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2Abt. Paläobotanik am Geologisch-Paläontologischen Institut, Westfälische Wilhelms-Universität Münster, Hindenburgplatz 57, D-48143 Münster, Germany; and 3Department of Ecology and Evolutionary Biology and Natural History Museum and Biodiversity Research Center, The University of Kansas, Lawrence, Kansas 66045-2106 USA
Received for publication April 14, 2000. Accepted for publication June 27, 2000.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Key Words: climber hooks • Early Permian • growth habit • Late Carboniferous • Pseudomariopteris busquetii • pteridosperms • reconstruction • Rotliegend • Stephanian
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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; Pfefferkorn et al., 1984
); some species, however, were much larger, with fronds that may well have been up to 7 m long (e.g., Laveine, 1986
). Other taxa had rather narrow and flexuous stems and have been suggested to be leaners (e.g., Wnuk and Pfefferkorn, 1984
). These forms may have gained support from leaning against larger trees and/or loosely intermingling with components of the surrounding vegetation, or they may have grown in dense stands (clumps), in which they supported each other by an intertwining of foliar parts (Wnuk and Pfefferkorn, 1984
; Stewart and Rothwell, 1993
). The pteridosperms also contained a larger number of true vines and lianas. Vine- to liana-like growth forms have been documented for compression taxa, based on gross-morphological features including narrow, flexuous stems, long internodes, and small fronds (e.g., Potonié, 1898
; Danzé-Corsin, 1953
) and/or specialized climbing organs such as climber hooks and tendrils (e.g., DiMichele et al., 1984
; Krings and Kerp, 1997, 1999
). Stem diameter and anatomy also suggest that some permineralized forms were vine- to liana-like (e.g., Baxter, 1949
; Rothwell and Taylor, 1972
; Stidd and Phillips, 1973
; Rothwell, 1975
; Pigg, Taylor, and Stockey, 1987
).
Detailed reconstructions depicting the growth habit of individual pteridosperm taxa typically address the tree-like or leaning forms (e.g., Pfefferkorn et al., 1984
). Complete reconstructions of vine- or liana-like forms are rare, although such pteridosperms are frequently found incorporated in overall reconstructions of Late Carboniferous and Permian coal-swamp forests (e.g., Potonié, 1899
[Frontispiece]; 1921 [Frontispiece]). Only a few scrambling and/or climbing taxa have been reconstructed in detail. One of these is Callistophyton sp., a Middle and Upper Pennsylvanian form from North America, which has been reconstructed as a scrambling shrub with adventitious roots that provided additional support (Fig. 1 in Rothwell, 1975
), and Blanzyopteris praedentata, a (?medullosan) compression taxon from the Stephanian of France, which has been characterized as a highly specialized tendril climber (Fig. 8 in Krings and Kerp, 1999
).
In this paper we present a growth habit reconstruction for Pseudomariopteris busquetii, a taxon with callistophytalean affinities (see below), that was quite common in the European upper Stephanian and Lower Permian (e.g., Kerp and Fichter, 1985
; Boersma, 1991
; Krings and Kerp, 2000
). Based on compression specimens from France and Germany, P. busquetii is reconstructed as a medium-sized scrambling/climbing plant that attained support by attaching its stems to other plants or by anchoring its fronds with climber hooks.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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; Langiaux, 1984
); the flora of the Basin has been described by Zeiller (1906)
and Langiaux (1984)
. Pseudomariopteris busquetii is a common element of this flora. The Commentry Basin is another of the intramontane basins in the Massif Central. The geology of this basin has been detailed by Fayol (1887)
and Desrousseaux (1938)
, among others. The Stephanian flora of Commentry has been described by Zeiller and Renault (1888–1890)
, and includes the original description of Diplotmema busquetii (Zeiller, 1888)
, which was later transferred to Pseudomariopteris. Most of Zeiller's material from Commentry and Blanzy-Montceau, including the type specimens, is deposited in the collections of the École Nationale Supérieure des Mines de Paris, at the University Lyon I, Villeurbanne, France, and is partly refigured here (specimen numbers preceded by EMP). In addition, specimens collected by Dr. Jean Langiaux (Gourdon, France), which are housed in the collections of the Musée des Fossiles in Montceau-les-Mines, France (specimen numbers preceded by L), were also examined.
