Paleontological inheritance of West Antarctica: Preliminary report of the newly found Mesozoic and Cenozoic fossil vertebrates from the James Ross Basin and Antarctic Peninsula.

MARCELO REGUERO; LEONEL ACOSTA BURLAILLE; CECILIA AMENABAR; EUGENIA ARNAUDO; MÓNICA. R. BUONO; MAGALI CARDENAS; CAROLINA ACOSTA HOSPITALECHE; ORNELA CONSTANTINI; JAVIER GELFO; PAULA BONA; JUAN JOSE MOLY; JOSE O´GORMAN; LAURA CHERNOGUBSKY; SERGIO SANTILLANA; MARIANELLA TALEVI; SOLEDAD GOURIC-CAVALLI; PABLO PUERTA

Kuala Lumpur

Congreso; XXXIV Scientific Committee on Antarctic Research Meeting; 2016

Penguins were and are a successful group of seabirds that conquest different ecological niches occupying marine coast in different cold and temperate environments around the world. Antarctic penguins are mainly represented by large and giant species, although in fact, the high diversity found during the Eocene in Seymour Island includes a wide spectrum of sizes. Fossil species are mostly known trough huge specimens, which are abundant during the Eocene, but small-sized penguins also lived in Antarctica at the same time. The finding of a tiny humerus in the upper Bartonian- Priabonian (Submeseta III Allomember, Submeseta Formation) of Seymour Island (West Antarctica) motivates the present study. Only three species of small−sized genera have been described in Antarctica: Delphinornis, Mesetaornis and Marambiornis, known only trough their tarsometatarsi. In addition, penguins equally sized are known also out of Antarctica: Eretiscus tonni from the early Miocene of Argentina, the Hakataramea penguin nominated by Tatsuro Ando as Pakudyptes hakataramea in his unpublished dissertation, from the latest Oligocene-earliest Miocene of New Zealand, and the modern species Eudyptula minor, habitant of New Zealand, Australia, Chatham Is., and Tasmania. However, the only similarity among them is size, and the systematic assignment of the MLP 00-I-1-19 to Eudyptula minor, Eretiscus tonni, and the Hakataramea penguin can be easily discarded because their fossa tricipitalis are bipartite whereas it is single in the Antarctic material. The huge difference in size precludes its assignment to any species of Tonniornis, Archaeospheniscus, Palaeeudyptes, and Anthropornis; that way, comparison will be only worth to make in detail with Marambiornis, Mesetaornis, and Delphinornis. Previous assignments published by Jadwiszczak using statistical approaches indicate a humerus of ca. 91 mm length for these species, whereas the MLP 00-I-1-19 only reaches 48.7 mm length. Some morphological differences can be pointed, for instance, the shaft is narrower proximal to the angulus preaxialis in the new specimen, whereas in Marambiornis, Mesetaornis, and Delphinornis it is constant in width, and the angulus preaxialis is more pronounced in the MLP 00-I-1-19 than in the other species. The textural aging and the ossification degree of the new specimen permit to recognize that this fossil belongs to an adult bird whose tiny size is not ought to an ontogenetic issue. These arguments favor the idea that the MLP 00-I-1-19 belong to a different species respect to the humeri previously assigned to Marambiornis, Mesetaornis, and Delphinornis. Nevertheless, a re-evaluation of the these taxa, considering all the material now available is necessary before the proposal of a new species. The evidence strongly suggests that the MLP 00-I-1-19 belongs to an un-described species.