The Eocene expansion of nautilids to high latitudes

A short-term return of environmental conditions similar to those of the end-Cretaceous is marked by the reappearance of nautiloid cephalopods in the lower-middle Eocene La Meseta Formation of Seymour Island, Antarctic Peninsula. Previous findings have been supplemented by a collections of 33 specimens. The nautiloids come from several horizons, the oldest sample apparently being located close to the base of the formation (Telm1), the most numerous coming from the Cucullaea bed of Telm2 and 3. A few specimens were collected from Telm4–6. The La Meseta Formation nautiloid assemblages developed apparently in response to one of the Eocene warmings and resulting transgression of a warm sea. The incursion of nautiloids into southern high latitudes was roughly coeval with their expansion to the northern European seas and the succession of faunas was parallel in both regions. on the analogy with the lower Eocene London Clay nautiloid assemblages an estimate of bathymetric evolution of the environment can be made by. The presence of a relatively shallow-water form similar to Cimomia imperialis close to the base of the lower-middle Eocene La Meseta Formation (Telm1) marks the beginning of the marine transgression. The dominant La Meseta species, Euciphoceras argentinae, was apparently an analogue of the English E. regale, the occurrence of which in the London Clay corresponds to the highest sea level stand. The presence of Aturia in the higher part (Telm4 and 5) of the La Meseta Formation suggests that cold oceanic waters possibly entered the area, accompanied by a sea-level drop. The last nautiloid (Telm6) is an Euciphoceras sp., interpreted to be indicative of shallower habitat depth limits. Both incursion of the nautiloids to, and their disappearance from the Eocene high latitudes were connected with a fundamental rearrangement of the geographic distribution of particular lineages.