Xg. Zhang et Enk. Clarkson, ONTOGENY OF THE EODISCID TRILOBITE SHIZHUDISCUS-LONGQUANENSIS FROM THE LOWER CAMBRIAN OF CHINA, Palaeontology, 36, 1993, pp. 785-806
The eodiscid Shizhudiscus longquanensis occurs abundantly in the Lower
Cambrian Shuijintuo Formation, Pengshui, Sichuan, China. Phosphatized
specimens in excellent preservation have been isolated from a single
limestone lens, and include a few protaspides and disarticulated examp
les of all subsequent growth stages. From this material the ontogeny o
f S. longquanensis is described and reconstructed. Of particular note
are two large spines on the axis of the transitory pygidium which even
tually become those of the second and third thoracic segments. The vis
ual surface first appears in the earliest meraspid, with a single lens
flanked by two half lenses. An immature specimen of Shizhudiscus sp.
from Shaanxi Province shows that this trilobite genus was already capa
ble of full enrollment in the degree 0 meraspid stage.