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.     

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).     

Fossil pollen records of extant angiosperms

The fossil record for angiosperm pollen types which are comparable to recent taxa is evaluated, following a similar survey published in 1970. Special attention is paid to the dating of the sediments. Evidence for 139 families is considered to be reliable, for others the records are cited as provisional, pending the accumulation of more evidence. Some published records are shown to be erroneous. In the early Cretaceous only types occur indicating the presence of plants ancestral to Magnoliidae and Liliatae. In the Turonian increased differentiation is evident, culminating in the Maestrichtian when evidence for the presence of most major taxa of angiosperms is available. In the Tertiary diversification at lower taxonomic level continues and identification with living taxa becomes more certain. Herbaceous groups tend to appear later in the record than woody ones.     

Leaf economic traits from fossils support a weedy habit for early angiosperms

Many key aspects of early angiosperms are poorly known, including their ecophysiology and associated habitats. Evidence for fast-growing, weedy angiosperms comes from the Early Cretaceous Potomac Group, where angiosperm fossils, some of them putative herbs, are found in riparian depositional settings. However, inferences of growth rate from sedimentology and growth habit are somewhat indirect; also, the geographic extent of a weedy habit in early angiosperms is poorly constrained. Using a power law between petiole width and leaf mass, we estimated the leaf mass per area (LMA) of species from three Albian (110-105 Ma) fossil floras from North America (Winthrop Formation, Patapsco Formation of the Potomac Group, and the Aspen Shale). All LMAs for angiosperm species are low (<125 g/m(2); mean = 76 g/m(2)) but are high for gymnosperm species (>240 g/m(2); mean = 291 g/m(2)). On the basis of extant relationships between LMA and other leaf economic traits such as photosynthetic rate and leaf lifespan, we conclude that these Early Cretaceous landscapes were populated with weedy angiosperms with short-lived leaves (<12 mo). The unrivalled capacity for fast growth observed today in many angiosperms was in place by no later than the Albian and likely played an important role in their subsequent ecological success.     

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.     

POLLEN WALL ULTRASTRUCTURE OF SELECTED DISPERSED MONOSULCATE POLLEN FROM THE CENOMANIAN,DAKOTA FORMATION,OF CENTRAL USA

Seven dispersed monosulcate pollen taxa from the Dakota Formation of Minnesota, Nebraska, and Kansas were examined ultrastructurally. Rugubivesiculites rugosus has gymnosperm affinities based on its anasulcate aperture and the presence and nature of the formation of sacci. Stellatopollis sp. has exine sculpturing restricted to taxa with angiosperm affinities and is monosulcate. The affinities of the other five monosulcate taxa are uncertain and the exines are tectategranular. The sulcus in many of the remaining five taxa are flanked by small flange-like sacci. These five taxa have features found in gymnosperms and also some features of primitive extant angiosperms. The combination of characters of the pollen types presented here does not entirely agree with our current concept of primitive pollen characters as understood from extant ranalean angiosperms.     

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 diversification of angiosperms in the western part of the Iberian Peninsula

The classic leaf fossil floras from the Cretaceous of the Lusitanian Basin, Portugal, which were first described more than one hundred years ago, have played an important role in the development of ideas on the early evolution of angiosperms. Insights into the nature of vegetational change in the Lusitanian Basin through the Cretaceous have also come from studies of fossil pollen and spores, but the discovery of a series of mesofossil floras containing well-preserved angiosperm reproductive structures has provided a new basis for understanding the systematic relationships and biology of angiosperms at several stratigraphic levels through the Cretaceous. In the earliest mesofossil floras from the Torres Vedras locality, which are of probable Late Barremian-Early Aptian age, angiosperms are surprisingly diverse with about 50 different taxa. In slightly later mesofossil floras, which are of probable Late Aptian-Early Albian age, the diversity of angiosperms is still more substantial with more than hundred different kinds of angiosperm reproductive structures recognized from the Famalicão locality alone. However, this early diversity is largely among angiosperm lineages that produced monoaperturate pollen (e.g., Chloranthaceae, Nymphaeales) and early diverging monocots (Alismatales). Eudicots are rare in these Early Cretaceous mesofossil floras, but already by the Late Cenomanian the vegetation of the western Iberian Peninsula is dominated by angiosperms belonging to various groups of core eudicots. The Normapolles complex is a particularly conspicuous element in both mesofossil floras and in palynological assemblages. In the Late Cretaceous mesofossil floras from Esgueira and Mira, which are of Campanian-Maastrichtian age, core eudicots are also floristically dominant and flowers show great organisational similarity to fossil flowers from other Late Cretaceous floras described from other localities in Asia, Europe and North America.     

CUTICULAR ANATOMY OF ANGIOSPERM LEAVES FROM THE LOWER CRETACEOUS POTOMAC GROUP. I. ZONE I LEAVES

Angiosperm leaf cuticles from the oldest part of the Potomac Group reinforce previous paleobotanical evidence for a Cretaceous flowering plant diversification. Dated palynologically as Zone I of Brenner (Aptian?), these remains show a low structural diversity compared to later Potomac Group and modern angiosperms. All cuticle types conform to a single plan of stomatal construction that is unusual in its extraordinary plasticity: both the number of subsidiary cells and their arrangement vary greatly on a single epidermis, such that the stomata might be classified as paracytic, anomocytic, laterocytic, and intermediate. Such stomatal diversity is uncommon in extant angiosperms but is known from a few Magnoliidae. Many species possess secretory cells comparable to the oil cells of modern Magnoliidae, and a few show the bases of probable uniseriate hairs. None of the cuticle types can be assigned to a single modern family, but several show similarities with Chloranthaceae and Illiciales. These results support the concept that subclass Magnoliidae includes some of the most primitive living angiosperms.     

