An arrowhead fruit from the late Miocene of Argentina

ROBLEDO, JUAN M.; CONTRERAS, SILVINA A.

Madrid

Congreso; 2nd Palaeontological Virtual Congress; 2020

A fossil achene (fruit) related to Sagittaria sp. wasfound in late Miocene sediments (Palo PintadoFormation) from the northwestern of Argentina.The sedimentary succession, 1200 m thick,crops out on both borders of the Calchaquí River(southern of Salta Province), between 25º41?01?S? 66º07?55?W and 25º40?59?S ? 66º05?49?W. ThePalo Pintado Fm. consists of sandstones alternatingwith siltstones and subordinately with conglomerates;it belongs to the Payogastilla Group,which is included between the Angastaco and theSan Felipe Formations.The achene originates from the basal portion ofthe Formation, at the Quebrada El Estanque locality.The fossil was preserved as an impressionthat shows 1 wing on each face and the beak ofthe achene ascending. It was also possible to observethe attachment scar to the bottom and thecurved seed inside of the fruit. The whole acheneis 2.3 mm in length x 1.1 mm in width, while theseed is 0.6 mm in length x 0.3 mm in width.The arrowheads grow in freshwater and slowcurrent wetlands (i.e., swamps and marshes).During the late Miocene, these plants wouldcoexist with other aquatic plants (i.e., Cabomba,Salvinia and Mayaca), previously recordedfrom the sediments of the Palo Pintado Formationattesting the great fossil diversity of aquaticplants preserved in its sediments. This reportrepresents the first record of an Alismataceaefossil in South America.