PROTEROCHAMPSA BARRIONUEVOI AND THE EARLY EVOLUTION OF THE CROCODILIA WILLIAM D. SILL INTRODUCTION During the months April through June of 1958 a joint expedition of the Museo Argentino de Ciencias Naturales and the Museum of Comparative Zoology explored continental deposits in the Province of Men-doza and San Juan in western Argentina. The last six weeks of the field season were spent in Triassic beds at Ischigualasto, a \'alley in the northeastern part of the prov-ince of San Juan. Fossils at this locality proved to be so abundant and so easily found that Romer (1962) has described it as a "paleontologist's dream." The crocodil-ians described in this paper were found there by Professor Bryan Patterson in the upper third of the Ischigualasto Formation, approximately 160 feet from the base. The formation consists of interbedded clays, shales, and some sandstone, characterized by the variegated green, white, brown, and red colors t\'pical of so many fossil bearing continental deposits. As regards age, Fren-guelli (1948) considered the formation to be upper Keuper; Romer (1960, 1962) states that it is certainly pre-Norian and probably pre-Carnian. Gomphodont cyno-donts and rhynchosaurs were found in abundance in the formation in the same general area as the material here discussed. The following year the Instituto Miguel Lillo of the Universidad de Tucuman sent two expeditions to the area. Under the direction of Dr. Osvaldo A. Reig a number of specimens were found, some of which have already been described (Reig, 1959; Casamiquela, 1960; Bonaparte, 1962, 1963). Reig (1959) published a preliminary ac-count of the ancestral crocodilian discussed here, giving it the name Pwterochampsa harrionuevoi. The material discussed in this paper con-sists of one complete, well preserved skull (but with parts of the ventral area badly fractured), together with 13 articulated vertebrae and ribs, MCZ 3408, and one partial skull, MACN 18165 (Museo Argen-tino de Ciencias Naturales). I am obliged to Arnold D. Lewis for preparation of the material, to Dr. Bernhard Kummel for the photography, to Dr. Edwin Colbert and The American Museum of Natural History for permission to examine Protosuchus, to Yale Peabody Museum for making available various mesosuchians for comparative study, and to Dr. K. A. Ker-mack of University College London for al-lowing me to examine the primitive croco-dilian from Wales. The manuscript has been read by Professors Bryan Patterson, Ernest Williams, and Alfred Romer. To all of these people I express my sincere thanks. The expedition was supported in part by the National Science Foundation, and in part by Life Magazine. Bull. MORPHOLOGY THE SKULL General remarks: The skull of Protero-champsa presents a remarkable combina-Mus. Comp. Zool.. 135(8): 415-446, April, 1967 415
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