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Ameghiniana

versión impresa ISSN 0002-7014

Ameghiniana vol.46 no.1 Buenos Aires ene./mar. 2009

 

ARTÍCULOS ORIGINALES

Leonardosia langei Sommer (Charophyta, Porocharaceae) from Corumbataí Formation (Guadalupian), Piracicaba, SP, Brazil: First record of an antheridium and of corticated thalli

Rafael Souza Faria1 and Fresia Ricardi-Branco2

Department of Geology and Natural Resources, Institute of Geosciences, P.O. BOX 6152. University of Campinas-Unicamp 13083-970, Campinas, SP, Brazil.
1MSc grant by CNPq, rafaelfaria@ige.unicamp.br
2fresia@ige.unicamp.br

Abstract. Fossilized portions of a charophyte found in close association with disperse gyrogonites identified as Leonardosia langei Sommer are described. One sample has an antheridium apparently connected to a thallus clearly corticated. Considering the close association and the lack of other carophyte species than L. langei the thalli are thought to belong to this species. The male structure is very rare and is recorded for the first time in L. langei and in the Porocharaceae. The samples consist of compressions/impressions from the Corumbataí Formation (Guadalupian of the Paraná Basin), found in the municipality of Piracicaba, in the Brazilian state of São Paulo. The presence of such algae provides evidence of some of the palaeoenvironmental conditions prevailing during the deposition of the Corumbataí Formation: a low energy environment, probably along the margin of a shallow inland sea not directly connected to the ocean.

Resumen. Leonardosia langei sommer (charophyta, porocharaceae) de la formación corumbataí (guadalupiano), picacicaba, sp, Brasil: primer registro de espermatogonio y talos corticados. Se describen segmentos fósiles de talos de carófitas fosilizados junto con girogonites aislados que fueron identificados como Leonardosia langei Sommer. Una de las muestras tiene un espermatogonio aparentemente conectado al talo, el que se encuentra claramente corticado. La presencia de espermatogonios es sumamente rara en el registro fósil y este constituye el primer hallazgo de una estructura reproductiva masculina para L. langei y dentro de la familia Porocharaceae. Así, al considerar la asociación estudiada y la ausencia de otras especies de carofitas fuera de L. langei, es posible que este pertenezca a esa especie. Los especímenes consisten en compresiones/impresiones y fueron colectados en capas de la Formación Corumbataí (Guadalupiano de la cuenca del Paraná), en el Municipio de Piracicaba, estado de São Paulo, Brasil. La presencia de este alga brinda además evidencias de las condiciones paleoambientales que predominaban durante la deposición de la Formación Corumbataí: un ambiente de baja energía, probablemente las áreas marginales de un mar interior de poca profundidad sin conexión directa con el océano.

Key words. Charophyta; Gyrogonites; Antheridium; Leonardosia langei; Corumbataí Formation; Permian.

Palabras clave. Charophyta; Girogonites; Espermatogonios; Leonardosia langei; Formación Corumbataí; Pérmico.

