The following is a list of the largest species in a group, where a group could be in a narrow definition like penguins or a much wider definition like reptiles. With no specific order:
1. Blue Whale
At 30 meters (98 ft) in length and 170 tonnes or more in weight, it is the largest whale and the largest known animal ever to have existed!
The Killer Whale, or Orca, is actually part of the Dolphins family, making it the largest species of the oceanic dolphin family. The largest Orca ever recorded was a male off the coast of Japan, measuring 9.7 m (32 ft) long and weighed 10 tonnes.
3. Emperor Penguin
The Emperor Penguin is one of the heaviest living birds as well as the largest penguin, with a maximum height of 1.35 m (4.3 ft) and weight of 46 kg (102 lb).
The largest living bird. A large male ostrich can reach a height of 2.8 m (9.2 ft) and weigh over 156 kg (345 lb). Eggs laid by the Ostrich can weigh 1.4 kg (3 lb) and are the largest eggs in the world today.
5. Saltwater Crocodile
The largest living reptile. The males of this species can reach sizes of up to 7 m (23 ft) and weigh as much as 2,000 kg (4,400 lb). Females are much smaller and often do not surpass 3 m (9.8 ft).
The largest living rodent, native to most of the tropical and temperate parts of South America east of the Andes, always near water. Full-grown capybaras can reach 1.5 m (4.9 ft) long and 0.9 m (3.0 ft) tall at the shoulder and a maximum weight of 105 kg (232 lb).
7. Giant Golden-Crowned Flying Fox
Also known as the golden-capped fruit bat, is a rare megabat and the largest bat in the world. The species is endangered and only found in the Philippines. It has a wingspan of 1.5–1.7 metres (4 ft 10 in–5 ft 7 in) and weighing 0.7–1.2 kilograms (1.5–2.6 lb).
The eastern lowland gorilla is the largest living primate. Found at the mountainous forests of the eastern Democratic Republic of the Congo. Males weigh 163 kg (360 lb) on average while females usually weigh half as much. Males have a standing height of 1.76 meters (5 ft 9 in) on average and females stand at 1.60 meters (5 ft 3 in) or less.
9. Green anaconda
The heaviest snake in the world with range from 30 to 70 kg (66 to 150 lb) in an average-range adult. The green anaconda is also one of the world’s longest snakes, reaching more than 6.6 m (22 ft) long. It is the largest snake native to the Americas.
10. Giant Huntsman Spider
The world’s largest spider by leg-span with a 30 centimeter (12 inches) leg-span (!!), and 4.6 centimeters (1.8 inches) body-length. The Huntsman appears to be a cave dweller and was discovered in Laos in 2001. It is part of the Heteropoda genus.