dinosaurs are birds -- 1/31/24
Today's selection -- from The Rise and Fall of the Dinosaurs by Steve Brusatte. The highly controversial idea that today’s birds are related to dinosaurs:
“The realization that birds are dinosaurs is probably the single most important fact ever discovered by dinosaur paleontologists. Although we've learned much about dinosaurs over the past few decades, this is not a radical new idea pushed by my generation of scientists. Quite the opposite: it's a theory that goes back a long way, to the era of Charles Darwin.
“The year was 1859. After two decades of sitting around and stewing over the observations he made as a young man sailing the world on the HMS Beagle, Darwin was finally ready to go public with his startling discovery: species are not fixed entities; they evolve over time. He even had a mechanism to explain evolution, a process he called natural selection. That November, he laid it all out in the Origin of Species.
“This is how it works. All populations of organisms are variable in their features. For instance, if you look at a bunch of rabbits in nature, they will have slightly different fur colors, even if they all belong to the same species. Sometimes one of those variations confers a survival advantage—say, darker fur that helps a rabbit camouflage itself better—and because of that, the individuals with that feature have a better chance of living longer and reproducing more. If that variation is heritable—if it can be passed on to offspring—then over time it will cascade throughout the population so that the entire rabbit species is now dark-haired. Dark hair has been naturally selected, and the rabbits have evolved.
“This process can even produce new species: if a population is somehow divided and each subset goes its own way, evolving its own naturally selected features until the two subsets are so different that they're unable to reproduce with each other, they have developed into separate species. This process has brought into being all of the world's species over the course of billions of years. It means that all living things—modern and extinct—are related, cousins on one grand family tree.
“Elegant in its simplicity, so far-reaching in its implications, today we regard Darwin's theory of evolution by natural selection as one of the fundamental rules underpinning the world as we know it. It's what produced the dinosaurs, what molded them into such a fantastic variety of species that were able to rule the planet for so long, adapting to drifting continents, shifting sea levels, changes in temperature, and the threats from competitors hoping to snatch their crown. Evolution by natural selection is also what produced us, and don't be mistaken, it continues to operate right now, constantly, all around us. It's why we're so worried about superbugs that evolve resistance to antibiotics, why we're always in need of new medicines to stay a step ahead of the bacteria and viruses that will do us harm.
|Various feathered non-avian dinosaurs, including Archaeopteryx, Anchiornis, Microraptor and Zhenyuanlong
“Some folks still dispute the reality of evolution today—and I won't say any more about that— but whatever disagreements we have now pale in comparison to what was happening in the 1860s. Darwin's book—written in beautiful, accessible prose for public consumption—sparked a fury. Some of society's most cherished notions about religion, spirituality, and humankind's place in the universe suddenly seemed up for debate. Evidence and accusations flew back and forth, and both sides were on the lookout for a trump card. For many of Darwin's supporters, the ultimate proof of his new theory would be ‘missing links,’ transitional fossils that capture, like a freeze frame, the evolution of one type of animal into another. These would not only demonstrate evolution in action, but could visually convey it to the public in a way that no book or lecture ever could.
“Darwin didn't have to wait long. In 1861, quarry workers in Bavaria found something peculiar. They were mining a type of fine limestone that breaks into thin sheets, which was used at the time for lithographic printing. One of the miners—now nameless to history—split open a slab and found a 150-million-year-old skeleton of a Frankenstein creature inside. It had sharp claws and a long tail like a reptile but feathers and wings like a bird. Other fossils of the same animal were soon found in other limestone quarries that sprinkled the Bavarian countryside, including a spectacular one that preserved nearly the entire skeleton. This one had a wishbone, like a bird, but its jaws were lined with sharp teeth, like a reptile. Whatever this creature was, it seemed to be half reptile, half bird.
