Paralia flatoniana sp. nov., a new species from the late Eocene of Texas with discussion on ecology and initial valves

Abstract

A new Paralia Heiberg species, Paralia flatoniana sp. nov., is documented from a late Eocene diatomite and mudstone deposit in east central Texas. Paralia represents up to 63% of the assemblage in the diatomite samples and 34% in the mudstone. Numerous Paralia initial valves are present adding an unusual component to this assemblage as they are infrequently reported from samples containing populations of fossil Paralia. A third valve type observed attached to Paralia chains is also illustrated and discussed. Intact chains are common and preservation of the frustules is very good with limited indication of dissolution or transport. An average valve diameter of 19.0 µm (7.1–37.7 µm range), the presence of numerous initial valves and preservation of fine morphological structures suggest an environment with often high in situ productivity rather than a transported assemblage. Morphologically similar species Paralia crenulata and Paralia thybergii share many mantle characteristics with P. flatoniana while the valve face details of Paralia fausta are similar. Paleogeography and – ecology of the Eocene Gulf of Mexico and volcanism to the west provided a temperate coastal nutrient-rich shelf environment favourable for Paralia.