dinosaur


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dinosaur
Skeletons of various non-avian dinosaurs Top: Tyrannosaurus, Diplodocus Top middle row: Triceratops, Microraptor Bottom middle row: Stegosaurus, Parasaurolophus Bottom: Argentinosaurus, Deinonychus

Skeletons of various non-avian dinosaurs
Top: Tyrannosaurus , Diplodocus
Top middle row: Triceratops , Microraptor
Bottom middle row: Stegosaurus , Parasaurolophus
Bottom: Argentinosaurus , Deinonychus

Temporal occurrence
Upper Triassic to Upper Cretaceous (birds to the present )
235 to 66 (or 0) million years
Locations
  • Worldwide
Systematics
Land vertebrates (Tetrapoda)
Amniotes (Amniota)
Diapsida
Archosauria
Ornithodira
dinosaur
Scientific name
Dinosauria
Owen , 1842
Orders

The dinosaurs (Dinosauria, from ancient Greek δεινός deinós , German 'terrible, mighty' and ancient Greek σαῦρος sauros , German 'lizard' ) are a group of terrestrial vertebrates that lived in the Middle Ages from the Upper Triassic around 235 million years ago to the Cretaceous-Palaeogene Border dominated the mainland ecosystems about 66 million years ago .

In the traditional system , the dinosaurs are extinct as a branch of reptiles considered, although they are in the morphology of the recent differ significantly, so living reptiles and with the most recent reptiles, especially lizards and snakes are not particularly closely related. From a cladistic point of view, both reptiles ( Sauropsida ) and dinosaurs include the birds that emerged from small theropod dinosaurs .

Thus not all dinosaurs perished during the mass extinction at the end of the Middle Ages , but with the birds a special line of development of the dinosaurs survived to this day. This line has proven to be extremely adaptable and successful: the birds make up about a third of all recent terrestrial vertebrate species, are represented in all terrestrial ecosystems and, with the penguins, also have a group that is strongly adapted to life on and in the water.

In zoology , which is mainly concerned with recent animals, and especially in ornithology , however, for pragmatic reasons, birds are still regarded as a separate class and not as dinosaurs or reptiles, with which they have less in common than with mammals. The same applies to general language usage.

An informal separation of birds and dinosaurs in the classical sense is also common in modern vertebrate paleontology. In order to do justice to the cladistic point of view, the latter are also referred to as " non-avian dinosaurs ". Therefore “non-bird dinosaurs” are always meant when “dinosaurs” are mentioned in the following.

Paleontologists acquire knowledge of the dinosaurs by examining fossils , which have been passed down in the form of fossilized bones, skin and tissue prints, and from trace fossils , i.e. footprints, eggs, nests, stomach stones or fossilized feces . Dinosaur remains have been found on every continent , including Antarctica , since the dinosaurs were formed at a time when the entire mainland was united in the supercontinent Pangea .

In the first half of the 20th century, dinosaurs were considered cold-blooded , sluggish and not very intelligent animals. However, numerous studies since the 1970s have shown that they are active animals with increased metabolic rates and adaptations that allow social interactions. Dinosaurs have become a part of global pop culture and have featured in some exceptionally successful books and films such as Jurassic Park .

Description of the dinosaurs

Reconstructed dinosaur socialization at " Two Medicine " in Montana (USA)

The English anatomist Richard Owen established the taxon "Dinosauria" in April 1842. According to today's cladistic view, dinosaurs include all descendants of the last common ancestor of Triceratops and birds. Alternatively, it has been suggested to define the dinosaurs as all descendants of the youngest common ancestor of Megalosaurus and Iguanodon , as these are two of the three genera Owen named when he first described the dinosaurs. Both definitions take the same taxa to the group of dinosaurs together: the theropods (bipedal carnivores ), Sauropodomorphen (mainly large herbivores with long necks and tails), Ankylosaurier (four-legged herbivore with massive skin tanks) Stegosaurus (four-legged, bone plates bearing herbivores), Ceratopsia ( four-legged herbivores with horns and neck shields) and ornithopods (two- or four-legged herbivores).

The dinosaurs exhibited an immense variety of shapes. Some were herbivores , others carnivores ; some were quadruped , others biped , and still others, such as Iguanodon , could move in both bipeds and quadrupeds. Many had armor, horns, bone plates, shields, or sails. Although they are known to be gigantic in size, their size varied considerably; so many dinosaurs were only as big as humans or smaller.

However, this diversity of forms was in fact limited to terrestrial habitats. Only a few species show certain adaptations to life in and in fresh water. They didn't really control the airspace either (the pterosaurs are a separate group). How well the Archeopteryx , often referred to as the first bird, but still quite dinosaur-like, was able to actively fly ( i.e. generate dynamic lift ) is a matter of dispute. Accordingly, it must be assumed that its previously unknown, possibly already relatively bird-like immediate ancestors could not fly well or not at all actively. The "four-winged dinosaurs" of the Lower Cretaceous ( Microraptor , Changyuraptor ), which belong to a different line of development than Archeopteryx , could probably not fly actively, but only glide from tree to tree.

As of 2006, 527 genera of dinosaurs had been scientifically described out of an estimated total of around 1850 genera . A study from 1995 estimates the total number at 3400 - many of which, however, have not survived as fossils. On average, there are currently two new genera per month and at least 30 new species per year.

Group-specific characteristics

Compared to their closest relatives within the archosaurs ( Lagosuchus , Scleromochlus and the pterosaurs ), the representatives of all dinosaur groups are characterized by a number of common derived features (synapomorphies):

  • Skull features : the post frontal is missing; In the palate , the ectopterygoid overlaps the wing bone (pterygoid); the head of the quadratum is exposed in a side view; Reduction of the post-temporal opening (fenestra posttemporalis, an occipital opening).
  • Characteristics of the postcranial skeleton (the skeleton without the skull (cranium)): the shoulder joint socket is oriented backwards; the hand is asymmetrical with shortened outer fingers (IV and V) - these are completely absent in higher theropods ; the tibia shows a comb-like elevation (cnemial ridge) at the front upper end; the astragalus (a tarsus bone ) has an upward process; the middle metatarsal (where toe III attaches) is bent in an S-shape.

