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Paleobotany |
í Kva
ek2,5ina Da
ková42National Museum, Prague, Václavské nám. 68, 115 79 Praha 1, Czech Republic; 3Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK; 4Academy of Sciences, Rozvojová 135, 165 00 Praha 6, Lysolaje, Czech Republic
Received for publication January 10, 2005. Accepted for publication September 1, 2005.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSSYSTEMATICSGINKGOALEAN AFFINITYFACIES-ASSOCIATED PLANT REMAINSWHOLE-PLANT RECONSTRUCTIONLITERATURE CITED |
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) Kvaek, J., ginkgoalean short shoots of Pecinovicladus kvacekii Falcon-Lang, and ginkgoalean trunk wood of Ginkgoxylon gruettii Pons and Vozenin-Serra in monodominant taphocoenoses at four geographically distant localities suggests that these remains all belong to one plant. This is supported by the close morphological and anatomical similarity between the different organs. Facies analysis of plant assemblages indicates that our Cretaceous tree occupied a water-stressed coastal salt marsh environment. It therefore represents the first unequivocal halophyte among the Ginkgoales.
Key Words: Cenomanian • Cycadopites • Eretmophyllum • Ginkgoales • Ginkgoxylon • Late Cretaceous • Nehvizdyella • Pecinovicladus
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSSYSTEMATICSGINKGOALEAN AFFINITYFACIES-ASSOCIATED PLANT REMAINSWHOLE-PLANT RECONSTRUCTIONLITERATURE CITED |
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). Peak diversity was attained in the Mesozoic Era, when ginkgoaleans comprised more than 13 genera (Tralau, 1968
) and grew over much of the Pangean supercontinent (Royer et al., 2003
). Although sterile ginkgoalean foliage is very common in Mesozoic strata, associated reproductive structures have only been documented very rarely. Furthermore, although fossil assemblages comprising both vegetative and reproductive organs are documented at some sites, only a few Mesozoic gingkoaleans have been reconstructed to date.
In this paper, we describe a new genus of ginkgoalean ovuliferous reproductive structure, Nehvizdyella bipartita gen. et sp. nov., from the Late Cretaceous (Cenomanian) of the Czech Republic. These fertile remains occur in facies-association with several other ginkgoalean morphotaxa, which all show strong morphological and anatomical similarities. Associated morphotaxa include tongue-shaped leaves referable to Eretmophyllum obtusum (Velenovsk) Kvaek, J., pollen of Cycadopites-type, woody short shoots of Pecinovicladus kvacekii Falcon-Lang, and mature trunk wood of Gingkoxylon gruettii Pons and Vozenin-Serra (Ulin et al., 1997
; Kvaek, 1999
; Falcon-Lang, 2004
). Based on these additional materials, we propose a whole-plant reconstruction for the ginkgoalean tree and utilize facies data to assess its paleoecology.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSSYSTEMATICSGINKGOALEAN AFFINITYFACIES-ASSOCIATED PLANT REMAINSWHOLE-PLANT RECONSTRUCTIONLITERATURE CITED |
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ech et al., 1980
). Palynological data indicate a late middle Cenomanian age for these beds (Pacltová, 1977
, 1978
). The four main sites are Hloub
tín Brickpit (50°06'45'' N, 14°32'02'' E), a disused brick pit in the eastern part of Prague (material collected by Hlutík, 1973–1974), and three large working quarries, Pecínov Quarry near Rynholec (50°08'00'' N, 13°54'34'' E), Kamenná Panna Quarry near Horouany (50°07'17, 14°44'09'' E), and Vyehoovice Brickpit (50°07'17'', 14°45'12'' E) east of the village of the same name (Fig. 1).
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n and 
piáková, 1996
). Palaeovalley-fill successions (Ulin et al., 1997
; Ulin and Nichols, 1997
) comprise the deposits of a variety of continental (braided rivers, meandering streams and floodplains, and anastomosed fluvial systems) and coastal environments (tidally influenced braided rivers, supratidal marshes, tidal flats, ebb-tidal deltas, estuaries, and lower shoreface). The ginkgoalean plant fossils were extracted from mudstone units interpreted as supratidal marsh facies at all four sites (Nguyen Tu et al., 2002
). Ginkgoaleans form the dominant fossil component of these beds, which also contain the remains of the conifer Frenelopsis alata (K. Feistmantel) Knobloch, a few angiosperms, and a putative gnetalean (Ulin et al., 1997
; Falcon-Lang et al., 2001
).
