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Floodplain deposits of the Anfiteatro de Ticó Formation (Baqueró Group, Aptian), in Patagonia (Argentina), are rich in plant remains and contain some of the oldest angiosperm records of southern Gondwana. Many gymnosperm and pteridophyte species, as well as three morphotypes of medium sized angiosperm leaves, have already been described from this unit at different fossiliferous outcrops. We report two new angiosperm morphotypes from the Bajo Tigre locality. Both morphotypes (AT1 and AT2) consist of nano- to microphyllous leaves, nearly elliptic, with untoothed margins and pinnate brochidodromous venation. These leaves mostly exhibit characteristics of a high first or low second rank vein system. This combination of characters is associated with early angiosperm evolution. Morphotype AT1 is similar to one of the brochidodromous morphotypes from the La Cantera Formation (uppermost Aptian), which could be possibly conspecific. Morphotype AT2 has gross features already observed in leaf records from the younger Kachaike Formation (Albian ̶ lower Cenomanian) though they differ in lamina shape and secondary venation features. The angiosperm leaves of the Anfiteatro de Ticó Formation suggest that the early stages of angiosperm evolution in Patagonia had included forms with more than one type of growth habit. [ABSTRACT FROM AUTHOR]

Abstract: Dichotomous rachises bearing Eremopteris golondrinensis Archangelsky foliage in organic connection with probable microsporangiate structures were collected in the mid to late Permian La Golondrina Formation at Laguna Castellanos locality in southern Patagonia. The fertile bodies are receptacles slightly curved distally that bear 4–5 sessile, erect and oblong to elliptic sporangia-like bodies parallel to each other. They are fused laterally and apparently are enveloped by a delicate layer of conjunctive tissue that holds them together and have no visible dehiscence marks. These structures are here interpreted as putative microsporangiate organs. The novel information allows the emendation of the diagnosis of E. golondrinensis by adding new data on the morphology of the frond and its reproductive organs. As the genus Eremopteris has recently been emended excluding this species, a new genus, Kladistamuos with a new combination, K. golondrinensis is proposed here. Kladistamuos is therefore considered to be another SW Gondwana plant fossil of a putative ‘pteridospermous’ affinity, having distally attached fertile organs that differentiate it from the Euramerican species of Eremopteris. [Copyright &y& Elsevier]

Abstract: A scanning and transmission electron microscopy-based ultrastructural study of Arcellites humilisVillar de Seoane and Archangelsky, 2008, from the Kachaike Formation and Piedra Clavada Formation (Albian-Cenomanian) from several localities in Patagonia (Argentina), is presented in this paper. TEM-photographs of thin-sectioned specimens show a thick spore body wall composed of three layers: a thin and dense exine, an inner granular perine sublayer with irregularly disposed small channels and lacunae, and an outer alveolate perine sublayer with channels perpendicular to the external surface. Transverse sections of the A. humilis wall are compared with fossil and extant species of Marsileaceae. We show that the wall ultrastructure is similar in A. humilis, A. santacrucensis, A. disciformis, A. stellatus and Regnellidium upatoiensis. However, the body wall and acrolamella of A. humilis are more similar to those of R. diphyllum Lindman than to those of the Marsilea L. or Pilularia L. species. Water ferns such as members of the Marsileaceae played an important role in aquatic or semi-aquatic niches in Patagonian Cretaceous floras, suggesting that high humidity and temperature prevailed during the Albian-Cenomanian in this region of Argentina. [Copyright &y& Elsevier]

Six angiosperm pollen types studied with SEM are recorded in the Cretaceous (early Aptian) Ticö flora on the basis of material recovered from two localities: Anfiteatro de Tico and Bajo Tigre. Clavatipollenites dominates, with four types described. The other two types, based on single specimens, were referred to Retimonocolpites and to the Anacostia type. Comparisons are made with similar species found in other Cretaceous paleofloristic regions and with other Aptian pollen assemblages from Patagonia. The chlorantha-ceous affinity of Clavatipollenites agrees with known paleobotanical, sedimentological, and paleoclimatical data obtained for the same fossiliferous horizons of the Anfiteatro de Ticö Formation studied here. During the early Aptian, a warm and humid paleoclimatic belt extended to latitudes greater than 60°S in SW Gondwana. This belt is known to have persisted until the late Aptian in southern Patagonia. The angiosperm pollen variety is further underscored by fossil leaves found in two of the horizons studied here, suggesting that angiosperms may have existed during the Barremian in SW Gondwana (Patagonian Province). [ABSTRACT FROM AUTHOR]

Abstract: The araucarian pollen grain Cyclusphaera radiata Archangelsky is emended based on newly discovered material from the Piedra Clavada Formation of Albian age in Santa Cruz province, Argentina. The general morphology and ultrastructure of the pollen were studied by means of transmitted light, scanning, and transmission electron microscopy. C. radiata is discoid with an equatorial thickening and two large opposite apertures, with radial thickenings in one of them and two central apertural occlusive opercula-like structures. Beneath there is a thick amorphous electron-dense nexine. The combination of characters seen in this pollen type is very unusual, and no parallels are known in fossil or extant gymnosperm grains. Functional interpretation of the apertural exine suggests that the radial thickenings and apertural membranes were involved in harmomegthy, the opercula-like structures in germination, and the apertural nexine perhaps as a strengthening layer. A hypothetical pollination mechanism is also presented for C. radiata. The paleobiogeography of this taxon shows that during the Mesozoic, the plants that produced these grains inhabited an extensive area of Gondwana that included South America, Africa, India and Antarctica. [Copyright &y& Elsevier]

Abstract: The schizaeaceous extant genus Mohria has a distribution restricted to South Africa and Madagascar area. Its cicatricose spores are characterised by their large size and muri with hollow longitudinal channels unknown in other schizaeaceous genera. Fossil spores that sometimes have been referred to Mohria lack this typical character and therefore the determinations were discarded. Early Cretaceous (Albian) sediments from Patagonia, referred to the Piedra Clavada Formation of the Austral Basin, contain spores that have the characters now found in Mohria. These fossils are hereby assigned to the new genus Palaeomohria that includes several morphological types. The paleogeographical proximity of South Africa and Patagonia in Southwestern Gondwana persisted from the Permian to the Early Cretaceous, during a time when floras of both regions had significant similarities. In this context, the finding of Mohria-like spores in Patagonia suggests that the distribution of this fern was more extended in the past and became restricted while the continents shifted apart during the Cretaceous/Tertiary. The two living Mohria species may then represent relict taxa of a much more varied and rich group that flourished during the Early Cretaceous in SW Gondwana. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]