The ecology of Cainozoic ferns

Review of Palaeobotany and Palynology 119 (2002) 51^68 www.elsevier.com/locate/revpalbo

The ecology of Cainozoic ferns Margaret E. Collinson  Department of Geology, Royal Holloway University of London, Egham, Surrey, TW20 0EX, UK

Abstract The ecology of Cainozoic ferns is documented (excluding that based only on nearest living relatives). Freefloating water ferns (of the modern genera Azolla and Salvinia) are widespread in the Cainozoic. They are represented by whole plants and dispersed or interconnected megaspores and microspore massulae in freshwater facies associated with a range of aquatic angiosperms. Acrostichum (a fern characteristic of mangroves today) was clearly associated with lakes and freshwater marshes in the Cainozoic. In southern England an Acrostichum/Typha association existed comparable to that which is rare today, e.g. in the Florida Everglades. Other Cainozoic ferns also grew at the margins of lakes and in mires, especially well-represented by the Princeton Chert flora (Dennstaedtiaceae, Dryopteridaceae, blechnoids and Osmunda). In North America ferns such as Onoclea and Osmunda were associates of freshwater swamp forests dominated by taxodiaceous trees. These ferns, along with Woodwardia and the extinct Coniopteris, had a Cainozoic circum-Arctic distribution to very high palaeolatitudes. The Eocene fern flora of Yellowstone National Park, USA, grew in a disturbed volcanogenic terrain but the same ferns also occurred in backswamp settings. Gleicheniaceae were part of a fire-prone vegetation in the Miocene of Australia but other Cainozoic Gleicheniaceae are very poorly understood. Relatively little is known about the Cainozoic ecology of the Marattiaceae, Matoniaceae, Dipteridaceae, Dicksoniaceae and Cyatheaceae despite their Mesozoic importance. The Cainozoic record of tree ferns (proven by stem fossils) is very patchy but does include members of the Cyatheaceae, Dicksoniaceae and Osmundaceae (Aurealcaulis, which grew in swampy floodplain forests). Although the epiphytic habit had evolved in extinct families of ferns in the Carboniferous there is no convincing evidence for fossils of epiphytic ferns in the Cainozoic. The fern Lygodium (for which a climbing habit is often inferred from morphological similarity with modern Lygodium) was widespread in the Cainozoic in North America, Chile, Europe, Australia and probably China. However, there are no rachis fossils to confirm or refute the interpretation that Palaeogene to Miocene Lygodium was a climber. 1 2002 Elsevier Science B.V. All rights reserved. Keywords: fern; fossil; palaeoecology; pteridophyte; Tertiary

1. Introduction Cainozoic fern ecology is discussed under three main headings: ¢rstly, the recognition of Cainozoic fern communities or ferns from distinct habitats (e.g. free-£oating aquatics, wetlands and

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swamps; ¢re prone, volcanogenic and other disturbed settings); secondly, the Cainozoic fate of those ferns which were ecologically dominant in the Mesozoic; and thirdly, the recognition of selected fern habits (e.g. epiphytic, climbing and tree) in the Cainozoic. Evidence is drawn from fern macrofossils and mesofossils, from wellunderstood sedimentological successions, where facies association is well-documented and taphonomic factors have been considered. Inferences

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based only on near living relatives or only on the dispersed spore record are excluded (with a few exceptions) because these o¡er less adequate evidence for interpretation of ancient plant ecology.

2. Fern communities and habitats 2.1. Water ferns A major modernisation occurred between the Late Cretaceous and Tertiary with loss of Late Cretaceous taxa, e.g. Hydropteris, Glomerisporites, Ghoshispora, Azollopsis, Ariadnaesporites, Parazolla etc. (Collinson, 2001a). Cainozoic £oras include only the modern genera Azolla and Salvinia of the heterosporous water ferns. The fossil record of Azolla and Salvinia is unequivocal due to the preservation of whole fertile plants and numerous dispersed megaspores and massulae. The dispersed material can be securely assigned because of the records of identical/closely comparable entities in whole fossil plants. The record has been reviewed by Collinson (1980, 1991, 1996a, 2001a). The whole plants are almost indistinguishable (in terms of habit and functional morphology indicative of habitat) from living relatives. Facies associations of fossils are in complete support of their growth in tranquil freshwaters including lakes and ponds. A few examples only are mentioned here, those for which the most extensive ecological interpretations can be made. Whole fertile plants of Azolla schop¢i Dijkstra and Azolla velus (Dijkstra) Jain and Hall are recorded from the Palaeocene Ravenscrag Formation of Saskatchewan, Canada (McIver and Basinger, 1993, see 2.2.3.1. Onoclea, Osmunda and associated ferns for more details of this £ora). The two species co-occur at one of the sub-localities. The Azolla were associated with other £oating aquatic plants including Quereuxia (synonym Trapago) (see also Stockey and Rothwell, 1997), a Pistia-like plant and Spirodela ( = Limnobiophyllum see Kvac›ek, 1995; Stockey et al., 1997). These whole fossil angiosperms are interpreted as free £oating (to rooted in very shallow water) aquatics based on their growth habit, nature of preserva-

tion of complete plants, facies associations and presence of aerenchyma (Limnobiophyllum) and leaf heteromorphy with one type ¢liform (Quereuxia). Whole fertile plants of A. schop¢i were also recorded from shales in the Palaeocene site of Genessee, Alberta, Canada, in association with Limnobiophyllum (Chandrasekharam, 1974). In this case preliminary observations showed a general stratigraphic sequence from deciduous broadleaved trees to Metasequoia to the free-£oating association (Chandrasekharam, 1974). The fern Botrychium from shales at this site was fully described by Rothwell and Stockey (1989) but its ecological context was not discussed. Whole fertile plants of Azolla stanleyi Jain and Hall were part of a lacustrine free-£oating vegetation on an oxbow lake, in the Palaeocene of Jo¡re Bridge, Alberta, Canada. The sediments also included Limnobiophyllum as well as Ricciopsis (an aquatic liverwort) just a few centimetres below the Azolla-bearing horizons (Ho¡man and Stockey, 1994a,b, 1997, 1999; Stockey et al., 1997). The Azolla fossils are the last occurring in the sedimentary sequence which suggests that they were the last colonisers of the lake open waters prior to in¢ll by sediment-laden waters (Ho¡man and Stockey, 1999). In the Eocene/Oligocene transitional strata of southern England whole fertile Azolla prisca Fowler (1975) plants occur in the Insect Limestone of the Bembridge Marls Member, Bouldnor Formation, of the Isle of Wight. The Insect Limestone is interpreted as a lacustrine deposit of impersistent water bodies (see McCobb et al., 1998). The Insect Limestone also frequently contains reproductive structures of Typha, Potamogeton and Sparganium (personal observation) as well as Typha-like foliage. Dispersed megaspores and associated microspore massulae of A. prisca are present along with these taxa and numerous other fossils whose near living relatives are freshwater free-£oating, marginal, emergent or rooted aquatics (e.g. Nymphaeaceae, Stratiotes (Hydrocharitaceae), Alismataceae, Juncaceae, Charophytes) in ¢ne-grained sediments containing freshwater gastropods e.g. Lymnaea and Planorbis and ostracods (Collinson, 1983, 1990, 1992; Collinson et al., 1993b; Collinson and Hooker, 1987, 2000;