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; Germer and Engel, 1986
; Laveine, 1989
). The P. busquetii specimens come from the upper Rotliegend (Nahe Group, N 4, probably the highest stratigraphic occurrence of the taxon) and were collected in the quarry of the Eimer Brickwork Company at Sobernheim (now Bad Sobernheim), Rheinland-Pfalz, Germany (cf. Kerp, 1988
), and are kept in the Laboratory of Palaeobotany and Palynology, University of Utrecht, The Netherlands (specimen numbers preceded by LPPU), and the Paleontology Museum Nierstein, Germany (collection Stapf, specimen numbers preceded by PMN). |
RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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, emend. Krings et Kerp, 2000
, is a late Paleozoic pteridosperm foliage taxon used for small bipartite and bipinnate fronds with mariopteroid pinnules. Although a few occurrences have been reported elsewhere, the distribution of Pseudomariopteris seems to be largely restricted to Europe and North America. The genus first appears in the latest Westphalian, being widely distributed in the Stephanian, and is last recorded from the Lower Permian (Boersma, 1991
). Pseudomariopteris busquetii (Zeiller, 1888)
Danzé-Corsin 1953
, emend. Krings et Kerp, 2000
, the type species and most common taxon of the genus, has been reported from the upper Westphalian D to the upper Rotliegend (cf. Krings and Kerp, 2000
). However, most of the records older than Stephanian B are questionable (Boersma, 1991
). The species seems to be most common in the European upper Stephanian, having been reported from various basins in France, Germany, Spain, Austria, Croatia, and Russia (Boersma, 1991
).
The pteridospermous affinity of P. busquetii is the result of small platyspermic seeds, which have been found attached to pinnules or pinna axes of a specimen from the Stephanian of Blanzy-Montceau (cf. Krings and Kerp, 2000
). The position of these seeds in P. busquetii (Figs. 9, 10) suggests a callistophytalean affinity given their occurrence in a similar position in Dicksonites (see, e.g., Figs. 1–6 in Langiaux, 1986
), a genus that is interpreted as the compression counterpart of Callistophyton (Meyen and Lemoigne, 1986
).
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The growth habit
Pseudomariopteris busquetii had a vine- to liana-like growth habit based on the slender stems, which range from only 1.0 to 1.5 cm in diameter (Figs. 6, 11). Although the fronds were relatively small (usually in the range of 15–25 cm long, Figs. 1, 3, 6), it appears unlikely that stems of this diameter were self-supporting. Rather, the plant obtained support from anchoring the fronds to some other plant(s) in the surrounding vegetation by means of specialized (up to 1.5 cm long) climber hooks, developed from apical extensions (prolongations sensu Boersma, 1972
) of pinna axes. These hooks may occur on the interior as well as on the exterior side of the frond. Specimens with well-developed climber hooks are known from Commentry (Fig. 1, arrows, and Fig. 2) and Blanzy-Montceau (Figs. 4, 6, 7, arrows), but also from various other sites, e.g., the Stephanian C of Plötz near Halle, Germany (Fig. 9 in Remy and Remy, 1977
) and the upper Stephanian of the Schulterkofel, Carnian Alps, Austria (fig. 2 in Boersma, 1991
). Interestingly, climber hooks are not consistently present in P. busquetii; some fronds have none and the pinnae terminate in small pinnules (e.g., Fig. 11, small arrows; Krings and Kerp, 2000
, Pl. III, 2). We hypothesize that the presence of climber hooks on the frond may be dependent on the stage of development of the plant; in some stages development of the hooks may have been suppressed. On the other hand, a number of extant climbing plants (e.g., many climbing Araceae) possess the ability to change the leaf morphology when they grow from one microhabitat into another, e.g., when they gain or loose contact with trees (Ray, 1987
). Thus, the development of climber hooks in P. busquetii may also have been controlled by environmental factors, perhaps by the type of vegetation in which the plant was growing, and thus the availability of certain types of support conditions. In this respect it is especially interesting to note that the large specimen from Sobernheim (Fig. 11) lacks climber hooks. This specimen shows a stem that bears two "pseudo-pairs" of fronds (large arrows), i.e., two closely spaced fronds, followed by a longer internode. The frond axes all are directed toward one side of the stem and the fronds were positioned more or less horizontally. The fact that the lowermost frond lies in the same plane as the main axis of the specimen is no doubt a preservational feature, as clearly indicated by torsion of the frond axis below the bipartition. The appearance of this specimen suggests that the stem was attached to a support medium, perhaps by twining or by means of adventitious roots. Orientation of the leaves to one side, toward the sunlight and free space and (as far as possible) away from the support, is commonly found in extant scrambling/climbing plants with firmly attached stems (e.g., Givnish and Vermeij, 1976
). The inconsistency of climber hooks and the information gathered from the large specimen from Sobernheim suggest that the scrambling/climbing mode of P. busquetii may have changed during the life of a single plant, or that individuals of P. busquetii could a priori express a variety of growth strategies, each dependent upon conditions in the respective habitat of growth.
