An Asteroid Extinguished All The Dinosaurs Except For Birds. Here’s Why

On nan last time of nan Cretaceous period, immoderate 66 cardinal years ago, Earth was teeming pinch a dazzling assortment of dinosaurs. In North America, nan superpredator Tyrannosaurus rex stalked its favourite prey, nan three-horned Triceratops. In Asia, agile raptors eyed herds of duck-billed and armored herbivores, and a menagerie of miniature carnivores and works eaters roamed nan European islands. South of nan equator long-necked behemoths heavier than pitchy airplanes shook nan crushed arsenic they walked. And each complete nan world feather-covered dinosaurs flaunted their plumage, immoderate flapping and flying done nan air.

Then, suddenly, nan Age of nan Dinosaurs was over. A monolithic asteroid slammed into nan Gulf of Mexico, triggering a concatenation guidance of carnage: earthquakes, tsunamis and wildfires followed by years of acheronian and cold. It was astir apt nan worst infinitesimal successful Earth history, and earlier agelong 3 retired of each 4 type were extinct. The asteroid was truthful catastrophic that it spawned 1 of nan top myths successful science, 1 truthful pervasive and repeated truthful perpetually that astir of america deliberation it is true. It is nan story that dinosaurs are gone, felled 1 and each during nan end-Cretaceous extinction.

In fact, immoderate dinosaurs survived nan asteroid apocalypse. Although canonical type specified arsenic T. rex and Triceratops perished, members of 1 dinosaur group managed to endure: birds. Why did birds persevere erstwhile each azygous different type of dinosaur died? Scientists person puzzled complete this mobility for decades. The enigma has deepened successful nan past 30 years arsenic paleontologists person uncovered scores of feathery and winged dinosaurs that were intimately related to birds and akin successful galore aspects of biology and behavior, though not really portion of nan avian lineage. Some of these dinosaurs could moreover fly. What, then, allowed birds unsocial to flight nan destiny of their family?

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Recently an reply has emerged, based connected caller investigation into fossils, genetics and ecology. Many birds were flying complete nan heads of T. rex and Triceratops erstwhile nan asteroid hit, and astir died alongside their dinosaur cousins. The only birds to make it retired of nan Cretaceous were modern-style species. Their endurance came down to circumstance: wherever they happened to unrecorded and nan features they happened to person served them successful bully stead erstwhile nan world went to hell.

Researchers person agelong contemplated nan narration betwixt modern birds and extinct dinosaurs. In nan 1860s scientists of Charles Darwin’s procreation noted striking similarities successful nan skeletons of today’s birds and those of mini meat-eating dinosaurs from nan Jurassic and Cretaceous periods, which spanned nan clip betwixt 201 cardinal and 66 cardinal years ago. In nan 1990s nan thought that birds evolved from dinosaurs became mainstream, bolstered by nan find successful China of dinosaur skeletons base feathers that had been buried by prehistoric volcanoes and fossilized successful pristine condition.

Over nan past 25 years farmers successful China’s Liaoning Province person unearthed thousands of these feathered dinosaurs from their fields. Working pinch my precocious workfellow Junchang Lü, I’ve had nan pleasance of studying galore of them and naming a caller species, a adjacent comparative of Velociraptor that we christened Zhenyuanlong. It is simply a stunning specimen, pinch wispy, hairlike feathers coating astir of its assemblage and quills lined up connected nan arms to shape mini wings. As I gawked astatine nan fossil successful nan backmost room of a Chinese museum, ray illuminating nan feathers, I genuinely understood nan typical relationship betwixt dinosaurs and birds.

These plumaged creatures show nan communicative of really birds evolved from dinosaurs. It was 1 of nan grandest evolutionary transitions successful nan history of life: ferocious ground-living carnivores shrank their bodies, webbed themselves successful downy fluff, germinated wings and took to nan skies.

I’ve been moving to understand this astounding translator for nan amended portion of nan past 2 decades, starting pinch my Ph.D. thesis, supervised by nan precocious Mark Norell, which produced a ample family character of early birds and their adjacent dinosaur relatives. This character showed that birds evolved from dinosaurs piecemeal complete tens of millions of years. Many keystone features of birds today—feathers, wings, wishbones, hollow skeletons, überefficient lungs, large brains—are really dinosaur features that person developed for a litany of reasons complete a agelong long of clip and were only later repurposed to shape a flying machine.

