Ã - 2002 - review of palaeobotany and palynology(4)

Fern ecological implications from the Lower Jurassic inWestern Hubei, China

Yongdong Wang �

Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China

Abstract

The Lower Jurassic Hsiangchi Formation in western Hubei, China is well known for its abundant and diversefossil ferns, including Marattiaceae, Osmundaceae, Matoniaceae, Dipteridaceae and Dicksoniaceae. Through recentcollections and investigation of the fossil plants in this area, an autochthonous/hypoautochthonous fern communityhas been recognised from the upper part of the Hsiangchi Formation in Zigui, Hubei. This community is dominatedby the matoniaceous ferns of the genus Phlebopteris ; Dipteridaceous ferns mainly characterised by Dictyophyllumrank second in abundance. Marattiaceae (Marattia) and Osmundaceae (Todites and Cladophlebis) are often dispersedspatially among the dominant ferns, whereas the small and slender herbaceous Dicksoniaceae, characterised byConiopteris, are sparsely distributed within the community. This fern community colonised the fluviatile peat-formingenvironment and indicates a tropical to subtropical climate with warm and humid conditions, which is favourable forthe peat accumulation. It is also a representative fern community recognised from the Southern Floristic Province inChina during late Early Jurassic period. . 2002 Elsevier Science B.V. All rights reserved.

Keywords: fern; ecology; peat accumulation; Hsiangchi Formation; Lower Jurassic; China

1. Introduction

Abundant living ferns characterise the south-western region of China today including Yunnan,Sichuan and Hubei Provinces. During the Meso-zoic, £oras including ferns were well developed inthe Triassic and Jurassic of this region. In westernHubei, fossil ferns have been described from EarlyMesozoic strata along the Three Gorges Area ofthe Yangzte River. Among them, the remarkableEarly Jurassic £ora from the Hsiangchi Forma-tion in the Zigui Basin is well known for its abun-dance and diversity of fossil plants. According to

the previous studies and the available data, theHsiangchi Flora is composed predominantly of¢licopsids and bennettitaleans, as well as a sizablenumber of ginkgoaleans (Sze, 1949; Wu et al.,1980; Meng, 1987). Ferns are one of the domi-nant elements of this £ora, including Marattia-ceae, Osmundaceae, Matoniaceae, Dipteridaceaeand Dicksoniaceae. Previous studies of ferns inthis £ora were based mainly on the gross mor-phology of impression specimens. In recent years,a lot of well preserved compression and impres-sion specimens of ferns were collected from ZiguiBasin in western Hubei, where the type locality ofthe Hsiangchi Formation is located. Some ofthem, such as Marattia and Phlebopteris were in-vestigated on their fertile organs and in situspores using light, scanning and transmission elec-

0034-6667 / 02 / $ ^ see front matter . 2002 Elsevier Science B.V. All rights reserved.PII: S 0 0 3 4 - 6 6 6 7 ( 0 1 ) 0 0 1 3 3 - 6

* Corresponding author. Fax: +86-25-3357026.E-mail address: [email protected] (Y.D. Wang).

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tron microscope techniques (Wang, 1999; Wangand Mei, 1999; Wang et al., 2001).As an important part of the £ora and the in-

dicator plants for the environment, the fossil fernswere less emphasised for their ecology in westernHubei. The purpose of the present paper is tostudy the fern ecological implications from theupper part of the Lower Jurassic Hsiangchi For-mation in western Hubei, based mainly on newcollections and relevant published data. Throughthe analysis of the mode of burial, and the indi-cators of the sedimentary features, a special eco-logical community dominated by the Matoniaceaewas recognised in this region, from which the cli-matic conditions can be inferred.

2. Geological setting, sedimentology andstratigraphy

The present fossil locality is in Zigui County,western Hubei, the eastern part of the ThreeGorges Area of the Yangtze River. This area istectonically located in the southeastern marginalregion of the ancient Yangtze Plate, along the

