Theropoda
| Theropoda | ||||||||||||
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Life picture of Daspletosaurus torosus from the late Upper Cretaceous North America |
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| Upper Triassic to Upper Cretaceous ( Norium to Maastrichtian ; birds up to now ) | ||||||||||||
| 228 to 66 (or until today) million years | ||||||||||||
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| Theropoda | ||||||||||||
| Marsh , 1881 |
The Theropoda ( Greek θήρ thēr 'wild animal', πούς poús 'foot', Germanized Theropods ) are a systematic group (taxon) that is traditionally assigned to the lizard basin dinosaurs (Saurischia). They moved on two legs and were mostly carnivores . Conversely, almost all carnivorous dinosaurs belonged to this group, including the largest land-dwelling carnivores of all time with lengths of around 15 meters. However, many theropoda were small compared to other dinosaurs, often measuring only 2 to 6 meters.
From a cladistic point of view, the theropods also include the birds that have evidently emerged from non-flightable theropods in the Jura . According to this, the theropoda (and thus the dinosaurs) not only survived the mass extinction at the end of the Cretaceous period , but also currently represent over a third of all recent terrestrial vertebrate species, represented by over 10,000 living species of modern birds . However, the following article is largely limited to fossil representatives of the Mesozoic Era that did not belong to birds (“non-avian theropods” in the sense of the English neologism non-avian theropods ).
In the course of the popularization of the dinosaurs from the middle of the 19th century, numerous live reconstructions of well-known theropod genera such as Megalosaurus , Tyrannosaurus , Allosaurus , Deinonychus and Velociraptor were created , which have shaped the public image of the Theropoda ever since.
features
General
The Theropoda in their general physique retained the original physique of the dinosaurs and their ancestors in many respects. Compared to other dinosaur groups such as the Sauropodomorpha or the Ornithischia , they showed little specialization. Theropods were consistently biped , so their locomotion took place exclusively with the hind legs, which were therefore longer than the front limbs in all theropods. The front legs were unusable for locomotion, which corresponds to the original posture of the dinosaurs.
The Theropoda had the greatest diversity within the dinosaurs in terms of body size. Many were relatively small, some representatives such as Microraptor and Parvicursor measured less than a meter and weighed only a few kilograms. The largest theropods, however, could reach lengths of up to 15 meters, including Tyrannosaurus , Carcharodontosaurus , Giganotosaurus and Spinosaurus . However, sizes are often hypothetical, as many of their representatives only found very incomplete skeletons. Weight estimates are generally difficult for extinct animals; the weight of the largest theropods is estimated to be 5 to 8 tons.
skull
The Theropoda usually had a relatively large skull . Compared to other dinosaurs, the construction of the skull is rather unspecialized and shows little changes compared to the primitive skull of the Archosauria (" triapsid skull "). As with all Archosauria addition to the Diapsiden typical two cranial windows behind the eye socket an additional skull opening in front of the eye socket (Präorbitalfenster or Antorbitalfenster) available, resulting in a lighter, clasp-like skull structure. An evolutionary innovation ( synapomorphism ) of the Theropoda is the lacrimal bone (os lacrimale) reaching up to the top of the skull and an additional antorbital opening, the maxillary window. The eyes of the theropods were comparatively large, especially those of the Coelurosauria , and some of them were oriented forward - as with many carnivores. The improved spatial vision enabled a more precise estimate of the distance to possible prey. The middle ear cavity was also often greatly enlarged. From this it can be concluded that the Theropoda had a comparatively good sense of sight and hearing. Another synapomorphy of the Theropoda is the construction of the articular knot on the occiput (condylus occipitalis), which together with the atlas forms the upper head joint . This is large and round and thus ensures increased mobility of the head - presumably in combination with strong neck muscles. The theropod skull also shows a certain mobility of the individual elements to each other ( skull kinesis ), which facilitated the devouring of larger prey, since the theropods could not chew their food to chew.
Some representatives of the Theropoda had cranial crests or horn-like outgrowths on the top of the head. These outgrowths differed significantly in their construction, sometimes they were very fragile - like the combs of Dilophosaurus or Oviraptor - sometimes very robust - like the horns of Ceratosaurus or Carnotaurus . These skull structures presumably played a role in the interaction with conspecifics.
teeth
The theropod's teeth were flattened on the sides and curved slightly backwards. They also had a serration on the leading edge - that is, with small spikes that were roughly at right angles to the cutting edge - and therefore very sharp. The shape of the serration along the incisal edge differed between groups. Many smaller representatives had small, pointed spikes that were suitable for tearing activities, while in the Tyrannosauridae , for example, the serrations were more rounded and blunt. The structure of the teeth, however, is primeval, the same pattern can be found, for example, in representatives of the Crurotarsi , basic crocodile ancestors . The teeth of the closely related prosauropods also show a serration of the teeth, but the notches are at an angle of about 45 ° upwards to the cutting edges or run in different directions.
From the structure of the teeth it can be seen that most theropods were carnivores. They used their teeth to grab their prey, to kill and also to tear the pieces of meat; the more blunt teeth of some representatives could also have been used to crush bones. The herbivorous therizinosaurs, on the other hand, had small, spatula-shaped teeth.
