INTRODUCTION

The conifer family Araucariaceae occurs exclusively in the Southern Hemisphere today, but it was widely distributed in both hemispheres during the Mesozoic (Stockey 1982, 1994; Stockey and Ko 1986; Hill 1995; Del Fueyo and Archangelsky 2002; Kunzman 2007a, 2007b). The mid-Jurassic through Cretaceous record is particularly rich in many regions, but early Mesozoic occurrences are uncommon and often ambiguous, especially in North America. Rare araucarian ovulate cones and cone scales have recently been described from the Late Triassic Chinle Formation of Arizona and New Mexico (Axsmith and Ash 2006) and the Lower Jurassic Moenave Formation of Utah (Tidwell and Ash 2006). Putative araucarian megafossils have also been reported from the Newark Supergroup of eastern North American (e.g., Wanner and Fontaine 1900; Bock 1954), but these are not generally accepted as convincing evidence for the family (Cornet 1986; Stockey 1994; Axsmith and Ash 2006). It is in this context that an unambiguous araucarian bract-scale complex from the Lower Jurassic Holyoke Dam locality of Massachusetts is described. Although known from a single specimen, this discovery is significant as the first certain megafossil of the Araucariaceae from the Newark Supergroup and one of the few early Mesozoic examples from all of North America. Furthermore, this bract-scale is similar to those of Araucaria section Eutacta and may represent the earliest known representative of this clade.

The extant species of Araucaria are commonly placed taxonomically among four sections; Eutacta, Intermedia, Araucaria (= Columbea) and Bunya (Endlicher 1847; Wilde and Eames 1952). Several characters, including aspects of the bract-scale morphology, are often used to distinguish among the sections. These classic delimitations are generally concordant with more recent molecular phylogenies (Gilmore and Hill 1997; Setoguchi et al. 1998; Kunzmann 2007b); however, relationships within the genus (i.e., between the sections) remain unclear. Fossil species of Araucaria (as well as Araucarites – see below) are represented by impression/compression remains of vegetative and reproductive organs from the Jurassic of the Northern and Southern Hemispheres, and most of these have been assigned to one of the sections of Araucaria (see Stockey 1982; Del Fueyo and Archangelsky 2002). These early records, along with the fossil described here, allow for estimates of phylogenetic/stratigraphic congruence, such as that presented below.