Are Dolphins and Whales the Same? A Detailed Explanation of the Differences in Appearance and the Identity of the Killer Whale

When it comes to marine mammals, most people probably think first of dolphins and whales. So, have you ever wondered, are dolphins and whales the same? What are the differences in appearance between the two? Is the killer whale a dolphin or a whale?

In fact, both dolphins and whales belong to the order Cetacea. This is a group of mammals that live in water, sharing the same physiological characteristics as land mammals, such as breathing with lungs and giving birth to live young, and they also possess special physiological structures evolved to adapt to an aquatic environment.

Cetacea is the branch of all mammals best adapted to aquatic life. Their appearance resembles that of fish, and they are completely unable to live on land. They include some of the largest animals on Earth, while most are medium-sized. All extant members of Cetacea have forelimbs shaped into flippers, completely degenerated hind limbs, a horizontal tail fin at the end of the tail, usually a vertical dorsal fin on the back, and nostrils relocated to the top of the head.

Extant Cetacea can be further divided into two suborders, namely the baleen whales and the toothed whales. The division of these two major groups is academically based mainly on differences in their feeding methods. The main morphological feature of baleen whales is that they have no teeth in the mouth, but instead have specialized baleen, which can be used to filter plankton, so they are filter feeders. Baleen whales have two blowholes, are mostly larger in size, and include the largest animals in the world. The toothed whales include most living cetaceans and had already appeared by the Late Miocene. Their main features are that they have more or fewer teeth in the mouth, an asymmetrical skull, only one blowhole, and are predatory. The number and arrangement of their teeth vary depending on diet. There are 13 families and about 79 species extant worldwide. 

The toothed whales are relatively diverse, with most members being relatively small in size, though a few species are very large. Many members of the toothed whales have relatively limited distributions, with quite a few species restricted to coastal areas, and some restricted to the open ocean or rivers, but some are distributed worldwide and can appear in many kinds of waters.

At present, there is some disagreement about the family classification of toothed whales. Broadly, they can be divided into three relatively distinct groups: dolphins, beaked whales, and sperm whales, with each group divided into one or more families.

In other words, dolphins belong to the class Mammalia, order Cetacea, suborder Odontoceti, family Delphinidae, commonly known as dolphins. They are the most species-rich family in Cetacea and the one most familiar to people, with nearly 62 species distributed across the world's oceans. Body length is 1.2 to 4.2 m, and body weight is 23 to 225 kg. Most members are relatively small in size, including the smallest cetaceans, and feed on fish or mollusks, while some are larger and can prey on other marine mammals. In terms of appearance, the family Delphinidae can be distinguished as long-beaked, short-beaked, and beakless, and most have a dorsal fin on the back, while a few have no dorsal fin.

From this it can be seen that dolphins and whales are in fact just called by different names, just like the eagle and the hawk, or the dog and the wolf: they are originally of the same lineage, similar yet not identical, following the same principle. The small ones are called dolphins, and the large ones are called whales, said to be divided by a body length of around 5 m after reaching adulthood.

So, is the killer whale actually a dolphin or a whale?

The killer whale is a large toothed whale. Because of its extremely fierce temperament, it is also called the bad whale, killer whale, murderer whale, orca, and so on. According to biological taxonomy, the killer whale belongs to the order Cetacea, family Delphinidae. If whales refer to the order Cetacea, then the killer whale is both a member of the dolphin family and also a whale.