north coast of the Tethys Ocean (Wang et al.,1996). The Jurassic strata are well developed inwestern Hubei, attaining a maximum thicknessof 6000 m and are mainly distributed in the Ziguiand Jinmen^Dangyang Basins, which crop out,respectively, along the western and eastern limbsof the Huangling Anticline (Fig. 1). In Zigui Ba-sin, the Jurassic is principally distributed in Ziguiand Xingshan Counties on both the northern andsouthern banks of the Yangtze River. The Juras-sic strata consist of an extensive succession of redclastic sediments of the Middle to Upper Jurassic.At the base is a coal-bearing sequence of the Low-er Jurassic, which was known as the HsiangchiGroup or the Hsiangchi Coal Series (Lee, 1924).According to systematic stratigraphic investiga-tions (Chen et al., 1979; Wu et al., 1980; Mengand Zhang, 1987), the Hsiangchi Group is com-posed of two biostratigraphic units: the UpperTriassic Shazhenxi Formation below and theLower Jurassic Hsiangchi Formation above (seealso ¢g. 2 of Wang, 1999). The Hsiangchi Forma-tion is composed of grey to greyish sandstones,siltstones, mudstones and carbonaceous shales, in-tercalated by coal seams as well as thin layers of

Fig. 1. A sketched geological map showing locality and the distribution of the Jurassic strata in western Hubei, China (simpli¢edafter Meng and Zhang, 1987). 1, Lower Jurassic; 2, Middle Jurassic; 3, Upper Jurassic; 4, granite; 5, Pre-Sinian to Sinian;6, fault.

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Y.D. Wang /Review of Palaeobotany and Palynology 119 (2002) 125^141126

siderite, with a total thickness of about 200 m.The base of this formation consists of a layer ofconglomerate and/or conglomeratic sandstone.Sedimentological analysis indicates that during

the Jurassic period, the Three Gorges Area of theYangtze River was characterised by a long-livedterrestrial depositional environment, resulting in aseries of stream and lake deposits (Gao et al.,1999). The Lower Jurassic Hsiangchi Formationrepresents meandering stream deposits, whichbear the typical normal sequential succession(Fig. 2). The basal part is the lag gravel of thestream bed deposit. Upward, the lithologychanges to point bars deposits of thick sandstone,£ood plain deposits of thick mudstone, or £uvia-tile peat marsh with carbonaceous mudstones and

coal seams. This kind of succession repeats inseveral rock packages from the basal to the upperpart of the formation.Abundant fossils are reported from the Hsiang-

chi Formation, including plants, spore^pollen,megaspores and bivalves. According to Wu etal. (1980) and Meng (1987), the plants from theHsiangchi Formation are characterised by a Pti-lophyllum^Coniopteris assemblage (Table 1). Thespore and pollen grains of the Hsiangchi Forma-tion are represented by a Dictyophyllidites^Clas-sopollis^Cerebropollenites assemblage in the lowerpart, and a Dictyophyllidites^Cyathidites^Classo-pollis assemblage in the upper part of the forma-tion (Zhang and Zhang, 1987) (Table 1). Themegaspores from the lower part of the formation

Fig. 2. Lithostratigraphy and sedimentology of the Lower Jurassic Hsiangchi Formation in western Hubei.

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Y.D. Wang /Review of Palaeobotany and Palynology 119 (2002) 125^141 127

are dominated by Nathorstisporites hopliticusJung, Horstisporites planatus (Marcinkiewicz)Marcinkiewicz and Trileites sp., which indicatean early Early Jurassic age, whereas the upperpart of the formation is represented by Bacutri-letes harrisii Yang and Sun, Bacutriletes clavatusMarcinkiewicz, Bacutriletes onodios (Harris) Yangand Sun and Verrutriletes aurantium (Harris) Po-tonie¤ (Yang and Sun, 1987). The bivalves of thisformation are characterised by a Sibriconcha ano-dontoides^Qiyangia xiangxiensis assemblage (Yu,1987) (Table 1). All of this fossil evidence indi-cates that the geological age of the Hsiangchi For-mation is Early Jurassic. The upper part of theformation is therefore corresponding to the lateEarly Jurassic, and is suggested to be Toarcian.

3. Materials and methods

All of the fossil plant material for this studycame from recent collections from the type local-ity of the Hsiangchi Flora in the town of Xiangxi,Zigui County, Hubei Province (Fig. 1). Fossilferns have been collected from the upper part ofthe Hsiangchi Formation. They were mostly pre-served as compressions as well as impressions in abed of grey shale and black mudstone about 50cm in thickness (see Wang, 1999). All the fossilfern material is well preserved including both ster-ile and fertile pinnae. In addition, some bennetti-talean leaves, such as Ptilophyllum, Pterophyllum,Otozamites, Anomozamites, nilsssonialeans includ-ing Nilssonia, ginkgoaleans Sphenobaiera andBaiera, as well as pteridospermous leaves Cteno-

zamites are frequently found with good preserva-tion associated with ferns.In addition, the fern specimens described by Sze

