Featured Research

from universities, journals, and other organizations

Clues To Horse Extinctions Point To Gritty Grass, Climate Change

October 19, 1997
Johns Hopkins University
A Johns Hopkins paleobiologist has uncovered clues that the horses (and camels and rhinos) that roamed North America millions of years ago went extinct because of climate change that radically changed their food supply. This new understanding of the extinctions is relevant to today's discussions of global warming.

Johns Hopkins paleobiologist Steven Stanley has sleuthed outclues to the evolution of horses, coming up with a new solutionfor an enduring mystery: What caused the extinction of manyequine species and other mammals 6 million years ago?

Like the protagonist in an evolutionary detective thriller,Stanley pursued a hunch that apparently had never occurred toother scientists. His long shot hit a bull's-eye, enablingStanley to learn how shifting climate and changing vegetationlikely altered the fate of horses in North America millions ofyears ago.

Stanley, a professor in the Johns Hopkins Department of Earth andPlanetary Sciences, pieced together the findings of otherscientists and connected those data in a way no otherresearchers had done previously. When taken together, the datapaint a picture of how Earth's changing climate and vegetationmay have been directly involved in the dramatic evolutionarytrends of horses and other animals.

The time was marked by the largest extinction rate of NorthAmerican mammals in the last 30 million years; about 60 genera,containing numerous species, perished.

Some scientists believe that changing atmospheric concentrations of carbondioxide could have helped bring about the climatic shifts that Stanleybelieves were directly linked to changes in the vegetation thriving in NorthAmerica. Because the extinctions apparently were brought about by thosechanges in vegetation, the lesson is that carbon dioxide-linked global warming-- if it is occuring again today as many scientists believe -- could have aprofound impact on future extinction rates.

Stanley will touch on his theory during a 1:35 p.m. talk onSunday, Oct. 19, at the start of the annual meeting of theGeological Society of America. The talk will be in the SaltPalace Convention Center, in Salt Lake City, Utah.

Contrary to the popular belief that horses were foreign to theNew World until they were brought here by the Spaniards, theanimals actually evolved in North America, spreading to Europe bycrossing the Bering land bridge that once connected Alaska andSiberia. But they later died out in North America near the end ofthe Ice Age.

Well before their disappearance, however, their life history tookan abrupt turn that killed off all but those horses with thelongest teeth. In fact, numerous other mammals, including camelsand rhinos, suffered the same fate in North America.

Scientists have known that the extinctions were somehow relatedto expanding grasslands and shrinking forests. Grasses possess agritty compound called silica, which is contained in sand and isused to make glass. As animals chew grass, the silica wears downtheir teeth. Therefore, animals with longer teeth live longerbecause their teeth don't wear down as fast, and they cancontinue to feed.

For tens of millions of years, as the Earth's climate becamecooler and dryer, the trend toward expanding grasslands andreceding forests continued in North America. About 13 millionyears ago, the 15 or so species of horses in North America weresplit between those with long teeth and those with shorter teeth.Also at that time, a few new species emerged that had very longteeth.

As grasslands expanded, the horses with long teeth lived longerbecause they were best adapted to eating grasses instead ofleaves. Living longer enabled them to produce enough offspring toguarantee survival of their species and the evolution of newspecies.

By 11 million years ago, only the horses especially adapted toeating grasses -- those with the long and very long teeth -- wereliving in North America.

"Then, there is this sudden event, 6 million years ago, more orless, and what you see is a big extinction pulse, a big drop intotal diversity, and the survivors are all the ones with verylong teeth," Stanley said.

The conventional wisdom has suggested that the long-toothedhorses disappeared because of expanding grasses. But that justdidn't make sense, Stanley said, because the horses with longteeth were especially adapted to eating grasses.

"So, why would more grass be a problem for them?" Stanley asked.

Somehow, something about the grasses must have changed, hereasoned.

Meanwhile, other scientists had discovered that, as the climatebecame dryer and cooler, a different type of grasses began todominate North America. Those grasses, known as C-4 grasses,which thrive in dryer climates, replaced many of the previouslydominant grasses, known as C-3 grasses.

"I thought, well, this seems like a long shot, but I wonder ifthere are on average more silica bodies in the C-4 grasses thanC-3 grasses," Stanley said.

His hunch proved correct. Stanley found that, on average, C-4grasses contain about three times as many of the silica particlesas do C-3 grasses.

"Think about a species that was doing all right eating C-3grasses. Maybe it lived 10 years on average and produced enoughcolts to reproduce the species. Well, what happens if that horseis suddenly only living seven years, or six years? It may notproduce enough colts to perpetuate its species.

"I think that's what happened. I think there was a big grinddown."

The title of his talk is, "Geobiology: Studying the deep historyof the earth-life system."

Story Source:

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

Cite This Page:

Johns Hopkins University. "Clues To Horse Extinctions Point To Gritty Grass, Climate Change." ScienceDaily. ScienceDaily, 19 October 1997. <www.sciencedaily.com/releases/1997/10/971014094121.htm>.
Johns Hopkins University. (1997, October 19). Clues To Horse Extinctions Point To Gritty Grass, Climate Change. ScienceDaily. Retrieved September 30, 2014 from www.sciencedaily.com/releases/1997/10/971014094121.htm
Johns Hopkins University. "Clues To Horse Extinctions Point To Gritty Grass, Climate Change." ScienceDaily. www.sciencedaily.com/releases/1997/10/971014094121.htm (accessed September 30, 2014).

Share This

More Plants & Animals News

Tuesday, September 30, 2014

Featured Research

from universities, journals, and other organizations

Featured Videos

from AP, Reuters, AFP, and other news services

California University Designs Sustainable Winery

California University Designs Sustainable Winery

Reuters - US Online Video (Sep. 27, 2014) Amid California's worst drought in decades, scientists at UC Davis design a sustainable winery that includes a water recycling system. Vanessa Johnston reports. Video provided by Reuters
Powered by NewsLook.com
Argentina Worries Over Decline of Soybean Prices

Argentina Worries Over Decline of Soybean Prices

AFP (Sep. 27, 2014) The drop in price of soy on the international market is a cause for concern in Argentina, as soybean exports are a major source of income for Latin America's third largest economy. Duration: 01:10 Video provided by AFP
Powered by NewsLook.com
Mama Bear, Cubs Hang out in California Backyard

Mama Bear, Cubs Hang out in California Backyard

Reuters - US Online Video (Sep. 27, 2014) A mama bear and her two cubs climb trees, wrestle and take naps in the backyard of a Monrovia, California home. Vanessa Johnston reports. Video provided by Reuters
Powered by NewsLook.com
'Crazy' Climate Forces Colombian Farmers to Adapt

'Crazy' Climate Forces Colombian Farmers to Adapt

AFP (Sep. 26, 2014) Once upon a time, farming was a blissfully low-tech business on Colombia's northern plains. Duration: 02:05 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.


Breaking News:

Strange & Offbeat Stories

Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News


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