Reconstruction of Pseudomariopteris busquetii, A Vine-Like Late Carboniferous-Early Permian Pteridosperm

by Michael Krings, Thomas N. Taylor, Edith L. Taylor, Hans Kerp
Citation
Title:
Reconstruction of Pseudomariopteris busquetii, A Vine-Like Late Carboniferous-Early Permian Pteridosperm
Author:
Michael Krings, Thomas N. Taylor, Edith L. Taylor, Hans Kerp
Year: 
2001
Publication: 
American Journal of Botany
Volume: 
88
Issue: 
5
Start Page: 
767
End Page: 
776
Publisher: 
Language: 
English
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Abstract:

RECONSTRUCTION BUSQUETZZ, A

OF PSEUDOMARZOPTERZS
VINE-LIKE LATECARBONIFEROUS-EARLY

PERMIAN

'Abt. Palaobotanik am Geologisch-PalaontolqischenInstitut, LVestfiilische \Villrelmc-L'niversitat Munster, Hindenburgplatz 57,
D-48143 Munster, Germany; and
'Department of Ecology and Evolutionary Biology and Natural History Museum and Biodiversity Research Center,
The University of Kansas, Lawrence, Kansas 66045-2106 USA

The growth habit of the Lare Carboniferous-Early Permian pteridosperm Pselidor7zcii-iol~te1'i~r on

bzi~qciefii is reconstructed based compression material from the upper Stephanian of the Blanzy-h4ontceai1 and Commentry Basins (Massif Central, France), and the upper Rotliegend of the Saar-Nahe Basin (Nahe Group, N 4, Rheinland Pfalz, Germany). Psettclo~nnrioprer.ir bt~.rqilefii was a medium- sized, vine- to liana-like plant with slender stems to which small bipartite fronds were attached. What is moyt interesting is that the species used at least two different strategies to both anchor and support the plant body. Most specimens possess specialized climber hooks developed from apical extensions of the pinna axes, indicating that the fronds were used to attach the plant. A few specirnens suggest that the stem may also ha~e had some capacity for attachment. In the absence of suitable supports, honever. P. bt~sqtirtiiwas apparently able to grow in dense stands or thickets in which the indi\idual plants supported each othet

Key words: climber hooks; Early Permian: growth habit; Late Carboniferous; Pseziiloiizariopteris busclur~rii; pteridospernms; re

construction; Rotliegend; Steplranian.

There are several reconstructions depicting the growth habit of Late Carboniferous-Early Permian pteridosperms based on both impressionlcompression fossils and permineralized spec- imens. Historically it was widely accepted that pteridosperms were self-supporting trees similar to modern tree ferns. Today, however, it is understood that pteridosperms were more mor- phologically diverse and displayed several fundamentally dif- ferent growth forms. Some taxa were small to medium-sized, upright, self-supporting trees with fronds in the range of 1-2 m long (e.g., Stewart and Delevoryas, 1956; Pfefferkorn et al., 1984); some species, however, were much large]; 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 je.g., Wnuk and Pfefferkorn, 1984). These forms may have gained support from leaning against larger trees andlor loosely intermingling with compo- nents 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 compres- sion taxa, based on gross-morphological features including narrow, flexuous stems, long internodes, and small fronds je.g., Potonie, 1898; DanzC-Corsin, 1953) andlor specialized

I Manuscript received 14 April 2000; revision accepted 27 June 2000.

The authors thank all colleagues who made material available, especially Drs. Jeari Langiaux (Gourdon. France), Abel Prieur (Villeurbanne, France), and Johan van der Burgh (I;trecht. The Netherlands). and Ms. Henri J. Doner-Hedrick (Lawrence. KS, USA) for drawing the reconstruction. This research was suol3orted bv the Alexander von Hunrboldt Foundatiorl (Feodor Lvnen ~esearch ~ellowshi~

to M.K.), the German Science Foundation (DFG g&s Ke 58412-1 and Ke 58412.2 to H.K.I. and the National Science Foundation

-~ ~

(NSF-grant OPP-9614847 to E.L.T. and T.N.T.). "Author for correspondence (fax: ++49-251-832 1739: e-mail: kringsmuni-muenster.deI.