(1949), Wu et al. (1980) and Wu (1991) fromthe same locality of the Hsianhchi Formationwere also re-examined for comparison and discus-sion. They were housed in the PalaeobotanicalCollection, Nanjing Institute of Geology and Pa-laeontology, Academia Sinica, Nanjing, China(NIGPAS). Besides megaplant material, the paly-nological data published by Li and Shang (1980),Zhang and Zhang (1987) were also considered tore£ect the £oral composition of ferns.In order to reveal the abundance of the fossil

fern groups, the statistical analysis of the recentcollection is applied giving the percentage of eachfern taxa on generic level.The selected specimens are ¢gured herein with

registration numbers PB6724, PB18090, PB18139and PB18894^PB18916, which are housed in Pa-laeobotanical Collection, NIGPAS, Nanjing, Chi-na.

4. Floral composition of the Hsiangchi Formationand its fern diversity

The Lower Jurassic Hsiangchi Formation iswell known for its southern-type £ora in China.Newberry (1865/1866) was the ¢rst to describeplant fragments, collected by Pumpelly from Zi-gui, Hubei (possibly derived from the HsiangchiFormation). According to Schenk (1867), thespecimens collected by Richthofen in China,were derived also from the same formation. Sze

Table 1Fossil assemblage zones recognized in the Lower Jurassic Hsiangchi Formation in western Hubei

Megaplants Spores and pollen grains Megaspores Bivalvas(Wu et al., 1980;Meng, 1987)

(Zhang and Zhang, 1987) (Yang and Sun, 1987) (Yu, 1987)

Ptilophyllum^Coniopterisassemblage

Upper part: Dictyophyllidites^Cyathidites^Classopollisassemblage

Upper part: Bacutriletes harrisii,Bacutriletes clavatus, Bacutriletesonodios, Verrutriletes aurantium

Sibireconcha anodontoides^Qiyangia xiangxiensisassemblage

Lower part: Dictyophyllidites^Classopollis^Cerebropollenitesassemblage

Lower part: Nathorstisporiteshopliticus, etc.

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(1949) made a systematic study on the fossil £oraof the Hsiangchi Group in western Hubei. After-wards, Wu et al. (1980) and Meng (1987) contrib-uted greatly to the study of the fossil plants fromthis locality and horizon. Presently, over 72 spe-cies belonging to 31 genera have been reportedfrom the formation (according to Meng, 1987).Among them, cycadophyta and ferns are thedominant groups, ginkgoales and conifers arecommon, pteridosperms are quite rare and onlyrepresented by Ctenozamites. The cycadophytaare characterised by bennettitalean leaves, suchas Pterophyllum, Anomozamites, Otozamites, Pti-lophyllum, Tyrmia, Weltrichia, Zamites, Ctenis,Mironeura, and Nilssonialeans (Nilssonia). Theginkgoaleans are represented by Ginkgoites,Baiera, Sphenobaiera, the Czekanowskialeans byCzekanowskia, Phenicopsis, Ixostrobus and Ste-norachis. The conifers are only known as Podoza-mites, Ferganiella, Swedenborgia and Eladocladus.It is noteworthy that the fossil plants in the

Lower Jurassic Hsiangchi Formation show a re-markable vertical diversity in western Hubei andthe equatorial horizon in adjacent areas of theYangtze River. Available data (Wu et al., 1980;Huang, 1983, 1988; Meng et al., 1994) and thepresent investigation show that ginkgoaleanplants are abundant in the lower part of theHsiangchi Formation, whereas ¢licaleans and cy-cadoaleans are more common and predominant inthe upper part of the formation.Among the ferns, over 20 species belonging to

nine genera have been reported so far from theHsiangchi Formation. They are grouped into ¢vefamilies, including Marattiaceae, Osmundaceae,Matoniaceae, Dipteridaceae and Dicksoniaceae.Sze (1949) described 18 species belonging to thegenera Marattiopsis ( =Marattia), Sphenopteris( =Todites), Cladophlebis, Laccopteris ( =Phlebop-teris), Dictyophyllum, Clathropteris and Coniopte-ris. Some of them were revised in the work by Wuet al. (1980), in which eight species were de-scribed, including Marattiopsis asiatica Kawasaki,Todites princeps (Presl) Gothan, Cladophlebis den-ticulata (Brongniart) Fontaine, Phlebopteris poly-podioides Brongniart, Clathropteris obovata Oishi,Thaumatopteris sp., Coniopteris cf. hymenophyl-loides (Seward), Coniopteris cf. murrayana (Brong-