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Hooker et al., 1995). This association testi¢es to the importance of Azolla as a free-£oating aquatic plant throughout the Late Eocene and Eocene/ Oligocene transition in southern England. Although whole fertile plants of Salvinia are known from the late Cretaceous onwards (Weber, 1973; Collinson, 2001a) this genus does not occur as whole plants in association with the Palaeogene Azolla noted above. The distribution map for fossil Salvinia (Shaparenko, 1956; and see Collinson, 2001a, for additional references) suggests that Salvinia was restricted to slightly lower palaeolatitudes. Dispersed Salvinia megaspores and clumps of microspore massulae do occur in the Palaeocene/Eocene transitional strata of southern England (Van Bergen et al., 1993; Batten and Collinson, 2001; Collinson, 2000b) but these occurrences may be associated with the short-lived warm climate excursion known as the LPTM (Collinson, 2000b). Eocene fertile Salvinia plants are known from France and the USA whilst Salvinia-like foliage occurs in the Eocene of Tennessee, Washington State and Wyoming, USA, former USSR and Nigeria. Salvinia occurs in association with Spirodela ( = Limnobiophyllum) and other aquatics in pond settings within a backswamp environment of a wet distal £oodplain in the Eocene of the Bighorn Basin, Wyoming (Wing, 1984; Farley, 1990; see also Davies-Vollum and Wing, 1998 for further study of this setting). Azolla is not recorded from this community by Wing (1984) but it is listed as a £oristic component in the Eocene Bighorn Basin £oodplains by Wing et al. (1995) and specimens of fertile Azolla plants were found in a channel ¢ll in the Willwood Formation at Elk Creek Crossing, west of Manderson in July 2001 (Collinson, personal observation). However, Salvinia plants were not found on the same bedding plane as the Azolla. The large leaves of Zingiberopsis were the most abundant associated fossils. Associated vegetative remains and megaspores and massulae of Salvinia occur in the Late Cretaceous/Early Tertiary Deccan Intertrappean Series (Collinson, 2001a, for further details). Azolla species also occur in the Intertrappean Series but not speci¢cally in the same samples as Salvinia. Dispersed megaspores and massulae of Salvinia

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were recorded in ‘every worthwhile sample’ from the Golden Valley Formation, Eocene, USA. Azolla megaspores and massulae were also recorded but many Salvinia-bearing samples lacked Azolla (Jain and Hall, 1969). Salvinia and Azolla (including whole fertile plants covering bedding surfaces, especially of Salvinia) occur in the Early Miocene of the B|¤lina ( = former Maxim Gorkij) mine in North Bohemia, Czech Republic (Bufiz›ek et al., 1971, 1988, 1992; Kvac›ek, 1998). Here Azolla and Salvinia are dominants in a community including Limnobiophyllum and other free-£oating £owering plants Lemna, Hydrochariphyllum and Elaphantosotis (Kvac›ek, 1995, 1998). Salvinia and Azolla are clustered by statistical analyses of the fossil £oras (Hubbard and Kvac›ek, 1998; Boulter et al., 1993). However, Kvac›ek (pers. commun., 2001) notes, based on his ¢eld observations, that the two genera rarely occur together on the same bedding surface. Overall the fossil evidence, therefore, suggests that, although growing in the same community, Cainozoic Azolla and Salvinia only rarely grew intermixed on the water surface. It seems likely that the two genera grew in slightly di¡erent areas of the water surface, possibly related to variations in the amount of open water, the water depth or the associated vegetation and the shade which it produced. The Cainozoic record of Marsiliaceae (see Collinson, 2001a) is based only on dispersed megaspores from the Oligocene onwards in Germany and former USSR. Some have attached microspores. The ecology of the parent plants is di⁄cult to infer as there are no Cainozoic sporocarps, foliage or whole plants, only dispersed spores. Furthermore, ecology cannot easily be inferred via modern relatives as the modern genera range through from wetlands to areas with very temporary or intermittent water supply, supporting drought-resistant species (Kramer in Kramer and Green, 1990). The £oating aquatic homosporous fern Ceratopteris has no macrofossil record but dispersed spores named Magnastriatites are very distinctive and can be used as tracers for this genus (Collinson, 2001a). However, there is no proof that

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these spores were produced by ancient aquatic ferns. 2.2. Wetland and swamp ferns 2.2.1. Acrostichum in freshwater wetlands Eocene Acrostichum was undoubtedly a fern capable of growing in freshwater from records in the UK, USA and Germany (Collinson, 2001a, 1996a). Material from the Middle Eocene Clarno Chert has aerenchymatous rootlets and the stems, petioles, foliage fragments, sporangia, spores and paraphyses have all been documented in permineralised material (Arnold and Daugherty, 1963). Material from the Late Eocene of England consists of compression fossils showing clumps of sporangia with paraphyses and in situ spores in association with fragments of foliage (Collinson, 1978, 2001a). The records of sterile pinnules from Germany come from lacustrine settings including the Maar lake of Eckfeld, Lake Messel and the wetlands of the Geiseltal (Frankenha«user and Wilde, 1993). Acrostichum also occurs in a freshwater setting (freshwater diatomites) in the latest Eocene Kuclin £ora, near B|¤lina, North Bohemia (Czech Republic) (Bufiz›ek et al., 1990). In the Late Eocene of England the Acrostichum is judged to have formed an association with Typha in extensive marshes (Collinson, 1983, 1990 ; Collinson et al., 1993b). There is absolutely no evidence for association of Acrostichum with the Nypa-dominated mangroves of Europe. An entirely di¡erent fern, an as yet unidenti¢ed possible dennstaedtioid, may have been associated with mangroves on the basis of occurrence in the London Clay Formation and the Brussels sands with many Nypa fruits and pollen. However, this is not an exclusive co-occurrence; this fern may have grown in both settings or may merely have been transported into the Nypa-containing sediments (Collinson, 1993, 1996a,b, 2001a). Detrended Correspondence analysis of Indonesian Eocene palynomorphs by Lelono (2000) suggested that plants producing Acrostichum-like spores grew in both freshwater and brackish conditions like the modern genus does today in the

