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Premise of research. The southern conifer family Podocarpaceae inhabits wet environments and is highly diverse in its vegetative and megasporangiate structures. The Podocarpaceae are today divided into a tropical clade and a prumnopityoid clade. We study the morphology and anatomy of leaves and megasporangiate cones at postpollination and the maturity of two native Patagonian Podocarpaceae, Saxegothaea conspicua (tropical clade) and Lepidothamnus fonkii (prumnopityoid clade). We aim to add to the knowledge of the South American Podocarpaceae and to interpret their unique morphologies to aid in our understanding of the deep and cryptic fossil record of the family and its relationships with other conifer families. Methodology. Specimens of S. conspicua and L. fonkii were collected in natural and cultivated populations of southern Chile and imaged using different macro- and microscopic techniques, including epifluorescence, bright-field, and scanning electron microscopy. Pivotal results. Leaf and megasporangiate cone anatomy and morphology are described in detail for both species. For S. conspicua , we observed a helical to slightly planate leaf arrangement with leaf reorientation, expanded leaves without accessory transfusion tissue, an apparent lack of vascularization of the epimatium (which is bikeeled and does not surround the ovule completely), and nonsaccate pollen germinating on the bract toward the protruding nucellus. For L. fonkii , we observed the absence of leaf hypodermis and resin canals, the presence of a micropylar hook in the ovule and seed integument, bisaccate pollen germinating within the ovule, cone bracts reduced in number and size, and a basal receptacle-like structure. Conclusions. Leaf arrangement in Saxegothaea shows an intermediate condition between the primary helical phyllotaxis common in the family and the secondary planate arrangement seen in most podocarps with expanded leaves. Lepidothamnus fonkii was determined to have a false receptacle (i.e., a receptacle-like structure originated from vegetative basal bracts rather than by sterile ovuliferous complexes). The presence of a false receptacle in L. fonkii is a morphological novelty in Podocarpaceae. [ABSTRACT FROM AUTHOR]

The Podocarpaceae are a morphologically diverse conifer family that have a cryptic fossil record reported since the Permian. We reviewed the fossil record of Podocarpaceae, tested the affinities of its oldest records using phylogenetic analyses, compiled macrofossil occurrence records, and investigated the diversity, distribution, and morphology of Podocarpaceae through time. We found that Permian, Triassic, and some Jurassic fossils referred to Podocarpaceae should not be placed in the family. Our total-evidence phylogenetic analyses, which sampled all major conifer lineages, recovered the Triassic Rissikia and the Jurassic Nothodacrium as stem-group conifers and the Jurassic Mataia as part of the Araucariales stem group. We further discuss the phylogenetic position of the Mesozoic enigmatic conifers Pararaucaria (Cheirolepidiaceae) and Telemachus (Voltziales), which were recovered most frequently in the conifer stem group. We conclude that the earliest reliable Podocarpaceae occurrences are from the Jurassic of both hemispheres and have scale-like leaves. Most extant genera appear in the fossil record between the Late Cretaceous and the Early Cenozoic. Many extant leaf morphologies appear in the Early Cretaceous, coeval with angiosperm diversification, consistent with the hypothesis that expanded leaves in Podocarpaceae are adaptive responses for light harvesting in angiosperm-dominated environments today. [ABSTRACT FROM AUTHOR]

Goeppertella has been postulated as a monophyletic group, whose precise position within the Gleichenoid families Dipteriaceae and Matoniaceae, remains poorly understood. Previously described Goeppertella specimens are based on frond fragments and its fertile morphology is represented by a few, poorly preserved specimens. We describe a new species based on the largest collection of fertile specimens known to date and discuss the evolutionary history of the genus based on the additional reproductive characters provided by the fossils described. Plant impressions were collected in Early Jurassic sediments of Patagonia, Argentina. The specimens were described, and silicone rubber casts were developed to examine in detail vegetative and reproductive features. The new species was compared with other Goeppertella species. Finally, a backbone analysis was performed in the context of a previously published combined matrix of Dipteridaceae, using the maximum parsimony criterion. The new species is described based on a combination of features that have not been previously reported. The vegetative morphology shows affinities with most fossil and extant Dipteriaceae, contrasting with the reproductive morphology which is more comparable with the scarce number of fossil dipteridaceous forms and it is more spread in the sister family, Matoniaceae. The backbone analysis indicates that the position of the new species vary among different positions among Dipteridaceae and Matoniaceae. Additional analyses, discriminating the signal of reproductive and vegetative character, are provided to discuss the base of this uncertainty. We consider Goeppertella as a member of the family Dipteridaceae since we interpret most shared features with Matoniaceae as plesiomorphic conditions for the family. In contrast, most shared features with Dipteridaceae represent apomorphies for the group. Thus, Goeppertella would represent an early diverging genus in Dipteridaceae, considering the venation characters as the most important in order to define the family. [ABSTRACT FROM AUTHOR]

