Dinosauria

The dinosaurs (Dinosauria, from the Greek δεινός deinós 'terrible' and σαῦρος sauros 'lizard': 'terrible lizards') are a group of saurops that appeared during the Triassic period. Although the exact origin and early diversification is the subject of active research, current scientific consensus places their origin between 231 and 243 million years ago. They were the dominant terrestrial vertebrates for 135 million years, from the beginning of the Jurassic about 200 million years) to the end of the Cretaceous (66 million years ago), when most groups of dinosaurs went extinct during the Cretaceous-Paleogene mass extinction that ended the Mesozoic Era. The fossil record indicates that birds evolved from theropod dinosaurs during the Jurassic period, and many taxonomists therefore consider birds to form a subgroup of dinosaurs. Some birds survived this event, and their descendants continue the lineage. from dinosaurs to the present day.

Dinosaurs are a taxonomically, morphologically, and ecologically diverse group of animals. Using fossil evidence, paleontologists have identified nearly five hundred different genera and more than a thousand different species of non-avian dinosaurs. Dinosaurs are represented on every continent by both extant species and fossil remains.

Some are herbivorous, others carnivorous or omnivorous. The first dinosaurs were bipedal, but many groups included quadrupedal species, and some could alternate between the two types of locomotion. Horns or crests are common to all groups of dinosaurs, and some groups developed skeletal modifications such as bony armor and spines. Evidence suggests that egg laying and nest building were traits shared by all dinosaurs. Many dinosaurs were large in size—the largest sauropod dinosaur could have reached a length of 58 meters and 9.25 meters in height. However, the idea that non-avian dinosaurs were all gigantic is an error based on bias. conservation, as large, strong bones are more likely to last until fossilized. Many dinosaurs were quite small: Xixianykus, for example, was about fifty cm long.

Although the word dinosaur means 'terrible lizard,' the name is a bit misleading, since dinosaurs are not lizards. Instead, they represent a separate group of reptiles that, like many extinct forms, do not display features traditionally seen as reptilian, such as splayed limb stance or ectothermy. In addition, many prehistoric animals, including mosasaurs, ichthyosaurs, pterosaurs, plesiosaurs, and pelycosaurs (Dimetrodon), are popularly thought of as dinosaurs, but are not taxonomically classified as such. Throughout the first half of the 20th century, before birds were recognized as dinosaurs, most of the scientific community believed that dinosaurs had been slow-moving and cold-blooded. However, most research since the 1970s has indicated that all dinosaurs were active animals with high metabolisms and numerous adaptations for social interaction.

Ever since the first dinosaur fossils were recognized in the 19th century, mounted fossil skeletons have been the main attraction in many museums around the world, and dinosaurs have become a permanent part of world culture. The large size of some groups, as well as their seemingly monstrous and fantastical nature, have ensured regular appearances of dinosaurs in best-selling books and in films such as Jurassic Park. The public's continuing enthusiasm for these animals has led to significant funding for scientific research on dinosaurs, and new discoveries are regularly reported in the media.

Etymology

The taxon Dinosauria was formally named in 1842 by paleontologist Sir Richard Owen, who used it to refer to the "distinct tribe or sub-order of the reptile saurians" that was later recognized in England and throughout the world. The term derives from the Greek words δεινός (deinós, meaning 'terrible', 'powerful', or 'great fear') and σαῦρος (sauros, meaning 'lizard'). ' or 'reptile'). Although the taxonomic name has often been interpreted as referring to the teeth, claws, and other fearsome features of dinosaurs, Owen was simply meant to evoke their size and majesty.

Definition

Skeleton Triceratops horridus, American Museum of Natural History, United States

From the point of view of phylogenetic taxonomy, dinosaurs are generally defined as the group consisting of all descendants of the most recent common ancestor (LCMA) of Triceratops and modern birds. it has been proposed that the Dinosauria be defined with respect to the ACMR of Megalosaurus and Iguanodon, because these were two of the three genera cited by Richard Owen in recognizing the Dinosauria. Definitions include the same group of animals: "Dinosauria = Ornithischia + Saurischia", which encompasses theropods (mostly bipedal carnivores and birds), ankylosaurians (armoured herbivorous quadrupeds), stegosaurs (herbivorous quadrupeds with plates on their backs), ceratopsians (horned and frilled quadrupedal herbivores), ornithopods (bipedal or quadrupedal herbivores, including "duckbills"), and sauropodomorphs (mostly large long-necked and tailed herbivorous quadrupeds).

In the 21st century, birds are recognized as the sole survivors of the lineage of theropod dinosaurs. In traditional taxonomy, birds were considered a separate class that had evolved from the dinosaurs, a distinct superorder. However, most contemporary dinosaur-related paleontologists reject traditional-style classification in favor of phylogenetic nomenclature; this approach requires that for a group to be natural, all descendants of group members are also included in the group. Birds are therefore considered dinosaurs, and dinosaurs are therefore not extinct. Birds are classified as belonging to the Maniraptora subgroup, which are coelurosaurs, which are theropods, which are saurischians, and which are dinosaurs.

Overview

In phylogenetic taxonomy, birds are included in the Dinosauria group.

Dinosaurs can generally be described as archosaurs with limbs held erect below the body. Many groups of prehistoric animals are popularly thought of as dinosaurs, such as ichthyosaurs, plesiosaurs, mosasaurs, pterosaurs, and pelycosaurs (Dimetrodon), but they are not scientifically classified as dinosaurs, and none had the characteristic erect-limb posture of true dinosaurs. Dinosaurs were the dominant terrestrial vertebrates of the Mesozoic, especially in the Jurassic and Cretaceous periods. Other groups of animals were restricted in size and niches; mammals, for example, rarely exceeded the size of a cat, and were generally carnivorous rodents the size of small prey.

Dinosaurs have always been a highly diverse group of animals; According to a 2006 study, more than 500 genera of non-avian dinosaurs had been identified with certainty to date, and the total number of genera that could be preserved in the fossil record has been estimated at around 1850; thus nearly 75% would not yet have been discovered. An earlier study predicted that around 3,400 genera of dinosaurs existed, including many that have not been preserved in the fossil record. As of September 17, 2008, they have been named 1047 different species of dinosaurs. Some were herbivorous, others carnivorous, including granivorous, ichthyophagous, insectivorous, and omnivorous. Although dinosaurs were ancestrally bipedal (as are all modern birds), some prehistoric species were quadrupedal, and others, such as Ammosaurus and Iguanodon, could walk just as easily. on two or four legs. Cranial modifications such as horns and crests are common dinosaur features, and some extinct species had bony armor. Although known for their large size, many Mesozoic dinosaurs were human-sized or smaller, and modern birds are generally small. Today dinosaurs are found buried on every continent, and fossils show that they had achieved global distribution by at least the early Jurassic period. 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 semi-aquatic habits.

Distinctive Anatomical Features

All dinosaurs known to date share certain modifications of the ancestral archosaur skeleton.

Although some genera developed adaptations that made structural differences even more pronounced, these basic features are considered typical of the superorder Dinosauria; such qualities common to members of a taxon (taxonomic group) are called synapomorphies of that group.

A detailed evaluation of the interrelationships among S. Nesbitt archosaurs confirmed or found the following twelve unequivocal synapomorphies, some previously known:

• in the skull is presented a supratemporal fose (excavation) opposed to the supratemporal fenestra, the main opening at the top of the rear skull
• epipophysis, oblique processes of rear pointer in the upper corners, present in the previous vertebrae (frontal) of the neck, behind the atlas and the axis, the first vertebrae of two mouths
• vertex of the ridge of the upper-ectoral (a projection in which the muscles unite deltopectoral) located at the level or more than 30% of the length of the humerus (arm bone)
• radio, lower arm bone, shorter than 80% of the length of the humerus
• fourth trocánter (projection where the caudofemoralis muscle attached to the inner rear axis) in the femur (bone of the thigh) is an acute breeze
• asymmetrical trocánter with lower distal margin, forming a more pronounced angle to the axis
• in the astrágalo and the calcáneo, upper ankle bones, proximal joint facet, of the upper connecting surface, so that the butne occupies less than 30% of the cross width of the element
• the exocciptials (bones at the back of the skull) do not join along the middle line in the soil of the endocranial cavity, the inner space of the cranial box
• in the pelvis, the proximal joint surfaces of the ischion with the ilion and pubis are separated by a large concave surface (on the upper side of the ischion between contacts with the pubic hip bone and the ilion is found a part of the open joint)
• cnemial crest in the tibia (excellent part of the upper surface of the spinilla) and arches arranged anterolaterally (curves in the front and outer part)
• different orientation of the proximodistal (vertical) chant present on the back side of the distal end of the tibia (the back surface of the lower end of the tibia)
• concave joint surface for the calcáneo perone (the upper surface of the calcáneo, where the perone plays, has a hollow profile).

