Generally speaking, ichthyosaurs are between 2 meters and 4 meters (although some species are smaller and some species are more than 4 meters long). Its head is like a dolphin with a long toothed kiss. Ichthyosaurus had a long, pointed mouth, conical teeth on the upper and lower jaws, and the whole skull looked like a triangle. Like today's tuna, it is suitable for fast swimming, with a disc-shaped vertebral body and slightly concave sides. A vertebra is like a string of plates strung on a rope, and the caudal vertebra is long, narrow and flat. Some ichthyosaurs seem to be suitable for deep diving. They have a pair of big round eyes on both sides of their heads, which can reach 30 cm in diameter. At present, the largest eye among living vertebrates is that of a blue whale, with a diameter of only 15 cm. Therefore, ichthyosaurs can prey on squid, fish and other prey in the dark night or deep sea. Some scientists estimate that ichthyosaurs can dive to 500 meters in the ocean (Ryosuke Algae, 2000). It is estimated that the swimming speed of ichthyosaurs can reach 40 kilometers per hour. Like cetaceans today, they breathe air and germinate embryos (some fossils of adult ichthyosaurs include fetuses). Although ichthyosaurs are reptiles and their ancestors laid eggs, it is not surprising that ichthyosaurs germinated by themselves. All marine animals that breathe air either go to the coast to lay eggs (such as turtles and some sea snakes) or have to give birth directly in the water (such as dolphins and whales). Because of the streamlined shape of ichthyosaurs, they are unlikely to climb to the shore to lay eggs.
According to Ryuke Algae's estimation, a 2.4-meter-long pterodactyl weighed between 163 and 168 kg, while a 4-meter-long eye dragon weighed between 930 and 950 kg.
Although ichthyosaurs look like fish, they are not fish. Stephen Jay Gould said that ichthyosaur was his favorite example of convergent evolution. The similar structures here are similar, but the sources are different. He pointed out:
"(Ichthyosaurus) and fish are so similar that their dorsal fin and caudal fin evolved in the same place have the same hydrodynamic design. These structures are particularly striking because they have never evolved. The ancestors of terrestrial reptiles had no boards on their backs and no blocks on their tails as their predecessors. "
In fact, at first people thought that the ichthyosaur had no dorsal fin, because there was no hard bone tissue in the dorsal fin of the ichthyosaur. It was not until the exceptionally well-preserved ichthyosaur fossils unearthed in Holzmeiden, Germany in the AD 1890' s that traces of its dorsal fin appeared. The local special preservation environment allows traces of soft tissue to be left behind.
Ichthyosaurs have flippers, which may be used for stabilization and steering, rather than acceleration, which may mainly come from shark-like caudal fins. Its caudal fin is divided into two pieces, of which the lower piece is supported by the coccyx.
In addition to obvious similarities with fish, ichthyosaurs and dolphins also have similar signs of evolution. The appearance of these two animals is similar, which may indicate that their activities are similar, and perhaps they occupy similar niches.
The main food of many ichthyosaurs is cephalopods, which are close relatives of squid belonging to the subclass Ammoniaceae in ancient times. Some early ichthyosaurs had teeth that could crush shellfish. Their staple food may be fish. Some large species have powerful jaws and teeth, which means they also eat small reptiles. Because ichthyosaurs vary greatly in size and have lived for such a long time, their recipes may be very extensive. Typical ichthyosaurs have big eyes protected by corneal rings, which seems to indicate that they mainly hunt at night.
Anterior fin of ichthyosaur
The earliest ichthyosaurs had hands and feet, or flippers. Paleontologists used to have various names for this. In the past ten years, they have gradually formed a conventional name. The front pair is called the front fin and the back pair is called the back fin.
Ichthyosaurs may be manipulated by their forefins when swimming, just like existing fish and whales (dolphins and whales). Some paleontologists speculate that ichthyosaurs must have used their hands and feet to propel their bodies. However, their shoulders and arms don't seem to be as strong as vertebrates.
