Utah State Today - University News

Utah State University Logo

ARTsySTEM: The Changing Climates of the Arts and Sciences

This exhibits showcases works of art that share a…


The Dorothy and Herbert Vogel Collection: Fifty Works for Fifty States

This exhibit showcases, for the first time, the…


Utah Wilderness 50 Photographic Exhibition

This exhibit features 50 photographs that were selected…


New Student Orientation: SOAR

New Student Orientation for new incoming students and…


New Student Orientation: SOAR

New Student Orientation for new incoming students and…

More events


Blogger Facebook Twitter You Tube RSS

USU Biologist Says Mammal Size Exploded After Dino Demise

Thursday, Dec. 02, 2010

dinosaur size
Following the demise of dinosaurs, terrestrial mammals exploded in size, according to an international, NSF-funded study co-directed by USU biologist Morgan Ernest. Image courtesy IMPPS.
Morgan Ernest
Ernest holds a kangaroo rat at the NSF-funded Portal, New Mexico Long-Term Ecological Research Project, where she is principal investigator in charge. Ernest has long studied the role of body size in structuring mammalian communities.

An international research team co-directed by Utah State University biologist Morgan Ernest found that the extinction of dinosaurs some 65 million years ago paved the way for mammals to get bigger – much bigger.

“The demise of dinosaurs provided vast evolutionary opportunities for mammals,” says Ernest, associate professor and co-director of graduate programs in USU’s Department of Biology.

“Mammals evolved to sizes nearly thousand times larger than had been seen before.”

The team’s study, published in the Nov. 26, 2010, issue of the journal Science, is the first to quantitatively explore the pattern of body size of mammals after the end of the Dinosaur Age.

Funded by a National Science Foundation Research Coordination Network grant, the research brought together paleontologists, evolutionary biologists and macroecologists from 13 universities and institutions throughout the world.

“It is well known in biology that size profoundly influences everything from how quickly a species reproduces to its vulnerability to extinction,” Ernest says. “The aim of our group is to bring together a diverse group of scientists to investigate unanswered questions about the evolution of size in mammals.”

She and team members found that mammals grew from a size of about 22 lbs. when sharing the earth with dinosaurs to a whopping maximum of 17 tons afterwards. Moreover, the pattern was surprisingly consistent across space, time and trophic groups and lineages.

“In addition to the strong consistency in the patterns across continents, I was particularly struck by the relationship between the evolution of size in carnivores and herbivores,” Ernest says. “The evolution of maximum size in carnivores tracked increases in size in herbivores, though carnivores remained ten times smaller than their potential prey.”

To document what happened to mammals after the extinction of dinosaurs, she and the team spent three years collecting 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, mammoths and mastodons; Xenarthra, anteaters, tree sloths and armadillos; as well as a number of other extinct groups.  

“These sorts of comprehensive datasets are important because they allow us to ask questions on a scale not previously possible,” Ernest says.

The maximum size of mammals began to increase sharply about 65 million years ago, peaking about 34 million years ago in Eurasia during the Oligocene Epoch and again about 10 million years ago in Eurasia and Africa during the Miocene Epoch.

Indricotherium transouralicum, a hornless rhinoceros-like herbivore believed to be the largest mammal that ever walked the earth, weighed in at approximately 17 tons. It stood about 18 feet high at the shoulder and lives in Eurasia some 34 million years ago.

“The results of the study give clues as to what sets the limits on maximum body size on land; namely, the amount of space available to each animal and the climate they live in,” Ernest says.

The colder the climate, the bigger the mammals seem to get as larger animals conserve heat better.

“The results also show that no one group of mammals dominates the largest size class,” she says. “The absolute largest mammal belongs to different groups over time and space.”


Related Links

IMPPS RCN Research Network
USU Department of Biology
USU College of Science  

Contact: S. K. Morgan Ernest, 435-797-8751, morgan.ernest@usu.edu

Writer: Mary-Ann Muffoletto, 435-797-3517, maryann.muffoletto@usu.edu

     email icon  Email story       printer icon  Printer friendly

Send your comment or question:

We welcome your response. Your comment or question will be forwarded to the appropriate person. Please be sure to provide a valid email address so we can contact you, if needed. Your response will NOT be published online. Thank you.

NOTE: Do Not Alter These Fields, they are used to limit spam: