Potomac Group Research Articles

New information and family relationship (Hymenophyllaceae) for the fossil fern genus Acrostichopteris Fontaine and a new species from the Lower Cretaceous (Albian) of Spain.

Reinvestigation of previously described fossil plants using improved techniques can provide insights for additional characters resulting in better family assignments and relationships to modern plants, as in this new study of the fossil fern Acrostichopteris from the mid-Cretaceous. The discovery of new species within genera provides additional characteristics for comparisons and support for family assignments. Fossil material was uncovered from the matrix (degagement) for the specimens described here. Material was removed from the matrix and mounted for examination by scanning electron microscopy (SEM). Spores were extracted and prepared for examination with light, fluorescence, and SEM. Characters for the previously described material from the Potomac Group in the USA and the new material from Spain were compared with those of other fossils assigned to the genus. The genus, described by Fontaine in 1889, reexamined by Berry in 1911, and assigned to the Schizaeaceae by Reed in 1947, is reassigned to the family Hymenophyllaceae on the basis of characteristics of the pinnules, sori, sporangia, and spores. We describe a new species in the genus from the Lower Cretaceous (Albian) of Spain that most likely belongs in this family, based on characteristics of the pinnules and the sori. A summary of all the species previously assigned to the genus is included. Assignment of this fossil to the family Hymenophyllaceae is based on all characters known and comparison to modern species, provides the time for appearance of characteristics within the family, and indicates diversification of Hymenophyllum species in the mid-Cretaceous.

Extinct seed plant diversity in the Early Cretaceous: An enigmatic new microsporangiate fossil with Decussosporites pollen in situ

A new microsporangiate cone, Renbernia zhoui, is described from the mesofossil flora extracted from exposures of the Potomac Group at Puddledock, Virginia, U.S.A., which are of Early Cretaceous (early-middle Albian) age. The cone consists of densely arranged dorsiventrally flattened laminar, flabelliform microsporangiophores that bear two elongate microsporangia on the presumed abaxial surface. The microsporangia are separated by sterile tissue that expands apically into a prominent hood-like sterile extension. The microsporangia have extrorse valvate dehiscence and both microsporangia and sterile apical expansion are covered by a short stiff hairs. In situ pollen resembles Decussosporites, elliptical with a long median colpus on the presumed distal surface flanked laterally by two equally long lateral colpi. A short transverse colpus on the presumed proximal surface links the two lateral colpi and divides the grain into two parts creating the appearance of two sacci. Renbernia zhoui is similar to Brenneria potomacensis described from the slightly older Drewry's Bluff and Dutch Gap mesofossil floras from the Potomac Group that also has Decussosporites-type pollen in situ. However, Renbernia microsporangiophores are more distinctly laminar and have sporangia that are more prominently elongated and with a hood-like apical extension of sterile tissue. The in situ pollen is also much smaller, the pollen wall is much more distinctly perforate-foveolate rather than more or less psilate, and in Renbernia the saccus-like structures are not inflated. The relationship of Brenneria and Renbernia, as well as the possible link between Decussosporites-type pollen and pollen of Eucommiidites (Erdtmanithecales) is discussed.

A Lower Cretaceous palynoflora from Carregueira (Lusitanian Basin, westernmost Iberia): taxonomic, stratigraphic and palaeoenvironmental implications

Here we describe a new Lower Cretaceous palynoflora from the Lusitanian Basin, located in the westernmost sector of the Iberian Peninsula. The spore-pollen assemblage was extracted from samples collected in the Carregueira clay pit complex, located near the village of Juncal, western Portugal, from sedimentary deposits belonging to the Figueira da Foz Formation. A rich and well-preserved palynoflora, typical of non-marine fluvial environments, was recovered. Fifty-eight species and morphological groups of palynomorphs in 43 genera were recognized. The palynoflora is dominated by fern spores and conifer pollen. Angiosperm pollen is scarce and mainly represented by Afropollis, Clavatipollenites, Stellatopollis and Senectotetradites. Comparisons with described marine sections in Portugal suggest that the fossil horizon is lower Albian, corresponding to a hiatus between Zone I and Zone II in the Potomac Group of the eastern USA. The same beds contain a mesofossil flora dominated by angiosperm seeds, fruits and flowers. A similar contrast in the relative abundance of angiosperm mesofossils and pollen is seen at other Portuguese localities but is not evident in the Potomac Group. The palynoflora and the sedimentological data suggest deposition in wet lowland environments in a moderately humid regional setting.