niart) Brongniart and Coniopteris. sp. Meng(1987) also described Phlebopteris ziguiensis fromZigui Basin as well as Coniopteris chenyuanensisMeng, Cladophlebis dangyangensis Meng, Clado-phlebis complicata Meng from Dangyang Basinin western Hubei.Recently, several osmundaceous ferns belong-

ing to Todites and cf. Osmundopsis were describedfrom the Hsiangchi Formation in Zigui, westernHubei (Wu, 1991). Wang (1999), Wang and Mei(1999) and Wang et al. (2001) published detailedresults of the fertile organs and in situ spores ofMarattia asiatica and Phlebopteris polypodioides.A further study on matoniaceous ferns in thisregion is under preparation (Wang and Van Ko-nijnenburg-van Cittert, 2002).In this investigation, the following taxa (includ-

ing nine genera of ¢ve families) are recognisedfrom the upper part of the Hsiangchi Formationbased on recent collections from Zigui County,western Hubei (Table 2).

4.1. Marattiaceae

Marattia asiatica (Kawasaki) Harris is the onlyrepresentative member of the Marattiaceae recog-nised from the Hsiangchi Formation. Specimensascribed to this species were originally describedas Marattiopsis muensteri by Sze (1949) and Ma-rattiopsis asiatica by Wu et al. (1980). They wereall impressions and yield no information of fertilestructures. A recent study by Wang (1999) andWang et al. (2001) revealed detailed structuresof fertile organs and in situ spores of this species.Both sterile and fertile specimens of Marattia

asiatica are found in the upper part of the Hsiang-chi Formation. The pinnae are linear and narrowin shape, and reach a length of over 15 cm (PlateI, 1). They vary from 24 to 30 mm wide in thelower region and near the pinna base, and grad-ually taper from the base to the apical region. Thebase is asymmetrical and auriculate (Plate I, 5).The fertile pinnae are especially well preserved,including the linear, bivalved synangia, whichare attached on the secondary veins of the pinnamargin (Plate I, 4). A synangium is composed of25^40 pairs of sporangia, which yield a largenumber of monolete spores with a granular exine

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(Wang, 1999). Though specimens of M. asiaticaare always found with pinnae in western Hubei, itseems that this plant has fronds that are at leastbipinnate with a possible third pinna rachis asreported by Kimura and Tsujii (1980, 1984) ofspecimens from the Early Jurassic of Japan. Sim-ilar fronds were also found in Marattia anglica(Thomas) Harris from the Jurassic of Yorkshire(Van Cittert, 1966).

4.2. Osmundaceae

About four species of the Osmundaceae arerecognised from the Hsiangchi Formation. To-dites princeps is the most common one in ourcollection. The specimens of this species aremainly represented by sterile pinnae, though the

fragmentary fertile pinnule were ¢gured by Wu etal. (1980) and Wu (1991). The frond is bipinnatewith anadromic branching of the pinnules andsphenopterid venation (Plates I, 2, 6, and II, 1).The specimens described as Sphenopteris modestaby Sze (1949), were similar in gross morphologyto T. princeps and were attributed to the latter byWu et al. (1980).Specimens of Todites leei Wu are also bipinnate

with pecopterid frond architecture and simple ve-nation (only fork one time) (Plate II, 3), the fertilepinnules are strongly reduced (Wu, 1991). Toditeswilliamsonii (Brongniart) Seward was described byWu (1991) from the Hsiangchi Formation. Thesterile pinnae are catadromic in pinna and venat-ion branching. The fertile pinnules are narrowand much smaller than sterile ones. Another os-

Table 2List of fern taxa recognized in this study from the upper part of the Lower Jurassic in Western Hubei

Families Genera and species

(1) Marattiaceae Marattia asiatica (Kawasaki) Harris(2) Osmundaceae Todites princeps (Presl) Gothan

Todites leei WuTodites williamsonii (Brongniart) SewardCladophlebis denticulata (Brongniart) Fountaine

(3) Matoniaceae Phlebopteris ziguiensis Wang and Van Konijnenburg-van Cittert ex. MengPhlebopteris muensteri (Schenk) Hirmer and HoerhammerPhlebopteris polypodioides BrongniartPhlebopteris sp.

