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Millions of years ago, scaly, lizard-like dinosaurs ruled the Earth. Over time, some of those dinosaurs sprouted feathers and took to the skies—and while their reptilian cousins died off, those ancient avians survived to become the birds we know and love today.

Recent decades have seen an explosion in research uncovering new details about the prehistoric birds that once roamed the planet and the evolutionary journey that brought them into the modern age. Cutting-edge technology has played a crucial role, says Daniel Field, who studies bird evolution at the University of Cambridge. Advanced scanning methods can capture minute details from fossil samples, while large-scale genome sequencing helps dig into the evolutionary relationships that tie together this whole family tree.

In many ways, the steady flow of research continues to complicate the picture of bird evolution, says Jingmai O’Connor, a paleontologist and curator at Chicago’s Field Museum. “It was easier for us to make very simple, little, neat answers when we had very little data,” O’Connor says. “And then you get more data, and you’re like, ‘Whoa. It’s weird. It’s complex.’” While scientists have gained new insights, they’re also left with many fundamental questions, including how one line of birds survived the dinosaurs’ mass extinction.

Of course, none of this would be possible without the fossils themselves. Luckily, “people just keep finding amazing new stuff,” Field says. As 2024 wraps up, we’re rounding up some fossil finds reported this year that are helping to build out our knowledge of the dinosaur-to-bird pipeline. “It’s kind of like birdwatching,” Field says. “But birdwatching through geological time.”

No teeth? No problem

The early birds that first evolved from dinosaurs looked pretty similar to today’s avians—with a couple twists. Many had tiny teeth lining their upper and lower beaks, as well as small claws poking out from their wings, says Alex Clark, a doctoral student at the University of Chicago. “Picture a robin with teeth, with little velociraptor hands,” Clark says. “You’re loosely getting there.”

So when scientists examined a 120-million-year-old avian fossil from China, they were surprised to find it didn’t have any chompers in its beak. The specimen was around 50 million years older than any toothless birds previously known, suggesting that a lack of teeth was a more common feature than scientists had realized. “It’s occurring more often and earlier than we thought in early bird evolution,” Clark says.

He and his co-authors described the new species in a , naming it Imparavis attenboroughi in honor of naturalist David Attenborough. The species belongs to an ancient bird group known as the enantiornithines, or “opposite birds,” a separate lineage from modern birds that thrived in the age of the dinosaurs but died off when the asteroid hit. Finds like this one show there’s still a lot to learn about this long-extinct group, says O’Connor, a co-author: “They’re just really weird birds.”

Soft as a feather, sharp as a scale

As dinosaurs dropped their scales and grew feathers, their skin became softer to support these new coverings. A fossil find shed light on a previously unknown step in that process: A dinosaur that likely sported patches of soft skin under its feathered tail, but kept areas of reptile-like skin across other parts of its body.

The fossil from a Psittacosaurus, or “parrot lizard,” is unusual, because it has soft tissue that remains preserved in three dimensions. “While numerous fossils of feathers have been studied, fossil skin is much more rare,” study author Maria McNamara, a paleontologist at University College Cork, said in a . The high-quality sample allowed researchers to examine its layers and uncover this mix of skin types. The researchers suggest that this patchwork approach would allow dinosaurs to keep some of the benefits of their scaly skin, which protected them from damage and disease even as they started to experiment with growing feathers.

The oldest birds of prey?

The Hell Creek formation in Montana is famous for its big dinosaur fossils like T. rex and triceratops. Now, the fossil trove has turned up evidence of the animals that soared over these species’ heads.

In an , researchers described two new species from the site: Avisaurus darwini and Magnusavis ekalakaenis, hawk-sized avians that lived around 68 million years ago. Though they only found one foot bone from each, scientists learned a lot by looking at a particular bump on the fossils—a tubercle where the bone would connect to muscle. In this case, that connecting muscle would control how the bird flexed its foot and moved its lower limb closer to the body, explains Clark, the lead author of the study.

On both, those bumps were huge and placed low on the bone. This pattern is similarly found in modern raptors, who use their powerful feet to pin down prey and haul them through the air. “If you're a hawk or an owl, whatever you're carrying, you want to bring as close as you can to the body to reduce drag,” Clark says. The team suggests that these ancient birds might have used their powerful feet to pick up small mammals or maybe even baby dinosaurs—which would make them the oldest predatory birds yet discovered.

Peering into ancient bird brains

Scientists have long wanted to better understand how birds evolved their distinctive brains, which allow them to navigate during flight and perform complex behaviors—but a lack of ancient bird skulls has made that difficult. A new fossil in Brazil could help fill in gaps: The fossil bird, described in a , was found with its skull in excellent condition, offering clues to the brain it once contained. 

The species, Navaornis hestiae, lived around 80 million years ago—about the midway point between the iconic Archaeopteryx, one of the oldest known birds, and the avians of today. Its remains were preserved in three dimensions, unlike other skull fossils from this period, which are “compressed like a pancake, or roadkill,” says study author Luis Chiappe, a paleontologist at the Natural History Museum of Los Angeles County. 

After scanning the skull and modeling the brain, researchers found that while Navaornis had a slightly expanded forebrain, it still had a pretty small cerebellum—a brain area that’s key for flight navigation in birds today, explains Field, a co-author on the study. The bird may have compensated with massive inner-ear structures that could help retain balance. Overall, Chiappe says, the fossil shows how avian brains of this period combined modern-looking features with structures that are clearly ancient: “This is like building the Empire State Building using adobe bricks.”

A bigger, badder terror bird

Tens of millions of years ago, stretches of South America were dominated by the terror birds—avian predators that were fast, flightless, and fierce. In November, scientists unveiled a chunk of leg bone that showed these creatures got even bigger, and spread even farther, than previously thought. 

After scanning and modeling the leg fragment, which was discovered by a rancher and fossil collector in Colombia, the bird could have stretched over 8 feet tall and weighed more than 340 pounds. Though it’s hard to tell from one piece of bone, researchers think the leg “may correspond to the largest terror bird that ever existed” and represent a new species in the terror bird family. The fossil find also expanded the known range of the South America’s terror birds nearer to the equator, suggesting these hunters also lived in tropical environments along with more temperate zones.

The fragment offers a clue to this bird’s downfall, too. Its leg displays a bite mark that probably came from a Purussaurus—a supersized crocodile relative whose bite was twice as powerful as a Tyrannosaurus rex, enough to take down even this hefty ancient avian. 

The “giga-goose,” revealed

Over a century ago, paleontologists uncovered the bones of a massive bird, twice the size of an ostrich, that roamed Australia 50,000 years ago. But without a well-preserved skull, they had many questions about Genyornis newtoni, including what it ate and how it related to modern birds. This June, scientists finally after finding a new fossil skull in the salt lake where the species was first discovered. The big reveal? The species was essentially a massive goose, which the researchers a “giga-goose.”  

The researchers’ analysis suggested the bird had a strong bite, good for crushing soft plants and fruit, and aquatic adaptations that helped keep water out of its ears and throat. It also suggests that a changing climate may have led to the giga-goose’s eventual demise as wetlands dried up. When the species went extinct, it put an end to the reign of the mihirungs—massive, flightless birds that roamed Australia for millions of years.