Article

Growth architecture and silhouette of Jurassic conifers from La Matilde Formation, Patagonia, Argentina

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  • National University of Patagonia San Juan Bosco - CONICET
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... Several reports of vegetative reproduction in fossil gymnosperms have been published, including epicormic resprouting and production of root shoots. Epicormic resprouting has been recorded in Woodworthia [26,27], Glossopterids [28], Araucaria mirabilis [29], Cuyoxylon [30], a new tree taxon [31] and an unspecified conifer genus [32]. Root suckering has been recorded in Notophyllum krauselii [33,34] and Austrocupressinoxylon barcinense [35]. ...
... Comparison was made between these structures and epicormic structures in extant gymnosperms. Falaschi et al. [29] indicated the occurrence of both total (new orthotropic leaders) and partial (epicormic shoots) reiteration in Araucaria mirabilis. Most studies considered the buds to be preventitious but it was also suggested they may have been of adventitious origin [28][29][30]. ...
... Falaschi et al. [29] indicated the occurrence of both total (new orthotropic leaders) and partial (epicormic shoots) reiteration in Araucaria mirabilis. Most studies considered the buds to be preventitious but it was also suggested they may have been of adventitious origin [28][29][30]. ...
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Article
Gymnosperms are generally regarded as poor resprouters, especially when compared to angiosperms and particularly following major disturbance. However, is it this clear-cut? This review investigates two main aspects of gymnosperm resprouting: (i) various papers have provided exceptions to the above generalization—how frequent are these exceptions and are there any taxonomic trends?; and (ii) assuming gymnosperms are poor resprouters are there any anatomical or physiological reasons why this is the case? Five of six non-coniferous gymnosperm genera and 24 of 80 conifer genera had at least one species with a well-developed resprouting capability. This was a wider range than would be expected from the usual observation ‘gymnosperms are poor resprouters’. All conifer families had at least three resprouting genera, except the monospecific Sciadopityaceae. Apart from the aboveground stem, buds were also recorded arising from more specialised structures (e.g., lignotubers, tubers, burls and underground stems). In some larger genera it appeared that only a relatively small proportion of species were resprouters and often only when young. The poor resprouting performance of mature plants may stem from a high proportion of apparently ‘blank’ leaf axils. Axillary meristems have been recorded in a wide range of conifer species, but they often did not form an apical dome, leaf primordia or vascular connections. Buds or meristems that did form often abscised at an early stage. While this review has confirmed that conifers do not resprout to the same degree as angiosperms, it was found that a wide diversity of gymnosperm genera can recover vegetatively after substantial disturbance. Further structural studies are needed, especially of: (i) apparently blank leaf axils and the initial development of axillary meristems; (ii) specialised regeneration structures; and (iii) why high variability can occur in the resprouting capacity within species of a single genus and within genera of the same family.
... This is particularly relevant because present vegetation at high latitudes (above 60 • ) is uncommon (particularly in the southern land masses), illustrating paleoecological and paleoclimatological shifts in the colonization of land through Earth history. Low/middle latitude studies of fossil forest exist, especially involving Paleozoic examples (Cúneoand Andreis, 1983;Gastaldo, 1986;DiMichele et al., 2007, to summarize a few of them), Mesozoic (McKnight et al., 1990;Keller and Hendrix, 1997;Roberts and Hendrix, 2000;Ash and Creber, 2000;Lehman and Wheeler, 2001;Artabe et al., 2007;Brea et al., 2008;Falaschi et al., 2011) and Cenozoic sites (Mosbruggeret al., 1994). Most of these studies have provided an enormous amount of data that help our understanding of tree communities, in particular lycopods in the Paleozoic, and conifers and to lesser degree angiosperms in the Mesozoic and Cenozoic. ...
... However, in spite of the preservation of the spatial arrangement of the trees, perhaps some of the largest known in the fossil record, little research was focused on the taphonomy, structural features and spatial distribution. Preliminary reports by Cúneo (1991) and Cúneo and Panza (2008) offered a first view on the structure and general nature of the "forest"; while Falaschi et al. (2011) provided a detail survey on the architecture of the La Matilde Jurassic "forest" with consideration on the systematic affinities of the trees. The goal of this contribution is to present a quantitative analysis of the araucarian trees preserved in this area of south-central Patagonia, and to reconstruct the stand structure and the taphonomical process responsible of their preservation. ...
... Similarly, Burns (1991) found that cohorts of A. araucana are established after disturbances by fire or windthrow (see also Armesto et al., 1995). Falaschi et al. (2011) extensively described the architectural pattern of dominant trees in TL2. The Araucaria mirabilis trees are characterized by monopodial orthotropic trunks and small plagiotropic branches arranged in pseudowhorls (i.e., Massart's Model). ...
Article
The structure and taphonomy of araucarian stumps and logs from the Jurassic of Patagonia are analyzed. Density measurements of these trees indicate that they were organized into woodlands that occupied extensive paleosurfaces affected by repetitive volcanism from nearby areas. At least two episodes of araucarian woodlands were identified, both terminated by explosive volcanism. As a result, fallen trees and stumps were immediately covered by massive ash falls that favored rapid silicification. The abundance of Araucaria mirabilis seedcones in the surroundings suggests that araucarian woodlands produced this type of cone. Paleoecological, sedimentological, and paleoclimatical data are used to better understand the life history of one of the best well preserved examples of Jurassic tree vegetation. The continuous association of araucarian trees with cheirolepidaceous conifers during most of the Jurassic and Early Cretaceous suggests that the Patagonian landscape was covered by open woodlands or closer forests as the dominant plant formation.
... The first evidence for the presence of more than one araucarian species in the Patagonian assemblage comes from the description of two distinct growth architectures of araucarian trees based on the Agathoxylon record from the La Matilde Formation in which the petrified forest was buried (Falaschi et al. 2011). The distinction of two architectural types is still valid although the proposed affiliation of Agathoxylon wood and Pararaucaria patagonica cones as 'Morphotype B' (Falaschi et al. 2011) is recently contradicted by the results of Escapa et al. (2012). ...
... The first evidence for the presence of more than one araucarian species in the Patagonian assemblage comes from the description of two distinct growth architectures of araucarian trees based on the Agathoxylon record from the La Matilde Formation in which the petrified forest was buried (Falaschi et al. 2011). The distinction of two architectural types is still valid although the proposed affiliation of Agathoxylon wood and Pararaucaria patagonica cones as 'Morphotype B' (Falaschi et al. 2011) is recently contradicted by the results of Escapa et al. (2012). Pararaucaria patagonica cones do not belong to Araucariaceae but to Cheirolepidiaceae. ...
... Pararaucaria patagonica cones do not belong to Araucariaceae but to Cheirolepidiaceae. 'Morphotype A' is reconstructed from Agathoxylon matildense, Araucaria mirabilis and branches with Brachyphyllum type foliage (Falaschi et al. 2011) However, these distinct growth patterns in araucarian wood (Falaschi et al. 2011) compelled us to carefully reinvestigate Cerro Cuadrado araucarian seed cones to detect the actual species diversity. More-over, the presence of likely unnamed fossil species is also indicated by specimens that have been published as "unidentified" cones from Cerro Cuadrado collections by Daniels & Dayvault (2006). ...
