María Jimena Franco

Leños Fósiles De Leguminosas de la Formación Ituzaingó, Entre Ríos, Argentina: Implicancias Paleoecológicas y Paleobiogeográficas

Abstract. FOSSIL WOODS OF LEGUMINOSAE FROM THE ITUZAINGÓ FORMATION, ENTRE RÍOS, ARGENTINA: PALEOECOLOGICAL AND PALEOBIOGEOGRAPHIC IMPLICATIONS. The family Fabaceae is among the best represented in the fossil record of the Cenozoic of Argentina and in particular of the Ituzaingó Formation. This paper describes four types of permineralized by silicification woods related to this family, Menendoxylon vasallensis Lutz, Anadenantheroxylon villaurquicense Brea, Aceñolaza y Zucol emend., Prosopisinoxylon americanum sp. nov. and Gleditsioxylon paramorphoides sp. nov. Two new fossil species were recognized and the diagnosis of Anadenantheroxylon villaurquicense was amended. The specimens were found in the Ituzaingó Formation (Pliocene—Pleistocene), Entre Rios, Argentina, and have only preserved the anatomy of secondary xylem. Some anatomical features were related with the presence of a seasonal and dry climate. From paleogeographic and paleoecological features of distribution of most related extant genera, it is proposed that during the Pliocene—Pleistocene developed a heterogeneous environment characterized by having arboreal elements linked to Chaco, riparian and component of Seasonally Dry Tropical Forests (SDTF). The presence of the studied fossil wood in the Ituzaingó Formation (Pliocene—Pleistocene) in the Paraná Basin shows a rich flora linked to SDTF southermost of its current distribution, supporting the hypothesis that had a greater extent in South American continent during the late Cenozoic.

Maderas fósiles de Lauraceae de la Formación Ituzaingó (Plioceno - Pleistoceno), cuenca del río Paraná, Argentina

Fossil woods of Lauraceae from the Ituzaingo Formation (Pliocene - Pleistocene), Parana river basin, Argentina. Six fossil woods with Lauraceae affinity from the fluvial sediments of the Ituzaingo Formation were described. The specimens were found in Hernandarias and Curtiembre fossiliferous localities, in Entre Rios, Argentina. Combination of characters present in the specimens allowed us to distinguish the Lauraceae from other dicotyledonous families and to assign them to two different fossil species: Laurinoxylon artabeae (Brea) Duperon-Laudoueneix & Duperon 2005 and a new genus. The Vulnerability Index (V) and Mesomorphy Ratio (M) were calculated, and they indicated that the two species were adapted to wet environments. Comparison with the nearest living relatives suggests the existence of a flora linked to a watercourse, with riparian components.

First record of fossil woods from the Mariño Formation (Miocene), Mendoza, Argentina and their palaeobiogeographical implications

The first Miocene records of silicified fossil woods from the Mariño Formation, Potrerillos area, Andes Precordillera, Mendoza province, Argentina are described. Rhaphithamnoxylon artabeae gen. et sp. nov. is described as the first fossil wood referable to Verbenaceae from Argentina. This new fossil species is related to extant Rhaphithamnus Miers, sharing the following anatomical features: diffuse porosity, distinct growth ring boundaries, numerous small to very small vessels, commonly in radial multiples, 1–3 seriate rays, and heterocellular and scarce paratracheal axial parenchyma. Rhaphithamnus contains only two extant species: R. spinosus (A.L. Juss.) Moldenke, which occurs in the Valdivian forests of Chile and Argentina, and R. venustus (Philippi) Robinson, which is endemic to the Juan Fernández Islands. Representatives of Verbenaceae are distributed predominantly in the Americas from Patagonia (Argentina) to Canada, and they are inferred to have originated in South America. The fossil wood described herein provides new age and geographical constraints on the raphithanoid lineage within Verbenaceae. Other fossil woods recorded from the Mariño level are retained under open nomenclature, as they possess a combination of mostly solitary broad vessels, and smaller vessels in radial multiples or in clusters, with numerous, vasicentric to confluent axial parenchyma, and heterocellular, high rays. Thus, they have features akin to dicotyledonous lianas or vine-like or small shrub species.

Small Celastraceae and Polygonaceae twigs from the Upper Cenozoic (Ituzaingó Formation) of the La Plata Basin, Argentina

Abstract Two new wood types from the Late Cenozoic of the Ituzaingó Formation, La Plata Basin, Northeast Argentina add to our knowledge of South American Cenozoic plants. The materials were preserved by siliceous cellular permineralization, and they were prepared for microscopic examination by surface polishing and in thin sections. The anatomy of these new species was described. The relationship and comparison with the nearest living relatives (NLRs) are discussed. Maytenoxylon perforatum Franco gen. and sp. nov. is described as the first fossil wood referable to Celastraceae from South America. This new fossil species is related to extant Maytenus Molina. The other fossil twig, Ruprechtioxylon breae Franco sp. nov., has features of the Polygonaceae family and particularly resembles the extant specie Ruprechtia laxiflora Meisn. The occurrence of these fossil woods in south-eastern South America suggests that a relatively warm and dry to seasonally dry climate prevailed over this region of Gondwana during the Upper Cenozoic. It also provides new evidence for the hypothesis of the more wide distribution of Seasonally Dry Tropical Forest (SDTF) during the Upper Cenozoic.