Ostracods (aquatic microcrustaceans with a calcified, bivalved shell) are among the most common fossils in nonmarine deposits worldwide since the Middle-Late Jurassic. This dissertation deals with the taxonomy and systematics of Late Mesozoic nonmarine ostracods with emphasis on the Lower Cretaceous of the North American Western Interior Basin, and their utilization and application. The taxonomic revision of the genera Theriosynoecum Branson 1936 and Cypridea Bosquet 1852, particularly of taxa from the Lakota and Cedar Mountain formations and conducted from the perspective of application, resulted in a breakthrough in the consideration of their utility. Inconsistent taxonomy was determined to have been the main reason hampering their application. The understanding and verification that these ostracods are not as endemic to North America as erstwhile believed in combination with an upgraded taxonomic concept, is the key to their successful manifold application and the interpretation of their paleobiology, evolution, paleobiogeography, and paleoecology. The results of the revision signify considerable progress in the taxonomy and systematics of these ostracod groups, the supraregional correlation and Early Cretaceous North American biostratigraphy based on their representatives, and the assessment of the further application potential of the latter in the basin as well as worldwide.
The timespan represented by the hiatus between nonmarine Upper Jurassic (to Early Berriasian?) and unconformably overlying Lower Cretaceous deposits throughout the North American Western Interior foreland basin has been under discussion for the entire 20th century and remains controversial to date. Ostracod correlations to well dated western European strata (Purbeck/Wealden of England and “German Wealden” of NW-Germany), mainly based on representatives of Cypridea, strongly suggest a much higher maximum age for some Lower Cretaceous formations of the Western Interior foreland basin, i.e., Berriasian to Early Valanginian instead of Barremian or Aptian. These biostratigraphic results have considerable consequences on a wide scope of basin-related geologic and paleontologic topics. The ostracods also help to expedite our understanding of animal (e.g. early mammals and dinosaurs) and plant (angiosperms) evolution on the North American continent.
The research progress marks the advent of a refined ostracod-based biostratigraphy in the nonmarine Lower Cretaceous of the WI Interior Basin and the revival of the variegated application of these ostracods on regional to global scale.
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