... Further material from this deposit has also been obtained by amateur and commercial fossil collectors and distributed widely around the world in private and institutional collections. In more recent years, permineralized remains from Cerro Cuadrado and associated localities have provided key insights into the anatomy, development, and reproductive biology of Jurassic araucarian (Stockey, 1975(Stockey, , 1977(Stockey, , 1978Stockey and Taylor, 1978;Zamuner and Falaschi, 2005;Falaschi et al., 2011) and podocarp (Gnaedinger, 2007) conifers. These woods in turn have contributed to models of climatic and vegetation evolution through the Mesozoic of Patagonia (Iglesias et al., 2011). ...
Article
Longitudinally aligned borings attributed to the ichnotaxon Dekosichnus meniscatus in the inner secondary wood of a silicified Middle–Late Jurassic conifer from Argentina contain finely granular frass particles arranged in meniscoid laminae. Synchrotron X-ray computed tomographic reconstruction of the borings reveals new characters of this ichnotaxon, such as opposing orientations of menisci in some adjacent borings, regular spacing of minor and major meniscoid laminae, a scarcity of tunnel branching, and rare occurrences of cylindrical–spherical terminal chambers on excavations. Architectural and distributional features of the galleries suggest excavation by cerambycid beetle larvae, thus representing one of the earliest potential fossil records of this group. The borings are confined to the inner wood of a young tree that experienced a moderately seasonal climate in a volcanically influenced landscape. By detecting subtle heterogeneities in composition, this study demonstrates that high-energy synchrotron X-ray tomography can characterize anatomical features and complex ecological interactions within even densely permineralized (silicified) plant fossils.
... The area has a succession comprised of volcanic and volcaniclastic rocks from the Jurassic, and continental and marine sedimentary rocks from the middle Cretaceous-Eocene that are covered by widely extended Cenozoic basaltic lava flows (Panza et al., 2001). The oldest rocks are from the Upper Jurassic and correspond to continental tuffs and reworked tuffs from the La Matilde Formation (Falaschi et al., 2011). Above the Jurassic rocks, tuffs from the Baqueró Group (Lower Cretaceous) were deposited in which several levels of stacked silicified paleosols occur (Césari et al., 2011;Pérez Loinaze et al., 2013). ...
Article
Arid and semi-arid regions constitute an area where approximately 20% of the global population lives and the groundwater represents the only source of fresh water supply in many cases. In Extra-Andean Patagonia, located in the south extreme of South America, the landscape dominated by basaltic plateaus is associated with wet meadows, which are the only source of fresh water for rural inhabitants in a region characterized by arid conditions. The aim of this work was to define the geological and geomorphological controls that condition the formation of wet meadows associated with basaltic plateaus in a sector of the Extra-Andean Patagonian. For this, fieldworks were carried out that included geological profiles, rock sampling and geomorphological description of the sectors associated with wet meadows. The perennial character of wet meadows is supported by lithostratigraphic, structural and geomorphological controls that regulate the recharge, storage, flows and discharge of the groundwater that sustains them. The subhorizontal position of the basaltic plateau and the presence of fractures allow the rapid infiltration of rainwater that recharges the aquifers. The lithology, structure and paleorelief of the underlying rocks to the basalts determine the storage and flow of groundwater. Despite the great extension of the basalt plateaus and their homogeneity, there are different geological-geomorphological combinations in the underlying rocks that give rise to a great variety of controls of the water flows that sustain the wet meadows. The data obtained provide new information for the knowledge of wetlands and water resources in arid environments such as Extra-Andean Patagonia, where wet meadows provide water supply of local people, livestock and vegetation, constituting a relevant ecosystem service.
... The fossils from the La Matilde Formation consist of plants (including the famous in situ stumps and seed cones from the Petrified Forest Natural Monument "Madre e Hija" or "Cerro Cuadrado"; e.g., Cúneo and Panza 2008;Falaschi et al. 2011;Kloster and Gnaedinger 2018), invertebrates, vertebrates (i.e., the anuran Notobatrachus degiustoi; originally described by Reig in Stipanicic andReig 1955, 1957;Báez and Nicoli 2004), and ichnites from invertebrates and vertebrates. Among the latter, four ichnites are regarded as of dinosaurian origin (Delatorrichnus goyenechei, Sarmientichnus scagliai, Wildeichnus navesi, and Grallator isp.) and two are mammalian, or from close mammalian relatives (Ameghinichnus patagonicus and A. manantialensis) (Casamiquela , 1964ade Valais , 2011. ...
Chapter
The sparse record of archaic Mesozoic South American mammals extends from the latest Early Jurassic to the latest Cretaceous, involving about 115 Ma, which can be further extended to about 160 Ma, including the post-K/Pg evidence. We review here the distribution, predicted time of origin, and likely place of origin for the lineages covered in the preceding chapters during that span of time and against the evolving geological backdrop of continental drift and paleogeography. Size, dental diversity, and likely dietary specializations of the Mesozoic South American mammals are discussed in the context of Mesozoic mammals in general. A few of the many surprising advances in comparative genetic and molecular evolution are discussed as part of a holistic view of early mammalian evolution to which fossils can, and should, be integrated. Social, financial, and geographical issues affecting paleontological research in South America, early mammals, in particular, are highlighted. We recognize that we are still in the early stages of development and that much of what we know about Mesozoic South American mammals is likely to be drastically altered by finds in the continent or underrepresented areas from formely Gondwanan landmasses such as Antarctica or Africa. Their scarce mammalian fossil record has hampered their full incorporation into an integrated view of early mammalian evolution. The relatively robust paleontological community present in several South American countries, relatively inexpensive nature of the discipline, and extensive outcrops are likely to ensure continuity of a synergistic research agenda. The potential for novel data, regional strengths in systematics, and the global resurgent importance of time as integral to model-based phylogenies are auspicious signs for the future of Mesozoic mammal research in South America.
... The fossils from the La Matilde Formation consist of plants (including the famous in situ stumps and seed cones from the Petrified Forest Natural Monument "Madre e Hija" or "Cerro Cuadrado"; e.g., Cúneo and Panza 2008;Falaschi et al. 2011;Kloster and Gnaedinger 2018), invertebrates, vertebrates (i.e., the anuran Notobatrachus degiustoi; originally described by Reig in Stipanicic andReig 1955, 1957;Báez and Nicoli 2004), and ichnites from invertebrates and vertebrates. Among the latter, four ichnites are regarded as of dinosaurian origin (Delatorrichnus goyenechei, Sarmientichnus scagliai, Wildeichnus navesi, and Grallator isp.) and two are mammalian, or from close mammalian relatives (Ameghinichnus patagonicus and A. manantialensis) (Casamiquela , 1964ade Valais , 2011. ...