Cretaceous Fungal Scutella from the Lower Potomac Group Zone 1: Stomatothyrium placocentrum gen. et sp. nov., a Dothideomycete Colonizer of Conifer Stomata

Premise of research. Mesozoic to Cenozoic fungi forming scutella, shield-like coverings of sporulating tissue on leaf surfaces, offer insights into the diversification of filamentous ascomycetes. We found a new fungal sporocarp type consisting of radiate scutella growing from the stomata of leaves of a conifer in a survey of dispersed plant cuticles from the Lower Cretaceous of Virginia. Here, we interpret the new morphotype and compare it with other fossil groups and with extant taxa.Methodology. We isolated fragments of conifer cuticles colonized by the fungus from macerated clays of the Potomac Group, lower Zone 1 (Aptian, 125–113 Ma), and studied them using light microscopy. We analyzed the anatomy of scutella of living taxa and compared the fossils with extant taxa producing either rhizothyria, asexual sporocarps that release spores from below the outer edge of the scutellum, or thyriothecia, sporocarps that release spores through dorsal cracks or an ostiole.Pivotal results. Stomatothyrium placocentrum gen. et sp. nov. has a radial arrangement of scutellum hyphae, characteristic of extant and fossil thyriothecial species in Dothideomycetes (Ascomycota). The scutella develop cracks on the dorsal surface that may show the dehiscence mechanism. Unusually for dehiscence in Dothideomycetes, the cracks follow the scutellum circumference rather than its radius. Each scutellum arises from a host plant stoma, appearing first as a hyphal columella that broadens into a flat scutellum disk on the leaf surface. The morphotype is common, and we found more than 63 specimens at different developmental stages on cuticle fragments.Conclusions. Its unique morphology suggests that S. placocentrum gen. et sp. nov. represents a now extinct group of leaf-dwelling Dothideomycetes that formed thyriothecia. This discovery contributes to our understanding of the range of character combinations of early epiphyllous Ascomycota.

Extending the fossil record for foliicolous Dothideomycetes: Bleximothyrium ostiolatum gen. et sp. nov., a unique fly‐speck fungus from the Lower Cretaceous of Virginia, USA

Fossils can reveal long-vanished characters that inform inferences about the timing and patterns of diversification of living fungi. Through analyzing well-preserved fossil scutella, shield-like covers of fungal sporocarps, we describe a new taxon of early Dothideomycetes with a combination of characters unknown among extant taxa. Macerated clays from the Potomac Group, lower Zone 1, from the Lower Cretaceous (Aptian, 125-113 Ma) of Virginia USA yielded one gymnospermous leaf cuticle colonized by 21 sporocarps of a single fungal morphotype. We inferred a tree from nuclear ribosomal DNA of extant species, and coded morphological characters to evaluate alternative, equally parsimonious placements of the fossil in a molecular constraint tree of extant species. Bleximothyrium ostiolatum gen. et sp. nov. has an ostiolate scutellum of radiate, dichotomizing hyphae. Unlike otherwise similar extant and fossil taxa, B. ostiolatum has tangled hyphae at its scutellum margin. Scutella of B. ostiolatum are connected to superficial mycelium, to intercalary and lateral appressoria, and to extensive subcuticular "mycélium en palmettes". The gymnospermous host has characters consistent with identity as a non-papillate ginkgophyte or cycad. Bleximothyrium ostiolatum is the oldest known fossil fly-speck fungus that occurs on plant cuticles and has the radiate, ostiolate scutellum known only from Dothideomycetes. Its combination of characters, its scutellum margin, and mycélium en palmettes are unknown in other extant and fossil species, and Bleximothyrium ostiolatum likely represents a new group of fly-speck fungi that may now be extinct.

