PALEOBIOGEOGRAPHY OF THE GENUS POSEIDONAMICUS (OSTRACODA)

Ostracoda are one of the few taxonomic groups that provide abundant, continuous deep-sea fossil records. Despite intensive studies over the course of deep-sea drilling programs, taxonomic identification of deep-sea ostracodes at the species level remains challenging. Here we focus on Poseidonamicus, a typical deep-sea genus with subtle interspecific differences. Based on prior studies of its taxonomic framework, we approach this genus by (1) creating an atlas to delineate paleobiogeographical distribution of all known Poseidonamicus species, and (2) updating taxonomic information for Poseidonamicus in the North Atlantic Ocean. Our compilation includes over 3000 taxonomically harmonized records of 25 Poseidonamicus species from over 60 deep-sea sites, spanning from the Eocene to modern. The atlas shows that while the genus is cosmopolitan, many Poseidonamicus species are confined to either the Indo-Pacific, Atlantic, or Southern Oceans. Although majority of the records are from the Atlantic Ocean, Poseidonamicus appears to be more diverse in the Pacific with the oldest record (~40 Ma) from the Tasman Sea. In the Pliocene–Quaternary North Atlantic, there are records of only four Poseidonamicus species, including the species Poseidonamicus parasculptus Huang et al. 2022. Identifying Poseidonamicus and likely other deep-sea ostracodes will require improved understanding of not only surface ornamentation and lateral outline but also differences related to body size, sex, and ontogeny. Taxonomy work is important to future work on understanding the evolution of Poseidonamicus and other deep-sea ostracodes along with the evolution of the deep ocean.