During the latter part of the 19th century, the waters off the coast of the Antarctic Peninsula began to be visited by ships searching for new whaling grounds. During the austral summer of 1892–1893, two of these early whaling expeditions visited the Seymour Island region on the northeast tip of the peninsula. The Norwegian ship Jason, commanded by Captain C. A. Larsen, reached Antarctica in November 1892; after sailing south along the east side of the peninsula as far as the sea ice would allow, the crew returned to Seymour Island in mid-November and landed on the east side of the island in search of seals. While ashore, Captain Larsen collected the first fossils from the continent of Antarctica. Although he never published any account of his discovery, we know many of the particulars of Larsen’s discovery from Dr. Donald, one of two naturalists assigned to the Dundee Whaling Expedition that arrived in the area shortly after the discovery. In 1901, explorer/scientist Otto Nordenskjöld organized the Swedish South Polar Expedition (1901–1903) to explore the Seymour Island region. Nordenskjöld’s expedition was forced, due to the loss of his ship, the Antarctic, to spend 2½ years in Antarctica. During his forced stay, he explored Seymour Island and the surrounding area and made a number of important scientific discoveries. Although the Swedish South Polar Expedition was one of the most scientifically successful expeditions in the annals of Antarctic exploration, Nordenskjöld did not succeed, due to chance and circumstances beyond his control, in exploiting the truly remarkable fossil deposits that are present on Seymour Island.

The Upper Cretaceous-lowermost Tertiary López de Bertodano and Sobral Formations Seymour Island, Antarctic Peninsula, contain one of the most important marine faunas known for this interval of the Earth’s history. Faunal data from this sequence are providing important new understanding of the origin and biogeographic history of the marine biota of the Southern Hemisphere and insight into the faunal transition at the end of Cretaceous time. The bivalves described herein where collected during four expeditions (1975, 1982, 1983–1984–1985) to Seymour Island. In addition, the collections made by the Swedish South Polar Expedition, 1901–1903, housed in the Naturhistoriska Riksmuseet, Stockholm, were also examined during the course of this study. This chapter describes 13 new species and 2 genera of bivalves: Nucula (Leionucula) hunickeni n. sp., Australoneilo casei n. sp., Austrocucullaea n. gen. oliveroi n. sp., Cucullaea ellioti n. sp., Pinna freneixae n. sp., Phelopteria feldmanni n. sp., Entolium seymourensis n. sp., E. sadleri n. sp., Acesta shackletoni n. sp., A. webbi n. sp., Seymourtula n. gen. antarctica (Wilckens), Lahillia huberi n. sp., Marwickia woodburnei n. sp., Cyclorisma chaneyi n. sp., Surobula n. gen. nucleus (Wilckens), Thracia askinae n. sp. Twenty-one previously described species are redescribed and figured, and their taxonomy revised.

Dimitobelus (Dimitocamax) seymouriensis n. sp., a new subgenus and species of Dimitobelidae, a belemnite family restricted to the Cretaceous Southern Hemisphere, is described from the Campanian-Maastrichtian López de Bertodano Formation of Seymour Island, Antarctic Peninsula. The subgenus D. (Dimitocamax) n. subgen. is erected for those species of Dimitobelus possessing a regular hastate form and Actinocamax-like alveolar regions. D. (Dimitocamax) n. subgen. had a restricted stratigraphic and geographic distribution in contrast to the wider distribution of D. (Dimitobelus) Whitehouse.

Twelve species of brachiopods have been collected from the La Meseta Formation (Eocene) of Seymour Island, Antarctica, arrayed in one inarticulate and nine articulate genera. None of these brachiopods is known to reside currently in the region near Seymour Island. Modern congeneric descendants of some of these taxa are found in both shallow- and deep-water habitats in a wide variety of Southern Hemisphere localities. These adaptations to a broad spectrum of habitats and the restriction to lower latitudes may have been triggered by changing conditions in the region subsequent to the development of the circum-Antarctic current following deposition of the La Meseta Formation. The articulate brachiopod genera ?Probolarina, Tegulorhynchia, ?Plicirhynchia, and Terebratulina are noted from the La Meseta Formation for the first time, although the latter three genera have been identified previously from the Tertiary beds of nearby Cockburn Island, Antarctica.

This chapter augments the work of Blake and Zinsmeister (1979) on asteroids of the upper Eocene La Meseta Formation, Seymour Island, Antarctic Peninsula. Buterminster elegans n. gen. n. sp. (Goniasteridae) is described, and small Zoroaster aff. Z. fulgens (Zoroasteridae), a four-armed Ctenophoraster downeyea (Astropectinidae), and an undetermined species of Sclerasterias (?) (Asteriidae) are reported and evaluated. Asteroids are rare in most fossil faunas but common in the La Meseta Formation; the poor record of asteroids is attributed to body construction and habits rather than to a geologically recent diversification. Asteroids, especially members of the Asteriidae, are important in determining structure of many modern communities. The presence of an asteriid species in the La Meseta Formation fauna suggests a community structure parallel to certain modern examples. Elsewhere, the La Meseta Formation has been inferred to have been deposited in moderately high-energy, shallow water; in contrast, modern Sclerasterias (in Antarctica), Zoroaster, and Ctenophoraster are known only from relatively deeper waters. Three small Zoroaster aff. Z. fulgens are preserved with their arms extended above the disc, apparently buried while suspension-feeding. This posture is rare among asteroids and has not been reported among modern members of the Zoroasteridae. Morphologic differences between La Meseta Formation asteroids and their closest modern biologic allies are relatively minor, suggesting slow evolution. Modern species closely related to the fossil species are known from southern oceans; no major biogeographic changes are evident.