Liliana Villar de Seoane

Comparative study of extant and fossil conifer leaves from the Baqueró Formation (Lower Cretaceous), Santa Cruz Province, Argentina

Abstract A comparative study of fossil leaves of Tomaxellia biforme Archangelsky, 1966, which belong to the family Cheirolepidiaceae, and those of Athrotaxis ungeri (Halle) Archangelsky, 1963, Sequoia sempervirens (D. Don) Endlicher and Taxodium mucronatum Tenore, fossil and extant species, respectively, included within the family Taxodiaceae is presented, using light microscopy (LM) and scanning and transmission electron microscopy (SEM and TEM). The fossil materials occur in the Baquero Formation (Lower Cretaceous), Santa Cruz Province, Argentina. The morphological, anatomical and ultrastructural analyses indicate great similarities between the Cheirolepidiaceae and Taxodiaceae leaves.

Early Cretaceous riparian vegetation in Patagonia, Argentina

Early Cretaceous riparian vegetation in Patagonia, Argentina. An autochthonous plant as-semblage found at the Bajo Grande locality, Anfiteatro de Tico Formation, Baquero Group, Early Aptian of Santa Cruz province, Argentina, is described. Sedimentological data show an alternation of sandstone and lime-stone, with recurrent fossil levels associated to a fluvial system. The frequent flood in areas close to the levee had an influence on the vegetation growing along the banks of the channels. A plant assemblage composed of Ricciopsis grandensis nov. sp. (bryophyte), Adiantopteris tripinnata nov. sp., Schizaeaceae pinnules (ferns), and the gnetalean fructification Ephedra verticillata nov. sp. was found in this paleoenvironment. The taphonomical studies suggest that the plant assemblage was autochthonous, and it grew and was buried in an area near a levee. This result is congruent with environmental data provided by living representative of the fossil taxa analyzed.

Equisetites pusillus sp. nov. from the Aptian of Patagonia, Argentina

Compressions of fertile equisetacean branches belonging to the new species Equisetites pusillus are described using light microscopy. The specimens were collected at the Estancia Bajo Tigre locality in strata referred to the Anfiteatro de Tico Formation, Baquero Group (Aptian) from the Santa Cruz province, Argentina. The fertile stems bear an oval and solitary terminal cone with spores. The spores are alete, circular and without elaters. Equisetites pusillus sp. nov . is compared with other fossil equisetacean taxa from Argentina and elsewhere. The spores are compared with those of two extant Equisetum species from Argentina, and also with other mesozoic taxa. The compressions were found in sediments rich in organic matter, deposited in shallow waters surrounded by environments colonized by sphenophytes, ferns and bryophytes. This type of landscape was frequent during the Aptian originating a common type of deposit (lenticular) in the Anfiteatro de Tico Formation.

Cuticle ultrastructure of the Bennettitales from the Anfiteatro de Ticó Formation (Early Aptian), Santa Cruz Province, Argentina

Abstract Cuticle ultrastructure analysis of Dictyozamites crassinervis Menendez, Otozamites parviauriculata Menendez, Zamites decurrens Menendez, Ptilophyllum longipinnatum Menendez, Pterophyllum sp. , Cycadolepis coriacea Menendez and Williamsonia bulbiformis Menendez (receptacle and bract) was made using transmission electron microscopy, allowing the extension of the original descriptions. The specimens occur in the Anfiteatro de Tico Formation, Baquero Group (Early Aptian), Santa Cruz Province, Argentina. Each leaf species and the scale-leaf were compared with other bennettitalean taxa from the Baquero Group and the Springhill Formation (Early Cretaceous of Patagonia). The comparison was extended to fossil and extant Cycadales. The ultrastructural analysis has indicated a close relationship among the following taxa: Dictyozamites , Otozamites and Zamites ; Ptilophyllum and Pterophyllum ; and Cycadolepis with the bract of Williamsonia . The ultrastructural comparison between the specimens found in the Baquero Group and the Springhill Formation has demonstrated the occurence of different processes of fossilization.