Abstract: A new species of anatomically preserved Cupressaceae is described from the Upper Cretaceous Raritan Formation (New Jersey, USA). The fossils are charcolified isolated ovuliferous complexes that were studied by [...]

Copyright of Ameghiniana is the property of Argentine Paleontological Association / Asociacion Paleontologica Argentina and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The conifer family Cupressaceae encompasses seven subfamilies. Five of them were once considered to constitute the family Taxodiaceae, later eliminated because of its paraphyletic nature but remaining as an informal category for early‐diverging Cupressaceae lineages. Among the taxodiaceous subfamilies, Athrotaxoideae shows a unique morphology in its ovuliferous complexes (OCs) and a phylogenetically unexplored fossil record. We describe the new genus and species Patagotaxodia lefipanensis, based on OC adpressions associated with leafy branches collected at the Maastrichtian section of the Lefipán Formation (Patagonia, Argentina), and we refer it to Athrotaxoideae. We include Patagotaxodia in total evidence phylogenetic analysis to test its affinity, and we recover it within the subfamilies Athrotaxoideae or Cunninghamioideae. However, we argue that the characters supporting the athrotaxoid affinity are more meaningful in a taxodiaceous systematic context. This placement is also supported by taxon inclusion‐exclusion experiments. We discuss the position of other Cretaceous athrotaxoid records. With basis on the morphological insights provided by the OC morphology of extant and extinct Athrotaxoideae, we study the evolution of the OC morphology in the family in a phylogenetic context and discuss the results in the light of the fossil record of the family. We discuss how and when the different morphologies appeared in the family. Based on phylogenetic, temporal, morphological, and ontogenetic evidence, we conclude that the OC morphology shown by the subfamily Athrotaxoideae is intermediate between two of the most common morphologies within extant and extinct Cupressaceae species, one of which would show adaptative advantages over basal morphologies. [ABSTRACT FROM AUTHOR]

We discuss a recent assessment by Dörken et al. (2021) regarding the affinities of the Eocene fossil species Huncocladus laubenfelsii from Laguna del Hunco (Patagonia, Argentina). We originally (Andruchow-Colombo et al. , 2019) assigned this species to the conifer family Podocarpaceae as the first certain South American macrofossil record of the phyllocladoid lineage (Huncocladus + Phyllocladus), based on a combination of numerous macro- and micromorphological vegetative characters. However, Dörken et al. (2021) rejected the podocarpaceous affinity of H. laubenfelsii and considered it to be more closely related to the cycad genera Bowenia or Eobowenia. Their assessment was based almost entirely on two cuticular characters, with only superficial consideration of the abundant additional evidence available that included several diagnostic macromorphological features. We review the two characters mentioned by these authors, and other features, and find that their suggestion is contradicted by the available evidence, maintaining our original assignment. Critical characters include presence/absence of a midvein, secondary venation pattern, arrangement and general morphology of the photosynthetic structures, and morphology and disposition of epidermal cells. [ABSTRACT FROM AUTHOR]

