摘要
Lower Triassic conodont biostratigraphy has been well studied around the world in the past decades, but the Induan-Olenekian boundary （IOB） remains undecided. The Novispathodus waageni group has been taxonomically re-assessed based on abundant new materials from the Jianshi and Chaohu sections, South China. New study shows that Nv. waageni typically possesses： （1） an approximately equi-dimentional P1 blade element, （2） an accurate upper profile with denticle height descending in both directions, （3） a denticulated posterior edge （lower denticles posterior of the highest denticle）, and （4） a round basal cavity outline. Of the three proposed subspecies of the waageni species, both Nv. waageni waageni （Sweet, 1970） and Nv. w. eowaageni （Zhao and Orchard, 2005） are valid, and the former differs clearly from Nv. w. eowaageni in having （1） a slightly higher length/height ratio （holotype=1.30 ： 1.23）, （2） a thicker blade, sometimes with medial thickening, （3） fewer （broader） denticles per unit length, （4） generally recurved denticles, not straight and upright, （5） highest denticles closer to posterior, （6） common differentiation of a posterior cusp, and （7） more sinuous basal profile, with increased posterior upturning. A third subspecies illustrated as Nv. waageni n. subsp. A sensu Goudemand, 2014 is not conspecific with older individuals of Nv. w. eowaageni, and also cannot be as- signed to the Nv. waageni group. Abundant new materials demonstrate a clear ontogenic process for Nv. w. eowaageni, indicating that Nv. w. eowaageni occurring in the Induan-Olenekian boundary （IOB） succession is rather stable. Small, earlier individuals （i.e., those from Bed 225 in Jianshi） are referred to as Nv. w. eowaageni Morphotype A, and are thought to have likely evolved from Ns. dieneri Morphotype 3, and to be the precursor of mature elements ofNv. w. eowaageni. The first appearance datum of Nv. w. eowaageni therefore is an ideal mark defining the IOB.
Lower Triassic conodont biostratigraphy has been well studied around the world in the past decades, but the Induan-Olenekian boundary （IOB） remains undecided. The Novispathodus waageni group has been taxonomically re-assessed based on abundant new materials from the Jianshi and Chaohu sections, South China. New study shows that Nv. waageni typically possesses： （1） an approximately equi-dimentional P1 blade element, （2） an accurate upper profile with denticle height descending in both directions, （3） a denticulated posterior edge （lower denticles posterior of the highest denticle）, and （4） a round basal cavity outline. Of the three proposed subspecies of the waageni species, both Nv. waageni waageni （Sweet, 1970） and Nv. w. eowaageni （Zhao and Orchard, 2005） are valid, and the former differs clearly from Nv. w. eowaageni in having （1） a slightly higher length/height ratio （holotype=1.30 ： 1.23）, （2） a thicker blade, sometimes with medial thickening, （3） fewer （broader） denticles per unit length, （4） generally recurved denticles, not straight and upright, （5） highest denticles closer to posterior, （6） common differentiation of a posterior cusp, and （7） more sinuous basal profile, with increased posterior upturning. A third subspecies illustrated as Nv. waageni n. subsp. A sensu Goudemand, 2014 is not conspecific with older individuals of Nv. w. eowaageni, and also cannot be as- signed to the Nv. waageni group. Abundant new materials demonstrate a clear ontogenic process for Nv. w. eowaageni, indicating that Nv. w. eowaageni occurring in the Induan-Olenekian boundary （IOB） succession is rather stable. Small, earlier individuals （i.e., those from Bed 225 in Jianshi） are referred to as Nv. w. eowaageni Morphotype A, and are thought to have likely evolved from Ns. dieneri Morphotype 3, and to be the precursor of mature elements ofNv. w. eowaageni. The first appearance datum of Nv. w. eowaageni therefore is an ideal mark defining the IOB.
基金
supported by four NSFC grants (Nos.41473006, 41572091, 41673011, 41772007)
one grant from the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Wuhan)
