-Evidence of insect-fern interactions are described for the fi rst time from late Miocene strata of Salta Province, Argentina. Two ichnospecies are defi ned to include fossil traces of surface feeding and hole feeding, located between the secondary veins and adjacent with the primary vein of two species of fossil ferns, Blechnum serrulatiformis Anzótegui & Horn and Thelypteris interrupta (Willd.) Iwatsuki. The fi rst ichnospecies corresponding with surface feeding presents oblong traces and both ends are rounded; occupying the entire intercostal space. This type of phytophagy is found for the fi rst time in the fossil record of ferns. The second ichnospecies is similar in shape and location to the previous ichnotaxon, except that all herbivorized tissues are absent. At last, a review of the fossil record of insect-fern associations is performed.Key words: insect-fern interactions, fossil traces, surface feeding, hole feeding.RESUMO -Descreve-se pela primeira vez evidência de interações inseto-samambaia no Mioceno superior da Província de Salta, Argentina. Duas icnoespecies são propostas para incluir rastros fósseis de alimentação superfi cial e alimentação em orifícios, localizadas entre as veias secundárias e adjacentes à veia primária em duas espécies de samambaias fósseis, Blechnum serrulatiformis Anzótegui & Horn e Thelypteris interrupta (Willd.) Iwatsuki. A primeira espécie corresponde à alimentação superfi cial, apresenta rastros oblongos com ambos os extremos arredondados e ocupa todo o espaço intercostal. Este é o primeiro registro de alimentação superfi cial em samambaias fósseis. A segunda espécie similar na sua forma e localização ao icnotáxon previamente descrito, exceto que todas as camadas de tecido herbivorizado estão ausentes. Finalmente, uma revisão do registro fóssil das associações inseto-samambaia também é realizada.Palavras-chave: interação inseto-samambaia, traços fósseis, alimentação superfi cial, alimentação em orifício.
The study of plant-insect interactions provides valuable information about the ecology of feeding behavior and the relationships between the host plant and the producer insect. Records of feeding traces are relatively rare for the Miocene of South America. Here, new records of plant-insect interactions on dicot leaves and fern fronds from the middle and late Miocene of Argentina are presented. In total, 1204 dicot and fern impressions were analyzed including 384 from the San José Formation and 856 from the Palo Pintado Formation. Traces of arthropod herbivory are found on 303 foliar impressions, 288 from the Palo Pintado Formation and just 15 from the San José Formation. Forty-four percent of all traces were found on Thelypteris interrupta (Willd.) Iwatsuki 1963 (Thelypteridaceae), followed by Cedrela fissiliformis Anzótegui and Horn 2011 (Meliaceae) (15.1%) and Schinus herbstii Anzótegui 1998 (Anacardiaceae) (11.3%). Thelypteris interrupta is associated with a low diversity of Damage Types, mainly hole and window feedings, indicating a monospecific relationship with the trace maker. On the other hand, the high abundance and diversity of damage types found on C. fissiliformis and S. herbstii denote that these plants were hosting a more diverse group of arthropods. Likewise, the lower number of traces identified in the San José Formation corresponds to the xeric conditions established during the middle Miocene in northwestern Argentina. These conditions changed in the late Miocene, at least in some regions, to a humid climate, promoting an increase in phytophagy that is evidenced by the abundance recorded in the Palo Pintado Formation.
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