Step 1: Recall the meaning of viviparous versus oviparous.
Viviparous animals give birth to live young that developed inside the mother, while oviparous animals lay eggs that develop outside the body.
Step 2: Classify the three distractor animals.
Scoliodon the dogfish, Pteropus the fruit bat, and Panthera the big cats are all live bearing animals, so they are viviparous and get eliminated.
Step 3: Identify the odd one out.
Echidna belongs to the monotremes, the small group of mammals that lay eggs despite nursing their young with milk, so it is the one animal here that is not viviparous.
Final answer: Option 1, echidna.