Whales and dolphins have fascinated us for generations. These magnificent beings can reach lengths of up to almost 100 feet (the blue whale), and are incredibly intelligent. Cetaceans are a large and diverse group that are divided into two suborders: the baleen whales (also known as Rorquals), and the toothed whales. These two groups have a common ancestor but have not been able to interbreed for many millions of years and, as a result, they have several traits that are quite different. For example baleen whales have two nasal openings that make up the blowhole, while toothed whales only have one. Baleen whales also possess a symmetrical skull and lack sternal ribs although it does have a sternum that is made up of one bone. The sternum of the toothed whale is much larger and contains sternal ribs. Toothed whales also have an asymmetrical skull perhaps due to the single nostril. Baleen whales tend to swim slower than toothed whales. The top swimming speed for a whale is just over thirty miles an hour but they can not travel at these speeds for long.
Cetaceans have been evolving for about 54 million years. As strange as it may sound, whales and dolphins actually started as a land animal! They are one of the best, if not the best example of gradual evolution in mammals. Many fossils can be found in what used to be a shallow sea called the Tethys Sea, separating India from Asia, now known as the Himalayan Mountain range. As the fossils became exposed through erosion, archaeologists began to discover small marine mammals. These marine mammals had characteristics that were uniquely cetacean accompanied by small hind legs! From this site we have made huge leaps in what we know about ancient cetaceans. We now believe that baleen and toothed whales diverged around 35 million years ago. When you remember that modern humans have only split from chimpanzees around 5 million years ago, you can understand how different these two types of marine mammals really are.
The Baleen Whales
Baleen whales are the largest of the cetaceans and contain the largest animals that have ever lived! It is believed that whales are large because it is easier for a mammal to maintain body heat in a cold, aquatic environment if they have less surface area in proportion to body mass. The more mass an animal has, the more heat it can produce and the less surface area it has, body heat will not be able to escape as easily.
The most distinctive feature of a baleen whale is, of course, their baleen plates. These whales have developed bristly plates instead of teeth, which they use as a filter. This is a useful adaptation because although these creatures are enormous, they prefer some of the tiniest organisms in the sea such as krill or plankton. A baleen whale simply has to swim through a group of krill with its mouth open, close its mouth when it is full and push the seawater out of its mouth through the baleen fibers. All that remains is a mouthful of tasty krill to swallow. Baleen can range in length from 30 centimeters (Minke Whale) to 4.5 meters (Bowhead whale). Baleen is not made from bone, in spite of its other name, “Whalebone”. It is actually made of keratin which is the same protein that makes up our hair and nails. Baleen is one of the primary reasons that many millions of whales have been killed. It was used in a variety of products, from corsets to strings in tennis rackets.
Lastly, baleen whales are known for their intriguing and hypnotic songs. They were once thought to be mute, because these whales lack vocal chords. It is still unclear exactly how they vocalize or even how they can hear. Baleen whales have a waxy plug that closes off its ear canal. They also lack the sound- receiving bone found in the lower jaw of toothed whales. However they do it, baleen whales can make a wide variety of sounds including moans, clicks, bellows, snorts, bubbling, knocks, yelps and grunts. Blue whales possess the loudest voice on earth. They can reach volumes of 180 decibels. Humans are not able to hear these vocalizations however because the blue whale's voice is at a frequency as low as 10Hz, too low for us to pick up. The reason baleen whales make such loud calls is not clear but it is believed to be a form of long distance communication with other members of its species. Some also believe it is a form of echolocation but this has not been proven. Humpback whales are the most famous cetacean singers. Their mournful songs can be heard day or night, sometimes for 24 hours or more with almost no breaks. Each song can last from a few minutes to as long as half an hour. When the song is finished, the humpback will start at the beginning and sing it all over again. These calls have been closely studied and we have learned there are between two and nine components to each song which are always found in the same order but are often gradually improved and polished. Humpback whales in an area sing similar tunes and seem to incorporate the improvements of others into their own songs, while two humpback whales from different areas sound completely different. In spite of our attempts to understand this behavior, we do not understand the meaning of these complex vocalizations.