Everglades. There is, however, some doubt as to the certainty with which Acrostichum-like dispersed spores can be reliably assigned to Acrostichum rather than to other ferns. Macrofossils of Acrostichum have, in some cases, been used to infer brackish or coastal palaeoenvironments (Awasthi et al., 1996; Petrescu et al., 1995) when this clearly need not be the case. I know of no unequivocal examples of the occurrence of Acrostichum macrofossils in sediments which would indicate a mangrove setting for Palaeogene Acrostichum plants. 2.2.2. Dennstaedtiopsis and the Princeton Chert ferns ^ marginal emergent aquatics and lake margin plants Rothwell et al. (1994) and Pigg and Stockey (1996) note at least ¢ve fern species in the Middle Eocene Princeton Chert £ora, British Columbia, Canada. The chert contains a number of in situ emergent aquatic plants (Cevallos-Ferriz et al., 1991) and was formed within a lacustrine succession probably in the shallow nearshore environment (Cevallos-Ferriz et al., 1991). One of the ferns Dennstaedtiopsis aerenchymata Arnold and Daugherty, is a dennstaedtioid which has aerenchyma in the rhizomes and petioles (CevallosFerriz et al., 1991; Pigg and Stockey, 1996; Arnold and Daugherty, 1964). This fern also occurs in the lacustrine Clarno Chert (Arnold and Daugherty, 1964) and the presence of aerenchyma is likely to indicate an aquatic habitat (CevallosFerriz et al., 1991). A second fern, a blechnoid (Rothwell and Stockey, pers. comm., 2000), referred to as ‘fern B’ in previous work, also has aerenchyma (Cevallos-Ferriz et al., 1991). Apart from the free-£oating heterosporous ferns (see above) these are the only Cainozoic aquatic ferns. They were presumably marginal emergents. Other ferns in the Princeton Chert include Makotopteris Stockey et al. (1999), of the Athyriaceae, which was referred to in earlier works as Diplazium, Diplazium-like or ferns A and D (Pigg and Stockey, 1996; Rothwell et al., 1994). Makotopteris lacks aerenchyma and occurs associated with Pinus remains and it is interpreted to have grown on the forest £oor at the lake margin (Stockey et al., 1999).

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2.2.3. Ferns of swamp or marsh environments 2.2.3.1. Onoclea, Osmunda and associated ferns In the Eocene of Axel Heiberg, Canadian High Arctic, (palaeolatitude 80‡N) a succession of coaly layers includes well-preserved in situ tree stumps and litter mats. Osmunda, and other ferns including Onoclea, occur in an angiosperm (with many Betulaceae, especially Alnus) ^ fern association which is part of a mosaic including a taxodiaceous peat-forming swamp (Metasequoia with or without Glyptostrobus) and a mixed coniferous community (Greenwood and Basinger, 1993, 1994). In some samples both Osmunda and Onoclea reached 25^50% of the plant material recorded (Greenwood and Basinger, 1993). The Betulaceae-fern community was interpreted to either re£ect slightly higher peat with a locally lower water table (cf. the taxodiaceous peat-accumulating swamp) or to possibly re£ect early succession following disturbance (Greenwood and Basinger, 1994). Analogies were made with the modern swamp^marsh communities in the Florida Everglades, an analogy accepted by recent studies on fossil mammals from Axel Heiberg (Eberle and Storer, 1999). McIver and Basinger (1999), in their review of Tertiary High Arctic vegetation, refer to peat layers with thick mats of Betulaceae, Osmunda and other ferns as lowland forests within a broad swamp environment. Basinger (pers. comm., 2001) reports that the ferns (Onoclea and Osmunda) are most commonly seen as largely fern-dominated mats, which argues for an open, fern-dominated community. If they had grown as a fern understory the fossil assemblage would, in contrast, be expected to be dominated by litter from deciduous canopy trees. The fern communities may have grown at the margins of, or in clearings within, the forests. McIver and Basinger (1999) also indicate that Osmunda occurred in streamsite overbank and £oodplain facies and was typical of vegetation in the area from the Late Palaeocene to the Late Eocene. Basinger (1991) also noted the occurrence of Osmunda in siltstone £oras (as well as in the leaf litter £oras) and interpreted these as part of a vegetation which inhabited the better-drained £oodplains. A similar occurrence of Onoclea is represented

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by whole plant fossils (fertile and sterile) from the Palaeocene site of Munce’s Hill in Alberta, Canada (Rothwell and Stockey, 1991). These fossils are so complete that their identity with modern Onoclea sensibilis L. has been established (Rothwell and Stockey, 1991). Some of the plants were inundated by £ooding and their fronds were bent over and preserved in place attached to rooted rhizomes. This is one of the few cases of conclusive proof of the herbaceous habit for a Cainozoic fern. The fossils occur in ¢ne- to medium-grained siliciclastics in a £uvial succession. They are in association with Betulaceae (especially Palaeocarpinus-like plants); a Metasequoia-like plant, the latter including in situ seedlings described by Falder et al. (1999); Jo¡rea seedlings ; and with in situ rooted Equisetum (Falder et al., 1999; Rothwell and Stockey, 1991). Jo¡rea, an unidenti¢ed fern and a possible bryophyte has also been recorded. Onoclea is represented by more than 2000 specimens (Rothwell and Stockey, 1991). It was suggested that the Onoclea formed the understory of a well-established taxodiaceous swamp on a £oodplain, su⁄ciently near a river channel for periodic £ooding but far enough away to allow establishment of stable forests. Falder et al. (1999) interpreted the rooted Onoclea, Equisetum and Metasequoia-like seedlings as growing in marshy habitats near the margins of oxbow lakes in £oodplain environments. There is no indication that these Onoclea were part of a peat-forming community. Onoclea stands in riparian settings are also represented in the Palaeocene/Eocene transitional strata of Mull, Scotland (Boulter and Kvac›ek, 1989). Another occurrence of seedlings of Jo¡rea along with Metasequoia and Glyptostrobus fossils is in the Late Palaeocene of Jo¡re Bridge, Alberta, Canada (Ho¡man and Stockey, 1999). Osmunda also occurs at this site but Onoclea is not recorded. A di¡erent fern is recorded, identi¢ed as Dennstaedtia blomstrandii (Heer) Hollick ( = Coniopteris (Dicksoniaceae) see discussion in Collinson, 2001a). The fern fossils occur in units interpreted as the distal margin of a crevasse splay, between a £uvial channel and a shallow oxbow lake, where it encroached into a taxodiaceous swamp. The ferns were interpreted as swamp for-

