Roberto E. Yury-Yáñez

Eocene Birds from the Western Margin of Southernmost South America

Abstract This study presents the first record of Eocene birds from the western margin of southernmost South America. Three localities in Magallanes, southern Chile, have yielded a total of eleven bird remains, including Sphenisciformes (penguins) and one record tentatively assigned to cf. Ardeidae (egrets). Two different groups of penguins have been recognized from these localities. The first group is similar in size to the smallest taxa previously described from Seymour Island, Marambiornis Myrcha et al., 2002, Mesetaornis Myrcha et al., 2002, and Delphinornis Wiman, 1905. The second recognized group is similar in size to the biggest taxa from Seymour Island; based on the available remains, we recognize the genus Palaeeudyptes Huxley, 1859, one of the most widespread penguin genera in the Southern Hemisphere during the Eocene. The stratigraphic context of the localities indicates a certain level of correlation with the geological units described on Seymour Island. The newly studied materials cast more light on the paleobiogeography of the group, extending the known ranges to the South American continent. In addition to the newly discovered birds, the presence of several taxa of elasmobranchs previously recovered exclusively from Eocene beds in the Southern Hemisphere help to clarify the age of the studied localities, widely discussed during the last decades. This paper verifies the presence of extensive Eocene sedimentary successions with fossil vertebrates along the western margin of southern South America, contrary to the previous assumption that such a record is lacking in Chile.

A new species of chimaeriform (Chondrichthyes, Holocephali) from the uppermost Cretaceous of the Lopez de Bertodano Formation, Isla Marambio (Seymour Island), Antarctica

Abstract We describe a new chimaeriform fish, Callorhinchus torresi sp. nov., from the uppermost Cretaceous (late Maastrichtian) of the López de Bertodano Formation, Isla Marambio (Seymour Island), Antarctica. The material shows it is distinct from currently known fossil and extant species of the genus, whereas the outline of the tritors (abrasive surfaces of each dental plate) shows an intermediate morphology between earlier records from the Cenomanian of New Zealand and those from the Eocene of Isla Marambio. This suggests an evolutionary trend in tritor morphology in the lineage leading to modern callorhynchids, during the Late Cretaceous-Palaeogene interval.

NEW CHONDRICHTHYANS FROM THE UPPER CRETACEOUS (CAMPANIAN-MAASTRICHTIAN) OF SEYMOUR AND JAMES ROSS ISLANDS, ANTARCTICA

Abstract We present new records of chondrichthyans recovered from strata of Maastrichtian age of the López de Bertodano Formation, Seymour (=Marambio) Island, and from levels of latest Campanian age of the Santa Marta Formation, James Ross Island, both located in the eastern Antarctic Peninsula. The material from Marambio Island comprises an associated assemblage with the first records of an indeterminate odontaspidid different from Odontaspis, as well as the genera Pristiophorus, Squatina, Paraorthacodus, and the species Chlamydoselachus tatere from the López de Bertodano Formation. Also, the studied section provides a well-constrained age for several taxa already recognized in the López de Bertodano Formation only by scattered samples of Maastrichtian age for the first time. The assemblage from Marambio Island is representative of one of the latest environmental conditions during the end of the Cretaceous in the coastal seas of the Larsen Basin before major changes that began after the K/P boundary. In addition, the finds from James Ross Island comprise the southernmost records of the neoselachians Cretalamna sp., Centrophoroides sp., as well as the holocephalans Callorhinchus sp. and an indeterminate rhinochimaerid, extending the occurrence of some of these taxa into the late Campanian, being their oldest record of the Weddellian Biogeographic Province.

Endocranial morphology of Pygoscelis calderensis (Aves, Spheniscidae) from the Neogene of Chile and remarks on brain morphology in modern Pygoscelis

The endocranial anatomy of Pygoscelis calderensis, a fossil species from the Bahía Inglesa Formation (Middle Miocene–Pliocene) of Chile, South America, was described through CT scans. Reconstructions of the fossil P. calderensis and endocasts for the living Pygoscelis adeliae, and Pygoscelis papua are provided here for the first time. Comparisons with the extant congeneric species P. adeliae, Pygoscelisantarctica and P. papua indicate that the morphological pattern of the brain and inner ear of the extant pygoscelids has been present already in the Middle Miocene. The neurological morphology suggests that the paleobiology of the extinct form would have been similar to the extant species. It was probably true for diet, feeding behaviour and diving kinematics.