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124-732: Dinosaur faunas of the Judithian age may represent the peak of dinosaur evolution in North America. Hadrosaurs were universally the dominant herbivore of the period and comprised more than half of "a typical assemblage." This was also the period of greatest genetic diversity among large herbivorous dinosaurs. Just in Montana and Southern Alberta were ten genera of ceratopsians and ten genera of hadrosaurs. Thomas M. Lehman has observed that Corythosaurus and Centrosaurus haven't been discovered outside of southern Alberta even though they are

248-555: A clade ( monophyletic group) including birds, though the precise definition of this clade varies between authors. Others prioritize the clade Sauropsida , which typically refers to all amniotes more closely related to modern reptiles than to mammals . The earliest known proto-reptiles originated from the Carboniferous period, having evolved from advanced reptiliomorph tetrapods which became increasingly adapted to life on dry land. The earliest known eureptile ("true reptile")

372-607: A gazetteer compiled by Chang Qu  ( 常璩 ) during the Western Jin Dynasty (265–316), reported the discovery of dragon bones at Wucheng in Sichuan Province. Villagers in central China have long unearthed fossilized "dragon bones" for use in traditional medicines . In Europe , dinosaur fossils were generally believed to be the remains of giants and other biblical creatures. Scholarly descriptions of what would now be recognized as dinosaur bones first appeared in

496-510: A sacrum composed of three or more fused vertebrae (three are found in some other archosaurs, but only two are found in Herrerasaurus ); and a perforate acetabulum , or hip socket, with a hole at the center of its inside surface (closed in Saturnalia tupiniquim , for example). Another difficulty of determining distinctly dinosaurian features is that early dinosaurs and other archosaurs from

620-447: A temnospondyl ). A series of footprints from the fossil strata of Nova Scotia dated to 315  Ma show typical reptilian toes and imprints of scales. These tracks are attributed to Hylonomus , the oldest unquestionable reptile known. It was a small, lizard-like animal, about 20 to 30 centimetres (7.9 to 11.8 in) long, with numerous sharp teeth indicating an insectivorous diet. Other examples include Westlothiana (for

744-421: A "pillar-erect" configuration of the hip joint, where instead of having a projection from the femur insert on a socket on the hip, the upper pelvic bone was rotated to form an overhanging shelf. Dinosaur fossils have been known for millennia, although their true nature was not recognized. The Chinese considered them to be dragon bones and documented them as such. For example, Huayang Guo Zhi  ( 華陽國志 ),

868-488: A controversial taxon that was recently confirmed to exist after archived photos were uncovered. Bruhathkayosaurus was a titanosaur and would have most likely weighed more than even Marrapunisaurus . Recent size estimates in 2023 have placed this sauropod reaching lengths of up to 44 m (144 ft) long and a colossal weight range of around 110 000 – 170 000  kg ( 240 000 – 370 000  lb), if these upper estimates up true, Bruhathkayosaurus would have rivaled

992-448: A corresponding inwardly facing distinct head on the femur. Their erect posture enabled early dinosaurs to breathe easily while moving, which likely permitted stamina and activity levels that surpassed those of "sprawling" reptiles . Erect limbs probably also helped support the evolution of large size by reducing bending stresses on limbs. Some non-dinosaurian archosaurs, including rauisuchians , also had erect limbs but achieved this by

1116-632: A dinosaur. In it he described and named a sauropod tooth , " Rutellum impicatum ", that had been found in Caswell, near Witney , Oxfordshire. Between 1815 and 1824, the Rev William Buckland , the first Reader of Geology at the University of Oxford, collected more fossilized bones of Megalosaurus and became the first person to describe a non-avian dinosaur in a scientific journal . The second non-avian dinosaur genus to be identified, Iguanodon ,

1240-537: A femur of Tyrannosaurus preserved soft, flexible tissue within, including blood vessels , bone matrix , and connective tissue (bone fibers) that had retained their microscopic structure. This discovery suggested that original soft tissues could be preserved over geological time, with multiple mechanisms having been proposed. Later, in 2009, Schweitzer and colleagues reported that a Brachylophosaurus femur preserved similar microstructures, and immunohistochemical techniques (based on antibody binding) demonstrated

1364-422: A group known as archosaurs, which also includes modern crocodilians. Within the archosaur group, dinosaurs are differentiated most noticeably by their gait. Dinosaur legs extend directly beneath the body, whereas the legs of lizards and crocodilians sprawl out to either side. Collectively, dinosaurs as a clade are divided into two primary branches, Saurischia and Ornithischia. Saurischia includes those taxa sharing

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1488-482: A more recent common ancestor with birds than with Ornithischia, while Ornithischia includes all taxa sharing a more recent common ancestor with Triceratops than with Saurischia. Anatomically, these two groups can be distinguished most noticeably by their pelvic structure. Early saurischians—"lizard-hipped", from the Greek sauros ( σαῦρος ) meaning "lizard" and ischion ( ἰσχίον ) meaning "hip joint"—retained

1612-583: A now lost partial vertebral neural arch described in 1878. Extrapolating from the illustration of this bone, the animal may have been 58 meters (190 ft) long and weighed 122 400  kg ( 269 800  lb). However, recent research have placed Amphicoelias from the long, gracile diplodocid to the shorter but much stockier rebbachisaurid. Now renamed as Maraapunisaurus , this sauropod now stands as much as 40 meters (130 ft) long and weigh as much as 120 000  kg ( 260 000  lb). Another contender of this title includes Bruhathkayosaurus ,

1736-433: A period of time, with estimates ranging from 5–10 million years to 21 million years. When dinosaurs appeared, they were not the dominant terrestrial animals. The terrestrial habitats were occupied by various types of archosauromorphs and therapsids , like cynodonts and rhynchosaurs . Their main competitors were the pseudosuchians , such as aetosaurs , ornithosuchids and rauisuchians, which were more successful than

1860-652: A potential food source, radiated in the Late Triassic. Early sauropodomorphs did not have sophisticated mechanisms for processing food in the mouth, and so must have employed other means of breaking down food farther along the digestive tract. The general homogeneity of dinosaurian faunas continued into the Middle and Late Jurassic, where most localities had predators consisting of ceratosaurians , megalosauroids , and allosauroids , and herbivores consisting of stegosaurian ornithischians and large sauropods. Examples of this include

1984-656: A presentation about fossil reptiles to the British Association for the Advancement of Science in 1841, but reports of the time show that Owen did not mention the word "dinosaur", nor recognize dinosaurs as a distinct group of reptiles in his address. He introduced the Dinosauria only in the revised text version of his talk published in April 1842. With the backing of Prince Albert , the husband of Queen Victoria , Owen established

