New Zealand Eocene, Oligocene and Miocene macrofossil and pollen records and modern plant distributions in the Southern Hemisphere.
New Zealand has a record of floral and vegetation changes through the Cenozoic that is perhaps the most continuous in the Southern Hemisphere. Well-preserved plant macrofossils including fertile fern fronds, leaves with cuticles, flowers (sometimes with in situ pollen), and wood, as well as dispersed spores, pollen, and epiphyllous fungal microfossils provide an excellent record of changing vegetation, environments and climate on an isolatcd oceanic archipelago.
Paleobotanical investigations have become increasingly important in current debates about the age and origin of the New Zealand flora and its importance in understanding the history of modern Southern Hemisphere plant distributions. A relatively young (post-Oligocene) and therefore solely immigrant biota has been proposed (e.g. Pole, 1994). This idea was based on the suggestion that New Zealand may have been totally submerged during the late Oligocene (e.g. Waters & Craw, 2006; Landis et al., 2008) and has gained some support from molecular phylogenetic studies indicating relatively recent divergence dates for a range of plant lineages with sister groups in Australasia and the Pacific (e.g. Wright et al., 2000, 2001; Wagstaff et al., 2002; Wagstaff, 2004; Knapp et al., 2007). However, there have been few systematic studies of paleofloras that span the relevant time period to support or refute these views. In this review we focus on three recently discovered sites in southern New Zealand with exceptional fossil deposits of late Eocene, Oligocene, and early Miocene age (Fig. 1). The aim is to describe their floras and affinities to the modern flora of New Zealand and coeval floras on other Southern Hemisphere landmasses.
The three sites are the Pikopiko Fossil Forest (Fig. 2), the Newvale Mine leaf beds (Fig. 3), and a diatomite deposit at Foulden Maar (Fig. 4). All contain organically preserved plant (and some animal) macrofossils which can be reliably identified. At each site the deposits can be dated with some precision, the paleoenvironment determined, and the flora and fauna placed in an ecological context. These deposits span a key time interval from late Eocene to early Miocene. Between late Eocene and late Oligocene time, the New Zealand land area was reduced to a minimum for the Cenozoic, perhaps to a series of islands occupying an area between 20,000 [km.sup.2] (about the size of New Caledonia) and 50,000 [km.sup.2] (about the size of Tasmania) (Lee et al., 2001). By the early Miocene, initiation of the major Pacific-Australian plate boundary had resulted in an increase in land area up to approximately that of the present. From the Eocene through to the early Miocene the New Zealand region was low-lying, with the altitudinal range gradually increasing to about 1,000 m by the early Pliocene and 3,000 m by the early Pleistocene (Lee et al., 2001).
Critical to understanding the dynamics of the biota during the marine transgression is the fossil record for terrestrial systems before and after the land area minimum event. Evidence for continuity or turnover of taxa and communities is needed to assess better the likelihood of a localized mass extinction event in Oligocene New Zealand due either to loss of land and/or any contemporaneous climatic changes. Similarly, although such an event is not easily disproved, the adoption of a 'total evidence' approach using both micro- and macrofossils allows for a much clearer understanding of local and regional floras, as well as for explaining patterns in terms of ecology, edaphic conditions, taphonomy and paleoclimatology and their relevance to wider changes in the Southern Hemisphere at this time.
Materials and Methods
The fossil material studied here comes from three different geological units (Figs. 2, 3 and 4), and collecting and preparation methods differ for each site. Blocks of Pikopiko mudstone were split to expose the leaves. Cuticles were prepared by soaking pieces in warm 30 % hydrogen peroxide or 50 % nitric acid followed by treatment with potassium hydroxide. After the two cuticle layers separated, they were rinsed, cleaned with a fine paintbrush and stained in 0.1% crystal violet before mounting on microscope slides in phenol-glycerine jelly. If the cuticles fragmented, cell sieves were used to process the fragments. For some leaves, pieces of cuticle were placed on stubs for electron microscopy.
Large blocks of Newvale lignite were broken using a hammer and observed for leaves. Small pieces of the leaves were removed and prepared for light microscopy or SEM using 30 % hydrogen peroxide. In some cases when there were thick cuticles, the material was not stained.
The Foulden diatomite was split using a knife or cut into blocks to partially expose leaves or flowers. A paintbrush and water was used to expose the leaf further. Cuticles were prepared by soaking a piece of the leaf in warm 6 % hydrogen peroxide with a few crystals of tetrasodium pyrophosphate. Cleaned, stained cuticles were mounted on glass slides under coverslips in phenol-glycerine jelly. Leaves were photographed with a digital SLR camera, the mounted cuticles were photographed on a Leica microscope fitted with a digital camera and some unmounted cuticles were placed onto a stub, sputter coated with gold and palladium and examined and photographed with a Cambridge $360 Stereoscan electron microscope.
Most palynological preparations were made at GNS Science, Lower Hutt. Palynomorphs were extracted using standard palynological procedures (e.g. Moore et al., 1991) and mounted in phenol-glycerine jelly on glass slides. Pollen examination and identification was done using a Zeiss Axioplan 2 imaging photomicroscope using various lenses.
Plant fossils figured in this paper are held in the Geology Museum (OU), University of Otago, Dunedin, New Zealand.