Chapter
Dryolestoids are iconic members of the Mesozoic mammalian associations in South America. They achieved a large taxonomic diversity in this region with disparate dental and cranial morphotypes ranging from the classical role of sharp-toothed insectivores to bunodont, complex dentitions reflecting omnivore/herbivore adaptations. The South American radiation of dryolestoids, the meridiolestidans, are among the most abundant Cretaceous mammals, surviving the K/Pg mass extinction and continuing until the Miocene as minor members of the South American biotas. New specimens have been recently discovered, some of them including associated upper and lower jaws, and exceptionally preserved skulls. These high-quality fossils provide crucial intraspecific dental variation, both along the tooth row and from upper to lower, allowing critical re-interpretation of some taxa originally named on the basis of isolated teeth or very incomplete material. The Cretaceous diversity of meridiolestidans has been grossly overestimated, with taxa based on different dental positions of what was later determinied to be a single taxon. One relatively poorly known Late Cretaceous taxon, Groebertherium, shares many features with the classical Holartic dryolestoids and may represent a Late Jurassic/Early Cretaceous foundational morphology expected for meridiolestidans.
... The fossils from the La Matilde Formation consist of plants (including the famous in situ stumps and seed cones from the Petrified Forest Natural Monument "Madre e Hija" or "Cerro Cuadrado"; e.g., Cúneo and Panza 2008;Falaschi et al. 2011;Kloster and Gnaedinger 2018), invertebrates, vertebrates (i.e., the anuran Notobatrachus degiustoi; originally described by Reig in Stipanicic andReig 1955, 1957;Báez and Nicoli 2004), and ichnites from invertebrates and vertebrates. Among the latter, four ichnites are regarded as of dinosaurian origin (Delatorrichnus goyenechei, Sarmientichnus scagliai, Wildeichnus navesi, and Grallator isp.) and two are mammalian, or from close mammalian relatives (Ameghinichnus patagonicus and A. manantialensis) (Casamiquela , 1964ade Valais , 2011. ...
Chapter
Non-mammaliaform cynodonts, formerly called “mammal-like reptiles,” illustrate earlier states of the morphological architecture in the mammalian lineage. These mammalian forerunners show unique character combinations without direct counterparts among living vertebrates reflecting adaptations long lost along the millions of years of cynodont history. The fossil record from South America, originating mostly from the Middle to Late Triassic of Argentina and Brazil, is one of the most prolific worldwide. SA non-mammalian cynodonts are systematically diverse, including approximately 40 species that present great morphological disparity in skull shape, tooth morphology, pattern of tooth replacement, masticatory mechanisms, and locomotory architectures. In this chapter, we summarize the record of SA non-mammaliaform cynodonts.
... At least one example from the fossil record suggests that the results of this study can be useful in assessing fossil serotiny among extinct groups of conifers. The Middle Jurassic La Matilde Formation in Patagonia, Argentina, contains well-preserved remains of the conifer Pararaucaria patagonica, the cones of which have been found attached to the base of large-diameter branches (see fig. 10 in Falaschi et al. 2011). Pararaucaria belongs to an extinct conifer family (the Cheirolepidiaceae; see Escapa et al. 2012) that produced seed cones at the tips of ramified small-diameter branches with scale leaves, as in modern Cupressaceae sensu stricto (Escapa and Leslie 2017). ...
... The oldest rocks are upper Jurassic and correspond to the La Matilde Formation of the Bahía Laura Volcanic Complex (e.g. Falaschi et al., 2011). They are constituted by continental tuffs, and reworked tuffs and constituted the floor of the valleys in the study area (Panza et al., 2001). ...
Article
Extra-Andean Patagonia, located in the south end of South America, is a wide arid region where the basaltic plateau landscape dominates. Associated with the basaltic plateaus, wet meadows and shallow lakes make up environments of relevance due to the ecosystemic services they provide. The aim of this work was to define the processes and factors that condition the hydrodynamics and hydrogeochemistry of wet meadows and shallow lakes in a sector of the Patagonian plateau basalts. For this, detailed geological and geomorphological studies were carried out and water was sampled at 29 points for the analysis of major ions and, in some samples, stable isotopes of the water molecule. Values of δ¹⁸O and δ²H similar to the local meteoric line in the water of wet meadows indicate that rainwater quickly infiltrates through the fractures of the basaltic plateaus and stores in the underlying sediments. Groundwater discharge occurs in the scarp zone due to changes in sediment permeability. The weathering of silicates in basalts, ion exchange in the sediment clays, and the dissolution of soluble salts provided by the dust control water chemistry of this wetland. Water from wet meadows drains into saline endorheic basins of sodium chloride composition where the isotopic signal is indicative of evaporation percentages close to 95%. The high evaporation rates cause the precipitation of evaporitic salts at the edges of shallow lakes with carbonate, sulfate, and chloride species controlled by the dominance of sodium in the water.
... These are features shared by extant Araucariales, which includes the Podocarpaceae and Araucariaceae (see comparisons in table 1). Additional vegetative and reproductive organs assignable to Araucariaceae and Podocarpaceae are found in the La Matilde Formation (e.g., wood, leafy branches, cones; Zamuner Falaschi et al. 2011;Kloster and Gnaedinger 2018). Further refinement of the systematic affinities of the nodules based on the preserved morphological characters, especially considering the morphological variability known to be present in fossil and extant Podocarpaceae and Araucariaceae, is not possible (Spratt 1912;Dickie and Holdaway 2011;tables 1, 2). ...
Article
Premise of the Research: Despite their ecological significance in modern terrestrial ecosystems, knowledge about the evolution of arbuscular mycorrhizae based on the fossil record is still scarce, especially concerning the case of root nodules harboring arbuscular mycorrhizal fungi as in some extant gymnosperms and angiosperms. Exceptionally preserved conifer nodular roots were found in the Jurassic fossil-bearing chert deposits of the Deseado Massif (Santa Cruz, Argentina), raising the possibility to study them in association with arbuscular mycorrhizal fungi. The aim of this study is to describe the plant organs and their fungal partners, and to discuss the ecological significance of the interactions observed, particularly with respect to their occurrence in the hot-spring settings. Methodology: Thin sections of chert samples from the ‘Cañadón Nahuel’ locality of the La Matilde Formation, Deseado Massif (Santa Cruz, Argentina) were observed using light microscopy. Pivotal Results: The cortex of the nodules are occupied by several glomeromycotan fungal structures. The structures occur in a specific zone of the cortex - towards its center -, and includes intracellular hyphal coils and arbuscules. Glomoid spores, and coenocytic hyphae possibly penetrating the epidermal cells are also described and analyzed. Conclusions: The root nodules have affinities with the Araucariales, representing the oldest record of such structures for this conifer clade. This is also the first record nodules harboring arbuscular mycorrhizal fungi for the Jurassic; it extends our knowledge of the fossil record of this particular type of fungal association.
... Of note is the world renowned petrified forest of the Middle Jurassic La Matilde Formation at the Monumento Natural Bosques Petrificados locality, which has become famous for its high amount and enormous in situ trunks as well as fallen logs, which have been assigned to Agathoxylon matildense (Zamuner and Falaschi 2005). Furthermore, the finding of numerous large logs that show branches of all order allowed Falaschi et al. (2011) to suggest that these Araucariaceae trees were composed of a main, orthotropic stem bearing up to seven plagiotropic branches in pseudowhorls. In addition, the outer bark anatomy of some of these trees has revealed a conspicuously banded periderm structure (Singer andArchangelsky 1958, hibbett et al. 1997). ...