The bones of hands and feet changed greatly during the evolution of ichthyosaurs. From the phylogenetic tree above, we can clearly observe the evolution of ichthyosaurs' hands and forefins: (1) The bones of the lower arm became shorter and shorter; (2) The phalanges became shorter and shorter, and finally became disc-shaped; (3) The number of phalanges began to increase in the early stage of evolution; (4) The thumb disappears, and then a new joint appears next to the remaining phalanges.
The main food of ichthyosaurs
According to the limited substances left in the stomach of ichthyosaur fossils, we can analyze what ichthyosaur ate. As early as 1853, Coles found something special in ichthyosaur fossils, which was thought to be scales at that time. But later, scientists discovered that these are actually small hooked structures from squid tentacles (extinct cephalopods, mostly arrow stones).
Since then, more data show that ichthyosaurs mainly feed on squid. Even the Jurassic Temnodontosaurus, which is 10 meter long, is no exception, although they also eat large vertebrates from time to time. Besides squid, ichthyosaurs also eat fish and other marine animals.
Simply put, many ichthyosaurs are natural enemies of squid, just like whales today.
Reproduction of ichthyosaurs
The specimen of ichthyosaur not only proves that ichthyosaur gave birth to a live baby, but also further proves that, like whales and dolphins, Xiaoyulong came out as Mr. Tail. However, it is important to note that individuals who "save production" may not be producing at the time of their death. On the contrary, it is very likely that they died during pregnancy, but later in the process of decomposition, the baby was pushed out of the birth canal by the gas produced in the mother's body. This kind of "born after death" is very common among whales washed up on the beach today.
Specimens preserved in the baby's head instead of tail show that ichthyosaurs sometimes have dystocia. Probably like whales and dolphins, Xiaoyulong was "triggered" to breathe for the first time until its head came out of its mother's cloaca. Therefore, if the baby's head sticks out first, it is very likely to be drowned. 1995 after studying ichthyosaur embryos, Dr. D.Charles Deeming and his colleagues pointed out that if this happens, the mother will also die, because the dead baby will stay in the cloaca later, and the mother's activities will be hindered. The baby's decay will last for a long time, making her bleed and poisoned. Maybe sometimes the baby who came first did survive, because there is a record of success in giving birth first among dolphins.
Another possible problem is the abnormal delivery of too many babies. Live birth is a very tense and dangerous process, especially for aquatic animals that breathe air. Deming and his colleagues also pointed out that a child may lead to the death of mother ichthyosaur.
Every year in mid-June, pregnant female ichthyosaurs will swim to the land surface with large coral reefs and seaweed in droves and give birth as soon as possible. This environment not only provides a rich food source for the small fish dragons, but also provides them with shelter. However, this place is not suitable for adult big-eyed ichthyosaurs to hunt. Accustomed to hunting in the vast and dark deep sea, it is difficult for them to adapt to the bright sunshine and narrow space on the land surface, so they will leave soon after giving birth to the small fish dragon. The first thing Xiao Yulong did after she left her mother was to float to the surface to catch her breath. They were born alive and can swim freely. Like all animals' babies, the ratio of their heads to their eyes is larger than that of adult individuals. In the early days of newborn ichthyosaurs, caves and passages in coral reefs became ideal places for them to avoid predators. In a few months, Xiaoyulong will grow up and live in the open sea.
Discover history
The earliest description of ichthyosaurs is 1699 fossil fragments found in Wales.
1708 The earliest vertebrate fossils were published twice, which are suspected to be the remains of the great flood. 18 1 1 year, mary anning discovered the first complete ichthyosaur fossil in Lyme Regis, which is the Jurassic coast today. Since then, she has found three different fossils.
1905, the dinosaur expedition of the University of California discovered 25 fossils in Nevada, with shallow Triassic strata. Today, some of these fossils are on display at the Archaeological Museum of the University of California. Other fossils are still buried in the stone bed today and can be visited in the state-owned Berlin Yulong Park in Naixian County. 1977, Nevada designated the Triassic zhaoxuelong as a state fossil. Nevada is the only state with a complete 17 meter long nylon. 1992 A Canadian ichthyologist discovered the largest ichthyosaur fossil to date, which was 23 meters long.
