Carbon isotopes support the presence of extensive land floras pre-dating the origin of vascular plants

Multiple lines of evidence indicate that Earth's land masses became green some 2.7 Ga ago, about 1 billion years after the advent of life. About 2.2 billion years later, land plants abruptly appear in the fossil record and diversify marking the onset of ecologically complex terrestrial communities that persist to the present day. Given this long history of land colonization, surprisingly few studies report direct fossil evidence of emergent vegetation prior to the continuous record of life on land that starts in the mid-Silurian (ca. 420–425 Ma ago). Here we compare stable carbon isotope signatures of fossils from seven Ordovician–Silurian (450–420 Ma old) Appalachian biotas with signatures of coeval marine organic matter and with stable carbon isotope values predicted for Ordovician and Silurian liverworts (BRYOCARB model). The comparisons support a terrestrial origin for fossils in six of the biotas analyzed, and indicate that some of the fossils represent bryophyte-grade plants. Our results demonstrate that extensive land floras pre-dated the advent of vascular plants by at least 25 Ma. The Appalachian fossils represent the oldest direct evidence of widespread colonization of continents. These findings provide a new search image for macrofossil assemblages that contain the earliest stages of land plant evolution. We anticipate they will fuel renewed efforts to search for direct fossil evidence to track the origin of land plants and eukaryotic life on continents further back in geologic time.     

Cord‐forming Palaeozoic fungi in terrestrial assemblages

The fossil record paints a thin picture of early terrestrial life. Useful diagnostic features are rare in the organic‐walled fossils of the first land colonizers, and at first glance the Silurian–Devonian Tortotubus protuberans seems no exception. Now, new material from New York, Gotland and Scotland reveals the ontogenesis and affinity of this problematic organism. Its filamentous early stages (previously referred to Ornatifilum lornensis) demonstrate simple septal perforations and a bilayered cell wall; threads of entwined filaments, bounded by an elaborately sculptured surface, arose via the retrograde growth and subsequent proliferation of secondary branches. This morphology and pattern of growth together indicate an affinity with the ‘higher’ fungi (Dikarya) and document the formation of differentiated mycelium. The presence of complex mycelial fossils in the earliest Silurian corroborates the likely contribution of fungi to the colonization of land and the establishment of modern sedimentological systems; their rise seemingly accompanied the diversification of early embryophytes and the vegetation of the terrestrial biosphere.     

The dawn of symbiosis between plants and fungi

The colonization of land by plants relied on fundamental biological innovations, among which was symbiosis with fungi to enhance nutrient uptake. Here we present evidence that several species representing the earliest groups of land plants are symbiotic with fungi of the Mucoromycotina. This finding brings up the possibility that terrestrialization was facilitated by these fungi rather than, as conventionally proposed, by members of the Glomeromycota. Since the 1970s it has been assumed, largely from the observation that vascular plant fossils of the early Devonian (400 Ma) show arbuscule-like structures, that fungi of the Glomeromycota were the earliest to form mycorrhizas, and evolutionary trees have, until now, placed Glomeromycota as the oldest known lineage of endomycorrhizal fungi. Our observation that Endogone-like fungi are widely associated with the earliest branching land plants, and give way to glomeromycotan fungi in later lineages, raises the new hypothesis that members of the Mucoromycotina rather than the Glomeromycota enabled the establishment and growth of early land colonists.     

Enigmatic occurrence of Permian plant roots in Lower Silurian rocks,Guizhou Province,China

Pinnatiramosus qianensis Geng, 1986, is a plant with a complex, extensive pinnate branching system and pitted tracheids, collected from marine Lower Silurian (Llandovery; c. 430 Ma) rocks in Guizhou Province, China. It challenges long‐held theories on the origin and early evolution of vascular plants in the Silurian and Devonian. However, there is a hypothesis that the fossils were not syngenetic with the entombing rock, but were the rooting systems of much younger plants, probably of Permian age. New sections and collections of P. qianensis have been subjected to detailed analyses, which indicate that P. qianensis belongs to an early Permian (c. 285 Ma) rooting system growing down into lower Silurian rocks.     

