This dataset supplement to the paper "Major Shifts in Equatorial Atlantic and Pacific Calcareous Nannofossil Assemblages across the Early Eocene Climatic Optimum (EECO; ~53–49 Ma)" (Paleoceanography and Paleoclimatology). Data Set S1. Age-Depth Models This dataset includes input age-depth tie points and output age models for ODP Sites 1258 and 865, generated using Undatable (Matlab software, Version 1.1; Lougheed & Obrochta, 2019; https://doi.org/10.1029/2018PA003457). Undatable input age-depth tie points and output age models for all sites (Sites 1258, 865, 1210, 1263, U1410, 589, 762, U1510, 1135, 690, 207) compared in this study are contained in two zipped folders: cm- and meter-depth scale version (the latter consist of only the age-depth plots). The age-depth models presented in this study can be reproduced by loading the input files into the Undatable graphical user interface (GUI) and applying the settings specified in the header row of the output files, including the number of Monte Carlo iterations, xfactor, and bootstrapping parameters. Data Set S2. Calcareous Nannofossil Census Data This dataset contains raw census data, total calcareous nannofossil absolute abundance estimates (N/g), and genus-level census counts (%) from ODP Sites 1258 and 865.