Mammals gradually expanded in size and diversity after the dinosaur extinction

Mammals thrived under the feet of dinosaurs

An explosion of fossil finds reveals that ancient mammals evolved a wide variety of adaptations allowing them to exploit the skies, rivers and underground lairs.

Air sacs and lightweight bones helped some dinosaurs grow to enormous sizes

After the Triassic extinctions, new species with birdlike anatomy evolved from smaller, early dinosaurs. This anatomy allowed for more efficient breathing and lighter skeletons, favoring the evolution of larger organisms.

Variations in beak shape helped birds survive the dinosaur extinction event

The asteroid that struck Earth 66 million years ago killed some avian dinosaurs. The smaller species endured by reproducing more quickly and adapting to the environment. Their different beaks allowed them to eat more varied foods for survival.

Dinosaurs would likely still roam Earth if the Chicxulub asteroid had hit elsewhere

Some scientists argue that the asteroid's impact would have been less severe if it had struck the ocean instead of shallow seas. In this scenario, small dinosaurs might have become urban survivors, living in cities alongside humans, much like pigeons or rats do today.

Dinosaurs emerged 245 million years ago when Earth’s continents were still conjoined

Once the supercontinent split apart, dinosaurs evolved into thousands of species as they adapted to their changing environments. All non-avian dinosaurs went extinct about 66 million years ago following an asteroid impact, while avian dinosaurs evolved into today’s birds.

Without dinosaurs, plants could produce fleshy fruits with bigger seeds

Previously disturbed by massive herbivores, denser and darker forests shifted plant evolution, reaching the greatest diversity of seed sizes, fruit sizes, and fruit types about 50 million years ago.

There are lots of weird ideas about dinosaur extinction, like hungry, hungry caterpillars

One of the great historical puzzles is this: why did the dinosaurs go extinct? Whether an asteroid, poison plants, volcanos and climate change, or something else, it's still a mystery. Scientists have been debating this question for almost a hundred years. One insect scholar suggests that caterpillars are the culprits.

Georges Cuvier used his knowledge of anatomy to prove extinction had occurred

Extinction had been viewed as impossible because a divine plan for the world would not rationally involve the loss of any of God’s creations. However, mammoth and mastodon bones differed from elephants’, and it seemed impossible that such creatures could be hiding elsewhere on Earth.

There have been five mass extinction events in Earth’s history

Each extinction event has resulted in the loss of at least 70% of Earth’s species at the time of the event, often due to significant changes in global temperatures. The most recent event occurred 66 million years ago and wiped out all non-avian dinosaurs.

What did the world of the dinosaurs look like?

Mesozoic means "middle life" and this is the time of the dinosaurs. This era includes the Triassic, Jurassic, and Cretaceous Periods, names that may be familiar to you. It ended with a massive meteorite impact that caused a mass extinction, wiping out the dinosaurs.

Supermountains the size of the continental US may have sparked complex life on Earth

Geological records show that the Nuna and the Transgondwanan Supermountains existed around the same time as two major jumps in species complexity on the planet: the rise of large organisms and the Cambrian explosion, respectively. Researchers believe that the erosion of these mountains deposited major nutrients into the oceans and boosted oxygen levels, both of which supported more complex species.

Large animals like giraffes and elephants have evolved unique cancer defenses

One may expect the larger an animal is, the more likely it is to develop cancer—simply because there are more cells and more chances for a dangerous mutation. However, some large animals show cancer rates almost 10 times lower than humans—a phenomenon known as Peto's Paradox.

Larger animals like giraffes, elephants, and blue whales have developed a unique defense against cancer, a phenomenon known as Peto's Paradox

Humans won't develop more than 5 fingers because it would impact too many body parts

All modern animals have five or fewer digits on each of their limbs. Roughly 348 million years ago, at least two species had eight: the Ichthyostega and the Acanthostega. According to Dollo's law, complex evolved features are very unlikely to recur in evolution. Researchers believe humans won't develop more than five digits because it would impact other body parts too much.

View a directory of more than 300 dinosaurs

This resource details each dinosaur's taxonomy, type, diet, and habitat, from Aardonyx to Zuniceratops. More well-researched dinosaurs include information on when they were discovered alongside their size, behaviors, and other noteworthy findings.

Bringing dinosaurs back to Mongolia

The Gobi Desert, which crosses Mongolia and China, was a dinosaur hotspot, offering visitors splendid freshwater lakes and a lush, humid climate. These past verdant vast valleys have become the largest dinosaur fossil reservoir in the world, and with that title comes those seeking to remove such items, whether for personal satisfaction or scientific study. This article explains the fight to restore Mongolia's fossil heritage.

Humans may be the ultimate invasive species

Originating in East Africa, Homo sapiens migrated across the world beginning about 60,000 years ago and directly harmed countless species by consuming resources and modifying ecosystems to serve our needs. While meeting the definition of an invasive species, some ecologists argue the opposite, claiming that humans have helped preserve numerous species.

Three examples of how humans are still evolving

For much of nature, natural selection and "survival of the fittest" still play a dominant role; only the strongest can survive in the wild. As little as a few hundred years ago, the same was true for humans, but what about now?