This fossilized skull of Asteriornis, nicknamed nan Wonderchicken, represents nan oldest known personnel of nan family to which modern chickens and ducks belong.

Daniel J. Field, University of Cambridge

By 150 cardinal years ago, nan fossil grounds reveals, existent birds had evolved, specified arsenic nan iconic Archaeopteryx, which soared complete nan lagoons of modern-day Germany. One singular talent distinguished these birds from different dinosaurs: not only could they passively glide for illustration immoderate of their feathered dinosaur kin, but they besides could flap their wings to supply nan assistance and thrust needed to get—and stay—airborne.

For nan adjacent 85 cardinal years aliases much due birds lived alongside their dinosaur cousins. The first ones, including Archaeopteryx, looked for illustration miniature velociraptors, pinch steak-knife teeth, crisp claws and long, bony tails. Over clip immoderate birds underwent refinements that amended adapted them to nan air. Their arms sewage longer, their wings broader, their wing-flapping muscles bigger, their bodies lighter. Their tails shortened to a fatty nubbin anchoring an aerodynamic rudder, and they traded teeth for beaks. Some became warm-blooded and started increasing astatine absurdly accelerated rates.

Meanwhile these Jurassic and Cretaceous birds colonized caller habitats connected nan ground, successful nan h2o and peculiarly successful nan trees, wherever a group called nan enantiornithines established a caller measurement of life, eating plants and bugs and nesting precocious successful nan canopy. By nan waning days of nan Cretaceous genuinely modern birds had appeared connected nan scene. Species specified arsenic Vegavis and Asteriornis, members of nan aforesaid group arsenic ducks and chickens, honked and flapped alongside galore primitive, slow-growing holdovers pinch agelong tails, teeth and claws. Between nan primitive holdovers and nan modern newcomers, nan Cretaceous boasted a staggering array of birds.

Then catastrophe struck. The culprit was a 10-kilometer-wide asteroid, a leftover crumb from nan commencement of our star strategy that happened to intersect Earth. When nan asteroid smashed into what is now nan Yucatán Peninsula of Mexico, it detonated pinch nan unit of much than 1 cardinal atomic bombs. Fire and brimstone filled nan first days of nan aftermath. Dust from nan collision and soot from wildfires clogged nan atmosphere, blocked retired nan sun and plunged nan satellite into a wintertime that lasted years. If you were live that day, your full type had only a 25 percent chance of continuing. Pterosaurs—the aerial reptiles that evolved flapping formation earlier birds—all died, arsenic did nan ocean-living reptiles and coil-shelled ammonites. And truthful did astir each dinosaur.

Paleontologists person based on astir nan velocity of nan end-Cretaceous extinction and whether nan asteroid was nan slayer aliases a wrongfully accused bystander to an extinction arena that was already underway. Based connected caller evidence, I americium assured that decease came fast—instantaneously, successful geological terms—and that nan asteroid was so to blame.

For much than a decade my colleagues and I person prospected nan badlands of northwestern New Mexico, wherever nan pastel-striped rocks sphere furniture aft furniture of dinosaur fossils starring up to nan extinction. In 2025 our team, led by geologist Andrew Flynn of New Mexico State University, described a vibrant organization of dinosaurs successful that area accurately dated to little than a fewer 100 1000 years earlier nan asteroid. They were thriving. There were nutrient eaters and works eaters, ones pinch horns and others pinch duck bills, mini raptors, apex-predator tyrannosaurs, and moreover a long-necked sauropod, Alamosaurus, that was 1 of nan largest animals to ever unrecorded connected land. There is nary motion that thing was amiss. And past their skeletons vanish from nan rocks, and only 1 type of dinosaur fossil remains: nan fragile, hollow bones of birds.

To understand why birds endured erstwhile nan nonavian dinosaurs went extinct, we first must see nan wide roster of victims and survivors—not conscionable dinosaurs but nan entirety of nan animal kingdom that existed correct earlier nan asteroid struck. The overarching shape is clear: if you were big, you died. Every terrestrial animal larger than a Siberian husky grounded to make it done nan Cretaceous and into nan adjacent interval of time, nan Paleogene.

