BLUE WHALE: THE LARGEST MAMMAL GETTING LARGER

published in Proceedings of the Royal Academy of Sciences, reported by Discovery news

Evolutionary biologist Alistair Evans of Monash University in Melbourne reports that while most mammals are smaller than they were during the last Ice Age, 100,000 years ago, blue whales are larger—and becoming still larger.

Evans and his researchers estimated the body size of hundreds of species in 28 different orders of animals in 20 time periods over the past 70 million years.  They used teeth, skulls, and limb bones to determine the size of the animals and compared the data to the size of current species.

Findings:  It took whales 5 million generations—30 million years–to evolve from about 55 pounds to 190 tons, the current weight for a blue whale.  In contrast, it took 10,000 million generations for a land mammal to grow 5000 times larger.

Evans believes that when dinosaurs and their marine cousins went extinct 65 million years ago, mammals used the opportunity to take over the space those creatures had previously occupied.

He also believes that ocean currents boosting the amount of krill around Antarctica may be responsible for the expanding length and girth of the blue whale.  Compared to land animals. larger size is further facilitated for marine animals because their weight is supported by water—fewer body modifications are needed to handle the increasing weight.

Evans cites advantages to increasing in size.  “It’s more efficient to be big,” he says.

An animal’s metabolic rate decreases with size, meaning it doesn’t have to eat as much food per gram of tissue, which means an animal can eat more abundant low energy-dense foods, like trees, leaves and grass.

Why are most mammal species smaller than they were 100,000 years ago?  Evans suggests it may be because the largest mammals have been hunted to extinction, or because the weather is warmer and there’s less metabolic advantage to being big.

The last finding of note from the research:  Mammals evolving to smaller size since the last Ice Age evolved much faster than those evolving to larger size. 

LORED.

published in Proceedings of the Royal Academy of Sciences, reported by Discovery news

Evolutionary biologist Alistair Evans of Monash University in Melbourne reports that while most mammals are smaller than they were during the last Ice Age, 100,000 years ago, blue whales are larger—and becoming still larger.

Evans and his researchers estimated the body size of hundreds of species in 28 different orders of animals in 20 time periods over the past 70 million years.  They used teeth, skulls, and limb bones to determine the size of the animals and compared the data to the size of current species.

Findings:  It took whales 5 million generations—30 million years–to evolve from about 55 pounds to 190 tons, the current weight for a blue whale.  In contrast, it took 10,000 million generations for a land mammal to grow 5000 times larger.

Evans believes that when dinosaurs and their marine cousins went extinct 65 million years ago, mammals used the opportunity to take over the space those creatures had previously occupied.

He also believes that ocean currents boosting the amount of krill around Antarctica may be responsible for the expanding length and girth of the blue whale.  Compared to land animals. larger size is further facilitated for marine animals because their weight is supported by water—fewer body modifications are needed to handle the increasing weight.

Evans cites advantages to increasing in size.  “It’s more efficient to be big,” he says.

An animal’s metabolic rate decreases with size, meaning it doesn’t have to eat as much food per gram of tissue, which means an animal can eat more abundant low energy-dense foods, like trees, leaves and grass.

Why are most mammal species smaller than they were 100,000 years ago?  Evans suggests it may be because the largest mammals have been hunted to extinction, or because the weather is warmer and there’s less metabolic advantage to being big.

The last finding of note from the research:  Mammals evolving to smaller size since the last Ice Age evolved much faster than those evolving to larger size. 

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