Mudstone specimens dominated by ginkgoalean foliage (Eretmophyllum) were treated in a solution of natrium carbonate. Other specimens were macerated for 8 h in diluted Schulze's solution and then stored in glycerine. After approximately 1 month, macerated specimens became partially translucent, although optimum translucence was not obtained until after 5 months of maceration and treatment in glycerine. Cuticles from the seed integument were then prepared using standard Schulze techniques (Kvaek, 1999
, 2000
). In addition to the ovules themselves, pollen grains that adhered to the seeds after maceration were separated using a dissecting needle with a human hair glued to its tip (Zetter, 1989
; Zetter et al., 2002
). Associated lignified and charred wood was also collected, and treated using standard HF techniques (Falcon-Lang et al., 2001
). Resultant material was examined using an Olympus (Japan) SZX 12 binocular microscope, an Olympus (Japan) BX 50 light microscope, a Phillips (Germany) 515 SEM, and a Hitachi (Japan) S-3200 SEM. All specimens and preparations were deposited in the palaeobotanical collections of the National Museum, Prague (F 00003–15, F 00112–133, F 00189–191, F 02281, F 02293, F 02481–2483, F 02497–2500, F 02856, F 02886, F 02910– 13, F 02926, F 02958, F 02972, F 03010–18, F 03038).
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SYSTEMATICS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSSYSTEMATICSGINKGOALEAN AFFINITYFACIES-ASSOCIATED PLANT REMAINSWHOLE-PLANT RECONSTRUCTIONLITERATURE CITED |
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Type
Nehvizdyella bipartita gen. et sp. nov.
Generic diagnosis
Compound ovuliferous reproductive organ consisting of a main axis and two short secondary axes, each terminated by a large cupule-like structure. Each cupule encloses one orthotropous ovule. Seeds consist of sclerotesta and sarcotesta.
Species
Nehvizdyella bipartita gen. et sp. nov. (Figs. 2– 11)
Synonym
Nehvizdya obtusa (Velenovsk) Hlutík pro parte—seeds, megasporangiophores, Hlutík 1986
: 100, pl. 1, figs. 1, 2, 6, text-fig. 8.
Specific diagnosis
Compound ovuliferous reproductive structure consisting of a main axis, stout and thick, which bears two short, apical secondary axes, each terminated by a cupule-like structure enclosing an ovule. In early developmental stages, the entire ovule, except the micropylar area, is embedded in the cupule. Ovule is orthotropous with micropyle facing distally. Seeds ovoid, having sclerotesta and sarcotesta. Remains of sarcotesta consisting of putative parenchymatous tissue. Outer cuticle of sarcotesta thick, bearing polygonal cells and stomata. Inner cuticle of sarcotesta very thin, bearing elongated cells. Sclerotesta hard and fragile. All the ovuliferous organs including main axis contain numerous resin bodies.
Holotype
Designated here F 03010, National Museum, Prague, (Figs. 3–5).
Paratype
Designated here F 03011, National Museum, Prague, (Fig. 2).
Type horizon
Late Cretaceous (Cenomanian), Peruc-Korycany Formation.
Type locality
Horouany, Kamenná Panna Quarry near Nehvizdy (holotype F 03010, paratype F 0301, F 03012–14, F 03018), Czech Republic (50°07'17'', 14°44'09'' E).
Other material
Prague, Hloubtín Brickpit (F 00189–91); Pecínov, unit 3 (F 03015–17), Vyehoovice Brickpit (F 02497–99).
Etymology
Derived from bipartite nature of the organ.
Description
The holotype of Nehvizdyella bipartita (F 03010) is a 15 mm long ovuliferous reproductive structure bearing two cupules (Fig. 3). The main axis is 6 mm long and 2 mm in diameter and has fine longitudinal striations. Secondary axes, 3–5 mm long and 2 mm in diameter, are dichotomously attached to the terminal part of the main axis. Each secondary axis is wrinkled, and its apical part gradually passes into the cupule-like structure. The holotype shows two cupules. The larger cupule is 8.5 mm in diameter and bears the remains of a seed. The smaller cupule (Figs. 4–6) is 4.5 mm in diameter encloses an orthotropous ovule (2.5 mm in diameter). There is an ovoid mass of tissue (1 mm in diameter), which differs from the surrounding cells (Fig. 5). It is interpreted as a nucellus or proembryo. The micropyle and pollen chamber are situated in the terminal part of the ovule (Fig. 4a, b). Other studied material includes five additional reproductive axes with or without seeds or ovules. They vary in length from 11 mm up to nearly 20 mm (paratype F 03011, Fig. 2). Their main axes are 5–9 mm long and 1–2 mm in diameter. Secondary axes are 2–3 mm in length. Cupule-like structures bearing mature seeds are 4–8 mm in diameter and have a well-cutinized rim (Fig. 6). All the ovuliferous organs except sclerotesta contain numerous resin bodies (Fig. 5).