While primitive dinosaurs have all of these characteristics, the bone structure of later forms can differ greatly, so that some of the characteristics listed are no longer present or understandable.

Pelvic anatomies and gaits of different groups of terrestrial vertebrates

In addition, there are several other traits that many dinosaurs have in common but are not referred to as common derived traits because they are also found in some non-dinosaurs or are not found in all early dinosaurs. These include the elongated shoulder blade (scapula), three or more sacral vertebrae in the area of ​​the pelvic girdle (three sacral vertebrae were found in some other archosaurs, but only two in Herrerasaurus ) or an open (perforated) acetabulum (closed in Saturnalia ).

The legs of the dinosaurs stood vertically under the body, similar to that of most mammals - but different from most other reptiles, whose legs are spread outwards ( straddling gait ). Their upright posture made dinosaurs easier to breathe when moving, which likely allowed stamina and activity levels to surpass those of other spread-legged reptiles. In addition, the straight position of the legs may have supported the evolution of gigantism, as this relieved the legs.

Fossil evidence

Triceratops skeleton in New York's American Museum of Natural History

Paleontologists gain knowledge of the dinosaurs by studying fossils , with bone findings playing a prominent role - they provide important data on kinship relationships, anatomy and physique, biomechanics and much more.

The trace fossils , such as tooth prints on the bones of prey, skin prints, tail prints, and above all fossil footprints, which are by far the most common trace fossils , provide further clues, especially about the behavior of the dinosaurs . Trace fossils make it possible to study dinosaurs from a different perspective, as the animal was alive when the traces were left - while bones always come from dead animals. Further information is obtained from fossil eggs and nests, from coprolites (fossilized feces) and gastroliths (stomach stones that were swallowed by some dinosaurs to break up the food).

Evolution and systematics

origin

For a long time, many scientists thought that dinosaurs were a polyphyletic group and consisted of archosaurs that were not closely related to one another - today, dinosaurs are viewed as a separate group.

The early dinosaurs Herrerasaurus (large), Eoraptor (small), and a Plateosaurus skull

The first dinosaurs may have emerged as early as the Middle Triassic about 245 million years ago from original members of the avemetatarsal / ornithodiric line of archosaurs, as attested by the East African Nyasasaurus , which is either the earliest dinosaur or its closest known relative. The fossils of the oldest undoubted dinosaurs Eoraptor and Herrerasaurus come from the Ischigualasto Formation in Argentina, which is around 230 million years old (late Triassic) . Eoraptor is considered to be the most original representative and probably looked very similar to the common ancestor of all dinosaurs. So the first dinosaurs are likely to have been small, bipedal carnivores. This view is confirmed by the finds of primitive, dinosaur-like ornithodirs such as Marasuchus and Lagerpeton . While these genera are classified outside of dinosaurs, they were likely closely related to the common ancestor of all dinosaurs.

When the first dinosaurs appeared, the niches of the terrestrial ecosystems were occupied by different species of primitive archosaurs and therapsids : aetosaurs , cynodonts , dicynodonts , ornithosuchids , rauisuchids and rhynchosaurs . Most of these groups died out in the Triassic; so there was a mass extinction at the transition between Carnian and Norian , in which the dicynodonts and various basal archosauromorphs such as the prolacertiforms and rhynchosaurs disappeared. This was followed by another mass extinction at the transition between the Triassic and Jurassic, in which most of the other early archosaur groups, such as aetosaurs, ornithosaurs, phytosaurs and rauisaurs died out. These losses left a terrestrial fauna consisting of crocodylomorphs , dinosaurs, mammals, pterosaurs, and turtles.

The early dinosaurs likely occupied the niches vacated by the extinct groups. It used to be thought that the dinosaurs drove back the older groups in a long competition - this is now considered unlikely for several reasons: the number of dinosaurs did not increase gradually, as it would have done if other groups had been displaced; rather, their number of individuals in the Carnian made up only 1–2% of the fauna, while after the extinction of some older groups in the Norium they made up 50–90%. Furthermore, the upright position of the legs, long considered a key adaptation of the dinosaurs, was also pronounced in other contemporary groups that were not so successful (aetosaurs, ornithosaurs, rauisuches and some crocodylomorphs).

Systematics and phylogenesis

Ornithischia pelvis structure.svg
Double-jet basin of the Ornithischia
Saurischia pelvis structure.svg
Three-jet basin of the Saurischia


Simplified systematics of dinosaurs

Like most reptiles today, the dinosaurs are counted among the diapsids . These differ from the synapsids (from which the mammals emerged) and from the anapsids (today's turtles) by two skull windows arranged in pairs behind the eyes. Within the diapsids they are counted among the archosaurs ("ruler's reptiles"), which are equipped with two additional skull windows. Today's remnants of this group of reptiles are, besides the crocodiles, the birds. The dinosaurs themselves are traditionally divided into two orders, Saurischia (also lizard pelvis dinosaur) and Ornithischia (also bird pelvis dinosaur). These differ primarily in the pelvic structure . The Saurischia have retained the pelvic structure of their ancestors and can be recognized by the protruding pubis and ischium bones . The pubis and ischium bones of the ornithischia, however, both run parallel to one another and obliquely backwards.

What follows is a simplified family-level classification of dinosaurs. A more detailed list down to the genus level can be found in the article Systematics of the Dinosaurs .

Dinosauria

Evolution, paleobiogeography and paleoecology

The evolution of the dinosaurs after the Triassic was influenced by changes in vegetation and the location of the continents. In the late Triassic and early Jurassic, all continents were united to form the large land mass of Pangea , which resulted in a globally uniform dinosaur fauna, which was mainly composed of carnivorous coelophysoids and herbivorous prosauropods . Bare-seeded plants , especially conifers, became popular as a possible source of food during the Late Triassic. Prosauropods could not process the plant material in the mouth and relied on other means of breaking down food in the digestive tract. The homogeneity of the dinosaur faunas continued into the middle and late Jurassic: among the carnivorous theropods, the ceratosaurs , the spinosauroids and the carnosaurs dominated , while among the herbivores the stegosaurs , the ornithics and the sauropods were common. Important well-known fauna of the late Jurassic include those of the Morrison Formation in North America and the Tendaguru Beds in Tanzania . Faunas from China, however, already show some differences such as the specialized Sinraptoriden among the carnivores and unusual, long-necked sauropods such as Mamenchisaurus among the herbivores. Ankylosaurs and ornithopods became increasingly popular, but the prosauropods became extinct. Conifers and other groups of plants such as ferns and horsetail were the dominant plants. In contrast to prosauropods and sauropods, ornithics developed mechanisms that allowed food to be processed in the mouth. Cheek-like organs held the food in the mouth, and jaw movements could grind the food.

