Earth and Atmospheric Sciences, Department of


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A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Earth and Atmospheric Sciences, Under the Supervision of Professor David K. Watkins. Lincoln, Nebraska: December, 2012

Copyright (c) 2012 Bobbi Jo Brace


The calcareous nannofossil genus Biscutum is ubiquitous in mid to Upper Cretaceous pelagic sediments and is an important paleoceanographic proxy for surface water fertility. Most work on the evolution of Biscutum has been conducted on high latitude sections or Lower Cretaceous or Jurassic sediments, leaving a gap in the understanding of Biscutum evolution in mid-latitudes during the mid to Late Cretaceous. This study documents the evolution of Biscutum during the mid to Late Cretaceous in a mid-latitude composite section from North America. Six new species of Biscutum are presented herein, in addition to an emended Biscutum constans species concept. An interval of diversification occurred in which five new species evolved in the mid-Cretaceous temperate latitudes. Evidence from other publications suggests a second diversification occurred in the high latitudes during the Campanian. This suggests that there was a distinct shift in the sites of evolutionary activity within Biscutum, from the mid-latitudes in the mid-Cretaceous to high latitudes in the Late Cretaceous. The appearance of these high latitude taxa during part of their evolutionary ranges in the temperate latitudes suggests that these episodes are relatively brief migratory appearances during the Campanian.

Adviser: David K. Watkins