New giant penguin bones from Antarctica: systematic and paleobiological significance

ACOSTA HOSPITALECHE, C.

Mendoza

Congreso; 4th International Palaeontological Congress, Cretaceous-Tertiary palaeobiogeographic connections with Antarctica Symposium; 2014

A tarsometatarsus (MLP 12-I-20-116) and a fragmented humerus (MLP 12-I-20-288) of striking dimensions assigned to Palaeeudyptes klekowskii were collected in the DPV 13/84, Marambio (Seymour) Island, Antarctica. They come from the middle Eocene- earliest Oligocene Submeseta Formation, equivalent to the uppermost part of the former La Meseta Formation, according to new stratigraphic proposal. Body mass and body length (maximum measurements from the tip of the toes to the end of the bill, with the neck and legs outstretched) were calculated. The most conservative values were used for diving duration estimations. The tarsometatarsus with 91.3 mm length, is the most massive tarsometatarsus known for Palaeeudyptes (59- 82.4 mm), constituting the largest one ever described. Subtle differences were obtained by using each measurements selected for calculations. The tarsometatarsal width indicates a body mass of 114.38 kg and 2.01 m length, whereas the anteroposterior width points toward a body mass of 116.21 kg and 2.02 m of total length. It seems an extremely high value for both calculated parameters. Nevertheless, given that the living Emperor penguin reaches 46 kg and 136 cm in length ?equivalent to near 116 cm in height-, and its tarsometatarsus is only about 50 mm length, the estimated values based on an almost double sized tarsometatarsus are not beyond the expected assessment. Assuming that the humerus proportions are not sensitive to significant intraspecific variation, it seems possible to calculate an approximate length of 259.2 mm for the MLP 12-I-20-288 on the basis of the measurements taken in the co-specific MLP 11-II-20-07, and scaling its size from the width of the proximal epiphysis. Dimensions of the humerus are also huge, although these values are only estimates and cannot be taken as absolute. The most conservative values were here taken for further paleobiological calculations in order to prevent overestimations. The tarsometatarsus would belong to a penguin with high diving skills; capable of making longer breath-hold dives than other heavy animals. It was estimated that regular dives take 16.6 minutes duration (with potential and maximum dives of 40 minutes). These approximations are consistent with the generalized idea that Antarctic large penguins were piscivores. They had probably used pursuit diving techniques for the capture of large fish. Gigantism would confer it certain advantages for survival within the colony, a more effective defense against predators, and greater ability to catch prey.