Where the seeds are attached to an axis, they are always aborted at some stage of maturation. Fully mature seeds only occur in a detached state, typically filled with sediment (Fig. 10), which probably penetrated through the broken sclerotesta after burial. Furthermore, mature seeds are not usually preserved intact and therefore rarely occur in bulk-macerated material. The generally poor preservation of mature seeds is probably linked to the development of the sclerotesta, which would have accentuated fragmentation during attrition resulting from sedimentary transport, maceration, and postsedimentary compression. Another similar case of differences between the preservation of immature and mature seeds has been noted by Rothwell and Holt (1997)
in Maastrichtian assemblages from Alberta, Canada.
The detached seed compressions (Fig. 10) are circular or slightly elliptic, 9–10 mm in diameter. They show two layers of coalified matter (Fig. 11). The inner layer, consisting of shiny black coalified matter, is usually 0.1 mm thick. It is interpreted as sclerotesta. The outer layer, consisting of faint (porose) matter, 0.2–4 mm thick, is interpreted as sarcotesta. It is covered by a thick cuticle (Fig. 11). The outer cuticle of the sarcotesta is easily macerated and comprises stomata surrounded by 6–7 subsidiary cells (15–25 µm by 20–35 µm) interspersed between isodiametric cells (10–25 x 20–35 µm, Fig. 8). The inner cuticle of the sarcotesta is poorly preserved and has elongated cells (Fig. 9). The sclerotesta is fragile and has a thin cuticle, which is difficult to prepare.
Some seeds are preserved intact (e.g., F 03018, Fig. 7), but do not possess sclerotesta, and when macerated, have a short, central stalk (2–3 mm). These fossils are interpreted as immature seeds.
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GINKGOALEAN AFFINITY |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSSYSTEMATICSGINKGOALEAN AFFINITYFACIES-ASSOCIATED PLANT REMAINSWHOLE-PLANT RECONSTRUCTIONLITERATURE CITED |
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; Stewart and Rothwell, 1993
). The ovuliferous organ is characterized by bifurcating axes, that each bear one ovule; seeds with haplocheilic stomata, axes and seeds bearing resin bodies; and associated leaves having two vascular bundles in petioles and dichotomizing venation. Further evidence for ginkgoalean affinity is given by the facies-association of this ovuliferous organ and foliage with a variety of unequivocally ginkgoalean organs including pollen, foliage, woody short shoots, and trunks (details discussed later). The most remarkable feature of Nehvizdyella is the upward-oriented cupule-like structure. It is striated and probably built of nonwoody tissues. It encloses the ovule, and in later developmental stages supports a seed. Based on its position and function, we suggest that it is homologous with the collar of extant Ginkgo. Similarity of Nehvizdyella to extant Ginkgo is evident in terms of the number of seeds per axis and their large size (length 20–22 mm in Ginkgo, 9–10 mm in Nehvizdyella). However, Nehvizdyella differs from Ginkgo in having ovules, which are mostly enclosed in a cupule-like structure, and in being facies-associated with the Eretmophyllum type of leaves (details discussed later). Although morphologically similar, Nehvizdyella bipartita is probably only distantly related to extant Ginkgo biloba. Reduction of the number of seeds per ovuliferous structure, the increasing size of the seeds, and the unification and expansion of the leaf lamina are probably general trends in several lineages of the Ginkgoales.
Nehvizdyella is most similar to ovuliferous reproductive structures associated with the genus Grenana Samylina from the Middle Jurassic of Angren, which have similarly sized seeds embedded in a large cupule (Appendix S1, see Supplemental Data accompanying online version of article). Grenana was originally described as a pteridosperm (Samylina, 1990
), but later Zhou (1997)
reinterpreted it as a member of the Ginkgoales. Although Nehvizdyella could be closely related to Grenana, detailed comparison between these two taxa is problematic because the holotype of Grenana angrenica Samylina (number 813/1N13) is a sterile leaf compression (Samylina, 1990
). Although the aforementioned reproductive structures, including seeds and cupules, are facies-associated with the leaves, they never occur in an attached state. It is important to note that fig. 1 of Samylina (1990)
is merely a hypothetic reconstruction and does not represent an actual specimen. Consequently, we consider the reinterpretation of Grenana by Zhou (1997
, p. 185) to be misleading. We maintain that the genus Grenana is best reserved for the foliage alone and that the facies-associated reproductive structures should be classified as a new taxon.
