Eocladopyxis peniculatum Morgenroth, 1966, Early Tertiary Ancestor of the Modern Dinoflagellate Pyrodinium bahamense Plate, 1906

Eocladopyxis peniculatum Morgenroth, 1966, represents one of the earliest known ancestors of the modern pyrodinioid dinoflagellate Pyrodinium bahamense Plate, 1906, and may be in the direct lineage leading to the modern species. Both the modern and the fossil species occur most abundantly in semi-enclosed, shallow-water bays with restricted circulation with the open ocean, suggesting that certain members of the Eocladopyxis-Pyrodinium complex may have evolved under, and are indicators of, marine-brackish, near-shore conditions. As known, E. peniculatum is restricted to the Paleocene and Eocene. Eocladopyxis peniculatum Morgenroth, 1966, Early Tertiary ancestor of the modern dinoflagellate Pyrodinium bahamense Plate, 1906 INTRODUCTION Investigation of the Aquia (Late Paleocene) and Nanjemoy (Early Eocene) Formations of the Virginia and Maryland coastal plains has revealed large numbers of specimens in some strata of the dinoflagellate cyst Eocladopyxis peniculatum Morgenroth, 1966. Excellent preservation of the cysts allows new information to be added to the original description. As now understood the species has the same unique tabulation as the modern pyrodinioid dinoflagellate Pyrodinium bahamense Plate, 1906, and resembles the resting spore (=cyst) of the modern species in several respects (see Discussion and comparison with similar species). So similar is E. peniculatum to P. bahamense in tabulation, morphology, and preference of ecological conditions that the fossil may be in the direct lineage which produced the modern species.