... According to the combined phylogenetic analysis of Escapa and Catalano (2013), when only considering extant species, the plesiomorphic configuration of the crown group of the genus Araucaria seems to be the papery-thin wing morphology for the cone scale complexes and a broad multiveined morphology for the leaves (Fig. 8). However, a rhomboidal (scale-like) morphology appears to be a more plausible basal leaf morphology when taking into account the oldest fossil record assigned to the genus or associated with it, as it is the case of several Brachyphyllum species (Kendall, 1949;Calder, 1953;Townrow, 1967;Harris, 1979;Gee and Tidwell, 2010;Falaschi et al., 2011;Sender et al., 2015). The reconstructed basal configuration for the crown group of the clade comprised by the species of section Eutacta would be thin-winged cone scale complexes and single-veined scale-like leaves (Fig. 8). ...
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Article
PREMISE OF THE STUDY: We describe a new araucarian species, Araucaria lefipanensis, from the Late Cretaceous flora of the Lefipán Formation, in Patagonia (Argentina) based on reproductive and vegetative remains, with a combination of characters that suggest mosaic evolution in the Araucaria lineage. METHODS: The studied fossils were found at the Cañadón del Loro locality. Specimens were separated into two leaf morphotypes, and their morphological differences were tested with MANOVA. KEY RESULTS: The new species Araucaria lefipanensis is erected based on the association of dimorphic leaves with cuticle remains and isolated cone scale complexes. The reproductive morphology is characteristic of the extant section Eutacta, whereas the vegetative organs resemble those of the sections Intermedia, Bunya, and Araucaria (the broad-leaved clade). CONCLUSIONS: The leaf dimorphism of A. lefipanensis is similar to that of extant A. bidwillii, where dimorphism is considered to be related to seasonal growth. The leaf dimorphism in A. lefipanensis is consistent with the paleoclimatic and paleoenvironmental reconstructions previously suggested for the Lefipán Formation, which is thought to have been a seasonal subtropical forest. The new species shows evidence of mosaic evolution, with cone scale complexes morphologically similar to section Eutacta and leaves similar to the sections of the broad-leaved clade, constituting a possible transitional form between these two well-defined lineages. More complete plant concepts, especially those including both reproductive and vegetative remains are necessary to understand the evolution of ancient plant lineages. This work contributes to this aim by documenting a new species that may add to the understanding of the early evolution of the sections of Araucaria.
... The Bahía Laura Group is integrated with an early stage of andesitic to basaltic-andesitic effusive and intrusive magmatism (Bajo Pobre Formation) followed by extensive dacitic and rhyolitic volcanic rocks, ignimbrites and domes conforming a LIP (large igneous province) of acidic rocks that covered most of Patagonia (Pankhurst et al., 1998) known as the Chon Aike Formation. Stratigraphically upward, in the Deseado Region this volcanic complex is interestratified with lacustrine and alluvial fan deposits of the Bajo Grande and La Matilde Formations, interpreted as upper Bathonian-Kimmeridgian to Hauterivian rocks (Panza, 1998;Falaschi et al., 2011), while in the subsurface of the Golfo San Jorge basin the uppermost Jurassic and Lower Cretaceous units are represented by the Las Heras Group (Fig. 2). The later is a lacustrine unit preserved in variably-oriented (E-W, NNW-SSE or NE-SW) half-grabens, filled by black shales and wedge-shaped, sandstone bodies (Figari et al., 1999;Bellosi et al., 2002) conforming the "main rifting event" of the Golfo San Jorge basin, informally known as the "Neocomian Basin" (Gianni et al., 2015a). ...
Article
We use three-dimensional (3D) seismic reflection data to analyze the structural style, fault kinematics and growth fault mechanisms of non-colinear normal fault systems in the South Flank of the Golfo San Jorge basin, central Patagonia. Pre-existing structural fabrics in the basement of the South Flank show NW-SE and NE-SW oriented faults. They control the location and geometry of wedge-shaped half grabens from the “main synrift phase” infilled with Middle Jurassic volcanic-volcaniclastic rocks and lacustrine units of Late Jurassic to Early Cretaceous age. The NE-striking, basement-involved normal faults resulted in the rapid establishment of fault lenght, followed by gradual increasing in displacement, and minor reactivation during subsequent extensional phases; NW-striking normal faults are characterized by fault segments that propagated laterally during the “main rifting phase”, being subsequently reactivated during succesive extensional phases. The Aptian-Campanian Chubut Group is a continental succession up to 4 km thick associated to the “second rifting stage”, characterized by propagation and linkage of W-E to WNW-ESE fault segments that increase their lenght and displacement in several extensional phases, recognized by detailed measurement of current throw distribution of selected seismic horizons along fault surfaces. Strain is distributed in an array of sub-parallel normal faults oriented normal to the extension direction. A Late Cretaceous-Paleogene (pre-late Eocene) extensional event is characterized by high-angle, NNW-SSE to NNE-SSW grabens coeval with intraplate alkali basaltic volcanism, evidencing clockwise rotation of the stress field following a ∼W-E extension direction. We demonstrate differences in growth fault mechanisms of non-colinear fault populations, and highlight the importance of follow a systematic approach to the analysis of fault geometry and throw distribution in a fault network, in order to understand temporal-spatial variations in the coeval topography, potential structural traps, and distribution of oil-bearing sandstone reservoirs.
... Reports of Jurassic fungi include fungal trace fossils (Martill, 1989) and lichen-like organisms and lichen-forming fungi (Preat et al., 2000;Wang et al., 2010), as well as more readily identifiable fungal remains such as spores and hyphae (Stockey, 1980;Traverse and Ash, 1994;Ibáñez and Zamuner, 1996;García Massini et al., 2012). In addition, Jurassic fossil wood has been described with particular decay patterns that have been interpreted as the result of fungal activity (e.g., Müller-Stoll, 1936;Süss and Philippe, 1993;Falaschi et al., 2011). Few reports, however, provide a detailed description of the fungi. ...
Article
Well-preserved fungi occur in permineralized conifer axes from the Lower Jurassic of northern Victoria Land, Antarctica. The fungus is characterized by septate hyphae extending through the vascular ray system via penetration of cross-field pits. Tyloses are present in large numbers and might have been effective as a physical restraint to the spread of the fungus. However, knotted fungal hyphae within and around the tyloses suggest that the fungus was able to surmount the barriers. Hyphae are also present in the secondary phloem. This plant–fungal interaction contributes to a better understanding of the antagonistic relationships that existed between pathogenic fungi and conifers in the Jurassic paleoecosystems of Antarctica, as well as providing evidence of interactions between fungi and tyloses in Mesozoic wood.
... Notable Early Jurassic paleobotanical localities areTaquetrén and Cerro Bayo in Chubut, Piedra Pintada in Neuquén, and Roca Blanca in Santa Cruz (Bonetti 1964, Herbst 1965, Escapa et al. 2008b), all of which share many elements with the Middle Jurassic Hope Bay flora of Antarctica (Halle 1913b, Gee 1989, Rees & Cleal 2004, Hunter et al. 2005). The remaining Jurassic record comes mostly from the late Early–early Middle Jurassic Cã nadónnad´nadón Asfalto (Frenguelli 1949, Escapa et al. 2008c, C ´ uneo et al. 2013b) and Middle Jurassic La Matilde formations (Feruglio 1937, Feraud et al. 1999, Falaschi et al. 2011), and the small Late Jurassic record from the Cã nadónnad´nadón Calcáreo Formation (Escapa et al. 2013). ...
