A new species of the fossil fern Millerocaulis (Osmundales: Osmundaceae) from the Snow Hill Island Formation (Upper Cretaceous) of James Ross Island, Antarctic Peninsula

A small permineralized stem containing an ectophloic-dictyoxylic siphonostele and petiole bases with an homogeneous sclerotic ring, referable to the fossil genus Millerocaulis Erasmus ex Tidwell emend. Vera, was recovered from the siltstones of the Gamma Member of the Snow Hill Island Formation (Marambio Group, Upper Cretaceous) of Santa Marta Cove, James Ross Island. The presence of high numbers of xylem strands, leaf traces per cross section, wide cauline xylem strands and lack of sclerenchyma in the petiole bases (apart from the sclerotic ring) at least until the fourth petiolar cycle allow its separation from other known species of the genus Millerocaulis, defining a new taxon Millerocaulis santamartaensis sp. nov.. This new taxon represents the fourth species of the genus identified from Antarctica. The fossil bearing strata are interpreted as upper Campanian to lower Maastrichtian. As a result, M. santamartaensis sp. nov. represents the youngest evidence of the presence of this genus of stem-Osmundaceae almost until the end of the Cretaceous.