Nesbitt found a number of potential new synapomorphies, and discounted a number of previously suggested synapomorphies. Some of these are also present in silesaurids, which Nesbitt recovered as a sister group to the Dinosauria, including a large anterior trochanter, metatarsals II and IV of subequal length, reduced contact between the ischium and pubis, the presence of a cnemial crest. on the tibia and from an ascending process on the talus, and many others.

Skull diagram of a typical diapsy.
j: yugal, p: parietal bone, po: postorbital bone, q: square bone, qj: quadratojugal bone, sq: squamous bone.

A variety of other skeletal features are shared by dinosaurs. However, because they are common to other groups of archosaurs or were not present in all ancestral dinosaurs, these features are not considered synapomorphies. For example, like diapsids, ancestral dinosaurs had two pairs of temporal fenestrae (openings in the skull behind the eyes), and as members of the diapsid group Archosauria, they had additional openings in their snouts and lower jaws. In addition, several features thought to be synapomorphies are now known to have appeared before dinosaurs, or were absent in early dinosaurs and evolved independently by different groups of dinosaurs. These include an elongated scapula or shoulder blade, a compound sacrum by three or more fused vertebrae (in some other archosaurs three are found, but in Herrerasaurus only two are found) and a perforated acetabulum, or hip socket, with a hole in the center of its surface interior (which, for example in Saturnalia, is presented closed). Another difficulty in clearly determining dinosaur characteristics is that the earliest dinosaurs and other Late Triassic archosaurs are often poorly understood although they were similar in many ways; these animals have sometimes been misidentified in the literature.

Hip and postures of the later extremities: (from left to right) typical reptiles (extensive), dinosaurs and mammals (erect), and rauissuchiana (erect)

Dinosaurs stood upright with their hind legs erect in a manner similar to most modern mammals, but unlike most other reptiles, whose limbs spread to either side. of the images. This posture is due to the development of a lateral frontal recess in the pelvis (usually an open socket) and a corresponding distinct head toward the frontal interior of the femur. Their upright position allowed early dinosaurs to breathe easily while moving, thus which probably gave them extra stamina and activity levels that exceeded those of the "extensive" reptiles. Probably erect limbs also helped support the evolution of large size by reducing bending stresses on the limbs. Some non-dinosaurian archosaurs, including Rauisuchians, also had erect limbs but achieved this feature by " erect pillar" of the hip joint, where the upper pelvic bone, instead of projecting the femur attachment from a hip socket, was rotated to form a protruding platform.

Evolutionary history

Origins and evolutionary beginnings

Skeleton Marasuchus lilloensis, an ornithodox similar to dinosaurs.

Some primitive dinosaurs: Herrerasaurus (beginning) Eoraptor (in front) and a skull Plateosaurus.

Dinosaurs diverged from their archosaur ancestors in the mid to late Triassic period, approximately 20 million years after the Permian-Triassic mass extinction wiped out an estimated 95% of all life on Earth. Radiometric dating of the rock formation that contained the fossils of the early dinosaur genus Eoraptor has yielded a date of 231.4 million years, establishing its presence in the Triassic fossil record. Paleontologists believe that Eoraptor resembles the common ancestor of all dinosaurs; that is, if so, the first dinosaurs were small, bipedal predatory animals. The discovery of small dinosaur-like ornithoderes such as Marasuchus and Lagerpeton in the Middle Triassic strata of Argentina supports this idea; analyzes of the fossils of these animals suggest that these animals were indeed small bipedal predators. Dinosaurs may have appeared as early as 243 million years ago, which is indicated by Nyasasaurus remains from that period, although known fossils of this animal are too fragmentary to determine whether they were truly it was a dinosaur or a very close relative of one of them.

When dinosaurs first appeared, they were not the dominant land animals. Terrestrial habitats were occupied by various types of archosauromorphs and therapsids, such as cynodonts, and there were also rhynchosaurs. Their main competitors were pseudosuchians, such as ethosaurs, ornithosuchians, and rauisuchians, which were more successful than dinosaurs. Many of these animals would disappear during the Triassic, in one of two extinction events. The first, about 215 million years ago, saw the demise of a wide variety of basal archosauromorphs, including protorosaurs. This was followed by the Triassic-Jurassic mass extinction (about 200 million years ago), in which several other groups of early archosaurs became extinct, including ethosaurs, ornithosuchids, phytosaurs, and rauisuchians. Rhynchosaurs and dicynodonts survived (at least in some areas) as late as the early Norian and early Rhaetian, respectively, but the exact date of their extinctions is uncertain. These losses resulted in a terrestrial fauna composed of crocodylomorphs, dinosaurs, mammals, pterosaurs, and turtles. The first lineages of primitive dinosaurs diversified during the Carnian and Norian epochs in the Triassic, possibly as they filled the niches of the groups. that were becoming extinct.

Evolution and paleobiogeography

The evolution of dinosaurs after the Triassic was accompanied by changes in vegetation and the position of the continents. In the Late Triassic and Early Jurassic, the continents were connected to a single landmass known as Pangaea, and there was virtually only one type of dinosaur fauna composed mostly of coelophysoid carnivores and primitive sauropodomorph (prosauropod) herbivores. Gymnosperm plants (particularly conifers), a potential source of food, spread in the Late Triassic. Early sauropodomorphs did not have sophisticated mechanisms for processing food in their mouths, so they must have used other means to break up food throughout their digestive tract. The general homogeneity of the dinosaur fauna continued through the Middle Jurassic and early Jurassic. Late Jurassic, times when many localities had predators such as ceratosaurs, megalosauroids, and carnosaurs, while herbivores were generally stegosaur ornithischians and large sauropods. Examples of these faunas are found in the Morrison Formation in North America and the Tendaguru Formation in Tanzania. The dinosaurs of China show some differences, with specialized theropods such as metriacanthosaurids and unusually long-necked sauropods such as Mamenchisaurus. Ankylosaurs and ornithopods were becoming more common, but prosauropods had become extinct. Conifers and pteridophytes were the most common plants. Sauropods, like their prosauropod ancestors, did not process food orally, but ornithischians were evolving various ways to handle food in their mouths, including possible cheek-like structures to hold food in the mouth and jaw movements to chew it. Another notable Jurassic evolutionary event was the appearance of birds proper, descendants of the manirraptor coelurosaurs.

During the Lower Cretaceous and with the successive breakup of Pangea, the dinosaurs began to differentiate more on each continent. The early part of this era saw the spread of ankylosaurs, iguanodonts, and brachiosaurids across Europe, North America, and North Africa. The latter were supplemented or replaced in Africa by the large spinosaurid and carcharodontosaurid theropods, and the rebachisaurid and titanosaur sauropods, also found in South America. In Asia, manirraptorous coelurosaurs such as dromaeosaurids, troodontids, and ovirraptorosaurs became the most common theropods, while ankylosaurids and primitive ceratopsians such as Psittacosaurus became dominant herbivores. Meanwhile, Australia was home to a basal ankylosaur fauna, "hypsilophodontids" and iguanodontians. Stegosaurs appear to have gone extinct at some point between the end of the Early Cretaceous and the beginning of the Late Cretaceous. An important change that occurred during the Lower Cretaceous, and would be amplified in the Upper Cretaceous, was the evolution of flowering plants. At the same time, various groups of herbivorous dinosaurs developed more sophisticated ways to process food in their mouths. Ceratopsians employed a method of chopping food with teeth stacked into dental batteries, while iguanodonts refined their method of crushing food with dental batteries, which would be taken to the extreme by hadrosaurids. Some sauropods also evolved such batteries, of which of which the best example is the rebbakisaurid Nigersaurus.