Melloniflora, a New Extinct Multiparted Flower from the Early Cretaceous of Virginia, USA

Premise of research. The Puddledock mesofossil flora from Virginia is the richest source for studying structurally preserved plant fossils in the Early Cretaceous Potomac Group sequence. Together with other mesofossil floras from the Potomac Group and also from Portugal, it is key for direct assessment of the structure, relationships, and reproductive biology of early angiosperms. In this study, a new multiparted floral structure from the Puddledock locality is analyzed, and its phylogenetic relationships are discussed.Methodology. The fossil was extracted from unconsolidated clays and sands through sieving in water. Adhering sediment was removed using HF and HCl followed by rinsing in water. External and internal features were studied using scanning electron microscopy and synchrotron radiation X-ray tomographic microscopy. Phylogenetic analyses were carried out by adding the features of the fossil flower to an existing morphological data set for extant angiosperms.Pivotal results. A new taxon, Melloniflora virginiensis gen. et sp. nov., is established on the basis of a small multiparted floral structure that has several series of free stamens (ca. 50) and carpels (21) borne on a flattened receptacle. Stamens have a broad, short base, and dehiscence is introrse. Ovules are borne in two rows on either side of the ventral suture of the carpels. Abundant secretory cells occur in all tissues. Melloniflora is related to extant early-diverging members of the Magnoliales but also has features found among extant taxa of other early-diverging angiosperm lineages such as Austrobaileyales.Conclusions. Melloniflora adds to the knowledge of plants related to extinct magnoliids from the Early Cretaceous. It shows a combination of features not seen in any extant taxon. Melloniflora contributes to the evidence of considerable extinct diversity at an early stage in angiosperm evolution, especially among clades that today are represented by only a few relatively species-poor lineages.

Evidence for an extinct lineage of angiosperms from the Early Cretaceous of Patagonia and implications for the early radiation of flowering plants.

The pinnately lobed Aptian leaf fossil Mesodescolea plicata was originally described as a cycad, but new evidence from cuticle structure suggests that it is an angiosperm. Here we document the morphology and cuticle anatomy of Mesodescolea and explore its significance for early angiosperm evolution. We observed macrofossils and cuticles of Mesodescolea with light, scanning electron and transmission electron microscopy, and used phylogenetic methods to test its relationships among extant angiosperms. Mesodescolea has chloranthoid teeth and tertiary veins forming elongate areoles. Its cuticular morphology and ultrastructure reject cycadalean affinities, whereas its guard cell shape and stomatal ledges are angiospermous. It shares variable stomatal complexes and epidermal oil cells with angiosperm leaves from the lower Potomac Group. Phylogenetic analyses and hypothesis testing support its placement within the basal ANITA grade, most likely in Austrobaileyales, but it diverges markedly in leaf form and venation. Although many Early Cretaceous angiosperms fall within the morphological range of extant taxa, Mesodescolea reveals unexpected early morphological and ecophysiological trends. Its similarity to other Early Cretaceous lobate leaves, many identified previously as eudicots but in some cases pre-dating the appearance of tricolpate pollen, may indicate that Mesodescolea is part of a larger extinct lineage of angiosperms.

A new epiphyllous fly-speck fungus from the Early Cretaceous Potomac Group of Virginia (125–112 Ma): Protographum luttrellii, gen. et sp. nov.

ABSTRACT Fly-speck fungi reproduce via thyriothecia that consist of sporogenous tissue appressed to cuticle surfaces of plant leaves and covered by a shield-like scutellum. Thyriothecial scutella likely evolved repeatedly in Dothideomycetes (Ascomycota), and their morphology varies by lineage. Fly-speck fungi have an exceptionally good fossil record that begins in the Mesozoic. The interpretation of scutellum characters in fossils may provide insights into origins of Dothideomycetes and help calibrate the timing of ascomycete evolution. From sediments of the Lower Cretaceous (125–112 Ma) Potomac Group of Virginia, from Dutch Gap Canal, lower Zone 1, we found scutella similar to those of extant Aulographaceae (Dothideomycetes), attached to a single piece of dispersed coniferous cuticle. We analyze hyphae and scutellum development among four extant Aulographaceae species for comparison with the fossil. The excellent preservation of fungi on the leaf cuticle surface allows us to infer a developmental sequence for the fossil. Scutellum development begins with coordinated growth of multiple neighboring generator hyphae and continues with hyphae producing two-dimensional pseudomonopodial, dichotomous, radial growth. Asci and ascospores were not found. We coded states for seven morphological characters using direct observations of the fossil and eight extant taxa, and using the literature for 28 others. We inferred a phylogeny using nuclear 18S and 28S rDNA of 36 extant taxa, 34 Dothideomycetes and two Arthoniomycetes. The phylogeny includes newly determined sequences from five species, two from Aulographaceae. With a branch-and-bound search, we inferred the most parsimonious placements of the fossil given the molecular tree topology. The parsimony analysis constrained by the rDNA phylogeny places the fossil taxon among stem lineages near Aulographaceae or among the known living members of Aulographaceae. We describe the fossil morphotype as Protographum luttrellii, gen. et sp. nov. The fossil provides the oldest evidence of morphological characters restricted among extant fungi to Aulographaceae.