Premise: The sooty molds are a globally distributed ecological group of ascomycetes with epiphyllous, saprotrophic habit, comprising several phylogenetically distant taxa (i.e., members of the classes Dothideomycetes and Eurotiomycetes). Their fossil record extends almost continuously back to the early Cretaceous; however, they are hypothesized to have originated in the early Mesozoic. Here, we describe new specimens of sooty molds associated with conifer leaves from Jurassic hot spring deposits of Patagonia, Argentina. Methods: Thin sections of chert samples from the La Matilde Formation, Deseado Massif (Santa Cruz, Argentina) were observed using light microscopy. Results: The fungi occur on the surface and axils of leafy twigs with podocarpaceous affinities, forming dense subicula comprised by opaque moniliform hyphae. Additionally, several asexual and sexual reproductive structures are observed. On the basis of vegetative (i.e., dense subicula composed of moniliform hyphae; hyphae composed of opaque cells deeply constricted at the septa) and reproductive characters (i.e., poroconidial and sympodioconidial asexual stages and diverse spores), two morphotypes were identified with affinities within lineages of the subphylum Pezizomycotina that encompass the ecological group of sooty molds, and a third morphotype was within the phylum Ascomycota. Conclusions: This finding extends the fossil record of sooty molds to the Jurassic and their geographic fossil range to the South American continent. In particular, their association with podocarpaceous conifers is shown to be ancient, dating back to the Jurassic. This new record provides an additional reference point on the diversity of interactions that characterized Jurassic forests in Patagonia. [ABSTRACT FROM AUTHOR]

Premise: Eocene floras of Patagonia document biotic response to the final separation of Gondwana. The conifer genus Araucaria, distributed worldwide during the Mesozoic, has a disjunct extant distribution between South America and Australasia. Fossils assigned to Australasian Araucaria Sect. Eutacta usually are represented by isolated organs, making diagnosis difficult. Araucaria pichileufensis E.W. Berry, from the middle Eocene Río Pichileufú (RP) site in Argentine Patagonia, was originally placed in Sect. Eutacta and later reported from the early Eocene Laguna del Hunco (LH) locality. However, the relationship of A. pichileufensis to Sect. Eutacta and the conspecificity of the Araucaria material among these Patagonian floras have not been tested using modern methods. Methods: We review the type material of A. pichileufensis alongside large (n = 192) new fossil collections of Araucaria from LH and RP, including multi‐organ preservation of leafy branches, ovuliferous complexes, and pollen cones. We use a total evidence phylogenetic analysis to analyze relationships of the fossils to Sect. Eutacta. Results: We describe Araucaria huncoensis sp. nov. from LH and improve the whole‐plant concept for Araucaria pichileufensis from RP. The two species respectively resolve in the crown and stem of Sect. Eutacta. Conclusions: Our results confirm the presence and indicate the survival of Sect. Eutacta in South America during early Antarctic separation. The exceptionally complete fossils significantly predate several molecular age estimates for crown Eutacta. The differentiation of two Araucaria species demonstrates conifer turnover during climate change and initial South American isolation from the early to middle Eocene. [ABSTRACT FROM AUTHOR]

Background. In extant ecosystems, complex networks of ecological interactions between organisms can be readily studied. In contrast, understanding of such interactions in ecosystems of the geologic past is incomplete. Specifically, in past terrestrial ecosystems we know comparatively little about plant biotic interactions besides saprotrophy, herbivory, mycorrhizal associations, and oviposition. Due to taphonomic biases, epiphyte communities are particularly rare in the plant-fossil record, despite their prominence in modern ecosystems. Accordingly, little is known about how terrestrial epiphyte communities have changed across geologic time. Here, we describe a tiny in situ fossil epiphyte community that sheds light on plant-animal and plant-plant interactions more than 50 million years ago. Methods. A single silicified Todea (Osmundaceae) rhizome from a new locality of the early Eocene (ca. 52 Ma) Tufolitas Laguna del Hunco (Patagonia, Argentina) was studied in serial thin sections using light microscopy. The community of organisms colonizing the tissues of the rhizome was characterized by identifying the organisms and mapping and quantifying their distribution. A 200 X 200 mm grid was superimposed onto the rhizome cross section, and the colonizers present at each node of the grid were tallied. Results. Preserved in situ, this community offers a rare window onto aspects of ancient ecosystems usually lost to time and taphonomic processes. The community is surprisingly diverse and includes the first fossilized leafy liverworts in South America, also marking the only fossil record of leafy bryophyte epiphytes outside of amber deposits; as well as several types of fungal hyphae and spores; microsclerotia with possible affinities in several ascomycete families; and evidence for oribatid mites. Discussion. The community associated with the Patagonian rhizome enriches our understanding of terrestrial epiphyte communities in the distant past and adds to a growing body of literature on osmundaceous rhizomes as important hosts for component communities in ancient ecosystems, just as they are today. Because osmundaceous rhizomes represent an ecological niche that has remained virtually unchanged over time and space and are abundant in the fossil record, they provide a paleoecological model system that could be used to explore epiphyte community structure through time. [ABSTRACT FROM AUTHOR]

