Dinosaur

• 1. Introduction

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  Dinosaurs are a diverse group of warmblooded reptiles, and the largest of them stretched to lengths of 39.7 meters and heights of 18 meters. They were the largest land animals of all time. Yet for most of the 20th century, scientists pictured them as sluggish, cold-blooded creatures dragging their tails through the mud. That image was wrong, and the story of how it collapsed runs through marl pits in New Jersey, the deserts of Mongolia, and a femur that bled soft tissue 66 million years after the animal died. How did a reptile clade come to include over 11,000 species of living birds? Why did one paleontologist spend his entire fortune racing a rival to dig up bones? And how do we know a creature was warm-blooded from the texture of its thigh bone? The answers begin with a single word coined in 1842.

• 2. Terrible Lizard

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  Sir Richard Owen coined the term dinosaur in 1842, drawing on words that mean terrible lizard. He intended it to evoke not only their fearsome teeth and claws but also their size and majesty. Owen had given a presentation on fossil reptiles to the British Association for the Advancement of Science in 1841, but reports of the time show he did not use the word dinosaur there. He introduced Dinosauria only in the revised text of his talk, published in April 1842. Owen recognized that three finds, Iguanodon, Megalosaurus, and Hylaeosaurus, shared distinctive features. He decided to present them as a distinct taxonomic group. With the backing of Prince Albert, the husband of Queen Victoria, Owen later established the Natural History Museum in London to display the national collection of dinosaur fossils. The fossils themselves had been turning up far earlier than anyone understood. Chinese authors long recognized the remains of prehistoric animals as dragon bones, used as ingredients in Traditional Chinese Medicine. A gazetteer compiled by Chang Qu during the Western Jin Dynasty reported dragon bones at Wucheng in Sichuan Province. In Europe, such fossils were generally believed to be the remains of giants and other biblical creatures. Part of a Megalosaurus femur was recovered from a limestone quarry near Chipping Norton, Oxfordshire, in 1676. It was sent to Robert Plot, professor of chemistry at the University of Oxford, who correctly judged it too large for any known species. He concluded it must be the thigh bone of a huge human, perhaps a Titan from legend.

• 3. The Bone Wars

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  In 1858, William Parker Foulke discovered the first known American dinosaur in marl pits in the small town of Haddonfield, New Jersey. The creature was named Hadrosaurus foulkii, one of the first nearly complete dinosaur skeletons ever found. It was clearly bipedal, which overturned the belief that dinosaurs walked on four feet like other lizards. Foulke's discovery sparked a wave of enthusiasm in the United States known as Dinosaur Mania. That mania curdled into a fierce rivalry between Edward Drinker Cope and Othniel Charles Marsh, both racing to find new dinosaurs in what became known as the Bone Wars. Their fight lasted more than 30 years and ended in 1897, when Cope died after spending his entire fortune on the hunt. The two men's methods were crude. Their diggers often used dynamite to unearth bones, damaging or destroying many valuable specimens, since blasting easily wrecks fossil and stratigraphic evidence. Despite this, their contributions were vast. Marsh unearthed 86 new species and Cope discovered 56, a total of 142 new species. Cope's collection now sits at the American Museum of Natural History in New York City, while Marsh's resides at the Peabody Museum of Natural History at Yale University.

• 4. The Renaissance

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  John Ostrom discovered the bird-like dromaeosaurid theropod Deinonychus and described it in 1969. Its anatomy pointed to an active predator that was likely warm-blooded, a sharp break from the prevailing image of dinosaurs as slow and dim. World War II had paused paleontological research, and afterward attention drifted toward fossil mammals rather than dinosaurs. Robert T. Bakker pushed the new view forward with a series of studies arguing for active lifestyles, later summarized in his 1986 book The Dinosaur Heresies. In a 1968 paper, Bakker argued that sauropods, long depicted as sprawling aquatic animals with tails dragging on the ground, were endotherms living vigorous terrestrial lives. Major new discoveries fueled the surge. Paleontologists worked previously unexplored regions including India, South America, Madagascar, Antarctica, and most significantly China. The number of named genera climbed sharply in the 1990s, with up to 30 new species named each year by 2008. Between 2009 and 2020, an average of 9.3 new sauropodomorph species were named each year. More sauropodomorphs were named between 1990 and 2020 than in all previous years combined. The renaissance brought a new way of sorting these animals. Cladistics, a method of classification based on ancestry and shared traits, replaced the older rank-based Linnaean system. Reference books such as David B. Weishampel and colleagues' The Dinosauria, released in 1990 and 2004, made the research accessible and spurred further interest.

• 5. Two Hips

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  Dinosaurs split into two primary branches, Saurischia and Ornithischia, distinguished most noticeably by their pelvic structure. Early saurischians were lizard-hipped, from the Greek sauros for lizard and ischion for hip joint, retaining a pubis bone directed forward. Saurischia includes the theropods, exclusively bipedal with a wide variety of diets, and the sauropodomorphs, long-necked herbivores. Ornithischians were bird-hipped, from the Greek ornis for bird, with a pubic bone oriented to the rear that superficially resembled a bird's pelvis. They were primarily herbivores. The terms hide a twist: despite being called bird-hipped, Ornithischia does not contain birds. Birds belong to Saurischia, the lizard-hipped dinosaurs, having evolved from earlier dinosaurs with lizard hips. Under phylogenetic nomenclature, dinosaurs are usually defined as the group consisting of the most recent common ancestor of Triceratops and modern birds, plus all its descendants. This sweeps in ankylosaurians, the armored herbivorous quadrupeds, stegosaurians, the plated herbivores, ceratopsians with their neck frills, the thick-skulled pachycephalosaurians, and the duck-billed ornithopods. Research by Matthew G. Baron, David B. Norman, and Paul M. Barrett in 2017 proposed a radical revision. Their analysis placed Ornithischia closer to Theropoda than to Sauropodomorpha, and they resurrected the clade Ornithoscelida to hold Ornithischia and Theropoda together.