climbing organs such as climber hooks and tendrils (e.g., Dihlichele 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 in- dividual pteridosperm taxa typically address the tree-like or leaning forms (e.g., Pfefferkorn et al., 1984). Co~nplete reconstructions of vine- or liana-like forms are rare, although such pteridosperms are frequently found incorporated in overall re- constructions of Late Carboniferous and Permian coal-swamp forests (e.g., Potonik, 1899 I Frontispiece]; 1921 [Frontispiece]). Only a few scrambling and/or climbing taxa have been reconstructed in detail. One of these is Culli.rto17hyton sp., a Middle and Upper Pennsylvanian form from North America, which has been reconstructed as a scrambling shrub with ad- ventitious roots that provided additional support (Fig. 1 in Rothwell, 1975), and Blanzyol?teris praedentcitc~, a (?medul- losan) 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 Pseuclor~zni-iopteri.c Dlisqiietii, 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 com- pression specimens from France and Germany, P. D~tsquetiiis reconstructed as a medium-sizcd scrambling/clin~bing plant that attained support by attaching its sterns to other plants or by anchoring its fronds with climber hooks.

MATERIALS AND METHODS

Specimens of Ps~iiiiori~nrio/~ter.is

hztsqtlefii colrre from the Stephanian of the Blanzy-Morrtceau and Co111ment1.y Basins (Massif Central, France) (e.g..

Figs. 1, 7, 4. 6, 7, 9. 10), and the upper Rotliegelid of the Saar-Nahe Basin (Rheinland-Pfalz, Germany) (e.g., Figs. 3, 5, 8, 11). The Blanzy-Montceau Basin is one of several intratnontane basins in the French Massif Central. The coal-bearing strata have been dated as late Stephailia11 (Branchet, 1983: Lan- giaux. 1984); the flora of the Basin has been described by Zeiller (1906) and Langiaux (1984). Pse~tilonzar-iopter-i.c Ousqcterii is a common element of this flora. The Colnmentry Basin is another of the intrarnontalie basins in the Massif Central. The geology of this basin has been detailed by Fay01 (1887) and Desrousseaux (1938), among others. The Stephanian flora of Commentry has been described by Zeiller and Renault 11888-1890). and includes the original description of Di~~lot~neiiin

husquerii (Zeiller, 18881, which was later transferred to Pseu~loiizariopteris.Most of Zeiller's ~naterial from Colnmentry and Blanzy-Montceau. including the type specimens. is deposited in the col- lectiolls of the &ole Nationale Superieure des Mines de Paris, at the Uni- versity Lyon I, Villeurbanne, France, and is partly refigured here (specimen numbers preceded by EMP). I11 addition, specimens collected by Dr. Jean Larigiaux (Gourdon, France), which are housed in the collections of the Muste des Fossiles in Montceau-les-Mines, France (specimen numbers preceded by L), were also examined.

The Saar-Nahe-Lorraine Basin is the largest late Paleozoic intramontane basin of northwestern and central Europe; plant-bearing strata there range from the upper Westphalian B to the upper Rotliegend (Kerp and Fichtei; 1985; Gerrner and Engel, 1986; Laveine. 1989). The P. bitsq~retii 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 Eiiner Brickwork Company at Sobernheim (now Bad Sobernheim). Rhein- land-Pfalz, Germany (cf. Kerp, 19881, and are kept in the Laboratory of Pa- laeobotany and Palynology, University of Utrecht. The Netherlantls (specimen numbers preceded by LPPU), and the Paleontology Museurn Nierstein, Ger- many (collection Stapf, specimen ~iumbers preceded by PMN).

RESULTS AND DISCUSSION

Pseudomariopteris busquetii (Zeiller) Danz.6-Corsin, emend Krirzgs et Kerp-PseudomariopteI.is Danze-Corsin 1953, emend. Krings et Kerp, 2000, is a late Paleozoic ptcri- dosperm foliage taxon used for small bipartite and bipinnate fronds with marioptcroid pinnules. Although a few occurrenc- es have been reported elsewhere, the distribution of Pseudomariopteris scems 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). Pseudomarioptel-is bzisyuetii (Zeiller, 1888) Danzt-Corsin 1953, emend. Krings et Kcrp, 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. b~rsquetiiis the result of small platyspermic seeds, which have been found attached to pinnules or pinna axes of a specimen from the Stephanian of

BLrSQIIETII RECONSTRlJCTIOIV 769

Blanzy-Montceau (cf. Krings and Kerp, 2000). The position of these seeds in P. busquetii (Figs. 9, 10) suggests a callis- tophytalean 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 Callisto-phyton (Meyen and Lemoigne, 1986).

