Diversity in obscurity: fossil flowers and the early history of angiosperms

In the second half of the nineteenth century, pioneering discoveries of rich assemblages of fossil plants from the Cretaceous resulted in considerable interest in the first appearance of angiosperms in the geological record. Darwin''s famous comment, which labelled the ‘rapid development’ of angiosperms an ‘abominable mystery’, dates from this time. Darwin and his contemporaries were puzzled by the relatively late, seemingly sudden and geographically widespread appearance of modern-looking angiosperms in Late Cretaceous floras. Today, the early diversification of angiosperms seems much less ‘rapid’. Angiosperms were clearly present in the Early Cretaceous, 20–30 Myr before they attained the level of ecological dominance reflected in some mid-Cretaceous floras, and angiosperm leaves and pollen show a distinct pattern of steadily increasing diversity and complexity through this interval. Early angiosperm fossil flowers show a similar orderly diversification and also provide detailed insights into the changing reproductive biology and phylogenetic diversity of angiosperms from the Early Cretaceous. In addition, newly discovered fossil flowers indicate considerable, previously unrecognized, cryptic diversity among the earliest angiosperms known from the fossil record. Lineages that today have an herbaceous or shrubby habit were well represented. Monocotyledons, which have previously been difficult to recognize among assemblages of early fossil angiosperms, were also diverse and prominent in many Early Cretaceous ecosystems.     

Cretaceous floras containing angiosperm flowers and fruits from eastern North America

A recent innovation in paleobotanical studies of the Cretaceous has been the use of bulk sediment disaggregation and sieving techniques. This approach has identified numerous Cretaceous floras that contain well-preserved plant fossil debris (“mesofloras”), and many of these have yielded abundant fossil angiosperm flowers, as well as angiosperm fruits, seeds and dispersed stamens. On the Atlantic Coastal Plain of eastern North America recent research has identified a new series of fossil floras of Campanian age from central Georgia. These form part of a rich sequence of mesofloras that range in age from early Aptian (or perhaps late Barremian) to Campanian. Detailed studies of fossil flowers from these floras have clarified the systematic relationships of Cretaceous angiosperms and identified source plants of several characteristic dispersed angiosperm pollen grains. Taxa referable to extant angiosperm families appear suddenly in the Albian and Cenomanian, and the number of extant angiosperm families that can be recognized increases rapidly through the Late Cretaceous. Based on the record of Cretaceous fossil flowers, “modernization” of angiosperm lineages occurred much earlier than had been inferred previously from studies of dispersed fossil pollen. Major extinct monophyletic “higher” taxa of Cretaceous angiosperms have not yet been recognized.     

Integrating Early Cretaceous fossils into the phylogeny of living angiosperms:Magnoliidae and eudicots

Over the past 25 years, discoveries of Early Cretaceous fossil flowers, often associated with pollen and sometimes with vegetative parts, have revolutionized our understanding of the morphology and diversity of early angiosperms. However, few of these fossils have been integrated into the increasingly robust phylogeny of living angiosperms based primarily on molecular data. To remedy this situation, we have used a morphological dataset for living basal angiosperms (including basal eudicots and monocots) to assess the most parsimonious positions of early angiosperm fossils on cladograms of Recent plants, using constraint trees that represent the current range of hypotheses on higher-level relationships, and concentrating on Magnoliidae (the clade including Magnoliales, Laurales, Canellales, and Piperales) and eudicots. In magnoliids, our results confirm proposed relationships of Archaeanthus (latest Albian?) to Magnoliaceae, Endressinia (late Aptian) to Magnoliales (the clade comprising Degeneria, Galbulimima, Eupomatia, and Annonaceae), and Walkeripollis pollen tetrads (late Barremian?) to Win-teraceae, but they indicate that Mauldinia (early Cenomanian) was sister to both Lauraceae and Hernandiaceae rather than to Lauraceae alone. Among middle Albian to early Cenomanian eudicots, we confirm relationships of Nelumbites to Nelumbo, platanoid inflorescences and Sapindopsis to Platanaceae, and Spanomera to Buxaceae. With the possible exception of Archaeanthus, these fossils are apparently not crown group members of living families but rather stem relatives of one or more families.     

Evolution of the angiosperms: calibrating the family tree.