The genus Nehvizdyella is also similar to the ginkgoalean ovuliferous reproductive structures Umaltolepis Krassilov from the Lower Cretaceous of Siberia (Krassilov, 1972
) and Toretzia Stanislavski from the Triassic of Ukraine (Stanislavsky, 1973
); they all have one or two ovules per axis (Appendix S1). However, Umaltolepis differs from Nehvizdyella in having a bract supporting the ovule, in having bracts at the base of the seed-bearing axis, and by the absence of a cupule-like structure. Toretzia differs from Nehvizdyella in having inverted anatropous seeds and in lacking cupule-like structures. Additionally, both Toretzia and Umaltolepis differ from Nehvizdyella in having linear ribbon-like leaves named Pseudotorellia.
Of the other fossil ginkgoalean reproductive structures described in the literature, all differ substantially from Nehvizdyella (Appendix S1). Schmeisneria Kirchner and Van Konijnenburg-Van Cittert from the Jurassic of Germany has small orthotropous ovules, and is locally attached to short shoots of Glossophyllum or Eretmophyllum type (Kirchner and Van Konijnenburg-Van Cittert, 1994
). Yimaia Zhou and Zhang from the Middle Jurassic of China shows eight to nine sessile anatropous ovules, attached to or facies-associated with Baiera and Ginkgoites foliage (Zhou and Zhang, 1988
, 1992
). Karkenia Archangelsky from the Lower Cretaceous of Argentina has numerous small anatropous ovules per axis and is facies-associated with a variety of foliage types including Sphenobaiera, Ginkgodium, and Eretmophyllum (Archangelsky, 1965
; Del Fueyo and Archangelsky, 2001
). It probably represents a distinct, perhaps ancestral, lineage within the Ginkgoales, together with the Palaeozoic genus Trichopitys (Zhou, 1997
).
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FACIES-ASSOCIATED PLANT REMAINS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSSYSTEMATICSGINKGOALEAN AFFINITYFACIES-ASSOCIATED PLANT REMAINSWHOLE-PLANT RECONSTRUCTIONLITERATURE CITED |
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Pollen
Cycadopites sp. (Figs. 12–17)
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Horizon and locality
Late Cretaceous (Cenomanian) Peruc-Korycany Formation, at Horouany, Kamenná Panna Quarry near Nehvizdy.
Description
Eleven pollen grains and their fragments were found adhering to the exterior of the seed of Nehvizdyella bipartita. They were the only pollen grains adhering on seed no. F 03018. Pollen grains were photographed during maceration of the seed cuticle, so they are in various modes of preservation and fragmentation.
Pollen grains are boat shaped with a single sulcus, not more than 30 µm in diameter (Figs. 12–16). The sulcus occupies the entire length of the grain and is slightly concave (Figs. 12, 13). The pollen surface is scabrate, and microverrucate (Fig. 12). Auricular projections observed by Sahashi and Ueno (1986)
are visible and have a reticular-like sculpture on the germinal aperture. This sculpture is also present in an internal part of the sulcus (Fig. 17).
Discussion
The pollen grains attached to seeds of Nehvizdyella bipartita agree with the genus Cycadopites Wodehouse (ex Wilson and Webster, 1946
) in having the same size and shape and one colpus and a similar exine pattern. The genus was based on material from the Palaeocene of Red Lodge, Carbon County in Montana, USA (Wodehouse, 1933
; Wilson and Webster, 1946
) and later emended by Krutzsch (1970)
and Nichols et al. (1973)
. The type species, Cycadopites follicularis Wilson and Webster 1946
, differs from the present Cycadopites sp. in larger size and rather smoother surface. The most similar pollen taxa to Cycadopites sp. are Cycadopites fragilis Singh and Cycadopites nitidus (Balme) de Jersey (1964)
, which are commonly encountered in the same supratidal marsh facies that contain N. bipartita in the Bohemian Cretaceous Basin (e.g., Pacltová and Svobodová, 1993
; Svobodová, 1990
, 1992
; Svobodová et al., 1998
; Ulin et al., 1997
). They both agree in general morphology with the material described herein attached to N. bipartita, having nearly smooth or faintly granulate exine.
