FIRST RECORD OF METRIORHYNCHUS (REPTILIA: CROCODYLIFORMES) IN THE BATHONIAN (MIDDLE JURASSIC) OF THE EASTERN PACIFIC

Abstract

Jurassic marine reptiles are best known from the study of European Jurassic collections. The record of these reptiles encompasses most of the period, but that of Aalenian–Bathonian rocks is quite incomplete (Andrews, 1913; Brown, 1981; Buffetaut, 1982; Godefroit, 1994; Bardet, 1995; O'Keefe, 2001; McGowan and Motani, 2003). South American marine reptiles of the early Middle Jurassic are especially significant because they contribute to fill this gap of taxonomic and paleogeographic information (Fernandez, 1994, 1999, 2003; Spalletti et al., 1994; Gasparini, 1997; Gasparini et al., 2000). The largest amount and diversity of Jurassic marine reptiles of the Southern Hemisphere was found in northwestern Patagonia, in the Neuquen Basin (Yrigoyen, 1991; Fig. 1). These reptiles dominate in Tithonian rocks cropping out at numerous sites of the basin (Gasparini and Fernandez, 1996; Spalletti et al., 1999). On the contrary, Middle Jurassic marine reptiles are restricted to Chacaico Sur area, southeast of the Neuquen Province (Fig. 1). There, until present, ichthyosaurs, plesiosaurs, and a crocodile vertebra were found in the upper part of Los Molles Formation, Cuyo Group (Lower Bajocian), and pliosaurs and plesiosauroids were found in the lower part of Lajas Formation, Lower Callovian (Gasparini and Spalletti, 1993; Fernandez, 1994, 1999; Spalletti et al., 1994; Gasparini, 1997). Figure 1 —The Neuquen Basin in west-central Argentina, showing the location of Chacay Melehue section. The crocodile remains proceed from Los Molles Formation. Base map from Digregorio et al. (1984) Recently, during field work performed by the biostratigraphy students of the Geological Sciences Department (University of Buenos Aires) in the area of Chacay Melehue, Neuquen Province (Fig. 1), two of the authors (MC and DL) took part in the finding and extraction of the skull and postcranium …