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) suggests that fronds were up to 30 cm long; most fronds are in the range of 15–25 cm in length (Figs. 1, 3, 6). A small, 
9 cm long frond with well differentiated individual pinnules from Sobernheim is illustrated in Fig. 5. Based on the differentiation of the pinnules we suggest that the frond was mature and, thus, demonstrates considerable heterophylly for P. busquetii. Heterophylly, which is a conspicuous feature of many extant climbing plants (e.g., Cremers, 1973, 1974
; Ray, 1987
; Lee and Richards, 1991
), has also been demonstrated for the tendril-climbing Stephanian pteridosperm Blanzyopteris praedentata (Krings and Kerp, 1999
). Heterophylly may arise by a number of different mechanisms (Steeves and Sussex, 1989
; Winn, 1999
), which argues against assigning a specific ecological or functional significance to within-individual variation of frond/leaf size and shape in fossil plants. For example, heterophylly in P. busquetii may be an expression of heteroblastic development or a programmed ontogenetic change in morphology (cf. Steeves and Sussex, 1989
; Winn, 1999
), and the small frond may have come from a juvenile plant. On the other hand, heterophylly in P. busquetii may be a mechanism of adaptation. Based on studies of extant tropical vines/lianas it is known that in favorable conditions these plants may produce specialized, elongate shoots ("Sucher" sensu Goebel, 1923
), which grow in length rather quickly during their "search" for suitable support media (i.e., exploratory growth); such shoots are often characterized by having small and/or undifferentiated leaves (Raciborski, 1900
; Goebel, 1923
). As growth continues, larger and/or more fully differentiated leaves are developed once suitable support is achieved. Thus, heterophylly in P. busquetii also could indicate that this species produced specialized, exploring shoots (perhaps in order to transition from one support tree into the foliage of neighboring trees), which were characterized by having small fronds.
It remains an unsolved question as to what were the most frequently used support media for the scrambling/climbing Pseudomariopteris busquetii plants, since no specimens have ever been found attached to their support(s). The vegetation that occurs with P. busquetii from Blanzy-Montceau and Commentry was structurally diverse, including larger pteridosperms, pecopterid tree-ferns, cordaites, calamites, and a few arborescent lycopsids (Zeiller, 1888, 1906
; Langiaux, 1984
). All of these plants may have provided suitable supports for vines and lianas. It is probable, however, that stands of calamites or the fronds of larger tree ferns and pteridosperms were particularly suitable support media since their structure provides an ideal trellis-like system for small fronds that used multiple anchoring sites, i.e., climber hooks. Fronds with numerous climber hooks could presumably effectively anchor by extending out on the support medium (e.g., on a larger tree fern frond), or by hanging in a thicket, suspended between components of one or several supports (e.g., in fern or pteridosperm foliage or in calamite branching systems and foliage). In addition, plants may have gained support from stem attachment (by twining or with adventitious roots) to larger tree trunks and perhaps even rock surfaces. Some of the cordaites, pteridosperms, and tree ferns of the Blanzy-Montceau and Commentry floras possessed stems that certainly provided suitable support for twining plants or root climbers. The stems of tree ferns with prominent root-mantles have been demonstrated elsewhere to be a frequently used support medium for climbing plants in the late Paleozoic (Rößler, 2000)
. However, whereas stems with adventitious roots may attach to tree trunks or even to rock surfaces, twining stems are more or less restricted to stems/trunks of other plants.