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Article
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 it be significantly modified, the original isolation concept is still repeated in much current literature. The persistence of the idea inspired us to present here an integrated paleobiogeographic account of Jurassic to Paleogene mammals, reptiles, and plants from 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 ...
Article
This paper describes a petrified trunk collected from a conglomerate bed of the Springhill Formation (Berriasian– Valanginian) in the Estancia El Álamo locality, Santa Cruz Province, Argentina. The fossil trunk is classified within the ubiquitous genus Agathoxylon and the wood anatomy shows a close affinity to that of Araucariaceae. This Patagonian wood has a distinct combination of anatomical characteristics unique among all known species from the Jurassic and Cretaceous of Western Gondwana allowing to diagnose a new fossil taxon Agathoxylon mendezii sp. nov. Sedimentological and megafloristic proxies of the Springhill Formation suggest that Agathoxylon mendezii sp. nov. grew under a warm and wet climate, which indicates a subtropical to temperate palaeoenvironment. However, the large number of frost rings in the earlywood of this araucarian tree suggests that the palaeoenvironment at Estancia El Álamo was subjected to recurrent disturbances, most likely caused by regional continuous volcanic activity originating from volcanoes located far away to the west. This activity would have produced periodic stratospheric veils that promoted rapid decreases in surface air temperature; the wood response to such stressful conditions would have been the formation of numerous (at least five) frost rings. Although recurrent eruptions in Patagonia during the Early Cretaceous are well recorded, this study is the first to register eruptions recorded in a coniferous wood.
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The South American fossil record of Mesozoic mammals and close relatives is one of the best for Gondwana. Early mammals and relatives are found in about a dozen localities in Argentina, Brazil, Bolivia, Chile, and presumably Peru, including a broad sample of non-mammaliaform cynodonts of the Triassic age. Mesozoic mammals span from the latest Early Jurassic to the latest Cretaceous, furthermore some of those archaic lineages unexpectedly survived the end of the Cretaceous period, remaining as minority elements in the Paleocene–Miocene faunal associations. The fossiliferous localities bearing these fossils are presented in this chapter, highlighting the geological setting, age, and their faunal associations.
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Anatomically preserved conifer-like leaves from the Middle Jurassic La Matilde Formation at the Barda Blanca locality in the Gran Bajo de San Julián area, southern Patagonia are described here. Leaves are assigned to conifers based on the following foliar features: thick-walled epidermal cells, a sclerenchymatic hypodermis, resin canals and transfusion tracheids associated with the vascular bundle. General mesophyll anatomy and inferred morphology suggest a similarity to large, broad, linear-lanceolate, multi-veined conifer-like leaves. The general foliar habit indicates an affinity with the large, multi-veined leaves of the Araucariaceae; especially with those exhibited by the species of the Araucaria sections, Araucaria and Bunya. Anatomically, the permineralized leaves exhibit xeromorphic foliar features, including thick-walled epidermal cells, an isobilateral mesophyll with well-developed palisade cells and mechanical tissue. The general leaf anatomy shown by the Patagonian specimens along with sedimentological data may suggest that during the deposition of the La Matilde Formation at the Barda Blanca locality, the parent plant was well adapted to the environmental conditions, which probably consisted of a high light intensity with an adequate quantity of water in the soil, which increased the maximum leaf conductance of CO2.
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Early diversification of modern conifer lineages occurred during the Late Triassic and Early Jurassic, and worldwide ecosystems were dominated by conifers throughout the Jurassic. The knowledge about the palaeobiology and palaeoecology of basal representatives of those clades, however, has only recently begun to be developed due to the relative scarcity of complete plant reconstructions for many of these conifer families. In regards to the Cupressaceae sensu lato, some reconstructions have been proposed, although none has linked all plant organs. One of the oldest records of this family is the genus Austrohamia, described from the Lower Jurassic of Argentina and China. The original material consists of impressions of leafy branches, organically attached to ovulate and pollen cones. This conifer has a combination of characters that support its assignation to the Cunninghamioideae subfamily, the most basal member of the Cupressaceae stem group. In this paper, we describe permineralized woods from the same strata where Austrohamia minuta was found in the Cañadón Asfalto Basin, Chubut Province, Argentina. The fossil woods were assigned to the genus Protaxodioxylon, due to homoxylic pycnoxylic secondary xylem, with distinct growth rings, radial tracheid pitting of mixed type, abundant axial parenchyma, taxodioid cross-fields and uniseriate homocellular rays. Consistent with the differences in other Protaxodioxylon species, we propose a new specific taxon for the Patagonian specimens. This genus has often been related to the taxodiaceous Cupressaceae. This linkage, together with the fact that all the conifer impressions from these strata correspond to Austrohamia, reinforces the idea that the wood belongs to the same biological entity as A. minuta. From this interpretation, Austrohamia represents the most complete Mesozoic Cupressaceae to date.
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The discovery of 16 cylindrical conifer seed cones at the Estancia Vilán locality in the Late Jurassic Cañadón Calcáreo Formation of Chubut Province, Patagonia, Argentina, provides anatomically preserved specimens, allowing for the description of a second species of Pararaucaria (Cheirolepidiaceae). The new species, Pararaucaria delfueyoi, is similar in general features to the type species, Pararaucaria patagonica, but has a specifically diagnostic combination of characters that include cone size, seed number, features of histology, and seed size. Specimens are cylindrical with a narrow axis that bears helically arranged bract/scale complexes. The bract and scale diverge from the axis at ∼90° and separate from each other almost immediately. The ovuliferous scale extends toward the margin of the cone and then arches over to enclose two inverted nonwinged seeds within a pocket of tissue. Although the specimens are abraded such that the distal regions of the ovuliferous scales are not preserved, this combination of morphological and histological characters allows for the assignment of P. delfueyoi to the Cheirolepidiaceae with confidence. The co-occurrence of this cone with an undescribed species of Araucaria extends the geographic and stratigraphic ranges of this association, which previously has been known only from the Middle Jurassic of Santa Cruz Province of Patagonia. This extends the knowledge of anatomical variation among seed cones of Cheirolepidiaceae and improves our understanding of homology relationships for conifer seed cone structures.
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Fungal–arthropod–plant interactions are described from the Middle Jurassic Monumento Natural Bosques Petrificados, Santa Cruz, Patagonia, Argentina. Fossils consist of a silicified araucarian log that appears differentially decayed and displays galleries bored in patterns resembling those produced by extant wood-boring beetles. Galleries are filled completely with frass that is reworked into smaller galleries containing spherical to ellipsoidal coprolites. The coprolites are of possible mite origin and contain fungal and plant remains. Fungi are also found growing from the walls of the smaller galleries and from the coprolites. Identifiable fungal propagules include asexual structures typical of extant imperfect fungi. Comparison with modern wood with similar patterns suggests a xilophagous role for the wood borer, whereas the smaller galleries and coprolites likely are products of a smaller xylophagous/fungivorous woodborer. Decay patterns in the silicified woods are like those produced by extant saprotrophic and pathogenic wood-rotting fungi in modern ecosystems. The fungus on the walls of the galleries and on the coprolites most likely was saprotrophic. However, additional indirect and direct interactions (i.e., phorisms) similar to those between conifers, mites, beetles, and fungi in modern ecosystems could be hypothesized. This report provides unique direct fossil evidence of multitrophic fungal–arthropod–plant interactions and suggests the possibility that complex interactions like those in modern conifers might have been in place by at least the Jurassic. These results underscore the importance of fungi as key elements of past ecosystems, acting as drivers of biological cycles and symbionts with a variety of organisms.