Fossil Site 1: Pikopiko Fossil Forest
Fossil forests are rare in New Zealand, and this is the only known example of an in situ forest of Eocene age. The Pikopiko Fossil Forest, near Tuatapere in western Southland (46.101[degrees]S, 167.700[degrees]E) was an evergreen lowland forest growing on fertile alluvial floodplain soils during the late Eocene (~35 Ma). The fossil forest and associated leaf beds occur in the lower part of the coal-bearing alluvial sediments of the Beaumont Formation. More than 200 fossil trees spaced 2-5 m apart and distributed over a 30x 120 m area are represented by calcite-cemented concretions up to 60 cm diameter and 80 cm high that extend down into coal and leaf-bearing mudstone. Fine-medium arkosic sand surrounding the concretions represents the fill of a south-flowing river channel that eventually smothered the growing forest, uprooting and toppling smaller trees that grew in the area (Fig. 2). The alluvial succession, part of a 100+ m thick lacustrine delta-plain assemblage, is overlain by >200 m of predominantly muddy lacustrine sediment of the Orauea Formation (Lindqvist & Beggs, 1999).
The age of the Beaumont Formation at Pikopiko is considered to be late Eocene on the basis of stratigraphic position, the relative abundance of Nothofagidites matauraensis pollen, and the lack of index species of Oligocene age.
Fossil Site 2: Newvale Lignite Mine, Newvale Leaf Bed
The Newvale leaf bed is a thin (c. 50 cm thick) horizon of densely packed leaves that occurs near the top of the 17 m thick W6 lignite seam within the Gore Lignite Measures at the open cut Newvale Mine, Waimumu, Southland (46.143[degrees]S, 168.752[degrees]E) (Fig. 3). In eastern Southland lignite-bearing sediments extend over 2,700 [km.sup.2] (Isaac & Lindqvist, 1990), in some areas subdivided into discrete coalfields. In the Waimumu Coalfield, the Gore Lignite Measures consist of 10 major seams or seam groups separated by sandstone and mudstone that are overlain by 60 m or more of quartzose sandy conglomerate (Isaac & Lindqvist, 1990: Fig. 63). The coal typically contains large quantities of wood, some in situ stumps, and an abundance of large and small blocks and blebs of resin.
The Gore Lignite Measures accumulated on a low-lying coastal plain, at a similar latitude to that of present day southern New Zealand (~46[degrees]S). There is no evidence for high relief, although there may have been low ridges up to 100-200 m in the hinterland. According to Isaac and Lindqvist (1990: p. 165), the Gore Lignite Measures were mainly deposited "in a range of fluvial channel, overbank splay, floodplain and swamp environments, as indicated by the presence of in situ terrestrial plant remains, lateral persistence of the multiple coal seams, common root-penetrated seat earths, large scale upward-fining clastic sequences typical of fluvial cyclothems, and the paucity of marine fauna. The depositional setting was a prograding deltaic plain, which advanced across a shallow marine shelf during Late Oligocene-Early Miocene time." The extensive, multiple coal seams such as those exposed in the Newvale mine are typical of the middle Gore Lignite Measures and probably formed as "blanket peats, in lower to middle delta plain inter-channel areas" (Isaac & Lindqvist, 1990: p. 165).
The age of the middle Gore Lignite Measures ranges from late Oligocene to early Miocene based on studies ofpalynofloras of Oligocene and Miocene strata of Otago and Southland (Pocknall & Mildenhall, 1984; Mildenhall & Pocknall, 1989). Palynofloras from Seam W6 in the Newvale Mine, which includes the leaf beds described here, were placed in the Proteacidites isopogiformis Zone (Pocknall in Isaac & Lindqvist, 1990), which is now considered to be late Oligocene to early Miocene in age.
Fossil Site 3: Foulden Maar
Foulden Maar, a partly eroded early Miocene maar crater near Middlemarch, Otago (45.527[degrees]S, 170.222[degrees]E) (Fig. 4) is infilled with a thinly laminated diatomite deposit that preserves a remarkable range of fossil plants and animals. Plant fossils include diatoms, algae, pollen-beating flowers, bark, stems, fruit, fungi, and numerous leaves with very well-preserved cuticle. The fauna includes siliceous sponge remains, fish and numerous, as yet undescribed insects (Kaulfuss et al., 2010a, b). The diatomite contains a rich assemblage of mostly evergreen rainforest plants that grew on relatively nutrient-rich basalt-derived soils around the lake margins. Most of the plant remains probably blew or fell directly into the lake from overhanging trees (Lee et al., 2010b).
The maar volcano that created the lake erupted through hard schist basement rock that was overlain by thin Paleogene sandstone. Associated basalts are dated at 23.2 [+ or -] 0.2 Ma by [sup.40]mr/[sup.39]Ar and palynostratigraphy supports an early Miocene age for the lake sediments (Lindqvist & Lee, 2009). Two cores drilled in June 2009 revealed about 130 m of laminated diatomite representing at least 120,000 years of deposition over the life of the lake which was a closed system with little terrigenous siliclastic sediment input.
Fossil Site 1: Pikopiko Fossil Forest
Forest litter preserved in the mudstone contains numerous angiosperm leaves, fragmentary fern fronds, wood and probable araucarian bark (Fig. 5). The leaves include dicots with close affinities to familes such as Myrtaceae (aft. Metrosideros and Syzygium), Lauraceae, Atherospermataceae (Laurelia) and monocots, including a palm (aft. Calamus) and leaves and stems of a liane (Smilax or Ripogonum). Pollen of Casuarina, several types of Proteaceae and Nothofagus (both Fuscospora and Brassospora) is present.