During the early Cretaceous Pangea continued to break apart, making the dinosaur faunas of different continents more and more different. The ankylosaurs, iguanodonts and brachiosaurids spread over Europe, North America and North Africa. Theropods such as the large spinosaurids and carcharodontosaurids were added later, especially in Africa; In addition, sauropod groups such as the Rebbachisauriden and the titanosaurs gained in importance. In Asia, maniraptors such as the dromaeosaurids , troodontids and oviraptorosaurs became common, ankylosaurs and early ceratopsians such as Psittacosaurus became important herbivores. Meanwhile, Australia became home to primitive ankylosaurs, hypsilophodonts, and iguanodons . The stegosaurs apparently became extinct in the late Lower Cretaceous or early Upper Cretaceous . A great change in the Lower Cretaceous brought the appearance of flowering plants . At the same time, various groups of herbivores were developing dental batteries, which consisted of stacked replacement teeth. The ceratopsians used the tooth batteries for cutting, while they were used for grinding, especially with hadrosaurids . Some sauropods have also developed tooth batteries; they are most pronounced in Nigersaurus .

There were three large dinosaur faunas in the Upper Cretaceous. In North America and Asia, the tyrannosaurs and various types of smaller maniraptors dominated the carnivores, the herbivores were predominantly ornithic and consisted of hadrosaurids, ceratopsians, ankylosaurs and pachycephalosaurs . In the southern continents, the abelisaurids were the predominant predators and titanosaurs the predominant herbivores. Finally, the fauna of Europe consisted of dromaeosaurids, rhabdodontids (Iguanodontia), nodosaurids (Ankylosauria) and titanosaurs. Flowering plants continued to expand, and the first grasses appeared at the end of the chalk. Hadrosaurids, which ground food and ceratopsian, which merely cut off food, became very abundant and diverse in North America and Asia towards the end of the Cretaceous. Some theropods developed into herbivores or omnivores (omnivores), such as the therizinosaurs and the ornithomimosaurs .

Feathered dinosaurs and origins of birds

The first dinosaur to be considered a bird, Archeopteryx , lived in the late Jurassic of Central Europe (see Solnhofen limestone ). It probably developed from early representatives of the maniraptors , a group of very bird-like theropods from the relatively modern subgroup Coelurosauria . Archeopteryx exhibits a mosaic of features from birds and theropods, but is so similar to theropods that at least one fossil with no clearly recognizable featherprints has been mistakenly attributed to the Compsognathus , a small non-avian dinosaur . Although the first near-complete specimen of Archeopteryx was found back in 1861, the idea that birds descended from dinosaurs did not gain general acceptance until much later, after being revisited by John Ostrom in 1970 . To date, numerous anatomical similarities between theropod dinosaurs and Archeopteryx have been demonstrated. Similarities are particularly evident in the structure of the cervical spine, the pubis, the wrist, the shoulder girdle, the fork bone and the sternum.

From the 1990s onwards, a number of feathered coelurosaurid theropods were discovered, which provide further clues to the close relationship between dinosaurs and birds. Most of these finds come from the Jehol Group in northeast China, a mighty series of sediments that is famous for its excellently preserved fossils. Some of the representatives with down-like feathers ( proto-feathers ) found in the Jehol group are relatively original coelurosaurs and not particularly closely related to birds, for example the Compsognathide Sinosauropteryx , the Therizinosauroide Beipiaosaurus and the tyrannosauroids Dilong and Yutyrannus ; the latter is by far the largest feathered dinosaur according to current knowledge (as of June 2015), which comes from the Yixian Formation (Barremium to early Aptium) of Liaoning Province. This shows that primitive plumage seems to be an original feature of theropods, or at least that of celurosaurs, and that many other theropods, of which only skeletal parts are known today, were also feathered during their lifetime, but their plumage has not been passed down in fossil form. The fact that the sediments of the Jehol group were only deposited in the Lower Cretaceous and are therefore geologically younger than the Solnhofen limestone and Archeopteryx does not change that . Finds of "feathered dinosaurs" are generally rare, which is very likely due to the fact that soft tissues such as skin and feathers only fossilize under particularly favorable conditions, as apparently prevailed in the sediments of the Jehol group and in the Solnhofen limestone. Many of the feathered non-bird dinosaurs in the Jehol group would therefore be the oldest plumed representatives of their lines of development, although all geologically older representatives of these lines and their common ancestors also had feathers.

The contour feathers so typical for birds can only be found in representatives of the coelurosaur subgroup Maniraptora, which includes the oviraptorosaurs, the troodontids, the dromaeosaurids and the birds. Proto feathers probably developed originally for thermal insulation , the contour feathers especially for optical communication with other species. The function of generating lift when flying or sailing through the air did not take over until later in evolution. In Microraptor gui , a chicken-sized dinosaur from the Jehol group, not only the arms and hands but also the legs are designed as wings fitted with contour feathers, and it is assumed that Microraptor sailed from tree to tree on these four wings . However, Microraptor , although geologically younger than Archeopteryx , is not considered a bird. Its bird-like appearance is instead based on a parallel development ( convergence ) within the Maniraptora. With Jeholornis there was also an early “real” bird in the Jehol group.

The fact that Microraptor is not regarded as a bird is not due to the fact that it was only capable of locomotion by gliding flight, but rather to its skeletal anatomy, which identifies it as a dromaeosaurid. After all, Archeopteryx's flying skills are also controversial. One hypothesis about the development of the flight ability of the "real" birds states that this has developed from gliding. The ancestors of Archeopteryx , possibly even Archeopteryx itself, would have been glider pilots as well.