Growing evidence of morphological diversity in angiosperm flowers, seeds and pollen from the mid Cretaceous and the presence of derived lineages from increasingly older geological deposits both imply that the timing of early angiosperm cladogenesis is older than fossil-based estimates have indicated. An alternative to fossils for calibrating the phylogeny comes from divergence in DNA sequence data. Here, angiosperm divergence times are estimated using non-parametric rate smoothing and a three-gene dataset covering ca. 75% of all angiosperm families recognized in recent classifications. The results provide an initial hypothesis of angiosperm diversification times. Using an internal calibration point, an independent evaluation of angiosperm and eudicot origins is performed. The origin of the crown group of extant angiosperms is indicated to be Early to Middle Jurassic (179-158 Myr), and the origin of eudicots is resolved as Late Jurassic to mid Cretaceous (147-131 Myr). Both estimates, despite a conservative calibration point, are older than current fossil-based estimates.     

Integrating Early Cretaceous fossils into the phylogeny of living angiosperms: Magnoliidae and eudicots

Over the past 25 years, discoveries of Early Cretaceous fossil flowers, often associated with pollen and sometimes with vegetative parts, have revolutionized our understanding of the morphology and diversity of early angiosperms. However, few of these fossils have been integrated into the increasingly robust phylogeny of living angiosperms based primarily on molecular data. To remedy this situation, we have used a morphological data set for living basal angiosperms (including basal eudicots and monocots) to assess the most parsimonious positions of early angiosperm fossils on cladograms of Recent plants, using constraint trees that represent the current range of hypotheses on higher-level relationships, and concentrating on Magnoliidae (the clade including Magnoliales, Laurales, Canellales, and Piperales) and eudicots. In magnoliids, our results confirm proposed relationships of Archaeanthus (latest Albian?) to Magnoliaceae, Endressinia (late Aptian) to Magnoliales (the clade comprising Degeneria, Galbulimima, Eupomatia, and Annonaceae), and Walkeripollis pollen tetrads (late Barremian?) to Winteraceae, but they indicate that Mauldinia (early Cenomanian) was sister to both Lauraceae and Hernandiaceae rather than to Lauraceae alone. Among middle Albian to early Cenomanian eudicots, we confirm relationships of Nelumbites to Nelumbo, platanoid inflorescences and Sapindopsis to Platanaceae, and Spanomera to Buxaceae. With the possible exception of Archaeanthus, these fossils are apparently not crown group members of living families but rather stem relatives of one or more families.     

The identification of fossil angiosperm pollen and its bearing on the time and place of the origin of angiosperms

Studies in the 1970's reporting the occurrence of fossil pollen types in the Cretaceous, coupled with surveys of extant pollen morphology of primitive flowering plants, laid the foundation for proposing a Lower Cretaceous origin of angiosperms. Over the last 30 years, morphological, ultrastructural, and ontogenetic studies of both extant and fossil pollen have provided an array of new characters, as well as greater resolution in defining character polarities. Moreover, a range of fossil pollen types exhibiting angiosperm characters occur in low frequency within Triassic and Jurassic sediments. The pollen data provide evidence of a pre-Cretaceous origin of angiosperms. Speciation and extinction rates were likely equal during the Triassic and Jurassic, resulting in the paucity of angiosperm pollen types from different geographic areas in the Atlantic – South American/African rift zone. It was not until the Lower Cretaceous that origination rates exceed extinction rates, resulting in the subsequent diversification of angiosperms and the origin of the eudicots.     

中国白垩纪被子植物花粉的宏演化

根据中国白垩纪被子植物花粉产出记录与形态构造分析以及与世界其它地区产出顺序比较,假设中国白垩纪被子植物花粉的宏演化序列,共划分为１０个发育阶段,归于７个形态演化期：１）欧特里夫期至早巴列姆期的无口器类演化期（含：１：１网纹无口器粉发育阶段）;２）晚巴列姆至晚阿普梯期的单沟类演化期（含：２：１。棒纹粉发育阶段;２．２,星粉－棒纹粉发育阶段）;３）早,中阿尔必期的三沟类演化期（含：３．１,三沟粉类－星     

Early Cretaceous angiosperm invasion of Western Europe and major environmental changes

