Evolution and distribution of the conodonts Sweetognathus and Iranognathus and related genera during the Permian, and their implications for climate change

The conodont genus Sweetognathus, which is characterized by pustulose ornamentation on a wide, flat-topped carina, originated in the earliest Permian as S. expansus from Diplognathodus edentulus. The Asselian through Artinskian part of the Sweetognathus lineage is well represented in Kansas by the successive evolution of S. expansus, S. merrilli, S. aff. S. merrilli, S. whitei and S. bucaramangus. Sweetognathus and Iranognathus lineages were mainly confined to tropical areas from the Kungurian onward. The Kungurian and Guadalupian part of the Sweetognathus lineage is well represented in South China by the successive evolution of S. whitei (Artinskian), S. guizhouensis (lower Kungurian), S. subsymmetricus (upper Kungurian), S. iranicus hanzhongensis (Roadian) and S. fengshanensis (Capitanian). An additional lineage in West Texas is represented by the evolution of S. sulcatus to S. aff. adjunctus to S. adjunctus and to S. bicarinum. In the Urals and northwestern Pangea, the late part of the Sweetognathus lineage is represented by rare specimens of S. bogoslovskajae (upper Artinskian–lower Kungurian). During the late Artinskian, S. whitei radiated into S. toriyamai and S. bucaramangus, and also gave rise to Neostreptognathodus pequopensis and probably Pseudosweetognathus costatus. Neostreptognathodus? exsculptus may have evolved from Adetognathus paralautus through Adetognathus? telfordi sp. nov. Iranognathus, characterized by a narrow carina with poorly developed denticles and bearing subtle and smaller pustulose micro-ornament, replaced Sweetognathus at or near the Guadalupian/Lopingian boundary. It probably also evolved from Diplognathodus in the topmost Guadalupian. A lineage of Iranognathus? sp. nov. A to I. erwini can be recognized for the Guadalupian and Lopingian boundary interval. A lineage of Iranognathus? sp. nov. A to I. movschovithschi to I. sosioensis to I. tarazi is found throughout the Guadalupian and Lopingian boundary interval and the Wuchiapingian of South China. Sweetognathus and Iranognathus tend to develop homeomorphic accessory nodes iteratively during lowstand periods of global sea level near the Artinskian/Kungurian and Guadalupian/Lopingian boundaries and in the late Wuchiapingian. Sweetognathus and Iranognathus seem to be equatorial warm-water inhabitants. Distribution patterns reflect glaciation in Gondwana during the Asselian and Sakmarian, a warm climate during the Artinskian, cooling in North Pangea during the Kungurian and later Permian, slight amelioration during the Guadalupian, warming during the Wuchiapingian, and cooling during the Changhsingian in the peri-Gondwana region. Definitions for most of the important Sweetognathus species are refined. Three new species and subspecies, Iranognathus? sp. nov. A, Adetognathus? telfordi sp. nov., Gullodus duani sp. nov., are described.