The killer whale spine is bulky and regular. It has 7 cervical vertebrae (the first 4 of which are “welded” together), 11 dorsal vertebrae, 10 lombo-sacred (in the sacrum area), and 23 caudal. The spine is therefore made of 51 vertebrae. According to the studies, the number varies from 50 to 52.

The vertebrae are linked together thanks to an inter vertebral disc. This gives a remarkable flexibility. However the apophysis being short, the moves are limited, especially at the lateral level.

The skeleton study of the killer whale is not that simple, as the sacred vertebrae are nearly identical to the caudal. The spine is regular in size from top to bottom with no sudden reduction in the bone sizes. This is due to the disappearance of the pelvis and the posterior members and to the need to support the whole mass in motion.

The first 7 pairs of ribs are linked to the sternum and have the double articulation principle. The other 6 pairs are are called floating.

The shoulder blade is very developed. It is flat and very large in order to facilitate the pectoral fin mobility as well as the muscular development in this area. Note the disappearance of the clavicle.

Every anterior member is very simple and efficient. As with human beings, we can find the humerus, ulna and the radius. They are not fixed together but are very short.

However, the hand is very developed. Made of 5 carpus, 5 metacarpus and 5 fingers. The hand is very elongated and the central fingers are the longest (number 2 & 3). All the bones are fixed and are on the same plan. Therefore, the bones do not move and it is the muscle contraction fixed to the humerus (and of the humero-scapular articulation) that will allow the moves in the pectoral fins. It is therefore impossible to bend it. It would be like having 2 arms in a plaster (except that the orcas would be better!!). The bones configuration of the pectoral fin (anterior member), clearly shows the link with the orcas’ terrestrial ancestor.

The skull of the odontoceti seems to have migrated to the back, if we compare it to other mammals.

This is actually called “telescoping”, which is the shifting of part of the superior bones of the skull to the back. This is due to the pressure from the maxillary and pre-maxillary.
It is not a reduction of the skull volume, merely a reorganisation. Some bones have disappeared while others have developed. The whole skull is short and high.

The frontal part is actually a bony plate nesting the orbits

One of the specificities of the killer whale skull is its asymmetry (but common with odontoceti). The orca’s face is asymmetric. Concerning the bone area, the left nasal orifice is larger than the right one. Therefore the blowhole is situated slightly on the left hand side. It’s the reason why orcas sometimes tilt a bit on the right hand side to breathe, in order to orientate the blowhole in a zenith position (axis perpendicular to the surface) Obviously this is very slightly and it is not easily spotted. The asymmetry is as much in the bone of the nasal canals that it is in the softer parts. About the bones on the face, these on the left hand side are thicker when these on the right hand side are larger. Hence the discrepancy on the left.

It is important to remember that although the FACE and the SKULL of the killer whale are ASYMETRICS, IT IS SYMETRIC INSIDE THE SKULL. The asymmetry is therefore not modifying the cerebral hemispheres.

The orcas’ skeleton is then very simple but terribly efficient. Sturdy, powerful, even though the whole does not move freely. The most mobile parts are the area operating the pectoral fins. The superior jaws can also open vertically but its moves horizontally are very limited. Actually only the extension and flexion moves are made possible by the articulations. The limitation of lateral moves is necessary to avoid the loss power (generated by the caudal fin). The archeocetes, who were flexible and did not have a “welded”, had to swim like our existing eels, using a lot of energy for a small motion. The skeleton of the killer whale, as we know it today, is an evolution that made the animal highly efficient in the marine environment.