Structural, physiological, and stable carbon isotopic evidence that the enigmatic Paleozoic fossil Prototaxites formed from rolled liverwort mats

New structural, nutritional, and stable carbon isotope data may resolve a long-standing mystery-the biological affinities of the fossil Prototaxites, the largest organism on land during the Late Silurian to Late Devonian (420-370 Ma). The tree trunk-shaped specimens, of varying dimensions but consistent tubular anatomy, first formed prior to vascular plant dominance. Hence, Prototaxites has been proposed to represent giant algae, fungi, or lichens, despite incompatible biochemical and anatomical observations. Our comparative analyses instead indicate that Prototaxites formed from partially degraded, wind-, gravity-, or water-rolled mats of mixotrophic liverworts having fungal and cyanobacterial associates, much like the modern liverwort genus Marchantia. We propose that the fossil body is largely derived from abundant, highly degradation-resistant, tubular rhizoids of marchantioid liverworts, intermixed with tubular microbial elements. Our concept explains previously puzzling fossil features and is consistent with evidence for liverworts and microbial associates in Ordovician-Devonian deposits, extensive ancient and modern marchantioid mats, and modern associations of liverworts with cyanobacteria and diverse types of fungi. Our interpretation indicates that liverworts were important components of Devonian ecosystems, that some macrofossils and microfossils previously attributed to "nematophytes" actually represent remains of ancient liverworts, and that mixotrophy and microbial associations were features of early land plants.     

Composition and dynamics of the great Phanerozoic Evolutionary Floras

Factor analysis of a data set representing the global distribution of vascular plant families through time shows the broad pattern of vegetation history can be explained in terms of five Evolutionary Floras. The Rhyniophytic (=Eotrachyophytic) Flora represents the very earliest (Silurian and earliest Devonian) vascular plants, notably the Rhyniophytopsida. The Eophytic Flora represents the early (Early–Middle Devonian) mainly homosporous land plants, notably the Zosterophyllopsida, Trimerophytopsida and early Lycopsida. The Palaeophytic Flora represents the Late Devonian and Carboniferous vegetation, which saw the introduction of heterospory among the spore producing plants and of early gymnosperms. The Mesophytic Flora first appeared in the Late Carboniferous and Permian macrofossil record, although there is palynological evidence of these plants having grown earlier in extra‐basinal habitats and was dominated by gymnosperms with more modern affinities. The Cenophytic Flora that first appeared during Cretaceous times was overwhelmingly dominated by angiosperms. The end‐Devonian, end‐Triassic and end‐Cretaceous mass‐extinction events recognized in the marine fossil record had little impact on the diversity dynamics of these Evolutionary Floras. Rather, the changes between floras mainly reflect key evolutionary innovations such as heterospory, ovules and angiospermy.     

The microfossil record of early land plants

Dispersed microfossils (spores and phytodebris) provide the earliest evidence for land plants. They are first reported from the Llanvirn (Mid-Ordovician). More or less identical assemblages occur from the Llanvirn (Mid-Ordovician) to the late Llandovery (Early Silurian), suggesting a period of relative stasis some 40 Myr in duration. Various lines of evidence suggest that these early dispersed microfossils derive from parent plants that were bryophyte-like if not in fact bryophytes. In the late Llandovery (late Early Silurian) there was a major change in the nature of dispersed spore assemblages as the separated products of dyads (hilate monads) and tetrads (trilete spores) became relatively abundant. The inception of trilete spores probably represents the appearance of vascular plants or their immediate progenitors. A little later in time, in the Wenlock (early Late Silurian), the earliest unequivocal land plant megafossils occur. They are represented by rhyniophytoids. It is only from the Late Silurian onwards that the microfossil/ megafossil record can be integrated and utilized in interpretation of the flora. Dispersed microfossils are preserved in vast numbers, in a variety of environments, and have a reasonable spatial and temporal fossil record. The fossil record of plant megafossils by comparison is poor and biased, with only a dozen or so known pre-Devonian assemblages. In this paper, the early land plant microfossil record, and its interpretation, are reviewed. New discoveries, novel techniques and fresh lines of inquiry are outlined and discussed.     