Cycadopites fragilis was originally described from the Lower Cretaceous of Alberta (Singh, 1964
) and is characterized by a sulcus extending the whole length of the grain and a smooth surface. Cycadopites nitidus was originally described from the Lower Cretaceous of Australia (Balme, 1957
). It is characterized by a narrow sulcus extending the full length of the distal surface, which is slightly expanded at the extremities, and a faintly granulate exine. These two types of pollen primarily differ only in terms of size, and we therefore suggest that the two Czech species likely represent taphonomic or ontogenetic variants. This view has been previously discussed by Norris (1967)
, who identified a similar intergradational relationship between two other Cycadopites pollen species. In summary, we suggest that C. fragilis and C. nitidus in the Cretaceous Bohemian Basin of the Czech Republic were probably produced by the same species that bore N. bipartita organs.
According to the morphological classification scheme introduced by Thomson and Pflug (1953)
the pollen grains described here are also similar to the genus Monocolpopollenites Pflug and Thomson in Thomson and Pflug 1953
. However, Monocolpopollenites differs from our material in its shorter sulcus and in having marginal folds. It is also smaller and confined mostly to pollen derived from monocots.
Foliage
Eretmophyllum obtusum (Velenovsk) Kvaek, J., 1998
(Figs. 18–24)
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1885
, pl. 1, fig. 8, National Museum, Prague, refigured herein (Fig. 18).
Type locality
Nehvizdy (old sandstone quarry in east surroundings of the village).
Type horizon
Late Cretaceous (Cenomanian), Peruc-Korycany Formation.
Other material
Nehvizdy (holotype F 00003, F 00004–7, F 00012, 13); Prague, Vysoany (F 00010); Lipenec (F 00008, 9); Kralupy and Vltavou (F 00014, 15); Prague, Hloubtín (Velenovsk type collection-F 00011); Prague, Hloubtín Brickpit (F 00112–133, F 00189–191, F 02856); Horouany, Kamenná Panna Quarry (F 02886, F 02958, F 02972); Pecínov Quarry, unit 3 (F 02281, F 02293, F 2481–3, F 02497–2500, F 02856).
Description
Leaves of Eretmophyllum obtusum are large (up to 11 cm long and up to 2.5 cm at their widest point), tongue-shaped, coriaceous, and entire-margined with a typically obtuse apex and cuneate base (Figs. 18, 19). The massive well-pronounced petiole (3 mm in diameter) contains two veins (Fig. 19). The veins dichotomously branch near the base of leaf, run subparallel to leaf lamina, and converge near the apex at a high angle. Up to 8–12 veins per cm occur in the medial part of the leaf. The adaxial cuticle is very heavily cutinized, composed of polygonal, isodiametric to slightly elongate cells, that are arranged in longitudinal rows with anticlinal walls that are straight or slightly bent (Fig. 23). The abaxial cuticle is also heavily cutinized, with costal and intercostal bands (Fig. 20). Intercostal cells are polygonal, elongate, and occur in longitudinal rows. Costal bands are constructed of strongly cutinized polygonal, isodiametric cells, and stomata, which are randomly scattered or arranged in short rows (Fig. 24). Stomata are haplocheilic, deeply sunken, and surrounded by 4–6 subsidiary cells (Fig. 22). Subsidiary cells are strongly cutinized and typically bear papillae that form a raised coronal rim (Fig. 21). Numerous circular or spindle-shaped resin bodies occur in the mesophyll tissue (Fig. 20).
Discussion
These tongue-shaped leaves were first described from the Cenomanian of Bohemia as Podozamites obtusus (Velenovsk, 1885
), but their ginkgoalean affinity was later established by Velenovsk and Viniklá (1926
, 1927
). Believing that the leaves were not arranged in bundles and given their superficial similarity to Glossophyllum, Hlutík (1977)
erected the genus Nehvizdya for this foliage type. In his revision of gymnosperm foliage from the Bohemian Cenomanian, Kvaek (1998
, 1999
) transferred these fossil leaves to the genus Eretmophyllum, introducing a new combination Eretmophyllum obtusum (Velenovsk) Kvaek J. (2000)
. Gomez et al. (2000)
attempted to distinguish Eretmophyllum from Nehvizdya on the basis of the presence or absence of papillae on subsidiary cells as the differential character. However, this character is variable among genera in the Ginkgoales, and the suggested splitting of Nehvizdya and Eretmophyllum is consequently not accepted herein. The ginkgoalean affinity of Eretmophyllum is based on its dichotomous venation, which arises from the two main petiole veins, and its cuticle having haplocheilic stomata (Thomas, 1913
).
Short shoots
Pecinovicladus kvacekii Falcon-Lang, 2004
(Figs. 25–34)
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Type locality
Pecínov Quarry, unit 3.
