How do we know that birds are dinosaurs?


Picture of the article titled

illustration: Benjamin Curry

The ferocious tyrannosaurus and towering sauropod dinosaurs are long gone, but dinosaurs continue to play among us.Of course we are talking about birds, but why we should consider birds is not entirely clear bona fide dinosaur. There are many reasons for this.

There is no doubt that birds are legal dinosaurs, not some branch of evolution.After the mass extinction caused by asteroids 66 million years ago, all non-avian dinosaurs were wiped out, but some birds—perhaps Ground-dwelling birds-Managed to survive, they No time wasted Take over as soon as their relatives are gone.

“Those little guys singing outside your window are the dinosaurs we left behind these days,” Adam Smith, curator of the Campbell Geological Museum at Clemson University, explained in an email. “Birds are just a type of dinosaur. Saying “birds are descendants of dinosaurs” is similar to saying that people are descendants of mammals. Simply put, all birds are dinosaurs, but not all dinosaurs are birds. “

This warbler doesn't mind being called a dinosaur.

This warbler doesn’t mind being called a dinosaur.
image: U.S. Fish and Wildlife Service

The connection between birds and dinosaurs is hardly a recent revelation. In the late 19th century, British naturalist Thomas Henry Huxley dared to propose that birds evolved from dinosaurs.Riley Black wrote In 2010, his idea of ​​the origin of birds “is not a perfect prediction of our current knowledge”, but Huxley, a skilled anatomist, clearly makes sense.

In fact, since then, scientists have identified many characteristics that can easily locate birds as dinosaurs in the phylogenetic tree. Kate Lyons, an assistant professor at the Lincoln School of Biological Sciences at the University of Nebraska, said that “not just a smoking gun” allows paleontologists to say that birds are dinosaurs, because there are “multiple evidences” that show this conclusion, as she said As written to me in the email.

Steven Brussart, a paleontologist at the University of Edinburgh, said that by applying the same reasoning that bats are mammals, we know that birds are dinosaurs.

Look at this dinosaur. Specifically, a brown boobies.

Look at this dinosaur. Specifically, a brown boobies.
image: NOAA/NMFS/OPR

“Yes, birds are small, have feathers, have wings, and can fly. This is different from the dinosaur image we are used to,” he wrote in an email. “Bats are analogy to mammals-they are small, have wings, and can fly. They don’t look like dogs, elephants or primates, but they are still mammals.”

In fact, bats have many characteristics unique to mammals, such as hair, molar teeth, three small ear bones, and the ability to feed their cubs with milk. Similarly, birds have characteristics that can only be seen in theropod dinosaurs, Brussat explained.

Like feathers.

Indeed, although there is no single “smoking gun” that can classify birds as dinosaurs, the presence of feathers may be the most exciting thing. The fossil record is full of examples of feathered non-avian dinosaurs, and because feathers are unique to birds, scientists can associate them as dinosaurs.

Skeptics might argue that the appearance of feathers in birds and non-avian dinosaurs is Convergent evolution, Where similar features appear independently in unrelated species.Smith said that in this case, convergent evolution is unlikely, because “many of the non-avian dinosaurs with well-preserved feathers found are species that have been independently assumed to be close relatives of birds,” including Raptor with Chinese Dragon Bird.

The artist's interpretation of the Mongolian Velociraptor.

Artist’s interpretation Mongolian Velociraptor.
illustration: Fred Willem (Fair use)

He added: “Feathers are extremely complex structures. Although convergent evolution often leads to similar structures—even entire animals—which look very similar on the surface, there is no example of convergent evolution that replicates structures on the scale. Kind of fidelity.”

As Andre Rowe, a PhD student in the School of Earth Sciences at the University of Bristol, explained in an email, phylogeny—the study of evolutionary relationships between species—provides further evidence that birds are dinosaurs.with all due respect Jurassic ParkPaleontologists cannot extract and analyze ancient dinosaur DNA, but they can examine the key features shared between species indicated by bones and anatomy.Based on these key characteristics, scientists “almost certainly say that birds belong to the theropod dinosaur lineage,” Luo said, referring to carnivorous dinosaurs, such as Tyrannosaurus, Allosaurus, with Lower jawImportantly, the bones of theropods and birds “have not changed abruptly in their evolutionary relationship, but have gone through a smooth transition over millions of years,” he added.