The origin and early evolution of tracheids in vascular plants: integration of palaeobotanical and neobotanical data

Although there is clear evidence for the establishment of terrestrial plant life by the end of the Ordovician, the fossil record indicates that land plants remained extremely small and structurally simple until the Late Silurian. Among the events associated with this first major radiation of land plants is the evolution of tracheids, complex water-conducting cells defined by the presence of lignified secondary cell wall thickenings. Recent palaeobotanical analyses indicate that Early Devonian tracheids appear to possess secondary cell wall thickenings composed of two distinct layers: a degradation-prone layer adjacent to the primary cell wall and a degradation-resistant (possibly lignified) layer next to the cell lumen. In order to understand better the early evolution of tracheids, developmental and comparative studies of key basal (and potentially plesiomorphic) extant vascular plants have been initiated. Ultrastructural analysis and enzyme degradation studies of wall structure (to approximate diagenetic alterations of fossil tracheid structure) have been conducted on basal members of each of the two major clades of extant vascular plants: Huperzia (Lycophytina) and Equisetum (Euphyllophytina. This research demonstrates that secondary cell walls of extant basal vascular plants include a degradation-prone layer ('template layer') and a degradation-resistant layer ('resistant layer'). This pattern of secondary cell wall formation in the water-conducting cells of extant vascular plants matches the pattern of wall thickenings in the tracheids of early fossil vascular plants and provides a key evolutionary link between tracheids of living vascular plants and those of their earliest fossil ancestors. Further studies of tracheid development and structure among basal extant vascular plants will lead to a more precise reconstruction of the early evolution of water-conducting tissues in land plants, and will add to the current limited knowledge of spatial, temporal and cytochemical aspects of cell wall formation in tracheary elements of vascular plants.     

The role of mid-palaeozoic mesofossils in the detection of early bryophytes

Recently discovered Silurian and Devonian coalified mesofossils provide an additional source of data on early embryophytes. Those reviewed in this paper are considered of some relevance to understanding the early history of bryophytes while highlighting the difficulties of recognizing bryophytes in often very fragmentary fossils. The first group comprises sporophytes in which terminal sporangia contain permanent dyads and tetrads. Such spores (cryptospores) are similar to those found dispersed in older Ordovician and Silurian strata, when they are considered evidence for a land vegetation of embryophytes at a bryophyte grade. The phylogenetic significance of plants, where the axes associated with both dyad- and tetrad-containing sporangia are branching, a character state not found in extant bryophytes, is discussed. The second group comprises axial fossils, many with occasional stomata, in which central conducting strands include G-type tracheids and a number of novel types of elongate elements not readily compared with those of any tracheophyte. They include smooth-walled, evenly thickened elongate elements as well as those with numerous branching +/- anastomosing projections into the lumen. Some of the latter bear an additional microporate layer, but the homogenized lateral walls between adjacent cells are never perforate. Such cells, which occur in various combinations in central strands, are compared with the leptoids and hydroids of mosses, hydroids of liverworts and presumed water-conducting cells in coeval Lower Devonian plants such as Aglaophyton. It is concluded that lack of information on the chemistry of their walls hampers sensible assessment of their functions and the affinities of the plants. Finally, a minute fossil, comprising an elongate sporangium in which a central cylindrical cavity containing spores and possible elaters terminates in a complex poral dehiscence apparatus, is used to exemplify problems of identifying early bryophytes. It is concluded that further progress necessitates the discovery of pre-Upper Silurian fossils with well-preserved anatomy, as well as a re-evaluation of criteria used to assess existing and new Devonian fossils for bryophyte affinity.     

Physiological correlates of the morphology of early vascular plants

RAVEN, J. A., 1984. Physiological correlates of the morphology of early vascular plants. The early evolution of vascular land plants is considered in relation to the physiological problems of life on land. The universal characteristics of vascular plants (xylem, cuticle, stomata, intercellular air spaces, long-distance symplastic transport and alternation of generations) are discussed in terms of the essential properties of a homoiohydric phototroph. Likely precursors of vascular plants, and the physico-chemical and biotic environment in which they occurred, are outlined prior to a discussion of the selective forces acting on the evolution of vascular plants in the Upper Silurian and Lower Devonian. Emphasis is placed on biochemical and structural 'pre-adaptations' which may have occurred in the precursors of vascular plants and on which natural selection could have acted with lignified xylem, stomata, etc., as the end-products. Guiding principles in the analysis include the physiology of extant plants, physico-chemical constraints, and compatibility with the fossil record. It is concluded that the likely sequence of acquisition of vascular plant characteristics was: heteromorphic alternation of generations with an erect sporophyte; cuticularization of sporophyte; evolution of xylem; occurrence of intercellular air spaces with pores in the epidermis; stomatal activity of the pores. Endodermis and phloem-type long-distance transport probably originated around stages (3)-(5).     

