Consider the following statements: 1. Some species of turtles are herbivores. 2. Some species of fish are herbivores. 3. Some species of marine mammals are herbivores. 4. Some species of snakes are viviparous. Which of the statements given above are correct?

Let's analyze each statement:

1. Some species of turtles are herbivores. This is correct. Many species of turtles, especially terrestrial tortoises (e.g., Aldabra giant tortoise) and some aquatic turtles (e.g., green sea turtle in its adult stage), are primarily herbivorous, feeding on plants, fruits, and algae.

2. Some species of fish are herbivores. This is correct. There are numerous herbivorous fish species that graze on algae and aquatic plants, such as parrotfish (coral reef herbivores), certain carp species, and many aquarium fish.

3. Some species of marine mammals are herbivores. This is correct. Manatees and dugongs, often referred to as 'sea cows', are prominent examples of marine mammals that are strictly herbivorous, feeding on seagrass and other aquatic vegetation.

4. Some species of snakes are viviparous. This is correct. While many snakes are oviparous (egg-laying), a significant number of snake species are viviparous, meaning they give birth to live young. Well-known examples include boa constrictors, anacondas, and most vipers.

Since all the statements are factually correct, the correct answer is D.