Maytenoxylon (Celastraceae) in the Early Danian Salamanca Formation, Patagonia, Argentina

BREA, M.; RAINGEMBORN, M.S.; IGLESIAS, A.

Buenos Aires

Congreso; XII Congreso de la Asociación Paleontológica Argentina; 2021

Asociación Paleontológica Argentina

The early Danian Salamanca Formation crops out in several areas of the Golfo San Jorge Basin, Patagonia. Among its southernmost exposures there is the Laguna Manantiales locality, in the northern Santa Cruz Province. In this area, the Salamanca Formation is condensed in a ~17 m thick section and composed of glauconitic sandstones and siltstones of estuarine paleoenvironments. It overlies the Baqueró Formation (Lower Cretaceous) and conformably underlies pedogenizedcontinental strata of the Río Chico Group (Paleocene??Eocene). The Salamanca Formation uppermost silty facies preserve leaf compressions and cuticles, while marine fauna has been found in the basal section of the unit. In the middle section, within glauconitic sandy facies, silicified woods with very good anatomical preservation have been recovered. The previously studied microflora has indicated to be diverse and compositionally dissimilar in relation to other areas in the basin, with an important continental source. In this contribution, we describe a wood piece (more than 20 cm in diameter) with a particular combination of character: simple perforated ray cells and dimorphic fibres in parenchymatous bands alternating with other normal fibres, distinctive of Celastraceae. The presence of wood diffuse-porous; distinct growth rings; vessels mainlysolitary, occasionally in radial multiples and in clusters; exclusively simple perforation plates; non-septate and septate fibres; axial apotracheal and paratracheal parenchyma (diffuse, scanty paratracheal and vasicentric); and heterocellular rays; all links the fossil to the genus Maytenoxylon Franco (that is related to the extant genus MaytenusMolina). Maytenoxylon is known from a single small twig (less than 2 cm in diameter) specimen from the late Miocene in northeastern Argentina.Maytenus is now widely distributed in the Americas, Africa, Indian Ocean margins, Micronesia, and Australasia, with species mostly adapted to ever-wet conditions, but others linked to gallery forests in marked dry season climates. On the other hand, the Celastraceae are pantropical with Upper Cretaceous to Paleogene fossil records in the Northern Hemisphere. The new specimen corresponds to the oldest record for the family in the Southern Hemisphere and the oldest record ofMaytenoxylon, thereby rooting the whole lineage that includes Maytenus. The new early Paleocene Patagonian record suggests a revision of the Northern Hemisphere as presumed centre of origin and dispersal for the Celastraceae.