Reinterpretation of Malvinoconularia cahuanotensis (Braniša and Vanek) from the Devonian Altiplano and Western Andean Cordillera, Bolivia, South America

Juliana De Moraes Leme¹, Marcello Guimarães Simões¹ and Heyo Van Iten²

¹ Depto. Zoologia, IB, UNESP, CP 510, Rubião Júnior, 18618-000, Botucatu, SP, Brasil. leme@ibb.unesp.br-btsimoes@ibb.unesp.br

² Department of Geology, Hanover College, Hanover, IN 47243, USA. vaniten@hanover.edu

Abstract. The holotype of Malvinoconularia cahuanotensis (Braniša and Vanek) (Devonian, Bolivia), the type species of the monospecific genus Malvinoconularia Babcock et al., is redescribed and refigured. M. cahuanotensis exhibits several gross morphological features that together are uniquely shared with Reticulaconularia baini (Babcock and Feldmann). In both taxa, the transverse ribs are nodose, the interspaces bear longitudinal ridges (bars or crests) that are collinear (line up) across the transverse ribs, and the longitudinal centerline (midline) of the faces is marked by a subdued ridge. Additionally, the two species may also be similar in the anatomy and external ornament of the corner sulcus. The slightly undulose geometry of the transverse ribs of M. cahuanotensis also is exhibited by certain specimens of Reticulaconularia; however, whether this feature is primary or taphonomic in origin is unclear at present. Together, these similarities suggest that the genus Malvinoconularia probably is a junior synonym of the genus Reticulaconularia.

Resumen. Reinterpretación de Malvinoconularia cahuanotensis (Braniša y Vanek) del Devónico de Bolivia, América del Sur. El holotipo de Malvinoconularia cahuanotensis (Braniša y Vanek) (Devónico, Bolivia), la especie tipo del género Malvinoconularia Babcock et al., es reinterpretado y refigurado. M. cahuanotensis exhibe varios rasgos morfológicos que en conjunto son compartidos únicamente con Reticulaconularia baini (Babcock y Feldmann). En ambos taxones las costillas transversas son nodosas, los interespacios poseen aristas longitudinales (barras o crestas) que son colineares a las costillas transversas, y las caras presentan una pequeña elevación externa sobre su línea media. Además, estas especies parecen ser similares en la anatomía y ornamentación externa del surco marginal. La geometría suavemente ondulada de las costillas de M. cahuanotensis es también exhibida por ciertos especímenes de Reticulaconularia, aunque aún no es claro si esta característica es primaria o tafonómica en su origen. En conjunto, estas similitudes sugieren que Malvinoconularia es un sinónimo junior de Reticulaconularia.

Key words. Bolivia; Devonian; Conulariids; Cnidaria; Systematics.
Palabras clave. Bolivia; Devónico; Conuláridos; Cnidaria; Sistemática.

Introduction

Devonian strata of Bolivia have long been known for their exceptionally abundant and well preserved invertebrate fossils, particularly in comparison with equivalent strata in other parts of the Malvinokaffric Realm (Sharpe, 1856; Bernard, 1895; Kayser, 1897; Reed, 1904, 1925; Thomas, 1905; Schwarz, 1906; Knod, 1908; Clarke, 1913; Kozlowski, 1913, 1923; Douglas, 1920; Richter and Richter, 1942; Boucot, 1971; Méndez-Alzola and Sprechmann, 1973; Cooper, 1977; Eldredge and Ormiston, 1979; Babcock et al., 1987; Leme, 2002; Rodrigues, 2002; Rodrigues et al., 2003; Leme et al., 2004). The most common fossils in the Bolivian rocks are trilobites, rhynchonelliform brachiopods, molluscs, and conulariids (d'Orbigny, 1842; Ulrich, 1892; Kozlowski, 1923; Braniša, 1965; Babcock et al., 1987; Babcock, 1993). Conulariids are very common in the Belén, Icla, and Sicasica formations (figure 1), where they generally occur in hard siliceous concretions (Ulrich, 1892; Kozlowski, 1923; Braniša, 1965; Babcock et al., 1987; Babcock, 1993). In the most recent review of the conulariids of these strata, Babcock et al. (1987) described six species: Conularia albertensis Reed, 1925, C. quichua Ulrich, 1890, (in Steinmann and Doderlein), Paraconularia africana (Sharpe, 1856), P. ulrichana (Clarke, 1913), Reticulaconularia baini (Ulrich, 1892), and Malvinoconularia cahuanotensis (Braniša and Vanek, 1973). Malvinoconularia cahuanotensis originally was placed in the genus Metaconularia (Braniša and ,Vanek 1973), and was erected on the basis of three specimens, all from the Lower Devonian Belén Formation. Unfortunately, Braniša and Vanek's holotype and nearly all other specimens, originally reposited in collections of the Yacimientos Petrolíferos Fiscales Bolivianos (YPFB, Santa Cruz de La Sierra, Bolivia), have been lost (José Oliveira and Hugo Barba, YPFB, oral communication, 2003). Only one actual specimen, the holotype of Malvinoconularia cahuanotensis (YPFB 5630; Braniša and Vanek, 1973, Fig. 2.1-4), currently is available for study.