Kristi Curry Rogers, a vertebrate paleontologist at McAlester College in Minnesota, wrote in an email: “Going back in time, we can trace the evolution of basic bird body plans. To some of the earliest dinosaurs.” “Like dinosaurs, birds walked with their legs directly under their bodies. Dinosaurs made the birds grow faster.”

All birds are dinosaurs, but not all dinosaurs are birds. Here, the tyrannosaurus skeleton is installed next to the triceratops skeleton at the Natural History Museum of Los Angeles.

All birds are dinosaurs, but not all dinosaurs are birds. Here, the tyrannosaurus skeleton is installed next to the triceratops skeleton at the Natural History Museum of Los Angeles.
image: Matthew Dillon (Fair use)

Holly Woodward Ballard, associate professor of paleontology and anatomy at the University of Oklahoma, said: “We know that birds are dinosaurs because they have more characteristics than extinct dinosaurs compared to other living animals. .”

In fact, there are many other features that need to be considered-such as “wishbone, bone hollowed out by airbags, and rotatable wrist”, allowing the dinosaur to “fold the arm and stick it to the body”, Brussart said .

In an email, paleontologist and evolutionary biologist Jessica Theodore from the University of Calgary described these and other unique characteristics of dinosaurs. For example, structures that allow birds to bend their hands backwards at the wrists to fold their wings are also present in wingless arms. Netherbone DragonShe explained that biologists can track this structural change “through theropod evolution.”

Comparison between the airbags of Majungasaurus and ducks.

Comparison between the airbags of Majungasaurus and ducks.
Image: Gina Drecky/NSF

Kat Schroeder, a PhD student in the Department of Biology at the University of New Mexico, described the fusion of certain vertebrae into the sacrum and coccyx as one of the most important evolutionary adaptations of birds.

“The same sacrum is the fusion of the vertebrae above the hips. It hardens the back and helps flight. The coccyx is the fusion of the last coccyx. It supports the tail feathers. This actually exists in some non-avian dinosaurs, such as Egg thief with Ornithosaurus There may be feather fans instead of long or pointed tail fans,” she wrote in an email.

“Birds have small flanges on the ribs, called uncinate processes, which provide some mechanical advantages for the respiratory muscles of the ribs.” They also exist in Egg thief with Chilong, As Theodore explained. More importantly, “bird bones have many other structural similarities with dinosaurs in their bones, all of which put them together for phylogenetic analysis,” she said.

evidence of meditation As Luo reminded me, in some dinosaurs, animals rest on their nests to keep their eggs warm and protected. This is a behavior of modern birds. In addition, both dinosaurs and birds use gizzard stones (stones that are swallowed to help digestion), “because these stones will grind up food that has been ingested,” he said.

As I mentioned before, scientists cannot study the DNA of ancient dinosaurs, but they can study the DNA of modern dinosaurs.

“The evidence that birds are really just little dinosaurs that learn to fly comes from dinosaur fossil records and the bodies and genomes of existing birds,” Curry Rogers explained. “When we look at modern birds, we can see that little souvenirs of their more ferocious history are deeply locked in their genes-the extinct developmental program used to build longer tails and teeth.”

She added: “It’s all there-written on the bones and bodies of dinosaurs, alive and extinct!”

So next time the hummingbird comes to your feeder, please feel free to welcome this little bird as a visiting dinosaur. You can also claim that you tasted a dinosaur after chewing some chicken wings, or that you were attacked by a dinosaur when a goose scared you away from her nest. When the Toronto Blue Jays play against the Baltimore Orioles, you can call this game a battle of dinosaurs.

It sounds strange, but you have science to support you.

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