There were three main types of dinosaur faunas in the Late Cretaceous. On the northern continents of North America and Asia, the major theropods were tyrannosaurids and various types of small manirraptor theropods, while herbivores were predominantly ornithischians such as hadrosaurids, ceratopsians, ankylosaurids, and pachycephalosaurs. On the southern continents that resulted from the breakup of Gondwana, the most common theropods were abelisaurids, and titanosaur sauropods were the most common herbivores. Finally, in Europe, the fauna consisted of dromaeosaurids, rhabdodontid iguanodonts, nodosaurid ankylosaurs, and titanosaur sauropods were predominant. Flowering plants irradiated with great success, and the first types of grasses appeared at the end of the Cretaceous. Hadrosaurids and ceratopsians became highly diverse in North America and eastern Asia. Theropods also evolved omnivorous and herbivorous forms, prominent among these being the thericinosaurs and ornithomimosaurs.

The Cretaceous-Tertiary mass extinction, which occurred approximately 66 million years ago at the end of the Cretaceous, caused the extinction of all groups of dinosaurs except the Neornite birds (or perhaps almost all, see on this below). Some other groups of diapsids, such as crocodilians, sebecosuchians, turtles, lizards, snakes, sphenodonts, and choristoderes, also survived the extinction event.

The surviving lineages of Neornite birds, including the ancestors of modern ratites, ducks and chickens, and a wide variety of waterfowl, diversified rapidly early in the Paleogene period, filling ecological niches left vacant by the extinction of groups of Mesozoic dinosaurs such as enantiornite arboreal birds, hesperornitiform waterfowl, and even large terrestrial theropods (which would be the case of Gastornis, dromornithids, and "terror birds"). However, mammals also evolved rapidly at this time, surpassing Neornite birds in dominating most terrestrial niches.

Classification

Dinosaurs (including birds) are archosaurs, like modern crocodiles. Archosaur diapsid skulls have two holes located where the jaw muscles attach, called the temporal fenestra. Most reptiles (including birds) are diapsids. Mammals, with only a temporal fenestra, are called synapsids; and turtles, without a temporal fenestra, are anapsids. Anatomically, dinosaurs share many other archosaur features, including teeth that borne from sockets rather than as direct extensions of the jaws. Within the Archosauria group, the dinosaurs are most significantly differentiated by their gait. The legs of dinosaurs extend directly under the body and are straight, while the legs of lizards and crocodiles extend outward, sticking out.

Many other kinds of reptiles lived in the Mesozoic era, side by side with the dinosaurs. Some of these are commonly, but incorrectly, thought of as dinosaurs, including plesiosaurs (which are not closely related to dinosaurs) and pterosaurs, which developed separately from reptilian ancestors in the late Triassic.

Dinosaurs are divided into two orders, Saurischia and Ornithischia, both of which are based on hip structure. Saurischians (Greek for Lizard Pelvis) are dinosaurs that initially retained the hip structure of their ancestors. They include all theropods (bipedal carnivores) and sauropods (long-necked herbivores). Ornithischians (Greek for Pelvis of bird) are the other order of dinosaurs, most of which were herbivorous quadrupeds.

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  Pelvic structure in Saurischia (left side).

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  Pelvis saurisquia de Tyrannosaurus (left side).

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  Pelvic structure in Ornithischia (left side).

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  Pelvis ornitisquia de Edmontosaurus (left side).

Taxonomy

The following is a simplified classification of dinosaur groups based on their evolutionary relationships, and organized based on the list of Mesozoic dinosaur species provided by Holtz (2008). more detailed version. The cross (†) is used to signify groups that have no living members.

• Dinosauria

• Saurischia (“lagarto saucer”; includes Theropoda and Sauropodomorpha)

• Theropoda (“pie of beast” all bent; most were carnivores)

Art print of six dromaeosaurid theropods: from left to right Microraptor, Dromaeosaurus, Austroraptor, Velociraptor, Utahraptorand Deinonychus

• †Herrerasauria (first bipedal carnivores)
• †Coelophysoid (small, first theropods; including Coelophysis and close relatives)
• †Dilophosauridae (first crested and carnivorous theropodes)
• †Ceratosauria (generately developed schools, the dominant southern carnivores of Cretaceous)
• Tetanurae (“rigid buds”; includes most theropods)

• †Megalosauroid (first groups of large carnivores including semiaquatic thornsaurids)
• †Carnosauria (Allosaurus and other close relatives, such as Carcharodontosaurus)
• Coelurosauria (“ollow tail lizards”; theropods with feathers, with a wide range of niches and body sizes)

• †Compsognathidae (first common coelurosaurs with reduced front extremities)
• †Tyrannosauridae (“Prayer lizards”);Tyrannosaurus rex and other close relatives; previous limbs were reduced)
• †Ornithomimosauria (“birds” imitators lizards”; mostly without teeth; carnivores to possible herbivores)
• †Alvarezsauroidea (insectivorous pecans with reduced previous limbs each with an increased claw)
• Maniraptora (“with the hands of a thief”; they had long and thin arms and fingers)

• †Therizinosauria (bipe greeks with large hand and small head claws)
• †Oviraptorosauria (“lagartos egg thieves”; mostly teethless; their diet and lifestyle are uncertain)
• †Archaeopterygidae (small, winged theropodes or primitive birds)
• †Deinonychosauria (“lagartos corridors”; small to medium size; similar to birds, with a distinctive claw on the toe)
• Avialae (“bird rooms”; modern birds and extinct relatives)

• †Scansoriopterygidae (small primitive avians with long third fingers)
• †Omnivoropterygidae (“omnivorous”; first large short-tailed aviators)
• †Confuciusornithidae (small toothless avians)
• †Enantiornithes (“opposite birds”; primitive arboreal flying aviators)
• Euornithes (“true birds”; advanced flying birds)

• †Yanornithiforms (Dented Chinese Cretaceous birds)
• †Hesperornithes (water vessels specializing in immersions)
• Birds (modern, modern picturing birds and their extinct relatives)

Artistic impression of four macronarian sauropods: from left to right Camarasaurus, Brachiosaurus, Giraffatitanand Euhelopus

• †Sauropodomorpha (“in the shape of a lizard’s paw”; small-headed herbivores, long neck and tail)

• †Guaibasauridae (small, primitive, omnivorous sauropodomorphs)
• †Plateosauridae (“plane lizards”; primitive, strictly biped “prosautropods”).
• †Riojasauridae (small, primitive sauropodomorphs).
• †Massospondylidae (small, primitive sauropodomorphs).
• †Sauropoda (“with lizard leg”; very large and heavy, usually more than 15 meters (49.2 feet) long; quadruped)

• †Vulcanodontidae (primitive neuropodes with extremities as pillars)
• †Eusauropoda (“true neuropodes”).

• †Cetiosauridae.
• †Turiasauria (European group of Jurassic and Cretaceous sauropods)
• †Neosauropoda (“new sauropodes”).

• †Diplodocoid (“double-beam lizards”; elongated skulls and tails; usually narrow and similar teeth to a pencil)
• †Macronaria (square cells; spoon or pencil-shaped teeth).

• †Brachiosauridae (long-armed large-necked)
• †Titanosauria (diverse; forned, with broad hips; more common in the Late Cretaceous of the Southern Continents)

Artistic imprint of six ornitopods and one heterodontosaurus. Left Extreme: Camptosaurus, left: Iguanodon, center background: Shantungosaurus, front-end center: Dryosaurus, right: Corythosaurusmore to the right (small): Heterodontosaurus, more to the right (large) Tenontosaurus.

• †Ornithischia (“bird-sided”; various bipedal and quadruped herbivores)

• †Heterodontosauridae (“different toothbrushes”; small herbivorous/omnivorous basal ornitopods with prominent similar to canine teeth)
• †Thyreophora (“coat carrier”; decorated dinosaurs; mostly quadruped)

• †Ankylosauria (listed as primary armor; some had claw-style tails)
• †Stegosauria (paints and dishes as main armor)

• †Neornithischia (“new orniquios”)

• †Ornithopoda (“bird”; various sizes; bipedals and quadruped; evolved a chewing method using flexible skulls and numerous teeth)
• †Marginocephalia (“heads with rebound”; characterized by cranial growth)

• †Pachycephalosauria (“gross-headed lizards”; biped with dome-shaped growths or cranium knots)
• †Ceratopsia (hot pressure, a rostral bone, merged neck vertebrae and two roots teeth)

Biology

Knowledge about dinosaurs has been gained from a variety of skeletal and non-skeletal fossil records, such as fossilized bones, footprints (imprints), feces (coprolites), stones used to aid digestion (gastroliths),), feathers, impressions of skin, internal organs, and soft tissue. Several fields of study contribute to our paleontological understanding of dinosaurs, including physics (especially biomechanics; dinosaur mass, velocity, and blood flow), chemistry, biology and Earth sciences (of which paleontology is a sub-discipline). Two topics of particular interest and study have been the size of dinosaurs and their behavior.

