How do we know that birds are dinosaurs?



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Illustration: Benjamin Currie

Cruel tyrannosaurs and tall sauropods are long gone, but dinosaurs are still having fun in our environment. We’re talking about birds, of course, but it’s not entirely obvious why we should consider them birds good faith dinos. Here are many reasons why.

Make no mistake, birds are legitimate dinosaurs, not some evolutionary offshoot. All non-avian dinosaurs were taken care of after a mass extinction caused by asteroids 66 million years ago, but some species of birds – probably birds living in the ground“They managed to survive, too.” he wasted no time in taking power after their relatives disappeared.

“Those little guys singing in front of your window are the dinosaurs we have left these days,” Adam Smith, curator at Campbell University’s Campbell Geological Museum, explained in an email. “Birds are just one species of dinosaur. To say “birds are descended from dinosaurs” is similar to saying that humans are descended from mammals. Simply put, all birds are dinosaurs, but not all dinosaurs are birds. “

This weasel doesn't mind being called a dinosaur.

This weasel doesn’t mind being called a dinosaur.
Picture: American Fish and Wildlife Service

That birds are somehow related to dinosaurs is hardly a recent discovery. In the late 19th century, English naturalist Thomas Henry Huxley dared to suggest that birds evolved from dinosaurs. As science writer Riley Black wrote In 2010, his ideas about the origins of birds “did not perfectly await our current knowledge,” but Huxley, a skilled anatomist, was clearly on to something.

In fact, scientists have since identified a multitude of traits that, like birds, settle comfortably like dinosaurs on a phylogenetic tree. Kate Lyons, an assistant professor at Lincoln University’s University of Nebraska School of Biological Sciences, says “there’s not just one smoking rifle” that allows paleontologists to say birds are dinosaurs because “multiple evidence” suggests that, as she wrote to me. in e-mail.

Paleontologist Steven Brussatte of the University of Edinburgh says we know that birds are dinosaurs by applying the same rationale that says bats are mammals.

Look at this dinosaur.  Specifically, a brown bomb.

Look at this dinosaur. Specifically, a brown bomb.
Picture: NOAA / NMFS / OPR

“Yes, birds are small, they have feathers, wings and flies, and that is different from the picture of dinosaurs we are used to,” he wrote in an e-mail. “Bats are an analogy of mammals – they are small, they have wings and they fly and they don’t look at all like a dog or an elephant or a primate, but they are still mammals.”

Indeed, bats have many features exclusive to mammals, such as hair, canines, three tiny ear bones, and the ability to feed young to milk. Likewise, birds have traits that are only seen in theropod dinosaurs, Brussatte explained.

Like feathers.

In fact, although there is no “smoking rifle” that would tie birds like dinosaurs, the presence of feathers is probably the most smoking thing of all. The fossil record is filled with examples of feathered non-bird dinosaurs, and since feathers are unique to birds, scientists are able to link them both like dinosaurs.

Skeptics may argue that the appearance of feathers in both birds and non-avian dinosaurs is a consequence convergent evolution, in which similar traits occur independently in unrelated species. Smith says convergent evolution in this case is unlikely because “many non-avian dinosaurs have been found to have preserved feathers of the exact species that were already assumed to be close relatives of birds,” including Velociraptors i Sinosauropteryx.

The artist's interpretation of Velociraptor mongoliensis.

The artist’s interpretation Velociraptor mongoliensis.
Illustration: Fred Wierum (Fair use)

To which he added: “Feathers are ridiculously complex structures, and although convergent evolution often results in similar structures – and even entire animals – that appear quite similar on the surface, there is no example of convergent evolution duplicating structures at that scale, with that kind of fidelity . “

Phylogenetics – the study of evolutionary relationships between species – provides further evidence that birds are dinosaurs, as Andre Rowe, a doctoral student at the School of Earth Sciences at the University of Bristol, explained in his email. With all due respect Jurassic Park, paleontologists are unable to isolate and analyze the DNA of ancient dinosaurs, but can examine key characteristics shared between species, as shown by their skeletons and anatomy. Based on these key characteristics, scientists “can say with almost certainty that the birds belong to the dinosaur theropod lineage,” Rowe said, referring to dinosaurs that eat meat like T. rex,, Allosaurus, i Compsognathus. Most importantly, the skeletons of theropods and birds show “no sudden changes in their evolutionary relationship, but a smooth transition over millions of years,” he added.

“Going back in time, we can trace the evolution of the basic plan of a bird’s body all the way back to some of the earliest dinosaurs,” wrote Christie Curry Rogers, a vertebrate paleontologist at Macalester College in Minnesota, in an email. “Just like dinosaurs, birds walk by keeping their feet directly under their bodies, and dinosaurs have given birds an extra little boost in growth rates.”

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

All birds are dinosaurs, but not all dinosaurs are birds. Here, the skeleton of a Tyrannosaurus is placed next to the skeleton of the Triceratops at the Natural History Museum in Los Angeles.
Picture: Matthew Dillon (Fair use)

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

In fact, many other characteristics need to be considered – things like “bone bones, bones hollowed out by air sacs and rotating wrists”, allowing dinosaurs to “fold their arms around their bodies”, according to Brussatte.

In an email, paleontologist and evolutionary biologist Jessica Theodor of the University of Calgary described these and other dino-specific characteristics. For example, a structure that allows birds to bend their arms backwards at the wrist, which they do to bend their wings, is also found in wingless arms. koelurosauri, and biologists can track the modification of this structure “through the evolution of theropods,” she explained.

Comparison of Majungasaurus and duck air sacs.

Comparison of Majungasaurus and duck air sacs.
Graphically: Zina Deretsky / NSF

Kat Schroeder, a doctoral student in the Department of Biology at the University of New Mexico, described the fusion of certain vertebrae into the synacrum and pigostyl as one of the most significant evolutionary adaptations in birds.

“Synsacrum is a fusion of the vertebrae over the hips, which stiffens the back and helps in flight, and the pigostil is a fusion of the last tail vertebrae that supports the tail feather, which is actually found in some non-avian dinosaurs like Oviraptorosauri i Ornithomimosaurs which may have had fans of feathers instead of long tails or fans on the tips of their tails, ”she wrote in an email.

“Birds have small flanges on the ribs, called non-galvanized processes, which provide a certain mechanical advantage to the breathing of the rib muscles,” and are also found in oviraptors i dromaeosaurs, as Theodor explained. Moreover, “bird skeletons have other structural similarities with dinosaurs in the skeleton, which puts them all in phylogenetic analyzes,” she said.

Evidence of Fr. tiring among some dinosaurs, in which animals rest over nests to keep their eggs warm and protected, behavior has been seen in modern birds, as Rowe reminded me. Also, dinosaurs and birds used stomach stones (stones that are swallowed to help digestion), “because the stones would break down food that had already been ingested,” he said.

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

“The evidence that birds are actually just tiny little dinosaurs that have learned to fly comes from dinosaur fossil records, as well as from the bodies and genomes of living birds,” Curry Rogers explained. “When we look at modern birds, we can see small memories of their cruel history locked deep in their genes – extinct development programs to build longer tails and teeth.”

To which she added: “Everything is fine there – written in the bones and bodies of dinosaurs, living and extinct!”

So the next time a hummingbird reaches your feeder, feel free to greet the tiny bird as a guest dinosaur. You can also claim to have tasted dinosaurs after eating chicken wings or that a dinosaur attacked you when a goose scared you away from its nest. And when the Toronto Blue Jays face the Baltimore Orioles, you’re totally good at calling the game a dinosaur battle.

It may sound strange, but you have a science that supports you.


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