A Llandovery to Ludlow age for the Niur Formation in the Derenjal Mountains (east-central Iran) is proposed based on new conodont data and previous work on other fossils. The uppermost part of the studied section yielded no diagnostic conodonts but may be Pridoli in age. Some intervals can be dated more precisely: Unit 11 (at least its upper part) is middle Telychian in age and corresponds to the Pterospathodus amorphognathoides lennarti Zone; the lowermost part of Unit 16 is earliest Ludlow in age and corresponds to the Kockelella crassa Zone; the uppermost Unit 16 is late Ludlow (Ludfordian) in age and corresponds to the Ozarkodina snajdri Interval Zone. The Llandovery–Wenlock boundary lies between units 12 and 13 based on sedimentological evidence. The precise location of the Wenlock–Ludlow boundary in the section is not clear but lies below Unit 16. Present-day Iran was located far away from Baltica and Laurentia, on the other side of the Rheic Ocean. This ocean does not seem to have been a major migration barrier for most organisms including the conodonts.
