Blue shark skull

This post is a bit overdue since this specimen has been completed for almost a year now, but I still wanted to write a few lines about it. It was my first large shark skull (and one of my first shark skulls for that matter, since I only started experimenting on numerous catshark specimens a few months later), and I made several mistakes in the process which I'll discuss a bit here.

I found this specimen quite unexpectedly while out to buy some food during the summer of 2013. I always check the fish department as well in case they might have anything of interest, and got really excited when I noticed the large shape on the stall. Although it's meat is sold on a regular basis around here (I'm located on the Mediterranean coast) it was the first time I saw the head in a shop, and the guys there were nice enough to give me the head for free.

Blue shark (Prionace glauca) head.

Close up on the snout showing the ampullae of Lorenzini. The medial rostral cartilage is also visible through the skin.

Dissection of the head, with palatoquadrate and right optic capsule exposed.

The first mistake I made with this specimen was to attempt a complete dissection of the head. While it can be done, it often leads to broken structures in the skull, since in some areas the skin is a lot tougher than the cartilage underneath, especially around the rostrum and orbital processes. Doing so, I damaged one of the preorbital processes, which are fairly developed in this species.

The second mistake was to apply too much heat to the jaw which separated at the joints. Fortunately, the teeth didn't fall out, which is also a common occurrence when too much heat is applied. This is why you can't clean shark jaws by boiling them as Quinn is doing in Jaws.

Re-articulation of the jaw joints.

The jaws can be glued back in place, and on large skulls I use wire as well for additional strength. Even then, the jaws will be much more fragile and delicate than if the ligaments are preserved. The palatoquadrate and meckel's cartilage are carefully drilled and wired with brass wire and glued back together. The same process can be used for the hyomandibulars and to glue the jaw to the chondrocranium. On large specimens, I prefer to remove the jaw from the chondrocranium for proper cleaning. This way I can also apply heat to the chondrocranium without damaging the jaws.

Gluing the hyomandibulars back in place on a blacktip reef shark (Carcharhinus melanopterus).

 Another issue with the blue shark is the tendency of the chondrocranium to warp a lot as it dries. Freeze drying might reduce this issue, but every specimens I've been able to see so far displayed a high degree of distortion.

Dorsal view of a blue shark skull, showing important distortion.

Anyway, it was still a very interesting specimen to work on. I hope to get my hands on a second one later one so I can clean it properly without repeating the same mistakes.

The finished specimen. I also kept the ceratohyals and basihyal and might glue them back later.