One horizon from the upper Rotliegend of Sobernheim (Pseudomariopteris horizon, cf. Kerp, 1988
) indicates that P. busquetii also may have grown in dense stands (clumps) or thickets in which neighboring stems and fronds provided support. In this horizon bedding planes are often completely covered with P. busquetii fronds, but remains of larger pteridosperms, tree ferns, or calamites, which could have supported vines or lianas, are comparatively rarely present. This suggests that P. busquetii may have had a similar appearance to stands of certain extant Rubus species (e.g., R. fruticosus, R. idaeus, or R. trivialis). These species, which are often vigorously growing, may, if no suitable support media (e.g., large bushes, trees) are available, form thickets of intertwining stems (canes) and leaves that can sometimes become extensive (e.g., Dierschke, 1988
). The individual plants within such thickets support each other and in this way may attain a height that no single plant could achieve alone. The plants in such thickets may be more competitive than individuals restricted to a creeping or semi-erect and arching habit. One of the few additional plants present in the Pseudomariopteris horizon at the Sobernheim locality is Dicksonites pluckenetii, believed to be the compression equivalent of the permineralized taxon Callistophyton (cf. Meyen and Lemoigne, 1986
). This pteridosperm also has been characterized as having a scrambling habit (Rothwell, 1975
). This suggests that the thickets or stands may have consisted of several species with similar growth habits. The growth conditions for P. busquetii in the Pseudomariopteris horizon from Sobernheim were apparently very similar to those of Karinopteris sp. in the Indiana paper shale (USA), where the cuticular (or "paper") coal is made up almost completely of Karinopteris sp. with few remains of larger plants present (DiMichele et al., 1984
).
The reconstruction
The drawing presented here (Fig. 12) shows a Pseudomariopteris busquetii plant climbing up the stem and into the foliage of a tree-like pteridosperm. The reconstruction depicts P. busquetii as being a large vine (or a small liana) that used two basically different strategies during development in order to anchor its body to the stem and into the foliage of the tree.
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Comparisons
Vine- or liana-like growth habits have repeatedly been suggested for mariopterid pteridosperms, based on the relatively narrow nature of the frond-bearing stems (e.g., Potonié, 1898, 1899
; Danzé-Corsin, 1953
) and/or the presence of apical extensions of pinna axes, commonly interpreted as climber hooks (e.g., Zeiller, 1906
; DiMichele et al., 1984
; Josten, 1991
). However, to date no detailed reconstructions of growth form and growth strategies have been elaborated for any one species. The reconstruction of Pseudomariopteris busquetii presented here depicts a growth form and growth strategies that were apparently widely distributed among mariopterid pteridosperms. Several gross-morphological features, which are characteristic of P. busquetii and important for our understanding of its growth form, have also been documented for other mariopterid taxa. Most striking is the presence of specialized climber hooks (usually, but not always, developed from apical extensions of pinna axes). Similar climber hooks have been reported from a large number of taxa, e.g., numerous species of Mariopteris from the Late Carboniferous of France and Germany (e.g., Mariopteris carnosa, M. nervosa [Corsin, 1932
], M. daviesi, M. sauveuri [Josten, 1991
], M. muricata [Zeiller, 1886
; Danzé-Corsin, 1953
]), Karinopteris acuta from the Namurian of Germany (Schultka, 1995
), Karinopteris sp. from the Middle Pennsylvanian Indiana paper shale, USA (DiMichele et al., 1984
), and Pseudomariopteris cordato-ovata from the Stephanian of France (Krings and Kerp, 2000
). Boersma (1972)
regards climber hooks as a typical feature of mariopterid pteridosperms. Although the climber hooks may display considerable interspecific morphological variability, they all suggest a scrambling/climbing growth form similar to that of P. busquetii. Moreover, all taxa noted above display the same inconsistency in the presence of climber hooks. This adds support to the concept that climber hooks characterize a phase in the growth of these pteridosperms. In addition, several mariopterid specimens with narrow and slender stems (up to 2.0 cm in diameter) have been reported, e.g., stem fragments of Karinopteris sp. from the Indiana paper shale (DiMichele et al., 1984
), and stem portions with attached frond(s) of Mariopteris andraeana (Danzé-Corsin, 1953
, Pl. LXXVII, 4), M. carnosa (Corsin, 1932
, Pl. LXVIII,1), M. guillaumei (Corsin, 1932
, Pl. LXXXV, 1), M. muricata (Zeiller, 1886
, Pl. XXI, 1, Pl. XXIII, 1), and M. roussini (Danzé-Corsin, 1953
, Pl. LXXVIII, 1a) from the Late Carboniferous of France. Of special interest is a specimen from the Westphalian of northern England, reported by Cleal and Thomas (1999)
. This highly informative specimen shows a slender stem with mariopterid fronds still attached, still wound around the stump of an arborescent lycopsid.