(4) Dipteridaceae Dictyophyllum nilssonii (Brongniart) GoeppertDictyophyllum nathorstii ZeillerDictyophyllum rugosum Lindley and HottonClathropteris obovata OishiClathropteris platyphylla (Goeppert) NathorstHausmannia ussuriensis KryshtofovichHausmannia buchii AndraeThaumatopteris spp.

(5) Dicksoniaceae Coniopteris hymenophylloides (Brongniart) SewardConiopteris murrayana (Brongniart) BrongniartConiopteris chenyuanensis MengConiopteris sp.

Plate I. Marattia (Marattiaceae) and Todites, Cladophlebis (Osmundaceous) from the Lower Jurassic Hsiangchi Formation. All¢gures U0.95 unless otherwise indicated. (1,4,5) Marattia asiatica (Kawasaki) Harris. (1) A larger fertile pinna from the collec-tion of Wu et al. (1980) with a length of over 15.5 cm; PB6724. (4) A fragmentary but well preserved fertile pinna showing theoutline of synangia (from Wang, 1999, plate II, ¢gure 6); PB18090. U2.85. (5) A sterile pinna with asymmetric and auriculatebase (from Wang, 1999, plate I, ¢gure 6); PB18139. (2,6) Todites princeps (Presl) Gothan; PB18894 (2), PB18896 (6). (3) Clado-phlebis denticulata (Brongniart) Fountaine; PB18895.

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mundaceous species, cf. Osmundopsis sturi (Raci-borski) was described by Wu (1991) based on thefragmentary specimens. However, re-examinationof the material shows that Wu’s specimens arefertile pinnae of Todites (probably T. williamso-nii). Unfortunately, the specimens are too smallto show the essential details needed for furtheridenti¢cation. Cladophlebis denticulata (Brong-niart) Fountaine is at least bipinnate and has alarger frond than Todites ; and the pinnules aretypically sickle shaped with a denticulate margin(Plate I, 3).

4.3. Matoniaceae

Phlebopteris is the only representative genus ofthe Matoniaceae in the Hsiangchi Formation.Phlebopteris ziguiensis Wang and Van Konijnen-burg-van Cittert ex. Meng is very common in thepresent collection. The specimens are character-ised by larger fronds (length of pinnae over 14.5cm, number of pinnae 6^10, even 15, length ofpinnules over 22 mm) with palmate or pedateshape. From 10 to 17 pinnae arise from themain rachis of the frond (Plates II, 2, 6, and III,1, 2). The fertile pinnae are well preserved includ-ing sori with ca. eight sporangia. Sze (1949) ¢rstdescribed one fragmentary specimen as Laccopte-ris cf. polypodioides, which was transferred asPhlebopteris polypodioides Brongniart (Wu et al.,1980) (Plate III, 5). The fertile organs and in situspores of P. polypodioides were studied by Wangand Mei (1999) based on newly collected material.Another member, Phlebopteris muensteri (Schenk)Hirmer and Hoerhammer, has a frond of thesame shape and size as P. ziguiensis, but withlonger and narrower pinnules (Plate III, 3). Speci-mens of P. polypodioides and P. muensteri are lessabundant than those of P. ziguiensis in the presentcollection. In addition, the young curved leaves(genus Spiropteris) are frequently found in closeassociation with Phlebopteris fronds or pinnae

(Plate II, 4, 5). The creeping roots and stems arefound in the same fossiliferous bed (Plate III, 4).Such evidence probably suggests almost autoch-thonous fossils.

4.4. Dipteridaceae

In western Hubei, four genera are recognisedfor the family Dipteridaceae as Dictyophyllum,Hausmannia, Clathropteris and Thaumatopteris.The most common species is Dictyophyllum nils-sonii (Brongniart) Goeppert. Specimens of thisspecies are frequently found with larger pinnaeor fronds (Plate IV, 1). The laminae of the pin-nules are thick. The midribs of pinnules are prom-inent and broad; the main lateral veins arise fromthe midrib at an angle of about 60‡. The second-ary lateral veins form a network of irregular po-lygonal meshes, in which the ¢nest veins are visi-ble (Plate IV, 3). In fertile pinna, the sporangiaare very well preserved, covering the whole part ofpinnules (Plate IV, 4). In addition, Dictyophyllumnathorstii Zeiller and Dictyophyllum rugosumLindley and Hutton are recognised in associationwith Dictyophyllum nilssonii, but they are notabundant. Hausmannia ussuriensis Kryshtofovichis common in the present collection. The fan-shaped lamina shows clear organisation of pri-mary and secondary veins and typical meshes(Plate V, 1, 2). The petiole and lamina are wellpreserved (Plate V, 3).