The Pikopiko Fossil Forest also has 20 pteridophyte miospore types and at least eight species of fern macrofossils (Cieraad, 2003), at least two of which are fertile (Fig. 6). Dispersed fern spores are common fossils in New Zealand, but their presence must be interpreted with caution as spores may be transported widely. In contrast, fern macrofossils indicate local plants, as fronds decompose in situ. The diversity and abundance of ferns at Pikopiko implies that fems were abundant in the forest understory, as in modern New Zealand rainforests.
A diverse range of epiphyllous fungi including Asterina, Entopeltacites, Callimothallus, Meliolinites, Quillonia, Trichopeltinites, various other microthyriaceous shields, fungal germlings and an assortment of spores, setae and hyphae indicates high rainfall and humidity and a climate that was at least marginally subtropical. This is further supported by the presence of pollen of Cupanieidites (Sapindaceae: tribe Cupaniae) and Malvacipollis (Austrobuxus-type=Picrodendraceae), the predominance of mesophyll-sized leaves in the leaf beds and palm leaves and fruits similar to the largely tropical rattan, Calamus. The Pikopiko Fossil Forest grew on an alluvial plain not far above sea level, and was situated at a paleolatitude of about 50[degrees]S. Analysis of the vegetation at Pikopiko suggests humid subtropical conditions in southern New Zealand during the late Eocene. This corresponds with estimated sea surface temperatures for southern New Zealand in the range of 21-22[degrees]C (Hornibrook, 1992). The Pikopiko site confirms that Southern Hemisphere terrestrial climates were humid and had temperature regimes equivalent to current subtropical zones at mid latitudes in the late Eocene.
Fossil Site 2: Newvale Lignite Mine, Newvale Leafoed
The leaf layers at the Newvale site (Fig. 7) represent litter horizons that are believed to have been laid down in pools on the surface of an ombrotrophic forest mire that formed on an extensive low-lying coastal plain with oligotrophic soils (Ferguson et al., 2010). Highly acidic water ponded in depressions would have prevented microbial decay of the foliage which represents the swamp forest community growing within a few meters of the site. Although no fern macrofossils have been seen in the Newvale leafbeds, spores include Cyatheaceae, Davalliaceae, Dicksoniaceae, Gleicheniaceae, Osmundaceae, Hymenophyllaceae, Polypodiaceae and Psilotaceae. Gymnosperm taxa represented by both leaves and pollen comprise at least eight conifers including Dacrycarpus, Dacrydium, Halocarpus, Microcachrys, Podocarpus and Phyllocladus (Jordan et al., 2011). Numerous detached leaves of Agathis are present, and amber colored resin found throughout the Gore Lignite Measures is likely to be derived from Agathis, which has a long history in the New Zealand region (Lee et al., 2007).
The angiosperm macrofossils (Fig. 7) are suggestive of a sclerophyll-dominated evergreen woodland and include Nothofagus (Brassospora-type), Gymnostoma, epacrid Ericaceae and species of Cunoniaceae and Sapindaceae (Ferguson et al., 2010; Jordan et al., 2010). The Newvale locality provides the first New Zealand macrofossil record of leaves belonging to an extinct species of Dianella/Phormium (Maciunas et al., 2009). One of the surprising finds in the Newvale leafbed was a diverse range of Proteaceae leaves, as the modern New Zealand flora includes just two species in two genera: Knightia and Toronia. These fossil records include the first extra-Australian record of Banksia (Tribe Banksieae) (Carpenter et al., 2010b), and two new species with affinities to Tribe Persoonieae (Carpenter et al., 2010a). Several other taxa are also present, including possible Beauprea, a genus that is now confined to New Caledonia.
In addition to the leaf fossils, the extensive pollen list from Newvale includes Aquifoliaceae (Ilex), Gyrostemonaceae, Meliaceae (Dysoxylum), Monimiaceae, Myrtaceae, Rubiaceae (Coprosma) and Restionaceae.
In contrast to the fossil forests that surrounded Pikopiko and Foulden Maar, there are no Lauraceae leaves at Newvale, possibly a function of the locally oligotrophic soils. The climate signal from Newvale indicates warm temperate to marginally subtropical conditions with plenty of rain.
Fossil Site 3: Foulden Maar
Cuticle preparations from more than 630 leaves indicate that most are from trees and lianes with moderately thick cuticles that generally have both upper and lower surfaces preserved. Most leaves are of eudicots, but there are a few ferns, two conifers, and at least five monocots, including the first records globally of organically-preserved fossil orchid leaves (Conran et al., 2009a).
One specimen of fern bearing sporangia with distinctive in situ spores has been identified as a new species of the epiphytic fern, Davallia (Conran et al., 2010b) (Fig. 6). Unlike most ferns, the fronds of Davallia fall from the plant soon after senescence, and are likely to have dropped into the lake from overhanging branches. This fertile frond has also made it possible to classify a spore type of previously uncertain affinity. Narrow strap-like branching fronds may represent a second type of fern, Schizaea, but in the absence of fertile material this cannot be confirmed. Spores indicate that other ferns that lived in the vicinity of Foulden Maar included tree ferns (Dicksoniaceae; Cyatheaceae), together with Gleicheniaceae, Psilotaceae and Schizaeaceae.
At least two different podocarps are represented by leaf macrofossils. Isolated leaves of the broad-leaved Podocarpus travisiae (Pole, 1993a) are relatively common (Fig. 6); these leaves are much larger than those of any extant Podoearpus species in New Zealand. Recently, foliage of a second podocarp with well-preserved cuticle has also been collected (Fig. 6). This is a new species of Prumnopitys, a tall forest tree genus that has two representatives in the modern New Zealand flora.