Premise of research. A new Early Jurassic species of Cupressaceae is reconstructed from the Cañadón Asfalto Formation in Argentina, based on impressions of foliage and attached and dispersed seed and pollen cones. Methodology. Over 230 specimens were examined using reflected-light microscopy and epifluorescence. Relevant extant taxa were studied for structural comparisons using herbarium specimens and living material from botanical gardens. Relationships of the new conifer were assessed in the context of currently known fossil and living taxa and used to evaluate morphological trends in the early evolution of Cupressaceae. Pivotal results. The new species, Austrohamia asfaltensis D.L. Contreras, I.H. Escapa, R.C. Iribarren, & N.R. Cúneo, has helically arranged, dorsiventrally flattened leaves that are rotated into semiplanar orientation, seed cones consisting of helically arranged coriaceous ovuliferous complexes that each bear two seeds and have a distinct abaxial keel and acuminate apex, and pollen cones that occur in clusters subtended by keeled bracts. Specimens show evidence that normal vegetative shoot growth continues from the pollen cone clusters, a condition that appears to characterize living Cunninghamia and some extinct conifers but not Taiwania. The new species is assignable to the genus Austrohamia , which shares a combination of characteristics consistent with the Cunninhamioideae and Taiwanioideae subfamilies of the Cupressaceae. It is distinct from other Austrohamia species, most notably by having seed cones that are twice as large and with many more ovuliferous complexes. Conclusions. The new species expands the known morphological diversity of Austrohamia , which is the oldest recorded genus of Cupressaceae based on reproductive material, and provides a new early occurrence of the family in the Southern Hemisphere. The development of a whole-plant concept enabled morphological comparisons over a broad range of traits and with taxa known from different combinations of organs, which has provided additional insights into the early evolution of Cupressaceae. [ABSTRACT FROM AUTHOR]

Premise of research. Today, mosses are the second most speciose lineage of land plants and are important components of many ecosystems. However, in spite of their diversity and ecological importance in the modern biota, mosses are rare in the fossil record, especially prior to the Cenozoic. Therefore, every new report of a pre-Cenozoic moss deeply enriches our understanding of their evolution. Pre-Cenozoic permineralized mosses represent particularly exciting discoveries because a thorough understanding of the organism is possible. Here, we present the first permineralized Jurassic moss. Methodology. A single chert block from the Cañadón Nahuel locality of the Jurassic (178–151 Ma) Deseado Massif in Santa Cruz Province, Patagonia, was polished, and the plants within were examined, revealing a moss gametophyte shoot. A thin section of this chert block was cut and subsequently examined using light microscopy. Pivotal results. We describe Heinrichsiella patagonica gen. et sp. nov., an acrocarpous moss with a novel combination of gametophyte features that suggests basal affinities within either the family Polytrichaceae or the family Timmiellaceae. Both of these families are members of a grade within subphylum Bryophytina basal to subclass Bryidae. Heinrichsiella is the oldest member of this grade by at least 15 million years. Conclusions. Heinrichsiella patagonica is the first report of a moss from the Jurassic Deseado Massif hydrothermal cherts of Patagonia. This fossil reveals that stem group members of extant acrocarpous moss families lived during the Jurassic, implicating the Jurassic as a critical time for understanding the evolution of higher-level moss taxa. [ABSTRACT FROM AUTHOR]

