C. Letenneur (MNHN)
The giant sperm whale Leviathan melvilleiis is illustrated attacking a medium-size baleen whale off the coast of the area now occupied by Peru.
Originally designed to live on land, marine mammals are a diverse, charismatic group of animals that include more than 120 species. The animals share key characteristics of land mammals. They have hair, breathe air, give birth to live young, which feed off mother's milk when young. They have warm bodies and usually thick blubber to keep their body temperatures high. The bottlenose dolphin is probably the most widely recognized marine mammal, easily spotted just offshore from beaches around the world. Small groups of 20 or less can live in close proximity to shorelines, but groups living more offshore can reach several hundred. Bottlenose dolphin calves stay with their mothers for up to six years, learning how to hunt and become good dolphin citizens. Full-grown dolphins reach eight to 12 feet in length and can weigh up to 1,430 pounds. The bottlenose dolphin is protected in U.S. waters.
What makes them "marine" depends on the animal. They either live mostly in the sea or, like polar bears, depend on the ocean for food. The largest in the group are whales -- including humpback whales. These massive animals reach up to 50 feet in length and weigh up to 79,000 pounds. To maintain their weight, the animals feed on tons of krill and fish. They neared extinction due to whaling, but have recovered somewhat since a 1966 moratorium on whaling was introduced.
While polar bears live mostly on land or ice, they are excellent swimmers and have been known to swim up to 45 miles a day. The massive animals, weighing up to 1,500 pounds, hunt mostly seals. In recent years, biologists have observed that the bears are swimming now more than ever as melting stretches the distances between Arctic ice flows. Because they depend on sea ice to hunt seals, the polar bear is considered threatened as global warming melts and thins ice in this region.
This member of the weasel family is also the smallest marine mammal, with females weighing about 60 pounds and males weighing up to 90 pounds. They may be small, but they're also clever. They're the only marine mammals known to use tools. They use stones to break open clams and store food they gather in the folds of their armpits! Another feature that sets them apart is their lack of blubber. These marine mammals depend mostly on their fur to stay warm. That feature makes them particularly vulnerable to oil spills, which can compromise their fur's insulating effect.
Immediately recognizable by its long tusks and whiskers, the sea walrus is a hefty, flippered member of the Odobenidae family and is, in fact, the last living member of this group. Since both the males and females have big tusks and not much for teeth, the animals feed by sucking up shellfish from the ocean floor. So, just what are those tusks for? The longer they are (they grow to be up to four feet long in males), the higher an animal is ranked in the group. Males attack each other with their tusks to establish dominance. The ivory appendages are also handy for poking holes in the winter ice and for helping the animals pull themselves out of the water.
Manatees, also known as sea cows, are gentle herbivores that live in marshy areas in tropical and subtropical waters. The average adult manatee can weigh up 1,200 pounds and is around 10 feet long. Because of their slow metabolism, these animals can only survive in warm waters. Due to the unusually long, cold winter this year in part of the southeastern United States, populations of manatees throughout Florida were devastated. During the day, manatees usually like to stay close to the surface. At night, manatees will often sleep about three to 10 feet below sea level. This is why these gentle animals are so often accidentally injured, maimed or killed by passing boats.
Found up and down the North American coastlines, these marine mammals spend half of their lives swimming. Although they can reach up to six feet in length and weigh around 180 pounds, when on land and in plain sight harbor seals may not be easy to spot. Their spotted brown or tan fur allows harbor seals to blend in with sand and rocks. Unlike their very vocal relatives -- sea lions and elephant seals -- harbor seals are quiet creatures that make little noise. They like to hang out on beaches, sand bars and rocks during low tide to bask in the sun and sleep, but they never go far from the water. At the slightest sign of danger, they will quickly slip back under the waves. These expert swimmers have been known to plunge to depths of more than 1,600 feet and stay underwater up to 28 minutes.
- Unlike modern sperm whales, this one had teeth in both jaws and might have eaten like killer whales.
- The 10-foot sperm whale skull fossil is the largest ever found.
- Its main food might have been baleen whales.
The massive skull and jaw of a 13-million-year-old sperm whale has been discovered eroding from the windblown sands of a coastal desert of Peru.
The extinct cousin of the modern sperm whale is the first fossil to rival modern sperm whales in size -- although this is a very different beast, say whale evolution experts.
"We could see it from very far," said paleontologist Olivier Lambert of the Muséum National d'Histoire Naturelle in Paris, France, who led the team which found the fossil.
The giant 3-meter (10-foot) skull of what's been dubbed Leviathan melvillei (in honor of the author of "Moby Dick") was found with teeth in its top and bottom jaws up to 36 centimeters (14 inches) long. The discovery is reported in the July 1 issue of the journal Nature.
Living sperm whales have teeth only in their lower jaws and are specialized to feed on giant squid, Lambert explained. They suck down squid like large spaghetti noodles rather than catch the prey with their teeth. The much toothier fossil sperm whales, however, may have eaten more like a outsized-orca, or killer whale: chomping great big bites out of its prey.
"These are very unusual attributes," said cetacea evolution expert Ewan Fordyce of the University of Otago in New Zealand. "It's remarkably big. That is unexpected."
Another sign that this ancient whale had a killer bite is the large hole in the skull to accommodate a large jaw muscle.
"This was a hunting predator that took chunks out of prey," said Fordyce.
It most likely fed on baleen whales, Lambert and his colleagues report, and lived in the same waters as the monster-sized shark called Carcharocles megalodon.
To learn more about its eating habits, Fordyce said it would be useful to look at the microscopic wear patterns on the teeth. If the wear lines are horizontal, it probably sucked in prey like today's whales. But if the wear lines are vertical, it would suggest a biter, like the orca.
"Many fossil sperm whales have been found in the past," said Lambert. "Most have been much smaller than modern sperm whales."
There have also been discoveries of isolated large sperm whale teeth fossils before, said Lambert. Those made it clear to researchers there was a bigger animal out there waiting to be found. And now they have found it.
"I think it's a great advance," said Fordyce of the discovery.
The fossil appears to also be a distant relative of today's sperm whales, said Fordyce, rather than a direct ancestor.