OSTEOHISTOLOGICAL VARIATION IN ANTARCTIC EOCENE STEM PENGUINS: PALAEOECOLOGICAL IMPLICANCES

CERDA, I.A.; TAMBUSSI, C.P.; DEGRANGE, F.J.

Córdoba

Congreso; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2013

Asociación Paleontológica Argentina

In this contribution, the microanatomical and histological structure of Antarctic Eocene stem penguin tarsometatarsi is examined. Our aim is to characterize the bone microstructure of fossil penguins and determine what this can tell us about the process of secondary adaptation to an aquatic life of these vertebrates. Eight adult tarsometatarsi belonging to eight fossil species (Palaeeudyptes gunnari, P. klekowski, Anthropornis grandis, A. nordenskjoeldi, Archaeospheniscus wimani, Microdytes exilis, Delphinornis arctowskii and D. larseni) were transversally sectioned at level of the mid-shaft and studied under normal and polarized light. The compactness percentage (area occupied by bone/total area*100) of each bone was also estimated. The sampled bone comes from the Antarctic Anthropornis nordenskjoeldi Biozone (La Meseta Formation, ~ 34.2 Ma). The thin sections reveal that the medullary cavities occupied less than 6% of the transversal section in Anthropornis spp., A. wimani and P. gunnari and more than 20% in Delphinornis spp., P. klekowski and M. exilis. Primary bone in all the samples consists of well vascularized fibro-lamellar bone. Secondary reconstruction is high and several specimens exhibit dense Haversian bone tissue. Medullary cavities are coated by a thick layer of lamellar bone tissue. The variation in the cortical compactness is the most striking difference among the sampled. Although several causes can explain the observed microanatomical variation (e.g., ontogeny, biomechanic), we interpret that such variation is related to differential adaptations to the aquatic life. Taxa with more massive bones (e.g., Anthropornis spp., Palaeeudyptes ssp.) were possibly adapted to deeper and more prolonged diving excursions.