Fossils as keys to evolution in fungi.

Both flagellated and nonflagellated fungi have an extensive fossil record, which is, however, unevenly documented and often difficult to interpret. Recent work on Silurian, Devonian and Carboniferous terrestrial assemblages has provided plausible evidence for all major groups of extant fungi in the Paleozoic. Key events in fungal macroevolution thus probably took place in the early Paleozoic or the late Precambrian, and the likelihood of finding definitive fossil evidence for them is small. The fossil record also provides evidence for morphological conservatism and early establishment of a spectrum of intimate associations between fungi and vascular plants. A model for the origin of terrestrial fungi involving two distinct lines of biotrophs in lichen-like symbioses with algae is proposed.     

内蒙古达茂旗巴特敖包地区包尔汉图剖面牙形刺生物地层

内蒙古达茂旗(达尔罕茂明安联合旗)巴特敖包地区志留纪、泥盆纪碳酸岩相地层发育,本区珊瑚、腕足类、层孔虫等底栖大化石的研究工作已有一定基础。但志留纪、泥盆纪地层在时代确定和对比上还存在很多问题,必须用主导化石门类牙形刺加以解决。研究表明：包尔汉图剖面的顶部属泥盆系无疑,应归入阿鲁共组,而不是西别河组;巴特敖包地区的海侵,始于罗德洛统卢德福德阶(Ludfordian)早期。本剖面没有发现文洛克世和罗德洛世早期的海相沉积。本文描写了一个志留纪牙形刺新种：Ozarkodina uncrispa sp．nov．。     

Microconchid encrusters colonizing land plants: the earliest North American record from the Early Devonian of Wyoming,USA

Caruso, JA. & Tomescu, AM.F. 2012: Microconchid encrusters colonizing land plants: the earliest North American record from the Early Devonian of Wyoming, USA. Lethaia, Vol. 45, pp. 490–494. Plant fossils in the Early Devonian Beartooth Butte Formation (Wyoming, USA) are colonized by microconchid encrusters which are found on several plant taxa, at two fossil localities in the formation, and whose tube coil diameters range from 230 to 1170 μm. Colonization is densest on broad Drepanophycus devonicus stems where microconchid individuals encompassing broad size ranges co‐occur in close vicinity. This indicates exposure to microconchid colonization and, therefore, submergence of the plant material for relatively extended periods of time prior to burial. For in situ preserved Drepanophycus, this suggests that the plants grew partially submerged and their submerged parts were colonized by microconchids while still alive. In turn, this indicates that by the Early Devonian microconchids were colonizing freshwater environments. The Beartooth Butte Formation provides the first record of plant colonization by microconchids in North America and, along with only one other Early Devonian record from Germany, the oldest evidence for microconchids colonizing plant substrates. □Devonian, encrusters, microconchid, vascular plants, Wyoming.     

The origin of herbivory on land： Initial patterns of plant tissue consumption by arthropods

The early fossil record of terrestrial arthropod herbivory consists of two pulses. The first pulse was concentrated during the latest Silurian to Early Devonian （417 to 403 Ma）, and consists of the earliest evidence for consumption of sporangia and stems （and limited fungivore borings）. Herbivorization of most of these tissues was rapid, representing 0 to 20 million-year （m.y.） lags from the earliest occurrences of these organs in the fossil record to their initial consumption （Phase 1）. For approximately the next 75 m.y., there was a second, more histologically varied origination and expansion of roots, leaves, wood and seeds, whose earliest evidence for herbivorization occurred from the Middle-Late Mississippian boundary to the Middle Pennsylvanian （327 to 309 Ma）. The appearance of this second herbivory pulse during the later Paleozoic （Phase 2） is accompanied by major lags of 98 to 54 m.y. between times of appearance of each of the four organ and tissue types and their subsequent herbivory. Both pulses provide a context for three emerging questions. First is an explanation for the contrast between the near instantaneous consumption of plant tissues during Phase 1, versus the exceptionally long lags between the earliest occurrences of plant tissues and their subsequent herbivorization during Phase 2. Second is the identity of arthropod herbivores for both phases. Third is the cause behind the overwhelming targeting of seed-fern plant hosts during Phase 2. Regardless of the answers to these questions, the trace fossil record of plant-arthropod associations provides primary ecological data that remain unaddressed by the body-fossil record alone.     