Size

Scale diagram comparing the greatest known dinosaurs of the five main nails and a human.

Current evidence suggests that the average size of dinosaurs varied through the Triassic, Early Jurassic, Late Jurassic, and Cretaceous periods. Predatory theropod dinosaurs, which occupied many of the terrestrial carnivore niches during the Mesozoic, frequently They fell into the 100 to 1,000 kg (kilogram) category when classified by their estimated weight into order-of-magnitude-based categories, while Holocene mammalian predators fall into the 10 to 100 kg category. The statistical mode Mesozoic dinosaur body masses range from one to ten metric tons. This contrasts sharply with the size of mammals throughout the Cenozoic, whose mass was estimated by the Smithsonian Institution's National Museum of Natural History to be between 2 to 5 kg.

However, the meaning of "average size" is not so easy to pin down. Current observations suggest different values for each of the geological periods involved.

The estimated [weights] of medium dinosaurs range between 500 kg and 5 tons [...] Eighty percent of the biomass of the Morrison Formation of the West of the United States consisted of Stegosaurus and sauropods; the latter averaged 20 tons [...]. The typical large porte of dinosaurs and the comparatively small size of modern mammals has been quantified by Nicholas Hotton. Based on 63 dinosaur genres, Hotton data show an average mass exceeding 395.9 kg (the weight of a medium grizzly bear), and a medium generic mass of about two tons (comparable to a giraffe). This contrasts markedly with extinct mammals (788 genera) whose average mass is 631 grams (a small rodent). The smaller non-avian dinosaur found to date was greater than two thirds of all current mammals; most dinosaurs were greater than all living mammals except for 2 percent of individuals.

Sauropods were the largest and heaviest dinosaurs. For most of the age of the dinosaurs, even the smallest sauropods were larger than any other animal in their habitats, and the largest were an order of magnitude more massive than any other creature that ever walked the Earth. Giant prehistoric mammals such as Paraceratherium (the largest known land mammal) were dwarfed next to giant sauropods, and only modern whales match or surpass sauropods in size. There are several proposed advantages to the large size of sauropods, including protection from predation, reduced energy use, and longevity, but perhaps the most important of these were related to their diet. Large animals are more efficient at digesting than small ones, since food spends more time in their digestive systems. This also allows them to subsist on food of lower nutritional value than small animals. Sauropod remains are found mainly in rock formations that are interpreted as dry or seasonally dry environments, so the ability to eat large amounts of nutrient-poor plants would have been advantageous in such ecosystems.

Big and small

Scientists will probably never know which were the largest and smallest dinosaurs that ever lived. This is because only a small percentage of the animals become fossilized, and many of these remain buried. Few of the specimens that are recovered are complete skeletons, and impressions of skin and other soft tissue are very rare. Reconstructing a complete skeleton by comparing the size and morphology of the bones of the best-known and most closely resembling species is an inexact art, and the reconstruction of the muscles and other organs of the living creature is at best an art. process of establishing informed assumptions.

Comparative size Giraffatitan with an average human.

The tallest and heaviest known dinosaur with complete skeletons is Giraffatitan brancai (previously classified as a species of Brachiosaurus). Its remains were discovered in Tanzania between 1907 and 1912. Bones of several similarly sized individuals were incorporated into the skeleton now mounted and on display at the Natural History Museum in Berlin; this skeleton is 12 m (meters) tall and between 21.8 and 22.5 m long, and would belong to an animal that would weigh between 30,000 and 60,000 kg (kilograms). The longest complete dinosaur is a 27 m long specimen of a Diplodocus, which was discovered in Wyoming in the United States and has been on display at the Carnegie Museum of Natural History in Pittsburgh since 1907.

There were much larger dinosaurs, but our knowledge of them is based on a small number of fragmentary fossils. Many of the largest recorded specimens of herbivores were all discovered in the 1970s onwards, and include the enormous Argentinosaurus, which may have weighed between 80,000 and 100,000 kg (kilograms); some of the longest include the 33.5 m (metre) Diplodocus hallorum (formerly known as the Seismosaurus) and the 33 m Supersaurus long; and among the tallest, is Sauroposeidon with 18 m in height, which could have reached a sixth-story window. The heaviest and longest of them all could have been Amphicoelias fragillimus, known only from a partial vertebra (the neural arch) described in 1878 and as of December 2016 missing. Extrapolating from the illustration of this bone, the animal could have been 58 m long and weighed about 120,000 kg. The largest known carnivorous dinosaur was Spinosaurus, reaching a length of over 16 m., and with a weight of 8150 kg.

Other large carnivorous dinosaurs include the theropods Giganotosaurus, Carcharodontosaurus, and Tyrannosaurus. Therizinosaurus and Deinocheirus were among the tallest among theropods.

Not including birds (Avialae), the smallest known dinosaurs were about the size of pigeons. Not surprisingly, the smallest non-avian dinosaurs were those most closely related to birds. Anchiornis huxleyi, for example, had a skeleton with a total length of less than 35 cm (centimeters). A. huxleyi is recognized as the smallest non-avian dinosaur described in an adult specimen, with an estimated weight of 110 g (grams). Smaller non-avian herbivorous dinosaurs include Microceratus and Wannanosaurus, each about 60 cm long.

Behavior

A land nest of the Hadrosaurido Maiasaura peeblesorum was discovered in 1978.

Many modern birds are highly social, often living in flocks. There is a general consensus that some behaviors that are common in birds, as well as in crocodiles (birds' closest living relatives), were also common among extinct groups of dinosaurs. Interpretations of the behavior of animal species known from fossil remains are generally based on the posture of their skeletons and habitat, computer simulations of their biomechanics, and comparisons with modern animals that have similar ecological niches.

The first evidence that herd behavior was common in various groups of dinosaurs other than birds came in 1878 with the discovery of 31 specimens of Iguanodon bernissartensis, ornithischians thought to have perished together at a site in Bernissart, Belgium, after having fallen into a deep flooded sinkhole where they drowned. Other sites of mass death were discovered later. These, along with several fossilized footprints, suggest that herd behavior was common in various dinosaur species. Tracks of hundreds or even thousands of herbivores indicate that hadrosaurids may have moved in large groups, such as American bison or springbok. Sauropod tracks document that these animals traveled in groups composed of different species, at least in Oxfordshire, England, although this is not evidence of a specific herd structure. Congregating in groups may have evolved for self-defense, for purposes migration, or to provide protection for young. There is evidence that many types of slow-growing dinosaurs, including various theropods, sauropods, ankylosaurs, ornithopods, and ceratopsians, formed aggregations of immature individuals. One example is a site in Inner Mongolia where the remains of about 20 Sinornithomimus, ranging in age from one to seven years, have been found. This association has been interpreted to correspond to a social group that became trapped in the mud. The interpretation of dinosaurs as social animals has also been extended to carnivorous theropods, depicting them as group hunters that cooperated to bring down large prey. However, this lifestyle is not common among modern birds, crocodiles, and other reptiles, and taphonomic evidence suggests that the putative mammalian-style group hunting suggested for dinosaurs such as Deinonychus and Allosaurus can also be interpreted as the result of fatal disputes between feeding animals, as has been observed in several modern predatory diapsids.

Artistic recreation of two Centrosaurus apertus locked in combat.

The crests and ruffs of some dinosaurs, such as marginocephalians, theropods, and lambeosaurines, may have been too fragile to have been used for active defense, and thus were probably used for sexual displays or aggression, although little is known about them. mating and territorialism in dinosaurs. Head bite wounds suggest that at least theropods fought in aggressive confrontations.