4.5. Dicksoniaceae

The extant Dicksoniaceae are tropical tree fernswith erect trunks and arborescent trunk habit.The Mesozoic dicksoniaceous ferns are, however,mostly smaller and shorter herbaceous plants.Only one genus Coniopteris is recorded in theHsiangchi Formation, which includes Coniopterishymenophylloides Brongniart, Coniopteris mur-rayana (Brongniart) Brongniart, Coniopteris che-

Plate II. Todites (Osmundaceae) and Phlebopteris (Matoniaceae). All ¢gures U0.95. (1) Todites princeps (Presl) Gothan, showingthe thick rachis and the pinnae; PB18897. (3) Todites leei Wu. A small specimen with thick rachis and clear venation; PB18898.(2,6) Phlebopteris ziguiensis Wang and Van Konijnenburg-van Cittert ex. Meng. (2) The petiole and 11 pinna rachises; PB18899;(6) A completely preserved frond with 17 pinnae; PB18902. (4) A young curved leaf Spiropteris (left) and the associated pinnaeof Phlebopteris ziguiensis (right); PB18900. (5) A young curved leaf; PB18901.

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nyuanensis Meng, and Coniopteris sp. Amongthem, C. hymenophylloides is the most commonone with both the sterile and fertile pinnae pre-served (Plate V, 4^6). All of these species are verysmall and slender in growth form, less than 20 cmtall.

5. Ecology implications

5.1. Fossil preservation and burial mode

As already mentioned, the ferns from the upperpart of the Hsiangchi Formation are preserved inthe peat-forming environments (Fig. 2). Fossils, ingeneral, are abundant and diversi¢ed in these lith-ologies. All of the fern fossils are found in thesame horizon, including not only the sterile leaveswith clear venation, but also the fertile leaves withgood reproductive organs of sporangia and in situspores (Plates I, 1, 4, and IV, 4; Wang, 1999;Wang and Mei, 1999). The larger fronds of Ma-toniaceae and Dipteridaceae are nearly completelypreserved including petiole and the radiation ofpinnae (Plates II, 2, 6, III, 1, and IV, 1). Evensmaller fronds of Phlebopteris also show petioleand pinnae (Plate III, 2). Sometimes, small pinnaeof Todites are found together with Phlebopteris inthe same slab (Plate III, 3). Smaller fronds, suchas those of Coniopteris, are also found with wellpreserved sori (Plate V, 4). The young curvedleaves (Plate II, 4, 5) and the roots of ferns (PlateIII, 4) are frequently associated with the fernfronds. In the fossil-bearing bed, ferns and othergymnospermous leaves, especially bennettitaleansare always closely associated and irregularly ar-ranged along the bedding surface. These indicatethat the fossil plants were subject to minimaltransport. Therefore, we consider that the fossilferns were deposited near their living area. This

suggests an autochthonous or hypoautochthonousburial in the present fossil-bearing horizon of theHsiangchi Formation.

5.2. Structural analysis and the fern community

Statistical analysis based on relative abundancedata were given using over 340 fern specimenscollected from the upper part of the HsiangchiFormation (Fig. 3). The Matoniaceae is the dom-inant group (42.6% of total fern specimens), rep-resented by Phlebopteris. The Dipteridaceae ranksecond (26.8%), but with greater of diversity, in-cluding Dictyophyllum, Hausmannia, Clathropterisand Thaumatopteris. The Marattiaceae are rela-tively abundant (14.7%) and are characterised byMarattia asiatica. The Osmundaceae (9.1%) andDicksoniaceae (5.3%) are less common.According to palynological data (Li and Shang,