Several times in the history of the development of the Theropoda there has been a loss of teeth. This concerns on the one hand the Ornithomimosauria (whose most original representatives however still had the foremost teeth of the lower jaw), and on the other hand the Oviraptorosauria . What exactly these toothless theropods ate is controversial; see the section on nutrition . Even modern birds - unlike many of their Mesozoic ancestors - are toothless.
Trunk skeleton
As with all dinosaurs, the hind limbs were placed vertically under the body, the body was balanced directly above the pelvis . The spine was kept almost horizontal; In order to still allow a good view to the front, the neck was bent in a bird-like S-shape - older reconstructions show the Theropoda with a downwardly inclined spine and a tail dragging on the floor, which, according to recent findings, might be wrong. One synapomorphism (a commonly derived trait) of the theropods was that there were five or more sacral vertebrae . The tail was usually long and had a large number of caudal vertebrae. In the Tetanurae ("stiff tails"), the more species-rich of the two subgroups of theropods, the tail was stiffened and was held more or less horizontally above the ground.
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This stiffening was achieved on the one hand by the fact that the tail vertebrae were connected by long bone rods ( zygapophyses ) reaching forwards and backwards and on the other hand by chevron bones (V-shaped appendages on the underside of the caudal vertebrae). In modern birds, the last caudal vertebrae have grown together to form a pygostyle ; a similar structure is also found in some non-avian theropods such as Nomingia and Beipiaosaurus . However, these are likely to be convergent developments.
The skeleton of the Theropoda is characterized by the fact that the long limb bones are thin-walled and hollow, and the vertebrae are also hollowed out. The vertebrae were already pneumatized in basal representatives like Majungasaurus , that is, partly filled with protuberances (diverticula) of an air sac system . Similar finds were also made at Mirischia . This is an indication that at least the Theropoda (but possibly also other dinosaurs) had a respiratory system similar to that of birds, with a permanent, unidirectional air flow in that part of the lungs where the main part of the gas exchange took place ("flow-through lung").
limbs
The shoulder area of the theropods was characterized by a strap- like shoulder blade . In addition, there was usually a boomerang-shaped fork leg (furcula) - which was once seen as a pure bird feature. A fork bone is already known from basal representatives such as the Coelophysoidea .
In the construction of the pelvis , as with all pelvic dinosaurs (Saurischia), the pubic bone (Os pubis) originally protruded forwards. In the course of the development of the Theropoda there has been a rotation, with the Deinonychosauria it points downwards and with the birds it finally points backwards. The basin of today's birds is confusingly similar to that of the bird basin dinosaur , the second subgroup of dinosaurs. Nevertheless, birds evolved from lizard pelvis and not from bird pelvic dinosaurs, the similarity is only superficial.
Synapomorphies of the Theropoda in the structure of the forelimbs were, on the one hand, the enlarged hand, which makes up up to 50% of the length of the entire arm, and, on the other hand, a tendency for the fourth and fifth fingers to recede to their complete absence. The hand thus typically consisted of rays (finger, digiti) I, II and III (counted from the thumb), with the first ray being partially movable, i.e. semi- opposable . In the Tyrannosauridae , the third finger was also regressed and Alvarezsauridae like Mononykus ("a claw") only had a well-developed finger beam. The remaining fingers were greatly elongated and, thanks to large indentations at the top of the front end of the metacarpal bones, extremely mobile. Many Theropoda, often the smaller representatives, were characterized by long arms with large hands and slender fingers. In these animals, the gripping function of the hand - including catching prey - played a major role. (In birds, the arms are particularly heavily modified to adapt to flying, so they have a carpometacarpus made of fused carpal and metacarpal bones.)
In contrast, some large theropods such as the Abelisauroidea and the Tyrannosauridae exhibited greatly reduced forelimbs. The arms of these animals were so short that they couldn't even reach their mouths - they were certainly of no importance in the hunt. The question of the function of these reduced arms has not been fully clarified. According to one theory, this feature is biomechanical : In order to maintain balance due to the greatly enlarged and therefore heavier head, the arms had to be made smaller. It is noticeable that these short arms were very strong and muscular. Possibly they were used to straighten up from the assumed sleeping position (lying on your stomach). Other theories, however, see their function in holding the partner tight during the mating.
The hind limbs were always longer than the front limbs. Most of the time, the lower leg was longer than the thigh (particularly in the Troodontidae and Ornithomimosauria ), which suggests that these animals could achieve high speeds. The foot was characterized by a compact, narrow and usually elongated middle foot (metatarsus) - with the mesotarsal ankle joint, which characterizes the ornithodira (dinosaurs and pterosaurs) . Toes II, III and IV were symmetrically directed forward and had a characteristic number of phalanges (phalangeal formula 3, 4, 5). These toes were the walking toes, because the inner, first toe was only short and did not touch the ground and the outer, fifth toe was reduced to a small bone. The typical theropod foot was therefore functionally tridactyl. In modern birds, the first toe usually points backwards ( anisodactyly ), but other toe arrangements have also developed in this group.
The toes ended in sharp claws or claws made of horn that sat on pointed, curved bone cones. A peculiarity developed within the Deinonychosauria . Here the second toe was equipped with a particularly large and sharp claw and also had a special joint. This made it possible to lift the toe when moving (functional didactyly) in order to avoid wear and tear, and a high degree of mobility when hunting. The bipedal and three-toed ornithopods from the group of bird's pelvis dinosaurs lack long claws, which is important for the assignment of fossil footprints .