Introduction

The Charophyta are green algae of special interest when studying the evolution of plants, since they are close related to the ancestors of the Embryophyta (Graham, 1985). These algae occur worldwide, sometimes abundantly, in fresh and brackish water. They have erect slender cylindrical stems with short branchlets arising from whirled nodes and are fixed to the substratum by rhizoids. Their reproductive organs are antheridia and oogonia (Feist, 2005). The female organ is particulary important for palaeontology because once fertilization occurs, it deposits calcium carbonate in the walls surrounding the zygote to form the gyrogonite, and this structure is commonly fossilized (Horn af Rantzien, 1956; García, 1994). These gyrogonites make the Charophyta fossil record the most complete and best studied of the calcareous algae, with the exception of the Dasycladales (Feist, 2005). Because of their unique morphology (Horn af Rantzien, 1956), these easily identified structure have become the focus of many studies in palaecological and palaenvironmental reconstructions (García, 1994, Soulié-Märsche et al., 2002).
Permian charophytes are relatively rare in the fossil record of the world, although Leonardosia is a common genus in Permian strata in Russia, Brazil, Paraguay, China and Kazakhstan (Feist and Grambast-Fessard, 2005). This genus and its type species, Leonardosia langei, were described by Sommer (1954). Although in Sommer (1954) the taxa were not assigned to any known family, a subsequent work (Grambast, 1962b) has assigned them to the Porocharaceae. Sommer's samples were found in Teresina Formation (Paraná Basin), in the region of Ponta Grossa, in the Brazilian state of Paraná, and when he described them, he mentioned the occurrence of vegetative parts associated with the gyrogonites, although he found no evidence of connection between the structures. In fact, he based almost all of his description of the taxa on the morphology of the fertilized female reproductive organs (as is usually the case in the systematics of fossil Charophyta).
In 1974, the first occurrence of L. langei in the state of São Paulo was reported by Ragonha and Soares, who analyzed gyrogonites from the Teresina Formation in the municipality of Anhembi. As did Sommer (1954), these researchers studied only compressions and impressions of the gyrogonites. In 1997, Zampirolli et al. obtained the first silicified specimens; these were found in the municipality of Fartura, also in the state of São Paulo, from strata of the Teresina Formation.
This paper presents a systematic analysis of the portions of charophyte thalli found in close association with disperse gyrogonites assigned to L. langei. Considering the lack of charophyte species other than L. langei in the Corumbataí Formation, as well as in other Permian strata of the Paraná Basin, this close association between the gyrogonites and the thalli fragments strongly suggests that they belong to the same species. The presence of vegetative parts associated with L. langei gyrogonites was noted by Sommer (1954) but it was not explored. The present paper thus provides the first description of cortication in portions of L. langei thalli.
Sample CP1/61G shows an antheridium cast on the margin of a thallus fragment, possibly connected with it organically. The uncertainty arises from the fact that no node can be distinguished at the point of attachment. In any case, the presence of the male reproductive organ is very important. These are rarely present in the fossil record, although casts of them have been found in Clavatoraceae and Pinnoputamenaceae (Guerlesquin and Feist, 2005). The present findings permit the first description of a fossil antheridium for a Porocharaceae.

Geological setting

The Paraná Basin is an intracratonic basin of sediments accumulated from Silurian to Cretaceous times. It extends for some 1.750.000 km2 throughout Brazil, Argentina, Uruguay and Paraguay. In Brazilian territory, it occupies 1.150.000 km2 in the states of Rio Grande do Sul, Santa Catarina, Paraná, Mato Grosso, Mato Grosso do Sul, Goiás, Minas Gerais and São Paulo (Petri and Fúlfaro, 1981; Zalán et al., 1991).
The Passa Dois Group, which contains the unit where the fossils were found, consists of a sediment sequence deposited during the Cisuralian-Lopingian, often referred to as the "continentalization" interval of the Paraná Basin. This group reaches a maximum thickness of over 1400 m (Rohn, 2007) and covers the south of Brazil, Uruguay, Paraguay, and possibly, the north of Argentina (Zalán et al., 1991). It is composed by the Irati, Serra Alta, Teresina and Rio do Rasto formations, although the difficulty in distinguishing the lithofacies of the Serra Alta and Teresina formations along the northern edge of the basin has led to the adoption of the term Corumbataí Formation for the two.
The Corumbataí Formation is characterized mainly by grey to red siltstones, interlaminated shales and fine sandstones with flaser-wavy-lenticular-bedding. It probably represents the deposition along the margins of an inland epicontinental sea. It was probably influenced by climatic variations which would have been common in the context of the gradual aridization of the Paraná Basin, and which could have control variations in water level and salinity. In these marginal sites, wave energy was minimal, damped by friction along a broad shallow shelf. No formally described fossil from the formation can be considered as truly marine, so this inland sea was probably not directly connected to the ocean (Rohn, 2007).
The Corumbataí Formation was deposited during the Early Guadalupian (Rohn, 2007) and is included in the Lycopodiopsis derbyi Zone (Rohn and Rösler, 2000). Corumbataí Formation represents part of the phytogeographic Southamerican-Indian Unity from Stage 4 defined by Cúneo (1996) for the Late Paleozoic of Gondwana.

