William J. Zinsmeister

Cenozoic High Latitude Heterochroneity of Southern Hemisphere Marine Faunas

Discovery of 11 genera, in five classes within the Mollusca, Echinodermata, and Arthropoda in upper Eocene rocks on Seymour Island, Antarctica, previously known only from Late Cenozoic in mid-latitudes, suggests that the high latitude region of the Southern Hemisphere acted as a center of origin and dispersal for a broad spectrum of taxa. Precursors to modern deep- and shallow-water mid-latitude forms evolved and flourished in the high latitudes until conditions in lower latitudes favored their dispersal. These observations of Antarctic marine invertebrates corroborate those recently made about terrestrial mammals and plants in the Arctic.

Fossil Land Mammal from Antarctica

A fossil land mammal, apparently the first found in Antarctica, belongs to the extinct marsupial family Polydolopidae. The fossils were recovered from rocks about 40 million years old on Seymour Island, in the northern Antarctic Peninsula. The newly discovered marsupials support theories that predicted their former presence in Antarctica and strengthen proposals that Australian marsupials perhaps originated from South American species that dispersed across Antarctica when Australia still was attached to it, prior to 56 million years ago.

Cretaceous paleogeography of Antarctica

Abstract During the Early Cretaceous, Antarctica formed the center piece of a large landmass extending from South America across the southern latitudes to Australasia. The eastern sector of this austral landmass was dominated by broad craton consisting of East Antarctica and Australasia. The western sector which was composed of the Antarctic Peninsula and southern South America consisted of a magmatic arc along a zone of subduction extending along the southeastern Pacific. West Antarctica from the base of the Antarctic Peninsula to East Antarctica consisted of several crustal blocks that are believed to have formed a land bridge between the magmatic arc and the craton. Marie Byrd Land and New Zealand which were probably connected across the Campbell Plateau underwent a period of intense orogenic activity during the Early Cretaceous which was followed by an extended period of quiescence and erosion. The Late Cretaceous heralded the final breakup of the southern continents and isolation of Antarctica. Although rifting between Australia and Antarctica began in the Jurassic and continued throughout the Cretaceous, the final separation of Australia probably did not occur until the late Eocene. Paleontologic and geophysical evidence indicate that New Zealand became isolated from Antarctica prior to the end of the Cretaceous. Controversy exists as to the relationship of the Antarctic Peninsula with southern South America during the Late Cretaceous. Paleontologic data clearly shows that the plates were adjacent with active migration of terrestrial faunas taking place. Although faunal interchange between South America and the Antarctic Peninsula ceased during the Early Tertiary with the development of a shallow seaway, complete separation of the two plates did not occur until development of deep sea conditions developed in the Middle Tertiary.