Paleobiological aspects of an Early Jurassic Equisetum species from Patagonia, Argentina

Abstract

We describe Equisetum dimorphum sp. nov. from the Lower Jurassic of Chubut province, Patagonia, Argentina. This new species is based on fertile and vegetative remains preserved as impressions of stems, leaves, strobili,transversal sections of the stems showing their anatomy, and terminal pagoda-like structures. The fine-grainedsedimentary matrix also helped to preserve detailed impressions ofepidermal features. The preserved morphological characters allow a whole plant reconstruction and assignment to Equisetum. E. dimorphumshows a mosaic of morphological characters that are commonly present on other Mesozoic forms and representatives of the two extantEquisetumsubgenera,e.g., sunken stomata and a blunt strobilus apex. Compared to other well-known Mesozoic equisetalean taxa, Equisetum dimorphum appears to be most closely related to a groupof Jurassic Equisetum-like plantsincluding Equisetum laterale Phillips 1829, and Equisetites ferganensis Seward, 1907. Additional evidence for the morphological stasis of the fertile and vegetative organs of extant horsetails is supplied with this new material, adding further support to the hypothesis that the living horsetails are a successful group that morphologically have not changed much over time and that have been present, nearly worldwide, since Jurassic times.