A CAMBRIAN ODYSSEY: GOGIID (EOCRINOIDEA; ECHINODERMATA) DISPERSAL IN CAMBRIAN STAGES 4 AND 5 BETWEEN SOUTH CHINA AND WESTERN LAURENTIA

Gogiid echinoderms are important members of the Cambrian Fauna (especially Stages 4 and 5). They are found primarily in Western Gondwana, Western Laurentia and are especially numerous and diverse on the South China (Yangtze) Plate where most species are wholly or moderately well documented in their ontogeny. Major characters used in understanding ontogeny and phylogenetic classification include, a) length and composition of the stalk, b) morphology of the attachment disc, c) morphology and order of emplacement of sutural pores, d) morphology of thecal plates, and e) straight vs spiraled brachioles. We have sufficient data to compare lineages between Laurentia and South China. In every case features supporting species lineages, originate and appear to be older in species on the South China (SC) plate than its sister lineage in Western Laurentia (WL). Some clear examples include Protogloboeocrinus (SC) - Gogia ojenai (WL); Guizhoueocrinus (SC) - Gogia prolifica; Globoeocrinus (SC) - Gogia spiralis (WL); Sinoeocrinus (SC) - Gogia palmeri (WL) and Balangicystis (SC) - Lyracystis (WL). However, modification of thicker stalks into thinner stem-like structures, despiriling of brachioles, asymmetrical increase in numbers of brachioles and evolution of shorter and broader thecae commonly originate in western Laurentia. The mechanics of these relationships is not clearly understood. While low latitude (Equator to 10ᵒ N) surface currents would naturally move potential larvae east to west, (and as viewed on a paleogeographic map e.g. McKerrow et al., 1992 or Torsvik and Cocks 2013) there is little evidence for gogiids in Siberia and Eastern Laurentia. There are several possibilities to explain this absence. First, environmental conditions may have been inappropriate for dense colonization of gogiids in these areas. Second, gogiids may not be preserved because of unfavorable sedimentological facies. These areas may have served as physical barriers between South China and Western Laurentia and the route between the two areas may have been via subducted islands and island arcs (distribution by island hopping) but presence of such geographic entities is hypothetical. The biogeographical connection between the two areas is real but has yet to be fully explained