Leaf Cuticle Anatomy and the Ultrastructure of Ginkgoites ticoensis Archang. from the Aptian of Patagonia

The leaf cuticle of the Ginkgoites ticoensis Archang. type material from the Aptian Anfiteatro de Ticó Formation in Patagonia, Argentina, is fully characterized with additional scanning and transmission electron microscopic observations. Many new anatomical and ultrastructural cuticular features are identified in the four-lobed leaf of G. ticoensis: the leaf shows a hypostomatic and papillate laminae, straight and pitted anticlinal and granulate periclinal walls, actinocytic stomata with between five and seven papillate, striate subsidiary cells, and guard cells with anticlinal smooth walls. The TEM studies on ordinary epidermal cells, papillae, subsidiary cells, and guard cells reveal general ultrastructural features of Ginkgoaceae: an outer polylamellate layer A made with A1 and a granular inner layer A2; A1 with an upper part A1U with continuous and straight translucent lamellae; a lower part A1L with significantly disrupted and waving translucent lamellae; and the fibrillar cuticular layer B1 as the innermost part. Ten ultrastructural characters are detailed and ranked by the use of confidence intervals based on 30 statistical measurements. A three-dimensional reconstruction of the cuticle is also provided. Because of the anatomical and ultrastructural fine details shown in the G. ticoensis cuticle, new elements are given to suggest its probable family affinity and to enhance the specificities of Ginkgo and Ginkgoites.

Estudios cuticulares de Ginkgoites Seward del Cretácico Inferior de Patagonia

Cuticular studies of Ginkgoites Seward from the Lower Cretaceous of Patagonia. The anatomy and ultrastructure of the leaf cuticles of Ginkgoites ticoensis Archang. and G. skottsbergii Lund. is studied. Both taxa were collected in Santa Cruz province, G. ticoensis from the Anfiteatro de Tico Formation (Aptian) and G. skottsbergii from the Kachaike Formation (Albian). The cuticular studies were made by means of electronic microscopy (SEM, TEM). These observations showed that G. ticoensis has hypostomatic leaves, papillae on both cuticles, and monocyclic stomata with 5-7 papillate subsidiary cells; while G. skottsbergii presents amphistomatic leaves, and monocyclic to dicyclic stomata with 6-8 subsidiary cells partially papillate. At the ultrastructural level the cuticular membrane has three layers, which are clearly distinct in both species. Comparisons with the leaf cuticle of other ginkgoalean taxa are also made.

Ginkgoites patagonica (Berry) comb. nov. from the Eocene of Patagonia, Last Ginkgoalean Record in South America

Premise of research. The ginkgophytes are an ancient group of gymnosperms with a long history starting during the late Paleozoic and reaching the present with the unique species Ginkgo biloba L. In order to better characterize the early and middle Eocene (ca. 52.2 and 47.7 Ma) leaf species Ginkgo patagonica Berry from northwest Patagonia, Argentina, new specimens were studied, focusing on their morphological and anatomical characters. Methodology. The specimens were studied with LM, epifluorescence, SEM, and TEM. Pivotal results. The diagnosis of the species Ginkgoites patagonica comb. nov. is enlarged to include anatomical and ultrastructural epidermal characters. Herein, the species Ginkgo patagonica is shown to have characteristics that clearly separate it from the genus Ginkgo L., and it is therefore recombined to the genus Ginkgoites Seward. Conclusions. Eocene Ginkgoites patagonica was present in plant communities, and it is the last representative of a still poorly understood southern ginkgophyte lineage that was distinct from the ancestors of G. biloba of the Northern Hemisphere.

Estudios palinológicos del Grupo Baqueró (Cretácico Inferior), provincia de Santa Cruz, Argentina: X. Polen de Gymnospermae y Apéndice Final

Palynological studies from the Baquero Group (Lower Cretaceous), Santa Cruz Province, Argentina. X. Pollen of Gymnospermae and final Appendix. In the present paper, the palynological study of Gymnosperm pollen from the Anfiteatro de Tico Formation is completed. The material was collected in Anfiteatro de Tico and Estancia Bajo Tigre localities from the Santa Cruz Province. The Anfiteatro de Tico Formation, the basal unit of the Baquero Group, has an Aptian age. The study includes 9 genera and 11 species. One new genus ( Ticoites ), and three new species ( Araucariacites spinosus , Ephedripites acutus and Ticoites gamerroi ) are described. Also, Dilwynites granulatus Harris is cited for the first time in the Lower Cretaceous of Argentina. This paper, the final contribution of the series, indicates the presence of a wide variety of gymnosperms, a group that nowadays is almost extinct in Patagonia due to large recurrent climatic changes that have occurred since the Aptian.