Material and methods

The fossils studied here were extracted from an outcrop (figure 1) in the lower portion of the Corumbataí Formation, located along the Hermínio Petrim Road (SP 308) linking the cities of Piracicaba and Charqueada (22°37'27"S / 47°42'03,3"W). They were collected by Dra.Rosemarie Rohn and graduate students of the State University of São Paulo (UNESP) and are deposited in the Paleobotanic Section of the Scientific Paleontological Collection of the Geosciences Institute, of the State University of Campinas, in Campinas, São Paulo, Brazil. The compressions/ impressions 12 separate gyrogonites and associated portions of thalli were studied.


Figure 1. Location of the outcrop from which was collected the studied assemblage/ localización del afloramiento donde fueron colectados los fósiles estudiados.

Results

Gyrogonites

Sistematic paleontology

The classification adopted here follows Feist and Grambast-Fessard (1991), with the modifications published in Feist and Grambast-Fessard, 2005.

Phylum CHAROPHYTA Migula, 1987
Class CHAROPHYCEAE Smith, 1938
Order CHARALES Lindley, 1836
Suborder CHARINEAE Feist &
Grambast-Fessard, 1991
Family POROCHARACEAE Grambast, 1962
Subfamily STELLATOCHAROIDEAE Grambast, 1962

Genus Leonardosia Sommer, 1954

Type species. Leonardosia langei Sommer, 1954.

Generic characters (according to Feist and Grambast- Fessard, 2005). Apical neck very long, more than one third of the gyrogonite length; apical neck broad at base, then decreasing in width toward top. Apical pore small or closed. Basal plate unknown. General shape subglobular. Size large.

Range. Upper Carboniferous (Pennsylvanian) to Upper Permian (Feist and Grambast-Fessard, 2005).

Geographic distribution. Russia, Brazil, Paraguay, China, Kazakhstan (Feist and Grambast-Fessard, 2005).

Synonymy. listed in Feist and Grambast-Fessard, 2005: 1984. Paracuneatochara Wang: p. 55. 1993. Acutochara Saidakovsky: p. 78. 1993. Luichara Kisielevsky: p. 100.

Leonardosia langei Sommer, 1954
Figure 2


Figure 2. Gyrogonite compressions of Leonardosia langei / compresiones de girogonites de Leonardosia langei 1, Sample / muestra CP1/68. 2, CP1/61G. 3, CP1/64. 4, CP1/63. 5, CP1/68. 6, Interpretative drawing of picture 1 / dibujo esquemático de la fotografia 1. .7, Interpretative drawing of picture 2 / dibujo esquemático de la fotografia 2. 8, Interpretative drawing of picture 3 / dibujo esquemático de la fotografia 3. 9, Interpretative drawing of picture 4 / Dibujo esquemático de la fotografia 4. 10, Interpretative drawing of picture 5 / dibujo esquemático de la fotografía 5. Scale bar / escala = 1 mm.

Holotype, type locality and stratigraphy. Sommer, 1954, pl. 16, 12 (Number 1030, Paleobotanic Collection, Divisão de Geologia e Mineralogia, Departamento Nacional de Proteção Mineral, Rio de Janeiro). Samples from Ponta Grossa, Paraná, Teresina Formation.

Samples studied, locality and stratigraphy. CP1/60, CP1/61A, CP1/61G CP1/62, CP1/63, CP1/64, CP1/68 e CP1/74. Outcrop along Hermínio Petrim Road (22°37'27"S / 47°42'03,3"W), lower portion of Corumbataí Formation.

