Mass Extinction That Killed the Dinosaurs Also Led to 'Explosive Radiations of Frogs'

Leon Brooks, Wikimedia Commons // Public Domain
Leon Brooks, Wikimedia Commons // Public Domain

You know what they say: Life finds a way. In this case, we're talking about frog life. Scientists say the mass extinction event that killed off so many dinosaurs may have paved the way for "explosive radiations of frogs," including the nearly 90 percent of species alive on Earth today. They published their report in the journal Proceedings of the National Academy of Sciences.

Previous research has suggested that the frog family party started about 100 million years ago. These studies based their conclusions on analysis of modern frogs' mitochondrial DNA, which can provide a sort of road map to an organism's evolutionary past. But sometimes that map is hard to read or even outdated.

To get a clearer picture, researchers from China and the U.S. decided to look at genes inside the nuclei, rather than the mitochondria, of frogs' cells. They compared nuclear (nucleus-based) genes among 301 different frog species, including one from each of the 55 major branches of the frog family tree.

Oddly enough, branches and trees may have been the key to the frogs' success. Analysis of the frogs' genetic histories suggests that the party really only started about 66 million years ago—just after so many of the dinosaurs were wiped out. It also reveals that nearly 90 percent of frog species today trace their genetic roots to just three frog lineages that survived the mass extinction.

But the researchers say it wasn't necessarily the dinosaurs' disappearance that made our planet a more frog-friendly place. The catastrophe that killed the thunder lizards also killed a lot of other things, including primitive prehistoric plants.

"We think the world was quite impoverished as a result of the [extinction event]," co-author David Wake of UC-Berkeley said in a statement, "and when the vegetation came back, angiosperms dominated. That's when trees evolved to their full flowering."

Seeing their opportunity, frogs began moving into the trees. And up there, they thrived.

Around the same time, Wake says, frog species that stayed on the ground learned their own neat trick: direct development, or skipping the tadpole stage, which requires access to water.

"This certainly draws renewed attention to the positive aspects of mass extinctions: They provide ecological opportunity for new things. Just wait for the next grand extinction and life will take off again. In which direction it will take off, you don't know."

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Andrea Piacquadio / Pexels.com

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The Reason Some People Never Return Shopping Carts, According to Science

Abandoned shopping carts could be a sign of social dysfunction.
Abandoned shopping carts could be a sign of social dysfunction.
adisa/iStock via Getty Images

On the spectrum of aberrant behavior, leaving a shopping cart in the middle of a parking space doesn’t quite rise to the level of homicide. But poor cart etiquette is nonetheless a breakdown of the social fabric, one in which some consumers express little regard for others by failing to return a cart to its proper place. Why does this happen?

In a piece for Scientific American, Krystal D’Costa examined some plausible reasons why shoppers avoid the cart receptacle. It might be too far from where they parked, they might have a child that makes returning it difficult, the weather might be bad, or they might have physical limitations that make returning it challenging. Alternately, they may simply believe it’s the job of the supermarket or store employee to fetch their used cart.

According to D’Costa, cart returners might be motivated by social pressure—they fear a disapproving glance from others—or precedent. If no other carts have been tossed aside, they don’t want to be first.

People who are goal-driven aren’t necessarily concerned with such factors. Their desire to get home, remain with their child, or stay dry overrides societal guidelines.

Ignoring those norms if a person feels they’re not alone in doing so was examined in a study [PDF] published in the journal Science in 2008. In the experiment, researchers observed two alleys where bicycles were parked. Both alleys had signs posted prohibiting graffiti. Despite the sign, one of them had markings on the surfaces. Researchers then stuck a flyer to the bicycle handles to see how riders would react. In the alley with graffiti, 69 percent threw it aside or stuck it on another bicycle. In the alley with no graffiti, only 33 percent of the subjects littered. The lesson? People might be more likely to abandon social order if the environment surrounding them is already exhibiting signs of neglect.

In another experiment, researchers performed the flyer trial with a parking lot that had carts organized and carts scattered around at separate times. When carts were everywhere, 58 percent of people left the flyers on the ground compared to 30 percent when the carts were cared for.

Social examples are clearly influential. The more people return carts, the more likely others will do the same. There will, of course, be outliers. Some readers wrote to D’Costa following her first piece to state that they didn’t return carts in order to keep store workers busy and gainfully employed, ignoring the fact that the primary function of those staff members is to get the carts from the receptacle and back to the store. It’s also rarely their primary job.

Until returning carts becomes universally-accepted behavior, random carts will remain a fixture of parking lots. And ALDI will continue charging a quarter deposit to grab one.  

[h/t Scientific American]