Abstract: Penguins (Aves: Spheniscidae) are pelagic, flightless seabirds, restricted to the southern hemisphere (Antarctic and sub-Antarctic areas, New Zealand, Australia, and nearby islands, as well as parts of South America and South Africa). They spend much of their life at sea, but return to islands and coasts to breed. Penguins are terrestrial as juveniles and aquatic as adults. To improve hydrodynamics, penguins tuck in their necks while swimming. They thus attain an ichthyosaur or cetacean body shape: characterised by telescoped cervicals. This mechanism is also used on land, associated with the posture of these birds. Our study of neck structure and cervical vertebrae morphology (morphological description, biometry and contour analysis) of the King Penguin ( Aptenodytes patagonicus ), Gentoo Penguin ( Pygoscelis papua ), Macaroni Penguin ( Eudyptes chrysolophus ) and Humboldt Penguin ( Sphensicus humboldti ) shows a highly specialised fitting in adults, which develops during ontogenesis. The growth of penguins proceeds by stages and there are key stages with regard to the design of the neck. Despite a common main structure, some characteristics vary between species. Distribution of cervical vertebrae can be defined by six modules. There are differences in modularity between species and also within species between different ontogenetical phases.