Whales belong to Chordata phylum, Vertebrate phylum, Mammalian phylum and Euvertebrate phylum, including about 98 viviparous mammals living in oceans and rivers. There are more than 30 species in China waters. Except a few whales that live in fresh water, all kinds of whales live in the sea? .
The definition of whale itself is vague. Whales can include all cetaceans, as well as cetaceans of specific families. Whales also include all dolphins. Whales are mainly divided into two types: mysterious whales and toothed whales.
There are few species of baleen whales, but they are huge. At present, the smallest known species is more than 6 meters long, and the world's largest animal, the blue whale, also belongs to the baleen whale. However, the shape of toothed whales is quite different, the smallest species is only about 30cm, and the largest sperm whale is more than 20m long. Whales do not belong to fish, but to mammals.
Extended data
Whales rely on keen hearing to survive underwater, but different whales show great differences in hearing ability. Baleen whales can receive infrasound waves with a frequency that is too low for humans to detect, which enables them to communicate over long distances, while toothed whales rely on ultrasonic waves, which are too high for humans to hear.
According to the report published in the Journal of Contemporary Biology on June 8, 2007, researchers found evidence from the fossils of early extinct whale species, which can prove that the differences in whale hearing ability only appeared after they evolved into complete aquatic animals.
Based on the study of "prehistoric whales" who can live both in water and on land, the researchers found that their auditory system is more similar to their close relatives on land, even cloven-hoofed animals such as pigs, hippos and camels.
Researchers analyzed the remains of primitive whales 45 million years ago, which were found in deep-sea sediments in Togo, West Africa. The researchers studied the bones of two early cetaceans and the cavity surrounding the auditory organs.
The scanned images enable them to analyze the cavity of the petrous part of the temporal bone to protect hearing and balance organs.
Baidu Encyclopedia-Cetaceans