From a behavioral point of view, one of the most valuable dinosaur fossils was found in the Gobi desert in 1971. It includes a Velociraptor attacking Protoceratops i>, providing evidence that dinosaurs did indeed attack each other. Additional evidence of attacks on living prey is found in the partially healed tail of an Edmontosaurus, a hadrosaur dinosaur; the tail was damaged in such a way that it shows that the animal was attacked by a tyrannosaurid but managed to survive. Cannibalism among some dinosaur species was confirmed by tooth marks found in Madagascar in 2003, on the theropod Majungasaurus.

Comparisons with the scleral rings of modern dinosaurs, birds, and reptiles have been used to infer the daily activity patterns of dinosaurs. Although it has been suggested that most dinosaurs were active during the day, these comparisons have shown small predatory dinosaurs such as dromaeosaurids, Juravenator and Megapnosaurus to be likely nocturnal. Medium- and large-sized herbivorous and omnivorous dinosaurs such as ceratopsians, sauropodomorphs, hadrosaurids, and ornithomimosaurs may have been cathemeral, i.e. active for short intervals throughout the day, although it is inferred that the small ornithischian Agilisaurus would have been daytime.

Based on available fossil evidence for dinosaurs such as Oryctodromeus, it appears that some ornithischian species appear to have adopted a partially fossorial (burrowing) lifestyle. Many modern birds are arboreal, and this it was the same for many Mesozoic birds, especially enantiornites. Although some species of bird-like dinosaurs appear to have also been arboreal (including dromaeosaurids such as Microraptor ) many non-avian dinosaurs appear to have been before all terrestrial locomotion. A good understanding of how dinosaurs moved on land is key to modeling dinosaur behavior; the science of biomechanics, in particular, has provided significant insight in this area. For example, studies of the forces exerted by muscles and gravity on the skeletal structure of dinosaurs have investigated how fast dinosaurs could run, whether diplodocids could create sonic booms by waving their whip-like tails, and whether sauropods could float.

Communication

Artistic recreation of a striking visual display in a Lambeosaurus magnicristatus.

Living birds are well known to communicate using primarily visual and auditory cues, and the wide diversity of visual display structures among extinct groups of dinosaurs suggests that visual communication was always important in dinosaur biology. On the other hand, less is known about vocalization in dinosaurs. In 2008, paleontologist Phil Senter examined evidence for vocalization in Mesozoic animal life, including dinosaurs. Senter found that, unlike popular portrayals of roaring dinosaurs in movies, many Mesozoic dinosaurs may not have been capable of creating any type of vocalizations (although the hollow crests of lambeosaurines may have functioned as resonance chambers used for a wide range of sounds). To reach this conclusion, Senter studied the distribution of vocal organs in birds and modern reptiles. He found that the vocal cords in the larynx likely evolved multiple times among reptiles, including crocodilians, which are capable of producing guttural roars. Birds, on the other hand, lack a larynx. Instead, their sounds are made with the syrinx, a vocal organ found only in birds, and unrelated to the larynx, meaning it evolved independently of the vocal organs of reptiles. The syrinx depends on the avian air sac system to function; specifically, it requires the presence of a clavicular air sac near the furcula. This air sac leaves distinctive markings or openings in the bones, including a characteristic hole in the upper arm bone (humerus). Although the extensive air sac system is a unique feature of saurischian dinosaurs, the clavicular air sac required for vocalization does not appear in the fossil record until enantiornite birds (with the exception of Aerosteon, which probably evolved its clavicular air sac independently of birds for reasons other than vocalization).

The earliest dinosaurs with a syrinx to make sounds are enantiornite birds, and thus archosaurs of the avian line (Ornithodira) did not make vocal calls. Instead, several lines of evidence suggest that dinosaurs primarily used visual communication, through distinctive-looking (and possibly brightly colored) horns, ruffs, crests, sails, and feathers. This is similar to what is seen in some modern reptiles such as lizards, which are mostly silent (although like many dinosaurs, they have a well-developed sense of hearing) but use complex display behaviors and bright colors to communicate..

In addition, dinosaurs were able to use other methods of making sounds to communicate. Other animals, including reptiles, use a wide variety of non-vocal sounds, including hissing, snapping or squeaking with their jaws, using elements in the environment (such as splashing), and flapping their wings (something possible in manirraptor dinosaurs). winged).

Reproductive biology

Nest of a chorlitejo (Charadrius).

All dinosaurs lay amniotic eggs with hard shells composed primarily of calcium carbonate. The eggs are usually laid in a nest. Many species create elaborate nests, shaped like a bowl, dome, plateau, bed, mound, or burrow. Some modern bird species do not make nests; A cliff-dwelling species, the common guillemot lays its eggs on bare rock, and the male emperor penguin cares for its eggs by placing them between his belly and feet. Primitive birds and many of the non-avian dinosaurs frequently laid their eggs in communal nests, in which mostly males incubated the eggs. Although modern birds only have one functional oviduct and lay one egg at a time, the most primitive birds and dinosaurs had two, such as crocodiles. Some non-avian dinosaurs, such as Troodon, exhibited repetitive clutches, in which adults might deposit a pair of eggs every day or two, then ensure they hatched simultaneously by postponing their incubation until all the eggs would have been laid.

When laying eggs, females would develop a special type of bone between the hard outer bone layer and the marrow of their limbs. This medullary bone, which is rich in calcium, is used to make the shell of the egg. The discovery of this feature in a Tyrannosaurus rex specimen provided evidence of medullary bone in extinct dinosaurs and, for the first time, allowed paleontologists to establish the sex of a fossil dinosaur specimen. Subsequent research has found medullary bone in the carnosaur Allosaurus and the ornithopod Tenontosaurus. Because the dinosaur lineage that includes Allosaurus and Tyrannosaurus diverged from that leading to Tenontosaurus very early in dinosaur evolution, this suggests that the production of medullary tissue is a general feature of all dinosaurs.

Fossils interpreted as an oviraptor Citipati nesting at the American Museum of Natural History. The smallest fossil to the extreme right shows the inside of one of the eggs.

Another widespread trait among modern birds is paternal care for newly hatched young. Jack Horner in 1978 discovered a nesting area of Maiasaura (the "good mother lizard") in Montana, United States, demonstrating that parental care continued for a long time after birth. among ornithopods, indicating that this behavior may have been common among dinosaurs. There is evidence that other non-theropod dinosaurs, such as the titanosaurs of Patagonia, also nested in large groups. A specimen found in Mongolia of the oviraptorid Citipati osmolskae was discovered in an incubation posture similar to that of chickens in 1993, indicating that they used an insulating layer of feathers to keep the eggs warm. The assumption that parental care outside a common trait in dinosaurs is supported by other findings. For example, a dinosaur embryo belonging to the prosauropod Massospondylus was found without teeth, indicating that young were required to be fed by their parents. Track trails have also confirmed parental care among ornithopods of the Isle of Skye in northwest Scotland. Nests and eggs have been found for several of the major groups of dinosaurs, and it seems likely that all dinosaurs cared for their young to some degree before or shortly after hatching.

Physiology

Because both crocodilians and modern birds have four-chambered hearts (albeit modified in crocodilians), it is likely a trait shared by all archosaurs, including dinosaurs. Although all birds they have high metabolisms and are "warm-blooded" (endothermic), there has been a vigorous debate since the 1960s as to how far back this feature goes in the dinosaur lineage. Scientists have differed on whether non-avian dinosaurs were endothermic, ectothermic, or a combination of both.

After the discovery of the first non-avian dinosaurs, paleontologists initially considered them to be ectothermic. This alleged "cold-blooded" was used to imply that dinosaurs were relatively slow and lazy organisms, although many modern reptiles are actually fast and agile despite relying on external sources of heat to regulate their body temperatures. The idea of slow dinosaurs continued to prevail until Robert T. "Bob" Bakker, one of the first to propose dinosaur endothermy, published an influential paper on the subject in 1968.

Recent evidence indicates that even non-avian dinosaurs and birds thrived in cold climates, and at least some of the earliest species must have been able to regulate their body temperatures by internal biological means (aided by the mass of the animals in the larger species and feathers or other insulating elements in the smaller species). Evidence for endothermy in Mesozoic dinosaurs includes the discovery of "polar dinosaurs" in Australia and Antarctica as well as analysis of blood vessel structures within fossil bones that are typical of endotherms. Scientific debate has continued regarding the specific ways in which temperature regulation evolved in dinosaurs.