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est understory plants. The swamp facies is carbonaceous mudstone and there is no evidence in the present outcrop of a major peat-forming habitat (Ho¡man and Stockey, 1997; Ho¡man and Stockey, 1999). The ferns Onoclea, Osmunda, and Coniopteris, along with Woodwardia, had a circum-Arctic distribution in the Late Palaeocene and Eocene (Collinson, 2001a). The ¢rst three clearly inhabited swamp and marshy settings, including both peat-forming and clastic conditions. The subtle di¡erences, which determine the speci¢c occurrences, probably relate to speci¢c local habitats rather than to latitude or geographic location. Onoclea, Woodwardia, Osmunda, Dennstaedtia americana (also probably Coniopteris see above) along with Dennastra McIver and Basinger and three unidenti¢ed ferns, all occur in the pond, swamps and forests of the alluvial plain of the Ravenscrag Formation (Palaeocene, Saskatchewan, Canada) (McIver and Basinger, 1993). However, only Onoclea and Woodwardia are represented by more than 10 specimens. They cooccur at sampling level locality US-30 in shales. These were probably forest understory ferns (McIver and Basinger, 1993) associated with broad-leaved deciduous forests. Taxodiaceous conifers were present in the vegetation but were only dominant in swamps at higher levels in the sequence (McIver and Basinger, 1993, p. 7). Fedotov (1970) described Woodwardia (and a fern named Polypodiopteris Krassilov and Fedotov) from clays lenses within, and a clay seam above, coals from Amur Province, Soviet Far East. These ferns were associated with taxodiaceous conifers and angiosperms. Other Woodwardia records are summarised by Kvac›ek (1994) and Collinson (2001a) but most have not been considered from a palaeoecological perspective. In the Miocene of the Most Basin, North Bohemia, Czech Republic, Woodwardia sometimes occurs in layers suggesting that it grew in pure stands in swamps or marshes (Kvac›ek and Hurn|¤k, 2000, p. 35). Cyclosorus (see 2.2.3.2. Thelypteridaceae) exhibits similar occurrences and the fern Blechnum dentatum also occurs in the coalbearing sequences. In contrast, Osmunda parschlugiana occurs in more sandy facies suggesting

a riparian setting (Kvac›ek and Hurn|¤k, 2000; Hurn|¤k and Kvac›ek, 1999). In contrast, these ferns are sometimes very rare, for example in a backswamp vegetation dominated by a Nyssa^ Taxodium association (Sakala, 2000) which suggests fern preference for more open habitats. Rothwell et al. (1996), Pigg and Tcherepova, (2000) and Pigg and Rothwell (2001) have studied ferns from permineralised peats (lake margin or swamp margin accumulations) from the Yakima Canyon Locality in the Miocene of Washington State, USA. At this site Osmunda wehrii Miller (Miller, 1982; Pigg and Tcherepova, 2000) produced larger trunks around which two other rhizomatous ferns were found in the same matrix (Pigg and Rothwell, 2001). The fern Woodwardia is represented by foliage, rhizomes with attached stipes and fertile pinnules with indusiate sori, all of which led to its determination as the modern species Woodwardia virginica (Pigg and Rothwell, 2001). The other fern (Weissiea) is represented by rhizomes and stipes with onocleoid anatomy. The fern community, habitat and its £oral association is considered very similar to that of the present day (Pigg and Rothwell, 2001). In the Eocene of the Bighorn Basin, Wyoming, USA ferns are found in £oodplain settings which include backswamp environments (Wing, 1984; Farley, 1990; Wing et al., 1995; Davies-Vollum and Wing, 1998; Wing, 1998). Wing et al. (1995) give a full list of plant-bearing localities, depositional environments and £oras. These £oras include Onoclea, Woodwardia, and Dennstaedtia americana (? = Coniopteris see above), as well as Cnemedaria, Lygodium, Allantodiopsis, and ferns named Asplenium eolignitum and ‘tatman fern’. For further discussion see 3.1. Open settings and volcanogenic terrains. A diversity of fern spores in the lignite sequences in the Neogene of the Rhineland (Ashraf and Mosbrugger, 1995) testi¢es to a diversity of ferns in peat-forming vegetation. Suggested modern a⁄nities for the spores include Osmunda, Schizaeaceae (Lygodium and Anemia), Pteridaceae, Gleicheniaceae and Polypodiaceae. Older reconstructions only include Woodwardia, Osmunda and Lygodium, the latter in Sequoia woodland, the former two in the Myricaceae/Cyrillaceae

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shrubland and Woodwardia in the Nyssa/Taxodium swamp (Teichmu«ller, 1991). These communities are sustained with some modi¢cation in recent work (Mossbrugger, 1995) although references reviewed by Mossbrugger et al. (1994) indicate a greater involvement of other conifers. Fern associates are not mentioned. Recent approaches studying in situ Miocene peat-forming forests (Mossbrugger et al., 1994) and charcoal (Figuerial et al., 1999) could be expanded to provide more detailed information on the fern component of this vegetation. 2.2.3.2. Thelypteridaceae Pole (1992, 1993) recorded the fern Pneumatopteris (which is treated as a subgenus of Cyclosorus Link, Thelypteridaceae, by Smith in Kramer and Green, 1990) in the early Miocene of New Zealand. In some cases he documented bedding surfaces covered with the in situ fern growing directly on a peat-swamp surface which had been overwhelmed by rise in water level/sedimentation. This was compared to modern fern ¢elds and raised bogs in New Zealand (Pole, 1993). Cyclosorus is also a component of the Geiseltal (see 2.2.3.3. Geiseltal ferns in a lignite-forming sequence) fern £ora in a peat-forming sequence. Cyclosorus (under the name Pronephrium) occurs in particular layers in baked clays in coal-bearing sequences, indicating that it formed dense stands in swamps or marshes in the Miocene of North Bohemia (Czech Republic) (Kvac›ek and Hurn|¤k, 2000, pp. 4 and 35). The Cyclosorus-like ferns are rather widespread in the Cainozoic record (Collinson, 2001a for summary) so more detailed surveys of their ecology should be possible in future. 2.2.3.3. Geiseltal ferns in a lignite-forming sequence Barthel (1976) described the Gesieltal ferns in what is still the most valuable monograph of a Cainozoic fern assemblage. In a section in the former Muecheln West pit (studied in May 2000) ferns occurred in abundance in a discrete horizon (Senckenburg Museum, Frankfurt, ¢eld number GII-7), a well-laminated clayey coal within an extensive lignite sequence including massive lignite (Wilde, Riegel and Collinson personal observa-

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tion). Field observations indicated that Ru¡ordia was very prominent in this assemblage along with Lygodium and Blechnum (and much rarer other ferns). We did not encounter Osmunda, Acrostichum or Cyclosorus ( = Abacopteris in Barthel 1976, see Collinson, 2001a) in this ¢eld study although all are present in Geiseltal material (Barthel, 1976). This Osmunda belongs to subgenus Plenasium, a di¡erent subgenus to that in the circum-Arctic £oras (see review in Collinson, 2001a). Other ferns described by Barthel (1976) were represented by only a few specimens and may not have been very important ecologically. However, no Onoclea, Woodwardia or Coniopteris are recorded at Geiseltal. These taxa are also lacking in the much poorer, but co-eval, assemblages from England. Together with the distinctive Osmunda subgenus this shows that the Geiseltal ferns indicate both geographic and latitudinal differences in Cainozoic wetland fern associations. Like the ferns of the circum-Arctic £oras these ferns certainly did not grow exclusively in peatforming habitats. Ru¡ordia (under the name Anemia), Lygodium, Osmunda and other ferns from the Eocene in England, e.g. in the Bournemouth group, are from siliciclastic £uvial to lacustrine sequences (Gardner and Ettingshausen, 1879^ 1882; Chandler, 1955; Collinson, 1996b). Ru¡ordia, Lygodium, Osmunda, Acrostichum and others occur in the Maar lake of Eckfeld and the lake of Messel (Eocene, Germany) (Wilde, 1989; Wilde and Frankenha«user, 1998; Frankenha«user and Wilde, 1993). Interestingly, Lygodium is more abundant at Eckfeld than at Messel and the opposite is true for Ru¡ordia, possibly related to the existence of a steep-sided Maar at Eckfeld but a marginal herbaceous wetland at Messel (Frankenha«user and Wilde, 1993).

