Ontogenetic change in valve characters in three new species of Baffinicythere (Ostracoda, Crustacea) from Northern Japan

• Published in: Journal of Paleontology
• Main Author: Irizuki, Toshiaki
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1996
• Subjects: Paleontology; Arctic
• Online Access: http://dx.doi.org/10.1017/s0022336000038385; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022336000038385

The genus Baffinicythere is a northern high-latitude marine ostracode, which includes four species: B. howei Hazel, B. ishizakii new species, B. reticulata new species, B. robusticostata new species. The first species occurs only in late Pliocene to Recent sediments of the Arctic and northern Atlantic Oceans. The remaining three species are abundant in the Plio–Pleistocene formations of northern Japan, which yield cold-water molluscan faunas. Detailed morphological analyses and paleogeographic distribution of the three new species indicates that: 1) B. reticulata has some primitive characters relative to the other two species; 2) B. ishizakii and B. robusticostata seem to have had different strategies as regards rate of ontogenetic size increase; 3) the left valve outlines can be resolved into two components, ontogenetic shape changes and species-specific distinctions among the species; and 4) B. robusticostata invaded areas inhabited by B. reticulata and may have excluded it during the late Pleistocene. The Atlantic species B. howei has not been recorded from northern Japan. Comparisons of B. reticulata and B. howei , based on their pore distribution and reticulate sculptures, suggest that B. reticulata could have migrated to the Arctic Province after the Bering land barrier had been breached and then evolved rapidly into B. howei.