BACKGROUND AND AIMS: At the beginning of the Late Cretaceous, angiosperms already inhabited all the environments and overtopped previously gymnosperm-dominated floras, especially in disturbed freshwater-related environments. The aim of this paper is to define what fossil plant ecology occurred during the early Cretaceous in order to follow the early spread of angiosperm taxa. METHODS: Floristic lists and localities from the Barremian to the Albian of Europe are analysed with the Wagner's Parsimony Method. KEY RESULTS: The Wagner's Parsimony Method indicates that (a) during the Barremian, matoniaceous ferns formed a savannah-like vegetation, while angiosperms composed freshwater aquatic vegetation; (b) during the Late Aptian humid phase, conifers increased, while matoniaceous ferns decreased, reflecting the closure of the vegetation; and (c) from the Albian, warmer and drier conditions induced the recovery of the matoniaceous ferns, while core angiosperms first developed in floodplains. CONCLUSIONS: During the late Early Cretaceous (Barremian-Albian), angiosperms showed a stepwise widening of their ecological range, being recorded first during the Barremian as aquatic plant mega-remains and at the Cenomanian onwards occurred in all the environments.     

江汉盆地渔洋组上部的古新世孢粉组合

20世纪70至80年代,几乎所有关于江汉盆地跑马岗组和渔洋组的古生物文献都将其时代确定为晚白垩世。李伟同在深入地研究了跑马岗组标准剖面上的轮藻化石后提出跑马岗组大部分属于古新统。取自层位与跑马岗组相当的渔洋组上段上部的岩芯样品经分析后获得了丰富的孢粉化石。这一组合总的面貌与王大宁等获得的晚白垩世渔洋组的第三组合区别明显,而与古近纪的新沟嘴组的第四组合相似处很多。在该孢粉植物群中,常见于当地的晚白垩世分子,如希指蕨孢属、克拉梭粉属、江汉粉属、刺参粉属、鹰粉属等没有或极少见到。而在本组合常见的南岭粉属、五边粉属、漆树粉属等多出现在我国南方古新世地层中。因此,其时代很有可能为古新世。如果是这样,渔洋组上部有可能跨越了白垩系和古近系界线。从当前孢粉植物群含有很多亚热带成分以及麻黄粉属以及胡颓子粉属、忍冬粉属等看,它反映了江汉盆地当时偏干旱的亚热带气候。     

Erdtmanitheca portucalensis,a new pollen organ from the Early Cretaceous (Aptian–Albian) of Portugal with Eucommiidites-type pollen

A new lignitised, slightly compressed pollen organ, Erdtmanitheca portucalensis, with affinities to extinct Erdtmanithecales from the Early Cretaceous (Aptian–Albian) of Vale de Água (Lusitanian Basin, western Portugal), is described. The pollen organ is composed of loosely arranged microsporophylls radiating from a central core. The estimated number of microsporophylls is about 100–150. The microsporophylls are sessile and ellipsoidal to barrel-shaped with a flattened or slightly apically depression containing about ten narrow sporangia. The sporangia enclose abundant well-preserved pollen grains of Eucommiidites-type. Pollen grains found in situ are elliptical in equatorial outline, about 16.0–27.2 μm long and 11.9–16.4 μm wide. The main (distal) colpus is long with expanded rounded ends. It is flanked by two subsidiary colpi in an almost equatorial position. The surface of the pollen wall is psilate and occasionally punctate. The ektexine is composed of a distinct tectum, granular infratectal layer and a thin foot layer. The endexine is thick and laminar. The new Early Cretaceous Portuguese pollen-organ is similar in several respects to that of Erdtmanitheca texensis described from the Late Cretaceous of Texas, USA. The new fossil species further documents the importance of the Bennettitales-Erdtmanithecales-Gnetales group in the Early Cretaceous floras of Portugal extending the stratigraphic and geographical distribution of the genus with regard to systematic and phylogenetic significance of the Eucommiidites-producing plants that may have been co-occurring with the Early Cretaceous diversification of angiosperms. It is ascertained that perforate tectum occurs in pollen grains with a well-developed foot layer as well as in pollen grains in which a foot layer is poorly developed or lacking, and that pollen features do not support a separation of the Erdtmanithecales seeds and pollen organs.     