1980; Zhang and Zhang, 1987), dispersed sporeswith known ¢licalean a⁄nities from the upperpart of the Hsiangchi Formation are representedby Dictyophyllidites, Concavisporites, Converruco-sisporites, Marattisporites, Todisporites, Granula-tisporites, Osmundacidites and Cyathidites. Basedon comparative analysis with fossil in situ spores(e.g. Van Konijnenburg-van Cittert, 1975, 1978,1989, 1993, 1996; Ash et al., 1982; Litwin, 1985;Balme, 1995; Schweitzer et al., 1997; Wang, 1999;Wang and Mei, 1999), the dispersed spores alsoindicate the source data as Marattiaceae, Osmun-daceae, Matoniaceae, Dipteridaceae and Dickso-niaceae. Furthermore, such data support theabundance of ferns in the Hsiangchi Formationsimilar to that found for megafossils as shownin Fig. 3.Comparison with the nearest living relatives

and their living habitats suggest that the fossilferns from the upper part of the Hsiangchi For-mation are all herbaceous and hydrophytic. They

Plate III. Phlebopteris (Matoniaceae). All ¢gures U0.95. (1) A larger frond of Phlebopteris ziguiensis Wang and Van Konijnen-burg-van Cittert ex. Meng, showing the long, thick petiole and nine radiating fertile pinnae; PB18903. (2) A small frond of Phle-bopteris showing the petiole and 11 pinnae rachises; PB18904. (3) A pinna of Phlebopteris muensteri (Schenk) Hirmer and Hoer-hammer. In the right lower part of the ¢gure (arrow), there is a fragmentary pinna of Todites princeps (Presl) Gothan; PB18905.(4) The creeping root that is frequently found in association with Phlebopteris pinnae; PB18907. (5) A pinna of Phlebopteris poly-podioides Brongniart; PB18906.

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are a typical peat-forming fern community domi-nated by the Matoniaceae. This community isecologically characterised by perennial herbaceousspecies specialised for growth on shaded £oor of awet, tropical to subtropical forest. These fernsmostly prefer high humidity and low light condi-tions. Phlebopteris and Dictyophyllum with largerfronds are more abundant and have higher coverin this community. The Marattiaceae and Osmun-daceae are often dispersed among the community.Coniopteris of the Dicksoniaceae is smaller andslender in size, and is distributed sparsely in thecommunity, probably on the marginal landaround the swamp. A reconstruction of thepresent fern community is suggested and shownin Fig. 4.

5.3. Climatic condition

During the Late Triassic to Middle Jurassic, thewestern Hubei belonged to the Southern FloristicProvince of China, i.e. the Maritime FloristicProvince proposed by Zhou (1984) or the Euro-Sinian Region proposed by Vakhrameev (1991).Fossil ferns are abundant and diverse in the

Hsiangchi Formation and are represented by thepresent fern community described herein that istypical of the Southern Floristic Province, whichis indicative of the climatic condition.The living relatives of the above ferns are

mainly restricted to tropical and subtropical re-gions. The Matoniaceae is a relict family of theMalesian region with two genera. The Dipterida-ceae is restricted to the Indo-Malayan region andsouthern China. The Marattiaceae are tree fernsranging in the palaeotropics from Africa to thePaci¢c. The Osmundaceae are all perennials,which includes three extant genera: Osmunda isdistributed throughout most temperate and trop-ical regions; Todea and Leptopteris are native inSouth Africa and Australia. Extant members ofthe Dicksoniaceae are mainly tree ferns, distrib-uted in tropical and subtropical regions. Thoughthe Mesozoic ferns di¡er from the extant relativesin gross morphology, their climate tolerances are,however, very similar. In general, the peat-form-ing fern community described above dominatedby the Matoniaceae apparently indicates a tropi-cal to subtropical warm and humid climate, whichis conductive for coal formation and accumula-tion. As western Hubei is located on the northcoast of the Tethys Ocean during the Early Juras-sic, the warm and humid marine current is favour-able for the development of a fern community ina coal swamp environment. However, at the sametime, few ferns have been distributed in theNorthern Floristic Province of China due to thelittle e¡ect of the marine currents there.In addition, sedimentary studies (Meng et al.,

1994) indicate that the clay minerals of the upperpart of the Hsiangchi Formation are characterisedby the humid climate indicator minerals, kaoliniteand illite (35% and 20%, respectively) as well assiderate, whereas the arid or dry climate indica-tors, such as chlorite and hydromica, are uncom-mon. These ¢ndings agree with the climatic con-ditions suggested by the fossil fern community.

Plate IV. Dictyophyllum nilssonii (Brongniart) Goeppert (Dipteridaceae). 1 and 2, U0.95; 3 and 4, U2.85. (1) A larger frondshowing the basal part of four pinnae; PB18908. (2) A pinna near the apical part of a frond; PB18909. (3) Enlargement of 2showing the venation and the impression of sori. U2.85. (4) Enlargement of a fertile pinna showing two pinnules that are cov-ered by sporangia; PB18910.