2108-599: A review paper by Paul Sereno in 1998, were accompanied by increases in the number of published phylogenetic trees for dinosaurs. Dinosaur fossils are not limited to bones, but also include imprints or mineralized remains of skin coverings, organs, and other tissues. Of these, skin coverings based on keratin proteins are most easily preserved because of their cross-linked , hydrophobic molecular structure. Fossils of keratin-based skin coverings or bony skin coverings are known from most major groups of dinosaurs. Dinosaur fossils with scaly skin impressions have been found since

2232-490: A section of the clade Amniota : The section that is left after the Mammalia and Aves have been hived off. It cannot be defined by synapomorphies , as is the proper way. Instead, it is defined by a combination of the features it has and the features it lacks: reptiles are the amniotes that lack fur or feathers. At best, the cladists suggest, we could say that the traditional Reptilia are 'non-avian, non-mammalian amniotes'. Despite

2356-549: A series of studies that likewise argued for active lifestyles in dinosaurs based on anatomical and ecological evidence (see § Physiology ), which were subsequently summarized in his 1986 book The Dinosaur Heresies . New revelations were supported by an increase in dinosaur discoveries. Major new dinosaur discoveries have been made by paleontologists working in previously unexplored regions, including India, South America, Madagascar, Antarctica, and most significantly China. Across theropods, sauropodomorphs, and ornithischians,

2480-603: A sister group to Dinosauria, including a large anterior trochanter, metatarsals II and IV of subequal length, reduced contact between ischium and pubis, the presence of a cnemial crest on the tibia and of an ascending process on the astragalus, and many others. A variety of other skeletal features are shared by dinosaurs. However, because they either are common to other groups of archosaurs or were not present in all early dinosaurs, these features are not considered to be synapomorphies. For example, as diapsids , dinosaurs ancestrally had two pairs of Infratemporal fenestrae (openings in

2604-565: A tiny gecko, Sphaerodactylus ariasae , which can grow up to 17 mm (0.7 in) to the saltwater crocodile , Crocodylus porosus , which can reach over 6 m (19.7 ft) in length and weigh over 1,000 kg (2,200 lb). In the 13th century, the category of reptile was recognized in Europe as consisting of a miscellany of egg-laying creatures, including "snakes, various fantastic monsters, lizards, assorted amphibians, and worms", as recorded by Beauvais in his Mirror of Nature . In

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2728-490: A universally agreed-upon list of their distinguishing features, nearly all dinosaurs discovered so far share certain modifications to the ancestral archosaurian skeleton, or are clearly descendants of older dinosaurs showing these modifications. Although some later groups of dinosaurs featured further modified versions of these traits, they are considered typical for Dinosauria; the earliest dinosaurs had them and passed them on to their descendants. Such modifications, originating in

2852-463: A variety of waterbirds , diversified rapidly at the beginning of the Paleogene period, entering ecological niches left vacant by the extinction of Mesozoic dinosaur groups such as the arboreal enantiornithines , aquatic hesperornithines , and even the larger terrestrial theropods (in the form of Gastornis , eogruiids , bathornithids , ratites, geranoidids , mihirungs , and " terror birds "). It

2976-784: Is Pentaceratops , the only known Judithian ceratopsian from New Mexico . Only the rarer species among modern mammal communities would be able to distinguish different latitudinal zones, and some of these taxa are likely too rare to fossilize. This lack of provinciality exists despite the strong temperature gradient. Restrictions in herbivorous dinosaur distribution may be due to foliage preferences, narrow tolerance for variation in climate or other environmental factors. The restrictions on herbivorous dinosaur distribution must have been due to ecological factors rather than physical barriers because carnivorous dinosaurs tended to have wider distributions, especially smaller forms. As of his 2001 paper, restrictions in dinosaur occurrences based on distance from

3100-430: Is 39.7 meters (130 ft) long. There were larger dinosaurs, but knowledge of them is based entirely on a small number of fragmentary fossils. Most of the largest herbivorous specimens on record were discovered in the 1970s or later, and include the massive Argentinosaurus , which may have weighed 80 000 to 100 000 kilograms (88 to 110 short tons) and reached lengths of 30 to 40 meters (98 to 131 ft); some of

3224-699: Is a synapsid ). None of them had the erect hind limb posture characteristic of true dinosaurs. Dinosaurs were the dominant terrestrial vertebrates of the Mesozoic Era , especially the Jurassic and Cretaceous periods. Other groups of animals were restricted in size and niches; mammals , for example, rarely exceeded the size of a domestic cat and were generally rodent-sized carnivores of small prey. Dinosaurs have always been recognized as an extremely varied group: over 900 non-avian dinosaur genera have been confidently identified (2018) with 1124 species (2016). Estimates put

3348-465: Is an inexact art, and reconstructing the muscles and other organs of the living animal is, at best, a process of educated guesswork. The tallest and heaviest dinosaur known from good skeletons is Giraffatitan brancai (previously classified as a species of Brachiosaurus ). Its remains were discovered in Tanzania between 1907 and 1912. Bones from several similar-sized individuals were incorporated into

3472-755: Is based in part on preservation bias , as large, sturdy bones are more likely to last until they are fossilized. Many dinosaurs were quite small, some measuring about 50 centimeters (20 inches) in length. The first dinosaur fossils were recognized in the early 19th century, with the name "dinosaur" (meaning "terrible lizard") being coined by Sir Richard Owen in 1842 to refer to these "great fossil lizards". Since then, mounted fossil dinosaur skeletons have been major attractions at museums worldwide, and dinosaurs have become an enduring part of popular culture . The large sizes of some dinosaurs, as well as their seemingly monstrous and fantastic nature, have ensured their regular appearance in best-selling books and films, such as

3596-459: Is between 1 and 10 metric tons (1.1 and 11.0 short tons). This contrasts sharply with the average size of Cenozoic mammals, estimated by the National Museum of Natural History as about 2 to 5 kg (4.4 to 11.0 lb). The sauropods were the largest and heaviest dinosaurs. For much of the dinosaur era, the smallest sauropods were larger than anything else in their habitat, and the largest

3720-617: Is derived from a variety of fossil and non-fossil records, including fossilized bones, feces , trackways , gastroliths , feathers , impressions of skin, internal organs and other soft tissues . Many fields of study contribute to our understanding of dinosaurs, including physics (especially biomechanics ), chemistry , biology , and the Earth sciences (of which paleontology is a sub-discipline). Two topics of particular interest and study have been dinosaur size and behavior. Current evidence suggests that dinosaur average size varied through

3844-479: Is equivalent to the more common definition of Sauropsida, which Modesto and Anderson synonymized with Reptilia, since the latter is better known and more frequently used. Unlike most previous definitions of Reptilia, however, Modesto and Anderson's definition includes birds, as they are within the clade that includes both lizards and crocodiles. General classification of extinct and living reptiles, focusing on major groups. The cladogram presented here illustrates