View a breakdown of the identified species on Earth

Over 2 million species have been documented by scientists, but there may be as many as a billion distinct species. The vast majority of the species on Earth are insects, while mammals form the smallest group.

Cats began cozying up to humans around 10,000 years ago

The feline family is a hugely diverse group of lions, panthers, and kitties that have spread all over the world. The ancestors of the cats we love today helped solve rodent problems when humans first invented agriculture. They've been worshipped, loved, and scorned by humans since.

Humans aren't the only mammals who go through menopause, but it's rare in the animal world

While scientists are unsure how many mammals actually experience menopause, they do know for sure that humans aren't the only ones. Orcas and some toothed whales (like belugas and narwhals) go through menopause. And a recent study found chimpanzees also experience the condition, though it's late in life.

Explore these collections of early human fossils

The human fossil record is filled with massive gaps, leaving archaeologists tiny samples to try and glean the history of our species. At this site, you can browse through the human fossil collection, including 3D rotatable scans of hundreds of fossils from different species of early humans.

Watch visualization of different-sized asteroid impacts

The animations range from a 4-meter-wide asteroid that would burn up in the atmosphere with the impact of 0.6 Hiroshima nuclear bombs to a 940-kilometer asteroid the size of the dwarf planet Ceres, which would produce a mass extinction event.

Tardigrades average about half a millimeter in size, with rear legs used for grasping

Their physiology and size, which is even smaller in the tun state, allow them to be carried by the wind and latch onto moist surfaces. They have been found in ocean trenches approximately 5 kilometers deep and at altitudes of six kilometers in the Himalayas.

The Chernobyl exclusion zone has become a unique wildlife refuge

Within the area—roughly the size of Yosemite National Park—animals such as wolves, bears, and feral dogs descended from the pets left behind have gradually adapted to low-level radiation. Eastern tree frogs in the area have darker skin than usual, which may have helped protect them from ionizing radiation.

The deep-sea fangtooth has the largest teeth of any marine species relative to body size

From transparent fish to the heaviest worms on the planet, these seven creepy creatures lurk in the deep sea. Learn all about them and the unique traits that help them survive and hunt.

Indefinite cloning of some endangered species may not sustain their longevity because cloning success rates decrease as genetic mutations accumulate.

See how each of the more than two million known species relates to each other—and to common ancestors—in this zoomable tree of life.

After NASA's Voyager 1 captured Earth as a single pixel as it left the solar system in 1990, astronomer Carl Sagan used the image to reflect on humanity's fragility and the responsibility to protect 'the only world we've ever known.'

Watch how viruses like Ebola can spill over from animals to humans—and vice-versa.

Before humans, the Soviet Union and the United States sent animals—including apes, dogs, and cats—to space during the Space Race.

Poison ivy will likely become both larger and more resilient due to climate change.

Some Pokémon have been named after real and fictional organisms, while some real-world species have been named after Pokémon, such as Chilicola charizard and Binburrum zapdos.

Fish populations in the Great Barrier Reef have increased after installing waterproof speakers on the ocean floor that played recordings of sounds from healthy coral reefs.

Volcanic activity may have triggered the Black Death by spewing gases that led to crop failures in Europe, thus forcing the import of grain ships with plague-infested fleas.

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

Most of the observable universe's volume consists of voids and supervoids—enormous regions of space with little to no galaxies, stars, or light.

The animatronic shark from Steven Spielberg's 'Jaws,' the first modern blockbuster, was a complex underwater apparatus called 'Bruce.'

About 12.5% of US adults experience a phobia in their lifetime, a diagnosis that hinges on the intense fear interfering with daily life and persisting for at least six months.

Shooting stars, or meteors, are fragments of asteroids and comets that burn up as they enter Earth's atmosphere, creating streaks in the sky called meteor showers.

The power and influence of the American presidency have expanded significantly over time—far beyond what the founders envisioned.

SpaceX's S-1 or 'prospectus' revealed many previously unknown details about the company, including its unprofitability despite doing $18.7B in revenue in 2025, exactly how many voting shares Elon Musk will have in the company (roughly 85%), and more.

Dozens of S&P 500 stocks, including Coca-Cola and Walmart—known as the dividend aristocrats—have increased dividends every year for 25 years

See a 3D reconstruction of Tenochtitlan, the Aztec capital that was home to an estimated population of 200,000 to 400,000.

While atoms are normally made of protons, neutrons, and electrons, exotic ones have been built with antimatter—alternate versions of normal matter that live for fractions of a second and are about a billion times as rare.

Fast-casual restaurant Chili's is experiencing a resurgence, with its parent company recently reporting a nearly 32% increase in sales, thanks to passionate Gen Z fans on TikTok.

Walt Disney's early film 'Alice's Wonderland' was a groundbreaking innovation in the silent film era

For centuries, it was common to sleep in two shifts: a few hours at the beginning of the night, and a longer period beginning around midnight

The syncytiotrophoblast is the outer layer of the placenta and the largest human cell, spanning an area about twice that of a king-sized bedsheet.

For centuries, Niagara Falls has been a magnet for daredevils seeking to conquer one of nature's most powerful wonders, with its 200-foot drop and water rushing at 32 feet per second with 280 tons of force.