The frond architecture of P. bzlsqlletii is well known from several complete bipartite fronds (e.g., Figs. 1, 3, 6). More- over, a few specimens provide information on the growth habit of the plant because they contain stem fragments with attached fronds (c.g., Figs. 6, 11). The reconstruction of P, riusquetii presented here is based on a synthesis of data from these larger specimens and comparisons with extant plants.

The growth habit-Pseuclomarioptel-is bztsq~fetiihad 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 ob- tained 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 ex- terior side of the frond. Specimens with well-developed climb- er hooks are known from Colnmentry (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 Plotz near Halle, Germany (Fig. 'in Remy and Remy, 1977) and the upper Stephanian of the Schulterkofel, Carnian Alps, Austria (fig. 2 in ~oersina, 1991). Interestingly, climber hooks are not con- sistently 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, P1. 111, 2). We hypothesize that the presence of climber hooks on the frond may be de- pendent 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 Araceac) possess the ability to change the leaf morphology when they grow from one microhabitat into an- other, e.g., when they gain or loose contact with trees (Ray, 1987). Thus, the development of climber hooks in P. bclsquetii may also have been controlled by environmental factors, per- haps 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

Figs. 1-5. Pseudonzar.iopteris husqitetii (Zeiller) Danze-Corsin, emend. Kririgs et Kerp from the upper Stephaniali of the Commentrq- and Blanzy-Montceau Basins, France, and from the upper Rotliegend (Nahe Group, N 4) of the quarry of the Eilner Brickwork Company, Bad Sobernheim, Saar-Nahe Basin, Germany.

1. Complete frond with climber hooks (arrows); lectotype of P. husqiterii, originally figured by Zeiller (1888, PI. IV, 7). Doyot Colliery, Commeritry Basin. EMP mithout collection number. X0.75. 2. Detail of Fig. 1, showing a pinna terminating in a climber hook. X4. 3. Nearly complete frond froin Sobernheim, originally figured by Kerp and Fichter (1985, PI. 18, 1). PMN without collection number. X 1. 4. Pilina terminating in climber hook, originally figured by Zeiller (1906, PI. VIII, 2). Sainte Helkne Colliery, Blanzy-Montceau Basin. EMP without collection number. X 1. 5. Very small frond with well differentiated pillnules from Sobernheim, originally figured by Ksings and Kerp (2000, PI. 111, 3). LPPU 6910E. X 1.

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 spec- imen suggests that the stem was attached to a support medium, perhaps by twining or by means of adventitious roots. Orien- tation of the leaves to one side, toward the sunlight and free space and (as far as possible) away from the support, is com- monly found in extant scramblinglclimbing plants with firmly attached stems (e.g., Givnish and Vermeij, 1976). The incon- sistency of climber hooks and the information gathered from the large specimen from Sobernheim suggest that the scram- blinglclimbing mode of P. busqcietii 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 de- pendent upon conditions in the respective habitat of growth.

Several complete rather small, bipartite fronds of Pseiidornariopteris bcisquetii are known. The largest isolated frond portion illustrated (fig. 109 in Remy and Remy, 1977) 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

u

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 ten- dril-climbing Stephanian pteridosperm Blanzyopteris pmederz- tata (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 eco- logical or functional significance to within-individual variation of frondlleaf size and shape in fossil plants. For example, het- erophylly 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 vinesllianas 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 spe- cialized, exploring shoots (perhaps in order to transition from one support tree into the foliage of neighboring trees), which were characterized bv having small fronds.

u

It remains an unsolved question as to what were the most frequently used support media for the scramblinglclimbing Pseudonzariopteris biisquetii plants, since no specimens have ever been found attached to their support(s). The vegetation that occurs with P. busqiietii from Blanzy-Montceau and Corn- mentry was structurally diverse, including larger pterido- sperms, 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 cala- mites or the fronds of larger tree ferns and pteridosperms were particularly suitable support media since their structure pro- vides an ideal trellis-like system for small fronds that used multiple anchoring sites, i.e., climber hooks. Fronds with nu- merous 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 pteri- dosperm foliage or in calamite branching systems and foliage). In addition, plants may have gained support from stem attach- ment (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. he stems of tree ferns with promineilt root-mantles have been demon- strated elsewhere to be a frequently used support medium for climbing plants in the late Paleozoic (RoBler, 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 stemsltrunks of other plants.