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3968-570: Is now at the American Museum of Natural History in New York City, while Marsh's is at the Peabody Museum of Natural History at Yale University . World War II caused a pause in palaeontological research; after the war, research attention was also diverted increasingly to fossil mammals rather than dinosaurs, which were seen as sluggish and cold-blooded. At the end of the 1960s, however,

4092-644: Is often stated that mammals out-competed the neornithines for dominance of most terrestrial niches but many of these groups co-existed with rich mammalian faunas for most of the Cenozoic Era. Terror birds and bathornithids occupied carnivorous guilds alongside predatory mammals, and ratites are still fairly successful as midsized herbivores; eogruiids similarly lasted from the Eocene to Pliocene , becoming extinct only very recently after over 20 million years of co-existence with many mammal groups. Dinosaurs belong to

4216-554: The Aquillapollenites and Normapolles palynofloral provinces. An association between Centrosaurus and Corythosaurus is characteristic of southern Alberta. Earlier research had found that lambeosaurines are less common in contemporary Montanan strata and with different centrosaurs as Monoclonius takes the place of Centrosaurus . Inland environments also differed, with the contemporary Two Medicine Formation preserving an inland fauna characterized by Maiasaura and

4340-528: The Jurassic Park franchise. Persistent public enthusiasm for the animals has resulted in significant funding for dinosaur science, and new discoveries are regularly covered by the media. Under phylogenetic nomenclature , dinosaurs are usually defined as the group consisting of the most recent common ancestor (MRCA) of Triceratops and modern birds (Neornithes), and all its descendants. It has also been suggested that Dinosauria be defined with respect to

4464-437: The blue whale and Perucetus colossus as one of the largest animals to have ever existed. The largest carnivorous dinosaur was Spinosaurus , reaching a length of 12.6 to 18 meters (41 to 59 ft) and weighing 7 to 20.9 metric tons (7.7 to 23.0 short tons). Other large carnivorous theropods included Giganotosaurus , Carcharodontosaurus , and Tyrannosaurus . Therizinosaurus and Deinocheirus were among

4588-666: The Anisian epoch of the Triassic, approximately 243 million years ago, which is the age of Nyasasaurus from the Manda Formation of Tanzania. However, its known fossils are too fragmentary to identify it as a dinosaur or only a close relative. The referral of the Manda Formation to the Anisian is also uncertain. Regardless, dinosaurs existed alongside non-dinosaurian ornithodirans for

4712-457: The Carnian pluvial event . Dinosaur evolution after the Triassic followed changes in vegetation and the location of continents. In the Late Triassic and Early Jurassic, the continents were connected as the single landmass Pangaea , and there was a worldwide dinosaur fauna mostly composed of coelophysoid carnivores and early sauropodomorph herbivores. Gymnosperm plants (particularly conifers ),

4836-613: The Ischigualasto and Santa Maria Formations of Argentina and Brazil, and the Pebbly Arkose Formation of Zimbabwe. The Ischigualasto Formation ( radiometrically dated at 231–230 million years old ) has produced the early saurischian Eoraptor , originally considered a member of the Herrerasauridae but now considered to be an early sauropodomorph, along with the herrerasaurids Herrerasaurus and Sanjuansaurus , and

4960-555: The Late Jurassic epoch , and are the only dinosaur lineage known to have survived the Cretaceous–Paleogene extinction event approximately 66 mya. Dinosaurs can therefore be divided into avian dinosaurs —birds—and the extinct non-avian dinosaurs , which are all dinosaurs other than birds. Dinosaurs are varied from taxonomic , morphological and ecological standpoints. Birds, at over 11,000 living species , are among

5084-484: The Late Triassic epoch are often poorly known and were similar in many ways; these animals have sometimes been misidentified in the literature. Dinosaurs stand with their hind limbs erect in a manner similar to most modern mammals , but distinct from most other reptiles, whose limbs sprawl out to either side. This posture is due to the development of a laterally facing recess in the pelvis (usually an open socket) and

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5208-645: The Morrison Formation of North America and Tendaguru Beds of Tanzania. Dinosaurs in China show some differences, with specialized metriacanthosaurid theropods and unusual, long-necked sauropods like Mamenchisaurus . Ankylosaurians and ornithopods were also becoming more common, but primitive sauropodomorphs had become extinct. Conifers and pteridophytes were the most common plants. Sauropods, like earlier sauropodomorphs, were not oral processors, but ornithischians were evolving various means of dealing with food in

5332-487: The Natural History Museum, London , to display the national collection of dinosaur fossils and other biological and geological exhibits. In 1858, William Parker Foulke discovered the first known American dinosaur, in marl pits in the small town of Haddonfield, New Jersey . (Although fossils had been found before, their nature had not been correctly discerned.) The creature was named Hadrosaurus foulkii . It

5456-611: The Pietraroja Plattenkalk of Italy. It preserves portions of the intestines, colon, liver, muscles, and windpipe. Concurrently, a line of work led by Mary Higby Schweitzer , Jack Horner , and colleagues reported various occurrences of preserved soft tissues and proteins within dinosaur bone fossils. Various mineralized structures that likely represented red blood cells and collagen fibres had been found by Schweitzer and others in tyrannosaurid bones as early as 1991. However, in 2005, Schweitzer and colleagues reported that

5580-853: The Reptile Database . The study of the traditional reptile orders, customarily in combination with the study of modern amphibians , is called herpetology . Reptiles have been subject to several conflicting taxonomic definitions. In Linnaean taxonomy , reptiles are gathered together under the class Reptilia ( / r ɛ p ˈ t ɪ l i ə / rep- TIL -ee-ə ), which corresponds to common usage. Modern cladistic taxonomy regards that group as paraphyletic , since genetic and paleontological evidence has determined that birds (class Aves), as members of Dinosauria , are more closely related to living crocodilians than to other reptiles, and are thus nested among reptiles from an evolutionary perspective. Many cladistic systems therefore redefine Reptilia as

5704-676: The United States and displayed in Pittsburgh 's Carnegie Museum of Natural History in 1907. The longest dinosaur known from good fossil material is Patagotitan : the skeleton mount in the American Museum of Natural History in New York is 37 meters (121 ft) long. The Museo Municipal Carmen Funes in Plaza Huincul , Argentina, has an Argentinosaurus reconstructed skeleton mount that

5828-418: The amniotic egg . The terms Sauropsida ("lizard faces") and Theropsida ("beast faces") were used again in 1916 by E.S. Goodrich to distinguish between lizards, birds, and their relatives on the one hand (Sauropsida) and mammals and their extinct relatives (Theropsida) on the other. Goodrich supported this division by the nature of the hearts and blood vessels in each group, and other features, such as

5952-427: The largest and smallest dinosaurs to have ever existed. This is because only a tiny percentage of animals were ever fossilized and most of these remain buried in the earth. Few non-avian dinosaur specimens that are recovered are complete skeletons, and impressions of skin and other soft tissues are rare. Rebuilding a complete skeleton by comparing the size and morphology of bones to those of similar, better-known species