3. Disturbed and open settings 3.1. Open settings and volcanogenic terrains Extensive fern communities sometimes termed ‘fern prairies’ are known from Cretaceous £oras from volcanogenic terrains and it has been suggested that many of the ferns of these commun-

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ities (Schizaeaceae, Gleicheniaceae, Dicksoniaceae) were opportunists colonising open and disturbed ground (see Collinson, 1996a for discussion). Wing et al. (1993) described the £ora entombed in situ by a mid-Maastrichtian (Late Cretaceous) tu¡. Here distinct sub-communities included ferns with cf. Anemia fremontii (Schizaeaceae) on an organic silt substrate and Gleicheniaceae and Dipteridaceae (including Hausmannia) on a peat substrate. The vegetation was interpreted as an open fern and palm-dominated vegetation. The only Cainozoic fern-rich £ora of which I am aware where comparable volcanogenic settings (Fritz and Harrison in Wing and Greenwood, 1993) might be found is the Eocene £ora from Yellowstone National Park. Wing (1987) (p. 759) points to an assemblage of 10^15 pteridophytes in this early Eocene £ora, supported by a diversity of some 28 species of fern spore. It was suggested that fern abundance might be linked to the frequency of disturbance by volcanic events (Wing, 1987). Knowlton (1899) described 10 species of fern based on macrofossils from the Eocene of Yellowstone National Park. Although this £ora has not been subjected to a detailed systematic revision the most up to date systematic assignments for those species are set out by Collinson (2001a). The most abundant ferns are now referred to Thelypteris ( = Cyclosorus) and Allantodiopsis erosa. Cnemidaria and Lygodium are also present. These four ferns also occur in the Eocene of the Bighorn Basin, Wyoming (Wing et al., 1995; Wing, 1998; Davies-Vollum and Wing, 1998) in samples from alluvial £oodplains. A full list of fern-containing samples and their depositional environments is given in Wing et al. (1995). Ferns occur in tabular carbonaceous beds which re£ect virtually year round wet environments in a Glyptostrobus-dominated backswamp (Davies-Vollum and Wing, 1998; see also Wing, 1984; Farley, 1990 and Wing et al., 1995). In one sample set most ferns occur sporadically but Lygodium is widespread (Davies-Vollum and Wing, 1998, table 3). According to Davies-Vollum and Wing (1998) there is no evidence for transport of plant material from the river channel into the backswamp. Allantodiopsis also occurs in the levee/crevasse splay environ-

ments (Wing, 1984; Farley, 1990) which would support the indication that this fern was tolerant of disturbed settings. Allantodiopsis is also known in the Late Palaeocene of Big Multi Quarry, Wyoming, in a £oodplain setting. Allantodiopsis occurs in four samples from the same metre sampling level (18 m) as a degraded ash indicative of volcanic activity but it is lacking earlier in the succession (Wilf et al., 1998, ¢gure 3, table 2., p. 526, mid left column). Disturbance, either through volcanic events or through clastic input from £ooding events, may have in£uenced the habitats of these ferns. However, their occurrence in the backswamp argues against an exclusive association with open or disturbed settings. Furthermore, this fern association is quite di¡erent from the Late Cretaceous examples. A detailed study of the Eocene fern £ora of Yellowstone in its sedimentological context would be a very valuable addition to the understanding of Cainozoic fern ecology. 3.2. K/T boundary, ferns and ¢res A fern spore spike originally sparked the argument that the K/T transition was associated with ecological disturbance (Tschudy et al., 1984). My own work on the Cretaceous/Tertiary boundary at Teapot Dome, Wyoming, shows that an abundance of fern spores occurred below, at and above the K/T boundary along with an abundance of fusain. Some of the fusain seems to be from fern rachides (Collinson, pers. obs.). For further discussion see Collinson (1996a). A recent temporary exposure, at Scalers Hill, near Cobham, Kent, S. England, of latest Palaeocene/early Eocene strata, has revealed a rarely seen lignitic sequence (Cobham lignite). Here I have recovered a very high proportion of fern spores associated with huge abundance of charcoal (macroscopic and microscopic), some of which again seems to be derived from fern rachides. The spores are of the Cicatricosisporites R. Potonie and Gelletich type. The spores conform to the type recognised as present in Cainozoic Ru¡ordia plants (R. subcretacea (Saporta) Barthel) and the modern genus Anemia according to Dettmann and Cli¡ord (1991, 1992) because

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they show anastomoses of adjacent mural sets in the radial region both on the distal faces and in the equatorial region. In contrast, Mesozoic Ruffordia spores show mural sets separated by a groove in the equatorial region. Collinson (2001a) discusses the close similarity between Cainozoic Ru¡ordia and Anemia noting that R. subcretacea falls into a clade including Anemia and Mohria according to Skog (1992). The fern charcoal is not evidently related to the dominant spore type and no charred fern foliage or reproductive structures have yet been recovered. The Cicatricosisporites-producing ferns clearly cannot have been exclusively associated with ¢re-prone environments because the spore type is widespread and certainly not typically associated with fusain. Riegel and his students have also recently documented a high abundance of fern spores in association with charcoal in palynological preparations from the Lower Eocene lignites and clastic interbeds of Helmstedt, Germany, deposited in a coastal plain. The lignite seams are heterogeneous and the co-occurrence of fern spore spikes and charcoal are interpeted as indicating a highly disturbed mire environment (Riegel, 2000; HammerSchiemann, 1998; Riegel et al., 1999). Here the fern spores are of the Laevigatosporites haardtii type (associated with abundant Stereisporites spores, botanical a⁄nity suggested with Sphagnum). The botanical a⁄nity of L. haardtii is usually stated as Polypodiaceae sensu lato. Spores of this type are found in situ in the fern Cyclosorus stiriacus (Unger) Ching and Takhtajan (Thelypteridaceae) in the Eocene lignite-bearing sequences of the Geiseltal and other sites (Barthel 1976, plate LXXIX, ¢gures 4^6, under the generic name Abacopteris). Cyclosorus-like ferns of the Thelypteridaceae were quite widespread in the Cainozoic (Collinson, 2001a) and may have been the source of this very abundant dispersed spore type. The clearest example of Cainozoic ferns associated with ¢re is an occurrence of up to three species of Gleicheniaceae macrofossils in the Miocene of the Latrobe Valley, Victoria, Australia (Hill and Jordan, 1998; Blackburn and Sluiter, 1994). The fossils occur in coals of the Yallourn and Morwell coal seams. The details of this material are in an unpublished report (Blackburn, 1985).

