Content area
Full text
Articles
Introduction
Bactritid cephalopods are considered a key group of the middle-upper Paleozoic. In addition to the interesting phylogenetic aspects concerning their origin, their important role in the evolutionary history of cephalopods has been especially debated (e.g., Erben, 1964; Kröger and Mapes, 2007; Kröger et al., 2011; Klug et al., 2015). The present consensus assumes they evolved from an orthocerid group during the latest Silurian-Early Devonian, and, in turn, gave rise to ammonoids during the Devonian and to coleoids in the Mississippian (Erben, 1966; Mapes, 1979; Doguzhaeva, 2002; Kröger and Mapes, 2007; Klug et al., 2015).
In contrast to the rich records from Laurentia and northern Gondwana, bactritids are very poorly known from southern Gondwana. Particularly in South America, the only certain reference is a report of the genus Bactrites Sandberger, 1843 from the Pennsylvanian of Perú (Thomas, 1928). Although Cecioni (1953) reported Eobactrites? from supposedly Early Devonian beds of the Lipeón Formation (Turner, 1960) in northwestern Argentina, that genus is considered a synonym of Bactroceras Holm, 1898 (e.g., Evans, 2005), and accordingly belongs to the Orthocerida (Kröger and Mutvei, 2005). Furthermore, those beds are known to be Silurian in age (Rickards et al., 2002).
A moderately small collection of non-ammonoid cephalopods from the Lower Devonian of west-central Argentina (Precordillera Basin) has recently been studied. Here, we describe bactritid cephalopods, which constitute the first Devonian record of the group in South America. Preliminarily reported orthocerids, pseudorthocerids, and oncocerids from this collection (Cichowolski and Rustán, 2014), as well as recently recognized lamellorthoceratids will be discussed at length in a forthcoming contribution.
With a long history of paleontological investigation, the rich records of the Argentine Precordillera have provided the best source of information on Devonian marine faunas from Argentina (e.g., Vaccari et al., 1994; García-López and Fernández-Martínez, 1995; Herrera, 1995a, b; Sánchez et al., 1995; Herrera et al., 1998; Rustán and Vaccari, 2010, 2012; Rustán et al., 2011a, b; Carrera et al., 2013; Salas et al., 2013; Carrera and Rustán, 2016). However, in spite of this extensive paleontological record, no cephalopods other than the wastebasket genus Orthoceras have been reported from this basin to date (Thomas, 1905; Keidel, 1921; García, 1945; Leidhold and Wetten, 1947).
Paleobiogeographic analyses of Devonian faunas from the Precordillera and elsewhere in...