Comparison between the aerial bags of an abelisaurid and a bird.

In saurischian dinosaurs, active metabolisms are supported by the evolution of the avian respiratory system, characterized by an extensive system of air sacs that extends into the lungs and invades many of the bones in the skeleton, making it lighter. Early avian-type respiratory systems with air sacs may have been able to sustain higher levels of activity than in mammals of similar size and build. In addition to providing a very efficient oxygen supply, the rapid airflow may have been an effective cooling mechanism, which is essential in animals that are active but too large to dissipate all the excess heat through their skin.

Like other reptiles, dinosaurs are primarily uricotelic, meaning their kidneys remove nitrogenous waste from their bloodstream and excrete it as uric acid instead of urea or ammonia as in other animals, through the ureters to the intestines. In many extant species, uric acid is excreted along with the feces as a semisolid waste. However, at least some birds (such as hummingbirds) may be facultatively ammoniotelic, excreting most nitrogenous waste as ammonia. They also excrete creatine, rather than creatinine as in mammals. This material, as well as waste from the intestines, exits through the cloaca. Other than this, many species regurgitate pellets, and fossil pellets possibly from dinosaurs are known from as far back as the Cretaceous period.

Diseases

• In August 2020, malignant cancer was first discovered in a dinosaur. The cancerous bone in which it was discovered was the butne of a Centrosaurus apertusA dinosaur with horns that lived 76 to 77 million years ago. [1]

Origin of birds

The possibility that dinosaurs were the ancestors of birds was first suggested in 1868 by Thomas Henry Huxley. After the work of Gerhard Heilmann in the early 20th century, the theory of birds as descendants of dinosaurs it was abandoned in favor of thecodont ancestors, the key piece of evidence being the supposed lack of a clavicle in dinosaurs. However, as later discoveries have shown, clavicles (or a single fused furcula, derived from two separate clavicles) were not actually absent.; had already been found in 1924 in Oviraptor, but had been misidentified as interclavicle. In the 1970s, John Ostrom revived the theory of dinosaurs as ancestors of birds, which won momentum during the following decades with the advent of cladistic analysis, and a great increase in discoveries of small theropods and primitive birds. They have been of special relevance fossils from the Yixian Formation, where multiple theropods and primitive birds have been found, often with feathers of some kind. Birds share more than a hundred distinct anatomical features with theropod dinosaurs, by the 21st century generally considered their relatives closest prehistoric.

The closest group to them is the manirraptor coelurosaurs. The dinosaurian origin of birds is supported not only by paleontological evidence but also by protein sequences obtained from Tyrannosaurus rex proteins. > and Brachylophosaurus canadensis which show that they are related to birds, although the latter two may be more closely related to each other than to birds. The phylogeny gave the following result:

A minority of scientists, notably Alan Feduccia and Larry Martin, have suggested other evolutionary pathways, including revised versions of Heilmann's proposal of basal archosaurs, or that manirraptor theropods were the ancestors of birds, but not were not dinosaurs, but rather convergent with them.

Feathers

Several non-avian feathered dinosaurs, including Archaeopteryx, Anchiornis, Microraptor and Zhenyuanlong

Feathers are one of the most recognizable features of modern birds, and a trait that was shared by all other groups of dinosaurs. Based on the current distribution of fossil evidence, it appears that feathers were an ancestral dinosaur trait, although one that may have been selectively lost in some species. Direct fossil evidence of feathers or feather-like structures has been discovered in a great variety of species in many groups of non-avian dinosaurs, both among the saurischians and the ornithischians. Simple, branched, feather-like structures are known from heterodontosaurids, primitive neonthischians, theropods, and primitive ceratopsians. Evidence for true feathers, blades similar to the flight feathers of modern birds, has only been found in the Maniraptora theropod subgroup that includes oviraptorosaurs, dromaeosaurid troodontids, and birds. Feather-like structures known as pycnofibers have also been found in pterosaurs, suggesting the possibility that feather-like filaments might have been common in the avian lineage and evolved before the appearance of dinosaurs themselves. Research on the genetics of American crocodiles has also revealed that pterosaurs Crocodilian scutes do possess feather-keratins during embryonic development, but these keratins are not expressed by the animals before hatching.

Archaeopteryx was the first fossil found that revealed a possible relationship between dinosaurs and birds. It is considered a transitional fossil, showing characteristics of both groups. Released two years after Darwin's seminal On the Origin of Species, its discovery spurred the fledgling debate between supporters of evolutionary biology and creationism. This bird is as old as the dinosaurs, with no clear feather impression in the surrounding rock, at least one specimen was mistaken for Compsognathus. Since the 1990s an increasing number of them have been found. non-avian feathered dinosaurs, which provided additional evidence for the direct relationship between dinosaurs and modern birds. Most of these specimens have been exhumed in the Liaoning province of northeast China, which was part of an isolated continent during the Cretaceous. Although traces of feathers have been found only in the Yixian Formation and a few other sites, it is likely that similar dinosaurs in other parts of the world were also covered in feathers. The lack of fossil plumage remains on a planetary scale may be due to the fact that delicate structures such as skin, hair, and feathers are not preserved by the usual fossilization conditions, making their presence in the fossil record difficult.

The description of feathered dinosaurs has not been without controversy; perhaps the biggest critics have been Alan Feduccia and Theagarten Lingham-Soliar, who have proposed that some feather-like fossils are supposedly the result of the breakdown of collagen fibers under dinosaur skin, and that the paddle-feathered Maniraptoran dinosaurs were not actually dinosaurs, but convergent with dinosaurs. However, his views have not generally been accepted by other researchers, to the point of questioning the scientific nature of Feduccia's proposals..

Skeleton

Because feathers are generally associated with birds, feathered dinosaurs are often labeled and described as the missing link between birds and dinosaurs. However, the multiple skeletal features shared by the two groups are also an important clue to paleontologists. Areas of the skeleton with significant similarities are the neck, pubis, wrist (carpus lunate), upper arm and shoulder girdle, furcula, and keel. The comparison of dinosaur and bird skeletons through cladistic analysis reinforces the theory of the relationship between the two groups.

Soft tissues

Pneumatophores in the left iliac bone of ilium Aerosteon riocoloradensis

Large meat-eating dinosaurs possessed a complex system of air sacs similar to those found in modern birds, according to 2005 research led by Patrick O'Connor of Ohio University. The lungs of bipedal carnivorous theropod dinosaurs with legs (similar to those of birds) probably pump air into empty sacs in their skeletons, as in birds. What in the past was formally considered a unique trait of birds was present in some form in their ancestors, O'Connor said. In 2008, scientists described Aerosteon riocoloradensis, the skeleton of which has provided the clearest evidence yet for a dinosaur with a respiration system similar to that of birds. A CT scan revealed the presence of air sacs within the body cavity of the Aerosteon skeleton.

Evidence of behavior

Fossils of troodontids Mei and Sinornithoides show that some dinosaurs slept with their heads tucked under their arms. contributed to keeping the head warm, it is also characteristic of modern birds. Several deynonsaurian and oviraptorosaur specimens have also been found preserved on top of their nests, probably chewing the cud in a similar manner to birds. The ratio of egg volume to adult body mass among these dinosaurs suggests that eggs they are incubated primarily by the male, and that the young were very precocious, similar to many modern ground-dwelling birds.

Some dinosaurs are known to use gizzard stones, like modern birds. These stones are eaten by animals to aid digestion and break down tough foods and fibers once they enter the stomach. When found in association with fossils, these stones are called gastroliths.