Integument and thermoregulation
Probably the most drastic change in the theories about the appearance of the Theropoda concerned the integument , i.e. the skin. In Sinosauropteryx 1996 Bird theropods no-signs were a first time in a spring dress discovered in the following years were more feathered dinosaurs described one plumage are known around 15 representatives signs so today. Different types of feathers - from simple, hair-like structures to contour feathers - are known. (Feathers rarely fossilize as a soft structure, these finds have so far been limited to a few sites.)
Most of the feathered theropods show no signs of adapting to flight in their physique, so that the plumage was originally probably used for thermoregulation . It is also conceivable, however, that the plumage would later take on other functions, for example privacy protection or signaling when communicating with fellow species.
According to the theories of Richard Prum and Alan Brush, the springs have gone through five stages of development (see also evolution of the spring ):
- In the first step, simple, cylindrical, hair-like hollow rods were formed.
- In a second step, tufts of elongated threads were created, which sat on a common quill (calamus). These tufted feathers resembled the down of today's birds, but did not yet have any secondary branches.
- In the third step, two types of springs were developed. On the one hand, these are the earliest contour springs with spring branches sitting on the spring shaft - but still without the toothing. On the other hand, the tufted feathers with secondary rays were also created, which are still found today in the form of down .
- The fourth step consisted in the development of a cover spring with interlocking arc and hook rays. This resembled the contour feather of today's birds, but in contrast to it was still symmetrical.
- In a fifth step, the asymmetrical feather found in today's birds with an outer and an inner vane was developed.
Further investigations have led to presumed correspondences between the development of the feather and the general development of the theropods (see cladogram in the systematics section ). The Coelurosauria are likely to have been equipped with a plumage, which corresponds to the fact that Sinosauropteryx (which is classified as Compsognathidae and thus as a basal Coelurosaur) had simple feathers of type 1 or 2. Signs of these simple feathers were also found in Dilong , an ancient representative of the Tyrannosauroidea . Feathers of type 2 or 3 were found in the therizinosaur Beipiaosaurus , and those of level 4 in the oviraptorosaur Caudipteryx . In the Deinonychosauria , signs of the asymmetrical feathers of type 5 have already been discovered in Microraptor , which were also discovered in the earliest bird Archeopteryx .
The question of whether the dinosaurs were generally warm-blooded or cold -blooded has not yet been finally clarified (see also warm-blooded dinosaurs ). Since the discovery of the feathered dinosaurs, it has been assumed that at least in the feathered coelurosauria there was some kind of internal temperature regulation and that thermoregulation was almost as effective as that of birds in the more highly developed theropods . Other theropods may, in the opinion of some paleontologists, have developed a different method of thermoregulation: the elongated vertebral processes of some theropods such as Spinosaurus and Acrocanthosaurus may have supported a back sail that served this purpose. However, these views are controversial.
According to some researchers, however, the largest Coelurosauria such as Tyrannosaurus may not have had feathers. In large animals, the ratio of surface area to volume is smaller than in smaller ones. Since the heat escapes through the surface of the skin, larger animals are more at risk of overheating, as plumage hinders the heat dissipation. (For the same reasons, even the largest mammals such as elephants and rhinos are almost hairless.) This scheme also fits that within the (feathered) Coelurosauria there were no longer any giant forms with the exception of the Tyrannosauridae .
What the skin of the non-Coelurosauria within the theropods looked like is not known exactly. One representative, Carnotaurus from the Abelisauroidea group , showed signs of scaly skin.
Paleobiology
distribution and habitat
The theropods were spread all over the world, fossil finds are known from all continents - with Cryolophosaurus also from the Antarctic. The early worldwide distribution is related to the fact that at the time of the development of the theropods all continents were still connected in the great continent of Pangea . Since the breakup of this continent, different theropod faunas have developed on the individual land masses. The Abelisauroidea are known almost exclusively from the former southern continent Gondwana , while other groups such as the Tyrannosauroidea are only known from the northern continent Laurasia . Since fossil finds are generally rarer in the southern hemisphere, no precise information on the area of distribution can be made for many theropod taxa.
There is also an enormous range of places where the theropods are deposited. In addition to river beds, floodplains and the vicinity of lakes, finds were also made in places that suggest a dry, desert-like habitat. A habitat preference of the theropods as a whole group is - if it exists at all - not known.
Social behavior
Speculations about the social behavior of Theropoda are, as with all animals known only from fossil finds, difficult. Even finds of the remains of several animals in one place do not have to indicate a group life, but can also be due to deposition technology. Most of the finds come from individual animals. However, there are two representatives in which mass concentrations of hundreds of animals have been discovered: Coelophysis in Ghost Ranch, New Mexico and Allosaurus in Cleveland-Lloyd Quarry ( Utah ). The interpretation of these mass finds is controversial, in addition to an interpretation as an indication of hunting in groups, the possibility that it was about dwindling water sources, where many animals have gathered and finally died of thirst, are considered; or that it was a trap of some kind that attracted the animals and from which they could no longer escape. Finds of several Deinonychus , among other things in connection with the possible prey animal Tenontosaurus , were regarded as an indication of hunting in groups.