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Much of the material is charcoali¢ed, especially foliage. One horizon, a dark coal near the base of the Yallourn Seam, is dominated by Gleichenia rhizomes, rachises and pinnules with laminations of monocotyledonous stems and leaves in the surrounding coal. The association was traced for more than 1 km without signi¢cant changes (Blackburn, 1985). One species is represented by rhizomes, rachises, pinnae with pouch like pinnules with narrow elliptical openings, and spores, and the fronds show characteristic pseudodichtotomous branching with buds in the axils. This species was considered very similar to modern Gleichenia dicarpa which occurs today in permanently wet sclerophyll forests where its distribution is strongly in£uenced by ¢res (Blackburn, 1985; Blackburn and Sluiter, 1994). The Gleichenia associations were interpreted as open shrubby Gleichenia-Restionaceae moor with fern thickets existing under a ¢re-prone setting (Blackburn and Sluiter, 1994; Blackburn, 1985). Where ¢res were less frequent the Gleichenia also colonised the margins of open water as well as drier areas. In the case of very infrequent ¢res the Gleichenia persisted at open water margins but was replaced on the drier sites by angiosperms and conifers (Blackburn and Sluiter, 1994, ¢gure 14.21). In my opinion all these examples are indicative of the association of ferns with disturbance by ¢re in the Cainozoic. The ferns concerned (with the probable exception of the Australian Miocene Gleicheniaceae) were not exclusively associated with ¢re-prone environments but were able to tolerate, or take advantage of, the disturbance caused by ¢res through colonisation of ¢re-prone settings.

4. Cainozoic fate of ecologically important Mesozoic ferns This topic was discussed in detail by Collinson (2001a) who concluded that the Matoniaceae, Marattiaceae and Dipteridaceae had probably reached their modern restricted distribution by the early Tertiary. However, nothing is known about their Tertiary ecology. Dispersed spores are only su⁄ciently distinct to act as possible trac-

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ers in the Matoniaceae but Cainozoic Matonisporites species all lack the apical and interradial thickenings which would be diagnostic indications for Matonia. Phlebopteris-like spores also occur in other ferns, e.g. Dicksoniaceae, and so cannot be used to trace Cainozoic Matoniaceae. Only one example from the middle Eocene of Java (Lelono, 2000) may represent Matonia-like Matoniaceae but it has rugose ornament. Cainozoic Dicksoniaceae, Cyatheaceae and Gleicheniaceae are poorly represented (Collinson, 2001a). They are discussed in 3.2. K/T boundary, ferns and ¢res and 5.3. Tree ferns. Cainozoic Osmundaceae are discussed in 2.2.3. Ferns of swamp or marsh environments and 5.3. Tree ferns.

5. Fern habits 5.1. Epiphytic ferns There is little evidence for Cainozoic epiphytic ferns (see reviews by Collinson, 1996a, 2001a, for the Cainozoic fossil fern record). Some fossil spores are sometimes suggested to represent epiphytic ferns on the basis of their resemblance to spores of modern epiphytes. However, these spores would need to be shown to be diagnostic, i.e. to carry unique synapomophies, for a taxon (clade) which is exclusively epiphytic at the present day. A possible example is the Neogene spores from Borneo named Scolocyamus magnus Playford which are large, monolete and have conspicuous elongate exinous spines, some of which bifurcate or branch irregularly at their tips. This morphology is considered to be unique to the modern species Stenochlaena areolaris (Harrington) Copel which is an epiphyte on Pandanus in the Phillipines and New Guinea (Playford, 1982). Although spores may act as tracers for epiphytecontaining clades their presence does not prove that the ancient members of the clades were epiphytic. Poole and Page (2000) described a single stipe/ rachis fragment (rachis type E) from the Eocene London Clay Formation, England, for which they proposed an a⁄nity with the family Polypodiaceae. On this basis of family a⁄nity they pro-

posed a probable epiphytic habit for the parent fern. Collinson (2001a) considered that the rachis characters were probably inadequate evidence for the family recognition. Modern Polypodiaceae include both terrestrial and epiphytic ferns and the presence of a fossil rachis does not prove that the parent fern was an epiphyte. Obviously the ideal situation would be to discover fossils in place on trunks as for the Permian Psaronius ecosystem (Ro«ssler, 2000) and it seems remarkable that such data are so few in the fossil record. The same is the case for £owering plants where there are hardly any records of epiphytes (Collinson et al., 1993a; Collinson, 2000a, 2001b). This is possibly due to the relatively recent evolution of this trait or to bias in the fossil record. Fern epiphytes are recorded on Permian Psaronius tree^fern trunks (Ro«ssler, 2000) but the epiphytic habit in more advanced ferns may have evolved relatively recently. 5.2. Climbing ferns Lygodium macrofossils with dimorphic fronds are very common and widespread in the Paleogene and Miocene (Collinson, 2001a). Currently fossils are referred to several species though di¡erences are minor, e.g. presence (Lygodium dinmorphyllum Churchill including L. skottsbergii Halle) of a petiolule in southern hemisphere material and absence in the northern hemisphere L. kaulfussii Heer. These fossils carry a variety of synapomorphies for the genus, especially sporangial and soral characteristics (Rozefelds et al., 1992; Manchester and Zavada, 1987). This fossil material has strong dimorphism between sterile and fertile pinnae and thus compares very closely with modern L. palmatum. All modern Lygodium have indeterminate growth of the rachis which is twining (Kramer in Kramer and Green, 1990). It is therefore arguable that the fossils were climbing ferns based on the nearest living relatives and the near identity of the fossils with modern species. However, I have not been able to ¢nd any record of pinnules attached to the rachis in fossils. In some modern Lygodium pinnae are deciduous so the absence of fossil pinnae attached to rachis is not unexpected and is somewhat comparable to the