Extinction of major groups

The discovery that birds are a type of dinosaur showed that dinosaurs in general are not, in fact, extinct as is commonly claimed. However, all non-avian dinosaurs as well as many groups of birds became extinct suddenly about 66 million years ago. It has been suggested that because small mammals, squamatas, and birds occupied ecological niches suitable for their small body size, non-avian dinosaurs never evolved a diverse fauna of small-bodied species, leading to their downfall, when they were seen. affected by large-bodied terrestrial tetrapods, as a consequence of the mass extinction event. Many other groups of animals also became extinct at this time, including ammonites (nautilus-like molluscs), mosasaurs, plesiosaurs, pterosaurs, and many groups of mammals. Significantly, the insects did not suffer any appreciable loss in their population, leaving food available for other survivors. This mass extinction is known as the Cretaceous-Paleogene mass extinction. The nature of the event that caused this mass extinction has been widely studied since the 1970s; to the 21st century, several related theories are supported by paleontologists. Although the consensus is that an impact event was the primary cause of the extinction of the dinosaurs, some scientists cite other possible causes, or support the idea that a confluence of several factors was responsible for the sudden disappearance of dinosaurs from the fossil record..

At the height of the Mesozoic, there were no ice caps, and sea levels were 100 to 250 m (meters) higher than today. The planet's temperature was also much more uniform, with a difference of only 25 °C (45 °F) between polar and equatorial temperatures. On average, atmospheric temperatures were also much warmer; the poles, for example, were 50 °C (90 °F) warmer than today.

The atmospheric composition during the Mesozoic was also very different. Carbon dioxide levels were up to twelve times higher than today, and oxygen made up 32-25% of the atmosphere, compared to 21% today. However, by the end of the Cretaceous, the environment was changing dramatically. Volcanic activity slowed, causing a cooling trend as atmospheric carbon dioxide levels fell. Oxygen levels in the atmosphere also began to fluctuate and eventually dropped considerably. Some scientists believe that climate change, coupled with lower oxygen levels, could have directly caused many species to disappear. If dinosaurs had respiratory systems similar to those typical of modern birds, it might have been particularly difficult for them to adapt to lower respiratory performance, considering the enormous amount of oxygen their bodies required.

Asteroid collision

The crater of Chicxulub on the Yucatan peninsula, a place of impact of the meteorite that would have caused the extinction of the dinosaurs.

The asteroid collision theory, which was popularized in 1980 by Walter Alvarez and colleagues, links the late Cretaceous extinction to a bolide impact approximately 65.5 million years ago. Alvarez and others suggested that a sudden increase in iridium levels, recorded worldwide in rock strata from this period, was direct evidence of the impact. Most indications as of 2016 suggest that a five- to fifteen kilometers in diameter impacted with Earth near the Yucatán peninsula, creating the 170 km (kilometers) diameter Chicxulub crater and triggering the mass extinction. Scientists do not know for sure whether the dinosaurs were thriving or failing. decline before astronomical impact. Some scientists suggest that the meteorite caused a long and unnatural drop in atmospheric temperature, while others, on the other hand, affirm that it would have caused an unusual heat wave. Some scientists propose that the meteorite impact caused extinctions both directly (by heat from the meteor impact) and indirectly (by global cooling due to the fact that matter ejected from the impact crater reflected thermal radiation from the Sun). Although the rate of extinction cannot be inferred from the fossil record alone, several models suggest that the extinction was extremely rapid, taking hours rather than years.

Deccan Traps

Prior to 2000, arguments that the Deccan Traps caused the extinction were generally tied to the theory that the extinction was gradual, as the Traps were thought to have started about 68 million years ago and lasted about two million. However, there is evidence that two-thirds of the Deccan Traps were created in a million-year period, approximately 65.5 million years ago, so these eruptions would have caused a fairly rapid extinction, possibly within a period thousands of years, but still a longer period than would be expected from a single meteor impact.

The Deccan Traps could have caused the extinction through various mechanisms, including the release of dust and sulfuric aerosols into the air, which could have blocked sunlight, reducing the photosynthetic capacity of plants. In addition, the volcanism of the Deccan Traps could have caused carbon dioxide emissions that would have increased the greenhouse effect once dust and aerosols had disappeared from the atmosphere. Before the mass extinction of the dinosaurs, the release of gases Volcanics during the formation of the Deccan Traps contributed to an apparently massive global warming. Some data indicate an average temperature increase of about 8 °C (degrees Celsius) in the last half million years before the impact [at Chicxulub.

In the years when the Deccan Traps theory was related to a slower extinction, Luis Walter Álvarez (who died in 1988), responded that paleontologists were being misled by the little data they had. Although his claim was initially not well received, subsequent intensive field studies of the fossiliferous strata reinforced his argument. Eventually, most paleontologists began to accept the idea that the mass extinctions of the late Cretaceous were due primarily, or at least in part, to a massive impact of the Earth against a bolide. However, even Walter Alvarez conceded that there were other big changes to Earth even before the impact, such as a drop in sea level and large volcanic eruptions that created the Deccan Traps in India, and that these changes could have contributed to the extinctions.

Lack of adaptation to changing conditions

By the middle Cretaceous, flowering plants became an important part of terrestrial ecosystems, which had previously been dominated by gymnosperms such as conifers. Dinosaur coprolites (fossilized dung) indicate that while some ate angiosperms, most herbivorous dinosaurs fed mainly on gymnosperms. Statistical analyzes by Lloyd et al. concluded that, contrary to previous studies, dinosaurs did not diversify much in the Late Cretaceous. Lloyd et al. suggested that the failure of dinosaurs to adapt to changing ecosystems doomed them to extinction.

Possible survivors of the Paleocene

Non-avian dinosaur remains are occasionally found in sediments above the K-T boundary. In 2000, Fassett and colleagues reported the discovery of a hadrosaur leg bone fossil in the San Juan Basin, New Mexico, and he described this single find as evidence of Paleocene dinosaurs. The formation in which the bone was discovered was dated to the early Paleocene epoch, approximately 64.5 million years ago. If the bone was not redeposited in that stratum by reworking of older materials, it would be evidence that some dinosaur populations could have survived for at least half a million years into the Cenozoic era. Other evidence includes the discovery of dinosaur remains in the Hell Creek Formation up to 1.3 meters above the K-T boundary (equivalent to 40,000 years later). Similar discoveries have come from other parts of the world, including China. However, many scientists deny that there were dinosaurs in the Paleocene, arguing that these bones were reworked, that is, that erosion took them out of their initial location and were buried again in later sediments, or they think that, even if it was true, the presence of a group of dinosaurs in the Lower Paleocene would not change much for practical purposes.

Study

Dinosaur fossils have been known for millennia, though their true nature was not understood. The Chinese, who call dinosaurs konglong (恐龍, or 'terrible dragon'), considered them to be dragon bones and documented them as such. For example, Hua Yang Guo Zhi, a book written by Zhang Qu during the Western Jin Dynasty, documented the discovery of dragon bones at Wucheng in Sichuan province. excavated dinosaur bones for decades, thinking they belonged to dragons, to make traditional medicines. Dinosaur fossils were generally believed in Europe to be the remains of giants and other creatures that perished in the Great Flood.

William Buckland

The megalosaur was the first dinosaur to be formally described, in 1677, when a portion of a bone was recovered from a limestone quarry in Cornwall, near Chipping Norton, England. This bone fragment was correctly identified as the lower end of the femur of an animal larger than anything living in modern times. The second genus of dinosaur to be identified, Iguanodon, was discovered in 1822 by Mary Ann Manto, the wife of English geologist Gideon Mantell. He recognized the similarities between his fossils and the bones of modern iguanas. Two years later, the Reverend William Buckland, professor of geology at Oxford University, unearthed more fossilized megalosaur bones and became the first person to describe dinosaurs in a scientific journal.

The study of these "great fossil lizards" became of great interest to European and American scientists, and in 1842 the English paleontologist Richard Owen coined the term "dinosaur." He recognized that the remains that had been found so far, Iguanodon , Megalosaurus , and Hylaeosaurus , shared a number of distinctive features, so he decided to group them as a taxonomic group of their own. With the support of Prince Albert of Saxe-Coburg-Gotha, husband of Queen Victoria, Owen established the Natural History Museum in South Kensington, London, to display the national collection of dinosaur fossils and other items on biology and geology.

In 1858 the first dinosaur was discovered in what is now the United States in some marl pits in the small town of Haddonfield, New Jersey (although the fossils had been found earlier, their nature had not been properly established). The creature was named Hadrosaurus foulkii, after the find's author, William Parker Foulke. It was an extremely important discovery: the first nearly complete dinosaur skeleton found, demonstrating a clearly bipedal posture (the first had been discovered in 1834 in Maidstone, England). It was an expensive revolutionary discovery, until then, most scientists thought that dinosaurs walked on all fours, like other reptiles. Foulke's discoveries triggered a wave of 'dinosaur mania' in the US. in the United States.