The above-mentioned ridges and outgrowths on the top of the skull probably played a role in the interaction with conspecifics. While the fragile crests of many animals probably served no other purpose than display, it is conceivable that the more robust horns were used for direct fighting. Whether it was about the mating privilege, the establishment of a group hierarchy or other purposes, must remain speculation.
Some theropods show signs of sexual dimorphism . For example, there are two forms of some Coelophysoidea , one with a long head and neck and more powerful limbs, and another with a short head and slimmer limbs. This could be a slightly different physique for males and females. There could also have been similar differences between the sexes in Tyrannosaurus . The more robust form is identified as females due to the wider basin.
Locomotion
As mentioned at the beginning, the Theropoda moved only with the hind limbs. Only the toes touched the ground, so they were toe walkers (digitigrad). From Ichnofossils (fossil footprints) shows that the hind legs were kept under the body. The step width was very narrow, one foot was often placed in front of the other. The legs could only be moved in one plane (forwards-backwards). Due to the construction of the joints, it was not possible for the Theropoda to rotate the limbs outwards, as mammals can.
There have been various attempts to calculate the speeds of dinosaurs using skeletal structures and Ichnofossils, for example by Robert McNeill Alexander and RA Thulborn. According to these calculations, the smaller theropods could have reached up to 40 km / h, the ornithomimosauria even up to 60 km / h. Lower speeds are assumed for larger Theropoda, but these calculations are controversial.
With some Deinonychosauria like Microraptor it is conceivable that they could also climb trees and do gliding flights.
Brain size
The Theropoda are the dinosaurs with the comparatively largest brains. JA Hopson developed the encephalization quotient (EQ) to calculate the size of the brain . This is a calculation method that works with the size of the skull cavity and allometric factors - larger living beings have comparatively smaller brains than smaller ones. The crocodiles , whose EQ = 1, is used as a comparison value . All theropods have an EQ> 1 (for comparison: among the dinosaurs only some representatives of the ornithopods have an EQ> 1, all other dinosaurs are below. Sauropodomorpha have the smallest EQ , followed by ankylosauria and stegosauria ). Within the Theropoda, the Dromaeosauridae have the highest EQ with 5.8, a value that is comparable to ostriches .
nutrition
The Theropoda were the only group of dinosaurs (with the possible exception of a few primeval representatives, see below) to eat mostly meat. Due to the wide range of body types and sizes, they have undoubtedly developed different nutritional strategies. Isolated fossil finds such as bite marks or coprolites sometimes allow conclusions to be drawn about the diet, but in many cases the type of prey acquisition and the question of possible prey remains speculative. D. Fastovsky and JB Smith have identified five morphotypes of carnivorous theropods. This is not a relational classification, which is why the types are not given names.
- Morphotype 1 includes the extremely large representatives with a length of over 10 meters. This type has a tendency to have a large skull, short forelimbs and a reduced number of fingers; well-known examples from this group are Tyrannosaurus , Tarbosaurus , Carcharodontosaurus and Giganotosaurus . This type includes what is known today as the largest land-dwelling carnivores of all time; there are no modern analogies to these animals. Their diet is often controversial, with some representatives, especially the Tyrannosauridae , it is discussed whether they were scavengers or whether they killed their prey themselves. Some of the clues that might speak in favor of a scavenging diet include the broad teeth, which were suitable for crushing bones, and the structure of the limbs. In contrast to most of the other Theropoda, the upper and lower legs were almost the same length, which suggests slow movement.
- Morphotype 2 includes the medium-sized, around 3 to 8 meter long theropods. They also had a rather large skull, compared to type 1 the hind limbs were slimmer and the lower legs were significantly longer than the thighs. The hands were also often well developed. Examples of this type are Allosaurus , Albertosaurus , Dilophosaurus , Ceratosaurus and Carnotaurus . The representatives of this type were almost certainly active hunters, speculations are in the direction of large prey, for example, sauropods .
- Morphotype 3 includes rather small theropods (2 to 6 meters in length). The skull was large, the eyes fixed forward. They had long arms and large hands with three grasping fingers, they were slim and their tails were noticeably stiff. On the specialized second toe, they had a sharp, flexible claw. Examples are Deinonychus , Troodon , Velociraptor or Utahraptor . According to John H. Ostrom, these are “ultimate killing machines” . These animals are likely to have been fast runners and agile, skillful hunters, and they may also have caught prey in groups. For this type there are concrete references to the prey animals, including the famous "fighting dinosaurs" (A Protoceratops is attacked by a Velociraptor , both animals died in battle, possibly by a sandstorm.)
- Morphotype 4 also includes rather small animals, 2 to 6 meters long. Like type 3, they had a slim build and long arms with large hands, but differed in their smaller skull and comparatively short hind limbs. Representatives of this type are among others Coelophysis , Compsognathus or Megapnosaurus . The type 4 animals were also active hunters, who presumably fed on small animals such as lizards , therapsids (including mammals ) or insects . The remains of a lizard found in the abdominal cavity of a Compsognathus and the fossils of small animals in the abdomen of Coelophysis , which for a long time were mistaken for its young, provide concrete evidence .