Description. Only lateral compressions/impressions of 12 gyrogonites were analyzed, as the few basal and apical views were too poorly preserved for study. These show a very long apical neck and, in general, a prolate morphology; the length of the polar axis (LPA) measures from 660 to 1480 μm (average of 996,7 μm; standard deviation of 266,8 μm), with the width of the equatorial diameter (LED) having a range of 420 to 960 μm (average of 740 μm; standard deviation of 163,8 μm). Seven to eight convolutions are visible.

Comparison. A comparison with the original description of the type species of Sommer (1954) leaves, clears that the gyrogonites described here are related to Leonardosia langei. The best preserved have the characteristic lageniform aspect of Sommer´s description. This author found gyrogonites ranging from 800 to 1700 μm in length and 700 to 1100 μm in width, but he did not report the averages. Ragonha and Soares (1974) found an average length of 1220,60μm (standard deviation of 123,93 μm) and an average width of 924,20 μm (standard deviation of 62,23 μm) for the 16 lateral compressions/impressions that they studied. Considering these two papers, the gyrogonites described here are a bit smaller. Zampirolli et al. (1997) also found smaller gyrogonites.

Discussion. The small size of the gyrogonites found here in relation to those studied by Sommer (1954) and Ragonha and Soares (1974) may be explained by the influence of environmental conditions as the smaller specimens of Zampirolli et al. (1997) were linked to a possible relation with salinity conditions, although the possibility of a new species was not eliminated. Moreover, the poor preservation of the present samples and the small number of gyrogonites makes it difficult to reach definite conclusions about average size (as can be seen in the large standard deviations for both length and width). A greater variation in length than in width was also observed by Ragonha and Soares (1974); who suggested that this variation might reflect pre-fertilization lengthening of the apical portion of the spiral cells to form a neck, thus permitting the penetration of the antherozoids. This would suggest that variations in length would reflect differential levels of maturation rather than inherent morphological differences. However, such an explanation ignores the fact that when a gyrogonite is detached from the thallus, it must presumably have undergone fecundation; hence, differences could not be due to level of maturation since all gyrogonites are by definition in the same developmental phase.

Thalli portions

Description. The samples analyzed here consist of compressions/impressions of portions of thalli, mainly branchlets, which are clearly corticated. The cortication is not easily classified, but seems to show contiguous isodiametrical cortical cells.
Sample CP1/60 and its counterpart CP1/61A show various branchlets apparently grouped together in a single thallus (figure 3). The superimposition of the branchlets makes it difficult to distinguish one from another or from a central axis. The diameter of each branchlet extends from less than 300 μm to more than 650 μm. It is not possible to see the nodes in the cast of the thallus, although two regions do seem to be possible node regions, since the branchlets are apparently attached to it and extend out of the central portion.


Figure 3. Thalli portions of Leonardosia langei, sample CP1/60 / porciones de talos de Leonardosia langei, muestra CP1/60. 1, Panoramic view. The branchlets are superimposed, except for two regions which can be possible node regions (see the arrows indicating the possible nodes) / vista panorámica. Los talos están sobrepuestos, excepto en dos lugares, posiblemente regiones asociadas con nudos (indicados por flechas). Scale bar / escala = 10 mm. 2, A detail of the anterior picture showing one of the possible node regions (arrow indicating the node). The branchlets extend out of the central portion / detalle de la fotografía anterior donde se puede apreciar un posible nudo (indicado por flecha). Scale bar/ escala = 5 mm. 3, Another detail of picture 1 where the branchlets are more clearly distinguishable. Here again the arrow point a possible node / detalle de la fotografía 1 en la cual las características de los talos son claramente observadas, una vez que no se encuentran sobrepuestos. La flecha indica un posible nudo. Scale bar / Escala = 5 mm. 4, A detail of the branchlets showing cortication / detalle de los talos donde se aprecia la corticación. Scale bar / escala = 1mm. 5, Interpretative drawing of picture 1 / dibujo esquemático de la fotografía 1. Scale bar / Escala = 10 mm. 6, Interpretative drawing of picture 2 / dibujo esquemático de la fotografía 2. Scale bar / escala = 5mm. 7, Interpretative drawing of picture 3 / dibujo esquemático de la fotografía 3. Scale bar / escala = 5 mm. 8, Interpretative drawing of picture 4 / dibujo esquemático de la fotografía 4. Scale bar / escala = 1 mm.

