Classroom paragraph reading. Some dinosaurs walked on two feet like their ancestors, while others walked on four feet. Some dinosaurs were tens of meters long and heavy.

Theropoda belongs to sauropoda, which lived from Middle Triassic to Cretaceous. They are all carnivorous dinosaurs, walking on two feet, with sharp claws at the toes, sharp teeth like daggers or knives in their mouths, and serrated teeth at the front and rear edges. Tyrannosaurus rex is its famous representative. Most theropod dinosaurs retain some primitive features of primitive dinosaurs, such as dagger-shaped teeth with serrated edges; All known theropods dinosaurs walked on two feet. In the next 1.65 billion years, their body structure showed the same characteristics as theropod dinosaurs: bipedal walking and grasping hands. The taxonomic status of Erigeron is still controversial. Some research results support the theory that Elodea belongs to primitive theropod dinosaurs, but Elodea lacks some characteristics of sauropod dinosaurs and real theropod dinosaurs, which proves that Elodea split from sauropod dinosaurs before they split.

True theropod dinosaurs have many characteristics. The ancestors of dinosaurs, Primitive Dragon and Lei Long, probably walked on the ground with four toes. After the advanced theropod dinosaurs, the new theropod dinosaurs all walked with three toes in the middle of their hind feet. The first and fifth toes degenerate and atrophy. There is an extra opening in the nasal cavity of Neotheropod dinosaur, which is likely to be used to assist heat exchange in combination with the air chamber system formed by soft tissue. New evidence shows that all new theropods dinosaurs may have chest wishbones. In birds, the chest wishbone is used to assist flight, and the chest wishbone of theropods is likely to be used to assist forelimbs to resist prey.

The new theropod is divided into two categories: Ceratosaurus and Ceratosaurus. Ceratosaurus is divided into two types: bone dragon and new ceratosaurus. Osteoporosis lived before the end of Jurassic, and its maxilla had special grooves. The osteophytes, Shi Xiu Jayotis and Sejilong are petite, less than one meter long. Large osteophytes, such as Liang Long and Godzilla, can reach 6 meters in length and weigh nearly a meal. Medium-sized brachiosaurus is about 3-4 meters long, such as brachiosaurus and Ankylosaurus. Osteoporosis is relatively light and can move quickly.

Most Neoceratosaurus dinosaurs were stout; The lightweight dragon, which lived at the end of Jurassic, was slender and its forelimbs were close to those of Pterosaur. Slender dragon may be a primitive new ceratosaurus, or it may be a late osteoporosis dragon. The most famous Jurassic Neotriceratops is Ceratosaurus, which lived in western North America in the late Jurassic. Ceratosaurus shared many features with Neocerasaurus in the late Belarusian period and stron in Arberry, such as lumbar enlargement. Abercrombies came from Gondwana in Cretaceous and probably lived in Europe. Small dinosaur with sickle-shaped claws similar to deinonychus. The large Abelian dinosaur was the most successful carnivorous dinosaur in the southern continent in the late Cretaceous, which was found in South America, India and Madagascar. Large Abercrombies have similar characteristics to Tyrannosaurus rex, such as fused nasal bones and degenerated forelimbs. The famous large Abercrombie includes the beef-eating dragon Abercrombie, and the newly discovered Ma Jun Craniosaurus and Wang Shenglong.

Although most of them are classified into Ceratosaurus and Osteoporosis, they all become Ceratosaurus. There is a theory that the relationship between Neoceratosaurus and Ceratosaurus is closer. The skull and hind limbs of Neotriceratops are similar to Cephalopods, but they do not have the characteristics of Cephalopods. In terms of time, Xu Gulong mainly lived in the Late Triassic and Early Jurassic. Neotriceratops and Ceratosaurus mainly lived after the Middle Jurassic. However, if the new Ceratosaurus is combined with Brachiosaurus and different from Brachiosaurus, it means that a large number of features of Ceratosaurus and Brachiosaurus on vertebrae and hind limbs are the result of convergent evolution, or the original features of Neotheropoda dinosaurs, which no longer exist in Brachiosaurus.

Cephalotaxus fortunei, as its name implies, has a tough and stiff tail. The spikes on the tail of a dinosaur with a strong tail were elongated, forming a hard structure in the second half of the tail. One structure may be that dinosaurs kept their balance better when turning and increased their flexibility. Some pterodactyls, pterosaurs and fast-moving lizards also have this structure. Ceratosaurus dinosaurs had large forelimbs, called Ceratosaurus, and their teeth were relatively concentrated in the first half of the upper and lower jaws. As Comrade Kate said.

