Rubén Cúneo

Coniferous Ovulate Cones from the Lower Cretaceous of Santa Cruz Province, Argentina

Two types of coniferous ovulate cones borne on leafy twigs are described from the Lower Cretaceous Kachaike Formation in Santa Cruz Province, Argentina. The fossils are impressions and compressions with well‐preserved cuticles. Morphology, anatomy, and ultrastructure were studied using LM, SEM, and TEM. Ovulate cones were assigned to Athrotaxis ungeri (Halle) Florin of the taxodiaceous Cupressaceae and Kachaikestrobus acuminatus gen. et sp. nov. of the Cheirolepidiaceae. This latter taxon is characterized by terminal elongate cones borne on twigs with Brachyphyllum leaves, cone scales densely and helically disposed, broad bracts with an accentuated acuminate apex fused at their bases to eight‐lobed ovuliferous dwarf shoots shorter than the bracts, and an epimatium covering at least one ovule that has preserved only the outer integument and the megaspore membrane. The ultrastructure of the bract and ovuliferous dwarf shoot cuticle is composed of three layers. Comparisons of K. acuminatus with other cheirolepidiaceous ovulate cones showed closest resemblance to Hirmeriella muensteri (Schenk) Jung. These Patagonian cone scales appear to have some of the most ancestral characters in the family. By the early Albian, A. ungeri and K. acuminatus were part of a plant assemblage dominated by ferns and a few subordinate angiosperms. The finding of A. ungeri in the Kachaike Formation extends its distribution during the Lower Cretaceous in Patagonia. These fossils also show that at that time, the taxodiaceaous Cupressaceae and the Cheirolepidiaceae still were well represented in southern South America.

Triassic floras of Antarctica: Plant diversity and distribution in high paleolatitude communities

ABSTRACT Continental Triassic sequences in Antarctica are among the most continuous and best represented in Gondwana. Triassic fossil plants have been collected sporadically from Antarctica since the beginning of the twentieth century, but our knowledge of the vegetation during this time has dramatically increased during the last three decades. Here we review the fossil record of Triassic plants as representatives of natural groups from sites along the Transantarctic Mountains, using the fossils as evidence for successive vegetational changes through the Triassic, taking into account that these plant communities were living under particular high-latitude (70° or higher) paleoclimatological conditions, including a polar light regime. Even though our knowledge of the Triassic floras of Antarctica is still incomplete, this survey shows that these floras were remarkably diverse. Lycopsids, equisetaleans, ferns, seed ferns, ginkgoaleans, and conifers were major components of the landscape in Antarctica during this time. The diversity of gymnosperms is exceptional, with almost every major clade of seed plants present, despite the high paleolatitude; however, each clade is often represented by only one or a few genera. The occurrence of permineralized peat, along with compression-impression floras, has increased our knowledge of the morphology, reproductive biology, and evolution of many of the plants in these floras. In general, floral changes in Antarctica during the Triassic can be recognized elsewhere in Gondwana, especially in South America, although a strict correlation based on macrofossils is still not possible. Thus, this contribution represents the first attempt to bring together information on Triassic floras from continental Antarctica (excluding the Antarctic Peninsula) within a biostratigraphic framework and thereby to compare these floras with those from lower latitudes.

Polyspermophyllum, a new Permian gymnosperm from Argentina, with considerations about the dicranophyllales

Abstract Polyspermophyllum gen. nov., a new primitive seed plant, is described. The material was found in early Permian strata, Chubut province, Argentina. It includes twigs that bear long, linear, once dichotomized leaves with two marginal longitudinal grooves in a compact helix. The fertile structures have proximal portions similar to sterile leaves and ultimate trusses with axes being several times dichotomized (or trichotomized) and bearing subsphaerical bodies composed of a distally curved segment (peduncle) enclosing a single oval structure (ovule). The vegetative organs ar closely comparable to taxa that have been referred to different genera while the fertile organs resemble those of the late Palaeozoic Trichopitys and Dicranophyllum . It is suggested that the Dicranophyllales are a primitive order of seed plants, including two families, the Trichopityaceae and the Dicranophyllaceae, in which Polyspermophyllum is placed. Possible relationships with Paleozoic pteridosperms and Mesozoic ginkgophytes are discussed, especially with regard to a putative “pre-ginkgophytic” line, already established during the Carboniferous in all palaeofloristic regions, viz. Angara, Equatorial Belt and Gondwana.

Leaf Architecture and Epidermal Characters of the Argentinean Species of Proteaceae

We describe the leaf architecture (venation and cuticle) of the eight extant species of Argentinean Proteaceae and discuss the diagnostic value of the characters. Proteaceae leaves are characterized by several architectural features. The leaves are ovate to oblong‐lanceolate or elliptic, with coriaceous texture, and have normal‐marginal petiole; the apexes vary between acute and obtuse, while the bases are acute to decurrent. They have pinnate simple first‐category venation, lack agrophic veins, have well‐developed areoles, and have two‐or‐more‐branched freely ending ultimate veins. Furthermore, all species have brachyparacytic stomata restricted to the abaxial surface of the leaves and multicellular trichomes. Cuticle features that differ among the species are the presence or absence of glands and papillae, and stomata size in relation to epidermal cell size. Architectural and cuticular features are also useful for differentiating tribes, subtribes, genera, and species within the subfamily Grevilleoideae. A key for the identification of Argentinean Proteaceae based only on leaf and cuticle characters is presented.