Macrofossil impressions of caytonialean leaves and micro- and megasporangiate organs from the Early Jurassic Taquetrén locality in Patagonia, Argentina, are described based on more than 300 hand specimens. Leaves of the organ-genus Sagenopteris are described using both discrete and continuous features allowing us to erect the species Sagenopteris trapialensis sp. nov. Associated microsporangiate organs of Caytonanthus type are the first recorded for South America and are characterized by a unique combination of architecture, size and type of dehiscence. Two specimens, one resembling an isolated Caytonia cupule, and the other a Caytonia axis, are also described. The availability of a collection with numerous specimens has proven to be an important tool in order to fully understand the intraspecific morphological plasticity of the studied species. The striking morphological resemblance of both vegetative and reproductive organ-genera with their Northern Hemisphere counterparts suggests that they were part of the same lineage, which was widely distributed during the Jurassic. Well-defined whole-plant concepts are still needed to advance the goal of deciphering the internal relationships of caytonialeans in particular, and their relationships with other groups of seed-plants in general, and thorough macro-morphological characterization of the organs that compose them, as we present here, may be of valuable use in achieving it. [ABSTRACT FROM AUTHOR]

Premise of research. The Río Genoa Formation of Argentine Patagonia hosts Early Permian fossil assemblages that document levels of plant diversity rare among coeval floras. Ongoing work to exhaustively characterize the diversity of these assemblages is key to understanding Permian vegetation and plant evolution. A new fern type identified in the Río Genoa Formation exhibits a novel combination of characters that required taxonomic assessment. Methodology. Observations and measurements of vegetative and reproductive morphology of compression fossils were used in a comparative framework to address the taxonomic placement of the fossils. Pivotal results. The new fern, Floratheca apokalyptika gen. et sp. nov., is characterized by small pinnules with a free base, weakly lobed margin, highly decurrent midvein, and rarely branched lateral veins, as well as radially symmetrical synangia with stellate dehiscence, consisting of six spindle-shaped sporangia. This unique combination of characters distinguishes Floratheca from the more than 25 Permo-Carboniferous marattialean genera known from compressions. Floratheca exhibits variable synangium morphology during development and variation in pinnule base morphology due to a combination of adaxial-abaxial asymmetry of ultimate rachises and taphonomic effects. Conclusions. Floratheca is one of only three late Paleozoic bona fide marattialean compression genera endemic to Gondwana and the second late Paleozoic endemic South American marattialean with preserved fertile structures. Floratheca adds to an increasing diversity of fossils that diminish the disparity between the Southern and Northern Hemispheres, in terms of the extent and intensity of exploration of the plant fossil record, currently skewed taxonomically toward Northern Hemisphere taxa. Variability of synangium and pinnule base morphology in Floratheca cautions against potential taxonomic inflation produced by establishment of new taxa based on small numbers of specimens and incomplete understanding of development and taphonomy. [ABSTRACT FROM AUTHOR]

Premise of research. Numerous leaf remains of pteridosperms occur at a new locality of the Early Jurassic Cañadón Asfalto Formation, in Patagonia, Argentina. Fossils consist of adpressions with superb cuticular preservation and are herein assigned to Lepidopteris (Peltaspermaceae). Methodology. Fossils were studied using normal light, epifluorescence, and scanning electron microscopy. The cuticles of 25 specimens were chemically prepared following standard methods. The remains were described in detail and compared with other pteridosperm genera and Lepidopteris species. Pivotal results. We erect Lepidopteris scassoi sp. nov. Elgorriaga, Escapa et Cúneo, based on its novel combination of characters. Among other features, L. scassoi has a bipinnate-tripinnatifid architecture, smooth rachis, 1–3 pairs of intercalary pinnules, and entire to deeply lobed pinnules with pinnate venation. Fronds are amphistomatic with a 0.5–0.7∶1 adaxial to abaxial ratio; stomata occur scattered on rachides and pinnules and have a ring of usually seven subsidiary cells with papillae oriented toward the stomatal pit; and the guard cells are sunken. A single solid papilla is usually present on epidermal cells of pinnules and pinnae. Structures resembling isolated Peltaspermum disks, with similar stomata as L. scassoi , were found in the same locality. Conclusions. We interpret L. scassoi and other members of its lineage as fast-growing, long-lived shrubby to herbaceous plants that thrived in waterside environments. Lepidopteris scassoi represents the youngest occurrence of the genus by more than 20 Myr. Lepidopteris and Dicroidium lineages, dominant in Southern Hemisphere Triassic ecosystems, show a similar overall pattern of origination (Late Permian), diversification (late Early-Middle Triassic), and decline (Late Triassic), with relict occurrences during the Early Jurassic. The systematic affiliation of a considerable number of Mesozoic pteridosperm records remains contentious, and future efforts should be oriented toward a better understanding of the position of each group on the gymnosperm tree of life. [ABSTRACT FROM AUTHOR]

