The ancients regarded dolphins as sea pigs. However, modern scientists have found that dolphins and pigs have the same ancestor, so it is no problem to call them sea pigs. According to modern biological classification, pigs are carved pig species of Artiodactyla. The ancestors of whales such as dolphins and blue whales are more like relatives of hippos according to the ancient Pakistani whales (with limbs and amphibians). At that time, hippopotamus belonged to the family Hippopotamus of the suborder Pig.
So it makes sense to say that whales are sea pigs, dolphins are small sea pigs and hippos are river pigs.
At present, some biologists have kidnapped Hippophae rhamnoides from the suborder Porcine and merged with cetaceans to create the concept of cetaceans or Hippophae rhamnoides. This is a deliberate deprivation of the existence of porcupines and an obliteration of the foresight of ancestors. Although the word dolphin meant "kill and eat meat" in the eyes of the ancients.