The mid-Paleocene fruit and seed flora from the Fort Union Formation of Newell’s Nook, southeastern Montana, USA

Abstract

The middle Paleocene Newell’s Nook biota of the Tongue River Member of the Fort Union Formation, southeastern Montana, is best known for its early Tiffanian mammalian fauna. Here, we describe an informative fruit and seed assemblage from this locality. These records refine the lower stratigraphic boundary for several plant genera known more widely from the Fort Union paleobotanical localities of less certain stratigraphic assignment within the upper Paleocene and help to fill a gap in our knowledge about the mid-Paleocene floristic composition of the Rocky Mountain and Great Plains region. Recognized plant taxa belong to the families Characeae, Taxaceae, Menispermaceae, Sabiaceae, Hamamelidaceae, Cercidiphyllaceae, Vitaceae, Cucurbitaceae and Juglandaceae. Several morphotypes remain uncertain as to familial position. Based on the dispersal syndromes of extant relatives, about 2/3 of these fruits were adaptive for animal dispersal, with hard seeds or endocarps covered by a fleshy outer layer. Dry seeds and nuts were likely part of the diet of small mammals. The Newell’s Nook locality presents another rare example of a North American Paleocene fruit and seed locality and provides insights to the dietary habits and ecology of the co-occurring fauna of this time.