On February 20, 1824, English naturalist and theologian William Buckland addressed the Geological Society of London and described a huge jaw and limb bones unearthed in a slate quarry in the village of Stonesfield, near Oxford.
Buckland recognized that these fossils belonged to a huge ancient reptile and gave it a formal scientific name: Megalosaurus, which means “great lizard.” With that, the first dinosaur was officially recognized, although the word actual dinosaur would not be coined until the 1840s. “It was the beginning of our fascination with dinosaurs,” said Steve Brusatte, a paleontologist at the University of Edinburgh. “Her announcement of him opened the floodgates and began an avalanche of fossils, and people went looking for other giant bones in England and beyond.”
In the intervening 200 years, dinosaur science has flourished, providing information about what these creatures were like, how they lived, how they evolved, and what doomed them. Dinosaurs walked the planet from about 231 million years ago to 66 million years ago during the Mesozoic Era. Their bird descendants remain with us today. “Our understanding of dinosaurs has changed significantly since the 19th century,” said paleontologist Emma Nicholls of the University of Oxford’s Natural History Museum, home of the Megalosaurus fossils that Buckland studied.
“Buckland and other gentlemen naturalists of the early 19th century would be surprised at how much we now know about dinosaurs,” Brusatte added. Megalosaurus is a good example. Buckland thought it was a lizard about 20 meters (66 feet) long, walked on four legs, and could live on land or in water. Scientists now know that it was neither a quadruped nor a lizard, but belonged to the group of theropods that includes carnivorous dinosaurs such as Tyrannosaurus and Spinosaurus and was about 30 feet (9 meters) long.
“It ran on its hind legs, chasing its prey, using its claws and toothy jaws to subdue its victims,” Brusatte said. Buckland, like others at the time, did not understand how long dinosaurs had lived, believing the Earth was only a few thousand years old. Scientists now know that the Earth is about 4.5 billion years old. Megalosaurus lived about 165 million years ago.
“It took several decades for geologists to understand that the Earth was truly ancient and that life had evolved over vast periods of time. The dinosaurs and the other fossils discovered were a big boost in this radical change in people’s understanding about their place in the world,” Brusatte said. ‘DINOSAURIA’
The English naturalist Richard Owen recognized that fossils found in southern England of Megalosaurus and two other large land reptiles, Iguanodon and Hylaeosaurus, formed a common group, calling them “Dinosauria” in an 1841 conference and a publication the following year. The subsequent discovery of fossils of Hadrosaurus and Dryptosaurus in the US state of New Jersey demonstrated that at least some dinosaurs were bipedal, changing the perception that they resembled reptilian rhinoceroses. Beginning in the 1870s, the first complete skeletons of large dinosaurs (first in the American West, then in Belgium and elsewhere) demonstrated the distinctive anatomy and diversity of dinosaurs.
In the 1960s, the identification of the small carnivorous dinosaur Deinonychus shook dinosaur science and helped usher in a period of research called the “Dinosaur Renaissance.” He showed that dinosaurs could be small and agile. Some were remarkably similar anatomically to early birds such as Archeopteryx, confirming how birds evolved from small feathered dinosaurs. It also sparked a debate about whether dinosaurs were warm-blooded like birds, contradicting the ancient view that they were slow, clumsy and cold-blooded. “In the following decades, there was increasing work on dinosaur growth, on the use of computed tomography, on analytical methods for reconstructing evolutionary relationships and biomechanical function, all of which helped create a vision more dynamic and biological of dinosaurs as living beings,” said University of Maryland paleontologist Thomas Holtz.
Paleontologists place cranial fossils in CT scanners to build digital models of dinosaur brains and ears, gaining a better understanding of dinosaur senses such as sight, hearing and smell. Researchers can now also determine the color of dinosaurs if their skin or feathers are well enough preserved to retain microscopic bubbles of pigment-containing melanosomes in the cells. There are currently more than 2,000 known species of dinosaurs and paleontology is a vibrant international science. Notable fossil finds are being made in places such as China, Argentina, Brazil, South Africa and Mongolia.
“In terms of discoveries about dinosaurs in recent decades, the most important in my opinion is the discovery that at least the carnivorous dinosaurs, the theropods, had feathers instead of scales and that some had very well-developed feathers on their backs. arms even though they were, for various reasons, unable to fly,” said paleontologist Hans-Dieter Sues of the Smithsonian Institution’s National Museum of Natural History in Washington. “Presumably these feathers, which were often colorful, provided insulation for the body and, at least in some species, were used for display,” Sues added.
THE KILLER ASTEROID The extinction of the dinosaurs had long baffled scientists, with several hypotheses proposed, from the plausible to the ridiculous. Some even proposed that shrew-sized mammals of the time ate dinosaur eggs.
In 1980, researchers identified a layer of sediment dating back to the end of the age of dinosaurs that contained high concentrations of iridium, an element common in meteorites, indicating that a huge space rock had hit Earth. The 180-kilometer-wide Chicxulub crater on Mexico’s Yucatan Peninsula was later identified as the site of the asteroid impact that wiped out three-quarters of Earth’s species, including dinosaurs. If that asteroid had not passed by Earth, would dinosaurs still rule, rather than the mammals (including eventually humans) who inherited a shattered world?
“It almost certainly is,” Holtz said. “Mammals emerged shortly after the first dinosaurs, but spent many tens of millions of years in their shadow. Mesozoic mammals were very successful and diverse, but only with smaller body sizes.” “Dinosaurs would have had to deal with the eventual drought and cooling of the world, and with it the reduction of forests and their replacement by grasslands,” Holtz added. “But these changes appear to have been gradual enough that dinosaurs would have had the opportunity to develop adaptations to the new conditions, just as large mammals did.”
Scientists have evaluated dinosaur metabolism using a formula based on body mass, as revealed by the mass of thigh bones, and growth rates, as shown by growth rings in fossil bones similar to those of the trees. The research suggested that dinosaurs were intermediate between today’s cold- and warm-blooded animals. Scientists have also refined their assessment of the size of several dinosaurs, including the group of sauropods that counted among them as the largest land animals in Earth’s history. A 2023 study based on limb bone dimensions crowned Argentinosaurus, which measured about 115 feet (35 meters) long, as heavyweight champion at approximately 76 metric tons.
Even after two centuries, the research is far from over. “Outside the realm of new technologies, there are still many wastelands in various corners of the world that are largely unexplored paleontologically,” Holtz said. “These regions will reveal new species from the age of dinosaurs. There are almost certainly entire groups of dinosaurs that we currently know nothing about waiting to be discovered.”
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