Edward Drinker Cope

Othniel Charles Marsh

Illustration of Marsh of 1896 of the bones StegosaurusA dinosaur he described and named in 1877.

That obsession with dinosaurs was exemplified by the great rivalry between Edward Drinker Cope and Othniel Charles Marsh who competed to see who could discover the most dinosaurs, a confrontation that later became known as the War of the Bones. The dispute probably originated when Marsh publicly pointed out that Cope's reconstruction of the Elasmosaurus skeleton had a flaw: Cope had inadvertently placed the head of a plesiosaur where the caudal end of the skeleton should have been. animal. That fight between the two scientific diggers lasted more than 30 years, ending in 1897 when Cope died after having spent all of his fortune in the search. Marsh won the competition primarily because he was better funded due to his relationship with the United States Geological Survey. Unfortunately, many valuable specimens were destroyed due to the crude methods of both paleontologists; for example, its excavators often used dynamite to unearth bones (a method modern paleontologists would find appalling). Despite their crude methods, Cope and Marsh's contributions to paleontology were enormous; Marsh discovered 86 new dinosaur species and Cope found 56, a total of 142 new species. As of 2016, Cope's collection is in the American Museum of Natural History in New York, while Marsh's is on display at the Peabody Museum of Natural History, Yale University.

Since 1897, the search for dinosaur fossils has spread to every continent, including Antarctica. The first Antarctic dinosaur to be discovered, the ankylosaurid Antarctopelta Oliveroi, was found on Ross Island in 1986, although it was not until 1994 that an Antarctic species, the theropod Cryolophosaurus ellioti, was formally described and named in a scientific journal.

Places of special dinosaur research as of 2016 include southern South America (particularly Argentina) and China. The latter in particular has given many exceptional specimens of feathered dinosaurs due to the unique geology of its fossiliferous strata, as well as an ancient arid climate especially favorable for fossilization.

"Rebirth" of the dinosaurs

The field of dinosaur research has enjoyed a surge of activity that began in the 1970s and is ongoing. This was prompted, in part, by John Ostrom's discovery of Deinonychus, an active predator that may have been "warm-blooded" (endothermy), in stark contrast to the still prevailing image of dinosaurs as slow, "cold-blooded" (ectothermy). Vertebrate paleontology became a field of global science. Important new dinosaur discoveries have been made by paleontologists working in previously unexploited regions, including India, South America, Madagascar, Antarctica, and most importantly, China (China's surprisingly well-preserved feathered dinosaurs have further cemented the relationship between dinosaurs and their living descendants, modern birds). The extensive application of cladistics, which rigorously analyzes the relationships between biological organisms, has proven extremely useful in classifying dinosaurs. Cladistic analyses, along with other modern techniques, help to compensate for the fact that the fossil record is often incomplete and fragmentary.

In popular culture

Outdated statues Iguanodon created by Benjamin Waterhouse Hawkins for the Crystal Palace Park in 1853

The battles that may have happened between the Tyrannosaurus rex and Triceratops they are a recurrent theme in popular science and the representation of dinosaurs in culture.

According to the general view, dinosaurs were fantastic-looking creatures and often enormous in size. Thus, they have captured the public imagination and have become a lasting part of the culture. Just three decades after the first scientific descriptions of dinosaur remains, sculptures of them were erected in London's Crystal Palace Park that were so popular with the public that small-scale replicas were sold, becoming one of the first examples of merchandising. of derived products. In the decades since, dinosaur exhibits have been held in parks and museums around the world, responding to and reinforcing public interest. The popularity of dinosaurs has long had a reciprocal effect on knowledge of dinosaurs as well. The competition between museums for the public's attention led directly to the Bone Wars of the 1880s and 1890s, and the resulting contribution to knowledge of these animals was enormous.

Dinosaurs hold an important place in modern culture. The word "dinosaur" It is used colloquially to refer to something very old or very big. Public interest in these reptiles led to their inevitable entry into popular culture. Beginning with a passing mention of the megalosaur in the opening paragraph of Charles Dickens's Bleak House in 1852, dinosaurs have appeared in a wide variety of works of fiction. Arthur Conan Doyle's 1912 book The Lost World, the iconic 1933 film King Kong, the 1954 film Godzilla and its many sequels, the 1990 best seller Jurassic Park and its film version, which was for a short time the highest-grossing film of all time, are just a few prominent examples of the long lore of dinosaurs in fiction. Dinosaurs are ubiquitous in advertising, and many companies try to use dinosaurs to sell their own products or to paint rivals as slow-moving, blurry, or outdated.

Dinosaurs have also appeared in cartoons, especially after the dinosauromania sparked by the George Lucas and Steven Spielberg film The Search for the Enchanted Valley. The film, which follows the adventures of a group of young dinosaurs to reach the "Great Valley", was so successful that by September 2008, twenty years after the original, twelve sequels had already been released. Other children's shows about dinosaurs were Denver, the Last Dinosaur , or Barney and His Friends , as well as the Disney Pixar feature film, A Great Dinosaur. Dinosaurs have also made appearances in Power Rangers and, more predominantly, in The Flintstones. Finally, it should be noted that the reduction in the costs associated with special effects has allowed the creation of television documentaries about dinosaurs, such as Walking Among Dinosaurs or When Dinosaurs Roamed America, that reproduce the appearance of dinosaurs with unprecedented fidelity.

The word dinosaur is used in the English language as a pejorative, to designate people, ideas, or styles that have long since become outdated. For example, members of the punk movement have mocked the style of representatives of the progressive rock movement, calling them "dinosaurs".

At the beginning of the 21st century, archaeological excavations began to be actively organized in China and Mongolia, where a multitude of other species of winged dinosaurs inhabiting the early Cretaceous period were found. This period can be conditionally called the second renaissance that followed after the first, in the 1970s. The discovery that dinosaurs were ancestors of birds and had more perfect behavior in comparison with simple reptiles again sparked public interest and influenced the work of a new generation of paleoartists.

In 2014, the Australian film Dinosaur Island was released, becoming the first non-documentary film to feature winged dinosaurs.

Religious conceptions

Various religious groups have views on dinosaurs that differ from those held by the vast majority of scientists, often due to conflicts with the Creation stories of their sacred writings. However, most of the scientific community rejects these religiously inspired interpretations of dinosaurs.

Because it is a modern term derived from Greek, the Bible does not use the word "dinosaur", but some Christians interpreted the Hebrew word tanniyn /tan ˈnin/ as a reference to dinosaurs. In Spanish translations, tanniyn can be translated as 'sea monster' or ' serpent', but it is usually translated as 'dragon'. These creatures are mentioned nearly thirty times in the Old Testament, and are said to live both on land and in water. At another time, the Bible describes a huge creature called Behemoth (Job 40: 15-24), who "keeps his tail stiff, like a cedar"; the Behemoth is described as first among the works of God and impossible to capture (v. 24). Some Bible scholars identify the Behemoth as an elephant, hippopotamus, or bull, but since these animals have very slender tails, they cannot be compared to the size of a cedar; creationists generally identify the Behemoth with sauropod dinosaurs. Other creationists refer to the Behemoth as a Brachiosaurus, as the Bible tells Job that "it is God's masterpiece", stating that it is the largest animal God created. However, some scholars they believe that the reference to cedar actually refers to its needle-like leaves, which resemble the spiky hair found on the tail of modern elephants, rhinos, and hippopotamuses. Other critics claim that the word "tail" is a euphemism. by the animal's penis, and which should be understood as a description of its virility.

The leviathan is another creature mentioned in the Old Testament; his description attributes to him a variety of characteristics of a dinosaur, a dragon, and a sea serpent. Some scholars identify Job's leviathan 41 with the Nile crocodile, or point out that it has seven heads and that it is purely mythological. As in the case of the Behemoth, creationists have sometimes attempted to associate the leviathan with the dinosaurs.

Many Muslims also acknowledge the existence of dinosaurs and other extinct animals within the limits of Islamic creationism, according to which Allah would have created "creatures of different species" (including dinosaurs) having colonized the entire Earth with them. However, they went extinct before the first human was created.