BIZARRE PERMIAN AMMONOID SUBFAMILY AULACOGASTRIOCERATINAE FROM SOUTHEAST CHINA

Abstract

Since the 1960s, Chinese researchers have reported a series of bizarre paragastrioceratids associated with the endemic pseudohaloritids and/or kufengoceratins from the Permian Restricted-Sea area of Southeast China. They include Aulacogastrioceras Zhao and Zheng, 1977; “ Paragastrioceras ” carinatum Chao, 1965 (invalid name, = Chekiangoceras carinatum Ruzhencev, 1974, type species of the genus Chekiangoceras Ruzhencev, 1974); “ Paragastrioceras ” dongwuliense Zhao and Zheng, 1977; and Nodogastrioceras Ma and Li, 1998 (= Yongpingoceras Ma and Li, 1998; including “ Paragastrioceras ” dongwuliense ). All these taxa share the following characteristic features: 1) an eight-lobed paragastrioceratid suture; 2) a variably shaped, evolute conch, and prominent sculpture with transverse ribs, nodes, and coarse strigae in all ontogenetic stages, suggesting an affinity with the subfamily Paragastrioceratinae; 3) and, by contrast, a conspicuous ventral sinus formed by growth lines and constrictions, indicating a phylogenetic relationship to the subfamily Pseudogastrioceratinae. These endemic Chinese paragastriocertids constitute a separate subfamily, distinct from both Paragastrioceratinae and Pseudogastrioceratinae, for which the subfamily Aulacogastrioceratinae is herein proposed. The genus Nodogastrioceras was established by Ma and Li (1998) on the basis of specimens from the Hutang Formation of northeast Jiangxi. Actually, forms identical to the type species, N. discum Ma and Li, 1998, had been known since the 1950s from the Kufeng Formation in outcrops and quarries south of Longtan town, an eastern suburb of Nanjing, Jiangsu. However, most of these specimens are preserved as impressions that do not show sutures and ventral characteristics, and they were typically identified as “ Paragastrioceras ” by previous authors, based on conch shape and sculpture. The latter identification was problematic, however, because the fossil-bearing Kufeng Formation is no older than Middle Permian (Roadian), whereas true Paragastrioceras Tchernow, 1907 is restricted to the Lower Permian (Asselian through Kungurian). Chao (1965) had even considered …