paper may elucidate the relation between respective genera.

Figures

Fig. 2. Stratigraphy of the lower and middle part of the Požár−3 section with ranges of stratigraphically most important cosmopolitan conodonts in relation with the range of Lanea carlsi. The samples are marked on the right side of the column. The sample numbers are marked on the right side of the column. For convenience the sample prefix (4Po) is omitted. The samples with other prefixes (from different samplings and re−samplings) are given in full (i.e., PZ14, PZ16, and R52.0).