Pteridium (Dennstaedtiaceae) from Miocene of Patagonia (Río Negro, Argentina): the southernmost evidence of bracken fern in South America

Abstract

With only four species, Pteridium is one of the most-known fern genera for its role as pioneer in ecological succession and for being an aggressive weed. Despite its current wide distribution that extends to almost the entire world, there is a relatively small number of fossil records of macrofossils and palynological assemblages related to or compared with this genus. The majority of these belong to Oligocene ─ Pliocene deposits from the United States, Europe, Asia and New Zealand and only one has been described for South America, in upper Pliocene? – Quaternary deposits from Brazil. In this contribution, we describe the oldest and southernmost record of Pteridium for South America, based on frond impressions from Miocene deposits of the Ñirihuau Formation, exposed in the North Patagonian Andes (Argentina) and interpreted as deposited in alluvial, lacustrine, deltaic, and fluvial environments. We illustrate the finding and compare it with previous records of Pteridium and Pteris and with the current Neotropical species Pteridium esculentum. Additionally, we characterise the palaeoenvironmental framework in which the palaeoflora developed and we discuss the association of the fossil with other taxa fossils found in the same deposits, and of Pteridium with other species in current floras.