The Baleen whales are part of the Mysticeti suborder, which consists of: The blue whale, fin whale, right whale, minke whale, humpback whale, bowhead whale, sei whale, Bryde's whale, and the gray whale.
The Toothed Whales
Toothed whales are a very diverse group! These whales live in a variety of habitats and have developed unique appearances and behavior. Of course they all contain teeth, and one species, the Narwhal, has actually developed a tusk! These whales can range in size from 18 meters in length (the sperm whale) to 140 centimeters in length (the vaquita or Gulf of California porpoise).
It is believed that only these cetaceans are capable of echolocation underwater. Echolocation is an amazing ability that consists of a dolphin or whale emitting a series of clicks that bounce off the environment and send information to the animal when it picks up the echo. Toothed whales use a several different frequencies to gather information about a target depending on the target's distance from the whale and how much information the whale desires. This, scientists say, helps to form a detailed “image” in the mind of the animal. For example, a dolphin will use low frequency echolocation when it is simply scanning its surroundings. When it finds something of interest, it will focus on the object and begin to use a higher frequency click which will provide a more detailed “picture”. In this manner, a toothed whale is able to see inside an animal and judge its quality as a source of food. This is assumed to be the reason behind a dolphin's fascination with pregnant women.
This shows what echolocation sounds like.
When talking about toothed whales it is impossible to give a broad description of traits that are found in all toothed whales. We will start with the sperm whales. This is actually a group of three species including the sperm whale, the pygmy sperm whale and the dwarf sperm whale. These cetaceans are the only specimens that have an organ that produces the wax- like substance called spermaceti. Scientists believe this oil, which is unlike anything produced by baleen whales, is used to regulate buoyancy during deep dives. It may also be used to focus echolocation. Sperm whales are able to reach depths of 3,000 meters to reach their favorite prey, squid. The dwarf sperm whale is the smallest, with a length of 2.1 to 2.7 meters. The pygmy sperm whale is around 3 meters while the more commonly known sperm whale can reach 18 meters! Sperm whales have an abnormally long gestation period- about 16 to 17 months.
Another interesting group of toothed whales is the beaked whales. Beaked whales are very seldom seen and scientists believe they are either very rare or spend most of their lives at great depths and avoid humans. These whales seem to be evolving a reduced number of teeth and in fact, females of many beaked whale species have no teeth at all. The males of these species usually have two to four teeth on the bottom jaw that tend to be elaborate and usually stick out of the whale's mouth. These enigmatic whales are hard to find and new species have been discovered in recent years.
The beluga whale and the narwhal are sometimes called the “White whales”. They can be found in the arctic sea and tend to be around 5 meters long. They are characterized by a round head with a short beak, lack of a dorsal fin and small round pectoral fins. Beluga whales are possibly the most vocal of all the cetacean species and has earned the nickname “sea canary” for its high pitched whistles and squeaks that can sound like a bird. It also has the ability to turn its head independently from its body like we can because its seven neck vertebrae are not fused as they are in most cetaceans. The narwhal is an unusual looking whale because it has a very large tusk sticking straight out in front of it. This is actually one of the two upper teeth these whales have and it usually begins to grow at around one year old in narwhal males. Occasionally females will have one as well and sometimes males may even have two tusks! The tusk usually reaches a length of 2 or 3 meters and is thought to be a tool for competing for females.
Porpoises and dolphins are similar but not the same. Porpoises have no beaks, have spade- shaped teeth, are typically smaller than dolphins and have a more stocky build. Except for the finless porpoise, all porpoises have a well defined dorsal fin, small pectoral fins and live mainly along coastlines. There are 33 species of dolphin including the misnamed Killer Whale. They vary greatly in color and body shape but all have conical shaped teeth. Some dolphins and porpoises have taken to living in the great rivers of the world. Dolphins are very social and active animals and frequently leap out of the water especially during travel. They are easiest to keep in captivity and have been the subject of many experiments. Dolphins have been known to save humans from drowning or from shark attacks and some have even formed a partnership with local fishermen. To watch a video about this, check out my hub "The Amazing Intelligence of Cetaceans"
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peachy from Home Sweet Home on August 03, 2020:
I read somewhere that big whales are often bullied by the orca
David Sproull from Toronto on August 10, 2011:
Voted up. Nice hub !