The majority of the plant macrofossils are isolated, more-or-less complete, compressed mummified leaves. About 45 % of the leaves are from the family Lauraceae, including several very common species with affinities to Cryptocarpa and Litsea (Conran et al., 2010a; Bannister et al., 2012). The remainder come from a diverse range of families (Fig. 8), including Araliaceae, Cunoniaceae, Elaeocarpaceae, Euphorbiaceae, Menispermaceae, Myrsinaceae, Myrtaceae, Proteaceae and Sterculiaceae. The site has also yielded over 80 insect fossils to date (Kaulfuss et al., 2010b) and many of the leaves show evidence of insect damage by chewing or leaf mining and some bear in situ scale insects (Harris et al., 2007). There are also several leaf taxa with prominent domatia (indicating possible associations with beneficial leaf mites) as well as some plants with conspicuous extra-floral nectaries (Fig. 9).
Although monocot leaf fossils are rare globally, the Foulden site includes several types, including Astelia, Cordyline, orchids, Ripogonum and Typha (Conran et al., 2009b). Cuticular analysis shows that the Astelia is related to A. alpina and A. linearis, but differs from modern species (Maciunas et al., 2011). Similarly, preliminary investigations of the Cordyline, Luzuriaga and Ripogonum leaves suggest that they may also represent several new species. The orchid leaves are the first unequivocal vegetative orchid fossils (Conran et al., 2009a) and are derived from two separate genera of epiphytic orchids within subfamily Epidendroideae, Dendrobium and Earina.
Another feature of this site is the presence of very well-preserved fossil flowers, several of which have anthers with in situ pollen; such fossils are very rare globally (Balme, 1995). The first flower to be described, Fouldenia staminosa is considered to probably belong to Rutaceae (Bannister et al., 2005). An inflorescence with the in situ pollen type Nyssapollenites endobalteus was assigned to Euphorbiaceae, subfamily Acalyphoideae. Distinctive leaves from the same site were referred to the MallotusMacaranga clade (Euphorhiaceae: Acalyphoideae) as Mallorangafouldenensis, with associated fruits described as Euphorbiotheca mallotoides. These are all likely to be sourced from the same small trees or shrubs growing close to the lake edge (Lee et al., 2010a). There are also other flowers from the site with affinities to Euphorbiaceae, Loranthaceae (aft. Alepis), Onagraceae (Fuchsia), Picrodendraceae, Monimiaceae (Hedycarya), Lauraceae and additional Rutaceae.
A number of pollen types occur in clumps of 20 or more grains and are likely to have come from anthers or parts of cones, indicating that the source plants grew close to the deposition site. These include taxa that are not as yet represented by macrofossils such as Microalatidites paleogenicus (Phyllocladus), Haloragacidites harrisii (Casuarinaceae), and Nothofagidites cranwelliae (Nothofagus subgen. Brassospora), Proteacidites minimus (Knightia-type), as well as several which are also present as macrofossils: Podocarpidites sp. (Podocarpus or Prumnopitys), Nyssapollenites endobalteus (Mallotus/Macaranga) (Lee et al., 2010a), Diporites aspis (Fuchsia), Rhoipites alveolatus (Euphorbiaceae), Hedycarya and Gothanipollis perplexus (Loranthaceae). It is unlikely that anthers containing pollen could have been blown more than a few tens of meters from the host plant and in several cases, the anthers and pollen are still inside their flower.
Saprophytic fungi as spores and perithecia within cuticular envelopes and epiphyllous fungi are also present. However, epiphyllous fungi are much less common than at Pikopiko, suggesting the climate was less humid. The high tree diversity and dominance by Lauraceae around the lake is supportive of a warm temperate to subtropical notophyll vine forest (Webb et al., 1984) similar to those of southeastern Queensland and northern New South Wales. These forests are generally also found on richer, basaltic soils in high rainfall areas (Specht & Specht, 1999).
Records of Plant Groups
Representatives of tree fern families such as Cyatheaceae and Dicksoniaceae, and forest taxa including Gleicheniaceae, Hymenophyllaceae and Osmundaceae have been important components of the forest understory in New Zealand since at least the late Eocene and possibly since the late Cretaceous (Mildenhall, 1980; Cieraad & Lee, 2006). This is demonstrated by the diversity of ferns preserved as forest litter at the Pikopiko site with more than 8 different fern macrofossils (Cieraad, 2003) and more than 20 spore types. Other families, including the epiphyte Davallia (Davalliaceae) are recorded from at least the late Oligocene to the present (Conran et al., 2010b). The modern New Zealand fern flora includes some 200 species in -60 genera, but, in contrast to dicot angiosperms, few ferns appear to have become extinct in New Zealand, perhaps because of its constantly mesic climate through the Cenozoic. However, this conflicts to some extent with studies by Brownsey (2001) and Perrie and Brownsey (2007), who concluded that the ancestors for most of the extant New Zealand ferns apparently arrived within the last ~30 million years. Further planned work on well-dated fossil fern lineages--particularly integrating the taxonomy of spores preserved on fertile fronds--will further elucidate the history of ferns in New Zealand.
