Variable noding and palaeoecology of a Middle Jurassic limnocytherid ostracod: implications for modern brackish water taxa

No less than seven junior synonyms exist of Theriosynoecum kirtlingtonense Bate, 1965. This taxonomic confusion has been brought about by variations i n the degree and patterns of noding within a single species, which was wide spread both geographically - from the south of England to the Hebrides - an d in the palaeoenvironments it occupied - from freshwater to polyhaline. A critical analysis is undertaken of the taxonomy of Theriosynoecum kirtlingt onense within a framework of palaeoenvironmental constraint, using only tho se bio-characters which are invariable at the intraspecific level. The dist ribution of the species in a section of the upper Bathonian Forest Marble F ormation at Tarlton in Gloucestershire, is investigated, The population age structure was used to determine those levels in which the species occurs a s an autochthonous component, and its variable noding investigated with res pect to salinity variations. All aspects of noding in this limnocytherid an d in the Neogene to Recent brackish water species Cyprideis torosa (Jones, 1850) are compared and contrasted and both are shown to be related fundamen tally to salinity. (C) 1999 Elsevier Science B.V. All rights reserved.