How do we know birds are dinosaurs? - petsitterbank

How do we know birds are dinosaurs?

Image for the article How do we know birds are dinosaurs?

illustration: Benjamin Currie

Wild tyrannosaurs and towering sauropods have long since disappeared, but dinosaurs continue to frolic in our midst. We are talking about birds, of course, but it is not entirely clear why we should look at birds as such bona fide Dinosaurs. Here are the many reasons for that.

Make no mistake, birds are real dinosaurs and not evolutionary offshoots. All non-avian dinosaurs were wiped out after the asteroid-induced mass extinction 66 million years ago, but some species of birds – likely ground-dwelling birds—Has managed to survive, and so did she no time wasted to take over as soon as their relatives were gone.

“Those little guys who sing outside your window are the dinosaurs we have today,” Adam Smith, curator at Clemson University’s Campbell Geology Museum, explained in an email. “Birds are just a kind of dinosaur. To say “birds are descended from dinosaurs” is like saying that humans descended from 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: US Fish and Wildlife Service

That birds are somehow related to dinosaurs is not a new revelation. In the late 19th century, the English naturalist Thomas Henry Huxley ventured the claim that birds evolved from dinosaurs. As a science writer, Riley Black wrote In 2010 his ideas about the origins of birds were “not a perfect anticipation of our current knowledge,” but Huxley, a seasoned anatomist, was clearly prepared for something.

In fact, since then scientists have identified a variety of traits that as birds position themselves comfortably in the phylogenetic tree as dinosaurs. Kate Lyons, assistant professor at the University of Nebraska’s Lincoln School of Biological Sciences, says there is “not just one smoking weapon” that enables paleontologists to label birds as dinosaurs, as there is “multiple evidence” of this. as she wrote to me in an email.

University of Edinburgh paleontologist Steven Brussatte says we know birds are dinosaurs using the same reasoning that tells us that bats are mammals.

Look at this dinosaur.  More precisely, a brown booby.

Look at this dinosaur. More precisely, a brown booby.
image: NOAA / NMFS / OPR

“Yes, birds are small and have feathers and wings and fly, and that’s different from what we’re used to seeing of dinosaurs,” he wrote in an email. “Bats are the analogy to mammals – they’re small, have wings, and fly, and they don’t look like a dog, elephant, or primate, but they’re mammals nonetheless.”

In fact, bats display many characteristics reserved only for mammals, such as hair, molar teeth, three tiny ear bones, and the ability to milk cubs. Likewise, birds have features only seen in theropod dinosaurs, Brussatte explained.

Like feathers.

While there isn’t a single “smoking weapon” to refer to birds as dinosaurs, the presence of feathers is probably the most smoking thing of all. The fossil record is filled with examples of non-avian feathered dinosaurs, and since feathers are unique to birds, scientists can link the two together as dinosaurs.

Skeptics may argue that the appearance of feathers in both birds and non-avian dinosaurs is a result of. is convergent evolution, in which similar traits appear independently of one another in unrelated species. Smith says convergent evolution is unlikely in this case because “many of the non-avian dinosaurs found with preserved feathers are the very species independently believed to be close relatives of birds,” including Velociraptors and Sinosauropteryx.

Artistic interpretation of Velociraptor mongoliensis.

And he added, “Feathers are ridiculously complex structures, and while convergent evolution often results in similar structures – and even whole animals – that appear quite similar on the surface, there are no examples of convergent evolution duplicating structures on scale, with that kind of loyalty. “

Phylogenetics – the study of evolutionary relationships between species – provides further evidence that birds are dinosaurs, Andre Rowe, a graduate student from the University of Bristol’s School of Earth Sciences, explained in an email. With all due respect Jurassic Park, Paleontologists are unable to extract and analyze ancient dinosaur DNA, but they can study the key features shared between species, such as their skeletons and anatomy reveal. Based on these key traits, scientists “can reasonably safely say that birds belong to the theropod lineage,” Rowe said of carnivorous dinosaurs such as T-rex, Allosaurus, and Compsognathus. It is important that theropod and bird skeletons “show no sudden changes in their evolutionary relationship, but rather a smooth transition over millions of years,” he added.

“If we go back in time, we can trace the evolution of the basic bird body plan back to some of the earliest dinosaurs,” wrote Kristi Curry Rogers, vertebrate paleontologist at Macalester College, Minnesota, in an email. “Just like dinosaurs, birds walk with their legs right under their bodies, and dinos gave the birds an extra little growth spurt.”

All birds are dinosaurs, but not all dinosaurs are birds.  Here a Tyrannosaurus skeleton is mounted next to a Triceratops skeleton in the Los Angeles Natural History Museum.

As Holly Woodward Ballard, associate professor of paleontology and anatomy at the University of Oklahoma, put it, “We know that birds are dinosaurs because they share more traits with extinct dinosaurs than other living animals.”

In fact, there are many other features to consider – things like “wishbones, bones hollowed out by air sacs, and wrists that can rotate,” says Brussatte.

In an email, University of Calgary paleontologist and evolutionary biologist Jessica Theodor described these and other dinosaur-specific traits. The structure that allows birds, for example, to bend their hands back on the wrist to fold their wings is also found in the arms of wingless Coelurosaurs, and biologists can see the modification of this structure “through the evolution of theropods,” she said.

Comparison between the majungasaurus and a duck's air sacs.

Comparison between the majungasaurus and a duck’s air sacs.
graphic: Zina Deretsky / NSF

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

“The synsacrum is the fusion of the vertebrae above the hips that stiffens the back and aids in flight, and the pygostyle is a fusion of the last caudal vertebrae that supports the tail feathers that are actually found in some non-avian dinosaurs like that Oviraptorosaur and Ornithomimosaur who may have feather fans instead of long tails or fans on the tips of their tails, ”she wrote in an email.

“Birds have small flanges on their ribs called uncinate processes that give mechanical advantage to the respiratory muscles of the chest,” and they are also found in Oviraptors and Dromaeosaursas Theodor explained. In addition, “bird skeletons have a number of other structural similarities to skeletal dinosaurs, all of which bring them together in phylogenetic analyzes,” she said.

Proofs for brooding In some dinosaurs, where animals rest over their nests to keep their eggs warm and protected, there is behavior observed in modern birds, as Rowe reminded me. Dinosaurs and birds also both used gizzard stones (stones that are swallowed to aid digestion) “because the stones would grind up food already ingested,” he said.

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

“The evidence that birds are really just tiny little dinosaurs that learned to fly comes from the fossil record of dinosaurs and the bodies and genomes of living birds,” said Curry Rogers. “When we look at modern birds, we can see little mementos of their more cruel history, ingrained in their genes – extinct development programs to build longer tails and teeth.”

And she added, “It’s all right – written on the bones and bodies of dinosaurs, alive and extinct!”

So the next time a hummingbird comes to your bird feeder, feel free to say hello to the little bird as a visiting dinosaur. You can also claim that you tried dinosaurs after eating some chicken wings, or that you were attacked by a dinosaur when a goose chased you from its nest. And when the Toronto Blue Jays take on the Baltimore Orioles, it’s good to call the matchup the battle of the dinosaurs.

It will sound strange, but you have the science to help you out.


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