“This Jurassic hybrid was named Archaeopteryx, and it became a sensation. Darwin included it in later editions of the Origin of Species as evidence that birds had a deep history which could be explained only by evolution. The strange fossil also caught the eye of one of Darwin's best friends and most vociferous supporters. Thomas Henry Huxley is perhaps best remembered as the man who came up with the term agnosticism to describe his uncertain religious views, but in the 1860s he was popularly known as Darwin's Bulldog. It was a nickname he gave himself, because he was unrelenting in his defense of Darwin's theory, taking on anyone—in person or in print—who maligned it. Huxley agreed that Archaeopteryx was a transitional fossil, linking reptiles and birds, but he went one step further. He noticed that it bore an uncanny resemblance to another fossil discovered in the same lithographic limestone beds in Bavaria, a small flesh-eating dinosaur called Compsognathus. So he proposed his own radical new idea: birds descended from dinosaurs.
“Debate continued for the next century. Some scientists followed Huxley; others didn't accept the link between dinosaurs and birds. Even as a deluge of new dinosaur fossils emerged from the American West—the Jurassic Morrison dinosaurs like Allosaurus and its many sauropod compatriots, the Cretaceous Hell Creek congregation of T. rex and Triceratops—there didn't seem to be enough evidence to settle the question. Then, in the 1920s, a book by a Danish artist made the simplistic argument that birds couldn't have come from dinosaurs because dinosaurs apparently didn't have collarbones (which birds fuse into wishbones), and although it may sound a little absurd, that viewpoint held sway until the 1960s (and today we realize that dinosaurs did indeed have collarbones, so the point is moot). As Beatlemania swept the globe, protesters marched for civil rights in the American South, and war raged in Vietnam, the consensus was that dinosaurs had nothing to do with birds. They were just very distant cousins that looked kind of similar.
“That all changed in 1969, that tumultuous year of Woodstock. Revolution was afoot, as societal norms and traditions were being challenged throughout the West. That spirit of rebellion also percolated into science, and paleontologists started to see dinosaurs differently. Not as the dim-witted, dull-colored, slow-moving wastes of space that defined a pointless era of prehistory, but as more active, dynamic, energetic animals that ruled their world through talent and ingenuity, creatures that were very similar in many ways to living animals—particularly birds. A new generation—led by an unassuming Yale professor named John Ostrom and his rambunctious student Robert Bakker— completely reimagined dinosaurs, even making the argument that dinosaurs lived together in herds, had keen senses, cared for their young, and may have been warm-blooded like us.
“The catalyst for this so-called Dinosaur Renaissance was a series of fossils unearthed a few years before, in the mid-1960s, by Ostrom and his team. They were out in far southern Montana, close to the border with Wyoming, prospecting in colorful rocks formed on a floodplain during the Early Cretaceous, some time between 125 and 100 million years ago. They found over a thousand bones of a dinosaur—a dinosaur that was astonishingly birdlike. It had long arms that looked almost like wings and the lithe build indicative of a fast-running dynamo of an animal. After a few years of studying the bones, Ostrom announced them in 1969 as a new species: Deinonychus, a raptor. It was a close cousin of Velociraptor, which was discovered in the 1920s in Mongolia and described by Henry Fairfield Osborn (the New York aristocrat who named T. rex), but in these pre-Jurassic Park times, it had yet to become a household name.
“Ostrom realized the enormous implications of his find. He used Deinonychus to resurrect Huxley's idea that birds evolved from dinosaurs, which he argued in a series of landmark scientific papers in the 1970s, a lawyer making his case by meticulous presentation of incontrovertible evidence. Meanwhile, his flamboyant former student Bakker went a different route. The cowboy-hatted, hippie-haired child of the Sixties became an evangelist. He preached the dinosaur-bird connection--and the new image of dinosaurs as warm-blooded, big-brained evolutionary success stories--to the public with a Scientific American cover story in 1975 and a wildly successful book in the 1980s, The Dinosaur Heresies. Their contrasting styles caused considerable friction between them, but together Ostrom and Bakker revolutionized how everyone viewed dinosaurs. By the end of the 1980s, most serious students of paleontology had come around to their way of thinking.”