With this norm successful mind, we tin spot why nonavian dinosaurs—including galore of nan feathered dinosaurs—were marked for death. Because of their mostly hefty size, they needed to eat important quantities of food, which was difficult erstwhile nan onshore burned and ecosystems collapsed. These animals could not easy burrow aliases shelter their ample bodies from nan fires and different biology demolition that happened instantly aft nan impact. And astir of them took respective years to turn into adults, which worsened nan likelihood that a azygous individual could persist done nan interminable asteroid-induced winter.

Birds, however, had galore of nan other attributes. Their mini size meant they didn’t request to eat hundreds of pounds of nutrient each time and could amended negociate thin times. They could fly, truthful moreover if they couldn’t excavation burrows, they could motorboat themselves acold distant from immoderate contiguous danger. Certainly these assets gave birds a limb up compared pinch nan different dinosaurs and nan various different animals that died. Case closed?

Rebecca Gelernter

Not exactly, because of 1 nagging problem. The end-Cretaceous was not a elemental communicative of birds surviving while nan nonbird dinosaurs died. In fact, galore birds were besides extinguished successful nan occurrence and fury of nan asteroid. Most of them—maybe astir each of them—followed T. rex to nan grave. One estimate puts nan standard of vertebrate extinction from this catastrophe astatine much than 90 percent. If it weren’t for immoderate plucky survivors, birds mightiness person gone nan measurement of their dinosaur cousins, and location would beryllium nary sparrows astatine your vertebrate feeder, fried chickenhearted dinners aliases pet parakeets today. So we must reframe nan question: Why did only a fewer birds survive?

Once again we tin comparison victims pinch survivors, this clip among birds. Well-sampled rocks of nan latest Cretaceous, spanning from our team’s section sites successful New Mexico northbound to Montana and into Saskatchewan, person yielded much than a twelve chopped type of birds. They scope from archaic forms that retained teeth and agelong tails to highly precocious members of nan modern groups. The extinction is marked by a bladed statement successful nan rocks, saturated pinch nan uncommon constituent iridium, delivered to Earth by nan asteroid. Above it only a azygous type of vertebrate fossil is ever seen again: members of nan modern-day lineages. All different birds disappear; ne'er would location beryllium different vertebrate pinch teeth successful its jaws aliases sickle claws connected its fingers aliases agelong broomstick tails. And that’s existent everyplace successful nan world.

The only birds that carried connected into nan Paleogene are nan alleged crown group: members of nan modern lineages, nan parts of nan vertebrate family character that are still surviving and expanding today. Much of what we cognize astir nan founding members of nan vertebrate crown group comes from 2 precocious discovered fossils making love to nan very extremity of nan Cretaceous.

The first is Vegavis, primitively described from a scramble of bones embedded successful a concrete-hard nodule plucked from nan crystal fields of Antarctica successful nan 1990s and supplemented past twelvemonth by a breathtakingly preserved fossil skull described by Christopher Torres of nan University of nan Pacific successful Stockton, Calif., Julia Clarke of nan University of Texas astatine Austin and their colleagues. The 2nd is Asteriornis—nicknamed nan Wonderchicken—found wrong limestone blocks wrested from a quarry adjacent nan Belgian-Dutch separator and described by Daniel J. Field of nan University of Cambridge and his squad successful 2020. Both are members of nan duck and chickenhearted family and frankincense firmly ensconced successful nan family character of today’s birds.

Vegavis and Asteriornis are emblematic of nan birds that faced down nan asteroid. They were mini for birds of their time, had beaks alternatively of teeth, and lived successful aliases adjacent nan water. And they knowledgeable a fast-paced life successful which they grew from hatchling to big wrong 1 year, arsenic shown by nan deficiency of immoderate yearly maturation rings wrong their bones.

Many birds were besides extinguished by nan occurrence and fury of nan asteroid. Why did only a fewer survive?

Vegavis, which is known from much complete fossils, was additionally a beardown flier pinch ample wings and powerful thorax muscles. It has been recovered pinch a petrified syrinx, nan vertebrate vocal organ, successful its chest, indicating that it could person honked and squawked and made different analyzable vocalizations. Antarctica was warmer successful nan Cretaceous than it is today, but still, Vegavis was intelligibly a robust vertebrate that was capable to tolerate nan acheronian winters of nan precocious latitudes. So successful galore ways nan first crown-group birds were special—and their characteristic mightiness person been nan fount of their resiliency.

