ABSTRACT
Introduction ....................................................................................................................................225 Methods and Materials...................................................................................................................226 Results ............................................................................................................................................228 Discussion ......................................................................................................................................232 Conclusions ....................................................................................................................................236 Acknowledgements ........................................................................................................................236 References ......................................................................................................................................236
With a fossil record known to extend as far back as the Early Palaeocene (61 Ma; Slack et al., 2006), Sphenisciformes (penguins) is among the oldest of extant avian clades. Penguins exhibit a remarkable range of adaptations to life in the marine environment, including flattened limb bones, feathers that are unique among birds and solid bones (Davis and Renner, 2003). This latter characteristic has been a feature of the group from earliest times, and to some extent explains their abundance in the fossil record compared with some other avian clades (Fordyce and Jones, 1990). Despite this, the origin, early evolution and systematics of penguins remain poorly understood.
