At the root of the early penguin neck: a study of the only two cervicodorsal spines recovered from the Eocene of Antarctica

Abstract

The spinal column of early Antarctic penguins is poorly known, mainly due to the scarcity of articulated vertebrae in the fossil record. One of the most interesting segments of this part of the skeleton is the transitional series located at the root of the neck. Here, two such cervicodorsal series, comprising reinterpreted known material and a new specimen from the Eocene of Seymour Island (Antarctic Peninsula), were investigated and contrasted with those of modern penguins and some fossil bones. The new specimen is smaller than the counterpart elements in recent king penguins, whereas the second series belonged to a large-bodied penguin from the genus Palaeeudyptes. It had been assigned by earlier researchers to P. gunnari (a species of “giant” penguins) and a Bayesian analysis—a Bayes factor approach based on size of an associated tarsometatarsus—strongly supported such an assignment. Morphological and functional studies revealed that mobility within the aforementioned segment probably did not differ substantially between extant and studied fossil penguins. There were, however, intriguing morphological differences between the smaller fossil specimen and the comparative material related to the condition of the lateral excavation in the first cervicodorsal vertebra and the extremely small size of the intervertebral foramen located just prior to the first “true” thoracic vertebra. The former feature could have resulted from discrepancy in severity of external pneumatization. Both fossils provided valuable insights into the morphology and functioning of the axial skeleton in early penguins.

• Antarctic Peninsula
• La Meseta Formation
• Palaeogene
• early Sphenisciformes
• cervicodorsal vertebrae.

Acknowledgements

I would like to thank Andrzej Gaździcki, Warsaw, Poland, for transferring specimen IB/P/B-0981 to the collection at the University of Bialystok and Andrzej Tatur, Warsaw, for his assistance in determining the position of the collecting site (so-called “shelves”). Marcelo Reguero, La Plata, Argentina, is thanked for inviting me to study the La Plata collection and his helpful suggestions on a submitted typescript of this paper. I am also greatly indebted to Daniel Ksepka, Raleigh, USA, the second reviewer, for his valuable comments and suggestions.