Figure 1. Map showing the distribution of Devonian strata in Bolivia / mapa exhibiendo la distribución de los estratos del Devónico en Bolivia.

According to Babcock et al. (1987, p. 219), the monospecific genus Malvinoconularia differs from all previously described conulariid genera "by [1] having rods [transverse ribs] that usually abut at the midline, [2] widely spaced rods, [3] large apical angles (37 to 43º), and [4] subtle thickenings of [the] integument which run the length of the exoskeleton and [5] by lacking spines [interspace bars, ridges, or crests]." However, reexamination of the holotype of M. cahuanotensis shows that it exhibits anatomical features that were not noted previously or may have been misinterpreted (Braniša and Vanek, 1973; Babcock et al., 1987). Furthermore, comparison of this specimen with specimens of Reticulaconularia baini shows that it and other species of Reticulaconularia exhibit most of the characteristics attributed by Babcock et al. (1987) to Malvinoconularia, and that these two taxa share several anatomical features not shared with other conulariids. Based in part on these new observations, presented below, we argue that Malvinoconularia may be a junior synonym of Reticulaconularia.

Materials and methods

The present study is based on direct examination of the holotype of Malvinoconularia cahuanotensis and 78 specimens of Reticulaconularia baini, all from Bolivia (see Appendix). Most of the R. baini specimens are from the Icla Formation, though some may be from the Belén Formation of the Altiplano and Western Andean Cordillera. Specimens were examined and photographed using reflected light microscopy. Use of anatomical terminology in this paper generally is consistent with precedents to be found in Sinclair (1940a, 1940b, 1942, 1948, 1952), Moore and Harrington (1956), Bischoff (1978), Van Iten (1991a, 1991b, 1992a, 1992b), Jerre (1993), Van Iten et al. (1996, 2000), Leme (2002), and Leme et al. (2004). Finally, all examined specimens are reposited in collections of the Yacimientos Petrolíferos Fiscales Bolivianos (YPFB), Santa Cruz de La Sierra, Bolivia, and Museo de Historia Natural Alcide d'Orbigny, Cochabamba, Bolivia.

Previous descriptions of Malvinoconularia

Braniša and Vanek (1973). The original description of Metaconularia cahuanotensis reads as follows: "The faces are not uniform in size, with bent edges. The corners are marked by broad shallow furrows, across which the transverse ridges are clearly continuous. These ridges are slightly variable in thickness. The transverse ridges are slightly arched adaperturally, and are offset along the midline. Midline of faces inconstantly marked by faint groove; on inner side (internal mould) enclosed by well-developed septal ridge. The interspaces, because of the close spacing of the transverse ridges, are represented only by shallow grooves. Faces with accessory longitudinal lines in outer surface. Apical angle: about 14º. Transverse ridge spacing: 10-11/5 mm".
Babcock et al. (1987). Based on examination of a single specimen (YPFB 5630), Babcock et al. (1987) erected the new, monospecific genus Malvinoconularia, with type species M. cahuanotensis Braniša and Vanek (1973). Their description of the genus Malvinoconularia reads as follows (Babcock et al., 1987, p. 219): "Conulariids with rods [transverse ribs] widely spaced; 18 to 24/cm; undulose; fewer than 30% alternate at midline; greater than 70% abut. Apical angles large, approximately 37 to 43º. Nodes present and closely spaced. Adapertural and adapical spines absent. Several narrow, subtle thickenings of integument run longitudinally along the exoskeleton".