Huncocladus laubenfelsii gen. et sp. nov. is described from the early Eocene (52 million years old) Laguna del Hunco site in Patagonia, Argentina, on the basis of a compression fossil with cuticle remains. The taxon has several similarities with Phyllocladus , together with characters that are absent in extant Phyllocladus species but are otherwise typical of the enclosing scale-leaved clade. Consequently, Huncocladus is interpreted as a relative of Phyllocladus , possibly belonging to its stem group. This view is supported by a phylogenetic analysis of Podocarpaceae, which recovers Huncocladus as sister to Phyllocladus within the here-termed phyllocladoid clade (Phyllocladus + Huncocladus). Huncocladus laubenfelsii is the first macrofossil record of the phyllocladoid lineage in South America or anywhere in the western hemisphere, vastly extending its historical range and constituting an additional lineage shared between Eocene Patagonia and extant and extinct Australasian and South-east Asian rainforests. The disappearance of phyllocladoids from South America adds to the general extinction pattern described previously for southern hemisphere Podocarpaceae, associated with the family's low drought tolerance in the face of climate change (i.e. aridification). Huncocladus is the oldest record of the phyllocladoids, and it represents a new reference point for temporal calibration and biogeographic inference for the evolution of conifers and Australasian rainforests. [ABSTRACT FROM AUTHOR]

A new species of anatomically preserved Cupressaceae is described from the Upper Cretaceous Raritan Formation (New Jersey, USA). The fossils are charcolified isolated ovuliferous complexes that were studied by means of a combination of SEM images and micro-computed tomography (micro-CT), allowing the observation of morphological and anatomical characters. Each ovuliferous complex bears 3-4 anatropous winged seeds, disposed in one row on a thin medial part of the adaxial side of the ovuliferous complex. Based on the combination of characters such as ovuliferous complex morphology, arrangement of vascular tissues and resin canals, seed number and their morphology, orientation and disposition, these fossils are placed within a new species of the fossil genus Athrotaxites. The developmental stage of the specimens is analyzed base on comparisons with living representatives of the subfamily Athrotaxoideae (i.e., Athrotaxis spp.), which supports a post-pollination stage for these fossils. In addition, the new species is compared with other extant and extinct representatives of basal cupressaceous subfamilies. This new record from the Upper Cretaceous sediments of New Jersey further supports a wider distribution of the subfamily Athrotaxoideae during the middle part of the Mesozoic, as it has been also noted for other basal representatives of the family Cupressaceae. [ABSTRACT FROM AUTHOR]

Copyright of Botany is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A letter to the editor is presented in response to the article "Puzzling rocks and complicated clocks: how to optimize molecular dating approaches in historical phytogeography" by Q Wang, and K.-S. Mao in a 2016 issue.

We here describeMarattiopsis patagonicasp. nov. (Marattiaceae) based on vegetative and fertile foliage impressions from the Lower Jurassic of Chubut Province, Patagonia, Argentina. The new species exhibits a unique combination of vegetative and reproductive features, including a prominent basal auricle; finely undulate, denticulate, to serrulate pinnule margins; interstitial fibres (venuli recurrentes) alternating with regular veins; submarginal position and distinctive relative length of synangia (about 12–20% of the pinnule width); and relatively small number of sporangia pairs per synangium (usually 14 or 16). The new species is assigned to the morphogenusMarattiopsis, since it shows no characters that would allow an unambiguous placement in any of the modern genera,Marattias.s.,Ptisana, orEupodium. The newly established paraphyly of theMarattias.l. species has a profound impact on the classification of fossil species. In this context, we provide a brief assessment of the significance of the fossilMarattiopsisfor phylogenetic and biogeographical interpretations. It appears that essentially modern marattioid ferns, includingMarattiopsis, which are commonly considered to be typical elements of tropical areas of the northern hemisphere during the Mesozoic, may have left an important but largely ignored fossil record in subtropical Gondwana. [ABSTRACT FROM AUTHOR]