Until recently, most data on the history of conifers in New Zealand came from pollen evidence. However, recent studies of organically preserved macrofossils, including those from the Newvale and Foulden Maar floras, have expanded the record considerably. All but one of the 10 conifer genera living in New Zealand today were present in the late Oligocene-early Miocene (Lee et al., 2008; Lee et al., 2010b; Jordan et al., 2011). At Pikopiko, bark of probable Araucaria is preserved, and pollen indicates the presence of Podocarpaceae, Ephedra and Wollemia. Foliage and wood preserved at Newvale indicate a diverse range of podocarps including Dacrycarpus, Dacrydium, Halocarpus, Microcachrys, Phyllocladus, Podocarpus, and Agathis. The pollen record adds Ephedra to the list.
At Foulden Maar, the large-leaved and now extinct Podocarpus travisiae dropped leaves into the lake, as did a species of Prumnopitys, but the pollen record suggests that Agathis/Araucaria, Dacrydium, Dacrycarpus, Ephedra, Halocarpus, Microcachrys, Pherosphaera and Phyllocladus also grew in the region.
At least five genera that had a long history in New Zealand are now locally extinct: Araucaria, Lagarostrobos, Microcachrys, Pherosphaera, Retrophyllum, Wollemia and the enigmatic gymnosperm Ephedra. Fossil evidence from the three sites discussed in this paper suggests that the extant diversity of conifers of New Zealand results from a combination of the depletion of a much more diverse mid-Cenozoic flora and the late Cenozoic diversification of some groups (Lee et al., 2010c). These new conifer macrofossils and pollen from New Zealand thus provide key data for interpreting Southern Hemisphere conifer evolution and biogeography.
The monocot flora of the Southern Hemisphere until now has been rather poorly documented. At Pikopiko, prickly leaves and fruits of a calamoid palm indicate a much wider geographic range for this taxon in the past (Hartwich et al., 2010), and a much warmer climate for southern New Zealand in the late Eocene. At Newvale, large, strap-like leaves of a monocot (possibly Cordyline) remain to be identified, but leaves of Dianella/Phormium are present (Maciunas et ah, 2009), as well as pollen attributed to Phormium. At Foulden Maar, organically preserved leaves of a diverse range of monocots have greatly expanded our knowledge of Southern Hemisphere monocot history. These include large trees (Cordyline), a liane (Ripogonum), the forest floor herbs/epiphytes Astelia and Luzuriaga, two genera of epiphytic orchids (Dendrobium and Earina), and the perennial emergent macrophyte, Typha. The presence of leaves and pollen of Luzuriaga at the Foulden site provides another link between New Zealand and southern South America. To date, all monocot fossils apart from the palms appear to be closely related to taxa still living in New Zealand.
Eudicots and Basal Angiosperms
The most diverse plant macrofossils at the Pikopiko, Newvale and Foulden sites are eudicot and basal angiosperms, which include a wide range of taxa that are now extinct in New Zealand. In the angiosperm flora in general, about 50% of the plant families living in New Zealand between 25 and 20 million years ago are now no longer present there (Lee et al., 2001). Old World, widespread and/or tropical elements that have now vanished include the families Aquifoliaceae, Polygalaceae and Santalum (Santalaceae sensu stricto), as well as Nothofagus subgenus Brassospora. Modern, largely Australian components now absent in New Zealand included numerous rainforest and sclerophyllous Proteaceae genera, as well as Casuarinaceae and Gyrostemonaceae. There was also a significant New Caledonian element, with endemic genera such as Strasburgeria (Strasburgeriaceae: formerly endemic, but now including the previously endemic New Zealand family Ixerbaceae, APG III, 2009) and the genus Beauprea (Proteaceae).
Casuarinaceae The Casuarinaceae are no longer present in the New Zealand flora, but fossil evidence from pollen indicates that this family was widespread in New Zealand in the Cenozoic from the early Paleocene to the Pleistocene (Raine et al., 2008), with abundant Gymnostoma-like fruiting cones present in some OligoceneMiocene deposits (Campbell & Holden, 1984) and Casuarina/Alloeasuarina from the Miocene of Lake Manuherikia (Pole, 1993d). Macrofossil stems assigned to Gymnostoma show that this taxon was also a common component of the vegetation at Newvale (Ferguson et al., 2010).
The Casuarinaceae are considered to be a Gondwanan family (Steane et al., 2003), but their sister taxa in the 'higher' Hamamelididae (= Fagales sensu APG III, 2009) such as the Betulaceae and Juglandaceae are regarded as predominantly Laurasian whereas the Myricaceae are widespread, but absent from Australasia (Manos & Steele, 1997). There are four extant Casuarinaceae genera, supported by both morphology and molecular data (Sogo et al., 2001; Steane et al., 2003), with Gymnostoma appearing in the fossil record prior to the cryptosomatic genera (Guerin & Hill, 2003; Wilf et al., 2007; Pole, 1993d). Representatives of the family were apparently widespread in South America, New Zealand and Australia in the Paleocene and Eocene (Zamaloa et al., 2006; Wilf et al., 2007), and were also common in the Oligocene of Antarctica (Hill & Scriven, 1995; Grube & Mohr, 2007) and the Miocene of southern Africa (Coetzee & Praglowski, 1984). The South American palynological record ranges from the early Paleocene to Eocene of Patagonia (Argentina and Chile) and megafossils are known from the early Eocene. The family appears to have become extinct in South America soon after the early Eocene climatic optimum (Zamaloa et al., 2006), disappearing from Africa at the end of the Miocene (Coetzee & Praglowski, 1984).
