Small animals thrive after mass extinctions, say scientists

A new study suggests that mass extinction of ancient larger animals led to the dominance of tiny species. 

Courtesy Bob Nicholls
An illustration of small sharks and fishes of the Mississippian Period, more than 300 million years ago. Researchers found shrinkage in sizes of some groups of species following a mass extinction.

From blue whales to elephants, most of the world’s most massive species are facing extinction.

A new study of fish fossils suggests that when large vertebrates become extinct, evolution does not replace them for many years.

Researchers, after analyzing fish that lived about 350 million years ago, have concluded that a mass extinction known as the Hangenberg event caused large species to die off while smaller species survived.

"Rather than having this thriving ecosystem of large things, you may have one gigantic relict, but otherwise everything is the size of a sardine," said Lauren Sallan, an environmental scientist at the University of Pennsylvania, in a news release.

Her findings suggest that the smaller fish had a unique advantage over their larger counterparts: they breed much, much faster than their giant cousins.

"The end result is an ocean in which most sharks are less than a meter [three feet] and most fishes and tetrapods are less than 10 centimeters," or smaller than a grapefruit, said Dr. Sallen. "Yet these are the ancestors of everything that dominates from then on, including humans."

Paleontologists have long debated the changes in the body sizes of animals over time.

One theory, known as Cope's rule, says a species tends to enlarge over time to avoid predation and to become better hunters.

Another theory says that all things being equal, animals become larger in the presence of increased oxygen, or in colder climates.

Another idea, known as the Lilliput Effect, holds that after mass extinctions, there will inevitably be a temporary trend toward small body size. It’s named after a fictional island in the book “Gulliver’s Travels” that’s inhabited by tiny people.

Many scientists believe that we are on the brink of – if not in the midst of – a sixth mass extinction. This summer, scientists released a report indicating that humans are chiefly to blame for the mass extinction that is already underway.  

But these same scientists say that aggressive conservation efforts may yet stave off a true mass extinction. Humpback whales, for example, were recently recommended for removal from the endangered species list

"This will require rapid, greatly intensified efforts to conserve already threatened species and to alleviate pressures on their populations – notably habitat loss, overexploitation for economic gain, and climate change," wrote the research team, including scientists from Stanford, Princeton, and Berkeley, in their report.

If the present extinction does eliminate the planet's largest animals, the new study suggests they will not be replaced any time soon.

"It doesn't matter what is eliminating the large fish or what is making ecosystems unstable," Sallan said. "These disturbances are shifting natural selection so that smaller, faster-reproducing fish are more likely to keep going, and it could take a really long time to get those bigger fish back in any sizable way."

You've read  of  free articles. Subscribe to continue.
Real news can be honest, hopeful, credible, constructive.
What is the Monitor difference? Tackling the tough headlines – with humanity. Listening to sources – with respect. Seeing the story that others are missing by reporting what so often gets overlooked: the values that connect us. That’s Monitor reporting – news that changes how you see the world.

Dear Reader,

About a year ago, I happened upon this statement about the Monitor in the Harvard Business Review – under the charming heading of “do things that don’t interest you”:

“Many things that end up” being meaningful, writes social scientist Joseph Grenny, “have come from conference workshops, articles, or online videos that began as a chore and ended with an insight. My work in Kenya, for example, was heavily influenced by a Christian Science Monitor article I had forced myself to read 10 years earlier. Sometimes, we call things ‘boring’ simply because they lie outside the box we are currently in.”

If you were to come up with a punchline to a joke about the Monitor, that would probably be it. We’re seen as being global, fair, insightful, and perhaps a bit too earnest. We’re the bran muffin of journalism.

But you know what? We change lives. And I’m going to argue that we change lives precisely because we force open that too-small box that most human beings think they live in.

The Monitor is a peculiar little publication that’s hard for the world to figure out. We’re run by a church, but we’re not only for church members and we’re not about converting people. We’re known as being fair even as the world becomes as polarized as at any time since the newspaper’s founding in 1908.

We have a mission beyond circulation, we want to bridge divides. We’re about kicking down the door of thought everywhere and saying, “You are bigger and more capable than you realize. And we can prove it.”

If you’re looking for bran muffin journalism, you can subscribe to the Monitor for $15. You’ll get the Monitor Weekly magazine, the Monitor Daily email, and unlimited access to

QR Code to Small animals thrive after mass extinctions, say scientists
Read this article in
QR Code to Subscription page
Start your subscription today