Most sauropods belong to specialized "ornopods". Hard-tailed dragon, not belonging to theropoda, includes Megalodon and Chiroptera. The dinosaurs of Megalodon got together and became Tyrannosaurus Rex. These dinosaurs were usually huge, with powerful forelimbs and thumbs. This kind of dinosaur includes Megalodon shark found in Britain in Jurassic period, Tyrannosaurus Rex found in North America in late Jurassic period and Zijilong in Piani. Rocker arm dragon is a very special cephalosaurus. Their forelimbs have huge claws, slender noses and fangs. The teeth in the front of the upper and lower jaws of Spinosaurus are larger than the other teeth in the mouth, and at the same time form a "hoop" structure, which is similar to a senior crocodile, indicating that Spinosaurus may have eaten fish. Like modern crocodiles, Spinosaurus had the ability to prey on large terrestrial animals. Fish scales and the remains of young Iguanodon were found in the abdominal cavity of heavy claw dragon fossils. Chiropterosaurus includes Spinosaurus, a superstar in JP3, and Diptera found in Britain similar to E Long in North Africa. Spinosaurus, such as Keelung, was also found in South America. The giant raptor found in Argentina may be a member of Spinosaurus.

There are a large number of derived features in the feet of birds and animals, including specialized carpal bones and crescent-shaped wrist joints, which increase the range of motion of hands. There is a hole in the jawbone of ornithopods in many places, which does not exist in China-style Lei Long, Ceratosaurus and non-ornithopods. The cavity in the vertebra of theropoda is more complex, forming a more complex air chamber structure than other theropoda. There are two kinds of animals and birds' feet, carnivorous dragon and empty-tailed dragon. These two names are used to distinguish between large and small theropods. Now these two names are no longer based on size. Carnivorous dinosaurs include Allosaurus and its relatives, and empty-tailed dinosaurs include highly specialized theropods.

Carnivorous dinosaurs are characterized by a highly specialized spine and a snout with an air cavity. Many carnivorous dragons have horns on their noses and tear bones. Ichthyosaurus had a horn crown bent forward on its head, and Monospinosaurus had a huge hollow crown in the center of its head. Advanced carnivores, such as Allosaurus and Pterosaur, had only three fingers, while primitive carnivores had a fourth metacarpal bone, such as Tyrannosaurus China. This feature shows that the disappearance of the fourth finger appears independently in higher carnivorous dragons and empty-tailed dragons. At present, the largest known theropod is sauropod, which lives in the southern behemoth of North Africa and South America in the late Cretaceous. The latter is larger than the largest known Tyrannosaurus rex 10- 15%. Although carnivorous dinosaurs were the most common theropods from the Middle Jurassic to the Early Cretaceous, no known carnivorous dinosaurs survived after the first stage of the Late Cretaceous (about 654.38 billion to 94 million years ago). The theropod dinosaurs that lived at the top in the late Cretaceous were Tyrannosaurus rex (North America and Asia) and abercromby (South America, Africa, India and Europe).

Empty dinosaurs have many different characteristics in prison. Compared with other kinds of theropod dinosaurs, sauropod dinosaurs have larger brain cavities, slimmer forelimbs, and dentate bones under the coccyx face forward and backward, forming a harder tail than lower sauropod dinosaurs. Some low-level sauropods, advanced egg-stealing dragons, Kamakura dragons and other empty-tailed dragons all have feathers, which shows that many empty-tailed dragons have primitive feathers. Some primitive sauropods living in Jurassic and Cretaceous are not closely related to higher sauropods. Some primitive empty-tailed dragons, such as sauropod, bird-loving dragon and empty-tailed dragon, are petite and less than 1.8 meters long. Others reach the size of typical carnivorous dinosaurs and ceratosaurus, such as Triceratops and Wounded Dragons.

The remaining empty-tailed dinosaurs are called hand-stolen dinosaurs, including some of the most specialized dinosaurs. Hand raptors include Bird Dragon, Tyrannosaurus Rex, Egg Stealing Dragon, Kamakura Dragon, Toothed Dragon, Long Ben Dragon and abala Spinosaurus. The characteristics of hand raptor include a smaller tail vertebra, slender forelimbs, a second jaw in the mouth and nose, and a constantly changing brain cavity. Although some hand-eating dinosaurs still kept their carnivorous habits, such as Tyrannosaurus Rex and Liang Long, there is some evidence that other groups of hand-eating dinosaurs are probably omnivorous or herbivorous.