Onshore–offshore correlations of Cretaceous fluvial-deltaic sequences, southern Baltimore Canyon trough

We evaluate Cretaceous depositional sequences on approximately 4400 km (∼2700 mi) of newly released multichannel seismic profiles and five wells on the continental shelf in the southern Baltimore Canyon trough and tie the data to three wells drilled onshore in the Maryland coastal plain. Seismic geometries coupled with facies and biostratigraphy from the wells are used to delineate mid-Cretaceous (Aptian–Turonian) depositional sequences and paleogeography. Beneath these sequences, 400–1000 m (1300–3300 ft) of Lower Cretaceous sedimentary rocks underlie the modern shelf. They thicken along strike to the southwest, implying a southern sediment source. Aptian to Cenomanian sediments were deposited in shelf to nearshore settings. A landward movement of the depocenter and a shift toward facies indicative of deeper paleodepths marks a 107-yr mid-Cretaceous transgression, within which we identify five sequences. A composite maximum flooding surface (MFS) within the uppermost of these retrogradational units is associated with the Cenomanian–Turonian boundary and ocean anoxic event 2. Shingled, lower Turonian seismic reflections prograde across the outer shelf, downlapping onto the composite MFS, and are truncated by a mid-Turonian sequence boundary. The Upper Cretaceous section thickens seaward and along strike to the northeast, implying a northern source and little Late Cretaceous accommodation beneath the modern shelf. Mid-Cretaceous strata offshore Maryland are likely sand-prone, considering their proximity to the correlative fluvial facies of the onshore Potomac Group. These potential reservoir sands are capped by regional confining units generated by 107-yr global mean sea-level flooding events and are excellent targets for supercritical carbon storage.

An Historical Geoarchaeological Approach to Sourcing an Eighteenth Century Building Stone: Use of Aquia Creek Sandstone in Christ Church, Lancaster County, VA, USA

Historic Christ Church in Lancaster County, VA (1735), is one of America’s best-preserved examples of colonial Georgian architecture. Among its many architectural highlights is the beautiful stone trim that adorns the brick church’s doorways and windows. As it ages, conservation of original stone architectural elements is becoming necessary. The goal of this study is to determine the source of the exterior stones so appropriate matches can be acquired when repairs or replacement of some elements are needed. It will also help elucidate Christ Church’s construction history. We compared stone samples from Christ Church’s steps and keystones to samples taken from the famous Aquia Creek quarry on Government Island in Stafford County, VA, that provided the stone for America’s first federal buildings (e.g., White House, Capital, Treasury). We used standard petrographic thin-section analysis to compare the samples’ grain size, sorting, and mineralogy. Both stones are moderately sorted, medium sand sized, subarkose sandstones. Based on this as well as historical evidence, we suggest that the steps at the north, south, and west doors as well as the stone elements around the windows and doors of the church are made of the Cretaceous Aquia Creek sandstone quarried on Government Island. Within the quarry, the sandstone most likely came from the upper Patapsco Formation of the Potomac Group rather than the lower Patuxent Formation. This information should be kept in mind as Aquia Creek sandstone has a history of premature weathering and may require shorter term maintenance and longer term replacement.

Geminispermum, an Early Cretaceous (early–middle Albian) cupulate unit from the angiosperm-dominated Puddledock flora of eastern North America

Abstract A new genus and species, Geminispermum virginiense, is described based on a well-preserved coalified cupulate reproductive unit recovered from the Early Cretaceous (early–middle Albian) Puddledock locality, Virginia, U.S.A. The reproductive unit is bisymmetrical and consists of an axis that bifurcates into two cupule-bearing stalks, each in the axil of a bract. Each cupule stalk bears a single non-valvate cupule recurved towards the center of the reproductive unit. The cupule opens distally by a short transverse slit with a distinct upper margin. Each cupule almost completely encloses a single orthotropous seed that is free from the cupule except at the base. The nucellus is also free from the integument except at the basal point of attachment. Geminispermum combines features of the ovulate structures of Caytoniales, Umkomasiales (= Corystospermales, including Doyleales) and Petriellales, but cannot be included in any of these existing orders as they are currently understood. The recurved, closed, non-valvate cupules are particularly similar to those of Caytonia, Petriellaea and Reymanownaea in external morphology, but differ in being one-seeded. The cupules of Geminispermum differ from the one-seeded cupules of Umkomasiales in being non-valvate and in having only a single cupule per bract. Geminispermum is perhaps most similar to the one- or two-seeded non-valvate cupules of Ktalenia from the Early Cretaceous of Argentina, but Ktalenia is poorly preserved, details of cupule architecture are uncertain, and the cupules appear to be associated with a single strongly dissected bract. Geminispermum is currently the only unequivocal seed plant cupule recovered from the Early Cretaceous Potomac Group and is distinct from all previously described cupulate reproductive structures.

