Why Are There No More Dinosaurs?

CHLOE EFFRON / DINOSAURS: ISTOCK
CHLOE EFFRON / DINOSAURS: ISTOCK

WHY? is our attempt to answer all the questions every little kid asks. Do you have a question? Send it to why@mentalfloss.com.

Actually, there are still dinosaurs: Birds! But let’s talk about that a little later. Scientists have found clues in rocks and fossils that tell us that by 65 million years ago, the climate (CLY-met), or usual weather, of the Earth had changed a lot, becoming cooler and drier. That was hard on the heat-loving dinosaurs. But that’s not why almost all of the dinosaurs became extinct, or disappeared forever. Scientists think a terrible event occurred that killed them off.

In 1991, scientists discovered a huge 110-mile-long crater, or hole, in the Gulf of Mexico. They think this crater was made by a giant, fiery, 6-mile-wide asteroid (AST-er-oyd) from space that smashed into the Earth about 65 million years ago. The impact was more powerful than any bomb we have ever known. Scientists believe this event killed most plant and animal life—including the dinosaurs. The asteroid probably caused shockwaves, earthquakes, fireballs, wildfires, and tidal, or really big, waves. It also sent huge amounts of dust and gas into the atmosphere, which is like a big blanket of air that surrounds the Earth. That was really bad for the planet.

The dust blocked sunlight, making the planet very cold and dark. Then, over time, the gases trapped heat, causing the Earth to get even hotter than it was before the asteroid hit. This change was deadly for most dinosaurs, and they became extinct. But birds survived. Many millions of years earlier, they had evolved (ee-VOL-ved), or changed slowly over time, from one group of dinosaurs. And when the dinosaurs disappeared, mammals diversified (die-VERSE-uh-fide), or changed, into many different kinds of animals—including us, many millions of years later. So the next time you see a bird swoop by, wave hello to the little flying dinosaur!    


Lost Your Wallet? You Might Be More Likely to Get It Back If There's Cash Inside

iStock/tzahiV
iStock/tzahiV

Few things can incite more panic than discovering you’ve lost a wallet or purse containing money, identification, credit cards, and/or keys. You wonder if anyone will find it—and if they do, whether they’ll decide to retain your cash using the playground ethics of the "finders keepers" rule.

An ambitious new study in the journal Science has provided at least a partial answer. If your wallet has cash inside, it’s actually more likely for people to return it than if it didn’t have any.

Researchers at the University of Michigan conducted an exercise in civic honesty, dispatching 13 assistants to 355 cities in 40 countries across the globe. At each destination, the assistants were armed with clear wallets that held things like grocery lists and business cards along with an email address. Some wallets had no money inside. Others contained about $13.45 in the local currency. The assistants gave the wallets to employees at banks, hotels, post offices, museums, and police stations, explaining they had “found” the wallet and were in too big of a hurry to contact the owner themselves. They passed the responsibility to the person receiving the wallet. All told, 17,303 wallets were left as proverbial bait to see what the employees might do.

Of the wallets without cash inside, researchers received an email seeking to return roughly 40 percent of them. About 51 percent of the employees attempted to return the wallets containing $13.45 in cash.

These percentages fluctuated by country. In Denmark, 82 percent of wallets with cash were returned. In the United States, the figure was 57 percent. When researchers upped the stakes by including $94.15 in wallets for areas in the U.S., Britain, and Poland, the return rate went up to 72 percent.

It’s difficult to infer motivations for why people returned wallets with more money than less, or none. In a survey, researchers found that people in general described wanting to avoid feeling like a thief by keeping the money. (Respondents were different than the employees who were left with the wallet.) That would explain why returns increased as the dollar amount went up.

The study was limited by the fact that the wallets were left with people who could have presumably been held accountable for not returning them. The research assistant could have returned to inquire about the wallet’s status, while no such concern exists for people finding a wallet in the street. Still, it does indicate that people feel a measure of sympathy for—and moral obligation to—lost money and will make an effort to see it returned.

[h/t Science News]

Some Fish Eggs Can Hatch After Being Pooped Out by Swans

iStock/olaser
iStock/olaser

A question that’s often baffled scientists is how certain species of fish can sometimes appear—and even proliferate—in isolated bodies of water not previously known to harbor them. A new study has demonstrated that the most unlikely explanation might actually be correct: It’s possible they fell from the sky.

Specifically, from the rear end of a swan.

A study in the journal Ecology by researchers at the Unisinos University in Brazil found that killifish eggs can, in rare cases, survive being swallowed by swans, enduring a journey through their digestive tracts before being excreted out. This kind of fecal public transportation system explains how killifish can pop up in ponds, flood waters, and other water bodies that would seem an unlikely place for species to suddenly appear.

After discovering that some plants could survive being ingested and then flourish in swan poop, researchers took notice of a killifish egg present in a frozen fecal sample. They set about mixing two species of killifish eggs into the food supply of coscoroba swans living in a zoo. After waiting a day, they collected the poop and dug in looking for the eggs.

Of the 650 eggs they estimated to have been ingested by the swans, about five were left intact. Of those, three continued to develop. Two died of a fungal infection, but one survived, enduring 30 hours in the gut and hatching 49 days after being excreted.

Because killifish eggs have a thick outer membrane, or chorion, they stand a chance of coming through the digestive tract of an animal intact. Not all of what a swan ingests will be absorbed; their stomachs are built to extract nutrients quickly and get rid of the whatever's left so the birds can eat again. In rare cases, that can mean an egg that can go on to prosper.

Not all fish eggs are so durable, and not all fish are quite like the killifish. Dubbed the "most extreme" fish on Earth by the BBC, killifish have adapted to popping up in strange environments where water may eventually dry up. They typically live for a year and deposit eggs that can survive in soil, delaying their development until conditions—say, not being inside a swan—are optimal. One species, the mangrove killifish, can even breathe through its skin. When water recedes, they can survive on land for over two months, waddling on their bellies or using their tails to "jump" and eat insects. A fish that can survive on dry land probably doesn't sweat having to live in poop.

The researchers plan to study carp eggs next to see if they, too, can go through a lot of crap to get to where they’re going.

[h/t The New York Times]

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