- The animals of morphotype 5 are also rather small (2 to 6 meters). Its most striking feature is the toothless, lightly built skull. Her body was slim, her arms were long and her large hands had three grasping fingers. The Oviraptorosauria belong to this group . The physique clearly indicates active hunters (they resemble Type 3 except for the toothlessness and lack of toe claw), but what these animals ate is uncertain. The beak is unsuitable for the original hypothesis that they fed on eggs. Other theories interpret the beak as a tool for cracking clams , but this is controversial as no evidence of water has been found in many fossil sites. Ultimately, the diet of these animals remains unclear, assumptions are in the direction of lizards, mammals and other small animals.
The Spinosauridae represent a special case within the carnivorous Theropoda . Their teeth are conical, with the foremost teeth being greatly enlarged. Due to the similarities with crocodiles , it is assumed that some of these animals ate large fish. In fact, fish scales and remains of a young iguanodon were found in the abdominal cavity of Baryonyx , suggesting a mixed diet of fish and land animals.
Although the great majority of theropods were carnivores, two groups have developed in which, in contrast to the others, a plant-based (herbivorous) diet is assumed:
- The ornithomimosauria were toothless except for a few basal representatives, their mouth ended in a bird-like beak. Their build was slim and geared for high speeds, their forelegs weak, but possibly suitable for pulling branches. With them were Gastrolithen (stomach stones) found. Conjectures about the diet of these animals go in the direction of herbivores or omnivores, similar to today's ostriches , with which they are often compared. However, some researchers have also discovered evidence of a comb-shaped structure in the beak, which could be a sign of filtering food intake. This would be consistent with the majority of ornithomimosaurs being found near freshwater habitats. However, these finds are controversial.
- The second herbivorous theropod group were the therizinosauria . They had small, spatula-shaped teeth, the hands were noticeably large and had long claws. The pelvis was turned caudally (back), which enlarged the trunk, which created more space for a long digestive tract. Their presumed way of life is sometimes compared to giant sloths. Presumably they pulled branches with their long claws to get at the food.
Reproduction and development
Like probably all dinosaurs and also today's birds, the theropods lay eggs. Several skeletons of representatives of the Oviraptorosauria have been discovered over nest. In the past, the animals were thought to be egg-eaters, hence the name, which means “egg thief”. Today, the findings are interpreted as meaning that the parents incubated the eggs. The nests consisted of up to 22 eggs, the adult animal was positioned above the center of the nest and held its arms around the nest. Other fossil nests were also found, but they cannot be assigned to any particular group.
The development of the Theropoda is characterized by a presumably relatively rapid growth, the size of the hatchling to the adult animal increasing by 10 to 15 times. The young animals also differed in their physique; so they had different skull proportions with smaller jaws, a shorter neck and longer hind legs. Finds of young animals are known only from a few representatives, for example from the Coelophysoidea Megapnosaurus and Coelophysis or from Tyrannosaurus , so that much information about the development must remain very vague.
Systematics
External system
The Theropoda were described with a stem-based definition as "all taxa that are more closely related to Passer domesticus [= house sparrow] than to Cetiosaurus oxoniensis [a sauropod]" . Within the dinosaurs, they are traditionally classified in the group of lizard dinosaurs (Saurischia), which also includes the sauropodomorpha . This descent can be shown in the following cladogram :
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There are some primeval dinosaurs such as the Eoraptor and the Herrerasauridae (with Herrerasaurus and Staurikosaurus ), whose systematic classification is controversial. There are studies with different results for these early representatives from the early Upper Triassic , so they are sometimes considered to be outside the dinosaurs, sometimes as the basal representatives of the theropods and sometimes as the basal representatives of the pelvic dinosaurs. A phylogenetic study by Max C. Langer classifies these controversial species as the lizard dinosaur, but sees the Theropoda as more closely related to the Sauropodomorpha than with them, which is why they are classified as basal lizard dinosaurs (and not as theropods). Due to the incomplete material, there is no consensus on this systematic question.
In 2017, a fundamentally new phylogenetic system of dinosaurs was proposed. According to this hypothesis, the Theropoda are no longer assigned to the Saurischia, but together with the bird pelvic dinosaurs form the Ornithoscelida, the sister group of the lizard dinosaurs:
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Internal systematics and history of development
If the controversial representatives mentioned above are counted among the theropods, as described by Sereno et al. suggested, then the remaining theropods are considered to be the sister group of these representatives and are summarized as Neotheropoda .
Apart from that, the Theropoda can be easily divided into two groups, the Ceratosauria and the Tetanurae . The Ceratosauria represent an early split, here again two taxa are distinguished. On the one hand, there are the Coelophysoidea , a group of smaller dinosaurs that were widespread in the Upper Triassic and Lower Jurassic and, apart from the controversial groups, are the oldest theropods. The second taxon of the Ceratosauria are the Neoceratosauria . In addition to early representatives such as Ceratosaurus , these include the Abelisauroidea , which in the Cretaceous period was one of the dominant predators on the southern continents that emerged from the great continent of Gondwana . The systematics within the Ceratosauria is not undisputed, it is also unclear whether they are monophyletic .