Recognising angiosperm clades in the Early Cretaceous fossil record

Studies of the earliest Cretaceous angiosperms in the 1970s made only broad comparisons with living taxa, but discoveries of fossil flowers and increasingly robust molecular phylogenies of living angiosperms allow more secure recognition of extant clades. The middle to late Albian rise of tricolpate pollen and the first local dominance of angiosperm leaves mark the influx of near-basal lines of eudicots. Associated flowers indicate that palmately lobed ‘platanoids’ and Sapindopsis are both stem relatives of Platanus, while Nelumbites was related to Nelumbo (also Proteales) and Spanomera to Buxaceae. Monocots are attested by Aptian Liliacidites pollen and Acaciaephyllum leaves and Albian araceous inflorescences. Several Albian–Cenomanian fossils belong to Magnoliidae in the revised monophyletic sense, including Archaeanthus in Magnoliales and Virginianthus and Mauldinia in Laurales, while late Barremian pollen tetrads (Walkeripollis) are related to Winteraceae. In the basal ANITA grade, Nymphaeales are represented by Aptian and Albian flowers and whole plants (Monetianthus, Carpestella and Pluricarpellatia). Epidermal similarities of lower Potomac leaves to woody members of the ANITA grade are consistent with Albian flowers assignable to Austrobaileyales (Anacostia). Aptian to Cenomanian mesofossils represent both crown group Chloranthaceae (Asteropollis plant) and stem relatives of Chloranthaceae and/or Ceratophyllum (Canrightia, Zlatkocarpus, Pennipollis plant and possibly Appomattoxia).     

The ecophysiology of early angiosperms

Angiosperms first appeared during the Early Cretaceous, and within 30 million years they reigned over many floras worldwide. Associated with this rise to prominence, angiosperms produced a spectrum of reproductive and vegetative innovations, which produced a cascade of ecological consequences that altered the ecology and biogeochemistry of the planet. The pace, pattern and phylogenetic systematics of the Cretaceous angiosperm diversification are broadly sketched out. However, the ecophysiology and environmental interactions that energized the early angiosperm radiation remain unresolved. This constrains our ability to diagnose the selective pressures and habitat contexts responsible for the evolution of fundamental angiosperm features, such as flowers, rapid growth, xylem vessels and net-veined leaves, which in association with environmental opportunities, drove waves of phylogenetic and ecological diversification. Here, we consider our current understanding of early angiosperm ecophysiology. We focus on comparative patterns of ecophysiological evolution, emphasizing carbon- and water-use traits, by merging recent molecular phylogenetic studies with physiological studies focused on extant basal angiosperms. In doing so, we discuss how early angiosperms established a roothold in pre-existing Mesozoic plant communities, and how these events canalized subsequent bursts of angiosperm diversification during the Aptian-Albian.     

Accelerated evolution of early angiosperms: Evidence from ranunculalean phylogeny by integrating living and fossil data

The new discovery of angiosperm remains in the Jehol Biota of northeastern China contributes to our understanding of the origin and early evolution of flowering plants. The earliest eudicot genus with reproductive organs, Leefructus, was recently documented from the Lower Cretaceous Yixian Formation at 125.8–123.0 Ma, and was reconsidered to be close to the extant family Ranunculaceae based on gross morphology. However, this hypothesis has not been tested using a cladistic approach. To determine the possible allies of Leefructus within extant eudicots, we constructed a 66 morphological data matrix. Molecular and morphological analyses of extant Ranunculales combined with the fossil suggest that it has an affinity with the Ranunculaceae. The earliest fossil record of the eudicots is 127–125 Ma based on tricolpate pollen grains. Thus, we suggest a hypothesis that the basal eudicots might have experienced an accelerated evolution and diversification during the latest Barremian and earliest Aptian, leading to the stem groups of at least six extant families or lineages, 10–15 Myr earlier than currently documented. Angiosperms have undergone multiple uneven pulses of radiation since their origin. Many key character innovations occurred in different stages that could have triggered those radiations in concert with various biotic and abiotic factors.     