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Premise of the study: Seed cone morphology and anatomy reflect some of the most important changes in the phylogeny and evolutionary biology of conifers. Reexamination of the enigmatic Jurassic seed cone Pararaucaria patagonica reveals previously unknown systematically informative characters that demonstrate affinities with the Cheirolepidiaceae. This paper documents, for the first time, internal anatomy for seed cones of this important extinct Mesozoic conifer family, which may represent the ghost lineage leading to modern Pinaceae. Methods: Morphology and anatomy of cones from the Jurassic La Matilde Formation in Patagonia are described from a combination of polished wafers and thin section preparations. New photographic techniques are employed to reveal histological details of thin sections in which organic cell wall remains are not preserved. Specific terminology for conifer seed cones is proposed to help clarify hypotheses of homology for the various structures of the cones. Key results: Specimens are demonstrated to have trilobed ovuliferous scale tips along with a seed enclosing pocket of ovuliferous scale tissue. Originally thought to represent a seed wing in P. patagonica, this pocket-forming tissue is comparable to the flap of tissue covering seeds of compressed cheirolepidiaceous cones and is probably the most diagnostic character for seed cones of the family. Conclusions: Pararaucaria patagonica is assigned to Cheirolepidiaceae, documenting anatomical features for seed cones of the family and providing evidence for the antiquity of pinoid conifers leading to the origin of Pinaceae. A list of key morphological and anatomical characters for seed cones of Cheirolepidiaceae is developed to facilitate assignment of a much broader range of fossil remains to the family. This confirms the presence of Cheirolepidiaceae in the Jurassic of the Southern Hemisphere, which was previously suspected from palynological records.
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The study of an Araucaria araucana-dominated primary forest in central Chile evidenced that more than a quarter of the biggest trees have several vertical axes. Although the trunk usually dominates, the occurrence of other vertical axes makes the silhouette quite different of the classical umbrella-like one. Most of Mesozoic landscape reconstructions display trees supposedly related to the Araucariaceae, and illustrate them with bottlebrush or parasol like shapes. Beyond a more realistic aspect of such reconstructions, the observation of vertical reiterations has several architectural and palaeobiological implications.
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Here we describe impressions of vegetative and fertile organs of Equisetaceae coming from the Monumento Natural Bosques Petrificados locality, La Matilde Formation (Middle Jurassic), Santa Cruz Province. They are very frequent in tuffaceous laminated levels with assymmetrical ripple marks, micro-crossbedding and bioturbations associated with shallow lacustrine environment. Stems are herbaceous, grass-like and have extremely small dimensions: diameter 1,3 mm, internodes 0,9 cm long, cross section hexagonal with 6 carinae and valeculae and 6 leaves per node fused into a leaf sheath. No branching was observed. The material is mostly vegetative, but three specimens with mature strobili show hexagonal, verticilate sporangiophores. The observed characters allow us to assign them to a new species of Equisetites: E. minimus n.sp. The stems lie parallel to the bedding planes or cross them suggesting life position. They probably grew in dense, monotypic communities, with an essentially vegetative reproduction.
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A new plant concept for the extinct conifer species Emporia lockardii (Mapes&Rothwell) Mapes&Rothwell (Emporiaceae) is developed from fossils collected at the Late Pennsylvanian Hamilton Quarry, Kansas. Emporia lockardii has lateral plagiotropic branches with simple and forked leaves, simple pollen cones, and compound ovulate cones. Stems have an endarch eustele with dense wood surrounding a septate pith. Leaves display position-dependent heterophylly with forked leaves on penultimate shoots and simple leaves on ultimate shoots. All leaves are amphistomatic with two stomatal bands and papillate epidermal cells on the adaxial surface and two basal stomatal bands and numerous trichome bases on the abaxial surface. Pollen cones are simple and have helically arranged microsporophylls and adaxial pollen sacs. Prepollen is monolete and monosaccate, and it conforms to the sporae dispersae genus Potonieisporites Bharadwaj. Ovulate cones are compound with helically arranged, forked bracts that subtend bilaterally symmetrical, axillary dwarf shoots with one to three narrow megasporophylls interspersed among numerous sterile scales. Ovules are terminal, inverted, and bilaterally symmetrical. This new reconstruction together with additional conifer reconstructions from the Hamilton Quarry locality indicate that the genus Emporia has a particularly high species diversity for walchian conifers. These findings support previous hypotheses that propose drier habitats as sites for the first appearances of plants that become dominant during the late Permian and Mesozoic.
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Study of an Araucaria araucana-dominated primary forest in central Chile evidenced that more than a quarter of the biggest trees have several vertical axes. Although the trunk usually dominates, the occurence of other vertical axes makes the silhouette quite different of the classical umbrella-like one. Most of Mesozoic landscape reconstructions display trees supposedly related to the Araucariaceae, and illustrate them with bottlebrush or parasol like shapes. Beyong a more realistic aspect of such reconstructions, the observation of vertical reiterations has several architectural and palaeobiological implications.
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Two anatomically preserved gymnosperm trunks with clusters of epicormic shoots are described from the Late Permian of Antarctica. The best-preserved trunk is 14 cm long. It has a small circular parenchymatous pith and 9 cm of secondary xylem that contains at least 50 growth rings. The second specimen is slightly smaller (11 3 8 cm) and has 20 growth rings. Both specimens have pycnoxylic wood and produced more than 50 small shoots in a delimited zone on the surface of the trunk. Shoots have a wide parenchymatous pith that may be solid to septate with endarch primary xylem forming 8–10 sympodia and a small amount of secondary xylem similar to that of the parent trunk. The shoots branch and increase in number toward the outside of the trunk. Evidence based on anatomical comparisons and association at the site indicates that the specimens probably represent trunks of some glossopterid, the dominant group of seed ferns during the Permian in Gondwana. This is the first report of clusters of epicormic shoots in a Paleozoic gymnosperm. The ability to produce a large number of young shoots that were capable of developing into new branches indicates that these high-latitude trees possessed an architectural plasticity that allowed them to respond quickly to short-or long-term environmental stress.