Palynology of the Baqueró Group (upper Aptian), Patagonia Argentina: An integrated study

A palynological study on samples obtained from the Anfiteatro de Ticó and Punta del Barco formations (Baqueró Group, Macizo del Deseado area, Santa Cruz Province) is carried out. A total of 162 taxa are identified in this work, including the recognition of 59 not previously reported in the unit. Furthermore, 9 new species are proposed: Coptospora santacrucensis sp. nov., Crybelosporites corrugatus sp. nov., Cycadopites grossus sp. nov., Cyclusphaera annularis sp. nov., Cyclusphaera punnulosa sp. nov., Densoisporites patagonicus sp. nov., Peromonolites globosum sp. nov., Retitriletes ornatus sp. nov. and Taurocusporites inaequalis sp. nov. Continental algae, recovered from the Anfiteatro de Ticó Formation, are illustrated for the first time. Comparisons with other Lower Cretaceous palynological zones from regions located at similar paleolatitudes (e.g. Australia, India) and from the Potomac Group (USA) are carried out. Finally, changes in the floral composition across the Baqueró deposits are analyzed considering a context of progressive increase of volcanic activity that most certainly had some effect in the dynamics of the floristic community.

New plant fossils from the Lower Cretaceous of the Parnaíba Basin, Northeastern Brazil: Southern Laurasia links

ABSTRACT: This study reports on the presence of a diverse set of gymnosperm and angiosperm macrofossils from the Codo Formation, Parnaiba Basin, whose assemblage was previously known only by the occurrence of pollen grains, spores, wood fragments, leaves and roots associated with Nympheaceae. In the Brejo municipality, northeastern Maranhao State, marl levels attest a transitional to marginal lacustrine environment, with occasional marine ingressions, demonstrated by the presence of crustaceans, gastropods and fishes. The plant fossils are preserved exclusively by molds and impressions, and its diversity is represented by few specimens, suggesting taphonomic processes of selection and transportation. The taphoflora is composed of Gnetales (?Drewria), conifers (Cupressinocladus and Brachyphyllum), and basal angiosperms (Nympheales, Magnollids, and/or basal Eudicots), which support an upper Aptian - ?Albian age. It displays affinities with both the well-known flora of the Araripe Basin (Santana Formation) as well as those ones identified in deposits from the south of North America (Potomac Group), suggesting that terrestrial links persisted in the equatorial areas of the Pangea at the end of the Early Cretaceous.

Early Cretaceous (Albian) spores and pollen from the Glen Rose Formation of Texas and their significance for correlation of the Potomac Group

ABSTRACTBecause the Gulf Coast Lower Cretaceous is dated by ammonites, it has great potential as a reference section for correlating continental sequences such as the Potomac Group and dating events in the rise of angiosperms. Middle Albian terrestrial palynofloras from Oklahoma have been described in detail, but the early Albian interval, represented in the Glen Rose Formation of Texas, is less well known. Samples from two localities on the Paluxy River, which correlate with horizons containing late early Albian ammonites, are dominated by Classopollis and Exesipollenites, but angiosperm pollen is the next most common terrestrial element, and there are several index spore species for Zone II in the Potomac Group. Among the angiosperms, reticulate monosulcates are most common and diverse, but there are also several tricolpate species. Stratigraphically important angiosperms include the Clavatipollenites rotundus group and reticulate tricolpates, which appear in the upper part of Potomac Zone I and the dated earliest Albian of England and Portugal. However, there are also tricolpates with striate-reticulate sculpture, a pollen type that is not known from upper Zone I but appears in the late early Albian of Portugal. This assemblage contrasts with floras from Potomac Zone II and the middle Albian (lower Fredericksburg Group) of Oklahoma, where tricolpates overtook monosulcate angiosperms in species diversity. These results confirm arguments based on the Portuguese section that there is a significant hiatus between Potomac Zones I and II, and that this gap is at least partly late early Albian. The dominance of Classopollis and Exesipollenites and the occurrence of isolated Northern Gondwanan elements (Sergipea, Tucanopollis) suggest that Texas lay in a transition zone between Southern Laurasia and the hotter and drier Northern Gondwana province, but regional studies are needed to disentangle geographic and climatic factors from effects of the lagoonal local environment.

