T88 Echinoderm Paleobiology I: In Honor of the Career of James Sprinkle

Monday, 5 November 2018
8:00 AM - 12:00 PM
Room 142

GOGIID (EOCRINOIDEA:ECHINODERMATA) CLADISTICS AND DISPERSAL DURING CAMBRIAN STAGES 4 AND 5: A MIGRATIONAL ODYSSEY BETWEEN SOUTH CHINA AND WESTERN LAURENTIA

Paper number: T88-4
Program: Technical Sessions
Time: 8:45 AM – 9:00 AM

Authors

Abstract

The oldest and most primitive gogiids originated on the South China (Yangtze) Plate (SC) and subsequently migrated to western Laurentia (WL) and to a lesser degree to western Gondwana. Their sparseness or absence in Avalonia, Baltica, Siberia, and eastern Gondwana is problematic. Gogiids are especially common in South China where complete (or nearly so) ontogenies of most genera have been reported and demonstrate their importance in constructing an accurate phylogenetic picture of the group. Major characters used in inferring the phylogeny include: a) size, shape and plate pattern of the distal attachment disk or nub: b) evolution of size, shape, plate pattern and transition of the stalk (tumid) to stem (thin with narrow lumen): c) morphology, order including areas of emplacement, of sutural pores (epispires): d) morphology of thecal plates: and e) emplacement pattern, number, and straight or coiled brachioles. Sufficient data is present to compare clades/subclades between the South China and western Laurentia and in every case major character lineages originate in south China. However, some characters are accentuated in western Laurentian gogiids, e.g. thinning of more tumid stalks into slender stem-like structures, despiraling of brachioles into straight feeding structures, asymmetrical departure from the 2-1-2 ambulacral pattern, and evolution of relatively shorter broader thecae. Examples of widely seperated sister species include: Protogloboeocrinus yin (SC) – Gogia ojenai (WL); Guizhoueocrinus yui (SC) -- Gogia prolifica (WL); Globoeocrinus globuilus (SC) – Gogia spiralis (WL); Sinoeocrinus lui (SC) – Gogia palmeri (WL) and Balangicystis rotundus (SC) – Lyracystis radiata (WL). An important paleoeclogical modification in western Laurentian gogiids is that, spiral or straight, brachioles are narrower (food groove width 0.5 or less ) than their counterparts from South China (food groove width 0.5 to ca. 0.8 mm). This suggests that nutritional planktonic organisms in western Laurentia may have been different and/or smaller and resident gogiids generally adapted to it. This adaptation may explain why gogiid migration seems to be unidirectional from South China to western Laurentia, the reverse may have presented feeding difficulties.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-317824

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