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1 Department of Geology and Geophysics, University of Calgary, Calgary, Alberta, Canada T2N 1N4 charles.henderson{at}ucalgary.ca
2 Nanjing Institute of Geology and Palaeontology, Nanjing, China 210008
Conodonts have been restudied in order to define the base of the Changhsingian Stage boundary at Meishan, Changxing County, Zhejiang Province, China. The Changhsingian represents the second and last stage of the Upper Permian, which is also known as the Lopingian Series. A sample-population based taxonomic approach has been used and described. This approach usually views the entire collection within a given sample as a population and recognizes the most consistent and stable characters within that ‘sample-population’ for identification. Three related conodont species, Clarkina longicuspidata Mei & Wardlaw in Mei et al. 1994, C. wangi (Zhang 1987) and C. subcarinata (Sweet in Teichert et al. 1973) have been redefined and redescribed using this new approach that recognizes carinal development as an apomorphic character for these taxa. A consistent change in denticulation has been observed between Clarkina longicuspidata and Clarkina wangi wherein C. longicuspidata has a prominent gap in front of the cusp, whereas C. wangi has a ‘wall’-like carina. The carinal change may have resulted from a heterochronic process involving acceleration, since juvenile descendants exhibit features of ancestral adults; the change may be related to the evolution of other biota that may represent potential food sources for the conodont animal, given the apparent importance of the conodont carina for food processing. It is suggested that the base of the Changhsingian Stage could be defined within the C. longicuspidata-C. wangi lineage, based on the newly refined taxonomy. This boundary occurs close to the flooding surface that represents at least the second parasequence within the Changxing Limestone. The proposed boundary is close to, but not identical with, the traditionally defined boundary.