283I.283II.284III.284IV.287V.288288References288 Summary: Evolutionary divergence‐age estimates derived from molecular ‘clocks’ are frequently correlated with paleogeographic, paleoclimatic and extinction events. One prominent hypothesis based on molecular data states that the dominant pattern of Southern Hemisphere biogeography is post‐Gondwanan clade origins and subsequent dispersal across the oceans in a metaphoric ‘Green Web’. We tested this idea against well‐dated Patagonian fossils of 19 plant lineages, representing organisms that actually lived on Gondwana. Most of these occurrences are substantially older than their respective, often post‐Gondwanan molecular dates. The Green Web interpretation probably results from directional bias in molecular results. Gondwanan history remains fundamental to understanding Southern Hemisphere plant radiations, and we urge significantly greater caution when using molecular dating to interpret the biological impacts of geological events. [ABSTRACT FROM AUTHOR]

The idea that South America was an island continent over most of the Cenozoic, during which its unusual mammalian faunas evolved in isolation, is outstandingly influential in biogeography. Although large numbers of recent fossil discoveries and related advances require that the original isolation concept be significantly modified, it is still repeated in much current literature. The persistence of the idea inspired us to present here an integrated paleobiogeographic account of mammals, reptiles, and plants from the Jurassic to the Paleogene of Patagonia, which has by far the richest fossil record on the continent. All three groups show distribution patterns that are broadly consistent with South America's long separation history, first from Laurasia by the Late Jurassic, then from Africa and India-Madagascar during the late Early Cretaceous, and finally from Antarctica and Australia during the early-middle Eocene, after which "isolation" finally commenced. We highlight areas of promising future research and provide an updated view of South American isolation. [ABSTRACT FROM AUTHOR]

A common problem in phylogenetic analysis is the presence of unstable taxa that are depicted in multiple positions in optimal topologies. These uncertainties are reflected in strict consensus trees with polytomies that hamper the interpretation of the phylogenetic results. We propose a protocol for detecting unstable branches (either terminal taxa or clades) and identifying particular characters related to their instability in cladistic analysis. This procedure is based on an iterative evaluation of the agreement of triplets among the optimal topologies (i.e. most-parsimonious trees, MPTs) and examination of character optimizations on these trees. Different types of characters underlying the unstable behaviour of taxa are detected: those with conflicting scorings that support alternative positions of problematic taxa and those with missing data in the unstable taxa that could reduce their instability if they are scored. The entire process is automated through a TNT script that provides a list of characters related to the instability of each unstable taxon. The outcome of this procedure can be used as a guide for further research efforts focused on the revision or addition of (morphological or molecular) phylogenetic data for elucidating the affinities of unstable taxa. © The Willi Hennig Society 2009. [ABSTRACT FROM AUTHOR]

A Middle-Late Jurassic fossil plant assemblage is described from the Bahía Laura Complex at the Laguna Flecha Negra locality, Santa Cruz Province. The fossil assemblage is autochthonous, preserved in volcaniclastic sediments in the fringes of a geothermal landscape. Taxonomic study of the palaeoflora revealed 17 taxa. The recognized species have been previously described in Jurassic localities of Gondwana and illustrate the diversity of plant communities that lived in a volcanic setting. The dominant elements of this flora are microphyllous conifers of the families Araucariaceae and Cheirolepidiaceae. Fossil leaves of Cycadeoidales co-dominate the community. There is a low diversity and abundance of ferns. Composition of the plant community is compared to coetaneous floras of the Bahía Laura Complex to analyse geographical variations in the diversity of Middle-Late Jurassic assemblages of Santa Cruz Province, and a relative uniformity is recognized. Forest landscapes were dominated by conifer trees, with cycadeoids as small trees or shrubs. The herbaceous understory was dominated by fern communities with low species diversity; Equisetales and Isoetales appeared as subordinated elements. Microphyllous conifers and cycadophytes, as well as a low diversity of ferns, are indicative of relatively dry weather. • New Middle-Late Jurassic megaflora is described for Patagonia Argentina. • Forest landscapes appear to be dominated by conifer trees and small cycads. • Megafloras of the Bahía Laura Complex are analysed and compared. • Climatic signature of megafloras indicate dryer weather than the Late Triassic. [ABSTRACT FROM AUTHOR]