6076-459: The paleo-shoreline had already been well documented. Vaguely distinguished inland-versus-coastal dinosaurs had been discussed previously in the scientific literature . Terrestrial sedimentary strata from the Judithian to the Lancian are generally regressive throughout the entire sequence the preserved changes in fossil communities represent not only phylogenetic changes but ecological zones from

6200-474: The submontane habitats to near-sea level coastal habitats. Modern life at high elevations in lower latitudes resembles life at low elevation in higher latitudes. There may be parallels to this phenomenon in Cretaceous ecosystems , for instance, Pachyrhinosaurus is found in both Alaska and upland environments in southern Alberta. Northern and Southern animal biomes approximately correspond respectively with

6324-1733: The "family tree" of reptiles, and follows a simplified version of the relationships found by M.S. Lee, in 2013. All genetic studies have supported the hypothesis that turtles are diapsids; some have placed turtles within Archosauromorpha, though a few have recovered turtles as Lepidosauromorpha instead. The cladogram below used a combination of genetic (molecular) and fossil (morphological) data to obtain its results. Synapsida ( mammals and their extinct relatives) [REDACTED] † Millerettidae [REDACTED] † Eunotosaurus † Lanthanosuchidae [REDACTED] † Pareiasauromorpha [REDACTED] † Procolophonoidea [REDACTED] † Captorhinidae [REDACTED] † Paleothyris † Araeoscelidia [REDACTED] † Claudiosaurus [REDACTED] † Younginiformes [REDACTED] † Kuehneosauridae [REDACTED] Rhynchocephalia ( tuatara and their extinct relatives) [REDACTED] Squamata ( lizards and snakes ) [REDACTED] [REDACTED] † Eosauropterygia [REDACTED] † Placodontia [REDACTED] † Sinosaurosphargis † Odontochelys † Proganochelys Testudines ( turtles ) [REDACTED] † Choristodera [REDACTED] † Prolacertiformes [REDACTED] † Rhynchosauria [REDACTED] † Trilophosaurus [REDACTED] Archosauriformes ( crocodiles , birds , dinosaurs and extinct relatives) [REDACTED] [REDACTED] The placement of turtles has historically been highly variable. Classically, turtles were considered to be related to

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6448-530: The "lizard-hipped" dinosaurs—birds evolved from earlier dinosaurs with "lizard hips". The following is a simplified classification of dinosaur groups based on their evolutionary relationships, and those of the main dinosaur groups Theropoda, Sauropodomorpha and Ornithischia, compiled by Justin Tweet. Further details and other hypotheses of classification may be found on individual articles. Timeline of major dinosaur groups per Holtz (2007) . Knowledge about dinosaurs

6572-453: The 18th century, the reptiles were, from the outset of classification, grouped with the amphibians . Linnaeus , working from species-poor Sweden , where the common adder and grass snake are often found hunting in water, included all reptiles and amphibians in class "III – Amphibia" in his Systema Naturæ . The terms reptile and amphibian were largely interchangeable, reptile (from Latin repere , 'to creep') being preferred by

6696-677: The 1970s , however, has indicated that dinosaurs were active animals with elevated metabolisms and numerous adaptations for social interaction. Some were herbivorous , others carnivorous . Evidence suggests that all dinosaurs were egg-laying , and that nest -building was a trait shared by many dinosaurs, both avian and non-avian. While dinosaurs were ancestrally bipedal , many extinct groups included quadrupedal species, and some were able to shift between these stances. Elaborate display structures such as horns or crests are common to all dinosaur groups, and some extinct groups developed skeletal modifications such as bony armor and spines . While

6820-409: The 19th century. Samuel Beckles discovered a sauropod forelimb with preserved skin in 1852 that was incorrectly attributed to a crocodile; it was correctly attributed by Marsh in 1888 and subject to further study by Reginald Hooley in 1917. Among ornithischians, in 1884 Jacob Wortman found skin impressions on the first known specimen of Edmontosaurus annectens , which were largely destroyed during

6944-584: The Eastern US may have resembled those of Texas except completely lacking in ceratopsians. Parasaurolophus and Kritosaurus are also present in northern latitudes, so evidently exchange between them occurred, but both are uncommon outside of the southern biome. Dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria . They first appeared during the Triassic period , between 243 and 233.23  million years ago (mya), although

7068-501: The English paleontologist Sir Richard Owen coined the term "dinosaur", using it to refer to the "distinct tribe or sub-order of Saurian Reptiles" that were then being recognized in England and around the world. The term is derived from Ancient Greek δεινός (deinos)  'terrible, potent or fearfully great' and σαῦρος (sauros)  'lizard or reptile'. Though

7192-480: The French. J.N. Laurenti was the first to formally use the term Reptilia for an expanded selection of reptiles and amphibians basically similar to that of Linnaeus. Today, the two groups are still commonly treated under the single heading herpetology . It was not until the beginning of the 19th century that it became clear that reptiles and amphibians are, in fact, quite different animals, and P.A. Latreille erected

7316-577: The Greek ornitheios (ὀρνίθειος) meaning "of a bird" and ischion (ἰσχίον) meaning "hip joint"—had a pelvis that superficially resembled a bird's pelvis: the pubic bone was oriented caudally (rear-pointing). Unlike birds, the ornithischian pubis also usually had an additional forward-pointing process. Ornithischia includes a variety of species that were primarily herbivores. Despite the terms "bird hip" (Ornithischia) and "lizard hip" (Saurischia), birds are not part of Ornithischia. Birds instead belong to Saurischia,

7440-501: The Late Cretaceous, was the evolution of flowering plants . At the same time, several groups of dinosaurian herbivores evolved more sophisticated ways to orally process food. Ceratopsians developed a method of slicing with teeth stacked on each other in batteries, and iguanodontians refined a method of grinding with dental batteries , taken to its extreme in hadrosaurids. Some sauropods also evolved tooth batteries, best exemplified by

7564-781: The MRCA of Megalosaurus and Iguanodon , because these were two of the three genera cited by Richard Owen when he recognized the Dinosauria. Both definitions cover the same known genera: Dinosauria = Ornithischia + Saurischia . This includes major groups such as ankylosaurians (armored herbivorous quadrupeds), stegosaurians (plated herbivorous quadrupeds), ceratopsians (bipedal or quadrupedal herbivores with neck frills ), pachycephalosaurians (bipedal herbivores with thick skulls), ornithopods (bipedal or quadrupedal herbivores including " duck-bills "), theropods (mostly bipedal carnivores and birds), and sauropodomorphs (mostly large herbivorous quadrupeds with long necks and tails). Birds are