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paucity of the fossil record of deciduous angiosperm leaves attached to branches. Nevertheless, in the absence of the rachis evidence, it is possible that Paleogene to Miocene Lygodium with dimorphic fronds had not developed the indeterminate twining rachis. This possibility receives some support from phylogenies based on molecular studies (Wikstro«m et al., 2002-this issue). I know of no other examples of possible climbing fern macrofossils in the Cainozoic. Caveats discussed under epiphytic ferns also apply to attempts to recognise climbing ferns from the dispersed spore record. Dispersed spores of Polypodiidites usmensis (van der Hammen) Hekkel are similar to those of Stenochlaena palustris (Burm.f.) Bedd. (Blechnaceae), a climbing fern of peat swamps of tropical Asia, Australia and Polynesia (Playford, 1982). In swamp settings in those geographic areas P. usmensis might represent S. palustris but similar spores are found in other Polypodiaceae, e.g. Microsorum (Anderson and Muller, 1975) so it is inappropriate to use this form taxon as indicative of a climbing fern. In contrast, fossil spores of Stenochlaenidites papuanus (Cookson) Khan are judged to be very distinctive by palynologists working in South East Asia and to represent fossils (latest Oligocene onwards) related to the modern species Stenochlaena milnei Underw. and S. cumingii Holttum, both climbing ferns (Morley, 1998, 2000; and see discussion in Collinson, 2001a). Whilst these spores may act as tracers for the palaeobiogeography of the clade (Morley, 1998, 2000; Collinson, 2001a) their presence does not prove the existence of a climbing habit for the ancient parent fern. 5.3. Tree ferns The existence of tree ferns in the Cainozoic is certainly proven from trunk fossils assigned to the Dicksoniaceae/Cyatheaceae complex and to Osmundaceae (Collinson, 1996a, 2001a). However, there are very few fossils compared to the Mesozoic examples and no extensive assemblages of Cainozoic tree ferns. The most well-represented and well-understood tree ferns of the Cainozoic are those determined as Aurealcaulis Tidwell and Parker emend Tidwell

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and Medlyn for which there are three known species in the Palaeogene (Palaeocene and ?Lower Eocene) of Wyoming and New Mexico, USA (Tidwell and Parker, 1987; Tidwell and Medlyn, 1991; Tidwell and Ash, 1994). This genus is assigned to the Osmundaceae although it possesses unique anatomical characters which are not represented in the modern family or in other fossil Osmundaceae. The Wyoming specimens have trunks ranging from about 5 cm up to 61 cm across (stems 16^27 mm diameter), with the longest fossil specimen being 1.8 m long and 30 cm wide. This specimen does not taper at either end and the narrow width compared to the widest specimen suggests that the trees could have been several metres tall in life. One specimen of the Wyoming species was rooted in situ in a lignite bed. Other specimens were in situ in siliciclastic horizons of the same £uvial sequence. The growth site was interpreted as a forest that grew under swampy conditions on a £at £ood plain at low elevation (up to 1300 m) in a subtropical to warm temperate climate (Tidwell and Parker, 1987). Glyptostrobus and the fern Allantodiopsis erosa (a⁄nity uncertain ^ see discussion in Collinson, 2001a) were associated with the Aurealcaulis. Other Cainozoic Osmundaceae are also represented by stem fossils which can be assigned to all three modern subgenera of Osmunda (see review in Collinson, 2001a). These stems are all of small stature with stem diameter maximum 15 mm (Miller, 1971), and small known axis diameters for example maximum 63 mm (for Osmunda dowkeri (Caruthers) Chandler) (Miller, 1971; Chandler, 1965). Many are represented by just a few specimens and their palaeoecology has rarely been fully evaluated. See 2.2.3.1. Onoclea, Osmunda and associated ferns for further discussion of Osmunda. Other Cainozoic permineralised axes have been assigned to the Cyatheaceae or Dicksoniaceae (see review in Collinson, 2001a). Fossil tree ferns of these families (including four Cainozoic examples) are listed in Tidwell and Nishida (1993) and are included in a cladistic analysis by Lantz et al. (1999). According to Lantz et al. (1999) the fossils Cibotium oregonense Barrington (Upper Eocene, Oregon, USA) and Cyathodendron texanum Ar-

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Table 1 Summary of key conclusions concerning the ecology of Cenozoic ferns

See text for further details and for other ferns not shown here, especially in the wetland and swamp category. Details of illustrations: Free-£oating water ferns: Azolla prisca Reid and Chandler emend Fowler, whole plant and enlarged fertile fragment, modi¢ed from Reid and Chandler (1926), leaves about 1 mm long; Salvinia reussii Ettingshausen, reconstruction from Collinson (1991), surface-£oating leaves up to 2.5 cm long. Wetland and swamp ferns: Osmunda lignitum (Giebel) Stur, pinna (left), reconstruction modi¢ed from Barthel (1976), pinna length 10^20 cm; Acrostichum (top) acrostichoid sporangial cluster with distinctive sterile paraphyses (drawn from illustrations in Collinson, 1978) and fragment of sterile frond with characteristic venation (modi¢ed from Frankenha«user and Wilde, 1993); Onoclea sensibilis L. plants, with sterile and fertile fronds, rooted in situ, and detail of frond venation (modi¢ed from Rothwell and Stockey, 1991), fronds 32^45 cm long; Ru¡ordia subcretacea (Saporta) Barthel, large fossil frond (modi¢ed from Gardner and Ettingshausen, 1879^1882), maximum frond length 80 cm.

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Table 1 (Continued).

Ferns in ¢re-prone settings: Sketch of charcoali¢ed Gleichenia foliage based on unpublished photographs in Blackburn (1985), pinnules 0.5^0.75 mm long and broad. Possible epiphytic ferns: Scolocyamus magnus spore, (drawn from illustrations in Anderson and Muller, 1975; Playford, 1982), spore 60 Wm long; London Clay Rachis type E in transverse section (drawn from illustration in Poole and Page, 2000), rachis 3 mm wide. Possible climbing ferns: Lygodium dinmorphophyllum Churchill, sterile and fertile pinnules (left) (modi¢ed from Rozefelds et al., 1992); L. kaulfussi Heer, sterile pinnule (right) (modi¢ed from Frankenha«user and Wilde, 1993), sterile pinnule lobes 5^10 mm wide, sorophores 4^14 mm long. Tree ferns: Reconstruction and transverse stem section of Aurealcaulis (left) modi¢ed from Tidwell and Parker (1987); Trunk fragment (max 25 cm long) of Protopteris laubei (Engelhardt) Stenzel, sketch based on illustrations in Knobloch et al. (1996); Petiole base anatomy of Cibotium oregonense Barrington from Tidwell and Nishida (1993).