Were location circumstantial reasons that fast-growing waterbirds pinch beaks could defy nan asteroid? Recent studies by Field, Derek Larson of nan University of Toronto and their colleagues propose that 2 factors were critical: residence and diet. Where you lived and what you ate mightiness person dictated your destiny astatine nan extremity of nan Cretaceous. Crown-group birds had nan winning combos.

Let’s see residence first. The effects of nan asteroid touched each corners of Earth, but nary situation had it worse than forests. They were pummeled, first by daze waves adjacent nan effect area and past globally by fires and acerb rainfall complete nan pursuing days and weeks. Any trees that survived nan onslaught would person been slow starved of nan sunlight they needed to photosynthesize their food. A plague of fungi preserved successful nan fossil grounds marks nan wide die-off of forests. It astir apt took hundreds of years for them to turn backmost erstwhile nan sunlight returned.

All animals that frequented trees would person been successful trouble—their shelter, nesting grounds and nutrient sources would person disappeared. Many Cretaceous birds, peculiarly nan archaic long-tailed species, were tree-living specialists. But not Vegavis, Asteriornis, and different early crown-group birds, which lived astir nan h2o and connected nan ground. Their homes would person been damaged but not destroyed.

Now connected to diet. When nan agelong wintertime descended, ecosystems built connected a instauration of photosynthesizing plants collapsed. When nan plants died, plant-eating animals had nary food, truthful they besides died. Then nan nutrient eaters succumbed, pinch nan losses cascading up nan nutrient concatenation until nan full web went kaput. But 1 works assets remained disposable for those that could return advantage of it: seeds.

Most plants would person died quickly, and animals that ate leaves, stems, shoots, fruits, aliases different parts of a increasing works were retired of luck. Not truthful pinch seeds. As we spot successful modern-day disasters, seeds tin stay viable successful nan ungraded for decades and let ecosystems to return aft a occurrence aliases volcanic eruption. Because crown-group birds had sharp, mobile nutcracker beaks, they would person been capable to utilization seeds arsenic food, whereas astir different animals—including nan archaic toothed birds—could not.

When you adhd it each together, survivorship astatine nan end-Cretaceous meant winning an unhinged crippled of poker. Each type sat astatine nan proverbial array pinch a manus of cards: wherever they lived, what they ate, really they grew and behaved. But nan platform was frozen—they couldn’t tie immoderate caller cards, because location was nary clip to accommodate done nan accustomed processes of earthy selection, of genes shaping occurrence complete nan generations.

Instead nan rules of nan crippled were elemental but brutal: What manus did you clasp erstwhile nan calamity struck? If you were slow-growing, incapable to burrow aliases shelter, lived successful nan trees aliases had to eat a batch of nutrient (especially plants), past crippled over. The nonavian dinosaurs, including astir feathered dinosaurs, recovered themselves successful this business contempt their resounding power complete nan erstwhile 150 cardinal years. So, too, did galore bona fide flapping, flying birds.

But if you grew fast, could shelter aliases alert distant from danger, lived connected nan crushed aliases successful nan water, and could eat seeds, past immoderate of those assets would person been beneficial and improved your likelihood astatine nan poker table. And if you held all of those cards? You had a royal flush. Crown-group birds conscionable truthful happened to clasp this hand, and they won nan game—and pinch it nan opportunity to evade extinction, unrecorded different time and spawn a caller dynasty of dinosaurs.

After nan impact, erstwhile nan soot clouds cleared and sunlight brightened a blighted land, treatment could begin. Winter gave measurement to rebirth. Seeds grew into trees, trees into forests, forests into analyzable ecosystems. Within a fewer 1000 years Earth was brimming pinch life again. And this caller world thrummed pinch birdsong.

In New Mexico, supra those Cretaceous rocks bursting pinch dinosaur bones, are mudstones from nan ensuing Paleogene, formed connected riverbanks and successful jungle swamps. These Paleogene layers are afloat of fossils, too—not nan dagger teeth of tyrannosaurs and nan elephantine backbones of sauropods but nan jaws and teeth of mammals. Our furry ancestors held their ain winning poker manus erstwhile nan asteroid struck: they were mini burrowers that were tin of increasing accelerated and could eat astir anything.