Fig. 3. Statistical result showing the relative abundance (per-centage) of the fern specimens collected from the Lower Ju-rassic Hsiangchi Formation in western Hubei. A, Marattia-ceae; B, Osmundaceae; C, Matoniaceae; D, Dipteridaceae;E, Dicksoniaceae.

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Furthermore, the above-mentioned vertical di-versity of fossil plants in the Hsiangchi Formationshows a variation of climate condition. Duringthe early stage of Early Jurassic, the sedimentarybasin in Zigui was characterised by high and pre-cipitous terrain as well as developed rivers andcreeks, and the climate was pleasantly cool withlower humidity. This condition was favourable forthe growth of ginkgoaleans and conifers, whereasthe growth of cycadophytes and ferns was re-strained. During the late stage of Early Jurassic,the basin was marked by smooth terrain, lakesand swamp were widely distributed. The climatechanged to warm and humid, which was favour-able for development of ferns and cycadophytes

as well. The fern community recognised in thisstudy from the Hsiangchi Formation is, therefore,a representative fern ecology community in theSouthern Floristic Province of China during theEarly Jurassic.

6. Concluding remarks

(1) Ferns are the conspicuous to dominantcomponents of the Early Jurassic Hsiangchi For-mation in western Hubei, China, including at leastnine genera in ¢ve families, such as Marattiaceae,Osmundaceae, Matoniaceae, Dipteridaceae andDicksoniaceae.

Fig. 4. A suggested reconstruction of the fern community dominated by Matoniaceae in the upper part of the Lower JurassicHsiangchi Formation in western Hubei. 1, Matoniaceae; 2, Dipteridaceae; 3, Marattiaceae; 4, Osmundaceae; 5, Dicksoniaceae.

Plate V. Hausmannia (Dipteridaceae) and Coniopteris (Dicksoniaceae). All ¢gures U0.95. (1^3) Hausmannia ussuriensis Kryshtofo-vich. (1,2) Showing the primary and secondary venation as well as typical meshes; PB18911 (1), PB18912 (2). (3) Part of a frondshowing half of the lamina and petiole; PB18913. (4^6) Coniopteris hymenophylloides (Brongniart) Seward. (4) A bipinnate fertilefrond with sori and a sterile pinna; PB18914. (5,6) Bipinnate sterile fronds with pinnae; PB18915 (5), PB18916 (6).

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(2) Ferns are abundant, diverse and well pre-served in the upper part of the Hsiangchi Forma-tion. The nature of the preservation and the asso-ciated sedimentary conditions suggest that fernsfrom this horizon represent an autochthonous orhypoautochthonous £uviatile peat-forming com-munity dominated by Phlebopteris of the Mato-niaceae.(3) This fern community indicates a warm and

humid, tropical to subtropical climate. It is a re-markable and representative fern community rec-ognised for the late Early Jurassic in the SouthernFloristic Province of China.

Acknowledgements

I would like to offer my sincere thanks to Dr.Johanna H.A. Van Konijnenburg-van Cittert(Utrecht) and Dr. Margaret Collinson (London)for their kind invitation and encouragement of thepresent contribution to the special volume, ‘FernEcology through Time’. Special thanks are due toProf. Zhou Zhiyan (Nanjing) for his kind sugges-tions and valuable comments on this study. I amalso grateful to Prof. Meng Fansong (Yichang),Prof. Liu Lujun, Mr. Mei Shengwu, Ms. Leng Qin(Nanjing) for their help and assistance in collectingfossil materials. I thank Prof. David L. Dilcher(Florida Museum of Natural History, Universityof Florida), Prof. William A. DiMichele (NationalMuseum of Natural History, Smithsonian Institu-tion, USA) and Dr. Johanna H.A. Van Konijnen-burg-van Cittert (University of Utrecht) for theircritical review and valuable suggestions to themanuscript. This work was financially supportedby the National Natural Science Foundation ofChina (NSFC) (39900007), the Talent TrainingFund from NSFC (990202), the Special Funds ofPalaeontology and Palaeoanthropology (SFPP)from CAS (990202), as well as the InnovationResearch Fund from NIGPAS, Nanjing, China(000213). This study was also partly supported bythe Executive Office of State Council ThreeGorges Project Construction Committee, and theChina Yangtze Three Gorges Project Develop-ment Corporation of China.

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