Size of Mammals Exploded after Dinosaur Extinction

Scientific Computing ^ | 12/1/10

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The largest land mammals that ever lived, Indricotherium and Deinotherium, would have towered over the living African elephant. The tallest on diagram, Indricotherium, an extinct rhino relative, lived during the Eocene to the Oligocene Epoch (37 to 23 million years ago) and reached a mass of 15,000 kg, while Deinotherium (an extinct proboscidean, related to modern elephants) was around from the late-Miocene until the early Pleistocene (8.5 to 2.7 million years ago) and weighed as much as 17,000 Courtesy of Alison Boyer/Yale University

Researchers demonstrate that the extinction of dinosaurs 65 million years ago made way for mammals to get bigger – about a thousand times bigger than they had been. The study, which is published in the prestigious journal Science, is the first to show this new pattern of increased body size of mammals after the exit of the dinosaurs.

"Basically, the dinosaurs disappear and all of a sudden there is nobody else eating the vegetation. That's an open food source and mammals start going for it, and it's more efficient to be an herbivore when you're big," says paper co-author Jessica Theodor, associate professor in the Department of Biological Sciences at the University of Calgary.

Theodor says as well as confirming the dramatic growth in mammalian size after the dinosaurs, the study shows that the ecosystem is able to reset itself relatively quickly. "You lose dinosaurs 65 million years ago, and within 25 million years the system is reset to a new maximum for the animals that are there in terms of body size. That's actually a pretty short time frame, geologically speaking," she says. "That's really rapid evolution."

Theodor says mammals grew from a maximum of about 10 kilograms when they were sharing the earth with dinosaurs to a maximum of 17 tons afterwards. "Nobody has ever demonstrated that this pattern is really there. People have talked about it but nobody has ever gone back and done the math," says Theodor one of the 20 researchers from around the world who worked on the study. "We went through every time period and said OK, for this group of mammals what's the biggest one? And then we estimated its body mass."


  In order to document how big mammals grew after the 'competitive release' caused by the extinction of dinosaurs, researchers collected data on the maximum size for major groups of land mammals on each continent, including Perissodactyla, odd-toed ungulates such as horses and rhinos; Proboscidea, which includes elephants, mammoth and mastodon; Xenarthra, the anteaters, tree sloths, and armadillos; as well as a number of other extinct groups. The results give clues as to what sets the limits on mammal size on land; the amount of space available to each animal and the climate they live in. The colder the climate, the bigger the mammals seem to get, as bigger animals conserve heat better. It also shows that no one group of mammals dominates the largest size class – the absolute largest mammal belongs to different groups over time and space.

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That's mighty big of them...

[frogjerk]

Mammals, like politicians, get big and fat when they don't have to work for their food.

[mountainlion]

I hate exploding rats.

[Frantzie]

All of them are some of my favorites - elephants, whales and hippos plus rhinos too.

[DCBryan1]

Exploding mammal.

[Red Badger]

It sure did................

[DCBryan1]

Exploding mammal.

[a fool in paradise]

Steroid abuse most likely...

[a fool in paradise]

Theodor says as well as confirming the dramatic growth in mammalian size after the dinosaurs, the study shows that the ecosystem is able to reset itself relatively quickly. "You lose dinosaurs 65 million years ago, and within 25 million years the system is reset to a new maximum for the animals that are there in terms of body size. That's actually a pretty short time frame, geologically speaking," she says. "That's really rapid evolution."

Yet we are told that humans have a distinct BMI that must be maintained. Gettin' bigger isn't in that equation and men and women must be the exact same size.

[Riodacat]

The speed at which the average American has grown in size in the past 50 years, it won't take 25 million years before we're the size of dinosaurs.

[Conservative Tsunami]

Don't even go there, sucka!"

[bravo whiskey]

sixe of us economy exploded after congressional dinosaurs died.

[Nervous Tick]

>> it won’t take 25 million years before we’re the size of dinosaurs.

Considering who we elected POTUS, it looks like average brain size is keeping pace with our devolution to dinosaurs as well.

[deltaromeo11]

That was hilarious! Fiction based on fiction. Wooh, those scientists keeping us entertained. Can I have grant to study the effect of incorrect presuppositions on the results of a study from a prestigious journal of science?

[Oberon]

Ping for later.

[azhenfud]

"The largest land mammals that ever lived, Indricotherium and Deinotherium, would have towered over the living African elephant. The tallest on diagram, Indricotherium, an extinct rhino relative, lived during the Eocene to the Oligocene Epoch (37 to 23 million years ago) and reached a mass of 15,000 kg, while Deinotherium (an extinct proboscidean, related to modern elephants) was around from the late-Miocene until the early Pleistocene (8.5 to 2.7 million years ago) and weighed as much as 17,000 Courtesy of Alison Boyer/Yale University

Researchers demonstrate that the extinction of dinosaurs 65 million years ago made way for mammals to get bigger – about a thousand times bigger than they had been."

Is it me or is something @$$ backward here. The modern elephant silhouette is SMALLER than that of the ancients'. Similarly, modern rino's are smaller than their predecessors.

[WayneS]

“They blowed up REAL good...”

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Yes, IF it were purely linear the largest mammals would be alive right now.

But it's not purely linear. The climate has changed, the number of competitors has changed, the available food supplies have changed, species have gone extinct for causes not necessarily related to size.

Current conditions have a different optimal size than past conditions.

Animals adapted accordingly, or died out.

[GraceG]

Everyone knows some animals were too big to fit on the boat ....

That is why Dinos and these large mammals are extinct...

/sarc

[Vermont Lt]

Oh, that is going to leave a mark....