One horizon from the upper Rotliegend of Sobernheim (Pseiidomariopteris 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 sup- port. In this horizon bedding planes are often completely cov- ered with P. busquetii fronds, but remains of larger pterido- sperms, 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. jruticosus, 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., Dier- schke, 1988). The individual plants within such thickets sup- port 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 creep- ing or semi-erect and arching habit. One of the few additional plants present in the Pseudonzariopteris horizon at the Sob- ernheim locality is Dicksonites pluckenetii, believed to be the compression equivalent of the permineralized taxon Callisto-phyton (cf. Meyen and Lemoigne, 1986). This pteridosperm also has been characterized as having a scrambling habit

Figs. 6-10. Pseudoiiznriopterk busquetii (Zeiller) DanzC-Corsin, emend. Krings et Kerp frorn the upper Stephanian of the Blanzy-Montceau Basin, France, and from the upper Rotliegend (Nahe Group, N 4) of the quarry of the Eirner Brickwork Company, Bad Sobemheim, Saar-Nahe Basin, Germany. 6. Complete frond with clirnber hooks (ai~ow) attached to a stem portion, originally figured by Zeiller (1906, P1. VIII, 1). Sainte-HClhne Colliery, Blanzy-Montceau Basin. EMP without collection number. X0.5. 7. Specimen with well-developed climber hooks (arrows), originally figured by Krings and Kerp (2000, P1. 11, 4). Blanzy-Montceau Basin. L 2705. X 1. 8. Pinnae of P. busquetii from Sobernheim showing the pinnule venation, originally figured by Krings and Kerp (2000, P1. 111, 4). LPPU 1251. X2.5. 9, Specimen with two platysperrnic seeds attached (arrows), originally figured by Krings and Kerp (2000, P1. V, 1-3). Blanzy-Montceau Basin. L 271 1. X 1. 10. Detail of Fig. 9, showing one of the seeds. X5.

(Rothwell, 197.5). This suggests that the thickets or stands may have consisted of several species with similar growth habits. The growth conditions for P. b~irquetiiin the Pseudornariopteris hori~on 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 com- pletely of Karinopteris sp. with few remains of larger plants present (DiMichele et al., 1984).

Tlze reconstruction-The drawing presented here (Fig. 12) shows a Pseudonzariopteris busquetii plant climbing up the stem and into the foliage of a tree-like pteridosperm. The re- construction depicts P. husquetii as being a large vine (or a small liana) that used two basically diffcrent strategies during development in order to anchor its body to the stem and into the foliage of the tree.

We hypothesize that the plant initially climbs up along the stem of the support tree. Since adventitious roots have not been found to date in stem soecimens of P. busauetii, the

L ,

reconstruction depicts the plant as gaining support from stem attachment by twining. Based on the Sobernheim specimen (Fig. 11), the fronds borne on the attached stem portion are positioned almost in pairs and lack climber hooks. In the up- permost region of the stem of the support tree, however, where the vinelliana is about to transition into the tree's foliage, the fronds start to bear climber hooks. The reconstruction of P. Ousyzietii in the foliage depicts the plant as suspended between several fronds of the support tree to each of which it is at- tached by means of numerous climber hooks. The foliage of the tree presumably could not provide reliable support for a medium-sized climber which firmly anchored its stems with adventitious roots or by twining. Especially the natural ab-

scission of fronds by the tree, or loss of fronds of the tree due to breaking, would be disadvantageous for firmly attached vines/lianas. Thus, a rather flexible anchoring system with multiple anchoring sites, catching and ratcheting between the support's fronds. and the distribution of the mass of the vine/ liana over a large poi-tion of the support tree's foliage would appear to be much more effective. Following Zeiller's largest climber hook-bearing specimen of P. bzlsquetii from Blanzy- Montceau (1906, P1. VIII, 1, partly refigured here in Fig. 6). the fronds are here reconstructed as being alternately (?heli- cally) arranged.