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7688-401: The Middle to Late Triassic epochs, roughly 20 million years after the devastating Permian–Triassic extinction event wiped out an estimated 96% of all marine species and 70% of terrestrial vertebrate species approximately 252 million years ago. The oldest dinosaur fossils known from substantial remains date to the Carnian epoch of the Triassic period and have been found primarily in

7812-519: The Triassic, Early Jurassic, Late Jurassic and Cretaceous. Predatory theropod dinosaurs, which occupied most terrestrial carnivore niches during the Mesozoic, most often fall into the 100-to-1,000 kg (220-to-2,200 lb) category when sorted by estimated weight into categories based on order of magnitude , whereas recent predatory carnivoran mammals peak in the 10-to-100 kg (22-to-220 lb) category. The mode of Mesozoic dinosaur body masses

7936-583: The United States, known as dinosaur mania. Dinosaur mania was exemplified by the fierce rivalry between Edward Drinker Cope and Othniel Charles Marsh , both of whom raced to be the first to find new dinosaurs in what came to be known as the Bone Wars . This fight between the two scientists lasted for over 30 years, ending in 1897 when Cope died after spending his entire fortune on the dinosaur hunt. Many valuable dinosaur specimens were damaged or destroyed due to

8060-657: The anapsid condition has been found to occur so variably among unrelated groups that it is not now considered a useful distinction. By the early 21st century, vertebrate paleontologists were beginning to adopt phylogenetic taxonomy, in which all groups are defined in such a way as to be monophyletic ; that is, groups which include all descendants of a particular ancestor. The reptiles as historically defined are paraphyletic , since they exclude both birds and mammals. These respectively evolved from dinosaurs and from early therapsids, both of which were traditionally called "reptiles". Birds are more closely related to crocodilians than

8184-666: The best-known genera are remarkable for their large size, many Mesozoic dinosaurs were human-sized or smaller, and modern birds are generally small in size. Dinosaurs today inhabit every continent, and fossils show that they had achieved global distribution by the Early Jurassic epoch at latest. Modern birds inhabit most available habitats, from terrestrial to marine, and there is evidence that some non-avian dinosaurs (such as Microraptor ) could fly or at least glide, and others, such as spinosaurids , had semiaquatic habits. While recent discoveries have made it more difficult to present

8308-455: The body . Other prehistoric animals, including pterosaurs , mosasaurs , ichthyosaurs , plesiosaurs , and Dimetrodon , while often popularly conceived of as dinosaurs, are not taxonomically classified as dinosaurs. Pterosaurs are distantly related to dinosaurs, being members of the clade Ornithodira . The other groups mentioned are, like dinosaurs and pterosaurs, members of Sauropsida (the reptile and bird clade), except Dimetrodon (which

8432-429: The bone as the lower extremity of the femur of a large animal, and recognized that it was too large to belong to any known species. He therefore concluded it to be the femur of a huge human, perhaps a Titan or another type of giant featured in legends. Edward Lhuyd , a friend of Sir Isaac Newton , published Lithophylacii Britannici ichnographia (1699), the first scientific treatment of what would now be recognized as

8556-421: The class Batracia (1825) for the latter, dividing the tetrapods into the four familiar classes of reptiles, amphibians, birds, and mammals. The British anatomist T.H. Huxley made Latreille's definition popular and, together with Richard Owen , expanded Reptilia to include the various fossil " antediluvian monsters", including dinosaurs and the mammal-like ( synapsid ) Dicynodon he helped describe. This

8680-467: The common theropods, and ankylosaurids and early ceratopsians like Psittacosaurus became important herbivores. Meanwhile, Australia was home to a fauna of basal ankylosaurians, hypsilophodonts , and iguanodontians. The stegosaurians appear to have gone extinct at some point in the late Early Cretaceous or early Late Cretaceous . A major change in the Early Cretaceous, which would be amplified in

8804-713: The dinosaur subgroup Maniraptora , which are coelurosaurs , which are theropods, which are saurischians. Research by Matthew G. Baron, David B. Norman , and Paul M. Barrett in 2017 suggested a radical revision of dinosaurian systematics. Phylogenetic analysis by Baron et al. recovered the Ornithischia as being closer to the Theropoda than the Sauropodomorpha, as opposed to the traditional union of theropods with sauropodomorphs. This would cause sauropods and kin to fall outside traditional dinosaurs, so they re-defined Dinosauria as

8928-427: The dinosaurs' modern-day surviving avian lineage (birds) are generally small due to the constraints of flight, many prehistoric dinosaurs (non-avian and avian) were large-bodied—the largest sauropod dinosaurs are estimated to have reached lengths of 39.7 meters (130 feet) and heights of 18 m (59 ft) and were the largest land animals of all time. The misconception that non-avian dinosaurs were uniformly gigantic

9052-686: The dinosaurs. Most of these other animals became extinct in the Triassic, in one of two events. First, at about 215 million years ago, a variety of basal archosauromorphs, including the protorosaurs , became extinct. This was followed by the Triassic–Jurassic extinction event (about 201 million years ago), that saw the end of most of the other groups of early archosaurs, like aetosaurs, ornithosuchids, phytosaurs , and rauisuchians. Rhynchosaurs and dicynodonts survived (at least in some areas) at least as late as early –mid Norian and late Norian or earliest Rhaetian stages , respectively, and

9176-483: The early pachyrhinosaur Einiosaurus . Farther south was characterized by lower taxonomic diversity in communities where lambeosaurines were less common and centrosaurs were completely lacking. There Kritosaurus , Parasaurolophus , and Pentaceratops are the dominant fauna. The giant eusuchian Deinosuchus is also "conspicuous" in the southern biome. Farther south, in Texas, Kritosaurus predominates. The biomes of

9300-554: The early proposals for replacing the paraphyletic Reptilia with a monophyletic Sauropsida , which includes birds, that term was never adopted widely or, when it was, was not applied consistently. When Sauropsida was used, it often had the same content or even the same definition as Reptilia. In 1988, Jacques Gauthier proposed a cladistic definition of Reptilia as a monophyletic node-based crown group containing turtles, lizards and snakes, crocodilians, and birds, their common ancestor and all its descendants. While Gauthier's definition

9424-574: The early saurischian Alwalkeria , are known from the Upper Maleri and Lower Maleri Formations of India. The Carnian-aged Chañares Formation of Argentina preserves primitive, dinosaur-like ornithodirans such as Lagosuchus and Lagerpeton in Argentina , making it another important site for understanding dinosaur evolution. These ornithodirans support the model of early dinosaurs as small, bipedal predators. Dinosaurs may have appeared as early as

9548-403: The end of the Cretaceous, caused the extinction of all dinosaur groups except for the neornithine birds. Some other diapsid groups, including crocodilians , dyrosaurs , sebecosuchians , turtles, lizards , snakes , sphenodontians , and choristoderans , also survived the event. The surviving lineages of neornithine birds, including the ancestors of modern ratites , ducks and chickens , and

