Journey of Life - Seas of Life 8
Steve travels back 3.8 billion years to when life began. Journeying round the oceans, he explores life's first laboratory and discovers how the incredible variety of sea creatures arose, from the first microbes to hagfish and dolphins.
The incredible thing is, eighty percent of its genes are inside us too, including those that form the human heart, but where is the backbone? The key to that inheritance is found inside its tiny young. It's these little squirts that have a tail with a flexible rod inside- the earliest hint of a backbone.
With this flimsy backbone, the first true vertebrates emerged, amongst which were the jawless fish.
These jawless hagfish are deep-sea creatures that live way beyond our reach. Here, more than a mile below the ocean surface, they are scavenging on the carcass of a dead whale. They might look more like worms than fish, but five hundred million years ago, jawless wonders like these ruled the seas.
Today they sometimes rise up to the shallows and in Sweden's cold dark fjords, they come face to face with fishermen. And if they're caught by a predator, just watch what they can do.
"Their primitive backbones are so flexible, they can literally tie themselves in knots"
And a slipknot can sometimes be a lifesaver. Being made of flexible cartilage rather than bone, that spine's a whole lot bendier than mine.
"Here we go. A nice little granny knot there."
And if tying a knot isn't enough to escape the predator's grasp, then the hagfish has another trick up its sleeve.
"Er, look at that"
"That is incredible. It's a really unique defense mechanism. The hagfish secretes mucus from glands either side of its body. And this mucus starts to swell when it contacts water. It also contains these high-tensile fibers that form a shield of slime.
One hagfish can jellify a whole bucket of seawater. But despite these extraordinary adaptations, jawless-fish had soon had their day. About four hundred million years ago, they were sidelined by the results of a new and deadly development. Somewhere out there. A brand-new kind of fish was evolving. Its front two-gill arches gradually grew and encircled the mouth, becoming the first biting jaws. Such early jawed fish became the sharks. |
