Carolina Acosta Hospitaleche

First articulated skeleton of Palaeeudyptes gunnari from the late Eocene of Isla Marambio (Seymour Island), Antarctica

Abstract The first articulated skeleton of a penguin from the late Eocene of Antarctica is described. MLP 96-I-6-13 comes from the upper Submeseta Allomember (La Meseta Formation) of Isla Marambio (locality DPV 10/84). The significance of this finding in the context of the Anthropornis nordenskjoeldi biozone is discussed. An osteologic description of the recovered elements and a brief discussion of its systematic determination are provided. MLP 96-I-6-13 is the first articulated skeleton with sure specific assignment to Palaeeudyptes gunnari (Wiman, 1905), a species previously known only through isolated tarsometatarsi and included in the groups of Wiman.

PALAEOSPHENISCUS PATAGONICUS (AVES, SPHENISCIFORMES): NEW DISCOVERIES FROM THE EARLY MIOCENE OF ARGENTINA

Abstract The penguin skeleton studied here constitutes the fourth partial skeleton found in Patagonia, and the third one with an associated humerus and tarsometatarsus. The finding of this partial skeleton identified with certainty as Palaeospheniscus patagonicus Moreno and Mercerat, 1891 (Aves, Sphenisciformes) allows the first description of elements other than the tarsometatarsus. The material comes from the basal sector of the Gaiman Formation (Early Miocene), located along the Atlantic coast of Chubut Province, south of Rawson city. This unit comprises a succession of shales, fine tuffs, sandstones, tuffaceous sandstones, and coquinas deposited in a shallow marine environment. These beds contain abundant marine vertebrates (sharks, dolphins, rays, birds), mollusk casts, and oyster beds. The skeleton includes: rostrum, two thoracic vertebrae, right coracoid without the distal end, left humerus, right femur, right tarsometatarsus, left fragmentary scapula, left coracoid, left radius without the distal end, proximal portion of left ulna, proximal end of left femur, and preacetabular part of the synsacrum. P. patagonicus would have been a medium-sized penguin weighing about 5 kg that inhabited the breeding colonies established in the nearby Bryn Gwyn area during the early Miocene. Despite the abundance of penguin remains known for Argentina, and the fact that they are among the birds with a better fossil record, this skeleton is an exceptional case. This finding allows a readjustment of the taxonomic criteria applicable to fossil and living species.

Skeletal morphoanatomy of the Brown Skua Stercorarius antarcticus lonnbergi and the South Polar Skua Stercorarius maccormicki

The Brown Skua Stercorarius antarcticus lonnbergi and the South Polar Skua Stercorarius maccormicki, which breed sympatrically in the Southern Hemisphere, are difficult to identify in the field because of their similar coloration and external morphology. Although several morphological and biological aspects have been previously discussed, no data have been published about their skeletal anatomy. In this paper we make a comparative description of the cranial and appendicular skeleton of both skua species. As a result, and although the differences are small, it has been found that some characters of the skull and the thoracic and pelvic limbs, allow the distinction between S. antarcticus lonnbergi and S. maccormicki.

A traumatic fracture in a giant Eocene penguin from Antarctica

Abstract A fractured femur of a giant fossil penguin from the Anthropornis nordenskjoeldi Biozone (Late Eocene), Isla Marambio (Seymour Island), Antarctica (La Meseta Formation) is described. Palaeoecological, palaeopathological and taphonomical implications derived from the analysis of the kinds of fractures identified are also discussed. The main fracture has irregular margins, indicating there was collagen in the bone at the time of the impact. In this fracture, a mineral deposit was also identified as a fracture hematoma. According to the antemortem classification of fractures, it was produced by an indirect mechanism, provocating a “butterfly wing” or “third fragment” fracture. The remaining fractures are assigned to times of biostratinomic and fossil diagenesis.