The Tetanurae ("stiff tails", due to the caudal vertebrae connected by bone rods and thus stiffened) are a well documented, probably monophyletic group that first appeared in the early Jurassic. Apart from a few basic representatives, two lines of development can be recognized within the Tetanurae, the Spinosauroidea and the Avetheropoda . The Spinosauroidea (or Megalosauroidea), whose association was only recognized in 1998, are divided into the Megalosauridae - a taxon of medium-sized Theropoda from the Jurassic, which includes Megalosaurus and Eustreptospondylus - and the Spinosauridae , a group from the Cretaceous Period crocodile-like elongated head, some of whose representatives may have fed on fish.
The Avetheropoda or Neotetanurae are characterized by an additional window in the upper jaw and by other features in the skull, pelvis, and caudal vertebrae. They are divided into two sub-taxa, the Carnosauria and the Coelurosauria . These two terms were previously used to roughly divide the Theropoda into larger and smaller representatives; in modern systematics they denote restricted, more precisely defined taxa. The Carnosauria are relatively large Theropoda and are characterized by enlarged nostrils, they comprise three larger groups. These are the Sinraptoridae , which are mainly attested to from the late Jurassic in Asia, the Allosauridae , including the well-known Allosaurus , and the Carcharodontosauridae , to which some of the largest known theropods are counted with Carcharodontosaurus and Giganotosaurus .
The Coelurosauria are the taxon in which, according to fossil records, the development of feathers began. Within this group, the Compsognathidae , a group of very small animals from the Upper Jurassic and Lower Cretaceous, represent the sister group of the other representatives. In addition to some basal representatives such as Ornitholestes , the Coelurosauria also include the Tyrannosauroidea , the Ornithomimosauria and the Maniraptora . The Tyrannosauroidea, whose best-known representative is Tyrannosaurus , were partly very large theropods, in which the later representatives were characterized by a massive head and short forelimbs. The ornithomimosaurs formed a taxon of ratite-like , presumably herbivorous or omnivorous dinosaurs.
The Maniraptora are characterized by the mostly greatly elongated forelimbs and hands. They include the Oviraptorosauria , the Therizinosauria , the Deinonychosauria and the birds (Aves or Avialae). The Oviraptorosauria form a taxon of mostly toothless dinosaurs, the Therizinosauria or Segnosauria had very elongated claws on the forelegs and probably ate plants. The Deinonychosauria were rather smaller, predatory animals, which were characterized by a large claw on the second toe and to which Velociraptor and Deinonychus are counted. From a phylogenetic point of view, birds also belong to the Maniraptora. Controversial within the Maniraptora is the position of the Alvarezsauridae , which combine bird-like with primeval features, but are not easy to classify due to their specialized, greatly shortened arms.
The Theropoda classification is neither complete nor undisputed. Many groups are covered by weak matches, and new discoveries can provide new insights that require rearrangement. Different researchers have opinions and classification systems that differ greatly from one another. A possible theropod cladogram looks like this:
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The oldest undoubted Theropoda - the Coelophysoidea - appeared in the Upper Triassic in the Norium (about 228 million years ago). From this point in time the theropods are known from almost the entire Mesozoic era , the non-avian theropods became extinct with the mass extinction of the dinosaurs at the end of the Cretaceous Period . (For discussions of the reasons for this extinction, see Cretaceous-Tertiary Boundary and The Extinction of the Dinosaurs .)
The evolution of birds
The great majority of researchers assume that birds in the cladistic sense are theropods and thus dinosaurs . This means that some theropods, such as the Deinonychosauria, are more closely related to the birds than to the other representatives of this group and that the theropods without the birds are a paraphyletic group, i.e. do not include all descendants of a common ancestor. Many features that occur only in birds within recent animals (for example feathers , the forkbone or hollow, pneumatized bones) are also found in some or even all Theropoda. In the course of their development, the birds have developed significantly in some traits - especially in connection with flight ability - for example in the sternum with a keel or in the fusion of the metacarpal bones to the carpometacarpus . Numerous forms of mosaic are known - especially from the Cretaceous period - that make this gradual development clear, for example the "primeval bird" Archeopteryx , Confuciusornis , the Enantiornithes and a few others. Some taxa such as the Oviraptorosauria or the Alvarezsauridae , which are usually counted among the non-avian theropods, are included in the birds in some classifications.
A minority of researchers, including the paleoornithologist Alan Feduccia , is of the opinion that birds did not evolve from theropods, but from a basal group of archosauria , and that some bird-like theropods are not theropods, but rather flightless birds adapted to continuous locomotion. Due to the numerous anatomical similarities, however, the majority of scientists assume a theropod ancestry.
Theropoda and humans
History of discovery and research
Part of a thigh bone - presumably from Megalosaurus - was found as early as 1677, examined by Robert Plot and mistaken for the bone of a giant. At the beginning of the 19th century, further remains of this genus, including a jaw fragment with teeth, were found, and were first scientifically described by William Buckland in 1824 as Megalosaurus . In 1842 Richard Owen coined the term Dinosauria for this and two other genres.