Evolutionary history
Early ichthyosaurs looked more like lizards with fins than fish or dolphins. These fossils were found in the early and middle Triassic strata in Spizbergen, Canada, China, Japan and Norway. These early species include Tidal Lake Dragon, Gryphon and Utah Dragon. These belong to ichthyosaurs, but not to ichthyosaurs (algae dragon interface,1997; Early ichthyosaurs evolved into real ichthyosaurs in the late Triassic or early Triassic. These ichthyosaurs quickly differentiated into many species, including the 65,438+00-meter-long Cymbospondylus, which looked like a sea snake, and smaller and more typical species, such as Mixosaurus. The ichthyosaurs in the late Triassic include the ancient Sast ichthyosauridae and Californosaurus, which is more like dolphins. Experts still disagree whether these ichthyosaurs showed an evolutionary process, in which Sastre ichthyosaurs were relatively nonspecific and gradually evolved into more advanced species (Maisch and Matzke, 2000), or whether they were two parallel species developed from the same ancestor (Nicholls and Manabe, 200 1).
In Kannik and Norikian, the Saxosauridae reached a great length. Many fossils were found in the Cannicci formation in Nevada, and the ordinary plesiosaur was 15 meters long. On both sides of the Pacific Ocean, the Cannic Sast ichthyosauridae was found. A Tibetan Himalayan dragon was found in Tibet. These ichthyosaurs, with a body length of 10 to 15 m, may belong to the same genus as Shannylon (Sargassum longzhijie et al.,1999; Lucas, 200 1 year, 1 17 to 1 19 pages). Shonisaurus sikanniensis, found in British Columbia, is 2 1 m long and is by far the largest marine reptile.
By the end of Nolik, these giant animals (and their little relatives) seemed to have disappeared. Letichthyosaurs were also found in Britain, which were very similar to those in the early Jurassic. Like dinosaurs, ichthyosaurs and plesiosaurs survived the extinction at the end of Triassic and immediately diversified to fill the gap in the early Jurassic.
The ichthyosaur painted by Heinrich Hald
The early Jurassic was the peak of ichthyosaurs, just like the late Triassic. At that time, ichthyosaurs included four families and many species, and their lengths ranged from 1 m to1m. Its genera include Eusaurus, ichthyosaurus, Leptosaurus, Pterosaur and Temnodontosaurus, a large carnivorous fish. At the same time, there are also relatively primitive Suevoleviathan left in the early stage, which has not changed much compared with their ancestors in Nolik stage. All these animals have streamlined bodies like dolphins. However, primitive animals may be slimmer than later developed species such as pterosaurs or ichthyosaurs.
There were still ichthyosaurs in the Middle Jurassic, but the diversity decreased. At this time, the representative ichthyosaurs include the four-meter-long Ophthalmosaur and its adjacent genera, which are similar to ichthyosaurs and have a perfect "water drop" streamlined body. Bigeyed ichthyosaurs have very large eyes, and these animals can prey in dark deep water (Dragon Interface Algae, 2000).
The diversity of ichthyosaurs seemed to continue to decline in Cretaceous. So far, only one genus has been found in Cretaceous ichthyosaurs: platypterosaurus. Although distributed all over the world, there are few species. These ichthyosaurs disappeared in the extinction event in the middle Cretaceous. Interestingly, animals with poor hydrodynamic performance such as Canglong and plesiosaur survived and thrived. Maybe ichthyosaur became the victim of its specialization. They can't compete with the extremely fast bony fish. But black dragon's strategy of waiting for an opportunity to attack is more effective for teleost (Linghan-Soglia, 1999).
Popular culture
In jules verne's Journey to the Center of the Earth, there is a description of the struggle between ichthyosaurs and plesiosaurs.
In the video game half-life, there is an underwater alien animal called ichthyosaur.