Penguin cranial remains from the Eocene La Meseta Formation, Isla Marambio (Seymour Island), Antarctic Peninsula

Abstract Widely accepted ideas about trophic preferences of early penguins suggest that all Eocene sphenisciforms were piscivorous. However, recent findings from the La Meseta Formation (Eocene) of Antarctica, support the presence of at least two different morphotypes that may have evolved as a niche partitioning strategy, which is consistent with the high diversity recorded. The first of them corresponds to a medium–large sized penguin, resembling the Neogene species in configuration. Another morphotype is represented by extremely large penguins with very long and slender bills, clearly linked to fish catching habits.

Ontogenetic variations of the head of Aptenodytes forsteri (Aves, Sphenisciformes): muscular and skull morphology

The emperor penguin (Aptenodytes forsteri) is the largest extant penguin among living species breeding in winter, at Antarctic high latitudes. Despite several studies made on this species, musculature and skeletal anatomy are barely known, especially in non-adult specimens. To address this shortfall, dissections and comparative descriptions were made on crania and mandibles of individuals of different ontogenetic stages: chicks, juveniles, and adults. The results presented here show significant differences in musculature between the age groups, and the proportions between bill and cranium also change along postnatal ontogeny.

Skull morphology and ontogenetic variation of the Southern Giant Petrel Macronectes giganteus (Aves: Procellariiformes)

The Southern Giant Petrel Macronectes giganteus is the largest Procellariidae around the world. Beyond the most striking features on the skull, the strong hooked bill with tubular, dorsally-placed, external nostrils, these petrels have been the focus of diverse studies, except osteological ones. Even less is known about the osteology in juveniles and chicks. A comparative description of the skull anatomy of the Southern Giant Petrel M. giganteus, highlighting the differences along each postnatal ontogenetic stage, is given here. As a result, we found that the shape of the skull does not vary among the compared stages and that there is a progression in the fusion of the elements of the skull and mandible. Besides, less obvious results show a little intraspecific variation among specimens of the same ontogenetic stage, involving osteological features such as the quantity and shape of foramina within pneumatic bone surfaces, and the fact that general size is not associated with sexual dimorphism. The beak acquires its characteristic development and sturdiness from early stages. Conversely, the fossae glandulae nasalis is only developed in juveniles and adults, being absent in earlier stages.

Comparison of the skull of Brown Skua ( Catharacta antarctica lonnbergi ) and South Polar Skua ( Catharacta maccormicki ): differentiation source identification and discriminant analysis

Many contributions try to emphasize the similarities and differences between the Brown Skua Catharacta antarctica lonnbergi¸ and the South Polar Skua Catharacta maccormicki. Most of the morphological information of these species is based on field observation and referred to their external appearance. Few studies deal with their morphometry, mostly using characters measured in live birds, but the information about skeletal features is scarce. In the present study, skull differences between the Brown Skua and the South Polar Skua are quantified through independent quantitative analyses. Shape differences were evaluated in a geometric morphometrics test, while linear metric parameters were used to analyze the differences between species in a principal component analysis, and finally, in a discriminant test. Geometric morphometrics analysis cannot separate groups, whereas linear morphometrics divide well two different groups, showing significant differences. Notwithstanding, the most significant result was obtained using the discriminant analysis, which differentiates the species using simple equations which contain combined measures that can be easily obtained.

New data on the humerotriceps of penguins and its implications in the evolution of the fossa tricipitalis

Abstract A paddle-shaped wing, the general morphology of the humerus, and the muscles involved in wing movement are among the most characteristic adaptations to diving in penguins. Particularly, the humeral fossa tricipitalis and the musculus humerotriceps are clear examples of muscular rearrangement accompanying skeletal changes. In extant Spheniscidae, we were able to identify two heads of this muscle attaching within a different compartment of the bipartite fossa. Since the partition of the fossa appeared as a novelty during the Miocene, we propose that this might have had implications for underwater flight contributing to wing-propelled diving efficiency.