The Antarctic’s Gondwanan cousin: a new Dynomenidae (Crustacea, Dromioidea) from the Santa Marta Formation, James Ross Basin, Antarctica

Abstract The James Ross Basin, situated in the northwestern portion of the Antarctic Peninsula, holds one of the most complete sedimentary records of the Cretaceous, and hosts exceptionally well-preserved and diverse fossil assemblages, particularly notable for high southern latitudes. The Santa Marta Formation (Santonian–Campanian) harbors a rich decapod crustacean fauna, including Anomura, Astacidea, Achelata, Brachyura, and Glypheidea. Among brachyuran crabs, only four families have been described on James Ross Island: Homolodromiidae, Necrocarcinidae, Prosopidae, and Raninidae. This work focuses on a brachyuran from the Marambio Group, a part of the Santa Marta Formation. The material presented here was collected during the 41 st Brazilian Antarctic Operation by researchers of the PALEOANTAR project. The site consists of a sequence of intercalated volcanic sandstones, siltstones, and tuffs, interpreted as a set of volcanoclastic deposits formed in a deltaic environment. The specimen described here with a well-preserved ventral surface, Sabellidromites santamarta new species, is assigned to the Dynomenidae based on uropods as calcified dorsal plates, a reduced, obliquely subdorsal fifth pereopod (fourth pereopod not reduced), and characteristics of the dorsal carapace. The occurrence of Sabellidromites santamarta n. sp. in the Santonian–Campanian of Antarctica suggests biogeographic exchanges of the dynomenid fauna between the Northern and Southern hemispheres during the Late Cretaceous. UUID: http://zoobank.org/5c53c84a-af78-432f-ba1a-795008a3db70