Tuzoia From Lower Cambrian Guanshan Fauna Of Eastern Yunnan, China

Tuzoia was a large bivalved arthropod witch existed widely in the Cambrian seas all over the world. Two species of Tuzoia from Lower Cambrian Guanshan Fauna of Eastern Yunnan were systematically studied in this thesis, including one species Tuzoia sinensis redescribed and the other species indeterminate Tuzoia sp. described and compared. Differences and relationships of the two species were discussed in the thesis, which may indicate that Tuzoia sp. was a juvenile of Tuzoia sinensis.Through observation on the Tuzoia fossils from Guanshan fauna, some new biological structures and detailed informations were found:1. Dorsal spines of each carapace of Tuzoia sinensis were integrated with the carapace, which were protruding from the dorsal margin and were deduced to be angled;2. There were frills along the lateral ridge of Tuzoia sinensis, which were composed by a series of broad-based spines, of which the sections showed oblate oval shape.3The ventral margin between broad-based marginal spines was bearing small jagged spines rather than being smooth.Some iron mineral crystals were showed in the SEM images. The material composition of the carapace was analysed by EDS and there tended to be no calcium in the carapace.Isoxy was compared with Tuzoia to show the differences of reticulate pattern between the two genus:There were sub-reticulate pattern in each polygon of Isoxy auritus whereas the bottoms of Tuzoia sinensis’polygons were smooth.Combining with the former studies, the physiological and hydrodynamic functions of the biological structures of Tuzoia sinensis were discussed:1. The lateral ridge and the spines probably played a stability-strengthening role in swimming;2. The reticulate pattern gave the carapace enough strength with fewer material and interfered the formation of vortexes behind the organism, which gave it stronger ability of swimming and predation.