Ericaceae The Ericaceae are a major component of Australasian sclerophyllous heathlands, with Late Cretaceous fossil pollen suggesting a very long presence of the family in the region. However, a molecular phylogeny for Dracophyllum (Wagstaff et al., 2010) suggests that the extant members of the group are very young, with only a recent radiation into New Zealand. Jordan et al. (2010) described two new macrofossil species of latest Oligocene-early Miocene age from the Newvale site--Cyathodophyllum novae-zelandiae (tribe Styphelieae) and Richeaphyllum waimumuensis (tribe Richeeae)--but noted that they were not closely allied to living taxa in New Zealand and argued for caution in using fossil Ericaceae pollen as evidence for ancestral lineages of extant taxa.
Lauraceae The Lauraceae have ~55 genera and ~2,250 species, with centers of diversity in Asia and Central to South America, both with >25 genera (Rohwer, 1993). There are 11 genera in Australia and six in New Caledonia, with two extending to New Zealand. Several large genera are largely pantropical (e.g. Beilschmiedia, Cryptocarya, Litsea), but some, such as Litsea and Lindera, have been shown from molecular evidence to be polyphyletic and in need of revision (Li et al., 2004, 2008). The family is known from Cretaceous fossils in a number of regions (Drinnan et al., 1990; Eklund, 2000; Doyle & Endress, 2010), including Antarctica (Francis et al., 2008) and the Paleocene of the now submerged Ninetyeast Ridge in the mid-Indian Ocean (Carpenter et al., 2010c) and south-east Australia. There is a well developed and diverse Lauraceae flora known from the Paleocene onwards in Australia (e.g. Hill, 1986; Christophel, 1989; Vadala & Greenwood, 2001; Carpenter et al., 2007). Although flowers are sometimes reported, fossil pollen is extremely rare, as little pollen is produced, it is thin-walled and fossilizes very poorly (Macphail, 1980; Herendeen et al., 1994; Eklund, 2000).
The near absence of lauraceous pollen in the Cenozoic record of the Southern Hemisphere due to poor preservation means that a significant section of the vegetation may be unaccounted for by the palynological record. Nevertheless, the family is present as leaf impressions, macrofossils and dispersed cuticle (e.g. Holden, 1982; Pole, 1993b, 1996, 2007), with Pole (2007) recognizing 25 extinct cuticle-based taxa from the Miocene of South Island. At the three sites examined in this study from southern New Zealand, Lauraceae are present at Pikopiko absent from Newvale, but diverse at Foulden, where at least 10 species in ~3 genera are present (Conran et al., 2010a; Bannister et al., 2012). This is a significant difference from the present, where there are only 3 extant species in two genera, Beilschmiedia (2) and Litsea (1); this is generally assumed to be a response to range contraction and/or local extinction in response to cooling (Carpenter et al., 2007).
Loranthaceae Pollen of Cranwellia and Gothanipollis occur at all sites. The family is ancient and Cranwellia pollen is recorded in New Zealand from the Maastrichtian to the early Pleistocene. Similarly, Gothanipollis has been present in New Zealand since the upper Eocene, where it is thought to represent genera such as the Elytranthe complex and Korthalsella (Mildenhall, 1980). The presence at Foulden Maar of a flower with in situ Gothanipollis pollen further strengthens the case for Loranthaceae long term occupancy, as the flower itself resembles the extant New Zealand endemic genus Alepis (Bannister et al., 2010), a member of the bird-pollinated Elytranthe group of genera (Vidal-Russell & Nickrent, 2008).
Myrtaceae The Myrtaceae are a prominent component of the modern New Zealand flora and appear to have had a long fossil history there. Mildenhall (1980) reported Eucalyptus pollen from the Miocene-early Pleistocene of New Zealand. Pole (1993c) found Miocene-aged Myrtaceae leaf impressions, some of which resembled Eucalyptus and Metrosideros, as well as fruits that he attributed to Eucalyptus. Pole et al. (2008) later described seven Myrtaceae leaf cuticle parataxa, an associated leaf and fruits from several early Miocene sediments, relating them to the modern genera Syzygium and Metrosideros. A postulated New Zealand origin for Metrosideros followed by repeated wind dispersal and subsequent radiation events from there to New Caledonia and the Pacific in the mid-late Cenozoic and during Pleistocene glaciations is also supported by molecular data (Wright et al., 2000, 2001). Pollen and leaves resembling Metrosideros occur at the Eocene Pikopiko site, and leaves similar to members of both genera occur at Newvale and Foulden Maar. Fruits and seeds of both genera are relatively common at Foulden Maar, and pollen with affinities to the modern Australasian genera Leptospermum and/or Kunzea is also present there.
Nothofagaceae At all three sites, pollen of Nothofagus species representing the three subgenera Brassospora, Fuscospora and Lophozonia is abundant. At Foulden Maar, although the pollen is common and there are pollen clumps suggesting proximity of the donor trees to the lake, there is to date no evidence of macrofossil remains. Nothofagidites cranwelliae and N. matauraensis (subgenus Brassospora) occur at all three sites, while leaves with distinctive cuticle that can be reliably assigned to N. brassii occur in the Newvale leafbed (Ferguson et al., 2010). This indicates that conditions at all sites were warm and wet.