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Seed ferns (pteridosperms) make up a heterogeneous group of broadleaf gymnosperms. Our attempts to reconstruct these extinct plants here summarize research over many years on the best-known seed ferns. We have named each reconstructed plant after its best-preserved ovulate fructifications, because these are the most reliable parts for identification of seed plants. We envisage Early Carboniferous (about 352 million years ago) Stamnostoma huttonense as a large tree, foresting elevated terraces and other well-drained areas of coastal plains. Swampy lagoon margins of the same coast probably were wooded with lycopods and small shrubby seed ferns such as Lyrasperma scotica. Of comparable age, but on well-drained ashy soils flanking inland volcanoes, was the early successional Calathospermum fimbriatum. Unlike these other plants, which were probably pollinated and dispersed by wind and water, arthropods may have played a role in the reproduction of C. fimbriatum. Earliest Late Carboniferous (about 320 million years old) Lagenostoma lomaxii is reconstructed as a bushy understory shrub in swamps of arborescent lycopods. Latest Late Carboniferous (about 296 million years old) Pachytesta illinoensis was a tree probably growing on elevated and nutrient-rich areas in and around permanently waterlogged swamps of marattiaceous tree ferns. Pachytesta illinoensis had large prepollen probably dispersed by insects. Its fleshy ovules may have been dispersed by large amphibians, reptiles, or fish. Another seed fern of these latest Carboniferous swamps, Callospermarion pusillum, is reconstructed as an early successional scrambling vine. Its pollen probably was dispersed by wind, and its numerous small seeds scattered widely by wind and water. In contrast to these Euramerican plants of tropical and subtropical climates, Late Permian (about 245 to 253 million years old) Dictyopteridium sporiferum was a dominant tree of cool temperate swamp woodlands of intermontane valleys in the southern hemisphere. Large air chambers in its roots enabled it to grow in waterlogged soils. Woodlands of southern hemisphere mid-continental lowlands during Late Triassic time (225 to 230 million years ago) included abundant trees of Umkomasia granulata, and a shrubby understory including Peltaspermum thomasii. Middle Jurassic (175 to 183 million years old) Caytonia nathorstii is reconstructed as a tree of lowland mixed conifer-broadleaf forest in a subtropical, seasonally wet paleoclimate. Its ovules were enclosed in berrylike cupules, which may have been pollinated and dispersed by small animals. From these examples, it is apparent that seed ferns were exceptionally diverse broadleaf plants which occupied a variety of niches now occupied by angiosperms.
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A new species of extinct conifer plants, Emporia royalii sp. nov. Hernandez‐Castillo, Stockey, Mapes et Rothwell (Emporiaceae: Voltziales), is described from the rich fossil biota of the Late Pennsylvanian, Hamilton Quarry, Kansas. This conifer has lateral plagiotropic branches with simple and forked leaves, “age‐dependent heterophylly,” simple pollen cones, and compound ovulate cones. Stems have an endarch eustele, dense wood, and secretory cells arranged in nests or plates in the pith. Leaves are amphistomatic with two adaxial stomatal bands and two longitudinal abaxial rows of stomata with numerous trichome bases. Pollen cones are simple and have helically arranged microsporophylls with adaxial pollen sacs. Prepollen is monolete and monosaccate (Potonieisporites Bharadwaj). Ovulate cones are compound with bilaterally symmetrical axillary dwarf shoots that bear up to 45 sterile scales and 1–2 sporophylls and occur in the axils of helically arranged bracts with forked tips. Ovules are inverted and winged and resemble those of Emporia lockardii and Emporia cryptica. Emporia royalii is compared to other Euramerican walchian Voltziales, and a summary of the Emporiaceae and evolution of Paleozoic conifers is given. This is the fifth species of extinct conifer plants to be reconstructed from the Hamilton Quarry, making it the only Paleozoic locality in the world with numerous conifers all of which have been characterized as complete or nearly complete plants.
Article
Beck, C. B. (U. Michigan, Ann Arbor.) Reconstructions of Archaeopteris, and further consideration of its phylogenetic position. Amer. Jour. Bot. 49(4): 373–382. Illus. 1962.—Two reconstructions, one of a branch bearing the basal part of 3 leaves and the other of the habit, are presented with the evidence upon which they are based. An analysis is made of some features which characterize the ferns. These, and characters of Archaeopteris, are considered in the light of present knowledge of evolutionary trends, and the conclusion is reached that Archaeopteris was neither a primitive fern nor a fern ancestor. Additional evidence is discussed which supports the view that the plant was a progymnosperm.
Article
Phellinus pini var. cancriformans and P. pini var. pini on white fir Abies concolor and balsam fir A. balsamea, respectively, initiated a nonspecific host response in phloem and xylem. Although many barrier zones are formed, often several within one annual ring, the fungus was not effectively compartmentalized. Successful penetration or evasion of barrier zones resulted in canker enlargement by both fungi. Phellinus pini var. cancriformans caused a typical white rot decay of heartwood in white fir whereas P. pini var. pini in balsam fir caused a selective delignification of wood. -from Author
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The size-dependent variations of plant height L and mass M with respect to basal stem diameter D are important to the analysis of a broad range of ecological and evolutionary phenomena. Prior examination of some of the world's largest trees suggests that the scaling relationships L proportional to D-2/3 and M proportional to D-8/3 hold true, ostensibly as functional adaptations for mechanical stability. This concept remains engrained in the literature in the form of null hypotheses (or predictive models), despite numerous examples showing that the 2/3 and 8/3 rules are violated by small and intermediate-sized plants. Here, we present a growth-hydraulic model that provides more accurate and biologically realistic predictions of L and M. This model also sheds light on why L, D, and M scale differently across species and habitats as a result of differences in absolute size.
Article
Describes the architectural model as being the growth pattern which determines the successive architectural phases. This model defines the way by which a plant elaborates its form and is an inherent growth strategy. The architectural unit is interpreted as the specific expression of the model. Reiteration is interpreted as a morphogenetic process which allows total or partial duplication of the architectural unit; the process is called the reiterated complex. Trauma can be the cause; otherwise the phenomenon is known as adaptive reiteration. -S.J.Yates
Article
A diverse assemblage of permineralized conifer remains has been discovered in late Palaeozoic limestones from the mid-continent of North America, near Hamilton, Kansas. Ovulate cones described as Lebachia lockardii sp. nov., support the structural homologies among cordaites, primitive conifers, and modern conifers proposed by Florin, and reveal anatomical features that are remarkably similar to those of many extant conifers. Features not recognized from previously described cones of Lebachia are dorsiventral, bilaterally symmetrical fertile shoots, inverted orientation of the ovules, and the true bilateral symmetry of the ovules. In both morphological structure and cuticular features the specimens show more variability than has previously been documented for a single conifer species and this calls to question the reliability of features previously employed for generic separation of Lebachia from Ernestiodendron. The specimens also provide the first histological evidence for ovule abscission in Palaeozoic gymnosperms, and allow for the interpretation of several aspects of ovule ontogeny and early conifer reproductive biology. -Authors
Article
Two theories advanced on the mode of regeneration of Araucaria are examined in the light of ecological studies made in New Guinea. The first theory postulates that they are `living' fossils dependent for their regeneration on natural catastrophes. According to the second theory, they are integral components of the forest whose regeneration patterns are similar to those of their angiosperm associates. The two species of Araucaria, A. hunsteinii and A. cunninghamii, occur over a wide latitudinal and altitudinal range, chiefly as emergents over several broad-leaf forest types. Optimum development of Araucaria is normally found in forest types whose canopy is reduced in density and height as compared with that of the tropical lowland rain forest. In two of these types studied in detail the size class distribution of Araucaria and the angiosperms is similar. There is an adequate representation of seedlings, saplings and young trees. Autecological studies indicate that conditions favouring seedling development are found in the forest rather than in the open. Seed dispersal is limited to within 60-80 m of the parent tree. It is therefore concluded that the Araucarias are integral components of the forest types in which they occur, and that their capacity to colonize large openings created by natural catastrophes is very limited.