After patiently biding their clip successful nan shadows, surviving underfoot of dinosaurs for 150 cardinal years but rarely, if ever, getting bigger than a location cat, mammals abruptly had their opportunity. A cardinal years aft nan asteroid effect location were mammals nan size of cattle, and these upstarts rushed to capable ecological niches vacated by nan dormant dinosaurs. But they would not beryllium alone.

Survivorship astatine nan extremity of nan Cretaceous meant winning an unhinged crippled of poker.

Every outpouring I task into nan New Mexico badlands, and complete nan years I’ve developed an oculus for spotting nan teeth of Paleogene mammals. But nary matter really galore I find, location has not been a azygous time erstwhile I’ve eclipsed nan haul collected by my friend Thomas Williamson, precocious retired curator astatine nan New Mexico Museum of Natural History and Science. Williamson is nan world master connected these mammals that took complete from nan dinosaurs, an accolade earned done decades of grueling hikes done nan godforsaken pinch his eyes glued to nan ground. He is truthful obsessed that he would return his copy boys, Ryan and Taylor, heavy into nan badlands erstwhile they were young, multitasking childcare pinch fossil hunting. He trained them conscionable arsenic he would later train me.

On 1 of their family outings, erstwhile nan twins were 10 years old, Taylor grew saturated aft galore hours of fruitless searching. He wandered disconnected by himself to look for rattlesnakes. Having nary luck, he stopped for a bath break. That’s erstwhile he tripped complete a trove of fossils—countless pieces of bony of each shapes and sizes peeking retired of nan godforsaken floor. His celebratory screams echoed done nan quiet canyons, yet reaching his dad.

Williamson later returned pinch a shovel to cod bagfuls of rock, which he passed done sieves astatine nan museum, picking retired each and each fossil. Among nan bones were immoderate different ones, paper-thin and hollow inside. One of them looked for illustration a stub of tailbones smashed together, and others contained fused chunks of manus and wrist. These were not nan bones of mammals; they belonged to a bird.

Williamson and 2 of his colleagues, Daniel Ksepka of nan Bruce Museum successful Greenwich, Conn., and Thomas Stidham, now astatine Austin College successful Texas, gave this vertebrate a name: Tsidiiyazhi abini. It intends “little greeting bird” successful Navajo, a tribute to those who person called this region of Paleogene jungle turned godforsaken location for galore centuries. Living conscionable a fewer cardinal years aft nan asteroid, it was a mini perching bird, a budgie-size type that had returned to nan trees aft nan forests regrew. It was truthful good suited to nan canopy that it could rotate 2 of its toes backward to grip branches, an different expertise that gave distant its identity: it was a mousebird. Mousebirds beryllium to nan vertebrate crown group, and six type of them are still live coming successful sub-Saharan Africa.

Finding a mousebird successful New Mexico a fewer cardinal years aft nan asteroid has startling implications. Mousebirds are profoundly nested successful nan family character of modern birds, meaning that by nan clip mousebirds came into existence, galore of their much primitive crown-group cousins would person already branched off. If location were mousebirds successful nan early Paleogene, location must person been early members of different lineages, too: flamingo and grebe, hawk and eagle, pigeon and dove, owl, and galore more. Indeed, if you analyse nan astir up-to-date genealogies of today’s birds—such arsenic nan 1 presented successful 2024 by Josefin Stiller of nan University of Copenhagen and her colleagues based connected full genomes of hundreds of species—many awesome groups of modern birds are implied to person originated correct aft nan end-Cretaceous extinction successful an exuberant burst of evolution.

With nan asteroid successful nan rearview mirror, their dinosaur cousins and ancestors gone and mammals now nipping astatine their wings, nan birds that bested nan end-Cretaceous asteroid were free to diversify pinch gusto. They experimented pinch caller flying styles and diets, expanded into uncharted environments, and fashioned nan instauration of today’s vertebrate diversity—more than 10,000 species, astir doubly nan number of mammals.

So acold this communicative is mostly implied by DNA and family trees. Other than Taylor’s Tsidiiyazhi and a fewer different scrappy specimens, we haven’t yet recovered galore fossils of these early Paleogene birds. Doing truthful will beryllium challenging because these birds were mini and vulnerable and astir apt did not easy petrify into stone. But if nan mentation is true, past nan fossils should beryllium retired there, concealed successful nan rocks, waiting for a caller procreation of paleontologists (or their kids) to find them. I’ll beryllium looking nan adjacent clip my students and I are successful New Mexico.