One of the richest and best preserved late Campanian-Maastrichtian ammonite faunas of the world occurs within the Lopez de Bertodano Formation on Seymour Island. The excellent exposure of this sequence has offered an opportunity for detailed stratigraphic study of the fauna, providing a stratigraphic control unavailable for most other Southern Hemisphere strata of similar age.
Ammonites are restricted to the Cretaceous portion of the Lopez de Bertodano Formation, becoming more abundant and increasing in diversity within a 600-m interval below the Cretaceous-Tertiary boundary. The ammonite-rich levels are divided into three zones (from oldest to youngest: Pachydiscus ootacodensis, P. riccardi and P. ultimus zones), extending from the late Campanian-Maastrichtian to the latest Maastrichtian.
The taxonomic study of this fauna shows a predominance of endemic taxa of the family Kossmaticeratidae, including the species Maorites tuberculatus Howarth, M. seymourianus (Kilian and Reboul), M. densicostatus (Kilian and Reboul), M. weddelliensis n. sp., Grossouvrites gemmatus (Huppe) and Gunnarites bhavaniformis (Kilian and Reboul). These taxa, together with the members of the family Desmoceratidae Kitchinites (Kitchinites) darwini (Steinmann) and K. (K.) laurae n. sp., are mostly restricted to the margins of the Late Cretaceous Weddellian Province that extended from southern South America to Australia.
Cosmopolitan genera described in this work become more abundant up section and include the species Anagaudryceras seymouriense n. sp., Zelandites varuna (Forbes), Pseudophyllites loryi (Kilian and Reboul), Diplomoceras lambi Spath, Pachydiscus (Pachydiscus) ootacodensis (Stoliczka), P. (P.) riccardi n. sp. and P. (P.) ultimus n. sp.