Paleobiology

size

Size of known dinosaurs in relation to humans

Although dinosaurs varied significantly in size, as a group they were large. By one estimate, the average dinosaur weighed one to ten tons, the average Cenozoic mammal only two to five kilograms. Some dinosaurs were gigantic; especially the long-necked sauropods, which included the largest land animals in the history of the earth.

According to Cope's rule , in the course of the evolution of an animal group there is a general tendency to increase the size of its representatives as a result of inter- and intra-species competition . However, this alone does not explain the gigantism of the dinosaurs, unprecedented in the history of the earth and evolution. In this regard, the question arises as to why the animals became so large and how this size could be achieved. As for the why , it is believed that the sauropods' giant growth provided digestive benefits. Since sauropods did not chew their plant-based food, which was rather difficult to digest, a longer stay in an expansive digestive tract enabled more intensive use (better digestion ) of the food than with smaller herbivores. This would have allowed a specialization in very low-nutrient vegetable foods. In terms of how , a bird-like airbag system including air-filled bones ( pneumatization , especially in the skull in the case of the large theropods) made the gigantism of the dinosaurs possible. The sauropods would also have saved jaw muscles by eating without chewing, which allowed a relatively small, light head, which in turn allowed the necks to become so long, with the neck length as a characteristic, among other things, possibly subject to sexual selection , i.e. H. Males with the longest necks would have had the greatest success in mating (a form of intra-species competition). Furthermore, an increase in weight of up to 30 tons in 20 years can only be achieved in the sauropods if the metabolic rates in young animals were very high (similar to birds or mammals), but had decreased with increasing body size in order to avoid overheating ( see surface rule ; see also dinosaur physiology ).

It will probably never be possible to say with certainty which of the largest or smallest dinosaurs were. The tradition through fossils is often very incomplete, only very few dinosaurs are known to have complete skeletons - of what are probably particularly large species, mostly only bone fragments are found. Paleontologists can compare the shape and size of bones with those of better-known species to estimate the size, but this is imprecise. The weight of the animals is even more difficult to estimate, as it depends, among other things, on how a model is provided with muscles and tendons, the location of which paleontologists have to find out using muscle attachment points on the bones.

Giraffatitan in the Berlin Natural History Museum after the revision was completed in 2007

The largest and heaviest dinosaur, known for good skeletal findings, is the sauropod Brachiosaurus (also known as Giraffatitan ). A skeleton, which consists of the bones of different individuals of roughly the same size, is exhibited in the Berlin Natural History Museum and is over 13 meters high and 23 meters long; such an animal would probably have weighed 30 to 60 tons. The longest dinosaur known from complete skeletons is Diplodocus , a skeleton find shows a length of 27 meters. Even larger sauropods are only known from skeletal fragments. One of the largest dinosaurs could have been Argentinosaurus , sometimes estimated to weigh up to a hundred tons; the 33.5 meter long Diplodocus hallorum (formerly Seismosaurus ) could possibly have belonged to the longest dinosaurs together with the 33 meter long Supersaurus .

There were also giants among the carnivorous dinosaurs. The largest theropod known from almost complete skeletal finds is the approximately 12 meter long Tyrannosaurus rex , but there are also skeletal fragments here that suggest even larger genera. Perhaps the largest known theropod was Spinosaurus with a length of 16 to 18 meters and a weight of eight tons, other very large theropods include Giganotosaurus , Mapusaurus and Carcharodontosaurus .

The smallest dinosaurs were the size of a chicken - the theropods Microraptor and Parvicursor were both less than two feet long. The smaller dinosaurs ate almost exclusively carnivorous food .

behavior

Statements about the behavior of the dinosaurs are based on the keeping of skeleton finds, on trace fossils such as fossil footprints, on the habitat in which the animals lived, on computer simulations of biomechanics and on comparisons with recent animals in similar ecological niches. Many hypotheses about the behavior of dinosaurs are controversial in the specialist literature. But there is also a growing set of behavioral assumptions that most researchers agree with.

The discovery of an Iguanodon mass grave in Bernissart ( Belgium ) in 1878 gave the first indication of herd life among dinosaurs. Today, many other indications of herd life in many types of dinosaurs are known; in addition to other mass graves, many parallel tracks have been discovered. Hadrosaurids probably migrated in large herds, similar to today's springbok or American bison ; a mass grave of Maiasaura from Montana (USA) contains the remains of at least 10,000 individuals. Sauropod tracks from Oxford (England) show that these sauropods migrated in mixed herds of different species. Perhaps dinosaurs formed herds as a defense against predators, to protect the young, or for periodic migrations. Certain carnivorous dinosaurs are also often shown sociable, although they may have hunted down larger prey in a group. In any case, group hunting of the dinosaurs' closest living relatives, birds and crocodiles, is quite unusual, and alleged evidence of group hunting in the theropods Deinonychus and Allosaurus could be the result of fatal clashes between eating animals, as in common to modern reptiles.

A Maiasaura nesting site was discovered in 1978

A Maiasaura nest colony that Jack Horner discovered in Montana (USA) in 1978 shows that some dinosaurs looked after and protected their young long after they had hatched. In Mongolia in 1993 the skeleton of the oviraptorid Citipati was discovered in a brooding position over its eggs; this could indicate insulating feathers that kept the eggs warm. Other finds also show parental care. For example, in Liaoning, China, an adult specimen of the Ceratopsier Psittacosaurus was found along with 34 juveniles - the large number of offspring could indicate that the adult cared for the offspring of different individuals, similar to today's ostriches . The Auca-Mahuevo discovery site in Patagonia contained thousands of nests with eggs that are ascribed to sauropods and give evidence of large nesting colonies of these dinosaurs, similar to those of today's penguins . Sauropods, however, probably did not practice parental care, which is assumed not least because of the size of the parent animals compared to the young.

The varied crests and shields of some dinosaurs, such as those of marginocephalia , theropods, and lambeosaurines , were perhaps too fragile for active defense. It is more likely that they were used for sexual display or intended to intimidate conspecifics - but little is known about the mating and territorial behavior of the dinosaurs. Bite wounds on the skulls of some theropods suggest active aggressive confrontation, at least in these dinosaurs. Communication between dinosaurs also remains mysterious, but is an active area of ​​research. For example, recent studies have shown that the lambeosaurine head combs may have served as a resonance enhancer for a wide range of calls.