Present description

The holotype of Malvinoconularia cahuanotensis (figure 2.A-D) can be redescribed as follows: Pyramidal theca having four faces that differ in width, with one set of opposing faces (the major faces; Babcock and Feldmann, 1986) approximately 1.3 times as wide as the other set of opposing faces (the minor faces); theca slightly compressed both parallel and perpendicular to its long axis, with several low, broad transverse folds, probably produced by secondary compaction parallel to the longitudinal axis of the theca (figure 2.C), crossing the faces; apical region and apertural margin missing; minimum original length of the theca approximately 4.2 cm. Apical angles of the major and minor faces approximately 51º and 37.5º, respectively. Midline of the faces marked discontinuously by a very low external ridge (figure 2.C). Transverse ribs finely nodose, slightly undulated, confluent at the midlines, widely spaced (figures 2.C, 2.D), with 4 ribs/mm within approximately 10 mm of the former apex and 3-3.5 ribs/mm elsewhere; transverse ribs on the faces chevron-like (figure 2.D); in some places (figure 2.B1), inflected toward the aperture on the shoulders of the corner sulcus; geometry of the transverse ribs in the corner sulcus proper cannot be determined owing to poor preservation of this feature; rib nodes on the faces hemispherical, generally numbering 4/mm. Interspaces locally (near the corners) showing narrow, bar-like longitudinal ridges (interspaces ridges) that line up across the transverse ribs and are more or less parallel to the corners (figure 2.B1-3); interspaces of the two major faces also exhibit four subdued, relatively broad longitudinal ridges that likewise extend across the full width of the interspaces and are collinear (line up) across the transverse ribs (figure 2.A). Corner sulcus relatively deep, possibly angulated (figure 2.B1); edges (shoulders) of the corner sulcus also angulated (figure 2.B1). Schott (apical wall; Babcock and Feldmann, 1986) absent.

Figure 2. Malvinoconularia cahuanotensis (Braniša and Vanek, 1973) and Reticulaconularia baini (Ulrich, 1892) from the Devonian of Bolivia. A-D, M. cahuanotensis (YPFB 5630). A, General view of the specimen showing the "subtle thickenings" on one of the faces (white arrow) / vista general del especimen presentando "subtle thickenings" (espesamientos longitudinales) en el peridermo (flecha blanca); B1, General view of the same specimen with transverse ribs on the faces inflected toward the aperture on the shoulders of the corner sulcus (white arrow) /vista general del mismo especimen con costillas que se doblan en dirección a la abertura en el surco de las aristas (flecha blanca); B2, Detail of the collinear alignment of the interspace ridges (crests), extending across the full width of the interspaces and lining up across the transverse ribs (white arrow), (x1.6) / detalle del peridermo exhibiendo elevaciones colineares a través del interespacio (crestas) (flecha blanca); B3, Same detail of B2 showing the collinear alignment of the interspace ridges (white arrow), (x2.0) / mismo detalle del B2 exhibiendo elevaciones colineares a través del interespacio (crestas) (flecha blanca); C, Side view of the holotype, a relatively complete specimen showing the subdued longitudinal external ridge at the facial midline (white arrow) / vista del holotipo, presentando una pequeña elevación externa en la línea media (flecha blanca); D, Theca showing the "undulate" transverse ribs (white arrow) / Peridermo exhibiendo costillas "onduladas" (flecha blanca). E-G, R. baini. E, View of the specimen (YPFB 3139) showing the "undulate" transverse ribs (white arrow), (x25.0) / vista del especimen (YPFB 3139) presentando costillas "onduladas" (flecha blanca); F, Same specimen of E, with the transverse ribs inflected toward the aperture on the shoulders of the corner sulcus (white arrow), (x25.0) / mismo especimen del E con costillas que se doblan en dirección a la abertura en el surco de las aristas (flecha blanca); G, Specimen (YPFB 461) with the longitudinal external ridge at the facial midline (white arrow), (x 15.0) / especimen (YPFB 461) con elevación externa en la línea media (flecha blanca). Scale bar = 1 cm / escala = 1 cm.