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nold (Upper Eocene, Texas, USA) both belong in a paraphyletic dicksoniaceous grade whilst Alsophilocaulis calveoli Menendez (Tertiary, Argentina) and Dendropteridium cyatheoides Bancroft (Late Tertiary, Kenya) belong in a cyatheaceous clade. Ferns assigned to the genus Protopteris were not included in the analysis because too few characteristics could be scored. Tidwell and Nishida (1993) and Lantz et al. (1999) list only Cretaceous Protopteris but P. laubei (Engelhardt) Stenzel comes from the Late Eocene of the Stare¤ Sedlo Formation in Bohemia (Knobloch et al., 1996). All of these Cainozoic examples are based on single or few, transported, fragmentary specimens. The sizes of the specimens suggest that these were indeed tree ferns, for example P. laubei has a maximum axis diameter of 8.5 cm (devoid of root mantle) and length 20 cm whilst Dendropteridium specimen length is 30 cm. However, none of the occurrences enable detailed palaeoecological inferences or more speci¢c extrapolations of stature for these tree ferns. Wing and Greenwood (1993) refer to cyatheaceous tree ferns as one of the frost-sensitive elements in the Sepulcher £ora from Yellowstone National Park (see 3.1. Open settings and volcanogenic terrains for other Yellowstone ferns). This observation was based on specimens in the United States National Museum and the £ora is based on an unpublished work of Dorf (Wing, 1987, appendix 1) to which I have not had access. Cnemidaria foliage fossils (or even the dispersed spores of Kulyisporites) could be interpreted as tree ferns on the basis of nearest living relatives (Collinson, 2001a). However, in the absence of trunk fossils there is no proof that the ancient representatives of this clade were trees.

6. Conclusions Key conclusions on Cainozoic fern ecology are summarised in Table 1. Ferns were subordinate to £owering plants in Cainozoic £oras (in terms of abundance, diversity, and proximity to depositional settings). This has resulted in comparative lack of understanding of Cainozoic fern ecology in contrast to Mesozoic and Palaeozoic ferns.

Some Cainozoic water, wetland and swamp ferns are very well-understood but this record is geographically restricted with little evidence from the southern hemisphere. Cainozoic ferns clearly acted as colonisers of disturbed settings, including ¢re-prone areas, and more detailed studies are needed of appropriate fern £oras. Cainozoic tree ferns are documented but there are very few examples. Claims for Cainozoic epiphytic ferns rely on nearest living relatives, mostly extrapolated from the dispersed spore record. Work is needed to document Cainozoic epiphytism in general. Samples from fossil trees, comparable to the Permian Psaronius ecosystem, (Ro«ssler, 2000) would be ideal. Cainozoic Lygodium is very well-represented by geographically and temporally widespread specimens of dimorphic fertile and vegetative pinnae. It is frequently assumed to be a climbing fern like the modern Lygodium. Until this is substantiated by fossils of twining rachises it remains possible that early Lygodium did not exhibit the climbing habit.

Acknowledgements I would like to thank Dave Christophel, Dave Greenwood, Bob Hill, Zlatko Kvac›ek, Walther Reigel, Gar Rothwell, Ruth Stockey and Anthony Vadalla for information and literature on Cainozoic ferns. Dave Christophel loaned slides of the Australian Miocene charred Gleichenia whilst Bob Hill, Dave Greenwood and Anthony Vadalla provided copies of parts of the unpublished report by Blackburn (1985). Meinholf Helmund and Volker Wilde are thanked for the opportunity to visit the Geiseltal site. Volker Wilde, Karin Schmidt, Berndt Simoneit, Angelika Otto and Jerry Hooker assisted with the field work. Specimens collected on this trip are stored in the Senckenberg Museum, Frankfurt, Germany. National Geographic is thanked for funding for the helicopter support for work at Teapot Dome, and Jack Wolfe, Bob Spicer, Sian Davies-Vollum, Ian Vollum and Peter Lang are thanked for assistance with fieldwork. Sharon Rose and other staff of Alfred McAlpine, AMEC and Channel Tunnel Rail Link are thanked for permission to visit the

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site at Scalers Hill, Kent, and for their considerable assistance on the site. Jerry Hooker, Steve Tracey and Jackie Skipper gave freely of their time and effort to provide vital assistance with fieldwork at Scalers Hill. References Anderson, J.A.R., Muller, J., 1975. Palynological study of a Holocene peat and a Miocene coal deposit from NW Borneo. Rev. Palaeobot. Palynol. 19, 291^351. Arnold, C.A., Daugherty, L.H., 1963. The fern genus Acrostichum in the Eocene Clarno Formation of Oregon. Contrib. Mus. Paleontol. Univ. Mich. 18, 205^227. Arnold, C.A., Daugherty, L.H., 1964. A fossil dennstaedtioid fern from the Eocene Clarno Formation of Oregon. Contrib. Mus. Paleontol. Univ. Mich. 19, 55^88. Ashraf, A.R., Mosbrugger, V., 1995. Palynologie und palynostratigraphie des Neogens der Niederrheinischen bucht. Teil 1 Sporen. Palaeontographica B 235, 61^173. Awasthi, N., Guleria, J.S., Prasad, M., Srivastava, R., 1996. Occurrence of Acrostichum Linn., a coastal fern in the Tertiary sediments of Kasauli, Himachal Pradesh, north-west Himalaya. Palaeobotanist 43, 83^87. Barthel, M., 1976. Farne und Cycadeen. Abh. Zentr. Geol. Inst. 26, 1^507, Atlas 91 pls. Basinger, J.F., 1991. The fossil forests of the Buchanan Lake formation (early Tertiary), Axel Heiberg Island, Canadian high arctic: preliminary £oristics and paleoclimate. In: Christie, R.L., McMillan, N.J. (Eds.), The Fossil Forests of Tertiary Age in the Canadian Arctic Archipelago. Geological Survey Bulletin of Canada 403, pp. 39^66. Batten, D.J., Collinson, M.E., 2001. Revision of Palaeocene species of Minerisporites, Azolla and associated plant microfossils from the Netherlands, Belgium and the United States. Rev. Palaeobot. Palynol. 115, 1^32. Blackburn, D.T., 1985. Palaeobotany of the Yallourn and Morwell Coal Seams. Palaeobotanical Project ^ Report 3. State Electricity Commission of Victoria, Melbourne. Blackburn, D.T., Sluiter, I.R.K., 1994. The Oligo-Miocene £oras of southeastern Australia. In: Hill, R.S. (Ed.), History of the Australian Vegetation Cretaceous to Recent. Cambridge University Press, Cambridge, pp. 328^367. Boulter, M.C., Kvac›ek, Z., 1989. The Palaeocene £ora of the Isle of Mull. Spec. Pap. Palaeontol. 42, 1^149. Boulter, M.C., Hubbard, R.N.L.B., Kvac›ek, Z., 1993. A comparison of intuitive and objective interpretations of Miocene plant assemblages from north Bohemia. Palaeogeogr. Palaeoclim. Palaeoecol. 101, 81^96. Bufiz›ek, C., Konza¤lova¤, M., Kvac›ek, Z., 1971. The genus Salvinia from the Tertiary of the North-Bohemian Basin. Sb. Geol. Ve›d. Paleontol. (Cz.) 13, pp. 179^222, +8 plates. Bufiz›ek, C., Konza¤lova¤, M., Kvac›ek, Z., 1988. Azolla remains from the lower Miocene of the North-Bohemian Basin, Czechoslovakia. Tert. Res. 9, 117^132.

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