Hippopotamus is huge, with a body length of 4m, a shoulder height of 1.5m and a weight of about 3 tons. It has a stout body, short limbs, four toes on its feet, a huge head, small eyes and ears, a particularly large mouth, a small tail, huge lower canine teeth, a body length of 50-60cm, a weight of 2.5kg and a skin thickness of about 40-50mm, except for kissing. Lactation 1 year, sexual maturity of 4-5 years old, life expectancy of 30-40 years.

Tyrannosaurusrex, also known as Tyrannosaurus Rex, is the only effective species in the model species, or Tyrannosaurus Rex. It is a large carnivorous dinosaur, about 13 meters long and weighing about 7 metric tons. It lived in the last 3 million years of the Maastricht stage at the end of Cretaceous, about 68.5 million to 65.5 million years ago, before the Cretaceous-Tertiary extinction event.