A troodontid fossil from China showed that this tiny theropod tucked its head under its arms when it slept to keep it warm; similar to today's birds. One of the most valuable dinosaur fossils for behavioral research was discovered in 1971 in the Gobi desert and contains a velociraptor that attacked a protoceratops ; the find shows the animals approximately in life. Further evidence of the hunt for live prey is provided by a partially healed tail injury to an Edmontosaurus belonging to the hadrosaurs - the tail was bitten by a tyrannosaur , but the animal survived. Cannibalism has been demonstrated in some theropods such as Majungasaurus ; in 2003 , bite marks were found in Madagascar .

New finds such oryctodromeus show that some herbivorous species seem in a building lived underground, while some bird-like species may have been arboreal as Microraptor and the enigmatic Scansoriopterygiden . However, most of the dinosaurs moved on the ground. A good understanding of the mode of locomotion is key to behavioral research, and biomechanics has made significant advances in this area. There have been studies of the forces exerted by muscles and the weight on the skeleton, which have been used to estimate how fast dinosaurs could run. It was also investigated whether diplodocids could produce a sonic boom with their tail or whether sauropods could swim. For theropods, scratch marks in the sediment of a lake have shown that they could swim.

physiology

There has been a vigorous discussion about temperature regulation in dinosaurs since the 1960s . Although the theory that dinosaurs could regulate their body temperature in the first place was originally rejected by scientists, dinosaur warm-bloodedness (endothermia) is the most common view today, and the debate has focused more on the mechanisms of thermoregulation.

When the first dinosaurs were discovered, scientists believed that dinosaurs were cold-blooded (ectothermic) animals - "terrible lizards," as their name suggests. Dinosaurs were imagined as slow, sluggish animals and compared to reptiles that have to warm up in the sun in order to be able to move actively. The notion of cold- blooded dinosaurs prevailed until Robert "Bob" Bakker , an early advocate of warm-blooded dinosaurs, published influential work on the subject.

Findings from Antarctica and Australia , where “polar dinosaurs” were found that had to survive a cold six-month winter there, provide evidence of warm-bloodedness . Finds from the Cretaceous Period in northern Alaska have only recently been made which show that the same species as in the rest of North America lived in these regions, which were already cold at the time . In addition, the skeletal structure of many dinosaurs - especially the theropods - suggests a high level of activity, which also suggests a high metabolic rate. Likewise, the blood vessel structures typical of warm-blooded animals in dinosaur bones could be demonstrated. A not insignificant number of smaller dinosaurs also had insulating plumage. It is possible that some dinosaurs were warm blooded but others were not.

The debate is complicated by the fact that warm blood can be based on more than one mechanism. Most discussions compare dinosaur warm-bloodedness to that of average-sized birds or mammals, which use energy to keep their body temperature above ambient. Small mammals and birds also have insulation in the form of fat, fur or feathers, which reduces heat loss. In any case, large animals like elephants have a completely different problem - if an animal becomes larger, the volume increases much faster than the surface of the skin (Haldane's principle). At a certain point, the heat produced by the body exceeds the heat loss through the skin, so that the animals are threatened with overheating. Especially with regard to sauropods, the theory is discussed that large dinosaurs were warmer than the environment (gigantothermal) due to their sheer size , without having had special adaptations such as mammals or birds. In 2011, researchers in Science reported that the body temperature of some large herbivorous dinosaurs was determined to be 36 to 38 degrees. At the beginning of 2020 a publication was published in which the isotope distribution in fossil egg shells was used to determine the temperature under which these shells were formed in the body of female dinosaurs. The temperature of the natural environment was determined from the isotope distribution in the shells of invertebrates, and the result was that the body temperature of the female dinosaurs was 10 to 15 ° higher than the ambient temperature.

Theropods, and probably also sauropods, had air sacs that carried air through the lungs like bellows . Since this feature is known only in birds among animals living today, it is considered to be a further indication of the ancestry of the birds from the dinosaurs. It is also interpreted as an indication that larger dinosaurs like the sauropods could have been warm-blooded, since evaporation in the air sacs is an effective cooling mechanism.

Computed tomographic examinations of cavities in the chest region of the ornithopod Thescelosaurus in 2000 showed the remains of a complex, four-chambered heart. While there is disagreement among experts as to the accuracy of the results, the presence of a four-chambered heart in both birds and crocodiles could indicate that dinosaurs also had one.

Histological studies on dinosaur bones provided evidence of close physiological parallels between female dinosaurs and birds in eggshell production. In female birds, as a result of the release of estrogen in the period before oviposition, a very calcium-rich bone substance grows in the leg bones, on the inside of the hard outer bones (cortical bones) into the medullary cavity . This bone substance is called medullary bone and is rich in proteoglycans and glycoproteins , to which the calcium ions are bound, and poor in collagen . Medullary bone serves as a reservoir in which calcium is stored, which is necessary for the formation of the eggshells. Bone substance, which is interpreted as medullary bone, was also found in the leg bones of a Tyrannosaurus rex . This suggests that calcium storage functioned similarly in dinosaurs and birds. In addition, the presence of medullary bone in fossil birds or dinosaurs can be used to identify female animals. After further research, medullary bone was also discovered in Allosaurus and the pelvic dinosaur Tenontosaurus . Since these two genera each belong to one of the two main lines of the dinosaurs, it is assumed that medullary bones for calcium storage arose very early in the dinosaur revolution and that almost all dinosaurs may have had this characteristic. The fact that this bone substance was also found in not yet fully grown animals allows the conclusion that dinosaurs reached sexual maturity relatively early in their individual development.

Soft tissue and DNA

Scipionyx skeleton with skin prints in Milan, Italy (2007)

One of the best examples of soft tissue imprints in a dinosaur fossil was discovered in Petraroia , Italy . The find described in 1998 comes from the small, very young celurosaur Scipionyx and shows impressions of various sections of the intestine, the liver, the muscles and the trachea.