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.     

Palynofloras from the upper Barremian-Aptian Nishihiro Formation (Outer Zone of southwest Japan) and the appearance of angiosperms in Japan

Palynomorphs are reported for the first time from the Nishihiro Formation (Wakayama Prefecture, Outer Zone of southwest Japan). The Nishihiro Formation consists of brackish to shallow marine deposits, dated as late Barremian to Aptian from geological correlations. Spores prevail in the assemblage, representing Filicopsida (mainly Cyatheaceae and Anemiaceae), Marchantiopsida and Lycopsida. The pollen assemblage is dominated by Coniferales, whereas Gnetales and Bennettitales/Cycadales are only rarely observed. Moreover, we report angiosperm pollen grains of the genus Retimonocolpites for the first time in the Early Cretaceous sediments of Japan. Pollen grains of the Retimonocolpites Group are typical of early angiosperms and commonly found in assemblages from the early to mid-Cretaceous of all paleofloristic provinces. Until this paper, the oldest angiosperm fossils in Japan were represented by a single seed and a wood reported from the Albian of Hokkaido. The oldest reliable angiosperm pollen grains were reported in Hokkaido from the Cenomanian, and in Honshu from the Coniacian. Thus, Retimonocolpites pollen grains reported in the present study represent the oldest record of angiosperms in Japan. They indicate an appearance of the angiosperms in Japan older than thought until now, which is consistent with that proposed elsewhere in eastern Asia.     

Paleobiogeographic relationships of angiosperms from the Cretaceous and early Tertiary of the North American area

The biogeographic affinities of the Cretaceous and early Tertiary angiosperm floras of the North American area (which includes Meso-America, and the Greater Antilles) have been the subject of considerable interest. Although recent treatments of isolated taxa have shown affinities between North American, European, east Asian and Neotropic floras, the relationships have not been quantified. This study compiles the records of fossils whose familial relationships seem secure. This provides a carefully culled, and uniformly presented review of the Cretaceous and Paleogene record from 1950 to 1989 and supplements LaMotte (1950). A subset of these records, which showed compelling evidence of subfamilial relationships, was analyzed to quantify the relationships of the Cretaceous, Paleocene, Eocene and Oligocene floras to other regions. The analysis suggests that for the entire period 24% of the fossil species had affinities with extant taxa from the Northern Hemisphere; 10% with taxa from the Northern Hemisphere that have a few species in South America; 17% with taxa from Eurasia; 3% with taxa with a disjunct Eurasian-South American pattern; 19% with taxa from South America and/or Africa; 8% with taxa from South America and/or Africa that have an important sister group in southeast Asia; 5% with taxa from the Old World; and 13% with taxa having other distribution patterns. Those fossils with affinities to Laurasian taxa are mostly found in the northern and western portions of the North American area. The fossils with affinities to South American and/or African taxa are found in the southern portions of North America, Meso-America, and the Greater Antilles. The taxa with disjunct distributions show both patterns. These patterns suggest that during this time there were wide-spread temperate elements, found throughout Laurasia; Boreotropical flora elements, distributed in North America, Europe and along the Tethys seaway to southeast Asia; and West Gondwana elements which show dispersion from South America across the proto-Caribbean. The paleobotanical data are compatible with current geological, paleontological and biogeographical studies.     

辽西早白垩世义县组Ruffordia和Nageiopsis的发现及其地层意义

报道辽西义县组两种颇具地层意义的植物化石。Ruffordia goeppertii(Dunker)Seward和Nageiopsis exgr.samioides(Fontaine)berry,根据植物化石认为义县组的时代应属于早白垩世。     

Seed size,pollination costs and angiosperm success

Summary Seed plants capture pollen before seeds are dispersed and abort unpollinated ovules. As a result, each seed is associated with an accessory cost that represents the costs of pollen capture and the costs of aborted ovules. Accessory costs may explain the minimum seed size among species, because these costs are likely to comprise a greater proportion of total reproductive allocation in species with smaller seeds. For very small propagules, the costs of pollination may not be worth the benefits, perhaps explaining the persistence of pteridophytic reproduction at small propagule sizes. The smallest angiosperm seeds are much smaller than the smallest gymnosperm seeds, both in the fossil record and in the modern flora. This suggests that angiosperms can produce pollinated ovules more cheaply than gymnosperms. Pollination becomes less efficient as a species decreases in abundance, and this loss of efficiency is greater for species with a higher accessory cost per seed. We propose that the greater reproductive efficiency of angiosperms when rare can explain why angiosperm-dominated floras were more speciose than the gymnosperm-dominated floras they replaced.     

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.     

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.     

The early evolution of the angiosperm flower

An unexpected variety of new fossil flowers from the Lower and mid-Cretaceous and new results on the structure, development and biology of the flowers of extant primitive angiosperms are leading to modifications of earlier concepts of early flower evolution. Most fossil flowers conform best to those of the angiosperm subclass Magnoliidae, diverse though they may be. The unusual variety in organ number and organ arrangement patterns is a characteristic not only of the fossils but also of the extant Magnoliidae. It is a feature of the still 'open' organization of the flower (without intricate synorganization of parts) at this evolutionary level, and not an expression of only distant phylogenetic relationship. On the other hand, many other predominant features of modern angiosperms are lacking in both earliest fossils and most extant Magnoliidae.     

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.