Basal eudicot leaves from the latest Aptian earliest Albian? of Patagonia

LLORENS, M.; CÉSARI, S.N.; PASSALIA, M.; VERA, E.I.; PEREZ LOINAZE, V.S.

San Luis

Congreso; Reunión Anual de Comunicaciones de la Asociación Paleontológica Argentina; 2017

Asociación Paleontológica Argentina, Universidad Nacional de San Luis

Eudicots diverged early in the evolution of flowering plants and represent more than 70% of the extant angiosperm species. The fossil record seems to indicate that basal eudicots were already present and relatively diverse in low-latitudes by the latest Barremian-earliest Aptian. In Patagonia, the oldest and accurately records of this clade correspond to tricolpate pollen grains from the early Albian. An assemblage of putative basal eudicots (aff. Ranunculales) has been recognized from the uppermost levels of Punta del Barco Formation (Baqueró Group) at Meseta Baqueró locality, Santa Cruz Province, Argentina (Paleobotanical Collection at Museo Argentino de Ciencias Naturales Bernardino Rivadavia, BAPb 13400-13407). A radiometric age previously obtained in the same stratigraphic section about fourty meters below suggests that the assemblage may be close to the latest Aptian?earliest Albian limit. It consists of imprints of nanophyll leaves, with a broad petiole, deeply dissected blade, rounded sinuses and craspedodromous venation. These leaves are mostly preserved disarticulated but also attached to a short stem suggesting that they belonged to a small, probably herbaceous plant. By the indistinct disposition of the fossil plants within the stratum it is possible that they were found in situ, buried by the fall of volcanic ash. The fossil evidence of Ranunculales-like leaves is as old as the earliest records of eudicots. Among them, there are forms recognized in the late Aptian ? earliest Albian of North America, and from the middle Albian of Europe, both records strongly comparable to those of Meseta Baqueró.