Concluding remarks
The Late Carboniferous–Early Permian pteridosperm Pseudomariopteris busquetii possessed a vine- to liana-like growth habit and used at least two different strategies to anchor itself to a support medium. In the absence of suitable supports, however, P. busquetii also was able to grow in dense stands (clumps) or thickets in which the individual plants supported each other. Morphological similarities between P. busquetii and other mariopterids suggest that the growth form may have been widely distributed among this group of pteridosperms, perhaps even characteristic of the general appearance of mariopterid pteridosperms.
Based on local abundance in the fossil record (e.g., DiMichele et al., 1984
; Kerp and Fichter, 1985
), mariopterid pteridosperms may have played an important role in some Late Carboniferous and Early Permian coal-swamp forest ecosystems. We assume that they represented part of a rather vigorously growing, sprawling, scrambling and/or climbing type of vegetation that may be structurally comparable to the vegetation that can be found prevailing at edges or in disturbed areas (e.g., treefall gaps) of contemporary temperate and tropical forest ecosystems. If so, mariopterid pteridosperms would have locally contributed to the structural complexity of the late Paleozoic coal-swamp forest vegetation.
Vine- to liana-like growth habits have to date been documented for a large number of Late Carboniferous and Early Permian pteridosperm taxa. The scrambling/climbing aids used by these pteridosperms include scrambling and twining stems, climber hooks, tendrils, and tendrils terminating in adhesive pads (cf. Kerp and Krings, 1998
). These reports, including the data presented here on the growth habit of Pseudomariopteris busquetii, clearly demonstrate that scrambling and/or climbing growth habits were common in this group of seed plants. Moreover, they demonstrate that the various modes of attachment, developed by pteridosperms in the late Paleozoic, and a number of morphological adaptations of these plants to the special physiological requirements of a scrambling/climbing growth habit (cf. Krings and Kerp, 1997, 1999, 2000
), are very similar with those that exist in extant angiosperms.
The fossil record of woody plants rarely provides specimens in organic attachment and, thus, concepts relating to whole plant biology are often difficult to determine. Nevertheless, more and more Paleozoic and Mesozoic taxa are being "assembled" and we are gaining increasing resolution about the community structure in which these organisms lived. The data presented here on the mariopterid pteridosperm Pseudomariopteris busquetii indicate that certain morphological structures (e.g., climber hooks, orientation of the fronds, and heterophylly) are related to how these plants grew in the community in which they lived and that certain of these structures can be attributed directly to the growth phase of the plant. Such information is especially important as it relates to the identification of disarticulated plant fossils, especially foliage types, since structural and morphological features are the basis of generic and specific identifications. Historically, paleobiologists have placed increasing emphasis on the structure/function relationships of various morphological features, and this emphasis has contributed to a more biological understanding of ancient plants. As paleobotanists have pieced together the floral elements and subsequently characterized the communities in which they once lived, they also have attempted to interpret ecosystem dynamics on a broad scale. We are now entering a phase within the discipline in which understanding plant/plant relationships may be possible in some instances. The ability to interpret various structures and their relationship to stages in the growth of the plant, as evidenced by the pteridosperm discussed here, provides a new source of information about both the plants and the ecosystems in which they grew.
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FOOTNOTES |
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4 Author for correspondence (fax: ++49-251-832 1739; krings{at}uni-muenster.de
).
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LITERATURE CITED |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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