In the middle of the 19th century, the next theropods were discovered with Troodon in North America and Compsognathus (and Archeopteryx ) in Solnhofen (Germany). The " Bone Wars ", a dispute between the paleontologists Edward Drinker Cope and Othniel Charles Marsh at the end of the 19th century, brought further representatives of this group to light, as Cope described Coelophysis and Marsh Allosaurus , Coelurus and Ceratosaurus . In 1881 Marsh coined the term Theropoda ("animal feet"), initially for all known dinosaurs from the Triassic and the carnivorous dinosaurs from the Jurassic and Cretaceous . At the beginning of the 20th century, other finds were made, including Tyrannosaurus and Albertosaurus in North America, Elaphrosaurus in Tendaguru (Tanzania) and Spinosaurus and Carcharodontosaurus by Ernst Stromer von Reichenbach in Egypt.
Systematic studies by Friedrich von Huene appeared in 1914 and 1920 . This divides the Theropoda into two groups, the small "Coelurosauria" and the large "Carnosauria". This system was valid until the 1980s, but is now considered obsolete, but the terms are still used for differently defined taxa. Also in 1920 Charles W. Gilmore published the first comprehensive study of North American theropods. The interwar period saw further discoveries of theropods, including Dromaeosaurus in North America and Oviraptor and Velociraptor in Asia . In 1932 Friedrich von Huene published his monograph on Saurischia in which he summarizes the taxonomy, distribution and development of the Theropoda. This work remained authoritative until the 1960s.
Since the 1960s, the diversity and complexity of the theropoda has been increasingly recognized, many old genera have been re-examined. The most spectacular discovery during this time was probably Deinonychus by John H. Ostrom . Its work should turn the previous image of the theropods upside down. He saw in them agile, nimble animals instead of the prevailing opinion that they were clumsy and slow. Ostrom has also re-suggested the theses on the warm-bloodedness of at least some dinosaurs and the ancestry of birds.
Many new theropods were also discovered in the 1970s and 1980s, for example Tarbosaurus , the Abelisauroidea on the southern continents or Baryonyx . In 1986 Jacques Gauthier first introduced cladistics into the dinosaur systematics; it was also he who first defined the theropoda as "birds and all saurischia that are more closely related to birds than to sauropodomorpha ". In 1996 a feathered dinosaur was described for the first time with Sinosauropteryx , later others like Protarchaeopteryx , Caudipteryx , Shuvuuia , Sinornithosaurus and Microraptor were discovered. Sciurumimus was first described in 2012 ; the holotype , an exceptionally well-preserved young animal, was found in 2009 or 2010 in Painten , Bavaria .
In addition to numerous new finds and improved investigations of old theropods, further cladistic systematic studies appeared, among others by Thomas R. Holtz and Kevin Padian . In recent times, in addition to anatomical and systematic questions, paleo-ecological studies have become important, which investigate the way of life of these animals and their interaction with other living beings. It is to be expected that further information about the appearance, way of life and systematics of these animals can be obtained in the future through new finds and analyzes.
Theropoda in culture
Since the dinosaurs first came into the public eye in the 19th century, they have enjoyed great interest and popularity worldwide. Among the best known and most popular dinosaurs are many theropods. This is also reflected in their role in fictional works (by Arthur Conan Doyle's book The Lost World ( The Lost World , 1912) to the modern Jurassic Park -Verfilmungen) or popular scientific works, such as the BBC series Dinosaurs - In Empire of the Giants (English title: Walking with dinosaurs ), reflected. See dinosaurs in the media for the reasons for the popularity of these animals .
literature
- David B. Weishampel , Peter Dodson , Halszka Osmólska : The Dinosauria . 2nd edition. University of California Press, Berkeley CA et al. 2004, ISBN 0-520-24209-2 .
- David E. Fastovsky , David B. Weishampel : The Evolution and Extinction of the Dinosaurs. 2nd edition. Cambridge University Press, Cambridge 2005, ISBN 0-521-81172-4 .
- Wilfried Westheide , Reinhard Rieger (Hrsg.): Special zoology. Part 2: vertebrates or skulls. Spectrum - Akademischer Verlag, Heidelberg et al. 2004, ISBN 3-8274-0307-3 .
Web links
- Theropoda on palaeos.com ( Memento from August 20, 2010 in the Internet Archive )
- James O. Farlow, Stephen M. Gatesy, Thomas R. Holtz, Jr., John R. Hutchinson, John M. Robinson: Theropod Locomotion. In: American Zoologist. 2000 40 (4), pp. 640-663. (Full text)
Individual evidence
- ^ Gregory S. Paul : The Princeton Field Guide To Dinosaurs. Princeton University Press, Princeton NJ 2010, ISBN 978-0-691-13720-9 , pp. 71-161, online .
- ^ Wilhelm Gemoll : Greek-German school and hand dictionary. 9th edition, reviewed and expanded by Karl Vretska . With an introduction to the history of language by Heinz Kronasser. Freytag ua, München ua 1965. Note: The stem ποδ- of the noun πούς is not recognizable in the nominative, but in the genitive ποδός .
- ↑ Frederick C. Mish (Ed.): Merriam-Webster's collegiate dictionary. 11th edition. Merriam-Webster, Springfield MA 2008, ISBN 0-87779-809-5 , p. 1297.