Extinct fishes and reptiles living in the Mesozoic sea are classified into the suborder Amphibia. 182 1 year, Koenig thought they were animals between fish and reptiles, and created the word ichthyo-saurus. Ju Yewei once described ichthyosaurs vividly: "ichthyosaurs have dolphin kisses, crocodile teeth, lizard heads and sternum, whale-like limbs and fish-shaped spines." It has been pointed out that they are an ancient reptile.
1835, h.-m.d.de Blainville listed ichthyosaurs as an independent class (ichthyosauria) and included them in Vertebrate subfamily. Four years later, richard owen, a famous British vertebrate paleontologist, merged ichthyosaurs and pterosaurs into a class called enaliasauria, which included two orders: ichthyosaurs and plesiosaurs. With the increase of ichthyosaur fossils, the taxonomic status of ichthyosaurs has been re-recognized. In 1956, A.S. Romer listed them as orders belonging to parapsida. 1968, Roche studied the skull structure of a complete ichthyosaur in late Cretaceous in North America. He classified ichthyosaurs as adjustable holes.
At present, there is no reliable clue about the origin of ichthyosaurs. The earliest known fossils were highly specialized in the late Early Triassic. So their ancestors should have appeared before Triassic. According to the morphological structure, ichthyosaurs may have originated from Ceratosaurus.
The Jurassic ichthyosaur is a typical ichthyosaur. Their shapes are similar to those of some large fast-swimming fish. Their bodies are spindle-shaped, their skin is bare, their triangular heads have a sword-like kiss, their mouths have conical teeth, and their teeth fall off. There are abundant ichthyosaur fossils in Jurassic marine strata in Germany, and they are well preserved. On clay slate, the soft part of the body is often clearly printed from the side, and a fleshy dorsal fin and an inverted tail composed of a series of downward folded coccygeal vertebrae can be clearly seen. This adaptation pattern of fish dragon, which embodies fast swimming, lasted from Triassic to Cretaceous, with only quantitative changes. For example, their individuals get bigger, their curved tail fins get bigger and their forelimbs get longer.
The body structure of ichthyosaurs shows that they have completely lost the ability to land. At present, the reproduction mode of ichthyosaurs is considered to be ovoviviparous. The ichthyosaur fossils unearthed in Wü rttemberg, Germany prove this inference. In the abdominal cavity of well-preserved ichthyosaur bones, besides some of their prey, such as cephalopods and fish, there are also ichthyosaur larvae, some of which have degenerated into cloaca.
As for the classification of ichthyosaurs, the current consensus is that they are divided into two categories according to the connection between limb bones and fin feet, that is, wide feet and narrow feet, which are divided into five families. ① Polypodidae, ② Panlong, ③ Brachiosauridae, ③ Saxosauridae, ④ Ichthyosauridae, and ⑤ Brachiosauridae.
The first three families mainly lived in Triassic and were primitive ichthyosaurs. Generally speaking, they are small in size and primitive in shape. The latter two families mainly include some progressive ichthyosaurs in Jurassic and Cretaceous.
The discovery and research of ichthyosaur fossils in China are relatively late. The first ichthyosaur fossil was named Maotai Mixed Dragon by Yang Yu 1964. 1964, ichthyosaur fossils were discovered in Tibet on a fixed date. 1966, a large ichthyosaur named Tibetan Himalayan ichthyosaur was collected in Longtu, nyalam county. 1965, a small ichthyosaur, Chaohu Guishan ichthyosaur, was found in the early Triassic strata of Chao County, Anhui Province, which is the earliest known genus in the world.
As a marine animal, ichthyosaurs are distributed all over the world. From its appearance in the late Early Triassic to its extinction in the late Cretaceous, it has been a very successful animal in the ocean. At the end of Mesozoic, they went extinct with dinosaurs and pterosaurs.