In 2005, Dr. Mary Higby Schweitzer and her team presented for the first time flexible fabric material from a dinosaur that was found in a 68 million year old leg bone of a Tyrannosaurus rex from the Hell Creek Formation in Montana (USA). After rehydration, the material became elastic again, and after several weeks of treatment to remove the minerals (demineralization), intact structures such as blood vessels, bone matrix and bone fibers were found. More detailed examinations under the microscope also showed that even microstructures at the cellular level have been preserved. Thomas Kaye et al. question the results in a recently published study - according to these researchers, the alleged tissue material is bacterial biofilms . The bacteria once colonized the cavities in the bone that were previously occupied by real cells. The researchers also interpret the structures that Schweitzer interpreted as blood vessels due to their iron content as framboids - rounded, microscopic mineral structures.

Successful recovery of dinosaur DNA has been reported in two cases, but neither of these studies has been confirmed. In any case, the theoretical peptide rhodopsin of a dinosaur has already been cloned, using the genes of crocodiles and birds, the closest living relatives of the dinosaurs today, as the basis for the phylogenetic derivation of this peptide. The rhodopsin expressed and purified in cell culture was shown to be active in functional tests. Various proteins have also been discovered in dinosaur fossils, including the red blood pigment hemoglobin . The possibility of cloning dinosaurs , as in Michael Crichton's famous novel DinoPark (filmed as Jurassic Park in 1993 ), can be ruled out for the near future due to a lack of genetic information.

Life expectancy and growth rates

In the course of more than a century of research into the fossil remains of dinosaurs, much information has been gained about the neurology , possible behavior and physiology of these primeval creatures. Empirical data on individual development (for example on reaching sexual maturity and growth rates) and on general life expectancy were still largely lacking at the beginning of the 21st century. In order to estimate the age of individual individuals and, moreover, the mean life expectancy of the corresponding species, histological examinations and in particular the determination of age based on growth lamellae ( skeletochronology ) are of particular importance.

In the case of the closest living relatives of the dinosaurs, birds and crocodiles , the life expectancy of a certain species correlates with the maximum attainable body size of its individuals (the larger, the older), and experience shows that representatives of some of the largest species can get very old (sometimes more in captivity than 100 years). From this one could deduce similar life spans and a similar size correlation for dinosaurs. However, the results of histological investigations do not agree with such purely phylogeny-based conclusions; the data from recent archosaurs cannot easily be extrapolated to dinosaurs. Nevertheless, the findings from histological investigations of recent archosaurs are important for the correct interpretation of the observations made on histological sections of fossil dinosaur bones (principle of actualism ).

Recordings of histological sections of the shin bones of the theropod Aniksosaurus with clearly visible growth
lamellae (arrows)

It has been known since the 19th century that many species of dinosaur reached enormous sizes. How fast they grew, at what age they were fully grown, or whether they continued to grow until their death was unknown for a long time. Skeletochronological investigations on dinosaur bones, i.e. counting growth lamellae ( lines of arrested growth , literally: 'lines of stopped / braked growth'), which ideally indicate the age of the animal like the annual rings of a tree trunk, have now been able to rudimentarily address this gap in knowledge to fill. So it has been determined for the gigantic late Cretaceous theropod Tyrannosaurus that he grew particularly quickly in "puberty", in the second third of life (between 14 and 18 years), with a daily weight gain of at least two kilograms, and that at the age of about 20 years ago and at a weight of 5 tons the growth slowed drastically, he was in fact fully grown. Its maximum age is said to have been 28 years, so it would have been surprisingly short given its size. For smaller, geologically older representatives of the tyrannosaurids , even lower maximum ages were calculated. The life expectancy of the large Triassic " prosauropod " Plateosaurus is estimated to be at least 27 years.

Whether in a certain dinosaur taxon the strong slowdown in body growth (reaching the so-called asymptotic size or somatic maturity ) also coincided with reaching sexual maturity cannot be determined by counting growth rings alone. However, the discovery of medullary bone (a calcium-rich bone tissue in the medullary cavity of the leg bones of female birds) in various species of dinosaurs now enables the age of sexual maturity to be determined relatively clearly, at least in female individuals. Medullary bone serves as a calcium store for the secretion of calcareous eggshells and should therefore only be found in sexually mature animals. In combination with the skeletochronology for Tenontosaurus (a bird pelvic dinosaur ), Allosaurus and Tyrannosaurus (both lizard dinosaurs ), sexual maturity was determined at the age of 8, 10 and 18 years, respectively. This suggests that dinosaurs likely became sexually mature a few years before they reached asymptotic size. The fact that this pattern also occurs in medium-sized to large mammals and, above all, that dinosaurs reached sexual maturity and asymptotic size significantly earlier than modern reptiles would if they were similarly large, allows the conclusion that dinosaurs have warm-blooded amniotes like mammals physiologically - metabolically were probably more similar than recent reptiles.

die out

The Chicxulub crater after measurements of the gravity anomaly
Artist's impression of the Dekkan-Trapp volcanism (Source: NSF )

In the past 550 million years there have been five major mass extinctions , each of which resulted in at least 40% of all genera becoming extinct. Most famous is the Cretaceous-Paleogene mass extinction about 66 million years ago, in which an estimated 50% of the genera and 20% of the families disappeared, including all non-avian dinosaurs. Various hypotheses have been put forward to clarify the causes of this mass extinction. Most current theories see the cause in a meteorite impact or increased volcanism , some include both events. The rapid drop in sea level could also have contributed to the mass extinction, as the great shallow seas disappeared and land bridges formed.

In a thin, dark clay layer from the time of the mass extinction at the Cretaceous-Paleogene boundary found the physicist Luis Walter Alvarez and his son, geologist Walter Alvarez , an enrichment of the very rare elsewhere in the earth's crust heavy metal iridium (see iridium anomaly ) . In their study published in June 1980, they postulated that this iridium could have come to earth through a meteorite, the impact of which triggered the mass extinction. The hypothesis was underpinned in 1991 by the discovery of the 180 km diameter Chicxulub crater on the edge of the Yucatan Peninsula in the Gulf of Mexico , which was formed at the appropriate time by the impact of a 10 km meteorite. Various considerations have been made regarding the possible short and medium-term consequences for the ecosystems of the time . An initially strong heating of the atmosphere is assumed to be the direct consequence of the impact ("firestorm"), followed by a strong cooling, which has since been proven, because the atmosphere is darkened by dust and thus the solar radiation ( insolation ) is reduced by 10 to 20% for a few years became (" nuclear winter "), with negative effects on the photosynthesis rates of terrestrial plants and unicellular marine algae, the primary producers of terrestrial and marine ecosystems. Another direct and indirect consequence of the impact were likely severe and extremely severe earthquakes and tsunamis that occurred thousands of kilometers from the site of the impact.