Kenilanthus, a new eudicot flower with tricolpate pollen from the Early Cretaceous (early-middle Albian) of eastern North America

A new Early Cretaceous flower, Kenilanthus marylandensis, is described from the fossil plant bearing sequence exposed in early-middle Albian Potomac Group sediments at the Kenilworth (Bladensburg) locality, Maryland, USA. The flower is small, actinomorphic, pentamerous, and isomerous, and contains both pistillate and staminate parts. The receptacle is slightly dome-shaped and bears one whorl of five tepals, with a possible additional whorl toward the outside, ten stamens in two whorls of five, and one whorl of five free carpels. Stamens have elongate, tetrasporangiate, dithecate anthers that arc slightly inwards towards the centre of the flower. Thecae protrude and are oriented outwards. Pollen grains are small, tricolpate and reticulate with a graded, heterobrochate reticulum and segmented, spiny muri. Carpels are elongate with abundant stomata on the outer surface, and each carpel has a broad oblique base. Ovules are numerous in each carpel and are borne on two marginal placentae that extend along either side of the ventral suture. Kenilanthus has a combination of features that occur among different early-diverging eudicot lineages, suggesting a phylogenetic position close to the base of the eudicot clade, but its precise phylogenetic position is difficult to resolve.

First records of the angiosperm genus Sapindopsis Fontaine (Platanaceae) in western Eurasia from middle to latest Albian deposits of Spain

The genus Sapindopsis was originally described from Albian deposits of the Potomac Group in the United States, and leaves of this genus have been found in Albian to Cenomanian deposits from western North America, the Middle East and Asia, but until now they were unknown in Europe. The pinnatifid and compound leaves of Sapindopsis reported here from the middle to uppermost Albian Escucha and Utrillas formations in northeastern Spain constitute the first records of this genus in western Eurasia. Two types of Sapindopsis have been found in Spain. The older type, here described as Sapindopsis turolensis sp. nov., has pinnatifid leaves, up to four pairs of opposite lobes, a trilobed apex with palinactinodromous venation and decurrent lobe bases that continue as a wide wing of foliar tissue on the rachis. These leaves are most similar to Sapindopsis magnifolia from the middle Albian of the Potomac Group, but they differ in characters of the lobes and venation. The younger type, Sapindopsis type A, is more similar to pinnately compound Sapindopsis leaves from late Albian localities in the Potomac Group but differs in having lobes rather than true leaflets, with a narrow wing of laminar tissue decurrent onto the rachis, and randomly oriented tertiary veins. All these features are shared with leaves from Quantico, Virginia. The sedimentological setting, palaeoenvironmental conditions and plant assemblages containing Sapindopsis in eastern North America and western Laurasia were generally similar during the middle and late Albian, differing mainly in the presence of tidal influence at the Spanish localities.

Evidence for an ancient association between leaf mining flies and herbaceous eudicot angiosperms

We describe an early angiosperm and a leaf mine ichnofossil from the Lower Cretaceous Potomac Group of Virginia, USA. The descriptions are based on a fossil leaf that was first reported in 1895 but identified as a fragment of a fossil fern. The new genus and species of angiosperm, Vernifolium tenuiloba Jud and Sohn, gen. et sp. nov., was likely herbaceous and is based on a twice odd-pinnatifid leaf with glandular teeth at the tips of the lobes, and minute resin bodies covering the lamina. Leaf architectural features and sedimentological context indicate that this leaf was produced by an herbaceous eudicot angiosperm, possibly associated with Ranunculales. The leaf mine Phytomyzites wardi Sohn and Jud, ichnosp. n. is a full depth linear-blotch mine with frass, a trace of puparium inside the blotch mine section, and feeding/oviposition-related puncture marks. The features of the mine are most consistent with those produced by agromyzid flies. This fossil extends the record of agromyzid flies by about 40 myr. Furthermore, data from molecular studies suggests that the ancestral hosts for agromyzid flies are asterids, with several later host-shifts to feeding on Ranunculaceae, but this fossil provides evidence that agromyzid flies or their ancestors were feeding on herbaceous basal eudicots similar to modern herbaceous ranunculids during the Early Cretaceous, prior to the appearance and diversification of asterids.