Coinparisons-Vine-or liana-like growth habits have re- peatedly been suggested for nlariopterid pteridosperms, based on the relatively narrow nature of the frond-bearing stems (e.g., PotoniC, 1898, 1899; DanzC-Corsin, 1953) and/or the presence of apical extensions of pinna axes, commonly inter- preted as climber hooks (e.g., Zeiller, 1906; DiMichelc et a]., 1984; Josten, 1991). However. to date no detailed reconstruc- tions of growth form and growth strategies have been elabo- rated for any one species. The reconstruction of Pseudornariopteris husquetii presented here depicts a growth form and growth strategies that were apparently widely distributed among mariopterid pteridosperms. Several gross-morphologi- cal features, which are characteristic of P. busquetii and im- portant for our understanding of its growth form, have also been documented for other mariopterid taxa. Most striking is the presence of specialized cliiuber hooks (usually, but not always, developed from apical extensions of pinna axes). Sim- ilar climber hooks have been reported from a large number of taxa, e.g.. numerous species of Mariopteris from the Late Car- boniferous of France and Germany (e.g., Mariopteris carnosa, M.rletvosa [Corsin. 19321: M. daviesi, M. sauveuri [Josten. 19911, M. rnuricata [Zeillel; 1886; DanzC-Corsin, 1953]), Karirzopteris acuta from the Namurian of Germany (Schultka, 1995), Karinopteris sp. from the Middle Pennsylvanian Indi- ana paper shale, USA (DiMichele et al., 1984), and Pseudonznriopteris cordato-ovuta from the Stephanian of France (Krings and Kerp, 2000). Boersma (1972) regards climber hooks as a typical feature of mariopterid pteridosperms. Al- though the climber hooks may display considerable interspe- cific moi-phological 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 con- cept that climber hooks characterize a phase in the growth of these pteridosperms. In addition, several mariopterid speci- mens 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 (DanzC-Corsin, 1953, P1. LXXVII, 4), M. carnosa (Corsin, 1932, P1. LXVII1,I). M. g~iillazirn~i(Corsin, 1932, Pl. LXXXV, I), M. muricatu (Zeillel; 1886, P1. XXI, 1, PI. XXIII,

I), and M. ro~issini(DanzC-Corsin, 1953. PI. LXXVIII, la) from the Late Carboniferous of France. Of special interest is a specimen from the Westphalian of northern England, reported by Cleal and Thornas (1999). This highly informative specimen shows a slender stem with mariopterid fronds still attached, still wound asound the stump of an arborescent ly- copsid.

Concluding remarks-The Late Carboniferous-Early Permian pteridosperm Pseucloinario1~teris busquerii possessed a vine- to liana-like growth habit and used at least two differ- ent strategies to anchor itself to a support medium. In the ab- sence 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 sin~ilar- ities between P. busquetii and other masiopterids suggest that the growth form may have been widely distributed among this group of pteridosperms. perhaps even characteristic of the gen- eral appearance of mariopterid pteridosperms.

Based on local abundance in the fossil record (e.g., Di- Michele et al., 1984; Kerp and Fichter, 1985). mariopterid pte- ridosperms may have played an important role in some Latc Carboniferous and Early Permian coal-swamp forest ecosys- tems. We assume that thcy represented part of a rather vigor- ously growing, sprawling, scrambling and/or climbing type of vegetation that may be structurally comparablc to the vegeta-

Fig. 1l. Stem portion of Pscudoi~tal-iopteris busquetii (Zeiller) Danzt-Corsin, emend. Krings et Kerp bearing two "pseudo-pairs" of fronds, originally figured by Krings and Kerp (2000, P1. IV, 1). Note that the fronds are positioned allnost in pairs and directed to one side (large arrows), and the pinnae lack climber hooks but terminate in small pin~iules (small arrows). Upper Rotliegend (Nahe Groi~p, N 4) of the quarry of the Eimer Brickwork Company, Bad Sobernheim, Saar-Nahe Basin, Germany. LPPU 14274. X0.8.

tion 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 docu- mented for a large number of Late Carboniferous and Early Permian pteridosperm taxa. The scramblinglclirnbing 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 Pseudomnriopt~ris busquetii, clearly demonstrate that scrambling andlor climbing growth habits were common in this group of seed plants. Moreover. thev demonstrate that the various modes of attach-

, ,

ment, developed by pteridosperms in the late Paleozoic, and a number of morphological adaptations of these plants to the special physiological requirements of a scramblinglclimbing 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 "as- sembled" and we are gaining increasing resolution about the community structure in which these organisms lived. The data presented here on the mariopterid pteridosperm Pse~clon~arioptel-is busquetii indicate that certain mosphological struc- tures (e.g., climber hooks, orientation of the fronds, and het- erophylly) are related to how these plants grew in the com- munity in which they lived and that certain of these struct~~res can be attributed directly to the growth phase of the plant. Such inforination 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. paleobiol- ogists have placed increasing emphasis on the structurelfunc- tion relationshins of various mor~holo~ical

Seatures. and this emphasis has c'ontributed to a mire bGlogica1 undesstanding of ancient plants. As paleobotanists have pieced together the floral elements and subsequently characterized the communi- ties 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 plantlplant 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 pte- ridosperm discussed here, provides a new source of informa- tion about both the plants and the ecosystems in which they grew.

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