Mesofossils from the Maastrichtian of the La Colonia Formation, Chubut, Argentina

DE BENEDETTI, F.; ZAMALOA, M.C.; GANDOLFO, M.A.

General Roca, Río Negro

Encuentro; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2023

Asociación Paleontológica Argentina

The record of mesofossils is remarkably scarce and comes mainly from the Northern Hemisphere. Deposits of the La Colonia Formation have yielded a suite of fossil anthers and coprolites. Herein, we describe and estimate the possible botanical affinities of these mesofossils based on their morphological characteristics, preservation, and comparisons with putative living relatives. They come from the Upper Cretaceous (Maastrichtian) outcrops of the La Colonia Formation, Chubut Province, Argentina, and were recovered by picking after filtration. The suite is composed of six anthers and ten coprolites. Four anthers contain reticulated monoporate pollen with affinities to the monocots, probably related to the family Typhaceae, while the other two contain microreticulate tricolpate/tricolporate pollen, linked to a family of eudicots of uncertain affinity. The ten coprolites contain 1) reproductive structures of aquatic ferns, 2) psilate trilete spores, 3) microfoveolate/microreticulate tricolporate pollen, 4) microreticulate pollen of indistinct aperture, 5) scabrate/punctate tricolporate pollen, and 6) anthers with scabrate/punctate tricolporate pollen. The fine-grained horizons of the La Colonia Fm. are associated with lagoon systems that preserved a diverse biota composed of invertebrates, vertebrates, and plants. Plant communities were dominated by angiosperms and aquatic ferns, other pteridophytes, gymnosperms, and algae were also well represented. The specimens were recovered from massive to finely laminated sediments, probably deposited by suspension in stagnant freshwater bodies. These findings represent the most diverse and abundant record of anthers and spore and pollen coprolites from the Late Cretaceous of the Southern Hemisphere and the first records of coprolites with reproductive structures of aquatic ferns worldwide.