9672-451: The exact date of their extinction is uncertain. These losses left behind a land fauna of crocodylomorphs , dinosaurs, mammals, pterosaurians, and turtles . The first few lines of early dinosaurs diversified through the Carnian and Norian stages of the Triassic, possibly by occupying the niches of the groups that became extinct. Also notably, there was a heightened rate of extinction during

9796-511: The exact origin and timing of the evolution of dinosaurs is a subject of active research. They became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201.3 mya and their dominance continued throughout the Jurassic and Cretaceous periods. The fossil record shows that birds are feathered dinosaurs , having evolved from earlier theropods during

9920-453: The fetus develops within the mother, using a (non-mammalian) placenta rather than contained in an eggshell . As amniotes, reptile eggs are surrounded by membranes for protection and transport, which adapt them to reproduction on dry land. Many of the viviparous species feed their fetuses through various forms of placenta analogous to those of mammals , with some providing initial care for their hatchlings. Extant reptiles range in size from

10044-433: The field of dinosaur research experienced a surge in activity that remains ongoing. Several seminal studies led to this activity. First, John Ostrom discovered the bird-like dromaeosaurid theropod Deinonychus and described it in 1969. Its anatomy indicated that it was an active predator that was likely warm-blooded, in marked contrast to the then-prevailing image of dinosaurs. Concurrently, Robert T. Bakker published

10168-486: The hip structure of their ancestors, with a pubis bone directed cranially , or forward. This basic form was modified by rotating the pubis backward to varying degrees in several groups ( Herrerasaurus , therizinosauroids, dromaeosaurids, and birds ). Saurischia includes the theropods (exclusively bipedal and with a wide variety of diets) and sauropodomorphs (long-necked herbivores which include advanced, quadrupedal groups). By contrast, ornithischians—"bird-hipped", from

10292-460: The hypothesis that turtles belong to a separate clade within Sauropsida , outside the saurian clade altogether. The origin of the reptiles lies about 310–320 million years ago, in the steaming swamps of the late Carboniferous period, when the first reptiles evolved from advanced reptiliomorphs . The oldest known animal that may have been an amniote is Casineria (though it may have been

10416-432: The last common ancestor of Triceratops horridus , Passer domesticus and Diplodocus carnegii , and all of its descendants, to ensure that sauropods and kin remain included as dinosaurs. They also resurrected the clade Ornithoscelida to refer to the group containing Ornithischia and Theropoda. Using one of the above definitions, dinosaurs can be generally described as archosaurs with hind limbs held erect beneath

10540-558: The late 17th century in England. Part of a bone, now known to have been the femur of a Megalosaurus , was recovered from a limestone quarry at Cornwell near Chipping Norton , Oxfordshire, in 1676. The fragment was sent to Robert Plot , Professor of Chemistry at the University of Oxford and first curator of the Ashmolean Museum , who published a description in his The Natural History of Oxford-shire (1677). He correctly identified

10664-508: The late 19th century, a number of definitions of Reptilia were offered. The biological traits listed by Lydekker in 1896, for example, include a single occipital condyle , a jaw joint formed by the quadrate and articular bones, and certain characteristics of the vertebrae . The animals singled out by these formulations, the amniotes other than the mammals and the birds, are still those considered reptiles today. The synapsid/sauropsid division supplemented another approach, one that split

10788-499: The latter are to the rest of extant reptiles. Colin Tudge wrote: Mammals are a clade , and therefore the cladists are happy to acknowledge the traditional taxon Mammalia ; and birds, too, are a clade, universally ascribed to the formal taxon Aves . Mammalia and Aves are, in fact, subclades within the grand clade of the Amniota. But the traditional class Reptilia is not a clade. It is just

10912-734: The living reptiles, there are many diverse groups that are now extinct , in some cases due to mass extinction events . In particular, the Cretaceous–Paleogene extinction event wiped out the pterosaurs , plesiosaurs , and all non-avian dinosaurs alongside many species of crocodyliforms and squamates (e.g., mosasaurs ). Modern non-bird reptiles inhabit all the continents except Antarctica. Reptiles are tetrapod vertebrates , creatures that either have four limbs or, like snakes, are descended from four-limbed ancestors. Unlike amphibians , reptiles do not have an aquatic larval stage. Most reptiles are oviparous , although several species of squamates are viviparous , as were some extinct aquatic clades  –

11036-478: The longest were the 33.5-meter (110 ft) long Diplodocus hallorum (formerly Seismosaurus ), the 33-to-34-meter (108 to 112 ft) long Supersaurus , and 37-meter (121 ft) long Patagotitan ; and the tallest, the 18-meter (59 ft) tall Sauroposeidon , which could have reached a sixth-floor window. There were a few dinosaurs that was considered either the heaviest and longest. The most famous one include Amphicoelias fragillimus , known only from

11160-477: The most abundant Judithian dinosaurs in the region. Large herbivores like the ceratopsians and hadrosaurs living in North America during the Late Cretaceous had "remarkably small geographic ranges" despite their large body size and high mobility. This restricted distribution strongly contrasts with modern mammalian faunas whose large herbivores' ranges "typical[ly] ... span much of a continent." Another example

11284-479: The most complete theropod specimens, while North American localities have produced the most complete sauropodomorph specimens. Prior to the dinosaur renaissance, dinosaurs were mostly classified using the traditional rank-based system of Linnaean taxonomy . The renaissance was also accompanied by the increasingly widespread application of cladistics , a more objective method of classification based on ancestry and shared traits, which has proved tremendously useful in

11408-495: The most diverse groups of vertebrates. Using fossil evidence, paleontologists have identified over 900 distinct genera and more than 1,000 different species of non-avian dinosaurs. Dinosaurs are represented on every continent by both extant species (birds) and fossil remains. Through the first half of the 20th century, before birds were recognized as dinosaurs, most of the scientific community believed dinosaurs to have been sluggish and cold-blooded . Most research conducted since

11532-509: The most important advantage was dietary. Large animals are more efficient at digestion than small animals, because food spends more time in their digestive systems. This also permits them to subsist on food with lower nutritive value than smaller animals. Sauropod remains are mostly found in rock formations interpreted as dry or seasonally dry, and the ability to eat large quantities of low-nutrient browse would have been advantageous in such environments. Scientists will probably never be certain of

11656-478: The most recent common ancestor of a certain taxonomic group, are called the synapomorphies of such a group. A detailed assessment of archosaur interrelations by Sterling Nesbitt confirmed or found the following twelve unambiguous synapomorphies, some previously known: Nesbitt found a number of further potential synapomorphies and discounted a number of synapomorphies previously suggested. Some of these are also present in silesaurids , which Nesbitt recovered as

11780-458: The mouth, including potential cheek -like organs to keep food in the mouth, and jaw motions to grind food. Another notable evolutionary event of the Jurassic was the appearance of true birds, descended from maniraptoran coelurosaurians. By the Early Cretaceous and the ongoing breakup of Pangaea, dinosaurs were becoming strongly differentiated by landmass. The earliest part of this time saw