Dinosaurs like birds are similar to modern ostriches and other flightless birds. Primitive ornithosaurus, such as the pelican dragon in the early Cretaceous, had 220 tiny teeth, while the late ornithosaurus had no teeth at all. Dinosaurs like birds have small heads, long necks, compact bodies and long legs. Unlike modern birds, ornithosaurus had a slender tail and forelimbs, and three fingers on its hands. Bird dragon's hand is unique, with three fingers almost equal in length, forming a claw ring structure similar to that of modern sloths. Although it is impossible for a bird-shaped dinosaur to live in a tree, its forelimbs may be used to grab branches and help eat leaves and fruits. The foot bones of the bird dragon are sunken, which can play a role in shock absorption when running. Bird-like dinosaurs are one of the fastest dinosaur groups.

Tyrannosaurus rex is another kind of dinosaur, which has the same foot bone characteristics. Although the shape of Tyrannosaurus rex is far from that of ornithosaurus, its hind legs are almost the same as that of ornithosaurus, and juvenile Tyrannosaurus rex also has the same slender hind legs as ornithosaurus. The structure of Tyrannosaurus Rex's hind legs shows that they can also move quickly, but adult Tyrannosaurus Rex often uses size and strength instead of speed when hunting. Derived features in the pelvis and skull of Tyrannosaurus rex show that they are the closest relatives to the bird dragon. Evolutionary Tyrannosaurus Rex has incised teeth on its front jaw, a super powerful lower jaw and thick teeth (different from the thin teeth of a typical theropod). Its tiny forelimbs only have the body structure of a two-fingered Tyrannosaurus Rex, which indicates that it only hunts directly with its mouth. Although the late Tyrannosaurus rex was 12 meters long, fossils show that the early Tyrannosaurus rex was about 3 meters long, and it evolved into a huge body only after the extinction of carnivorous dinosaurs.

The remaining population of hand raptors is called hand raptors. They have long forelimbs and enlarged sternum. Egg-stealing dragons, including feathered tail-feathered dragons, have short and square skulls, while advanced egg-stealing dragons have no teeth in their mouths. Many egg-stealing dragons have gorgeous crowns and hatch eggs like birds. There is still controversy about the eating habits of the egg stealing dragon. Some egg-stealing dinosaurs also had the same foot bone structure as bird dragons, indicating that they could move quickly.

The location of Kamakura is only a taxonomic problem, which has the characteristics of higher sauropods, protosauropods and ornithopods. Through the analysis of the recently discovered lower Kamakura and higher Kamakura, it is proved that they belong to the hand-stolen dragon and have the closest relationship with the egg-stealing dragon. The tooth morphology of Kamakura dragon is very similar to that of sauropods and birds-buttock dinosaurs, indicating that Kamakura dragon is a herbivorous dinosaur. Kamakura's pubic bone faces backward, increasing the volume of abdominal cavity. Most kamakura (except some primitive species) have short and wide feet, which shows that they move slowly.

Toothed dragon is a highly evolved empty-tailed dragon. Their tail roots are very active, and their feet have retractable sickle claws, just like dragons and birds. The teeth of odontosaurus had small dentate protrusions instead of serrations, which were similar to those of Kamakura. There is an inflatable cavity in the brain cavity of the sunken sole bone, which is similar to that of a bird dragon. Unlike other hand raptors, odontosaurus had shorter forelimbs (compared with the length of femur), which was similar to the original cephalosaurus. The eating habits of odontosaurus are also controversial. Some scholars think that odontosaurus is a carnivorous dinosaur similar to Liang Long, while others think that odontosaurus is an omnivorous dinosaur whose food includes meat, insects and plants. The slender hind limbs of odontosaurus showed that they could move quickly. The odontosaurus had a big brain cavity and was once considered as the smartest dinosaur. However, there is little information about the brain cavities of many other hand raptors, so it is uncertain whether the brain cavities of odontosaurus are larger than those of other hand raptors, or whether hand raptors generally have enlarged brain cavities.

