The different videos help to identify the different bones that can be found at the level of the skull in porpoise, seal, human and dog. We have use common colours for homologous bones meaning you should be able to make comparisons. From a theoretical point of view, all the mammals should have the same bones. It is however not easy to distinguish all of them because they can fuse. For this reason, it is not easy to distinguish for example the different part of the so-called “sphenoid”. We also try at best to place both names used by biologists and name used by vets and/or physicians. Different modifications can be found in the head of marine mammals and are related to their way of life in open sea. The most important one is probably the position of the nares (blowhole). In terrestrial mammals, nares are usually found rostrally and directed downward. While swimming, this position is energetically expensive, as you need to lift your head to place your nose out of the water to take a breath. In marine mammals, nares are directed horizontally or even vertically, limiting the effort to breath. The most extreme cases are found in cetaceans, which nose has migrated to the top of the skull. Whales therefore do not need to emerge the complete head to breathe. This would at any rate be difficult for marine mammals with fused cervical vertebrae, preventing the flexibility of their neck. Marine mammal skulls are also characterized by elongated upper jaws (maxillaries, premaxillaries) and lower jaws (dentaries) that result in a long mouth. Dolphins have numerous sharp teeth. Just as for crocodiles, this mouth ‘design’ is ideal for catching evasive prey, such as fast-moving fish or squid. Dolphins lack incisors, canines, premolars and molars, all of which are found in terrestrial mammals. Instead they have a single kind of tooth with a single cuspid (tip) meaning they can hardly chew their food.
We thank Dr Alicia Quievy, Dr Thierry Jauniaux, Prof Stefan Huggenberger and Prof Annick Gabriel for their assistance.