Albian angiosperm pollen from shallow marine strata in the Lusitanian Basin, Portugal

The evolution of angiosperms significantly changed the composition of the terrestrial vegetation during the mid-Cretaceous. In contrast to the wealth of information available on the biology and systematic relationships of early angiosperms, the temporal patterns of their evolution and radiation are poorly constrained. Here we present a continuous angiosperm pollen record from well-dated shallow marine deposits in the Lusitanian Basin, Portugal. The São Julião section provides a solid stratigraphic framework to track angiosperm pollen distribution patterns from the early Albian to early Cenomanian at mid-latitudes. In comparison to previous angiosperm pollen records from the Lusitanian basin, the section shows an extended late Albian succession and provides new insights into the diversification of early angiosperms during this important interval. Productive palynological samples were analysed and 79 different angiosperm pollen types have been recorded. Throughout the Albian angiosperm pollen represent only a minor component of the total palynoflora. The early Albian pollen record is characterized by highly diverse assemblages of monoaperturate pollen of monocot or “magnoliid” affinity and by the first appearance of polyporate and tricolpate pollen of eudicot affinity. A distinct diversification phase among tri- and poly-aperturate pollen (e.g., Cretacaeiporites, Retitrescolpites, Rousea, Striatopollis and Tricolpites) and the presence of conspicuous pollen grains assigned to Dichastopollenites characterize the middle and late Albian palynological assemblages. Thus, the section records a striking sequence of appearances of important angiosperm pollen morphologies. Monocolpates, polyporates and tricolpates appear in the early Albian whereas tricolporates appear from the early part of the late Albian onwards. Furthermore, well-constrained biostratigraphic ranges of selected angiosperm pollen from mid-latitudes are presented. In view of these new data, the temporal framework of the palynological Subzones II-B and II-C in the Potomac Group succession from the Atlantic Coastal Plain, eastern USA is revised to a middle to late Albian age.

Fossil evidence for a herbaceous diversification of early eudicot angiosperms during the Early Cretaceous.

Eudicot flowering plants comprise roughly 70% of land plant species diversity today, but their early evolution is not well understood. Fossil evidence has been largely restricted to their distinctive tricolpate pollen grains and this has limited our understanding of the ecological strategies that characterized their primary radiation. I describe megafossils of an Early Cretaceous eudicot from the Potomac Group in Maryland and Virginia, USA that are complete enough to allow reconstruction of important life-history traits. I draw on quantitative and qualitative analysis of functional traits, phylogenetic analysis and sedimentological evidence to reconstruct the biology of this extinct species. These plants were small and locally rare but widespread, fast-growing herbs. They had complex leaves and they were colonizers of bright, wet, disturbance-prone habitats. Other early eudicot megafossils appear to be herbaceous rather than woody, suggesting that this habit was characteristic of their primary radiation. A mostly herbaceous initial diversification of eudicots could simultaneously explain the heretofore sparse megafossil record as well as their rapid diversification during the Early Cretaceous because the angiosperm capacity for fast reproduction and fast evolution is best expressed in herbs.

Mid-Cretaceous megaspore floras from Maryland, USA

AbstractBulk maceration of unconsolidated Potomac Group sediments collected from 12 samples of middle–late Albian and early Cenomanian age on the Elk Neck Peninsula, Maryland, yielded 14 genera and 18 species of megaspores. The identified megaspores have affinities to both heterosporous ferns, e.g., Arcellites and Molaspora, and to heterosporous lycopsids, e.g., Erlansonisporites, Minerisporites, and Paxillitriletes. Morphological variation within species is high, and most morphotypes differ from established taxa in one or more characters. Two new species—Dijkstraisporites praetextus and Verrutriletes diversus—are proposed. The composition of these middle–late Albian and early Cenomanian floras is a mixture of taxa previously recorded from Aptian and Santonian floras in North America. In addition, a fragmentary strobilus of selaginellalean affinity containing a megaspore and microspores is described.