1. ichthyosaurs in ancient oceans
It was found that ichthyosaurs began to exist in the ancient ocean 230 million years ago. This primitive ichthyosaur, Hunlong, was found in Maotai, Guizhou Province, China, which is rich in Maotai liquor. Its head is long and its neck is short. Its body now looks like a dolphin. Their limbs have become flippers that are good at swimming. Ichthyosaurs feed on fish, mussels or other vertebrates in the ocean. Mixed dragon is the smallest group in the whole ichthyosaur family, with a body length of less than 1 m, and the longest is only more than 2 meters.
From the vast ocean, a sharp animal with a long nose appeared. It looks like a dolphin now, with a long mouth and sharp teeth. This animal is actually a reptile, a reptile that lives in water, just like a modern mammal whale. The name of this animal is fish lizard, or "ichthyosaur". You see, its limbs have become very strong fins to adapt to swimming in the water, and its tail has become like a fish's tail. The body of ichthyosaur is streamlined, like a fish, but it is not a fish, because it does not breathe with gills, but breathes air with lungs like reptiles on land at that time. Besides, ichthyosaurs don't lay eggs in water like fish. Instead, mother ichthyosaur left the eggs in her body so that she could hatch them safely. After their children were born, they lived in the ocean all their lives. They are very comfortable in the sea, and some ichthyosaurs can grow to more than 13 meters.
In the ancient ocean at that time, there was another reptile called earthworm. This inappropriate name was given by early paleontologists, meaning "lizard on land". Some people call it "sea crocodile". As you may already know from these nicknames, it must look like a modern crocodile. But in addition to the crocodile-like body, its four feet have become paddle-like fins, and with that big tail, it can swim freely in the water. This aquatic reptile, like the colorful dragon, usually lives in the ocean all its life except laying eggs on the shore.
At that time, there was a short-headed fish dragon living in the ocean. Its head is short and thick, and its mouth has rows of teeth like buttons. It turned out to be a ichthyosaur that lived on the bottom of the sea and ate mollusks for a living. It uses button-like teeth to "break" the shell of a mollusk and swallow the fresh meat inside. Although the short-headed fish's faucet is small, it is not small, and its limbs are much longer than other ichthyosaurs of its time. Some sauropods can grow to 10 ~ 14 meters. Compared with the mixed dragon, it is a "big man".
The most common ichthyosaur family is the real ichthyosaur that lived 65.438+0.5 billion years ago, and it is the typical ichthyosaur we often talk about. Its streamlined body and bare skin are very suitable for swimming in the water. It has a long head with long nostrils, and its mouth is full of sharp and big teeth, as many as 200. Ichthyosaurus had two big eyes and a structure called scleral ring to protect them, which showed that Ichthyosaurus had strong vision. Its hearing is also better than other reptiles. No wonder some people boast that it is the overlord in the sea of "seeing all directions and listening to all directions"! How did ichthyosaurs swim in the sea? Is it like a fish or a dolphin Scientists tell us that it swims more like a modern penguin. A few years ago, some ichthyosaur fossils were found in a quarry under a British museum, with necks, forelimbs and tails. After careful study, it was found that ichthyosaurs used their forelimbs as "directional rudder" and their big tails as propellers. If it wants to swim slowly, it paddles with its two forelimbs. If it wants to move forward quickly, it shakes its big tail vigorously and flies away like an arrow across the water.
Ah, a little head emerged from the sea, followed by a slender neck, swam to the shore and climbed up the rock. Its body is flat, and its four fins like seals are wide and powerful. It was with them that it climbed up the rocks on the shore. Who is this strange-looking guy? It is another overlord in the ocean-plesiosaur. A scientist described it as "a big snake wearing a turtle". It is a fierce carnivore, which can not only eat fish, but sometimes catch pterosaurs that sneak into the sea to prey! Plesiosaurs lived on the earth for 1. 1 100 million years. All the oceans and lakes in the world have left their shadows. Together with the last dinosaur, they died out 65 million years ago.
