A restudy of Oryctocephalus indicus (Reed,1910)

Since both Chinese[1]and American Palaeontolo-gists[2]proposed separately to mark the beginning ofthe Middle Cambrian based on the first appearancedatum (FAD) ofOryctocephalus indicus[3]in thesame year ,the suggestion has been considered seri-ously and adoptedfrequently[4—18].The InternationalSubcommission on Cambrian Stratigraphy (ISCS) hasorganized the Working Group,chaired by L.B. Mc-Collum,to select candidate sections that bear poten-tial to become a GSSPfor the traditional Lowe…     

A new section of Kaili Formation （Cambrian） and a biostratigraphic study of the boundary interval across the undefined Cambrian Series 2 and Series 3 at Jianshan,Jianhe County,China with a discussion of global correlation based on the first appearance datum of Oryctocephalus indicus （Reed, 1910）

A trilobite biostratigraphic study of a new section of the Kaili Formation at Jianshan, Chuandong Village, Jianhe County, Guizhou is reported. Additional occurrences of key species associated with the Ovatoryctocara granulata-Bathynotus holopygus Zone and the overlying Oryctocephalus indicus Zone that were originally defined from the trilobite assemblages at the WuliuZengjiayan section of the Kaili are reported from this new section. The first appearance datum （FAD） of Oryctocephalus indicus occurs at the 44.52 m above the base of the unit. Based on study of abundant specimens （n = 800） from the Kaili Formation, we argue that Oryctocephalus indicus is a widespread taxon with a global distribution. O. reticulatus （Lermontova, 1940） from the middle part of the Kounamkites Zone of the Amganian Stage in the Molodo River region of Siberia and O. americanus （Sundberg and McCollum, 2003） from Nevada, North America are similar to representatives of O. indicus which occur in the O. indicus Zone of the Kaili Formation. O. reticulatus and O. americanus are here synonymized with O. indicus （Reed, 1910）. This study strengthens the Wuliu-Zengjiayan section of the Kaili Formation as a candidate section for a Global Stratotype for the base of the unnamed Cambrian Series 3.     

A restudy of Oryctocephalus indicus (Reed, 1910)

Restudy on morphology of Oryctocephalus indicus (Reed, 1910), based on specimens from Guizhou, China and Nevada USA, suggests that the subspecies regarded previously as Oryctocephalus indicus indicus (Reed, 1910), O. indicus latus Zhao et Yuan 2002, and O. indicus kobayashi Saito, 1934, are synonymous, and Oryctocephalus americanus Sundberg et McCollum, 2003 is a similar form of O. indicus. Oryctocephalus indicus is rediagnosed as having a glabella that is subconical in outline and tapering forward slightly; a thorax that comprises 12 segments, and a small pygidium that bears 2?3 axial rings with a terminal piece and a postaxial ridge. Oryctocephalus indicus is widely distributed in eastern Guizhou and ranges through a great interval of Kaili Formation. Its first appearance is almost identical with these events of trilobite extinction-recovery occurring at the end of the Early Cambrian, the alternation of acritach assemblages, the change of trace elements (REE) and stable isotopes (carbon) at the Wuliu-Zengjiaya section. As one of the key forms for defining the traditional Lower - Middle Cambrian boundary (the base of Cambrian Series 3 and Stage 5 in the new Cambrian chronstratigraphic standard), O. indicus has received detailed study and has more advantages than other species such as Ovatoryctocara granulata Tchernysheva, 1962 or Arthricocephalus chauveaui Bergeron, 1899.