A new fossil flower from the Turonian of New Jersey: Dressiantha bicarpellata gen. et sp. nov. (Capparales)

Recent discoveries of fossil reproductive structures from deposits of the Raritan Formation in New Jersey (Turonian, Upper Cretaceous, ~90 million years BP) include a previously undescribed representative of the Order Capparales. The fossils are usually charcoalified with three-dimensional structure and excellent anatomical details. In the present contribution, we introduce a taxon represented by fossil flowers that have a combination of characters now found in the families of the Order Capparales sensu Cronquist. The fossil species is characterized by an unique suite of characters, such as the presence of a gynophore, arrangement of the sepals, unequal petal size, monothecal anthers, and a bicarpellate gynoecium, that are found in extant families of the Order Capparales. This new taxon constitutes an important addition to our understanding of Cretaceous angiosperm diversity and represents the oldest known fossil record for the Capparales. Heretofore, the oldest known capparalean was from the Late Tertiary sediments of North America.     

Paisia,an Early Cretaceous eudicot angiosperm flower with pantoporate pollen from Portugal

A new fossil angiosperm, Paisia pantoporata, is described from the Early Cretaceous Catefica mesofossil flora, Portugal, based on coalified floral buds, flowers and isolated floral structures. The flowers are actinomorphic and structurally bisexual with a single whorl of five fleshy tepals, a single whorl of five stamens and a single whorl of five carpels. Tepals, stamens and carpels are opposite, arranged on the same radii and tepals are involute at the base clasping the stamens. Stamens have a massive filament that grades without a joint into the anther. The anthers are dithecate and tetrasporangiate with extensive connective tissue between the tiny pollen sacs. Pollen grains are pantoporate and spiny. The carpels are free, apparently plicate, with many ovules borne in two rows along the ventral margins. Paisia pantoporata is the oldest known flower with pantoporate pollen. Similar pantoporate pollen was also recognised in the associated dispersed palynoflora. Paisia is interpreted as a possibly insect pollinated, herbaceous plant with low pollen production and low dispersal potential of the pollen. The systematic position of Paisia is uncertain and Paisia pantoporata most likely belongs to an extinct lineage. Pantoporate pollen occurs scattered among all major groups of angiosperms and a close match to the fossils has not been identified. The pentamerous floral organisation together with structure of stamen, pollen and carpel suggests a phylogenetic position close to the early diverging eudicot lineages, probably in the Ranunculales.     

The rise to dominance of the angiosperm kingdom: dispersal,habitat widening and evolution during the Late Cretaceous of Europe

Coiffard, C. & Gomez, B. 2009: The rise to dominance of the angiosperm kingdom: dispersal, habitat widening and evolution during the Late Cretaceous of Europe. Lethaia, Vol. 43, pp. 164–169. The earliest fossil records of angiosperms in Europe occur in the Barremian and consist of freshwater wetland plants. From the Barremian onwards, angiosperms show a stepwise widening of their ecological range with the result that they inhabited most environments by the Cenomanian. Nevertheless, most angiosperms had still restricted habitats, while a few angiosperm trees were confined to disturbed environments, such as channel margins. A Wagner’s Parsimony Method analysis performed on a fossil plant and locality database from the Turonian to the Campanian of Europe indicates continued decrease in richness of ferns and gymnosperms compared with angiosperms, turnover between conifer and palm trees in freshwater‐related swamps at about the Cenomanian/Turonian boundary, and spreading of angiosperm trees through the floodplains. The ecological range of angiosperm trees was increased, being recorded in channel margins from the Cenomanian and spreading over floodplains (e.g. Platanaceae) and swamps (e.g. Arecaceae) by the Campanian. These new ecological ranges and successions went with innovative architectures, such as dicot trees and palm trees. Most living core angiosperm families had their earliest representatives in the Late Cretaceous, which should be considered as the dawn of modern angiosperm forests. □Core angiosperms, Europe, Late Cretaceous, palms, Wagner’s Parsimony Method.     

Mesofossils with platanaceous affinity from the Dakota Formation (Cretaceous) in Kansas, USA

The Platanaceae holds a basal position in the phylogeny of eudicots and therefore is of great interest to angiosperm systematists. The fossil record of the family is found in strata ranging from the Cretaceous to Recent in America, Europe and Asia. The research on the Platanaceae in the Dakota Formation can be traced back to 19th century; however, mesofossils of reproductive organs of the Platanaceae were never reported in the Midwest of North America before. This paper reports several specimens of Friisicarpus (Platanaceae) from the Dakota Formation in Kansas, USA. It complements the existing fossil records, and provides more information on reproductive biology of the family. The comparison with similar fossils from eastern North America and Europe provides some hints on biostratigraphy of the Cretaceous.     