2. Discovery of ichthyosaur fossils
There is a story that a farmer saw what looked like huge animal footprints on the rocks of his pasture. He immediately called a scientist. The scientist looked at it for a while and said to the farmer, this is a big guy. This prehistoric animal must have walked on two legs. Its feet are like a duck's webbed feet. Later, I learned that it was a hadrosaur. Scientists also found that this big guy can easily walk through the soft soil. Maybe this place used to be a beach, because there is a small sand crab fossil near the footprint.
Another time, a farmer in New England also found some strange footprints, which had been petrified. But no one had heard of dinosaurs at that time, so it was impossible to name these big and strange feet.
Later, decades later, after the first dinosaur skeleton was discovered, people associated these strange footprints with dinosaurs.
The first "dragon" skeleton was discovered by Mary, an English 12 year old girl. This beautiful little girl lives by the sea. Little Mary often helps her father collect shell fossils from rocks by the sea. They make a living by selling fossils in tourist areas. 18 1 1 year One day, Mary found the skeleton of a strange animal in the rock, which looked like the fossil of an ancient reptile that once lived in the ocean. Through the research of scientists, it is confirmed that this fossil is indeed the remains of a marine reptile. After its death, its bones were buried in the seabed by sediments and became fossils in rocks. I don't know how many millions of years have passed, and the rocks on the seabed have been lifted for many meters and exposed to the water. Under the weathering of the sun and rain, some rocks have been broken, forming today's cliffs by the sea. The reptile bones in this ancient ocean are just on the surface of this cliff, and it was discovered by lucky Mary. Later, scientists put these bone fossils together, only to know that this is a ichthyosaur fossil that has been extinct for 200 million years.
What's the name of this fossil that Mary found? At that time, scientists named animals and plants in Latin or Greek. Therefore, this fossil is no exception, giving it a name "Ichth-Ysaurus", which means "fish" in Greek, and "saurus" means "lizard" in Greek. So early paleontologists translated it as "fish lizard". Later it was translated into ichthyosaur.
Mary is famous for it. She was very excited and determined to find some important fossils again. After several years of hard work, she discovered the skeleton fossils of pterosaurs, another reptile flying in the sky. She is indeed a great discoverer of paleontological fossils. If she were here now, she would surely win the Nobel Prize.
Soon after, an English woman, Mrs Mantell, found some extra-large teeth in the rocks. They think that tooth is very similar to a tooth called an iguana. They named this ancient reptile Iguanodon. Later they found many Iguanodon fossils. When a complete Iguanodon skeleton was excavated, they found that this Iguanodon was completely different from the original Iguanodon except for its teeth.
As more and more giant reptiles are discovered, a scientist thinks it is necessary to name all these giant monsters. He decided to call them dinosaurs, which means "terrible lizards". Paleontologists in China translated it as dragon.
3. New discovery of ichthyosaur "graveyard"
Most reptiles are oviparous, that is, most reptiles reproduce by laying eggs. Generally speaking, reptiles lay their eggs in the sand or in their nests, but ichthyosaurs are different. They can't lay eggs underwater, nor can they climb to land to lay eggs. So, how do they reproduce? 140 years ago, a very complete ichthyosaur fossil was found in rocks. Strangely, there is a tiny ichthyosaur that looks very similar in the belly of the big fish dragon. At that time, some people thought that the big fish dragon swallowed the small fish dragon. Later, scientists discovered more than 300 ichthyosaur bones near Holzmaden, Germany. In addition to a large number of ichthyosaur bones and skin fossils, they also accidentally discovered some female ichthyosaur bones with larvae in their abdomen. There are more than 20 such bone specimens.
Almost all adult female ichthyosaurs found in ichthyosaur "graveyard" have little dragons in their body cavities. Even four small fish dragons were found in the abdominal cavity of a female dragon named Tetraodon. Three of them are in the body cavity, 1 is about to be born. Its body is outside the body, but its head is in its mother's stomach. The fossils of nature truly record the reproduction of ichthyosaurs. Through the study of these specimens, scientists determined that Xiao Yulong did not leave her mother's body quickly at birth. During childbirth, Xiao Yulong's tail first gradually extended from the mother, but the whole body did not come out until Xiao Yulong had deliberately used the tail fin and fin foot. The soon-to-be-born ichthyosaur is bigger, and the child born to a 3-meter-long female ichthyosaur can reach 0.5 ~ 0.7 meters. 1988, a Swiss paleontologist found many dragon fossils in the Alps. More than 200 million years ago, it was still a warm ocean, and magic dragon, who looked a bit like a dolphin, was swimming freely. Now many people are speculating that marine reptiles like ichthyosaurs may be "oviparous" animals, which was very progressive at that time.
