THE YANGTZEPLACOGNATHUS CRASSUS (CONODONTA) ZONE, DARRIWILIAN OF THE CENTRAL PRECORDILLERA, SAN JUAN, ARGENTINA. Elements of Yangtzeplacognathus crassus (Chen and Zhang) were recovered from samples collected in the San Juan Formation at three section in the Central Precordillera, San Juan Province, Argentina. The last meters of the San Juan Formation are exposed at the Quebrada del río de Las Chacritas, Cerro La Chilca and Quebrada Del Aluvión where these gray limestone strata are represented by grainstone, packstone-wackestone y dolopackstone. These limestone outcrops correspond to different carbonate ramp facies, from distal ramp, middle ramp, and lagoon. The key conodont Yangtzeplacognathus crassus documents the Yangtzeplacognathus crassus Zone in these sections, pointing towards a middle Darriwilian age for the conodont-bearing strata in the San Juan Formation and allowing correlation among these sections. The middle Darriwilian biostratigraphic frame of Baltica and central-south China is verified for the argentine Precordillera.