Type horizon
Late Cretaceous (Cenomanian), Peruc-Korycany Formation.
Other material
Pecínov Quarry, unit 3, F 02910, F 02911, F 02913-F 02926.
Description
Pecinovicladus kvacekii consists of 7–13 mm diameter shoots comprising pith, xylem, periderm, leaf traces, and branch traces (Fig. 25). The 1.6–2.2 mm diameter pith is parenchymatous. The xylem layer is 0.5–1.8 mm in radius (Fig. 26). Mucilage ducts (70–110 µm in diameter, >1.1 mm high) surrounded by axial parenchyma occur in the inner part of the secondary xylem (Fig. 27). Xylem comprises scalariformly-thickened primary and metaxylem succeeded by pycnoxylic secondary xylem composed of irregularly arranged tracheids (7–26 µm in diameter). Tracheids have 1–2-seriate, alternate or mixed, circular, bordering pitting on the radial walls (Fig. 28). Cross-fields comprise 1–6 taxodioid or cupressoid pits per field (Fig. 29). Axial parenchyma, arranged in vertical files may locally contain inflated cells, 25–45 µm in diameter, containing crystalline molds (Fig. 30). Rays are very short (1–7 cells high) and uniseriate, being spaced 5–11 tracheids apart (Fig. 31). The cambial zone, 55 µm radius, contains inflated parenchyma and rhombic crystal molds. The 2.5 mm radius periderm comprises parenchyma, resin-filled fibers and sieve cells.
Leaf traces, comprising an oval adaxial xylem strand and a crescent-shaped abaxial phloem strand, are 1.0–1.5 mm in diameter at the point of departure from the secondary xylem, and arranged with a 5/13 helical phyllotaxy (Figs. 25, 32). Leaf bases preserved on the exterior of the axis, 2.7–3.5 mm wide and 1.45 mm thick, comprise xylem, phloem, mesophyll and epidermis (Fig. 33). The vascular bundle ramifies into >6 veins at the leaf base. Some shoot specimens have fewer leaf traces, but have secondary branch traces (1.8–2.1 mm diameter) comprising a 0.8 mm diameter pith and a 0.8 mm radius secondary xylem layer. A few secondary branches are positioned in the leaf axil (bracts) and may represent the detached peduncle of reproductive structures (Fig. 34).
The gingkoalean affinity of this morphotaxon is indicated by a combination of features including, most importantly, the presence of inflated axial parenchyma in the secondary xylem, which demonstrably once contained crystalline druses (Gunckel and Wetmore, 1946
; Greguss, 1955
; Scott et al., 1962
). Additional ginkgoalean features are irregularly arranged files of wide and narrow tracheids in the secondary xylem (Srivastava, 1963
), and very short rays (Mastogiuseppe et al., 1970
).
Mature wood
Ginkgoxylon gruettii Pons and Vozenin-Serra 1992
(Figs. 35–38)
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Type locality
Carrière du Bouillard, Nord d'Angers, France.
Type horizon
Late Cretaceous (Cenomanian), Jumelles and Brissac Formation.
Material studied
F 03038, National Museum, Prague.
Horizon and Locality
Late Cretaceous (Cenomanian) Peruc-Korycany Formation, at Prague, Hloubtín Brickpit.
Description
Mature ginkgoalean wood is known from a single trunk specimen, 13 cm in diameter and >1.09 m in length, preserved in the salt marsh peat facies at Hloubtín Brickpit. Anatomically, the wood is pycnoxylic, consisting only of tracheids and rays. In radial longitudinal section (RLS), tracheids are characterized by uniseriate bordered pits which are typically spaced at least one pit diameter apart (Fig. 35). Both borders (9–10 µm in diameter) and apertures (2–3 µm in diameter) are circular. Rays are composed of parenchyma cells that are 50–75 µm long, 20–30 µm high, and 20– 30 µm wide, and have well-preserved cross-field pitting. Typically 2–8 circular cupressoid pits, each 5–6 µm in diameter, occur clustered in the cross-field region (Fig. 36). Chains of inflated axial parenchyma, 3–12 cells in length are common (Fig. 37). Axial parenchyma cells are large (25–45 µm in diameter), locally thick-walled (up to 8 µm thick), and may contain moldic preservation of crystalline druses. In tangential longitudinal section (TLS), rays are uniseriate and short (1–12 cells high). Tangential tracheid pits are absent. In transverse section (TS), rays are spaced 90–210 µm apart, and may be up to 3–4 mm long. Tracheids have tangential diameters of 14–22 µm and radial diameters of 12–21 µm. Middle lamellae are present between adjacent trachieds indicating that the wood is lignified, not charred. Growth rings are absent over several centimetres, but subtle growth interruptions do locally occur with an irregular spacing (Fig. 38).