Several hypotheses about the causes of the extinction are specifically related to the fact that the impact took place on a carbonate shelf platform . Their sediment sequence now houses an abundant oil deposit in the immediate vicinity of the Chicxulub crater , which probably already existed at the end of the Cretaceous period. Therefore, based on isotope studies of organic carbon from sediments of the Cretaceous-Paleogene border area, a thesis was formulated that the impact burned large amounts of petroleum. The resulting soot rose into the stratosphere and spread there worldwide. This, and not the fine rock dust ejected from the impact crater, was the main cause of the worldwide darkening and cooling after the impact. Because the mighty sediment pile of the Yucatan carbonate platform also contains anhydrite and gypsum (calcium sulfate, CaSO 4 ) , the heat of impact could have produced large amounts of sulfur dioxide (SO 2 ) and trioxide (SO 3 ), which occurred in the following weeks and months would have led to acid rain worldwide , causing acidification of soils and waters and thus considerably worsening the living conditions, especially for plants and algae. Using a computer climate model has been determined that no dust or soot, but above all durable sulfuric acid - aerosols in the atmosphere in the months after the impact of a drop in average annual global surface temperature would have caused at least 26 ° C. As a result, the earth experienced a perennial, almost global period of permafrost, with dramatic consequences for both land and marine life.

An indication of the volcanism theory is the enormous Dekkan-Trapp volcanism of the Indian Dekkan plateau, which extracted at least two million cubic kilometers of basalt ( flood basalt , Trapp ). In addition to reduced solar radiation, large amounts of carbon dioxide could have entered the atmosphere, which would have had a strong greenhouse effect . A recent study links the Chicxulub impact directly to the Dekkan-Trapp volcanism. According to this, the long “smoldering” Dekkan-Trapp recorded a new maximum of activity due to the energy released by the meteorite impact of at least 3 × 10 23 joules and the tectonic shock waves triggered by it. According to this hypothesis, the geologically short-term ejection of 70% of all Dekkan-Trapp flood basalts, reaching into the Paleogene over thousands of years, is due to this event.

The actual extinction likely happened in a relatively short period of time and "at least in North America instantly by geological standards". Although some dinosaur bones were found in 64.5 million year old Cenozoic layers and subsequently interpreted by some researchers as an indication of a slow extinction, this thesis was violently contradicted on the grounds that the bones were eroded from Mesozoic deposits and new in the Cenozoic layers has been embedded. Far more controversial is the question of whether the dinosaurs were already in decline at the end of the Cretaceous period or whether they were in full bloom. Current research has shown that the rate of new species formation in dinosaurs was already exceeded by the normal background rate of extinction 50 million years before the end of the Cretaceous Period. Exceptions to this gradual decrease in species diversity are the hadrosaurs and the ceratopsia , specialized herbivores that created numerous new species in the recent Cretaceous. Despite these exceptions, the dinosaurs as a taxon were apparently relatively vulnerable to global catastrophe at the time.

Dinosaurs and humans

Miniature sheet "dinosaur" of Deutsche Post of 4 August 2008, series "For the Youth". Plateosaurus , Tyrannosaurus , Triceratops , Diplodocus

No other group of extinct animals has such an important cultural significance as the dinosaurs. Since the dinosaurs first came into the public eye in the 19th century, they have enjoyed great interest worldwide and are so popular that there is sometimes talk of a "dinomania" that continues to this day.

Almost as well known as the dinosaurs themselves is the fact that they became extinct in a very short time. Therefore, the name dinosaur is often used as a metaphor for ways of thinking and acting or for things that are perceived as backward-looking and no longer contemporary, such as the dinosaur of the year .

Discovery story

The first dinosaur fossils were found hundreds, probably thousands of years ago, and their true nature was not recognized. In China of the Eastern Jin Dynasty , Cháng Qú (常 璩) reported in his book Huàyángguó zhì ( Chinese  華陽 國 志  /  华阳 国 志 ) in the 4th century about the discovery of " dragon bones " from the Sichuan province , which may have come from dinosaurs . Villagers in central China have been digging up dragon bones for decades to make traditional medicine. The ancient Greeks and Romans also found corresponding fossils that provided material for their legends and sagas.

Excavation activities in the Spanish fossil site Lo Hueco 2007

In 1677, manufactured Robert Plot , the first formal description of a dinosaur fossil in that near Cornwell in Oxfordshire ( England discovered) and today Megalosaurus attributed. Although he first assigned the large bones to an elephant that had come to Britain with the Romans, Plot later recognized an apparent resemblance to human bones and ascribed it to a giant of the biblical pre-flood. One of the first to know about this group of prehistoric giant reptiles and to research them was the English doctor Gideon Mantell . As early as 1822 he found the first fossil tooth, which he named Iguanodon a few years later and after other discoveries . 1824 amateur paleontologist described William Buckland with Megalosaurus first time a dinosaur in a scientific journal. The term Dinosauria was coined by another, the English anatomist Richard Owen . In 1842 he merged Megalosaurus and Iguanodon with another genus, Hylaeosaurus , into a group he named Dinosauria.

Othniel Charles Marsh
Edward Drinker Cope

In 1858, the first almost complete dinosaur skeleton was discovered in North America . This as Hadrosaurus foulkii find from described Haddonfield ( New Jersey ) showed that this dinosaur probably was bipedal, and revolutionized the public image of the dinosaurs - previously set to be dinosaurs like Megalosaurus as a huge, four-legged running, waranähnliche beings before. This discovery sparked true dinomania (dinosaur enthusiasm) in the United States.

