Cambrian trilobite Ovatoryctocara granulata Tchernysheva, 1962 and its biostratigraphic significance

摘要: Abstract The genus Ovatoryctocara Tchernysheva, 1962, and its key species granulata are revised. occurs near the base of Zone ranges up into lower portion Kounamkites in Siberian Platform. O. also appears southeastern Guizhou, South China, but northern Greenland may represent an indefinite species. Specimens from Newfoundland cannot be identified to level. including two cranidia three pygidia part Aoxi Formation at Yaxi Village, Shizhu Town, eastern Tongren, northeastern were previously assigned granulata, which is now reassigned as a new yaxiensis sp. nov. It bears following main features: glabella club-shaped, slightly expanded medially, with four pairs lateral furrows, S1–S3 triangular pits, S4 shallow, connecting axial furrow; shorter palpebral lobe situated little anterior midway facial suture across fixigenae, longer posterolateral area (exsag.); semielliptical pygidium consisting seven rings terminal piece eight marginal tips giving sawtooth-like shape margins dorsal view. Although widely distributed species, FAD for global stage boundary, still has some disadvantages. First, distribution not wide that Oryctocephalus indicus (Reed, 1910). Second, specimens common only Siberia. Third, stratigraphic range been studied detail all continents. Fourth, relatively small easily affected by post-burial distortion. Last least, there exists obviously facies change between (lower Amgan Stage; deeper water facies) underlying Anabaraspis splendens (Toyonian shallow Nevertheless, correlation utility China Siberia discussed.