Xanthe's Shark Braincase

To begin with, Xanthe's Shark Briancase was a bit of a mystery. It was found on the beach at Colac Bay.

We had a few clues:

  • It looked like a skull - it had an exit hole at the back for a spinal chord.

  • The hole faced backwards rather than downwards - suggested an animal with a horizontal spine.

  • It was spongey and flexible l - it felt like cartilage.

  • We knew some fish skeletons are made of cartilage instead of bone.

  • It was found on a beach.



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In Google Images we typed...


fish+skull+cartilage

Bingo! up popped the image below image which looked

very similar to Xanthe's find...

... a photograph of shark's chondrocranium or braincase.

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In Xanthe's shark braincasethe rostrum is missing.

Everything else is recognizable.

The hole at the back right of the braincase is the foramen magnum.

Foramen is Latin for 'hole'. Magnum is Latin for 'big'.

The foramen magnum is the big hole where the spinal chord

leaves the brain into the spine.


Visit this site to see the braincase in more detail.

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1. rostrum - the stiff snout.

2, 3 and 4 - form the cavity for the shark's eyes

5. Occipital condyle - these two bumps show where the

skull meets the first bone of the spine. They help the

head to move as it should.

6. basal plate - the base of the skull

7. nasal capsule - part of a shark's nostril and sense of

smell.

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Xanthe's shark chondrocranium has probably come from a

Dogfish Shark.


Cartilage vs Bone

Cartilage is made of tough, flexible tissue. You can feel it in your

ears and nose. Fish have bones.

For the shark, a skeleton made of cartilage has lots of advantages:

  • cartilage is lighter, stronger and more flexible than bone.

  • A lighter skeleton prevents the shark from sinking.

  • A flexible skelteton allows the shark to turn in tighter circles

when hunting prey.

The Shark's Sixth Sense

The shark has all the senses that we have, plus one

more - an electrical sense.


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Tiny pores on its snout lead to jelly-filled sacs called

ampullae of Lorenzi. These can detect weak electrical

fields. All animals send out electrical 'vibes'.

A struggling or scared animal's electrical 'vibes' are

very strong and the shark can sense them easily with

ts snout.


Heaps more information about sharks here