Late paleozoic atmospheres and biotic evolution

The latter half of the Paleozoic era is marked by notable evolutionary advances, followed by the greatest of all mass extinctions and the subsequent establishment of Mesozoic‐Cenozoic faunas of very different aspect. Current models suggest marked changes in concentration of oxygen and carbon dioxide in the Paleozoic atmosphere. Atmospheric oxygen is thought to have increased from 15% in the mid‐Devonian to near 35% by the end of the Carboniferous, followed by a decline to 17% near the end of the Permian. Atmospheric carbon dioxide was near 0.5% in the early Paleozoic, declining to less than 0.3% in the Devonian, and then more steeply downward to a minimum near 0.04% at the end of the Carboniferous. The principal causes of these changes were the advent and expansion of land plants, deposition of carbonates and continental weathering. Notwithstanding quantitative uncertainties, it seems clear that a major pulse of high oxygen concentration and associated shifts in carbon dioxide characterized the late Paleozoic atmosphere. Atmospheres with such different compositions have markedly different physical characteristics. These changes have major implications for the physiologies of contemporary organisms. The fossil records of various taxa indicate dramatic changes in the biosphere that coincide in time with the inferred changes in composition of the atmosphere. Major changes in phenotype observed in numerous lineages of animals and plants, including accelerated radiations in fresh water and on the land, are inferred to have occurred in response to these changes in the atmosphere. The morphologies, physiologies, and inferred behavior of many organisms preserved in the fossil record are in good accord with expectations based on hyperoxic, low carbon dioxide conditions of the Carboniferous atmosphere and with a return to lower oxygen levels by the end of the Permian.     

ALTERNATION OF GENERATIONS IN LAND PLANTS: NEW PHYLOGENETIC AND PALAEOBOTANICAL EVIDENCE

Current ideas on the evolution of alternation of generations in land plants are reviewed in the context of important recent advances in plant systematics and the discovery of remarkable new palaeobotanical evidence on early embryophyte life cycles. An overview of relationships in major groups of green plants is presented together with a brief review of the early fossil record as a prelude to discussing hypotheses of life cycle evolution. Recent discoveries of life cycles in the early fossil record are described and assessed. The newly discovered gametophyte and sporophyte associations are based on exceptionally well-preserved material from the Rhynie Chert, Scotland (Middle Devonian: 380–408 Myr) and compression fossils from other Devonian localities. These data document diplobiontic life cycles in plants at the ‘protracheophyte’ and early tracheophyte level of organization. Furthermore, the early fossils have a more or less isomorphic alternation of generations, a striking departure from life cycles in extant embryophytes. This unexpected similarity between gametophyte and sporophyte calls for a cautious approach in identifying ploidy level in early groups. Viewed in a systematic context, the neontological and palaeontological data contribute towards the formulation of a coherent hypothesis of life cycle evolution in major, early embryophyte groups. Evidence from extant groups strongly supports a single direct origin of the diplobiontic life cycles of land plants from haploid, haplobiontic life cycles in ancestral ‘charophycean algae’. The interest of the new palaeobotanical data lies in its relevance to life cycle evolution at the restricted level of vascular plants rather than at the more general level of embryophytes (vascular plants plus ‘bryophytes’). The occurrence of morphologically complex, axial gametophytes in early vascular plants is consistent with the moss sister-group proposed in some cladistic analyses. Similarities of moss gametophytes to fossils in the vascular plant stem-group are discussed, and it is argued that the late appearance of mosses in the macrofossil record may be due to the problem of recognizing stem-group taxa. The new palaeobotanical evidence conflicts with previous hypotheses based on extant groups that interpret morphological simplicity as the plesiomorphic condition in the gametophytes of vascular plants. These new data indicate that a significant elaboration of both gametophyte and sporophyte occurred early in the tracheophyte lineage, and that the gametophytes of extant ‘pteridophytes’ are highly reduced compared to those of some of the earliest ‘protracheophytes’. Vestiges of this early morphological complexity may remain in the gametophytes of some extant groups such as Lycopodiaceae.     