• 6. Giants And Featherweights

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  The tallest and heaviest dinosaur known from good skeletons is Giraffatitan brancai, whose remains were discovered in Tanzania between 1907 and 1912. The mount on display at the Museum fur Naturkunde in Berlin stands 12 meters tall and runs 21.8 to 22.5 meters long. The Museo Municipal Carmen Funes in Plaza Huincul, Argentina, holds an Argentinosaurus reconstruction that measures 39.7 meters long. Argentinosaurus itself may have weighed 80,000 to 100,000 kilograms. The tallest, Sauroposeidon, reached 18 meters and could have peered into a sixth-floor window. Some contenders are known only from fragments. Amphicoelias fragillimus, described from a now-lost partial vertebral neural arch in 1878, was extrapolated to a possible 58 meters and 122,400 kilograms. Recent research reclassified it as a stockier rebbachisaurid, renamed Maraapunisaurus, measuring as much as 40 meters and 120,000 kilograms. Bruhathkayosaurus, a controversial titanosaur confirmed after archived photos were uncovered, was estimated in 2023 to reach lengths of up to 44 meters, possibly rivaling the blue whale as one of the largest animals ever. Size ran to the other extreme as well. The smallest dinosaur known is the bee hummingbird, just 5 centimeters long with a mass of around 1.8 grams. The smallest known non-avialan dinosaur described from an adult specimen is Anchiornis huxleyi, weighing an estimated 110 grams with a skeletal length of 34 centimeters. The largest carnivore was Spinosaurus, reaching 12.6 to 18 meters, and the largest ornithischian was probably the hadrosaurid Shantungosaurus giganteus at 16.6 meters.

• 7. Eggs And Herds

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  All dinosaurs laid amniotic eggs, usually in a nest. Bob Makela and Jack Horner's 1978 discovery of a Maiasaura nesting ground in Montana showed that parental care continued long after birth among ornithopods. The name Maiasaura means good mother lizard. A specimen of the oviraptorid Citipati osmolskae, found in a chicken-like brooding position in 1993, suggested these animals used an insulating layer of feathers to keep eggs warm. Some species, such as Troodon, practiced iterative laying, producing a pair of eggs every one or two days and delaying brooding until all were laid so they hatched together. Females laying eggs grow a special calcium-rich tissue called medullary bone, used to make eggshells. Its discovery in a Tyrannosaurus skeleton let paleontologists establish the sex of a fossil dinosaur for the first time. Group behavior left its own traces. The 1878 discovery of 31 Iguanodon at Bernissart in Belgium, thought to have drowned together in a flooded sinkhole, offered early evidence of herding. A site in Inner Mongolia yielded over 20 Sinornithomimus aged one to seven years, interpreted as a social group trapped in mud. Some of the most vivid fossils capture single dramatic moments. One found in the Gobi Desert in 1971 preserved a Velociraptor attacking a Protoceratops. Cannibalism among the theropod Majungasaurus was confirmed by tooth marks found in Madagascar in 2003.

• 8. Soft Tissue And The Bird Connection

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  In 2005, Mary Higby Schweitzer and colleagues reported that a femur of Tyrannosaurus preserved soft, flexible tissue, including blood vessels and bone matrix that retained their microscopic structure. In 2009 the team reported similar microstructures in a Brachylophosaurus femur, where immunohistochemical techniques demonstrated proteins such as collagen, elastin, and laminin. Both specimens yielded collagen sequences viable for molecular phylogenetic analysis, which grouped them with birds, exactly as expected. The bird connection had been proposed long before. Thomas Henry Huxley first suggested in 1868 that dinosaurs were the ancestors of birds. The idea was later abandoned after Gerhard Heilmann's work, which leaned on the supposed lack of clavicles in dinosaurs. That evidence proved false; clavicles had been found as early as 1924 in Oviraptor but misidentified as an interclavicle. Birds share over a hundred distinct anatomical features with other theropod dinosaurs and are most closely allied with maniraptoran coelurosaurs. Archaeopteryx was the first fossil to reveal a potential connection, a transitional form displaying features of both groups. It came to light just two years after Charles Darwin's On the Origin of Species, published in 1859. One specimen was so dinosaur-like that, lacking a clear feather impression, it was mistaken for the small theropod Compsognathus. Feathers themselves appear to have been an ancestral dinosaurian trait. Simple branched structures are known from heterodontosaurids, primitive neornithischians, theropods, and primitive ceratopsians, while true vaned feathers turn up only in the theropod subgroup Maniraptora. The richest evidence comes from the lagerstatten of the Jehol Biota, where Xing Xu and colleagues described hundreds of specimens bearing feather-like impressions. Among modern birds, more than 10,800 species carry that lineage forward, the only branch of dinosaurs to survive the Cretaceous-Paleogene extinction event.