Discussion. The present description differs from the descriptions of Braniša and Vanek (1973) and Babcock et al. (1987) in several ways. One of these concerns the anatomy of the longitudinal centerline, or midline, of the faces (figure 2.C). According to Braniša and Vanek (1973), the midline is marked by a discontinuous "faint groove" associated with a "well-developed septal ridge". Although it is no longer possible (apparently) to examine the full suite of specimens assigned by Braniša and Vanek (1973) to Metaconularia cahuanotensis, we found no evidence of a faint groove or internal ridge at or near the midlines of YPFB 5630. Instead, the midlines of at least some of the faces of this specimen appear to be slightly and discontinuously raised (figure 2.C). In many other conulariids (e.g., many species of Conularia and Paraconularia; e.g., Babcock and Feldmann, 1986) having transverse ribs that arch or point toward the aperture on the faces, the summit of the ribs more or less coincides with the midline. In YPFB 5630, the summit of many of the chevron-like transverse ribs is noticeably displaced from the geometrical centerline (figure 2.D). Also, none of the transverse ribs on this specimen is disrupted (offset) at or near the midline (figure 2.D).
A second point of disagreement concerns the anatomy of the interspaces. According to Babcock et al. (1987), the interspaces of Malvinoconularia lack longitudinal ridges (referred to by these authors as "spines"). However, as shown here in figures 2.B1-3, relatively narrow, bar-like interspace ridges clearly are present in YPFB 5630. [These ridges may correspond to the "accessory longitudinal lines" noted by Braniša and Vanek (1973)]. Moreover, these ridges line up (are collinear) across the transverse ribs (figure 2.B1-3).
Babcock and Feldmann (1986) also noted the presence of eleven "subtle thickenings" running along the length of each face (Babcock et al., 1987, fig. 6; this paper, figures 2.1, 2.3). Inspection of YPFB 5630 shows that these features probably are not sites of actual thickening, but instead are subtle folds or corrugations that are somewhat similar to the interspace ridges (crests) of other conulariids (e.g., Reticulaconularia). Thus, YPFB 5630 exhibits both bar-like interspace ridges and broader, subtler longitudinal ridges (figure 2.A). While the interspace ridges probably are primary anatomical features, the broad longitudinal ridges may be artifacts of transverse compaction. Owing, unfortunately, to the fact that there is only specimen of Malvinoconularia available for study, we cannot resolve this problem.
A third difference involves the geometry of the transverse ribs within and near the corner sulcus. According to Braniša and Vanek (1973), the transverse ribs are "clearly continuous" across the corner sulcus. Babcock et al. (1987) did not describe the corner sulcus, and continuity of the ribs across the sulcus is not evident in their published photographs (Babcock et al., 1987, figure 6, p. 220). In YPFB 5630, the corner sulcus is distorted (by compaction) and/or partially obscured by rock matrix, and thus without further preparation (possibly) it cannot be determined whether the transverse ribs are in fact continuous across the sulcus (as is the case in many other conulariids such as Conularia and Metaconularia; e.g., Van Iten et al., 1996). However, on the rounded shoulders (edges) of one of the corner sulcus (figure 2.B1), some of the transverse ribs are inflected (bent) toward the apertural end of the theca. Such bending generally is displayed by conulariids, including Climacoconus, Paraconularia, and Reticulaconularia, whose transverse ribs terminate within the corner sulcus (e.g., Van Iten et al., 1996; Van Iten et al., 2000).
Finally, Babcock and Feldmann (1986) noted that the transverse ribs of Malvinoconularia are slightly undulated. Similar undulation of the transverse ribs, though perhaps not as pronounced as in YPFB 5630 (figure 2.D), also is exhibited by certain specimens of Reticulaconularia (figure 2.E). Again, however, it is not clear whether these features are primary or are artifacts of preservation (see Simões et al., 2003).

The genus Reticulaconularia Babcock and Feldman

According to Babcock et al. (1987), Malvinoconularia cahuanotensis is most similar to Reticulaconularia. The original diagnosis of this genus (Babcock and Feldmann, 1986, p. 447) reads as follows: "Conulariids with rods that are widely spaced, 12-39/cm. 30-80% of rods alternate at midline; 20- 70% abut. Apical angles large, 22-59º. Nodes and adapertural spines present and widely spaced; adapical spines not known." At present, Reticulaconularia contains three species: R. penouili (Clarke, 1907), R. sussexensis (Herpers, 1949), and R. baini (Babcock et al., 1987).
In a recent study comparing Reticulaconularia with the monospecific genus Changshaconus Zhu, 1985 (Devonian, China), Van Iten et al. (2000) noted five additional characteristics of Reticulaconularia: (1) midline of the faces marked by an external ridge; (2) nodes located at the ends of the interspace furrows (as opposed to the interspace bars or ridges); (3) long axes of the interspace ridges generally line up across the transverse ribs; (4) interspace ridges extend across the full width of the interspaces; (5) interspace ridges inclined at high angles (approximately 70º) to the transverse ribs. Van Iten et al. (2000) argued further that Changshaconus and Reticulaconularia may have been more closely related to each other than either genus was to any other conulariid, and suggested that one or both genus names may have to be abandoned in order to eliminate paraphyly.
Based on the two descriptions previously published and on direct examination of 78 specimens of R. baini from the Devonian of Bolivia (Appendix), we summarize the common characteristics of the three species placed by Babcock and Feldmann (1986) in the genus Reticulaconularia as follows: Conulariids with four faces; apical angles range from approximately 22º (minor faces) to 59º [major faces; see however Simões et al. (2003) for a discussion of the limitations of the use of the apical angles to diagnose conulariid species]. Transverse ribs finely nodose, chevron-like or bell-shaped on the faces, numbering from 39 ribs/mm in the apical region and from 12 to 21 ribs/mm elsewhere; transverse ribs generally cross the midlines without disruption or offset (figure 2.G); transverse ribs inflected toward the aperture on the shoulders (edges) of the corner sulcus and terminate within the corner sulcus, where the ends of the transverse ribs of one face alternate and interlock with the ends of the transverse ribs of the adjacent face (figure 2.F). Midlines marked by a low external ridge (figure 2.G). Interspaces with interspace ridges (bars or crests) that extend across the full width of the interspaces and are collinear (line up) across the transverse ribs (figure 2.F). Corner sulcus deep, angulated (figure 2.F), with shoulders (edges) also angulated (figure 2.F). Schott not observed.