Onagraceae Diporate pollen representing the genus Fuchsia is known from the Oligocene of New Zealand (Mildenhall, 1980). Pollen assigned to an extinct Fuchsia species is present at Newvale and at Foulden Maar; it occurs in anthers where Fuchsia-type flowers are also present. The modern New Zealand and Tahitian Fuchsia species represent an early-divergent lineage from the South American members of the genus (Godley & Berry, 1995; Berry et al., 2004). This presents a further example of an apparently ancient New Zealand-South American link.
Proteaceae The Proteaceae are an iconic Southern Hemisphere plant family with major centers of diversity in Australia (~45 genera, >800 species), South Africa (16 genera, ~400 species) and, to a lesser extent, New Caledonia (9 genera) and South America (8 genera). The recent discovery of macrofossils of at least seven genera at the Newvale and Foulden sites (Carpenter et al., 2010a, b) confirms and expands the existing pollen record, demonstrating that representatives of at least four of the five Proteaceae subfamilies and seven of the 11 tribes defined by Weston and Barker (2006) were present in New Zealand, indicating high local diversity at the tribal level in Paleogene to Neogene New Zealand. The family has a very extensive fossil record on the larger continental areas of Gondwana, including
Antarctica (e.g. Dettmann & Jarzen, 1990; Jordan et al., 1998; Hill & Brodribb, 2001; Gonzalez et al., 2007; Grube & Mohr, 2007), but the molecular biogeography suggests complex patterns of vicariance and dispersal, with the divergence of Australian, New Zealand and New Caledonian taxa in the Eocene consistent with a shared, ancestral flora, but contrary to a vicariance scenario (Barker et al., 2007). However, the relatively common occurrence of pollen from the now New Caledonian endemic genus Beauprea, the Stenocarpus-like leaf at Foulden and the Banksia and Persoonioideae leaves from Newvale strengthens the links between these two land masses and the possibility for interchange between Australasian floras at least into the Oligocene, as suggested by Ladiges and Cantrill (2007) and Pole (2010). Similarly, the Gevuina-like leaf at Foulden Maar provides a further link to southern South America.
Although the total amount of sediment excavated from the three sites so far occupies a volume of less than 20 m 3, the information gained from the exceptionally well-preserved leaves, flowers and fruits has added greatly to our knowledge of the floristic diversity of New Zealand in the mid Cenozoic. The vegetation at each site represents quite different paleoenvironments, although all three sites were at low elevations and probably quite close to the paleocoastline. The diverse vegetation at these sites confirms that the climate in mid-southern latitudes was much warmer than it is today (probably warm temperate to subtropical), agreeing with Hornibrook (1992) and Pole (1996, Pole et al. 2008).
In the late Eocene, the mesophyll vine forest-like vegetation (MVF) with tropical palm genera like rattans, together with the abundance of epiphyllous fungi, strongly suggests humid and warm, subtropical conditions on the fertile alluvial plains at the Pikopiko site. The less complex simple notophyll vine forest-like vegetation (SNVF) at Foulden Maar was also diverse and appears to represent a similar style of Lauraceae-dominated forest to Pikopiko, but the abundance of fern macrofossils, spores and palm macrofossils at Pikopiko shows that the two sites were different. Their floras (SNVF versus MVF) suggest that the climate at Foulden Maar was slightly cooler and more subtropical/warm temperate (Webb, 1978; Webb et al., 1984), but still capable of maintaining a highly diverse rainforest ecosystem on the basaltic soils close to the lake, albeit one with nearby Nothofagus or Podocarpaceae-dominated forests, possibly growing on less fertile soils over schists.
In contrast, the oligotrophic mire at Newvale is unusual in the apparent absence of Lauraceae and the dominance of more numerous sclerophyllous taxa, probably reflecting local edaphic conditions, especially the more acidic and poorer soils. It has long been thought that the evolution of widespread sclerophylly was initially an adaptation to low soil fertility, particularly phosphorous, with the ability to withstand aridity and fire seen almost as a secondary adaptation of the sclerophyllous habit (Loveless, 1962; Beadle, 1981; Specht & Rundel, 1990; Hill, 1998). The absence for any evidence for fire (such as charcoal) at the Newvale site further supports this.
Understanding the history of the New Zealand flora is essential for gaining an understanding of the history of the vegetation of the rest of the Southern Hemisphere. Integration of the macrofossil record with that from spores and pollen gives a much clearer picture of the vegetation at three contrasting depositional sites of mid-Cenozoic age, as well as providing accurate dating calibration points for molecular phylogenies of the families and genera present there.
Some research has suggested that groups such as various ferns (Perrie & Brownsey, 2007), Phyllocladus (Wagstaff, 2004) and Dracophyllum (Wagstaff et al., 2010) have arrived in New Zealand relatively recently--perhaps within the last 10 million years. However, improved 'earliest appearance' fossil records will affect the calibration of dated molecular phylogenies, pushing some of these dates further back in time. For example, the evolutionary history of monocots is the subject of intense international research. There is particular interest in family Orchidaceae, which, although representing the second largest family of flowering plants with c. 25,000 species, has, until recently, had virtually no fossil record. This apparent lack of fossils has reinforced the idea that they are likely to be a recently evolved group, even though DNA studies suggest that they may instead be one of the oldest families of monocots (Ramirez et al., 2007). Our discovery in the Foulden Maar sediments of organically preserved leaf macrofossils representing two genera of epiphytic orchids (Conran et al., 2009a) provides the first robust evidence for timing clade diversification of the largest subfamily of orchids (Epidendroideae; c.f. Gustafsson et al., 2010) and is consistent with an ancient (Late Cretaceous) origin for Orchidaceae as proposed by Ramirez et al. (2007).