FIRST REPORT OF FEEDING TRACES IN PERMIAN BOTRYCHIOPSIS LEAVES FROM WESTERN GONDWANA

Abstract The genus Botrychiopsis consists of leaves with substantial heteromorphism, present in late Paleozoic Gondwanan floras. The genus is recorded in paleofloras from Australia, India, South Africa, Brazil, and Argentina, and occurs from the latest Mississippian to the early Permian. Here, we report and analyze the first record of plant-insect interactions found in the Botrychiopsis-type leaves from the basinal deposits of Permian Argentina and Brazil. The samples are from three different Permian deposits: Arroyo Totoral, Bajo de Véliz (Argentina), and Morro do Papaléo (Brazil). Evidence of insect-plant interactions was present in only eight of 154 specimens analyzed. We found evidence of margin and hole feeding damage made by insects. This represents the first evidence of plant-insect interactions in Botrychiopsis leaves from Permian Gondwanan deposits. The occurrence of herbivory only on the Permian species B. plantiana may indicate that consumption of these leaves began during this interval, not in the Carboniferous, as occurred with Cordaites leaves.

Reconstruction and Phylogenetic Significance of a New Equisetum Linnaeus Species from the Lower Jurassic of Cerro Bayo (Chubut Province, Argentina)

Abstract. We describe Equisetum dimorphum sp. nov. from the Lower Jurassic of Chubut Province, Patagonia, Argentina. This new species Is based on fertile and vegetative remains preserved as Impressions of stems, leaves, strobili, transversal sections of the stems showing their anatomy, and terminal pagoda-like structures. The fine-grained sedimentary matrix also preserved detailed Impressions of epidermal features. The morphological characters allow a whole-plant reconstruction and assignment to Equisetum. Equisetum dimorphum sp. nov. shows a mosaic of morphological characters that are commonly present in other Mesozoic forms and representatives of the two extant Equisetum subgenera, e.g., sunken stomata and a blunt strobilus apex. Compared to other well-known Mesozoic equisetalean taxa, Equisetum dimorphum sp. nov. appears to be most closely related to a group of Jurassic Equisetum-like plants including Equisetum laterale Phillips and Equisetites ferganensis Seward. Additional evidence for the morphological stasis of the fertile and vegetative organs of extant horsetails is supplied with this new material, adding further support to the hypothesis that the extant horsetails are a successful group that has undergone only little morphological changeover time and that has been present, nearly worldwide, since Jurassic times.

Exploring the interior of cuticles and compressions of fossil plants by FIB-SEM milling and image microscopy

We present the first study of cuticles and compressions of fossil leaves by Focused Ion Beam Scanning Electron Microscopy (FIB‐SEM). Cavities preserved inside fossil leaf compressions corresponding to substomatal chambers have been observed for the first time and several new features were identified in the cross‐section cuts. These results open a new way in the investigation of the three‐dimensional structures of both micro‐ and nanostructural features of fossil plants. Moreover, the application of the FIB‐SEM technique to both fossils and extant plant remains represent a new source of taxonomical, palaeoenvironmental and palaeoclimatic information.

Morphometric variables can be analyzed using cladistic methods: A reply to Adams et al.

It is apleasure to respond toAdamset al. (inpress). Because shape characters are often at least partially the results of heritable variation, there is no theoretical basis to discard them as phylogenetic markers (Rae,1998). Thus,weseeAdamset al.’s critiqueofour recent research (González-José et al., 2008) as largely methodological. Adams et al. focus on some potential methodological pitfalls that, in their view, do not support our proposal that our approach offered “an improvement over alternative methods” Adams et al. (in press: 1). Here, we acknowledge some of the points raised by Adams et al. (in press), especially the problem of sensitivity to rotation. However, when compared to previous alternative methods, our paper offered advances in addressing some theoretical issues, such as the inclusion of modularity and its relation to the character concept. In our view, this should be considered in future research in phylogenetics, particularly as methodologies improve. Adams et al. focus their criticism on the fact that there is no straightforward method to derive meaningful characters from morphometric variables. We are well aware of this issue, and acknowledged it in the Methods section of our paper, asserting that “principal components have a biological meaning, as orthogonal dimensions of variance, even though that is not equivalent to the meaning of a character” (González-José et al., 2008: Supplementary Information). In other words, Adams et al. (in press) correctly claim that rank-ordering of character states performed during principal component analysis is sensitive to the additions or deletions of taxa from the data matrix. They present a schematic representation of a rotational effect (Adams et al., in press: Fig. 1), showing that an alteration of the sample’s composition might significantly alter the orientation of variance-optimized shape traits. In this context, we fully acknowledge the significance of the criticism that our method is sensitive to rotation. Even though this is a crucial aspect, we note that new methods invariant to rotation are being developed based on finding, for each of the landmarks, the ancestral positions that minimize the distance between the ancestor anddescendant points along the tree (Catalano et al., 2010; Goloboff and Catalano, in press). We are well aware that such approaches still require considerable research and development, but we also believe that they offer advances over the practice of atomization of complex phenotypes into many arbitrary “characters” and forcing the discretization of naturally continuous traits. In summary, we validate Adams et al.’s (in press) cautions regarding the effects of rotation. Indeed, the use of Manhattan distances and its sensitivity to rotation is the most fundamental

FIB analysis of fossils plant remains: Technical and experimental aspects

We present a comprehensive study about the technical aspects of the application of focused ion beam (FIB) to the study of cuticles and compressions of fossil leaves. The technique allowed us to cross section and image fossil coalified plant remains with a spatial resolution within the 10 nm range, far higher than any other method employed so far. At various stages of the milling process, we observed significant gallium redeposition on the trench walls, particularly pronounced in the case of cavities. These highly unwanted artefacts can be greatly reduced, but not wholly eliminated, by lowering either or both the beam current and acceleration voltage; nevertheless, great care is needed when interpreting cross-sectional images.