According to biologists, three orders encompass 123 known species of living marine mammals.
|Family||Manatees & Dugongs||Eared seals,True Seals,Walruses & Bears||Whales & Dolphins|
|Genus and species||6 species||37 species||80 species|
Each animal and plant has its own scientific name that is instantly recognized by naturalists in the United States, Europe, or anywhere else in the world. This binomial system of taxonomy dates back to the 1750s, when Swedish naturalist Carl von Linne (Latinized to Carolus Linneas) adopted Latin, the scholarly language of the day, to describe organisms. Each organism is assigned a Genus name (which is capitalized) and a species name (in lower case). Both names are usually italicized. Organisms of the same genus are closely related (such as Canis for all dogs), while those with similar species names may share a common feature, such as color or shape (as inrubrumfor red). By looking for the root meaning of Latin names, students may deduce the characteristics of an organism or something about its origin or habits. For example, the humpback whale's scientific name is Megaptera novaeangliae,which translates to "big-winged New Englander." Its full taxonomy is:
|Suborder:||Mysteceti (baleen whales)|
|Family:||Balaenopteridae (Rorqual family)|
|Genus and species:||Megaptera novaeangliae|
The largest group of marine mammals are the whales and dolphins with 80 species. Baleen whales, long hunted by whalers, have been known for a long time. The last new species of baleen whales was discovered in 1879, Bryde's whales. New species of toothed whales are still being discovered. Eleven species have been described since 1990. Seven new species of beaked whales, family Ziphiidae, have been discovered in the 1900s.These secretive whales have just begun to reveal their habits and are rarely seen, let alone photographed. The most recent species of beaked whale, Mesoplodon peruvianus,was described in 1991.
New research techniques, including DNA testing,have helped taxonomists/marine mammalogists distinguish between species and identify new ones. DNA testing is also being used on individual whales to determine if individuals are closely related. in some cases, these tests have indicated that most of a population descended from just a few mothers, suggesting that the biodiversity of the species is threatened.
(*source: "Marine Mammal Biodiversity,"Oceanus, Vol. 38, No. 2, Fall/Winter, 1995)
How are whales and dolphins alike?
Both belong to the order Cetaceans (from the Latin word Cetus, meaning largesea animal.) There are baleen and toothed whales. Most of the largest whales (except the sperm whale) belong to the sub-order, baleen whales(Mysticeti.) They feed mostly on plankton (small floating animals) and krill (shrimplike creatures), which they strain from the sea water through plate-like baleen hanging from their upper jaws.
The toothed whales (Odonteceti) are usually small to medium sized, and encompass a broad variety of species, including dolphins, porpoises, narwhals, and river dolphins. They chase and eat a wide variety of prey as well, including fish, squid, shrimp, and even other cetaceans. By various estimates there are about 30-40 species of dolphins (Delphinidae),including some species we commonly call whales, such as killer whales (orcas), false killer whales, and pilot whales.
Dolphins have pointed rostrums and cone-shaped teeth, while porpoises have rounded rostrums and spade-shaped teeth. There are six species of porpoises (Phocoenidae).
Where did marine mammals come from?
Whales and dolphins have had an on-again, off-again relationship with the sea. Life evolved in the sea some 3 billion years ago. When opportunities for food opened up on land, some animals, including the dolphins and whales, moved onshore to take advantage of the food supply. These ancestors were distantly related to cows and horses and have been described as wolf-like in appearance. For some reason, probably again to find food, the descendants of these animals worked their way back into the sea, probably first foraging from shore before becoming full-fledged ocean dwellers. As new fossils are uncovered, scientists believe they may find further evidence that the ancestors of whales and dolphins moved on and off the land several times.
How old are whales?
A fossilized jawbone and teeth recently unearthed in the Himalayan foothills suggest whales originated about 53.5 million years ago. This find is 3.5 million years older than any fossils previously found. The fossil is a new whale species named Himalayecetus subathuensis.
How is a whale like a hippo?
Scientists agree that dolphins and whales descended from land animals that were ungulates (like horses, cows, hippos, and camels). Now some researchers are finding some striking similarities between hippos, which spend much of their time partially submerged in muddy pools, and dolphins, which spend most of their lives submerged in the ocean.
- Both may give off underwater sounds through fatty areas in their heads.
The dolphin transmits sounds through a fatty area on its forehead known as the melon. Bill Barklow thinks hippos, although they do have vocal cords, may also release sounds into the water through a roll of fat in their throats.
- Both may "hear" through their jaws.
Ken Norris of the University of California at Santa Cruz examined dolphin skulls to find evidence that sounds are conducted through the lower jaw to the dolphin's ears. Barklow found similar structures in hippos that he believes may make it possible for hippos to listen to sounds above the surface with their ears while simultaneously monitoring underwater sounds through its submerged jaw.
- They have a close blood match.
Jerold Lowenstein of the University of California at San Francisco has compared blood serum of whales with many ungulates, including cattle, pigs, and gazelles. He found whales were more similar to hippos than to any other group (although DNA studies have not confirmed this).
(source: "Snatching Scientific Secrets from the Hippo's Gaping Jaws," David M. Schwartz, Smithsonian,March, 1996)