11904-715: The now-splitting supercontinent Gondwana , abelisaurids were the common theropods, and titanosaurian sauropods the common herbivores. Finally, in Europe, dromaeosaurids, rhabdodontid iguanodontians, nodosaurid ankylosaurians, and titanosaurian sauropods were prevalent. Flowering plants were greatly radiating, with the first grasses appearing by the end of the Cretaceous. Grinding hadrosaurids and shearing ceratopsians became very diverse across North America and Asia. Theropods were also radiating as herbivores or omnivores , with therizinosaurians and ornithomimosaurians becoming common. The Cretaceous–Paleogene extinction event, which occurred approximately 66 million years ago at

12028-756: The number of named genera began to increase exponentially in the 1990s. As of 2008, over 30 new species of dinosaurs were named each year. At least sauropodomorphs experienced a further increase in the number of named species in the 2010s, with an average of 9.3 new species having been named each year between 2009 and 2020. As a consequence, more sauropodomorphs were named between 1990 and 2020 than in all previous years combined. These new localities also led to improvements in overall specimen quality, with new species being increasingly named not on scrappy fossils but on more complete skeletons, sometimes from multiple individuals. Better specimens also led to new species being invalidated less frequently. Asian localities have produced

12152-422: The other euryapsids, and given the older name Parapsida. Parapsida was later discarded as a group for the most part (ichthyosaurs being classified as incertae sedis or with Euryapsida). However, four (or three if Euryapsida is merged into Diapsida) subclasses remained more or less universal for non-specialist work throughout the 20th century. It has largely been abandoned by recent researchers: In particular,

12276-438: The pair's rough methods: for example, their diggers often used dynamite to unearth bones. Modern paleontologists would find such methods crude and unacceptable, since blasting easily destroys fossil and stratigraphic evidence. Despite their unrefined methods, the contributions of Cope and Marsh to paleontology were vast: Marsh unearthed 86 new species of dinosaur and Cope discovered 56, a total of 142 new species. Cope's collection

12400-408: The presence of proteins such as collagen, elastin , and laminin . Both specimens yielded collagen protein sequences that were viable for molecular phylogenetic analyses , which grouped them with birds as would be expected. The extraction of fragmentary DNA has also been reported for both of these fossils, along with a specimen of Hypacrosaurus . In 2015, Sergio Bertazzo and colleagues reported

12524-458: The preservation of collagen fibres and red blood cells in eight Cretaceous dinosaur specimens that did not show any signs of exceptional preservation, indicating that soft tissue may be preserved more commonly than previously thought. Suggestions that these structures represent bacterial biofilms have been rejected, but cross-contamination remains a possibility that is difficult to detect. Dinosaurs diverged from their archosaur ancestors during

12648-416: The primitive anapsid reptiles. Molecular work has usually placed turtles within the diapsids. As of 2013, three turtle genomes have been sequenced. The results place turtles as a sister clade to the archosaurs , the group that includes crocodiles, non-avian dinosaurs, and birds. However, in their comparative analysis of the timing of organogenesis , Werneburg and Sánchez-Villagra (2009) found support for

12772-422: The rebbachisaurid Nigersaurus . There were three general dinosaur faunas in the Late Cretaceous. In the northern continents of North America and Asia, the major theropods were tyrannosaurids and various types of smaller maniraptoran theropods, with a predominantly ornithischian herbivore assemblage of hadrosaurids, ceratopsians, ankylosaurids, and pachycephalosaurians. In the southern continents that had made up

12896-438: The reptiles into four subclasses based on the number and position of temporal fenestrae , openings in the sides of the skull behind the eyes. This classification was initiated by Henry Fairfield Osborn and elaborated and made popular by Romer 's classic Vertebrate Paleontology . Those four subclasses were: The composition of Euryapsida was uncertain. Ichthyosaurs were, at times, considered to have arisen independently of

13020-1404: The rocks that produced the Jehol (Early Cretaceous) and Yanliao (Mid-to-Late Jurassic) biotas of northeastern China, from which hundreds of dinosaur specimens bearing impressions of feather-like structures (both closely related to birds and otherwise, see § Origin of birds ) have been described by Xing Xu and colleagues. In living reptiles and mammals, pigment-storing cellular structures known as melanosomes are partially responsible for producing colouration. Both chemical traces of melanin and characteristically shaped melanosomes have been reported from feathers and scales of Jehol and Yanliao dinosaurs, including both theropods and ornithischians. This has enabled multiple full-body reconstructions of dinosaur colouration , such as for Sinosauropteryx and Psittacosaurus by Jakob Vinther and colleagues, and similar techniques have also been extended to dinosaur fossils from other localities. (However, some researchers have also suggested that fossilized melanosomes represent bacterial remains. ) Stomach contents in some Jehol and Yanliao dinosaurs closely related to birds have also provided indirect indications of diet and digestive system anatomy (e.g., crops ). More concrete evidence of internal anatomy has been reported in Scipionyx from

13144-450: The sauropodomorphs Bagualosaurus , Buriolestes , Guaibasaurus , Macrocollum , Nhandumirim , Pampadromaeus , Saturnalia , and Unaysaurus . The Pebbly Arkose Formation, which is of uncertain age but was likely comparable to the other two, has produced the sauropodomorph Mbiresaurus , along with an unnamed herrerasaurid. Less well-preserved remains of the sauropodomorphs Jaklapallisaurus and Nambalia , along with

13268-416: The sauropodomorphs Chromogisaurus , Eodromaeus , and Panphagia . Eoraptor 's likely resemblance to the common ancestor of all dinosaurs suggests that the first dinosaurs would have been small, bipedal predators . The Santa Maria Formation (radiometrically dated to be older, at 233.23 million years old ) has produced the herrerasaurids Gnathovorax and Staurikosaurus , along with

13392-571: The skeleton now mounted and on display at the Museum für Naturkunde in Berlin ; this mount is 12 meters (39 ft) tall and 21.8 to 22.5 meters (72 to 74 ft) long, and would have belonged to an animal that weighed between 30 000 and 60 000  kilograms ( 70 000 and 130 000  lb). The longest complete dinosaur is the 27 meters (89 ft) long Diplodocus , which was discovered in Wyoming in

13516-406: The skull behind the eyes), and as members of the diapsid group Archosauria, had additional openings in the snout and lower jaw. Additionally, several characteristics once thought to be synapomorphies are now known to have appeared before dinosaurs, or were absent in the earliest dinosaurs and independently evolved by different dinosaur groups. These include an elongated scapula , or shoulder blade;

