Ontogeny, functional morphology, and comparative morphology of lower (Stage 4) and basal middle (Stage 5) Cambrian gogiids, Guizhou Province, China

Abstract

Three gogiid eocrinoids, numbering in the thousands of specimens, are well known from the lower Cambrian (Stage 4) Balang Formation (Guizhoueocrinus yui) and basal middle Cambrian (Stage 5) Kaili Formation (Kaili Biota) (Sinoeocrinus lui and Globoeocrinus globulus) that resided on the Yangtze-South China Plate (modern Guizhou Province, China). In each species a complete ontogenetic sequence, using thecal height (TH) as a scale, juvenile stage (early, middle, and late substages), mature stage (early, middle, and late substages), and a gerontic stage can be identified. Sutural pores appeared in an orderly sequence; below the ambulacrals, above the stalk and generally over the theca, in that order. In younger species their emplacement and growth was commonly precocious relative to G. yui. Also, their shape ranges from circular to oval to triangular in a single growth sequence, after the establishment of the 2-1-2 pattern; brachioles were added in series of five and were also precocious in time of occurrence in younger species. Thecae in younger species tend to retain juvenile aspects relative to G. yui. All of these species lived in outer shelf settings in fine-grained, organic-rich siliciclastics.