This wood corresponds closely to Ginkgoxylon gruettii Pons and Vozenin-Serra from the Cretaceous (Cenomanian) of Anjou, France. This species differs from the Czech specimens in exhibiting rare biseriate trachied pitting, rare biseriate rays that are 1–26 cells high, and fewer cross-field pits (1–6). Such differences are of little taxonomic significance and likely reflect ontogenetic variability (Falcon-Lang, 2005a
). For these reasons, our mature woods are assigned to Ginkgoxylon cf. G. gruettii. This morphotaxon has also recently been discovered in Cenomanian deposits at Charente in western France (Perrichot, 2000
). One of the key features that allows this morphotaxon to be referred to the Ginkgoales is, as previously noted, the presence of druse-filled, inflated axial parenchyma chains (Gunckel and Wetmore, 1946
; Greguss, 1955
; Scott et al., 1962
).
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WHOLE-PLANT RECONSTRUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSSYSTEMATICSGINKGOALEAN AFFINITYFACIES-ASSOCIATED PLANT REMAINSWHOLE-PLANT RECONSTRUCTIONLITERATURE CITED |
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; Zhou, 1997
; Czier, 1998
). Some ginkgoalean taxa show a high degree of polymorphism with up to three genera of sterile foliage associated with one reproductive structure, and locally one genus of sterile foliage may have several associated reproductive structures (Zhou, 1997
). Consequently, analysis of isolated morphotaxa may result in either an overestimate or underestimate of biological diversity.
Whole-plant reconstruction
In this paper we demonstrate the common affinity of Nehvizdyella bipartita ovuliferous organs, Cycadopites pollen, Eretmophyllum obtusum leaves, Pecinovicladus kvacekii short shoots, and Ginkgoxylon gruettii trunk wood based on (1) the facies co-occurrence of parautochthonous remains at four sites, and (2) the precise anatomical correspondence between adjacent morphotaxa.
Specifically, Cycadopites pollen is found adhering to Nehvizdyella, whereas other pollen morphotaxa are absent. Furthermore, Cycadopites pollen is always highly abundant in the salt marsh facies dominated by Eretmophyllum. Leaf bases preserved on the external surface of Pecinovicladus are anatomically and morphologically identical to the leaf bases of Eretmophyllum, indicating a close association between the two morphotaxa (Falcon-Lang, 2004
). Furthermore, secondary axes preserved in leaf axils (bracts) on Pecinovicladus are of identical size and shape to the main axis of Nehvizdyella, and closely correspond anatomically. The secondary wood of Pecinovicladus is almost identical to Ginkgoxylon wood, the only minor differences probably being related to wood ontogeny (Falcon-Lang, 2005a
). Finally, Nehvizdyella bears the same type of stomata and contains the same type of resin bodies as leaves of Eretmophyllum, indicating a common affinity (compare Fig. 8 and Figs. 5, 20, 24).
Previous studies have also hinted at this same association, although only in part. For example, Velenovsk and Viniklá (1926
, 1927
) described poorly preserved isolated axes (putative long shoots) and seeds, which they tentatively associated with Eretmophyllum foliage. Preliminary cuticular studies of seed sarcotesta were carried out by Hlutík (1986)
, who also noted an association with Eretmophyllum foliage. In both cases, the seeds were of the same type as those described herein as Nehvizdyella bipartita. Hlutík (1986)
attempted a partial reconstruction of these remains, depicting them in terms of a long shoot with helically arranged leaves, a reconstruction based on Velenovsk and Viniklá (1926)
's poorly preserved specimen (which is now lost). During the course of our investigation, we did not find similar long shoot material. It is possible that the Nehvizdyella whole-plant possessed both short shoots and long shoots, as in recent Ginkgo, but in the absence of well-preserved long shoot material we are unable to confirm Hlutík's reconstruction.
Based on the fossil assemblage described, we maintain that the Nehvizdyella whole-plant was a small tree or large shrub. The maximum recorded trunk diameter of only 13 cm suggests a height of no more than a few meters given biomechanical considerations (Niklas, 1994
). Lateral branches with short shoots, and possibly long shoots, bore helically arranged tongue-shaped leaves up to 11 cm long with ovules locally positioned on stalks within the leaf axils. A representative branch of Nehvizdyella whole-plant is illustrated in Fig. 39.