Thus, understanding modern biogeographic distributions and relationships requires consideration of paleobiogeographic data such as that provided by these key sites in southern New Zealand. The sites described here represent strong edaphic contrasts and different levels of local environmental complexity, broadly similar in many regards to what is found in the present New Zealand landscape. However, they do confirm that the forest flora of modern New Zealand is depauperate compared to its apparent mid-Cenozoic diversity. This is particularly true when the larger modern land area and much broader range of habitats are taken into account. The palynomorph record taken in isolation gives a perspective on the regional vegetation, whereas pollen and spores when combined with associated macrofossils present a much more accurate picture of the plants growing at a particular fossil site.
The forest floras of these mid-Cenozoic New Zealand sites traverse the period of maximal marine transgression and associated edaphic factors, but provide no indication of total species turnover indicative of complete submergence at the end of the Oligocene. These sites show that there were considerable similarities in the floras present on either side of the land area minimum event, both micro- and macrofossil. In particular, the discovery of in situ pollen and spores allows for much more precise identification and mapping of the age range and paleodistribution of various pollen types, though there is still the need for caution, as even identified affinities for pollen types are not proof themselves of the long term continuity of a single taxon. Although it cannot be proven with certainty, the most parsimonious explanation for the pattern observed here is that there was land present continuously somewhere in the region for the taxa seen at these sites to inhabit throughout this period of New Zealand's history.
Nevertheless, there are still features relating to spatial and temporal heterogeneity of the vegetation in the fossil record that require further examination in order to disentangle the effects of climate, geology and ecology which may have contributed to the observed patterns and changes. New Zealand is one of very few places in the Southern Hemisphere possessing such a good and continuous record for both micro-and macrofossils, making it the ideal location to test these hypotheses about long-term change and floristic depletion and its causes.
Lagerstatten deposits with exceptionally well-preserved fossils, such as those at Pikopiko, Newvale and especially Foulden Maar provide crucial evidence for past climates, information on stratigraphic ranges of key plant and animal groups, and evidence for plant radiations and extinctions. They highlight the role that the New Zealand region has played in the development of Southern Hemisphere terrestrial paleobiodiversity. Importantly, fossils from these deposits provide well-dated calibration points and support for molecular phylogenies.
The three sites at Pikopiko, Newvale and Foulden Maar, spanning late Eocene to early Miocene, indicate that diverse, probably locally heterogeneous, mixed forest systems typical of New Zealand vegetation were present throughout most of the Cenozoic. Overall they provide no support for, or evidence of major floristic discontinuities that might be associated with total land submergence at any time during the last 30-20 million years, but the problem of relating fossils to extant taxa means that care must be taken in making generalizations. Although the forests were species-rich with angiosperms, conifers and, at Pikopiko, ferns, both macrofossil and palynomorph records always underestimate diversity. This suggests that there was no significant decrease in floristic complexity, especially as our study of these three exceptionally rich sites has involved searching though a few cubic meters of sediment or less from each locality. The true diversity must have been very much greater and this is the subject of ongoing research.
New Zealand's fossil floras allow us to place the history of the region into a wider Southern Hemisphere context both spatially and temporally. Although there is some evidence to suggest that several 'recent arrivals' may represent recent radiations, the presence of many groups in the fossil record prior to and during the land area minimum event and subsequent glaciations events still needs to be explained.
Acknowledgments We thank Mafia Zamaloa, Mafia Alejandra Gandalfo and colleagues for the invitation to speak at the VII Southern Connection conference in Bariloche, Argentina, and for inviting us to contribute a paper to this volume. We thank Mr. B. Highsted and Mr K. McLaren of Solid Energy for kindly allowing us access to Newvale Mine; and the Gibson family and Dr Darren Hughes, Featherston Resources Ltd for kindly allowing us access to the Foulden Maar fossil site. Ray Carpenter, Ellen Cieraad, David Ferguson, Aline Homes, Greg Jordan, Liz Kennedy, Bill Lee, Elizabeth Maciunas and Ian Raine provided information on various aspects of plant families, palynology and ecology. Liz Girvan is thanked for help with SEM work, Roger Tremain for preparing some palynological samples and Reinhard Zetter for the palynological SEM photographs. The Departments of Geology and Botany, University of Otago and the School of Earth and Environmental Sciences, The University of Adelaide are thanked for the provision of resources to undertake this research. Funding for this study was provided by a Marsden Grant from the Royal Society of New Zealand.
DOI 10.1007/s 12229-012-9102-7
Published online: 7 July 2012
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Daphne E. Lee (1,5), John G. Conran (2), Jon K. Lindqvist (1), Jennifer M. Bannister (3), Dallas C. Mildenhall (4)
(1) Department of Geology, University of Otago, PO Box 56, Dunedin, New Zealand
(2) Australian Centre for Evolutionary Biology and Biodiversity, School of Earth and Environmental Sciences DX 650 312, The University of Adelaide, Adelaide, SA 5005, Australia
(3) Department of Botany, University of Otago, PO Box 56, Dunedin, New Zealand
(4) GNS Science, PO Box 30368, Lower Hutt, New Zealand
(5) Author for Correspondence; e-mail: firstname.lastname@example.org
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|Author:||Lee, Daphne E.; Conran, John G.; Lindqvist, Jon K.; Bannister, Jennifer M.; Mildenhall, Dallas C.|
|Publication:||The Botanical Review|
|Date:||Sep 1, 2012|
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