First occurrence of Early Triassic conodonts from the Lang Son Formation, northeastern Vietnam

The Early Triassic conodonts Eurygnathodus costatus Staesche, E. hamadai (Koike), Neospathodus cristagalli (Huckriede), and Ns. pakistanensis Sweet are newly reported from the upper part of the Lang Son Formation in Lang Son City, northeastern Vietnam. This association and particularly E. costatus and E. hamadai indicate the lower Smithian (lower lower Olenekian). Thus, the geological age of the upper part of the Lang Son Formation ranges from Induan to early Olenekian, and the stage boundary lies within the upper part of the formation.