The ichthyosaur fossil was first discovered in Zurich, Switzerland in the18th century (1708), with only two spines. At that time, scientists didn't know each other. 100 years later (18 14), mary anning, a girl of 0/2 years old in England, found a complete ichthyosaur fossil in a suspended rock on the British coast, which only scholars realized.
According to the characteristics of Himalayan ichthyosaur and the invertebrate fossils born with it, scholars believe that the stratigraphic age of ichthyosaur fossils should be late Triassic, about 654.38+0.6 billion years ago. In other words, when Tibetan ichthyosaurs lived here, the Himalayan region was an ocean, not an ancient Himalayan sea. This sea is connected with the ancient Mediterranean Sea, and today's Atlantic Ocean and Pacific Ocean can be connected with each other through the ancient Himalayan Sea and the ancient Mediterranean Sea. The Himalayas we see today and its highest peak, Mount Everest, were formed after rising from the seabed. The Himalayas is a young mountain range, which keeps rising every year. From here, we really see the dialectics of "vicissitudes of life" and the examples of paleontology providing scientific arguments for paleogeography.
There is another interesting story about ichthyosaur. It was oviparous. We know that most reptiles are oviparous, but some poisonous snakes are oviparous. The so-called viviparous means that its fertilized eggs are not excreted like oviparous animals, but hatched by the external environment, but remain in the mother until they develop into small animals. This kind of reproduction seems to be viviparous, but when it develops in the mother, it is not provided with nutrition by the mother like viviparous animals, but mainly depends on the nutrition of the fertilized egg itself. It just "stores" the egg in the mother for hatching, and it is still oviparous in essence. It is reported that there is an embryo of ichthyosaur in a foreign ichthyosaur fossil, and even/kloc-0 female ichthyosaur and 7 ichthyosaur fossils have been found. Some of these seven small dragons are located outside the body of the big dragon, and some are still preserved in the abdominal cavity of the big dragon. This female ichthyosaur may die during childbirth.
Besides Tibet, ichthyosaur fossils have also been found in Anhui and Guizhou. The ichthyosaurs in Anhui were primitive and earlier, in the early Triassic, about 220 million years ago. Its discovery advanced the Triassic record of ichthyosaurs by 65438+ 1 100 million years.
Besides ichthyosaurs, there are plesiosaurs, Shanglong and Guizhou dragons in China.
Himalayan Himalayesaurus tibetensis is over 10 meter long and weighs about 3 tons. There are teeth as thick as a flat cone in the mouth. The whole skull is triangular, and the eyes are big and round. The vertebral body of the spine is like a plate with concave sides, and the whole spine is like a string of plates tied to a rope. Its limbs are flat and its shoulder blades are long, which is suitable for swimming. Its spindle-shaped body, paddle-like limbs and strong tail make it an unparalleled fast swimmer in the ancient Himalayan Sea.
Sast ichthyosauridae is the most widely distributed ichthyosaur in the Middle and Late Triassic, including many different species, ranging from several meters to more than ten meters long. Shastasaurus is a typical representative of this family. Its teeth are grooved, there is no fin on its back, and it has a half-moon tail fin, so it may swing like an eel.
In the last 10 million years of Triassic, Sast ichthyosaur quickly evolved from an ordinary creature to a terrible marine behemoth. They are big and strong, and they are dwarfed by the land animals of the same period-all kinds of early dinosaurs and dinosaurs that have just stepped onto the historical stage, compared with Sastre Leiyusaurus.