Ontogeny of the Middle Cambrian Trilobite Shantungia spinifera Walcott, 1905 from North China and Its Taxonomic Significance

Abstract

The cambrian trilobite Shantungia Walcott, 1905 is a monotypic genus, with S. spinifera Walcott, 1905 as the genotype and is characterized by its long frontal spine extending medially from the anterior cranidial border. The genus has hitherto been known restricted in occurrence to the traditional Drepanura Zone of North China (Walcott, 1913; Endo and Resser, 1937; Qiu et al., 1983; Zhang and Jell, 1987). As Drepanura Bergeron, 1899 is preoccupied by a collembolan insect and Neodrepanura Ozdikmen, 2006 was proposed as a replacement, this zone is referred to as the Neodrepanura Biozone herein. Recently collected trilobites from the Kushan Formation in Shandong Province of North China contain forty specimens of Shantungia spinifera , including protaspid and meraspid forms. Interestingly, the juvenile specimens of S. spinifera are morphologically closely comparable to the specimens recently assigned to Oculishumardia hunania Peng et al., 2003 from the uppermost middle Cambrian Liostracina bella Zone of South China (Peng et al., 2004). Peng et al. (2003) claimed that Oculishumardia is the oldest shumardiid and phylogenetically represents an intermediate stage between ptychoparioids and shumardiids. This note describes the ontogenetic development of Shantungia spinifera from North China and, based on this information, raises the possibility that Oculishumardia may represent meraspid stages of a damesellid trilobite and will explore its taxonomic and phylogenetic significance. All of the specimens examined in this study were collected from the Kushan Formation of the Tangwangzhai section, Shandong Province, China (Fig. 1). The Tangwangzhai section (116°51′42″E and 36°30′33″N) has served as the type section of middle Cambrian to Furongian (upper Cambrian) strata of North China and comprises the Changhia, Kushan, and Chaumitien formations in ascending order (Bureau of Geology and Mineral Resources of Shandong Province, 1996). The Kushan Formation in the section measures ca. 62 m in thickness and is generally …