@earthstory / earthstory.tumblr.com
Since I can’t actually get a dinosaur for Christmas… next best thing’s some new additions to my collection. :D
From top to bottom:
1. Tiger shark and London Shark teeth
2. Triceratops tooth (!!!)
3. Oh look, it’s a rock - nope, there’s a couple of gorgeous plant fronds in there
4. A few assorted crinoid pieces from the bag I got. They’re just so pretty. <3
I hope everyone had a lovely Christmas!
Here, have a nightmare.
Tonic immobility
Recently in Australian news, a diver named Cristina Zenato showed the world a perspective of sharks that goes against their vicious and dangerous reputation (http://bit.ly/1BhdcmF). While scratching the nose of a nearby shark, it appears to calm and rest its head in her lap. As she swims away, the shark follows her, almost like it is begging to be scratched some more. It goes into a calm, trance-like state which is scientifically called tonic immobility.
Tonic immobility is a natural state of paralysis that some animals may enter, where they become physically inactive and unresponsive to external stimuli. It has been hypothesised as a method of deterring predators by playing dead, an adaptive behaviour that is called thanatosis, but this response doesn’t appear to be the case with sharks. Sharks use electro-recepting organs called the Ampullae of Lorenzini to sense the electromagnetic field in the water around them and assist in hunting. These ampullae are a network of jelly-filled pores on the underside of the snout, around the nostrils and eyes.
Tonic immobility can be induced in many species of sharks, such as Lemon, Black-tip Reef, and Leopard sharks, and some species of rays by inverting them, thereby putting them in an unnatural pose that is thought to alter the sensory interchange with the environment, causing a 'limp' physical response. Similarly, by scratching or rubbing these organs, as Cristina does, it is thought that this overloads the shark’s sensory capacity and it enters this state of tonic immobility. This activity is used commonly in shark husbandry during handling, in order to calm the shark and reduce the possibility of injury. They can be kept in this state for at least 15 minutes before recovering.
Some studies have been made into tonic immobility in humans, describing it as a state of motor inhibition that occurs in response to fear. The scientists carrying out the studies proposed that inescapable traumatic life threats may invoke tonic immobility-like reactions in humans, using subjects with and without PTSD and recording their physiological response to a retelling of their most traumatising experience in life. Read about it here: http://bit.ly/1W7axsN
Source credit: http://bit.ly/1RtUXAA Image credit: visible pores are the Ampullae of Lorenzini on the underside of a Tiger Shark’s snout (http://bit.ly/1KqhWHo)
