Part Ⅱ Homology and structure in dinoflagellate cyst terminology

摘要

Research over the past three decades has produced a rich vocabulary for describing dinoflagellate cysts. Ideas about homology have exerted a strong influence on the development of this terminology. From wall structure to tabulation, some of these ideas are inconsistent with homology concepts in contemporary evolutionary biology. In this selective review of the descriptive terminology for fossil dinoflagellates, a practical and theoretically consistent terminology is proposed from among the present plurality of terms. We perceive tabulation as the number, distribution and topology of thecal plates and cyst fields because the expression of these characters is the same for both the motile planozygote and the non-motile cyst. The Kofoid system of labeling tabulation elements is favored over the Taylor-Evitt approach, where specific homologies must be assumed present between naturally occurring tabulations and the model. We apply the results of our analysis in descriptions of 12 morphologically diverse new taxa from the Miocene of Maryland and Virginia. The new genus Cousteaudinium is erected with Cousteaudinium aubryae as the type. The taxon Labyrinthodinium truncatum Piasecki 1980 is emended and a new subspecies, Labyrinthodinum truncatum subsp. modicum, is described. The other new species are: Cannosphaeropsis passio, Cerebrocysta pouhenii, Cerebrocysta satchelliae, Exochosphaeridium insigne, Impagidinium antecarcerem, Impagidinium arachnion, Llngulodinium multivirgatum, Pyxidiniopsis fairhavenensis, Spiniferites solidago and Sumatradinium hamulatum.