Sample CP1/61G and its counterpart CP1/62 show a group of branchlets that may belong to the same thallus, although this is not clear (figure 4). These branchlets also show cortication and have an average diameter of approximately 700 μm. At two points along the margin of these branchlets, one finds the cast of reproductive organs; at one point there is a cast of an antheridium and at other, there is one of a gyrogonite. The antheridium, seem to be organically connected to the thallus, but since the presence of a node in this region is not visible, the possibility of displacement during the process of fossilization of the algae must be considered. It shows no association with bracteoles or bract-cells of the thallus and is a globular-shaped organ with a diameter of approximately 625 μm, closely resembling those of extant species. The shield cells are not clearly distinguishable. The gyrogonite (visible only in sample CP1/61G) is apparently displaced, but located along the margin of a branchlet in a strategic position which leaves some doubt about a possible connection. It shows five convolutions in a lateral view. The width of the equatorial diameter (LED) reaches approximately 578 μm. Neither the length of the polar axis (LPA), nor the isopolarity index (LPA/LDE x 100) could be measured, due to the incomplete preservation of the apical portion of the gyrogonite.


Figure 4. Thalli portions of Leonardosia langei, sample CP1/61G / porciones de talos de Leonardosia langei, muestra CP1/61G. 1, Panoramic view. The branchlets are superimposed and there is no certainty if they belong to the same individual. At two points along the margin of these branchlets, one finds the impressions of reproductive organs / vista panorámica. Los talos se encuentran sobrepuestos y no existe certeza de que pertenezcan a un mismo individuo. Fueron resaltados dos puntos a lo largo de los talos, donde se pueden apreciar estructuras reproductoras. Scale bar / escala = 5 mm. 2, A detail of the anterior picture showing a gyrogonite near the margin of a branchlet. It is possible displaced / Detalle de la fotografía anterior mostrando un girogonite localizado cerca del margen del talo. Este posiblemente esta desplazado. Scale bar / escala = 2 mm. 3, A detail of picture 1 showing an antheridium organically connected to a branchlet / detalle de la fotografía 1 mostrando un espermatógonio orgánicamente conectado con el talo. Scale bar / escala = 2 mm. 4, An enlargement of the antheridium. The shield cells are not clearly visible, but its general form closely resembles those of extant charophytes / ampliación del espermatógonio. Los escudos no se están muy bien preservados, aunque su forma recuerda claramente a la de las carofíceas actuales. Scale bar / escala = 1mm. 5, Interpretative drawing of picture 1 / dibujo esquemático de la fotografía 1. Scale bar / escala = 5 mm. 6, Interpretative drawing of picture 2 / dibujo esquemático de la fotografía 2. Scale bar / escala = 2 mm. 7, Interpretative drawing of picture 3 / dibujo esquemático de la fotografía 3. Scale bar / escala = 2 mm. 8, Interpretative drawing of picture 4 / dibujo esquemático de la fotografía 4. Scale bar / escala = 1 mm.

Comparison. When describing Leonardosia langei, Sommer mentioned the presence of vegetative parts associated with the gyrogonites, but said little about them, except that they were abundant and showed no concrete proof of connection with the gyrogonites. In the present samples, the cortication of the thalli fragments, however, is clear.

