Featured Research

from universities, journals, and other organizations

When it comes to mammals, how big is too big?

Date:
June 16, 2013
Source:
Arizona State University
Summary:
Mammals vary enormously in size, from weighing less than a penny to measuring more than three school buses in length. Some groups of mammals have become very large, such as elephants and whales, while others have always been small, like primates. A new theory provides an explanation for why and how certain groups of organisms are able to evolve gigantic sizes, whereas others are not.

The southern elephant seal, Mirounga leonina, is the largest species of the mammalian order Pinnipedia, which is the second largest order of mammals. The males weigh up to 4,000 kilograms.
Credit: © Eduardo Rivero / Fotolia

Mammals vary enormously in size, from weighing less than a penny to measuring more than three school buses in length. Some groups of mammals have become very large, such as elephants and whales, while others have always been small, like primates. A new theory developed by an interdisciplinary team, led by Jordan Okie of Arizona State University, provides an explanation for why and how certain groups of organisms are able to evolve gigantic sizes, whereas others are not.

The international research team composed of palaeontologists, evolutionary biologists and ecologists examined information on how quickly an individual animal grows and used it to predict how large it may get over evolutionary time. Their research is published in the journal Proceedings of the Royal Society B.

The new theory developed from the observation that some animals live fast and die young, while others take their time and mature much later. This is called the slow-fast life-history continuum, where "fast" animals -- such as mice -- breed very quickly, while humans mature slowly and are relatively older when they first have children. The theory proposes that those species that are relatively faster are more likely to evolve a large size quicker than slow species, and that their maximum size will be greater.

The research team tested their theory using the fossil records of mammals over the last 70 million years, examining the maximum size of each mammal group throughout that time, including whales, elephants, rodents, seals and primates. They found that their theory was very well supported.

"Primates have evolved very slowly, and never got bigger than 1,000 pounds," said Okie, an exploration postdoctoral fellow in the School of Earth and Space Exploration at ASU. "The opposite was true of whales, which evolved their large size at the fastest rates recorded."

The theory also makes predictions about the relative risks of extinction for large animals compared to small. The maximum size of an animal is limited by the rate of mortality in the population. Because larger animals tend to breed less frequently than smaller animals, if the mortality rate doubles, the maximum size is predicted to be 16 times smaller.

"This is a really surprising finding," said co-author Alistair Evans of Monash University (Melbourne, Australia). "It points to another reason why many of the large animals went extinct after the last Ice Age, and their high risk of extinction in modern environments."

The research clarifies some of the differences among the main groups of mammals and makes further predictions about how changes in body size affect the evolutionary potential. In the future, this work will be extended to help explain how extinction risk may be reduced in changing climates.

The team was funded by a Research Coordination Grant from the US National Science Foundation. Financial support to Okie was provided by an Exploration Postdoctoral Fellowship from Arizona State University's School of Earth and Space Exploration and a National Aeronautics and Space Administration Astrobiology Institute Postdoctoral Fellowship.


Story Source:

The above story is based on materials provided by Arizona State University. Note: Materials may be edited for content and length.


Journal Reference:

  1. J. G. Okie, A. G. Boyer, J. H. Brown, D. P. Costa, S. K. M. Ernest, A. R. Evans, M. Fortelius, J. L. Gittleman, M. J. Hamilton, L. E. Harding, K. Lintulaakso, S. K. Lyons, J. J. Saarinen, F. A. Smith, P. R. Stephens, J. Theodor, M. D. Uhen, R. M. Sibly. Effects of allometry, productivity and lifestyle on rates and limits of body size evolution. Proceedings of the Royal Society B: Biological Sciences, 2013; 280 (1764): 20131007 DOI: 10.1098/rspb.2013.1007

Cite This Page:

Arizona State University. "When it comes to mammals, how big is too big?." ScienceDaily. ScienceDaily, 16 June 2013. <www.sciencedaily.com/releases/2013/06/130616210700.htm>.
Arizona State University. (2013, June 16). When it comes to mammals, how big is too big?. ScienceDaily. Retrieved April 24, 2014 from www.sciencedaily.com/releases/2013/06/130616210700.htm
Arizona State University. "When it comes to mammals, how big is too big?." ScienceDaily. www.sciencedaily.com/releases/2013/06/130616210700.htm (accessed April 24, 2014).

Share This



More Fossils & Ruins News

Thursday, April 24, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

New Pictures of Ship That Sank in 1888

New Pictures of Ship That Sank in 1888

AP (Apr. 24, 2014) — Federal researchers have released new images of the City of Chester, a steamship that sank in San Francisco Bay in 1888. Researchers recently found the shipwreck while mapping shipping routes. (April 24) Video provided by AP
Powered by NewsLook.com
Mich. Boy Unearths 10,000-Year-Old Mastodon Tooth

Mich. Boy Unearths 10,000-Year-Old Mastodon Tooth

Newsy (Apr. 20, 2014) — A 9-year-old Michigan boy was exploring a creek when he came across a 10,000-year-old tooth from a prehistoric mastodon. Video provided by Newsy
Powered by NewsLook.com
Couple Finds Love Letters From WWI In Attic

Couple Finds Love Letters From WWI In Attic

Newsy (Apr. 17, 2014) — A couple found love letters from World War I in their attic. They were able to deliver them to relatives of the writer of those letters. Video provided by Newsy
Powered by NewsLook.com
Erotic Art Offers Glimpse of China's 'lost' Sexual Philosophy

Erotic Art Offers Glimpse of China's 'lost' Sexual Philosophy

AFP (Apr. 16, 2014) — Explicit Chinese art works dating back centuries go on display in Hong Kong, revealing China's ancient relationship with sex. Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

More Coverage


From Tiny to Massive: Mammal Size Evolution Explained

June 25, 2013 — Scientists have added another piece to the evolutionary puzzle to explain why certain mammal families evolved to be very large, while others remained ... read more
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins