An arrowhead fruit from the late Miocene of Argentina

ROBLEDO, JUAN MANUEL; CONTRERAS, SILVINA A.

Congreso; 2nd Palaeontological Virtual Congress; 2020

A fossil achene (fruit) related to Sagittaria sp. was found in late Miocene sediments (Palo Pintado Formation) 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 alternating with siltstone and subordinately with conglomerates; it belongs to the Payogastilla Group, which is included between the Angastaco and the San Felipe Formations. The achene originates from the basal portion of the Formation, at the Quebrada El Estanque locality. The fossil was preserved as an impression that shows 1 wing on each face and the beak of the achene ascending. It was also possible to observe the attachment scar to the bottom and the curved seed inside of the fruit. The whole achene is 2.3 mm in length x 1.1 mm in width, while the seed is 0.6 mm in length x 0.3 mm in width. The arrowheads grow in freshwater and slow current wetlands (i.e., swamps and marshes). During the late Miocene, these plants would coexist with other aquatic plants (i.e., Cabom-ba, Salvinia and Mayaca), previously recorded from the sediments of the Palo Pintado Formation attesting the great fossil diversity of aquatic plants preserved in its sediments. This report represents the first record of an Alismataceae fossil in South America.