13640-434: The sole surviving dinosaurs. In traditional taxonomy , birds were considered a separate class that had evolved from dinosaurs, a distinct superorder . However, most contemporary paleontologists reject the traditional style of classification based on anatomical similarity, in favor of phylogenetic taxonomy based on deduced ancestry, in which each group is defined as all descendants of a given founding genus. Birds belong to

13764-515: The specimen's excavation. Owen and Hooley subsequently described skin impressions of Hypsilophodon and Iguanodon in 1885 and 1917. Since then, scale impressions have been most frequently found among hadrosaurids, where the impressions are known from nearly the entire body across multiple specimens. Starting from the 1990s, major discoveries of exceptionally preserved fossils in deposits known as conservation Lagerstätten contributed to research on dinosaur soft tissues. Chiefly among these were

13888-527: The spread of ankylosaurians, iguanodontians , and brachiosaurids through Europe, North America, and northern Africa . These were later supplemented or replaced in Africa by large spinosaurid and carcharodontosaurid theropods, and rebbachisaurid and titanosaurian sauropods, also found in South America . In Asia , maniraptoran coelurosaurians like dromaeosaurids, troodontids , and oviraptorosaurians became

14012-789: The structure of the forebrain. According to Goodrich, both lineages evolved from an earlier stem group, Protosauria ("first lizards") in which he included some animals today considered reptile-like amphibians , as well as early reptiles. In 1956, D.M.S. Watson observed that the first two groups diverged very early in reptilian history, so he divided Goodrich's Protosauria between them. He also reinterpreted Sauropsida and Theropsida to exclude birds and mammals, respectively. Thus his Sauropsida included Procolophonia , Eosuchia , Millerosauria , Chelonia (turtles), Squamata (lizards and snakes), Rhynchocephalia , Crocodilia , " thecodonts " ( paraphyletic basal Archosauria ), non- avian dinosaurs , pterosaurs , ichthyosaurs , and sauropterygians . In

14136-468: The study of dinosaur systematics and evolution. Cladistic analysis, among other techniques, helps to compensate for an often incomplete and fragmentary fossil record. Reference books summarizing the state of dinosaur research, such as David B. Weishampel and colleagues' The Dinosauria , made knowledge more accessible and spurred further interest in dinosaur research. The release of the first and second editions of The Dinosauria in 1990 and 2004, and of

14260-730: The tallest of the theropods. The largest ornithischian dinosaur was probably the hadrosaurid Shantungosaurus giganteus which measured 16.6 meters (54 ft). The largest individuals may have weighed as much as 16 metric tons (18 short tons). Reptile This is an accepted version of this page See text for extinct groups. Reptiles , as commonly defined, are a group of tetrapods with an ectothermic ('cold-blooded') metabolism and amniotic development . Living reptiles comprise four orders : Testudines ( turtles ), Crocodilia ( crocodilians ), Squamata ( lizards and snakes ), and Rhynchocephalia (the tuatara ). As of May 2023, about 12,000 living species of reptiles are listed in

14384-459: The taxonomic name has often been interpreted as a reference to dinosaurs' teeth, claws, and other fearsome characteristics, Owen intended it also to evoke their size and majesty. Owen recognized that the remains that had been found so far, Iguanodon , Megalosaurus and Hylaeosaurus , shared distinctive features, and so decided to present them as a distinct taxonomic group. As clarified by British geologist and historian Hugh Torrens, Owen had given

14508-849: The total number of dinosaur genera preserved in the fossil record at 1850, nearly 75% still undiscovered, and the number that ever existed (in or out of the fossil record) at 3,400. A 2016 estimate put the number of dinosaur species living in the Mesozoic at 1,543–2,468, compared to the number of modern-day birds (avian dinosaurs) at 10,806 species. Extinct dinosaurs, as well as modern birds, include genera that are herbivorous and others carnivorous, including seed-eaters, fish-eaters, insectivores, and omnivores. While dinosaurs were ancestrally bipedal (as are all modern birds), some evolved into quadrupeds, and others, such as Anchisaurus and Iguanodon , could walk as easily on two or four legs. Cranial modifications like horns and crests are common dinosaurian traits, and some extinct species had bony armor. Although

14632-585: The years following Gauthier's paper. The first such new definition, which attempted to adhere to the standards of the PhyloCode , was published by Modesto and Anderson in 2004. Modesto and Anderson reviewed the many previous definitions and proposed a modified definition, which they intended to retain most traditional content of the group while keeping it stable and monophyletic. They defined Reptilia as all amniotes closer to Lacerta agilis and Crocodylus niloticus than to Homo sapiens . This stem-based definition

14756-625: Was Hylonomus , a small and superficially lizard-like animal which lived in Nova Scotia during the Bashkirian age of the Late Carboniferous , around 318  million years ago . Genetic and fossil data argues that the two largest lineages of reptiles, Archosauromorpha (crocodilians, birds, and kin) and Lepidosauromorpha (lizards, and kin), diverged during the Permian period. In addition to

14880-452: Was an extremely important find: Hadrosaurus was one of the first nearly complete dinosaur skeletons found ( the first was in 1834, in Maidstone, England ), and it was clearly a bipedal creature. This was a revolutionary discovery as, until that point, most scientists had believed dinosaurs walked on four feet, like other lizards. Foulke's discoveries sparked a wave of interests in dinosaurs in

15004-485: Was an order of magnitude more massive than anything else that has since walked the Earth. Giant prehistoric mammals such as Paraceratherium (the largest land mammal ever) were dwarfed by the giant sauropods, and only modern whales approach or surpass them in size. There are several proposed advantages for the large size of sauropods, including protection from predation, reduction of energy use, and longevity, but it may be that

15128-592: Was close to the modern consensus, nonetheless, it became considered inadequate because the actual relationship of turtles to other reptiles was not yet well understood at this time. Major revisions since have included the reassignment of synapsids as non-reptiles, and classification of turtles as diapsids. Gauthier 1994 and Laurin and Reisz 1995's definition of Sauropsida defined the scope of the group as distinct and broader than that of Reptilia, encompassing Mesosauridae as well as Reptilia sensu stricto . A variety of other definitions were proposed by other scientists in

15252-615: Was not the only possible classification scheme: In the Hunterian lectures delivered at the Royal College of Surgeons in 1863, Huxley grouped the vertebrates into mammals , sauroids, and ichthyoids (the latter containing the fishes and amphibians). He subsequently proposed the names of Sauropsida and Ichthyopsida for the latter two groups. In 1866, Haeckel demonstrated that vertebrates could be divided based on their reproductive strategies, and that reptiles, birds, and mammals were united by

15376-450: Was purportedly discovered in 1822 by Mary Ann Mantell , the wife of English geologist Gideon Mantell , though this is disputed and some historians say Gideon had acquired remains years earlier. Gideon Mantell recognized similarities between his fossils and the bones of modern iguanas and published his findings in 1825. The study of these "great fossil lizards" soon became of great interest to European and American scientists, and in 1842

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