Terrestrial-marine teleconnections in the Devonian: links between the evolution of land plants,weathering processes,and marine anoxic events

The Devonian Period was characterized by major changes in both the terrestrial biosphere, e.g. the evolution of trees and seed plants and the appearance of multi-storied forests, and in the marine biosphere, e.g. an extended biotic crisis that decimated tropical marine benthos, especially the stromatoporoid-tabulate coral reef community. Teleconnections between these terrestrial and marine events are poorly understood, but a key may lie in the role of soils as a geochemical interface between the lithosphere and atmosphere/hydrosphere, and the role of land plants in mediating weathering processes at this interface. The effectiveness of terrestrial floras in weathering was significantly enhanced as a consequence of increases in the size and geographic extent of vascular land plants during the Devonian. In this regard, the most important palaeobotanical innovations were (1) arborescence (tree stature), which increased maximum depths of root penetration and rhizoturbation, and (2) the seed habit, which freed land plants from reproductive dependence on moist lowland habitats and allowed colonization of drier upland and primary successional areas. These developments resulted in a transient intensification of pedogenesis (soil formation) and to large increases in the thickness and areal extent of soils. Enhanced chemical weathering may have led to increased riverine nutrient fluxes that promoted development of eutrophic conditions in epicontinental seaways, resulting in algal blooms, widespread bottomwater anoxia, and high sedimentary organic carbon fluxes. Long-term effects included drawdown of atmospheric pCO₂ and global cooling, leading to a brief Late Devonian glaciation, which set the stage for icehouse conditions during the Permo-Carboniferous. This model provides a framework for understanding links between early land plant evolution and coeval marine anoxic and biotic events, but further testing of Devonian terrestrial-marine teleconnections is needed.     

The colonization of land by animals: molecular phylogeny and divergence times among arthropods

Background  

The earliest fossil evidence of terrestrial animal activity is from the Ordovician, ~450 million years ago (Ma). However, there are earlier animal fossils, and most molecular clocks suggest a deep origin of animal phyla in the Precambrian, leaving open the possibility that animals colonized land much earlier than the Ordovician. To further investigate the time of colonization of land by animals, we sequenced two nuclear genes, glyceraldehyde-3-phosphate dehydrogenase and enolase, in representative arthropods and conducted phylogenetic and molecular clock analyses of those and other available DNA and protein sequence data. To assess the robustness of animal molecular clocks, we estimated the deuterostome-arthropod divergence using the arthropod fossil record for calibration and tunicate instead of vertebrate sequences to represent Deuterostomia. Nine nuclear and 15 mitochondrial genes were used in phylogenetic analyses and 61 genes were used in molecular clock analyses.     

The Luoping biota: exceptional preservation, and new evidence on the Triassic recovery from end-Permian mass extinction

The timing and nature of biotic recovery from the devastating end-Permian mass extinction (252 Ma) are much debated. New studies in South China suggest that complex marine ecosystems did not become re-established until the middle–late Anisian (Middle Triassic), much later than had been proposed by some. The recently discovered exceptionally preserved Luoping biota from the Anisian Stage of the Middle Triassic, Yunnan Province and southwest China shows this final stage of community assembly on the continental shelf. The fossil assemblage is a mixture of marine animals, including abundant lightly sclerotized arthropods, associated with fishes, marine reptiles, bivalves, gastropods, belemnoids, ammonoids, echinoderms, brachiopods, conodonts and foraminifers, as well as plants and rare arthropods from nearby land. In some ways, the Luoping biota rebuilt the framework of the pre-extinction latest Permian marine ecosystem, but it differed too in profound ways. New trophic levels were introduced, most notably among top predators in the form of the diverse marine reptiles that had no evident analogues in the Late Permian. The Luoping biota is one of the most diverse Triassic marine fossil Lagerstätten in the world, providing a new and early window on recovery and radiation of Triassic marine ecosystems some 10 Myr after the end-Permian mass extinction.     

Evolution of New Zealand's terrestrial fauna: a review of molecular evidence

New Zealand biogeography has been dominated by the knowledge that its geophysical history is continental in nature. The continental crust (Zealandia) from which New Zealand is formed broke from Gondwanaland ca 80 Ma, and there has existed a pervading view that the native biota is primarily a product of this long isolation. However, molecular studies of terrestrial animals and plants in New Zealand indicate that many taxa arrived since isolation of the land, and that diversification in most groups is relatively recent. This is consistent with evidence for species turnover from the fossil record, taxonomic affinity, tectonic evidence and observations of biological composition and interactions. Extinction, colonization and speciation have yielded a biota in New Zealand which is, in most respects, more like that of an oceanic archipelago than a continent.