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n and Nichols, 1997
). These units were formed during periods of marine transgression and represent a saline, water-stressed environment (Ulin et al., 1997
). Tree-rings in facies-associated woods additionally suggest a seasonally dry subtropical climate (Falcon-Lang et al., 2001
). The ginkgoalean remains, especially Eretmophyllum obtusum leaves, occur in very high concentrations in these units, locally forming the dominant component of the peat (Kvaek, 1999
). These data, together with presence of roots below the peat and the taphonomic co-occurrence of organs with varying hydrodynamic properties (Nichols et al., 2000
), indicate that this is an autochthonous or parautochthonous assemblage. Therefore, the ginkgoaleans, together with co-occurring cheirolepid conifers, putative gnetaleans, and a few angiosperms, are best characterized as a mangrove or salt marsh community (Hlutík, 1986
) with trees adapted for growth in saltwater environments (Tomlinson, 1994
). No modern coniferopsids utilize the mangrove or saltmarsh strategy (Hogarth, 1999
), although rare putative examples have been reported from the fossil record (Falcon-Lang, 2005b
).
Carbon isotopic studies of plants from the salt marsh peat facies allow more detailed palaeoecological interpretation. The angiosperm, gnetalean, and cheirolepid conifer remains have highly positive 
13C values (–23
) compared to the mean value for the whole Peruc-Korycany Formation, consistent with growth under highly water-stressed conditions (Nguyen Tu et al., 1999
, 2002
). Additionally, these plants have very thick cuticles and show a variety of xerophytic characters including deeply sunken stomata (Ulin et al., 1997
). In contrast, 13C values for Eretmophyllum are consistently more negative (–25.5) than the other salt marsh plants, although more positive than for plants in freshwater facies (–27). Furthermore, Eretmophyllum, being a broadleaf, is less characteristically xeromorphic, although such characters as sunken, papillate stomata certainly suggest xeromorphy (Kvaek, 1999
). An additional xeromorphic character in Nehvizdyella is the enclosure of ovules in sterile tissues (presumably to limit water loss), a feature also seen in Alvinia bohemica, the ovuliferous cone of Frenelopsis alata (Kvaek, J., 2000
). Isotopic data perhaps imply that the Nehvizdyella tree grew in less saline regions of the salt marsh, either in a supratidal setting landward of the other trees, or adjacent to lower salinity drainage channels that locally cut into the salt marsh peat facies (Ulin et al., 1997
).
The absence of tree-rings in the woody cylinder of Pecinovicladus may suggest that all of the short shoots were less than 1 year old and were therefore seasonally shed as in Metasequoia. However, tree-rings are also absent in the mature wood, Ginkgoxylon gruettii so the age at which short shoots were shed cannot be assessed with certainty. Nor can the occurrence of discrete Eretmophyllum-rich laminae be used as an indicator of seasonal leaf shedding because this may simply represent a taphonomic phenomenon. Furthermore, Eretmophyllum leaf bases and leaf scars attached to Pecinovicladus show evidence for mechanical breakage rather than abscission, perhaps indicating an evergreen habit. Whilst the phenology of the Nehvizdyella tree cannot be determined with certainty, it is worth noting that all modern trees adapted to salt marsh or mangrove settings have a physiological necessity for an evergreen canopy. It is therefore likely that our Cretaceous ginkgoalean tree was similarly evergreen, in contrast to its nearest living relative, Ginkgo biloba.
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FOOTNOTES |
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ek, M. Philippe, and B. Gomez for stimulating discussions and S. Archangelsky for facilitating access to the type collection of Karkenia. Our warmest thanks go to J. Svoboda who drew the reconstruction of Nehvizdyella. J.K. acknowledges funding from the Czech Grant Agency (205/02/1465) and the Ministry of Culture of the Czech Republic (MK 00002327201). H.J.F.L. gratefully acknowledges receipt of a NERC Post-doctoral Fellowship (NER/I/S/2001/00738) held at the University of Bristol and a Timothy Jefferson Grant (2001) from the Geological Society, London. H.J.F.L. thanks D. O'Neill and the NRC-IMB facility in Halifax, Nova Scotia, Canada who facilitated SEM analysis of several specimens. 
5 Author for correspondence (jiri.kvacek{at}nm.cz
)
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LITERATURE CITED |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSSYSTEMATICSGINKGOALEAN AFFINITYFACIES-ASSOCIATED PLANT REMAINSWHOLE-PLANT RECONSTRUCTIONLITERATURE CITED |
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