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^ Richard O. Prum: Development and evolutionary origin of feathers. In: Journal of Experimental Zoology. Vol. 285, No. 4, 1999, ISSN 0022-104X , pp. 291-306, doi : 10.1002 / (SICI) 1097-010X (19991215) 285: 4 <291 :: AID-JEZ1> 3.0.CO; 2 -9 .
Richard O. Prum, Alan H. Brush: Which came first, the feather or the bird? In: Scientific American. Vol. 288, No. 3, 2003, ISSN 0036-8733 , pp. 60-69. - ↑ Xing Xu, Mark A. Norell , Xuewen Kuang, Xiaolin Wang, Qi Zhao, Chengkai Jia: Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids. In: Nature . Vol. 431, No. 7009, 2004, pp. 680-684, doi : 10.1038 / nature02855 , PMID 15470426 .
- ^ W. Desmond Maxwell, John H. Ostrom : Taphonomy and paleobiological implications of Tenontosaurus-Deinonychus associations. In: Journal of Vertebrate Paleontology. Vol. 15, No. 4, 1995, ISSN 0272-4634 , pp. 707-712, doi : 10.1080 / 02724634.1995.10011256 .
- ↑ Kenneth Carpenter : Variation in Tyrannosaurus rex. In: Kenneth Carpenter, Philip J. Currie (Eds.): Dinosaur Systematics. Approaches and Perspectives. Cambridge University Press, Cambridge et al. 1990, ISBN 0-521-36672-0 , pp. 141-145.
- ^ R. McNeill Alexander: Estimates of speeds of dinosaurs. In: Nature. Vol. 261, No. 5556, 1976, pp. 129-130, doi : 10.1038 / 261129a0 .
- ^ Richard A. Thulborn: Speeds and gaits of dinosaurs. In: Palaeogeography, Palaeoclimatology, Palaeoecology. Vol. 38, No. 3/4, 1982, ISSN 0031-0182 , pp. 227-256, doi : 10.1016 / 0031-0182 (82) 90005-0 .
- ↑ James A. Hopson: Relative brain size in dinosaurs; implications for dinosaurian endothermy. In: Roger DK Thomas, Everett Claire Olson (ed.): A Cold Look at Warm-Blooded-Dinosaurs (= American Association for the Advancement of Science Symposium. No. 28). Published by Westview Press for the American Association for the Advancement of Science, Boulder CO 1980, ISBN 0-89158-464-1 , pp. 287-310.
- ↑ Information on the encephalation quotient of the Theropoda
- ↑ David E. Fastovsky , Joshua B. Smith: Dinosaur Paleoecology. In: Weishampel, Dodson, Osmólska: The Dinosauria. 2004, pp. 620-624.
- ↑ John H. Ostrom: Deinonychus, the ultimate killing machine. In: Gary D. Rosenberg, Donald L. Wolberg (eds.): Dino Fest (= Paleontological Society. Special Publication. No. 7, ZDB -ID 2002145-8 ). Proceedings of a Conference for the General Public held March 24-26, 1994 at Indianapolis, Indiana. Paleontological Society et al., Knoxville TN et al. 1994, pp. 127-138.
- ↑ "all taxa closer to Passer domesticus than to Cetiosaurus oxoniensis ". Thomas R. Holtz , Halszka Osmólska: Saurischis. In: Weishampel, Dodson, Osmólska: The Dinosauria. 2004, p. 22, referring to the work of K. Padian and CL May and T. Maryańska.
- ↑ Max C. Langer: Basal Saurischia . In: Weishampel, Dodson and Osmólska (eds.): The Dinosauria . (2004), pp. 40-44.
- ^ The problem of diagnosing primitive theropods is discussed in detail and up to date in: Paul C. Sereno : The phylogenetic relationships of early dinosaurs: A comparative report. In: Historical Biology. Vol. 19, No. 1 = Special Issue: Early Dinosaur Evolution , 2007, ISSN 0891-2963 , pp. 145-155, doi : 10.1080 / 08912960601167435 .
- ^ Matthew G. Baron, David B. Norman, Paul M. Barrett: A new hypothesis of dinosaur relationships and early dinosaur evolution. In: Nature 543, 2017, pp. 501-506, doi : 10.1038 / nature21700 .
- ^ Paul C. Sereno, Catherine A. Forster, Raymond R. Rogers, Alfredo M. Monetta: Primitive dinosaur skeleton from Argentina and the early evolution of Dinosauria. In: Nature. Vol. 361, No. 6407, 1993, pp. 64-66, doi : 10.1038 / 361064a0 .
- ↑ simplified after Weishampel, Dodson and Osmólska: The Dinosauria. 2004.
- ^ Charles Whitney Gilmore : Osteology of the Carnivorous Dinosauria in the United States National Museum. With Special Reference to the Genera Antrodemus (Allosaurus) and Ceratosaurus (= United States National Museum Bulletin. No. 110, ISSN 0362-9236 ). Government Printing Office, Washington DC 1920, digitized .
- ^ Friedrich von Huene : The fossil reptile order Saurischia, their development and history (= monographs on geology and palaeontology. Series, no . 4, ZDB -ID 634428-8 ). Bornträger, Leipzig 1932.
- ↑ Jacques Gauthier : Saurischian Monophyly and the origin of birds. In: Memoirs of the California Academy of Sciences. No. 8, 1986, pp. 1-55, digitized .