Schenkeriphyllum glanduliferum, a new magnolialean angiosperm from the Early Cretaceous of Northern Gondwana and its relationships to fossil and modern Magnoliales

Abstract

A fossil angiosperm from the Aptian Crato Formation (Brazil), Schenkeriphyllum glanduliferum n. gen. n. sp. is described and phylogenetically analyzed. The taxon consists of branching axes with attached simple sessile, sheathing, narrowly ovate glanduliferous leaves with ethereal oil cells and solitary axillary medium sized flowers. Several of the multiparted flowering structures are reasonably well preserved in differing stages of maturity. Broad obovate tepals, (stamens?), glanduliferous staminodes (more than 30?) and free carpels are arranged on a flat to slightly convex receptacle. The gynoecium consists of ca. 12 to 20 free carpels. Among recent Magnoliales only Magnoliaceae share many characters of the flowering structures with Schenkeriphyllum. A phylogenetic analysis confirms that Schenkeriphyllum represents most likely a sister taxon to Endressinia for which the diagnosis is slightly emended. Both fossil taxa may represent together a sister clade to extant Magnoliaceae.

Introduction

Early Cretaceous angiosperm fossils have been described from several geographic areas (Crane et al., 1995, Dilcher, 2001). South American Early Cretaceous angiosperms include various dispersed pollen types and leaves that are considered to be approximately of late Aptian to late Albian age. In Argentina in upper Aptian strata angiosperm leaves are still rare and not diverse while in late Albian floras flowering plants exhibit a variety of differing leaf shapes (Archangelsky et al., 2009). Unequivocal magnolialean remains however have not yet been identified. Northern Gondwana floras with an angiosperm component that represents the paleoequatorial vegetation during the Cretaceous are known from Colombia (Pons, 1988, van Waveren et al., 2002) and from Brazil. In particular Endressinia brasiliana, a magnoliid taxon from the Crato Formation of Brazil has been described in detail (Mohr and Bernardes-de-Oliveira, 2004).

The old age of magnoliid fossils including dispersed pollen, such as Walkeripollis (Ward et al., 1989) is consistent with a basal placement with its origins deep in the Cretaceous (Friis et al., 1997). However, unambigous pre-Albian magnolialean fossils are overall relatively rare and the diversity of this group seems to increase mainly during the Late Aptian to Cenomanian (Friis et al., 2006, Doyle and Endress, 2010). This observation may reflect the systematic position in which extant Magnoliales, sister to Laurales, are seen today (Soltis et al., 2005). Magnoliales does not belong to the most basal groups such as Amborella and Nymphaeales (Endress, 2001), but to the Magnoliids that are one of the five clades of mesangiosperms (including Ceratophyllum, Chloranthaceae, monocots and eudicots).

Today Magnoliales comprise a group of several basal angiosperm families that consist of two main clades. One clade is represented by Myristicaceae. A second clade comprises Magnoliaceae, Eupomatiaceae plus Annonaceae, and Degeneriaceae plus Himantandraceae (Sauquet et al., 2003, Soltis et al., 2005). Molecular data and many morphological features reflect the close relationships among these families (Doyle and Endress, 2000).

Recently Friis et al. (2011) reviewed accounts of some of these early Cretaceous magnolialian fossils. Many of these remains consist, however, of dispersed pollen or isolated parts of flowers and are therefore not directly comparable with Schenkeriphyllum n. gen. that is preserved as a more or less complete plant, including axes, leaves and flowers. Selected relevant magnolialean early to mid-Cretaceous fossils are discussed and compared to Schenkeriphyllum below.