MACNBR   00242
MUSEO ARGENTINO DE CIENCIAS NATURALES "BERNARDINO RIVADAVIA"
Unidad Ejecutora - UE
artículos
Título:
An Early Cretaceous zamiaceous cycad of SW Gondwana: Restrepophyllum nov. gen. from Patagonia, Argentina.
Autor/es:
PASSALIA, M,; DEL FUEYO, GEORGINA M; S. ARCHANGELSKY.
Revista:
REVIEW OF PALAEOBOTANY AND PALYNOLOGY
Editorial:
ELSEVIER SCIENCE BV
Referencias:
Lugar: Amsterdam; Año: 2010 vol. 161 p. 137 - 137
ISSN:
0034-6667
Resumen:
<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0pt; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 85.05pt 70.85pt 85.05pt; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> The record of Cycadales in Patagonia begins in the Triassic and extends up to the Oligocene. In this area the group is highly diversified and includes several taxa represented by trunks, leaves and pollen cones. A new cycadalean genus et species, Restrepophyllum chiguoides, form the Aptian Anfiteatro de Ticó Formation, Santa Cruz province, Argentina, is here described. The fossil is a leaf compression with cuticle preserved. Its morphology, anatomy and ultrastructure are studied by means of light and electron microscopy. The leaf is lanceolate, dentate with a prominent midvein and decurrent laterals showing an open venation, simple or dichotomous. The cuticle is hypostomatic, and the abaxial is thinner than the adaxial. The stomata are irregularly distributed and indistinctly oriented between veins. They are haplocheilic, imperfectly to completely dicyclic; the suprastomatal aperture is raised over the epidermis and the guard cells are sunken. Scattered hairs and crystalliferous idioblasts are also observed. The epidermal cells show three layers, the outer and inner are lamellate and the middle is granulate. This novel cycad leaf is compared with similar fossil leaves from Gondwana and Euroamerica and also with similar extant cycad leaves. Based on the general morphlogy and the cuticle main characters Restrepophyllum chiguoides is assigned to the family Zamiaceae; moreover it is more closely related to the living Zamia (Chigua) restrepoi (D. Stevenson) Lindstrom than to any other member of the Cycadales. The paleophytogeographic evidence suggests a southamerican origin of Zamia/Chigua and a further migration to northern latitudes. This new type of leaf also suggests the putative existence of a Chigua clade that may be traced back to the Early Cretaceous when two cycadalean families, Zamiaceae and Stangeriaceae, were well established in Patagonia.