In the years that followed, a hostility began between two famous dinosaur researchers, Edward Drinker Cope and Othniel Charles Marsh , which escalated into the famous " Bone Wars ". Perhaps the argument began when Cope received sharp criticism from Marsh for placing the skull of the newly discovered, strange marine reptile Elasmosaurus on the wrong end of the body. This marked the beginning of resentment and jealousy between the two researchers, and their argument did not end until 30 years later in 1897 after Cope's death. Each of the two opponents and his team tried to find more and more dinosaur bones than the other - by all means. They mutually destroyed many bone finds, other bones fell victim to the dynamite with which bones were then blasted free. The result of the rivalry was 142 newly discovered dinosaur species, of which Marsh contributed 86 species and Cope 56 species.

Since then, dinosaur fossils have been found all over the world: For example, the Berlin Museum of Natural History started a large expedition led by Werner Janensch to German East Africa , today's Tanzania , which unearthed unique finds such as Brachiosaurus and Kentrosaurus . Other important discoveries were made in South America , Madagascar , India , Mongolia , China and also in Germany .

Although dinosaurs were initially thought of as lively, agile animals, that picture was changed by the discoveries of Marsh and Cope; Increasingly, dinosaurs were viewed as stupid, slow, and awkward creatures. Marsh even described a sauropod as a Morosaurus ("stupid lizard") because of its head, which appears ridiculously small in comparison to its body size , but Cope's name Camarasaurus was later used . It was not until the 1970s that scientific opinion returned to the original image of lively, active animals after John Ostrom described Deinonychus and the idea of ​​a warm-blooded dinosaurs emerging. This development sparked the dinosaur renaissance, a remarkable increase in activity within dinosaur research that continues to this day. Currently, most of the new finds come from China and South America, especially Argentina .

Dinosaurs in culture

Sculpture of a Megalosaurus from 1854 in Crystal Palace Park, London

Models

Crystal Palace Park in London first aroused broad public interest in dinosaurs , where in 1853 a primeval landscape was modeled with various, life-size models of extinct animals, which can still be admired today. The sculptor Benjamin Waterhouse Hawkins , with advice from Owen, made four models of dinosaurs. The popularity of the dinosaurs in Crystal Palace Park became so great that Hawkins was hired for a similar project in Central Park , New York. However, a new administration of the park dropped this plan and the half-finished models were destroyed.

Skeletons

Since the beginning of the 19th century, the exhibited skeletons of primeval mammals have attracted a large number of visitors. A lot of money could be made with travel exhibitions that roamed the US and Europe. Therefore, soon after the discovery of complete dinosaur skeletons, they should be exhibited. In 1868 Hawkins was commissioned to assemble dinosaur skeletons ( Hadrosaurus and Dryptosaurus ) for the first time and present them to the public. There was a real rush of visitors to a New York museum . In the following decades, these new attractions in the museums banished many skeletons of other primeval animals to the museum cellars, and in Germany in 2006 relics of the Egyptians could only compete with the popularity of dinosaur skeletons.

Literature and film

From the beginning of the 20th century, the dinosaur theme became economically more important and profitable in literature and film. One of the first and one of the most famous fantasy stories is Arthur Conan Doyle's novel The Lost World ( "The Lost World", 1912), which was filmed in 1925 in many cases. Like these, many other such stories are about the discovery of a hitherto isolated area, for example in the rainforest or on an island, where dinosaurs have survived until our time.

In the cartoon series Flintstones (1960–1966), which was also very successful in Germany , dinosaurs were part of the regular inventory. Later, a number of originated Hollywood -Action- films in which the dinosaurs, however, except for some, but not all performances in films of Jurassic Park - and Jurassic World scientific findings are not shown according to series, exaggerated and. So dinosaurs were mostly ahistorically depicted as man-eating monsters, often living together with cavemen. In 1954, the award-winning Czechoslovak fantasy film Journey into Primeval Times , in which children travel deeper and deeper into the past on a river , showed the primeval animals in the correct ages for the first time.

The latest dinosaur films are often documentaries , for example the BBC series Dinosaurier - Im Reich der Gianten (English title: "Walking with Dinosaurs" ), which has been produced at great expense and tries to show dinosaurs in their habitat. Only through the modern and often elaborate three-dimensional moving graphics ( Computer Generated Imagery ) is it possible to depict these creatures in a lifelike manner. Nevertheless, in the scientific field, the artisanal, often skillful and aesthetic illustration - in the English-speaking world this discipline is sometimes referred to as paleoart - has not lost its importance. Even in large cinema productions, storyboards are always used today . After the immense economic success of the film Jurassic Park , which is listed in the Internet Movie Database 2007 as the ninth most successful film worldwide, the "actor dinosaur" also conquered the world of computer games .

A dinosaur embodied the main character of the audio book series Mit em Batino unterwägs of Zurich's traffic education, produced between 1990 and 2006 .

The ABC dinosaur Xenegugeli gives the name to the Swiss animal ABC classic as a book, song album and app by Roland Zoss .

Detail of a sound table : "D / d" for "Dinosaur"

Images of a (regular grünhäutig shown) sauropods in the style of a children's book illustration are in reading learning materials ( initial sound table ) as an example word picture in the meaning dinosaurs or dinosaur used for the letter D, for. B. in an edition used in Bavarian elementary schools in 2014 . This implies that today the term “dinosaur” combined with the icon of the sauropod is generally assumed as part of the receptive vocabulary of German-speaking school beginners .

In April 2016, images of the heads of three dinosaur taxa considered exemplary were proposed for inclusion as emojis in the Unicode standard. In the proposal document, the heads of Tyrannosaurus rex and Brontosaurus ("Bronto") are shown as green-skinned, while those of Triceratops are brownish.

Private collecting and trading

Auction houses auction a handful of dinosaur skeletons every year.

See also

Portal: Dinosaurs and Relatives  - Overview of Wikipedia content on the topic of dinosaurs and relatives

literature

Web links

Wiktionary: Dinosaurs  - explanations of meanings, word origins, synonyms, translations
Commons : Dinosaur  album with pictures, videos and audio files

In German

In English

photos

  • Skeletal Drawing (pictures of the anatomy of the dinosaurs created by the paleontologist Scott Hartman)

Individual evidence

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This version was added to the list of articles worth reading on February 18, 2006 .