Paper No. 12
Presentation Time: 11:15 AM
ONTOGENY AND FUNCTIONAL MORPHOLOGY OF BASAL MIDDLE CAMBRIAN GOGIID EOCRINOIDS IN THE KAILI BIOTA, GUIZHOU PROVINCE, CHINA
The basal Middle Cambrian Kaili Formation, containing the Kaili Biota, is a Burgess Shale-like lagerstätten (Guizhou Province, southwest China). The coelomate portion of the biota is dominated by two species of gogiid eocrinoids: Sineoeocrinus lui and Sinoeocrinus globus. Sinoeocrinus lui (1200+ known specimens) has a cone-shaped attachment disk, a long slender variably plated holdfast, thecal sutural pores that sequentially appear in stages and undergo life long modification, and long straight brachioles sequentially numbering 4 (2-2 ambulacral pattern) in early juveniles and, 5,10 and 15 in late juveniles and mature specimens, ( 2-1-2 ambulacral pattern). Sinoeocrinus globus ( 3000+ known specimens) has a flattened pancake-like attachment disk, short, thick, holdfast uniformly composed of small platelets; most sutural pores appear in a single sequence and undergo limited modification; brachioles sequentially number 4 (2-2 ambulacral pattern) in early juveniles, or 5 or 10 in late juveniles and mature specimens (2-1-2 ambulacral pattern). Brachioles are spirally coiled and like S. lui, have tall pointed cover plates. Large sections of thecal plates may remain without sutural pores until well into maturity. In contrast to S .lui, this species demonstrates paedomorphic development, especially in the holdfast and thecal sutural pores. Sinoeocrinus lui commonly attached directly to the seafloor but will attach to inarticulate brachiopods, trilobite exuviae, or other organic debris. Theca and brachioles probably heeled over in the current from the bent holdfast so that brachioles streamed above but essentially parallel to, the seafloor. Sinoeocrinus globus commonly attached to inarticulate brachiopods, trilobite exuviae, or other organic debris; direct attachment to the seafloor is rare. The short robust holdfast precluded heeling over in the current but brachioles probably streamed nearly parallel to the seafloor.