Whale Evolution and Classification
Characteristic Shared Between Cetacean Species
Whales probably evolved from animals related to the Hippopotamus millions of years ago, and it seems as if their unusually small inner ear structures hold a key. Because they were not so likely to become dizzy when performing acrobatics underwater they were able to exploit an entirely new environment. In geological terms they adapted very rapidly to their new aquatic life, and by 30 million years ago they had established two completely different lines – the baleen whales and the toothed whales.
Marine Mammals
Several groups of mammal have secondarily adapted to an aquatic life-style. Whales, dugongs and the seals and sea-lions are all fully marine mammals, and the sea otters are almost there. These mammals are only distantly related to one-another (they are all mammals!), and the whales themselves are often distantly related to each other.
How Closely Related are the Whales
The different groups of whales are not very close relatives. The baleen whales separated from the toothed whales millions of years ago – long before we shared common ancestors with other great apes. Some species (such as the Gray Whale) even have a family (Eschrichtiidae) to themselves. For comparison we humans are in the same family as the chimpanzees and gorillas, but the gibbons are in a family of their own. So, although all whales share common ancestors millions of years ago, they are not necessarily closely related to each-other.
Toothed Whales
One of the characteristic features of the mammals is their teeth, and all whales started out with effective teeth. Most of the whales who pursue an active hunting life-style have retained their teeth, but they seem to have developed different uses in different species. Killer Whales certainly use their teeth as one would expect, but what is the function of the Narwhal’s tusk? It has been suggested that in some cases (Sperm Whales for example) the teeth might actually be more part of the echo-location system than structures used to grab prey.
Baleen Whales
Millions of years ago some whales replaced their teeth with sheets of baleen (made of the same stuff as our finger nails), so that they could filter small organisms from the plankton. Most still use their baleen plates in this way, but the Humpback now catches fish, while the Gray Whale filters sediment.
Characteristics Shared by All Whales
Certainly all living whales share certain characteristics, but no more so than all primates. If we are talking about DNA or body plans then it makes sense to talk about ‘whales’, but when we move on to the more interesting questions such as ‘how intelligent?’ or ‘do they have a language?’ we need to ask the question of each species individually. Indeed, if we move on to ask questions about behaviour we might need to focus on different populations within a species. Humans living traditionally in remote parts of the world behave differently from other human populations of city dwellers, and some pods of Killer Whales behave very differently from others!
(Click on the dark image below to view it!)