Article
Les, espèces actuelles de Conifères se développent conformément aux modèles de RAUH, MASSART, ATTIMS et MANGENOT. Cependant, les modalités, particulièrement nuancées, de l'expression de la plagiotropie conduisent souvent à des architectures intermédiaires entre plusieurs modèles. Cette originalité est peut-être liée au caractère archaïque de ce taxon.
Article
Resprouting is an efficient means by which woody plants regain biomass lost during disturbance, but there is a life history trade-off that occurs in all disturbance regimes between investment in the current generation through resprouting vs investment in future generations at the same or more distant sites. The relative allocation to resprouting vs seeding in woody plant communities is dictated by the nature of disturbance regimes. Resprouting is the predominant response to the least severe disturbance regimes, but is also a common response in disturbance regimes of high severity, those that destroy most or all above-ground biomass, and which occur at medium to high frequency. The response to disturbance either by resprouting or seeding is dictated by the site's productivity. We present a comprehensive model for relative allocation to resprouting vs seeding across a range of disturbance regimes. Competition between plants that mostly seed vs those that mostly resprout should accentuate differences in allocation along a gradient of disturbance frequency. However the patchy nature of disturbance in time and space, coupled with gene flow among populations undergoing different disturbance regimes, ensures that it is unlikely that either resprouting or seeding will be the sole response in most plant communities at most disturbance frequencies. Additional influences on resprouting in woody plant communities include changes in allocation during the lifespan of individual plants and phylogenetic constraints that are expressed as biogeographic patterns.
Article
A 1,3000 m thick sequence of andesitic to rhyolitic Jurassic volcanic and volcaniclastic rocks crops out in the Estancia El Fénix-Cerro Huemut area of central western Deseado Massif. The andesitic rocks have been assigned to the Bajo Pobre Formation and, in the lower part of the sequence, are interealated with ignimbrites and ash fall tuffs of the Chon Aike Formation of the Bahía Laura Group. Andesitic bodies represent lava flows, breccias, and dykes that cut the acid rocks. This zone is considered to have been a Jurassic effusive center that formed a high in the landscape at the time the ignimbrites at the top of the sequence were erupting. The simultaneity of the acid and the intermediate volcanic processes as well as the geochemical similarity of the products support the proposal to include the Bajo Pobre Formation within the Bahía Laura Group.
Article
Endogenous adventitious buds develop in situ from dedifferentiated parenchyma cells of the trunk-bark in the temperate trees Tilia platyphyllos, Acer pseudoplatanus and Fraxinus excelsior, as well as in the tropical cauliflorous trees Artocarpus integrifolia, Swartzia schomburgkii and Couroupita guinanensis. On aerial roots of Clusia rosea endogenous adventitious buds originate within the proliferated phelloderm beneath lenticels. In Salix alba, Fraxinus excelsior and Terminalia arjuna, exogenous dormant buds are overgrown during secondary growth and engulfed within the bark tissue, so that they give the impression of endogeny. In the leaf axils of young shoots of Araucaria angustifolia, superficial tissue layers divide and form axillary protrusions, which soon become parenchymatic and partly suberized. A few cells at their bases stay meristematic and develop as rudimentary endogenous bud primordia, which persist in the bark for many years. -Author
Article
Extract (1.) In a paper published in the Annals of Philosophy for November and December 1824*, I gave an account of the order and characters of the strata which occur beneath the chalk on the coast of part of the Isle of Wight and of Dorsetshire, and stated some reasons for supposing that a similar arrangement would be found to exist in the interior of England. The principal objects of that paper were; First, to distinguish as a separate group, the series of strata now called the Lower Green-sand;––which had previously been confounded either with the beds containing green particles immediately below the chalk, or with the sandy and ferruginous strata conspicuously exhibited on the coast at Hastings, and then called “Iron-sand.” Secondly, to indicate more clearly than had been done before, the peculiar characters of the group, which succeeds in a descending order to that just mentioned, and is remarkably distinguished by its fossils from the strata immediately in apposition with it, both above and below. For this latter group, which includes the Weald clay, the sand of Hastings, and the Purbeck limestone, and is well entitled to a separate denomination, I have adopted the name of “ Wealden,” proposed by Mr. Martin, in his valuable memoir on the West of Sussex †. (2.) The objects of the inquiries which have produced the following pages were, to compare some portions of the series of strata between the chalk and the Oxford oolite, in different parts of the South-east of
Article
Most leaf axils of most conifers are devoid of any bud-forming potential. Bycontrast, the numerous, apparently blank, leaf axils of the previouslyinvestigated species of the Araucariaceae possess unusual, if not unique,little-differentiated axillary meristems which have neither a bud-likeorganisation nor vascular or provascular connections with the central vascularcylinder. These meristems are exogenous in origin but are buried beneath thestem surface by the formation of localised periderms. Leaf axils fromplagiotropic branch shoots of juvenile and adult morphology and fromorthotropic leaders of adult morphology of the recently described Wollemi pine(Wollemia nobilis W.G.Jones, K.D.Hill & J.M.Allen)have been found to possess a anatomy similar to that previously described forthe Araucariaceae. Thus, W. nobilis is, on the basis ofits leaf axil anatomy, a typical member of the Araucariaceae.
Article
The Wollemi pine (Wollemia nobilis W.G. Jones, K.D. Hill & J.M. Allen) is shown to possess a unique architecture. The model is notdescribed by any of the 23 basic models previously described (Bell 1991), butcan be described by a modified Cook model whereby growth is rhythmic ratherthan continuous. This differs from all other extant members of Araucariaceae,which conform to the models of either Rauh or Massart. The branching andcoppicing habits can both be interpreted as adaptive reiterations. Both thearchitectural model and the two types of adaptive reiteration are advanced orautapomorphic conditions in the Wollemi pine.
Article
The cells of active plant meristems are characterised by their small size, thin walls and a full complement of organelles, most noticeably a large nucleus surrounded by densely staining, little-vacuolated cytoplasm. The axillary meristems of Araucaria cunninghamii Aiton ex D. Don (hoop pine) possess a similar ultrastructure, even though they quickly assume a near complete, potentially permanent quiescence following their detachment from the flanks of the actively dividing apical meristem. However, they differ from metabolically active cells in that those organelles and structures associated with cytokinesis and cell wall formation are either absent (microtubules) or infrequent and in an apparently inactive state (smooth endoplasmic reticulum, non-vesiculating dictyosomes, nuclei with a low heterochromatin to euchromatin ratio). In addition, storage products (starch, lipid globules), usually not present in metabolically active cells, are well developed. In addition to not developing a bud-like organisation, the meristems are also unlike typical axillary buds in that they have no vascular or provascular connections with the axial vascular tissues and are bounded adaxially by a group of thick-walled cells. While these cells constitute a physical barrier around the axillary meristems, they are nucleated and possess numerous simple pits that have a high plasmodesmatal frequency. Thus it appears that the meristems are not physiologically isolated, but are in cytoplasmic continuity with the remainder of the plant.