Una nueva Podocarpácea fértil (Coniferal) del Cretácico inferior de Patagonia

AMEGHINIANA (Impact Factor: 1.22). 01/1990; 27(1).


The new genus, Morenoa fertilis from the early Cretaceous beds of the Baqueró Formation (Santa Cruz Province, Argentina) is here described. This conifer is referred to the family Podocarpaceae on account of its vegetative as well as reproductive male organs that include bisaccate pollen grains. The ultrastructure of the leaf cuticle (of the Elatocldus type) and the pollen grains (of the Podocarpidites type) was studied with transmission electron microscopy. Comparision with fossil and extant taxa of the family are also made, including the other three fossil genera known in fertile state from the same formation. The excellent preservation of the closed pollen sacs permitted the recognition of still inmature tetrads and a high inner content of Ubisch bodies. Epiphyllous fungi were also recognized on the leaf epidermis suggesting a mild and humid climatic regime.Some degradation of the leaf cuticles was observed, possibly related in part to fungal activity.

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    • "The studies on the fossil leaf cuticular ultrastructure using transmission electron microscopy started with the pioneer work of Archangelsky et al. (1986). Since then, the leaf cuticular ultrastructure is known for a number of fossil taxa or groups, including pteridosperms (Taylor et al., 1989; Baldoni and Barale, 1996; Labe and Barale, 1996; Maheshwari and Bajpai, 1996; Bajpai, 1997; Guignard et al., 2001), bennettitaleans (Barale and Baldoni, 1993; Villar de Seoane, 2001), cycadaleans (Artabe and Archangelsky, 1992; Villar de Seoane , 1997b), ginkgoaleans (Taylor et al., 1989; Villar de Seoane , 1997a; Guignard and Zhou, in press), czekanowskialeans (Zhou and Guignard, 1998), as well as conifers (Archangelsky and Taylor, 1986; Archangelsky et al., 1986; Del Fueyo et al., 1990; Barale et al., 1992; Guignard et al., 1998; Villar de Seoane, 1998; Zhou et al., 2000). Most of the cuticle is marked [Vol. "
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    ABSTRACT: Transmission electron microscope studies of three types of pollen grains, i.e. Balmeiopsis, Callialasporites and Araucariacites, found in Early Cretaceous strata of Patagonia have shown that they possess several similar ultrastructural patterns. The nexine is uniformly lamellate and the sexine is composed of granular to vermiculate sporopollenin units. Sometimes granular elements may form ill defined collumella-like structures oriented radially near the surface of the grains. Balmeiopsis has a thickened equator that may contain a small empty space, while Callialasporites has rudimentary sacci formed by the separation of both exine layers. However, the inner surface of the sexine does not form an endoreticulum and there are no thin sporopollenin threads that fill the cavities between nexine and sexine. This type of primitive saccus is different from the eusaccate or protosaccate types found in gymnosperms. Araucariacites has the thinnest exine of the three and no equatorial thickening or rudimentary sacci. All three types belong to conifers and comparisons are made with fossil and extant members of the Podocarpaceae and Araucariaceae, two families that are now represented in the Andean region.
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    ABSTRACT: The ultrastructure of several in-situ bisaccate pollen grains produced by Triassic members of the Voltziales is described and illustrated. These include five species of Willsiostrobus (W. willsii, W. ligulatus, W. rhomboidalis, W. cordiformis, W. denticulatus), in addition to Darneya dentata and Sertostrobus laxus. All of the grains are protosaccate with ektexine elements extending from the inner surface of the saccus wall to the nexine. White line nexine lamellae show some uniformity in thickness among species suggesting a basic substructure to the exine. Sporoderm ontogeny in these grains is compared with that of modern bisaccate conifer pollen, and the development and function of the protosaccus are discussed.
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