Which of the following is a living fossil

Explanation

• A living fossil is an organism that has remained unchanged from earlier geographical time and its close relatives are extinct. 
• Coelacanth with lobed fins, is called the living fossil, as it was thought to be extinct and was considered as the only sole member alive of a taxon. 
• In 1938, South Africa, Coelacanth was caught, and these evolved into first amphibians which could live on both land and water.
• Limulus (King crab) has remained unchanged from almost 190 million years and thus is categorized as a living fossil. 
• Sphenodon (tuataras) is considered a living fossil as they possess primitive body plan i.e., its heart is primitive compared to other reptiles like snakes, lizards, etc.

Final Answer

Hence the correct option is D i.e., all the above as Coelacanth, Limulus and Sphenodon are all considered as living fossils. 

• Antidiuretic hormone or vasopressin plays an important role in regulating the water content in the body. Thus, it gets released when water loss is high or the body is dehydrating and increases water reabsorption.
• Adrenaline hormone is a stress hormone that prepares our body for the fight-or-flight response.