Comparisons of Reticulaconularia and Malvinoconularia

As noted above in the introduction, Babcock et al. (1987, p. 219) stated that Malvinoconularia differs from all other conulariid genera "by [1] having rods [transverse ribs] that usually abut at the midline, [2] widely spaced rods, [3] large apical angles (37º to 43º), and [4] subtle thickenings of [the] integument which run the length of the exoskeleton and [5] by lacking spines [interspace bars, ridges, or crests]". However, our work shows that characteristics 1-3 also are exhibited by species in the genus Reticulaconularia. Furthermore, some specimens of R. baini also exhibit subdued longitudinal ridges, which may or may not be primary anatomical features, and interspace bars (crests) and troughs are present in Malvinoconularia. Data presented in this and previous studies (Sinclair, 1942; Braniša and Vanek, 1973; Babcock and Feldmann, 1986; Babcock et al., 1987; Babcock, 1993; Van Iten et al., 2000) show further that Malvinoconularia and Reticulaconularia share the following anatomical similarities: (1) interspaces with interspace ridges (bars or crests) that line up (are collinear) across the transverse ribs; (2) midline of the faces marked by a more or less distinct external ridge; (3) transverse ribs with nodes; (4) transverse ribs commonly chevron-like. Finally, although the anatomy of the transverse ribs in the corner sulcus of Malvinoconularia is unclear, the geometry of the ribs on the shoulders of the corner sulcus is consistent with the hypothesis that the sulcus proper is similar to that of Reticulaconularia, in which the transverse ribs terminate and their ends are arranged in alternation.
In short, then, Malvinoconularia Babcock et al. (1987) exhibits all of the characters regarded by Babcock and Feldmann (1986) as diagnostic of Reticulaconularia, and many and possibly all of the characteristics attributed to this genus by Van Iten et al. (2000). For this reason, we conclude that Malvinoconularia cahuanotensis (Braniša and Vanek, 1973) might be placed in the genus Reticulaconularia. Thus, under the rules of priority of the International Code of Zoological Nomenclature (2000), Malvinoconularia should be considered a junior synonym of Reticulaconularia, and M. cahuanotensis a junior synonym of R. baini.

Appendix

List of examined material of Malvinoconularia cahuanotensis and Reticulaconularia baini. Specimens deposited in the paleontological collections of the Yacimientos Petroliferos Fiscales Bolivianos (YPFB), Santa Cruz de La Sierra, Bolivia, and the Museo de Historia Natural Alcide d'Orbigny (MHNC), Cochabamba, Bolivia / lista del material examinado de Malvinoconularia cahuanotensis y Reticulaconularia baini. Especímenes depositados en las colecciones paleontológicas de Yacimientos Petrolíferos Fiscales Bolivianos (YPFB), Santa Cruz de La Sierra, Bolivias y en el Museo de Historia Natural Alcide d'Orbigny (MHNC), Cochabamba, Bolivia.

Acknowledgments

The senior author thanks Yacimientos Petroliferos Fiscales Bolivianos (YPBF), and R. Suarez Soruco and R. Céspedes, for permission to examine the paleontological collections of the YPBF and the Museo de Historia Natural de Cochabamba Alcide d'Orbigny. The senior author also is indebted to Soruco and Céspedes for their assistance during her stay in Bolivia, and L. B. Simões for the photograph work. The authors also thank L.E. Babcock (Ohio State University) and an anonymous reviewer for their constructive comments to the final version. We also thank the Ameghiniana editor (F. Tortello) for his help with the Spanish version of the abstract. FAPESP and CNPq provided generous financial support for this project.

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Recibido: 6 de octubre de 2004.
Aceptado: 1 de abril de 2005.