Liang Long's forelimbs are long, with grasping hands, and the joints between the tail root and pelvis are highly mobile. The rest parts are connected by bone rods, forming a very tough structure, and the hind feet have sickle-shaped claws. All these characteristics prove that Liang Long is a very agile and active predator. The discovery of deinonychus shook the view that dinosaurs were slow to move. By comparing the similarities between Liang Long and Archaeopteryx, it is proved that birds originated from dinosaurs, and that Liang Long is one of the dinosaurs closest to birds. The pubic bone of a dragon is backward, just like a bird. Different from Kamakura and bird-buttock dinosaurs, the trend change of BengLong was probably used to change the attachment of pelvic bone, tail and hind limb muscles, so that BengLong could walk with knees instead of buttocks. The tail structure of Long Ben and early birds enabled them to turn more suddenly during running and enhanced their mobility.

Dinosaurs walked upright, similar to most modern mammals, while most other reptiles walked with their limbs extended to both sides. The buttock fossa of dinosaur faces to both sides, and the fourth largest trochanter of femur faces to the inside, and the two fit together to produce an upright gait. The upright gait allows dinosaurs to breathe while moving quickly, making them active animals, which has an advantage over animals that use extended gait on both sides. Upright gait can reduce the pressure on the limbs when bending, and help dinosaurs develop a huge body shape. Some non-dinosaur dinosaurs also independently developed an upright gait, such as crocodile Lloyd, but its hip fossa was downward and its femur was embedded in the hip fossa upward, forming a "columnar upright way" different from dinosaurs and mammals.

The biggest difference between dinosaurs and other reptiles lies in the posture of standing and the way of marching. Dinosaurs are completely upright, with their limbs directly under their bodies. This structure has more advantages than other reptiles (such as crocodiles, whose limbs extend outward) when walking and running. According to the different structural characteristics of dinosaur belts, they can be divided into sauropods and ornithopods.

The main difference between them lies in their belt structure:

The belt of sauropods is three-shot when viewed from the side. The pubic bone extends forward under the intestinal bone and the ischium extends backward, similar to lizards. Very ugly.

The waistband of ornithischia expands greatly in the front and back of the intestinal bone, and there is a large pubic protrusion on the front side of the pubic bone, which extends below the intestinal bone, and the back side extends parallel to the ischium to the front and bottom of the intestinal bone. So the pelvis is radiant from the side (there are other differences).

Sauropods are divided into sauropods and theropods.

Sauropods are divided into protosauropods and sauropods.

Theropod dinosaurs lived from the Late Triassic to the Cretaceous. They are all carnivorous dragons, walking on two feet, with sharp claws on their toes and well-developed heads, and they are the smartest one. There are teeth as sharp as daggers or knives in the mouth. Tyrannosaurus rex is a famous representative, and others, such as Allosaurus, southern behemoth and Spinosaurus, are also quite famous.

Pterosaurs can be divided into five categories: ornithopod, stegosaurus, Ankylosaurus, Ceratosaurus and pachycephalosaurus.

At present, the longest known carnivorous dinosaur, Spinosaurus, has a body length of 16 ~ 19 meters and a mass of 16~26.5 tons. The largest herbivorous dinosaur, a fragile double-chambered dragon, was 58 meters long and weighed 150- 180 tons. The smallest dinosaur is equivalent to a pigeon. At present, the smallest known adult dinosaur specimen belongs to the nearly bird dragon, and its weight is estimated to be about110g. Moreover, the smallest known herbivorous dinosaurs are Microceratosaurus and Venanosaurus, which are about 60 cm long.

A suborder of sauropods. Its huge body is the largest of all terrestrial vertebrates. Small head, long neck and tail, strong limbs, walking on all fours. Feed on plants. Mainly lives in swamps. Jurassic reached its peak and became extinct at the end of Cretaceous. China's famous Puzzled Dragon, Liang Long, Brachiosaurus, Tianshan Dragon, Mamenxilong and Panzulong all belong to this category.

All sauropods have similar body structures: small head and extremely long neck; A large, long, huge gastrointestinal tract; Thick columns of legs support a huge body; The tail is quite long, tapering and whipping from the base to the end. The belt is very thick, and it heals with the spine through four sacral vertebrae (five in some species), providing strong support for the body and tail. There are deep pits on both sides of the vertebral body of the spine to reduce the weight and maintain its structural strength. It used to be thought that sauropods were immersed in shallow water all day and supported their heavy bodies by the buoyancy of water, but some species seemed to be more suitable for living on hard ground. Sauropod has a long neck, so it can eat trees, even the tallest trees, a bit like modern giraffes. Its teeth are often small and thin, and the number is small. It seems that sauropods want to swallow stones or bacteria into the gastrointestinal tract to help crush or decompose the plant matter they eat.