Discussion. In corticated thalli, calcite can be incorporated into the elongated filaments around the internodal cells (Guerlesquin and Feist, 2005). The cortication seen in the vegetative portions described here may suggests the calcified state of the thalli at the time of deposition, which could explain such a rare preservation. However, clearly uncalcified tissue has also been preserved, as can be seen by the presence of an antheridium. Although antheridia in other families have been found, the present record is the first of a Porocharaceae antheridium.
In sample CP1/61G, if the apparent connection of the organs (even the gyrogonite) to the branchlets is accepted, then is possible to propose something about the biology of Leonardosia langei: if the branchlets belong to the same individual, then the alga is monoecious. If monoecious, it moreover be sejoined, as it appears to be in the fossil cast, or it could be conjoined, if one of the organs preserved has been exported from the node bearing the other. The distinction between monoecious and dioecious forms generally cannot be detected in the fossil record, except for clear examples of conjoined monoecy between the Clavatoraceae and Pinnoputamenaceae (Guerlesquin and Feist, 2005). So if these fossils are trully monoecius, they would represent the first record of monoecy in a Porocharaceae.

Paleoenvironmental aspects

The utility of charophytes in paleolimnology is clear (García, 1994). The degree of preservation can indicate the energy of the environment, and the presence of only a few specimens is an indication of reophile conditions. Considering the gyrogonites studied here, which were few in number and not very well preserved, one could conclude that their deposition might have occurred in a high energy reophile environment. However, if the good state of preservation of the thalli and of the antheridium (fragile structures) are considered, as well as the fact that both gyrogonites and vegetative portions are impressions, it is clear that they probably were not submitted to a long process of transportation nor deposited under high energy conditions. These characteristics lead the suggestion of parautochthonous preservation. Other plant fossils found in the same outcrop, which include lycopods and its megaspores (see Faria et al., 2007), also indicate low transport and a low energy deposition. This hypothesis agrees with other paleoenvironmental interpretations (Rohn, 2007) which consider that the Corumbataí Formation was deposited along the margins of an inland sea where wave energy was minimal, damped by friction along a broad shallow shelf. The present fossils also reinforce the hypothesis of no direct connection of this inland sea with the ocean as Leonardosia langei is a strictly freshwater genus (Lu and Zhang, 1990).

Conclusions

This paper represents a contribution to our knowledge of charophytes because it provides a record of casts of Leonardosia langei portions of thalli and of an antheridium in close association with various gyrogonites. Both the thalli and the antheridium are relatively rare in paleozoic strata. The antheridum, the first registered in Porocharaceae, may be organically connected to a branchlet.
Vegetative parts in association with L. langei were mentioned by Sommer (1954) when it was first descript, but these thalli were not described. Here the thalli have been shown to be corticated with apparently contiguous isodiametrical cortical cells.
These findings also provide evidence of some of the palaeoenvironmental conditions prevailing during the deposition of the Corumbataí Formation: a low energy environment, probably along the margins of a shallow inland sea with no direct connection with the ocean (most likely a coastal lagoon).

Acknowledgments

The authors would like to acknowledge the collaboration of R. Rohn Davies (Department of Applied Geology, State University of São Paulo) for granting access to the assemblage studied, as well as her assistance during the field work. They also acknowledge the suggestions of the referees Monique Feist (Institut des Sciences de L'Evolution, Université Montepellier) and A. García (School of Earth & Environmental Sciences, University of Wollongong). Their contributions have significantly improved the quality of the paper. We also like to thank The Brazilian National Council for Scientific and Technological Development (CNPQ) and the Foundation for the Support of Research in the State of São Paulo (Fapesp - Project"Bryophyta, Lycophyta and associated plant fossils from Upper Permian of Paraná Basin", 06/01365-9) for the financial support provided.

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Recibido: 6 de diciembre de 2007.
Aceptado: 15 de septiembre de 2008.