Convergent evolution and adaptive radiation of beetle-pollinated angiosperms

A literature review of 34 families of flowering plants containing at least one species pollinated primarily by beetles is presented. While the majority of species are represented by magnoliids and basal monocotyledons specialized, beetle-pollinated systems have evolved independently in 14 families of eudicotyldons and six families of petaloid monocots. Four, overlapping modes of floral presentation in plants pollinated exclusively by beetles (Bilabiate, Brush, Chamber Blossom and Painted Bowl) are described. Chamber Blossoms and Painted Bowls are the two most common modes. Chamber Blossoms, found in magnoliids, primitive monocotyledons and in some families of woody eudicots, exploit the greatest diversity of beetle pollinators. Painted Bowls are restricted to petaloid monocots and a few families of eudicots dependent primarily on hairy species of Scarabaeidae as pollen vectors. In contrast, generalist flowers pollinated by a combination of beetles and other animals are recorded in 22 families. Generalist systems are more likely to secrete nectar and exploit four beetle families absent in specialist flowers. Centers of diversity for species with specialized, beetle-pollinated systems are distributed through the wet tropics (centers for Brush and Chamber Blossoms) to warm temperate-Mediterranean zones (centers for Painted Bowls and a few Bilabiate flowers). It is unlikely that beetles were the first pollinators of angiosperms but specialized, beetlepollinated flowers must have evolved by the midlate Cretaceous to join pre-existing guilds of beetlepollinated gymnosperms. The floras of Australia and western North America suggest that mutualistic interactions between beetles and flowers has been a continuous and labile trend in angiosperms with novel interactions evolving through the Tertiary.     

A whole-plant monocot from the Lower Cretaceous

The Yixian Formation (the Lower Cretaceous) of China is world famous for its fossils of early angiosperms. Despite their great diversity, few of these fossils are preserved as whole plants, making our understanding of early angiosperms incomplete. Here, we report a fossil angiosperm, Sinoherba ningchengensis n. gen. n. sp. (Sinoherbaceae n. fam.), from the Yixian Formation of China. The fossil is of a whole plant, including physically connected root with fibrous rootlets, a stem with branches and nodes, leaves with parallel-reticulate veins, and a panicle of female flowers with an ovary surrounded by perianth. Morphological and phylogenetic analyses reveal that Sinoherba is an herbaceous monocot. This fossil underscores the great diversity of angiosperms in the Lower Cretaceous Yixian Formation and an earlier, pre-Cretaceous origin of angiosperms.     

Early Cretaceous Angiosperms of the Yanji Basin,Jilin Province

An assemblage of fossil plants was discovered in the Yanji Basin, Jitin Province, consisting mainly of pterid0Phytes, gymnosperms and a few angiosperms. The present paper deals with the angiosperms only; They are: Rogersia angunifolia, Saliciphyllum longifoliurn, Sapindopsis magnifolia, Sterculophyllurn eleganurn, ,Ficophyllum, "Sassafras", Ranunculophyllum pinnatisectum sp. nov., Clernatites lanceolatus sp. nov., and the fruits Carpolithus brookensis, Carpolithus sp. gymnosperm Sequoia as well, all angiosperms having the morphological features of early angiosperms. Most of them are similar to the elements of the Potomac Group in North America and to some extent approach the fossil plants of Neocomian in Mongolia. This assemblage is manifestly different from the Albian flora of Kolyma River (URSS) and Portugal of Europe because of belonging to different stages. Thus, the age of the Dalazi Formation of Yanji Basin is tentatively ascribed to Aptian. The characteristics of this assemblage indicate that the floras of Eurasia and North America had been closely related during the early Mid-Cretaceous and that the early angiosperms were widely distributed in the North Hemisphere. Judging from the characteristics of this assemblage and the deposition, the authors speculate that in Northeast China the climate was warm and humid during the early Mid-Cretaceous.